Hi Brian,
You not only have a variabilityof the Tg, but the Tg is a single number
locating a temperature range of about 45C over which the transformation
actually takes place.
This becomes important fot accelerated reliability testing of SMT solder
joints; you can not characterize the lading on the SJs if you run your test
temperature into this Tg-range. Thus, I recommend that the top cycle
temperature be Tg minus 25C.
Werner Engelmaier

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