Removing solder from printed circuit boards

[Marcel]

I stand corrected. In that case there is little advantage and HCl seems to be the only realistic approach.

I try to avoid HCl wherever possible in early stages of refining (recovering?) since Silver Chloride is a mess in the procedures lateron (filtering).

 

[Marcel]

Yes but that is easily mitigated by HCl and air.
My post was aimed at the Tin Oxide part of the discussion.

OK, got it!
Tin oxide should easily dissolve in sulphuric acid—the more concentrated and the higher the temperature, the better.
I dissolved it in concentrated sulphuric acid which was heated around 80° quite fast... (Wear protective gear!!!!)

 

[haveagojoe]

Yes but that is easily mitigated by HCl and air.
My post was aimed at the Tin Oxide part of the discussion.

Yes, I don't have a problem dealing with Copper (i) Chloride, only Tin Oxide; and possibly Iron and Nickel oxides, I am still trying to determine if they are part of my black powders. I think it may be an issue for me because my HCl is not concentrated enough.

 

[Yggdrasil]

Yes, I don't have a problem dealing with Copper (i) Chloride, only Tin Oxide; and possibly Iron and Nickel oxides, I am still trying to determine if they are part of my black powders. I think it may be an issue for me because my HCl is not concentrated enough.

If you have the time your HCl can easily be concentrated to 20ish % by evaporation.

 

[haveagojoe]

If you have the time your HCl can easily be concentrated to 20ish % by evaporation.

Yes that will be my next approach I think. For a long time I have been using 10% HCl thinking is fine but in fact it may be the cause of some of my issues it seems.
I will give Sulfuric a try for soldered boards but not hot! Too scary for me!

 

[VolkD]

Have you had problems with this?
I have never encountered any significant filter issues with AP.

If you put things in the AP that have minimal impurities, then there are no problems.

 

[VolkD]

Copper(I) has been a painful filtering experience for me as well sometimes. You should have added more HCl and bubbling is a must.

I agree, hydrochloric acid is certainly cheaper than your time spent resolving such a situation.

 

[VolkD]

I will give Sulfuric a try for soldered boards but not hot! Too scary for me!

Wait, I'll do one test first. If I succeed,...

 

[adam mizer]

I saw this solution demonstrated online and works fairly quick.
Have not tried it yet.
200-400ml 27% sulfuric acid per 1 liter water. (battery acid) or adjust your acid to 27%
200 grams Ammonium or Potassium or Sodium Nitrate per 1 liter water.
20 grams Urea (Carbamide) per 1 liter water.
No heating.
Stirring or movement helps with speed of solder removal but not necessary.

 

[Yggdrasil]

I saw this solution demonstrated online and works fairly quick.
Have not tried it yet.
200-400ml 27% sulfuric acid per 1 liter water. (battery acid) or adjust your acid to 27%
200 grams Ammonium or Potassium or Sodium Nitrate per 1 liter water.
20 grams Urea (Carbamide) per 1 liter water.
No heating.
Stirring or movement helps with speed of solder removal but not necessary.

I'm not sure this will be good.
You are basically making Nitric and adding that to your solder.
This will most likely result in MetaStannic acid.

 

[adam mizer]

Looked okay to me but he only did a small amount.
HERE

 

[GoIdman]

I have a lot of circuits of this type. You can see from the photo that there is gold plating under the solder. Since my modified AP method refuses to cooperate with the solder, I have to remove the solder first.
Any advice would be welcome.
Ideally, I would remove the solder to the point where the gold color is visible.View attachment 67486

The gold color will never be visible on soldered surfaces, since some of the gold is dissolved by the solder.

I would use two methods, both of them labor intensive, and not viable if you have large quantities.

1) use a drilling machine to clean out the big holes (1,2 mm drill bit or bigger depending on the dialeter of the holes, to cover the entire gold bearing surfaces) from solder and gold mixture and separate that for later processing (ex. cupelling to reclaim the dissolved gold silver mixture, then refine), cut off the clean part and separate that to be processed separately (with AP, then AR to refine), dispose the not needed PCB tailings.

2) heat the boards with a heat gun and knock it to something to remove the majority of the solder (refine reclaimed solder with cupelling for the gold silver mixture) and clean the holes and surface, then treat with the correct acids step by step to remove the remaining solder. Then if the boards are clean use AP.

The first method may be more viable, but as I said, is labor intensive and you need quantities to be worth your time.

Maybe a 3`rd method would be, but i`m not sure its a walk-able path, burn the whole boards then grind, use a shaker table to separate copper and junk, use smelting to concentrate the values then cupelling to reclaim the values. Any input from more experienced members? Is this method even worth to be tried?

I presume these are newer boards with silver mixture solder.

Pete

 

[Yggdrasil]

Looked okay to me but he only did a small amount.
HERE

Hmm a disturbing lack of use of gloves.
Maybe the Urea is working as an inhibitor of sorts.
But you can see that there are some solid slime's swirling around.