wwceramics. org/ACT Composites of 0-3 Connectivity talk, are influenced by the dielectric properties of the 4D1 iportant re materials is to ensure the electrical insulation of the sil- 载LDU8 chip and circuit pins. a low conductivity is needed roid leakage current, a low E, to minimize the ca- 06 itive coupling effects, and a low loss factor to reduce y un et investigated the dielectric prop 0D4 erties of epoxy composites with micrometer-sized and nanosized silica fillers. The epoxy-nanosilica composite had higher dielectric loss at a low frequency and 0.002 was attributed to the increased ionic conductivity caused by the contaminants from the sok-gel-synthesized nanosized silica. Chen et al. investigated the effect of properties of PTFE/SiO2 composites. They found that the loss factor and water absorption increase with decreasing filler particle size. The PTFE/silica composite, when treated with a 4.006 phenyltriethoxysilane coupling agent, increase tensile strength and CTE and the water absorption de creases without significant changes in the dielectric properties. Murali et al. prepared PTFE with nano and micrometer-sized silica composites and reported that the PTFE/silica nanocomposites have lower den- sity and higher losses and higher E, for <30 wt of fll ler. However, the composites prepared by filling silica Volume fraction of Sm2 07 are able to achieve only moderate relative permittivity Fig. 1. Variation of relative permittivity and loss tangent (a) cause d by its low Er (3.8-5.4). In order to obtain a Polbystyrene-Sm2Si 0,(6) Polyetbhylene-Sm2Si20r composites with higher Er for miniaturization of devices, the four possi different wolume fractions of the filler at I MHz(afier Thomas et al ") ble ways are to use fillers of a high En, increase the vol ume fraction of the filler, modify the polymer-ceramic filler materials with disk- or needle-type grains instead interfaces, dry the materials before processing, or change of spherical ones. These calculations estimated that the morphology of the filler grains. However, the first under mixture conditions where inclusion has 50 times approach with a higher filler concentration results in higher permittivity than the matrix, disk- and needle- oor Auidity and poor fexibility and low strength in the type fillers could produce 5 and 3. 4 times higher composite. Hu et al. for example could increase the mittivity than the spherical ones. However, the avail permittivity value of PpS polymer up to 13.5(1 GHz) ability of these kinds of ceramic fillers is very limited by addition of 70 wt% of Ba. 55Sro45TiO3(BST) pow- Furthermore, the chosen polymer exerts an effect on the der. It was reported that the mechanical properties de- achieved electrical properties. Figure I shows the vari- grade with increased filler loading 36.37 This problem ation of relative permittivity and tan 8 at 1 MHz for an be overcome by modifying the filler materials. Re- different volume fractions of the filler in the polyethyl- cently, Che et al. reported that a spherical powder ene/Sm2Si2O, and polystyrene/Sm2 Si2O, compos- with optimized particle size can increase Auidity and ites. The e. and tan s increase with an increase in cking. They reported that by using a composite di- the filler content. The polyethylene with a 0.4 volume electric from spherical powder of Cao.65Sro35 TiO3 and fraction of Sm2S2O7 showed an Er of 5.28 and a tan 8 of a thermoplastic polymer could increase the filler con- 0.005 at 8 GHz, whereas for the same volume fraction centration by over 5 vol% for a higher Er. On the other in polystyrene had values of 4.34 and 0.010, respec hand,theoretical calculations proposed that composites tively. The same kind of extrinsic reason, nar h very high E, values could be prepared by selecting polymer, ceramic, chemical, and mechanical coupling,talk, are influenced by the dielectric properties of the packaging materials. An important role of the packaging materials is to ensure the electrical insulation of the sil￾icon chip and circuit pins. A low conductivity is needed to avoid leakage current, a low er to minimize the ca￾pacitive coupling effects, and a low loss factor to reduce signal loss. Sun et al. 33 investigated the dielectric prop￾erties of epoxy composites with micrometer-sized and nanosized silica fillers. The epoxy–nanosilica composite had higher dielectric loss at a low frequency and was attributed to the increased ionic conductivity caused by the contaminants from the sol–gel-synthesized nanosized silica. Chen et al. 34 investigated the effect of filler particle size on the properties of PTFE/SiO2 composites. They found that the loss factor and water absorption increase with decreasing filler particle size. The PTFE/silica composite, when treated with a phenyltrimethoxysilane coupling agent, increased the tensile strength and CTE and the water absorption de￾creases without significant changes in the dielectric properties. Murali et al. 35 prepared PTFE with nano￾and micrometer-sized silica composites and reported that the PTFE/silica nanocomposites have lower den￾sity and higher losses and higher er for o30 wt % of filler as compared with the use of a micrometer-sized filler. However, the composites prepared by filling silica are able to achieve only moderate relative permittivity caused by its low er (3.8–5.4). In order to obtain a higher er for miniaturization of devices, the four possi￾ble ways are to use fillers of a high er, increase the vol￾ume fraction of the filler, modify the polymer–ceramic interfaces, dry the materials before processing, or change the morphology of the filler grains. However, the first approach with a higher filler concentration results in poor fluidity and poor flexibility and low strength in the composite. Hu et al. 26 for example could increase the permittivity value of PPS polymer up to 13.5 (1 GHz) by addition of 70 wt% of Ba0.55Sr0.45TiO3 (BST) pow￾der. It was reported that the mechanical properties de￾grade with increased filler loading.36,37 This problem can be overcome by modifying the filler materials. Re￾cently, Che et al. 38 reported that a spherical powder with optimized particle size can increase fluidity and packing. They reported that by using a composite di￾electric from spherical powder of Ca0.65Sr0.35TiO3 and a thermoplastic polymer could increase the filler con￾centration by over 5 vol% for a higher er. On the other hand, theoretical calculations proposed that composites with very high er values could be prepared by selecting filler materials with disk- or needle-type grains instead of spherical ones.39 These calculations estimated that under mixture conditions where inclusion has 50 times higher permittivity than the matrix, disk- and needle￾type fillers could produce 5 and 3.4 times higher per￾mittivity than the spherical ones. However, the avail￾ability of these kinds of ceramic fillers is very limited. Furthermore, the chosen polymer exerts an effect on the achieved electrical properties. Figure 1 shows the vari￾ation of relative permittivity and tan d at 1 MHz for different volume fractions of the filler in the polyethyl￾ene/Sm2Si2O7 and polystyrene/Sm2Si2O7 compos￾ites.40 The er and tan d increase with an increase in the filler content. The polyethylene with a 0.4 volume fraction of Sm2S2O7 showed an er of 5.28 and a tan d of 0.005 at 8 GHz, whereas for the same volume fraction in polystyrene had values of 4.34 and 0.010, respec￾tively. The same kind of extrinsic reason, namely polymer, ceramic, chemical, and mechanical coupling, Fig. 1. Variation of relative permittivity and loss tangent (a) Polystyrene–Sm2Si2O7 (b) Polyethylene–Sm2Si2O7 composites with different volume fractions of the filler at 1 MHz (after Thomas et al.40). www.ceramics.org/ACT Polymer–Ceramic Composites of 0–3 Connectivity 417