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Topic: Ferric Chloride  (Read 9303 times)

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Offline nobody_6.1

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Ferric Chloride
« on: January 31, 2007, 09:18:12 PM »
I use ferric chloride to etch circuit boards. My biggest problem is that after a few cicruit boards I need new etchant. It looks like the reaction for this is:

FeCl3 + Cu ? FeCl2 + CuCl followed by FeCl3 + CuCl ? FeCl2 + CuCl2

Is there a way to reclaim the Ferric chloride from the used etchant, maybe through electrolysis or something?

Thanks

Offline Borek

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Re: Ferric Chloride
« Reply #1 on: February 01, 2007, 04:36:14 AM »
Chances are simple aerating will work - at least it should oxidize Fe(II) to Fe(III). It will not remove copper from the solution.
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Offline woelen

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Re: Ferric Chloride
« Reply #2 on: February 01, 2007, 06:14:58 PM »
Replenish the solution with some acid every now and then and allow air-contact. There is no need to get rid of the copper, in fact, the copper in solution helps etching the PCB. Finally, you hardly won't need any additional FeCl3. The only thing used up is acid.

Initially the iron(III) acts as oxidizer, but lateron, the copper (II) in solution also acts as oxidizer. The esulting copper (I) compounds are VERY easily oxidized by oxygen from the air. So, essentially, oxygen from the air is your free oxidizer. The only non-free compound (after the initial FeCl3) is the acid. If the volume becomes too large, simply get rid of some (don't flush it down the drain, bring it to a proper waste processing facility).
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Offline nobody_6.1

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Re: Ferric Chloride
« Reply #3 on: February 02, 2007, 05:44:25 PM »
So I could just bubble air through the solution and occasionally add more FeCl3?

Offline woelen

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Re: Ferric Chloride
« Reply #4 on: February 03, 2007, 04:40:43 PM »
No need to add FeCl3 occasionally. You need an oxidizer to get it started and initially get copper (II) in solution, but once you have a lot of copper in solution, the only replenishment you need is occasionally adding some concentrated hydrochloric acid.

So, you start with FeCl3, dissolved in hydrochloric acid. Equally well (or even better) is adding some H2O2 to hydrochloric acid.
To this, you add copper and that will dissolve and after that you keep the stuff in contact with air.
Each time you want to use it, just keep it in a container, with air contact several hours before you immerse the PCB. After use you can store it in a tightly closed container (it gives off corrosive fumes, so you want it isolated, when not in use) and a few hours before using it again, you leave it in contact with air again to absorb oxygen. No need for annoying bubbling sessions.
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Re: Ferric Chloride
« Reply #5 on: February 19, 2007, 05:04:02 AM »
Interesting page on using just copper chloride for etching:

http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/index.html
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