Parametric study on relevant design and material parameters for reliable hard encapsulation of automotive power modules

Abstract

In power module packaging, the standard approach for encapsulation is potting by soft silicone gels with low vis-cosity and youngs modulus. Within the last decade, hard encapsulation realized by large area transfer-molding of epoxy mold compounds has established itself as an alternative due to potential cost reduction and reliability enhancement. Large-area potting of liquid hard encapsulant material is another option for realization of a hard encapsulation. Regardless of the used process technology the large substrate, heatsink and module size in general, multi-material stack-up, heavy cyclic thermal loads during operation, high temperature and high voltage operation possess challenges to the material choice for hard encapsulation. Delamination and brittle fracture of the encapsulant and damage of the encapsulated structure through the encapsulant are the main concerns within the material selection process. Thermo-mechanical simulations can support and provide guidance within this material selection process. Therefore comparative parametric simulations have been performed within this study in order to estimate the influences of geometric parameters, such as substrate metallization thickness and heatsink thickness, and process parameters, such as curing temperature of the potting material, onto the thermo-mechanical behavior of the encapsulated packages. The concept of calculating an “effective package coefficient of thermal expansion” is introduced in this study as a tool for effective selection of encapsulants. The obtained results can be used as a guideline for the selection of encapsulation materials for different module stack ups.