[sdiy] Audio circuits and basicelectronics knowledge recommendation.

David G Dixon dixon at mail.ubc.ca
Fri Mar 4 19:44:29 CET 2016

No chlorine is released from hydrochloric acid.  The chlorine in HCl is in
the form of chloride, which is the same thing in table salt.  If you use too
much peroxide, you may have a bit of gassing (oxygen) and this can carry out
some hydrogen chloride gas (the gaseous form of hydrochloric acid) which can
make your eyes water and make you sneeze.  It's best to do this etch in a
well ventilated area.  HCl is dangerous (as is any strong acid), so you have
to be careful.  We are adults -- take precautions.  The worst thing about
HCl is storing it.  If you store the jug near anything made of steel, it
will rust.  I keep mine out in the back yard.

Also, the least active agent in the solution is the chlorine.  Here's how
the HCl peroxide etching of copper works:

The peroxide oxidizes copper metal to copper II (cupric):

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

Then, the cupric oxidizes the copper metal to copper I (cuprous).  Cuprous
is not stable in water, but the chloride ions complex the cuprous, which
stabilizes it:

Cu + CuCl2 --> 2 CuCl

Hence, the copper leaches itself.  The peroxide just gets the process
started (and makes it go faster).  This process would not work with, for
example, sulfuric acid, because sulfate ions do not complex cuprous ions, so
the second reaction wouldn't work in a sulfate bath.  This only works in a
chloride bath -- hence, the need for HCl.

> -----Original Message-----
> From: rsdio at audiobanshee.com [mailto:rsdio at audiobanshee.com] 
> Sent: Thursday, March 03, 2016 10:12 PM
> To: David G Dixon
> Cc: 'Chris Juried'; 'Gordonjcp'; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Audio circuits and basicelectronics 
> knowledge recommendation.
> Why is hydrochloric acid better than ferric chloride? I've 
> long had the impression that HCl is highly dangerous.
> The active agent is the chlorine, which wants to bind with 
> copper more than iron (ferrous) molecules (or hydrogen?). 
> Some chlorine is always released in the process, even though 
> it wants the copper. The ferric chloride does leave behind a 
> lot of iron.
> By the way, Chris, lasers aren't bad at cutting PCB copper at 
> all, provided that the setup is designed for it. The LPKF 
> Protolaser S makes fast work of it, but there is a hood that 
> would stop any reflections. Of course, many people cut shiny 
> materials like plexiglass with lasers, so there's always a 
> need to protect against reflections.
> On Mar 3, 2016, at 7:30 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> > Don't use ferric chloride.  Use a combination of 
> hydrochloric (or muriatic) acid and a splash of high-strength 
> hydrogen peroxide (25% H2O2 can be bought at most health food 
> stores).  Once you've etched a couple of boards in this 
> solution, it starts to turn emerald green.  I just pour the 
> solution (which I store in a 1-Litre brown bottle) into a 
> pyrex glass dish in my laundry-room basin, then I put on one 
> rubber glove and swish the PCB in the solution until it is 
> etched.  No heaters, no bubbling.  It takes about 3 or 4 
> minutes of swishing to finish the etching.  It is pretty 
> gentle and doesn't over etch.  I've used the same solution 
> for six years.  I just occasionally add a splash of acid, and 
> every time I add a couple teaspoons of peroxide (which I keep 
> in the second fridge in the laundry room).  Some of the 
> solution sloshes out of the dish and goes down the drain, or 
> sometimes the bottle overflows slightly when refilling it 
> after the etch.  Just flush it with some water from the tap.  
> It won't hurt your pipes, and it's not particularly noxious 
> at the water treatment plant, especially since only a few 
> teaspoons of it are going down the drain.  It just contains a 
> bit of cupric chloride.
> > 
> >> From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] On 
> >> Behalf Of Chris Juried
> >> Sent: Thursday, March 03, 2016 2:50 AM
> >> 
> >> That's the process I have been using for some time now. I 
> would like to get away from using ferric chloride. 
> >>  
> >> From: Gordonjcp <gordonjcp at gjcp.net>
> >> Sent: Thursday, March 3, 2016 3:17 AM
> >> 
> >> On Wed, Mar 02, 2016 at 11:37:58PM +0000, Chris Juried wrote:
> >> > I would love to get my hands on a laser cuter for 
> prototyping. Any idea what these are running, on the entry 
> level machines?
> >> > 
> >> 
> >> Laser cutters aren't great at making PCBs because copper 
> is shiny.  What you want is a laser *printer*, some 
> press'n'peel and a couple of quid's worth of chemicals in a 
> sealable tub like a Chinese takeaway container.
> >> 

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