Influence of Crosslinking on Physical Properties

Linear thermal expansion coefficients oL of thermoset resins in mbb y and glassy states are plotted against oCE ) in Fig. 23. A unique phenomenon is ob ed in tltt relation between aL and q(E ) which is reversed above and below Tg. That is, in the rubbery state of thermoset resins with higher q(E ), aL tends to become smaller, while in the glassy state of thermoset resins with lower q(E ), aL becomes larger. 

In Fig. 26, dianges of spedfic volumes of thermoset resins undergoing curing and thermal shrinkage are hematical]y shown. Resins I and II are charactoized h and lower Tg values which result from accelerators giving high and Iowa- q(E ) values, resp rtively. 

According to the th ry of the iso-free-volume a value of fractional free volume 

Important characteristics required for encapsulation matoials, as discussed in Sect. 2, are summarized in the following. 

Thermal stress in encapsulation materials should be intrinsically small in order to prevent occurrence of cracks in packages or passivations layras, dis 4acetr t of aluminum wirings, short circuits between layers, or changes in device performance, caused by the pile-up of thmnal stress in the package. This bectnnes particularly acute with itKreases in packagir daisity. 

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