Synthesis and properties of vinyl siloxane modified cresol novolac epoxy for electronic encapsulation

Vinyl siloxane (VS) modified cresol novolac epoxy (CNE)and cresol novolac h ardener (CNH) resins are synthesized and both components are capable of fur ther crosslinking. The reaction kinetics for both components are studied so that they can crosslink simultaneously in a designed synthesis procedure. Through careful adjustment of a triphenylphosphine dosage, the glass-transi tion temperature (T-g) of CNE/CNH resins can be effectively controlled. Phe nomena characteristic of the existence of a diffusion-controlled reaction a re also observed. The relationships between the T-g and crosslinking densit y for the CNE/CNH resin are explicitly revealed through gel content and swe ll ratio experiments. CNE/CNH resins with a higher T-g have lower equilibri um moisture uptake because of the higher fraction of free volume. The coeff icient of diffusion also shows a similar but less apparent trend. The incor poration of VS incurs a 35% reduction in the equilibrium moisture uptake an d a 20% reduction in the coefficient of diffusion for the modified resin. T he VS-modified CNE/CNH resin possesses a lower Young's modulus and a higher strain at break than its unmodified counterpart does. This modified resin can help to alleviate the popcorning problems in integrated circuit package s, which results from hygrothermal stresses. (C) 2000 John Wiley & Sons.