Simulation-based lifetime curve for a power module to extend parameter regime beyond testing limitations

摘要

There are two important reliability tests commonly used in power electronics imposing thermomechanical stress: power cycling (PC), when heat is produced in chips by applied current, and passive thermal cycling (TC), when module baseplate is heated and cooled externally. Especially the latter is efficiently used to stress the large area solder interface between substrates and baseplate [1]. Both these tests are usually described by combination of minimal and maximal temperatures T_min, T_max and temperature swing AT. During experimental testing, one of the temperature limits (usually Tmin for TC and Tmax for PC) is held constant. Influence of the chosen reference temperature and its particular value on the expected lifetime is discussed in the current paper. FEM simulations are used to extend the lifetime prediction to the conditions not or hardly covered by standard reliability thermal cycling tests. In a first step, simulation is applied to compare the expected life time dependency on temperature swing per cycle for two scenarii of constant temperature range limits: fixed T_min and fixed Tmax. Furthermore, simulation is used to evaluate a pre-existing lifetime assessment and estimate the safety factor behind it.