Corrosion of Gold Plating on Beryllium Copper

A. It depends on a number of factors, probably including the required contact resistance; but yes, beryllium copper is used bare for some applications (perhaps with a benzotriazole ⇦ this on eBay or Amazon [affil links] or chromate top coat though). While it's possible to gold plate copper, it is most common to nickel plate it first anyway. Any reason you can't?

A. Agree, Nickel first before gold is the way to go if your application can handle a magnetic material under the Gold.

If not and you have to plate the gold directly on the BeCu, then you first must prepare the BeCu surface and the only good way to do that is after a standard cleaning process, add a 1 Oz/Gal Cyanide soak for 2 - 3 minutes lukewarm then go live directly into a Gold Strike. One of the 1-3 ASF Acid-Cyanide full DC varieties will work fine. But since Gold suffers diffusion and you have no (Nickel)barrier, if you want to get rid of the staining, you will need lay the Gold down thick, over 400 Microinches. That's a lot of Gold. Which is why a cheap layer of Nickel is usually used.

A. I am not familiar with plating of this particular part, but you are describing a very thin nickel coating which sounds like it would be porous and not very corrosion resistant.

A. I think if you increased the thickness of your nickel flash the problem would go away. It seems a little thin and the problem does not occur for a few months which would be about the right amount of time for the Cu to migrate through the thin nickel. Does anyone else agree?

A. 1-1.5 microns nickel is standard thickness for semiconductor device interconnect metallurgy such as solderball grid array interconnects, wirebond contact pads and pre-soldered leadframes, but BeCu is never found as the circuit trace material, so I agree, perhaps a thicker Nickel callout for BeCu engineering materials is in order. Perhaps a standard 100 - 400 microinch (2.5 - 10 micron) callout? Also, is the Nickel Electroless, Watts, or Sulfamate? Since you mentioned a flash, is it a Wood's strike all the way?

A. After soak cleaning, I dip BeCu in sodium Hydroxide till it turns black and then remove the smut by acid. Then it can go through normal plating cycle with excellent results.

BeCu is normally a spring material and bright nickel can cause problems. I use nickel bath without any additions with 5:1 pr current to deposit reasonably ductile nickel and then follow that with gold plating with PR current. During preplate, care is taken to avoid hydrogen pickup.

A. Hi - At a past employer we plated 100's of thousands of small BeCu parts for contacts. 50+ microinches of 1st Ni sulfamate and then same plus of Class II GOLD. In discussions with Brush Wellman (the authority on BeCu) we learned a few things:

1st - Heat Treat all BeCu where you can first. Seems irrelevant - but was not.

2nd - A Copper Sulphamate strike (not cyanide) after a real good 2% sulfuric acid cleaning helps

Then proceed with the 50+ Ni, rinse well, Au Strike (soft gold), then direct into Class II gold plate tank.

Hope this works for you.