Electrical Engineering Glass

glass possessing specific electrical properties and used in electrical engineering and electronics as an insulating and structural material.

Electrical insulating glass is used in the production of capacitors, hermetically sealed plug and socket units and input terminals, and insulators for power transmission lines; glass textiles and fiber glass reinforced plastic are used for insulating parts of electric machines and equipment. Fine wire may be produced with a thin glass insulation (2–5 micrometers thick). Nonalkaline and low-alkaline aluminosilicate glasses possessing high electrical resistance, moisture resistance, electric strength, and heat resistance are also used for electrical insulation.

Vacuum-tube glass is an important structural material in the construction of vacuum-tube instruments and the production of light sources. It is used to make electron tubes, electron-beam and X-ray tubes, photo-multipliers, particle counters, incandescent lamps, gasdischarge lamps, halogen lamps, and pulsed light sources. Electrode jackets, holders, and insulators as well as hermetically sealed output terminals of vacuum-tube and semiconductor devices with metal packages are also made of vacuum-tube glass. Such glasses should exhibit good dielectric properties and, in order to avoid cracking at seals, they should have coefficients of thermal expansion that match those of the metals or other glasses with which they are joined. Vacuum-tube glasses are divided into the following major groups based on their coefficient of thermal expansion a and, consequently, the feasibility of joining them to suitable metals (the figures in parentheses are α × 10⁷, in °C^–1): quartz glasses (6–10), tungsten glasses (37–40), molybdenum glasses (47–50), titanium glasses (72–75), platinum glasses (84–92), and iron glasses (110–120).

In order to join metals to glasses that have a considerably different coefficient of thermal expansion (for example, quartz glass), consecutive seals of several glasses with small differences in their coefficient of thermal expansion or special transition structures may be used. In the Soviet classification of vacuum-tube glasses, the coefficient of thermal expansion is indicated in the product designation (for example, S49–2 glass has α = 49 × 10^–7/°C). Bromosilicate, aluminosilicate, alkaline, and nonalkaline glasses containing oxides of, for example, alkaline-earth metals and lead may be used as vacuum-tube glasses. Quartz glasses and glasses with a high silica content (94–96 percent) are used in the production of powerful light sources.

In microelectronics, thin films of glass (1–50 micrometers thick) are used to provide interlayer electrical insulation, pack-ageless shielding for integrated circuits, and hermetic sealing of integrated circuit packages. Nonalkaline borate and borosilicate glasses with low melting points are used for the production of the films. Several types of integrated circuit packages are manufactured from glass.