--- In
Homebrew_PCBs@yahoogroups.com, "Steve" <alienrelics@...> wrote:
>
> --- In Homebrew_PCBs@yahoogroups.com, "James Bishop" <bishopaj@> wrote:
> >
> > This gave me an idea.. I wonder if it would be possible to replace the
> > laser diode in a laser printer with a uv one, and then run a
> > sensitised board through in place of the drum..
> >
> > What do you guys think? Am i crazy?
>
> Not crazy. I recall a past conversation on this but don't recall the
> outcome.
>
> I suspect exposure time would be a problem. Photoconductor drums are
> very sensitive, whereas photoresist is not.
>
> Aha... found something relevant. Someone calculated how much exposure
> time from a 2mW UV laser diode. Says approximately 25 seconds per
> square cm minimum. Way to slow for a laser printer. High sensitivity
> photoresist would require darkroom procedures.
>
> http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/1933
>
> It would also take a very large change in the mechanics of a laser
> printer. A laser printer works by shining laser or LED light onto a
> charged photoconductor drum, which causes charge to drain from the
> exposed areas. The unexposed, still charged areas then attract toner
> from another roller, then the paper is rolled across the
> photoconductor drum with a high voltage behind the paper to attract
> the toner to the paper. The paper then has a hot fuser roller melt the
> toner onto it.
>
> It seems that direct inkjet conversion would be much simpler,
> comparatively.
>
> But don't let anyone stop you from trying! There used to be lots of
> nay-sayers about direct inkjet printing, some of them quite vehement.
> All it really took to happen was the advent of pigmented ink and for
> someone to keep trying.
>
> Steve Greenfield
I'd expect the optics to be a bit of a trick. Note that the laser
diode in a laser printer is scanned, usually via either a rotating
mirror or a hologram, across the photoconductive drum. Trying to
focus a UV LED, and keep it pinpoint sharp as it traversed the
different distances across the face of the drum, might be a bit of a
trick (especially since UV is mostly invisible, and since some glass
lenses tend to not do a good job of transmitting UV). It could, of
course, be made to work, given a sufficient design, but there'd still
be concerns about the resolution causing broken traces.
I'd think that it might be easier to simply mount a UV LED on an
X-Y plotter, and "draw" the design onto the PCB directly. Of course,
you'd have to control the slew speed of the "pen" to ensure that
all areas were adequately exposed. And, there'd be some optics
design that would be needed, but this would be simplified since the
distance from the UV LED to the photosensitized board would remain
constant. Plus, you'd need to rework the pen up/down solenoid so
that it controlled power to the UV LED.
If you really wanted to get fancy, you could probably work up some
interchangeable apertures for the UV LED to allow plotting different
sized lines (If you really wanted to get fancy, you could work this
into the pen up/down solenoid control.).
Of course, this is basically reinventing a photo-plotter, which have
existed for decades.
Dave