Reliability assessment and thermal characterization of automotive power module package based on novel thick copper-ceramic substrate and hard epoxy encapsulation

Abstract:
Standard automotive power modules with sixpack topology and highest power density rely on metal ceramic substrates, direct liquid cooling by copper heat sinks and soft encapsulation by silicone gel. Variations of this packaging concept are often sought in order to adapt performance, reliability and cost of the power module to requirements set within a particular application. Therefore non-standard packaging options, such as novel thick copper substrates with copper metallization thicknesses up to 2 mm, aluminium heat sinks and hard encapsulation by epoxy potting, are assessed within this study. To evaluate wether these options are a viable alternative to standard packaging approaches, soft and hard potted modules based on thick copper substrates soldered onto an aluminium heat sink are compared, in terms of thermal performance and thermo-mechanical reliability, to standard soft potted power modules based on active metal brazed substrates soldered onto a copper heat sink. Thermal resistance measurements and thermal impedance finite element simulations are performed in order to compare thermal performance of the module types, differences in thermo-mechanical reliability are assessed via thermal shock tests. Further quantification of the influence of active metal brazed and thick copper substrates, heat sink material and epoxy potting onto damage of interconnection layers, such as substrate solder and sintered die attach layer, is done by thermo-mechanical finite element simulation of thermal shock test.