Electrical glass moisture absorption

Components of switches, relays, and connectors use glass fiber reinforced semicrystalline polymers, such as PA, PPS, PBT, and PET. The following requirements are important in these applications dimensional stability and precision, low moisture absorption, strength, resistance to creep, electrical insulating properties, and resistance to high working temperatures ( 85°C). 

PET and PBT are characterized by high strength, rigidity, and toughness low creep at elevated temperatures excellent dimensional stability low coefficient of friction good chemical, grease, oil, and solvent resistance minimal moisture absorption and excellent electrical properties. Reinforcement of these polymers with glass fibers enhances many of their properties (Table 15.16). 

This is a thermoplastic material, the correct name for which is poly-etheretherketone. PEEK is also regarded as a high-performing polymer, offering excellent chemical resistance, very low moisture absorption and good wear, abrasion and electrical resistance. It can be used continuously to 250°C in hot water and steam without permanent loss in physical properties. It is used to replace metal parts in the aerospace, automotive, oil and gas industries and is available reinforced with glass and carbon fibre. 

D. Electrical Properties Because of the water-resistant nature and low moisture absorption levels, most polyphenylene oxide alloys present good electrical properties over a wide range of humidity and temperature ranges. PPO has a low dielectric constant of 2.58 (at 23°C 60 Hz), a low dissipation factor of 0.00035 and a high glass transition temperature (T ) of approximately 212°C, which are suitable materials for insulating matrices for electrical and electronic devices. 

In addition to providing circuit interconnection, a multilayer printed wiring board (ML-PWB) provides the electrical and mechanical platform for the system. This means that the electrical and thermal properties of the ML-PWB material are very important for the proper functioning of the system. Among the properties of importance are dielectric constant, Du (also known as Er) dielectric loss, Df (or tan 8) glass transition temperature, Tg time to delamination,Txxx thermal decomposition temperature.Ta coefficient of thermal expansion, CTE and moisture absorption. The following sections discuss the importance of these properties to an ML-PWB snbstrate. 

Basically, PBT seems to have a unique and favorable balance of properties between nylons and POM resins. It has relatively low moisture absorption, extremely good self-lubrication, fatigue resistance, solvent resistance, and good maintenance of mechanical properties at elevated temperatures. When PBT was reinforced with glass fiber it has excellent maintenance of properties up to its crystal melting point. Key markets include under-the-hood automotive applications, which require thermal and solvent resistance, electrical and electronic applications, power tools, small and large appliance components, and athletic goods. 

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