Measurement Standard
RF dielectric characterization of unclad thin laminate material relies on a non-destructive clamping fixture that forms a temporary transmission line. The clamped stripline test evaluates the relative permittivity and loss tangent of flexible or rigid dielectric sheets without requiring permanent metallic cladding. A card under evaluation slides between two ground planes and a central resonator board, forming a balanced stripline structure.
Clamping pressure establishes uniform air gaps that eliminate parasitic air film errors during resonance detection. The procedure governs raw material qualification for high-frequency circuit boards.
Mechanical Clamping
Hydraulic or mechanical force clamps the substrate under test against a thin central conductor pattern etched on a dedicated card. Mechanical pressure compresses surface micro-roughness, driving out entrained air that would otherwise artificially depress the measured dielectric constant. Standardized clamping torque values maintain consistent internal geometries across repeated insertions.
Precise alignment pins prevent skew of the central strip relative to the outer ground plates during assembly. Variations in clamping force shift the resonant frequency, rendering calibrated torque application mandatory for reproducible loss calculations. Fabrication facilities utilize these measurements to verify incoming laminate lots prior to etching signal traces.
Frequency Limit
Cavity resonances inside the physical fixture bound the upper operational range of the measurement system. Beyond ten gigahertz, higher-order transverse electromagnetic modes propagate within the clamped volume, skewing S-parameter extraction. Thinner dielectric samples extend the usable frequency range by suppressing unwanted cavity modes.
