This is my first post on the forum! Hopefully I’m posting in the right place
I’m a sophomore in college, an EE student, and one of my hobbies is making printed circuit boards. A PCB is a thin fiberglass/paper composite board
that has a thin layer of copper on top. After designing the PCB on the computer, I put “etch resist” on the copper I want to stay on the board
(i.e. the traces) and then put the board in etchant so that all the rest of the copper is eaten away.
Sadly, I know almost nothing at all about chemistry. But from what I’ve read, it looks like mixing the hydrochloric acid - hydrogen chloride (HCL)
in water - with peroxide (H2O2) and then putting copper in it produces cucl2 (the etchant). Eventually it becomes cucl (which doesn’t eat copper?),
and so peroxide needs to keep being added to regenerate the oxygen and make it cucl2 again. Is that correct?
This chemical reaction produces chlorine gas which is not explosive, but is apparently not good at all to breathe. Exactly how bad it is to breathe, I
don't know.. I’ve read several places that repeated exposure could cause serious health conditions. Should I buy a respirator to filter out the
chlorine fumes? (I’m using this in my basement, which doesn’t have very good ventilation).
Another question that I was hoping someone could answer, is what I should do if I spill some of this (or a lot of it) on the workbench or floor, or on
myself for that matter. Is there something that can "neutralize" the acid?
So, to recap:
1) How bad is breathing the chlorine gas? (e.g. should I purchase a respirator?).
2) What protective equipment should I wear?
3) What should I do if I spill it?
Thanks for helping me understand what precautions I need to take when using this stuff. I'm worried about the long term affects of using this and I
want to take whatever precautions are necessary.
One other thing that I should mention is that I'm on a tight budget. For instance, there's no chance I could purchase a fume hood.
[Edited on 9-1-2011 by EE4ever]vulture - 9-1-2011 at 13:44
Chlorine gas is pretty toxic, but the question is whether you'll be releasing enough to make it a problem. It dissolves quite a bit in water. If you
get a gas mask, make sure your filters are rated against chlorine and do mind that their lifespan is very limited.
Wear safety goggles, gloves and a labcoat. Peroxide is nasty for the eyes in its own right, HCl doesn't make it better.
Spills should be neutralized with carbonate (baking soda). Vigorous gas evolution will be the result, this is CO2. Avoid contact of the mixture with
highly flammable substances (for example sawdust lying around in a workshop).
It's good to see engineers with some interest in chemistry. Sadly we have an engineer in a management position who thinks you can shut off chemical
reactions at night when you go home by pulling the plug.watson.fawkes - 9-1-2011 at 15:51
Very good information on this etchant is available here: http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/index.html. See TOC item 8.1, preparation by the "metal + air" method, where you are
substituting H2O2 solution for atmospheric O2.ldanielrosa - 9-1-2011 at 18:02
This is nice in that you can regenerate it by adding more hydrochloric acid, but you will eventually have more on hand than you need. You might want
to consider what you will do with your waste stream.
It is still toxic and corrosive as CuCl, so don't get caught flushing it down the toilet. I neutralize my excess with baking soda, then wash and dry
the copper carbonate for other uses. At the moment I'm making some copper sulfate from it with that dirty sulfuric acid drain opener to treat wood
that's already been bolted to concrete many years ago.
And yes, an aquarium bubbler will replace the hydrogen peroxide _and_ agitate the solution for a uniform etch.
For safety, don't put anything in your etching tank that you want to keep- _NO ALUMINUM!_. Use plastic tools- even stainless steel is not immune.
The fumes will contain HCl, which is unkind to lungs, eyes and metal. I haven't used a respirator for this.aonomus - 9-1-2011 at 20:29
Biggest warning I'd have for you that hasn't been mentioned already is that any metal tools in the same room will likely rust. A white 'frost' will
appear (HCl) and your metal surfaces that aren't oil coated will be corroded. Its a fact of life when dealing with HCl and the fact it has a vapor
pressure.Panache - 10-1-2011 at 01:08
a study of around 1500 WWI veterans, all of whom had been significantly exposed to Cl2 gas warfare, was monitored over their lifetime. No long term
effects were identified. It causes significant nausea almost immediately and you remain very unwell for several hours afterwards. A bicarbonate of
soda (1% soln if i remember) nebuliser can be used however no controlled study of its efficacy has been undertaken.
As the reaction produces gas simply perform your etching in a large PE or PP storage box with a snap top lid and run a small hose into a large
reservoir of 5% NaOH, ensuring the hose only marginally dips below the surface. This will destroy any excess cl2 generated. Also keep things cold as
is reasonable, as Vulture said, Cl has appreciable solubility in water, provided it is below room temperatue, above that it's solubulity drops
rapidly and is almost zero at 50c.bbartlog - 10-1-2011 at 10:01
If you use an aquarium bubbler you shouldn't have any chlorine fumes, just HCl. Not that that's healthy either. Actually I'm not quite clear on the
reaction that produces chlorine from H2O2 and HCl... do you really get H2O2 + 2HCl -> 2H2O + Cl2? I guess it seems plausible but it must proceed
fairly slowly, I've never heard of it as a chlorine gas generation method. bquirky - 10-1-2011 at 10:20
Why dont people like Ferric Chloride ? just dont drink it and keep it till next time.watson.fawkes - 10-1-2011 at 18:25
Why dont people like Ferric Chloride ? just dont drink it and keep it till next time.
For a modest fixed
cost of, roughly, an air pump, you replace buying ferric chloride with buying HCl, with lower per-unit cost. Also, the regenerated solution can be
used for electrolytic copper plating, if you have an application for that process.unionised - 11-1-2011 at 11:42
You forgot to add the cost of corroding everything in the room with HCl fumes driven from the mix by the air. (or Cl2 if you use H2O2)
HCl/air is OK if you can use it outside or in a fume cupboard.
The reaction of HCl and H2O2 is very concentration dependent.watson.fawkes - 11-1-2011 at 15:18
You forgot to add the cost of corroding everything in the room with HCl fumes driven from the mix by the air.
No, I didn't forget. I was answering a different question, one about benefits of a non-FeCl3 etchant, not one about the balanced
trade-offs of one etchant vs. another. That's a much larger question, with different answers for different people.bquirky - 11-1-2011 at 15:23
you can make ferric chloride from HCL iron scrap and an air bubbler too.
no h2o2 required EE4ever - 15-1-2011 at 11:21
Thanks for all of your replies.
Quote:
This is nice in that you can regenerate it by adding more hydrochloric acid, but you will eventually have more on hand than you need. You might want
to consider what you will do with your waste stream.
I don't think this will be much of a problem. I can always get a bigger container for the etchant if necessary. As for disposing it, I have no idea..
Maybe the dump would take it?
Quote:
Biggest warning I'd have for you that hasn't been mentioned already is that any metal tools in the same room will likely rust. A white 'frost' will
appear (HCl) and your metal surfaces that aren't oil coated will be corroded. Its a fact of life when dealing with HCl and the fact it has a vapor
pressure.
You forgot to add the cost of corroding everything in the room with HCl fumes driven from the mix by the air. (or Cl2 if you use H2O2)
I wasn't aware that this would happen Any ideas on how I can prevent this problem?
Quote:
HCl/air is OK if you can use it outside or in a fume cupboard.
Unfortunately I make a lot of boards during the winter when it's not feasible to do it outside. I also don't have a shed or anything outside, so I'm
been using this stuff (and storing it) in my basement. A fume cupboard is probably expensive to buy or make, and I can't afford to spend much right
now.
Quote:
The reaction of HCl and H2O2 is very concentration dependent.
It is important to point out that the only time that a cupric etchant is lost as waste is when it is dragged out through rinses or when it is
contaminated; in industry the copper salts are crystallized out when it is cooled and the bath is regenerated and reused.
I have attached a pdf that explains things pretty well.
Attachment: Cupric-Chloride.pdf (145kB) This file has been downloaded 672 times
Any ideas on how I can prevent this problem?