Etching, what chemical to use?

[haspelman]

Everybody is warning not to use ferrid chlorid but tu use instead Ammonium Persulphate or Sodium Persulphate.

Which one is better to use at room temperature? I wouldn't like using a heating of some kind.

[markr04]

I use Ammonium Persulphate. I mix a tiny bit (like 1/4 cup x 4 parts water) in a disposable plastic butter dish (my boards tend to be smallish anyway). This mixture can be used for 3-4 days I believe. Heating it does help, but it's not necessary. So I put some water in a slightly larger container and microwave it for 1 min and set the other bowl down in it. You don't need a heater.

Sodium Persulphate is supposed to work better with Sharpie/Etch Resist pens, but I don't have any problems with the ammonium version.

Mark

[phillip]

I use Ferric Chloride...works great.  I sit the little plastic dish in front of a heat lamp to heat it before etching.

Ferric Chloride is safe to use...it's only dangerous if you have copper pipes.  BUT it's very easy to neutralize...just slowly add regular baking soda to turn it into a harmless, environmentally safe form.  But remember to add the baking soda slow...it does the whole fizzing up thing like when adding baking soda to vinegar.

Phillip

[Mike Burgundy]

I like ammonium persulphate 'cuase it has a very clear indication of when it's spent (a certain shade of blue) and you can see through it to see how your pcb is doing. ferric chloride actually is a little bit better in how much you can actually etch with it (about 40% more, is my guess) but you can't see through it.
As far as getting rid of it is concerned, neutralising both with soda works, but I wouldn't really worry about it (although I'm a good boyscout and deliver it to the monthly neighbourhood hasmat-roundup)
Raising temperature has a profound effect on both - I actually do this "au bain marie" - I put the etching dish in a larger one which I periodically fill from a waterheater. This speeds up the process from an hour or more to minutes for fresh etchant.
hih

[jimbob]

Where would you buy this stuff? Hardware store? Walmart?

[haspelman]

Thank you for your answers. I think I will try Ammonium Persulphate. The trick with baking soda is good too!

[Paul Perry (Frostwave)]

Her is something I found on a graphic arts etching page:

"Ferric chloride is actually a salt, not an acid. It is usually supplied in liquid form at 45- or 46-Baumé (a measure of concentration) and can be diluted to 42-Baumé (as measured by a hydrometer) for etching use. For soft-ground etching a dilution to 32-Baumé is good. Ferric chloride is a sort of warm rust color when fresh and gradually turns dull brownish-green after much use. I usually top up used solutions with fresh ferric chloride and discard the excess rather than discarding the whole thing. This keeps a constant etching strength while conserving resources and minimizing waste. Used solution can be safely neutralized with baking soda (sodium carbonate), which precipitates out the remaining iron. Ferric chloride corrodes even 'stainless' steel, so sinks and pipes have to be plastic, or coated with WD-40 light oil (thanks to Dodie Warren for this latter suggestion).

Acetic acid (mixed with salt) is indispensable for brightening copperplates just before applying resist or etching grounds or ink to them. The mixture actually forms weak hydrochloric acid which lightly etches the surface, removing oxidation. Some people use vinegar or soy sauce instead of pure acetic acid, but the impurities complicate resist laydown in photogravure. A good working solution is eight parts water to one part each of acetic acid and salt by volume."
---end of quote

The salt & vinegar might be a nice way to clean up a tarnished pcb.

[Torchy]

I used to put salt'n'vinegar on my chips till it screwed up a batch of 4558s  :oops:  Sorry, UK joke I s'pose ...

[Hal]

Her is something I found on a graphic arts etching page:

"Ferric chloride is actually a salt, not an acid. It is usually supplied in liquid form at 45- or 46-Baumé (a measure of concentration) and can be diluted to 42-Baumé (as measured by a hydrometer) for etching use. For soft-ground etching a dilution to 32-Baumé is good. Ferric chloride is a sort of warm rust color when fresh and gradually turns dull brownish-green after much use. I usually top up used solutions with fresh ferric chloride and discard the excess rather than discarding the whole thing. This keeps a constant etching strength while conserving resources and minimizing waste. Used solution can be safely neutralized with baking soda (sodium carbonate), which precipitates out the remaining iron. Ferric chloride corrodes even 'stainless' steel, so sinks and pipes have to be plastic, or coated with WD-40 light oil (thanks to Dodie Warren for this latter suggestion).

Acetic acid (mixed with salt) is indispensable for brightening copperplates just before applying resist or etching grounds or ink to them. The mixture actually forms weak hydrochloric acid which lightly etches the surface, removing oxidation. Some people use vinegar or soy sauce instead of pure acetic acid, but the impurities complicate resist laydown in photogravure. A good working solution is eight parts water to one part each of acetic acid and salt by volume."
---end of quote

The salt & vinegar might be a nice way to clean up a tarnished pcb.

If I remember my chemistry correctly, Ferric Chloride is what is called an "anhydous acid."  This means that the iron attracts the hydroxide ions (OH-) more than the chlorine attaracts hydrogen ions.  Therefore, an aquious solution has an "acidic" pH.  While it is true that "ferric chloride" is a salt and not an acid, it is misleading, since we do not purchise ferric chloride, we buy an aquious solution of it, which is acidic.  

Its been a while though, I may be _totally_ wrong with that post :-D

Moral - I use ferric chloride.  I buy it at radio shack for a couple of dollars for a nice sized bottle.  It is one of their few reasonably priced items.  I hear they're going to phase it out soon, so stock up .  The fact that I can not see through it does not bother me - I simply move the dish its in so i can see.  Etching ususally takes something like 20-25 minutes, with a 65W lamp over my shallow dish.  I have had only wonderful results so far.