Homebrew_PCBs

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.
>

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.

No personal experience, but here is a link to building a bubble tank
http://www.thinktink.com/stack/volumes/voliii/equipmnt/bubltank/bubltank
.htm

Tim
[Denver, CO]

> -----Original Message-----
>
>
> 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.

In a message dated 06-May-02 00:28:32 Central Daylight Time,
adam_seychell@... writes:

> How about very small bubbles ?
>
>

Your holes are much too large. Try 0.040" holes (about 1 mm). But you might
need a LITTLE more air-pressure (1 psi?).


[Non-text portions of this message have been removed]

Adam
I use this tank http://www.web-tronics.com/lowcosetsysw.html
It does 2 double side boards in about 4min.
It has about 4 small holes at the bottom only and uses an aquarium
pump, low pressure.
There are as you call it sweet spots in the tank that etch faster than
others. But this is no real problem. I have forgot about it
and left for an hour. All it did was make my trace narrower.

Derek


[Non-text portions of this message have been removed]