Interfacial Microstructure and Joint Strength of Sn–3.5Ag–X (X = Cu, In, Ni) Solder Joint

Interfacial phase and microstructure, solder hardness, and joint strength of Sn–3.5Ag–X (X = Cu, In, Ni; compositions are all in wt% unless specified otherwise) solder alloys were investigated. Considering the melting behavior and the mechanical properties, five compositions of Sn–3.5Ag–X solder alloys were selected. To examine the joint characteristics, they were soldered on under bump metallurgy isothermally at 250 °C for 60 s. Aging and thermal cycling (T/C) were also performed on the solder joint. The interfacial microstructure of the joint was observed by scanning electron microscopy. X-ray diffraction and energy dispersive x-ray analyses were made toidentify the type of solder phase and to measure compositions. Excessive growth of an interfacial intermetallic layer in the Sn–3.5Ag–6.5 In solder joint led to a brittle fracture. In the other four solder joints, ductile fractures occurred through the solder region and the solder hardness was closely related with the joint strength.