Multilayer ceramics cofired materials

HTCC is an all-inclusive term to describe ceramic substrates that are consolidated at temperatures above about 1000°C. Applied to electronic packaging, this descriptor includes aluminum oxide, aluminum nitride (AIN), and a variety of other developmental or seldom-used materials. Until recently, discriminating between HTCC and low-temperatme cofired ceramics (LTCC) was elementary, as the firing temperatures differed by roughly 600°C. To confoimd that difference, an intermediate-firing multilayer ceramic, or medimn-temperature cofired ceramic (MTCC), has recently been introduced. Details on the processing and properties of this material will be discussed in Section 6.2 and Section 6.4. 

Figure 16. Cross section of thin-film multilayer interconnections on a pinned cofired ceramic substrate, with face-up tape-automated-bonded chip and thermal vias. (Reproduced with permission from reference 79. Copyright 1988 Materials Research Society.)...

Thermal vias in low-temperature cofired ceramic (LTCC) are fabricated in the same manner with the same constraints as in multilayer thick films. The only difference is the formulation of the via-fill material. 

High-temperature cofired ceramic (HTCC) packages make use of thermal vias in the same manner as in multilayer thick-film substrates. The via-fill material used in HTCC packages is a refractory material such as tungsten or moly-manganese. 

The multilayer systems use low-dielectric-constant materials similar to traditional ceramic substrates for dielectric layers and an internal circuit metallization designed to be cofired with the ceramic dielectric. Cofiring of metallization with a ceramic dielectric required development of compatible systems which would have matching shrinkage onsets, shrinkage rates, and total volumetric shriiikage. Since the metal thermal expansions are... 

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. 

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