JPH05298919

PURPOSE:To provide sufficient mechanical strength to a composite substrate, make its thermal expansion coefficient near that of silicon and its dielectric constant low, and fire at low temperature by making the composite circuit substrate using a cordierite-anorthite-boron-based composite and providing a fine structure to the composite circuit substrate wherein the anorthite is taken in the cordierite phase. CONSTITUTION:A composite circuit substrate is made of a cordierite-anorthite- boron-based composite material and has a fine structure wherein the anorthite is taken in the cordierite phase. The weight ratio of cordierite/anorthite is (50-95)/(5-50) and boron (calculated in terms of B2O3) to cordierite is 0.5-10wt.%. A cordierite-anorthite composite composition sol is prepared by mixing boehmite sol, silica sol, a water-soluble magnesium salt, and a water-soluble calcium salt, gelled, calcined, and sintered. As a result, the resulting composite circuit substrate has sufficient mechanical strength, thermal expansion coefficient near that of silicon, low dielectric constant, and can be sintered at low temperature.