Homebrew PCBs

I use ammonium persulfate which I think behaves almost identical to 
sodium persulfate, I have read there are some subtle differences with 
etching between the two. I have never heard of needing to "shock" the 
solution. What is the purpose of "shocking" ?

I've read that iron ions and some other metal contaminants can 
accelerate the decomposition of persulfate.  The pH of persulfate 
etchants are always acidic (very low pH) because of the decomposition 
products ,

2H20 + S208(2-) -> 2H(+) + 2S04(2-) + H2O2

You basically get sulfuric acid and peroxide which then further 
decomposes to release oxygen. Heat also speeds decomposition. I've got 
some solution for 2 years that I occasionally use for very light 
etching. The fact I've never heating the solution could be why its 
still showing some strength.
A common method of completely destroy persulfate is to boil them in 
solution for ten minutes or so.
You can switch to ferric chloride if you want an indefinite shelf 
life. Just put it in a etching tank so you never have to let the stuff 
  touch anything else but the PCB.
Recommended startup concentration for persulfate is 200g/liter of the 
salt.

Ron Amundson wrote:
> For some reason this didn't get posted last week, my apologies if it shows
> up twice, but I'm making boards on Wednesday, and would like some input.
> 
> In my Kepro datasheet, it says I can shock the solution by adding some spent
> Sodium Persulfate so I don't have to wait for it to stabilize.
> 
> I had some used solution which was 3 months old that I used to shock the
> bath. I know the shelf life for etching is 3 weeks, but can it still be used
> to add in adjusting the pH? The experience as shown below seemed to indicate
> its not possible, but I want to know if I need to look at some other reason
> for the slow etch rate.
> 
> I went ahead and etched, but it took forever. I was successful at 12/12, but
> the etching seem to take 15 - 20 minutes. When I had my techs making proto
> boards, it seemed we could etch in 2-4 minutes. The solution was at 105-110
> deg F. The board was quite small, and as I use huge ground planes and leave
> dead copper on the board to reduce waste, It seems it should have etched
> close to the 2 minute time frame rather than 20 minutes.
> 
>  I doing tray etching with manual agitation.
> 
> Thanks
> Ron
> 
> 
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