Degradation by Sn diffusion applied to surface mounting with Ag-epoxy conductive adhesive with joining pressure

Abstract

Shear and tensile tests were carried out on joints made with an isotropic conductive adhesive (ICA) consisting of Ag and epoxy: Sn–Pb plated components mounted on printed boards and tensile bars consisting of Sn plated Ni and Cu joined under various joining pressures. After 150 °C–100 h, shear strength degraded to 72% and Sn in the plating diffused slightly to the Ag fillers in the ICA for the component mounting. High joining pressure increased the initial tensile strength and volume percentage of Ag fillers in the ICA. After 150 °C–100 h, tensile strengths for all joining pressures degraded on average to 36% of the initial strengths. In the case of low joining pressures, an Ag–Sn intermetallic was formed at only the Ag–Sn contact points of the Sn/ICA interface; leading to reproducibility of the component mounting. The difference of degradation ratios between the mounted components and tensile bars could be explained by the offset of the Sn–Pb area at the component/ICA interface.