Avi,
You could use a non-contact setup like an equipment made by Quantox.  It
deposits a corona charge on the film and uses a Kelvin probe to measure the
capacitance.  If you already know the phyisical thickness, you can derive
the dielectric constant.

I am not sure if you would call this a true "physical measurement".
Goodluck.
Jaideep

At 04:41 PM 4/21/99 -0700, you wrote:
>     Hello all,
>
>     I am currently working with 15 micron thick, spin-on polyimide films.
>     The films are hard-baked following patterning. Since these films are
>     for a microwave/RF application (I'm fabricating tranmission lines on
>     the polyimide, substrate is Si), I'm interested in measuring the
>     dielectric constant and dielectric loss tangent for these films,
>     following the curing step. I would like to know the variation in
>     dielectric constant, loss tangent as a function of curing times,
>     temperatures, etc...
>
>     As far as I know the easiest way to do this is to fabricate a
>     capacitor, with the polyimide as the dielectric and perform
>     measurements usings the C-V meter.
>
>     An alternative approach is to fabricate transmission lines, measure
>     S-parameters, and extract the dielectric constant from the data...
>
>     I'd be interested in performing an actual physical measurement, if
>     possible, rather than rely on a functional device/component...
>
>     Any suggestions would be appreciated...
>
>     Thanks,
>
>     Avi Kane
>     Raytheon Systems Company
>     askane@west.raytheon.com
>
>
>