Acoustic Microscopy for Electronics - Alternative Applications
Non-destructive testing provides the foundation for any thorough failure analysis project. Without properly gathering initial data about the part - condition of the package and leads, electrical behavior, and so on - an analyst would be hard pressed to identify and track down a defect. Often, the use of acoustic microscopy for electronics component inspection can provide invaluable data about the condition of a part that directly leads to identifying the root cause of failure - for example, delamination of the package over the lead for an open-circuited signal. Looking for delamination is only one of the acoustic microscope's applications, however; properly applied, it can reveal much more.
As awareness increases about the presence of "grey-market" components in the market, it has become increasingly common to use acoustic microscopy for electronic component counterfeiting inspection. Since the ultrasonic waves the acoustic microscope uses are extremely sensitive to interface changes, it is often possible to determine whether a package has been "black-topped" - coated with a layer of black epoxy or other material, then re-marked - simply based on the appearance of the returning sound wave. Comparing the top and bottom of a package using acoustic microscopy can also reveal whether or not a part has had its original markings sanded off, based on a comparison of the surface texture of a component. In some cases, it's even possible to get an acoustic image of two sets of markings - the original device markings, and a second set of markings painted over the top after the fact.
The acoustic microscope can also be used to generate simulated cross-sections of a device. Typically, the microscope is run in either A-Mode (a waveform) or C-Mode (a top-down image); when run in B-Mode, the microscope collects data about all the interfaces along a given scan line, then uses acoustic time-of-flight information to construct an approximation of what a device would look like if it were cross-sectioned along that line. This can be beneficial for analyzing devices with very complex packaging, as it allows an analyst to see the way the various constituents of the device "stack up". A B-Mode image can also reveal some packaging anomalies like die tilt or coplanarity issues.
Without using acoustic microscopy for electronic component inspection, a wealth of non-destructive data would be lost. The acoustic microscope can provide much more data than just that pertaining to a failure; general construction quality, evidence of remarking or other package tampering, and other information can all be found with the proper application of the tool.
Derek Snider is a failure analyst at Insight Analytical Labs, where he has worked since 2004. He is currently an undergraduate student at the University of Colorado, Colorado Springs, where he is pursuing a Bachelors of Science degree in Electrical Engineering.