What type and thickness of gold plating over nickel?
Q. I'm looking for guidance on selecting the proper types and thickness for a gold over nickel plate. We are modernizing a 20 year old design that used gold over silver and had problems with the cheap silver undercoat tarnishing through too thin of a gold overcoat.
Hi, I'm an EE test engineer and am working a little out of my realm. I know that we want to use nickel as the undercoat for gold, but I don't know if it should be electroless or electroplated. I'm not sure what the optimum thickness for the nickel or gold are.
The copper alloy 260 or 270 ASTM B134 quarter hard pin being plated is about one inch long with a maximum diameter of about 0.09 inches and several areas turned down to different diameters, one as small as 0.035 inches. The pin serves as an electrical contact and a mechanical interlock. A wire is soldered on to one end.
Any help with the specifics, or if you can point me to a resource that can provide guidance, is appreciated.
We perform most of our operations to MIL-SPECS, so that's the perspective I come from. The nickel plating spec appropriate to your application is SAE-AMS-QQ-N-290 [link by ed. to spec at TechStreet] and it typically calls out a thickness from 30 to 150 microinches for an underplate. The nickel has to be of sufficient thickness to prevent migration of the copper through the gold which has an inherently microporous finish. The widely used gold spec is Mil-G-45204 [link by ed. to spec at TechStreet] and the thicknesses are from 20 microinches to 1.5 mils, a huge window. There are many considerations which go into determining the appropriate thickness such as soldering requirements, wear surfaces, environments and others most of which you already know about your part and reading the spec will point you in the right direction. Another excellent source would be the Metals Handbook (ASM). An off the cuff typical process would probably consist of degreasing, soak cleaner, deoxidize,cyanide copper strike, nickel underplate followed by a hard gold.
This is not meant to be a definitive answer, just a point in the general direction. GOOD LUCK.Bob Denney
avionics Tampa, Florida
A. Paul Stransky has also offered useful input on this subject, in his on-line article here, "Some Notes on Nickel Diffusion Barriers".
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. I believe all you need is 2 or 3 tenths of electroplated Watts nickel followed by a thin layer of gold. This is done routinely in the barrel for millions of pins subsequently used in connectors. I think you need enough gold to just protect the nickel until soldering time. Since the gold dissolves into the solder, contaminating the solder, you don't want too much around.Maybe you could use nickel followed by tin plate, and eliminate the gold altogether.
Falls Township, Pennsylvania
A. Do not use electroless nickel, it passivates and it can cause adhesion problems.
Make sure you plate the gold layer immediately after nickel cause if you wait between the two plating processes you will have adhesion problems again. Sara
April 19, 2012
A. Hi steve c,
I can share our process specs here for your reference incase you need some more info.:
for Electroless Nickel and Immersion Gold
Nickel thickness range= 100- 280 microinches
Nickel thickness target= 175 microinches
Gold thickness range= 2- 8 microinches
Gold thickness target= 3 microinches
for Electrolytic Nickel- Gold
Nickel thickness range= minimum= 100 microinches
Nickel thickness target= 150 microinches
Gold thickness range= minimum= 20 microinches
Gold thickness target= 25 microinches
C. de luna
February 8, 2012
Q. Nickel migration through Gold boundaries is causing solderability issues, specially after performing steam aging (100° C, 100% humidity for 8 hours). Is there a special plating scheme to prevent solderability issues of Ni/Au plated Tungsten?Dan Mendoza
- Pelham, New Hampshire
November 30, 2012
Q. Dear all. Please recommend non-destructive electronic gauge to measure plated gold only (or silver only) upon the nickel layer on the copper or brass plate.
I will be appreciate for any other recommendation of how to do this.
- Odessa, Ukraine