High performance conductive adhesives

Isotropic conductive adhesives (ICAs) have been developed as an alternative for traditional tin/lead (Sn/Pb) solders for electronic applications. Compared to mature soldering technology, conductive adhesive technology is still in its infant stage, therefore, there are some limitations for current commercial ICAs. Two critical limitations are poor impact performance and unstable contact resistance with nonnoble metal finished components. These limitations seriously hindered the wide applications of ICA's. No current commercial ICAs show both desirable impact performance and stable contact resistance. In this paper, novel conductive adhesives were formulated using mixtures of an epoxide-modified polyurethane resin and a bisphenol-F type epoxy resin and a corrosion inhibitor. Cure profiles, rheology, and dynamic mechanical properties of the conductive adhesives were studied using a differential scanning calorimeter (DSC), a rheometer, and a dynamic mechanical analyzer (DMA), respectively. Impact strength and contact resistance with several nonnoble metals (Sn/Pb, Sn, and copper) of these conductive adhesives were tested and compared to those of a commercial conductive adhesive. It was found that these in-house conductive adhesives showed superior impact performance and substantially stable contact resistance with nonnoble metal finished components during elevated temperature and humidity aging.