Patent ID: 7563353

Claim:
A method of forming an Sn—Ag—Cu ternary alloy thin-film on a base material, wherein said method includes the step of immersing said base material in a plating bath to form said Sn—Ag—Cu ternary alloy thin-film by electroplating entirely or partially on said base material, said plating bath contains at least an Sn compound, an Ag compound, a Cu compound, an inorganic chelating agent, and an organic chelating agent, said inorganic chelating agent is a polymerized phosphate-based chelating agent or a metal fluoro complex-based chelating agent represented by a chemical formula (I): MF X (X—Y)— (I) where M is an arbitrary metal, X is an arbitrary natural number and Y is an oxidation number of M, and at least 1 part by mass and at most 300 parts by mass of said inorganic chelating agent is contained relative to 1 part by mass of said Ag compound, and said organic chelating agent is a porphyrin, a dipivaloylmethane, a phthalocyanine or a compound represented by a chemical formula (II): R—(CH 2 CH 2 O) n -A (II) where R is an alkyl group having a carbon number of 8 to 30, A is CH 2 COONa or CH 2 SO 4 Na and n is a natural number, and at least 1 part by mass and at most 200 parts by mass of said organic chelating agent is contained relative to 1 part by mass of said Cu compound.