The bubbles are probably trying to force the surrounding liquid
to rise, causing turbulence and currents.
Glue in a vertical wall with the two vertical sides glued, 5cm
away from the enclosing side of the tank, and with a bottom
gap of 5cm. Keep the top side of the wall 5cm below the liquid
level. That way, the rising current caused by the bubbles
flows over the top of the wall and back down to the bottom
to be repeated. It should make the bubbles rise faster with
less turbulence and more laminar flow.
That said, my crappy dse bubble etcher with few bubbles
seems to etch double-sided boards evenly, using FeCl.
(1/2oz Cu, 6-8mins, room-temp, 1:1 dilution with water)
Adam Seychell wrote:
>
> Hi all,
>
> I'm trying to make a bubble etching tank that can etch uniformly. I've
> spend lots of my time experimenting with different designs and can't get
> uniform etching of double sided circuit boards. I tried large bubbles
> from 2 mm holes drilled in PVC pipe. They never go evenly on each side
> of the PCB. The bubbles also have a tendency to group together on one
> side of the tank and circularliquid downward on the opposed side. I also
> tried increasing tank width (from 50 mm to 200 mm) so the solution down
> flow does not interfere rising bubbles. This helped but the bubbles
> still don't flow evenly enough for my liking. I even tried using two
> rows of bubbles on each side of the PCB. All this makes the etching
> terribly non uniform. I was going to look into spray etching but I heard
> spray equipment design must deal with all the same problems. Has anyone
> tried putting stuff like plastic beads in the solution ? this may even
> up distribution. How about very small bubbles ?
>
> The only other method I've seen is to pump the etchant over the PCB like
> a river bed.
>