JP6305354B2 - Electrostatic withstand voltage test method and electrostatic withstand voltage test apparatus - Google Patents

Description

  The present invention relates to an electrostatic withstand voltage test method and an electrostatic withstand voltage test apparatus.

  Conventionally, an electrostatic withstand voltage test for measuring the withstand voltage of an electronic component against electrostatic discharge is performed when the electronic component is shipped. Regarding the electrostatic withstand voltage test, for example, in JP-A-2-103479 (Patent Document 1) and JP-A-2007-091012 (Patent Document 2), after accumulating electric charge in a capacitor using a power source, A configuration is described in which characteristics of an electronic component when the accumulated charge is discharged to the electronic component are measured, and whether or not the electronic component has failed is determined based on the measurement result.

Japanese Patent Laid-Open No. 2-103479 JP 2007-081012 A

  In a conventional electrostatic withstand voltage test, an electric charge for electrostatic discharge is accumulated in a capacitor by applying a voltage of about several kV to a capacitor having a capacitance of about several hundred pF based on international standards. The configuration is widely adopted.

  However, in the market, although an electrostatic withstand voltage test is performed at the time of product shipment, a failure of an electronic component due to static electricity may occur. One cause of failure due to static electricity is the fact that in recent years, the use of electronic components has led to higher voltages than those stipulated in the electrostatic withstand voltage test due to the acceleration of the increase in power consumption of products using electronic components. It may be applied to the part. Therefore, in the electrostatic withstand voltage test, it is required to reproduce a failure of an electronic component due to a high voltage, which is considered to have occurred in the market. However, in the conventional electrostatic withstand voltage test, since it is not easy to apply a voltage higher than the current several kV, there is a problem that it is difficult to reproduce an electrostatic failure occurring in the market.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electrostatic withstand voltage test apparatus and an electrostatic withstand voltage capable of reproducing a failure caused by static electricity occurring in the market. It is to provide a test method.

  In one aspect of the present invention, the electrostatic withstand voltage test method is an electrostatic withstand voltage test method for measuring a withstand voltage against electrostatic discharge of a device under test. In the electrostatic withstand voltage test method, a capacitor configured to change the capacitance is connected to a power source, and the capacitor is charged with electric charge, and the electric charge charged in the capacitor in the charging step is directed to the device under test. A step of measuring the electrical characteristics of the device under test during discharging of the capacitor, a step of determining failure of the device under test based on the electrical characteristics measured by the measuring step, The step of detecting the voltage of the power source when the device under test is determined to be faulty as the electrostatic withstand voltage of the device under test; and Increasing the capacitance. In the charging step and the discharging step, charging and discharging of charges are performed on the capacitor whose capacitance has been increased by the increasing step. In the determining step, the failure of the device under test is determined based on the electrical characteristics measured by the measuring step during the discharge of the capacitor with increased capacitance.

  According to another aspect of the present invention, there is provided an electrostatic withstand voltage test apparatus for measuring a withstand voltage against electrostatic discharge of a device under test, comprising a power source, a capacitor configured to change capacitance, and the capacitor connected to the power source. To form a charging path for accumulating electric charge in the capacitor and a discharge path for discharging the accumulated electric charge of the capacitor to the DUT by connecting the capacitor to the DUT. A switch, a measurement unit for measuring the electrical characteristics of the DUT when the discharge path is formed, and a failure of the DUT based on the electrical characteristics of the DUT measured by the measurement unit Judgment and judgment unit configured to detect the voltage of the power supply when the DUT is determined to be faulty as the electrostatic withstand voltage of the DUT, and when the DUT determines that the DUT is normal In With increasing capacitance of the capacitor, and a control unit for controlling the first switch to charge path and discharge paths for capacitors whose capacitance increases are selectively formed.

  The present invention can provide an electrostatic withstand voltage test apparatus and an electrostatic withstand voltage test method capable of reproducing a failure due to static electricity occurring in the market.

It is a figure which shows roughly the structure of the electrostatic withstand voltage test apparatus according to embodiment of this invention. It is a wave form diagram which shows an example of the electrical property of the electronic component measured by a measurement part. It is a flowchart for demonstrating the electrostatic withstand voltage test method according to this Embodiment. It is a figure which shows an example of the data of the electrostatic withstand voltage of an electronic component and the electrostatic capacitance of the capacitor of a selection state memorize | stored in the calculating part in an electrostatic discharge withstand pressure test. It is a flowchart which shows an example of a process of the data obtained by the electrostatic withstand voltage test method shown in FIG. It is a figure which shows roughly the structure of the electrostatic withstand voltage test apparatus according to the modification of this Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

[Configuration of electrostatic withstand voltage test equipment]
FIG. 1 schematically shows a configuration of an electrostatic withstand voltage test apparatus according to an embodiment of the present invention.

  Referring to FIG. 1, an electrostatic withstand voltage test apparatus 1 is a test apparatus for measuring the withstand voltage of an electronic component 2 that is a device under test during electrostatic discharge. The electrostatic withstand voltage test apparatus 1 includes a DC power supply 10, a plurality of capacitors C1 to C3, switches 12, 14, a charging resistor R1, and a discharging resistor R2. The electrostatic withstand voltage test apparatus 1 further includes a control unit 16, a measurement unit 18, and a calculator 20.

  DC power supply 10 is connected between high-voltage power line PL1 and low-voltage power line GL. The power line GL is typically constituted by a ground wiring. DC power supply 10 is configured to be able to switch the magnitude of the voltage output to power line PL <b> 1 in response to a control signal output from computing unit 20.

  The electronic component 2 that is a device under test is connected between the power line PL1 and the power line GL on the high voltage side. The electronic component 2 is, for example, a zener diode or a surge absorber that is an overvoltage protection element.

  The plurality of capacitors C <b> 1 to C <b> 3 are parts for storing electric charges for performing electrostatic discharge on the electronic component 2 that is a device under test. One terminal of each of the plurality of capacitors C1 to C3 is commonly connected to the power line GL. The other terminal of each capacitor is connected to the switch 14.

  The plurality of capacitors C1 to C3 have different capacitances. FIG. 1 illustrates a configuration in which the electrostatic withstand voltage test apparatus 1 includes three capacitors C1 to C3 having different capacitances. The three capacitors C1 to C3 are assumed to increase in capacitance in the order of the capacitor C1, the capacitor C2, and the capacitor C3 (C1 <C2 <C3).

  Here, the international standard regarding the electrostatic withstand voltage test stipulates that a capacitor having a capacitance of about several hundred pF is used as the capacitor mounted on the test apparatus. For example, in the international standard IEC61000-4-2, a capacitor having a capacitance of 150 pF ± 10% is used in an electrostatic withstand voltage test (human body model, HBM) assuming electrostatic discharge generated from the human body. It is prescribed. Further, in the MIL standard, it is specified to use a capacitor having a capacitance of 100 pF. In the present embodiment, a capacitor having a capacitance larger than the capacitance defined by the international standard is used for each of the plurality of capacitors C1 to C3. For example, each of the plurality of capacitors C1 to C3 has a maximum capacitance of about 1 μF.

  The switch 14 is a switch for selecting one capacitor among the three capacitors C1 to C3. The switch 14 is configured to be able to switch a capacitor to be selected according to a control signal from the control unit 16. As an example, the switch 14 includes three fixed contacts 14a to 14c and a movable contact 14d that selectively connects to the three fixed contacts 14a to 14c, as shown in FIG. The three fixed contacts 14a to 14c are connected to the other terminals of the three capacitors C1 to C3, respectively. By connecting the movable contact 14d to one of the three fixed contacts 14a to 14c in accordance with a control signal from the control unit 16, a capacitor connected to the fixed contact is selected. That is, the plurality of capacitors C1 to C3 correspond to “a plurality of capacitor elements”, and the plurality of capacitors C1 to C3 and the switch 14 realize a “capacitor” configured so that the capacitance can be changed.

  Switch 12 is connected between power lines PL1 and PL2 and switch 14. Switch 12 electrically connects the other terminal of the capacitor selected by switch 14 to one of power lines PL1 and PL2 in accordance with a control signal from control unit 16. As an example, as shown in FIG. 1, the switch 12 includes two fixed contacts 12a and 12b and a movable contact 12c that selectively connects the two fixed contacts 12a and 12b. Two fixed contacts 12a and 12b are connected to power lines PL1 and PL2, respectively. The movable contact 12 c is electrically connected to the movable contact 14 d of the switch 14. By connecting the movable contact 12c to one of the two fixed contacts 12a and 12b according to a control signal from the control unit 16, the other of the capacitors in the selected state is connected to the power line connected to the fixed contact. The terminals are electrically connected.

  As one mode of the switch 12, a case where the capacitor C1 is in a selected state by the switch 14 is assumed. In this case, the switch 12 electrically connects the other terminal of the capacitor C1 and the power line PL1 in accordance with a control signal from the control unit 16, thereby using the voltage supplied from the DC power supply 10 to the power line PL1. A charging path for charging is formed. As shown in FIG. 1, a charging resistor R1 is interposed in the charging path. For the charging resistor R1, for example, a resistance element having a resistance value of about several MΩ is used. Thereby, the capacitor C1 can be charged smoothly.

  On the other hand, the switch 12 electrically connects the other terminal of the capacitor C1 and the power line PL2 in accordance with a control signal from the control unit 16, so that the accumulated charge of the capacitor C1 is directed to the electronic component 2 via the power line PL2. A discharge path for discharge is formed.

  As shown in FIG. 1, a discharge resistor R2 is interposed in the discharge path. For the discharge resistor R2, for example, a resistance element having a resistance value of about several hundred Ω to several kΩ defined by an international standard for an electrostatic withstand voltage test is used. As an example, the international standard IEC61000-4-2 stipulates that a resistance element having a resistance value of 330Ω ± 10% is used. Further, in the MIL standard, it is specified that a resistance element having a resistance value of 1500Ω is used.

  As described above, according to the control signal from the control unit 16, the switch 12 has a charging path for accumulating charges in the capacitor selected by the switch 14, and a discharging path for discharging the charges accumulated in the capacitor. Are configured to be selectively formed.

  On the other hand, the switch 14 is configured to be able to switch the capacitance of a capacitor to be charged / discharged according to a control signal from the control unit 16. The electrostatic charge amount Q stored in the capacitor to be charged / discharged is represented by the product of the power supply voltage V supplied from the DC power supply 10 and the capacitance C of the capacitor (Q = C × V). That is, by switching the electrostatic capacity C of the capacitor to be charged / discharged using the switch 14 while the power supply voltage V is a constant voltage, the charge amount Q of static electricity generated in the capacitor can be changed. .

  As the switch 12, for example, a mercury relay switch having a small contact bounce is preferably used so as not to cause separation or disappearance of the discharge current. As a result, when electrostatic discharge is performed on the electronic component 2 that is the device under test, voltage fluctuation due to the influence of bounce of the contact can be suppressed, so that the measurement unit 18 can obtain highly reproducible electrical characteristics. it can.

  The switch 14 is preferably a high voltage switch that does not fail even when a high voltage is applied. This makes it possible to perform an electrostatic withstand voltage test using a capacitor having a small electrostatic capacity.

  The measurement unit 18 is a part for measuring electrical characteristics that appear in the electronic component 2 that is a device under test in a state where the above-described discharge path is formed. The measurement unit 18 is configured to be able to measure the voltage between the terminals of the electronic component 2 and the current flowing through the electronic component 2. In order to accurately measure the voltage and current waveforms, the sampling frequency in the measurement unit 18 is preferably 1 Gs or higher. The electrical characteristics of the electronic component 2 measured by the measurement unit 18 are sent to the calculator 20.

  FIG. 2 is a waveform diagram showing an example of electrical characteristics of the electronic component 2 measured by the measurement unit 18. FIG. 2 shows temporal changes in the current flowing through the Zener diode before and after failure of the Zener diode when electrostatic discharge is performed on the Zener diode which is the electronic component 2.

  Referring to FIG. 2, when a capacitor in a selected state is discharged, a discharge current flows through a Zener diode provided in the discharge path. A solid line k1 in the figure shows a current waveform before the Zener diode fails. A dotted line k2 in the figure shows an example of a current waveform after the Zener diode has failed.

  When the Zener diode fails due to electrostatic discharge (open failure or short-circuit failure), the resistance value of the Zener diode varies compared to before the failure. As can be understood from FIG. 2, the current waveform (dotted line k <b> 2) obtained by the measurement unit 18 in response to a change in the resistance value of the Zener diode also greatly changes from the current waveform before the failure (solid line k <b> 1).

  In the present embodiment, the computing unit 20 calculates, as a pulse width, the time from when the current starts to flow through the electronic component 2 until it converges to the original current value (ie, zero) in the current waveform shown in FIG. . Then, the computing unit 20 determines whether or not the electronic component 2 has failed based on the calculated pulse width. That is, the computing unit 20 corresponds to a “determination unit”.

  Here, the pulse width is determined by the time constant τ, which is the time taken for the current value to decay to about 37%, with the current value at the peak of the current waveform being 100%. The time constant τ can be calculated from the product of the capacitance of the capacitor and the total value of the resistance value of the discharge resistor R2 and the resistance value of the electronic component 2. According to this, it is understood that when the resistance value of the electronic component 2 fluctuates due to a failure, the time constant τ changes, and as a result, the pulse width changes.

  Since the time constant τ decreases as the capacitance of the capacitor decreases, the pulse width also decreases. As described above, by setting the sampling frequency of the measurement unit 18 to 1 Gs or more, even a waveform with a short pulse width can be measured with high accuracy.

  When the arithmetic unit 20 receives the current waveform indicated by the solid line k1 in FIG. 2 from the measurement unit 18, the arithmetic unit 20 calculates the pulse width PW1 of the current waveform. The computing unit 20 stores the calculated pulse width PW1 as a reference value representing the electrical characteristics before the electronic component 2 fails. When the calculator 20 receives the measured value of the current waveform of the electronic component 2 from the measurement unit 18 during the electrostatic discharge, the calculator 20 calculates the pulse width of the current waveform, and calculates the calculated pulse width and the reference value PW1. Compare

  At this time, if the electronic component 2 is out of order, the pulse width PW2 of the current waveform has a value different from the reference value PW1, as indicated by a dotted line k2 in FIG. Therefore, the computing unit 20 can determine whether or not the electronic component 2 has failed based on the result of comparing the calculated pulse width with the reference value PW1.

  For example, the arithmetic unit 20 determines that the electronic component 2 has not failed when the deviation between the calculated pulse width and the reference value PW1 is less than or equal to a predetermined threshold value. On the other hand, when the deviation between the calculated pulse width and the reference value PW1 exceeds a predetermined threshold, the calculator 20 determines that a failure has occurred in the electronic component 2. The computing unit 20 detects the power supply voltage of the DC power supply 10 when the electronic component 2 has failed as the electrostatic withstand voltage of the electronic component 2. The computing unit 20 stores the power supply voltage of the DC power supply 10 when the electronic component 2 fails and the capacitance of the selected capacitor. The power supply voltage of the DC power supply 10 (corresponding to the electrostatic withstand voltage of the electronic component 2) when the electronic component 2 fails has a one-to-one correspondence with the capacitance of the capacitor to be charged / discharged.

  Returning to FIG. 1, the arithmetic unit 20 switches the power supply voltage supplied from the DC power supply 10 to the power line PL <b> 1 based on the determination result that the electronic component 2 has not failed. The arithmetic unit 20 further generates a control signal for controlling the switching operation in the switches 12 and 14 and outputs the control signal to the control unit 16. Then, the computing unit 20 performs electrostatic discharge on the electronic component 2 under the switched power supply voltage and / or capacitance.

[Static test method]
Next, an electrostatic withstand voltage test method according to the present embodiment will be described. FIG. 3 is a flowchart for illustrating the electrostatic withstand voltage test method according to the present embodiment.

  Referring to FIG. 3, in order to perform an electrostatic withstand voltage test, first, electronic component 2 to be tested is set in electrostatic withstand voltage test apparatus 1 (see FIG. 1) in step S01. Specifically, as shown in FIG. 1, one terminal of the electronic component 2 is electrically connected to the power line PL2, and the other terminal of the electronic component 2 is electrically connected to the power line GL. Next, the measurement part 18 is electrically connected between two terminals of the electronic component 2 by step S02.

  In step S03, computing unit 20 sets an initial voltage for the power supply voltage supplied from DC power supply 10 to power line PL1. The initial voltage is a power supply voltage supplied from the DC power supply 10 at the start of the electrostatic withstand voltage test.

  When the initial voltage is set in step S03, the operation proceeds to step S04, and the computing unit 20 selects a capacitor that charges and discharges the electric component 2 for electrostatic discharge. The control unit 16 generates a control signal for selecting one of the three capacitors C1 to C3 based on an instruction from the arithmetic unit 20, and outputs the generated control signal to the switch 14. To do. For example, at the start of the electrostatic withstand voltage test, the control unit 16 generates a control signal for selecting the capacitor C1 having the smallest capacitance among the three capacitors C1 to C3. In this case, according to the control signal from the control unit 16, the switch 14 connects the movable contact 14d to the fixed contact 14a, so that the capacitor C1 connected to the fixed contact 14a is selected.

  In step S05, a charging path for accumulating electric charge in the selected capacitor is formed. Specifically, the control unit 16 generates a control signal for connecting the selected capacitor (for example, the capacitor C1) to the power line PL1 based on an instruction from the computing unit 20, and the generated control signal is switched to the switch 12. Output to. According to the control signal from the control unit 16, the switch 12 connects the movable contact 12c to the fixed contact 12a, whereby the selected capacitor C1 is electrically connected to the power line PL1. Thereby, a charging path for accumulating electric charge in the capacitor C1 is formed. The charge is charged in the capacitor C1 using the formed charging path.

  When the capacitor is charged in step S05, the process proceeds to step S06, and a discharge path for discharging the electric charge accumulated in the capacitor toward the electronic component 2 is formed. Specifically, the control unit 16 generates a control signal for connecting the selected capacitor (for example, the capacitor C1) to the power line PL2 based on an instruction from the computing unit 20, and the generated control signal is switched to the switch 12. Output to. According to the control signal from the control unit 16, the switch 12 connects the movable contact 12c to the fixed contact 12b, whereby the selected capacitor C1 is electrically connected to the power line PL2. As a result, a discharge path for discharging the electric charge accumulated in the capacitor C1 toward the electronic component 2 is formed. Electrostatic discharge is performed on the electronic component 2 using the formed discharge path.

  When the electrostatic discharge is started, the electrical characteristics of the electronic component 2 are measured by the measuring unit 18 in step S07. For example, the measurement unit 18 measures the current flowing through the electronic component 2 and sends the measurement result to the computing unit 20. The computing unit 20 calculates the pulse width PW1 of the current waveform (see FIG. 2) measured by the measuring unit 18, and stores the calculated pulse width PW1 as a reference value. At this time, the computing unit 20 stores the calculated pulse width (reference value) PW1 in association with the power supply voltage (initial voltage) of the DC power supply 10 when the electrostatic discharge is performed and the capacitance of the capacitor. It may be.

  As described above, when the pulse width PW1 in the current waveform before failure of the electronic component 2 is acquired as the reference value, the process proceeds to step S08, and the computing unit 20 sets the power supply voltage of the DC power supply 10 to a voltage higher than the initial voltage. Change to a value. The computing unit 20 increases the power supply voltage of the DC power supply 10 by a predetermined amount.

  In step S09, a charging path for accumulating charges in the capacitor using the changed power supply voltage is formed. As a result, electric charges are charged again in the selected capacitor using the formed charging path.

  When the capacitor is charged in step S09, a discharge path for the charge accumulated in the capacitor is formed in step S10, and electrostatic discharge is again performed on the electronic component 2 using the formed discharge path.

  When the electrostatic discharge is started, the calculator 20 calculates the pulse width of the current waveform measured by the measuring unit 18 in step S11. Then, in step S12, the arithmetic unit 20 compares the calculated pulse width with the reference value PW1, and determines whether or not the electronic component 2 has failed based on the comparison result. For example, the arithmetic unit 20 determines that a failure has occurred in the electronic component 2 when the deviation between the calculated pulse width and the reference value PW1 exceeds a predetermined threshold. When it is determined that the electronic component 2 is out of order (at the time of YES determination in step S12), the computing unit 20 determines that the power supply voltage of the current DC power supply 10 (corresponding to the electrostatic withstand voltage of the electronic component 2) by step S13. And the capacitance of the selected capacitor.

  On the other hand, when the deviation between the calculated pulse width and the reference value PW1 is less than or equal to a predetermined threshold value, the computing unit 20 determines that the electronic component 2 has not failed. If it is determined that the electronic component 2 has not failed (NO in step S12), the arithmetic unit 20 proceeds to step S14 and determines whether or not the power supply voltage can be further increased in the DC power supply 10. To do. When the current power supply voltage reaches the upper limit value of the voltage range that can be output by the DC power supply 10, the computing unit 20 determines that the power supply voltage cannot be increased. On the other hand, if the current power supply voltage does not reach the upper limit, the computing unit 20 determines that the power supply voltage can be increased.

  When it is determined that the power supply voltage of the DC power supply 10 can be increased (when YES is determined in Step S14), the arithmetic unit 20 returns to Step S08 and changes the power supply voltage of the DC power supply 10 to a higher voltage value. And the electrostatic discharge is performed to the electronic component 2 by performing the process of steps S09 to S11, and the pulse width of the current waveform of the electronic component 2 is calculated. By step S12, the arithmetic unit 20 determines the presence or absence of a failure of the electronic component 2 based on the calculated pulse width.

  On the other hand, when it is determined in step S14 that the power supply voltage of the DC power supply 10 cannot be increased (NO determination in step S14), the computing unit 20 replaces the capacitor in the selected state in step S15. Change to a capacitor with higher capacitance. That is, the computing unit 20 substantially increases the capacitance of the capacitor to be charged / discharged by switching the capacitor to be selected to a capacitor having a larger capacitance. For example, when the capacitor C1 is in the selected state, the arithmetic unit 20 switches the capacitor C2 having the second largest capacitance after the capacitor C1 to the selected state.

  The calculator 20 resets the initial voltage of the DC power supply 10 in order to start the electrostatic withstand voltage test using the capacitor (for example, the capacitor C2) switched to the selected state in step S16. The initial voltage to be reset is the initial voltage set in step S03 as long as the amount of static electricity accumulated in the capacitor after switching is larger than the amount of static electricity accumulated in the capacitor C1 before switching. It may be a higher voltage value or a lower voltage value.

  When the initial voltage is reset in step S16, an electrostatic withstand voltage test using the capacitor switched to the selected state is executed. That is, by executing the processes of steps S05 to S07, electrostatic discharge is performed on the electronic component 2 using the electric charge accumulated in the capacitor switched to the selected state. The computing unit 20 calculates the pulse width of the current waveform measured by the measuring unit 18, and stores the calculated pulse width as a reference value.

  Subsequently, by executing the processes of steps S08 to S11, the power supply voltage of the DC power supply 10 is increased and electrostatic discharge is performed based on the increased power supply voltage, and the pulse width of the current waveform of the electronic component 2 is calculated. . By step S12, the arithmetic unit 20 determines the presence or absence of a failure of the electronic component 2 based on the calculated pulse width. The processes in steps S05 to S12 and S14 to S16 are repeatedly executed until it is determined that the electronic component 2 is out of order (YES determination in step S12). When it is determined that the electronic component 2 has failed (when YES is determined in step S12), the computing unit 20 determines the power supply voltage (electronic component 2) of the DC power supply 10 when the failure is determined in step S13. And the electrostatic capacity of the selected capacitor.

  FIG. 4 is a diagram illustrating an example of data on the electrostatic withstand voltage of the electronic component 2 and the capacitance of the selected capacitor stored in the calculator 20 in the electrostatic discharge withstand voltage test. 4 indicates the power supply voltage of the DC power supply 10 when the failure of the electronic component 2 is determined (electrostatic withstand voltage of the electronic component 2), and the horizontal axis of FIG. 4 indicates that the failure of the electronic component 2 is determined. It shows the capacitance of the capacitor that is sometimes selected. In FIG. 4, data (actually measured values) obtained in the electrostatic discharge withstand voltage test are indicated by black rhombuses. Each data is obtained by conducting an electrostatic withstand voltage test on the same type of electronic component 2 using a plurality of capacitors having different capacitances.

  As can be understood from FIG. 4, a relational expression indicating the relationship between the electrostatic withstand voltage and the capacitance of the capacitor can be derived based on the data of the electrostatic withstand voltage of the electronic component 2 and the capacitance of the capacitor. FIG. 4 shows a curve indicating the relationship between the electrostatic withstand voltage of the electronic component 2 and the capacitance of the capacitor. FIG. 5 is a flowchart showing an example of processing of data obtained by the electrostatic withstand voltage test method shown in FIG. When a plurality of data is obtained in step S13 of FIG. 3 by performing an electrostatic withstand voltage test using a plurality of capacitors having different electrostatic capacities, in step S14, the computing unit 20 causes the electrostatic withstand voltage of the electronic component 2 to be obtained. And a relational expression showing the relationship between the capacitor and the capacitance of the capacitor. According to this, by using the derived relational expression, it is possible to estimate the electrostatic withstand voltage of the electronic component 2 when the electrostatic discharge is performed by setting the capacitor to be charged / discharged to an arbitrary capacitance. It becomes possible.

(Modification of the embodiment)
In the above-described embodiment, the configuration for determining whether or not the electronic component 2 has failed due to electrostatic discharge has been described based on the pulse width of the current waveform flowing through the electronic component 2, but the determination method is not limited thereto. For example, it is possible to determine whether or not the electronic component 2 has failed based on the voltage waveform of the electronic component 2. In this case, the reference value is calculated and stored based on the voltage waveform when the electronic component 2 is not out of order.

  Moreover, in embodiment mentioned above, about the structure which mounts the several capacitor | condenser element C1-C3 from which electrostatic capacitance mutually differs in the electrostatic withstand voltage test apparatus 1, and switches the capacitor | condenser element used as charging / discharging object using the switch 14. FIG. Although illustrated, as shown in FIG. 6, the electrostatic withstand voltage test apparatus 1 </ b> A has a configuration in which a single capacitor element C whose capacitance can be changed is mounted instead of the plurality of capacitor elements C <b> 1 to C <b> 3 and the switch 14. It is good. In the electrostatic withstand voltage test apparatus 1 </ b> A shown in FIG. 6, the capacitor element C is configured so that the capacitance can be changed in response to a control signal output from the control unit 16.

[Function and effect]
Hereinafter, the effects of the electrostatic discharge withstand voltage test apparatus and the electrostatic discharge withstand voltage test according to the present embodiment will be described.

  In recent years, the failure of electronic components due to electrostatic discharge that has occurred in the market is not due to the application of a high voltage of several kV to electronic components, but due to the amount of electrostatic charge that is discharged. Conceivable.

  For example, when the electronic component is a Zener diode, when a reverse voltage equal to or higher than the breakdown voltage is applied between the anode and cathode of the Zener diode, the charge starts to pass through the depletion layer generated by the PN junction due to the tunnel effect. The conduction resistance decreases. Therefore, no voltage higher than the breakdown voltage is applied between the anode and cathode of the Zener diode. Even in the case where the electronic component is a surge absorber, a voltage higher than the clamp voltage is not applied between the two terminals of the surge absorber because the conduction resistance decreases when a voltage higher than the clamp voltage is applied, as in the case of a Zener diode.

  For these reasons, the main mode of electrostatic failure in Zener diodes and surge absorbers is unlikely to be directly caused by the high voltage applied between the two terminals of the electronic component. This is thought to be caused by heat generation due to electric charges.

  Therefore, the electrostatic resistance of the Zener diode and the surge absorber can be known by gradually increasing the amount of static electricity generated by the electrostatic withstand voltage test apparatus and examining the amount of charge when the electronic component fails.

  Here, the charge quantity Q of static electricity generated by the electrostatic withstand voltage test apparatus includes the electrostatic capacity C of the capacitor for charging / discharging mounted in the electrostatic withstand voltage test apparatus and the voltage value V of the power source used for charging the capacitor. (Q = C × V). That is, it can be understood that there are two methods for increasing the amount of electrostatic charge: a method of increasing the voltage value V of the power supply and a method of increasing the capacitance C of the capacitor.

  However, in the method of increasing the voltage value of the power supply, it is necessary to mount a high voltage power supply of about several kV on the electrostatic withstand voltage test apparatus. Even if a high voltage power supply is used, the voltage value is limited so as not to exceed the withstand voltage of components such as resistors and switches. For this reason, the method of increasing the voltage value of the power source is not suitable for measuring the electrostatic withstand voltage in an electronic component that requires high static resistance such as an overvoltage protection element.

  In contrast, the method of increasing the capacitance of a capacitor does not require the use of a high-voltage power supply, and discharges electrostatic discharge while increasing the amount of electrostatic charge at a voltage value that is lower than the breakdown voltage of the components of the electrostatic withstand voltage test equipment. Can be done. The electrostatic withstand voltage test apparatus according to the present embodiment is equipped with a plurality of capacitors having different electrostatic capacities, and the capacitance of the capacitors can be increased by switching the capacitors to be charged and discharged. . Therefore, in the electrostatic withstand voltage test, it is possible to increase the amount of static electricity generated with a constant power supply voltage. As a result, an electrostatic discharge withstand voltage test can be performed on electronic components that require high electrostatic resistance, such as an overvoltage protection element such as a Zener diode or a surge absorber.

  In a conventional electrostatic withstand voltage test, electrostatic charges are generated in a capacitor having an electrostatic capacity of several hundred pF using a high voltage of several kV based on an international standard or the like. However, in the market, although an electrostatic withstand voltage test is performed, a failure of an electronic component due to electrostatic discharge may occur. This is considered to be due to the fact that a higher voltage than that stipulated by the international standard is applied to the electronic component in the market under the influence of the recent increase in power of products using the electronic component. Therefore, in the electrostatic withstand voltage test, it is required to reproduce a failure of an electronic component due to a high voltage, which is considered to have occurred in the market. However, in the conventional electrostatic withstand voltage test apparatus, as described above, since it is not easy to increase the voltage value of the power supply, there is a problem that it is difficult to reproduce a failure due to static electricity generated in the market.

  On the other hand, the electrostatic withstand voltage test apparatus and the electrostatic withstand voltage test method according to the present embodiment adopt a method of increasing the electrostatic charge amount by increasing the capacitance of the capacitor, so that the conventional electrostatic withstand voltage test apparatus is used. Thus, it is possible to generate a large amount of electrostatic charge that is difficult to realize at a voltage value lower than the breakdown voltage of the component parts. As a result, it is possible to apply a greater stress to the electronic component than can be provided by a conventional electrostatic withstand voltage test apparatus. As a result, it is possible to reproduce a failure caused by electrostatic discharge that could not be reproduced by a conventional electrostatic withstand voltage test.

  Moreover, since the conventional electrostatic discharge withstand voltage test apparatus is equipped with a high voltage power supply of about several kV, air discharge occurs between the high voltage side power line and the low voltage side power line (ground wiring). In order to avoid this, the insulation distance between the two power lines is set large, which causes a problem that the apparatus becomes large. Further, since the high voltage power supply is more expensive than the low voltage power supply, the apparatus cost becomes expensive. On the other hand, in the electrostatic withstand voltage test apparatus according to the present embodiment, as described above, a failure due to static electricity can be generated using a voltage lower than that in the conventional electrostatic withstand voltage test, and therefore a high voltage power supply is not necessarily required. Therefore, it is possible to reduce the size and cost of the electrostatic withstand voltage test apparatus.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  1, 1A electrostatic withstand voltage test equipment, 2 electronic components, 10 DC power supply, 12, 14 switch, 16 control unit, 18 measuring unit, 20 computing unit, C1 to C3, C capacitor (capacitor element), PL1, PL2, GL power line , R1 charging resistance, R2 discharging resistance.

Claims (10)

An electrostatic withstand voltage test method for measuring a withstand voltage against electrostatic discharge of a device under test,
Charging a charge to the capacitor by connecting a capacitor configured to change capacitance to a power source;
Discharging the electric charge charged in the capacitor toward the device under test by the charging step;
Measuring electrical characteristics of the device under test during discharge of the capacitor;
Determining a failure of the device under test based on the electrical characteristics measured by the measuring step;
Detecting the voltage of the power source when the device under test is determined to be faulty in the determining step as an electrostatic withstand voltage of the device under test;
When the test object is determined to be normal in the determining step, the method includes a step of increasing the capacitance of the capacitor,
In the charging step and the discharging step, charge and discharge of electric charge are performed on the capacitor whose capacitance has been increased by the increasing step,
An electrostatic withstand voltage test method, wherein, in the determining step, a failure of the device under test is determined based on the electrical characteristics measured by the measuring step during discharging of the capacitor having increased capacitance.   The electrostatic withstand voltage test method according to claim 1, further comprising a step of storing a capacitance of the capacitor and a voltage of the power source when the device under test is determined to be faulty in the determining step.   A step of deriving a relational expression indicating the relationship between the electrostatic withstand voltage of the device under test and the electrostatic capacity of the capacitor based on the electrostatic capacity of the capacitor and the voltage of the power source stored in the storing step; The electrostatic withstand voltage test method according to claim 2, further comprising:   The step of increasing is a case where the device under test is determined to be normal in the step of determining, and when the voltage of the power source cannot be increased, the capacitance of the capacitor is increased. Item 2. The electrostatic withstand voltage test method according to Item 1. The determining step is configured to compare the electrical characteristic measured by the measuring step with a reference value and determine a failure of the device under test based on a comparison result;
Further comprising setting the reference value based on the electrical characteristics of the normal device under test;
In the setting step, when the capacitance of the capacitor is increased by the increasing step, the charge charged in the capacitor having the increased capacitance is discharged toward the normal device under test. The electrostatic withstand voltage test method according to claim 1, wherein the reference value is reset based on the electrical characteristics at the time. The capacitor includes a plurality of capacitor elements having different capacitances from each other,
The step of charging is configured to charge the capacitor element by connecting one capacitor element selected from the plurality of capacitor elements to the power source,
The increasing step is configured to switch the capacitor element connected to the power source to a capacitor element having a larger capacitance,
6. The electrostatic withstand voltage according to claim 1, wherein in the charging step and the discharging step, charge and discharge are performed on the capacitor element switched to a selected state by the switching step. Test method. An electrostatic withstand voltage test apparatus for measuring the withstand voltage against electrostatic discharge of a device under test,
Power supply,
A capacitor configured to change capacitance,
A charging path for accumulating charges in the capacitor by connecting the capacitor to the power source, and a discharging path for discharging accumulated charges in the capacitor to the device under test by connecting the capacitor to the device under test. A first switch configured to selectively form;
A measurement unit for measuring electrical characteristics of the device under test when the discharge path is formed;
The failure of the device under test is determined based on the electrical characteristics of the device under test measured by the measuring unit, and the voltage of the power source when the device under test is determined to be faulty is determined as the device under test. A determination unit configured to detect the electrostatic withstand voltage of
When the determination unit determines that the device under test is normal, the capacitance of the capacitor is increased, and the charging path and the discharging path are selectively selected with respect to the capacitor having increased capacitance. An electrostatic withstand voltage test apparatus comprising: a control unit that controls the first switch so as to be formed.   The electrostatic withstand voltage test apparatus according to claim 7, further comprising a storage unit for storing the capacitance of the capacitor and the voltage of the power source when the determination unit determines that the device under test is faulty. The capacitor is
A plurality of capacitor elements having different capacitances;
A second switch for connecting one of the plurality of capacitor elements to the power source in a selected state;
When the determination unit determines that the DUT is normal, the control unit switches the second switch so that the selected capacitor element is switched to a capacitor element having a larger capacitance. The electrostatic withstand voltage test apparatus according to claim 7 or 8 to be controlled.   In the case where the determination unit determines that the device under test is normal and the control unit is unable to increase the voltage of the power source, the control unit causes the selected capacitor element to have more capacitance. The electrostatic withstand voltage test apparatus according to claim 9, wherein the second switch is controlled to switch to a larger capacitor element.

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