Composite materials high-temperature cofired

Ceramic-glass composite materials may be used to economically fabricate very complex multilayer interconnection structures. The materials in powder form are mixed with an organic binder, a plasticizer, and a solvent and formed into a slurry by ball or roll milling. The slurry is forced under a doctor blade and dried to form a thin sheet, referred to as green tape or greensheet. Further processing depends on the type of material. There are three basic classes of materials high temperature cofired ceramic (HTCC), low temperature cofired ceramic (LTCC), and aluminum nitride. 

The fact that this composite material can be cofired at temperatures of approximately 950°C represents a favorable characteristic. Hence, highly conductive metals such as copper and silver can be used to increase the conductivity compared with molybdenum. 

More recently, because of their high dielectric constants k > 20 000), lead-based relaxor ferroelectrics have been used as capacitor materials. These ceramics have the general chemical formula Pb(5i, 2)03) vvhere Bi is typically a low-valence cation and B2 is a high-valence cation. Compositions used in capacitor applications are frequently based on lead magnesium niobate, Pb(Mgi/3,Nb2/3)03, and lead zinc niobate, Pb(Zni/3,Nb2/3)03. Other substituents and modifiers are added so that dielectric layers of these materials can be densified at relatively low temperatures ( 900 °C). The low firing temperatures permit the use of relatively inexpensive cofired electrode materials, such as silver. Typically, tape casting is used in the preparation of the dielectric layers. 

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