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

A vinyl siloxane‐modified cresol novolac epoxy (CNE)/cresol novolac hardener (CNH) molding compound with both siloxane and epoxy components capable of further crosslinking is synthesized. Through careful adjustment of TPP dosage, the Tg of CNE/CNH resins can be effectively controlled. The VS‐modified CNE/CNH compound possesses a lower Young's modulus, a lower linear coefficient 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 mismatch. In addition to thermal mismatch, chemical shrinkage in a molding process is also an important factor that affects the interfacial strain between a compound and a substrate. The incorporation of vinyl siloxane (VS) incurs a 25% reduction in the equilibrium moisture uptake and a 16% reduction in the coefficient of diffusion for the VS‐modified compound. This modified compound can help alleviate the popcorning problems in IC packages resulting from hygrothermal stresses.