Lifetime prediction for power modules in wind-energy converters based on temperature variations in a large area substrate solder connection

Abstract

Accurately modelling the lifetime of a power module is a major concern in wind power applications. Their lifetime is typically modelled via empirical laws fitted to data, e.g. from power cycling tests. Often, those models are parametrized with respect to junction temperatures due to its measurability and failure mechanisms occurring close to the chip. Nevertheless, some module types are limited by their large area substrate solder between the baseplate and substrate metallization. They motivate to choose the substrate solder temperatures for a lifetime model instead. Furthermore, transient effects are conceivable which lead to an ambiguous relation between substrate solder and junction temperatures. Thus, for such a model, a substitution of junction temperatures with substrate solder temperatures is carried out to derive a model based on substrate solder temperatures. Afterwards, the influence on lifetime estimation is investigated. For this purpose, the thermal behavior of a PrimePack™2.XT during power cycling is studied, utilizing reduced order models. Lifetime calculations with a junction and a substrate solder temperature-based model on a mission profile from a wind application show that the latter yields a significantly higher lifetime. A shift in the ratio between substrate solder temperature and junction temperature during operation towards a lower regime compared to the power cycling test is identified as the root cause for this. It is shown that from a physical perspective, this result is realistic and a lifetime modelling with respect to substrate solder temperatures increases the accuracy of lifetime prediction in this case.