Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

James English <jimenglish123@...> writes:

> Does anyone out there have experience with exposing a photosensitive
> board through a negative to sunlight?

Sunlight is very variable, but in general, anyone doing UV exposure
should have a "transmission step wedge" - this is a plastic film with
various calibrated shades of grey printed on it. Using this, you can
calibrate ∗any∗ UV source and, with a little math, figure out the ideal
exposure time in one trial run.

http://www.stouffer.net/TransPage.htm - you want T2115 as that's the
most common one to see on film specs, and it's only $6.55.

http://www.thinktink.com/stack/volumes/volvi/filmimag.htm#Photo_resist
for instructions on how to calibrate.