Fatigue Mechanism of Die-Attach Joints in IGBTs Under Low-Amplitude Temperature Swings Based on 3D Electro-Thermal-Mechanical FE Simulations

Fatigue failure of insulated gate bipolar transistor modules (IGBTs) packages under low-amplitude temperature swings is of great significance for the reliability evaluation of IGBTs operating in actual power electronic devices. In this article, failure mechanism of die-attach joints in IGBTs under normal operating and accelerated aging was comparably investigated by a three-dimensional electro-thermal-mechanical coupled model. Results indicated that local viscoplastic deformation of solder alloys around stress concentrated areas caused by material microdefects is the root cause of fatigue of die-attach joints under low-amplitude temperature swings. Fatigue cracks can only initiate and propagate at those plastically deformed areas (activation points). Fatigue of die-attach joints is co-determined by the number of activation points and crack growth rate. Comparably, the whole die-attach solder is in viscoplastic deformation under accelerated aging and the number of activation points has reached its saturation. Fatigue of die-attach joints under accelerated aging is only determined by the crack growth rate. Due to the difference in failure mechanism, it is questionable to directly extend conventional life models to normal operating conditions. Accordingly, an energy-based physical life model for die-attach joints in IGBTs under low-amplitude temperature swings was proposed.