Abstract: In order to improve the properties of Sn-1.2Ag-0.6Cu solder,small amount of In(0~1.0%) was added to the base alloys,the melting temperatures of alloys were tested,and the effect of In on the wettability and microstructure of solder alloy was studied. The melting temperature decreases with the addition of In. At the same soldering temperature,the lower melting temperature is,the higher superheat is,thus the viscosity of liquid solder is decreased and fluidity is improved. The zero time of Sn-1.2Ag-0.6Cu in air is below 1s at 260℃,while the zero time of Sn-1.2Ag-0.6Cu-1.0In in N2 atomsphere is below 1s at 250℃,meeting the demand of IPC/EIA J-STD-003B. The Ag3Sn in Sn-1.2Ag-0.6Cu alloy becomes coarser with 1.0% In added,which is harmful to the mechanical properties. Thenefore,the content of In addition into the Sn-1.2Ag-0.6Cu is not higher than 1.0%.