Substrate materials metals

In appUcations in which electrical conductivity is required, metals, copper, tungsten, molybdenum, and Kovar [12606-16-5] are the preferred chip-carrier materials. Metals have exceUent thermal conductivities. Tables 2 and 3 Ust the various materials used for substrates, along with their mechanical, electrical, and thermal properties. 

Because of the high functional values that polyimides can provide, a small-scale custom synthesis by users or toU producers is often economically viable despite high cost, especially for aerospace and microelectronic appHcations. For the majority of iudustrial appHcations, the yellow color generally associated with polyimides is quite acceptable. However, transparency or low absorbance is an essential requirement iu some appHcations such as multilayer thermal iusulation blankets for satellites and protective coatings for solar cells and other space components (93). For iutedayer dielectric appHcations iu semiconductor devices, polyimides having low and controlled thermal expansion coefficients are required to match those of substrate materials such as metals, ceramics, and semiconductors usediu those devices (94). 

Impressed current anodes of the previously described substrate materials always have a much higher consumption rate, even at moderately low anode current densities. If long life at high anode current densities is to be achieved, one must resort to anodes whose surfaces consist of anodically stable noble metals, mostly platinum, more seldom iridium or metal oxide films (see Table 7-3). 

The two types of hot eorrosion eause different types of attaek. High-temperature eorrosion features intergranular attaek, sulfide partieles and a denuded zone of base metal. Metal oxidation oeeurs when oxygen atoms eombine with metal atoms to form oxide seales. The higher the temperature, the more rapidly this proeess takes plaee, ereating the potential for failure of the eomponent if too mueh of the substrate material is eon-sumed in the formation of these oxides. 

A SSIMS spectrum, like any other mass spectrum, consists of a series of peaks of dif ferent intensity (i. e. ion current) occurring at certain mass numbers. The masses can be allocated on the basis of atomic or molecular mass-to-charge ratio. Many of the more prominent secondary ions from metal and semiconductor surfaces are singly charged atomic ions, which makes allocation of mass numbers slightly easier. Masses can be identified as arising either from the substrate material itself from deliberately introduced molecular or other species on the surface, or from contaminations and impurities on the surface. Complications in allocation often arise from isotopic effects. Although some elements have only one principal isotope, for many others the natural isotopic abundance can make identification difficult. 

Anodically grown aluminum oxide (AI2O3) has also been used extensively as a template [3,32-37]. When grown on high-purity aluminum, this material has a hexagonal pattern of cylindrical pores, which extend through the thickness of the alumina (Fig. 1C and ID). These microporous alumina films can be removed from the substrate A1 metal and collected as a freestanding membrane [37,38]. 

Plastics. Part of the trend to substitute plastic and composite substrates for metals can be attributed to a desire to avoid the process of metallic corrosion and subsequent failure. Relatively little attention has been called to the possible failure modes of plastics under environments considered corrosive to metals. More extensive work should be conducted on the durability and life expectancy of plastic and composite materials under end-use environments. A further consideration is the potential for polymer degradation by the products of metal corrosion in hybrid structures comprising metal and polymer components. Since it is expected that coatings will continue to be used to protect plastic and composite substrates, ancillary programs need to be conducted on the mechanisms by which coatings can protect such substrates. 

The catallytic metallic Pd covers only a small fraction of the surface. The amount of Pd on the glass substrate (11) is 0.04 to 0.05 ixglcm . Assuming uniform distribution, this amount corresponds roughly to 0.3 of a monolayer of Pd on a glass substrate. The surface density of catalytic sites a depends on substrate material. For glass the maximum value of a was found to be 10 sites/cm. ... 

The simplest recording medium is a bilayer structure. It is constructed by first evaporating a highly reflective aluminum layer onto a suitable disk substrate. Next, a thin film (15-50 nm thick) of a metal, such as tellurium, is vacuum deposited on top of the aluminum layer. The laser power required to form the mark is dependent on the thermal characteristics of the metal film. Tellurium, for example, has a low thermal diffusivity and a melting point of 452 °C which make it an attractive recording material. The thermal diffusivity of the substrate material should also be as low as possible, since a significant fraction of the heat generated in the metal layer can be conducted to the substrate. For this reason, low cost polymer substrates such as poly (methylmethacrylate) or poly (vinyl chloride) are ideal. 

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