Online Condition Monitoring of Solder Fatigue in a Clip-Bonding SiC mosfet Power Assembly via Acoustic Emission Technique

In this work, an acoustic emission (AE) technique was applied to online condition monitoring (CM) of solder fatigue in a clip-bonding SiC mosfet power assembly during short and long power cycling tests (PCTs). Solder fatigue caused by PCTs was identified in the clip-bonding assembly via scanning acoustic tomography and scanning electron microscopy and successfully diagnosed via the AE-based online CM. By analyzing AE signals, junction temperature, and junction-to-case thermal resistance, it can be confirmed that the AE signal shows a superior sensitivity in initial fatigue diagnosis to the thermal or electrical signals. Meanwhile, two solder fatigue processes, cracking initiation and cracking acceleration, were identified based on the cumulative AE counts and AE energy during the long PCT. An abrupt increase in AE energy happened at the end stage of the long PCT due to a severe cracking process, which can be regarded as a prewarning of a failure point of the power assembly. In addition, the relationship between transitional thermal resistance and accumulative AE energy was investigated and shows a linear relationship. These results suggest that the AE technique can be a promising online CM approach to diagnose and predict solder fatigue in power assemblies during operation.