Acoustic Microscopy of High-Reliability Electronic Components

1. 1 Acoustic Microscopy of High-ReliabilityElectronic Components

2. 2 Immersion systems Squirter systems Systems for inspection aero composite structures Systems for inspection of tube and bar Systems for use in the railway and automotive industries Inspection of hollow railway axles Acoustic microscopes USL Expansion boards PM30 Pulser Receiver (with linear & log amplifiers) PHASYS phased array system Multiplexers USL Ultrasonic Sciences Ltd

3. 3 ACOUSTIC MICROSCOPE APPLICATIONS TO MICROELECTRONICS John Jones, ALTER Technology Group, UK Office ATG became involved in acoustic microscopy in 1998 whilst qualifying a GPS PEM for a Japanese space programme. ATG acquired an acoustic microscope in 2002 and have processed many thousands of components since then. In 2011 the microscope was upgrade by USL and now has new objectives and the latest software. ATG became involved in acoustic microscopy in 1998 whilst qualifying a GPS PEM for a Japanese space programme. ATG acquired an acoustic microscope in 2002 and have processed many thousands of components since then. In 2011 the microscope was upgrade by USL and now has new objectives and the latest software.

4. 4 A typical failure analysis sequence � electrical measurement has identified open circuits � radiographic inspection had found no defects � CSAM identified delamination of the die surface (pop-corning) � de-encapsulation and SEM confirmed that ball bonds had been torn from the die surface. The Dutch C17th scientist Snell described how light was refracted in an optical lens although it had been proposed earlier by an Arab scientist, Snell�s Law is the principle behind acoustic microscopy. Basically an ultrasound pulse (1MHz to 100MHz) applied to a solid body will be reflected back from any interfaces in that body. The amount of reflection depends on the acoustic impedance of the material and the quality of the bond at the interface. More importantly if the acoustic pulse passes from solid to air the phase of the signal will be seen to flip making acoustic microscopy a valuable tool for detecting voids and delaminations. The rest is down to the computing power of the acoustic microscope providing the type of images shown here. The Lucent microcircuit shown has delaminated during reflow soldering (pop-corning) tearing the bond wires from the silicon chip. The Dutch C17th scientist Snell described how light was refracted in an optical lens although it had been proposed earlier by an Arab scientist, Snell�s Law is the principle behind acoustic microscopy. Basically an ultrasound pulse (1MHz to 100MHz) applied to a solid body will be reflected back from any interfaces in that body. The amount of reflection depends on the acoustic impedance of the material and the quality of the bond at the interface. More importantly if the acoustic pulse passes from solid to air the phase of the signal will be seen to flip making acoustic microscopy a valuable tool for detecting voids and delaminations. The rest is down to the computing power of the acoustic microscope providing the type of images shown here. The Lucent microcircuit shown has delaminated during reflow soldering (pop-corning) tearing the bond wires from the silicon chip.

5. 5 CSAM and COMPONENT EVALUATION Radiographic Image The image shows the die, die attach, lead frame and the bond wires CSAM Image The image also shows the plastic tie bar used to support the lead frame and a heat spreader below the die Acoustic microscopy is complimentary to and not an alternative to radiographic inspection. The radiographic image can be used to assess the metal elements of this ACTEL FPGA. The lead frame, die, die paddle, die attach perimeter and bond wires are all very obvious. What the radiographic image does not show is that buried in the encapsulant is a plastic tie bar which holds the fine pitch lead frame in place during assembly of the part. Radiographic inspection also does not show the heat spreader below the die paddle. The grey scale CSAM images provides more detail than the colour image in the previous slide. The new software allows delaminations and voids to be superimposed in colour (red) on the grey scale image. Acoustic microscopy is complimentary to and not an alternative to radiographic inspection. The radiographic image can be used to assess the metal elements of this ACTEL FPGA. The lead frame, die, die paddle, die attach perimeter and bond wires are all very obvious. What the radiographic image does not show is that buried in the encapsulant is a plastic tie bar which holds the fine pitch lead frame in place during assembly of the part. Radiographic inspection also does not show the heat spreader below the die paddle. The grey scale CSAM images provides more detail than the colour image in the previous slide. The new software allows delaminations and voids to be superimposed in colour (red) on the grey scale image.

6. 6 CSAM and COMPONENT SCREENING This is a typical space upscreening lot with CSAM being performed before and after burn-in, thermal shock etc. The sample size is deliberately small. Because focussing the microscope and scanning the samples takes time there is a possibility that by the time the scan reaches the last row water may have ingressed into any delamination and the acoustic signal will not flip. ATG recommend a lower temperature but longer time bake because our observations have indicated that the predominant wear out mechanism in plastic encapsulated components is gold aluminium intermetallics. Residual Gas Analysis (RGA) of the impervious A/S bags found no significant change in the internal environment in 2 to 3 years. Had moisture ingressed into the plastic packages corrosion at least of aluminium bond pads would have been expected. Extensive testing of FPGA including HAST found no evidence of degradation (under taken for MIL/Avionics customers) This is a typical space upscreening lot with CSAM being performed before and after burn-in, thermal shock etc. The sample size is deliberately small. Because focussing the microscope and scanning the samples takes time there is a possibility that by the time the scan reaches the last row water may have ingressed into any delamination and the acoustic signal will not flip. ATG recommend a lower temperature but longer time bake because our observations have indicated that the predominant wear out mechanism in plastic encapsulated components is gold aluminium intermetallics. Residual Gas Analysis (RGA) of the impervious A/S bags found no significant change in the internal environment in 2 to 3 years. Had moisture ingressed into the plastic packages corrosion at least of aluminium bond pads would have been expected. Extensive testing of FPGA including HAST found no evidence of degradation (under taken for MIL/Avionics customers)

7. 7 CSAM and COUNTERFEIT COMPONENTS Counterfeit components are a big problem! Blatant counterfeits, no die, no bond wires, rebranding etc can occur to any level of component from pure commercial to space qualified. This type of counterfeit can detected by good incoming inspection processes, radiographic screening etc. However some counterfeits are being manufactured on the same production line as genuine product by sub contractors running extra shifts. These components may be functionally identical to the expected parts but fail to meet the full requirements of the original manufacturer�s data sheet. ATG experienced this when a Analog Devices ADG452B found it�s way into the supply chain as the more expensive wider temperature range BR version of the part. As a result of the examples above ATG instigated a data base recording all of the set up variables for each lot screened so that similar product/manufacturers could be compared and changes investigated. Counterfeit components are a big problem! Blatant counterfeits, no die, no bond wires, rebranding etc can occur to any level of component from pure commercial to space qualified. This type of counterfeit can detected by good incoming inspection processes, radiographic screening etc. However some counterfeits are being manufactured on the same production line as genuine product by sub contractors running extra shifts. These components may be functionally identical to the expected parts but fail to meet the full requirements of the original manufacturer�s data sheet. ATG experienced this when a Analog Devices ADG452B found it�s way into the supply chain as the more expensive wider temperature range BR version of the part. As a result of the examples above ATG instigated a data base recording all of the set up variables for each lot screened so that similar product/manufacturers could be compared and changes investigated.

8. 8 Because of the colour of the ferrite cracks could only be detected at high magnification after flooding the surface with IPA to enhance the cracks. This was taking 15 to 20 minutes per sample. Including set up time, CSAM was processing 20 isolators in the same time. The CSAM image also supplied further useful information of the quality of the bonding of the ferrite to the substrate and the magnet etc to the ferrite. Because of the colour of the ferrite cracks could only be detected at high magnification after flooding the surface with IPA to enhance the cracks. This was taking 15 to 20 minutes per sample. Including set up time, CSAM was processing 20 isolators in the same time. The CSAM image also supplied further useful information of the quality of the bonding of the ferrite to the substrate and the magnet etc to the ferrite.

9. 9 Although CSAM could be used to screen any ceramic capacitor, filter or surface mount monolithic inductor CSAM is extremely useful in screening the ceramic piece parts of filter connectors. Here you have two factors to consider. The filter connector is an expensive unit. If defective capacitors are used time and effort are wasted during assembly before the failure is found. Similarly if the completed filter connector is defective but the capacitor was good to start with manufacturer knows that there is a process problem. Although CSAM could be used to screen any ceramic capacitor, filter or surface mount monolithic inductor CSAM is extremely useful in screening the ceramic piece parts of filter connectors. Here you have two factors to consider. The filter connector is an expensive unit. If defective capacitors are used time and effort are wasted during assembly before the failure is found. Similarly if the completed filter connector is defective but the capacitor was good to start with manufacturer knows that there is a process problem.

10. 10 OTHER SCANNING ACOUSTIC MICROSCOPY APPLICATIONS The images shown so far were made using a single gate i.e. only part of the return signal was processed to form the image. But it is possible to set up multiple gates and generate multiple images.The images shown so far were made using a single gate i.e. only part of the return signal was processed to form the image. But it is possible to set up multiple gates and generate multiple images.

11. 11 And finally a solder problem � CSAM is commonly used by manufacturers of power semiconductors to assess solder die attach. CSAM can not only identify voids in solder, CSAM will also high light dewetting where a solder joint may look good optically and by radiographic inspection but the solder has not bonded to the surfaces being joined. Some success has been reported by other users in inspecting BGA soldering. And finally a solder problem � CSAM is commonly used by manufacturers of power semiconductors to assess solder die attach. CSAM can not only identify voids in solder, CSAM will also high light dewetting where a solder joint may look good optically and by radiographic inspection but the solder has not bonded to the surfaces being joined. Some success has been reported by other users in inspecting BGA soldering.

12. 12 Publications and Contacts COTS Reliability Assessment, CMSE Europe, 2010 � Ron Fidler and John Jones. Counterfeit Components, Encapsulation Considerations, UK COG Conference 2007 � John Jones Contacts COTS Reliability � ron.fidler@altertechnology.com COTS Reliability � john.jones@altertechnology.com CSAM Services � manuel.dominguez@alter-spain.com COTS Services � david.n@alter-spain.com (David Numez)

13. 13 USL Ultrasonic Sciences Ltd

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17. 17 USL Ultrasonic Sciences Ltd Unit 4 Springlakes Industrial Estate, Deadbrook Lane, Aldershot, Hampshire, GU12 4UH, England Tel: + 44 (0)1252 350550 Fax: + 44 (0)1252 350445 E mail: info@ultrasonic-sciences.co.uk Internet: http://www.ultrasonic-sciences.co.uk