Please be careful when etching PC boards

[ptricks]

I posted just a minute ago in another post about introducing other metals into an etchant solution. I feel so strongly about this that I had to make it a topic so maybe more people see it.

The very first thing you should do before using any etchant is to read up on any pitfalls in the safety or health area.  Muriatic acid and hydrogen peroxide is a popular etchant and is one I use myself, it works fast and is cheap and I have used it for years. The problem with this etchant are a couple different things:

It will burn skin if you leave it in on the skin for more than a second or two.
Fumes produced are dangerous if inhaled directly.
It is very dangerous if you are not careful about what you combine with it.
It will damage plumbing , metal sinks , including stainless steel , making them rust.

So what can you do to prevent damage or harm ?

First , wear gloves. I don't care how uncomfortable they are, or how safe you think you are, use gloves.

Second , eye protection. I know many will say that is overkill and at first I thought, I am careful enough, I am not going to get any on my face. Until the day when I was using one of those foam brushes to rub off some copper on a board area and the brush when hitting the edge of the board, flipped up and sprayed dots of etchant on my arms and face. If it had gotten in my eyes I could have had some serious issues.

Third , have a carton of baking soda near the work area. Baking soda can neutralize any spills of the acid almost immediately. I once had some etchant splatter onto my arm, it started burning in a few seconds, baking soda neutralized it immediately .  Water will work as well but it takes longer because unless you put the exposed area under running water you are just diluting the acid.

Fourth - know your etchant !
The muriatic+peroxide etchant is popular, its fast, and easily available, but I doubt many realize how dangerous it can be.
Introducing other metals besides copper is a big NO with this stuff. Aluminum in the solution will get so hot as to boil the etchant and produce hydrogen gas which it can then ignite. Acetone , something many use to clean boards, becomes an explosive if mixed with the etchant.

Fifth - disposal . Etchant should never be poured into the sink, dumped outside, or placed in the trash. I do not use new etchant with each board, instead I have used the same batch of etchant for the past  year and have done 30 or so boards in that same batch.  The peroxide added will off gas leaving the muriatic acid and that contains a lot of water as does the peroxide. If you can find a safe place to leave your etchant uncovered, the water will evaporate leaving a very strong acid solution. To re-use one only needs to increase the peroxide and sometimes a cap full of acid.  To dispose of you can leave the etchant to evaporate in a safe area. The result will be crystals of the copper that you removed from the boards. You can easily place those in a small container and take them to wherever you dispose of toxic materials in your area.

I haven't covered ferric chloride because it isn't as available as it once was. Most of the above applies to ferric chloride except it doesn't harm skin as much on contact and the aluminum reaction doesn't occur. 


Feel free to correct or add, be safe !

[Baliszoft]

Nice thought. I was also using this solution (even now very rarely) and i have to admit that i disposed it into the sink. I always diluted it with tap water (which turned its "funky" green color into nice "sea" blue what i actually liked a lot ). BTW HCL is widely used over here for example cleaning toilets (removing limesacle), etc.

[free_electron]

Simply use Sodium persulfate , which is the industrial etchant. All problems solved.

[Oracle]

I use only FeCl... And remember don't trow it to sewers or waste it: it's insoluble in water because it's a mixture it's a salt after all...

and, If you stain a dress, you have to use oxalic acid

[ElektroQuark]

I use only FeCl... And remember don't trow it to sewers or waste it: it's insoluble in water because it's a mixture it's a salt after all...

and, If you stain a dress, you have to use oxalic acid

There is no FeCl. There are FeCl2 and FeCl3. The FeCl3 is the one used for etching. It is used for water treatment too. FeCl3 is completely soluble in water, as thousands or other salt are.
In my work we make FeCl3 by tons.

[Psi]

FeCl3 will start to irritate your skin too after a little while.

It's acid after all, leaving any splashes on your skin is probably not the smartest idea.

Simply use Sodium persulfate , which is the industrial etchant. All problems solved.

I've never used sodium persulfate but ammonium persulfate is terrible stuff.
Only works when it's really hot and its hard to keep it hot without a heated bath system.
Also if you use the toner transfer method it pulls thin toner traces off the pcb during the etch (or the heat does).

[westfw]

As far as I know, pretty much any of the etchants that will etch copper will also cause stainless steel to corrode...

HCl is the acid produced by your stomach, which means both that it does a pretty good job of dissolving meat, and ... its toxicity is overrated.

The proportions are all wrong for making explosives.  Not that even a little bit of explosive can't ruin your day.

Used etchant is pretty similar to stuff they sell to put in your swimming pool.  HCl to adjust pH, copper to supress algae.

It can be really difficult to get accurate and useful information about chemical safety.  The "standards" (MSDS and similar) err on the side of caution, and will happily urge you to wear proper safety gear and avoid inhalation when handling "beach sand"...  Which can be pretty important when you do professional sand blasting for 8 hours per day, but not so much when you spend the weekend at the beach.

[Psi]

It can be really difficult to get accurate and useful information about chemical safety.  The "standards" (MSDS and similar) err on the side of caution, and will happily urge you to wear proper safety gear and avoid inhalation when handling "beach sand"...  Which can be pretty important when you do professional sand blasting for 8 hours per day, but not so much when you spend the weekend at the beach.

Exactly, it's quite annoying, overly cautions safety info isn't of much use to a hobbyist.

[Chris Wilson]

Thanks, good info, will be investigating the peroxide / muratic acid stuff at some stage. Cheers.

As for staining my dress, what can I say, my secret is out...... Should have kept the blinds down.... <LOL> 

[6502nop]

ptricks
Most of the above applies to ferric chloride except it doesn't harm skin as much on contact and the aluminum reaction doesn't occur.

Wanna bet?

The FeCl3 I used to use would cause my skin to discolor, as if I has just put on some spray tan crap (or OD'd on Heparin). As for the aluminum?

I had just got done pulling my PCB out of the soup, rinsed, and checked. I had a thought of what to do with the remaining stuff. I happened to have some foil in reach, and ripped about a square cm (half-inch) and tossed it in to see what would happen. At first, nothing (probably skin oils on the Al). After a couple of seconds, that little piece of foil was dancing around on top of the tub like a pat of butter on a hot plate, with the same ultimate end: total dissolution. It didn't smell that great, either - but nothing FeCl3 related does. If you want to try it yourself, be sure to cover the top, as the reaction of the foil creates a lot of spatter.

Short version: Wear gloves and eye protection, open ventilation, copper only!

I have recently switched over to using H2O2, vinegar, and salt (in a double-boiler config to warm the solution). Not as fast, but you can always whip up a batch whenever you need to by raiding the kitchen.

nop

[DarkPrince]

Simply use Sodium persulfate , which is the industrial etchant. All problems solved.

+1... I use this stuff. Should probably look into any potential bi-products but...  I take some safety measures. Granted as of the last few boards i'll probably step it up a bit for precautionary reasons.

[T4P]

In any case any mixture/liquid that is capable of etching/dissolving away copper is not meant to be handled without some latex gloves!
Even how stinky it might smell on your fingers but it literally saved my arse once ...

[ptricks]

I had just got done pulling my PCB out of the soup, rinsed, and checked. I had a thought of what to do with the remaining stuff. I happened to have some foil in reach, and ripped about a square cm (half-inch) and tossed it in to see what would happen. At first, nothing (probably skin oils on the Al). After a couple of seconds, that little piece of foil was dancing around on top of the tub like a pat of butter on a hot plate, with the same ultimate end: total dissolution. It didn't smell that great, either - but nothing FeCl3 related does. If you want to try it yourself, be sure to cover the top, as the reaction of the foil creates a lot of spatter.

What you saw was not a reaction to ferric chloride, it was a reaction to cupric chloride which is formed when the reaction between copper and ferric chloride occurs.   Cupric chloride is one of the best etchants you will ever find, once it is established it really doesn't need anything else added to it other than air, aquarium air stones can do that quite well, and it doesn't produce any odor when etching. The only downside is it is slower than other methods but I like not having to dump etchant every time I do a board. Like I said above, my etchant right now is now going on 30+ boards, just did another this morning and this stuff just keeps on working.  To make cupric chloride is pretty easy, don't dump the etchant when finished, supply it with air either from peroxide or air stones.   After a few boards it will turn dark green and remain that way until you add air again , then it will turn light green. 

I wish I had weighed the solution when I started, because after 30+ 2 sided boards, 2oz copper,  I wonder how much is really suspended in the solution, it has to be quite a bit.


Forgot to add that if someone wants to try copper chloride etchant and has the money you can take a shortcut. Copper sulfate is sold in hardware stores as root killer, you can't miss it, has a green color and is usually a powder. It isn't cheap though, about $15 USD for less than a pound. Easily converts to copper chloride.

[poorchava]

I use sodium persulfate myself, because it causes less over/under etching (anyway - etching copper under the masking layer).

Some people say that persulfate is better because it doesn't leave such nasty stains. I personally disagree, both of those will ruin any clothing they drip on. Always wear some kind of clothes which you are not sorry to ruin. I'd even say that persulfate is worse, because when in small quantity or not used very much it's practically transparent and can easily get unnoticed when you spill a few drops on your worktable.

btw. my father told me that back in worst years of communist/USSR "friendship" times (i guess around 1970s or so), when pretty much everything was hard to come by, they were using CAR BATTERY ACID (i guess sulfuric(VI) acid) to etch pcb's (masked with nail varnish). On the other hand many factories were existing only for the sole reason of giving people job rather than making a profit, so If you knew right people you could get a professional pcb made in single quantity for a bottle of vodka  (other thing is that professional pcbs were total shit back in those days)

[george graves]

It will burn skin if you leave it in on the skin for more than a second or two.

Naw - it's not that bad at all.  I've gotten a tear in my glove before and didn't realize it till I was done (10-15 mins?) - it didn't even turn red.

[Gall]

I use FeCl3*6H2O since it is easyto get here in Russia.

Works well and is perfectly safe. May damage clothes and things (permanent yellow spots) but nothing more. An accidental skin contact is almost harmless and results in a yellow spot too. Just wash hands immediately. The spot will go away soon.

FeCl3 is poisonous if ingested, of course.

Do not confude FeCl3*6H2O crystallohydrate (yellow) with anhydrous FeCl3 (black powder, may contain rust). Anhydrous FeCl3 does not dissolve in water, it comes in hydrolysis instead. The reaction is exotermic and produces lot of heat (may boil!). The resulting liquid will be unusable for etching. If you got anhydrous FeCl3 by mistake, you may still use it by dissolving in an acidic solution (Hydrochloric acid).