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.
Millimeter-Wave Laminates
Substrate Specification
High-frequency dielectric boards engineered for applications operating above thirty gigahertz provide very low attenuation and stable permittivity. Modern millimeter-wave laminates are manufactured using polytetrafluoroethylene or hydrocarbon resins filled with ceramic particles to ensure low losses. These materials are designed to be thin and have very smooth copper foil attached to them.
Signal Losses
At very high frequencies, the electromagnetic wave travels primarily along the skin depth of the conductor, making the copper foil roughness a major source of attenuation. The laminates use very low profile or rolled copper to keep losses to a minimum. Additionally, the dielectric constant must remain stable across a wide temperature range and are designed to avoid moisture absorption.
This stability prevents the shifts in transmission line impedance and phase velocity that would disrupt the performance of phased-array antennas. Typical thickness values range from five to twenty mils, which limits the radiation losses from the transmission lines.
Manufacturing Challenge
Processing these materials requires special drilling parameters and plasma etching to ensure through-hole plating adhesion. Because the resins are often softer than standard FR4, panels must be handled with care to prevent scratches and dimensional instability. Precise registration is necessary during multilayer lamination to align sub-millimeter features.