stefan_trethan@... wrote:
>>I've just done a bit of experimenting with the HCl I bought earlier, and
>>some 20 Vol (6%) H2O2 from the local Boot's emporium.
>>
>>A couple of small pieces of PCB material about 1.5 cm in area etched
>>completely in about 5 minutes at room temperature, with continuous
>>agitation
>>in a small container. I used about equal quantities of the 32% HCl and 6%
>>H2O2. The resultant solution is now green, indicating that there are
>>plenty
>>of cupric ions present. If I re-use the solution, adding some H2O2 from
>>time
>>to time when it goes blue (excess CuCl2), I should end up with a
>>reasonable
>>concentration of CuCl3 that I can use. I think that some PCB manufacturers
>>who use CuCl3 monitor the etchant by measuring the colour continuously and
>>oxidise it automatically.
>>
>>Leon
>>--
>>Leon Heller, G1HSM
>>leon_heller@...
>>http://www.geocities.com/leon_heller
>
>
>
> i find it strange that you didn't find hcl earlier.
> it is very easy to get here....
Yes, HCl is the "standard" when you need a strong acid. Its
volatile, so if you spill a bit it will soon evaporate,
unlike a sulfuric acid spill which will hang around for a
millennium. I know here is Australia its very easy to find.
Sold in 0.5L, 1L & 5L containers at most hardware stores,
some carry 20L drums for the builders.
> i think there is a important difference between cucl etching and hcl + h2o2
> etching.
> well, you can use h2o2 as a fast substitute for regenerating your cucl but
> if you only put it in when etching (to have active h2o2 in the etchant when
> the pcb is in) you will get much faster results because also the reaction to
> cucl2 is used (not only cucl2 to cu2cl2).
> i only guess that, but consider the following:
> if you have fresh hcl and fresh h2o2 it also works fast, so it must work off
> the solid copper without cucl2 present (yes, this is built instantly but for
> t=0+ there is 0).
>
> i think this is the explanation why it is so much faster.
> also if you have a perfect regenerated cucl bath it is not so fast as if
> there is h2o2 in.
In normal CuCl2 etching (without chemical oxidizer) then
the CuCl is a product of the etching, which films on the
copper surface and slows down etching. As you know the H2O2
instantly regenerates the etchant, by converting all the
CuCl back to green CuCl2. So I would agree with your
comments that H2O2 speeds up etching because CuCl is quickly
chewed up. In a pure solution of HCl and H2O2, then the
exact reaction with copper metal must be something more
complicated. I wonder if the etching speeds up as the CuCl2
concentration rises, from zero initially.
The air regenerated CuCl2 etching solutions need a very high
concentrations of copper for it to be effective. The color
looks a very dark green inside a container, and you can only
see it as clear transparent green liquid when looking
through no more than a few mm thick, such as a drop on to a
surface. The solubility of CuCl2 is amazingly high. At 0°
you can dissolve 700g in of cupric chloride dihydrate in 1
liter, thats eqivilent to holding 300g of elemental copper.
Adam