Introduction to High-Frequency & High-Speed PCB Materials

February 11, 2026

Part 1: Requirements for High-Frequency & High-Speed Materials

Printed circuit boards (PCBs) are widely used in various electronic devices, from phones and computers to complex machinery. If a PCB has defects or manufacturing issues, it can lead to final product failures and inconvenience. In such cases, manufacturers would have to recall these devices and spend additional time and resources to fix the faults. Therefore, PCB testing becomes an indispensable part of the circuit board manufacturing process, as it helps identify problems promptly, assists staff in quick resolution, and ensures high-quality PCBs.

Part 2: Dielectric Constant (Dk or Er)

This refers to the ability of an insulating material per unit volume to store electrostatic energy under a potential gradient. A lower Dk is better. For example, at 1MHz, PTFE (Teflon) has a Dk of approximately 2.5, while FR-4 is around 4.7.

Part 3: Dissipation Factor (Df)

This is a measure of the energy loss of alternating current (AC) in a functional context. It is a characteristic of the insulating material (resin).

Part 4: Conductor Surface Roughness

The roughness of the conductor surface contributes to resistance heating and signal energy loss (conductor loss). The smoother the surface, the better for signal transmission. However, surface roughness also affects the bonding strength between PCB layers; a rougher surface increases the bonding area and strength.

Part 5: Copper Foil

By Manufacturing Process:

Electrodeposited (ED) Copper Foil: Advantages: Low cost, various sizes/thicknesses. Disadvantages: Poor ductility, high stress, brittle.
Rolled-Wrought (RA) Copper Foil: Advantages: High ductility, excellent reliability for dynamic FPC applications, smooth surface beneficial for Microwave electronics. Disadvantages: Poor adhesion to substrate, higher cost, width limitations.

By Performance Type: High Temperature Elongation (HTE) foil, Double-Treated foil, Ultra-Thin foil, Reverse-Treated foil, Low-Profile foil, Standard ED foil.

Part 6: How Prepreg (PP) is Made

"PP" stands for Prepreg, short for preimpregnated. Using epoxy resin as an example: Liquid resin is mixed with hardeners, accelerators, solvents, and sometimes fillers to create varnish (A-stage resin). Fillers can improve flame retardancy and adjust Tg. Fiberglass cloth is impregnated with this A-stage resin and partially cured to form PP (B-stage resin), which is then layered with cores.