Im using a 25% hcl and 30% peroxide diluted to 3% for large boards and semi professional manufacturing. The process is not very critical but you shoul BE AWARE THAT CHLORINE GAS IS RELEASED when cupric chloride is forming. Do this in a VERY well ventilated area and if possible get a chemical mask, use protective googles, gloves,etc. Best clothes to wear in this case is pure polyester because its not afected by the acid, a large plastic apron, meat industry kind, is also a good idea.
When initially mixing hcl and h2o2 remember the triple A, Allways Add Acid to water, in other words, first put the water and the slowly add the acid or you will have a wild exotermic reaction.
Do not store this solution in metal or allow it to get in contact with metal. Do not use more than 3% h2o2 or the reaction with copper can go wild, i read somewhere that some rocket use peroxide and cooper as propeller.
Maintainig the solution s very simple, a green esmerald color is a good color, when it start to turn brown because of too much cooper retained, add more h2o2 until it goes ligth green again. From time to time you would see that besides having a ligth green color the etchant takes to much time to work, this is because the acid gets diluted (regeneration with h2o2 generates h2o as subproduct) and you simple have to had more hcl.
Tritation is a good form of control but I never done it yet.
I hope this helps and if anybody knows something better please share with the rest.
--- In Homebrew_PCBs@yahoogroups.com, Philip Pemberton <ygroups@...> wrote:
>
> Hi guys,
>
> Does anyone know off-hand what the required ratio of Hydrochloric Acid
> to Peroxide is when starting off a cupric chloride etch bath?
>
> I've tracked down these 'starter' chemicals on ebay:
> HCl:
> http://cgi.ebay.co.uk/BRICK-CLEANER-CEMENT-REMOVER-CONCRETE-REMOVER-ACID-/250631108343?pt=LH_DefaultDomain_3&hash=item3a5ac736f7
> or
> http://cgi.ebay.co.uk/Disclean-Brick-Cleaner-2-x-5lts-/390122417591?pt=LH_DefaultDomain_3&hash=item5ad51badb7
>
> H2O2:
> http://cgi.ebay.co.uk/2x200ML-Bell-Hydrogen-Peroxide-9-Anti-Septic-Bacterial-/130392225994?pt=UK_Health_HealthCare_RL&hash=item1e5bfb78ca
>
> This is 17.5% strength HCl, and 9% H2O2. Assuming this is strong enough
> to start a cupric chloride bath (with a sufficient amount of air and
> scrap copper provided), what sort of mix ratio would I need to make a
> viable etchant?
>
> Do I need to target a specific pH? That is, do I need to buy litmus
> paper and so on too?
>
> What about titration and specific gravity control -- is that necessary?
> I have some sodium hydroxide granules in the cupboard (CIF Photoresist
> Developer; I've been using MEGA CPD5 instead because it's less harmful
> and harder to screw up), but would need to hunt down a suitable
> indicator chemical and glassware...
>
> Thanks,
> --
> Phil.
> ygroups@...
> http://www.philpem.me.uk/
>