Substrate dissolution and shear properties of the joints between Bi-Ag alloys and Cu substrates for high-temperature soldering applications

The present study investigated interfacial reactions between Cu substrates and Bi-Ag alloys during soldering. Without forming intermetallic compounds (IMCs), the molten solder grooved and further penetrated along the grain boundaries (GBs) of the Cu substrate. An increase in Ag content enhanced GB grooving, raised the dissolution rate and also the amount of dissolved Cu in molten Bi. A stoichiometric Cu-Bi phase formed isothermally in liquid solders and considerably affected the Cu dissolution kinetics. The results also show that Bi-Ag/Cu joints possessed a better shear strength than the Pb-Sn/Cu, which implies that mechanical bonding by grain-boundary grooves was strong enough to withstand shear deformation.