Polystyrene-Silver composites for embedded capacitor applications

Abstract

Abstract -The present paper reports the preparation and characterization of Polystyrene-Silver composites for embedded capacitor applications. The composites have been prepared by ultrasonic mixing followed by hot pressing. The percolation threshold is found to be decreasing from 0.1 V f for silver of particle size < 250 µm to 0.07 V f for nano silver. The composites have temperature stable relative permittivity. Keywords-Embedded capacitor; nano-composite; dielectric; percolation; conductivity I. INTRODUCTION Technologies that enable the production of cost effective miniature electronic devices are highly desired for applications including telecommunications, network systems, automotive, and computer electronic devices. Embedded passive technology is a solution to the ever growing demands of miniaturization, increased functionality, and low cost. Among the embedded passives, embedded capacitors have crucial role because of the use of capacitors in multiple functions, such as decoupling, by-passing, filtering, frequency determining and timing capacitors. The material requirements for the embedded capacitor applications are high relative permittivity, reasonably low dielectric loss, and temperature stability of dielectric properties. The fabrication of conductor-insulator percolative composites has been recognized as the promising technique to achieve high relative permittivity [1]. In the context of high permittivity materials, several polymer-ceramic [2-4], polymer-metal [5-7] ceramic-metal [8, 9] and polymer-ceramic-metal [10, 11] composites have been studied. In polymer-ceramic composite, higher volume fraction of ceramic loading is required to achieve the high relative permittivity. The higher filler loading can lead to processability issues such as poor adhesion and dispersion which finally results in poor performance. But in polymer-metal and ceramic-metal composites small amount of metallic filler is quite enough to accomplish high permittivity. The high processing temperature limits the practical applications of ceramic-metal composites. Hence, polymer-metal composites are found to be promising for embedded capacitor applications. The present paper is focused on the development of a new polymer-metal composite for embedded capacitor applications. Polystyrene (PS) is chosen as the matrix and silver powder (Ag) of different particle size as filler. Polystyrene is a low loss polymer with good mechanical properties. Among the possible metallic fillers, Ag is promising when both the cost and properties are concerned. II. EXPERIMENTAL Silver particles of four different sizes viz. < 250 µm, 5-8 µm, 2-3.5 µm (Bought from Aldrich) and nano (synthesized) were used as filler.