Ben Davis wrote:

> ...So now I'm confused.  Does the chart indicate the rise of the trace
> temperature or does it indicate the rise above ambient of the environment?
> Perhaps someone from the IPC committee that worked on the 275 (Gary are you
> there?) could comment and/or elaborate on the charts...

Note 3 of figure 3-4 says:
"For general use, the permissible temperature rise is defined as the
difference between the maximum safe operating temperature of the laminate
and the maximum ambient temperature in the location where the panel will
be used."

I agree that this and the other notes could have been written in a less
ambigous way, however it seems evident to me that what you are seeing
as you look at the chart is that as the current rises the temperature
of the trace rises.  The trace itself is the only thing defined in even
the most superficial of ways here.  There is nothing said of the rest of
the environment (ie: thermal mass of surrounding parts, thermal conductivity
of the enclosure, air flow or heat transfer efficency, etc...), so, to
me, I don't see how any chart could ever hope to map the rise of the
ambient temperature due to current changes in a given conductor.

I would also welcome any comment from Gary or other authoratative source.
Or maybe just anyone with an opinion. :-)



      ____      [log in to unmask]   "Nudists are people who wear
     (.)(.)     voice: (512)251-2341      one-button suits."
--000-(oo)-000--fax:   (512)251-0498                 --Anonymous