From Electronic Materials and Processes Handbook, Third Edition

8.7 Properties of Substrate Materials

8.7.1 Aluminum oxide

Aluminum oxide, Al 2O 3, commonly referred to as alumina, is by far the most common substrate material used in the microelectronics industry, because it is superior to most other oxide ceramics in mechanical, thermal, and electrical properties. The raw materials are plentiful and low in cost and are amenable to fabrication by a wide variety of techniques into a wide variety of shapes.

Alumina is hexagonal close-packed with a corundum structure. Several metastable structures exist, but they all ultimately irreversibly transform to the hexagonal alpha phase. Alumina is stable in both oxidizing and reducing atmospheres up to1925 C.

Weight loss in vacuum over the temperature range of 1700 C to 2000 C ranges from 10 ?7 to 10 ?6 g/cm 2-sec. It is resistant to attack by all gases except wet fluorine to at least 1700 C. Alumina is attacked at elevated temperatures by alkali metal vapors and halogen acids, especially the lower-purity alumina compositions that may contain a percentage of glasses.

Alumina is used extensively in the microelectronics industry as a substrate material for thick and thin film circuits, for circuit packages, and as multilayer structures for multichip modules. Compositions exist for both high- and low-temperature processing. High-temperature cofired ceramics (HTCC) use a refractory metal, such as tungsten or molybdenum/manganese, as a conductor and fire at about 1800 C. The circuits are formed as separate layers, laminated together, and fired as a unit. Low-temperature cofired ceramics (LTCC) use conventional gold...

Products & Services
Aluminum Oxide and Alumina Ceramics
Aluminum oxide and alumina ceramics have excellent wear characteristics, chemical resistance, compressive strength, high-temperature properties, and dielectric strength. They are used widely because of their versatility and low cost. Their main drawback is its relatively poor thermal-shock resistance due to higher coefficients of thermal expansion and lower thermal conductivity (compared to other pure ceramic materials).
Zirconium Oxide and Zirconia Ceramics
Zirconium oxide and zirconia ceramics are extremely refractory compounds of zirconium and oxygen. Zirconia ceramics possess excellent chemical inertness and corrosion resistance at temperatures well above the melting point of alumina.
Silica, Quartz, and Silicate Materials
Silica, quartz and silicate materials include fused silica, quartz, kaolin or clay-based materials, cordierite, steatite, forsterite, sillimanite, zircon, porcelain, and fireclay. They are based on silicon dioxide and various chemical variations.
Specialty Ceramics
Specialty ceramics include nitrides, borides, carbon, zirconia, rare earth oxide (REO) materials and silicides as well as other specialized non-metallic compounds.
Thermal and Refractory Ceramics
Thermal and refractory ceramics are inorganic, engineered materials that are designed for high-temperature applications. They are used for thermal insulation and fire proofing, and also as structural materials. Additional applications include wear parts and tooling, electrical and electronic components, glass manufacturing, materials processing, corrosion protection, and ballistics.

Topics of Interest

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