Thoughts about stripping/deplating circuit boards.

[Nevadayote]

I've had the idea spinning in my skull that there should be a way to effectively use a stripping cell to deplate circuit boards. I know it can be done by a tedious process of using something like a pin probe anode contact. I've seen people doing that on video, but it takes forever! Also, it's kind of risky since the plated material has to be in the electrolyte while the user uses a probe to make electrical contact with the plated surface. I much prefer keeping my hands farther away from the acid!

What has come to mind is to make a sort of clamping rig out of plastic where the circuit board can be sandwiched in it with copper wool on the plated surface. The copper wool would be the anode contact and the plastic clamp would keep it pressed to the plated parts of the circuit board. The entire thing could then be laid into the cell. Deplating should only take a few seconds.

Does this seem doable?

 

[Yggdrasil]

I've had the idea spinning in my skull that there should be a way to effectively use a stripping cell to deplate circuit boards. I know it can be done by a tedious process of using something like a pin probe anode contact. I've seen people doing that on video, but it takes forever! Also, it's kind of risky since the plated material has to be in the electrolyte while the user uses a probe to make electrical contact with the plated surface. I much prefer keeping my hands farther away from the acid!

What has come to mind is to make a sort of clamping rig out of plastic where the circuit board can be sandwiched in it with copper wool on the plated surface. The copper wool would be the anode contact and the plastic clamp would keep it pressed to the plated parts of the circuit board. The entire thing could then be laid into the cell. Deplating should only take a few seconds.

Does this seem doable?

What are you going to strip?
The Gold or components?
If you are talking of a Sulfuric stripping cell the concentrated Sulfuric would not react with the Copper.
For other cells the Copper will probably dissolve.

 

[Nevadayote]

It's a sulfuric stipping cell to strip gold plate. The copper wool is simply to provide anode contact with the cold plated portions of an otherwise bare (components already removed) circuit board. Right now, I'm using AP to dissolve base metals and release gold foils and that works, but I'm simply exploring the possibility of using a stripping cell to do the same job.

 

[Yggdrasil]

It's a sulfuric stipping cell to strip gold plate. The copper wool is simply to provide anode contact with the cold plated portions of an otherwise bare (components already removed) circuit board. Right now, I'm using AP to dissolve base metals and release gold foils and that works, but I'm simply exploring the possibility of using a stripping cell to do the same job.

The stripping cell is not suited to depopulate as it will foul quickly.
Better depopulate with other means.
I'm still not convinced it is a good idea for whole PCBs.

 

[Nevadayote]

I would NOT be using the stripping cell to depopulate. The circuit board would not have any components on it whatsoever. Only the gold plating on contacts and traces is of any interest in this process. I use other means to strip components off of the boards.

 

[BShan]

Preface: I have only done small tests, and have not begun any recovery processes in earnest; I'm a hobbyist, been reading for a few years now.

My opinions:
I don't see why it wouldn't work. You'll lose some gold to the copper wool, but that's recoverable eventually. But if there's solder on the boards though, it won't recover the gold dissolved in the solder. That efficacy is where your other process wins over this one, as that gold in theory should be in the powder at the bottom of the AP bucket, if it was run long enough to dissolve the solder off of the boards too.

Random other things to think about:
* larger surface area of the sulfuric cell needed for boards, might increase the rate of water absorption by the electrolyte
* PCB might be porous enough to hold onto a decent amount of sulfuric when you pull them out (same problem with AP, though). With the copper wool and extra pieces, it might make rinsing more complicated, or cause your rinse to become acidic more quickly.
* heat will be generated, and I think probably localized to where the "action" happens; the plastic backing used to squish the wool onto the pcb surface might not like that

 

[Yggdrasil]

I would NOT be using the stripping cell to depopulate. The circuit board would not have any components on it whatsoever. Only the gold plating on contacts and traces is of any interest in this process. I use other means to strip components off of the boards.

I read you wrong, sorry about that.

Anyway it will not work completely since not all traces are connected everywhere on both sides.
Some traces goes only a certain distance and on one side. some are more wide spread.
Anyway the boards that need to be depopulated are few, most boards are only plated on the contact areas (fingers).
These are easily cut off and processed traditionally.

 

[BShan]

In my limited testing of stuff from the more modern era, most boards which have a lot of gold plating, is usually the very thin plating, suspected to be ENIG. Like, those digital processing boards on LCD screens which demux the signal to the actual rows and columns of pixels, are extremely thin gold which comes off in foils so delicate they turn to powder if you look at them wrong. It sure would take a lot of those for me to justify creating a whole separate process to recover the little bit of gold on there too.

But, if I had a huge stack of depopulated boards with full gold plating staring at me, it would be hard to emotionally justify sending them off to the scraplot, I surely understand that part! I have 2 boards in my work area, full plating on the back, I know full well how little is actually there, but it sure is pretty to see that much surface area of gold!

I've pondered an even worse idea: a "spongebath" way which doesn't rely on submersion. I decided it was way too finicky and no way could I do that without making a mess, which is crucial to avoid with something as strong as conc. sulfuric acid. Because of the small amount I have, I'm compromising with my emotions, and planning on just sanding off the gold, and tossing the sandpaper and copper powder in with my other copper and gold powders. But, a smarter person than me would probably just sell it off as-is.

 

[Nevadayote]

The copper wool will certainly hold onto more acid! A longer time to drain will be needed. As for the heat and plastic, I'm thinking of butchering a plastic cutting board and using two chunks of that to make the "clamp" that holds the copper wool to the circuit board. It's quite possible that the whole thing is much more trouble than it's worth. I think I'll give the idea a limited run soon and report my observations here.

 

[Nevadayote]

OK! My idea is pretty crappy as it turns out. The metal wool retains a huge amount of acid and does not drain hardly at all! That's a huge issue right there. Not at all safe and it makes the entire process very difficut. So, submerging in AP is still the best process I've tried. Yeah, AP takes time, but it much more easily managed. When I finish neutralizing the acid in the wool, I can get a look at the result. I expect that the gold got stripped, but it wasn't worth the hassle.

 

[patnor1011]

Try iodine/iodide leach. It is not quite cheap but iodine can be recovered back and reused. Eventually ferrocyanide leach can work too. I would certainly prefer to use those rather than hot concentrated sulfuric.