Depopulating PCB with acid

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GoldUser

Well-known member
Joined
Apr 7, 2022
Messages
81
Location
Vienna
Hello,

1. first I want to say hello to the forum. I do gold recovery from old electronics with a good chemistry graduate friend of mine. Im a programmer but I love Chemstry, Physics and Biology (mostly self-learned). I already obtained a lot of knowledge from all the wisdom everyone provided so far. So thank you all first of all. I know everyone takes PPE, etc. very serious so as a newbie I want to say that im fully aware of the dangers and only operate with respirator(outdoors), eye protection, gloves and more. But im open for improvements (just dont want to make this a safety thread :D)

2. I have a lot of PCB with gold plated on them. The problem is i want to remove/depopulate the resitors, capacitors, chips, etc. from the boards to get a clean solution and dont get all of it stuck in the filter at the end. My Idea was to put the boards in conc. HCL and remove the solder so that everything would fall out of the "socket". Ive never done this before so are there any tips for that? Temperature wise (do i need heat) or adding oxygen with an aquarium bubbler (im a litte afraid to oxidise some copper to copper oxide and further get copper chloride in my solution).
Maby additives or not?

I dont have the picture of mine but the PCB's are from PC displays. I added a picture from google. Mine though have some more gold plating on them.

Im sorry if this thread is already out there on the forum but i could not really find what im asking.
Thanks for everyone who takes time for this. I would really appreciate this :D

David

Edit: canedane pointed out that there is mostly flash plated gold on it which is not rly worth anything. Due to the fact we do this for fun and try this acid depopulation on diffrent kinds of PCB's I would still appreciate some tips regarding to the acid process of removing the components leaving the plating and the fiber.
 

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Hello David, welcome to the GRF.
The best you can do is to cut of the gold fingers, close to the edge. The gold at the picture is flash plated , and it is not worth to recover the gold, unless your labour is for fun and free.
Henrik
 
Hello David, welcome to the GRF.
The best you can do is to cut of the gold fingers, close to the edge. The gold at the picture is flash plated , and it is not worth to recover the gold, unless your labour is for fun and free.
Henrik
Hey,
thnaks for the fast reply :)
we just do this for the fun and take the gold we get in the end.
Is there any "kind of a rule" on how much of this flash plating is gold if I would have like a kilo of them.
Or any kind of information about flash plating.
David
 
Experiment: Use HCL + H2O bath to depopulate PCB creating Tin in solution and precious metal precipitate.

Process: Dilute HCL to 12-15% and soak PCB at ambient temperature. The boards were processed for 2-5 days depending on temperature, until components could easily by removed. (Completed)

Leach Solution: I expect this to contain mainly tin, hopefully without too much cadmium. I use electrolysis to recover the tin then reuse the solution on the next batch of PCB.

Slimes: First, process with H2SO4 and KNO3 to remove the lead and copper.
Second, process with HNO3 to place Silver into solution.
Third, treat with slightly diluted AR to recover the Gold.
Fourth, retain solids for future recovery of PGM.

Components: First use pyrolysis to ash the components.
Second, remove magnetic pieces
Third, crush to fine powder (crush, sift, crush etc)
Fourth, water flush to remove carbon
Fifth, process with H2SO4 and KNO3 to remove the lead and copper.
Sixth, process with HNO3 to place Silver into solution.
Seventh, treat with slightly diluted AR to recover the Gold.
Eight, retain solids for future recovery of PGM.




Does this seem reasonable?
 
Experiment: Use HCL + H2O bath to depopulate PCB creating Tin in solution and precious metal precipitate.

Process: Dilute HCL to 12-15% and soak PCB at ambient temperature. The boards were processed for 2-5 days depending on temperature, until components could easily by removed. (Completed)

Leach Solution: I expect this to contain mainly tin, hopefully without too much cadmium. I use electrolysis to recover the tin then reuse the solution on the next batch of PCB.

Slimes: First, process with H2SO4 and KNO3 to remove the lead and copper.
Lead are insoluble in Sulfuric acid and why use KNO3 if you have Nitric?
Second, process with HNO3 to place Silver into solution. Where do you expect the Silver to come from?
Third, treat with slightly diluted AR to recover the Gold. Are you thinking of Gold from components or foils?
Fourth, retain solids for future recovery of PGM. Very little PGMs jn modern electronics, mostly Pd from MLCCs and then only if they are high end and old.

Components: First use pyrolysis to ash the components. You have to sort the components, most do not need pyrolysis and have no PMs
Second, remove magnetic pieces
Third, crush to fine powder (crush, sift, crush etc)
Fourth, water flush to remove carbon
Fifth, process with H2SO4 and KNO3 to remove the lead and copper. As said before Lead do not dissolve if Sulfuric are present. It is an excellent electrode for Sulfuric cells. And Copper makes up most if the value in electronics
Sixth, process with HNO3 to place Silver into solution.
Seventh, treat with slightly diluted AR to recover the Gold.
Eight, retain solids for future recovery of PGM.




Does this seem reasonable?
Many concerns here.
HCl and H2O2 have to be used carefully so it don’t dissolve Gold, better to use plain HCl for the Tin, or even better use mechanic or heated depopulation.
I have commented in bold text in the quote.
Edit for spelling.
 
Experiment: Use HCL + H2O bath to depopulate PCB creating Tin in solution and precious metal precipitate.

Process: Dilute HCL to 12-15% and soak PCB at ambient temperature. The boards were processed for 2-5 days depending on temperature, until components could easily by removed. (Completed)

Leach Solution: I expect this to contain mainly tin, hopefully without too much cadmium. I use electrolysis to recover the tin then reuse the solution on the next batch of PCB.

Slimes: First, process with H2SO4 and KNO3 to remove the lead and copper.
Second, process with HNO3 to place Silver into solution.
Third, treat with slightly diluted AR to recover the Gold.
Fourth, retain solids for future recovery of PGM.

Components: First use pyrolysis to ash the components.
Second, remove magnetic pieces
Third, crush to fine powder (crush, sift, crush etc)
Fourth, water flush to remove carbon
Fifth, process with H2SO4 and KNO3 to remove the lead and copper.
Sixth, process with HNO3 to place Silver into solution.
Seventh, treat with slightly diluted AR to recover the Gold.
Eight, retain solids for future recovery of PGM.




Does this seem reasonable?
In a setup like that he could win the tin via electrolysis.
 
I am currently processing some 1970's fully plated boards from fluke testing equipment and tektronix communications equipment that only have gold fingers.
Usually it takes a day and a half to two days for the solder to dissolve at outside temperature. Most of the components will just fall off when i turn them upside down in a 5 gallon bucket of water.
The biggest problem so far is some of the black plastic board sockets do not mix well with the concentrated hydrochloric acid, they start fizzing and turn to liquid plastic mush that coats everything.
Always keep a eye on your boards when you first put them in the acid and if you see foam a fizzing above the plastic remove from the acid, rinse and remove the problem components and try again.
Another problem is when your acid gets too saturated with copper it will start plating copper on your gold plated traces and fingers.
Always pactice safety with the acid, nitrile or rubber chemical gloves, safety glasses, goggles, and do not breathe the fumes. I keep a two gallon bucket of water and sodium bicarbonate on hand in case acid splashes on me or to neutralize spills.
Yes it does work. However it's not fast and it is also has problems.
With my thick plated boards it's actually faster and easier to remove all components by hand, heat the board up a little bit and use a knife to loosen a corner and peel off the plating with pliers. Not all gold plating can be peeled off like that but some of the older high end testing equipment is thick enough to peel. From there I put the peeled plating in concentrated hydrochloric acid to remove everything that is not gold. If the reaction is slow to start I add a little over the counter hydrogen peroxide, just enough to start putting the copper into solution.
 
When I come across these LCD boards, they also have a layer of glue on top of the "fingers," which is used to adhere the conductive ribbons.
 
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