Homebrew PCBs

Markus Zingg wrote:
>>Hi Markus
>>
>>Question why are the anodes on your pics covert with clothes!
>> next the heated tanks do they have air agitation otherwise it get a 
>>more hot to the element as eslewere in the tank!
> 
> 
> Uh, yes, I forgot to answer this part. They are here to keep small
> copper wires that will be created by the process away from the PCB
> where they obviousely could create short cuts. For a homebrew station
> - due to the smaller number of runs - maybe not that much of an issue,
> but they were part of the anode package as I bought it.
> 
What small copper wires are you talking about ? I thought 
the anode and cathode (PCB) are well separated so there 
cannot be any possibility of contact.

Anode bags are very often used in many types of plating 
baths. I know that for bright acid copper sulfate plating 
the bags are used to inhibit solution flow around the anode 
surface and preserve the black (or dark brown) film that 
normally forms. I am using Macuspec 9241 brightener from 
Macdermid and the data sheet stresses that anode bags must 
be used. Well, since it didn't give any reasons why anode 
bags must be used I didn't believe it and so I didn't use 
any. Hmmm, yep, I soon learned why the bags are important. 
The black film on anodes that's formed during plating is 
very fragile and may easily strip off with air bubble 
agitation. In these conditions the film is continuously 
forming and releasing into the solution. After plating just 
one PCB I could see enough precipitate produced that the 
bottom of the tank was covered with a dark powder. I 
installed the proper anode bags and it solved the problem 
totally. I later read in plating books that the anode film 
in bright acid copper plating is important for correct 
dissolution of the anode.

Interesting , originally when I was plating with no 
additives (200g/L H2S04 , 75g/L CuS04.5H20), the anodes 
would not form this dark brown film, and would be more 
stable. But there were still some anode film and small 
amount of copper powder would release into the bath.

I also found that plating with low acid high copper
(75g/L H2S04 , 200g/L CuS04.5H20) then anodes dissolve much 
cleaner and remain pink, but of course this bath has 
terrible plating uniformity and is why no one uses it to 
plate PCBs.

The anode bags are normally polypropylene fabric, that looks 
very much like white denim. You could probably use 2 or 3 
layers of 100% polyester fabric. I would first put it in 
some 200g/L sulfuric acid for a week so that any thing in it 
that might react with the acid will do so before in goes 
into your plating tank.