Thermal Properties of Low Loss PTFE-CeO 2 Dielectric Ceramic Composites for Microwave Substrate Applications P. S. Anjana, 1 S. Uma, 2 J. Philip, 2 M. T. Sebastian 1 1 Materials and Minerals Division, National Institute for Interdisciplinary Science and Technology (CSIR), Thiruvananthapuram 695019, Kerala, India 2 Department of Instrumentation & STIC, Cochin University of Science and Technology, Cochin 682022, Kerala, India Received 28 June 2009; accepted 30 October 2009 DOI 10.1002/app.31690 Published online 26 May 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Polytetrafluroethylene (PTFE) composites filled with CeO 2 were prepared by powder processing technique. The PTFE is used as the matrix and the loading fraction of CeO 2 in the composite varied up to 0.6 volume fraction. The thermal conductivity and coefficient of ther- mal expansion were studied in relation to filler concentra- tion. The thermal conductivity increased and coefficient of thermal expansion decreased with increase in CeO 2 con- tent. For 0.6 volume fraction loading of the ceramic, the composite has a thermal conductivity of 3.1 W/m  C and coefficient of thermal expansion 19.6 ppm/  C. Different theoretical approaches have been employed to predict the effective thermal conductivity and coefficient of thermal expansion of composite systems and the results were com- pared with the experimental data. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 751–758, 2010 Key words: composites; dielectric properties; thermo- gravimetric analysis; differential scanning calorimetry; thermal properties INTRODUCTION The electronic packaging has continuously provided the impetus pushing the development of new mate- rials in a fascinating and rich variety of applica- tions. 1 Thermal considerations in the electronic pack- age have become increasingly important because integration of transistors has resulted in the escala- tion of power dissipation as well as an increase in heat flux at the devices. Hence the desire for improving thermal properties of materials for elec- tronic component parts is getting stronger and the material performance has become a critical design consideration for packages. 2 Historically, metal com- ponents in integrated circuit packages have provided thermal paths for the removal of heat; however, this mechanism has reached its maximum potential. As a result, the polymeric materials in the components are increasingly important as thermal paths for the removal of excess heat that builds up. Unfortunately, polymeric materials are inherently poor thermal con- ductors, and they must be modified to assist in heat removal from electronics. 3,4 Fillers play an important role in the production of polymeric materials. In addition to cost saving, other value-added properties are gained through the use of fillers. 5 Fillers can improve the mechanical 6,7 and thermal properties 8-10 as well as optical and electri- cal properties 11-13 of a polymeric material. Ceramic fillers are often added to polymers to increase the re- sultant thermal conductivity of the composites. 14 Considerable amount of literature is available on the thermal conductivity of polymers by fillers. 11-13,15 Thermally conductive, electrically insulative, cost effective, and design flexible ceramic particle loaded PTFE composites are increasingly used for electronic packaging and substrate applications. 16 PTFE exhib- its useful properties over the widest temperature range of any known polymer. PTFE has a high vir- gin crystalline melting point (325–335  C), extremely high shear viscosity (10 11 Poise at 380  C) in the melt, good thermal and chemical stability. 17,18 Its combina- tion of electrical properties (relative permittivity (e r ) ¼ 2.1 and dielectric loss (tan d) ¼ 10 5 at 800 MHz) is outstanding with high dielectric strength and extremely low dielectric loss. 19 However, the disad- vantages of PTFE substrate include low thermal con- ductivity (0.26 W/m  C), 17 high linear coefficient of thermal expansion (>100 ppm/  C) and low surface energy. 20,21 Addition of metallic fillers, although have high thermal conductivity adversely affect the dielectric properties of the composites. Hence ceramics having low thermal expansion coefficient, high thermal conductivity along with low dielectric Correspondence to: M. T. Sebastian (mailadils@yahoo. com). Contract grant sponsors: Council of Scientific and Industrial Research and Department of Science and Technology, New Delhi. Journal of Applied Polymer Science, Vol. 118, 751–758 (2010) V C 2010 Wiley Periodicals, Inc.