Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Lyman, congrats on your first photo-board.

You didn't say what your exposure tool was; but at the
1-mil level, you may well be running into effects of poor
collimation; as much as any other factor.

This can be somewhat ameliorated by increasing the distance
between the UV source and the board; but this will of course
reduce the received intensity, by the square of the distance.
(increases exposure time).

Also, many dry-films designed for PCB work will start running
out of resolution in the 1-mil range anyway. They've sacrificed
some resolution in order to gain easier processing, faster
exposure,
etc.. Nevertheless, I think you'll find that real artwork made
by
giving Gerber files to someone with a real laser photoplotter,
will
make a big difference compared to laser-printout, at the 1-mil
level.

If you need to do 1-mil or less on a regular basis, look into
liquid
resists as used by the semi industry. There are dozens, if not
hundreds, of choices. Some serious googling would be in order.

For exposure, I used 8 germicidal flourscent tubes, the 15-20w
size, mounted almost right next to each other; giving me an
active
area of about 12x15". Sockets were mounted in a wooden box
about 8" deep; with the bottom lined with bright aluminum
"flashing"
stock (roofing material).

This setup put the top surface of the socketed bulbs about 6"
from
the glass. This distance is probably a little close for 1-mil
work; but
virtually everything I did was 5-mil or larger; and exposures
were very
quick.... <g>

At that time, the germicidal bulbs ran around $15/each. The last

time I needed some, they no longer carried them at the "home
improvement" stores....I had to go to a lighting-supplier.

good luck with your process
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