Effect of anisotropy on extracted dielectric properties of PCB laminate dielectrics

The effect of anisotropy of fiber-glass-filled epoxy resin composites, typically used as laminate dielectrics for manufacturing of printed circuit boards (PCB) is studied. It is shown that the extracted dielectric properties, the dielectric constant (Dk) and the dissipation factor (Df), depend significantly on the measurement technique, and first of all, how the electric field in a test fixture or a test vehicle is oriented with respect to the glass fiber bundles in the composite dielectric. The comparison of the dielectric properties obtained using the traveling-wave technique based on the S-parameter measurements and the split-post dielectric resonator technique are shown, and the discrepancy between the results is explained from the point of view of anisotropy and composite mixing theory.