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Corrosion of Gold Plating on Beryllium Copper





Q. I'd like to find out regarding corrosion problems on gold plated beryllium copper plate.

Is it true that corrosion is unavoidable due to beryllium copper being a porous material, thus plating is difficult and brown stains & oxidation will occur eventually? My understanding is BeCu itself is a material with high corrosion resistance.

Thank You.

K H [last name deleted for privacy by Editor]
- Singapore
 

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 [on eBay or Amazon] 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?

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


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.

Dave Kinghorn
Dave Kinghorn
Chemical Engineer
SUNNYvale, California

 


Q. Hi Ted and Dave,

Thanks for your response. The BeCu I am looking at is with a nickel plate / flash of 1-1.5 µM and gold plate of 1-3 µM over it. After some time, about 4-6 months after plating, corrosion of brown stains are visible on the gold plate. Understood from the plating vendor that it is "unavoidable". Personally, I do not really agree on the statement from the plating vendor. Appreciate your kind advise.

Thank You.

Best Regards,

K H [last name deleted for privacy by Editor]
- Singapore
 

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.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


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?

Rick Richardson, MSF
Dayton, Ohio
 

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?

Dave Kinghorn
Dave Kinghorn
Chemical Engineer
SUNNYvale, California

 


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.

Vijay Deval
electroplaters - Pune, Maharashtra, India
 

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.

Daryll Saunders
- Beverly, Massachusetts, USA
May 30, 2013




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