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Tin Plated Stainless Steel Undercoats

We have customers that are requiring electro-tin plated stainless steel cases for their electronic components. They are plating in this sequence; Electro-tin (Mil-T-10727, Type I, .0003 min thk) over nickel (QQ-N-290, Cl 2) over copper (Mil-C-14550, Cl 3). Copper being on the base metal. It was our understanding copper does not adhere well to stainless and that the nickel should be deposited first on the stainless. Is this a correct assumption?

Norm Richarte
Product Designer - Hawthorne, California, USA
April 8, 2009

Your understanding is generally correct. For plating most metals over most stainless steels a Woods nickel strike is used. A Woods strike is an all chloride bath which is very aggressive and therefore adheres to the stainless. A strike is a thin plating.

The use of the copper without the strike is sometimes done if the stainless is a high copper alloy although adhesion (especially under duress) is marginal.

Gene Packman
process supplier - Great Neck, New York
April 15, 2009

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