Sorry for the late reply. I received the emails as a digest.
Thanks DJ for the answers to my question. I have been building PCB and Assemblies professionally for over 35 years, so I knew about the ink side close to the copper in order to limit diffraction of the light during exposure. That's why I selected to use an old scanner to do the exposure. The film is resting on the glass with the ink up, the PCB is then pressed against the film by the cover of the scanner. Seems to be working great so far. I am going to redesign the line of UV LEDs to have 8.5" capability which is the size of the scanner glass.
I will post pictures when I am done with the final version.
Jean-Paul
--- In Homebrew_PCBs@yahoogroups.com, DJ Delorie <dj@...> wrote:
>
> The R320 is limited to 1440 DPI (well, 5760x1440 but square pixels are
> nice) but that's probably still more resolution than needed for what we
> can home-brew. The R280 can do 5760x2880. Anyway, if your existing
> print software can be told to print at 1440 dpi, and your EDA software
> can produce a print of that resolution, you should be all set. The
> interesting factor will be if the print software can be told to put down
> more ink than normal (choose ultra glossy film if you have a choice).
> My software uses the smallest drop size but 100% coverage (no dithering
> or halftones).
>
> An unrelated thing you might think about is how you're holding the film
> against the PCB. I only get good results if I (1) print the film in
> reverse, so that the inked side is against the PCB, and (2) use a vacuum
> to hold the film tight against the pcb (gravity won't work).
>
> With a decent film (jetstar, silkjet, etc), high enough resolution, and
> enough ink, you should be getting jet black prints with crisp edges.
> With something to hold the inked side tight against the PCB, you should
> be getting crisp edges on your etch resist too.
>