# I can't seem to depopulate these circuit boards



## JBo (May 13, 2018)

Hi everyone. I spent about 48 hours trying to depopulate 500g of these clean cut circuit boards by doing a standard AP solution with 31.45% muriatic acid and 2% HCl in a 3:1 ratio respectively. I poured muriatic acid onto the circuit boards until the acid covered the top boards by about 1 cm, and then added 1/3 of the volume HCL I used of Muratic acid. But I can't even get a quarter of the boards clean after trying to run an aquarium pump through. Could someone give me a suggestion?


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## FrugalRefiner (May 13, 2018)

JBo said:


> Hi everyone. I spent about 48 hours trying to depopulate 500g of these clean cut circuit boards by doing a standard AP solution with 31.45% muriatic acid and 2% HCl in a 3:1 ratio respectively.


Did you make a mistake in typing this? AP stands for acid/peroxide. Muriatic acid and HCl are the same thing.

You also say you are trying to "depopulate" the boards. When we talk about depopulating boards, it refers to removing components like integrated circuits, surface mount components, etc. from the boards. I'm assuming you are actually trying to remove the gold foils from the boards.

Assuming you really used muriatic acid and hydrogen peroxide, you used too much peroxide. You only need a tiny amount, like a capful, to get the process started. The AP process is slow. Depending on other factors it can take days, weeks, or even months to dissolve the copper layer between the circuit board and the gold plating.

Dave


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## kernels (May 13, 2018)

As above, use an air bubbler and add an aquarium heater to the bucket, AP is very temperature dependent.

Also, those are likely ENIG gold over Copper, do you know how to process the gallons of toxic Copper waste you will create for a tiny amount of Gold ?


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## patnor1011 (May 14, 2018)

This plating is so thin you will likely not see any foils but it rather disintegrates to tiny specs and powder like. If I would have to guess I would say less than a gram worth of gold there. 
Give it about a week or two of soaking and check again. It also helps to stir them once or twice a day to make sure they are not stuck together and acid gets to all of the surfaces.


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## JBo (May 14, 2018)

Dave,

Whoops. Yeah I miss typed. I meant Muratic acid (HCl) and 2% hydrogen peroxide. 
Thanks for the advice! I'll add less hydrogen peroxide. I'm a newbie if you can't tell 

Also, do you think it's even worth processing these if they are ENIG? How much gold can I possible get fro them if I have 8.7 pounds of it?


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## JBo (May 14, 2018)

patnor1011 

Really?! That little even if I have 8.7 pounds of ENIG board?


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## IdahoMole (May 14, 2018)

Patnor is correct. The education will be more valuable than the gold so all is not lost. Process them to completion.

Jason


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