In the design of multilayer printed circuit boards (PCBs) for high-frequency and high-speed applications, material selection is critical to ensuring signal integrity, minimizing loss, and maintaining reliable performance. The unique challenges of high-frequency (HF) and high-speed (HS) environments—such as signal attenuation, dielectric loss, and electromagnetic interference (EMI)—require materials with specific electrical and physical properties.

　　Dielectric Substrates: The dielectric material between copper layers is the foundation for HF/HS performance. Key parameters include:

　　Dielectric Constant (Dk): A stable Dk across frequencies is essential for controlled impedance. Materials like Rogers RT/duroid (Dk=2.2–10.2) and Isola FR408HR (Dk=3.5–4.5) are widely used due to their low loss and frequency stability. For example, in 5G antenna modules, low-Dk materials (Dk<3) reduce signal delay and enable compact antenna arrays.

　　Dissipation Factor (Df): Low Df (e.g., <0.001 at 10 GHz) minimizes energy loss. PTFE-based composites (e.g., Rogers) and ceramic-filled laminates (e.g., Taconic TLY) are preferred for their ultra-low Df, making them ideal for radar systems and satellite communications.

　　Thermal Stability: High glass transition temperature (Tg > 170°C) and low coefficient of thermal expansion (CTE) are vital to prevent delamination and dimensional shift during high-power operation. Materials like Nelco N4000-13SI (Tg=170°C) and Arlon AD255 (Tg=280°C) are suitable for aerospace and industrial applications.

　　Copper Foil: The quality of copper foil directly impacts conductor loss and signal integrity:

　　Rolled Annealed (RA) vs. Electrodeposited (ED) Foil: RA foil has a smoother surface (roughness <1 μm), reducing skin effect loss at high frequencies. ED foil, while cheaper, has a granular surface that increases resistance in HF traces. For HS signals (e.g., 10 Gbps+), reverse-treated ED foil (RTF) with controlled roughness (e.g., 1.5–2 μm) balances cost and performance.

　　Thickness: Thin foils (18–35 μm) are preferred for HF applications to minimize conductor loss, while thicker foils (70–105 μm) may be used for power layers in mixed-signal boards.

　　Prepregs and Bonding Materials: These ensure reliable layer adhesion and consistent dielectric properties:

　　Glass Weave Style: Low-Profile (LP) or Very Low-Profile (VLP) glass fabrics (e.g., 1080, 2116) reduce microstrip roughness and dielectric discontinuities. In 100+ layer boards, VLP fabrics enable tighter impedance control.

　　Resin Systems: Halogen-free, lead-free soldering-compatible resins (e.g., FR4 with TG180+) are standard. For extreme environments, cyanate ester or benzocyclobutene (BCB) resins offer superior thermal and electrical performance, albeit at higher cost.

　　Specialized Materials for Emerging Technologies:

　　High-Temperature Applications: Polyimide-based materials (e.g., Pyralux) withstand up to 280°C, suitable for engine control units (ECUs) in aerospace.

　　Thermally Conductive Layers: Aluminum nitride (AlN) or silicon carbide (SiC) cores enhance heat dissipation in power-hungry HS systems like data center switches.

　　EMI Shielding Materials: Conductive coatings (e.g., nickel-graphite) or embedded shielding layers reduce radiated emissions in HF circuits, critical for compliance with FCC/CE standards.

　　Material selection must balance performance, cost, and manufacturability. For example, while PTFE-based laminates offer superior HF performance, their higher cost and limited availability may restrict use to aerospace or defense applications. In consumer electronics, FR4 derivatives with optimized Dk/Df (e.g., Isola 370HR) provide a cost-effective compromise for HS USB4 or PCIe 5.0 interfaces.