In a message dated 12/31/2002 10:03:08 PM Central Standard Time,
ghidera2000@... writes:
> Are the trace sizes I see on boards as big as they are simple due to
> limitations in the pcb making process and not for
> carrying current?<<
Yes! I think I heard, once, that 0.01" wide is about the practical limit for
small. I have SEEN formulae for calculating the minimum copper-width per
amp, but it was quickly clear that I'd never be working with currents
approaching those where calculating copper-width was necessary, so I did not
memorize, so, have forgotten.
>
> What trace sizes do you generally use for TTL circuits?<<
Surely, even 0.01" wide traces would be sufficient for even maximum fan-out
from TTL. However, not only for current-capacity, but to reduce EMI effects,
wider traces than that, say, up to 0.1", might be adviseable for Vcc traces
(+5VDC) for a dozen TTL IC's, particular "board ground-buss traces". But
"one-each" NON-solder-plated (i.e., "copper-only") traces? I'd want at
least, oh, 0.025" wide, as the integrity of the conductor would be tenuous,
if narrowerer, for home-brew!
> And actually, while I'm at it - what pad sizes do you like to use?
> PCB123's default pad size is 0.05 inch. Seems pretty small to me but, I'm
> just a noob :D <<
For my own "one-each" NON-PTH home-brew boards, I'd want a pad at least .065:
dia., as it is usually difficult to get registration just-so, so that the
hole doesn't sever the circumference of the pad when registration is clumsy
(been there, done that!). However, the couple of times in the past when I
have had professionally-made boards made, and I have used Bishop Graphics and
all that, and 2X artwork, and all is on a "guaranteed grid" of 0.025", then
0.05" dia. pads would be fine for something tiny like IC pins or 1/4 W. R's,
etc. There is nothing finer than the "wicking effect" of a solder-plated PTH
board! The pad COULD even be as small as, say, 0.01" larger dia. than the
hole-dia.! BUT, when we are talking about NON-PTH, you need SOME copper
there for the solder to adhere to, to make a "metallurgical bond" which will
conduct electricity! (Yes, surprise! That's what a PCB-trace is FOR!).
Took me some decades of tinkering and breadboarding to learn it, but for more
than two or three IC's and the usual amount of discretes therewith, a
"one-each" PCB is just too much hassle! Thus, the attraction of wire-wrap!
I agree, however, for just one to three IC's, often even a "one-each" PCB is
nicer. Or, if you have to make ten or more of "same board", then PTH
professional is the way to go. Whew, if I were 17, again, and knew all I
know now, of such home-brew hassle, I could be a whiz with a much nicer
personality!
Jan Rowland, old Troll
Any trouble soldering on pads that small?>
>
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