TABLE OF CONTENTS 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...
