Enclosure etching w/ Ammonium persulfate?

[the3secondrule]

I've done a bit of a search and haven't found anything conclusive. My local Jaycar (radioshack equivalent, I guess), sell ammonium persulfate as PCB etchant. Anyone used it for etching enclosures?

[muddyfox]

Over here it's called Sodium Persulphate and while I haven't tried it yet, I'm thinking it won't work on aluminum, only copper.

I'm sure our very own M-Kresol will come in with all guns blazing on this one. 

[muddyfox]

I'll just bump this, it appears that Felix has missed the fact that we need his expertise here! 

[muddyfox]

M-Kresol, front and center! 

[m-Kresol]

Hey guys,
thanks for the vote of confidence; I have missed somehow this thread.
I have never used it (in fact, I have my first etching with whatever chemical still ahead of me), but I think I can help to some extent.
If sodium or ammonium persulfate (also called peroxodisulfate) is dissolved in water you have the ions in solution. As the persulfate ion is not very stable and wants to be reduced to sulfate you can oxidize Copper to Cu2+ ions, which are water soluble.
The reason it may be hard to etch aluminum with it, is most probably the oxide layer aluminum generelly forms, which is working as a protecting layer so to speak and is only dissolved by bases (therefore etching with NaOH, sodium hydroxide).

According to the german wikipedia article the sodium persulfate is used instead of iron chloride, if you have fine lines on the pcb you want to etch. The iron chloride etches faster and therefore can etch also in masked areas (basically from the sides) and produce less sharp traces.

I would recommend sticking to sodium hydroxide for enclosure etching since we have people around with experience in doing so. Also, it should be way cheaper. And the persulfate is actually quite nasty stuff, since it's oxidizing!! We sometimes use an acid we call "piranha acid" to clean, which is basically the corresponding acid.

[muddyfox]

Is FeCl3 a base, then? Cause it eats through aluminum just fine...

I don't have access to NaOH, only persulphate (as no store here still sells FeCl3 anymore, something about EU laws and whatnot) so I guess I'm screwed when it comes to etching boxes....

[m-Kresol]

Ok, I LOVE being a chemist.
After writing the answer above, I went straight to the lab and tried everything myself. First, Oxone (TM) which is potassium persulfate with Al. Nothing at all. Put Copper in -> etched slowly, but clearly visible.
Then tried out Iron chloride with aluminium. Took a while, but it dissolves.
Then NaOH with aluminum -> violent reaction.
I took videos and will probably edit them together and upload them. Wanted to try doing so anyways, so why not with these videos.

FeCl3 is a so called Lewis Acid (electron acceptor). Actually, I didn't really tell you the whole truth above. It doesn't dissolve in all bases neither... it's chemically quite resistant, but fortunately the natural oxide layer is only a few microns thick. Also Chloride ions are one of the most aggressive corrosives. I forgot why, but I remember to learned something like that in conext with steel.

Have you tried to get NaOH in a pharmacy? I think they should have it. Also, drain pipe cleaners are often NaOH (the POWDER one!!! NOT the liquid, they often have other stuff as well). Make sure to check the label if you go for the later. Don't use anything with hypochlorite, since it gives Chlorine gas -> toxic.

[muddyfox]

Yes, I tried everywhere, no dice. Even though NaOH can be purchased all over the world, for some reason it's very frowned upon over here.

FeCl3 also gave me a rather deep etch in aluminum and I would have gone with that but like I said, EU put it's foot down and it's not obtainable anymore (either as liquid or granules).

I did try dunking an enclosure into a HCl+H2O2 (very little H2O2, tbh) and that almost got out of hand 
Frothed a lot (good thing I was holding it with some long pliers) and did a very deep etch but it also underetched and messed up the graphics. My kitchen has windows so I just held my breath and hoped for the best with chlorine gas. 

[m-Kresol]

I did try dunking an enclosure into a HCl+H2O2 (very little H2O2, tbh) and that almost got out of hand 
Frothed a lot (good thing I was holding it with some long pliers) and did a very deep etch but it also underetched and messed up the graphics. My kitchen has windows so I just held my breath and hoped for the best with chlorine gas. 

Whooaa, that is aggressive stuff! Hydrochloric acid alone would have done the job just fine. The H2O2 is only needed for really noble metals, such as Gold... But mostly likely the addition of H2O2 wasn't the reason for the underetching, HCl itself is strong enough. Might work more dilute...

What I don't get is, how you can obtain HCl and hydrogen peroxide, but not sodium hydroxide... I would really try drain pipe cleaner. Most often it really is just plain NaOH. But be careful! That stuff is corrosive! Handle with care, goggles and gloves only, when you want to etch with it!

[muddyfox]

What I don't get is, how you can obtain HCl and hydrogen peroxide, but not sodium hydroxide...

Well there you go... one of a gazillion nonsensical things about this place... 

I would really try drain pipe cleaner. Most often it really is just plain NaOH. But be careful! That stuff is corrosive! Handle with care, goggles and gloves only, when you want to etch with it!

I can only get two types of pipe cleaners here and they are both the yellow gooey stuff. I'm guessing there's all sorts of stuff in there that could mess up or even prohibit a reaction with aluminum but it's certainly worth a shot. Worst case scenario, nothing happens! 

[muddyfox]

Also, if I manage to get my hands on some NaOH, how does that work? What's the right ratio/mixture for safe etching of aluminum?

And, will it eat avay printer toner and nail polish?

[m-Kresol]

I can only get two types of pipe cleaners here and they are both the yellow gooey stuff. I'm guessing there's all sorts of stuff in there that could mess up or even prohibit a reaction with aluminum but it's certainly worth a shot. Worst case scenario, nothing happens! 

I would not recommend using those. It's
a) a health risk, if there's hypochlorites etc. in there
b) the outcome is questionable. You may destroy the enclosure..

Keep looking, I think you should be able to find the right stuff.

Also, if I manage to get my hands on some NaOH, how does that work? What's the right ratio/mixture for safe etching of aluminum?

And, will it eat away printer toner and nail polish?

It shouldn't eat away the printer toner. But again, I haven't done etching yet. I just used about 1g in 20 ml of water in the lab just now and the reaction is quite vigorous. If it etches slowly, but does work, it's fine and you can add more the next time. If it's too concentrated you might over-etch.

In this tutorial  he's using 40 g in 100 ml water (28.5 w% solution btw, not the declared 40 ) Seems to work fine...

[m-Kresol]

As promised, I quickly edited the videos I made in the lab and put them together. It basically shows how the etchants work with either Al or Cu. Not really fascinating or anything, but I wanted to try video editing a while now and this was a quite easy first start.
And please forgive me for being a total idiot filming with my phone standing upright. I had to clamp it in my fume hood and I did not think about it at the time.