Just in case some people here may be wondering how to speed up the etching process for PCB's, one way to do it is to use a bubble etcher. Basically all you have to do is install a perforated plastic tube in the bottom of your etching tank and force air through it. The bubbling action constantly agitates the etchant and thus greatly speeds up the etching process. I'm using some aquarium tubing with small holes drilled in it and I use an airbrush compressor as an air source in my small tank. For a larger tank you can use 1/2" ABS pipe and the exhaust of a canister style vacuum cleaner such as a Shop Vac for an air source. You should use an adjustable valve in the air line to regulate the flow so as not to spray etchant all over the place. In this type of tank the circuit board must be hung vertically in the etchant. Heating the etchant is also recommended. Have a good day.
Good morning, Rodney. Someone who's interested in this type of etching setup might want to look at the GC/Waldom Electronics Cat. No. 22-0394 "Professional" etching system. It uses a setup similar to the one you're talking about, with an aquarium heater and a small aquarium pump. I found it to be useful for small quantity ferric chloride board etching.
A couple of caveats about using this type of setup. First, heated etchant will emit fumes, which are corrosive. This kind of thing should only be done in a well-ventilated area, and away from computers or other electronics. Second, while the aquaruim controller provides pretty good temp control (once you get the dial setting right -- use a thermometer to get the controller to the right setting), the temp control only works well with a constant etchant level. As etchant evaporates, the level changes, and the temp control will be affected. Not only that, but if the etchant level gets too low, the glass of the aquarium heater will crack.
The aquarium heater itself hangs from the side of the etchant tank on the inside. If the glass of the heater comes in contact with the plastic tank, it can melt through, causing a disaster. GC now provides an O-ring to slip around the side of the glass heater to help avoid this problem. The O-ring should be used at all times. But, in order to be safe, the whole tank should be placed in a large pan which would catch the etchant in the event of a melt-through of the plastic tank (voice of bitter experience here).
One other note -- it's very important to physically place the aquarium pump over the level of the top of the etching tank. When power to the pump is turned off (or in the event of a power failure) etchant can back up the air tube into the pump. That's disastrous for the pump, and will cause failure in the near term.
This type of hobbyist system is good for small quantity, single sided boards where the minimum trace widths aren't too demanding. It's difficult in this type of setup to get a double-sided board to etch well. It can be of use to periodically flip the board over, turning it around and upside-down, to try to even out the etch. This setup also assumes you will have some scrap around your circuit, because the edge of the board in the aerator/holder doesn't etch.
Anyone using this setup for real should obtain a spare O-ring and a spare aquarium heater (which has been preset to the right temp) in case of component failure.
some etchant can become airborne when it's bubbled, making breathing rather dificult, proper ventilation will fix that.
depending on etchant formula it may be a good idea to heat it constantly or not, i not then heating to operating temperature. some produce heat when they work, constant heating could cause it to go exothermic, meaning it would boil and perhaps cause fire or explosion, maybe a gaseous acid as well. as long as you don't exceed a certain rate of copper absorbed in a set timeframe things should be fine with preheating.
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If you run the lines up and over the side of the tank there shouldn't be any back-flow of etchant but the check valve might also be a good idea. Keeping the air line fairly long might also be a good idea. I haven't seen any problem with back-flow in my system so far but I'm not using an aquarium pump.