Tin coating – also referred to as electro-tinning – is a type of surface treatment process. It produces a metallic coating of tin on the surface of metal components. The coating is produced in one of two electrolytes. One option is an alkaline solution producing a matt pure tin finish. The alternative is an acid solution containing organic brighteners. This option produces a bright finish.
What is tin plating used for?
Tin plating is mostly used for functional applications. However, in some applications the appearance of the surface is also important. This coating has a good resistance to oxidation in moderately corrosive environments. It’s commonly applied to equipment and machines used in the food industry. The main application of the tin coating however, is used for surfaces on which soldering is necessary – as well as electric contacts and switchgear.
The soft character and corrosion durability of the tin coating are appealing factors. It results in low and stable contact resistance compared to copper and brass surfaces. With copper and brass, the contact resistance with time increases due to the formation of a thin layer of corrosion products.
Tin coatings, which are deposited directly on zinc rich copper- alloys such as brass, have poor solderability. This is because the tin coating diffuses into the zinc rich areas of the brass. This also decreases the resistance of the coating to oxidation. This diffusion of the tin plating can be avoided by applying a nickel or pure copper barrier layer before the tin plating.
Electro-tinning can under certain circumstances spontaneously form long, thin (1-3 urn) threads of tin – so-called tin whiskers – which can create difficulties with current-division or short-circuiting in electronic components. An under coat of nickel applied before the tin coating counteracts the formation of whiskers.
Corrosion behaviour of tin coatings
Tin is a base metal compared to copper, copper-alloy and nickel and, therefore, is capable of protecting these metals where minor damages and perforations occur in the tin coating. The principal is known as cathodic protection.
The coating is more noble metal than steel under atmospheric conditions. Damage and voids that penetrate the tin coating will, therefore, result in galvanic corrosion and form rust on the steel surface where it is exposed to the environment. High tin thickness or undercoats of nickel reduces the amount of porosity to base metal of the coating. However, under highly corrosive conditions and/or requirements of long service life it is recommended that the components are manufactured in a corrosion-resistant material.
Application data for tin (Sn)
IMDS number: 756885
Melting point: 2320 C
Volume weight: 7,3 g/cm3
Max application temperature for tin: 1000 C
Specifications for tin coatings
The application of tin plating at E.C. Williams Ltd is carried out in accordance with the standards BS 1872, ISO 2093 (1986) as well as many industry specific specifications
If you would like to find out more about our tin coating services, then head to our website today. Or, call to speak to a member of our helpful and friendly team.
If you have found this blog helpful, you may wish to read our previous blog on Zinc Nickel Coating.