Homebrew PCBs

Hello,

Can I ask a really dumb question?

When I visit my board house (they're local and let me "tour" as I 
wish; a 900x certified facility) I see ALL their plating and etching 
baths using vertical board holders closely spaced in large tanks. 

No slanted walls, No bubbles. But here IS good recirculation of the 
etchant. (They do acid etching, AIRC)

If it works for them; why doesn't it work for us?

Ballendo

P.S. A buddy bought a commercial spray etcher from a closing low 
volume PCB fab house (They mostly stuffed boards, so were not really 
a PCB mfr. Had the spray etcher to be "complete" I guess.) 

Nothing special about it. Again boards/panels held vertically, with 
SS spray jets on each plexiglas side--might have been polycarb 
instead of acrylic? It WAS clear--and about 2' high by 3 feet wide 
and about 4-6 inches thick The spray nozzles were on about 8 inch 
centers The spray form was a flat cone, and they overlapped about 1/3 
cone. (So there was a spray line about every 2-2/3 inches)

I'm pretty sure it had a back and forth motion to the board holder; 
kinda like Markus Zingg's THP line setup, only 90 degrees turned Like 
duck decoys at an amusement park shooting range.

The etchant was clear (AP?)

Worked like a charm; but took up too much space for him so he sold it.

So the second question is, since we know spray etchers work, why are 
they so hard to duplicate?

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:
> On Fri, 15 Apr 2005 18:09:02 -0400, Alan King <alan@n...> wrote:
> 
> >
> >    Nope, would take some tests.  Just a flat plate in the bottom 
corner  
> > leaning
> > in at an angle should give an idea.  Just occurred to me off the 
top of  
> > my head
> > that the bubbles are giving less action from spreading out 
horizontally  
> > and
> > joining together as they rise when I read your last message.  A 
wedge  
> > pushing
> > them back towards the board should do a lot for it.
> 
> 
> Well, while it sounds like a good idea, it needn't necessarily 
really work  
> ;-) .
> 
> I think the bubbles will not stay attached to the board, unless you 
can  
> get that wedge very, very close.
> Which might actually work, like making the gap smaller than bubble  
> diameter. the flow of etchant is pretty high from the bubbles so it 
should  
> stay fresh.
> 
> 
> BUT this needs experimenting, and i can not just make the walls of 
the new  
> tank sloped a guessed angle.
> I think it is easier to make the tank straight and insert plastic 
plates  
> at a later time. It could be like a upside-down funnel shape at the 
bottom  
> of the board, herding all bubbles through a small gap between pcb 
and the  
> bubble-guide.
> 
> A possible problem i see with this is that one would need a very 
precise  
> board holder, if the board is not centered precisely it will cause 
trouble.
> 
> ST