Abstract: Ceramic substrates (1) for microelectronic modules are formed in multiple layers (7 & 9) fused into a unitary one-piece assembly. The layers contain the same ceramic material but in different purity so that one outer layer (9) is optimal in composition for bonding to a thick film conductor (11) and the other outer layer (7) is optimal in composition for bonding to a thin film conductor (13). In a dual composition substrate embodiment one layer is formed of a 96% alumina composition and the second layer is formed of a 99.6% alumina composition.

Abstract: The presently claimed invention relates to a method of producing, in large volumes and at low cost, transition metal carbide, nitride or carbonitride whiskers, preferably submicron, having excellent reinforcing properties. These whiskers are suitable for use as a reinforcement in a wide range of materials, including metals, intermetallics, plastics, ceramics and metallic bonded hard material. The basic idea is the use of a carbon source with a volatile part which volatiles at temperatures up to 1000.degree. C. Transition metal oxide or alkali compounds thereof in amounts to satisfy the stoichiometric requirements of the desired carbide or nitride is mixed with the carbon powder along with an alkali metal chloride powder as a volatilization agent for the metal and a catalyst for the whisker growth such as Ni or Co. The reactant powders are blended in some typical manner using a high speed blender so as to intimately mix them.