Understanding of electrically conductive adhesives: formulation, curing and conductivity

Use of Electrically conductive adhesives has been considered an environment friendly interconnection technique, one of the two potential alternatives. Fundamental understanding of conductive adhesives has lagged far behind their commercial utilization. For isotropically conductive adhesives (ICAs), the conductive particles in the adhesives are responsible for the electrical interconnection, while the polymer matrix mainly provides the mechanical interconnection. We have found from our previous studies that there is obvious relationship between the polymerization shrinkage of epoxy curing and the electrical conductivity finally established with the material. In this paper, several epoxy resin based curing systems were used as the matrices for the ICAs. They exhibited different curing peak temperatures, which would enable us to investigate the effects of curing process upon the resultant bulk resistivity of the ICAs. To eliminate the complex effect of lubricants in silver flakes, a spherical silver powder was used as the conductive filler. The experimental results indicated a strong correlation between bulk resistivity and curing temperature or curing kinetics, which could be explained by a proposed mechanism on the establishment of electrical conductivity of ICAs during the curing process.