Conductive silver-epoxy pastes: characteristics of alternative formulations

Abstract

Conductive silver-epoxy formulations containing 52 and 62 wt % silver flakes have been prepared and exposed to corrosive environments simulating as much as several decades of typical field exposure. The samples were then analysed by a variety of techniques and the results compared with previous data on pure silver and on a 72 wt % formulation. The corrosive sulphur gas diffused readily into the formulations to form silver sulphide at the surface of the flakes. Contact resistance values initially decreased with time, apparently as a result of softening and increased conductivity of the formulations due to water vapour adsorption. Contact resistance values were lower for high humidity exposure in the presence of H2S than in its absence, suggesting that the effect of water sorption is enhanced by dissolved H2S. The results indicate that low contact resistances and stable electrical performance are not reached within reasonable field lifetimes for these formulations, even though their characteristics are not markedly affected by corrosive environments.