What you want to do is not to *focus* the beam, but rather to "collimate
it". A focused beam comes together at a single point because all the 'rays'
are angled together. The rays in a collimated beam are all parallel to one
another.

With a collimated beam you could have multiple apertures to get different
line widths/pad shapes, very much like the old photoplotters.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Vern Jones" <soundres@FOOTHILL.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, January 13, 2003 2:47 PM
Subject: Re: [EE]: Direct UV plotting PCBs?


> A way to do this would be to enclose the led in a fixtire with the beam
> focused through a pinhole at the point where the beam would emerge from
> the fixture. Maybe a .25mm hole that would be above the surface of the
> board by a few microns. paint the inside of the LED fixture black to
> minimize reflections...
>
> Vern Jones, Sound Research http://www.foothill.net/~soundres
>
> mark@MBCC.CO.UK wrote:
> >
> > I think that using a UV LED as a plotter pen is a fantastic idea in
theory and certainly a project that I would attempt myself if I could
overcome a few problems I can foresee:
> >
> > > ... The beamwidth is
> > > 10 degrees for the narrow ones, which (if I've calculated correctly)
would
> > > give 0.4mm line width at 2.3mm ( (0.4/2) / tan(10/2) ) off the board
> > > surface.
> >
> > Your 'beam' would presumably need to be as narrow as the narrowest track
you wish to
> > Regards,
> > Mark Brown
> >
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