A Physics-of-failure based Prognostic Method for Power Modules

This paper describes a physics of failure (PoF) based prognostic method for power electronic modules. This method allows the reliability performance of power modules to be assessed in real time. A compact thermal model was firstly constructed to investigate the relationship between the power dissipation and the temperature in the power module. Such relationship can be used for fast calculation of junction temperature and the temperatures at each interface inside power modules. The predicted temperature profile was then analyzed using a rainflow counting method so that the number of thermal cycles with different temperature ranges can be calculated. A reduced order thermo-mechanical model was also constructed to enable a fast calculation of the accumulated plastic strain in the solder material under different loading conditions. The information of plastic strains was then used in the lifetime prediction model to predict the reliability of the solder interconnect under each regular loading condition. Based on the linear damage rule and the number of cycles calculated from the rain flow counting algorithm, the accumulated damage in the power module over the whole period of usage can be predicted. As a demonstration, this method has been applied to a typical IGBT half bridge module used in aircraft applications.