Abstract: Disclosed is an aluminum nitride circuit board which is advantageously used as a carrier for a part emitting a large volume of heat, the substrate of the circuit board is a sintered aluminum nitride substrate which comprises a basal part and projection rising from the basal part and offering a surface for application of a metallizing composition, a metallized layer thereof is formed on the upper side of the projection by applying the metallizing composition thereon and forming the applied layer of the composition by firing, the metallizing composition applied on the upper side of the projection is prevented from sagging down the lateral side of the basal part owing to the step formed with the projection and the basal part, the preclusion of the otherwise inevitable sagging of the composition contributes greatly to improving the circuit board's voltage withstanding property.

Abstract: This invention resides in a substrate structure comprising a ceramic tile, a conductor layer of copper or copper alloy directly joined to the surface of the ceramic tile, and an outgoing terminal connected to the conductor layer, which substrate structure is characterized by the fact that the part of the conductor layer to which the aforementioned outgoing terminal is joined is raised from the ceramic tile so as to bridge an empty space.