Homebrew PCBs

Stefan Trethan wrote:

> 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

If tools are corroding several meters away then it must be HCl gas, 
rather than splashes or wouldn't travel so far. What etchant are you 
running ? There should be almost no oder from a open jar of etchant at 
room temp. Keep HCl concentration under 2 Molar. If your stuck with a 
fuming etchant,(i.e an open container of etchant will corrode steel in 
its vicinity) then you have to keep it sealed. All I can recommend is 
keep the place well ventilated during etching, and seal air tight when 
not in use. You must of course also eliminate exterior splashes due to 
bubbles.