Development of a heat spreader for high power electronic modules using thermal vias

The Virginia Power Electronics Center at Virginia Tech has performed research to develop improved heat spreader designs for high power electronic modules. The objectives of this work are to maximize thermal conductivity, minimize thermal shear stresses, and improve mechanical toughness of the materials and interfaces used in the heat spreading structure. As a result of this research, a heat spreader design which uses a copper/molybdenum bi-metallic plate has been developed. The structure uses a low thermal expansion material as a base (molybdenum) with copper or metal matrix composite (MMC) filled vias which provide a low thermal resistance path between heat source and sink. The high elastic modulus of the base material acts to constrain the copper or MMC vias from thermal expansion, providing a significant reduction in thermally induced shear stresses at the heat spreader/power module interface. This paper presents the design layout and initial characterization data of the improved heat spreading structure. The processing techniques and bonding materials developed in the course of this research are described, as well as thermal and mechanical models describing the behaviour of the vias and bonding layers during power module operation