Circuit board and method of production therefor

A method of producing a circuit board, comprising

• a step of producing a first laminate comprising disposing a first metal layer on a first ceramic layer, and disposing a second metal layer on the first ceramic layer to a surface of the first ceramic layer opposite to a surface thereof on the side of the first metal layer, and pressurizing under heating, so as to produce the first laminate,
• a step of producing a second laminate comprising disposing a second ceramic layer on the first metal layer of the first, and pressurizing at a pressure of 1 to 20 MPa for a pressurizing time of 10 minutes to 30 hours under heating to a heating temperature of 150 to 260° C., so as to produce the second laminate in which the first metal layer is disposed between the first ceramic layer and the second ceramic layer, wherein a metal used in the first metal layer is at least one metal selected from the group consisting of copper, aluminum, nickel, iron, tin, gold, silver, titanium, and stainless steel, and wherein the second metal layer has a thickness of 0.2 to 5.0 mm,
• the second ceramic layer being a porous boron nitride layer having voids filled with a semi-cured material of a thermosetting composition.