# How to Reover Gold From Circuit Board



## kwxj61b (Mar 28, 2009)

Hi!
I have couple pieces of the same board. Can someone tell me the steps to get the gold out?
Thanks.


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## butcher (Mar 29, 2009)

I would unsolder few components (heat gun or pencil torch or propanne torch), and use acid peroxide, the Hcl/ bleach method, nice board.


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## meng2k7 (Mar 30, 2009)

hi

u can try steve's sulfuric cell.


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## AuMINIMayhem (Mar 30, 2009)

just an FYI, without seeing the board up close.. 

I've seen a lot of boards that "look" like they have a ton of gold plating on them, but after careful inspection there was actually a coating, like a conformal coating that had a slight amber appearance to it and made a copper substrate look gold  I'd test it with a SMALL drop of nitric 

solder flux and conformal coatings can tint things just enough to make them appear to be "golden".. 

*also after looking over your picture the gold tips on the connector are much more "gold" in appearance than the large area in question, again hard to tell by looking but are the two areas different shades, that may prove to be a red flag as well*


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## goldsilverpro (Mar 30, 2009)

Sure looks like gold, though, doesn't it?


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## g_axelsson (Mar 30, 2009)

Those boards are definitely gold plated. I can see the Ericsson logotype on one of the circuits. They are clearly telecom boards with a gold plated ground plane. All the holes in lines on the board are for grounding RF shielding boxes. Any isolation in the form of solder mask is destroying the function of the shield.

A lot of modern boards gets a protective coating of nickel and gold on the surfaces that are going to be soldered. It's called ENIG or electroless nickel immersion gold and is a thin protection against oxidation. It doesn't need to stand up to rubbing as fingers have to so it's usually quite thin. All this gold is dissolved into the tin when the board is soldered.
From another board...


> IPC-4552 ENIG specification:
> * Ni thickness: 3 - 6 microns [120 - 240 microinches].
> * Au thickness: 0.075 - 0.125 microns [3 - 5 microinches].
> * Recommended specification is 2 microinches minimum at -4 sigma from the mean for the gold with 3-5 being typical.


Other popular surface treatment is HASL (Hot Air Solder Levelling) and silver plated. Also gold flash seems to be popular. Gold flash is a thin plating of nickel and gold before the surface copper is etched. It is probably the method used on all boards with gold plate under the solder mask. (reference)
ENIG on the other hand is often added after the solder mask to not spend too much gold.


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## goldsilverpro (Mar 30, 2009)

I think g_axelsson knows what he is talking about. I was a gold plating specialist for 10 years and his post and the reference he gave (read it - very informative!) made a lot of sense to me. Assuming he is right, it also explains to me why people are having so much trouble with the gold under solder mask - it's almost non-existent. At $920 gold, 1 square inch of 3 micro" gold would be worth $.0276 and would weigh .00094 grams, if I calculated right. It would take 66 boards, each with a gold plated area under the mask of 4" x 4", to make 1 gram. Are these boards really worth messing with?

*Immersion plating* is exactly the same thing as cementation, except that the solution is formulated so that the gold bonds tightly to the nickel and eventually will form a barrier to prevent further penetration of the solution. As gold is deposited, nickel dissolves. At some point, when all the surface nickel is covered with gold, the gold stops plating. In the Reference, the gold thickness is said to be self-limiting. Since the rate of immersion deposition continually decreases before completely stopping, the thickness could be controlled by the time spent in the solution.

*Electroless plating* occurs from a bath that contains a reducing agent. The nickel is chemically reduced onto the copper (or onto the nickel already deposited) and forms a bond. Unlike immersion plating, no copper dissolves and the the nickel thickness is unlimited. True electroless gold baths work the same way. Here again, time in the tank determines thickness.

*Flash plating* is simply electroplating. It's thickness is easily controlled and is proportional to the current density (amps/sq.ft., e.g.) and to the time spent in the tank.

The adhesion of all 3 types of plating is dependent on how well the substrate was prepared (cleaning, removal of oxides, etc.) before plating. All 3 types of solutions are composed of multiple ingredients, which control such things as reduction, color, brightness, adhesion, and solution conductivity.

As far as adhesion is concerned, electroplating is usually the best, then electroless plating, then immersion plating.

Although being in this business for 40 years, I couldn't figure out WHY the large area under a solder mask would be covered with gold. There didn't seem to be any logical reason for it, unless you wanted to waste gold - and, believe me, PCB manufacturers have NEVER wasted gold. 

The reason that silver cementation on copper is not limited is that the silver continually sloughes off, thus providing fresh nickel sites for the silver to deposit. The copper is never completely covered with silver.


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## oldtimmer (Mar 31, 2009)

Interesting board. I was watching one for sale on ebay that looks just like this one.

Listing has just colsed:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=220385464278


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## SapunovDmitry (Mar 31, 2009)

I have processed alot of those boards. If you take off two RF gold plated details board still can yield about 250-300 gr. of gold per tonn.
I have processed some of those (1-2 samples in the CPU bucket) RF details and they appear to not dissolve in AR.Only plating has dissolved. It became shiny white. Maybe it is lead or tin plating above copper.Or maybe i had not enough AR after CPU processing.

PS. These are D-AMPS boards from Ericsson cell phones stations. Guys, I want to know as much as it is possible about exactly these boards. If you have some additional info about them please share it.Cause now we are processing 12-15 tonns of these boards per year.


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## AuMINIMayhem (Mar 31, 2009)

HA HA!! I love GSP's quick math! Wanna come over and balance my check-book? :lol: :lol: :lol: 

g-axel.. you are absolutely right.. I looked at the components again and was also able to see the Ericson logo on that one circuit.. so I would have to agree that you are correct that it is some form of gold plating.. I also tend to agree with GSP, that unless kwxjj61b has numerous pieces of that board, it may not be worth it's weight in the chemicals it would take to process such a large board.. that would probably go in my "hoarding stack".. the area of my basement where I'm keeping things assorted by how they are going to be processed and just collecting until I feel I have enough of whatever process to make it worth while.. 

Cheers!


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## kwxj61b (Mar 31, 2009)

I have about a ton of this. I used an electronic gold tester and it comes up w 22k gold. 
Guys, thanks for the tips.


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## koebeef (Mar 31, 2009)

That listing was a buddy of mine, he has a few hundred of them but cannot sell them because of a contract with the company. Anyways I told him to cut the board in half and sell the pieces but he cannot. Oh well, at least its not worth so much.


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## AuMINIMayhem (Apr 1, 2009)

kwxj61b said:


> I have about a ton of this. I used an electronic gold tester and it comes up w 22k gold.
> Guys, thanks for the tips.



SCORE!  

Cheers!


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## goldsilverpro (Apr 1, 2009)

So what does it mean that it tested 22K? It's certainly not solid 22K gold and the plating certainly isn't 22K. Sounds like the reading was erroneous and worthless. That's not what those electronic pen testers are designed for.


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## rainmaker (Apr 1, 2009)

Here's what I would do if I had these boards

1. depopulate 1 board

2. place that board in a caustic soda (lye) solution to remove the mask

3 place the board in nitric to remove any silver & most of your base metals

4. process the board in AP

5 weigh the gold to determine yield per board.


Have fun


Rainmaker


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## AuMINIMayhem (Apr 1, 2009)

rainmaker said:


> 2. place that board in a caustic soda (lye) solution to remove the mask
> 
> Rainmaker



or you can use Dynasolve :wink:  

http://goldrefiningforum.com/phpBB3/viewtopic.php?t=4553&highlight=


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