Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

On Sun, 19 Jun 2016 14:54:56 -0700, you wrote:

>What I’ve got seems to work fairly well – I think the only area I’m suffering is not understanding the process, and the relationship between the vinegar and salt and the peroxide. Today I put in a full 500ml bottle of peroxide and then dumped what was left of my cleaning vinegar in – I think it was close but not quite 1:1.. and that mixture went crazy on the board and did a perfect job. However, the board I put in was half the size of the previous.. so maybe the amount of copper present has an impact also. I put a bit of salt in and it just fizzed and fizzed away.
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The standard mix is hydrochloric acid (hydrogen ions and chlorine
ions), and then a lot of oxygen (H2O2, hydrogen peroxide) decomposes
into water and oxygen.

Acetic acid (no idea of the formula), decomposes into hydrogen ions
and acetate ions (probably wrong name).

Salt (NaCl) decomposes in water (or at least makes available) Sodium
ions (Na+) and chlorine ions (CL-).

Turns out that the sodium ions are probably ignored, the acetate ions
are ignored, (and if they're not, IIRC most acetates are soluble), and
what you're left with is Hydrogen ions, Chlorine Ions, and Oxygen.

These form the CuCl reaction which is exactly the same that you'd get
from HCL (muriatic acid) and Hydrogen Peroxide.

The difference (in this case) is that the household vinegar (or even
stronger stuff) gives you the strength of hydrogen ions that you'd get
from dilute HCl (muriatic acid). So if you can't find HCl, then
acetic acid (vinegar/glacial acetic acid, etc...) and salt (Cl- ions)
will substitute.

You're just making the effect of HCl with other household chemicals.

The problem with Muriatic Acid (HCl) is that it's concentrated, and
like all concentrated acids, has to be handled carefully.

Vinegar is of such a low concentration that you can resist it. (no
pun intended considering PCB work). It works rather slowly.

Increase the concentration and it works faster.

Faster makes the time you have between perfect and overetched a bit
more critical.

I've used both Ferric Chloride (which has HCl in it, BTW), and CuCl
(and the precursor, HCl and Peroxide), and I prefer the CuCl/peroxide
mix.

Cheaper.
Does not stain.
Available locally.
Lasts forever.

BTW: Ferric Chloride eventually becomes CuCl, from what I understand.

Harvey

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>Without a doubt it works.. the goal here was a) to be safer and b) avoid relying on things that are difficult or impossible to by in my silly small town.
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>Another thing I found helps per Quinn’s site is the foam brush on the board while it’s in the bath.
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>Side note: I’m glad I didn’t go with those $400 custom made PCBs I was thinking about.. I dissolved a piece of their sample in my etchant and the green of the fiber was nowhere near what it looked like in pictures. In fact, these cheapo Chinese boards were far closer.
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>Brad
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>From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
>Sent: Sunday, June 19, 2016 12:31 PM
>To: Homebrew_PCBs@yahoogroups.com
>Subject: RE: [Homebrew_PCBs] Etching with vinegar, peroxide and salt
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>Have you thought about using acetic acid ? isn’t that what vinegar actually is ?
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>I have glacial acetic here ,it is used for darkroom work. Stop bath is basically the same thing except it has indicator in it so you know when it goes bad I used to stick my fingers in it all the time when printing photo’s . it freezes at about 62 degrees I think ,so watch where you store it. The glacial you can water down to whatever strength you need ,stop bath you also water down. It comes in a small plastic bottle and you add a certain amount to like a half gallon of water . think the mix is only a couple ounces to half a gallon!
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>From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
>Sent: Sunday, June 19, 2016 12:58 PM
>To: Homebrew_PCBs@yahoogroups.com
>Subject: RE: [Homebrew_PCBs] Etching with vinegar, peroxide and salt
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>Yeah. I just have a hesitancy about muriatic, remembering some accidental burns years ago. :) I accidentaly splashed a bit of this vinegar stuff on my hand in a moment where I forgot to put on gloves and nothing happened. That kind of thing with muriatic would be very bad. It etches beautifully – just really slow.
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>From: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs@yahoogroups.com> [mailto:Homebrew_PCBs@yahoogroups.com]
>Sent: Sunday, June 19, 2016 9:02 AM
>To: Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs@yahoogroups.com>
>Subject: RE: [Homebrew_PCBs] Etching with vinegar, peroxide and salt
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>One explanation I was given is that the vinegar reacts with the chloride in salt and produces a very weak hydrochloric acid. I tried it but it took forever to see any effect on the copper. Much easier to go and get a gallon of muriatic acid for $10. I only use about an ounce at a time along with 3 oz of peroxide and get boards etched in about 5 minutes.
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