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Potassium hydroxide good for developing PCBs?

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Dago

Wed Nov 26 2008, 05:41PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

I accidentally bought KOH drain opener instead of the usual NaOH one, will KOH work for developing PCBs? What about the concentration, will the same concentration work (been using around 1%)?

And should the developing liquid stay good when stored in a bottle for longer periods of time (months to a year or something)?

Proud Mary

Wed Nov 26 2008, 05:54PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

30g KOH in 1000ml water @ 25Â°C, agitate for ~ two minutes.

Backyard Skunkworks

Wed Nov 26 2008, 06:04PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

I'm fairly sure there shouldn't be any problem using KOH.

KOH is a stronger base though, you won't need as much.

And if its drain cleaner, look out to make sure its not mostly made of sodium hypochlorite.

Bored Chemist

Wed Nov 26 2008, 06:07PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

KOH should work fine. In principle you need to use 56/40 times as much i.e. about 1.5%, but I doubt this will matter- it will just make a bit of difference to the development time.

How well it (or NaOH, they are very similar) stays fresh depends on a few things- the most important question is what do you store it in?
It slowly attacks glass so I wouldn't use that (it "glues" ground glass stoppers very quickly).
It atacks PET type bottles too so they are out.
It should not attack polythene bottles (a lot of milk bottlese these days are polythene). However that brings us to the second problem; how well can you keep CO2 from the air away from the stuff?
A lot of plastics are quite permeable to CO2.
The simple answer is don't bother to try to save it.
Use it to etch stuff then throw it away.

Proud Mary

Wed Nov 26 2008, 06:11PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I forgot to add that KOH PCB developers rapidly react with CO2 from the air, so in commercial use sealed development tanks are usually employed to extend the working life of the solution.

Shelf life of made up solutions should be very long if flasks are airtight.

Conundrum

Wed Dec 24 2008, 07:35PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Does this also apply to NaOH solution 10% in water? my "old" solution didn't work but freshly made did.

Regards, -A

mikeselectricstuff

Fri Dec 26 2008, 11:24AM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

Hydroxides are really lousy developers - silicate based ones are WAY better.
See

for more info.

aonomus

Tue Dec 30 2008, 05:13AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Using weak hydroxides contaminated with photoresist would do poorly imo. If you can't find NaOH pellets (ie: pure, not in aqueous solution).

If you really need something to neutralize your solution, take some sodium bicarbonate from the supermarket, heat it at a few hundred degrees for a few hours to dehydrate and force it to sodium carbonate (more neutralizing power) and slowly add it (it will offgas CO2, don't let it bubble out of control). Once you have fully neutralized the solution, you can evaporate water to get Copper carbonate, then heat it much more strongly to get rid of CO2 to give the oxide.

And according to some other documentation you can add the copper oxide to acidified etchant (low volume) to bring up the copper concentration to etch faster. Air regeneration works but you'd offgas some HCl, so 30% peroxide might work better.

Chris Cristini

Tue Dec 30 2008, 05:30AM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

Be careful I used to work for a place called sturm rugers and I was in the blueing department I used Potassium hydroxide all the time it is very corrosive I got some down one of my rubber boots and it ate the skin of the top of my foot its a big lawsuit and don't inhale to much it takes your breath away.

Backyard Skunkworks

Tue Dec 30 2008, 08:50AM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

crazy4 wrote ...

I got some down one of my rubber boots and it ate the skin of the top of my foot

Wow did you heal up alright?

The worst by far is getting KOH in your eyes though, it normally causes blindess unless neutralized/diluted VERY fast. That goes for NaOH too, alkali hydroxides are some of the nastiest common chemicals for skin contact; be sure to know what your doing and always wear protective equipment!

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