Silver plating on electrical contact springs.
I have been cycle testing spring probes used in circuit board testers to determine the best and longest lasting type of plating to be used on the spring itself.
So far, silver plate over a copper strike, on a spring wound from music wire ASTM 228 seems to give the best results. The silver springs even outlast raw unplated ones. I believe this is due to the lubricating properties of the silver, and it's malleability. Previously, we were plating gold over electroless and/or sulfamate nickel, and having problems with premature spring failure. I have two questions. One: does anyone know what the conductivity of silver sulfide (tarnish) is? And secondly: can anyone give any reason why not to plate these springs with silver.
Thanks to all for your input.Brian A. Jones
Test Connections Inc. - Upland, Ca U.S.A.
Silver should be fine to use as the plate and if you are getting the spring cycles you may not need to bake the parts after electroplating. Silver will form a very light chromate film (will pass current) if you just want more protection or if you need to bake and then need to snap the surface back.
Sorry, don't know the conductivity of the sulfide, but its not much of a conductor. 3M makes some protective papers that can be placed along with the parts in good packaging (sealed plastic bag 4 mils thick or more) and will increase the shelf life. Gold over the silver would also work (silver will, with time, come to the surface of the gold so you may need more than a flash).
Regards,Fred Mueller, CEF
Wendt Dunnington - Royersford, Pennsylvania
We have a problem with heavy tarnish on silver-plated spring contacts which are difficult to reach and impossible to abrade. Is there a chemical treatment which will reduce the silver sulfide to metallic silver? Would heating work?
- Elliot Lake, ON, Canada
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