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Rhodium Plated electrical contacts get spots (burns?)

Q. I'm experiencing issues with getting a decent electrical connection between two Rhodium plated components (~3V). One component is a pin (Al w/ Rhodium plate per MIL--R-46085B, Class 1, 0.000002" thick) and the other is a leaf spring (Phosphor Bronze w/ Rhodium plate per MIL-R-46085, class 3, 0.000002" thick). Over time, a small, black spot appears where the two contacts come together. Because there is no sliding/scrubbing between these contacts, the black spot must be removed more frequently than our customer specs allow (Dremel tool + polishing compound). These parts need to maintain electrical contact in both vacuum and atmospheric environments. They are typically in a clean room, so environmental contamination and temperature swings are not a major concern or contributing factor.

Has anybody experienced similar issues with non-sliding Rhodium plated contacts? If so, I'd like to hear about any solutions I might be able to leverage. I read in t

Can anybody suggest an alternate plating that is better suited to this application? I can freely change the leaf spring materials, but changing the pin is not an option at this point I'm afraid.

Many thanks in advance!

Paul Keady
- Hillsboro, Oregon, USA
December 15, 2011