In the reduction of the whiskers Sn film

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PROBLEM TO BE SOLVED : To provide a method of inhibiting formation of whiskers in Sn films.SOLUTION : A method of forming a pre-solder covering an electrical lead comprises : providing a metallic conducting lead having a surface; forming a tin layer covering the metallic lead surface, the tin layer including grains separated by grain boundary regions; and doping the tin layer with an average concentration of one or more dopants selected from among Al and rare earth elements such that the one or more dopants have a concentration substantially greater in the grain boundary regions than the average concentration.