WO2002048720A2 - Method and apparatus for detection of defects using localized heat injection of short laser pulses - Google Patents
Method and apparatus for detection of defects using localized heat injection of short laser pulses Download PDFInfo
- Publication number
- WO2002048720A2 WO2002048720A2 PCT/CA2001/001585 CA0101585W WO0248720A2 WO 2002048720 A2 WO2002048720 A2 WO 2002048720A2 CA 0101585 W CA0101585 W CA 0101585W WO 0248720 A2 WO0248720 A2 WO 0248720A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- heat
- sequence
- point
- points
- heat pulse
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/72—Investigating presence of flaws
Definitions
- the invention relates to the field of industrial inspection. More specifically, it relates to the inspection of the quality and integrity of junctions and connections, such as those for devices mounted on Printed Circuit Boards (PCB).
- PCB Printed Circuit Boards
- an object such as a populated circuit board may be inspected for defects by a procedure wherein such a board is heated in order to obtain a thermal image via an infrared (IR) camera.
- IR infrared
- the captured image is then compared to a standard thermal image of a known defect-free populated circuit board in order to evaluate the quality of the connections and junctions on the tested board.
- What varies in the state of the art is the way the object under inspection is heated.
- US patent 5,052,816 discloses a method and apparatus for junction inspection of electronic parts wherein a plurality of lead wires such as those from an IC (an integrated circuit) are irradiated by a fan beam at the same time.
- US patent 5,208,528 discloses a method for inspecting a PCB, and particularly for inspecting solder joints on the board. This method is characterized by the heating of the board, which is done either by pulsed or brief heating, or in a laminar fashion using a quartz lamp.
- US patent 5,246,291 teaches a bond inspection technique for a semiconductor chip wherein a bonding process heats each package lead bonded to each contact area and an IR camera captures an intensity image.
- a laser can also be used to heat the leads, heating a plurality of leads at once.
- US patent 5,984,522 discloses an apparatus for inspecting bump junctions in a semiconductor flip chip mounting wherein the surface of the semiconductor bare chip is irradiated with a laser light and radiation heat from the heated chip is detected with an IR camera. From the above referenced patents, it is clear that a thermal image can be captured by an IR camera and that this image can be used to detect defects on a PCB. What is also clear is that obtaining thermal images with respect to individual solder junctions would provide an enormous advantage over the state of the art. It would also be advantageous to be able to selectively heat a preselected area of a PCB adjacent to a predetermined solder joint or junction.
- an object of the present invention is to detect defects such as missing balls, misaligned balls, extra parts between balls, solder bridges between two adjacent balls, cracks at the junction ball-copper pad, and voids in balls of a ball-grid array component mounted on printed circuit boards.
- Another object of the present invention is to detect anomalies in junctions between flip chips and printed circuit boards. Accordingly, another object of the present invention is to use a light beam, collimated, converging or diverging, to deliver a heat pulse, or stream of heat pulses, to a very small area of a printed circuit board.
- a method for inspecting an object and detecting defects comprising: injecting a heat pulse by light beam at a selected point on the object; capturing a sequence of consecutive thermal images of the object to record heat diffusion over time resulting from the heat pulse; comparing the heat diffusion over time at the point on said object to a reference; and determining whether the object comprises any defects.
- the method is to be used for detecting anomalies in solder junctions of ball-grid arrays and flip chips mounted on printed circuit boards.
- the heat pulse is to be directed to the bottom surface of the board, producing infrared emissions at the top surface of the component as the heat is diffused through the board and the electronic component.
- An infrared camera captures a sequence of thermal images and compares the data to reference data gathered from known defect-free boards.
- an apparatus for inspecting an object and detecting defects comprising: a mounting for mounting the object; a pulsed laser source having a beam able to be positioned for providing a heat pulse at a precise location on the object; a thermal camera for capturing thermal images of the object; a frame grabber for capturing a sequence of image signals from the thermal camera; a memory unit for storing data representative of heat diffusion over time resulting from the heat pulse obtained from the sequence of image signals; and an analyzing unit for comparing the heat diffusion data to a reference data set, said reference comprising upper and lower limits of acceptable thermal heat diffusions of a specific area on the object.
- the apparatus also comprises an X-Y galvanometer to align the pulsed laser source with the precise location on the object.
- the apparatus can also comprise focusing optics to converge, diverge, and deflect the laser beam coming from the pulsed laser source, an optical power attenuator to adjust power of the heat pulse, and an input/output interface to control the X-Y galvanometer, the pulsed laser source, and the optical power attenuator.
- the mounting comprises register pins to properly fix in space the object under inspection.
- the mounting can also comprise a stage that allows the object to be moved in the x, y, and z directions.
- FIG. 1 is a schematic diagram illustrating an embodiment of the present invention
- FIG. 2 is a block diagram of the Computer system controlling the apparatus
- FIG. 3 is a schematic diagram illustrating an embodiment of the LASER unit
- FIG 4. is a schematic diagram illustrating heating a solder joint.
- Figure 1 illustrates an apparatus for inspecting the quality and integrity of junctions and connections of parts of a semi-conductor device, such as BGA and flip-chip, mounted on a PCB.
- a PCB 1 is mounted on a mounting plate 2, register pins 3 are used to properly align the board and to ensure a precise positioning in space with respect to the light beam and the camera.
- the junction points of the BGA 7 to the board are hidden and inaccessible visually.
- a computer system 14 selects a programmed ball position by setting the X-Y motor control circuit 13 of the X-Y galvanometer 12. The computer then fires the laser beam generator 4, powered by a LASER Radio Frequency (RF) power supply 5 and a LASER DC power supply 6, supplying an optical beam to an optical power attenuator 8.
- RF Radio Frequency
- the attenuator 8 is controlled by the motor control circuit 9 and transmits the optical beam to laser beam deflectors 10 and optics for a converging a beam 11 until the optical beam reaches an X-Y galvanometer 12.
- the galvanometer 12, controlled by the X-Y control circuit 13, is responsible for directing the optical beam towards a selected area of the mounting plate 2 and selectively heating one or more balls in the BGA 7 through the PCB 1.
- the IR camera 16 captures a thermal image, transforms the IR radiation of the thermal signature into electronic data and sends it to the computer system 14 to be captured and analyzed.
- the IR optics 15 maximize the field of view to get the maximum spatial resolution for the best performances.
- the main parts of the computer system 14, which are not explicitly shown in the figure, are a frame grabber to capture analog or digital data from the IR camera 16 and to store in the PC memory, an input/output Interface to control the Laser Pulses, the programmable optical power attenuator 8 and the X-Y galvanometer scanner 12 positions, and an application software to learn a "good" or acceptable thermal ball pattern and to compare the thermal ball pattern under test with some stored reference (dual threshold statistical acceptance criteria, min-max acceptance criteria or any mean to accept/reject a pixel or a pattern). Comparison between two thermal patterns is processed and done by the computer system 14.
- the computer system 14 captures and stores the specified sequence of images in the PC with the proper synchronization. These images are processed and some intermediate results of the test may be provided.
- the computer system 14 selects the next ball position to be inspected and the process is repeated.
- the BGA capture sequence and storage is completed and the computer processes all the specified balls and outputs a complete result for the entire BGA under inspection.
- the pulse duration may vary between 100 to 200 ms with an average power of 2 Watts with a CO 2 LASER, which means an energy between 200 to 400 mJ. This energy is concentrated on a spot size of around 1 mm to 4 mm in diameter at 1/e 2 at the nominal ball location.
- the time for the heat pulse to propagate is in the order of 200 to 500 ms.
- the IR camera 16 will capture consecutive images at a rate of 30 to 60 frames per second, depending on the transmit time of the heat.
- the LASER pulse is also synchronized with the frame timing of the camera.
- Another type of LASER such as YAG or a laser diode, can be used to implement the necessary heat source. In this case, the wavelength and power used changes.
- the laser instead of having an X-Y galvanometer to direct the laser beam to the board, the laser is fixed and it is the mounting plate that is moveable. The mounting plate, with the PCB in a fixed position on it, can move in the x, y, and z position in order to properly align the board and the laser.
- Figure 2 is a block diagram representing module 14 of figure 1.
- a frame grabber 44 captures a sequence of image signals from the thermal camera 43 and specific points in time following the heating of the board by the pulsed laser source 41.
- a memory unit 45 stores data representative of heat diffusion over time resulting from the heat pulse and obtained from the sequence of image signals. This information is then passed on to an analyzing unit 46 to compare the heat diffusion data to a reference data set.
- the reference data set comprises upper and lower limits of acceptable thermal heat diffusions for a specific area on the board and at a specific point in time following the heating. This reference data is collected from known defect-free boards and averaged out to produce an acceptable range.
- a controlling unit 47 controls all other modules within the computer system 14. It also controls the X-Y galvanometer 12, the laser beam generator 4, and the optical power attenuator 8.
- the controlling unit 47 may comprise a programmed sequence of points to which the laser beam must be targeted and is responsible for directing the laser beam to each of these points sequentially.
- FIG 3 is a physical description of the preferred embodiment of the laser unit.
- the RF LASER power supply 5 and the LASER beam generator 4 are connected by electrical cables.
- the LASER beam generator 4 generates sufficient optical power at such a wavelength to be able to induce a heat spot at the bottom surface of the PCB.
- the LASER may be a CO 2 LASER (10.6 ⁇ m wavelength) with a 25 to 50 Watts continuous waveform.
- the LASER beam deflector unit 10 comprises two small, flat mirrors 21 , each angled at 45 degrees in order to reflect the beam towards the optics for a converging LASER beam 11.
- the optics for a converging LASER beam 11 comprises several lenses 22 used to focus and collimate the beam before sending it into the X-Y galvanometer scanner 12.
- the X-Y galvanometer scanner 12 comprises of two orthogonal flat mirrors mounted on two motor axis (not shown). The two motors are positioned from the computer through proper electronic/electrical interfaces.
- the LASER beam is concentrated to have an adjustable spot size of around imm to 4mm in diameter at 1/e 2 . This light spot covers the area where the ball under inspection is located. When this area has been heated by the pulse, the X-Y galvanometer scanner 12 addresses the next ball to be inspected and the LASER is fired again for the same short period of time.
- the RF LASER power supply 5 provides the RF energy to stimulate the CO 2 LASER which will output the light beam during the time this RF energy is present. When this RF energy is absent, the LASER will stop lasing immediately.
- the RF LASER power supply 5 also monitors and controls the pulse duration and repetition rate through electronic signals coming from the computer input/output interface.
- the system of the present invention must be calibrated before a PCB is tested and analyzed.
- the calibration step is carried out in order to obtain and store in computer memory the parameter settings (i.e. intensity, shape, duration, repetition rate, etc.) for the comparison of the tested PCB with an acceptable range for a thermal signature.
- the acceptable range approximately 15 to 30 thermal images are taken of known defect free samples and the mean and the standard deviation are calculated for every pixel of each frame.
- the upper and lower limits of the acceptance range is then calculated (user will set the number of standard deviations) for every pixel and stored as the standard to which all tested boards are compared to.
- a first image is taken of the PCB before being heated by the laser.
- This first image is then subtracted from all subsequent images taken of the same board in order to take into account all ambient and variation effects.
- the heat injected must always be the same. This is only achievable when using a laser to heat the element.
- two thermal images are compared, they must have been taken at the same point in time. Therefore, the system is working with four variables: two positional (x, y), one thermal (heat intensity), and one for time.
- the threshold for the intensity of the laser is the damage threshold. That is, the amount of energy injected is only as high as the amount of heat applicable that will not cause any damage to the board or the elements.
- Figure 4 is a close-up schematic of the heating of a solder joint.
- a light beam 30 is positioned under a ball from a ball-grid array.
- the laser light pulse heats the small area 31. Heat propagates through the materials 32 and appears at the BGA top surface 33.
- a radiation pattern 34 is then captured by an infrared camera. From the drawing, the junction point between the ball and the PCB is quite clear.
- This particular embodiment makes use of transmissive heating. However, it is possible to do reflective heating. In this case, a light beam is placed above the BGA at an angle to the desired area to be heated in order to keep the path between the BGA and the infrared camera clear.
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
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- Investigating Or Analyzing Materials Using Thermal Means (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2002214889A AU2002214889A1 (en) | 2000-12-11 | 2001-11-15 | Method and apparatus for detection of defects using localized heat injection of short laser pulses |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US25466600P | 2000-12-11 | 2000-12-11 | |
US60/254,666 | 2000-12-11 |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2002048720A2 true WO2002048720A2 (en) | 2002-06-20 |
WO2002048720A3 WO2002048720A3 (en) | 2002-10-03 |
Family
ID=22965116
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/CA2001/001585 WO2002048720A2 (en) | 2000-12-11 | 2001-11-15 | Method and apparatus for detection of defects using localized heat injection of short laser pulses |
Country Status (2)
Country | Link |
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AU (1) | AU2002214889A1 (en) |
WO (1) | WO2002048720A2 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2005026747A2 (en) | 2003-09-16 | 2005-03-24 | Jacob Gitman | Electric ultimate defects analyzer detecting all defects in pcb/mcm |
EP1901060A1 (en) * | 2006-09-13 | 2008-03-19 | Ibea Ingenieurbüro für Elektronik und Automation GmbH | Thermographic detection system |
US7877217B2 (en) | 2003-09-16 | 2011-01-25 | Invisible Ltd. | Electric ultimate defects analyzer detecting all defects in PCB/MCM |
FR3105528A1 (en) * | 2019-12-23 | 2021-06-25 | Engie Green France | Method for detecting defects in an element made of composite material |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3803413A (en) * | 1972-05-01 | 1974-04-09 | Vanzetti Infrared Computer Sys | Infrared non-contact system for inspection of infrared emitting components in a device |
EP0089760A2 (en) * | 1982-03-18 | 1983-09-28 | United Kingdom Atomic Energy Authority | Transient thermography |
RU2073851C1 (en) * | 1992-11-24 | 1997-02-20 | Государственное научно-производственное предприятие "Исток" | Device for remote non-destructive flaw detection |
US5711603A (en) * | 1996-10-30 | 1998-01-27 | United Technologies Corporation | Nondestructive testing: transient depth thermography |
DE19841968C1 (en) * | 1998-09-14 | 2000-06-29 | Karlsruhe Forschzent | Two-dimensional quantitative mapping of laminar composite- and coating tenacity infers defects from high thermal resistance, when laser pulse induces measured heating profile on opposite side |
-
2001
- 2001-11-15 AU AU2002214889A patent/AU2002214889A1/en not_active Abandoned
- 2001-11-15 WO PCT/CA2001/001585 patent/WO2002048720A2/en not_active Application Discontinuation
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3803413A (en) * | 1972-05-01 | 1974-04-09 | Vanzetti Infrared Computer Sys | Infrared non-contact system for inspection of infrared emitting components in a device |
EP0089760A2 (en) * | 1982-03-18 | 1983-09-28 | United Kingdom Atomic Energy Authority | Transient thermography |
RU2073851C1 (en) * | 1992-11-24 | 1997-02-20 | Государственное научно-производственное предприятие "Исток" | Device for remote non-destructive flaw detection |
US5711603A (en) * | 1996-10-30 | 1998-01-27 | United Technologies Corporation | Nondestructive testing: transient depth thermography |
DE19841968C1 (en) * | 1998-09-14 | 2000-06-29 | Karlsruhe Forschzent | Two-dimensional quantitative mapping of laminar composite- and coating tenacity infers defects from high thermal resistance, when laser pulse induces measured heating profile on opposite side |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2005026747A2 (en) | 2003-09-16 | 2005-03-24 | Jacob Gitman | Electric ultimate defects analyzer detecting all defects in pcb/mcm |
US7877217B2 (en) | 2003-09-16 | 2011-01-25 | Invisible Ltd. | Electric ultimate defects analyzer detecting all defects in PCB/MCM |
EP1901060A1 (en) * | 2006-09-13 | 2008-03-19 | Ibea Ingenieurbüro für Elektronik und Automation GmbH | Thermographic detection system |
FR3105528A1 (en) * | 2019-12-23 | 2021-06-25 | Engie Green France | Method for detecting defects in an element made of composite material |
WO2021130458A1 (en) * | 2019-12-23 | 2021-07-01 | Engie Green France | Method for detecting faults in a composite material component |
Also Published As
Publication number | Publication date |
---|---|
AU2002214889A1 (en) | 2002-06-24 |
WO2002048720A3 (en) | 2002-10-03 |
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