Homebrew PCBs

"Mike Young" <mikewhy@...> writes:
> Has anyone measured the UV transmissive density of their artwork?
> One would think Laserjet toner should be opaque "enough", and
> dye-based ink jets will have difficulty achieving the required
> density. Is it a for sure certainty that laser printers should have
> no difficulty?

The disadvantage of laser printers (at least, based on looking at it
under a microscope) is that it's made of dry particles, so you don't
get a smooth opacity.  Ink drops, no matter how fast they dry, will
tend to pool together, resulting in a smoother mask, or at least
smoother edges.  My TT results always gave irregular edges.  Plus for
my laser printer at least, the imprecision of the toner transfer to
the paper limits how small a feature I can allow.  My inkjet, cheap
though it is, is still five times more precise than my expensive laser
printer.

Having said that, I was going to run tests with laser printed masks
too.  Hmmm... maybe I'll redo my latest test with a laser printed one,
on vellum (it's cheaper than laser transparencies).

Worst case with any of these, you run the test I just ran with a given
printed mask, and choose the exposure that puts you in the middle of
the sweet spot for results.  If your mask isn't opaque enough, you'll
just have to use a less-than-ideal exposure to avoid risking defects.