Homebrew PCBs

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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