Conductive adhesive materials for lead solder replacement. II

Several isotropic conductive adhesives were evaluated for SMT with MLC capacitors as lead containing solder replacements from the contact resistance and adhesion strength points of view. The contact resistance and adhesion strength depend on the different kinds of adhesives and adherent materials. Silver filled adhesives, which have low contact resistance, and nickel filled adhesives, which have a slightly higher contact resistance but no electromigration, containing phenolic resin as curing agent, have excellent stability of contact resistance to any adherent materials tested through reliability testing. As for adhesion strength, although Ag/Pd and Cu fired terminations give rather stable adhesion strength, that of Ni/Sn plated terminations falls during high temperature storage and thermal cycling. It can be estimated that the brittleness of the Ni/Sn intermetallic layer caused by Ni diffusion into the Sn layer results in serious adhesion strength degradation