Abstract: Wettability of SnAgCu/SnAgCuCe solders on Cu substrate and properties of solder joints were tested by diode laser soldering system. The solder joints reliability during thermal cycling test was investigated by diode laser soldering system and IR reflow soldering method respectively. The results indicate that, as the laser output power increases, the spreading area of lead-free solder increases, the optimal wettability and spreadability are obtained while the laser output power increases to a certain range. Moreover, the results indicate that the wettability and spreadability of the two kinds of solders on Cu substrate are improved with the increase of heating time under the condition of selected laser output power. For QFP256 devices soldered with diode laser soldering system, optimum power can be found, the optimum power for SnAgCu solders is 16.7 W, for SnAgCuCe solders, it is 17 W. Moreover, during thermal cycling, the reliability of soldered joints obtained by diode laser soldering is higher than that by IR reflow soldering.