Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

I started out with Ferric Chloride many years back, worked well but was very messy and stained anything it touched.  Never tried to regenerate it but did heat the solution to help things etch and discarded when used up.  Then I moved over to Ammonium Persulfate, much cleaner, has a very fast etch with minimal undercut but it needs to be heated quite hot to work well.  For really fast etching add a few PPM of a mercury II salt.   Once mixed the AP degrades and becomes useless in a couple of weeks.  Worked great in my splash etch tank, I did a lot of boards with the stuff. Also helped that I had a free source.   For the most recent boards I tried H202 and  HCL,  works good  but more corrosive than the AP.

The actual etchant in the H202-HCL is the  Cupric Chloride  ie. Copper(II) chloride CuCl2 that is formed in the solution.  The etchant gets better with use as more CuCl2 is formed.  The etching is the result of a
Redox reaction, the copper on the board is oxidized to Cu+ ions and goes into the solution  while the CuCl2 is reduced to CuCl.  The H202 or air bubblier oxidizes CuCl back to CuCl2 making more etchant out of the board copper  The HCl provides the additional Cl ions as more Cu  goes into solution.   At some point the solution will become over saturated and you will need to dilute it down or start over.

Notes:  Beauty supply H202 is not 30%  it is 30 or 40  "Volume"  which is I think about 10 - 12%
           To remove ferric chloride stains use Oxalic acid

Craig