Chemical tin

A Pcb surface treatment consisting of an electroless deposited tin layer, which protects the copper of the areas to be soldered from oxidization. Since during soldering the tin layer is melting, any oxidization of the tin during storage is not an issue. One disadvantage of this type of preventative measure is the intermetallic layer which is formed at the interface to the copper. This layer grows with each additional soldering process, and it is therefore possible that, in situations where repeated solder processes are required, the pad surfaces are no longer wettable. This worst case occurs when the intermetallic has grown up to the surface.