Build-up substrate materials are high-performing specialty materials that consist of inorganic reinforcing particulates evenly dispersed throughout a continuous thermoset polymer matrix. Build-up materials are of critical importance in high density interconnect applications and often serve as the dielectric layer in multilayer circuitry including interposers, substrate packaging, and redistribution layers. Thermoset buildup materials benefit from low coefficients of thermal expansion, high reliability, and are available as thin dielectrics allowing for high density circuitry. Typically, high concentrations of ceramic particulate reinforcement are necessary to yield a low rate of thermal expansion. Solid particles of silica have the disadvantage of silica naturally raising the dielectric constant of a composite material relative to the low loss polymer resin which contributes to a lower dielectric constant. The future of build-up material requires increasingly lower loss for applications such as machine learning, AI, 5/6G, and high-speed switching. Although not as obvious as dissipation factor, there is also an advantage of lowering the dielectric constant. Increasing densification and finer lines and spaces leads to increasingly higher transmission line losses. Lower dielectric constant dielectrics allow a reduction in dielectric thickness while maintaining a given trace width. In order to meet the rapidly growing needs of increasingly higher density interconnect with the lowest losses, lower dielectric constant and lower dissipation factor build-up materials can be achieved by designing the thermoset matrix with lower dissipation factor and replacing solid particulates of silica with micron sized hollow silica, effectively taking advantage of air within the dielectric medium. In this study, we investigate the dielectric, mechanical and thermal properties of thermoset polymer buildup films that have been reinforced with hollow silica particulates.
