Homebrew PCBs

That is a great "Hi-Tek" idea.

BUT, I subscribe to the K.I.S.S. method... keep it simple

I used to work in a professional PCB manufacturing lab and they also 
did things the simplest and cheapest ways.

For double sided PCBs you take both films (top/bottom) and register 
them together. Tape a scrap piece of PCB material to one edge. Now 
you have an exposure "set". All you need to do is slip in the PCB 
into the "set" and expose. We had a top/bottom exposure frame, lights 
underneath and in the lid.

We found that certain acrylics transmit the UV better than others. 
Quartz is the best, but extremely expensive. Lexan BLOCKS UV totally.
Glass works, but not as well as the acrylics. The only problem with 
acrylics was that it needed to be replaced occasionally since it 
would become "crazed" and brittle after a while.

John M...
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--- In Homebrew_PCBs@yahoogroups.com, Neil <cobra_neil@a...> wrote:
> Alright, call me crazy, but an idea just occurred to me, and I 
can't see why 
> it can't work.  To me, the most difficult (expensive, complicated, 
> unreliable, etc) part of creating a PCB is getting the pattern laid 
out on 
> the board so it can be exposed, etc.  The rest is science ... 
standard 
> procedure, standards times, standard results.  Yes, laying out the 
pattern 
> can be science, but at a higher price, and still takes time to line 
up the 
> image transparencies, etc.
> 
> So this idea just randomly came to me ... why not use a projector 
to project 
> the image on the board.  Use a positive-coated board and an XGA LCD 
> projector, with a UV bulb instead of the usual bulb.  I get quite 
good 
> results at 300dpi, so if we go with a projector resolution of 
1024x768 for 
> now, that's about 3.4" x 2.5".  There may need to be some optical 
> manipulation done to get it to focus clearly at that distance, and 
a bunch of 
> other little things sorted out (such as calibration for 
> non-linear/inconsistent pixel spread), but I can't see why it can't 
work.  
> No, it's not cheap, but I believe it would be really fast, going 
from 
> computer straight to PCB.
> 
> Maybe this has been thought of or done already?  Or maybe I'm going 
off the 
> deep end?
> 
> Cheers,
> -Neil.