Rheology and Thermal Conductivity of Diamond Powder-Filled Liquid Epoxy Encapsulants for Electronic Packaging

The traditional silica-based epoxy system used for electronic packaging has a poor thermal conductivity of less than 1 W/mK and no longer meets the increasingly stringent thermal management requirements of many packaging applications. The current commercial availability of low-cost diamond powders with very high-thermal conductivity makes it possible to consider diamond powder-filled epoxy for high-end product packaging. This paper reports the design, rheology, and experimentally determined thermal conductivity results on the multimodal diamond powder-filled epoxy system for liquid encapsulants. Rheology studies of the monomodal diamond powder in epoxy show the necessity of the use of surfactants when the powder sizes are below 10 mu m. A high-thermal conductivity of 4.1 W/mK was achieved for epoxy-filled by 68% volume loading of diamond powders, which required a multimodal particle size distribution (nine sizes). Comparative measurements of electronic junction temperatures of Si diodes sealed by the diamond powder-filled epoxy and commercial silica-epoxy show a much better thermal performance of the diamond-filled epoxy, which suggests the potential application of the diamond-filled epoxy for packaging high-end electronic products.