Removing solder from printed circuit boards

[IThinkSilver]

Try heating the boards in a moderate solution of sodium hydroxide (lye). This should remove it in less than an hour. You can experiment with the concentration and time to your liking.

 

[VolkD]

However, for the benefit of readers, and ultimately in the interest of safety, I think it would be beneficial to provide the formula for reactions when novel ideas are proposed, so that members can follow the logic of the proposal and discuss its potential. I worry that without understanding why chemicals are used, particularly in combination, a new approach could potentially become a recipe for disaster in the hands of an inexperienced reader.

Reaction: Hydrochloric acid + Copper(I) chloride (CuCl) + Sodium persulfate (Na₂S₂O₈)
1. Oxidation of copper(I) chloride (CuCl) to copper(II) chloride (CuCl₂)
- When copper dissolves in the AP process (HCl + H₂O₂), copper(I) chloride (CuCl) is formed, which is poorly soluble and brownish.
- The addition of sodium persulfate (Na₂S₂O₈) helps to oxidize CuCl back to copper(II) chloride (CuCl₂), which is highly soluble and greenish-blue in color.

Reaction: CuCl+Na2S2O8→2CuCl2+Na2SO42CuCl+Na2S2O8→2CuCl2+Na2SO4
- Persulfate (S₂O₈²⁻) strongly oxidizes Cu⁺ to Cu²⁺.
- CuCl₂ is soluble in HCl, which helps in further dissolving the copper.
- Na₂SO₄ (sodium sulfate) remains as a byproduct in the solution.
2. Further dissolution of copper in HCl + CuCl₂ + Na₂S₂O₈
When there is enough CuCl₂ in the solution, the copper dissolves faster, without the need for additional hydrogen peroxide.

Reaction: Cu+CuCl2→2CuClCu+CuCl2→2CuClCuCl+Na2S2O8→CuCl2+Na2SO4CuCl+Na2S2O8→CuCl2+Na2SO4
- CuCl₂ reacts with copper to form CuCl (a brownish residue).
- The persulfate oxidizes CuCl back to CuCl₂, allowing for continued dissolution.
- Copper therefore dissolves as long as there is enough CuCl₂ and an oxidant (Na₂S₂O₈) in the solution.

3. When to add hydrochloric acid (HCl)?
- Hydrochloric acid helps in two cases:
¤ If white or brown insoluble residues (CuCl, Cu₂O) appear.
¤ If the reaction slows down and the solution is oversaturated with CuCl₂.
- Adding HCl helps:
CuCl+HCl→[CuCl2]−CuCl+HCl→[CuCl2]−
¤ Prevents the precipitation of CuCl (brown residue).
¤ Allows better dissolution of copper.


Conclusion: How to optimize the process?

- If the solution is dark brown: Add Na₂S₂O₈ to oxidize CuCl to CuCl₂.

- If brown CuCl precipitates: Add HCl to stabilize it in [CuCl₂]⁻.
- If the dissolution of copper slows down: Add HCl and a little Na₂S₂O₈ to reactivate the reaction.

Result: More stable and faster AP process without excess peroxide!

Or you can also put it very simply and briefly:sodium persulfate is a strong oxidant that replaces turbo adding bubbles so successfully that adding peroxide for this purpose is not necessary. At the same time, it is not strong enough to dissolve gold.I am not yet completely convinced of this last statement, although tests confirm it. If it dissolves it, very very little. If it dissolves it, so little that I can say without a doubt that speed is worth paying for.Experience so far shows that the whole thing is sensitive to contamination. Any contamination extends the reaction time.Back to the topic: That is why there is a debate here about how to remove solder from printed circuit boards.

 

[VolkD]

Try heating the boards in a moderate solution of sodium hydroxide (lye). This should remove it in less than an hour. You can experiment with the concentration and time to your liking.

https://goldrefiningforum.com/threa...inted-circuit-boards.35832/page-2#post-389422

This was my first attempt. Not good enough.

 

[VolkD]

This is treated with hot air. All the elements are removed, instead of a scraper I used a paper towel. This way you remove more solder. Unfortunately this is not good enough either.

 

[Marcel]

Not drum scale but works decent for a small scale home user.

Awesome!
Speaking about time: Such a solution automatizes the recovery. You can let it run while doing something else. Other methods often do not take into account that follow-up steps , waste removal, buying, preparing chemicals etc. altogether cost time as well. While the dissolution with strong reagents may go much faster it is the question if the whole process from beginning to end is really a time saver.

 

[VolkD]

Such a solution automatizes the recovery. You can let it run while doing something else.

That's right, but the circuit board is still not cleaned well enough. There is still too much solder. Of course I'm talking about gold-plated circuits. In my case, the solder causes the reaction to last much longer than if they were clean.

 

[haveagojoe]

Reaction: Hydrochloric acid + Copper(I) chloride (CuCl) + Sodium persulfate (Na₂S₂O₈)
1. Oxidation of copper(I) chloride (CuCl) to copper(II) chloride (CuCl₂)
- When copper dissolves in the AP process (HCl + H₂O₂), copper(I) chloride (CuCl) is formed, which is poorly soluble and brownish.
- The addition of sodium persulfate (Na₂S₂O₈) helps to oxidize CuCl back to copper(II) chloride (CuCl₂), which is highly soluble and greenish-blue in color.

Reaction: CuCl+Na2S2O8→2CuCl2+Na2SO42CuCl+Na2S2O8→2CuCl2+Na2SO4
- Persulfate (S₂O₈²⁻) strongly oxidizes Cu⁺ to Cu²⁺.
- CuCl₂ is soluble in HCl, which helps in further dissolving the copper.
- Na₂SO₄ (sodium sulfate) remains as a byproduct in the solution.
2. Further dissolution of copper in HCl + CuCl₂ + Na₂S₂O₈
When there is enough CuCl₂ in the solution, the copper dissolves faster, without the need for additional hydrogen peroxide.

Reaction: Cu+CuCl2→2CuClCu+CuCl2→2CuClCuCl+Na2S2O8→CuCl2+Na2SO4CuCl+Na2S2O8→CuCl2+Na2SO4
- CuCl₂ reacts with copper to form CuCl (a brownish residue).
- The persulfate oxidizes CuCl back to CuCl₂, allowing for continued dissolution.
- Copper therefore dissolves as long as there is enough CuCl₂ and an oxidant (Na₂S₂O₈) in the solution.

3. When to add hydrochloric acid (HCl)?
- Hydrochloric acid helps in two cases:
¤ If white or brown insoluble residues (CuCl, Cu₂O) appear.
¤ If the reaction slows down and the solution is oversaturated with CuCl₂.
- Adding HCl helps:
CuCl+HCl→[CuCl2]−CuCl+HCl→[CuCl2]−
¤ Prevents the precipitation of CuCl (brown residue).
¤ Allows better dissolution of copper.


Conclusion: How to optimize the process?

- If the solution is dark brown: Add Na₂S₂O₈ to oxidize CuCl to CuCl₂.

- If brown CuCl precipitates: Add HCl to stabilize it in [CuCl₂]⁻.
- If the dissolution of copper slows down: Add HCl and a little Na₂S₂O₈ to reactivate the reaction.

Result: More stable and faster AP process without excess peroxide!

Or you can also put it very simply and briefly:sodium persulfate is a strong oxidant that replaces turbo adding bubbles so successfully that adding peroxide for this purpose is not necessary. At the same time, it is not strong enough to dissolve gold.I am not yet completely convinced of this last statement, although tests confirm it. If it dissolves it, very very little. If it dissolves it, so little that I can say without a doubt that speed is worth paying for.Experience so far shows that the whole thing is sensitive to contamination. Any contamination extends the reaction time.Back to the topic: That is why there is a debate here about how to remove solder from printed circuit boards.

Nice, that's helpful. But I was referring more to the recipes for dissolving solder; as Marcel pointed out the one @adam mizer posted with Urea doesn't seem to make a lot of sense.

 

[VolkD]

I've seen this on youtube. I think it's because someone does something, others copy it, and eventually it becomes a myth.Urea is a useful chemical, but as a neutralizer, I'm not sure what it's supposed to do here. If so, then you reduce the amount of acid or lower its concentration.