Hello,
The ""bible" for pcb design is "Printed Circuits Design" by Gerald
Ginsberg. Published by McGraw Hill, I paid 5 bucks for myt copy of
the '91 edition. You can pick up a copy inexpensively at ABEBOOKS.com
or similar.
Another decent book is Tim Williams, "The Circuit Designers Companion"
Ginsbergs book has several nomographs, one of which answers what
you've asked. But there ar additional considerations. Is the trace by
itself--means away from other traces? How much temperature rise can
you allow? Is the trace on an internal or external layer? What is the
copper "ounce" rating?
From page 40, the three nomographs will get you where you need to be.
Assuming external layer, nothing REALLY close by, and a worst case
temp rise of 60 degrees C. 7 amps requires a 70mil cross section.
With one ounce copper, that's a trace about .053 wide... With 2 oz.,
you need .028-.030 width.
At 20 degrees rise, you need 150 cross mils. So that's a trace
about .120 wide in 1 oz. copper. In 2 oz., it's only .060 wide.
Hope this helps,
Ballendo
P.S. Did you try putting "required PCB trace width" into a search
engine?
FWIW, there is a formula, but the nomographs are easier to use. The
formula is in ANSI/IPC D-949
--- In
Homebrew_PCBs@yahoogroups.com, Anthony Toft <toftat@c...>
wrote:
> is there a formula for how wide tracks should be? I need to make
> tracks capable of carrying 7+A at 12v How fat should they be?
> --
> Anthony Toft <toftat@c...>