Substrate Material
High-frequency dielectric substrates with ultra-low dissipation factors are designed to support electromagnetic wave propagation in the millimetric and sub-millimetric wave bands. For next-generation communications systems, sub-terahertz laminates utilize specialized glass reinforcement and polymer matrices to minimize dielectric absorption above one hundred gigahertz. These materials provide a highly stable dielectric constant across a wide temperature and frequency range.
This stability is critical to prevent signal attenuation and phase distortion in advanced radar and high-speed data links.
Transmission Performance
Transmission losses in high-frequency circuits are dominated by conductor skin effect and dielectric attenuation, which both increase dramatically at higher frequencies. Because the skin depth of the signal at these frequencies is extremely shallow, the copper surface of the laminate must be exceptionally smooth to prevent resistive losses. Conventional rough copper foils degrade signal propagation, making the use of rolled or very low profile copper foil mandatory on these substrates.
Furthermore, the absence of woven glass fibers in some designs helps eliminate the fiber weave effect, which otherwise causes phase imbalance between differential signal lines. These material optimizations ensure that signal path losses remain within acceptable limits for long-term transmission, protecting high-frequency transceivers from output power drops.
Fabrication Detail
Fabrication of printed circuit boards with these materials requires strict process control during lamination and drill steps. The toughness of the polymer matrices requires optimized drilling parameters to avoid resin smear and ensure clean hole walls for copper plating. Clean drill holes are necessary to prevent electrical opens and maintain high-frequency connection reliability.
Once drilled, boards undergo surface desmear and chemical activation to ensure strong adhesion of the copper plating in the through-holes.
