Finite element modelling of thermal fatigue effects in IGBT modules

The effects of progressive thermal fatigue of the solder layer interface on the thermal performance of power module packages have been investigated. Specifically, in the paper the analysis of an 800 A-1800 V IGBT module using finite element techniques is performed. The use of this technique for modelling fatigue effects is thus demonstrated, and a method for estimating the fatigue lifetime of soldered power modules based on the Coffin-Manson relation is also given. Assessed parameters in the three-dimensional model are the thermal resistance, heat flux distribution through the different layers and maximum die temperature. The critical crack length at which the thermal resistance significantly increases is determined from the two-dimensional model. The temperature excursion and shear strain of the solder layer are estimated from dynamic analysis. Finally, all achieved models are calibrated by comparison of predicted results with simple theory and direct temperature measurements.