Etching copper designs & circuit boards

A. I no longer have access to the reference, but look for an older book (say, 1970) on the manufacture of printed circuit boards, they might have a simple way to prepare and use sulfuric-peroxide and ammoniacal etchants. Proprietary chemicals, such as the organic stabilizers, are sold by chemical companies in the directories of these pages.

I found this in the 1941 Chemical Formulary:

I think you would be better off buying a proprietary formula from a supplier if you use a drum or so every month. They would be able to work up some costs for you if you called them. Look in our directories for phone numbers.

Purify "dug outs"? You mean like a dugout where baseball players sit?
Dug out canoes?
I would love to know.

Look in our (voluminous) resources for book lists where you can buy the latest and greatest.

If you were contemplating medium to high production, you could probably buy a few sections of a previously owned printed circuit board etching machine, and adapt it for your plates. It is only a pump distributing etchant to spray nozzles in a covered area over a sump, with a conveyor of little rubber wheels on a chain. You may already be doing this, but you could control the etching depth by making the speed of the conveyor fast enough so you need a few passes to finish the job. This would be a lot easier than dipping plates into tanks, if that is what you do. Of course, automating something takes all the fun out of it:-}

I don't know how this would change how you control pollution, but you can regenerate the ammonia and sulfuric-peroxide etches; I think you get copper sulphate crystals back.

A. Adam,

Operating parameters are: 140-155 g/l Copper 180-190 g/l Chlorides, hence, you mix ammonia chloride with water. This is an endotherm reaction, which means that it needs heat to mix. I think that the mixture of ammonia chloride solution (170-175 g/l chlorides) in conjunction with a pH adjustment (ammonia) to about 9, (temp 50 °C) will be enough to start the etching reaction. This way you can dissolve copper to desired concentration.

Then lower the pH to 8.5 (by not adding more ammonia or vent) and start etching. And maintain the copper by adding the ammonia chloride solution. Its critical that the copper, pH and chlorides are in spec. Otherwise sludge occurs. I think this will work if you don't want to use propriety chemicals, which contains speed enhancers and such. regards Peter

Thanks, Peter.

A. Adam, it's been decades since I've looked at it, but try to find Coombs' "Printed Circuits Handbook" in the library because, unless my memory is tricking me, it discusses all of the alternative etches for copper in depth.

Regards,

A. This process is called photo engraving and has some similarity to printed circuit board manufacture. Positive photoresist is available in an aerosol from various electronics supplies. I would suspect a lot of trial and error would be needed in the design of the etching tank in order to get uniform and deep etching of the plate. If you can afford very slow erosion then an electrowinning cell may be preferred over an oxidizing solution. That way the solution can be reused for the next photoengraved plate you wish to make.

A. The answer depends upon exactly what and how you are trying to measure. For example, I've frequently needed to measure the rate of sodium persulphate to etch the copper on circuit board laminate. I wanted about 50 millionths of surface removal, and used 3"x3" coupons. For this purpose I needed to weigh on an analytical balance which measured to 0.0001g. The point here is that you need an instrument which can determine the weight difference of the sample accurately enough for your purposes.

A. Another thing to consider is your customer requirements. For example, if you are an aerospace subcontractor(and I believe you are, among other customers, you may be doing your test to a Boeing "BAC" test procedure that may define the precision requirements. If your customers' specification reference an ASTM procedure, you need to review that. Nadcap requirements are more generic; you need to review the limits of your etch rate and order of magnitude...are the etch rate limits ± 0.1 inch/hour or 0.0001 inch/hour? You then fall back with standard calibration requirements....with the complication that you are converting weight loss to a linear dimension. Boils down to algebra.

A. Hi Jack.
(Hopefully you realize how dangerous it is to mix bleach with an acid, even a weak one like vinegar, because of the evolution of chlorine gas).
If you mix any acid (vinegar in this case) with any oxidizing agent (bleach in this case), I think you'll get the capacity to dissolve copper, which is what you did. The blue solution is due to copper ions in solution, the blue crystals are probably hydrated copper acetate [affil links].

Regards,