[ladyada] has republished an interesting snippet from the synthDIY mailing list. [David Dixon] discusses the actual chemistry behind ferric chloride based home circuit board etching. He concludes that ferric chloride is essentially a ‘one-shot’ oxidant. It can’t be regenerated and can be difficult to dispose of properly. The use of acidified copper chloride is a much better path and becomes more effective with each use, as long as you keep it aerated and top up the acidity from time to time. This etchant solution is actually the result of initially using hydrogen peroxide as an oxidant along with muriatic acid. You can see us using this solution in our etching how-to and while creating the board for our RGB lock. For more information on using hydrogen peroxide, check out [Adam Seychell]’s guide and this Instructable.
Aside: [ladyada] has added the receiver code to the Wattcher project page.
14 thoughts on “Ferric Chloride Etching Chemistry”
We used a similar thing in school if I remember correctly.
In my experience the most unpleasant part of the process is trying to pour the toxic etchant solution back into the jar and finding a place to put it. In the climate I live in it will freeze and burst the jar if left outside. Any suggestions for disposal? Others on the net suggest flushing it down the toilet or feeding it to your houseplants, which I personally don’t recommend. I ended up taking it to the borough waste disposal, and they had no clue what it was.
@dan – If you have a local university, they might have a suggestion or facility.
I think ‘down the sink with a cold water chaser’ is pretty common hobbyist practice.
err… Though Ive not met Limor, Im pretty sure ladyada is a “she” not a “he”
… no ignore me I just re-read it.. the he bit refers to David.
this stuff is pretty dangerous to the environment and plumbing, and in many places it’s forbidden by law to trow it in the sink, in whatever quantity.
@Dan: I use the seno SN3300 etch-in-a-bag kit (from MegaUK) for ease of disposal. It comes with ‘neutraliser powder’ (plaster of paris? cement?) which you add to the Ferric Chloride once it is exhausted. This sets into a solid (inside the plastic etchant bag) and you then drop it into the bin for disposal in land-fill.
Thank you Eliot
there’s an instructable about this, I don’t have the link handy.
Copper is a nasty thing to dump down the drain, let alone iron. Personally I’m a fan of the CuCl/HCl/H2O2 process, because to clean up all you have to do is boil off the acid, add water, neutralize and make basic with NaOH, filter, and dry. You get relatively pure CuO with some NaCl mixed in, and you can simply wash it a few times and use the CuO for other stuff.
Dissolve the CuO in sulfuric acid and you get a copper etchant solution.
Etching your own boards is only useful if you gotta have it right now. Otherwise use sparkfun and get a pcb made for you better than any board you can etch on your own. no more chemicals to etch, tin and the nasty process of baking the boards to make Vias right with the copper paste. then silk screening at home is a pita for the solder mask and legends.
Nope I can have PCB express or sparkfun make my boards for 1/2 the price I can.
use a fume hood or do your “aeration” out doors. I aerated my cupric chloride solution in my back shed and destroyed the finish on many hundreds of dollars worth of tools. The acid aerosol ate the finish off nearly everything made of steel, except for things with baked on paint or quality chrome finishes.
Yea, and I hope you had a breather on as well, think of what that was doing to your lungs.
Really, if you think before you do it, that shouldn’t have been an issue.
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