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FR-4

Flame Retardant 4 (FR-4) is reinforced glass epoxy that is standard throughout the PCB industry. It is highly desired due to its low costs, high dielectric strength, and great electrical insulation as it is also temperature resistant and moisture resistant, so it can be used in a wide range of applications. However, there are a few setbacks that make them unsuitable for high digital circuits or for the newer higher frequencies that are being developed (fifth generation or 5G wireless communication). It experiences high dielectric loss for microwave frequencies.

PTFE

Polytetrafluoroethylene (PTFE), also referred to as Teflon, are woven fiberglass/ceramic filled plastics that are acceptable replacements for FR-4 laminates when developing high speed PCBs. Their dielectric constant ratios are anywhere from 3.5 or lower, making them ideal for high frequency applications when requiring low signal loss and better impedance control. PTFE is also used for applications that will experience higher temperatures as it provides good mechanical stability. A downside with PTFE is that it costs more than FR-4, and although it has temperature stability, it will experience dielectric loss at higher temperatures and will have dimensional changes due to being a softer material.

Polyimide

We often talk about polyimide when it is used for rigid-flex and flexible PCBs. Yet this flexible polymer film also works well for hybrid, multilayer PCB applications. The material offers a high level of chemical resistance, works well with a wide range of temperatures, and has good electrical properties. Polyimide laminates are flexible and lightweight, making them suitable for portable applications. One of the major disadvantages for polyimide laminates are the costs, as they are more expensive than FR-4 and PTFE.

Hybrid multilayer PCBs often make use of circuit materials with very different values of dielectric constant (Dk). For example, some multilayer antenna circuits may consist of a low-Dk circuit material as the outside layer for radiating elements, a moderate-Dk circuit material internally for a stripline antenna feed line, and a high-Dk material for an internal layer for filter circuitry. The different Dk materials are often based on different resin systems. The outer, low-Dk layer may be PTFE material while the inner, moderateDk circuit layer is formed on a ceramic-filled hydrocarbon-based laminate. The bonding materials could be based on either type of material, although hydrocarbonbased bonding materials are more often used for their ease of circuit fabrication.

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3. Product application

Printed circuit boards (PCBs) with characteristic impedance control are widely used in high frequency circuit. PCB's that mixed high frequency material can reduce signal loss at high frequencies and meet the development needs of communication technology.

It is mainly used in the infrastructure field of transmission cores including WDM/OTN end-to-end intelligent optical transmission platform, MSTP/multi-service transmission platform, microwave fusion transmission radio frequency, data communication system platform, and other information communication industries.