Homebrew PCBs

On Sun, 28 Oct 2012 05:21:57 -0000, you wrote:

>I have been using H2O2 from the pharmacy / Muriatic Acid combo, 2:1 - works well and is easy to get, but it doesn't work after the initial use.  It seems every etch, I need to make a new batch.  The etchant turns into a bright lime green color on the first etch and it does what I need to pretty quick and it seems like there is decent activity - bubbles which only happens on the first time use, after that maybe bubbles when I first put in the pcb/Cu but they go away very quickly.
>
>After use, I will put the solution in a clear, sealed glass container and even if I use it the next day, after I start, 45min later my etch is still not done, so I dispose of it and make a new batch at which time I am done in 15mins.
>
>What am I doing wrong or where is the mixture out of balance?  Again, I just did an etch this evening and had to make a new batch, which is now a bright lime green color.

The etchant uses the oxygen from the peroxide to enable the etching.
To continue to etch with that solution, you need to bubble air through
it.  It will also help to heat the solution to 100 degrees F or so.

The solution will gradually turn a darker green.  If it turns olive
(IIRC), then the chemistry is out of balance.  The peroxide provides
oxygen only for the first day or so, at which point the etchant turns
into a CuCl etchant, which works very well, is a trifle slower, but
never wears out.  I think that there's a good review of this chemistry
in the group archives, which explanation is better than mine.

You'll find that if you add some relatively concentrated peroxide to
the etchant, it will start to work the way you expect, but the word is
concentrated.  Not really needed.

Some people take the peroxide etchant mix and deliberately add copper
to it, producing the CuCl etchant to start with.

You will eventually have to add either Muriatic acid to the mix to
replace the chloride ion, again, IIRC.

Harvey

>
>Thanks in advance,
>Bob