In-Situ Quasi-Optical Characterization of High-Frequency Printed Circuit Laminates
Non-destructive quasi-optical characterization captures true millimeter-wave permittivity tensors, preventing costly phase velocity errors before lamination.
Loss Tangent Verification
Dissipation Measurement
The systematic process of measuring the dielectric loss factor of board materials at target operating frequencies validates laminate performance. By conducting loss tangent verification, manufacturers ensure that high-frequency signals do not suffer from excessive attenuation due to heating of the board substrate. This validation is critical for radar and high-speed data systems.
Resonant Extraction
The verification process often uses a split-cylinder resonator or a strip-line resonator to isolate the material’s dielectric losses from conductor losses. Resonant methods measure the quality factor (Q-factor) of the cavity with and without the substrate sample inserted. A high Q-factor represents very low dissipation, whereas a lower Q-factor indicates higher dielectric loss.
Computations convert the measured shift in resonance frequency and bandwidth into the material’s loss tangent. The verification process must account for environmental conditions, particularly humidity, because absorbed moisture increases the measured loss factor. The test is typically executed across several panels in a production lot to confirm laminate uniformity.
Substrate Qualification
Laminates that do not meet the specified loss tangent limits are rejected to avoid thermal hotspots and signal corruption. It is especially vital when using ultra-low-loss materials that operate above twenty-four gigahertz. Correct verification maintains the signal reach and power budget of the design.