Split Post Cavity Resonance Corrections for Anisotropic Substrate Core Permittivity
Split post cavity resonance measures in-plane substrate permittivity; z-axis core corrections prevent multi-ohm stripline impedance errors on woven glass panels.
High-Frequency Laminate Testing
Evaluation Protocol
Dielectric assessment of raw clad or unclad substrates ensures that the electrical performance of high-frequency circuit boards matches design requirements. This procedure, called high-frequency laminate testing, determines the relative permittivity and loss tangent under conditions that replicate multi-gigahertz operation. The results confirm whether a specific batch of laminates is suitable for low-loss applications.
It prevents the costly fabrication of panels that would fail to meet attenuation specifications at microwave frequencies. These evaluations are usually performed on raw sheets before any photolithography or copper etching occurs, ensuring a baseline material quality check before assembly.
Test Fixturing
Resonant cavity fixtures or stripline cards hold the laminate sample during the electrical measurement. The choice of fixture depends on whether the dielectric is being evaluated along the in-plane or out-of-plane axis. Out-of-plane measurements are preferred for microstrip designs where the electric fields pass vertically through the board.
In-plane measurements help analyze coplanar designs.
Metrology Error
Instrument calibration and sample preparation are major sources of variation in these high-frequency measurements. Surface roughness of the copper foil cladding can falsely elevate the measured loss tangent if it is not compensated during calculation. Moisture absorption in the board material also skews the dielectric constant, necessitating dry-out baking before the evaluation starts.
Maintaining tight thickness tolerances on the test pieces ensures consistent results.