Homebrew PCBs

Yes, normal steel is a bad news around a copper acid plating 
tank. I only recognized this problem because I've been through 
these mistakes myself. Suitable construction materials are 
plastics (except nylon) and stainless as I mentioned earlier.

 From what I can see in the picture of your updated anode mounts, 
it looks ok to me. Get some PVC solvent cement (the smelly stuff 
used for gluing PVC pluming and irrigation pipes) and drip a 
little around where the copper anodes meets with the PVC 
shielding. That way your anodes should not prematurely dissolve 
at this location and cause them to fall to the bottom of the tank.

Make sure you are using stainless nuts/whashers holding copper 
posts to the black rectangular plastic frame.

As for a power supply, I used an old PC power supply with 5V 
output and a power resistor to change the current. The resistor 
was made by element wire mounted to a length of wood so I could 
connect an alligator clip at different positions to change the 
current. It was extremely crude, but at this stage I only need 
something that works because I have so many other things to worry 
about first, such as the getting the chemistry and process 
working. I'm still working on the more critical PCB processes, so 
the plating power supply will come some other day.

 From memory the power requirements for copper plating are;
cathode current density 1 to 2 A/dm^2
I think cell voltage with plating additives I'm using is around 
700mV at 2A/dm^2. I'll have to confirm this, but I'm sure it was 
under 1 volt. You definitely don't need a precision constant 
current source for this type of plating. A voltage source is ok, 
as the current can change +-%20 without worry. A bit of 
resistance in the line is enough to take care of current variations.

Adam


Markus Zingg wrote:

> Hi Adam,
> 
> After some testing, it turned out that you were absolutely right. Not
> that I really would have doubht it - It came even worse in that the
> anode bags - which were wicked around the iron on top of the anodes
> soaked up the solution. As a result the iron started to corrode....
> 
> I meanwhile have followed your sugestions. That is I made it slightly
> different in that I drilled four threads into the anodes from top, and
> screwd four solid copper wires into them. On top I also replaced the
> iron with plastic bars. The wires are now PVC insulated and I used
> glue to isolate the coper wire / anode interface.
> 
> You can see pictures of the changes here 
> 
> http://www.myhome.ch/mzingg/pcbstuff/tps/ 
> 
> click on "updates to the station"
> 
> While I think it's now done the way you meant, I still really
> apreciate your feedback!
> 
> There is another probelm left open with the powersupply. It turns out
> that the lamp regulator I use does not start up immediately and as a
> result the transformer first outputs about 3V. There are ~40 Amps when
> plating starts, and trying to regulate it down leads to the effect
> that I can only go down to 10 Amps at about 0.6 V. Below current stops
> flowing immediately. I'm now considering adding diodes in row to the
> cathode line to have the transformer operate at a higher voltage...
> 
> I first hoped that the fact that now that the anodes are floated
> completely this would change but it did not.
> 
> How did you do your power supply?
> 
> Markus
> 
> 
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>

Hi Adam,

Thank you very much for your feedback.

[snip]

> From what I can see in the picture of your updated anode mounts, 
>it looks ok to me. Get some PVC solvent cement (the smelly stuff 
>used for gluing PVC pluming and irrigation pipes) and drip a 
>little around where the copper anodes meets with the PVC 
>shielding. That way your anodes should not prematurely dissolve 
>at this location and cause them to fall to the bottom of the tank.

Ok, will try to get this.

>Make sure you are using stainless nuts/whashers holding copper 
>posts to the black rectangular plastic frame.

They are all stainless already.

>As for a power supply, I used an old PC power supply with 5V 
>output and a power resistor to change the current. The resistor 
>was made by element wire mounted to a length of wood so I could 
>connect an alligator clip at different positions to change the 
>current. It was extremely crude, but at this stage I only need 
>something that works because I have so many other things to worry 
>about first, such as the getting the chemistry and process 
>working. I'm still working on the more critical PCB processes, so 
>the plating power supply will come some other day.
>
> From memory the power requirements for copper plating are;
>cathode current density 1 to 2 A/dm^2
>I think cell voltage with plating additives I'm using is around 
>700mV at 2A/dm^2. I'll have to confirm this, but I'm sure it was 
>under 1 volt. You definitely don't need a precision constant 
>current source for this type of plating. A voltage source is ok, 
>as the current can change +-%20 without worry. A bit of 
>resistance in the line is enough to take care of current variations.

Thanks for the info about the PC power supply. I will first try to add
diodes in series to the kathode line to raise the overall voltage a
bit so as the regulator can operate better. If this fails, then a
complete redesign of the power supply will be the next step.

Markus

PS: I meanwhile updated the pages with pictures of the first PCB.
Looks like the much too high current created this effect.