Thermal conductivity electrical insulators

These adhesives consist of a polymerizable liquid matrix and large volume fractions -of electrically insulating thermally conductive filler. Typical matrix materials are epoxies, silicones, urethanes, and acrylates, although solvent-based systems, hot-melt adhesives, and pressure-sensitive adhesive tapes are also available. Aluminum oxide, boron nitride, zinc oxide, and increasingly aluminum nitride are used as fillers for these types of adhesives. The filler loading can be as high as 70 - 80 wt %, and the fillers raise the thermal conductivity of the base matrix from 0.17-0.3 up to about... 

In order to obtain a fundamental understanding of oxide surfaces, well-ordered thin oxide films, grown in ultrahigh vacuum (UHV) under well-controlled (clean) conditions, has turned out to be a successful approach ([8, 17, 38] and references therein). In contrast to many (insulating) bulk oxides, thin oxide films exhibit electrical and thermal conductivity sufficient for the application of surface sensitive imaging (e.g., STM) and spectroscopic methods (e.g., XPS Auger electron spectroscopy, AES and temperature-programmed desorption, TPD). 

The most important additive in an adhesive formulation is the filler. Fillers such as metal particles are used to render adhesives both electrically and thermally conductive while electrically insulative fillers such as metal oxides are used to provide thermal conductivity alone. Regardless of whether they are electrically conductive or not, fillers provide numerous simultaneous benefits, including the following ... 

Due to the exceptional properties of carbon nanotubes (CNTs), such as high electrical and thermal conductivity and excellent mechanical properties, they are expected to have great potential as fillers for polymeric matrices. CNTs are incorporated in electrically insulating polymer materials to achieve electrostatic dissipative behavior or electrical conductivity and improved mechanical properties. Current applications for such nanocomposites include electrostatically dissipative plastic housing or fuel lines, as well as lightweight and electrostatically paintable plastic components replacing metals in car panel applications. Incorporation of CNTs in polymers on an industrial scale is... 

Epoxy or polyepoxide is a thermosetting polymer formed from reaction of an epoxide resin with polyamine hardener. Epoxy is used in coatings, adhesives and composite materials. They have excellent adhesion, chemical and heat resistance, good mechanical properties and electrical insulating properties. Epoxies with high thermal insulation, thermal conductivity combined with high electrical resistance are used for electronics applications. There are a few studies conducted on OPE-epoxy composites. 

For high electric and thermal conductivity, metals such as gold (Au), copper (Cu), and aluminum (Al) are used widely. Magnetic metals such as nickel (Ni) and iron (Fe) are utilized to form magnetic actuators. Some metal thin films such as chromium (Cr) and titanium (Ti) are applied to enhance the adhesion of other metal thin films to a substrate. Doped polycrystalline silicon and metal silicides [12] have electric conductivities slightly inferior to metals but much better than insulators. They have also become integral materials for microelectronics. 

Conductive adhesives include electrically and thermally conductive materials. Most fillers that impart electrical conductivity also contribute to thermal conductivity, but thermally conductive adhesives that are electrically insulative are also available. 

Other advantages. Adhesives can be made to function as electrical and thermal insulators. The degree of insulation can be varied with different adhesive formulations and fillers. Adhesives can even be made electrically and thermally conductive with silver... 

The market for electrically insulating, heat conductive encapsulants based on beryllia grain-polymer mixtures is both small and restricted. While these composites have thermal conductivities 10-20 times higher than those of other filled plastics, the handling restrictions necessitated by the presence of beryllia limit their use. 

Some of the solid lubricants may provide better electrical and thermal conductivity, whereas most liquid lubricants are insulating. 

By nature, polymers are insulating materials and some of them are employed without any added fillers. However, most applications require either electrical or thermal conductivity or both. According to the final use, thermal stabiUty and resistance to aggressive environment can be important criteria to select a particular type of polymer. In fact, few adhesives have been specifically developed for the electronic industry. Instead, most materials were preexisting compositions that have been tested and incorporated in production processes. Specific requirements such as ionic contamination, water absorption, and better thermal stability appeared later. Major chemical companies and semiconductor manufacturers, in particular in the USA and Japan, launched variants of these polymers fulfilling the demand for organic materials with enhanced properties. 

Oxides are often chosen as insulation materials, for example as sheaths for resistive heaters, due to their low electrical and thermal conductivity. In MOS transitors (MOS = Metal-Oxide-Semi-conductor), a thin Si02 layer is deposited between a doped silicon substrate and the metallic gate to control the channel conductivity. In more complicated electronic devices, with several integration levels, Si02 is also used to make insulating dielectric layers. 

Pure ionic crystals are transparent well into the ultraviolet, and are good insulators with low electrical and thermal conductivities at room temperature. At high temperature the ionic conductivities can be appreciable. 

In insulators, there are no free electrons and consequently only phonons transmit heat. The maximum thermal conductivity of such a material can be calculated using the formulae above. In most cases, however, this turns out to be a relatively low value and most electrical insulators are relatively good thermal insulators. The notable exception is diamond with the highest thermal conductivity of any material. Because it is an electrical insulator, diamond conducts heat via phonons alone. 

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