In microelectronic circuit packages, circuits and units are prepared in packaging levels of increasing scale. Generally, the smallest scale packaging levels are semiconductor chips housing multiple microcircuits and/or other components. Such chips are usually made from ceramics, silicon, and the like. Intermediate package levels (i.e., “chip carriers”) comprising multi-layer substrates may have attached thereto a plurality of small-scale chips housing many microelectronic circuits. Likewise, these intermediate package levels themselves can be attached to larger scale circuit cards, motherboards, and the like. The intermediate package levels serve several purposes in the overall circuit assembly including structural support, transitional integration of the smaller scale microcircuits and circuits to larger scale boards, and the dissipation of heat from the circuit assembly. Substrates used in conventional intermediate package levels have included a variety of materials, for example, ceramic, fiberglass reinforced polyepoxides, and polyimides.
Dielectric materials used as coatings on the substrates must meet several requirements, including conformality, flame resistance, and compatible thermal expansion properties. Conventional dielectric materials include, for example, polyimides, polyepoxides, phenolics, and fluorocarbons. A common method of applying conformal coatings is by vapor deposition. Electrophoretic deposition has also been explored; however, polyimide resins such as bismaleimide resins, while desired for their superior dielectric and thermal stability properties, are intractable in most solvents, let alone aqueous dispersions, making electrophoretic deposition of such resins virtually impossible. Reactivity of the resins with amines increases the difficulty of formulation in both solvent based and aqueous dispersed coatings.
Accordingly, it would be desirable to provide a composition that provides the dielectric and thermal stability properties necessary for electronic circuit applications, while allowing for convenient electrophoretic deposition thereof.