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Gold plating for music wire springs

November 30, 2009

I am using a small OD spring (.5" long x .080 od x .012" wire) as a conductor between a ENIG finish PCB and a nickel plated brass or steel contacts. Our standard for the last year has been nickel plating, which has the best conductivity after Ag or Cu without the corrosion problems (non-conductive oxides).

This has worked fairly well, but recently it was brought to our attention that gold plating the springs would not add significantly to the cost, but it would decrease the resistance compared to nickel. We do a 4-wire resistance measurement to measure <2.0 ohms accurately, and we see some failures. Unfortunately I don't have data on resistance fail rates, but it's generally low and I'd like to get it to zero. It's for low voltage communication signals...3 to 5V, current in the milli-amp range.

My question is, do we need a layer between the music wire & the gold? I am inclined to keep the nickel plating & add the gold layer. Half the springs never deflect, and a few springs deflect a small amount (.050"), or about 10% of their length, so I'm not worried about fatigue, just corrosion. This is a consumer device used mostly in friendly environments.

Mark Bruneau
product designer/manufacturing support - S. Burlington, VT USA

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December 2, 2009

Mark,
It is true that gold will give you lower contact resistance, and good corrosion resistance. I think you are right regarding your inclination in keeping the nickel plate under the gold. The nickel will be the diffusion barrier thereby eliminating any migration of the steel or copper into the gold layer.
As far as cost goes, it would depend on how much gold is deposited, and the surface area of the springs. With gold hovering around $1200.00 a troy oz plus fab, mfg, and any other adders, it may be a cost issue. The company doing the plating could give you the cost increase. Good Luck!

Mark Baker
Fellow Plater - Syracuse, NY, USA