Tin is a soft, ductile, silvery-white metal that is not easily oxidized in air. It has good conductivity and corrosion resistance while enhancing solderability of substrates that are not otherwise easily soldered to.
Tin plating services can be broken up into two primary categories: Bright tin and matte (solderable) tin. Both deposits are electrolytically applied. Bright tin has a high degree of luster and is generally preferred for electrical contact applications such as busbars, terminals and switching components that are not soldered to. If bright tin is soldered, the codeposited organics in the deposit can burn resulting in a dewetting of the solder and a visible charring of the solder joint.
For solderable applications matte (solderable) tin is recommended, as it is free of the codeposited brighteners integral in bright tin deposits. For substrates alloyed with zinc (such as brass alloys) it is generally recommended to apply a diffusion barrier or nickel or copper to prevent zinc migration into the tin deposit to prevent formation of tin intermetallics. Surtronics recommends the use of sulfamate nickel as a diffusion barrier as it affords an excellent solder base for soldering applications. It is important to note that solderability of tin plated products is a perishable attribute that has a finite life. Surtronics can work with companies to help extend the soldering life of products as much as possible by properly specifying the deposit, preparing the substrate and packaging the plated components.
Tin deposits can have the potential to form filiform tin whiskers that propagate from the surface of the deposit. For applications where tin whiskers could negatively impact the function of the product, Surtronics offers tin/lead plating services that are immune to the potential for whisker growth. In addition, reflow of tin deposits can help minimize but not fully prevent the formation of tin whiskers.
