Power cycling failure analysis of double side cooled IGBT modules for automotive applications

A three-phase half-bridge insulated gate bipolar transistor (IGBT) module is designed and prototyped as the assembly of heat sink-substrate-post-chip-substrate-heat sink to realize high power density and good thermal performance for electric and hybrid electric vehicle applications. This paper reports the failure modes different from those fatigue of the chip-near interconnections in the conventional IGBT modules and a method to identify the weak points in two IGBT module samples during power cycling tests with timescale of seconds. Details presented include packaging structure and advantages of the designed IGBT module, conditions of the power cycling tests, thermal performance and power cycling lifetimes of the two module samples, small ranges containing the weak points to be determined with the recorded VCE parameters, the exact weak points, failure modes and mechanisms to be identified with optical microscopy and scanning electronic microscopy observation. The results obtained can be used as feedback to optimize the design and further improve the power cycling reliability of the present double side cooled IGBT module. The principle established through this work can also be applied to optimize the thermo-mechanical design and improve the reliability of other double side cooled power modules.