Effects of Joint Height on the Interfacial Microstructure and Mechanical Properties of Cu-Cored SAC305 Solder Joints

Abstract

In order to discuss the effects of Cu-cored solder with pure Ni coating and joint height on the interfacial microstructure and mechanical properties of joints, Cu/Sn-3.0Ag0.5Cu (SAC305)/Cu and Cu/Cu-cored + SAC305/Cu sandwich solder joints were prepared using a reflow process. The interfacial microstructure of the solder joints was investigated by scanning electron microscope with energy-dispersive x-ray spectroscopy. The results showed that, at as-reflowed joints, an intermetallic compound (IMC) of scallop-like Cu6Sn5 was formed at the Cu wire/solder interface, and a plane-like (Cux, &!nbsp;Ni1−x)6Sn5 IMC was formed at the Cu core/solder interface. Compared with SAC305 solder joints, Cu-cored solder joints showed more interface layers, a thicker Cu6Sn5 IMC layer, and higher tensile strength. With increasing joint height, the thickness of the IMC at the two interfaces decreased, and the tensile strength also decreased for Cu-cored solder joints. Mixed brittle/ductile fracture appeared in SAC305 and Cu-cored solder joints with height of 600 μm, but were suppressed and transformed into ductile fractures with increasing height of the solder joints.