Power Cycle Testing at Low Temperature Swings – Evaluating the Stability of SAC- and SnSb-based Chip Solder Layers

Abstract:
Results of a comprehensive power cycling study on two groups of standard baseplate modules are presented. The main difference between the two groups is the used chip solder material. Group A modules are built up with a common SAC solder, whereas the group B modules use a special SnSb-based material. At temperature swings between 70K and 110K only small differences between the two types of modules were seen with wire bond lift-off being the dominant failure mode. However, at a more application relevant temperature swing of 40K the power cycling test reveals a significant difference between both groups. The SAC-soldered modules fail between 4.5 and 6 million cycles due to solder fatigue, whereas the SnSb-based soldered modules withstand at least 15 million cycles to failure without reaching the 20 % increase in thermal resistance failure criterion. Apparently the SnSb-based solder material provides a superior stability in the low temperature swing regime. The test on the SnSb-soldered modules is still ongoing. Up to now the test took more than one and a half years of testing time.