22 Oct
1999
22 Oct
'99
11:51 p.m.
On Oct 22, 15:20, daniel wrote:
Making PCBs at home is a rediculous waste of time. I
have a vacuum
lightbox
here as well as a commercial processing system, a
silkscreening set up,
even
a wave solder machine in my home and nothing compares
to what the big
guys
can do and charge for the same thing.
If you're trying to emulate the way a professional PCB house will make
them, or if you need moderate to large quantities, I suppose I agree. But
for two or three boards, I strongly disagree. I've made dozens, possibly
hundreds of PCBs at home or at work, and it doesn't take that long, nor is
it very difficult. I certainly prefer it to wire-wrap. Of course, you
typically won't be able to get such fine lines, and putting two tracks
between the pins of a 0.1" pitch DIP isn't something I'd do. I wouldn't
consider using a professional PCB company for a one- or two-off unless it
truly was very special, or a prototype for something that later would be
made by the hundred.
I make same-size artwork on a decent laser printer, and expose that onto
sensitized boards. With a little care, registration is easily good enough
for double sided PCBs. It's even possible to do plated-through holes,
though I don't -- I use track pins, because the through hole stuff is
relatively expensive.
My last *production* company use to
make its own prototype doublesided PCBs in house and it wasn't worth it.
I
have a company I use now that will make me a double
sided PCB, GOLD
PLATED
contacts, solder mask both sides (pre-drilled of
course), and silk
screened,
and cut for less than a $1 a board in quantities of
500.
OK, but do they also charge $490 for a one-off prototype? Most companies
here charge according to the number of layers and amount of setup -- and
that's mostly related to the number of plated holes, not board area.
Pre-sensitised boards are useless as they usually come
flawed and the
coating thickness is not consitant. The company I use now for PCBs used
a
"roll" of sentised film that was
"ironed" onto a 3' X 3' board. Far
better
process.
Maybe, but I've never had a problem with pre-sensitised board. Sensitising
it myself with an aerosol turned out to be a less-than-clever idea, though
:-)
Don't forget a good GERBER and NC drill file is
needed and most PCB
manufacturers find little problems with the files that you may not
uncover
in
Most PCB houses here are perfectly happy with 2x size artwork, and many
will accept same-size, possibly with a small surcharge.
Marvin mentioned a number of ways to produce artwork. I've seen most of
them used. Dot matrix printers aren't usually very good in terms of
black/white contrast, nor sharpness (but often OK for x2 camera-ready
artwork). I once discussed using an offset litho press to print directly
onto flexible PCBs, but I don't know if the person I spoke to actually did
that -- it should certainly have much higher resolution than a silkscreen.
And people really do use tape on mylar film (well, maybe not much
nowadays, but it used to be common). Lots of hobbyists over here print
onto acetate or drafting film with a laser printer, and that works pretty
well -- it goes straight into my light box.
Daniel wrote "He drills the boards first, then photosensitizes
them. They get UV, then he develops them in water (I think it was). Then he
electroforms copper to create plate through holes, then tins, then gold
plates, I think then he did the solder mask on both sides (I am sure that
was silk screened) and finally the boards were silk-screened (layout), then
cut." That's a fairly typical commercial method, except it wouldn't be
water development. At home, it would be a weak solution of caustic soda,
but that "goes off" very quickly, so a more esoteric substance is used
commercially.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York