I've recently taken the plunge in this area myself because I wanted to make
my own H-bridge/control boards for small robots. I did quite a bit of
research and followed the path that appealed to me from the many choices
available. Rather than transparency film or acetate you can try tracing
paper. The standard weight is 90 gsm but 120 gsm is better if you can find
it. Tracing paper is sufficiently transparent to UV radiation for this
process. The Jetstar film is an interesting product, however. I bought the
MG Electronics (also located in the UK) UV lamp, as well as some of their
chemicals. The UV spectrum output is centered at 375 nm. It's cheesy, but
exposure frames are very expensive, especially for hobby work. A good
alternative is a used small tanning station if you can find one cheap. I was
tempted to build an exposure frame but cost-benefit considerations decided
against it, at least for the present. I've never found an accurate kitchen
timer so I bought a used darkroom timer. An alternative might be an
appliance timer but after searching online I couldn't find one suitable for
my purposes. BTW, Seichi Inoue, who has been mentioned in the past, I
believe, has an interesting homebuilt countdown timer for just this sort of
thing.

You don't need a red darkroom lamp to fasten the artwork to the
pre-sensitized board (cut to size) because the board is not as sensitive as
film, however, you do need subdued light and you might want to use a yellow
bug lamp or gold fluorescent lamp for this step.

Single lamp exposure times can be as high as 20 to 50 minutes, depending on
the type of lamp used and the distance from the lamp to the board. You *can*
use sunlight but it doesn't allow much control of the exposure. Exposure
times are on the order of 20-25 seconds in very bright conditions and you
have to be careful of bleed-through. You really need a light meter to
determine exposure times if you go this route. You might also need a light
meter to calibrate your setup using a UV lamp but once that is done you
don't need the light meter again. As an alternative, if you already have
some idea of the correct exposure time you can sacrifice a small strip of
board to make a step exposure reference, which should be marked and filed
for future reference.

As for wasting a sheet of transparency film: print artwork on ordinary
paper, lay a sheet of film over the print and mark boundaries, cut just the
portion of film you need, align and tape to a fresh sheet of paper and print
on that. For small boards you can probably get four (or more) prints per
film sheet this way.

As for other and cheaper methods, there is dry transfer and drawing the
artwork on the board with a Sharpie ;)

Cheers

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf Of
Peter Onion
Sent: Sunday, July 31, 2005 5:25 AM
To: Microcontroller discussion list - Public.
Subject: [EE] PCB newbie needs advice please.

While I've been building electronics projects for over 15 years, I've
never taken the step of moving from hand wiring on stripboard to making
my own PCBs.

However I now want to produce a number of simple PIC boards to
experiment with a network of communicating PICs, so it seems the right
time to investigate making my own PCBs.

<snip>
Peter Onion

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