Microstructure and mechanical properties of partial melted joint using offeutectic lead-free solders

This paper introduces the partial melting soldering process as a new solder ing technology and investigates the mechanism, mechanical properties, and i nterface reactions between Cu and off eutectic binary alloys: Sn-7 mass%Ag. Sn-3 mass%Cu, and Sn-2 mass%Ni. In order to show the possibility of the pa rtial melting soldering, reflow was conducted under various temperature con ditions between the eutectic and the liquidus temperatures. As a result, in termetallic compound layers were formed at the joint in their partial melti ng Lone. In cases ol. tile Sn-7Ag and Sn-3Cu solders, Cu6Sn5 intermetallic layers were formed, while the intermetallic layer formed between Sn-2Ni and Cu plate was a ternary compound of Sn-Ni-Cu. Hardness test showed that par tial melted joint was harder than the full melted joint, indicating that th e solid phase in the mushy zone had an effect of reinforcement. According t o the aging experiments, the growth rate of intermetallics of partial melte d joint was lower than that of full melted one. This indicates that the sol id phase in mushy zone also prevented excessive growth of the intermetallic s. Finally, shear test had been made to evaluate joint strength, showing th at the strength of the partial melted joint was almost 80% that of a full m elted joint.