CuCl etching

In early Jan there was a discussion here about using CuCl to etch PC boards. Sorry, I lost the original thread.

Someone mentioned a web page about this. I think that was my page. My site was in limbo at the time. I have finally gotten around to putting up some pages in a new location.

Here's the page on CuCl etching...

This information is all copied from a book of the 1980's. I did contact the author before posting. He goes into great detail on the process of keeping the chemistry right.

All the pictures on this page are from the book. When I did my version, I found some porous plastic tubing in an aquarium store. I ran a few rows horizontally across the bottom of the tank as a bubbler. I adapted an aquarium heater in a large test tube. The heater was adjusted to a level that could cook fish, but all the parts were there, so the conversion was pretty easy.

Interesting, What is more, when the cuprous chloride has been formed, you can bubble acetylene through the soultion to make cuprous acetylide - explosive, but not as good as the silver variety.

I prefer fulminate of mercury myself (remember the movie "Mister Roberts" ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
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I love to cook with wine.      Sometimes I even put it in the food.

Thanks for sharing. I think that was myself who commented in January. My design is slowly coming along, but I'm still not sure of several things yet so it is up in the air. So far it's looking like a five-division acrylic tank about

13"x10"x1" per tank - one for developer, etchant, stripper, tin plate, and rinse. (Not necessarily in that order or same thickness, of course.) The hard part has been figuring out a way to seal the etchant tank during bubbling so etchant doesn't splatter all over the place or run or drip. Since HCl fumes are so nasty, I also thought about piping the etchant air exhaust into a bubbler in the rinse tank - hopefully counteracting the effects of developer and stripper alkalinity on the rinse water anyways. It's a W.I.P.

I wanted to mention about disposal of excess CuCl - some peeps on sci.chemistry and I figure that adding magnesium to (rejuvinated) CuCl should produce harmless byproducts suitable for disposal. This has not been tested yet. A great place to get bulk magnesium is eBay of course. Whenever I get a chance to test this, I'll let us know the results.

Did you say CuCl wouldn't etch very fast for you? To make my initial batch I took the H2O2/HCl reducer path and added some copper. This sat in a polyethylene bottle next to my bathroom register (heater vent) for about a week, etching happily whenever I'd throw in some copper. Half a gallon ate all three conductors of a beefy 6' computer electrical cord and then some. It did seem to be very slow, but of course the solution parameters was and still is nowhere near the recommended. In hindsight, it would have been much simper to just buy some CuO from eBay and mix it with HCl, done.

It's pretty much stopped etching now, but the color is not anywhere near "olive-brown." It's more like a deep, slightly-opaque green, still in stark contrast to the "almost-glow-in-the-dark" bright translucent green when it started. I haven't been able to bubble it yet, and it still seems like the density is far too low (compared to the viscosity of FeCl), but we'll see what happens when it goes into the bubbler tank and gets some well-needed rejuvination and calibration. :)

Regards, Mark

A much safer alternative is ammonium tri-iodide. Take a pitri dish, add a few (read: one or two) iodine crystals, add just enough ammonia to cover. Ammonia in this case is household ammonia - the pure stuff would make the result far too unstable - breathing on it would set it off. Swirl gently, and after a few minutes the iodine crystals will turn purple. When wet, it is harmless. But once they dry, they become explosive. Apparently the molecules line up in very long chains when drying and are easily broken by physical force, creating a miniature atomic chain-reaction. The product of explosion is simple dis-assembly of the structure - it leaves an ammonia-and-iodine-stain on whatever unlucky thing touched it.

I read in sci.electronics.design that Jim Thompson wrote (in ) about 'Was: CuCl etching', on Sun, 13 Feb 2005:

That is not too surprising since it's a compound, mercuric isocyanate, formed from mercury and *ethyl alcohol*, with a little help from nitric acid.

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The good news is that nothing is compulsory.
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That is a problem. I never solved it. The HCl fumes are indeed nasty, and heating the solution makes it worse. The bubbling tends to create an aerosol of the solution too which can badly stain anything it contacts. I have some plumbing in my batroom, where I tried this, that now has a nice rust coating.

A tight cover and some kind of fume hood would definately be a good idea.

I guess you read the disposal idea from the book I copied? This was mainly in reference to FeCl but I guess would be ok for CuCl too. He talks about neutralizing it and then mixing it into concrete to make a brick that will contain the chemicals. I thought that was one of the best ideas I had heard.

Yes. I can't remember the times now but it seemed to take about twice as long as I ecpected FeCl would. Maybe there was some problem with my set-up, but I mixed the chemical per the article and tests showed acid level and density to be about right.

Ah.... those were the days, when schools really taught chemistry.

martin

"Facts are stupid things.." -- Reagan, '88

I read in sci.electronics.design that xray wrote (in ) about 'CuCl etching', on Sun, 13 Feb 2005:

HCl vapour is very highly soluble in water. So you can absorb it in a water bath to recover the acid. It's so soluble that you have to take precautions to stop the water climbing up the input pipe after it. I kid you not; it's called 'suck back'. What you do is to terminate the pipe only JUST under the surface of the water, so if the water climbs up the pipe the level in the bath drops and exposes the end of the pipe.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Hg(ONC)2

"Mercury Fulminate is made by dissolving mercury in concentrated nitric acid and pouring the warm solution into alcohol, under carefully defined conditions, in a roomy and suitable apparatus. After an initial period of quiescence a stormy reaction of a complex nature sets in, and eventually mercury fulminate begins to separate in small grey needles. At the end of the reaction the cooled mother-liquor is decanted and the fulminate collected on a filter and well washed with cold water. Large crystals are removed by passing the product through a fine screen, and the product is washed again until it is quite free from acid. The brownish-grey crystals obtained in this way are stored in linen bags under water. The density of the crystals is about 4.3 ..."

from Explosives by John Read, Pelican books 1942.

"Chandelon's process. 1 part by weight of mercury is dissolved in 10 parts of nitric acid (sp. gr. 1.4) at a gentle heat; the solution at a temperature of about 55 degrees, is poured in a capacious flask (its capacity must be at least equal to six times the volume of the liquid) containing 8.3 parts of alcohol (of sp.gr. 0.83). The flask is connected by a cork and tube with a stoneware condenser to recover spirit.

In about a quarter of an hour the reaction commences with a slight formation of gas bubbles; very soon the liquid boils, and the flask becomes filled with voluminous white vapour..."

from A dictionary of applied chemistry by TE Thorpe 1891