Synthesis and characterization of poly(epoxy-imide) crosslinked networks

Poly(epoxy imide)s were prepared by a reaction between a hydroxyl-group-containing soluble copolyimide and commercial epoxy resins at 220°C for 2 h. Poly(epoxy imide) thin films exhibited higher thermal stability and lower dielectric constants than a commercial flip-chip package material (U300). The thermal stabilities of the poly(epoxy imide)s were 1.4-2.0 times higher than that of U300. The thermal stability increased with increasing crosslink density and with decreasing bulky CF₃ groups (which were easily decomposable). The dielectric constants of the poly(epoxy imide)s were 1.1-1.3 times lower than that of U300, and this is highly desirable for the microelectronic packaging industry. The dielectric constant dramatically decreased when bulky CF₃ groups were added and when the functionalities of epoxy resins decreased. The residual stresses, slopes in the cooling curves, and glass-transition temperatures of the poly(epoxy imide)s were measured with a thin-film stress analyzer. Low residual stresses and slopes in the cooling curves were achieved with a higher crosslink density. However, in the presence of bulky CF₃ groups, the copolyimide backbone structure did not affect the residual stress values.