Hi Steve,
With the exception of the old lamp-type IR reflow machines, the interior of
components, except very small ones, will be cooler than the exterior. In the
lamp-type IR reflow machines heat transfer is entirely by radiation in a
wavelength range where absorption efficiency is very color-selective (large
differences in emissivity). Even the so-called IR-reflow ovens that have
radiation panels about 50% of the heat transfer is by convection. 
If the component leads are massive, however, the lead temperature and the
leadframe temperature in the component interior could be almost equal. 
In any case, do not use conductive epoxies for thermocouple attachment. That
could falsify your results depending on the geometry.  

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask] 

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