In-Situ Free-Space Dielectric Testing of Unclad Substrates
Non-destructive free-space characterization evaluates bulk dielectric properties of raw unclad laminates without etched coupon waste or copper interface errors.
Millimeter Wave Substrates
High Frequency Laminate
Specialized dielectric laminates designed for operation above thirty gigahertz provide the low dispersion and low signal attenuation required for automotive radar and advanced communications. These millimeter wave substrates feature extremely smooth copper foil and ultra-low-loss resin systems to minimize conductor losses at very high frequencies. The electrical performance of these materials depends heavily on maintaining a stable dielectric constant across the entire operating bandwidth.
Standard FR-4 laminates cannot be used at these frequencies due to excessive dielectric losses.
Dielectric Loss
Reinforcement fibers influence the electromagnetic consistency of the board structure. When working with millimeter wave substrates, the woven glass bundles in traditional composites cause localized variations in the dielectric constant. To solve this, manufacturers use spread-glass to ensure a homogeneous material profile.
Fabrication Detail
Surface roughness at the copper-dielectric interface becomes the dominant cause of signal degradation at short wavelengths. At millimeter wave frequencies, the skin depth of the signal is under one micron, meaning current flows almost entirely in the copper treatment layer. If millimeter wave substrates use rough copper foils to improve mechanical peel strength, the effective line resistance rises dramatically.
Circuit designers therefore specify low-profile or very-low-profile copper treatments to preserve signal integrity.