Passivation of tin layers

1. Characteristics and properties

Tin is a silver-white, shiny metal with a low hardness and a low melting point (232°C). Electrolytically produced tin layers show good corrosion resistance to atmospheric air, moisture, aqueous solutions, mineral acids and oxidizing acids. The passivation of tin layers is a post-treatment process which reduces the formation of oxides on tin and thus prevents discoloration and contact problems. The passivation layer has neither a negative influence on the very good optical properties nor on the insertion and withdrawal forces or soldering properties.

2. Benefits and areas of application

Tin is ideally suited for all types of electrical components where good solderability is required, as well as all current-carrying components and workpieces that come into direct contact with foodstuffs. Bright tin offers a technical surface with a decorative, glossy finish which also has a lubricating property which is particularly suitable for all plug contacts. Metoba offers a passivation coating for tin layers in order to prevent the tin layers from tarnishing at elevated temperatures, such as occur during thermal ageing tests, IR remelting tests, prolonged storage or water vapour ageing tests.

3. Basic material

After a material- and application-specific pretreatment, all stainless steels, steels, non-ferrous metals and their alloys as well as aluminium and zinc die-cast can be coated with bright tin without any problems.

In order to guarantee a long solderability of the tinned workpieces, it is absolutely necessary to deposit a diffusion barrier layer of usually 1-3µm nickel under the tin layer of brass materials in order to prevent diffusion of the zinc into the tin layer. The solderability is standardised according to DIN IEC 60068-2-20.

The passivation offered by Metoba can be applied to all deposited tin layers.

4. Required delivery condition

The goods provided must be largely metallically bright. Residual oils or residual impurities must be removable with conventional aqueous alkaline degreasers. Oils containing silicone, alkali/alkaline earth and high-pressure additives must be avoided at all costs.