Homebrew_PCBs

Here's a slightly odd question... well, it is Sunday night :)

I was thinking about mixing up a cupric chloride etch bath. Thing is,
while I have a ton of concrete cleaner (hydrochloric acid) and raw
copper (in the form of old copper wire), I don't have any hydrogen peroxide.

Now as I understand it, the H2O2 is used as a source of free oxygen to
accelerate the reaction between the HCl and Cu. Out of curiosity, would
it be possible to start a cupric chloride etching bath by bubbling air
through the HCl while adding copper (possibly heating the HCl to
accelerate the reaction)?

--
Phil.
ygroups@...
http://www.philpem.me.uk/

On Sun, 28 Jul 2013 23:12:45 +0100, you wrote:

>Here's a slightly odd question... well, it is Sunday night :)
>
>I was thinking about mixing up a cupric chloride etch bath. Thing is,
>while I have a ton of concrete cleaner (hydrochloric acid) and raw
>copper (in the form of old copper wire), I don't have any hydrogen peroxide.
>
>Now as I understand it, the H2O2 is used as a source of free oxygen to
>accelerate the reaction between the HCl and Cu. Out of curiosity, would
>it be possible to start a cupric chloride etching bath by bubbling air
>through the HCl while adding copper (possibly heating the HCl to
>accelerate the reaction)?

This is often considered the best writeup on the subject.
He mentions starting with HCl, Cu, and H2O2, but I've never
found a copy where he completed that section
He does cover starting with HCl, Cu and air.

href="http://techref.massmind.org/techref/pcb/etch/CuCl2.htm"

Keith Bowers WB4LSJ- Thomasville, NC

On 29/07/13 02:01, kabowers@... wrote:

> This is often considered the best writeup on the subject.
> He mentions starting with HCl, Cu, and H2O2, but I've never
> found a copy where he completed that section
> He does cover starting with HCl, Cu and air.
>
> href="http://techref.massmind.org/techref/pcb/etch/CuCl2.htm"

Ah. Looks like I should expect a ~10 day wait then.

I have managed to get my hands on 200ml of 9% H2O2 ("look, that's all I
can sell you, the law says so"), though I'm not convinced this will be
enough to start a 1-litre tank.

A quick scan through one of my old threads (from 2010, yeesh!) suggests
the mix ratio for 9% H2O2 / 17.5% HCl should be around 2 parts acid to
one peroxide. That gives me (2x200)+200 = 600ml of etchant, all being well.

I've got a few small boards to start with - I'll probably chuck in some
(stripped) scrap copper wire I have lying around, then the peroxide,
then the acid ("add acid to water"), give it an hour and maybe chuck in
the PCB.

That said, I suspect my heavily used FeCl3 bath is mostly CuCl2 at this
point. After getting rid of the precipitates a few months ago and adding
what I'd describe as "way too much" HCl, it turned green with a hint of
brown to betray its iron content. Very strange stuff and very prone to
foaming if the air pump is turned up to full...

--
Phil.
ygroups@...
http://www.philpem.me.uk/

On Thu, 01 Aug 2013 02:19:35 +0100, you wrote:

>On 29/07/13 02:01, kabowers@... wrote:
>> This is often considered the best writeup on the subject.
>> He mentions starting with HCl, Cu, and H2O2, but I've never
>> found a copy where he completed that section
>> He does cover starting with HCl, Cu and air.
>>
>> href="http://techref.massmind.org/techref/pcb/etch/CuCl2.htm"
>
>Ah. Looks like I should expect a ~10 day wait then.
>
>I have managed to get my hands on 200ml of 9% H2O2 ("look, that's all I
>can sell you, the law says so"), though I'm not convinced this will be
>enough to start a 1-litre tank.
>
>A quick scan through one of my old threads (from 2010, yeesh!) suggests
>the mix ratio for 9% H2O2 / 17.5% HCl should be around 2 parts acid to
>one peroxide. That gives me (2x200)+200 = 600ml of etchant, all being well.
>
>I've got a few small boards to start with - I'll probably chuck in some
>(stripped) scrap copper wire I have lying around, then the peroxide,
>then the acid ("add acid to water"), give it an hour and maybe chuck in
>the PCB.

Why bother to go that way when the copper from the boards you would
etch would do the same, and get the boards etched? With a lot of
oxygen available, you'll find that these boards will etch rapidly in
the fresh mixture. As the O2 from the peroxide dies off, the bubbled
air will substitute for that and you're building your CuCL2 etchant.

Around here it's used for reducing the PH of pools, and concrete
cleaning, still available in the big box home stores and pool supply
stores under both uses.

Worked for me.

Harvey

On 01/08/13 02:33, Harvey White wrote:

> Why bother to go that way when the copper from the boards you would
> etch would do the same, and get the boards etched? With a lot of
> oxygen available, you'll find that these boards will etch rapidly in
> the fresh mixture. As the O2 from the peroxide dies off, the bubbled
> air will substitute for that and you're building your CuCL2 etchant.

I mixed the stuff up yesterday, but I think the etchant might be a bit
short on oxygen - after an hour or so it turned a dark brown and pretty
much stopped reacting with anything.

I've left an aquarium air bubbler running overnight with the copper
removed. I'll see what that does but it doesn't look promising and I'm
out of H2O2... :-/

Thanks,
--
Phil.
ygroups@...
http://www.philpem.me.uk/

On 3/08/2013 9:16 a.m., Philip Pemberton wrote:

>
> On 01/08/13 02:33, Harvey White wrote:
> > Why bother to go that way when the copper from the boards you would
> > etch would do the same, and get the boards etched? With a lot of
> > oxygen available, you'll find that these boards will etch rapidly in
> > the fresh mixture. As the O2 from the peroxide dies off, the bubbled
> > air will substitute for that and you're building your CuCL2 etchant.
>
> I mixed the stuff up yesterday, but I think the etchant might be a bit
> short on oxygen - after an hour or so it turned a dark brown and pretty
> much stopped reacting with anything.
>
> I've left an aquarium air bubbler running overnight with the copper
> removed. I'll see what that does but it doesn't look promising and I'm
> out of H2O2... :-/
>

Try some sodium percarbonate, 1 teaspoon/50ml of water, readily
available as a cleaning agent. Add very slowly as it releases CO2 and O2.

On Sat, 03 Aug 2013 13:37:58 +1200, you wrote:

>On 3/08/2013 9:16 a.m., Philip Pemberton wrote:
>>
>> On 01/08/13 02:33, Harvey White wrote:
>> > Why bother to go that way when the copper from the boards you would
>> > etch would do the same, and get the boards etched? With a lot of
>> > oxygen available, you'll find that these boards will etch rapidly in
>> > the fresh mixture. As the O2 from the peroxide dies off, the bubbled
>> > air will substitute for that and you're building your CuCL2 etchant.
>>
>> I mixed the stuff up yesterday, but I think the etchant might be a bit
>> short on oxygen - after an hour or so it turned a dark brown and pretty
>> much stopped reacting with anything.
>>
>> I've left an aquarium air bubbler running overnight with the copper
>> removed. I'll see what that does but it doesn't look promising and I'm
>> out of H2O2... :-/
>>
>
>Try some sodium percarbonate, 1 teaspoon/50ml of water, readily
>available as a cleaning agent. Add very slowly as it releases CO2 and O2.

Not sure that this will work, but potassium persulfate is an etchant
in and of itself. In the states, it's used as a shock treatment for
swimming pools (the extra oxygen kills off stuff you don't want).

It's about the equivalent of 3 GPB per kilo, and as such (you need
almost that much for a single run), is rather expensive when compared
to muriatic acid/hydrogen peroxide mix. The rather expensive (when
new) etchant tank I have can't handle the HCL.

So does sodium percarbonate work as an etchant?

Ammonium persulfate and potassium persulfate (with trace ingredients)
are used as etchants. The trace ingredients come when you buy the
stuff to treat pools (and they don't tell you what is.....).

The persulfate etchants do not attack tin/lead, if I remember it
correctly.



Harvey

On 3/08/2013 2:35 p.m., Harvey White wrote:

>
> On Sat, 03 Aug 2013 13:37:58 +1200, you wrote:
>
> >On 3/08/2013 9:16 a.m., Philip Pemberton wrote:
> >>
> >> On 01/08/13 02:33, Harvey White wrote:
> >> > Why bother to go that way when the copper from the boards you would
> >> > etch would do the same, and get the boards etched? With a lot of
> >> > oxygen available, you'll find that these boards will etch rapidly in
> >> > the fresh mixture. As the O2 from the peroxide dies off, the bubbled
> >> > air will substitute for that and you're building your CuCL2 etchant.
> >>
> >> I mixed the stuff up yesterday, but I think the etchant might be a bit
> >> short on oxygen - after an hour or so it turned a dark brown and pretty
> >> much stopped reacting with anything.
> >>
> >> I've left an aquarium air bubbler running overnight with the copper
> >> removed. I'll see what that does but it doesn't look promising and I'm
> >> out of H2O2... :-/
> >>
> >
> >Try some sodium percarbonate, 1 teaspoon/50ml of water, readily
> >available as a cleaning agent. Add very slowly as it releases CO2 and O2.
>
> Not sure that this will work, but potassium persulfate is an etchant
> in and of itself. In the states, it's used as a shock treatment for
> swimming pools (the extra oxygen kills off stuff you don't want).
>
> It's about the equivalent of 3 GPB per kilo, and as such (you need
> almost that much for a single run), is rather expensive when compared
> to muriatic acid/hydrogen peroxide mix. The rather expensive (when
> new) etchant tank I have can't handle the HCL.
>
> So does sodium percarbonate work as an etchant?
>

Sodium Percarbonate (aka solid hydrogen peroxide) is a mixture of sodium
carbonate and hydrogen peroxide Na2CO3.5H2O2. When dissolved in water it
forms an aqueous solution of Sodium Carbonate and Hydrogen Peroxide. Mix
that with Hydrochloric acid and you get an aqueous solution of Salt,
hydrogen peroxide and gaseous carbon dioxide. 1Kg of percarbonate (costs
$8 / Kg in New Zealand, they probably give it away in USA) is equivalent
to 1 Litre of 35% hydrogen peroxide.

It's used in washing as a bleach
http://www.ebay.com/itm/Sodium-Percarbonate-Oxygen-Bleach-Oxyclean-Tide-1-2-lb-/190477839862?pt=LH_DefaultDomain_0&hash=item2c595d2df6

Looks like Oxy-Boost is 100% Sodium Percarbonate.

http://www.textfiles.com/uploads/oxiclean.txt

Steve Greenfield AE7HD

That's kinda how I did mine. Just keep bubbling air through it, it will
eventually turn bright green.

On 03/08/13 04:12, Kerry Koppert wrote:

> Sodium Percarbonate (aka solid hydrogen peroxide) is a mixture of sodium
> carbonate and hydrogen peroxide Na2CO3.5H2O2. When dissolved in water it
> forms an aqueous solution of Sodium Carbonate and Hydrogen Peroxide. Mix
> that with Hydrochloric acid and you get an aqueous solution of Salt,
> hydrogen peroxide and gaseous carbon dioxide.

My concern would be the effect it has on the pH of the solution. The
Na2CO3 is going to react with the HCl and pretty much eliminate it if
you add it straight to the etch bath. Then you have to do the titration
steps from Kasten's book (or Adam Seychell's writeup) and adjust the
acid level appropriately.

Mixing with HCl separately might be another option, then freeze it to
get rid of some of the water and reduce it to H2O2. Although that might
not be possible if the salt content is too high...

(Begin brain-dump - ob disclaimer: I'm not a chemist, this looks
plausible but peer review would be gratefully received!)

Na2CO3 + 2xHCl => (2x NaCl) + H2O + CO2

If that's right, there's twice as much salt generated as water... we're
not using pure solutions so that water and salt will be dissolved into
the water already present in the acid. The question is, how much will
the salt content shift the freezing point, and can a domestic freezer
get cold enough to separate out enough H2O2 to make this worthwhile?

In any case, I'm fairly certain Oxyclean or something like it could be
obtained from the local supermarket or hardware store...

Thanks,
--
Phil.
ygroups@...
http://www.philpem.me.uk/

On 03/08/13 19:11, DJ Delorie wrote:

>
> That's kinda how I did mine. Just keep bubbling air through it, it will
> eventually turn bright green.
>

Yep - that certainly seems to be happening. I checked on it a few
minutes ago and it's gone from sludge brown to a fairly bright green.
It's nowhere near see-through like you see on Adam Seychell's site, but
it looks like a liquid solution of a copper salt at least. No doubt I'll
have to adjust the acid concentration, but for now it's one step at a time.

I noticed the copper wire sat next to the tank has oxidised so that's
back in the tank. I'll see what happens there. At a guess, the oxidation
was CuCl or something like it - a bright blue/green powdery coating on
the plain copper which was easily rubbed off.

This is starting to get interesting :)

Thanks,
--
Phil.
ygroups@...
http://www.philpem.me.uk/

How about using copper sulfate in chimney cleaners instead of copper hydroxide? I think they also often contain TSP, aka TriSodium Phosphate.

Steve Greenfield AE7HD

Has anyone checked the Files or Links section for info on etchants?

I had archived this post in the Files/Etchants folder:

Making copper etchant with off-the-shelf 3% Hydrogen Peroxide and 30% Muriatic Acid

Originally posted on Homebrew_PCBs by dkesterline

Others will recommend using stronger H2O2, 30% or 50%. But I had a hard time finding it without paying extremely high hazmat delivery fees, so I experimented with using the weaker medical grade.

My acid (HLC, or Muriatic) is bottled at 31 point something percent strength. From what I've read you want between 10 and 15% in the final etchant. Generally that's accomplished by diluting the acid 50-50 with water and then adding up to a couple ounces per gallon of 30% H2O2.

I have successfully used 2 parts 3% medical H2O2 with one part 31% acid - no additional water. It's pretty close to the same mix when you're done. Etching times of 7-10 minutes.

With stronger H2O2 (30% or more) you can just add a little more to regenerate the mix. With the 3% stuff it has too much water and if you add enough to regenerate the CuCl it dilutes the mix to much. To get around that I usually just regenerate with a bubbler. (aquarium pump and a plastic "air stone")

By the way, I use a rubbermaid 5161 cereal keeper as an etch tank: http://tinyurl.com/3hbax About $5.50 at Walmart, holds a gallon and a half and can do a 9x9 inch board nicely. For a holder I usually just dangle them on a piece of plastic coated wire (cat5). Mostly just loose loops around opposite corners, but sometimes I drill a hole in the corner.

-Denny

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