--- In
Homebrew_PCBs@yahoogroups.com, "Leon Heller" <leon_heller@h...>
wrote:
>
>
>
> >From: Neil <cobra_neil@a...>
> >Reply-To: Homebrew_PCBs@yahoogroups.com
> >To: pcblist <Homebrew_PCBs@yahoogroups.com>
> >Subject: [Homebrew_PCBs] I have a dream...
> >Date: Fri, 23 May 2003 03:36:00 -0500
> >
>
> Even better would be something like a home-made laser plotter with a UV
> laser plotting directly onto the resist-coated PCB. Send it the
Gerber file
> and take out the exposed PCB a few minutes later, into the developer
and
> etchant, and one has an etched PCB. That's what I dream of!
>
> Leon
It would appear that several people are thinking along the same lines.
The LCD screen idea occurred to me (either with changing the
backlighting to a UV source or using one of the older overhead
projector LCD screens), as did using a TI Digital Mirror Device
(something that looks like it might already be in the works at some
companies for some photoprocessing equipment and PCB manufacturing).
Given the resolution needed, obviously you'd probably want an image
that could be stepped across the board -- no single DMD has sufficient
pixels to cover a good-sized board with thousandths-of-an-inch resolution.
As for the laser idea, well, that's something I've been thinking about
a lot lately, too. I recently dismantled a malfunctioning Laserjet
III and obtained the laser diode scanning assembly; replacing the
laser diode should be easy enough once Nichia and others start
mass-producing them, although I'll need to ask HP whether the optics
will pass UV light and focus it sufficiently.
The challenges would be installing the scanner on a precision-motion
shuttle with some sort of stepper motor for moving the laser down the
PCB as each line is "drawn" (maybe using the original LJIII stepper),
correctly spacing the optical assembly for accurate to-scale imaging
for several thicknesses of copper-clad board, and controlling the
whole deal based upon image or gerber files. It would also be nice to
know whether the laser scanning assembly is actually capable of
1/600th of an inch (or better) spot size focusing.
It would be necessary to slow down the laser scanning from that used
in the original LJ III; with a 2 mW laser and reasonably sensitive
(e.g. 50 mJoule/cm^2) photoresist, covering an entire board could take
more than an hour (25 seconds per square centimeter, give-or-take).
Of course, if one used higher-sensitivity resist, one could go faster.
It would be nice to be able to adjust speed to compensate.
I guess if I make it work, I'll let you guys know :)
Jonathan