The silicon nitride sintered material and production of sintered silicon nitride, and circuit board

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PROBLEM TO BE SOLVED : To provide a silicon nitride-based sintered compact having a high thermal conductivity in addition to high strength and high toughness, and to provide a method of producing the same. SOLUTION : In the silicon nitride-based sintered compact, fine particles having diameters of ≤100 nm, which are composed of Mg or at least one rare earth element selected from La, Y, Gd and Yb and oxygen, and which are each composed of an amorphous nucleus part and an amorphous peripheral part, are contained in an amount of ≥5 pieces/μm2in silicon nitride particles. The method of producing the silicon nitride-based sintered compact comprises blending 1 to 50 parts by weight of silicon nitride-based powder containing β-fraction in an amount of 30 to 100% and oxygen in amount of ≤0.5 wt.% and having an average diameter of 0.2 to 10 μm and an aspect ratio of ≤10, 99 to 50 parts by weight of an α-type silicon nitride powder having an average diameter of 0.2 to 4 μm, and a sintering aid including Mg and at least one kind of element selected from the group of Y and rare earth elements (RE), then keeping the blend for 1 to 10 h at 1, 400 to 1, 600°C under a nitrogen atmosphere of 0.5 MPa, thereafter, raising the temperature to 1, 800 to 1, 950°C with a temperature rising speed of ≤5.0°C/min, and sintering for 5 to 40 h at a temperature of 1, 800 to 1, 950°C. COPYRIGHT : (C)2004, JPO