Homebrew PCBs

Adam,

The sulfuric acid was like a thin syrup and was used at room 
temperature. It would take on a slight red-brown color as the epoxy 
level built up. We used a very narrow tall polyethylene tank with a 
floating polyethylene cover to keep the air out. The next two tanks 
were just a water dip. We would monitor the acid tank for proper 
specific gravity and adjust it as needed with fresh acid. These tanks 
never wore out. I built these tanks from the same polyethylene 
material that the acid drums were made of. 

The acid tank would always need additions to the operating level 
because so much was being dragged out due to the high viscosity. We 
would drain off the acidic water from the two static rinse tanks and 
use it for pH adjustments in our waste treatment system and to 
neutralize the caustic solutions when changing our cleaner 
conditioner tanks and photoresist stripper solutions. Safety was a 
big issue and the guy running this process wore a face shield, gloves 
and plastic apron. The panels were always held by a racking system 
and almost never touched so we had very few problems.

Tom
 
> Wow, concentrated sulfuric acid !.  Wasn't this a little dangerous 
> working with ?  Was it heated or at room temperature ?
> Conc. sulfuric is extremely hydroscopic and rips moisture out of 
the 
> air until the concentration reaches an equilibrium of about 30%. 
How 
> long did the tank last ? The acid is viscous like vegetable oil, 
dose 
> that cause a lot of the acid to stick to the PCB when you pull it 
out 
> ? I imagine a lot of acid would be used in this part of the process 
> and this acid would use up a lot of alkaline for neutralization.
> 
> I've seen what this stuff does to organic materials, like wood, 
paper. 
> I had a pin drop of conc. sulfuric  accidentally get on my finger 
> while pouring it from a bottle and it felt like someone jabbed me 
with 
> a hot soldering iron there. I was lucky to be right next to a water 
> tap so I was able to rinse it off in within a few seconds. I always 
> where a face mask and gloves now when handing the stuff, even a 
tiny 
> amount.