Homebrew PCBs

>I've got access to an XRay developer machine and was wondering about 
>this... The Film is pretty large so If at all possible I could make a PCB 
>1' by 1'
>or bigger but thats the biggest size of paper we got...

     Maybe...
     -Since the silver halides in x-ray film retain their inherent 
blue/UV sensitivity, you'd be able to expose the film without having to 
blast them with the x-ray machine. They may also have a sensitivity to 
green or other wavelengths, see package notes regarding phosphor screens, 
etc.

     -Most (not all) x-ray film has a sensitized emulsion on both sides 
of the film. This helps to increase density and contrast to improve 
viewability. This may be an advantage, or may not.

     -X-ray film tends to be fairly high-contrast, which would be useful 
for litho masks (the thing you'll use for your pcb exposure), although it 
may not be dense/black enough.

     -X-ray films typically have a pretty thick substrate, which makes 
for easier handling but could cause problems with double-sided emulsions 
and fine circuit traces. If you want to remove some emulsion from one 
side, straight chlorine bleach will eat it right off developed or not.

     -You *will* have to experiment with both exposure and development 
times, but x-ray developer chemistry is very similar to, if not the same 
as, regular black/white film chemistry. The fixer might be a little 
stinkier. Cut up a sheet and try different exposure/development times.

     You'll probably get better results with clear film than any sort of 
paper.

     If you can get the film, especially if they toss it because there's 
a code date (it's most likely still good), give it a try. The main 
difference between x-ray and photo film is the sensitization to x-ray 
wavelengths, and I have shot 8x10 x-ray film in a big camera. It *did* 
tend to be a bit grainy, so film resolution (the finest detail that the 
film can render) might come into play.

***
     Craig, I'm not sure who, if anyone, is still making litho film, but 
if you can get hold of some surplus imagesetting film it should do the 
trick. The backing tends to be thin, but it has very high resolution and 
nice density - it's litho film, after all. I have some of the red 
sensitive stuff (RLD = "red laser diode"), and dealing with the big roll 
in the dark green safelight (aka: the green darkness) is kind of a pain 
but better than total darkness.

     -Gary