I made a few photographic resist boards long ago, some in positive presensitized boards, some were sprayed by me with negative resist. I didn't have to spin the boards, just sprayed an even spray in a couple of thin coats.
I used an incandescent 75W "Gro" light, sounds like just what you describe. Takes a little longer than a brighter UV source, but that just makes the timing less critical, too.
I found the proper timing the old fashioned way - cover all but 1/10th of the board, expose for 40 seconds, move the cover to expose another 1/10th, after 10 seconds move it again, etc so I have 40, 50, 60, 70, 80, 90, 100, 110, 120, and 130 second exposure times. Then I used that info to refine and then shot for the center.
Hand-taped using drafting tape and rub-on patterns for positives. For negatives, I drew the outlines in drafting pen and filled in by hand.
Boards looked great. Made a few dozen that way. I often avoided drilling by using the semi-SMD method, clip DIP leads off just a little proud of the bottom, same with resistor leads and solder to the copper side. A few boards I used real SMDs.
Steve Greenfield
--- In Homebrew_PCBs@yahoogroups.com, "RDHeiliger" <rdheiliger@...> wrote:
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> I use a sun lamp in one of those aluminum reflector/clip on bulb holders as a uv source. At a foot away the exposure time is about 1 1/2 minutes for negative dry film. You don't have to build anything. Lay a piece of glass over the film and board for some weight.
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> RD
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