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etching printed circuit boards

One of the problems with making your own printed circuit boards is the difficulty of legally disposing of spent etchant. That might be easy in some places, expensive or impossible in others.

It occurred to me that there might be less problematic alternatives for dealing with printed circuit boards. For example, a few decades ago when I wanted to try to synthesize copper acetate for myself, I dropped pennies in vinegar and left them alone for a few weeks and copper acetate crystals grew on the pennies. (I know that pennies are not pure copper, so this might not have been pure copper acetate). The pennies never dissolved completely, but I was after crystals and didn't worry about completely digesting the pennies.

I was able hasten the process considerably by connecting the leads of a battery to a cupful of vinegar with copper wire. In fact, the wire dissolved completely. It produced a rich blue solution from which I obtained broccoli-like dendritic growth, but it would probably have just as well grown nice crystals under other conditions.

So, I was wondering what exactly would be wrong with dropping the printed circuit boards in vinegar (or perhaps somewhat more concentrated acetic acid) and trying to etch them that way. When you are done, you can just use the resulting solution to grow nice copper acetate crystals. The battery idea is also appealing, but it suffers from the obvious defect that once the copper near the electrode is gone, the rest of the copper is no longer connected to the battery. Maybe someone knows a clever way around that inconvenience.

Alternatively, consider the problem of disposing of actual spent ferric chloride or spent ammonium perchlorate. Some locales have no provision for disposing of such chemicals at special waste sites, which are dedicated to lists of specifically approved substances such as paint thinners, motor fuel, used tires, etc. Instead, one has to contract with a company specializing in toxic waste to get rid of it. That sounds like an expensive proposition and they might simply refuse to deal with an individual and the tiny quantities of spent etchant they generate.

Is there any reason why one can't simply try to use the spent etchant to grow large single crystals and add them to one's crystal collection? In fact, amateurs who etch their own printed circuit boards can have contests for the largest and most perfect single crystals, or the most interesting dendritic growth.

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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Reply to
Allan Adler
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dissolved

acid)

Electro-etching is one way decent amounts of copper can be removed from a board. Usually it's followed up by regular etchant to clean up the last bits. This method allows you to use less etchant because you remove most of the copper first, and don't wear out the etchant as quickly. I haven't tried it.

Reply to
Garrett Mace

Allan, while I applaud your rather extreme level of environmentally related political correctness, I really think you should get a closer grip on reality and realize that the copper laden waste residue created by amateur PC board etching wouldn't even create a glitch in a graph of the copper salt residue released into the waste water treatment systems by millions of copper pipe plumbed homes.

That said, you are correct in believing that you can electroplate or precipitate crystals or salts from spent etchant. Large PC shops have been since the early 1980s required to do just this, however the costs involved in this copper reclamation process have driven most of the industry into the use of additive copper PC fabrication processes rather than etching away the majority of surface area on a copper foil laminated panel.

The pollution produced by simply dumping small quantities of home produced spent etchant into a municipal waste water collection system is arguably no worse than that released into the same systems by millions of home darkrooms and drugstore sited photo processors. Simply neutralize the etchant by adding some lye or ammonia to it (in well ventilated conditions) prior to pouring it down the drain.

Important note: Never dump spent etchant into a domestic system that feeds into a residential septic tank for reasons that should be obvious.

Harry C.

p.s., Allan, stay away from using a solder plated resist on your PC boards, because lead salts present a far more serious disposal problem than does copper.

Reply to
Harry Conover

Copper does not dissolve in vinegar. Zinc does. Since you had some "insoluble stuff" left from dissolving pennies, you managed to get some dirty zinc acetate and separate all copper (3% of it, used for coating).

If you want to dispose spent etchant solution in a cheap and enviro-friendly way, you can mix it into concrete slush and leting it harden. While you are pouring your concrete mix, you can also include your mother-in law for more satisfying monolith.

Reply to
Muhammar

Yup, i know the problem. i my self don't have very much trouble in disposing of the etching due to a local dump that handles those kinds of problems. i did how ever develop 2 different X,Y,Z scanning tables. one is a sprayer that uses Blue Dye and sprays the protective coating onto the clad.. the other is a EDM (electro discharge Machine) that actually is using a plasma removable approach with the Clad submerged in a oil that is very easy cleaning afterwards. i use a small little fluid pump to circulate and filter the oil.. both work, i would rather use the EDM over my Blue Dye sprayer due to the mess it some times makes.. P.S. currently i am having noise emission problems with EDM but working on it.. :)

Allan Adler wrote:

Reply to
Jamie

Chemists were fairly unanimous in telling me, before I tried it, that it wouldn't work, muttering about oxidation potentials or something like that. I admit that the presence of other metals in pennies leaves that example inconclusive, but note that I also got copper wire to be completely digested by vinegar when I used a battery.

After I told some chemists about my experiences with it, they said something about the presence of oxygen in the water being the reason it worked when it shouldn't have. I don't know what reaction mechanisms are involved, so I really can't comment on this. However, I got into a conversation with someone specializing in the history of chemistry and he referred me to something called the Stockholm manuscript, an ancient Greek papyrus in which a process is described for making copper acetate by heating vinegar and letting the fumes corrode the the copper lid of the vessel.

Admittedly, a half remembered conversation from over two decades ago about a work I haven't read is not an argument against what Muhammar says. However, I happen to own a copy of a bilingual Greek-French edition of the Stockholm manuscript that I acquired in Paris in 1985 for just this reason but which I've always been too busy to read. Now that I have an excuse to do so, I'll start working through it. This process is likely to generate some other questions about obsolete chemical technology.

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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Reply to
Allan Adler

Harry, thanks for all the suggestions. Regarding my motivations, it is a matter of complying with the law and I don't know what the law is. For example, in Jan Axelson's book, "Making printed circuit boards", which I'm reading at the moment, it says on p.216, "Check with local officials on how to dispose of used etchant." Her book is aimed at amateurs and she still says that you have to find out the local regulations.

If I can find a local official who, in his/her official capacity, can tell me that simply neutralizing the etchant with lye or ammonia and pouring it down the drain is an acceptable way to dispose of it, then there is no problem. So far, finding out the law is a lot harder than any of the chemical issues.

Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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Reply to
Allan Adler

This is really useful information! I was wondering whether one could do it with an EDM but I have so little knowledge about the devices that I wasn't sure what one can or can't use it for. Everything I know about EDM comes from the catalogue for Lindsay Publications, which sells a book (24 pages, I think) on how to make your own EDM. Jamie, are you familiar with this book or did you learn some other way of making an EDM?

More questions: What kinds of fumes does it generate? Also, do the electrical discharges cause any damage to the underlying board itself? Was it your own idea to use this for making printed circuit boards or did you read about it somewhere and, in that case, where? If not, would you consider writing a more detailed article about your experiences making printed circuit boards this way? I think that that a sufficiently detailed and protracted explanation could get published by Lindsay Publications, just as they have published books (e.g. on how to cast your own pulleys) spawned by the Gingery series on making your own metal shop. It doesn't have to be

500 pages: some of their books are only a couple of dozen pages, e.g. the EDM book.

I guess this now also raises the following question, more pertinent to sci.chem: how might one use an EDM in chemical experiments? I'm sure there are lots of chemicals to try it on under various conditions, but just to keep the discussion a little more self-contained, what would happen if you grew a single crystal of spent etchant and applied an EDM to it? What would be the chemical effects on the crystal and what would be the products?

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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Reply to
Allan Adler

"Allan Adler" a écrit dans le message de news: snipped-for-privacy@nestle.ai.mit.edu...

regulations.

It often happens that you can use simple common sense. If you add garden lime you'll get a sludge of iron oxides/hydroxides that amount to no more than one of the minerals the Earth is made of.

While I'm on the subject, the original posting referred to electrolytic etching. This isn't really practical... because the objective is to create a certain number of electrically isolated tracks.

Regards

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Reply to
Chris R. Lee

well thanks for your interest on the EDM. no i wasn't aware of any published books on the idea use of EDM on clad boards., i got the idea back when i use to service some machine shop equipment. there they had 2 EDM's, one for rough cut and one for the fine cuts. they would make carbit dyes use in various operations like stamping out revits, nuts etc.. because the material is very hard it makes it difficult to use common milling processes.. so what they did was make for example Hex brass stock and use that for the quill (neg side) the stock material was placed in a holder at the base of the tank and then the tank was filled with insolating oil. after a short period of the brass probe inserting it self against the stock material with regulated currents and servo's on the drive you would have a nice near perfect hex hole of about 1 " in depth. this unit simply used rectified DC at around 400 volts low current. the second unit for the final was polishing used 400 cycles of pulsed Dc on the probe. the unit had 4 banks of Push-Pull 3-400Z tubes .. the whole theory is simply a plasma burn much like used today in plasma cutters etc.. using the insolated oils it cuts down alot on the splatter and carbon effects. i call it plasma, some simply call it electro discharge burn. i maybe miss using the terms but i think i get my point accross.

any ways i use 1 stepper motors to drive the X scan in bidirection scans to speed things up and the Y motor to move down the clad board. the head is a retractable hard point tip that is pulled in via a electromagnet to skip over the area's not required to be removed.. i use a current shunt circuit so that i know when the copper is fully removed. if a short out takes place the tip is retracted and inserted again.. when the area is complete the X scan moves to the next possition. this works well because low side of the board is clamped into the table for the current path. i need to remove the pin now an then and clean it up for better edges.. ./. my use of the blue dye actually works quite well too. how ever that means i need to use etching. :(

Allan Adler wrote:

Reply to
Jamie

I am interested in this, might be a neat way to convert my mini CNC mill to a quicker PCB maker. How fine of a cut do you get? What's the electrode made out of, and the best angle for the point? Best working voltages and oils? Any faster than milling?

Reply to
Garrett Mace

I agree with everything Harry wrote except for this bit about "neutralizing" etchant. I have seen this advice before, and there is no chemical basis for it. (ASSumption here: we're talking about ferric chloride or ammonium persulfate etchants, NOT something like nitric acid....) The mechanism of etching by these reagents is oxidative, so to "neutralize" etchant you'd add a reducing agent. Scrap iron would work. But it's probably unecessary anyway, as long as you flush down the drain with lots and lots of water (which you should do anyway). And most modern sewer pipes are PVC, which will not be affected by etchants.

Steve Turner

Reply to
Steve Turner

Copper does not dissolve to any great extent in non-oxidizing acids without some help. That help can be in the form of atmospheric oxygen or in the form of an electric current, either of which causes oxidation of the copper to the ionic form, which does dissolve in acids.

Copper does dissolve in nitric acid, but that's a special case -- nitric acid is a powerful oxidant.

Steve Turner

Reply to
Steve Turner

to

made

My experiment with a 24V supply, piece of copper-clad, blob of motor oil, and fine drill bit was rough but successful enough to warrant further investigation and experimentation. I'll go look for more information on EDM and see if I can convert my little mill to use this. I'll most likely use point-to-point outline removing (G code) instead of the scanning method you outlined below. I wonder what it will take to monitor the electrode current and modify TurboCNC to adjust Z accordingly...really this looks like a great application of hobby EDM, removing a foil of copper is going to be much faster than cutting a hunk of steel. The only thing I'm doing right now is wondering why I didn't think of it before, just last week I was discussing how to use continuity on copperclad to zero a Z axis very accurately. Never occurred to me to just increase the testing voltage and put a little acrylic tank on the mill.

Reply to
Garrett Mace

What would you recommend using for the resist?

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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  • in any way on MIT. Moreover, I am nowhere near the Boston *
  • metropolitan area. *
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Reply to
Allan Adler

you could try a mixture of sulphuric acid and hydrogen peroxide.

Reply to
CBarn24050

What? that would ruin a perfectly good batch of concrete!

--
We now return you to our normally scheduled programming.

Michael A. Terrell
Central Florida
Reply to
Michael A. Terrell

Thanks. At this point, I think the question of what can etch the copper has been abundantly answered. What hasn't been touched is the question of what is a suitable resist for use with the other proposed etchants. Can one use the same resists one uses with ferric chloride or are different resists required? Or, even better, is there a household substance one can use for a resist instead of the usual commercial resists?

E.g. assuming one can in fact use vinegar for the etchant, with either bubbled air or hydrogen peroxide to provide oxygen, what can one use for the resist? For example, might some kind of paint or ink be ok that one can apply through a mask? Or some kind of wax?

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

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  • Disclaimer: I am a guest and *not* a member of the MIT Artificial *
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  • in any way on MIT. Moreover, I am nowhere near the Boston *
  • metropolitan area. *
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Reply to
Allan Adler

Dale Trynor wrote: I could add one. I have etched PC board on occasion and have used a dilute nitric acid. Use it pure and its so fast it heats up and is likely to cause ones resists to lift off and also can produce a lot of noxious NO and NO2 gas. Reason I mention it is because its so easily made especially if you don't need it very concentrated and in hat case mixing sulfuric acid with nitrates will usually result in enough nitric acid for this type of thing. I have on occasion mixed sulfuric acid solution with ammonium nitrate fertilizer solution as a way of dissolving the base metals from old electronics so that I could recover the gold and it did work, although it was a bit slow.

I think I had used a resist pin when I did this myself using the dilute nitric acid but I am not really sure now. I think the nitric acid was less than 10% but could only guess now. Why don't you just try a small piece of PC board with different things you can find around the house and just draw or paint a line with each sample to see what works best. I have even tried tape at one time but it was a bit too time consuming to cut it into circuit patterns, it did work alto not really very well as in some places it had started to lift off the tape etching a bit more than I waned in some places, although it was still usable. The tape is a common type but I don't remember what its called.

I think I remember seeing kits with stick on patterns that one could use for this sort of thing alto its been so long ago that I am not sure anymore. I do still have a photocopy and then iron on type of paper for PC board resists that I never got around to using. Do note that you can buy special pins that contain electrically conductive silver powder that can even be soldered onto. I bought one of these for a little more than 10.00 long ago but never used it either as once its opened I didn't figure it would keep very long, now its probably spoiled anyhow.

If you have ever taken a tarnished copper item and put it into hydrochloric acid you would note just how good the acid is at removing tarnish. Acetic acid will similarly brighten a bit of tarnished copper. Because tarnish is copper oxide you will instantly realize that the acid is probably not really dissolving the metal but rather its oxide coating and if you remove this protective coating then another will quickly form only to also be dissolved off. I don't know if the acid might speed up this tarnishing rate somehow but its a good guess that hydrogen peroxide would help. Even ammonium hydroxide will dissolve copper and I believe its due to the same sort of reaction because of the way it will also dissolve copper oxide. You should have seen the amount of corrosion I accidentally caused to a brass lock by spilling ammonia near by.

Long ago I have even tried cutting holes in hardened steal using nitric acid as this is a bit to hard to drill. It was doing a great job except that the tape always failed when the acid got about 1/4 or so inches into the metal. Its amazing how fast this acid is when its nearly concentrated and gets warmed up and going. What's bizarre is that the really concentrated acid will pasivate iron so well it will even resists rusting for some time after treatment so you need to weaken it a bit with water to get it really vicious on iron. Cutting steel cable with this stuff or with a bit of hydrochloric acid added is so fast that its at least almost the sort of exaggerated stuff one would only expect to see on tv, but it for real. Yes I have had lots of entertaining times showing this to my friends. When using the concentrated acid on a small metal object it helps to astonish the audience as the very heavy and dark reddish brown nitrogen oxides tend to flow like water and are so toxic they can knock the fly's of a window when you hold the beaker up to them. Do these types of demonstrations out doors. You shouldn't have much trouble with very dilute solutions on small pieces of pc boards but its wise to place the container in a well ventilated area anywise if you chose to try this method.

Don't forget silver nitrate solution will rapidly deposit silver while it also dissolves copper and gives no gases or vigorous reactions to deal with and you can recycle your silver. The reduced silver particles should be easily removed.

Dale

Reply to
Dale Trynor

electrochemical

oxidizes

haven't

in

that

The electrode potentials given in CRC are for the standard conditions . If you are considering water as a source of hydroxide ions which is approximately about 10^-7 mole/liter in water at 25 C, , you will need Nernst equation to get the correct electrode potential for the conditions you are applying and then check the possibility of the reaction between copper and hydroxide ions. Though the reaction under standard conditions seems to be thermodynamically possible, but I never heard of copper being attacked by common alkalis except ammonia, which perhaps dissolves copper by the forming a blue complex rather than forming a oxide.

Reply to
Mohammed Farooq

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