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Abstract

A novel crystallizable glass composition for producing a novel low temperature co-fired glass-ceramic substrate having patterns of a low electrical-resistance conductor such as Ag, Ag-Pd, Au, and/or Cu is obtained. Being subjected to a firing process, the novel crystallizable glass can precipitate mullite as main crystalline phase, and at least one subordinate crystalline phase among forsterite, spinel, sapphirine, and similar crystalline phases. And also, the novel crystallizable glass powder composition with a inorganic filler as external additive having a minimum of 1.4 m.sup.2 /g. of mean specific surface area can precipitate both mullite phase and cordierite phase. The mixing weight ratio of the filler to the crystallizable glass powder is from 0.1/99.9 to 20/80. The crystallizable glass composition comprises following oxide components expressed in terms of percent by weight on the oxide basis; 45-58% of Al.sub.2 O.sub.3, 20-35% of SiO.sub.2, 5-15% of B.sub.2 O.sub.3, 5-20% of MgO, and 0-4% of alkali metal oxide. The substrates produced from the above compositions have high flexural strength, low dielectric constant, low loss factor, and controllable thermal expansion coefficient of ranging from about 30 to about 70.times.10.sup.- 7 /.degree.C. As for the substrate containing both mullite phase and cordierite phase, as the substrate has a low thermal expansion coefficient, it can be combined with AlN to produce a composite structure package.

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