DSC (differential scanning calorimetry) measures heat transfer to and from
the sample (at a programmed heat rate).  From what I understand, DSC will
give a broad range from the onset to the offset of the transition. Tg is
normally reported at the midpoint of the transition (peak at tan delta).
Laminate manufacturers use DSC because it's a cheaper piece of equipment
and it gives the broader glass transition range.

We don't specify Tg, we specify the onset temp.  We don't want our boards
getting soft and more flexible in their operating environment, and the
onset temp is the beginning of the transition.  Since DMA (Dynamic
Mechanical Analysis) measures modulus, it is more sensitive to changes in
the stiffness of the board, which is what we are concerned with.

TMA will measure the change in dimension (CTE) during heating.  The values
for CTE are lower below Tg and are higher above Tg for the laminate.  If
you are concerned with delams caused by the difference in CTEs, TMA is a
good tool to use.

Lynn Norman

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