Homebrew PCBs

In our lab plating tanks we used 1" PVC pipe with two rows of 1/16" holed on 
1" or shorter centers at 45\ufffd up from the bottom.  These were big tanks 
(about 80 gal) and the boiling action was pretty impressive with 1 to 2" 
diameter bubbles.  In a small tank this level of sparging would send the 
etchant all over the room.  If the bubble is too small it just doesn't rise 
and doesn't move the etchant around.  You want as big a bubble as you can 
get while not splashing stuff all over the place and keeping the agitation 
uniform over the surface of the board.  My guess is that for most small 
tanks you want bubbles between 1/8 and 1/4" or 3 to 6 mm diameter.  You have 
to drive the whole sparger bar though.  Make sure you have the air capacity 
for that.  Also make sure the sparger is very close to level.  Otherwise 
once the first couple of holes open up, air pressure drops and you may not 
drive the etchant out and open up the other holes so you are really only 
sparging one end of the tank.

I don't think you have to go down to 0.002" - I was doing this to help 
develop a test method for monitoring the sterile barrier characteristics of 
medical packaging, but it is relatively easy to do.  I have an old Unimat 
drill press to which I attach the tweezers from a resistance soldering unit. 
I just put a piece of stiff wire of the size I want in the tweezers, press 
it against the plastic and turn on the power.  It heats quickly and melts 
through the plastic.  Leave it in too long and the hole gets a lot bigger. 
For these real small holes I've been using tungsten because it's about the 
only thing stiff enough.  If you go up to .005" there are plenty of metals 
that are stiff enough that they won't bend when you push (gently) on them.

----- Original Message ----- 
From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Tuesday, March 08, 2005 3:37 AM
Subject: Re: [Homebrew_PCBs] bubbler - more even spread of bubbles


>
> On Mon, 7 Mar 2005 18:38:59 -0500, Earl T. Hackett, Jr.
> <hacketet@...> wrote:
>
>> Lots more smaller holes.  I've been making 0.002" holes with a hot wire.
>
>
> that's 0.05mm!!!! what wire did you use? how did you do that?
>
> Think and tinker says larger bubbles are desireable, they use a special
> hole pointed down 45 degree that allows a large bubble to assemble before
> breaking off.
>
> I'm not sure what is best, all i know is i have a uneven etch and i'd like
> to change that.
>