Plating Palladium Over Silver

Q. We have been asked to plate palladium over silver. The silver is on an aluminum substrate. We have experience plating various metals on aluminum substrates but have never been asked to plate this combination of metals. Can you give us any suggestions on how to do this? R. P.

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A. Since you indicate in your e-mail that you have experience plating on aluminum, we will skip that part of the process and address the plating of palladium. If you are looking for a suitable formulation for a palladium plating bath, you can find a number of formulations in the 2006 Edition of the Metal Finishing Guidebook and Directory, www.metalfinishing.com.

Palladium is known to form alloys with silver. This may cause diffusion problems as the parts age in use or in storage. You should discuss this issue with your customer. Typically, what is recommended when you have metals that can diffuse into other metals is to use a barrier layer. A typical barrier layer would be nickel.

This is an excellent example of why the modern plater must be part of the team when developing finishing processes. The engineer or individual who specified this particular combination of materials may not be aware of this issue of diffusion. This is where you as the plater can add your expertise and save your customer and yourself a lot of grief.