Homebrew PCBs

mihai_hagianu wrote:
> 
> Hi guys,
> 
> i have tryed before, and restarted now to experiment with
> electroetching, as an alternative method to FeCl3.
> 
> I and up with the same problem all the time. The electric courent is
> peeling off any stencils i'm using. I have tryed toner, different
> paints i've found here in the house(few oil based,acrilic,enamel), and
> even sticky tape( :) ).I have also tryed different acid for
> electrolite ( H2S04, HCl, acetic)in different concentrations, to see
> any improuvement, but the result is the same:
>  -if I put the board, with the selected stencil in the acid,without
> power connected to it, it lasts ok, 
> 
>  - if I apply electricity to it, to start electroetching, it works ok
> for a while, but after some time, the stencils are peeled off, for a
> reson i do not undestand nor can prevent yet.
> 
>  - I have tryed to electroplate the board, to check if the peeling
> happens, and of course it does not.
> 
>  - I have tryed different current densities, but the peeling still
> happends...some times sooner, sometimes later.
> 
> any ideeas what am I doing wrong ?
> 
> thanx,
> Mihai 
> 
> 
> 

Sounds like electrocleaning to me. Are there gas bubbles forming on the 
PCB copper surface when current is flowing ?

If so then it could be one or more of;
* Too high current density
* low ionic concentration
* missing ions that form soluble copper salts.

H2SO4 is the stuff to use. The sulfate ion won't gas (unlike chloride 
ion in HCl). The copper must go into solution so it needs a soluble 
counter ion, and sulphate from H2SO4 is perfect for the job. your 
cathode (negative terminal) can be any piece of copper. If you want to 
reclaim the copper then the cathode should be a flat sheet with high 
surface area to keep current density to minimum. Keep PCB current 
density < 20mA/cm^2 and agitate with air bubbles for cleaner dissolution 
of the copper. This will need some experimenting, but start with 150g/L 
H2SO4 acid (1/2 strength car battery acid).

Gas bubbles are used to advantage in electrocleaning as they scrub the 
surface and lift off any foreign material stuck to the surface. Usually 
done in alkaline solution so the metal to be cleaned cannot dissolve.