"Bruce W.1" bravely wrote to "All" (04 Apr 05 00:29:55)
--- on the heady topic of " Pattern a circuit board with a computer =
printer?"

BW From: "Bruce W.1"
BW Xref: aeinews rec.radio.amateur.homebrew:9114

BW Dave Platt wrote:
BW There are several.

One way is to laser-print the resist pattern onto a transparency (or
laser-print into paper and photocopy onto a transparency) and then use
the resulting transparency as a photographic mask, exposing a piece of
photosensitized PCB material to UV light through the mask. The
exposed photo-resist is then developed (chemically in many cases) and
the unexposed portion is washed away (or vice versa - depends on the
type of resist) and the board is etched.

Another way is to laser-print the resist pattern (mirrored
left-for-right) on a specialized sort of coated paper. The PC board
material is cleaned thoroughly, the printed paper is placed on the
board toner-side-down and carefully ironed onto the board - the resist
melts and sticks to the clean copper. The board is soaked in water,
and the coating on the paper releases the toner/resist and the paper
washes off of the board. The board is then etched. There are
commercial papers made for this purpose, I've heard of people using
some glossy-surfaced inkjet papers, and some folks even make their own
by brushing a liquid gelatin solution onto smooth paper.

It's also possible to use a flatbed plotter, with a special pen, to
draw resist patterns directly on PC board material.

BW =3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3 d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d=3d

BW I'm familiar with the photosensitized PCB material and UV light
BW method. But this is hardly an at-home kind of thing. I think I was
BW looking for the second method you mentioned.

Sure, it is doable at home. One method similar to the above
transparency is to simply print the pattern on thin tracing paper and
then oiling it. The oil makes the paper transparent and allows
exposure.

The most difficult but important thing in PCB making is to get an
accurate exposure time for the sensitized PCB. The way to determine
this is either with a calibrated UV source, or to expose a test strip.
Use a thin 1/4 " strip of PCB and cover it with a cardboard sheet,
slide the sheet back exposing 1/4" at a time. Use 1 minute increments.
The last segment uncovered will be 1 minute and the 1st will have the
longest exposure. Then develop the strip and note which was the best
exposure time.

I've even made exposures in the Sun. Just one problem I noticed with
this method is that the Sun moves and tends to undercut the traces, so
in the case of a transparency the toner side must go against the PCB
surface as otherwise the small gap allows the Sun's changing angle to
leak under. This doesn't happen so much with a fixed UV lamp. It helps
to do this at Noon so that the Sun's angle changes less and reduces
exposure time. It takes about 10 to 12 minutes in the midday Sun and
it takes about 2 to 3 minutes with a sunlamp, clothes drier UV lamp,
etc... It's a learning experience, good luck!

A*s*i*m*o*v

.... Powdered water -- just add ... hmmm ...