Microstrip Phase Velocity Fundamentals across Multi Layer Glass Stackups
Microstrip phase velocity depends on outer layer inhomogeneous dielectric fields, glass reinforcement architecture, copper roughness, and lamination compression.
High Frequency Dielectric Testing
Permittivity Measurement
Material characterization procedure evaluates the electrical response of an insulating substrate at gigahertz frequencies. High frequency dielectric testing determines the relative permittivity and loss tangent of the resin and reinforcement system used in the board. These values are essential for accurately predicting signal speed and attenuation in high speed digital designs.
Loss Quantification
Signal energy dissipates into the heat as it travels through the PCB material at high speeds. High frequency dielectric testing identifies the dissipation factor, which represents the efficiency of the material in preserving signal integrity. Materials with a high loss tangent cause rapid signal degradation, making them unsuitable for radar or telecommunications equipment.
Testing occurs across a wide range of temperatures to ensure the substrate remains stable under varying operational loads.
Resonant Extraction
Laboratory methods like the split cylinder resonator or the stripline test provide precise data for stackup calculations. During high frequency dielectric testing, a sample of the substrate is placed within a microwave cavity to measure how it shifts the resonant frequency. This shift allows for the calculation of the dielectric constant with high precision.
Advanced techniques also measure the anisotropy of the material, showing how properties change in the longitudinal and transverse axes. Designers use this data to select laminates that minimize phase distortion in multi gigabit per second links.