Abstract: A silicon nitride circuit board includes a silicon nitride substrate, a first copper layer over one surface of the silicon nitride substrate, and a second copper layer over the other surface of the silicon nitride substrate, in which a fracture toughness value Kc of the silicon nitride substrate is equal to or more than 5.0 MPa·m0.5 and equal to or less than 10.0 MPa·m0.5, and when a coefficient of linear expansion of the silicon nitride substrate is ?B (/° C.), a Young's modulus of the silicon nitride substrate is EB (GPa), a coefficient of linear expansion of the first copper layer is ?A (/° C.), and a coefficient of linear expansion of the second copper layer is ?C (/° C.), each of a heat shock parameter HS1 and a heat shock parameter HS2 is equal to or more than 1.30 GPa and equal to or less than 2.30 GPa.

Abstract: Disclosed is an aluminum nitride substrate for a circuit board, the substrate having aluminum nitride crystal grains with an average grain size of 2 to 5 ?m and a thermal conductivity of at least 170 W/m·K. The aluminum nitride substrate does not include a dendritic grain boundary phase and has a breakdown voltage of at least 30 kV/mm at 400° C. Also provided is a method for producing the aluminum nitride substrate, including the steps of heating a raw material containing an aluminum nitride powder to 1500° C. at a pressure of at most 150 Pa, then increasing and holding the temperature at 1700 to 1900° C. in a pressurized atmosphere of at least 0.4 MPa using a non-oxidizing gas, then cooling to 1600° C. at a cooling rate of at most 10° C./min.

Abstract: Disclosed is an aluminum nitride substrate for a circuit board, the substrate having aluminum nitride crystal grains with an average grain size of 2 to 5 ?m and a thermal conductivity of at least 170 W/m·K. The aluminum nitride substrate does not include a dendritic grain boundary phase and has a breakdown voltage of at least 30 kV/mm at 400° C. Also provided is a method for producing the aluminum nitride substrate, including the steps of heating a raw material containing an aluminum nitride powder to 1500° C. at a pressure of at most 150 Pa, then increasing and holding the temperature at 1700 to 1900° C. in a pressurized atmosphere of at least 0.4 MPa using a non-oxidizing gas, then cooling to 1600° C. at a cooling rate of at most 10° C./min.

Abstract: A circuit substrate which has a ceramic substrate and an Al circuit comprising Al or an Al alloy bonded to said ceramic substrate via a layer comprising Al and Cu.

Abstract: A circuit substrate which has a ceramic substrate and an Al circuit comprising Al or an Al alloy bonded to said ceramic substrate via a layer comprising Al and Cu.