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36 The PCB Magazine • July 2014 nate. The dielectric thickness was set to 25µm for all samples. As shown in Figure 2, the effect of the filler size on the BDV was clearly detect- able, and the BDV of the dielectrics composed of the larger size filler revealed a considerable improvement in BDV compared to the case of formulating with the smaller size filler. Lower BDV may result from non-uniform dispersion of the filler and it may induce the charging of the weak interface chemistry, probably repre- senting the filler agglomerates. We continue to work on improving the material to achieve rela- tively high BDV even with small size filler by controlling the suspension chemistry. Indirect evidence for the improvement of the filler distribution was sought by measur- ing capacitance change with temperature for samples fabricated with different suspension preparation routes. Temperature coefficient of capacitance (TCC) is an important material pa- RF CAPACITOR MATERIAL FOR USE IN PCBS continues Figure 2: BdV variation of polymer compositing with the filler size. Figure 3: temperature stability of capacitance of two samples prepared by different suspension preparation routes. Figure 4: SeM images (on the coating surface) of samples with (a) dispersion condition a and (b) dis- persion condition B.