Steve-
One of the tests that I perform on reflow systems when I evaluate them is an
IC internal temperature test.  I have a board with a QFP84 mounted on it.  I
have drilled down to the die and attached a thermocouple to the die with
conductive epoxy and filled the hole up with non-conductive epoxy.  I also
attach a thermocouple to one of the lead/pad interconnects of that device.  I
run the board through a typical profile and observe the difference between
the lead/pad interconnect temperature and the internal temperature (of the
die).

Some of the older Convection/IR systems, particularly those with a high
amount of IR (such as the lamp systems) would take the internal temperature
above the lead temp. though some did not.  Of all of the "newer" Convection
Dominant (Forced Convection) reflow systems, all of them allowed the die to
remain cooler than the interconnection - usually by at least 10 deg. C or
more.  Only one machine (no longer in production) brought the die up to
equilibrium with the lead.

Hope this helps.

Phil Zarrow
ITM, Inc.
Durham, NH

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