Homebrew_PCBs

Thus far I have had great success with toner transfer and CuCl from my
very first etch. I did a bunch of PCBs 30 years using a resist pen
and FeCl, but these are the first boards I have made since then. I
have, however, noticed something that I have not seen reported in all
that I have read on the topic.

I am using 20% HCl and "40 volume" hair developer which is 12% H2O2
plus a bunch of stabilizers. When mixed 2 parts H2O2 to one part HCl,
the product is very reactive and can etch 1 oz. copper in 30 seconds -
1 minute depending on the amount of action on the board. However,
this etchant seems to degrade rapidly over 24 hours. It will still
etch the following day, but *very* slowly -- 30 minutes or more to
etch the same 1 oz. copper.

Oddly, I have never seen the equation for the generation of CuCl2 with
H2O2, but I believe it to be roughly the following:

2 HCl + Cu + H2O2 -> CuCl2 + 2 H2O

I say roughly because there is clearly a gas produced during the etch.
While this could be water vapor, I am not certain of it.

In any case, I believe what is going on is that I am only producing a
minimal amount of CuCl2, and something is causing the H2O2 to degrade
when it sits. At this point, I merely have a (diluted) acidic
solution with very low CuCl2 content. This would explain the vast
difference in etch times when the only variable is time (the time it
sat on the shelf). I suspect that if I had etched more copper before
the H2O2 degraded, I would have produced more CuCl2, and thus would
have had a much more concentrated solution for future CuCl2 etching.

I *have* seen some references to people mixing up very small
quantities of 35% H2O2 + HCl, and I wonder if they are only using the
HCl + H2O2 phase, and not actually bothering with the CuCl2 etch.

I think in the future I will be mixing up much smaller batches of HCl
+ H2O2 and then perhaps tossing in some scrap copper to produce CuCl2
while the H2O2 is still present.

Any ideas if I am correct of this? Am I merely re-discovering common
knowledge of this list? Are there many people who only use the first
phase due to its insanely fast etch times?

-p.

On Mon, 12 May 2014 18:25:04 -0400, you wrote:

>Any ideas if I am correct of this? Am I merely re-discovering common
>knowledge of this list? Are there many people who only use the first
>phase due to its insanely fast etch times?
>
>

<snip>
This paper is a good place to start:

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

Also check old posts in this group; LOTS of discussion of the subject.

Keith Bowers WB4LSJ- Thomasville, NC

On Mon, May 12, 2014 at 8:14 PM, kabowers@... [Homebrew_PCBs]

> This paper is a good place to start:
>
> http://techref.massmind.org/techref/pcb/etch/CuCl2.htm

Yes, I found that page, along with this one:

http://www.xertech.net/Tech/CuCl_ech.html

which appear to be the two primary sources on CuCl2. Everything else
I found is more or less a re-hash of what is in those two documents.
However, neither of of these documents mention the high-speed initial
production of CuCl2 (or high-speed etching) when using strong H2O2. I
was able to find very little reference to this on the web, and what I
did find did not seem to cover the experiences I described in my
previous post.

> Also check old posts in this group; LOTS of discussion of the subject.

I did do some searching of the archives, but Yahoo's search isn't the
best and it is painful to try to follow a thread. In the past, I have
used a script to download the complete archives of Yahoo mailing
lists, build sensible message threads, and then search locally, but
unfortunately Yahoo's recent changes have broken that script. In any
case, I was able to find plenty of references to CuCl2 etching, but
was unable to find anything that covered what I was talking about.

-p.

I *have* seen some references to people mixing up very small

quantities of 35% H2O2 + HCl, and I wonder if they are only using the
HCl + H2O2 phase, and not actually bothering with the CuCl2 etch.

FWIW, I use 35% H202 to reoxygenate my CuCl2, 1 cap in about 500ml of the etchant before I start, and now and then add a cap of HCl.

Unfortunately my CuCl2 had a pretty rough adhoc start to life and no measurements were taken, but it works.  It's on my list if jobs to one day start a new batch with a bit more care and record it for posterity. 

When I do so, being of a "do it by feel" kind of person, I intend to start with a small amount of HCl (33%) and add (contrary to good practice, but necessary when done by observation) sufficient water until fuming is no longer evident, then add and mix 35% H202 1 cap at a time, until a wad of copper wire strands is being dissolved at a moderate rate, leave this to consume the copper and develop the characteristic green coloration (adding more copper or H202 as required).  Therein simply maintaining this useful rate of etch in normal operation by addition of small amounts of H202 and occasional HCl to renew the CuCl2 which has developed, as is my current practice.  I'm fairly confident that this simple observationally-based process would give a good result without the need for introducing maths, careful measuring, and chemistry equations into it :-)

NB: In my opinion, a moderate speed of etch is better than blazing fast, I don't care if it takes 10 minutes, if it means I have more chance to rescue a problem spotted during the etch, and to stop it when it's "just right".

 

With the visual/feel method, when the reaction slows down, how do I know if I need to add more HCl or H2O2?

.

Note that H2O2 is photo-sensitive, and should be stored in a light-proof
container. It will break down over time all by itself.

You don't need a *lot* of H2O2 to etch, so a 3% solution is enough if
you use the 2:1 ratio. The stronger H2O2 can be used a little at a time
to "freshen" the etchant just before you use it.

When I made my etchant, after I used it for circuit boards, I put about
half a pound of solid copper in it (3-4 liters of etchant) and let it
slowly dissolve, which gave me enough CuCl for the next etch. It took a
while but eventually worked. Once it's converted to a CuCl etchant, you
can refresh it with plain old air.

On Tue, May 13, 2014 at 3:54 PM, DJ Delorie dj@... wrote:

> Note that H2O2 is photo-sensitive, and should be stored in a light-proof
> container. It will break down over time all by itself.

Indeed. I have read that storing in a refrigerator is even better,
and 35% solution should be stored in the freezer. A 35% solution
should remain liquid at typical home freezer temperatures. Supposedly
the hair developer contains something that reduces the rate of natural
degradation. I do not know what (if any) effect this has on PCB
etching.

> You don't need a *lot* of H2O2 to etch, so a 3% solution is enough if
> you use the 2:1 ratio. The stronger H2O2 can be used a little at a time
> to "freshen" the etchant just before you use it.

If I am understanding the chemistry correctly, you do not need H2O2
for CuCl2 etching proper, but rather to "regenerate" the CuCl to
CuCl2. Any extra H2O2 remaining after the CuCl to CuCl2 conversion
will participate in the acid etch reaction. This may or may not be an
issue depending on your goals.

As an aside, where I am located 32 oz of 3% H2O2 (medical) costs $1.79
vs. $4.99 for 32 oz of 12% H2O2 (hair developer). As an oxygen
source, the hair developer is actually a somewhat cheaper. Not enough
to matter from a cost basis, but the more concentrated oxygen source
will result in your total etchant volume growing more slowly. Again,
this may or may not be an issue.

> When I made my etchant, after I used it for circuit boards, I put about
> half a pound of solid copper in it (3-4 liters of etchant) and let it
> slowly dissolve, which gave me enough CuCl for the next etch. It took a
> while but eventually worked. Once it's converted to a CuCl etchant, you
> can refresh it with plain old air.

Based on my experiences, using 12% H2O2 will convert raw copper to
CuCl2 *quite* quickly. Anyone looking to get started with CuCl2 in a
hurry should definitely prefer more concentrated H2O2.

-p.

"Peter Johansson rockets4kids@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com> writes:

> On Tue, May 13, 2014 at 3:54 PM, DJ Delorie dj@... wrote:
>> You don't need a *lot* of H2O2 to etch, so a 3% solution is enough if
>> you use the 2:1 ratio. The stronger H2O2 can be used a little at a time
>> to "freshen" the etchant just before you use it.
>
> If I am understanding the chemistry correctly, you do not need H2O2
> for CuCl2 etching proper, but rather to "regenerate" the CuCl to
> CuCl2. Any extra H2O2 remaining after the CuCl to CuCl2 conversion
> will participate in the acid etch reaction. This may or may not be an
> issue depending on your goals.

Right, initially you need the H2O2 because pure HCl will not etch
copper, you need a separate oxidizer. CuCl doesn't need an oxidizer to
etch, but it does need oxygen to regenerate.

> Based on my experiences, using 12% H2O2 will convert raw copper to
> CuCl2 *quite* quickly. Anyone looking to get started with CuCl2 in a
> hurry should definitely prefer more concentrated H2O2.

In my case, I was "done" with the etchant for a while. It wasn't fully
fresh any more, and it was going to sit for a while. The copper gave it
something useful to do while I was away, using only oxygen it had left
and whatever it got from contact with the air around it (i.e. not much).