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How to get tin plating on the internal diameter of fittings

October 12, 2011

We would like to get a Tin coating on brass fittings with a thickness of 10-15 microns.
In our current process we first apply a ground layer of Copper.

The problems we observe is that the tin coating on the outer diameter is sufficient. On the inner diameter of the fitting we are not able to have a plating thickness of around 2-3 micron.

Are there processes available to get a thicker tin layer on the inner diameter.

Hans Snijders
product designer - Almelo, Netherlands

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October 12, 2011

Hi, Hans.

Brighteners and addition agents in plating processes generally have a slight ability to improve throwing power. You may be using an acid tin bath, whereas an alkaline stannate bath might have somewhat better throwing power.

For the most part though, plating thickness is proportional to current density (per Faraday's Law), and the current takes the shortest path from the anodes to the surface of the part. The way to increase plating thickness on the inside of a part is with auxiliary anodes, i.e., small diameter positively charged electrodes running into the I.D. of the component. These will almost surely work, but may or may not be affordable in terms of labor and the cost of jigs.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey