# Gold plated?



## Slochteren (May 7, 2015)

I have this piece of militair scrap. Looks like gold plated. How can i be sure its gold plated? This size doesnt fit in my cell also before building a bigger one special for this piece i would like to know if its plated or not. The small pcb will be removed first offcourse and treated seperate.


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## g_axelsson (May 7, 2015)

Nice microwave circuit, I'm certain that it is gold on aluminum base, but I can be wrong.

Put a drop of nitric on the surface, if plated it will have a copper layer between the aluminum base and the gold plate and the gold will just flake off.
Search the forum for gold on aluminum for more help, it's been discussed before.

Göran


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## Anonymous (May 7, 2015)

It's a very good piece of board. Good yield per piece as opposed to good yield by weight.

Each of the components inside is usually a on copper plate with gold plate on both sides in addition to the gold plate on the chassis. You also may have PGMs in the traces. 

If you dismantle it completely, removing all the screws you may find that you have to pry the internal components out as they have a layer of heat paste between the components and the base. 

The dullness of the plating is a good indicator as to the thickness of the plate overall. The base metals vary on these- some are copper, some are aluminium and some actually have gold over silver before you reach the base metal. I have also heard of some that have gold/palladium/base too although I haven't had any of those yet so I cannot confirm the accuracy of that report.

I currently have over 80kg of similar units to process myself so I will follow your progress with great interest 8) 8) 

I hope that helps.

Jon


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## Slochteren (May 7, 2015)

g_axelsson said:


> Nice microwave circuit, I'm certain that it is gold on aluminum base, but I can be wrong.
> 
> Put a drop of nitric on the surface, if plated it will have a copper layer between the aluminum base and the gold plate and the gold will just flake off.
> Search the forum for gold on aluminum for more help, it's been discussed before.
> ...


 I put a drop off nitric(53%) on it but nothing happens, made some scratches but still no reaction, telling me there is something different or nothing between the plated and aluminum?

About the white "pcb" that is BERYLIUM OXIDE CERAMICS i read in another topic wenn it breaks and in dust its dangerous. Any idea how to seperate it from the plated metal without damaging it?


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## Lou (May 7, 2015)

Those traces _should_ be on alumina, not beryllia. No real easy way to check. There is a copper and nickel strike under the gold.

Once processed a bunch of the silver versions, believe they ran about $3.50-4/lb Ag back at $40 silver. If the gold thickness is the same as the silver, you could be in for a nice day.

These RF waveguides can be quite nice. 

Too bad you don't have a couple thousand pounds, would love to do those for you 

My advice to you is *not* to strip in a sulfuric cell. Best way to strip these is with 1:1 nitric/water and 1% w/v of that mix is HCl.


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## Slochteren (May 9, 2015)

Thx Lou..

till now i only did AP and gold plated pins in sulfiric cell.

What you are advising is new for me so i have some quistions about it before i mess up.

"My advice to you is not to strip in a sulfuric cell. Best way to strip these is with 1:1 nitric/water and 1% w/v of that mix is HCl"

The nitric i have is 53%, also i can put it straight in that (would be 1:1 +/-) or do i have to put that 53% 1:1 with water? 
What do you mean with w/v? 
Wenn i have 2 liter of that mix i add 20cc HCL(37%)

This solution will solve the aluminum? 

Thx Paul


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## Lou (May 9, 2015)

More nitric doesn't hurt, it just costs more. 

The idea here is that you want the aluminum passivated at all times and protected by a thin film of aluminum (III) oxide. Aluminum doesn't dissolve in nitric acid because nitric acid only oxidizes the surface and doesn't coordinate with the Al(III) ion, which chloride does. Essentially there's a war going between keeping the aluminum oxide passivated surface intact and the gold in solution as AuCl4-. Gold won't cement onto aluminum (or any metal that passivates) under such conditions. 

Truth be told, using this so called reverse aqua regia is so insanely dangerous that it's begging for it if you can't do your math right. I mean begging for a problem.

If you'd used the sulfuric cell, what would happen is you risk immediate and destructive attack (and probably a hydrogen gas fire) of the aluminum substrate by the sulfuric--sulfate anion DOES coordinate to aluminum to form aluminum (III) sulfate.


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## necromancer (May 9, 2015)

hope you are removing all those screws & ceramic boards before putting into your nitric bath :?: 

i have seen those before, some ceramic boards like those are also glued into place.

start clean & finish clean.


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