TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: (I) further comprises an underlayer between the substrate and the plating layer, where the underlayer is composed of a metal comprising nickel, chromium, iron, cobalt or their alloy. The thickness of the underlayer is 0.5 mu m or above. The tin layer is a tin single layer composed of tin only, and the tin single layer is formed in an uppermost layer. The tin layer is a tin and carbon mixture layer composed of tin and carbon, the tin and carbon mixture layer is formed in an uppermost layer, and a ratio of atom% of tin and carbon (Sn(at%)/C(at%)) is 0.01-2 when a composition analysis is performed from the uppermost layer side by a scanning electron microscope/ an energy dispersion type analyzer (SEM/EDX) under a condition of 15 kV acceleration voltage. The tin layer includes a tin single layer composed of tin only and a tin and carbon mixture layer composed of tin and carbon formed on the tin single layer, the tin and carbon mixture layer is formed in an uppermost layer, and a ratio of atom% of tin and carbon (Sn(at%)/C(at%)) is 0.01-2 when a composition analysis is performed from the uppermost layer side by SEM/EDX under a condition of 15 kV acceleration voltage. Preferred Method: The tin layer of the plating layer formed in the plating layer forming step is a tin single layer composed of tin only. The tin layer of the plating layer formed in the plating layer forming step is a tin and carbon mixture layer composed of tin and carbon, and the tin and carbon mixture layer is formed by a plating treatment by adding carbon and a cationic surfactant into a tin plating bath and adjusting the carbon content in the tin plating bath to 1-200 g/l. The tin layer of the plating layer formed in the plating layer forming step includes a tin single layer composed of tin, and a tin and carbon mixture layer composed of tin and carbon formed on the tin single layer, and the tin and carbon mixture layer is formed by a plating treatment by adding carbon and a cationic surfactant into a tin plating bath and adjusting the carbon content in the tin plating bath to 1-200 g/l.