To learn about transparencies, temperatures, and techniques for Toner
Transfer, I took the time to run a series of tests with my hacked
laminator:
http://www.delorie.com/pcb/transparencies/24 different transfers, with comparisons and the original (big) scans
of the results.
Summary (if you don't want to look at all the pictures :)
∗ no matter how hot the laminator is, you need multiple passes
∗ there's a fine line between "stuck" and "squished"
∗ cleaning the board and keeping dust off everything is still critical
(sigh)
∗ preheat the pcb
∗ don't put paper between the film and the rollers after the first
pass. You can probably make do without it for the first pass too,
but it helps keep the film in place. Tape would probably do if you
need to accurately align the film.
∗ you ∗can∗ apply a second layer of toner if you need to, if you can
align it sufficiently with the first.
∗ a mechanical bond is required; if the copper is too shiny the toner
won't stick.