RF Capacitor Material for Use in PCBs

 RF Capacitor Material for Use in PCBs

Abstract A novel ceramic-functional-particle-filled polymer composite material has been developed for the use either in discrete elements on the PCB or in being embedded within the packaging substrate for high-frequency circuit applications. This material provides the desired properties such as low loss at high frequencies (about 0.002 or less up to 10GHz) and high dielectric strength, among other improved properties. The electrical properties were influenced significantly by the ceramic-functional-particle (type and particle size/distribution in the polymer matrix). Their contributions to the electric strength and temperature stability of capacitance (which is an important material issue for practical device application) will be discussed. In addition, capacitance tolerance for manufacturing an embedded RF capacitor will be presented in terms of etching uniformity to minimize the variation of the capacitor electrode areas. Introduction Organic-based dielectric materials has been explored for the use either in discrete passive components on the PCB or in being embedded within the packaging substrate as part of RF/microwave circuits. Using ceramic-functional-particles (fillers), filled polymer composite material is merely a convenient and inexpensive way (to compete with ceramic chip capacitors) achieving low ESR (equivalent series resistance), high SRF (self-resonant frequency) for RF capacitor application that can support frequencies well above 1GHz. Besides, embedding fillers into the polymer enhances properties of dielectric materials (by optimizing filler chemistry and its distribution in the polymer matrix) such as temperature stability of capacitance for high precision RF circuit and dielectric strength (the maximum DC electric field strength applied across the dielectrics in RF capacitor) for a high voltage rating which is essential especially for servers, pico cell and femto cell in base station market space. Generally, fillers are widely accepted in various applications because of their advantage in addressing several limitations of polymers, making its way onto benefits such as better dimensional stability for polymer composite membrane, lower coefficient of thermal expansion (CTE) for build-up layer, increasing thermal conductivity for thermal interface materials (TIM), and improved stiffness for underfill materials. As for the fillers in RF capacitor application, it is presently based almost entirely on the simple perovskite BaTiO3 (barium titanate), but there is strong demand on the class of materials known as paraelectrics, mainly due to the fact that their dielectric properties are much more stable with regard to most operating conditions such as frequency, temperature and DC bias. -