Teflon & FR4
Teflon is the best known brand name of PTFE (Polytetrafluoroethylene) based formulas. It has excellent dielectric properties, especially at high radio frequencies, making it suitable for use as an excellent insulator in printed circuit boards used at microwave frequencies (it is also used in connector assemblies and cables). Combined with its high melting temperature, this usually makes the material the best high-performance substitute for the weaker and lower-melting-point polyethylene commonly used in low-cost applications. Most of the materials used in PCB’s are not pure PTFE but will have some small amount of micro-fiber glass impregnated into the substrate, or will be PTFE with woven glass reinforcement or ceramic filled. In general, and in comparison to the other types of high frequency materials, the nearly pure PTFE without woven glass can be one of the most challenging type of circuit material to use in PCB fabrication.