Aromatic polyesters were prepared and used to improve the brittleness of the cyanate ester resin. The aromatic polyesters include poly(ethylene phthalate) (PEP) and poly(ethylene phthalate-co-1,4-phenylene phthalate). The polyesters were effective modifiers for improving the brittleness of the cyanate ester resin. For example, inclusion of 20 wt % PEP (MW 19,800) led to a 120% increase in the fracture toughness (K IC ) with retention in flexural properties and a slight loss of the glass transition temperature compared to the mechanical and thermal properties of the unmodified cured cyanate ester resin. The microstructures of the modified resins were examined by scanning electron microscopy and dynamic viscoelastic analysis. The thermal stability of the modified resins was lower than that of the unmodified resin as determined by thermogravimetric analysis. The water absorptivity of the modified resin increased significantly, compared to that of the unmodified cured cyanate ester resin. The toughening mechanism was discussed in terms of the morphological and dynamic viscoelastic behaviors of the modified cyanate ester resin system.

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In flip chip packages, it is common practice for interconnects to be encapsulated with a liquid underfill material. This paper describes the effects of different underfill processes, i.e., the conventional capillary-flow underfill and two no-flow underfill processes, on flip chip packaging. The warpage of the package was examined, and the value of this during three different underfill encapsulating processes was measured. In addition, the interconnect reliability of the bump bonds after thermal-cycling was evaluated using a test circuit. The warpage of the package before curing varied depending on the assembly process, but that after curing was almost the same for all the processes studied. It was found that the interconnect reliability is closely related to the differences in the warpage arising from the assembly process, and that the smaller change in warpage introduced by the curing process gave a higher interconnect reliability for the bump bonds. Based on these findings, lower curing temperatures are considered to be more effective for improving the mountability of the package and the interconnect reliability.

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