The effect of adding an appropriate amount of Co element on the properties of Sn-0.7Cu lead-free solder alloy was studied.The microstructure of Sn-0.7Cu xCo(x=0%,0.002%,0.004%,0.02%,0.03%)alloy solder was observed using Axio Scope A1 microscope,differential scanning calorimeter,FAST system 3 weldability tester,high-temperature test chamber,and HITACHI 550i scanning electron microscope,and the melting point,weldability,and reliability performance were compared and analyzed.The results showed that adding a certain amount of Co element increased the melting point of Sn-0.7Cu and reduced its wetting performance,but the metallographic structure and reliability were improved.