Scanning Acoustic Microscopy for Solder Joint Failure Analysisand Design Improvements

摘要

This paper reports using Scanning Acoustic Microscopy forrnsolder joint failure analysis and process and designrnimprovements. There are reliability concerns associated withrnsolder voids or non-wetting of the solder to the bond padsrnwhich is particularly important for higher electrical power orrntemperature applications. Defects in solder can also occur andrngrow during operation and thermal cycling. Sonoscan is anrnattractive non-destructive test to characterize solder joints andrnis often used to study the growth of defects during life testrnsimulations. X-ray imaging cannot identify very smallrndefects, particularly non-wetting and delamination because ofrnpoor resolution. The instrument used in this study was a C-SAMrn(C-Mode Scanning Acoustic Microscopy) operating inrnreflection mode at 30-100 MHz. We have identified voidsrninherent in the solder layer as well as delamination at thernpackage to solder and solder to heat-sink interfaces. C-SAMrnresults confirmed that the delamination was caused by CTErnmismatch of the materials as well as the mechanical stressesrncaused by higher level package integration and modulernassemblies. Thermal cycling studies have shown that typicallyrnthe voids do not grow whereas delamination does. Thesernresults were used to improve thermal heat-sinking and productrnreliability by minimizing defects in solder joint by changes inrnprocess and mechanical designs.