Tom,

The thermal properties of PCB materials are dependant on the resin type
and glass content (I expect the electrical properties will also). Most
materials suppliers are still very poor at providing relevent materials
properties despite the use of simulation systems such as you described.

We have just measured some 1.6mm MAS FR4 material to have an SHC
varying from 1300J/kgK at 50C to 1650J/kgK at 130C (then remaining
constant up to over 200C). 

Thermal conductivity is orthotropic, but in general though thickness
temperature gradients are relatively small so the in plane (XY) figure
is most important (and is usually much more important than SHC). It is
also difficult to measure accurately. We tend to use a textbook figure
of 0.25W/mK.

If anyone else has any more data they are prepared to share I would
be prepared to create a WWW page collating the data.

David Whalley