Homebrew PCBs

On Tue, 28 Jun 2005 00:50:28 +0200, Adam Seychell  
<a_seychell@...> wrote:

>
> I've never notice actual mist from bubbling etchant. However, if your
> trying to minimize gaseous fumes then a sealed system is the only
> option. Bubbles do create a lot of splashes and fine droplets that will
> travel a surprising long distance. If you can sufficiently cover the
> etchant so that droplets run back in to the tank, then that should solve
> most of your problems. My spray etcher does creates a heck of lot of
> mist and it is not "closed loop". There is an air bubbler in the spray
> chamber for aerating the etchant and I get virtually no etchant escaping
> even though the "air" is continuously escaping. By far most etchant
> escapes from spillage as I withdraw the PCB. The trick was to install a
> double walled opening. The theory is that mist will immediately settle
> upon contact with a surface. So you all you have to do it make sure the
> mist is very likely to contact a surface.
> Now you won't be limited to corrosion resistant air pumps. And even
> aquarium pumps don't like acid. They usually have a zinc screw
> connecting the diaphragm to the oscillating arm, and I've found the
> valve flap material breaks down too. I can guarantee you'll get more
> problems then you'll solve trying to recirculate the etchant chamber  
> gases.
> Adam


well, i have taken the pump apart, cleaned it, and you were right the  
liquid did affect it, it "sticks" the valve flaps. They are silicone so i  
wouldn't worry and the screw was protected with silicone too.


In a way i want to run it open loop and avoid all the problems, but in a  
way i also want to avoid the fumes. If there is enough droplets in the air  
to clog the pump it will corrode my tools. My tank is more or less  
airtight, with a rubber seal.


Now the pump works better again, and would even be strong enough to power  
the bubbler (tho i can use shop air open loop).

What i wonder is if there is a way to make sort of a filter, maybe a  
bottle with cotton wool in it or something like that to catch the  
droplets. Maybe it would help to soak it in some weak NaOh, and let dry,  
to neutralize and droplets.

What do you think?

ST