On Fri, 28 Nov 2003 16:30:48 +0000, Dick
wrote:

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??

Basically, you are right, it is relatively simple.

Some standard glass will not pass certain bands of UV. Test first (put
a sliver of the glass partially over some sensitized material for a
standard exposure time and note any difference.)

You may not need the glass if the mask adheres well to the substrate.

You want enough spacing to get reasonably even coverage, but too much
will increase exposure time. Consistency is more important, so you can
develop a standard timing for the unit.

Consider mounting the lights to face down, as a safety precaution.
Also, you might add a microswitch and relay to prevent your box from
lighting up with the cover open. This would be a lot worse for your
eyes than a photocopier.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom