HEV power modules robust against cyclic thermo-mechanical stress

Abstract:
For the development of HEV power modules power-cycling stress tests and analyses of failure modes have been performed. This modules are fabricated in a two step sinter process first joining IGBTs and diodes to the topside of DCBs and secondly Ag-foils there on top. The investigations show, that the robustness against repetitive thermo-mechanical stress as required for HEV operation can be accomplished by the selection of surface patterns imprinted into the surface of the silver-foils. A failure mode resulting from avoidable deficiencies could be identified and distinguished from the failure mode appearing unavoidably due to principal material properties. This principal failure mode, the delamination between two AlCu-layers of the IGBT metallization appears to be facilitated by a creeping-based material transport within the AlCu-layers. This implicates its minor significance for temperatures below 0.4 Tmelt Al (373K).