Physics-of-failure based lifetime modelling for SiC based automotive power modules using rate- and temperature-dependent modelling of sintered silver

The new generations of automotive power modules pose new challenges and requirements for the die-related packaging technologies as well as the assessment of reliability and lifetime. The use of sintered silver for the die-related packaging in particular has proven promising and enables new designs such as a sintered die attach combined with a sintered top side interconnection comprising a copper foil and copper ribbon bonds. However, the empirical lifetime models for power modules developed over many years are not suitable any more. A holistic Physics-of-Failure approach can provide remedy as it allows for a significant reduction of testing time via finite element simulations. This approach requires a detailed understanding of the relevant failure mechanisms as well as an electrical, thermal and mechanical characterisation of the involved materials and subsequent field coupled modelling. A failure analysis of the complete power module revealed that the top side sinter layer connecting the copper foil to the semiconductor die is prone to degradation. Therefore, the core of this work is the mechanical characterisation of porous sintered silver and, in particular, the primary and secondary creep behaviour. A newly developed creep model which – for the first time – takes load reversal for primary creep into account is implemented with a subroutine. This allows for lifetime simulations within a Physics-of-Failure framework resulting in a first lifetime model on module level for a complex automotive power module employing sintered silver.