Mechanical characteristics of 96.5 Sn/3.5 Ag solder in microbonding

The mechanical characteristics of 96.5 Sn/3.5 Ag solder discussed include elongation, microstructure, and thermal fatigue life. A controlled-collapse chip joint was used as a vehicle to evaluate thermal fatigue life. 96.5 Sn/3.5 Ag solder with the addition of several mass% of gold was examined for tensile properties and microstructure. 63 Sn/37 Pb solder was also examined for comparison; it was found that although 63 Sn/37 Pb solder with more than 3 mass% of gold has a poor ultimate elongation, 96.5 Sn/3.5 Ag solder extends well. The influence of thermal fatigue on microbonding is discussed. After a temperature cycling test, the striations traced by thermal fatigue were observed on the fractured surface. Their intervals were as fine as 0.04-0.2 mu m. The crack propagation rate of the solder joint was calculated by the change in the intervals of the striations, and the life of each solder joint was estimated. The thermal fatigue life of 96.5 Sn/3.5 Ag solder was estimated to be about twice as long as that of 63 Sn/37 Pb solder.>