Journal of Alloys and Compounds 477 (2009) 677–682 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Microwave dielectric properties of PTFE/rutile nanocomposites S. Rajesh, V.S. Nisa, K.P. Murali, R. Ratheesh ∗ Microwave Materials Division, Centre for Materials for Electronics Technology (C-MET), Department of Information Technology, Government of India, Athani P.O., Thrissur, Kerala 680771, India article info Article history: Received 9 September 2008 Received in revised form 14 October 2008 Accepted 22 October 2008 Available online 9 December 2008 Keywords: Composite materials Dielectric properties PTFE Packaging abstract The effects of nano-size rutile ﬁller on the microwave dielectric properties of PTFE composites were investigated and the results were compared with that of micron size rutile ﬁlled composites. Nano-size rutile powder was prepared through sol–gel route and the ﬁlled PTFE composites were fabricated through SMECH process. Different characterization techniques such as powder X-ray diffraction, SEM, BET, TEM and TG/DSC were employed to analyze the nature of ceramic ﬁller. The dielectric properties of ﬁlled composites were evaluated at microwave frequency region using waveguide cavity perturbation technique. Different theoretical models have been employed to predict the variation of dielectric constant with respect to ﬁller loading. The moisture absorption characteristics of nano-rutile ﬁlled PTFE composites were measured as per IPC-TM-650 2.6.2 standards. Composites show high dielectric constant at X-band frequency region with relatively high loss tangent compared to micron size counterpart. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Packaging technology demands materials having high dielec- tric constant and appreciable loss tangent with improved thermal properties for the integration of passive components in to a single module. High dielectric constant is needed for circuit miniaturization and low loss tangent keeps the signal integrity. Polymer/ceramic composites, wherein the high dielectric constant, low coefﬁcient of thermal expansion and high thermal conductivity of ceramics can be combined with ﬂexibility, low moisture absorp- tion and high solvent resistance of the polymers, are reported to be best suited for packaging applications [1]. Most common polymer matrix used for the fabrication of electronic packages is brominated bisphenol epoxy resin. Bisphenol epoxy resin is a good choice at low frequency region but too lossy to use at frequencies >1GHz range [2]. Hence materials with improved dielectric properties are needed to cater the requirements of fast growing high frequency packaging industry. Poly(tetraﬂuroethylene) (PTFE) is a high performance ther- moplastic polymer with unique electrical properties. PTFE-based composites are widely used for the fabrication of microwave cir- cuit boards [3,4]. PTFE has low dielectric constant ε ′ r ∼ 2.1 and extremely low loss tangent tan ı ∼ 0.0003 which is stable over a wide range of frequencies [5]. The low loss tangent is a conse- ∗ Corresponding author. Tel.: +91 487 2201156; fax: +91 487 2201347. E-mail address: ratheeshr@yahoo.com (R. Ratheesh). quence of the symmetrical conformation of the polymer backbone, which effectively neutralizes the dipole forces of the C–F bonds yielding a net zero dipole moment [5]. The high linear coefﬁcient of thermal expansion (CTE ∼ 109 ppm/ ◦ C), low thermal conductiv- ity and poor stress relief restrict the wider usage of PTFE as such for microelectronic packaging. These impediments can be overcome by ﬁlling ceramic particulates in the PTFE matrix at appropriate loading fractions [3]. In our earlier studies, ∼5 m size rutile parti- cles (M/s. Sigma–Aldrich USA) were ﬁlled in the PTFE matrix and its microwave dielectric as well as mechanical properties were evalu- ated [6]. PTFE/rutile composites show a dielectric constant of 10.2 with loss tangent of 0.002 at optimum ﬁller loading (67 wt%). Even though the microwave dielectric properties of micron size partic- ulate ﬁlled PTFE composites are studied by many researchers, less attention has been paid to the role of nano-ﬁller on its electrical properties [7,8]. The upsurge of nano-phase materials in recent years attracted researchers to develop nanoparticle ﬁlled polymer composites for improved performance. The improvements in dielectric prop- erties of polymer nanocomposites could be due to increased interaction zone between polymer and ﬁller, changes in the polymer morphology, increased space charge distribution, etc. [9]. Although numerous reports are available on the dielectric properties of nanocomposites, mostly conducting ﬁller mate- rials are used as particulate ﬁllers to make the composites [10]. However in recent times, polymer/nanocomposites with non-conducting ﬁllers are also getting wide attention but the studies are mostly restricted in the low frequency region. Only very few literature are available which report the dielec- 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.10.092