Removing solder from printed circuit boards

[VolkD]

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.

 

[haveagojoe]

I use Hydrochloric acid but dilute Sulfuric would also work, probably faster. The problem would be that Sulfuric acid would also attack the solder mask, so when you get to the Copper Chloride etching stage there will be a lot more copper exposed.
For boards like that I chop them up with snips, cutting off all the bits with gold and no solder, and then process the soldered bits seperately. It depends how many you have to process I guess.

Edit to add: on the plus side for Sulfuric is that it won't attack the copper so there isn't a risk of releasing the foils prematurely, which can happen with HCl if you leave it too long.

Edit 2: an advantage with using HCl is that you can recycle it by dropping the tin out as tin oxide by bubbling air through it. The tin oxide is a whitish powdery precipitate which can easily be filtered out.

 

[VolkD]

Better than HCl alone is to add a little citric acid. Even better, instead of citric acid, add ammonium chloride. A little of each is best.Unfortunately, I don't have ammonium chloride. I know that it is a fertilizer used in agriculture, but unfortunately I can't find a connection between the chemical and commercial name.
I was hoping to find out about some other method.

I like turbo methods

 

[haveagojoe]

One of the problems is that during soldering the gold alloys slightly with the tin solder, so attempts to clean the solder off will never be completely successful, it won't be as good as the unsoldered pads and some tin will carry over into the Copper Chloride etch. There the bubbler will make it fall out as tin oxide, which gets mixed up with the foils.

You may have seen my recent post about an experiment of how to deal with that using Zinc:
https://goldrefiningforum.com/threa...-etches-experiment-writeup.35821/#post-388888

 

[Marcel]

I have made good experience using dilute sulfuric acid. It takes some time but will dissolve Tin and Lead. I do not use HCl because of the formation of Silver Chloride and the fact that it may also attack the copper.