Dipped copper wire of 0.25mm diameter into molten solder of 400°C and measured the time until copper wire is melts to cut. Under the listed measuring condition, the solder composition which has the least erosion is NP508Z (Sn-3.0Cu-0.25Ni). On the other hand, in turn, solder composition which has the most erosion is Sn. The more copper content in solder increases, the less erosion of copper occurs. Able obtain the same effect by adding small quantity of nickel.