Study on the effects of small swing of junction temperature cycles on solder layer in an IGBT module

This paper proposes a method to obtain the effect of junction temperature swing with low amplitudes on the power modules, so that the knowledge about the reliability characteristics of the modules and the lifetime model could be improved. Power cycling tests and finite-element analysis (FEA) models, for non-aged and aged IGBT modules, are designed to illustrate the failure mechanisms of the power modules and the stress distribution. IGBT modules in actual converters such as those in wind turbine systems are usually operated in a junction temperature swing range up to 40°C, therefore small swing junction temperature tests are designed to obtain the effects of small swings of junction temperature on the lifetime of IGBT modules. It is found that such relatively minor stress cycles, which happen frequently during normal operation, may not be able to directly initiate a crack but can contribute to the development of damage in die attach solder layer due to the stress concentration. The experimental results show that the effects of small swing of junction temperature are affected by the ageing state, stress level and load sequence.