THERMO-MECHANICAL FATIGUE INDUCED UNEXPECTED STRAIN HARDENING OF CU CLIP WIRING ON TRANSFER-MOLD TYPE EV POWER MODULES

Abstract

Power modules subjected to cyclic power operation experience thermomechanical fatigue. Herein, the epoxy molding compounds and creep behaviors of solder joints promoted the strain hardening of the Cu clip wiring and caused failure to the power module during the power operations. In the Cu clips, the grain size was refined by 90% from the failure stage compared to the initial state, and an increase in hardness was observed. The results indicate that constraints of EMC and the creep behaviors of solder joints are other critical factors for the role of bare Cu clip strain hardening of EV power modules.