Embedded Ceramic Passive on FR‐4 Using Aerosol Deposition

Abstract

Embedding various passive components, such as capacitors, filters, and inductors, in one circuit board, effectively achieves miniaturization, cost reduction, and higher performance in RF wireless communication products. Much R&D into embedded passives has been conducted using different circuit board technologies. However, no circuit boards developed to date satisfy all [of the requirements that is required of them. We propose a resin built-up circuit board that embeds ceramic film with passive functions to achieve low-cost RF modules in the next generation. These circuit boards make it possible to simultaneously obtain a fine pattern for miniaturization, improved performance, such as low transmission loss and high capacitance density, and cost reduction. The key required to achieve such a circuit is ceramic deposition. Our unique aerosol deposition (AD) method can provide passive ceramic elements embedded in the resin substrate. The film is formed by accelerated ceramic nano-particle aerosol bombardment. Many kinds of ceramics can be deposited on a substrate at room temperature. We present a novel AD approach to fabricating embedded capacitors on resin FR-4 substrates and the experimental results. We also discuss the correlation between the microstructure and dielectric properties of AD dielectric films deposited under various conditions. We confirmed that dense BaTiO 3 dielectric films with a dielectric constant of 400 could be formed on resin substrates at RT. Embedded capacitors on an FR-4 substrate, fabricated as a prototype with this AD film, had a capacitance density of 300 nF/cm 2 .