Analysis of thermal evolution in power semiconductor modules as lifetime and reliability tool

A method is presented for temperature calculations in systems with irregular rapidly varying chip-powers by solution of implicit integral equations, where the dissipated power may depend on chip-temperature itself. For discontinuous power evolution differential equation solvers pose problems in treating thermal equivalent circuits. When no thermal model exists, the method can start directly from measured cool down curves. For user specified mission profiles over long duration, semiconductor module lifetimes are estimated by thermal cycle counting and application of the Palmgren-Miner-rule. For simplified models of chip power dissipation thermal runaway can be observed in case of unfortunate system parameters. A general criterion is inferred for the thermal stability of the system with the help of a quasi steady-state model for the system´s cooling power described by a single thermal resistor.