Effect of Cooling Rate on Microstructure and Strength Properties of Tin-Silver-Copper Solder Ball Bonding

摘要

The microstructure and the strength property of Sn-3.5 mass percent Ag and Sn-2.5 mass percent Ag-0.8 mass percent Cu solder ball bonding formed at various cooling rates were investigated. The grain size of Sn phase and the lamellar space depended on the cooling rate R_c. The reaction layer was thinner and the grain size of Sn phase coarsened when solder balls containing Cu were used. The reaction layer formed between Sn-3.5 mass percent Ag and Cu pad was composed of (Ni-Au, Ag)_3Sn_4, (Ni-Au, Ag)_3Sn_2 and (Ni-Au, Ag)_3Sn precipitates. (Cu-Ni, Au, Ag)_6Sn_5 was formed in the bonding interface when the ball with Cu was used. The lamellar space in both balls became smaller at faster cooling rates and was proportional to R_c~((-1/2)). The micro Vickers hardness of the solder ball with Cu decreased slightly at the slower cooling rates because of the grain size and lamella coarsening. The shear strength of joint using Sn-2.5 mass percent Ag-0.8 mass percent Cu was a little higher than that using Sn-3.5 mass percent Ag at the slower cooling rate because of the fine lamellar structure.