Effective thermal modeling of discrete components under peak-pulsed power loading by subdomain consideration

Power diodes are subjected to massive sudden peak- pulsed powers (hundreds of watts for milliseconds) boosting junction temperatures within the diode package. If the maximum junction temperature is exceeded, the diode fails. To develop safe designs it is therefore of great importance to predict the diode\´s thermal behavior under peak-pulsed power loads. Due to the peak-pulsed thermal loading and poor thermal conductivity of the diode\´s encapsulation, thermal finite element (FE) analysis is very time-consuming. The small time scale of the transient thermal effect requires a high level of mesh refinement to capture the peak temperature effects, but at the same time the "far field" is undisturbed. In this work, the encapsulation effect on the total discrete package transient thermal behavior is approximated by a semi-analytic approach and taken into account in the FE model. This is done by applying time-dependent semi-infinite boundary conditions on a sub domain for the thermal solution, while the thermo-mechanical analysis is applied to the entire domain. Results are compared to an alternative approach which makes use of semi-infinite elements. It will be shown that the sub-domain consideration approach greatly reduces simulation time without significantly affecting the outcome of the calculations.