Dielectric constants printed wiring substrates

The use of polytetrafluoroethylene or PTFE for printed wiring substrate fabrication is a relatively well-established practice brought about by the need for improved high-frequency materials. The critical properties in this field of application are a low dissipation factor, a uniform dielectric constant which exhibits little variation with frequency over a wide bandwidth up to 15 GHz, combined with environmental and temperature stabilities. These properties can be achieved in a number of teflon/glass or teflon/glass/ceramic composites based on both fabrics and random glass. The dissipation factor at 1 MHz is more than 100 times less than a typical epoxy FR4, as shown in Table 9.4. 

Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

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