Printed wiring properties

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. 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

The most important application of parylenes is as a conformal coating for printed wiring assemblies. These coatings provide excellent chemical resistance, and resistance to fungal attack, hi addition, they exhibit stable dielectric properties over a wide range of temperatures. 

The electrical properties of polymers are important in many applications [1]. The most widespread electrical application of polymers is the insulation of cables. In recent years, high-performance polymers have become important in the electronics industry as encapsulants for electronic components, as interlayer dielectrics, and as printed wiring board materials. The dielectric constant (or permittivity) and the dissipation factor (or power factor or electrical loss tangent) tan 8, which are dimensionless quantities, are the key electrical properties. 

Kraft paper is widely used as a reinforcement. When saturated with phenolics, it is made into a common printed wiring board. When combined with melamine, it becomes a decorative high-pressure laminate used in furniture, countertops, and wall panels. Paper reinforcement is inexpensive and easy to machine, drill, and pxmch. It imparts good electrical properties, but it is sensitive to moisture and cannot withstand high temperatures. 

Saytex CP-2000 is widely used for printed wiring boards laminates made from FR4 epoxies. It is reacted into the epoxy, so that there is no potential for leaching out of the resin. The FR meets the German Dioxin Rule. It is environmentally acceptable, thermally stable at high temperatures and does not disrupt resin properties when soldered. It can be used as an additive in ABS and also as a raw material in brominated epoxy oligomers in ABS and high impact polystyrene (HIPS). 

UL746 A B C D E Underwriters Laboratories. Pol5mieric materials Short term property evaluations Long term property evaluations Use in electrical equipment evaluations Fabricated parts Industrial laminates, filament wound tubing, vulcanised fibre, and materials used in printed wiring boards... 

Grade FR-4 This grade is the most common grade used in printed wiring applications. It is made with epoxy resin and glass fabric reinforcement and has properties similar to G-10 but with a flame resistance of V-0. Rods and roUed tubes are available. 

Mitsubishi Gas Chemical (7) has developed a family of products which are stated to be a coreactive blend of triazine resin (terminology used to describe bisphenol A dicyanate and its prepolymers) and a bismaleimide resin. Properties of these resins are described in patents (8) and product literature (7). End uses suggested include electronic encapsulation, printed wiring board and structural composites. 

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