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38 The PCB Magazine • July 2014 RF CAPACITOR MATERIAL FOR USE IN PCBS continues capacitor laminate, uniformity of capacitance was investigated as a function of various capac- itor electrode areas (0.25 mm square ~ 3 mm square) which were prepared by the standard etching on the test board. Figure 6 shows a typi- cal result, showing the measured capacitance tolerance and calculated tolerance (expected) of capacitance. Actual measured uniformity of capacitance in smaller foot print of the capaci- tor showed a good correlation with an assump- tion that the etching variation is around ±7µm. Small footprint capacitors with tight tolerance is still being challenged, but the result in Figure 5 indicate that we can still achieve fairly uni- form capacitance values with proper process op- timization and control that will result in func- tional RF circuits. III. Conclusion The ceramic filled organic-based compos- ite material has been used to make RF capaci- tor laminates (to compete with ceramic chip capacitors). Using this material, we successfully achieved low DF of ~0.002 at GHz frequencies (up to 10GHz), higher dielectric strength and better TCC by optimizing size of the filler and controlling its distribution in the polymer matrix. This material can be applicable for the use either in discrete RF components or in be- ing embedded within the packaging substrate as an embedded RF capaci- tor material. PCB References 1. New 500 & 250V Multilayer Organic Capacitors (MLOCs), AVX Co., 2012. 2. P. N. Lee et al., "Design and modeling methodology of embedded passives substrate in a compact wire- less connectivity module," 61 st ECTC, May 31–June 3, 2011, FL USA, pp. 144–149. 3. Features and Applications of Polymer Thin Film Multi-Layer Ca- pacitor PML CAP, Rubycon Co., 2011. 4. J. Andresakis et al., "Use of high Dk, low loss composite material as used for embedded capacitors in high frequency applications," 41 st IMAPS, USA, 2008. 5. R. Ulrich, L. Schaper, D. Nelms, and M. Leftwich, "Comparison of paraelectric and fer- roelectric materials for applications as dielec- trics in thin film integrated capacitors," Inter. J. Microcircuits Electron Packag., Vol. 23, 2000, pp. 172–180. 6. S. J. Monte, "Titanate Coupling Agents," in Functional Fillers for Plastics, 2 nd ed., M. Xanthos, Ed. Germany: Wiley-Vch, 2010, pp. 91–114. 7. J. H. Hwang et al., "High Dk embedded capacitor materials in organic packaging sub- strate," 12 th Electronic Circuits World Conven- tion (ECWC12), US100, Taiwan, 2011. 8. J. Krupka et al., "Uncertainty of complex permittivity measurements by split post dielec- tric resonator technique," J. Europ. Ceram. Soc., Vol. 21, 2001, pp. 2673–2676. 9. S. George et al., "Dielectric mechanical, and thermal properties of low-permittivity polymer-ceramic composites for microelectron- ic applications," Int. J. Appl. Ceram. Technol., Vol. 7, 2010, pp. 461–474. Figure 6: capacitance variation with electrode area: calcula- tion vs. measurement result.