On the validity of rainflow counting-based lifetime assessment for power electronics assembly

The lifetime assessment of power electronics based on mission profiles is increasingly applied to obtain realistic lifetime predictions while considering application-close operational scenarios. Generally, mission profile-based lifetime is calculated by individual temperature cycles disassembled from the mission profiles using specific counting methods. Among the different methods, rainflow counting (RC) method is the most common algorithmic procedure for determining damage-relevant events in power electronics. However, the conventional RC method does not consider the mechanical sequential effect and transient effect on damage caused by time-dependent material properties, especially at high temperatures during power module operation. In this paper, we investigate the validity of using the RC method for mission profile-based lifetime assessment of power modules. Through finite element (FE) modeling, we explicitly calculate both effects driven by the mission profile. For the selected mission profiles, we find that the lifetime of bond wire calculated by the FE approach shows a difference of 9 %, which cannot be sensed by the conventional RC approach. Furthermore, through a comparison between different approaches, it appears that the lifetime calculated by the RC approach is higher than the lifetime assessed by the FE approach by around 20 %. Simultaneously at the solder, the deviation between both approaches reaches around 95 %.