Abstract
An insulated gate bipolar transistor (IGBT) power module has acquired fast switching and low conduction loss characteristics. Because of its electrical characteristic, 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 wire and the solder are subjected to thermo-mechanical stress which cause solder fatigue and bonding wire failure, and affect the reliability of IGBT under actual operation conditions. A 3-D finite element (FE) model was established base on real test samples. In order to reduce calculation time and increase the research efficiency, multi-point constraints (MPC) method were used to simulate and direct-field coupling thermal-structural FE analysis were conducted to analyze the temperature distribution of IGBT and the mechanical behavior of bonding wire under cyclic power cycling test. The simulation results found that the maximum junction temperature 112.5 ˚C was observed at the middle of IGBT chip under the load current of 40 A. The predicted temperature history and experiment results under the cyclic current load were identical, which indicates the reliability of direct-field coupling thermal-structural FE analysis. Then analyze the mechanical behavior of IGBT, the structural simulation results showed 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 bonding interface between the bonding wire and chip are 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.