Resist materials printed wiring

Hitachi has developed a heat-resistant material for printed wiring boards, consisting of an epoxy polymer containing nanosized silica, evenly dispersed by means of a sol-gel reaction. At 260 °C, the nanocomposite s elasticity was said to be about ten times higher than that of epoxy, and its thermal expansion coefficient was about one-third. 

Takahashi A, Satsu Y, Nagai A, Umino M and Nakamura Y (2005), Heat-resistant epoxy-silicon hybrid materials for printed wiring boards , IEEE Trans Electron Packag Manuf 28, 163-167. doi 10.1109/TEPM.2005.846831. 

The conditions under which the device is thermally characterized have to be clearly described. In fact, thermal resistance is made up of constant terms that are related to device and package materials and geometry in series with a number of variable terms. These terms are related to the heat paths from the package boundary to some point in the system that serves as the reference temperature and are determined by the method of mounting, the printed-wiring-board (PWB) if used, other heat generating components... 

These plastics exhibit low dielectric losses and stable dielectric constants over a broad range of temperatures and frequencies. The chemical resistance of the materials is their weakest point. Although resistant to most common solvents, acids and alkalis, they exhibit stress cracking in the presence of organic ketones, esters and chlorinated hydrocarbons. Polysulphones are used in the electronics field for connectors, chip carriers and capacitor dielectrics, and they are the first of the high temperature thermoplastics to be used for printed wiring board fabrication. 

However, conductive elastomers have only ca <10 of the conductivity of soHd metals. Also, the contact resistance of elastomers changes with time when they are compressed. Therefore, elastomers are not used where significant currents must be carried or when low or stable resistance is required. Typical apphcations, which require a high density of contacts and easy disassembly for servicing, include connection between Hquid crystal display panels (see Liquid crystals) and between printed circuit boards in watches. Another type of elastomeric contact has a nonconducting silicone mbber core around which is wrapped metalized contacts that are separated from each other by insulating areas (25). A newer material has closely spaced strings of small spherical metal particles in contact, or fine soHd wires, which are oriented in the elastomer so that electrical conduction occurs only in the Z direction (26). 

The markets for polyetherimides arise to an extent from stricter regulations concerning flammability and smoke evolution coupled with such features as high strength, toughness and heat resistance. Application areas include car under-the-bonnet uses, microwave equipment, printed circuit boards and aerospace (including carbon-fibre-reinforced laminated materials). The polymer is also of interest in flim, fibre and wire insulation form. 

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