418 International ournal of Applied Ceramic Technolog-Sebastian and Jantunen Vol.7,No.4,2010 to the dielectric properties of 0-3 ceramic-polymer com- different polymers were used with the same ceramic filler 0.008 It has been reported recently that there exist inter Er(Modified Lichtenecker 20 phase regions at polymer-filler interfaces in particulate- 0.006 filled polymer composites. The interphase consists of polymer molecules that are bonded or ori- Eg ented at the filler-Particle interface, giving rise to unique electrical and physical properties. The interphase region of the composite can have E, significantly differ- 00001暑 ent from that of the polymer phase due to the nature of the chemical bonding of the polymer molecules to the 0102030405060 Volume Percentage of BsT urface of the filler particles. Chemical coupling agents and surfactants such as silanes, organometallic chelating agents, etc. are generally used to enhance the compat ibility between the polymer phase and the dispersed 0.008 filler phase of Ite systems. Thus, in the r Modified Lichtenecker che interphase region of a polymer-ceramic composite is 0.006 comprised of polymer molecules and/or additives mo- cularly bonded to the surface of the filler, creating a 80.004 material with chemical, mechanical, and electrical char- acteristics different from those of the constituent phases Additionally, Kobune et al. /reported that vacuum dry- 0.000L 2 ng with silane surface treatment of the filler( BaZrO3 aTiO3-Ba(Fe1/Ta1)O3 )improved Er and tan 8 when a 0-3 epoxy composite was prepared. Volume Percentage of nano BST It has been reported that the use of nanosized filler Fig. 2. Variation of relative permitivity and los tangent(a) BSTc- particles in 0-3 type polymer-ceramic composites in- COC composites(b)BSTa-COC composite at I GHZ as a finction of structure. #8. 4s mposite loading and improves the micro- creases BST loading (after Hu et al. 2. BST, BaassSrods TrO Recently hu et al. investigated the effect of particle size of the filler on the dielectric properties and cies, but has hardly any effect at microwave frequencies ites. The composites with the BST nanopowder showed a mediate frequency, indicating the relaxation behavior of higher Er and loss factor at BST loading over 10 vol% the polymer matrix. The dielectric properties of the compared with using a normal BST powder as shown in composites are influenced not only by the relative per- Fig. 2. Figure 3 shows the microstructure of the compos- mittivity of the components but also by other factors The use of nanopowders yielded a more uniform and between the two phases. Therefore, the prediction of crostructure but in general the use of der increased the loss facto ative permittivity of the components and the volume fraction of the filler is very important but is a difficult task for electronic packaging applications. The follow Dielectric Properties of Polymer-Ceramic ing equations are commonly used to calculate the Er of the composites with a low filler content. 1. Jayasundere-Smith It was found that for the same filler ceramic load- g, the dielectric characteristics Em(1-)+6+2后 trongly depend on the type of polymer. Polar poly- celt mers increase the Er of the composites at low frequen 1-+3m-12+3(-m)to the dielectric properties of 0–3 ceramic–polymer com￾posites was reported by Teirikangas et al. 41 when three different polymers were used with the same ceramic filler. It has been reported recently that there exist inter￾phase regions at polymer–filler interfaces in particulate- filled polymer composites.42–46 The interphase region consists of polymer molecules that are bonded or ori￾ented at the filler–particle interface, giving rise to unique electrical and physical properties. The interphase region of the composite can have er significantly differ￾ent from that of the polymer phase due to the nature of the chemical bonding of the polymer molecules to the surface of the filler particles. Chemical coupling agents and surfactants such as silanes, organometallic chelating agents, etc. are generally used to enhance the compat￾ibility between the polymer phase and the dispersed filler phase of composite systems. Thus, in these cases, the interphase region of a polymer–ceramic composite is comprised of polymer molecules and/or additives mo￾lecularly bonded to the surface of the filler, creating a material with chemical, mechanical, and electrical char￾acteristics different from those of the constituent phases. Additionally, Kobune et al. 47 reported that vacuum dry￾ing with silane surface treatment of the filler (BaZrO3– BaTiO3–Ba(Fe1/2Ta1/2)O3) improved er and tan d when a 0–3 epoxy composite was prepared. It has been reported that the use of nanosized filler particles in 0–3 type polymer–ceramic composites in￾creases the composite loading and improves the micro￾structure.48,49 Recently, Hu et al. 24 investigated the effect of particle size of the filler on the dielectric properties and microstructure of cyclic olefin copolymer–BST compos￾ites. The composites with the BST nanopowder showed a higher er and loss factor at BST loading over 10 vol% compared with using a normal BST powder as shown in Fig. 2. Figure 3 shows the microstructure of the compos￾ites with 10 vol% BST nano and normal powder loadings. The use of nanopowders yielded a more uniform and homogeneous microstructure but in general the use of nanopowder increased the loss factor. Dielectric Properties of Polymer–Ceramic Composites It was found that for the same filler ceramic load￾ing, the dielectric characteristics of the composites strongly depend on the type of polymer. Polar poly￾mers increase the er of the composites at low frequen￾cies, but has hardly any effect at microwave frequencies. The loss tangent of the composites peaks at an inter￾mediate frequency, indicating the relaxation behavior of the polymer matrix. The dielectric properties of the composites are influenced not only by the relative per￾mittivity of the components but also by other factors such as the morphology, dispersion, and the interactions between the two phases.39 Therefore, the prediction of the relative permittivity of the composite from the rel￾ative permittivity of the components and the volume fraction of the filler is very important but is a difficult task for electronic packaging applications. The follow￾ing equations are commonly used to calculate the er of the composites with a low filler content. 1. Jayasundere–Smith equation50: eeff ¼ emð1 vfÞ þ ei vf 3em eiþ2em h i 1þ3 vf ðeiemÞ eiþ2em h i 1 vf þ vf 3em eiþ2em h i 1þ3 vf ðeiemÞ eiþ2em h i ð1Þ 0 10 20 30 40 50 60 0.000 0.002 0.004 0.006 0.008 (a) (b) Dielectric loss εr(Modified Lichtenecker) εr(Experimental) Volume Percentage of BST Loss tangent 5 10 15 20 Relative Permittivity 0 5 10 15 20 25 30 35 0.000 0.002 0.004 0.006 0.008 Volume Percentage of nano BST Dielectric loss εr(Modified Lichtenecker) εr(Experimental) Los tangent 2 4 6 8 10 Relative permittivity Fig. 2. Variation of relative permittivity and loss tangent (a) BSTc￾COC composites (b) BSTa-COC composite at 1 GHZ as a function of BST loading (after Hu et al.24). BST, Ba0.55Sr0.45TiO3. 418 International Journal of Applied Ceramic Technology—Sebastian and Jantunen Vol. 7, No. 4, 2010