Michael,

It's unlikely anyone could give you a generic model that would give you
what you want. You'll need to determine the heat transfer rate through
and out of the specific board construction you're using, as well as the
aggregate heat capacitance. Since your looking at a short time, on an
inner layer trace, I suppose you could assume "infinite" insulating
conditions to get a feel for the worst case.

When I did my heat rise software I had to create a model for one very
specific combination of materials and layers. To be accurate you'll have
to create a model and do Thermal FEA. An even better approach would be
to build a board with a buried thermocouple and get some real-time
measurements.

You may want to take a look at my circuit heat rise and flex thermal
analysis programs at:
http://www.geocities.com/CapeCanaveral/Launchpad/9641/program.html

Andy Magee
Flex Guru - Consulting
[log in to unmask]
(937) 435-3629

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