See inset notes below.

-----Original Message-----
<snip>
1. What is the "glass transition" ? What is the glass transitioning from and
to? I'm guessing it's the plastic stage that occurs in a material just
before it melts.
        > Glass transition refers to the point where the *epoxy* goes from a
glass-like state
        > to a highly plastic state. There are drastic changes to the
materials mechanical
        > properties at this point and some can cause PCB failures.
2. What is gained by a higher Tg in tetrafunctional and multifunctional
epoxy-glass?
        > Higher Tg materials are needed for applications where thermal
excursion (rapid                > temperature changes or wide opperating
temperature range)occur
3. What is meant by the prefixes "tetra" and "multi" as they're applied
here? Is it a reference to the number on bonds in the chemical structure of
the epoxy or glass?
        > Di-, Tetra-, and poly- or multi-functional are references to the
bonding structure
        > of the epoxy.


<snip>
Jeffrey A. McGlaughlin, C.I.D.
Sr. PCB Designer
Battelle Memorial Institute
Columbus Ohio
[log in to unmask]

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