Conduction path development in electrically conductive adhesives composed of an epoxy-based binder

Generation of electrical conductivity in electrically conductive adhesives (ECAs) composed of epoxy-based binders was investigated. Development of conduction paths for electrons in the ECAs was found to consist of two elementary processes, microstructure formation of a filler-network and development of inter-filler electrical conductivity. Microstructure formation of the filler-network occurred in the initial stages of the curing process through rearrangement of fillers, and this accompanied variation in the viscosity of the binder. Electrical conductivity in the ECAs can vary largely depending on the binder chemistry and the surface chemistry of the fillers, even though all the ECAs showed similar filler-network microstructures within the binder matrix. Results suggested that chemical factors controlled the electrical conductivity through inter-filler gaps. In addition, large decreases in electrical conductivity of the ECAs were observed with increasing curing time during isothermal curing for epoxy-based binder containing an acid anhydride curing agent. Kinetics for development of the inter-filler electrical conductivity varied depending on the chemical factors.