Interfacial microstructure and joint strength of Sn-3.5Ag-X (X = Cu, In, Ni) solder joint

Abstract

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 degreesC 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 to identify the type of solder phase and to measure compositions. Excessive growth of an inter-facial 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.