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Why are tungsten or molybdenum conductors cofired with alumina ceramic layers?

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Steps in doctor blading, a tape-casting process employed in the production of ceramic films. Ceramic powder and solvent are mixed to form a slurry, which is treated with various additives and binders, homogenized, and then pumped directly to a tape-casting machine. There the slurry is continuously cast onto the surface of a moving carrier film. The edge of a smooth knife, generally called a doctor blade, spreads the slurry onto the carrier film at a specified thickness, thereby generating a flexible tape. Heat lamps gently evaporate the solvent, and the dry tape is peeled away from the carrier film and rolled onto a take-up reel for additional processing.
advanced ceramics Steps in doctor blading, a tape-casting process employed in the production of ceramic films. Ceramic powder and solvent are mixed to form a slurry, which is treated with various additives and binders, homogenized, and then pumped directly to a tape-casting machine. There the slurry is continuously cast onto the surface of a moving carrier film. The edge of a smooth knife, generally called a doctor blade, spreads the slurry onto the carrier film at a specified thickness, thereby generating a flexible tape. Heat lamps gently evaporate the solvent, and the dry tape is peeled away from the carrier film and rolled onto a take-up reel for additional processing.

Tungsten and molybdenum are used as conductors in multilayer alumina packages because they are compatible with the high-temperature cofiring process required to create these structures.

To produce a monolithic package with internal conductive pathways, alumina layers are metallized with tungsten or molybdenum and then laminated together. This assembly must be fired at temperatures as high as 1,600° C (2,900° F). Tungsten and molybdenum are selected for this process because they can withstand these extreme temperatures without melting or degrading. Furthermore, the firing process is conducted in protective atmospheres of hydrogen or hydrogen-nitrogen gas specifically to prevent these metals from oxidizing at such high temperatures.1