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26 The PCB Design Magazine • August 2014 coating method for putting the ceramic-filled polymer composite material on the copper can minimize the material variation. In addition to the material variation, the process variation (mainly etching variation) in formation of the electrodes by the etching process in PCB manu- facturing will add to the tolerance. In order to understand the capacitance tolerance of the ca- pacitor laminate, uniformity of capacitance was investigated as a function of various capacitor electrode areas (0.25 mm square ~ 3 mm square) which were prepared by the standard etching on the test board. Figure 6 is a typical result, show- ing the measured capacitance tolerance and calculated tolerance (expected) of capacitance. Actual measured uniformity of capacitance in the smaller footprint of the capacitor showed a good correlation with an assumption that the etching variation is around ±7µm. Small foot- print capacitors with tight tolerance are still being challenged, but the result in Figure 5 in- dicate that we can still achieve fairly uniform capacitance values with proper process optimi- zation and control that will result in functional RF circuits. III. Conclusion The ceramic filled organic-based com- posite material has been used to make RF ca- pacitor laminates (to compete with ceramic chip capacitors). Using this material, we suc- cessfully 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 being embedded within the packaging substrate as an embedded RF capacitor material. PCBDESIGN References 1. New 500 & 250V Multilayer Organic Ca- pacitors (MLOCs), AVX Co., 2012. 2. P. N. Lee et al., "Design and modeling methodology of embedded passives substrate in a compact wireless 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 Capacitor 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 ferroelectric materials for applications as dielectrics 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 dielectric 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 microelectronic applications," Int. J. Appl. Ceram. Technol., Vol. 7, 2010, pp. 461–474. feature RF CAPACIToR MATERIAL FoR USE IN PCBS continues Figure 6: Capacitance variation with electrode area: calculation vs. measurement result.