WO2019171373A1 - In-situ systems and methods for detecting damage to solder joints - Google Patents

In-situ systems and methods for detecting damage to solder joints Download PDF

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Publication number
WO2019171373A1
WO2019171373A1 PCT/IL2019/050235 IL2019050235W WO2019171373A1 WO 2019171373 A1 WO2019171373 A1 WO 2019171373A1 IL 2019050235 W IL2019050235 W IL 2019050235W WO 2019171373 A1 WO2019171373 A1 WO 2019171373A1
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WO
WIPO (PCT)
Prior art keywords
pcb
piezoelectric sensor
sensor
piezoelectric
electrical parameter
Prior art date
Application number
PCT/IL2019/050235
Other languages
French (fr)
Inventor
Craig LOPATIN
Original Assignee
Technion Research & Development Foundation Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Technion Research & Development Foundation Limited filed Critical Technion Research & Development Foundation Limited
Publication of WO2019171373A1 publication Critical patent/WO2019171373A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/66—Testing of connections, e.g. of plugs or non-disconnectable joints
    • G01R31/70—Testing of connections between components and printed circuit boards
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
    • G01R29/22—Measuring piezoelectric properties

Definitions

  • aspects of the present disclosure generally relate to in-situ systems and methods for detecting damage to solder joints on a circuit board by monitoring the mechanical response thereof.
  • solder joints in electronic components and systems can be catastrophic.
  • Sources of failure of solder joints include fatigue due to vibration, overstress, and poor manufacturing practices. Improvements in design (e.g. better packaging, improved materials, and better control of manufacturing processes) are continuously being implemented, but the fact remains that solder joint failures still occur.
  • One way to prevent a solder joint failure from causing critical damage is by detecting the onset of damage, so that the component containing the defect can be removed before the damage results in a total loss of electrical conductivity of the solder joint.
  • test structures are fabricated near the components of interest.
  • the test structures are purposely fabricated weaker than the components of interest, so that failure of the test structure provides an indication that the components had been subjected to conditions whereat the solder joints could have been damaged.
  • a related approach is to monitor the electrical conductivity of some of the unused pins on an integrated circuit. This approach is more suited for monitoring the integrity of solder joints of field programmable gate arrays, which may have unused pins and, in addition, may include extra gates in the array which can be used to implement the monitoring circuit. Failure of monitored pins can be used as a trigger to remove the component.
  • Non-destructive methods such as acoustic microscopy, X-rays, and RF time domain reflectometry are also used to inspect solder joints.
  • a drawback of these methods, as currently practiced, is that the components need to be removed from the surface and examined in the laboratory.
  • aspects of the present disclosure relate to in- situ systems and methods for detecting damage to solder joints on a circuit board by monitoring the mechanical response thereof. More specifically, but not exclusively, aspects of the present disclosure, according to some embodiments thereof, relate to in- situ systems and methods for monitoring crack or fissure growth in solder joints on a printed circuit board (PCB) using one or more piezoelectric sensors.
  • PCB printed circuit board
  • the present disclosure teaches self-testing, in-situ systems to detect damage to solder joints on a PCB.
  • the PCB includes at least one piezoelectric sensor configured to be vibrated.
  • the piezoelectric sensor may be positioned on the substrate near a solder-joint mounted electronic component (EC) whose solder joints (mounting the EC on the substrate) are to be monitored.
  • the piezoelectric sensor is embedded within the substrate below the EC.
  • the EC is an integrated circuit (IC).
  • An alternating current passed through the piezoelectric sensor induces vibrations thereof, which may translate to vibrations of the substrate.
  • the vibration amplitude is affected by the strength of the connection between the EC and the substrate (in particular, by the integrity of the solder joints), and influences, in a measurable manner, electric parameters (for example, the impedance) characterizing the piezoelectric sensor.
  • the systems and methods of the present disclosure do not require removing the PCB from the device/system (e.g. an electronic/computational device or system) in which the PCB is installed (so that the monitoring is performed“in-situ”).
  • the disclosed system is“on-board” in the sense that the PCB includes all the components of the disclosed system (in particular, all the components of a sensor interrogator, which analyzes the output of the piezoelectric sensor).
  • the PCB is“self-testing” in the sense that both the measurements and the processing of the measurement outcomes are performed on the PCB.
  • the piezoelectric sensor is on-board but other components of the disclosed system (e.g.
  • components of the sensor interrogator may be off-board.
  • the components that are not positioned on the PCB may be positioned instead, for example, on a second PCB in the device/system wherein the PCB (including the piezoelectric sensor) is installed, so that the device/system may be viewed as self-testing.
  • the piezoelectric sensor is positioned on the PCB, the disclosed systems and methods allow for monitoring (optionally, in an effectively continuous manner) the integrity of solder joints on the PCB when the PCB is installed in an intended device/system, even when the device/system is operating. Consequently, the disclosed systems and methods allow for the real-time detection of the onset of damage to a solder joint (e.g.
  • An advance warning may be useful and even vital for devices/systems wherein failure may be dangerous and/or destructive, such as computational systems in vehicles, particularly, aerial vehicles, and implanted medical devices, such as cardiac pacemakers and defibrillators.
  • computational systems in vehicles particularly, aerial vehicles
  • implanted medical devices such as cardiac pacemakers and defibrillators.
  • the present disclosure further teaches self-testing integrated circuits (ICs).
  • Each lead of the IC may include a piezoelectric sensor attached thereto (and electrically decoupled therefrom), which may be sensitive to damage in an associated bonding wire and associated connection interfaces connecting the bonding wire to the lead and to a semiconducting die of the IC.
  • the connection interfaces connecting bonding wires to a semiconducting die may be suboptimal.
  • the IC further includes a sensor interrogator configured to analyze the outputs of the piezoelectric sensors, and which may be connected to the power and ground leads of the IC.
  • the IC may be tested for the above-specified types of damage (i.e.
  • a printed circuit board including a substrate, at least one electronic component (EC) solder-joint mounted on the substrate (connected to the substrate via solder joints), and at least one piezoelectric sensor attached (secured) to the substrate.
  • the piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor. A measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the EC.
  • the at least one EC is an integrated circuit (IC).
  • each of the at least one EC may be an IC, a switch, an amplifier, a filter, a rectifier, an inverter, a transistor, a resistor, a capacitor, an inductor, a diode, or any other discrete component. (That is, for example, when there are two ECs, one may be an IC and the other a diode, or one may be a resistor and the other a capacitor, or both may be resistors, and so on.)
  • the piezoelectric sensor includes a first terminal and a second terminal electrically coupling the piezoelectric sensor to the sensor interrogator. The sensor interrogator is configured to apply the input voltage to the first terminal.
  • the at least one piezoelectric sensor is attached to the substrate proximately to the EC.
  • the sensor interrogator includes the following components:
  • a signal generator configured to apply the input voltage.
  • a measurement unit configured to measure the electrical parameter.
  • a control circuitry functionally associated with the signal generator and the measurement unit and configured to process measurement data obtained by the measurement unit and to determine whether the measurement data are indicative of potential damage to the at least one solder joint.
  • control circuitry has stored in a memory therein electrical parameter baseline data.
  • the control circuitry is configured to determine whether the measurement data are indicative of potential damage to the at least one solder joint by evaluating a difference between the measured values of the electrical parameter and the electrical parameter baseline data.
  • a piezoelectric element in the piezoelectric sensor is surface bonded to the substrate or embedded within the substrate.
  • the EC is mounted on a top surface of the substrate and the piezoelectric element is surface bonded to a bottom surface of the substrate below the EC.
  • the EC is mounted on the substrate on a top surface of the substrate such as to form a gap between an EC body of the EC and the top surface.
  • the piezoelectric element is surface bonded to the top surface below the EC body.
  • the piezoelectric element is glued to the substrate or vacuum deposited on the substrate.
  • the signal generator is configured to apply a sinusoidal, or substantially sinusoidal, voltage signal or current signal. According to some embodiments, the signal generator is configured to sweep a frequency of the voltage signal across a range of frequencies.
  • a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz (e.g. the range of frequencies runs from 20 kHz to 800 kHz or the range of frequencies runs from 10 kHz to 10 GHz). According to some such embodiments, the minimum frequency is greater than about 100 kHz.
  • control circuitry is configured to repeatedly (i) command the signal generator to apply the input voltage the piezoelectric sensor (e.g. to the first terminal thereof) and (ii) command the measurement unit to measure the electrical parameter of the piezoelectric sensor, as long as the measurement data are not indicative of potential damage to the at least one solder joint.
  • the electrical parameter is an electrical impedance of the piezoelectric sensor, or a current through the (two) terminals of the piezoelectric sensor, or a voltage across the piezoelectric sensor.
  • the measured values of the electrical parameter are indicative of an integrity of, or damage to, solder material of the at least one solder joint.
  • the at least one EC includes a plurality of ECs and the at least one piezoelectric sensor includes a plurality of piezoelectric sensors.
  • Each of the plurality of piezoelectric sensors is attached to the substrate more closely (i.e. nearer) to a respective EC from the plurality of ECs than to any other one of the ECs.
  • the ECs in the plurality of ECs may differ from one another, e.g. one may be an IC, another may be a diode, two may be capacitors that differ in capacitance, and so on.
  • the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Each of the piezoelectric sensors is attached to the substrate such as to be closer (i.e. nearer) to a respective solder joint, from the at least one solder joint and associated with the at least one EC, than to any one of the other solder joints.
  • each of the at least one solder joint has a respective piezoelectric sensor, from the plurality of piezoelectric sensors, attached more closely thereto than to any one of the other solder joints.
  • the sensor interrogator is configured to allow interrogating each of the plurality of piezoelectric sensors one at a time.
  • the sensor interrogator includes a multiplexer mounted on the substrate. The multiplexer is electrically connected to the plurality of piezoelectric sensors such as to allow interrogating each of the plurality of piezoelectric sensors one at a time.
  • the control circuitry is configured to evaluate the difference between the measured values of the electrical parameter and the electrical parameter baseline data by computing a root-mean-square difference (RMSD) associated therewith.
  • RMSD root-mean-square difference
  • the signal generator and the measurement unit are configured for continuous monitoring of the at least one solder joint.
  • the PCB includes the sensor interrogator.
  • the sensor interrogator is located on the substrate and powered by an operating voltage of the PCB.
  • control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint associated with the EC.
  • the control circuitry is configured to trigger the output signal when the computed RMSD is greater than a threshold value.
  • the output signal is an electrical signal sent to an external computational component/system (e.g. an external processing circuitry, an external electronic circuitry, a second PCB, an external controller, a computational device, etc.).
  • the sensor interrogator further includes a light emitting diode (LED). The LED is functionally associated with the control circuitry and configured to receive therefrom a trigger signal to emit light as the output signal.
  • a system for detecting damage to one or more solder joints on a printed circuit board includes the PCB and the sensor interrogator, described above according to some embodiments, wherein at least some of the components of the sensor interrogator are off-board.
  • a system for detecting damage to solder joints on printed circuit boards includes a plurality of the PCB, described above according to some embodiments, and the sensor interrogator, described above according to some embodiments, wherein the sensor interrogator is off-board and configured to interrogate the at least one piezoelectric sensor on each of the plurality of PCBs, respectively.
  • a method for detecting damage to one or more solder joints on a printed circuit board includes steps of:
  • the at least one piezoelectric sensor is attached to the PCB.
  • the PCB includes at least one electronic component (EC) solder- joint mounted on the PCB.
  • the electrical parameter is sensitive to damage to at least one solder joint associated with the EC. - Determining potential damage to the at least one solder joint, or lack of damage, based on a measured value or measured values of the at least one electrical parameter.
  • the at least one EC is an integrated circuit (IC).
  • each of the at least one EC may be an IC, a transistor, a switch, an amplifier, a filter, a rectifier, an inverter, a resistor, a capacitor, an inductor, a diode, or any other discrete component.
  • the at least one piezoelectric sensor is attached to the PCB proximately to the EC.
  • the step of determining potential damage includes a sub-step of evaluating a difference between the measured values of the electrical parameter and electrical parameter baseline data. The difference is indicative of integrity of, or damage to, the at least one solder joint.
  • the method further includes an initial step of performing a baseline measurement to obtain the electrical parameter baseline data, the initial step includes sub-steps of:
  • the step of applying the input voltage, the step of measuring the electrical parameter, and the step of determining are repeated, optionally periodically, as long as, in the step of determining potential damage, no potential damage to the at least one solder joint has been determined.
  • a piezoelectric element in the piezoelectric sensor is surface bonded to the PCB or embedded within the PCB.
  • the EC is mounted on the PCB on a top surface of the PCB and the piezoelectric element is surface bonded to the PCB on a bottom surface of the PCB below the EC.
  • the EC is mounted on the PCB on a top surface of the PCB such as to form a gap between an EC body of the EC and the top surface.
  • the piezoelectric element is surface bonded to the top surface below the EC body.
  • a sinusoidal or substantially sinusoidal voltage signal, or current signal is applied to the piezoelectric sensor in the step of applying the input voltage.
  • a frequency of the sinusoidal voltage signal is swept across a range of frequencies.
  • a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz. According to some such embodiments, the minimum frequency is greater than about 100 kHz.
  • the PCB further includes a sensor interrogator electrically coupled to the at least one piezoelectric sensor and being configured to apply input voltages to each of the at least one piezoelectric sensors, to measure the electrical parameters associated with each of the at least one piezoelectric sensors, respectively, and to determine whether the measured values of the electrical parameter(s) are indicative of damage to one or more of the at least one solder joint.
  • a sensor interrogator electrically coupled to the at least one piezoelectric sensor and being configured to apply input voltages to each of the at least one piezoelectric sensors, to measure the electrical parameters associated with each of the at least one piezoelectric sensors, respectively, and to determine whether the measured values of the electrical parameter(s) are indicative of damage to one or more of the at least one solder joint.
  • the at least one EC includes a plurality of ECs and the at least one piezoelectric sensor includes a plurality of piezoelectric sensors.
  • Each of the piezoelectric sensors is attached to the PCB such as to be closer to a respective EC from the plurality of ECs than any other one of the ECs.
  • the at least one piezoelectric sensor includes a plurality of piezoelectric sensors.
  • Each of the piezoelectric sensors is attached to the PCB such as to be closer to a respective solder joint, from the at least one solder joint and associated with the at least one EC, than to any other one of the solder joints.
  • the method further includes a step of providing an output signal when in the step of determining potential damage it is determined that the measured values of the electrical parameter are indicative of damage to the at least one solder joint.
  • the output signal is an electrical signal sent to an external computational component/system.
  • the sensor interrogator further includes a light emitting diode (LED), and wherein the output signal is light emitted by the LED.
  • LED light emitting diode
  • the electrical parameter of the piezoelectric sensor is an electrical impedance of the piezoelectric sensor.
  • the step of applying the input voltage and the step of measuring the electrical parameter are performed simultaneously or substantially simultaneously.
  • the step of applying the input voltage and the step of measuring the electrical parameter are performed continuously.
  • the sub-step of evaluating the difference includes computing a root-mean-square difference (RMSD) associated with the measured values of the electrical parameter and electrical parameter baseline data and wherein the computed RMSD being greater than a threshold is indicative of potential damage to the at least one solder joint.
  • RMSD root-mean-square difference
  • a printed circuit board including a substrate, at least one electronic component (EC) solder-joint mounted on the substrate, and at least one piezoelectric sensor attached to the EC.
  • the piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor.
  • a measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the EC.
  • the at least one EC is an integrated circuit (IC).
  • each of the at least one EC is an IC, a switch, an amplifier, a filter, a rectifier, an inverter a transistor, a resistor, a capacitor, an inductor, or a diode.
  • the piezoelectric sensor is electrically connected to a pair of leads of the IC such as to allow actuation of the piezoelectric sensor.
  • the piezoelectric sensor is mounted on the EC.
  • the sensor interrogator is mounted on the EC.
  • the piezoelectric sensor is housed within the EC.
  • the sensor interrogator is housed within the EC.
  • an integrated circuit including a chip package housing therein a semiconducting die, at least one piezoelectric sensor, and a sensor interrogator.
  • the IC further includes a plurality of leads electrically coupled to the semiconducting die and extending from within the chip package (i.e. the inside of the chip package) to the outside thereof.
  • the at least one piezoelectric sensor is attached to at least one of the plurality of leads, respectively, such as to be electrically insulated therefrom.
  • the sensor interrogator is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor.
  • a measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint connecting the at least one of the plurality of leads, respectively, to (a substrate of) the PCB.
  • the semiconducting die, the at least one piezoelectric sensor, and the sensor interrogator are encapsulated within the chip package.
  • the piezoelectric sensor includes a first terminal and a second terminal electrically coupling the piezoelectric sensor to the sensor interrogator.
  • the sensor interrogator is configured to apply the input voltage to the first terminal.
  • the sensor interrogator includes the following components:
  • a signal generator configured to apply the input voltage.
  • a measurement unit configured to measure the electrical parameter.
  • a control circuitry functionally associated with the signal generator and the measurement unit and configured to process measurement data obtained by the measurement unit and to determine whether the measurement data are indicative of potential damage to the at least one solder joint.
  • control circuitry has stored in a memory therein electrical parameter baseline data.
  • the control circuitry is configured to determine whether the measurement data are indicative of potential damage to the at least one solder joint by evaluating a difference between the measured values of the electrical parameter and the electrical parameter baseline data.
  • a piezoelectric element in the at least one piezoelectric sensor is glued to the at least one of the plurality of leads.
  • the signal generator is configured to apply a sinusoidal, or substantially sinusoidal, voltage signal or current signal.
  • a frequency of the voltage signal is swept across a range of frequencies.
  • the range of frequencies runs from about 5 kHz to about 10 GHz.
  • control circuitry is configured to repeatedly (i) command the signal generator to apply the input voltage to the at least one piezoelectric sensor and (ii) command the measurement unit to measure the electrical parameter of the at least one piezoelectric sensor, when the IC is mounted on the PCB, as long as the measurement data are not indicative of potential damage to the at least one solder joint.
  • the electrical parameter is an electrical impedance of the piezoelectric sensor, or a current through the piezoelectric sensor, or a voltage across the piezoelectric sensor.
  • the measured values of the electrical parameter are indicative of an integrity of, or damage to, solder material of the at least one solder joint.
  • the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Two or more of the plurality of leads may each have attached thereon two or more piezoelectric sensors, respectively, from the plurality of piezoelectric sensors. According to some such embodiments, each of the plurality has attached thereon one piezoelectric sensor from the plurality of piezoelectric sensors.
  • the sensor interrogator is configured to allow interrogating each of the plurality of piezoelectric sensors one at a time.
  • the sensor interrogator includes a multiplexer. The multiplexer is electrically connected to the plurality of piezoelectric sensors such as to allow interrogating each of the plurality of piezoelectric sensors one at a time.
  • the control circuitry is configured to evaluate the difference between the measured values of the electrical parameter and the electrical parameter baseline data by computing a root-mean-square difference (RMSD) associated therewith.
  • RMSD root-mean-square difference
  • the at least one piezoelectric sensor is positioned proximately to at least one bonding wire electrically coupling the at least one of the plurality of leads, respectively, to the semiconducting die. The at least one piezoelectric sensor is thereby configured to detect damage to the at least one bonding wire and to connection interfaces connecting the at least one bonding wire to the at least one of the plurality of leads and to the semiconducting die.
  • the signal generator and the measurement unit are configured for continuous monitoring of the at least one solder joint. According to some embodiments of the IC, the signal generator and the measurement unit are configured for continuous monitoring of the at least one solder joint and the at least one bonding wire and the connection interfaces.
  • control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint.
  • control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint and/or the at least one bonding wire and/or the connection interfaces. According to some embodiments of the IC, the control circuitry is configured to trigger the output signal when the computed RMSD is greater than a threshold value.
  • the output signal is an electrical signal configured to be sent to processing circuitry external to the IC.
  • the IC further includes a light emitting diode (LED) attached to, or embedded on, the chip package.
  • the LED is functionally associated with the control circuitry and configured to receive therefrom a trigger signal to emit light as the output signal.
  • the method includes steps of:
  • a PCB having mounted thereon an IC including a chip package housing therein a semiconducting die and one or more piezoelectric sensors.
  • the IC further includes a plurality of leads electrically coupled to the semiconducting die and extending from within the chip package to the outside thereof such as to connect the chip package to the PCB via respective solder joints.
  • the one or more piezoelectric sensors are attached to one or more of the plurality of leads, respectively, such as to be electrically insulated therefrom. - Applying an input voltage to each of the one or more piezoelectric sensors.
  • the at least one electrical parameter being sensitive to damage to one or more of the solder joints, respectively.
  • the chip package further includes a sensor interrogator electrically coupled to the one or more piezoelectric sensors and configured to apply input voltages to each of the one or more piezoelectric sensors, to measure the electrical parameters associated with the one or more piezoelectric sensors, respectively, and to determine whether the measured values of the at least one electrical parameter are indicative of damage to the one or more of the solder joints.
  • a sensor interrogator electrically coupled to the one or more piezoelectric sensors and configured to apply input voltages to each of the one or more piezoelectric sensors, to measure the electrical parameters associated with the one or more piezoelectric sensors, respectively, and to determine whether the measured values of the at least one electrical parameter are indicative of damage to the one or more of the solder joints.
  • the one or more piezoelectric sensors are glued to the one or more of the plurality of leads, respectively.
  • the step of determining potential damage includes a sub-step of evaluating a difference between the measured values of the electrical parameter and electrical parameter baseline data. The difference is indicative of integrity of, or damage to, the one or more of the solder joints.
  • the method further includes an initial step of performing a baseline measurement to obtain the electrical parameter baseline data, the initial step includes sub-steps of:
  • the step of applying the input voltage, the step of measuring the electrical parameter, and the step of determining are repeated, optionally periodically, as long as, in the step of determining potential damage, no potential damage to the one or more of the solder joints has been determined.
  • a sinusoidal or substantially sinusoidal voltage signal, or current signal is applied to each of the one or more piezoelectric sensors in the step of applying the input voltage.
  • a frequency of the sinusoidal voltage signal is swept across a range of frequencies.
  • a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz. According to some such embodiments, the minimum frequency is greater than about 100 kHz.
  • the method further includes a step of providing an output signal when in the step of determining potential damage it is determined that the measured values of the electrical parameter are indicative of damage to the one or more of the solder joints (that is, to at least one of the monitored solder joints).
  • the output signal is an electrical signal sent to an external computational component/system.
  • the IC further includes a light emitting diode (LED).
  • the output signal is light emitted by the LED.
  • the LED is positioned on the chip package (e.g. glued thereon) or embedded thereon.
  • the electrical parameter is an electrical impedance of the piezoelectric sensor.
  • the step of applying the input voltage and the step of measuring the electrical parameter are performed simultaneously or substantially simultaneously.
  • the step of applying the input voltage and the step of measuring the electrical parameter are performed continuously.
  • the sub-step of evaluating the difference includes computing a root-mean-square difference (RMSD) associated with the measured values of the electrical parameter and the electrical parameter baseline data.
  • RMSD root-mean-square difference
  • the computed RMSD being greater than a threshold is indicative of potential damage to the one or more of the solder joints (that is, to at least one of the monitored solder joints).
  • the one or more piezoelectric sensors are positioned proximately to one or more bonding wires, respectively.
  • the bonding wires electrically couple the one or more of the plurality of leads, respectively, to the semiconducting die.
  • the one or more piezoelectric sensors are thereby configured to additionally detect damage to the one or more bonding wires and to connection interfaces connecting the one or more bonding wires to the one or more of the plurality of leads, respectively, and the semiconducting die.
  • the method further includes, prior to mounting the IC on the PCB, a step of testing the integrity of the one or more bonding wires and the connection interfaces associated therewith, by electrically connecting power and ground leads of the IC to an external power source, and (i) applying an input voltage to each of the one or more piezoelectric sensors, (ii) measuring at least one electrical parameter of each of the one or more piezoelectric sensors, each of the at least one electrical parameter being respectively sensitive to damage to the one or more bonding wires, respectively, and the respective connection interfaces associated therewith, and (iii) determining potential damage to each of the one or more bonding wires and the connection interfaces associated therewith, or lack of damage, based on a measured value or measured values of the at least one electrical parameter.
  • Certain embodiments of the present disclosure may include some, all, or none of the above advantages.
  • One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein.
  • specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages.
  • Figure la schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
  • Figure lb schematically depicts a cross-section of the printed circuit board of Fig. la, according to some embodiments;
  • Figure lc schematically depicts a cross-section of the printed circuit board of Fig. la, wherein a solder joint is damaged such that a pin end portion is loose, according to some embodiments;
  • Figure 2 schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
  • Figure 3 schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments
  • Figure 4 schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments
  • Figure 5a is a block diagram of a self-testing printed circuit board including one or more piezoelectric sensors configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
  • Figure 5b is a circuit diagram of electronic components of the self-testing circuit board of Fig. 5a, according to some embodiments;
  • Figure 6 is a block diagram of a self-testing printed circuit board including one or more piezoelectric sensors configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
  • Figure 7 is a block diagram of a system for detecting damage to solder joints on a printed circuit board, the printed circuit board including one or more piezoelectric sensors, according to some embodiments;
  • Figure 8 is a block diagram of a system for detecting damage to solder joints on a printed circuit board, the printed circuit board including one or more piezoelectric sensors, according to some embodiments;
  • Figure 9 is a flowchart of a piezoelectric sensor-based method for detecting damage to solder joints on a printed circuit board, according to some embodiments.
  • Figures 10a and 10b present experimental data demonstrating utility of the disclosed systems and methods in detecting damage to solder joints on circuit boards;
  • Figures 11 and 12 present experimental data demonstrating utility of the disclosed systems and methods in detecting damage to solder joints on circuit boards;
  • Figure 13a is a circuit diagram of an experimental system used to obtain the experimental data presented in Figs. 10a-12;
  • Figure 13b is a photograph of a circuit board of the experimental system of Fig. 13a;
  • Fig. 14a schematically depicts a self-testing integrated circuit including a plurality of piezoelectric sensors, according to some embodiments
  • Fig. 14b is a schematic, partial, cross-sectional view of a printed circuit board and the integrated circuit of Fig. 14a mounted thereon, according to some embodiments.
  • the expression“at least one of A and B”, is equivalent to“only A, only B, or both A and B”.
  • the expressions“at least one of A and B”,“at least one of A or B”,“one or more of A and B”, and“one or more of A or B” are interchangeable.
  • the words“include” and“have”, and forms thereof, are not limited to members in a list with which the words may be associated.
  • the term“about” may be used to specify a value of a quantity or parameter (e.g. the length of an element) to within a continuous range of values in the neighborhood of (and including) a given (stated) value.
  • “about” may specify the value of a parameter to be between 80 % and 120 % of the given value.
  • the statement“the length of the element is equal to about 1 m” is equivalent to the statement“the length of the element is between 0.8 m and 1.2 m”.
  • “about” may specify the value of a parameter to be between 90 % and 110 % of the given value.
  • “about” may specify the value of a parameter to be between 95 % and 105 % of the given value.
  • the terms“substantially” and“about” may be interchangeable.
  • a three-dimensional cartesian coordinate system (with orthogonal axes x, y, and z) is introduced. It is noted that the orientation of the coordinate system relative to a depicted object may vary from one figure to another. Further, the symbol Q may be used to represent an axis pointing“out of the page”, while the symbol ® may be used to represent an axis pointing“into the page”.
  • the term“printed circuit board” is used to refer in short to a printed circuit board assembly (i.e. the substrate (the“naked” printed circuit board) with electronic components, e.g. integrated circuits, mounted thereon).
  • the term“piezoelectric sensor” may refer to a piezoelectric element (e.g. a piezoelectric crystal, a PZT disc, or the like) and a pair of terminals attached to the piezoelectric element, e.g. to opposite surfaces thereof, such that, when the piezoelectric element is deformed (e.g. compressed), a potential difference (voltage) is generated between the terminals.
  • Piezoelectric sensors may be used in electro-mechanical impedance (EMI) sensing.
  • EMI sensing is based on the principle that the electrical impedance (i.e. voltage/current) of a piezoelectric sensor bonded to a structure is related to the mechanical impedance (i.e. force/velocity) of the structure.
  • the term“port” (e.g.“input port”, “output port”) with reference to a printed circuit board (PCB), is used in a broad sense to refer to both female components such as sockets, or male components such as fingers, and/or the like.
  • the ports are configured for receiving inputs from one or more external processing circuitries and/or sending outputs to one or more external processing circuitries (which may differ from the external processing circuitries from which the inputs are received).
  • a pair of input-output ports may be used to power PCB components between an operating voltage V cc and the ground.
  • Other input ports may be used to provide data/inputs, received from one or more external processing circuitries, to PCB components, particularly integrated circuits.
  • Other output ports may be used to send data/outputs from PCB components to one or more external processing circuitries.
  • the term“processing circuitry” may refer to one or more processors and memory components.
  • the term“external computational component/system” with reference to a described PCB refers to a computational component/system which is off-board, that is, not included in the PCB (e.g. not mounted on the substrate of the PCB), such as, for example, a second PCB or a processing circuitry included in the second PCB.
  • the term“measurement” and related forms thereof are used in a broad sense which includes both“direct measurements”, e.g. when a voltage across a resistor is measured using a voltmeter connected in parallel thereto, and“indirect measurements”, e.g. when the voltage across a circuit element is measured by directly measuring the voltage on a resistor connected in series to the circuit element and forming a voltage divider therewith.
  • “indirect measurement” is one wherein a second physical parameter - from which the (first) physical parameter can be derived/inferred or at least estimated - is directly/indirectly measured, e.g. indirect measurement of the electrical impedance may refer to a direct/indirect measurement of one or more other electrical parameters of the circuit element (e.g. the voltage across the circuit element) from which the electrical impedance can be derived/inferred.
  • PCB 100 includes a substrate 102, an integrated circuit (IC) 106, a piezoelectric sensor 110, and a sensor interrogator 114.
  • IC 106 is mounted on a substrate (e.g. using surface mount technology). More specifically, IC 106 includes pins 120 (not all are numbered). Pins 120 are soldered onto solder pads 124 (e.g. copper surfaces on substrate 102, shown in Fig. lb), respectively, using solder material 128, such as to form respective solder joints 130 (shown in Fig. lb).
  • the term“solder joint” may refer to an end portion of a lead or a pin (whereby the lead/pin is soldered onto a substrate of PCV, for example, to a conductive track (e.g. a copper trace) on the substrate or to a solder pad on the substrate) and a connection interface (e.g. a solder material connecting the lead/pin to the substrate).
  • the term“solder joint” may refer to the end portion of the lead/pin, the solder material (connecting the lead/pin to the solder pad), and the solder pad.
  • the term“pin” with reference to solder-joint mountable ECs refers to an exposed portion of a lead of the EC, that is, the portion of the lead which extends outside the body of the EC (e.g. in an IC, the pin may refer to the portion of the lead which is external to the chip package).
  • the term“solder joint” refers to the full extent of the pin (or the full extent of the exposed portion of the lead), the solder material, and the solder pad.
  • a solder joint is said to be associated with an EC when at least an end portion of a lead/pin of the EC forms part of the solder joint.
  • Piezoelectric sensor 110 is attached (secured) to substrate 102 proximately (near) IC 106. According to some embodiments, piezoelectric sensor 110 is surface bonded to, or embedded within, substrate 102. Piezoelectric sensor 110 includes a piezoelectric element 140 and a pair of terminals 142 attached to the piezoelectric element 140, e.g. on opposite sides thereof. Piezoelectric element 140 is electrically coupled to sensor interrogator 114 via electrical lines (e.g. copper traces) 144, as elaborated on below. Additional electrical lines, e.g. electrical lines connecting sensor interrogator 114 to the power and ground ports of the PCB, are not shown, and neither are the ports.
  • electrical lines e.g. copper traces
  • the term “attached”, particularly when used in reference to a piezoelectric sensor and a PCB, may refer to (i) a direct attachment of the piezoelectric sensor to the substrate of the PCB wherein the piezoelectric sensor contacts the substrate, as well as to (ii) an indirect attachment of the piezoelectric sensor to the substrate of the PCB wherein the piezoelectric sensor does not contact the substrate but instead contacts an intermediate component which may be directly attached to the substrate.
  • the terms“attached” and “secured” may be used interchangeably.
  • Sensor interrogator 114 is mounted on substrate 102. Sensor interrogator 114 is configured to apply an input voltage (e.g. a varying voltage signal) to one of terminals 142 (e.g. an input terminal configured to receive an input voltage from a signal generator) and to measure the electrical impedance of piezoelectric element 140 (or, according to some embodiments, one or more other electrical parameters of piezoelectric element 140), as elaborated on below.
  • Sensor interrogator 114 includes a signal generator (e.g. sine-wave generator) and a measurement unit, e.g. an impedance measurement unit, as elaborated on below.
  • Substrate 102 includes two surfaces: a top surface 152 (in some embodiments, also referred to as“component side”) and a bottom surface 154 (in some embodiments referred to as“print side”), below (i.e. opposite) to top surface 152.
  • a top surface 152 in some embodiments, also referred to as“component side”
  • a bottom surface 154 in some embodiments referred to as“print side”
  • Surfaces 152 and 154 are indicated in Fig. lb.
  • PCB 100 includes a plurality of ICs and a plurality of piezoelectric sensors.
  • Each of the piezoelectric sensors is located in/on substrate 102 proximately to a respective IC from the plurality of ICs (similarly to piezoelectric 110 positioning relative to IC 106).
  • Each of the piezoelectric sensors is sensitive to damage in solder joints of the respective IC.
  • Fig. lb is a (partial) transverse, cross-sectional view of PCB 100 taken along a line A-A (shown in Fig. la).
  • a region of a solder joint 130a (from solder joints 130) of a pin 120a (from pins 120) is also shown enlarged at the bottom of the Fig. la.
  • Solder joint 130a is shown in a damaged condition, with a solder material 128a of solder joint 130a exhibiting a crack C. Also indicated is a solder pad 124a of solder joint 130a.
  • piezoelectric sensor 110 is bonded to substrate 102 on top surface 152.
  • piezoelectric sensor 110 may be glued to, or deposited (e.g. vacuum deposited) on, top surface 152.
  • piezoelectric sensor 110 is embedded on top surface 152.
  • PCB 100 includes a plurality of solder-joint mountable electronic components (such as ICs, switches, amplifiers, filter, rectifiers, inverters, transistors, and the like, as well as resistors, capacitors, inductors, diodes, and other types of discrete components), and a plurality of piezoelectric sensors. More specifically, PCB 100 includes at least one additional electronic component (EC) beyond IC 106, and at least one additional piezoelectric sensor beyond piezoelectric sensor 110 and similar to piezoelectric sensor 110. Each piezoelectric sensor is located near a respective EC from the plurality of ECs (e.g. piezoelectric sensor 110 is located proximately to IC 106), being thereby configured for monitoring solder joint integrity (i.e. being sensitive to solder joint damage) in the respectively associated EC.
  • solder joint integrity i.e. being sensitive to solder joint damage
  • piezoelectric sensor 110 is positioned more closely to solder joint 130a than the rest of solder joints 130. According to some such embodiments, due to the positioning thereof, piezoelectric sensor 110 may be more sensitive to damage to solder joint 130a than damage to the rest of solder joints 130.
  • PCB 100 includes a plurality of piezoelectric sensors, such as piezoelectric sensor 110, each of the piezoelectric sensors being located proximately to a respective solder joint from solder joints 130.
  • PCB 100 includes two piezoelectric sensors.
  • a first piezoelectric sensor is located in proximity to a first solder joint attaching the power pin of the IC to the substrate, being thereby particularly sensitive to damage in the first solder joint.
  • the second piezoelectric sensor is located in proximity to a second solder joint attaching the ground pin of the IC to the substrate, being thereby particularly sensitive to damage in the second solder joint.
  • Fig. lc shows how a crack in a solder joint leads to the (associated) pin imposing a decreased mechanical constraint on the PCB. That is, the boundary conditions of the PCB change when any type of mechanical constraint changes, resulting in a different mechanical response and a changed vibration spectrum, as elaborated on below. More specifically, Fig. lc is a (partial) transverse, cross-sectional view of PCB 100 taken along line A-A with PCB 100 being in a state wherein solder joint 130a is damaged and with crack C present (piezoelectric sensor 110 is not shown in Fig. lc). The presence of crack C may result in a loosening of pin 120a attachment to substrate 102, as indicated by a dashed outline O.
  • Dashed outline O delineates a pin end portion 132a of pin 120a in a state wherein pin end portion 132a is not attached in full to solder pad 124a (i.e. only a left part of pin end portion 132a is attached to solder pad 124a). Also indicated is an IC body 134 (i.e. IC 106 excluding pins 120) of IC 106.
  • Fig. 2 is a (partial) transverse cross-sectional view of a PCB 200.
  • PCB 200 is similar to PCB 100 but differs therefrom in that the piezoelectric sensor of PCB 200 is embedded within the substrate of PCB 200 (instead of being attached on top of the substrate). More specifically, PCB 200 includes a substrate 202 similar to substrate 102, and a piezoelectric sensor 210 similar to piezoelectric sensor 110. PCB 200 further includes IC 106 and a sensor interrogator (not shown) similar to sensor interrogator 114. Piezoelectric sensor 210 is embedded within substrate 202 beneath IC 106.
  • piezoelectric sensor 210 is embedded within substrate 202 below solder pad 124a, such as to potentially be more sensitive to damage to solder joint 130a than damage to the rest of solder joints 130. According to some embodiments, below each of solder pads 124 a respective piezoelectric sensor, essentially similar to piezoelectric sensor 210, is embedded.
  • Fig. 3 is a (partial) transverse, cross-sectional view of a PCB 300.
  • PCB 300 is similar to PCB 100 but differs therefrom in that the piezoelectric sensor of PCB 300 is located on the bottom surface of the substrate of PCB 300 (instead of being attached on top of the substrate). More specifically, PCB 300 includes a substrate 302 similar to substrate 102, and a piezoelectric sensor 310 similar to piezoelectric sensor 110. PCB 300 further includes IC 106 and a sensor interrogator (not shown) similar to sensor interrogator 114. Piezoelectric sensor 310 is attached to a bottom surface 354 of substrate 302 beneath IC
  • Fig. 4 is a (partial) transverse, cross-sectional view of a PCB 400 similar to PCB 100.
  • PCB 400 includes a substrate 402 similar to substrate 102, an IC 406 similar to IC 106, a piezoelectric sensor 410 similar to piezoelectric sensor 110, and a sensor interrogator (not shown) similar to sensor interrogator 114.
  • An IC body 434 of IC 406 is elevated by solder joints 430 relative to substrate 402, such as to define a gap (indicated by a double -headed arrow G) between a top surface 452 of substrate 402 and a bottom surface 415 of IC body 434.
  • Piezoelectric sensor 410 is located in the gap between top surface 452 and bottom surface 415, being attached to top surface 452 of substrate 402 beneath IC body 434. Also indicated are pins 420, solder pads 424, and a solder material 428.
  • Figs, la-4 have focused on using piezoelectric sensors for monitoring the integrity of solder joints connecting pins/leads of an IC to a substrate of a PCB
  • the scope of the present disclosure also covers use of the above-described technology to monitor, in essentially the same way, solder joints used to connect other electric components (ECs) to a PCB, such as diodes, resistors, capacitors, inductors, transistors, switches, amplifiers, filter, rectifiers, inverters, and the like.
  • ECs electric components
  • the leads of an EC may be soldered to conductive tracks on a substrate of a PCB or to solder pads on the substrate.
  • the scope of the present disclosure covers both options, as well as any other option whereby an EC is similarly mounted on a substrate of a PCB via soldering.
  • “proximately to”,“in proximity to”, and“near” may be used interchangeably.
  • a piezoelectric sensor may be said to be positioned (e.g. mounted on a substrate) proximately to an electronic component (EC) (which is also mounted on the substrate), when positioned closer (nearer) to the EC than to any other EC which is secured to the substrate via a solder joint connection.
  • a piezoelectric sensor may be said to be positioned proximately to an EC, when positioned at a distance no greater than the smaller of the two planar dimensions of the EC - the planar dimensions being parallel to the surface of the PCB (e.g. the Av-plancs in Figs, la and lb).
  • the smaller of the two planar dimensions of IC 106 is given by a width W of IC 106.
  • a piezoelectric sensor may be said to be positioned proximately to a lead of an EC mounted on a substrate (e.g. a pin of an IC), when positioned closer to the lead than to any other lead (particularly of the EC).
  • a piezoelectric sensor may be said to be positioned proximately to a first lead of an EC, when positioned at a distance from the first lead of no more than 25 % of the distance between the first lead and a nearest neighbor second lead (i.e. a second lead which is closest to the first lead).
  • the distance between two nearest neighbor pins or leads may be referred to as the“inter-pin distance” or“inter-lead distance”.
  • Fig. 5a is a block diagram of a PCB 500.
  • Optional components are designated by boxes having dashed outlines.
  • PCB 500 may be similar to PCBs 100-400.
  • PCB 500 may be a specific embodiment of each of PCBs 100, 200, 300, or 400, respectively. Each possibility corresponds to a separate embodiment.
  • Fig. 5a may also be descriptive of functional interrelations between components in each of PCBs 100-400 (e.g. between piezoelectric sensor 110 and sensor interrogator 114 in PCB 100), according to some embodiments thereof.
  • PCB 500 includes a substrate 502, one or more ECs 506, one or more piezoelectric sensors 510, and a sensor interrogator 514.
  • Each of piezoelectric sensors 510 is located proximately to a respective EC from ECs 506.
  • sensor interrogator 514 includes a signal generator 521, an electrical impedance measurement unit 525, a micro-controller 529, and, in some embodiments, wherein PCB 500 includes more than a single piezoelectric sensor, also a multiplexer 533.
  • ECs 506 are depicted as including three ECs: an EC 506a, an EC 506b, and an EC 506c. It will be understood that ECs 506 may differ from one another.
  • EC 506a may be an IC
  • EC 506b may be a resistor
  • EC 506c may be a capacitor.
  • each of piezoelectric sensors 510 is distinguished accordingly to account for the possibility that in some embodiments, piezoelectric sensors may differ from one another, each being optimized to detect damage to the EC (of ECs 506) in proximity to which it is positioned. That is, in Fig.
  • piezoelectric sensors 510 include a piezoelectric sensor 510a positioned proximately to EC 506a, a piezoelectric sensor 510b positioned proximately to EC 506b, and a piezoelectric sensor 510c positioned proximately to EC 506c.
  • piezoelectric sensors 510 may differ from one another in their respective vibration spectrums.
  • each of ECs 506 (e.g. EC 506a, EC 506b, and EC 506c) is an IC.
  • Micro-controller 529 is functionally associated with signal generator 521, electrical impedance measurement unit 525, and multiplexer 533 (in embodiments including a plurality of piezoelectric sensors), and is configured to control operation thereof, e.g. to periodically instruct (command) signal generator 521 to initiate a sine wave sweep, to instruct multiplexer 533 which of the outputs of piezoelectric sensors 510 is to be routed to electrical impedance measurement unit 525, to receive measurement data from electrical impedance measurement unit 525, and so on.
  • Sensor interrogator 514 is designated by a box with a dotted outline to emphasize that sensor interrogator 514 is a collection of electronic components (e.g. signal generator 521, impedance measurement unit 525) which, according to some embodiments, are not housed within a single casing (housing). Nevertheless, the scope of the disclosure should be understood to cover also the options of some or all of the electronic components being housed within a common casing.
  • electronic components e.g. signal generator 521, impedance measurement unit 525
  • signal generator 521 and impedance measurement unit 525 may form a part of, or be replaced by, an impedance analyzer, such as the commercially available AD5933 impedance analyzer (in which case both the first terminals of each of piezoelectric sensors 510 and the second terminals of each of piezoelectric sensors 510 (via multiplexer 533) are connected to the impedance analyzer).
  • an impedance analyzer such as the commercially available AD5933 impedance analyzer (in which case both the first terminals of each of piezoelectric sensors 510 and the second terminals of each of piezoelectric sensors 510 (via multiplexer 533) are connected to the impedance analyzer).
  • An output port of signal generator 521 is electrically connected to a respective first terminal of each of piezoelectric sensors 510.
  • Signal generator 521 is configured to produce a voltage signal (or a current signal), and thereby induce a voltage between the terminals of each of piezoelectric sensors 510, respectively.
  • a respective second terminal of each of piezoelectric sensors 510 is electrically coupled to electrical impedance measurement unit 525.
  • the second terminals of piezoelectric sensors 510 are electrically coupled to electrical impedance measurement unit 525 via multiplexer 533.
  • signal generator 521 is a sine wave generator (e.g. configured to generate a sinusoidal voltage signal). According to some embodiments, signal generator 521 is configured to generate a swept sine signal, e.g. a sine voltage signal whose frequency increases from an initial frequency (e.g. 100 kHz) to a final frequency (e.g. 10 GHz).
  • a swept sine signal e.g. a sine voltage signal whose frequency increases from an initial frequency (e.g. 100 kHz) to a final frequency (e.g. 10 GHz).
  • Electrical impedance measurement unit 525 is configured to measure respective impedances of (or according to some embodiments, just the current through each of, or just the voltages across each of) piezoelectric sensors 510 and to communicate the obtained measurement data to micro-controller 529.
  • electrical impedance measurement unit 525 includes electronic components such as to allow electrical impedance measurement unit 525 to measure directly/indirectly the electrical impedance of the piezoelectric sensor selected by multiplexer 533.
  • impedance measurement unit 525 may include a sensing resistor, connected in series to multiplexer 533 (and thereby to the“selected” piezoelectric sensor from piezoelectric sensors 510) such as to form a voltage divider therewith, and a voltmeter configured to measure the voltage across the sensing resistor.
  • FIG. 5b A circuit diagram of the above described configuration, which constitutes a specific embodiment of components in PCB 500, is depicted in Fig. 5b.
  • signal generator 521 according to some embodiments thereof, multiplexer 533, according to some embodiments thereof, a sensing resistor 535, and a voltmeter 537 (and, according to some embodiments, additionally or alternatively to voltmeter 537 and sensing resistor 535, an ammeter 539).
  • one or more electrical switches 545 within multiplexer 533 are depicted.
  • a double -headed arrow B indicates the input voltage Vi, that is to say, the voltage applied by signal generator 521 at the input (first) terminal of each of piezoelectric sensors 510 (e.g.
  • a double-headed arrow D indicates the output voltage V 0 , that is to say, the voltage across sensing resistor 535.
  • micro-controller 529 includes processing circuitry and a memory (both not shown).
  • the processing circuitry may be an application specific integrated circuitry (ASIC), a programmable processing circuitry such as an FPGA, firmware, and/or the like, and is configured to process measurement data obtained by impedance measurement unit 525 and determine whether the measurement data are indicative of damage to at least one of the monitored solder joints.
  • the memory is a non-transitory memory.
  • the memory may include a solid-state memory, a magnetic memory, a photonic memory, and/or the like.
  • the memory includes both non-transitory memory components and transitory memory components.
  • the memory has stored therein electrical impedance baseline data (and/or baseline data of other electrical parameters), which are used by the processing circuitry as a reference to which the measurement data, obtained during the monitoring, is compared. Significant differences between the measurement data and the baseline data may be indicative of damage to one or more of the monitored solder joints, as elaborated on below.
  • Micro controller 529 may further include at least one filter configured to filter electrical signals, at least one voltage and/or current amplifier, at least one analog- to-digital electrical signal convertor, and/or at least one digital-to-analog electrical signal convertor.
  • micro-controller 529 is configured to analyze the spectrum of the measured electrical impedance(s) (or the spectrum of another physical quantity from which the measured impedance can be obtained, such as the RMS voltage spectrum of sensing resistor 535).
  • the memory in micro-controller 529 may have stored therein custom software for analyzing the spectrum, executable by the processing circuitry in micro-controller 529.
  • the custom software may be configured to identify features (or lack thereof) in the spectrum, which are typical of intact (undamaged) solder joints.
  • the spectrum associated with intact solder joints may include more features, such as peaks and troughs (valleys), or more distinct (pronounced) features, such as larger peak and troughs, as compared to the spectrum of damaged solder joints.
  • the electrical impedance spectrum associated with intact solder joints may be different from the electrical impedance spectrum associated with damaged solder joints, due to the stronger mechanical coupling between the PCB and the EC provided by intact solder joints as compared to that provided by damaged (e.g. loose) solder joints (in Fig. lc a loose pin end portion is depicted).
  • the decrease in the mechanical coupling (i.e. less constraint) between the PCB and the EC e.g. due to a crack in the solder material/joint, results in a different vibration spectrum of the PCB (and thus a different electrical impedance spectrum of the piezoelectric sensor).
  • the custom software may be configured to determine potential damage to one or more solder joints when a change is observed in the electrical impedance spectrum.
  • the software is configured to compare the measured spectrum with the baseline spectrum and identify differences there between, such as an absence of features, e.g. peaks and/or troughs, in the measured spectrum, which appear in the baseline spectrum, or attenuation (shrinking) of features in the measured spectrum as compared to the baseline spectrum.
  • the custom software may be configured to determine potential damage to one or more solder joints when one or more features, appearing in the baseline spectrum, are missing in the measured spectrum (or vice-versa) or appear significantly different (e.g. shrunk or enlarged) in the measured spectrum as compared to the baseline spectrum.
  • the baseline spectrum is obtained when the PCB is believed to be“healthy”, e.g. before use or immediately after fabrication.
  • the custom software may be configured to (i) compute a root-mean-square difference (RMSD) associated with the measured spectrum and the baseline spectrum, and, when the computed RMSD is greater than a threshold value, (ii) determine that the monitored solder joint(s) is potentially damaged, as elaborated on below in the Methods subsection.
  • micro-controller 529 is further configured to not only determine whether a monitored solder joint is damaged, but also to assess the degree of damage to the monitor solder joint (when the solder joint is determined to be damaged), e.g. whether the monitored solder joint is slightly damaged or severely damaged.
  • Micro-controller 529 is electrically coupled to an output port 551 of PCB 500.
  • the other input and output ports (e.g. sockets or fingers) of PCB 500 e.g. VC- (for powering PCB 500 elements, including sensor interrogator 514), GND (ground port), and input and output ports for providing inputs and relaying outputs from ECs 506, respectively, are not shown.
  • Micro-controller 529 is configured to send an output signal (via output port 551) to an external computational component/system, when the measured electrical impedance of one or more of piezoelectric sensors 510 is indicative of damage to one or more of the monitored solder joints.
  • sensor interrogator 514 requires only a single dedicated port (i.e. output port 551) on PCB 500.
  • Fig. 6 is a block diagram of a PCB 600.
  • PCB 600 is similar to PCB 500 but differs therefrom in that the output signal of the sensor interrogator of PCB 600 is not relayed via an output port of PCB 600 (in contrast to PCB 500 wherein the output signal from sensor interrogator 514 is relayed via output port 551).
  • PCB 600 includes a substrate 602 similar to substrate 502, one or more ECs 606 (e.g. three, as depicted in Fig 6: an EC 606a, an EC 606b, and an EC 606c) that may be similar to ECs 506, one or more piezoelectric sensors 610 (e.g.
  • a piezoelectric sensor 610a a piezoelectric sensor 610b, and a piezoelectric sensor 610c positioned near EC 606a, EC 606b, and EC 606c, respectively) that may be similar to piezoelectric sensors 510, and a sensor interrogator 614.
  • Sensor interrogator 614 includes a signal generator 621 similar to signal generator 521, an electrical impedance measurement unit 625 similar to electrical impedance measurement unit 525, a micro controller 629, optionally a multiplexer 633, and a light emitting diode (LED) 655.
  • LED 655 is electrically coupled to micro-controller 629.
  • Micro-controller 629 is configured to send a trigger signal to LED 655 when the measured electrical impedance of one or more piezoelectric sensors 610 is evaluated by micro-controller 629 as being indicative of damage to at least one of the monitored solder joints.
  • LED 655 is configured to emit light upon receiving the trigger signal. The emitted light constitutes the output signal.
  • a light detector 657 coupled to an external computational component/system (not shown), e.g. an external control circuitry, is positioned proximately to PCB 600 such that light emitted by LED 655 is incident on light detector 657.
  • sensor interrogator 614 requires no dedicated ports on PCB 600.
  • a PCB (not shown in the figures).
  • the PCB is similar to PCB 600 but differs therefrom in including a wireless transmitter instead of LED 655.
  • the wireless transmitter is functionally associated with a micro controller, similar to micro-controller 629, and is configured to transmit an output signal upon receipt of a trigger signal from the micro-controller.
  • ECs 606 may differ from one another (e.g. EC 606a may differ from EC 606b), essentially as described above with respect to ECs 506.
  • piezoelectric sensors 610 may differ from one another, essentially as described above with respect to piezoelectric sensors 510.
  • each of ECs 606 is an IC.
  • PCBs 500 and 600 are said to be“self-testing” in the sense of including electronic components capable of independently identifying damage to solder joints thereon the PCB, i.e. without requiring off-board measurements and processing of measurement data.
  • all of the components of the sensor interrogator are on-board (e.g. mounted on, attached to, or embedded in/on the substrate).
  • all the processing of measurement data measurements are performed off-board.
  • all the components of the sensor interrogator are off-board.
  • some of the processing of measurement data and/or some of the measurements may be performed off-board.
  • some of the components of the sensor interrogator are off-board.
  • the multiplexer and sensing resistor may be on-board while the rest of the sensor interrogator components may be off-board.
  • Fig. 7 is a block diagram of a PCB 700.
  • PCB 700 is similar to PCB 500 but differs therefrom in that, except for a multiplexer 733, PCB 700 does not include any other components analogous to components of sensor interrogator 514.
  • Interrogation (probing and analysis) of the piezoelectric sensor(s) on PCB 700 is performed by an off-board sensor interrogator (not shown), which, according to some embodiments, apart from being off-board, is essentially similar to sensor interrogator 514.
  • PCB 700 includes a substrate 702, one or more ECs 706 (e.g. three, as depicted in Fig 7: an EC 706a, an EC 706b, and an EC 706c), one or more piezoelectric sensors 710 (e.g. three as depicted in Fig 7: a piezoelectric sensor 710a, a piezoelectric sensor 710b, and a piezoelectric sensor 710c positioned near EC 706a, EC 706b, and EC 706c, respectively), and multiplexer 733.
  • Piezoelectric sensors 710 are electrically connected to an input port 763 whereby a voltage signal (e.g. sine wave signal) from an external signal generator can be provided.
  • a voltage signal e.g. sine wave signal
  • Multiplexer 733 is electrically connected to each of piezoelectric sensors 710 (through output ports thereof, not numbered) and configured to select between them. Multiplexer 733 is further electrically connected to additional input ports 767 and an output port 751. Multiplexer 733 is configured to receive (e.g. from an external control circuitry functionally similar to micro-controller 529), via additional input ports 767, a signal specifying which of the outputs of piezoelectric sensors 710 is to be forwarded (routed). The selected output is forwarded via output port 751, e.g. to an external impedance measurement unit. According to some embodiments, not depicted in Fig. 7, instead of multiplexer 733, PCB 700 includes a demultiplexer.
  • the demultiplexer is connected to input port 763, to piezoelectric sensors 710 (through input ports of piezoelectric sensors 710, not numbered), and to additional input ports 767.
  • the demultiplexer is configured to forward the input voltage signal (from input port 763) to a“selected” piezoelectric sensor, according to instructions conveyed to the demultiplexer via additional input ports 767.
  • Piezoelectric sensors 710 are also connected (via output ports thereof, not numbered) to output port 751.
  • ECs 706 may differ from one another (e.g. EC 706a may differ from EC 706b), essentially as described above with respect to ECs 506.
  • piezoelectric sensors 710 may differ from one another, essentially as described above with respect to piezoelectric sensors 510.
  • each of ECs 706 is an IC.
  • Fig. 8 is a block diagram of a PCB 800.
  • PCB 800 is similar to PCB 700 but differs therefrom in not including any components analogous to components of sensor interrogator 514. Interrogation of the piezoelectric sensor(s) on PCB 800 is performed by an off-board sensor interrogator (not shown), essentially as described with respect to
  • PCB 800 includes a substrate 802, one or more ECs 806 (e.g. three, as depicted in Fig 8: an EC 806a, an EC 806b, and an EC 806c), and one or more piezoelectric sensors 810 (e.g. three as depicted in Fig 8: a piezoelectric sensor 810a, a piezoelectric sensor 810b, and a piezoelectric sensor 810c positioned near EC 806a, EC 806b, and EC 806c, respectively).
  • Piezoelectric sensors 810 are electrically connected to an input port 863 whereby a voltage signal (e.g. sine wave signal) from an external signal generator can be provided.
  • Each of piezoelectric sensors 810 is electrically connected to a respective output port from output ports 851, whereby piezoelectric sensors 810 may be electrically coupled to an external multiplexer that functions essentially similarly to multiplexer 733.
  • ECs 806 may differ from one another (e.g. EC 806a may differ from EC 806b), essentially as described above with respect to ECs 506.
  • piezoelectric sensors 810 may differ from one another, essentially as described above with respect to piezoelectric sensors 510.
  • each of ECs 806 is an IC.
  • PCB 700 has the advantage over PCB 800 of requiring only n + 2 dedicated ports (ports 751,
  • n ml (the brackets denoting rounding up so that — 1 ⁇ k»g 2 m ⁇ n), whereas PCB 800 requires m + 1 ports (ports 851 and port 863) to the same end.
  • Fig. 9 is a flowchart of a method 900 for monitoring integrity of solder joints on a PCB and detecting potential onset of damage thereto, according to some embodiments. Dash- delineated boxes contain text corresponding to optional steps of method 900. Method 900 can be implemented using any one of PCBs 100-800, and PCBs similar thereto, as elaborated on below. Method 900 includes:
  • step 910 wherein an input voltage is applied to a terminal of a piezoelectric sensor (such as piezoelectric sensors 110, 510, or 710).
  • the piezoelectric sensor is attached to a substrate of a PCB (such as PCBs 100, 500, or 700).
  • an electrical parameter(s) e.g. electrical impedance
  • an electrical parameter(s) e.g. electrical impedance
  • Values of the electrical parameter(s) are affected by a mechanical coupling between the piezoelectric sensor and the substrate due to the attachment of the piezoelectric sensor to the substrate.
  • step 930 wherein it is determined whether the measured value(s) of the electrical parameter(s) are indicative of potential damage to one or more solder joints (such as solder joint 130a in PCB 100) whereby the EC (e.g. IC 106) is mounted on the PCB.
  • a step 935 wherein an output signal is provided (e.g. by a sensor interrogator such as sensor interrogator 114 or 514) contingent upon it being determined in step 930 that the measured values of the electrical parameter(s) are indicative of potential damage to one or more of the solder joints.
  • a sensor interrogator such as sensor interrogator 114 or 51
  • the piezoelectric sensor is attached to the substrate proximately to an EC mounted thereon.
  • Possible attachment locations of the piezoelectric sensor on the PCB are specified in Figs, la-4 and the accompanying descriptions thereof.
  • Possible attachment mechanisms e.g. surface bonding, embedding are also specified above in the descriptions of Figs. la-8.
  • step 930 the determination of whether the measurement data (measured values of the electrical parameter) are indicative of damage to one or more of the monitored solder joints may be performed by a processing circuitry, such as the processing circuitry described above with reference to micro-controller 529.
  • step 930 differences between the measurement data of the electrical parameter and electrical impedance baseline data are analyzed (evaluated). Appreciable differences between the two data (spectra) serve as an indicator of potential damage to one or more of the solder joints, essentially as described above in the description of the processing circuitry of micro-controller 529 and as elaborated on below.
  • RMSD root-mean-square difference
  • RMSD “damaged” spectrum
  • the m are the amplitudes of data points in the baseline spectrum, and the summation is over all pairs of data points (i.e. di and m with the same index) in the spectra. It has been shown in the literature that in many cases the RMSD increases monotonically as increasing levels of damage are found in a structure. By running tests in the lab (e.g. on many copies of a PCB), a RMSD threshold value, beyond which damage to the PCB is considered significant and unacceptable, can be determined.
  • steps 910, 920, and 930 are repeated (e.g. periodically) so long as the measurement data (obtained in step 920) are not indicative of potential damage to one or more of the monitored solder joints.
  • measurements can be taken continuously or substantially continuously (e.g. frequency scans (see below) are repeated without pause, or substantially without pause, between consecutive frequency scans). Continuous monitoring of a solder joint(s) (which involve continuous measurements of a respective piezoelectric sensor) is most beneficial when the PCB is subject to continuous vibration, during which time the solder joint(s) may start to fail (e.g. develop a crack).
  • steps 910, 920, and 930 are repeated one or two additional times for verification.
  • method 900 further includes an initial step 905, wherein the electrical parameter baseline data are obtained, e.g. by effecting a first sub step similar to step 910 and a second sub-step similar to step 920.
  • the measured values of the electrical parameter(s) obtained in the second sub-step may be stored (as electrical parameter baseline data) in a memory (e.g. non-volatile memory) of a micro controller, such as micro-controller 529 or 629 (or any micro-controller or control circuitry associated with a sensor interrogator, such as sensor interrogator 114, 314, or 714).
  • a sine wave generator is used to apply the input voltage in step 910.
  • the sine wave generator effects a frequency scan (i.e. produces a swept sine voltage signal whose frequency is e.g. increased from about 5 kHz to about 10 GHz or about 100 kHz to about 10 GHz), thereby obtaining a measured spectrum of the electrical parameter (the dependence of the measured values of the electrical parameter on the frequency of the applied input voltage signal).
  • the determination (in step 930) of whether the measured spectrum is indicative of damage to one or more of the solder joints includes checking (examining) the spectrum for features/structural patterns, or lack thereof, which are typical of intact (undamaged) solder joints. According to some embodiments, absence of one or more of the typical features is indicative of potential damage to one or more of the solder joints. According to some embodiments, presence of atypical features in the measured spectrum is indicative of potential damage to one or more of the solder joints.
  • step 930 the measured spectrum and baseline spectrum are checked for the presence/absence of common features e.g. peaks and/or troughs, or differences in the shape/size of the common features.
  • potential damage to one or more solder joints is determined when one or more features, appearing in the baseline spectrum, are missing in the measured spectrum or appear different (e.g. reduced in size) in the measured spectrum as compared to the baseline spectrum.
  • an obtained value of the RMSD (computed from the measured spectrum and baseline spectrum, as explained above) being above a threshold value is indicative of damage to one or more of the solder joints.
  • the obtained RMSD value (together with the RMSD threshold value) suffices to determine whether damage has occurred to one or more of the solder joints.
  • the output signal in step 935 is an electrical signal sent to an external computational component/system.
  • the output signal in step 935 is a light emitted by a LED and which is incident on a light detector functionally associated with an external computational component/system.
  • a single piezoelectric sensor is used to monitor solder joints of different ECs.
  • the piezoelectric sensor is located proximately to more than one EC.
  • the piezoelectric sensor may be located midway or substantially midway between two ECs.
  • Figs. 10a- 12 present experimental data demonstrating the feasibility of method 900 and indicating the utility of PCBs 100-800 for detecting damage to solder joints thereon.
  • Fig. 13a is a circuit diagram of the system used to obtain the data
  • Fig. 13b is a photograph of the experimental circuit board used.
  • Circuit board 1300 includes a piezoelectric sensor 1310 (STEMiNC type SMD05T04R111WL) glued thereto, an eight-pin dual-in-line-package (DIP) IC 1306 soldered to the board at pins 1, 4, 5, and 8, and a resistor 1369 (shown in Fig. 13b).
  • DIP dual-in-line-package
  • Resistor 1369 is not electrically connected to the sensor interrogator (or piezoelectric sensor 1310) and was used to demonstrate the sensitivity of the method to changes in the mechanical vibration spectrum of circuit board 1300 by first gluing one of resistor 1369 leads to circuit board 1300 and later soldering the second lead thereof to circuit board 1300 (thereby changing the boundary conditions of the board), as described below.
  • piezoelectric sensor 1310 and a (off-board) sensing resistor 1335 are electrically connected in series such as to form a voltage divider (similarly to piezoelectric sensors 510 and sensing resistor 535).
  • a swept sine voltage signal (generated by a signal generator 1321) was used to drive the voltage divider.
  • the resultant voltage across the sensing resistor was amplified (by an amplifier 1371), converted to a DC signal (by an RMS-to-DC converter 1375 (Analog Devices AD536)), and recorded (using a USB scope 1379).
  • Fig. 10a shows a voltage (presented in“arbitrary units” AU), measured across sensing resistor 1335, as a function of the drive frequency. More specifically, Fig. 10a shows the RMS (root-mean-square) voltage across the sensing resistor as a function of the drive frequency when resistor 1369 is not bonded to the PCB (i.e. before the epoxy glue was applied).
  • the electrical impedance of the piezoelectric sensor is approximately inversely proportional to the voltage V 0 across the sensing resistor ( Z ⁇ R s * (Vi / V render) ).
  • solder joint strength e.g. of an IC
  • Fig. 11 shows the effects of additionally soldering the second lead of resistor 1369 to the PCB.
  • Two spectra are shown.
  • the bottom spectrum corresponds to a first frequency scan, i.e. before the second lead was soldered (but with the first lead glued).
  • the top spectrum which is offset with respect to the bottom spectrum, corresponds to a frequency scan after the second lead was soldered.
  • the differences between the two spectra are especially noticeable in the regions highlighted in grey, wherein peaks are present in the top spectrum which are missing in the bottom spectrum, making it easy to distinguish the two spectra even by eye.
  • Fig. 12 shows the effect of soldering an additional pin (a fifth pin) of the IC to the PCB.
  • Two spectra are shown.
  • the bottom spectrum corresponds to a first frequency scan, i.e. before the fifth pin (pin 7) was soldered.
  • the top spectrum which is offset with respect to the bottom spectrum, corresponds to a frequency scan after pin 7 has been soldered.
  • the differences between the two spectra are particularly noticeable in the regions highlighted in grey. Given that the integrated circuit already had four pins soldered (pins 1, 4, 5, and 8), the fact that soldering an additional pin resulted in significant changes in the spectrum demonstrates the sensitivity of the disclosed methods to detect changes in solder joint strength.
  • control circuitry As used herein, according to some embodiments, the ter s “controller”, “micro controller”, and“control circuitry” are used interchangeably. As used herein, according to some embodiments, the terms“off-board” and“external”, with reference to components which are not located on a PCB (e.g. on the substrate thereof), are used interchangeably.
  • a PCB there is provided a PCB.
  • the PCB includes an EC mounted thereon by solder joints.
  • the EC includes a piezoelectric sensor attached thereto.
  • a piezoelectric element of the piezoelectric sensor is attached (e.g. glued) to a top surface of a body of the EC (e.g. to a chip package of an IC).
  • the piezoelectric element is attached to a bottom surface of the body of the EC.
  • the piezoelectric element is positioned within the EC.
  • the piezoelectric sensor is electrically coupled to a sensor interrogator, similar to the sensor interrogators described above, and which, according to some embodiments, is also positioned within the EC.
  • the piezoelectric sensor may be connected to the free pins such as to allow actuation thereof by a sensor interrogator external to the EC.
  • the mechanical coupling between the piezoelectric sensor and the EC allows for monitoring the integrity of the solder joints of the EC, the working principle being similar to that described above for piezoelectric sensors mounted on a substrate of a PCB.
  • Fig. 14a is a schematic, top view of a self testing integrated circuit (IC) 1400, according to some embodiments.
  • Fig. 14b is a schematic, partial, cross-sectional view of IC 1400 mounted on a PCB 1450 (or, more precisely, on a substrate 1452 thereof), according to some embodiments.
  • IC 1400 includes a chip package 1402, a semiconducting die 1404, leads 1410, bonding wires 1412, one or more piezoelectric sensors 1420 (for example, and as depicted in Fig. 14a, one per lead), a sensor interrogator 1422, and a light-emitting diode (LED) 1424.
  • Fig. 14a is a schematic, top view of a self testing integrated circuit (IC) 1400, according to some embodiments.
  • Fig. 14b is a schematic, partial, cross-sectional view of IC 1400 mounted on a PCB 1450 (or, more precisely, on a substrate 1452 thereof), according to some
  • chip package 1402 is outlined but otherwise depicted as transparent in order to show the components housed therein, and thereby facilitate the description.
  • Die 1404, piezoelectric sensor 1420, and sensor interrogator 1422 may be embedded in chip package 1402, e.g. embedded in a plastic encapsulate (e.g. a mold resin) or a ceramic encapsulate (the encapsulate is not shown).
  • die 1404 may be fixed to a support structure (header; not shown), which is encapsulated within chip package 1402, as known in the art of ICs.
  • Leads 1410 are electrically connected to die 1404 via bonding wires 1412 (for example, gold wires).
  • Leads 1410 extend outside of chip package 1402, the exposed portions thereof (i.e. the portions of leads 1410 located outside of (externally to) chip package 1402) constituting the pins which may be used to mount IC 1400 on a PCB (as shown, for example, in Fig. 14b).
  • Dashed arrows (single -headed and double-headed) denote in Figs. 14a and 14b functional relationships between components (e.g. electrical coupling, sending of information).
  • Each of piezoelectric sensors 1420 is attached to one of leads 1410, respectively.
  • piezoelectric sensors 1420a, 1420b, and 1420c are attached to leads 1410a, 1410b, and 1410c (from leads 1410), respectively.
  • Each of piezoelectric sensors 1420 may include a piezoelectric element (e.g. a piezoelectric crystal or PZT disc) and a pair of terminals attached to the piezoelectric element, which electrically couple (via electrical lines, e.g. electrical wires or traces; not shown) the piezoelectric element to sensor interrogator 1422. More specifically, each piezoelectric element is attached to one of leads 1410, respectively.
  • the attachment is such that the lead is electrically insulated from the piezoelectric element.
  • the piezoelectric element may be glued to the lead by means of an adhesive, which forms an electrically insulating layer between the lead and the piezoelectric clement (and the terminals).
  • the piezoelectric element When an alternating electrical current is passed through the piezoelectric element, the piezoelectric element vibrates and induces acoustic vibrations in the lead to which the piezoelectric element is attached.
  • the vibration spectrum of the piezoelectric element is affected by the strength of the mechanical coupling of the lead to the substrate, which in turn depends on the integrity of the solder joint joining the lead to the substrate (for example, as depicted in Fig. 14b, to a solder pad on the substrate).
  • an oscillating voltage is applied across the terminals of piezoelectric sensor 1420c, vibrations thereof are induced, which are imparted to lead 1410c.
  • the vibration spectrum of piezoelectric sensor 1420c depends on the integrity of a solder joint 1426c joining lead 1410c (by means of a solder material 1428c) to a solder pad 1456c on substrate 1452 (shown in Fig. 14b).
  • the vibration spectrum of a piezoelectric element is determined by (mechanical) boundary conditions characterizing the mechanical coupling of the piezoelectric element to the surroundings thereof.
  • the boundary conditions may also be affected, in a measurable manner, by the strength of the mechanical coupling of the respective lead to die 1404, that is, by the integrity of the connection provided by the bonding wire electrically coupling the lead to die 1404.
  • Each bonding wire may form, on a first end thereof, a connection interface with die 1404 and, on the second end thereof, a connection interface with the respective lead.
  • the boundary conditions may be affected, in a measurable manner, by the integrity of the bonding wire, as well as by the integrity of the connection interfaces attaching (e.g.
  • connection interface connecting a bonding wire to a semiconducting die may be particularly sensitive to damage (e.g. connection interface 1432c).
  • leads 1410 and/or semiconducting die 1404 may include bonding pads to which the ends of bonding wires 1412 are attached (i.e. the connection interfaces may include bonding pads).
  • each piezoelectric sensor may be attached to the respective lead proximately to the bonding wire electrically coupling the lead to the die, so as to increase the sensitivity of the piezoelectric sensor to structural damage in the bonding wire and to the strength of the respective connection interfaces joining the bonding wire to the leads and the semiconducting die (that is, to any structural damage to the connection interfaces).
  • piezoelectric sensor 1420c is attached to lead 1410c in proximity to bonding wire 1412c.
  • a piezoelectric sensor in a chip package may be said to be attached to a lead proximately to a bonding wire in the chip package, when positioned closer to the bonding wire than to the external portion of the lead.
  • Electrical lines 1438a and 1438b respectively connect sensor interrogator 1422 to leads 1410a and 1410b (the power lead and ground lead of IC 1400, respectively), which supply the power to operate sensor interrogator 1422, piezoelectric sensors 1420, and LED 1424 (as well as die 1404).
  • Sensor interrogator 1422 is configured to selectively apply an input voltage to each one of piezoelectric sensor 1420 (e.g. one at a time), and thereby induce vibrations of the respective piezoelectric element.
  • Sensor interrogator 1422 is further configured to measure the electrical impedance of each piezoelectric element or, according to some embodiments, one or more other electrical parameters of each piezoelectric element, essentially as described above in the description of Figs. 5a- 6 and in the description of method 900.
  • sensor interrogator 1422 includes a signal generator (e.g. sine-wave generator), a measurement unit (e.g. an impedance measurement unit), a micro-controller, and a multiplexer, functionally associated there between and with piezoelectric sensors 1420, essentially as described above, with respect to sensor interrogator 614 and piezoelectric sensors 610, in the description of Fig. 6.
  • a signal generator e.g. sine-wave generator
  • a measurement unit e.g. an impedance measurement unit
  • micro-controller e.g. an impedance measurement unit
  • multiplexer functionally associated there between and with piezoelectric sensors 1420, essentially as described above, with respect to sensor interrogator 6
  • LED 1424 may be positioned on chip package 1402 (e.g. glued thereon) or embedded thereon. It is noted that in Fig. 14a, LED 1424 is shown positioned on a side surface of chip package 1402, while in Fig. 14b, LED 1424 is shown positioned on the top surface of chip package 1402. (Similarly, in Fig. 14a, sensor interrogator 1422 is shown positioned to the side of die 1404, while in Fig. 14b, sensor interrogator 1422 is shown positioned above die 1404.)
  • LED 1424 is electrically coupled to sensor interrogator 1422 (e.g. to the micro controller included in sensor interrogator 1422).
  • Sensor interrogator 1422 is configured to send a trigger signal to LED 1424 when the measured electrical impedance of one or more of piezoelectric sensors 1420 is evaluated by sensor interrogator 1422 as being indicative of damage to one or more of the solder joints connecting leads 1410 to substrate 1452 (e.g. when the measured impedance of piezoelectric sensor 1420c is indicative of damage to solder joint 1426c (shown in Fig. 14b)) and/or to one or more of the bonding wires and/or the associated connection interfaces joining the leads to the die (e.g.
  • LED 1424 is configured to emit light upon receiving the trigger signal.
  • the emitted light constitutes an output signal indicating malfunction in the PCB (e.g. a crack in solder joint 1426c and/or damage to bonding wire 1412c).
  • PCB 1450 may further include a light detector (not shown) positioned thereon, such that light emitted by LED 1424 is incident on the light detector.
  • PCB 1450 may include a plurality of light detectors, particularly, in embodiments wherein PCB 1450 includes, in addition to IC 1400, other self-testing ICs similar to IC 1400.
  • the light detector(s) may be external to PCB 1450, essentially as described above with respect to PCB 600.
  • the light detector may be associated with an external computational component/system (e.g. external to PCB 1450).
  • two piezoelectric sensors may be attached to each lead, such that one of the piezoelectric sensors is positioned proximately to the bonding wire, and the other piezoelectric sensor is positioned proximately to a side surface of the chip packet, such as to be positioned proximately to the external portion of the lead.
  • the piezoelectric sensor positioned near the bonding wire may be more sensitive to damage to the bonding wire and to the connection interfaces connecting the bonding wire to the semiconducting die and the lead.
  • the piezoelectric sensor positioned near the side surface may be more sensitive to damage to the solder joint connecting the lead to the PCB substrate on which the IC is mounted.
  • the piezoelectric sensor e.g. piezoelectric sensor 1420c
  • the bonding wire e.g. bonding wire 1412c
  • the connection interfaces electrically coupling the lead (to which the piezoelectric sensor is attached) to the die
  • the testing of the integrity of the bonding wire and the connection interfaces may be performed prior to the mounting of IC 1400 on PCB 1450, e.g. immediately after fabrication of IC 1400.
  • Such testing may be performed by electrically coupling the power and ground leads (i.e. leads 1410a and 1410b) to an external power source.
  • an IC similar to IC 1400 which differs therefrom in not including a LED (such as LED 1424).
  • the output signal is communicated from the IC, via a lead of the IC, to other processing circuitry on the PCB (on which the IC is mounted), and therefrom, e.g. via a dedicated output port of the PCB, to an external computational component/system.
  • the lead is electrically coupled to the sensor in the IC, but, unlike leads 1410, is not electrically coupled to the die in the IC.
  • steps of methods according to some embodiments may be described in a specific sequence, methods of the disclosure may include some or all of the described steps carried out in a different order.
  • a method of the disclosure may include a few of the steps described or all of the steps described. No particular step in a disclosed method is to be considered an essential step of that method, unless explicitly specified as such.

Abstract

Disclosed is a printed circuit board including a substrate, at least one electronic component solder-joint mounted on the substrate, and at least one piezoelectric sensor attached to the substrate. The piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor. A measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the electronic component.

Description

IN-SITU SYSTEMS AND METHODS FOR DETECTING DAMAGE TO
SOLDER JOINTS
TECHNICAL FIELD
Aspects of the present disclosure, generally relate to in-situ systems and methods for detecting damage to solder joints on a circuit board by monitoring the mechanical response thereof.
BACKGROUND
Failure of solder joints in electronic components and systems can be catastrophic. Sources of failure of solder joints include fatigue due to vibration, overstress, and poor manufacturing practices. Improvements in design (e.g. better packaging, improved materials, and better control of manufacturing processes) are continuously being implemented, but the fact remains that solder joint failures still occur. One way to prevent a solder joint failure from causing critical damage is by detecting the onset of damage, so that the component containing the defect can be removed before the damage results in a total loss of electrical conductivity of the solder joint.
A number of approaches have been proposed for early detection of damage in solder joints. The most common approach is to monitor the electrical resistance of the solder joint, since a growing crack in the solder joint increases the resistance thereof. The problem with defect detection based on electrical resistivity measurements is that the solder joint has to be fairly well compromised (i.e. the crack has to be fairly large) before a detectible change in electrical resistance is possible. Thus, a defect might be detected too late. Also, implementing an in-situ system that can monitor the electrical conductivity of each solder joint is a difficult task.
Other approaches are based on the “canary” principle - the use of test structures fabricated near the components of interest. The test structures are purposely fabricated weaker than the components of interest, so that failure of the test structure provides an indication that the components had been subjected to conditions whereat the solder joints could have been damaged. A related approach is to monitor the electrical conductivity of some of the unused pins on an integrated circuit. This approach is more suited for monitoring the integrity of solder joints of field programmable gate arrays, which may have unused pins and, in addition, may include extra gates in the array which can be used to implement the monitoring circuit. Failure of monitored pins can be used as a trigger to remove the component. However, while“canary” methods provide an indication of whether the more critical solder joints are at risk, they do not provide information on individual solder joints. In particular, they do not take into account that there may be manufacturing defects in the solder joints, which could cause failure before failure of the test structure.
Non-destructive methods, such as acoustic microscopy, X-rays, and RF time domain reflectometry are also used to inspect solder joints. A drawback of these methods, as currently practiced, is that the components need to be removed from the surface and examined in the laboratory.
There remains a need for in-situ methods and systems for early and real-time detection of defects in solder joints, which are more sensitive than current methods and which can be used to inspect each solder joint in the entire system.
SUMMARY
Aspects of the present disclosure, according to some embodiments thereof, relate to in- situ systems and methods for detecting damage to solder joints on a circuit board by monitoring the mechanical response thereof. More specifically, but not exclusively, aspects of the present disclosure, according to some embodiments thereof, relate to in- situ systems and methods for monitoring crack or fissure growth in solder joints on a printed circuit board (PCB) using one or more piezoelectric sensors.
The present disclosure, according to some aspects thereof, teaches self-testing, in-situ systems to detect damage to solder joints on a PCB. The PCB includes at least one piezoelectric sensor configured to be vibrated. According to some embodiments, the piezoelectric sensor may be positioned on the substrate near a solder-joint mounted electronic component (EC) whose solder joints (mounting the EC on the substrate) are to be monitored. According to some embodiments, the piezoelectric sensor is embedded within the substrate below the EC. According to some embodiments, the EC is an integrated circuit (IC). An alternating current passed through the piezoelectric sensor induces vibrations thereof, which may translate to vibrations of the substrate. The vibration amplitude is affected by the strength of the connection between the EC and the substrate (in particular, by the integrity of the solder joints), and influences, in a measurable manner, electric parameters (for example, the impedance) characterizing the piezoelectric sensor.
Advantageously, the systems and methods of the present disclosure do not require removing the PCB from the device/system (e.g. an electronic/computational device or system) in which the PCB is installed (so that the monitoring is performed“in-situ”). According to some embodiments, the disclosed system is“on-board” in the sense that the PCB includes all the components of the disclosed system (in particular, all the components of a sensor interrogator, which analyzes the output of the piezoelectric sensor). In such embodiments, the PCB is“self-testing” in the sense that both the measurements and the processing of the measurement outcomes are performed on the PCB. According to other embodiments, the piezoelectric sensor is on-board but other components of the disclosed system (e.g. components of the sensor interrogator) may be off-board. In such embodiments, the components that are not positioned on the PCB may be positioned instead, for example, on a second PCB in the device/system wherein the PCB (including the piezoelectric sensor) is installed, so that the device/system may be viewed as self-testing. Since the piezoelectric sensor is positioned on the PCB, the disclosed systems and methods allow for monitoring (optionally, in an effectively continuous manner) the integrity of solder joints on the PCB when the PCB is installed in an intended device/system, even when the device/system is operating. Consequently, the disclosed systems and methods allow for the real-time detection of the onset of damage to a solder joint (e.g. the beginning of the formation of a crack in the solder joint) and the provision of an advance warning before the damage becomes critical. An advance warning may be useful and even vital for devices/systems wherein failure may be dangerous and/or destructive, such as computational systems in vehicles, particularly, aerial vehicles, and implanted medical devices, such as cardiac pacemakers and defibrillators. As a further advantage, it is noted that the systems and methods of the present disclosure allow for the in-situ monitoring of each critical solder joint on a PCB, or even of all the solder joints on the PCB.
The present disclosure further teaches self-testing integrated circuits (ICs). Each lead of the IC may include a piezoelectric sensor attached thereto (and electrically decoupled therefrom), which may be sensitive to damage in an associated bonding wire and associated connection interfaces connecting the bonding wire to the lead and to a semiconducting die of the IC. In particular, the connection interfaces connecting bonding wires to a semiconducting die may be suboptimal. The IC further includes a sensor interrogator configured to analyze the outputs of the piezoelectric sensors, and which may be connected to the power and ground leads of the IC. Advantageously, the IC may be tested for the above-specified types of damage (i.e. to the bonding wires and the connection interfaces) also prior to being mounted on a printed circuit board, by connecting the power and ground leads of the IC to an external power source. Thus, according to an aspect of some embodiments, there is provided a printed circuit board (PCB) including a substrate, at least one electronic component (EC) solder-joint mounted on the substrate (connected to the substrate via solder joints), and at least one piezoelectric sensor attached (secured) to the substrate. The piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor. A measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the EC.
According to some embodiments, the at least one EC is an integrated circuit (IC). According to some embodiments, each of the at least one EC may be an IC, a switch, an amplifier, a filter, a rectifier, an inverter, a transistor, a resistor, a capacitor, an inductor, a diode, or any other discrete component. (That is, for example, when there are two ECs, one may be an IC and the other a diode, or one may be a resistor and the other a capacitor, or both may be resistors, and so on.) According to some embodiments, the piezoelectric sensor includes a first terminal and a second terminal electrically coupling the piezoelectric sensor to the sensor interrogator. The sensor interrogator is configured to apply the input voltage to the first terminal.
According to some embodiments, the at least one piezoelectric sensor is attached to the substrate proximately to the EC.
According to some embodiments, the sensor interrogator includes the following components:
- A signal generator configured to apply the input voltage.
- A measurement unit configured to measure the electrical parameter. - A control circuitry functionally associated with the signal generator and the measurement unit and configured to process measurement data obtained by the measurement unit and to determine whether the measurement data are indicative of potential damage to the at least one solder joint.
According to some embodiments, the control circuitry has stored in a memory therein electrical parameter baseline data. The control circuitry is configured to determine whether the measurement data are indicative of potential damage to the at least one solder joint by evaluating a difference between the measured values of the electrical parameter and the electrical parameter baseline data.
According to some embodiments, a piezoelectric element in the piezoelectric sensor is surface bonded to the substrate or embedded within the substrate.
According to some embodiments, the EC is mounted on a top surface of the substrate and the piezoelectric element is surface bonded to a bottom surface of the substrate below the EC.
According to some embodiments, the EC is mounted on the substrate on a top surface of the substrate such as to form a gap between an EC body of the EC and the top surface. The piezoelectric element is surface bonded to the top surface below the EC body. According to some embodiments, the piezoelectric element is glued to the substrate or vacuum deposited on the substrate.
According to some embodiments, the signal generator is configured to apply a sinusoidal, or substantially sinusoidal, voltage signal or current signal. According to some embodiments, the signal generator is configured to sweep a frequency of the voltage signal across a range of frequencies.
According to some embodiments, a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz (e.g. the range of frequencies runs from 20 kHz to 800 kHz or the range of frequencies runs from 10 kHz to 10 GHz). According to some such embodiments, the minimum frequency is greater than about 100 kHz.
According to some embodiments, the control circuitry is configured to repeatedly (i) command the signal generator to apply the input voltage the piezoelectric sensor (e.g. to the first terminal thereof) and (ii) command the measurement unit to measure the electrical parameter of the piezoelectric sensor, as long as the measurement data are not indicative of potential damage to the at least one solder joint.
According to some embodiments, the electrical parameter is an electrical impedance of the piezoelectric sensor, or a current through the (two) terminals of the piezoelectric sensor, or a voltage across the piezoelectric sensor. According to some embodiments, the measured values of the electrical parameter are indicative of an integrity of, or damage to, solder material of the at least one solder joint.
According to some embodiments, the at least one EC includes a plurality of ECs and the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Each of the plurality of piezoelectric sensors is attached to the substrate more closely (i.e. nearer) to a respective EC from the plurality of ECs than to any other one of the ECs. (It will be understood that the ECs in the plurality of ECs may differ from one another, e.g. one may be an IC, another may be a diode, two may be capacitors that differ in capacitance, and so on.) According to some embodiments, the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Each of the piezoelectric sensors is attached to the substrate such as to be closer (i.e. nearer) to a respective solder joint, from the at least one solder joint and associated with the at least one EC, than to any one of the other solder joints.
According to some embodiments, each of the at least one solder joint has a respective piezoelectric sensor, from the plurality of piezoelectric sensors, attached more closely thereto than to any one of the other solder joints.
According to some embodiments, the sensor interrogator is configured to allow interrogating each of the plurality of piezoelectric sensors one at a time. According to some such embodiments, the sensor interrogator includes a multiplexer mounted on the substrate. The multiplexer is electrically connected to the plurality of piezoelectric sensors such as to allow interrogating each of the plurality of piezoelectric sensors one at a time. According to some embodiments, the control circuitry is configured to evaluate the difference between the measured values of the electrical parameter and the electrical parameter baseline data by computing a root-mean-square difference (RMSD) associated therewith.
According to some embodiments, the signal generator and the measurement unit are configured for continuous monitoring of the at least one solder joint.
According to some embodiments, the PCB includes the sensor interrogator. The sensor interrogator is located on the substrate and powered by an operating voltage of the PCB.
According to some embodiments, the control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint associated with the EC.
According to some embodiments, the control circuitry is configured to trigger the output signal when the computed RMSD is greater than a threshold value. According to some embodiments, the output signal is an electrical signal sent to an external computational component/system (e.g. an external processing circuitry, an external electronic circuitry, a second PCB, an external controller, a computational device, etc.). According to some embodiments, the sensor interrogator further includes a light emitting diode (LED). The LED is functionally associated with the control circuitry and configured to receive therefrom a trigger signal to emit light as the output signal.
According to an aspect of some embodiments, there is provided a system for detecting damage to one or more solder joints on a printed circuit board (PCB). The system includes the PCB and the sensor interrogator, described above according to some embodiments, wherein at least some of the components of the sensor interrogator are off-board.
According to an aspect of some embodiments, there is provided a system for detecting damage to solder joints on printed circuit boards (PCBs). The system includes a plurality of the PCB, described above according to some embodiments, and the sensor interrogator, described above according to some embodiments, wherein the sensor interrogator is off-board and configured to interrogate the at least one piezoelectric sensor on each of the plurality of PCBs, respectively.
According to an aspect of some embodiments, there is provided a method for detecting damage to one or more solder joints on a printed circuit board (PCB). The method includes steps of:
- Applying an input voltage to at least one piezoelectric sensor (e.g. to a first terminal thereof), respectively. The at least one piezoelectric sensor is attached to the PCB. The PCB includes at least one electronic component (EC) solder- joint mounted on the PCB.
- Measuring at least one electrical parameter of the piezoelectric sensor. The electrical parameter is sensitive to damage to at least one solder joint associated with the EC. - Determining potential damage to the at least one solder joint, or lack of damage, based on a measured value or measured values of the at least one electrical parameter.
According to some embodiments of the method, the at least one EC is an integrated circuit (IC).
According to some embodiments of the method, each of the at least one EC may be an IC, a transistor, a switch, an amplifier, a filter, a rectifier, an inverter, a resistor, a capacitor, an inductor, a diode, or any other discrete component.
According to some embodiments of the method, the at least one piezoelectric sensor is attached to the PCB proximately to the EC.
According to some embodiments of the method, the step of determining potential damage includes a sub-step of evaluating a difference between the measured values of the electrical parameter and electrical parameter baseline data. The difference is indicative of integrity of, or damage to, the at least one solder joint. According to some embodiments of the method, the method further includes an initial step of performing a baseline measurement to obtain the electrical parameter baseline data, the initial step includes sub-steps of:
- Applying an input voltage to the piezoelectric sensor.
- Measuring the electrical parameter of the piezoelectric sensor to obtain the electrical parameter baseline data.
- Storing in a memory the electrical parameter baseline data.
According to some embodiments of the method, the step of applying the input voltage, the step of measuring the electrical parameter, and the step of determining, are repeated, optionally periodically, as long as, in the step of determining potential damage, no potential damage to the at least one solder joint has been determined.
According to some embodiments of the method, a piezoelectric element in the piezoelectric sensor is surface bonded to the PCB or embedded within the PCB. According to some embodiments of the method, the EC is mounted on the PCB on a top surface of the PCB and the piezoelectric element is surface bonded to the PCB on a bottom surface of the PCB below the EC.
According to some embodiments of the method, the EC is mounted on the PCB on a top surface of the PCB such as to form a gap between an EC body of the EC and the top surface. The piezoelectric element is surface bonded to the top surface below the EC body.
According to some embodiments of the method, a sinusoidal or substantially sinusoidal voltage signal, or current signal, is applied to the piezoelectric sensor in the step of applying the input voltage.
According to some embodiments of the method, a frequency of the sinusoidal voltage signal is swept across a range of frequencies.
According to some embodiments of the method, a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz. According to some such embodiments, the minimum frequency is greater than about 100 kHz.
According to some embodiments of the method, the PCB further includes a sensor interrogator electrically coupled to the at least one piezoelectric sensor and being configured to apply input voltages to each of the at least one piezoelectric sensors, to measure the electrical parameters associated with each of the at least one piezoelectric sensors, respectively, and to determine whether the measured values of the electrical parameter(s) are indicative of damage to one or more of the at least one solder joint.
According to some embodiments of the method, the at least one EC includes a plurality of ECs and the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Each of the piezoelectric sensors is attached to the PCB such as to be closer to a respective EC from the plurality of ECs than any other one of the ECs.
According to some embodiments of the method, the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Each of the piezoelectric sensors is attached to the PCB such as to be closer to a respective solder joint, from the at least one solder joint and associated with the at least one EC, than to any other one of the solder joints.
According to some embodiments of the method, the method further includes a step of providing an output signal when in the step of determining potential damage it is determined that the measured values of the electrical parameter are indicative of damage to the at least one solder joint.
According to some embodiments of the method, the output signal is an electrical signal sent to an external computational component/system.
According to some embodiments of the method, the sensor interrogator further includes a light emitting diode (LED), and wherein the output signal is light emitted by the LED.
According to some embodiments of the method, the electrical parameter of the piezoelectric sensor is an electrical impedance of the piezoelectric sensor.
According to some embodiments of the method, the step of applying the input voltage and the step of measuring the electrical parameter are performed simultaneously or substantially simultaneously.
According to some embodiments of the method, the step of applying the input voltage and the step of measuring the electrical parameter are performed continuously.
According to some embodiments of the method, the sub-step of evaluating the difference includes computing a root-mean-square difference (RMSD) associated with the measured values of the electrical parameter and electrical parameter baseline data and wherein the computed RMSD being greater than a threshold is indicative of potential damage to the at least one solder joint.
According to an aspect of some embodiments, there is provided a printed circuit board (PCB) including a substrate, at least one electronic component (EC) solder-joint mounted on the substrate, and at least one piezoelectric sensor attached to the EC. The piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor. A measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the EC.
According to some embodiments, the at least one EC is an integrated circuit (IC).
According to some embodiments, each of the at least one EC is an IC, a switch, an amplifier, a filter, a rectifier, an inverter a transistor, a resistor, a capacitor, an inductor, or a diode.
According to some embodiments, wherein the EC is an IC, the piezoelectric sensor is electrically connected to a pair of leads of the IC such as to allow actuation of the piezoelectric sensor. According to some embodiments, the piezoelectric sensor is mounted on the EC. According to some such embodiments, the sensor interrogator is mounted on the EC.
According to some embodiments, the piezoelectric sensor is housed within the EC. According to some such embodiments, the sensor interrogator is housed within the EC.
According to an aspect of some embodiments, there is provided an integrated circuit (IC) including a chip package housing therein a semiconducting die, at least one piezoelectric sensor, and a sensor interrogator. The IC further includes a plurality of leads electrically coupled to the semiconducting die and extending from within the chip package (i.e. the inside of the chip package) to the outside thereof. The at least one piezoelectric sensor is attached to at least one of the plurality of leads, respectively, such as to be electrically insulated therefrom. The sensor interrogator is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor. When the IC is mounted on a printed circuit board (PCB), a measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint connecting the at least one of the plurality of leads, respectively, to (a substrate of) the PCB.
According to some embodiments of the IC, the semiconducting die, the at least one piezoelectric sensor, and the sensor interrogator are encapsulated within the chip package. According to some embodiments of the IC, the piezoelectric sensor includes a first terminal and a second terminal electrically coupling the piezoelectric sensor to the sensor interrogator. The sensor interrogator is configured to apply the input voltage to the first terminal. According to some embodiments of the IC, the sensor interrogator includes the following components:
- A signal generator configured to apply the input voltage.
- A measurement unit configured to measure the electrical parameter.
- A control circuitry functionally associated with the signal generator and the measurement unit and configured to process measurement data obtained by the measurement unit and to determine whether the measurement data are indicative of potential damage to the at least one solder joint.
According to some embodiments of the IC, the control circuitry has stored in a memory therein electrical parameter baseline data. The control circuitry is configured to determine whether the measurement data are indicative of potential damage to the at least one solder joint by evaluating a difference between the measured values of the electrical parameter and the electrical parameter baseline data.
According to some embodiments of the IC, a piezoelectric element in the at least one piezoelectric sensor is glued to the at least one of the plurality of leads. According to some embodiments of the IC, the signal generator is configured to apply a sinusoidal, or substantially sinusoidal, voltage signal or current signal.
According to some embodiments of the IC, a frequency of the voltage signal is swept across a range of frequencies.
According to some embodiments of the IC, the range of frequencies runs from about 5 kHz to about 10 GHz.
According to some embodiments of the IC, the control circuitry is configured to repeatedly (i) command the signal generator to apply the input voltage to the at least one piezoelectric sensor and (ii) command the measurement unit to measure the electrical parameter of the at least one piezoelectric sensor, when the IC is mounted on the PCB, as long as the measurement data are not indicative of potential damage to the at least one solder joint. According to some embodiments of the IC, the electrical parameter is an electrical impedance of the piezoelectric sensor, or a current through the piezoelectric sensor, or a voltage across the piezoelectric sensor.
According to some embodiments of the IC, the measured values of the electrical parameter are indicative of an integrity of, or damage to, solder material of the at least one solder joint.
According to some embodiments of the IC, the at least one piezoelectric sensor includes a plurality of piezoelectric sensors. Two or more of the plurality of leads may each have attached thereon two or more piezoelectric sensors, respectively, from the plurality of piezoelectric sensors. According to some such embodiments, each of the plurality has attached thereon one piezoelectric sensor from the plurality of piezoelectric sensors.
According to some embodiments of the IC, the sensor interrogator is configured to allow interrogating each of the plurality of piezoelectric sensors one at a time. According to some such embodiments, the sensor interrogator includes a multiplexer. The multiplexer is electrically connected to the plurality of piezoelectric sensors such as to allow interrogating each of the plurality of piezoelectric sensors one at a time.
According to some embodiments of the IC, the control circuitry is configured to evaluate the difference between the measured values of the electrical parameter and the electrical parameter baseline data by computing a root-mean-square difference (RMSD) associated therewith. According to some embodiments of the IC, the at least one piezoelectric sensor is positioned proximately to at least one bonding wire electrically coupling the at least one of the plurality of leads, respectively, to the semiconducting die. The at least one piezoelectric sensor is thereby configured to detect damage to the at least one bonding wire and to connection interfaces connecting the at least one bonding wire to the at least one of the plurality of leads and to the semiconducting die.
According to some embodiments of the IC, the signal generator and the measurement unit are configured for continuous monitoring of the at least one solder joint. According to some embodiments of the IC, the signal generator and the measurement unit are configured for continuous monitoring of the at least one solder joint and the at least one bonding wire and the connection interfaces.
According to some embodiments of the IC, the control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint.
According to some embodiments of the IC, the control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint and/or the at least one bonding wire and/or the connection interfaces. According to some embodiments of the IC, the control circuitry is configured to trigger the output signal when the computed RMSD is greater than a threshold value.
According to some embodiments of the IC, the output signal is an electrical signal configured to be sent to processing circuitry external to the IC.
According to some embodiments of the IC, the IC further includes a light emitting diode (LED) attached to, or embedded on, the chip package. The LED is functionally associated with the control circuitry and configured to receive therefrom a trigger signal to emit light as the output signal.
According to an aspect of some embodiments, there is provided a method for detecting damage to one or more solder joints connecting an integrated circuit (IC) to a printed circuit board (PCB). The method includes steps of:
- Providing a PCB having mounted thereon an IC including a chip package housing therein a semiconducting die and one or more piezoelectric sensors. The IC further includes a plurality of leads electrically coupled to the semiconducting die and extending from within the chip package to the outside thereof such as to connect the chip package to the PCB via respective solder joints. The one or more piezoelectric sensors are attached to one or more of the plurality of leads, respectively, such as to be electrically insulated therefrom. - Applying an input voltage to each of the one or more piezoelectric sensors.
- Measuring at least one electrical parameter of each of the one or more piezoelectric sensors. The at least one electrical parameter being sensitive to damage to one or more of the solder joints, respectively.
- Determining potential damage to the one or more of the solder joints, or lack of damage, based on a measured value or measured values of the at least one electrical parameter.
According to some embodiments of the method, the chip package further includes a sensor interrogator electrically coupled to the one or more piezoelectric sensors and configured to apply input voltages to each of the one or more piezoelectric sensors, to measure the electrical parameters associated with the one or more piezoelectric sensors, respectively, and to determine whether the measured values of the at least one electrical parameter are indicative of damage to the one or more of the solder joints.
According to some embodiments of the method, the one or more piezoelectric sensors are glued to the one or more of the plurality of leads, respectively. According to some embodiments of the method, the step of determining potential damage includes a sub-step of evaluating a difference between the measured values of the electrical parameter and electrical parameter baseline data. The difference is indicative of integrity of, or damage to, the one or more of the solder joints.
According to some embodiments of the method, the method further includes an initial step of performing a baseline measurement to obtain the electrical parameter baseline data, the initial step includes sub-steps of:
- Applying an input voltage each of to the one or more piezoelectric sensors (e.g. one at a time). - Measuring the electrical parameter of each the one or more piezoelectric sensors, respectively to obtain the electrical parameter baseline data.
- Storing in a memory the electrical parameter baseline data.
According to some embodiments of the method, the step of applying the input voltage, the step of measuring the electrical parameter, and the step of determining, are repeated, optionally periodically, as long as, in the step of determining potential damage, no potential damage to the one or more of the solder joints has been determined.
According to some embodiments of the method, a sinusoidal or substantially sinusoidal voltage signal, or current signal, is applied to each of the one or more piezoelectric sensors in the step of applying the input voltage.
According to some embodiments of the method, a frequency of the sinusoidal voltage signal is swept across a range of frequencies.
According to some embodiments of the method, a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz. According to some such embodiments, the minimum frequency is greater than about 100 kHz.
According to some embodiments of the method, the method further includes a step of providing an output signal when in the step of determining potential damage it is determined that the measured values of the electrical parameter are indicative of damage to the one or more of the solder joints (that is, to at least one of the monitored solder joints).
According to some embodiments of the method, the output signal is an electrical signal sent to an external computational component/system.
According to some embodiments of the method, the IC further includes a light emitting diode (LED). The output signal is light emitted by the LED. According to some such embodiments, the LED is positioned on the chip package (e.g. glued thereon) or embedded thereon. According to some embodiments of the method, the electrical parameter is an electrical impedance of the piezoelectric sensor.
According to some embodiments of the method, the step of applying the input voltage and the step of measuring the electrical parameter are performed simultaneously or substantially simultaneously.
According to some embodiments of the method, the step of applying the input voltage and the step of measuring the electrical parameter are performed continuously.
According to some embodiments of the method, the sub-step of evaluating the difference includes computing a root-mean-square difference (RMSD) associated with the measured values of the electrical parameter and the electrical parameter baseline data. The computed RMSD being greater than a threshold is indicative of potential damage to the one or more of the solder joints (that is, to at least one of the monitored solder joints).
According to some embodiments of the method, the one or more piezoelectric sensors are positioned proximately to one or more bonding wires, respectively. The bonding wires electrically couple the one or more of the plurality of leads, respectively, to the semiconducting die. The one or more piezoelectric sensors are thereby configured to additionally detect damage to the one or more bonding wires and to connection interfaces connecting the one or more bonding wires to the one or more of the plurality of leads, respectively, and the semiconducting die.
According to some embodiments of the method, the method further includes, prior to mounting the IC on the PCB, a step of testing the integrity of the one or more bonding wires and the connection interfaces associated therewith, by electrically connecting power and ground leads of the IC to an external power source, and (i) applying an input voltage to each of the one or more piezoelectric sensors, (ii) measuring at least one electrical parameter of each of the one or more piezoelectric sensors, each of the at least one electrical parameter being respectively sensitive to damage to the one or more bonding wires, respectively, and the respective connection interfaces associated therewith, and (iii) determining potential damage to each of the one or more bonding wires and the connection interfaces associated therewith, or lack of damage, based on a measured value or measured values of the at least one electrical parameter.
Certain embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In case of conflict, the patent specification, including definitions, governs. As used herein, the indefinite articles“a” and“an” mean“at least one” or“one or more” unless the context clearly dictates otherwise.
BRIEF DESCRIPTION OF THE FIGURES
Some embodiments of the disclosure are described herein with reference to the accompanying figures. The description, together with the figures, makes apparent to a person having ordinary skill in the art how some embodiments may be practiced. The figures are for the purpose of illustrative description and no attempt is made to show structural details of an embodiment in more detail than is necessary for a fundamental understanding of the disclosure. For the sake of clarity, some objects depicted in the figures are not to scale.
In the Figures:
Figure la schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments; Figure lb schematically depicts a cross-section of the printed circuit board of Fig. la, according to some embodiments; Figure lc schematically depicts a cross-section of the printed circuit board of Fig. la, wherein a solder joint is damaged such that a pin end portion is loose, according to some embodiments;
Figure 2 schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
Figure 3 schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments; Figure 4 schematically depicts a self-testing printed circuit board including a piezoelectric sensor configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
Figure 5a is a block diagram of a self-testing printed circuit board including one or more piezoelectric sensors configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
Figure 5b is a circuit diagram of electronic components of the self-testing circuit board of Fig. 5a, according to some embodiments;
Figure 6 is a block diagram of a self-testing printed circuit board including one or more piezoelectric sensors configured for monitoring integrity of one or more solder joints on the printed circuit board, according to some embodiments;
Figure 7 is a block diagram of a system for detecting damage to solder joints on a printed circuit board, the printed circuit board including one or more piezoelectric sensors, according to some embodiments;
Figure 8 is a block diagram of a system for detecting damage to solder joints on a printed circuit board, the printed circuit board including one or more piezoelectric sensors, according to some embodiments;
Figure 9 is a flowchart of a piezoelectric sensor-based method for detecting damage to solder joints on a printed circuit board, according to some embodiments; Figures 10a and 10b present experimental data demonstrating utility of the disclosed systems and methods in detecting damage to solder joints on circuit boards;
Figures 11 and 12 present experimental data demonstrating utility of the disclosed systems and methods in detecting damage to solder joints on circuit boards; Figure 13a is a circuit diagram of an experimental system used to obtain the experimental data presented in Figs. 10a-12;
Figure 13b is a photograph of a circuit board of the experimental system of Fig. 13a;
Fig. 14a schematically depicts a self-testing integrated circuit including a plurality of piezoelectric sensors, according to some embodiments; and Fig. 14b is a schematic, partial, cross-sectional view of a printed circuit board and the integrated circuit of Fig. 14a mounted thereon, according to some embodiments.
DETAILED DESCRIPTION
The principles, uses, and implementations of the teachings herein may be better understood with reference to the accompanying description and figures. Upon perusal of the description and figures present herein, one skilled in the art will be able to implement the teachings herein without undue effort or experimentation. In the figures, same reference numerals refer to same parts throughout.
In the description and claims of the application the expression“at least one of A and B”, (e.g. wherein A and B are elements, method steps, claim limitations, etc.) is equivalent to“only A, only B, or both A and B”. In particular, the expressions“at least one of A and B”,“at least one of A or B”,“one or more of A and B”, and“one or more of A or B” are interchangeable.
In the description and claims of the application, the words“include” and“have”, and forms thereof, are not limited to members in a list with which the words may be associated.
As used herein, the term“about” may be used to specify a value of a quantity or parameter (e.g. the length of an element) to within a continuous range of values in the neighborhood of (and including) a given (stated) value. According to some embodiments,“about” may specify the value of a parameter to be between 80 % and 120 % of the given value. For example, the statement“the length of the element is equal to about 1 m” is equivalent to the statement“the length of the element is between 0.8 m and 1.2 m”. According to some embodiments,“about” may specify the value of a parameter to be between 90 % and 110 % of the given value. According to some embodiments,“about” may specify the value of a parameter to be between 95 % and 105 % of the given value.
As used herein, according to some embodiments, the terms“substantially” and“about” may be interchangeable.
For ease of description, in some of the figures a three-dimensional cartesian coordinate system (with orthogonal axes x, y, and z) is introduced. It is noted that the orientation of the coordinate system relative to a depicted object may vary from one figure to another. Further, the symbol Q may be used to represent an axis pointing“out of the page”, while the symbol ® may be used to represent an axis pointing“into the page”.
As used herein, according to some embodiments, the term“printed circuit board” is used to refer in short to a printed circuit board assembly (i.e. the substrate (the“naked” printed circuit board) with electronic components, e.g. integrated circuits, mounted thereon).
As used herein, according to some embodiments, the term“piezoelectric sensor” may refer to a piezoelectric element (e.g. a piezoelectric crystal, a PZT disc, or the like) and a pair of terminals attached to the piezoelectric element, e.g. to opposite surfaces thereof, such that, when the piezoelectric element is deformed (e.g. compressed), a potential difference (voltage) is generated between the terminals. Piezoelectric sensors may be used in electro-mechanical impedance (EMI) sensing. EMI sensing is based on the principle that the electrical impedance (i.e. voltage/current) of a piezoelectric sensor bonded to a structure is related to the mechanical impedance (i.e. force/velocity) of the structure.
As used herein, according to some embodiments, the term“port” (e.g.“input port”, “output port”) with reference to a printed circuit board (PCB), is used in a broad sense to refer to both female components such as sockets, or male components such as fingers, and/or the like. The ports are configured for receiving inputs from one or more external processing circuitries and/or sending outputs to one or more external processing circuitries (which may differ from the external processing circuitries from which the inputs are received). A pair of input-output ports may be used to power PCB components between an operating voltage Vcc and the ground. Other input ports may be used to provide data/inputs, received from one or more external processing circuitries, to PCB components, particularly integrated circuits. Other output ports may be used to send data/outputs from PCB components to one or more external processing circuitries. As used herein, according to some embodiments, the term“processing circuitry” may refer to one or more processors and memory components.
As used herein, according to some embodiments, the term“external computational component/system” with reference to a described PCB, refers to a computational component/system which is off-board, that is, not included in the PCB (e.g. not mounted on the substrate of the PCB), such as, for example, a second PCB or a processing circuitry included in the second PCB.
As used herein, the term“measurement” and related forms thereof (e.g.“measure”), with reference to a physical parameter/quantity, are used in a broad sense which includes both“direct measurements”, e.g. when a voltage across a resistor is measured using a voltmeter connected in parallel thereto, and“indirect measurements”, e.g. when the voltage across a circuit element is measured by directly measuring the voltage on a resistor connected in series to the circuit element and forming a voltage divider therewith. Another example of an“indirect measurement” is one wherein a second physical parameter - from which the (first) physical parameter can be derived/inferred or at least estimated - is directly/indirectly measured, e.g. indirect measurement of the electrical impedance may refer to a direct/indirect measurement of one or more other electrical parameters of the circuit element (e.g. the voltage across the circuit element) from which the electrical impedance can be derived/inferred.
Self-testins printed circuit boards and systems Fig. la schematically depicts a partial, top-view of a printed circuit board (PCB) 100, according to some embodiments. PCB 100 includes a substrate 102, an integrated circuit (IC) 106, a piezoelectric sensor 110, and a sensor interrogator 114. IC 106 is mounted on a substrate (e.g. using surface mount technology). More specifically, IC 106 includes pins 120 (not all are numbered). Pins 120 are soldered onto solder pads 124 (e.g. copper surfaces on substrate 102, shown in Fig. lb), respectively, using solder material 128, such as to form respective solder joints 130 (shown in Fig. lb).
As used herein, according to some embodiments, the term“solder joint” may refer to an end portion of a lead or a pin (whereby the lead/pin is soldered onto a substrate of PCV, for example, to a conductive track (e.g. a copper trace) on the substrate or to a solder pad on the substrate) and a connection interface (e.g. a solder material connecting the lead/pin to the substrate). According to some embodiments, wherein the end portion of the lead/pin is soldered onto a solder pad on the substrate, the term“solder joint” may refer to the end portion of the lead/pin, the solder material (connecting the lead/pin to the solder pad), and the solder pad. As used herein, according to some embodiments, the term“pin” with reference to solder-joint mountable ECs, refers to an exposed portion of a lead of the EC, that is, the portion of the lead which extends outside the body of the EC (e.g. in an IC, the pin may refer to the portion of the lead which is external to the chip package). According to some embodiments, the term“solder joint” refers to the full extent of the pin (or the full extent of the exposed portion of the lead), the solder material, and the solder pad.
As used herein, according to some embodiments, a solder joint is said to be associated with an EC when at least an end portion of a lead/pin of the EC forms part of the solder joint.
Piezoelectric sensor 110 is attached (secured) to substrate 102 proximately (near) IC 106. According to some embodiments, piezoelectric sensor 110 is surface bonded to, or embedded within, substrate 102. Piezoelectric sensor 110 includes a piezoelectric element 140 and a pair of terminals 142 attached to the piezoelectric element 140, e.g. on opposite sides thereof. Piezoelectric element 140 is electrically coupled to sensor interrogator 114 via electrical lines (e.g. copper traces) 144, as elaborated on below. Additional electrical lines, e.g. electrical lines connecting sensor interrogator 114 to the power and ground ports of the PCB, are not shown, and neither are the ports.
As used herein, the term “attached”, particularly when used in reference to a piezoelectric sensor and a PCB, may refer to (i) a direct attachment of the piezoelectric sensor to the substrate of the PCB wherein the piezoelectric sensor contacts the substrate, as well as to (ii) an indirect attachment of the piezoelectric sensor to the substrate of the PCB wherein the piezoelectric sensor does not contact the substrate but instead contacts an intermediate component which may be directly attached to the substrate. As used herein, according to some embodiments, the terms“attached” and “secured” may be used interchangeably.
Sensor interrogator 114 is mounted on substrate 102. Sensor interrogator 114 is configured to apply an input voltage (e.g. a varying voltage signal) to one of terminals 142 (e.g. an input terminal configured to receive an input voltage from a signal generator) and to measure the electrical impedance of piezoelectric element 140 (or, according to some embodiments, one or more other electrical parameters of piezoelectric element 140), as elaborated on below. Sensor interrogator 114 includes a signal generator (e.g. sine-wave generator) and a measurement unit, e.g. an impedance measurement unit, as elaborated on below.
Substrate 102 includes two surfaces: a top surface 152 (in some embodiments, also referred to as“component side”) and a bottom surface 154 (in some embodiments referred to as“print side”), below (i.e. opposite) to top surface 152. Surfaces 152 and 154 are indicated in Fig. lb.
According to some embodiments, not depicted in Fig. la, PCB 100 includes a plurality of ICs and a plurality of piezoelectric sensors. Each of the piezoelectric sensors is located in/on substrate 102 proximately to a respective IC from the plurality of ICs (similarly to piezoelectric 110 positioning relative to IC 106). Each of the piezoelectric sensors is sensitive to damage in solder joints of the respective IC.
Fig. lb is a (partial) transverse, cross-sectional view of PCB 100 taken along a line A-A (shown in Fig. la). A region of a solder joint 130a (from solder joints 130) of a pin 120a (from pins 120) is also shown enlarged at the bottom of the Fig. la. Solder joint 130a is shown in a damaged condition, with a solder material 128a of solder joint 130a exhibiting a crack C. Also indicated is a solder pad 124a of solder joint 130a.
According to some embodiments, piezoelectric sensor 110 is bonded to substrate 102 on top surface 152. For example, piezoelectric sensor 110 may be glued to, or deposited (e.g. vacuum deposited) on, top surface 152. According to some embodiments, piezoelectric sensor 110 is embedded on top surface 152.
According to some embodiments, PCB 100 includes a plurality of solder-joint mountable electronic components (such as ICs, switches, amplifiers, filter, rectifiers, inverters, transistors, and the like, as well as resistors, capacitors, inductors, diodes, and other types of discrete components), and a plurality of piezoelectric sensors. More specifically, PCB 100 includes at least one additional electronic component (EC) beyond IC 106, and at least one additional piezoelectric sensor beyond piezoelectric sensor 110 and similar to piezoelectric sensor 110. Each piezoelectric sensor is located near a respective EC from the plurality of ECs (e.g. piezoelectric sensor 110 is located proximately to IC 106), being thereby configured for monitoring solder joint integrity (i.e. being sensitive to solder joint damage) in the respectively associated EC.
According to some embodiments, piezoelectric sensor 110 is positioned more closely to solder joint 130a than the rest of solder joints 130. According to some such embodiments, due to the positioning thereof, piezoelectric sensor 110 may be more sensitive to damage to solder joint 130a than damage to the rest of solder joints 130.
According to some embodiments, not depicted in the figures, PCB 100 includes a plurality of piezoelectric sensors, such as piezoelectric sensor 110, each of the piezoelectric sensors being located proximately to a respective solder joint from solder joints 130.
It is noted that damage to the solder-joints associated with the power pin (the pin through which operating voltage Vcc is supplied to the IC) and the ground pin of an IC may be more critical than damage to the solder-joints associated with other pins of the IC. Thus, according to some embodiments, PCB 100 includes two piezoelectric sensors. A first piezoelectric sensor is located in proximity to a first solder joint attaching the power pin of the IC to the substrate, being thereby particularly sensitive to damage in the first solder joint. The second piezoelectric sensor is located in proximity to a second solder joint attaching the ground pin of the IC to the substrate, being thereby particularly sensitive to damage in the second solder joint.
Fig. lc shows how a crack in a solder joint leads to the (associated) pin imposing a decreased mechanical constraint on the PCB. That is, the boundary conditions of the PCB change when any type of mechanical constraint changes, resulting in a different mechanical response and a changed vibration spectrum, as elaborated on below. More specifically, Fig. lc is a (partial) transverse, cross-sectional view of PCB 100 taken along line A-A with PCB 100 being in a state wherein solder joint 130a is damaged and with crack C present (piezoelectric sensor 110 is not shown in Fig. lc). The presence of crack C may result in a loosening of pin 120a attachment to substrate 102, as indicated by a dashed outline O. Dashed outline O delineates a pin end portion 132a of pin 120a in a state wherein pin end portion 132a is not attached in full to solder pad 124a (i.e. only a left part of pin end portion 132a is attached to solder pad 124a). Also indicated is an IC body 134 (i.e. IC 106 excluding pins 120) of IC 106.
Fig. 2 is a (partial) transverse cross-sectional view of a PCB 200. PCB 200 is similar to PCB 100 but differs therefrom in that the piezoelectric sensor of PCB 200 is embedded within the substrate of PCB 200 (instead of being attached on top of the substrate). More specifically, PCB 200 includes a substrate 202 similar to substrate 102, and a piezoelectric sensor 210 similar to piezoelectric sensor 110. PCB 200 further includes IC 106 and a sensor interrogator (not shown) similar to sensor interrogator 114. Piezoelectric sensor 210 is embedded within substrate 202 beneath IC 106.
According to some embodiments, piezoelectric sensor 210 is embedded within substrate 202 below solder pad 124a, such as to potentially be more sensitive to damage to solder joint 130a than damage to the rest of solder joints 130. According to some embodiments, below each of solder pads 124 a respective piezoelectric sensor, essentially similar to piezoelectric sensor 210, is embedded.
Fig. 3 is a (partial) transverse, cross-sectional view of a PCB 300. PCB 300 is similar to PCB 100 but differs therefrom in that the piezoelectric sensor of PCB 300 is located on the bottom surface of the substrate of PCB 300 (instead of being attached on top of the substrate). More specifically, PCB 300 includes a substrate 302 similar to substrate 102, and a piezoelectric sensor 310 similar to piezoelectric sensor 110. PCB 300 further includes IC 106 and a sensor interrogator (not shown) similar to sensor interrogator 114. Piezoelectric sensor 310 is attached to a bottom surface 354 of substrate 302 beneath IC
106.
Fig. 4 is a (partial) transverse, cross-sectional view of a PCB 400 similar to PCB 100. PCB 400 includes a substrate 402 similar to substrate 102, an IC 406 similar to IC 106, a piezoelectric sensor 410 similar to piezoelectric sensor 110, and a sensor interrogator (not shown) similar to sensor interrogator 114. An IC body 434 of IC 406 is elevated by solder joints 430 relative to substrate 402, such as to define a gap (indicated by a double -headed arrow G) between a top surface 452 of substrate 402 and a bottom surface 415 of IC body 434. Piezoelectric sensor 410 is located in the gap between top surface 452 and bottom surface 415, being attached to top surface 452 of substrate 402 beneath IC body 434. Also indicated are pins 420, solder pads 424, and a solder material 428.
While the above embodiments, depicted in Figs, la-4, have focused on using piezoelectric sensors for monitoring the integrity of solder joints connecting pins/leads of an IC to a substrate of a PCB, the scope of the present disclosure also covers use of the above-described technology to monitor, in essentially the same way, solder joints used to connect other electric components (ECs) to a PCB, such as diodes, resistors, capacitors, inductors, transistors, switches, amplifiers, filter, rectifiers, inverters, and the like. It will also be understood that the leads of an EC may be soldered to conductive tracks on a substrate of a PCB or to solder pads on the substrate. The scope of the present disclosure covers both options, as well as any other option whereby an EC is similarly mounted on a substrate of a PCB via soldering.
As used herein, according to some embodiments,“proximately to”,“in proximity to”, and“near” may be used interchangeably.
According to some embodiments, a piezoelectric sensor may be said to be positioned (e.g. mounted on a substrate) proximately to an electronic component (EC) (which is also mounted on the substrate), when positioned closer (nearer) to the EC than to any other EC which is secured to the substrate via a solder joint connection. According to some embodiments, a piezoelectric sensor may be said to be positioned proximately to an EC, when positioned at a distance no greater than the smaller of the two planar dimensions of the EC - the planar dimensions being parallel to the surface of the PCB (e.g. the Av-plancs in Figs, la and lb). Thus, for example, in Fig. 1A the smaller of the two planar dimensions of IC 106 is given by a width W of IC 106.
According to some embodiments, a piezoelectric sensor may be said to be positioned proximately to a lead of an EC mounted on a substrate (e.g. a pin of an IC), when positioned closer to the lead than to any other lead (particularly of the EC). According to some embodiments, a piezoelectric sensor may be said to be positioned proximately to a first lead of an EC, when positioned at a distance from the first lead of no more than 25 % of the distance between the first lead and a nearest neighbor second lead (i.e. a second lead which is closest to the first lead). The distance between two nearest neighbor pins or leads may be referred to as the“inter-pin distance” or“inter-lead distance”.
Fig. 5a is a block diagram of a PCB 500. Optional components are designated by boxes having dashed outlines. PCB 500 may be similar to PCBs 100-400. In particular, PCB 500 may be a specific embodiment of each of PCBs 100, 200, 300, or 400, respectively. Each possibility corresponds to a separate embodiment. The skilled person will appreciate that Fig. 5a may also be descriptive of functional interrelations between components in each of PCBs 100-400 (e.g. between piezoelectric sensor 110 and sensor interrogator 114 in PCB 100), according to some embodiments thereof.
PCB 500 includes a substrate 502, one or more ECs 506, one or more piezoelectric sensors 510, and a sensor interrogator 514. Each of piezoelectric sensors 510 is located proximately to a respective EC from ECs 506. According to some embodiments, sensor interrogator 514 includes a signal generator 521, an electrical impedance measurement unit 525, a micro-controller 529, and, in some embodiments, wherein PCB 500 includes more than a single piezoelectric sensor, also a multiplexer 533.
In Fig. 5a, as a non-limiting example, ECs 506 are depicted as including three ECs: an EC 506a, an EC 506b, and an EC 506c. It will be understood that ECs 506 may differ from one another. As a non-limiting example, EC 506a may be an IC, EC 506b may be a resistor, and EC 506c may be a capacitor. Further, each of piezoelectric sensors 510 is distinguished accordingly to account for the possibility that in some embodiments, piezoelectric sensors may differ from one another, each being optimized to detect damage to the EC (of ECs 506) in proximity to which it is positioned. That is, in Fig. 5a, as a non-limiting example, piezoelectric sensors 510 include a piezoelectric sensor 510a positioned proximately to EC 506a, a piezoelectric sensor 510b positioned proximately to EC 506b, and a piezoelectric sensor 510c positioned proximately to EC 506c. In particular, piezoelectric sensors 510 may differ from one another in their respective vibration spectrums.
According to some embodiments, each of ECs 506 (e.g. EC 506a, EC 506b, and EC 506c) is an IC.
Micro-controller 529 is functionally associated with signal generator 521, electrical impedance measurement unit 525, and multiplexer 533 (in embodiments including a plurality of piezoelectric sensors), and is configured to control operation thereof, e.g. to periodically instruct (command) signal generator 521 to initiate a sine wave sweep, to instruct multiplexer 533 which of the outputs of piezoelectric sensors 510 is to be routed to electrical impedance measurement unit 525, to receive measurement data from electrical impedance measurement unit 525, and so on.
Sensor interrogator 514 is designated by a box with a dotted outline to emphasize that sensor interrogator 514 is a collection of electronic components (e.g. signal generator 521, impedance measurement unit 525) which, according to some embodiments, are not housed within a single casing (housing). Nevertheless, the scope of the disclosure should be understood to cover also the options of some or all of the electronic components being housed within a common casing. For example, signal generator 521 and impedance measurement unit 525 may form a part of, or be replaced by, an impedance analyzer, such as the commercially available AD5933 impedance analyzer (in which case both the first terminals of each of piezoelectric sensors 510 and the second terminals of each of piezoelectric sensors 510 (via multiplexer 533) are connected to the impedance analyzer).
An output port of signal generator 521 is electrically connected to a respective first terminal of each of piezoelectric sensors 510. Signal generator 521 is configured to produce a voltage signal (or a current signal), and thereby induce a voltage between the terminals of each of piezoelectric sensors 510, respectively. A respective second terminal of each of piezoelectric sensors 510 is electrically coupled to electrical impedance measurement unit 525. According to some embodiments (wherein PCB 500 includes a plurality of piezoelectric sensors), the second terminals of piezoelectric sensors 510 are electrically coupled to electrical impedance measurement unit 525 via multiplexer 533.
According to some embodiments, signal generator 521 is a sine wave generator (e.g. configured to generate a sinusoidal voltage signal). According to some embodiments, signal generator 521 is configured to generate a swept sine signal, e.g. a sine voltage signal whose frequency increases from an initial frequency (e.g. 100 kHz) to a final frequency (e.g. 10 GHz).
Electrical impedance measurement unit 525 is configured to measure respective impedances of (or according to some embodiments, just the current through each of, or just the voltages across each of) piezoelectric sensors 510 and to communicate the obtained measurement data to micro-controller 529. The skilled person will understand that electrical impedance measurement unit 525 includes electronic components such as to allow electrical impedance measurement unit 525 to measure directly/indirectly the electrical impedance of the piezoelectric sensor selected by multiplexer 533. For example, impedance measurement unit 525 may include a sensing resistor, connected in series to multiplexer 533 (and thereby to the“selected” piezoelectric sensor from piezoelectric sensors 510) such as to form a voltage divider therewith, and a voltmeter configured to measure the voltage across the sensing resistor.
A circuit diagram of the above described configuration, which constitutes a specific embodiment of components in PCB 500, is depicted in Fig. 5b. Depicted are signal generator 521, according to some embodiments thereof, multiplexer 533, according to some embodiments thereof, a sensing resistor 535, and a voltmeter 537 (and, according to some embodiments, additionally or alternatively to voltmeter 537 and sensing resistor 535, an ammeter 539). Also depicted are one or more electrical switches 545 within multiplexer 533, according to some embodiments thereof. A double -headed arrow B indicates the input voltage Vi, that is to say, the voltage applied by signal generator 521 at the input (first) terminal of each of piezoelectric sensors 510 (e.g. an input terminal 542al (whereat Vi is applied) of piezoelectric sensor 510a; an output terminal 542a2 of piezoelectric sensor 510a is also indicated). A double-headed arrow D indicates the output voltage V0, that is to say, the voltage across sensing resistor 535. When the resistance Rs of sensing resistor 535 is small relative to the impedance of piezoelectric sensors 510 (i.e. Rs « 1 / (InfC), wherein /is the frequency of the voltage signal and C is the capacitance of the (selected) piezoelectric sensor), the voltage across the selected piezoelectric sensor is to a good approximation given by V The current I through the piezoelectric sensor and sensing resistor 535 is I = V0 / Rs The impedance Z of the (selected) piezoelectric sensor is thus (approximately) given
Figure imgf000033_0001
The impedance is therefore proportional to 1 / Vo. According to some such embodiments, it may suffice to obtain the spectrum of Vo (or, what amounts to the same thing, 1 / V0 ) without deriving Z.
According to some embodiments, micro-controller 529 includes processing circuitry and a memory (both not shown). The processing circuitry may be an application specific integrated circuitry (ASIC), a programmable processing circuitry such as an FPGA, firmware, and/or the like, and is configured to process measurement data obtained by impedance measurement unit 525 and determine whether the measurement data are indicative of damage to at least one of the monitored solder joints. According to some embodiments, the memory is a non-transitory memory. The memory may include a solid-state memory, a magnetic memory, a photonic memory, and/or the like. According to some embodiments, the memory includes both non-transitory memory components and transitory memory components. According to some embodiments, the memory has stored therein electrical impedance baseline data (and/or baseline data of other electrical parameters), which are used by the processing circuitry as a reference to which the measurement data, obtained during the monitoring, is compared. Significant differences between the measurement data and the baseline data may be indicative of damage to one or more of the monitored solder joints, as elaborated on below. Micro controller 529 may further include at least one filter configured to filter electrical signals, at least one voltage and/or current amplifier, at least one analog- to-digital electrical signal convertor, and/or at least one digital-to-analog electrical signal convertor. According to some embodiments, wherein signal generator 521 produces a swept sinusoidal, or substantially sinusoidal, voltage or current signal, micro-controller 529 is configured to analyze the spectrum of the measured electrical impedance(s) (or the spectrum of another physical quantity from which the measured impedance can be obtained, such as the RMS voltage spectrum of sensing resistor 535). The memory in micro-controller 529 may have stored therein custom software for analyzing the spectrum, executable by the processing circuitry in micro-controller 529. The custom software may be configured to identify features (or lack thereof) in the spectrum, which are typical of intact (undamaged) solder joints. The spectrum associated with intact solder joints may include more features, such as peaks and troughs (valleys), or more distinct (pronounced) features, such as larger peak and troughs, as compared to the spectrum of damaged solder joints.
Without committing to any theory, the electrical impedance spectrum associated with intact solder joints may be different from the electrical impedance spectrum associated with damaged solder joints, due to the stronger mechanical coupling between the PCB and the EC provided by intact solder joints as compared to that provided by damaged (e.g. loose) solder joints (in Fig. lc a loose pin end portion is depicted). Put another way, the decrease in the mechanical coupling (i.e. less constraint) between the PCB and the EC, e.g. due to a crack in the solder material/joint, results in a different vibration spectrum of the PCB (and thus a different electrical impedance spectrum of the piezoelectric sensor). The custom software may be configured to determine potential damage to one or more solder joints when a change is observed in the electrical impedance spectrum.
According to some embodiments, wherein the memory has stored therein an electrical impedance baseline spectrum (or a spectrum associated therewith/indicative thereof, such as the RMS voltage of sensing resistor 535 in Fig. 5b), the software is configured to compare the measured spectrum with the baseline spectrum and identify differences there between, such as an absence of features, e.g. peaks and/or troughs, in the measured spectrum, which appear in the baseline spectrum, or attenuation (shrinking) of features in the measured spectrum as compared to the baseline spectrum. The custom software may be configured to determine potential damage to one or more solder joints when one or more features, appearing in the baseline spectrum, are missing in the measured spectrum (or vice-versa) or appear significantly different (e.g. shrunk or enlarged) in the measured spectrum as compared to the baseline spectrum.
Generally, the baseline spectrum is obtained when the PCB is believed to be“healthy”, e.g. before use or immediately after fabrication. According to some embodiments, the custom software may be configured to (i) compute a root-mean-square difference (RMSD) associated with the measured spectrum and the baseline spectrum, and, when the computed RMSD is greater than a threshold value, (ii) determine that the monitored solder joint(s) is potentially damaged, as elaborated on below in the Methods subsection. According to some embodiments, micro-controller 529 is further configured to not only determine whether a monitored solder joint is damaged, but also to assess the degree of damage to the monitor solder joint (when the solder joint is determined to be damaged), e.g. whether the monitored solder joint is slightly damaged or severely damaged.
Micro-controller 529 is electrically coupled to an output port 551 of PCB 500. The other input and output ports (e.g. sockets or fingers) of PCB 500, e.g. VC- (for powering PCB 500 elements, including sensor interrogator 514), GND (ground port), and input and output ports for providing inputs and relaying outputs from ECs 506, respectively, are not shown. Micro-controller 529 is configured to send an output signal (via output port 551) to an external computational component/system, when the measured electrical impedance of one or more of piezoelectric sensors 510 is indicative of damage to one or more of the monitored solder joints.
Advantageously, sensor interrogator 514 requires only a single dedicated port (i.e. output port 551) on PCB 500.
Fig. 6 is a block diagram of a PCB 600. PCB 600 is similar to PCB 500 but differs therefrom in that the output signal of the sensor interrogator of PCB 600 is not relayed via an output port of PCB 600 (in contrast to PCB 500 wherein the output signal from sensor interrogator 514 is relayed via output port 551). More specifically, PCB 600 includes a substrate 602 similar to substrate 502, one or more ECs 606 (e.g. three, as depicted in Fig 6: an EC 606a, an EC 606b, and an EC 606c) that may be similar to ECs 506, one or more piezoelectric sensors 610 (e.g. three as depicted in Fig 6: a piezoelectric sensor 610a, a piezoelectric sensor 610b, and a piezoelectric sensor 610c positioned near EC 606a, EC 606b, and EC 606c, respectively) that may be similar to piezoelectric sensors 510, and a sensor interrogator 614. Sensor interrogator 614 includes a signal generator 621 similar to signal generator 521, an electrical impedance measurement unit 625 similar to electrical impedance measurement unit 525, a micro controller 629, optionally a multiplexer 633, and a light emitting diode (LED) 655. LED 655 is electrically coupled to micro-controller 629. Micro-controller 629 is configured to send a trigger signal to LED 655 when the measured electrical impedance of one or more piezoelectric sensors 610 is evaluated by micro-controller 629 as being indicative of damage to at least one of the monitored solder joints. LED 655 is configured to emit light upon receiving the trigger signal. The emitted light constitutes the output signal. According to some such embodiments, a light detector 657 coupled to an external computational component/system (not shown), e.g. an external control circuitry, is positioned proximately to PCB 600 such that light emitted by LED 655 is incident on light detector 657.
Advantageously, sensor interrogator 614 requires no dedicated ports on PCB 600.
According to some embodiments, there is provided a PCB (not shown in the figures). The PCB is similar to PCB 600 but differs therefrom in including a wireless transmitter instead of LED 655. The wireless transmitter is functionally associated with a micro controller, similar to micro-controller 629, and is configured to transmit an output signal upon receipt of a trigger signal from the micro-controller.
It will be understood that ECs 606 may differ from one another (e.g. EC 606a may differ from EC 606b), essentially as described above with respect to ECs 506. Similarly, it will be understood that piezoelectric sensors 610 may differ from one another, essentially as described above with respect to piezoelectric sensors 510.
According to some embodiments, each of ECs 606 is an IC.
PCBs 500 and 600 are said to be“self-testing” in the sense of including electronic components capable of independently identifying damage to solder joints thereon the PCB, i.e. without requiring off-board measurements and processing of measurement data. In particular, all of the components of the sensor interrogator are on-board (e.g. mounted on, attached to, or embedded in/on the substrate). According to some embodiments disclosed herein, depicted in Figs. 7 and 8, all the processing of measurement data measurements are performed off-board. According to some such embodiments, all the components of the sensor interrogator are off-board. According to some embodiments, some of the processing of measurement data and/or some of the measurements may be performed off-board. In such embodiments, some of the components of the sensor interrogator are off-board. For example, the multiplexer and sensing resistor may be on-board while the rest of the sensor interrogator components may be off-board.
Fig. 7 is a block diagram of a PCB 700. PCB 700 is similar to PCB 500 but differs therefrom in that, except for a multiplexer 733, PCB 700 does not include any other components analogous to components of sensor interrogator 514. Interrogation (probing and analysis) of the piezoelectric sensor(s) on PCB 700 is performed by an off-board sensor interrogator (not shown), which, according to some embodiments, apart from being off-board, is essentially similar to sensor interrogator 514.
More specifically, PCB 700 includes a substrate 702, one or more ECs 706 (e.g. three, as depicted in Fig 7: an EC 706a, an EC 706b, and an EC 706c), one or more piezoelectric sensors 710 (e.g. three as depicted in Fig 7: a piezoelectric sensor 710a, a piezoelectric sensor 710b, and a piezoelectric sensor 710c positioned near EC 706a, EC 706b, and EC 706c, respectively), and multiplexer 733. Piezoelectric sensors 710 are electrically connected to an input port 763 whereby a voltage signal (e.g. sine wave signal) from an external signal generator can be provided. Multiplexer 733 is electrically connected to each of piezoelectric sensors 710 (through output ports thereof, not numbered) and configured to select between them. Multiplexer 733 is further electrically connected to additional input ports 767 and an output port 751. Multiplexer 733 is configured to receive (e.g. from an external control circuitry functionally similar to micro-controller 529), via additional input ports 767, a signal specifying which of the outputs of piezoelectric sensors 710 is to be forwarded (routed). The selected output is forwarded via output port 751, e.g. to an external impedance measurement unit. According to some embodiments, not depicted in Fig. 7, instead of multiplexer 733, PCB 700 includes a demultiplexer. The demultiplexer is connected to input port 763, to piezoelectric sensors 710 (through input ports of piezoelectric sensors 710, not numbered), and to additional input ports 767. The demultiplexer is configured to forward the input voltage signal (from input port 763) to a“selected” piezoelectric sensor, according to instructions conveyed to the demultiplexer via additional input ports 767. Piezoelectric sensors 710 are also connected (via output ports thereof, not numbered) to output port 751.
It will be understood that ECs 706 may differ from one another (e.g. EC 706a may differ from EC 706b), essentially as described above with respect to ECs 506. Similarly, it will be understood that piezoelectric sensors 710 may differ from one another, essentially as described above with respect to piezoelectric sensors 510.
According to some embodiments, each of ECs 706 is an IC.
Fig. 8 is a block diagram of a PCB 800. PCB 800 is similar to PCB 700 but differs therefrom in not including any components analogous to components of sensor interrogator 514. Interrogation of the piezoelectric sensor(s) on PCB 800 is performed by an off-board sensor interrogator (not shown), essentially as described with respect to
PCB 700.
More specifically, PCB 800 includes a substrate 802, one or more ECs 806 (e.g. three, as depicted in Fig 8: an EC 806a, an EC 806b, and an EC 806c), and one or more piezoelectric sensors 810 (e.g. three as depicted in Fig 8: a piezoelectric sensor 810a, a piezoelectric sensor 810b, and a piezoelectric sensor 810c positioned near EC 806a, EC 806b, and EC 806c, respectively). Piezoelectric sensors 810 are electrically connected to an input port 863 whereby a voltage signal (e.g. sine wave signal) from an external signal generator can be provided. Each of piezoelectric sensors 810 is electrically connected to a respective output port from output ports 851, whereby piezoelectric sensors 810 may be electrically coupled to an external multiplexer that functions essentially similarly to multiplexer 733.
It will be understood that ECs 806 may differ from one another (e.g. EC 806a may differ from EC 806b), essentially as described above with respect to ECs 506. Similarly, it will be understood that piezoelectric sensors 810 may differ from one another, essentially as described above with respect to piezoelectric sensors 510.
According to some embodiments, each of ECs 806 is an IC.
Given that m piezoelectric sensors are used for the monitoring of the solder joints, PCB 700 has the advantage over PCB 800 of requiring only n + 2 dedicated ports (ports 751,
763, and 767) for the monitoring, where n =
Figure imgf000039_0001
ml (the brackets denoting rounding up so that — 1 < k»g2 m < n), whereas PCB 800 requires m + 1 ports (ports 851 and port 863) to the same end.
In Figs. 7 and 8, inputs into piezoelectric sensors 710 and 810, respectively, are represented by dashed-dotted lines to facilitate distinguishing the inputs from the respective outputs (represented by solid lines) of the piezoelectric sensors.
Methods
Fig. 9 is a flowchart of a method 900 for monitoring integrity of solder joints on a PCB and detecting potential onset of damage thereto, according to some embodiments. Dash- delineated boxes contain text corresponding to optional steps of method 900. Method 900 can be implemented using any one of PCBs 100-800, and PCBs similar thereto, as elaborated on below. Method 900 includes:
- A step 910, wherein an input voltage is applied to a terminal of a piezoelectric sensor (such as piezoelectric sensors 110, 510, or 710). The piezoelectric sensor is attached to a substrate of a PCB (such as PCBs 100, 500, or 700).
- A step 920, wherein an electrical parameter(s) (e.g. electrical impedance) of the piezoelectric sensor is measured (e.g. using a sensor interrogator such as sensor interrogators 114, 514, or the off-board sensor interrogator described in the description of Fig. 7). Values of the electrical parameter(s) are affected by a mechanical coupling between the piezoelectric sensor and the substrate due to the attachment of the piezoelectric sensor to the substrate. - A step 930, wherein it is determined whether the measured value(s) of the electrical parameter(s) are indicative of potential damage to one or more solder joints (such as solder joint 130a in PCB 100) whereby the EC (e.g. IC 106) is mounted on the PCB. - Optionally, a step 935, wherein an output signal is provided (e.g. by a sensor interrogator such as sensor interrogator 114 or 514) contingent upon it being determined in step 930 that the measured values of the electrical parameter(s) are indicative of potential damage to one or more of the solder joints.
According to some embodiments, the piezoelectric sensor is attached to the substrate proximately to an EC mounted thereon. Possible attachment locations of the piezoelectric sensor on the PCB are specified in Figs, la-4 and the accompanying descriptions thereof. Possible attachment mechanisms (e.g. surface bonding, embedding) are also specified above in the descriptions of Figs. la-8.
In step 930, the determination of whether the measurement data (measured values of the electrical parameter) are indicative of damage to one or more of the monitored solder joints may be performed by a processing circuitry, such as the processing circuitry described above with reference to micro-controller 529.
According to some embodiments, in step 930 differences between the measurement data of the electrical parameter and electrical impedance baseline data are analyzed (evaluated). Appreciable differences between the two data (spectra) serve as an indicator of potential damage to one or more of the solder joints, essentially as described above in the description of the processing circuitry of micro-controller 529 and as elaborated on below.
One way of quantifying the difference between the measurement spectrum and the baseline spectrum is the’’root-mean-square difference” (RMSD) method. The RMSD is given by
Figure imgf000040_0001
wherein the di are the amplitudes of data points in the
“damaged” spectrum, the m are the amplitudes of data points in the baseline spectrum, and the summation is over all pairs of data points (i.e. di and m with the same index) in the spectra. It has been shown in the literature that in many cases the RMSD increases monotonically as increasing levels of damage are found in a structure. By running tests in the lab (e.g. on many copies of a PCB), a RMSD threshold value, beyond which damage to the PCB is considered significant and unacceptable, can be determined.
According to some embodiments, steps 910, 920, and 930 are repeated (e.g. periodically) so long as the measurement data (obtained in step 920) are not indicative of potential damage to one or more of the monitored solder joints. According to some embodiments, when available power is not limited, measurements can be taken continuously or substantially continuously (e.g. frequency scans (see below) are repeated without pause, or substantially without pause, between consecutive frequency scans). Continuous monitoring of a solder joint(s) (which involve continuous measurements of a respective piezoelectric sensor) is most beneficial when the PCB is subject to continuous vibration, during which time the solder joint(s) may start to fail (e.g. develop a crack).
According to some embodiments, even when the measurement data turn out to be indicative of potential damage to one or more of the monitored solder joints, steps 910, 920, and 930 are repeated one or two additional times for verification.
According to some embodiments, method 900 further includes an initial step 905, wherein the electrical parameter baseline data are obtained, e.g. by effecting a first sub step similar to step 910 and a second sub-step similar to step 920. The measured values of the electrical parameter(s) obtained in the second sub-step may be stored (as electrical parameter baseline data) in a memory (e.g. non-volatile memory) of a micro controller, such as micro-controller 529 or 629 (or any micro-controller or control circuitry associated with a sensor interrogator, such as sensor interrogator 114, 314, or 714).
According to some embodiments, a sine wave generator is used to apply the input voltage in step 910. According to some embodiments, the sine wave generator effects a frequency scan (i.e. produces a swept sine voltage signal whose frequency is e.g. increased from about 5 kHz to about 10 GHz or about 100 kHz to about 10 GHz), thereby obtaining a measured spectrum of the electrical parameter (the dependence of the measured values of the electrical parameter on the frequency of the applied input voltage signal). In some such embodiments, the determination (in step 930) of whether the measured spectrum is indicative of damage to one or more of the solder joints includes checking (examining) the spectrum for features/structural patterns, or lack thereof, which are typical of intact (undamaged) solder joints. According to some embodiments, absence of one or more of the typical features is indicative of potential damage to one or more of the solder joints. According to some embodiments, presence of atypical features in the measured spectrum is indicative of potential damage to one or more of the solder joints.
According to some embodiments, wherein in step 910 a frequency scan is performed, in step 930 the measured spectrum and baseline spectrum are checked for the presence/absence of common features e.g. peaks and/or troughs, or differences in the shape/size of the common features. According to some embodiments, potential damage to one or more solder joints is determined when one or more features, appearing in the baseline spectrum, are missing in the measured spectrum or appear different (e.g. reduced in size) in the measured spectrum as compared to the baseline spectrum. According to some embodiments, an obtained value of the RMSD (computed from the measured spectrum and baseline spectrum, as explained above) being above a threshold value is indicative of damage to one or more of the solder joints. According to some embodiments, the obtained RMSD value (together with the RMSD threshold value) suffices to determine whether damage has occurred to one or more of the solder joints.
According to some embodiments, the output signal in step 935 is an electrical signal sent to an external computational component/system. According to some embodiments, the output signal in step 935 is a light emitted by a LED and which is incident on a light detector functionally associated with an external computational component/system.
According to some embodiments, a single piezoelectric sensor is used to monitor solder joints of different ECs. In such embodiments, the piezoelectric sensor is located proximately to more than one EC. For example, the piezoelectric sensor may be located midway or substantially midway between two ECs.
Experimental data demonstrating efficacy of the disclosed systems and methods
Figs. 10a- 12 present experimental data demonstrating the feasibility of method 900 and indicating the utility of PCBs 100-800 for detecting damage to solder joints thereon. Fig. 13a is a circuit diagram of the system used to obtain the data, and Fig. 13b is a photograph of the experimental circuit board used. Circuit board 1300 includes a piezoelectric sensor 1310 (STEMiNC type SMD05T04R111WL) glued thereto, an eight-pin dual-in-line-package (DIP) IC 1306 soldered to the board at pins 1, 4, 5, and 8, and a resistor 1369 (shown in Fig. 13b). Resistor 1369 is not electrically connected to the sensor interrogator (or piezoelectric sensor 1310) and was used to demonstrate the sensitivity of the method to changes in the mechanical vibration spectrum of circuit board 1300 by first gluing one of resistor 1369 leads to circuit board 1300 and later soldering the second lead thereof to circuit board 1300 (thereby changing the boundary conditions of the board), as described below.
Making reference again to Fig. 13a, piezoelectric sensor 1310 and a (off-board) sensing resistor 1335 are electrically connected in series such as to form a voltage divider (similarly to piezoelectric sensors 510 and sensing resistor 535). To obtain the data, a swept sine voltage signal (generated by a signal generator 1321) was used to drive the voltage divider. The resultant voltage across the sensing resistor was amplified (by an amplifier 1371), converted to a DC signal (by an RMS-to-DC converter 1375 (Analog Devices AD536)), and recorded (using a USB scope 1379).
To demonstrate the capacity of the disclosed methods to monitor the growth of a crack in a solder joint of an EC, five-minute epoxy glue was applied to one of the electrical leads of resistor 1369, which was otherwise not bonded to circuit board 1300, and frequency scans (e.g. sinusoidal voltage sweeps) were performed every few minutes.
Fig. 10a shows a voltage (presented in“arbitrary units” AU), measured across sensing resistor 1335, as a function of the drive frequency. More specifically, Fig. 10a shows the RMS (root-mean-square) voltage across the sensing resistor as a function of the drive frequency when resistor 1369 is not bonded to the PCB (i.e. before the epoxy glue was applied). As explained above, when the resistance of the sensing resistor is small compared to the electrical impedance of the piezoelectric sensor (at all of the scanned frequencies), the electrical impedance of the piezoelectric sensor is approximately inversely proportional to the voltage V0 across the sensing resistor ( Z ~ Rs * (Vi / V„) ).
A trough T is evident at about 23-24 kHz. Fig. 10b is an enlarged view of trough T at times t = 0 min (minutes), 3 min, 5 min, and 9 min, as measured from the time of the application of the epoxy glue (e.g. at t = 3 min the epoxy glue has been applied for 3 minutes). As can be seen, the trough becomes less deep as t increases, thereby facilitating distinguishing the measurement at t = 9 min from the measurements at earlier times, and consequently facilitating distinguishing the state in which the electrical lead of the sensing resistor is strongly bonded to the circuit from a state in which the electrical lead of the sensing resistor is loosely bonded or not bonded at all to the circuit board.
It is noted that even with the epoxy glue fully cured, the (adhesive) bonding of the resistor 1369 to the circuit board 1300 is significantly weaker than bonding provided by soldering. Therefore, reductions in solder joint strength (e.g. of an IC), for example, from fatigue or crack formation, are expected to be even more evident.
Fig. 11 shows the effects of additionally soldering the second lead of resistor 1369 to the PCB. Two spectra are shown. The bottom spectrum corresponds to a first frequency scan, i.e. before the second lead was soldered (but with the first lead glued). The top spectrum, which is offset with respect to the bottom spectrum, corresponds to a frequency scan after the second lead was soldered. The differences between the two spectra are especially noticeable in the regions highlighted in grey, wherein peaks are present in the top spectrum which are missing in the bottom spectrum, making it easy to distinguish the two spectra even by eye.
Fig. 12 shows the effect of soldering an additional pin (a fifth pin) of the IC to the PCB. Two spectra are shown. The bottom spectrum corresponds to a first frequency scan, i.e. before the fifth pin (pin 7) was soldered. The top spectrum, which is offset with respect to the bottom spectrum, corresponds to a frequency scan after pin 7 has been soldered. The differences between the two spectra are particularly noticeable in the regions highlighted in grey. Given that the integrated circuit already had four pins soldered (pins 1, 4, 5, and 8), the fact that soldering an additional pin resulted in significant changes in the spectrum demonstrates the sensitivity of the disclosed methods to detect changes in solder joint strength.
As used herein, according to some embodiments, the ter s “controller”, “micro controller”, and“control circuitry” are used interchangeably. As used herein, according to some embodiments, the terms“off-board” and“external”, with reference to components which are not located on a PCB (e.g. on the substrate thereof), are used interchangeably.
According to an aspect of some embodiments, there is provided a PCB. The PCB includes an EC mounted thereon by solder joints. The EC includes a piezoelectric sensor attached thereto. According to some embodiments, not depicted in the figures, a piezoelectric element of the piezoelectric sensor is attached (e.g. glued) to a top surface of a body of the EC (e.g. to a chip package of an IC). According to some embodiments, not depicted in the figures, the piezoelectric element is attached to a bottom surface of the body of the EC. According to some embodiments, the piezoelectric element is positioned within the EC. The piezoelectric sensor is electrically coupled to a sensor interrogator, similar to the sensor interrogators described above, and which, according to some embodiments, is also positioned within the EC. According to some such embodiments, wherein the EC includes free (unused) pins (which is often the case when the EC is an FPGA), the piezoelectric sensor may be connected to the free pins such as to allow actuation thereof by a sensor interrogator external to the EC. The mechanical coupling between the piezoelectric sensor and the EC allows for monitoring the integrity of the solder joints of the EC, the working principle being similar to that described above for piezoelectric sensors mounted on a substrate of a PCB.
Self-testing integrated circuits
Making reference to Figs. 14a and 14b, Fig. 14a is a schematic, top view of a self testing integrated circuit (IC) 1400, according to some embodiments. Fig. 14b is a schematic, partial, cross-sectional view of IC 1400 mounted on a PCB 1450 (or, more precisely, on a substrate 1452 thereof), according to some embodiments. IC 1400 includes a chip package 1402, a semiconducting die 1404, leads 1410, bonding wires 1412, one or more piezoelectric sensors 1420 (for example, and as depicted in Fig. 14a, one per lead), a sensor interrogator 1422, and a light-emitting diode (LED) 1424. In Fig. 14a, chip package 1402 is outlined but otherwise depicted as transparent in order to show the components housed therein, and thereby facilitate the description. Die 1404, piezoelectric sensor 1420, and sensor interrogator 1422 may be embedded in chip package 1402, e.g. embedded in a plastic encapsulate (e.g. a mold resin) or a ceramic encapsulate (the encapsulate is not shown). According to some embodiments, die 1404 may be fixed to a support structure (header; not shown), which is encapsulated within chip package 1402, as known in the art of ICs. Leads 1410 are electrically connected to die 1404 via bonding wires 1412 (for example, gold wires). Leads 1410 extend outside of chip package 1402, the exposed portions thereof (i.e. the portions of leads 1410 located outside of (externally to) chip package 1402) constituting the pins which may be used to mount IC 1400 on a PCB (as shown, for example, in Fig. 14b).
Dashed arrows (single -headed and double-headed) denote in Figs. 14a and 14b functional relationships between components (e.g. electrical coupling, sending of information).
Each of piezoelectric sensors 1420 is attached to one of leads 1410, respectively. For example, piezoelectric sensors 1420a, 1420b, and 1420c (from piezoelectric sensors 1420), are attached to leads 1410a, 1410b, and 1410c (from leads 1410), respectively. Each of piezoelectric sensors 1420 may include a piezoelectric element (e.g. a piezoelectric crystal or PZT disc) and a pair of terminals attached to the piezoelectric element, which electrically couple (via electrical lines, e.g. electrical wires or traces; not shown) the piezoelectric element to sensor interrogator 1422. More specifically, each piezoelectric element is attached to one of leads 1410, respectively. The attachment is such that the lead is electrically insulated from the piezoelectric element. For example, according to some embodiments, the piezoelectric element may be glued to the lead by means of an adhesive, which forms an electrically insulating layer between the lead and the piezoelectric clement (and the terminals).
When an alternating electrical current is passed through the piezoelectric element, the piezoelectric element vibrates and induces acoustic vibrations in the lead to which the piezoelectric element is attached. When IC 1400 is mounted on a substrate of a PCB, the vibration spectrum of the piezoelectric element is affected by the strength of the mechanical coupling of the lead to the substrate, which in turn depends on the integrity of the solder joint joining the lead to the substrate (for example, as depicted in Fig. 14b, to a solder pad on the substrate). Thus, for example, when an oscillating voltage is applied across the terminals of piezoelectric sensor 1420c, vibrations thereof are induced, which are imparted to lead 1410c. The vibration spectrum of piezoelectric sensor 1420c depends on the integrity of a solder joint 1426c joining lead 1410c (by means of a solder material 1428c) to a solder pad 1456c on substrate 1452 (shown in Fig. 14b).
More generally, the vibration spectrum of a piezoelectric element is determined by (mechanical) boundary conditions characterizing the mechanical coupling of the piezoelectric element to the surroundings thereof. For each of piezoelectric sensors 1420, the boundary conditions may also be affected, in a measurable manner, by the strength of the mechanical coupling of the respective lead to die 1404, that is, by the integrity of the connection provided by the bonding wire electrically coupling the lead to die 1404. Each bonding wire may form, on a first end thereof, a connection interface with die 1404 and, on the second end thereof, a connection interface with the respective lead. Thus, the boundary conditions may be affected, in a measurable manner, by the integrity of the bonding wire, as well as by the integrity of the connection interfaces attaching (e.g. by soldering) the bonding wire to the die and to the lead; for example, the integrity of bonding wire 1412c and connection interfaces 1432c and 1434c (shown in Fig. 14b) formed by bonding wire 1412c with die 1404 and with lead 1410c, respectively. In particular, the connection interface connecting a bonding wire to a semiconducting die may be particularly sensitive to damage (e.g. connection interface 1432c). According to some embodiments, leads 1410 and/or semiconducting die 1404 may include bonding pads to which the ends of bonding wires 1412 are attached (i.e. the connection interfaces may include bonding pads).
Thus, according to some embodiments, each piezoelectric sensor may be attached to the respective lead proximately to the bonding wire electrically coupling the lead to the die, so as to increase the sensitivity of the piezoelectric sensor to structural damage in the bonding wire and to the strength of the respective connection interfaces joining the bonding wire to the leads and the semiconducting die (that is, to any structural damage to the connection interfaces). For example, according to some embodiments, and as depicted in Figs. 14a and 14b, piezoelectric sensor 1420c is attached to lead 1410c in proximity to bonding wire 1412c. According to some embodiments, a piezoelectric sensor in a chip package may be said to be attached to a lead proximately to a bonding wire in the chip package, when positioned closer to the bonding wire than to the external portion of the lead. Electrical lines 1438a and 1438b respectively connect sensor interrogator 1422 to leads 1410a and 1410b (the power lead and ground lead of IC 1400, respectively), which supply the power to operate sensor interrogator 1422, piezoelectric sensors 1420, and LED 1424 (as well as die 1404). Sensor interrogator 1422 is configured to selectively apply an input voltage to each one of piezoelectric sensor 1420 (e.g. one at a time), and thereby induce vibrations of the respective piezoelectric element. Sensor interrogator 1422 is further configured to measure the electrical impedance of each piezoelectric element or, according to some embodiments, one or more other electrical parameters of each piezoelectric element, essentially as described above in the description of Figs. 5a- 6 and in the description of method 900. According to some embodiments, sensor interrogator 1422 includes a signal generator (e.g. sine-wave generator), a measurement unit (e.g. an impedance measurement unit), a micro-controller, and a multiplexer, functionally associated there between and with piezoelectric sensors 1420, essentially as described above, with respect to sensor interrogator 614 and piezoelectric sensors 610, in the description of Fig. 6.
LED 1424 may be positioned on chip package 1402 (e.g. glued thereon) or embedded thereon. It is noted that in Fig. 14a, LED 1424 is shown positioned on a side surface of chip package 1402, while in Fig. 14b, LED 1424 is shown positioned on the top surface of chip package 1402. (Similarly, in Fig. 14a, sensor interrogator 1422 is shown positioned to the side of die 1404, while in Fig. 14b, sensor interrogator 1422 is shown positioned above die 1404.)
LED 1424 is electrically coupled to sensor interrogator 1422 (e.g. to the micro controller included in sensor interrogator 1422). Sensor interrogator 1422 is configured to send a trigger signal to LED 1424 when the measured electrical impedance of one or more of piezoelectric sensors 1420 is evaluated by sensor interrogator 1422 as being indicative of damage to one or more of the solder joints connecting leads 1410 to substrate 1452 (e.g. when the measured impedance of piezoelectric sensor 1420c is indicative of damage to solder joint 1426c (shown in Fig. 14b)) and/or to one or more of the bonding wires and/or the associated connection interfaces joining the leads to the die (e.g. when the measured impedance of piezoelectric sensor 1420c is indicative of damage to bonding wire 1412c and/or at least one of connection interfaces 1432c and 1434c (shown in Fig. 14b)). LED 1424 is configured to emit light upon receiving the trigger signal. The emitted light constitutes an output signal indicating malfunction in the PCB (e.g. a crack in solder joint 1426c and/or damage to bonding wire 1412c).
PCB 1450 may further include a light detector (not shown) positioned thereon, such that light emitted by LED 1424 is incident on the light detector. According to some embodiments, PCB 1450 may include a plurality of light detectors, particularly, in embodiments wherein PCB 1450 includes, in addition to IC 1400, other self-testing ICs similar to IC 1400. According to some embodiments, the light detector(s) may be external to PCB 1450, essentially as described above with respect to PCB 600. The light detector may be associated with an external computational component/system (e.g. external to PCB 1450).
According to some embodiments, two piezoelectric sensors may be attached to each lead, such that one of the piezoelectric sensors is positioned proximately to the bonding wire, and the other piezoelectric sensor is positioned proximately to a side surface of the chip packet, such as to be positioned proximately to the external portion of the lead. The piezoelectric sensor positioned near the bonding wire may be more sensitive to damage to the bonding wire and to the connection interfaces connecting the bonding wire to the semiconducting die and the lead. The piezoelectric sensor positioned near the side surface may be more sensitive to damage to the solder joint connecting the lead to the PCB substrate on which the IC is mounted.
It is noted that in embodiments wherein the piezoelectric sensor (e.g. piezoelectric sensor 1420c) is sensitive to damage to the bonding wire (e.g. bonding wire 1412c) and the connection interfaces, electrically coupling the lead (to which the piezoelectric sensor is attached) to the die, the testing of the integrity of the bonding wire and the connection interfaces may be performed prior to the mounting of IC 1400 on PCB 1450, e.g. immediately after fabrication of IC 1400. Such testing may be performed by electrically coupling the power and ground leads (i.e. leads 1410a and 1410b) to an external power source.
According to some embodiments, there is provided an IC similar to IC 1400, but which differs therefrom in not including a LED (such as LED 1424). In such embodiments, upon detection of the onset of damage, the output signal is communicated from the IC, via a lead of the IC, to other processing circuitry on the PCB (on which the IC is mounted), and therefrom, e.g. via a dedicated output port of the PCB, to an external computational component/system. The lead is electrically coupled to the sensor in the IC, but, unlike leads 1410, is not electrically coupled to the die in the IC.
It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the disclosure. No feature described in the context of an embodiment is to be considered an essential feature of that embodiment, unless explicitly specified as such.
Although steps of methods according to some embodiments may be described in a specific sequence, methods of the disclosure may include some or all of the described steps carried out in a different order. A method of the disclosure may include a few of the steps described or all of the steps described. No particular step in a disclosed method is to be considered an essential step of that method, unless explicitly specified as such.
Although the disclosure is described in conjunction with specific embodiments thereof, it is evident that numerous alternatives, modifications and variations that are apparent to those skilled in the art may exist. Accordingly, the disclosure embraces all such alternatives, modifications and variations that fall within the scope of the appended claims. It is to be understood that the disclosure is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth herein. Other embodiments may be practiced, and an embodiment may be carried out in various ways.
The phraseology and terminology employed herein are for descriptive purpose and should not be regarded as limiting. Citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the disclosure. Section headings are used herein to ease understanding of the specification and should not be construed as necessarily limiting.

Claims

CLAIMS What is claimed is:
1. A printed circuit board (PCB) comprising a substrate, at least one electronic component (EC) solder-joint mounted on the substrate, and at least one piezoelectric sensor attached to the substrate; wherein the piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor, and wherein a measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the EC.
2. The PCB of claim 1, wherein the at least one EC is an integrated circuit (IC).
3. The PCB of claim 1, wherein each of the at least one EC is an IC, a switch, an amplifier, a filter, a rectifier, an inverter, a transistor, a resistor, a capacitor, an inductor, or a diode.
4. The PCB of any one of claims 1 to 3, wherein the at least one piezoelectric sensor is attached to the substrate proximately to the EC.
5. The PCB of any one of claims 1 to 4, wherein the sensor interrogator comprises the following components: a signal generator configured to apply the input voltage; a measurement unit configured to measure the electrical parameter; and a control circuitry functionally associated with the signal generator and the measurement unit and configured to process measurement data obtained by the measurement unit and to determine whether the measurement data are indicative of potential damage to the at least one solder joint.
6. The PCB of claim 5, wherein the control circuitry has stored in a memory therein electrical parameter baseline data, and wherein the control circuitry is configured to determine whether the measurement data are indicative of potential damage to the at least one solder joint by evaluating a difference between the measured values of the electrical parameter and the electrical parameter baseline data.
7. The PCB of any one of claims 1 to 6, wherein a piezoelectric element in the piezoelectric sensor is surface bonded to the substrate or embedded within the substrate.
8. The PCB of any one of claims 5 to 7, wherein the signal generator is configured to (i) apply a sinusoidal, or substantially sinusoidal, voltage signal or current signal, and (ii) sweep a frequency of the voltage signal across a range of frequencies, wherein a minimum frequency of the range is greater than about 5 kHz and a maximum frequency of the range is smaller than about 10 GHz.
9. The PCB of any one of claims 5 to 8, wherein the control circuitry is configured to repeatedly (i) command the signal generator to apply the input voltage to the piezoelectric sensor and (ii) command the measurement unit to measure the electrical parameter of the piezoelectric sensor, as long as the measurement data are not indicative of potential damage to the at least one solder joint.
10. The PCB of any one of claims 1 to 9, wherein the electrical parameter is an electrical impedance of the piezoelectric sensor, or a current through the piezoelectric sensor, or a voltage across the piezoelectric sensor.
11. The PCB of any one of claims 1 to 10, wherein the at least one EC comprises a plurality of ECs and wherein the at least one piezoelectric sensor comprises a plurality of piezoelectric sensors, each of the plurality of piezoelectric sensors being attached to the substrate more closely to a respective EC from the plurality of ECs than to any other one of the ECs.
12. The PCB of any one of claims 1 to 11, wherein the at least one piezoelectric sensor comprises a plurality of piezoelectric sensors, each of the piezoelectric sensors being attached to the substrate such as to be closer to a respective solder joint, from the at least one solder joint and associated with the at least one EC, than to any one of the other solder joints.
13. The PCB of any one of claims 11 and 12, wherein the sensor interrogator is configured to allow interrogating each of the plurality of piezoelectric sensors one at a time.
14. The PCB of any one of claims 1 to 13, wherein the PCB comprises the sensor interrogator, the sensor interrogator being located on the substrate and powered by an operating voltage of the PCB.
15. The PCB of claim 14, wherein the control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint associated with the EC.
16. The PCB of any one of claims 14 and 15, wherein the sensor interrogator further comprises a light emitting diode (LED), the LED being functionally associated with the control circuitry and configured to receive therefrom a trigger signal to emit light as the output signal.
17. A system for detecting damage to solder joints on one or more printed circuit boards (PCBs), the system comprising one or more of the PCBs according to any one of claims 1 to 13 and the sensor interrogator of any one of claims 1 to 13, wherein at least some of the components of the sensor interrogator are off-board, the sensor interrogator being configured to interrogate the at least one piezoelectric sensor on each of the one or more PCBs, respectively.
18. A method for detecting damage to one or more solder joints on a printed circuit board (PCB), the method comprising steps of: applying an input voltage to at least one piezoelectric sensor, respectively, the at least one piezoelectric sensor being attached to the PCB, the PCB comprising at least one electronic component (EC) solder- joint mounted on the PCB; measuring at least one electrical parameter of the piezoelectric sensor, the electrical parameter being sensitive to damage to at least one solder joint associated with the EC; and determining potential damage to the at least one solder joint, or lack of damage, based on a measured value or measured values of the at least one electrical parameter.
19. A printed circuit board (PCB) comprising a substrate, at least one electronic component (EC) solder-joint mounted on the substrate, and at least one piezoelectric sensor attached to the EC; wherein the piezoelectric sensor is electrically coupled to a sensor interrogator, which is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor, and wherein a measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint associated with the EC.
20. An integrated circuit (IC) comprising a chip package housing therein a semiconducting die, at least one piezoelectric sensor, and a sensor interrogator, the IC further comprising a plurality of leads electrically coupled to the semiconducting die and extending from within the chip package to the outside thereof; wherein the at least one piezoelectric sensor is attached to at least one of the plurality of leads, respectively, such as to be electrically insulated therefrom; and wherein the sensor interrogator is configured to apply an input voltage to the piezoelectric sensor and to measure at least one electrical parameter of the piezoelectric sensor, and wherein, when the IC is mounted on a printed circuit board (PCB), a measured value or measured values of the electrical parameter are indicative of an integrity of, or damage to, at least one solder joint connecting the at least one of the plurality of leads, respectively, to the PCB.
21. The IC of claim 20, wherein the sensor interrogator comprises the following components: a signal generator configured to apply the input voltage; a measurement unit configured to measure the electrical parameter; and a control circuitry functionally associated with the signal generator and the measurement unit and configured to process measurement data obtained by the measurement unit and to determine whether the measurement data are indicative of potential damage to the at least one solder joint.
22. The IC of claim 21, wherein the control circuitry has stored in a memory therein electrical parameter baseline data, and wherein the control circuitry is configured to determine whether the measurement data are indicative of potential damage to the at least one solder joint by evaluating a difference between the measured values of the electrical parameter and the electrical parameter baseline data.
23. The IC of any one of claims 20 to 22, wherein a piezoelectric element in the at least one piezoelectric sensor is glued to the at least one of the plurality of leads.
24. The IC of any one of claims 21 to 23, wherein the signal generator is configured to (i) apply a sinusoidal, or substantially sinusoidal, voltage signal or current signal, and (ii) sweep a frequency of the voltage signal across a range of frequencies, wherein a minimum frequency in the range is greater than about 5 kHz and a maximum frequency in the range is smaller than about 10 GHz.
25. The IC of any one of claims 21 to 24, wherein the control circuitry is configured to repeatedly (i) command the signal generator to apply the input voltage to the at least one piezoelectric sensor and (ii) command the measurement unit to measure the electrical parameter of the at least one piezoelectric sensor, when the IC is mounted on the PCB, as long as the measurement data are not indicative of potential damage to the at least one solder joint.
26. The IC of any one of claims 20 to 25, wherein the electrical parameter is an electrical impedance of the piezoelectric sensor, or a current through the piezoelectric sensor, or a voltage across the piezoelectric sensor.
27. The IC of any one of claims 20 to 26, wherein the at least one piezoelectric sensor comprises a plurality of piezoelectric sensors, and wherein two or more of the plurality of leads each have attached thereon a respective piezoelectric sensor from the plurality of piezoelectric sensors, and wherein the sensor interrogator is configured to allow interrogating each of the plurality of piezoelectric sensors one at a time.
28. The IC of any one of claims 20 to 27, wherein the at least one piezoelectric sensor is positioned proximately to at least one bonding wire electrically coupling the at least one of the plurality of leads, respectively, to the semiconducting die, the at least one piezoelectric sensor being thereby configured to detect damage to the at least one bonding wire and to connection interfaces connecting the at least one bonding wire to the at least one of the plurality of leads and to the semiconducting die.
29. The IC of any one of claims 21 to 28, wherein the control circuitry is configured to trigger an output signal when the measurement data are indicative of potential damage to the at least one solder joint, or to the at least one solder joint and/or the at least one bonding wire and/or the connection interfaces.
30. The IC of claim 29, wherein the IC further comprises a light emitting diode (LED) attached to, or embedded on, the chip package, the LED being functionally associated with the control circuitry and configured to receive therefrom a trigger signal to emit light as the output signal.
PCT/IL2019/050235 2018-03-04 2019-03-04 In-situ systems and methods for detecting damage to solder joints WO2019171373A1 (en)

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CN117153714A (en) * 2023-10-31 2023-12-01 宁波尚进自动化科技有限公司 Method, system, equipment and medium for detecting welding bonding

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Publication number Priority date Publication date Assignee Title
CN112924840A (en) * 2021-02-26 2021-06-08 航天科工防御技术研究试验中心 Light-emitting diode failure positioning method
CN117153714A (en) * 2023-10-31 2023-12-01 宁波尚进自动化科技有限公司 Method, system, equipment and medium for detecting welding bonding
CN117153714B (en) * 2023-10-31 2024-04-02 宁波尚进自动化科技有限公司 Method, system, equipment and medium for detecting welding bonding

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