At 09:13 AM 2/3/99 -0500, you wrote:
>Me too! And I'm talking black tape; not that new fangled red and blue
>stuff...
Red/Blue was an idea whose time came when it was already a bad idea. But it
was better than the amazingly obtuse practice of making separate artworks
for each side of a board, which would never have started up either if PC
Designers had been familiar with regular (paper!) printing techniques.
I.e., register pins, with padmaster artwork. Red/Blue required very finicky
camera work, I understand. I did it once, because I was a new designer and
the client asked for it. What a pain!
I eventually settled on designing on mylar (1-side frost) with pencil and a
mylar layer for each layer of the board, plus an "assembly" layer which had
component outlines, designators, and pads, all drawn moderately roughly. I
did up to 8-layer work this way. I had a grid below my mylar; the pencils
were just approximations of where I wanted the traces to go.
When the design was done, or at least looked done, I would make a padmaster
on clear, heavier mylar, from the original assembly layer. Pin register was
set up and a dupe made on a diazo machine (the dupe was exposed,
pin-registered, in a glass frame put in the sun for a few minutes). My wife
at the time eventually persuaded me to put the diazo machine out in a
laundry room.... I would also number all the vias on the assembly layer,
and I made dupes of the pencil trace layer drawings. The originals went to
someone, usually an artist I hired, who would realize the actual taped
pattern; and the dupe padmaster allowed more than one person to do this at
a time. The dupe pencil drawings were converted to a net list by a team of
children. My children. I had written a program in Basic which ran on a
Commodore VIC-20, to take the individual layer netlists and merge them into
a complete net list for the board. Anyone remember the VIC-20?
The complete net list was then marked off on copies of the original
schematics.
The process was *very* reliable, even more reliable than some present CAD
schemes unless someone really checks the CAD net list against a printed
copy of the schematic. All too often, schematics have invisible or subtle
errors that can be easily overlooked, like +12V on one sheet and +12 on
another.
I never had to do an SMT board this way, but the process could have been
adapted. But 2-thrus were a pain to do at 2:1, and 4:1 artwork had its own
problems, not the least being transporting them.
I did not go to CAD until 1988 or so. Never looked back, never again picked
up an Exacto knife to do PC work. I don't particularly miss getting blood
on the designs....
Interestingly enough, it was fairly routine for me to do 200 IC designs
this way, and pretty quickly. When I went to CAD, by some miracle, my job
mix changed and I was only doing relatively small designs. The one
exception I can remember was really a nuisance on a 286 PC. Now, with
faster computers and better software, large designs are not a problem.
[log in to unmask]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433
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