Hj. Tai et al., Synthesis and properties of a low hygrothermal stress epoxy molding compound for electronic encapsulation, POLYM COMP, 21(6), 2000, pp. 953-959
A vinyl siloxane-modified cresol novolac epoxy (CNE)/cresol novolac hardene
r (CNH) molding compound with both siloxane and epoxy components capable of
further crosslinking is synthesized. Through careful adjustment of TPP dos
age, the Tg of CNE/CNH resins can be effectively controlled. The VS-modifie
d CNE/CNH compound possesses a lower Young's modulus, a lower linear coeffi
cient of thermal expansion (LCTE), and a higher break strain than those of
its unmodified counterpart. The combination of lower mechanical moduli and
lower LCTE results in a 33% reduction in thermal stress caused by thermal m
ismatch. In addition to thermal mismatch, chemical shrinkage in a molding p
rocess is also an important factor that affects the interfacial strain betw
een a compound and a substrate. The incorporation of vinyl siloxane (VS) in
curs a 25% reduction in the equilibrium moisture uptake and a 16% reduction
in the coefficient of diffusion for the VS-modified compound. This modifie
d compound can help alleviate the popcorning problems in IC packages result
ing from hygrothermal stresses.