Thermal analysis and reliability assessment of power module under power cycling test using global- local finite element method

Insulated gate bipolar transistor (IGBT) power modules have acquired fast switching and low conduction loss characteristics. Because of these electrical characteristics, the IGBT has been widely applied in power supplies, e.g. hybrid electric vehicle, wind power generation, etc. However, the IGBT during rapid transient operation under high power can cause the IGBT chip to lead high junction temperature and high temperature gradients. Furthermore, because of the coefficient of thermal expansion (CTE) mismatch between the various material layers, the bonding wires and the solder joints are subjected to thermo-mechanical stress which cause solder fatigue and bonding wire failure, and then affect the reliability of IGBT under actual operation conditions. A 3-D finite element (FE) model was established base on real test samples. The simulation results found that the maximum junction temperature 112.5 °C is observed at the middle of IGBT chip under the load current of 40 A. Then analyze the mechanical behaviors of IGBT, the structural simulation results show that under a cyclic power environment, the stress concentration within the wire, caused by the CTE mismatch between the wire and the IGBT chip. Therefore, the wire/chip interface is the weaker portion of the power module. Finally, according to the life prediction models of literatures, this paper assessed the reliability of bonding wire in order to investigate the effects of thermal stress and strain on reliability during power cycling test.