The delta Tg is regulated in PCB manufacturing spec., but for IC substrate
there is not any spec. include this item. It is often 2-4 deg C. Also I
found the delta Tg measurement methos in IPC-TM-650 2.4.25. The IPC spec.
suggest that not apply this method on BT, polyimide materials, because they
may increase Tg further during measurement procedure.

However, I measured the delta Tg of substrate which made by BT core (4
layer substrate). The delta Tg is roughly 20 deg C in the first time. The
second run on the same sample is down to 4-6 deg C, and get smaller and
smaller for 3rd and 4 th run.

My questions are:

1. How can we know the curing extent of BT will noe affect the IC package
reliability? What is the best delta Tg we can accept, after substrate
manufacturing and after IC assembly?

2. Does anyone knows any spec. or any substrate supplier have this
regulation?


If you have any question or further discussion, please let me know.

Enigma P.

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