Homebrew PCBs

Stefan Trethan wrote:
>>The resistance on the rods does rise as copper plates
>>on to them. However, I've never had the copper content
>>up to the point that a rise in resistance became a
>>problem. Like I said, I do small runs and not large
>>runs that are going to saturate the solution with
>>copper. Besides, even if I did, an equilibrium would
>>be reached between copper on the rods and copper
>>remaining in solution: No more copper would plate out
>>onto the rods. But, the copper on the robs would not
>>be dissolved off the rods (Unless there was a decrease
>>in the current used to pull THAT amount of copper out
>>of the solution).
>>
>>Regards
>>
>>Marvin Dickens
>>
> 
> 
> Oh i didn't fear any problems with the resistance. i do not expect it to
> be significant.
> I just feared that the etchant will eat away the copper i plated.
> just like it is supposed to eat away the copper from the pcb.
> I guess you definitely need to take out the electrodes, or at least remove 
> the
> copper if you disconnect the power source for a while.
> 
> Have you measured which current/voltage you use? would be very interesting 
> to know that
> and maybe also the estimated electrode surface, and the bath volume, and 
> electrode distance.
> 


Read my earlier post of setting current density *ratios* between the anode 
and cathode. You can use large anode surface area to achieve low current 
density and avoid chlorine gas evolution. You can use small cathode surface 
area to achieve high current density and maximize plating efficiency. But 
avoid too high a cathode current density or hydrogen gas will evolve. The 
aim is to reduce the copper content to only about 50% to 75% of its 
original concentration because copper (2+) is needed to etch. Specific 
gravity measurement is the best way to know your copper levels. Sorry, I 
don't have any tables on sp.gr verses Cu content.

I would experiment with carbon rods anodes as these are cheaper and easier 
to get (see earlier post). The life of graphite rods should be very good 
provided chlorine gas is not evolving. You can use stainless steel for the 
cathode , but don't leave it in the solution for very long with the current 
disconnected or it will corrode. Another option is just plate on another 
piece of copper, e.g. a length of copper pluming pipe. I haven't tried 
plating copper onto titanium but I suspect it would just fall off as Marvin 
said.

Current and voltage for an arbitrary cell depend on too many factors to 
have any meaning. Electrode current densities and temperature are the key 
parameters you should be seeking.

Adam