Assessment of microstructure and shear strength for low melting point tin-free alloys on Cu

This study explores and compares two new alloys, namely 50In-50Bi and 17Sn-26In-57Bi (wt%), with melting peak temperatures of 95 and 82 °C, which are substantially lower than the melting points of lead-free solders commonly used for low-temperature applications. The microstructures and intermetallic compounds (IMCs) of the new alloys, which were reflowed on Cu substrates, were studied. Notable Bi3In5 and BiIn2 compounds were formed in the reflowed 50In-50Bi alloy. The IMCs detected at the interfaces of 50In-50Bi and 17Sn-26In-57Bi were Cu11(In, Bi)9 and Cu6(In, Sn)5, respectively. Shear tests were systematically performed on organic solderability preservative (OSP) Cu substrates with 300-μm openings. Investigation of the fracture surfaces of both alloys indicated that the 17Sn-26In-57Bi/OSP Cu system had the higher shear strength and the more ductile joints.