Effect of bismuth on wettability of Sn-2.5Ag-0.5Cu-0.5Bi quaternary solder alloy on Cu substrate

This study reports the investigation on Bismuth (Bi) addition into Sn–3.0Ag-0.5Cu (SAC305) ternary lead-free solder to improves its various performances. The effects of Bi addition on the wettability of the solder alloy was studied. The results showed that when the addition of Bi was 0.5 wt.%, the change in the melting temperature of Sn-2.5Ag-0.5Cu-0.5Bi (SAC-0.5Bi) solder was negligible, but the contact angles (θ) of the solder alloy decreased which were measured by using of the sessile drop method at various temperatures (250, 280 and 310°C) on Cu substrate in Ar atmosphere. Microstructures, inter-metallic phases, and melting temperatures of alloys were characterized by optic microscope and SEM and EDX, XRD, and DSC, and effects of the amount of Bi on microstructure were investigated. The lowest θ was obtained as 39.22° for the SAC-0.5Bi alloy at 310°C. As a result, the studies show that the wetting capability of SAC-0.5Bi quaternary alloy is better than SAC305 ternary alloy.