Tin Lead Plating
Tin lead plating is normally done to impart solderability to variety of base metal substrates. Tin lead plating is a silvery, blue-white metal that is ductile, solderable, and covers very well. The solderability of time can be affected by the substrate, since several metals tend to react with and migrate into the tin forming relatively non-solderable intermetallic layers. Of particular concern is tin plating over brass or zinc die-cast. The zinc will migrate into the tin and severely limit the shelf life of the finished parts. The migration can be mitigated by the common practice of applying an undercoat of copper or nickel or a combination of copper with a flash of nickel through which the zinc cannot migrate. Matte tin lead plating generally has better solderability, but bright tin is specified more because of its appearance. Tin does not tarnish easily, making it a good choice as a decorative finish.
Tin/Lead 60/40, 90/10, 93/7