FR4, being the most popular one, is not always used in high-frequency PCBs because this PCB laminate can degrade the signal performance at high frequencies. Not because they consist of any wrong conduction material, but the reality lies in the substrate dielectric properties. The dielectric itself attenuates the signal at high frequency. So, after a lot of research in this area, we got some really good materials. The three alternatives for high-performance PCBs are Rogers, PTFE, and Teflon laminates. They offer better dielectric control, lower signal loss, and superior thermal stability. But they differ a lot from the cost perspective from standard FR4. In this guide, we will get through:
Two key electrical properties of a laminate define how it will behave in high-frequency circuits:
1. Dielectric Constant (Dk or εr):
It determines the speed of signal propagation. Lower the value of Dk means faster signal speed, longer wavelength. The dielectric constant of a material also affects impedance calculation for traces. Rogers typically offers Dk = 2.2–6.5, PTFE/Teflon often ~2.1.
2. Loss Tangent (Df or tan δ):
It represents dielectric losses (how much RF energy is lost as heat). Lower loss tangent means higher efficiency. A table below is given for all FR4, Roger, and PTFE for comparison:
Rogers Corporation produces a wide range of high-frequency PCB laminates (e.g., RO4000, RO3000 series). The composition includes hydrocarbon-ceramic or PTFE composites. Because of the laminate properties, it is excellent from hundreds of MHz into tens of GHz due to low losses. Rogers has better stability to heat than any other high-frequency material. They are particularly used in radar, satellite, and precision RF technologies.
It is a type of polymer with an extremely low dielectric constant variation over frequency. It has the lowest losses among all but is more affected by heat. It has very good electrical signal handling properties, but is mechanically very soft in nature, because of which the copper layer may expand or contract as per temperature. It is commonly used in medical and radar applications.
Teflon is a brand name for PTFE (registered by DuPont/Chemours). In PCB terminology, "Teflon boards" are usually PTFE-based PCBs. Same low-loss, low-Dk characteristics as PTFE, but “Teflon” often refers to pure PTFE or PTFE composites. They need special manufacturing processes due to their softness. And commonly used in very high-frequency microwave boards (>10 GHz), aerospace communication.
Let’s take a real-world example: Designing a 50 Ω microstrip trace at 10 GHz. Let the thickness of the PCB be 0.8mm and the copper thickness if 35 μm. We’ll calculate the trace width required for 50 Ω impedance.
Dk = 3.48, Df= 0.0037, Using microstrip impedance formulas:
Dk = 2.1, Df = 0.0005, Using microstrip impedance formulas:
Dk ≈ 4.4, Df ≈ 0.017, Using microstrip impedance formulas:
