Homebrew PCBs

On 13/05/14 10:25, Peter Johansson rockets4kids@... 
[Homebrew_PCBs] wrote:
> 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".