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Author: Subject: Disposal of electroless plating solution (formaldehyde-based)
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[*] posted on 22-7-2022 at 13:48
Disposal of electroless plating solution (formaldehyde-based)


Hello,
I've been experimenting for a few years with electroless plating [1] for printed circuit boards. The process key step involves a plating bath with copper sulfate and formaldehyde [2], and I was thinking at ways to safely dispose of this solution.

The idea I had was to add an excess of concentrated NaOH solution to achieve two goals.
First, this plating bath is known to spontaneously decompose at too high pH, precipitating copper metal. This "feature" allows to get rid of the copper sulfate.
Second, if enough excess NaOH remains in solution, the Cannizzaro reaction should slowly destroy the formaldehyde, forming methanol and sodium formate.

The question I have is the following: is there anything obvious I may have missed? Do you think the resulting solution would be free of formaldehyde? Is there even a qualitative test for formaldehyde?


Anyway, to test my theory I decided to give the process a test. To a beaker I prepared 40mL of a concentrated sodium hydroxide solution, let it cool to room temperature, added it to around 60mL of the plating solution, and let it react overnight in a loosely sealed container (as part of reducing copper salts to copper, the solution releases hydrogen as a byproduct).
The next day the blue color of copper sulfate was almost completely gone (picture attached) and a copper dust collected at the bottom of the container, so it at least seems to work.

disposal.jpg - 135kB

[1] My video about the process I developed
https://youtu.be/Kn92cLf69iw

[2] Composition of the plating solution
- 2.52g copper sulfate pentahydrate
- 5.8g disodium EDTA
- 4 drops of Triton-X 100 (surfactant)
- 1.6mL of 37% formaldehyde
- enough water to reach 200mL
Solution is stored acidified with sulfuric acid, and a controlled amount of NaOH is added before use.

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Rainwater
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[*] posted on 22-7-2022 at 15:02


According to this lab disposal guide.
https://www.google.com/search?q=Hazardous+Laboratory+Chemica...

Pg. 239
By mixing the diluted solution with an excess of bleach formic acid will be produced.

Quote:

Slowly add diluted formaldehyde (10ml water for each 1ml formaldehyde) to an excess of household bleach. (25ml household bleach for each 1ml of formaldehyde). Stir for 20 minutes, and then wash the solution into the drain.

Personally i would try to collect and purify that acid but it says what it says amd you may have no use or want for it.

Do you want to recover any metals, copper, noble, PGM? Haven't watched the video yet but I use a palladium catalyst to start the plating process. So i try to save every atom.

http://www.sciencemadness.org/talk/viewthread.php?tid=65275
This thread is about measuring formaldehyde.




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[*] posted on 22-7-2022 at 15:31


If I may suggest a different method to apply your catalyst. By getting some empty felt tip pens and filling them with your palladium solution, then using your cnc to draw the traces, you can eliminate several steps. It would still require electroplating to thicken the traces where needed but would remove several steps involving etching.

I hand draw/drill many of my boards and discovered this method years ago. Signal traces are usually thick enough with just the initial plating. Power traces I thicken by including temporary traces bonding them together, electroplating with a solution of h2so4 + cuso4 + Polyethylene glycol + h2o at around 50ma cm². Then etch off the temporary traces

great tutorial

[Edited on 22-7-2022 by Rainwater]




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[*] posted on 23-7-2022 at 01:06


Quote: Originally posted by Rainwater  

Pg. 239
By mixing the diluted solution with an excess of bleach formic acid will be produced.

Personally i would try to collect and purify that acid but it says what it says amd you may have no use or want for it.

Do you want to recover any metals, copper, noble, PGM? Haven't watched the video yet but I use a palladium catalyst to start the plating process. So i try to save every atom.

http://www.sciencemadness.org/talk/viewthread.php?tid=65275
This thread is about measuring formaldehyde.


Thanks for the reply. Actually I expect the Cannizzaro reaction to occur quite slowly at room temperature, and heating the solution is a bad idea as it would let formaldehyde escape as a gas. Adding bleach after precipitating the copper seems a good idea to get rid of the remaining formaldehyde fast and I don't see any evident chemical incompatibilities with the plating bath composition.

As for the formic acid, I bought several years ago an 1L bottle of 85% formic acid and only used 100mL or so, so I won't try to recover milliliters of it from plating solution.

As for the PGM metals, one of the steps of the process does use palladium chloride, but I only made two 50mL batches of that solution, with 20mg of palladium chloride each. The first batch has gone bad, so I may try to recover palladium from it. I don't feel particularly confident I'll be able to recover such a small quantity but I make take it as a challenge someday I have nothing to do in the lab.

As for the formaldehyde titration thread thanks for that, I'll see if I can find something I can replicate in my lab.
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[*] posted on 23-7-2022 at 01:18


It looks like we've been experimenting with the same problem :D. Unfortunately I didn't find any complete tutorial like on the entire Internet and thus spent quite some time combining bits and pieces and filling the gaps with basically homebrew R&D to get it working. Was fun and rewarding, but took a very long time.

I'm not sure about the felt tip idea, as I need the catalyst to coat the hole walls to make through hole vias. Sure, I could load the felt tip with so much catalyst that it would almost drips, but that would make it impossible to draw closely spaced fine traces without shorting them together. Plus, the FR4 substrate I use is already copper clad, would need to source unclad board.

My current approach to manage the complexity of this process is to use it only when really needed. I can get away doing single sided boards for most of my projects, and those are super fast to do.

Quote: Originally posted by Rainwater  
If I may suggest a different method to apply your catalyst. By getting some empty felt tip pens and filling them with your palladium solution, then using your cnc to draw the traces, you can eliminate several steps. It would still require electroplating to thicken the traces where needed but would remove several steps involving etching.

I hand draw/drill many of my boards and discovered this method years ago. Signal traces are usually thick enough with just the initial plating. Power traces I thicken by including temporary traces bonding them together, electroplating with a solution of h2so4 + cuso4 + Polyethylene glycol + h2o at around 50ma cm². Then etch off the temporary traces

great tutorial

[Edited on 22-7-2022 by Rainwater]
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