摘要： This work investigates the effect of Indium (In) addition, 0.5 wt.% In, on the wettability of the Sn–3Ag–0.5Cu (SAC305) ternary pb-free solder alloy. Adding In to SAC305 decreased the contact angles (θ) of the Sn-2.5Ag-0.5Cu-0.5In quaternary pb-free 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 scanning electron microscope and energy dispersive X-ray spectroscopy, X-ray diffraction, and differential scanning calorimeter, and effects of the amount of In on microstructure were investigated. The results indicated that when the addition of In was 0.5 wt.%, the change in melting temperature of Sn–2.5Ag-0.5Cu–0.5In 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. The lowest θ was obtained as 45.22° for Sn–2.5Ag-0.5Cu– 0.5In alloy at 310 °C. The formation of intermetallic compounds (IMC) between the Pb-free solder alloys and the Cu substrate was observed. Thus, If the amounts of indium and silver are optimized, the Sn-2Ag-0.5Cu-0.5In quaternary solder alloy may be a suitable potential candidate to replace conventional Sn-3.0Ag-0.5Cu solder to provide economic gain in solder alloy production.