Comparison of power cycling and thermal cycling effects on the thermal impedance degradation in IGBT modules

Insulated gate bipolar transistor (IGBT) devices have gained leading position in traction and aerospace applications. The failure of these switches (IGBT) can reduce the efficiency of the system. Two most dominated failure mechanisms of IGBTs are solder fatigue and bond wire lift off. One of the major effects which influence these failure mechanisms is thermal impedance characteristics, which depends on the heat dissipation in the junction. In traction or aerospace application, the operational loads are not always constant. It results in the temperature cyclic in power converter, meaning that change in the device junction temperature. This change in temperature degrades the transient thermal resistance, and induces a mechanical stress especially at contacting surfaces of materials with different coefficient of thermal expansion. This may lead to degradation or complete failure of these components. The aim of this paper is to identify thermal impedance variation due to power cycling and thermal cycling. More importantly which temperature cyclic nature causes degradation in the thermal impedance, and its relation to semiconductor module failure mechanism.