A bonding layer for bonding resin is provided that is formed on a copper surface, and contains an alloy of: (a) copper; (b) tin; and (c) at least one type of metal (third metal) selected from the group consisting of: silver, zinc, aluminum, titanium, bismuth, chromium, iron, cobalt, nickel, palladium, gold, and platinum. The copper is contained in an amount of 1 to 50 atom %, the tin is contained in an amount of 20 to 98 atom %, and the third metal is contained in an amount of 1 to 50 atom %. The bonding layer has a thickness of not less than 0.001 nullm and not more than 1 nullm. Thus, adhesion between copper and resin can be enhanced.