A Pb-free Sn-based material part of a wiring conductor is provided at least at a part of a surface the wiring conductor, and the Sn-based material part includes a base metal doped with a transformation retardant element and an oxidation control element. The transformation retardant element is at least one element selected from a group consisted of Sb, Bi, Cd, In, Ag, Au, Ni, Ti, Zr, and Hf. The oxidation control element is at least one element selected from a group consisted of Ge, P, Zn, Kr, Cr, Mn, Na, V, Si, Al, Li, Mg and Ca. The wiring conductor is reflow processed, such that at least one of the Sn, the transformation retardant element and the oxidation control element is diffused to form an alloy.