Evaluation and Process Optimization of Heat-Curable Thermal Interface Materials for Advanced Packages

This research focused on evaluating 4 epoxy-based thermal interface materials for use between the ASIC and heat spreader in high-reliability flip-chip packages. The research methods included materials characterization, processing experiments and package builds. Experimental thermal conductivity measurements were performed using laser flash analysis on bulk and layered coupons to provide insight to interfacial thermal resistance. Layered samples incorporated two copper pads encapsulating the thermal interface material, thereby approximated a die-to-heat spreader interconnect. The best thermally performing material was incorporated into two different flip-chip package assemblies and exposed to solder reflow temperatures. The material was inspected for voids using confocal scanning acoustic microscopy. To achieve bondlines with low voiding, processing variables were studied including cure temperature ramp rate, cure pressure, and the inclusion of a pre-bake step before curing.