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Dr. H.

Sat Mar 06 2010, 09:04PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

as you might have seen - I've build an etching tank. The question now is - what to use for ething solution. I've been reading about sodium/amonium persulfate, hydrogen peroxide and hydrochloric acid, the "good" old ferric chloride.

What solutions do you guys use ? What do you like about them and what you don't ?

I personally am thinking of using sodium persulfate, but the thing I don't like is that it has a very limited life after desolving it in water ...

Cheers

Turkey9

Sat Mar 06 2010, 09:11PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I love the muriatic acid and hydrogen peroxide one because for one). it's easily made for cheap, ant two). it's very fast. I've even had luck reusing the stuff if you keep it in an opaque container. It takes much longer but it works! So you might be able to cycle the stuff through your tank for very long periods of time if it's not in direct light as that seems to turn it into nothing more than pretty looking liquid.

uzzors2k

Sat Mar 06 2010, 10:31PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

The life time of sodium persulfate isn't as ridiculously short as everyone makes it out to be. I mixed one large batch last summer and I've been etching PCBs in it since. I used it just last week actually. It looses some edge while in storage, but it certainly doesn't become useless. If it gets a little slow, just warm up the solution some more while etching. 50-60 degrees is about right.

IntraWinding

Sun Mar 07 2010, 09:09AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I like the the mix that you start off as HCl +H2O2. After you've built up the concentration of Copper Chloride (use some scrap copper wire) you regenerate by exposure to air and additions of HCl only, so very low cost. Well suited to a bubble tank. Someone else might tell you about relative speed of etch and relative tendency to undercut the mask, sensitivity to concentrations and temperature: I just use this for simplicity (and nice colours!).

Conundrum

Sun Mar 07 2010, 01:23PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

heh... i used the old peroxide bottle as the container (dark brown glass) so hopefully it will work fine.

i might try this later, does anyone know how much faster it is compared with persulphate?

thanks,
-A

Dr. H.

Mon Mar 08 2010, 08:21AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

Turkey9 - how much does it stain cloths and stuff ? (the main thing that I hate about Ferric chloride). Do you sacrafice trace quality (underetching) because of the very high speed of etching ? Does a simple permenent marker stands up to the solution ?

Uzzors - those are some really good news

. How do you store the solution ? What is a tipical time for etching a board with fresh/old solution (heated afcourse ) ?

Is the HCl +H2O2 really so sensitive to light ?

Cheers

uzzors2k

Mon Mar 08 2010, 01:15PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I store my etchant in one of those 1L motor oil bottles (hydraulic oil to be specific). Even if unlabeled no one is going to take a sip of the lovely blue water inside.

I keep the cap a little loose, or squeeze the bottle before sealing it. Just remember to check on it every few weeks or it might pop from the oxygen created! When it was fresh the bottle would puff up frequently, hardly at all now though.

I heat the solution using a hot water bath in the bathroom sink. I haven't measured the temperature of the water, but I assume it averages 50 degrees. At this temperature etching takes 15 - 30 minutes. It's not very fast, and I even optimize my boards to use as little etchant as possible by keeping the trace spacing as small as possible. If you had a jig to both stir and heat the etchant I'm sure the etch time could be halved.

IntraWinding

Mon Mar 08 2010, 05:02PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

If you store a solution containing H2O2 other than as its supplied (i.e. very pure, with added stabilisers) it might decompose releasing O2 with or without light, so just make sure not to store it in an airtight container! The thing is, you don't need any H2O2 after you've got a reasonable concentration of Copper Chloride, it just helps at the start. After that atmospheric Oxygen is all that's needed to change the Copper oxidation state back to the active one. In fact I didn't use any H2O2 when I first tried this as I happened to have made a large batch of a copper hydroxide previously which I could directly dissolve in Hydrochloric Acid. The reaction in use is analogous to the one you get with Ferric Chloride as far as I know, but it's certainly less messy as it doesn't form those weird colloidal precipitates you get with Ferric Chloride. I would still avoid getting it on your skin and clothes though! If you do lots of etching you might not have time to wait for atmospheric Oxygen to rejuvenate your etchant. In that case you can add some H2O2 as required.
This place looks good

IamSmooth

Mon Mar 08 2010, 11:51PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I use ammonium persulfate. I can get it dirt cheap on Ebay. It stores well in powdered form, and I can mix as much as I need when I am ready to etch.

Turkey9

Tue Mar 09 2010, 02:59AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

The stuff stains but it doesn't last for long... Light yellow color but it washes off your hands. Don't let the fresh mixture get on you though! I spilled some on me and it bleached my pants slightly. I've had great results as far as quality but it's pretty mean stuff. Normal marker doesn't stand up at all to the stuff and even some toner will get eaten through. I find that the toner from older printers works great! I'm using an HP IV or something that I got at the thrift store for 15 bucks and it works great!

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