How long can you keep ferric chloride?

[Shea]

At room temperature,that is. I've had some sitting in a jar for a couple of years now. I'll buy new ferric chloride if I have to, but I'd rather not waste what I have left of the old stuff if I don't have to.

Which reminds me of another question -- how should I dispose of the stuff?

Shea

[Liam]

Cut off a bit of PCB. Write a line across it with an etch resist pen. See if it still works. It probably will.

Which reminds me of another question -- how should I dispose of the stuff?

Depends where you live as to the rules. I always work on the basis that anything that goes into landfill (i.e. the trash) will be quite well diluted and absorbed by all the fuller's earth cat litter I send them every fortnight.

Liam

[Mark Hammer]

Provided it isn't exposed to air, there's no reason why FeCl shouldn't last years in a glass jar or the plastic bottle it came in. I find the biggest risk is that any water in it evaporates and the stuff becomes so think that the sludge is not easily separated from the still-viable etchant. I've added some hot water to it in past (though I imagine distilled water is probably better) to thin it out and it still works like a charm. Even speedier in some instances.

Used etchant is a real nuisance but you can render it less harmful by mixing it with baking soda (sodium bicarbonate). It will produce a rust-colored foam that will dry crunchy hard and can simply be placed in a garbage bag at the curb without fear of contaminating the environment. Just keep in mind that the chemical reaction is very strong, VERY quick, and the volume increases about eightfold. No exaggeration. So you will want to mix it with baking soda in a much bigger container. Remember that moment in "Jaws" where the late Roy Scheider says "We're gonna need a bigger boat"? That's how I felt the first time I mixed the stuff together. Best to do it in small volumes toget used to it at first.

Also be aware that you DO NOT want to spill the stuff on clothes or surfaces. A real bugger to get out.

[Shea]

Thanks for the replies.

Although I've been keeping this in a jar with the lid screwed on, it has lost volume over time, which I guess means some water has evaporated out and slipped past the the lid. And the lid has started to rust. What I have left in the bottom of the jar looks like a yellow fluid with brown sludge in it. I might try to revive it with some hot water like Mark suggested, but I'm leaning towards getting rid of it and starting over with something new. At least with the volume being small, it should be easier to get rid of now. And I wonder if some rust from the lid has fallen into the solution, and I don't know what effect that would have on it.

This method looks promising: http://www.instructables.com/id/Stop...--A-better-etc

The guy talks about it like it's the greatest thing since sliced bread.

[Mark Hammer]

There are so many downsides to use of ferric chloride, that when people stumble onto something that can do the same job without the disadvantages they are jumping for joy, and right to do so.

Though I have not tried any alternate solutions myself (and shame on me for that!), like ammonium persulphate, they work well. So feel free to try them. Personally, I only stick with FeCl because I know it well, know where to buy the stuff in town, and don't do a huge volume of etching.

[lowell]

can etchant be reused?

after etching a board can I dump the solution back into the bottle?

[Mark Hammer]

Ideally, what you want to do is separate the sediment (produced as a byproduct of etching) and the still-viable etchant. Part of that involves letting it settle for a few days. The other part involves carefully pouring off what is at the top of your etchant bath into the bottle for later use, without disturbing the grungy part a the bottom.

Once you have the still-usable stuff stored, you still need to disable the remainder with baking soda.

[lowell]

cool thanks mark.

[J M Fahey]

I have a 20 liter tank which lasts from one to three years, depending on the country's economy (that's to say how many boards go through it)
When it gets crusty on the surface and greenish instead of reddish (no doubt due to the ferric chloride becoming cupric chloride) and times start getting long, it's revived once with clorhidric/muriatic acid which makes it last some 3 extra months, but then it *MUST* be replaced.
I use granulated caustic soda/sodium hydroxide, which has the advantages over sodium bicarbonate of: not foaming, being *Much* stronger and cheaper and universally available to boot.
I spoon the stuff in, and mix well, until it gets into what looks like a paste of ground rust and mud.
My "test" probe is a piece of bright shiny copper board, when fully neutralized it comes out dirty but has not that classic reddish matte surface of half-etched copper.
Why spooning?
Because I count them, and after neutralizing the mix , I add extra 50% to 100% of what I already have, so I can be sure that my sludge now is alkaline (which will hurt neither pipes nor masonry) and composed of a rust-like iron compound, a neutralized copper salt, table salt and excess sodium hydroxide, an accepted pipe obstruction cleaner.
That can be thrown (diluted) into the sewer without causing a great echologic havoc.
The only case where it should not be used, is for houses with septic tanks, where "good" shit-eating bacteria will be poisoned by this mixture, and any other, including household lye, detergents, soap, etc.
But that's another problem.

[tedmich]

as a chemist, I appreciate the 1:2 muriatic acid (~28% HCl): H2O2 (3%) etchant

works great, starts out clear and easy to find. I toss it after one use

[J M Fahey]

Hi.
I use it too sometimes, for 1 or 2 boards, either in winter when heating those 20 liters isn't worth the 2 hours it takes or when I am at a friend's and he has no specific chemicals available.
Anyway I always neutralize it with an excess amount of caustic soda (bought at the hardware store at the same time I buy the muriatic acid).
Unfortunately it can't be kept, because peroxide is unstable and bubbles oxygen out even when not actually etching anything.
But for a one-use solution it canīt be beaten.

[rockin roy]

I used to sell it as a dry powder in one pound bags. They must have been twenty years old but worked just fine.
Nobody wants anyting thrown down the drain even though feric chlorides most common use is for water purification and sewage treatment.
I'd contact your local land fill about proper disposal, especialy if it has been used for etching.

[J M Fahey]

I got curious and found this on the mighty WIKI:
>>>When dissolved in water, iron(III) chloride undergoes hydrolysis and gives off heat in an exothermic reaction. The resulting brown, acidic, and corrosive solution is used as a coagulant in sewage treatment and drinking water production, and as an etchant for copper-based metals in printed circuit boards.<<<
Amazing.

[Lee_ranaldo]

I have a 20 liter tank which lasts from one to three years, depending on the country's economy (that's to say how many boards go through it)
When it gets crusty on the surface and greenish instead of reddish (no doubt due to the ferric chloride becoming cupric chloride) and times start getting long, it's revived once with clorhidric/muriatic acid which makes it last some 3 extra months, but then it *MUST* be replaced.
I use granulated caustic soda/sodium hydroxide, which has the advantages over sodium bicarbonate of: not foaming, being *Much* stronger and cheaper and universally available to boot.
I spoon the stuff in, and mix well, until it gets into what looks like a paste of ground rust and mud.
My "test" probe is a piece of bright shiny copper board, when fully neutralized it comes out dirty but has not that classic reddish matte surface of half-etched copper.
Why spooning?
Because I count them, and after neutralizing the mix , I add extra 50% to 100% of what I already have, so I can be sure that my sludge now is alkaline (which will hurt neither pipes nor masonry) and composed of a rust-like iron compound, a neutralized copper salt, table salt and excess sodium hydroxide, an accepted pipe obstruction cleaner.
That can be thrown (diluted) into the sewer without causing a great echologic havoc.
The only case where it should not be used, is for houses with septic tanks, where "good" shit-eating bacteria will be poisoned by this mixture, and any other, including household lye, detergents, soap, etc.
But that's another problem.

Have you tried mixing it with Muriatic Acid to increase it's performance?.
i know they use this tecnique in metal etching for instrumental panels in the industry.

[rockin roy]

You guys scare me

Chemicals are a real environmental problem (not like global warming) and making cocktails only makes it worse. I'd guess you are not worried about signal to ground plane so look at the real alternatives. First point to point looks good if cleanly laid out. There is also a tool that drills a hole into copper clad and makes a little round solder point at the same time. You could also use a universal breadboard.