industry collaborative groups seem possibilities. A few specific problems and the possible role of chemistry in their solution will illustrate some of the issues.

Multilayer Substrates for Electronics

The fabrication of high-performance microelectronic devices depends increasingly on a sophisticated technology in which individual components are located on complex substrates containing the necessary power distribution lines and interconnects. These substrates comprise multiple layers of ceramic (alumina), metal, and thin-film organic insulators. The fabrication of these substrates is made difficult by a number of problems, prominent among which is that of ensuring adhesion between the different components/These components commonly exhibit widely divergent coefficients of thermal expansion and fundamentally incompatible surface chemistries. Current adhesion promoters and coupling agents used in these devices are not entirely satisfactory, and the mechanisms of interfacial failure are being explored. This area represents an important opportunity for chemistry—the development of new series of coupling agents designed and optimized to improve adhesion between the ceramic, organic, and metallic components of these multilayer substrates.

The packaging of microelectronic components, which are commonly assembled on fiberglass-reinforced epoxy circuit boards, presents many other significant problems. As the density of circuit interconnects on these boards increases along with requirements for flexibility and durability, the intrinsic limitations of such boards become more evident. For instance, delamination resulting from adhesive failure at the epoxy-fiberglass interface during drilling of interconnect holes can cause short-circuiting between leads and consequently is a serious problem in large, high-density circuit boards. In the near term, development of improved, water-resistant coupling agents to improve adhesion between fiberglass and epoxy will improve this technology. In the long term, development of homogeneous substrates or composite substrates that have fewer problems with delamination will be important.

The production of ceramics for microelectronics presents additional problems. The most commonly used ceramic in microelectronics is alumina. It has a high dielectric constant which reduces the speed of electrical signal transmission. Ceramics with a lower dielectric constant would be preferable, but none of the present alternatives is as easily processed as alumina. The development of new, processable, low-dielectric-constant ceramics using organometallic ceramic precursors and sol-gel methods is attractive.

The microelectronic packaging requirements for low-temperature sintering, low dielectric constant, and controlled thermal expansion cannot be met by conventional ceramic materials such as alumina. New multiphase ceramic



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