SBIR Phase II: Multimodal High-Conductivity Filler for Epoxy Molding Compounds

This Small Business Innovation Research Phase II project will focus on developing more efficient semiconductor packaging materials, which is one of the key challenges of the electronics industry where increasing power and reduced size of integrated circuits is creating heat dissipation challenges. Most epoxy molding compounds used to encapsulate semiconductors contain fused silica (55-70% by volume) to maintain a compatible thermal expansion coefficient and impart moisture resistance. However, the resulting thermal conductivities of the composite compounds are very low (<1 W/mK). The low thermal conductivity of the epoxy molding compound increases the operating temperatures, which in turn decreases the reliability and processing speed of microprocessors. As semiconductor clock speeds continue to increase and chip sizes decrease, the need for higher thermally conductive molding materials has become a stark necessity. In Phase I of this project multi-modal distributions of high-conductivity diamond powder where optimized to obtain high packing densities (over 72% by volume) in epoxy molding compounds. The resulting thermal conductivities of diamond/epoxy composites were almost 8 times higher than conventional silica-filled epoxies and almost 30 times higher than the epoxy matrix. The thermal expansions of silica and diamond filler are similarly low, thus allowing better matching to silicon. In this Phase II project significantly higher thermal conductivities are to be achieved by optimizing the epoxy/hardener system with the diamond filler to improve bonding and thereby improving the heat transfer mechanism. The diamond filler will be used as a direct substitute for commercially available silica filler, requiring little or no modification of existing equipment or processing. The diamond/epoxy molding compound will effectively act as a heat-spreader. The diamond filler will allow higher switching speeds, thinner oxide gates and increased reliability of electronics. The project team will work with an epoxy molding compound (EMC) manufacturer to introduce the diamond filler into the commercial market towards the end of Phase II. Commercial markets for this EMC technology include high-performance aerospace, automobile and microelectronic packaging applications, where heat dissipation from the packaging material outweighs the increased material cost. The increased thermal conductivity offered by the diamond filler will benefit the business and scientific community by increasing computing speed and hardware reliability. Studies indicate that heat dissipation and associated thermal problems are the most critical factors in determining the efficiency and reliability of electronic devices. In terms of scientific and educational value, EMC's incorporating the optimized diamond filler will exhibit the maximum thermal conductivity obtainable and serve as the upper-limit benchmark in thermal conductivity for the composite material.