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Stripping Gold Braze

2004

I am looking for a formula for a stripper that will remove gold alloys, in the form of brazes, .001"-.002" thick, from various substrates, for purposes of re-working the parts. The stripper can be electrolytic or immersion. The solution must be selective and cannot attack the substrates, which can be 410SS, High Co or Ni superalloys, silver solder, kovar, nickel, or copper. The various alloys of gold are: 82Au/18Ni, 80Au/20Sn, and about 97Au/3Si(atomic percentage). It would also be nice to selectively strip only one of two adjacent, but electrically isolated, gold braze surfaces, electrolytically.

I've had no luck with cyanide formulations, whether lab made or proprietary. They're great for pure and/or thin gold layers, but hardly touch the thicker braze alloys.

I would certainly appreciate your ideas,

Chris Owen
Consultant - Houston, Texas

You might check PWA, GE, or rolls royce standard practices to see what they use. , in San Antonio, has a dual system of cyanide and boiling nitric acid that is proprietary and effective. They might do the stripping for your customer for a very small fee and the recovered gold.

James Watts
- Navarre, Florida
2004

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2004

James,

Thanks for your response. I used to consult for , San Antonio, and saw the nitric/cyanide method being used. I think there are a couple of patents on this same process issued to Fountain Plating. There's another old patent that uses a Hi-HNO3, Lo-HCl form of Aqua Regia, but it's slow and doesn't work too well on parts such as fuel manifolds, where the gold is mostly hidden from the solution. I basically asked the question hoping that some new method would appear.

The other metals and brazes that I mentioned appear on assembled I.C. packages. Same problem. To restore the packages for re-use, the gold braze must be selectively removed and the part re-plated. Do you know of anyone doing this?

Thanks,

Chris Owen
- Houston, Texas

I am not aware of any other method. I have always wondered if micro abrasive methods or wet very high pressure with abrasive added might be adapted with lots of trial and error. Any possibility the it could be lazered out, or EDM.

James Watts
- Navarre, Florida
2004