Homebrew PCBs

Markus Zingg wrote:
>>Markus Zingg wrote:
> 
> 
> You are right, I am using palladium activation. The palladium is 200
> EUR per 0.5 liter. That's expensive, but my 2.5 liter tank only needs
> 125ml per load. The remaining part is filled up with the pre-dip
> solution which is a lot cheaper. That said, the 200 EUR palladium is
> sufficient for four loads which last quite a while.

Thanks for the price info. I'd expected that price range. I 
remember once a friend looked into doing his own through 
hole plating using conventional electroless copper and got a 
shock when the sales person faxed him the prices :). You 
point out that the economics going down this path yourself 
is still small compared to professional made boards, which 
is all the matters at the end of the day.

I guess the importnat thing now is to take extra care not to 
comtaminate the palladium solution.

There is really no alternative because its not likely your 
going to develop your own chemistry and go through the years 
  of research that the manufactures once did. Its taken 
decades for these alternative electroless copper systems to 
make it in the industry. If your are interested in the 
subject you might like to read;

http://nr.stic.gov.tw/ejournal/ProceedingA/v23n3/365-368.pdf

> 
> I have to laminate it, then do the light exposure then developp it. I
> used the term "negative" becuase the exposed parts of the film are
> thereafter resisting to the developper and those which are not exposed
> to light will be taken away from the developper.

Yes, that's what people call a "negative" resist.

> 
>>From what you mentioned above I suspect your using dry film 
>>negative photoresist. Developer of this resist is 10g/L of 
>>Na2CO3 at 25~30\ufffdC and the stripper (remove all resist) is 
>>usually 10 to 30g/L of NaOH.
> 
> 
> I use  20g/L of Na2CO3
> and later on to strip 15g/L of NaOH
>

The strip solution is not critical, but from what I've read 
on all dry film data sheets is the developer should be 9 to 
11g/L NaCO3. If the instructions say 20g/L then use that.
For my developing method I pour 500 ml of warm water into a 
plastic tray and then add 50 ml of concentrate stock 
solution (100g/L NaCO3). I drop in the PCB and gently brush 
over with a 50 mm wide paint brush until I can clearly see 
all the copper. Then I continue brushing for another minute 
just to make sure all the (unexposed) resist is removed. 
I've had problems with resist residue if I don't do the 
extra brushing. Then the board is quickly rinsed and goes 
straight into the etchant. I found the resists can swell a 
the edges if rinsed for too long a time in fresh water. Once 
the bard goes into the acidic etchant then the resist film 
returns hard again.


Adam