New physical model for lifetime estimation of power modules

In this paper a physical model for lifetime estimation of standard power modules is proposed. The lifetime prediction is based on the assumption that the solder interconnections are the weakest part of the module assembly and that the failure cause is the inelastic deformation energy accumulated within the solder material. Unlike the well-known Coffin-Manson model, the proposed model can be used to physically explain the dependency of lifetime on the various properties of a temperature profile i.e. frequency, dwell-ramp time, minimum/maximum temperature. The model is based on Clech´s algorithm for simulation of stress-strain solder response under cyclical thermal loading and on the solder deformation mechanism map used to define the dominant failure mechanism under observed stress-temperature conditions. Either accelerated cycling tests or existing field databases are needed to parameterize the model. To verify the approach, the results of power cycling tests for a high power IGBT module found in literature are applied and the impacts of two mission profiles on the module lifetime are examined.