Thanks for the description. I've used HCl+CuCl and regenerate
with air. Specific gravity is about 1.25 to 1.30 Its not a fast
etchant, 30 minutes etch 35 um copper foil at 15°C in bubble
tank. I guess if there is some excess H202 in the etchant then it
works much faster, but when all the H2O2 used up, it etches only
with CuCl2, which produces dark brown Cu2Cl2.
You method of adding limited H202 and watching for dark brown
Cu2Cl2 is very effective in controlling the correct amount.
Adding way too much will only oxidize the HCl and end up with
chlorine gas !!!!.
You are correct in the HCl is consumed during etching, the
chloride must come from somewhere if your producing CuCl2.
From what I've read on CuCl2 +HCl etching the HCl concentration
has minor effect on etch rate, in fact some etchants run at
almost zero acid. So when you see any blue sludge, Cu(OH)2 you
know there isn't any acid. Just add concentrated stuff 35%.
If specific gravity goes above 1.30 then copper content is
getting high, some water will fix that, but the H2O2 additions
may keep the S.G from rising too high.
Looks like you have it all worked out.
The strongest H2O2 I found at hair styling supplier was 18% and
had it in 1 liter bottles. You will go broke buying from a
pharmacy. Finding industrial strength (35% - 50%) H2O2 in small
quantities is more difficult. The stuff decomposes so its not
worth buying in bulk.
Adam
Stefan Trethan wrote:
> On Mon, 05 Jan 2004 23:10:50 -0000, dkesterline <desterline@...> wrote:
>
>
>>>it also depends where you do your shopping, if muratic acid (HCl)
>>
>>is easy
>>
>>>to come
>>>by where you are and you can get H2O2 somewhere is most likely the
>>
>>cheapest
>>
>>>method.
>>>
>>
>>Muratic acid is widely used for cleaning masonary (bricks, block, etc)
>>and controlling PH in swimming pools. Most any masonary supply house or
>>pool chemical supplier should be able to sell you some in gallon jugs for
>>less then $5.
>>
>>H2O2 (hydrogen peroxide) should be available though any beauty supply
>>shop, though I'm not sure about the strength you need.
>
>
> I fear it is pretty thinned (no more than 10%)
>
>
>>Very weak peroxide is available in the Pharmacy for disinfectant. It's
>>not very strong, but if the recipie calls for water dilution, it might be
>>made to work.
>>
>>Since this is redily available, someone want to post a recipie? Maybe
>>some "Care and feeding" guidelines about the regeneration proccess?
>>
>
>
>
> The problem with diluted H2O2 (like 2% medical) is that you need a lot
> more. and the price is nearly the same as 35% stuff.
> the huge amount of water will keep your etchant growing.
>
> I bought 1 liter 35% at a chemist's shop for some 3 or 4 eur if i remember
> correct.
>
>
> I use a simplified CuCl process (as i think now - if wrong pease write).
>
> it works the following:
>
> for a start you make a 15% HCl solution (tap water is fine)
>
> Then you put a pcb in it.
>
> then you put H2O2 in it.
> for the first pcb you may need more than usual.
> start slow, you should see discoloration of the copper very quick.
> if you see bubbles forming it is more than enugh, stop adding h2o2.
>
>
>
> After some time the etchant will become green.
> as long as it is a bright green it etches and everything is fine.
> over time it gets darker, and darker, nearly brown.
> then it has stopped etching.
> if you add a few drops H2O2 you see immediately the conversion to bright
> green again.
> Add enough to get the whole amount bright green.
> but mind, stirr or agitate the container you are using.
> a few drops h2o2 can regenerate the whole container, you will see amazing
> effect when stirring.
>
> You will also see that localy near copper surfaces the etchant gets brown.
> if you agitate the brown drifts away and is diluted/regenerated and
> dissapears in the green again.
>
>
>
>
> Well, that pretty much is it. just add H2O2 to keep it bright green.
>
> If you add too much H2O2 the whole thing starts to "boil" at the copper
> surface.
> lots of bubbles and gas, clorine smell, no good at all.
> but if you have good ventilation and need a board in 10 seconds (no joke,
> bowl etching) this is a option.
>
>
> The H2O2 is volatile.
>
> After a etch when the board it out there is no new copper to be converted.
> any H2O2 still present has no where to go and will disappear over (not too
> long) time.
> therefore it is good to add only enough for one etch.
>
>
> While there is still copper left a certain (tiny) amount of H2O2 in the
> etchant
> is good. it immediately regenerates the brown etchant to green (Cu2Cl2 to
> CuCl2 i was told).
> But it can only work as long as Cu2Cl2 is produced. if there is no Cu2Cl2
> is left it is a fully
> regenerated etchant.
>
> So you see the reason for not adding too much. it will only produce oxygen.
>
> The echant stays in regenerated state in storage.
> so the CuCl2 is not lost between etches.
>
> It does also stay in used Cu2Cl2 condition. but air oxygen slowly
> regenerates it.
> If you add a bubbler (air pump) and let it run (hours to days) you can
> actually regenerate
> it only from air oxygen.
>
>
> I don't do that because H2O2 is so cheap, it is faster etching with it, and
> air bubbling adds problems (mist).
>
>
>
> There are two effects i can't fully describe:
>
> a) the "start up" why it works with plain HCl and H2O2 in the beginning.
> (but it really does, you need no day - long preparation)
> there is no CuCl2 present, it must directly convert it from copper, HCl and
> oxygen.
>
>
> b) the "blue" effect.
> Only once until now the etchant suddenly formed a blue soft sludge on the
> copper and
> refused etchnig. adding H2O2 did not help.
> Adding HCl did help, but i also needed some H2O2 again.
>
> I assume all Cl atoms were already used up and it din new HCl to get them.
>
>
> The catch is that the copper is not regenerated out the solution.
> the number of CuCL2 molecules steadily increases.
>
> If one Cu2Cl2 is regenerated 2 CuCl2 are produced.
> the clor needed is taken from the HCl.
> but with the hcl there is hydrogen. the hydrogen is taken by the oxygen
> from the H2O2.
> this leaves you with additional water.
>
> I hope this simple chemistry is correct, it is all i could come up with.
>
> the growth of the etchant is very low in fact, i would say nearly
> insignificant if some
> water vaporizes and some is taken out sticking to the boards.
> the consumption of H2O2 is also very low, only a few drops for a smaller
> board.
>
> the HCl consumption is not more, you will etch quite a few boards before
> the initial 15% are used up.
> you see i had the "blue" effect only once until now...
>
> to the handling:
> it is a strong etchant.
> i have fetched the pcb several times by now with bare hands and in only one
> second
> washed it immediately in water. nothing was to be seen on the hand.
> i strongly recomment not doing that anyways...
> Longer exposure is not tested, and i don't like being test rabbit.
>
> You can not use any metals in the tanks etc., no stainless steel or so.
> only plastic holds up well.
>
> For me this etchant is ideal with toner transfer - as it is as easy and
> fast.
> the toner takes no harm in the etchant.
> photoresist works too.
> Most ohp markers (edding etc) don't work too well.
> the best is the red staedtler ohp pen ink.
> with that you can correct your artwork if the toner transfer left errors.
>
>
>
> Feel free to ask any questions.
>
> Stefan
>
>
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