Polyimides are one class of high temperature materials that
have been extensively used in the microelectronics industry in
passivation and protection. The extremely good thermal stabilities,
along with desirable mechanical and electrical properties, have led to
their use in integrated circuits and thin film multi-layer packaging.
Due to rapid advances in the microelectronics industry, stringent
demands have been placed on the improvement of electric
performance of the packaging systems. This has resulted in a search
for materials with extremely low dielectric constants while
maintaining the desirable thermal and mechanical properties. In the
past, the incorporation of fluorine into polyimides has been shown to
decrease the dielectric constant. In this research, the concept of a
foamed morphology has been utilized to obtain a decrease in the
dielectric constant, by taking advantage of the low value for air. To
achieve compatibility with the microscopic features of the electronic
circuitry, polyimide foams with pore sizes in the nanometer regime
have been developed. Block and graft copolymers consisting of
thermally stable polyimide and labile poly(propylene oxide) were
synthesized to first develop the desired microphase separated
morphology. Both semicrystalline and fluorinated polyimides were
evaluated as low dielectric matrices with improved mechanical
properties and solvent resistance. The labile component was
degraded with thermal treatment in air, leaving behind pores where the size and shape were largely determined by the original
multiphase copolymer morphology.
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