Failure analysis and lifetime assessment of IGBT power modules at low temperature stress cycles

Lifetime models of high-power Insulated Gate Bipolar Transistors modules express the number of cycles to end of life as a function of stress parameters. These models are normally developed based on experimental data from accelerated power-cycling tests performed at predefined temperature stress conditions as, for example, with temperature swings above 60 degrees C. However, in real power converters applications, the power modules are usually stressed at temperature cycles not exceeding 40 degrees C. Thus, extrapolating the parameters of lifetime models developed using data from high-temperature stress cycles experiments might result in erroneous lifetime estimations. This paper presents experimental results from power cycling tests on high-power Insulated Gate Bipolar Transistors modules subjected to low temperature stress cycles of 30 and 40 degrees C. Therefore, devices experience still accelerated aging but with stress conditions much closer to the real application. Post-mortem failure analysis has been performed on the modules reaching end-of-life in order to identify the failure mechanism. Finally, the number of cycles to end-of-life obtained experimentally is fit with a state-of-the-art lifetime model to assess its validity at low temperature stress cycles. Challenges and limitations on data fitting to this lifetime model and the impact of various stress parameters on the anticipated failure are also presented.