The only time I've run into constraints with trace width is
with controlled impedence designs.  As a general rule I'm
afraid I'm not that well versed to say.

In regards to your trace width versus trace spacing ...
Trace spacing is determined by voltages on the trace.
If I read your question correctly, the trace can be as wide
as you want as long as the voltage on the trace doesn't change.
In other words, you could have a trace 1 inch wide for current
or temp requirements AND require only an 8mm spacing for voltage
requirements.

Regards,  Doug


JoAnn Amerson wrote:
>
> Once again I turn to you pleading for help.  The "powers that be" are
> requiring us to use a 12 mil wide trace as a minimum unless we
> absolutely cannot because of lack of space.  It seems our board
> vendors have difficulty meeting a width and trace at 8/8.  My pleas
> to look into other vendors fall upon deaf ears.  "They're too
> expensive!", they cry.  So we pay the price over-designing our
> boards.  Our boards are predominantly low current, low voltage.  8
> mil usually is more than enough but......I'm sure you've all run into
> this argument at one time or another.
>
> What I'd like to hear from everyone are reasons why we *shouldn't*
> use a wider trace than necessary - if there are any.  Other than it
> takes longer to route a board with wider traces.  They don't care
> about that.  What documentation can I offer to them to make our lives
> just a tad bit easier?  Or am I lost in wishful thinking?
>
> And also, today's dumb question:
> I know that spacing between traces is governed by voltage and the
> width is governed by current load and temperature rise above ambient.
>  If I use a 12 mil wide trace, can I still maintain an 8 mil wide
> space to the next trace?  Assume it meets the spacing for that
> voltage.  Or is the spacing always at least track width?
>
> I appreciate any and all responses on these issues.  :-)
>
> Jo

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