抄録
Tin-coated phosphor-bronze with good adhesion as deposited sometimes shows an almost complete lack of adhesion at the interface of the tin layer and the phosphor bronze substrate after aging at 100-200°C. In this paper, this adhesion failure is called“thermal peeling”, since peeling accompanies metallurgical changes caused by such thermal processes as diffusion and segregation. Main findings are summarized as follows.
1. Tin-coated phosphor-bronze with no copper undercoat is much less sensitive to thermal peeling than that with a thin (about 0.5μm) copper undercoat.
2. Plastic bending prior to aging increases thermal peeling: thermal peeling appears after aging for 4000 hours at 85°C even for tin-coated phosphor-bronze with no copper undercoat.
3.ε-Cu3Sn and η-Cu6Sn5 are formed between the tin layer and the surface of the phosphor-bronze.
4. Accumulations of phosphorus and the formation of Kirkendall voids having concentrated amounts of phosphorus and oxygen are found along the ε-Cu3Sn/phosphor-bronze interface.
5. It is suggested that surface segregation of phosphorus accelerates the formation of the Kirkendall voids, which in turn causes the thermal peeling.
