Low Stress Cycle Effect in IGBT Power Module Die-Attach Lifetime Modeling

Abstract

Operational management for reliability of power electronic converters requires sensitive condition monitoring and accurate lifetime modeling. This study adds to the second aspect by examining the effect of cyclic junction temperature variations ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> of low amplitude in different stages of the power module ageing process. 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 due to stress concentration. This agrees with the observation that the ageing process tends to accelerate toward the end of life. This study investigates the dependence of the ageing effect on the amplitude of ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> , the mean junction temperature T,,,, and the present health condition of the module, and proposes a lifetime model focusing on die-attach solder fatigue. It is assumed that the future-ageing process is independent of the operational history that has led to the current state of health. The model is intended for operational management of converter systems that are subjected to frequent low ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</sub> stress cycles and are supposed to be in service reliably for a long time with a slow ageing process. Experimental results validate the model.