Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Anthony Toft <toftat@c...> wrote:
> Well, I got about half a pint of HCl from a friend with a pool (I could
> only buy 2 gallons minimum) and made ~150ml of etchant (100ml of 3%
> H202, 50ml of 31.5% HCl) and it worked like a charm, what a difference
> new etchant makes, my tired old FeCl would have taken 20+ minutes, this
> took 5-10!

Glad to hear of your success.  That's definitely the HCL doing the
etching.  You can get 1 G quantities at home depot, lowes, ...

> 
> This appeared to be exothermic (it made it's own heat) will this stop?
> What is causing it (I think it's the reaction with the H202)? Will it
> produce heat next time?

I did not see it first time I used that etchant though I used about 3
liters so it could have masked heat production.  HCl boils around 50 C
so you definitely dont want the etchant warming up.  Note that mixing
acid and water is exothermic.  always add acid to water, never water
to acid.

> 
> There are bubbles in my storage container (I didn't aerate), what are
> they? Will they eventually explode the bottle if I don't vent them off?
> It's in a pint bottle that usually contains water.

I noticed bubbles when I had plenty of H2O2.  It will eventully go
flat.  I doubt that it will build up that much pressure but for piece
of mind, you can leave the lid slightly loose.  

> 
> Why did my latex gloves turn yellow where they got etchant on them?

Probably CuCl.  I would recommend something beefier than latex gloves.
 I use heavy duty ones intended for masons using HCl for acid washing.
 I'm going to get a lab apron next time I hit the chem supply place.

I'm interested in your second etching session.  If its anything like
mine (hope not) you will have to add H2O2.  My sessions with the same
recipe went something like this:

first session (3 L) - etched 6 boards, lots bubbling, fast etching,
odd discolorations of the copper (purple, black streaking).

2nd session (about 5 days later) - no etching at all.  Left a small
strip of copper clad in overnight there was very very slight etching.
 Discovered that etchant eats "airstone' plastics - makes a big mess.
 SG was 1.075 (way low)

3rd session (next day) - divided mixture in half (1.5 L), added 2 oz
of 30% h2o2.  Good etching action, some bubbles but took longer, maybe
25 minutes/board.  Did 3 boards 15X20 cm.  SG after was 1.1.

4th session (3 days later) - no etching  added 2 oz h2o2.  good action
some bubbles.

5th session (2/3 days later - tonight) - no etching.  I made a new
bubbler and bubbled the etchant overnight.  Tried again the next day.
slow etching (I was out of the h2o2).  It took 35 minutes to do one
15x10 cm board.  Etchant was a dark olive green.  I left the bubbler
on overnight - I really hope I can regen this stuff with out using
H2O2.  I'll check the SG tomorrow and hope that I see emerald green...

I'm not super happy with this stuff yet.  If I can either find a cheap
source of H2O2 or regen via bubbling, I will be much happier.  As it
stands, having to buy H2O2 at $4/oz really is bad economics.  But if
it can be made to work the the displosal benefits will make it all
worthwhile.

Phil