chrundle_the_great
Active member
In a fb gold recovery group someone mentioned using caustic soda to remove green board when there is gold plating underneath. Anyone have the steps or process to do this?
Gold plating under green boards and caustic soda
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chrundle_the_great
Active member
Will plain AP get to the gold and copper underneath the green board if NaOH is optional? I always assumed it would. This is why I asked here, you all are alot more knowledgeable than facebook
nickrpotts
Member
It really depends on the age and technology used on the PCB, most of the modern boards with solder mask (the green or other coloured coatings) are plated after the solder mask is applied, using electroless chemistry which deposit an even and usually slow and self limiting coating.
The gold plating is very thin, with a nickel under coat 3-5 microns thick and then less than 0.2micron in thickness for the gold. So there is no need to strip the solder mask as there is no gold underneath it.
Older PCB's were electrolytic plated and typically plated all over as defined by the circuit pattern, as they needed an electrical connection to enable the plating process to be carried out. These were typically greater than 1 micron in thickness, with old style end connectors or wire bondable pads 5 microns or thicker.
Also as Tggdrasil states, the NaOH can also be dangerous in this application, as this usually needs to be done at 80'c or hotter.
The gold plating is very thin, with a nickel under coat 3-5 microns thick and then less than 0.2micron in thickness for the gold. So there is no need to strip the solder mask as there is no gold underneath it.
Older PCB's were electrolytic plated and typically plated all over as defined by the circuit pattern, as they needed an electrical connection to enable the plating process to be carried out. These were typically greater than 1 micron in thickness, with old style end connectors or wire bondable pads 5 microns or thicker.
Also as Tggdrasil states, the NaOH can also be dangerous in this application, as this usually needs to be done at 80'c or hotter.
I have quite a few of these very old HP boards.... I was going to depopulate them first, then place them in copper II chloride (AP). This should remove the remaining solder in the thru holes and the green solder mask (which is covering gold). I do not want to use NaOH. What do you fine gents think?
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The AP will dissolve the Copper behind the Gold foils and the HCl in the AP will dissolve the Solder.
But that is it the green solder mask is not touched at all.
If you feel the need to remove that, you need hot NaOH solution 20% or so and it will take care of it.
But be careful hot Lye is no joke and this have to be done first.
Thank you. How about if I release the exposed gold foils first with AP, and see if it amounts to anything worthwhile - before proceeding to the solder mask issue.
Yggdrasil... Has anyone ever posted pictures of a fully exposed board free from all soldered electronics, solder, and green mask?
It would be pretty cool to get a visual on that. Also, does anyone have any specific dates when the circuitry stopped bearing gold?
No problem, and if you let it spend enough time in the AP the whole foil will release probably.
I have seen pictures of bare boards, new and depopulated.
If my mind don't play tricks on me, I think I have seen boards with fully exposed tracks too.
They are out there and Google will find them
I will do that and post my results under this thread in a few weeks.
Thanks fellas... There have been so many times that I've clipped off the fingers, pins, surface gold plating, and chips then just chucked the rest. Was wondering about why a gold plating under solder mask would still look copper in color.
In the consumer electronics I have examined, gold plating under solder mask is much less common than unplated copper under solder mask. laptop touchpads, and some older sound cards, are all I've encountered. I imagine for sound cards, it adds marketing value. Sound nerds love gold plating. Or I guess analog signal nerds love good connections.
I did run a test of 5 touchpads in "AP", and after a very very long time, the solder mask and theoretical foils detached with some physical abrasion. The solder mask remains adhered to the substrate where there is no copper to dissolve; the HCL does not seem to affect the solder mask's integrity. The solder mask was removeable by scraping the piece gently with my stir rod, but it did not just detach by itself.
My specific test pieces either were not gold plated, or the gold was too thin to release in a full foil.
With relation to this conversation, I would hypothesize that HCL will release the foils once it gets under the solder mask, but the solder mask will need to be physically abraded to detach from the board and physically release the foils. You would then be able to filter the solution and be left with chunks of solder mask with your foils.
I did run a test of 5 touchpads in "AP", and after a very very long time, the solder mask and theoretical foils detached with some physical abrasion. The solder mask remains adhered to the substrate where there is no copper to dissolve; the HCL does not seem to affect the solder mask's integrity. The solder mask was removeable by scraping the piece gently with my stir rod, but it did not just detach by itself.
My specific test pieces either were not gold plated, or the gold was too thin to release in a full foil.
With relation to this conversation, I would hypothesize that HCL will release the foils once it gets under the solder mask, but the solder mask will need to be physically abraded to detach from the board and physically release the foils. You would then be able to filter the solution and be left with chunks of solder mask with your foils.
In continuance with this subject, I physically depopulated many of these old HP boards to where I just have:
A) exposed thick gold plating on the top surface
B) a green solder mask covering thick gold plating on the bottom surface
C) remaining solder from the removed pins and connectors
I placed a sample board into a beaker and covered it with HCL for a few days and as you guys predicted, the solder dissolved.
My question is:
If I skip this HCL step and go straight to AP, will the tin in the solder foul my perfect batch of AP?
Thanking you in advance.
A) exposed thick gold plating on the top surface
B) a green solder mask covering thick gold plating on the bottom surface
C) remaining solder from the removed pins and connectors
I placed a sample board into a beaker and covered it with HCL for a few days and as you guys predicted, the solder dissolved.
My question is:
If I skip this HCL step and go straight to AP, will the tin in the solder foul my perfect batch of AP?
Thanking you in advance.
Yes.
Dave
Dave
I believe not, I have never removed the solder after depopulating by heat. Not much solder left then, but I always end up with some grey gunk.
It has not bothered me much though.
I guess it is a mix between Copper I Chloride and some undissolved Tin/Trash.
It cleans up nicely though, but I never use AR to dissolve the foils.
Edit for spelling
Oops, I see Dave beat me to it.
I have not noticed much fouling, so can you explain a bit more.
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I depopulated with a chisel, so I have considerably more solder present.
The copper chloride leach can be reused for a long time, as long as it remains a copper chloride leach. As other metals are dissolved in the solution, the chemistry changes.
Tin will also combine with gold that may dissolve into the solution, tying it up temporarily.
Dave
Tin will also combine with gold that may dissolve into the solution, tying it up temporarily.
Dave
Thanks Dave.
