| 摘要 |
<p>Copper-containing surfaces, such as a copper surface for use in an electrical circuit, are protected by the provision of a bismuth metal coating immersion-plated from a moderately to strongly acidic plating bath. The plating bath preferably contains dissolved bismuth, halide, and a sulfur-containing ligand as a complexing agent that promotes adhesion of the bismuth coating. The bath may be formed from a concentrate system combined with water. The concentrate system may be a two-component system having an acidic first component containing the bismuth, halide, and sulfur-containing ligand, and an alkaline second component containing an additional complexing agent (e.g., EDTA salt). Tarnish resistance of the plated bismuth can be improved by the application of an alkaline composition to neutralize residual acid. Plating thickness can be enhanced by pre-cleaning the surface to be plated with a pre-cleaner containing nitric acid.</p> |
