Effect of Filler on the Microwave Dielectric Properties of Polyethylene/Ceramic Composites M. T. Sebastian*, Sherin Thomas and Sumesh George Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram-695019, India. E-mail*:mailadils@yahoo.com Abstract: The present study investigates the effect of various ceramic fillers on the dielectric properties of polyethylene based composites. The fillers used were Sr9Ce2Ti I2036 (SCT), Ca[(LiI/3Nb 2lJ)o.sTio.2I03-a (CLNT) and Sm2Si207(SS) with relative permittivities 173, 38 and 12 respectively. The composites were synthesized by melt mixing and hot pressing methods. The effect of different volume fractions of the ceramic (vr = 0 - 0.5) on the dielectric properties of the composites was investigated at 8 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ceramic filler content. The relative permittivities obtained experimentally were compared with that of the theoretical predictions. I. INTRODUCTION The recent developments in the microelectronic industry demand high performance microwave materials for substrate and packaging applications. These materials should satisfy certain diverse requirements such as low relative permittivity to reduce the signal propagation delay, low dielectric loss for better device performance, high thermal conductivity to dissipate the heat generated and low or matching thermal expansion coefficient with that of silicon, moisture absorption resistance and high dimensional stability and mechanical flexibility [1-3]. Polymers are generally known to be good insulating materials for electronic packages due to their stable physical and chemical properties, low cost, low relative permittivity, ease of processing, adhesive properties etc.. However, the higher values of linear thermal expansion coefficient and low surface energy limit their practical applications [4]. These difficulties can be overcome to a certain extent by the addition of inorganic fillers such as ceramic particles into the polymer matrix. In order to develop suitable composites for packaging applications, the prime requirement is a filler having low relative permittivity, low dielectric loss, high thermal conductivity and good thermal stability. The present study is a comparison of the properties of polymer - ceramic composites with different ceramic fillers such as ｓｲ ＹｃｾｔｩＱＲＰ ＳＶ (SCT), Ca[(Li1/3Nb 2 13 )ogTi o 2]0 3 .& (CLNT) and Sm2Si207 (SS) with relative permittivities 173,38 and 12 respectively. II . EXPERIMENTAL The ceramics were prepared by the conventional solid state ceramic route. High purity Sm203, CaC0 3, SrC0 3 , Ce02, Li 2C03, Ti0 2, Nb 20s and Si0 2 were stoichiometrically weighed and were ball milled in polyethylene bottle using 978-1-4244-4819-7/09/$25.00 ©2009 IEEE yttria stabilized zirconia balls in distilled water (ethanol medium is used for CLNT) for 24 h. The slurry was dried at 100 °C in hot air oven and calcined in the temperature range 1150-1375°C/4h. The starting materials and polyethylene were mixed separately in a kneading machine. Different volume fractions (0 - 0.5) of ceramics were added to the melted polyethylene and blended at 150 °C for 45 minutes. The uniformly mixed composites were hot pressed under a pressure of 100 MPa at 150°C for 30 min. The surface morphology of the composites was studied by scanning electron microscope (JEOL-JSM 5600 LV, Tokyo, Japan). The microwave dielectric properties of the sample were measured by the cavity perturbation technique using HP 8510 C Network Analyzer (Agilent Technologies). III . RESULTS AND DISCUSSION Figures 1 (a) and (b) show the micro structural images of PE-O.3 vf Sm2Si207 and PE-O.5 vf CLNT polymer - ceramic composites. It can be seen that the ceramic particles are uniformly dispersed throughout the polymer matrix and at lower ceramic loading, a good adhesion is observed between the polymer and ceramic. However, as the filler content increases the ceramic particles form a continuous network and the packing of the particles grew denser. It is also found that the porosity of the composites increases with increase in the filler loading. Fig. I. SEM images of (a) PE-O.3 vfSm,Si,O" (b) PE-O.5 vfCLNT Authorized licensed use limited to: Regional Research Laboratory-RRL TVM. Downloaded on June 29,2010 at 04:27:48 UTC from IEEE Xplore. Restrictions apply.