Dielectric Material and Foil Surface Roughness Properties Extraction Based on Single-ended Measurements and Phase Constant ($\beta$) Fitting

Abstract

Dielectric substrate and foil surface roughness properties of fabricated printed circuit boards (PCB) are important for high-speed channel design. Several stripline-based extraction methods have been developed to characterize dielectric relative permittivity ($\varepsilon_{r}$), dielectric dissipation factor ($\text{tan}\delta$), and foil surface roughness correction factor ($K_{R}$) using measured S-parameters. However, the $\text{tan}\delta$ extraction still needs further improvement due to the difficulty in separation of dielectric and conductor loss. The authors found that the frequency-dependence of the stripline phase constant ($\beta$) is helpful to determine the $\text{tan}\delta$ without introducing high sensitivity to foil surface roughness. By introducing a causal dielectric frequency-dependent model, $\varepsilon_{r}$ and $\text{tan}\delta$ are extracted by fitting measured $\beta$. The foil surface roughness property (correction factor $K_{R}$) is obtained using the conductor loss calculated by subtracting extracted dielectric loss from the total loss. To demonstrate the feasibility of the proposed method examples are provided using simulation data and fabricated PCB.