Real-time life expectancy estimation in power modules

The environmental and operating conditions applied to power electronic modules, such as temperature changes, load cycling, vibration, etc., cause degradation and ultimately failure in particular at interfaces between dissimilar materials, such as wire bonds and in solder layers. In this paper a compact real-time thermal model is used to predict the temperatures of the active device junctions and inaccessible locations such as solder layers within the power module. The temperature estimates are combined with lifetime based reliability models to provide a tool for life consumption monitoring. A rainflow counting method is applied to the temperature vs. time data to extract the occurrence frequencies of different thermal cycling ranges. Knowledge of the life consumed for each different cycle then allows the remaining life time to be estimated under arbitrary operational conditions through application of the Palmgren-Miner accumulated damage rule. Example results for life consumption in power module substrate solder layers are presented.