--- In FreePCB@yahoogroups.com, "SapphireGin2" <sapphiregin2@...> wrote:
>
> To what point (or end) should I be concerned with thermal dissipation and
impedance values in the traces on my board? How do I calculate these values?
>
> - The two boards I am designing are 2" x 4" and 2" x 6" in size.
> - I am using some RS-232 and USB stuff mostly.
>
> Greg

The thermal issues depend entirely on your design. But if you aren't doing
anything weird, RS-232 and USB shouldn't require any thermal consideration.

Impedance is a different matter. RS-232 is fine, but USB has requirements for
impedance of the differential pair that carries the signal. I had to design a
board with USB traces once and I never did get it right. They spec a
differential impedance and IIRC a single ended impedance. But the differential
impedance of a pair of traces can be spec'd several different ways and I never
did find a good enough reference to understand all the considerations. We had
all sorts of expensive gear for measuring impedance and it did me no good since
I didn't know what I wanted to measure. The USB signal was full speed, not high
speed and in the end it worked just fine.

The short answer is, this can be complex, but it seems to be tolerant of wide
deviations if you aren't using high speed mode.

Rick