Synthesis and properties of a low hygrothermal stress epoxy molding compound for electronic encapsulation

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.