Conductivity Enhancement of Thermal Interface Material via Capillary Attraction

Our present work showed that capillary force could induce a conductive network in a silver-epoxy composite by adding a small amount of secondary fluid for the filler volume fraction as low as 5%. The electrical conductivity was enhanced from 10^-6 S/cm to 10² S/cm, transforming the polymer composite from insulating state to a conductive state. The thermal conductivity is improved by 2.5 times. Wetting properties such as wetting angle and interfacial tension between silver, epoxy and the secondary fluid were measured. A pronounced microstructure transition of filler network was also observed as the second liquid content gradually increased. With the aid of SEM-EDS analysis, the secondary liquid was found to be mainly distributed among the silver clusters and aggregates, which provided strong evidence to prove the existence of capillary bridging. These current findings not only provide a simple way to manipulate the conductive network formation, but also tremendously lower the consumption of silver flakes to the current 5 Vol%, which would bring a remarkable economic benefit to industry.