Homebrew PCBs

"trevwhite74" <trevor.white100@...> writes:
> Why do you need a vacuum system? Is this to make sure the mask layer
> is tightly against the board?

Yes, it just holds the mask tight against the board.  While the board
and glass are "flat" they're not the same flat, so before parts of the
mask were up a bit, and the exposure was fuzzy, resulting in wider
and/or narrower traces - i.e. shorts and breaks.

> I thought the visual light would show something similar to what
> would be happening with the UV.

Yeah, similar, but consider that the UV is much more intense.  I'm not
sure you can rely on the light/dark pattern you see as a reflection of
what the UV is doing.  I suppose if I could find some day-glo
paper... ;-)

> I have found some superflux UV LEDs that have a viewing angle of
> 100+ degrees so I was thinking I could

Remember that the wider the angle, the more important it is to keep
the mask tight - angled light will get under the mask and expose more
than you intend.  You want the UV source to be as co-linear as you can