Dowa Metaltech Co., Ltd.

Masaaki Izaki

Hiroto Narieda

Yuta Sonoda

A Cu-based materialis immersed into an alkali hydroxide solution with a concentration of 3.0 to 37.5 mass % and a HOsolution with a concentration of 3.0 to 50.0 mass % is added in the alkali hydroxide solution, a temperature of the alkali hydroxide solution when the Cu-based material is immersed ranges from 60 to 105&#xb0; C., a ratio A/B between a mol number A of alkali hydroxide in the alkali hydroxide solution and a mol number B of HOin the HOsolution is 10 or more, and where a mol number of Sn in the Sn layer is C and a mol number of Sn in the CuSn layer is D, B&#x2267;C&#xd7;2+D&#xd7;6.

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Tokyo, Japan

Masaaki Izaki