A method is described. The method is a method for making a constraining ceramic assembly. The method includes applying at least one metallic electrode to a substrate. The method also includes applying a porous ceramic layer to the substrate to cover the metallic electrode. The method also includes sintering the substrate, the porous ceramic layer, and the metallic electrode together at a sintering temperature above a melting point of the metallic electrode.

In an embodiment a method for producing a substrate includes forming a green sheet stack including first green sheets and second green sheets, wherein each of the first green sheets and the second green sheets contains a ceramic material as a main component, and wherein the second green sheets further contain a sintering aid in addition to the ceramic material.

It is an object of the present disclosure to provide a thin-film carbon foam and a method of manufacture the same. It is another object of the present disclosure to provide a stack carbon foam having fewer through holes and a method of manufacturing the same. The carbon foam of the present disclosure is, for example, a stack carbon foam being a stack of at least two monolayer carbon foams stacked one another, each monolayer carbon foam comprising linear portions and node portions joining the linear portions, or a carbon foam comprising linear portions and node portions joining the linear portions, wherein the ratio of the number of large through holes having a diameter of 1 mm or more to the surface area of the carbon foam is 0.0003/mm.sup.2 or less.

It is an object of the present disclosure to provide a thin-film carbon foam and a method of manufacture the same. It is another object of the present disclosure to provide a stack carbon foam having fewer through holes and a method of manufacturing the same. The carbon foam of the present disclosure is, for example, a stack carbon foam being a stack of at least two monolayer carbon foams stacked one another, each monolayer carbon foam comprising linear portions and node portions joining the linear portions, or a carbon foam comprising linear portions and node portions joining the linear portions, wherein the ratio of the number of large through holes having a diameter of 1 mm or more to the surface area of the carbon foam is 0.0003/mm.sup.2 or less.

In an embodiment a method for producing a substrate includes forming a green sheet stack including first green sheets and second green sheets, wherein each of the first green sheets and the second green sheets contains a ceramic material as a main component, and wherein the second green sheets further contain a sintering aid in addition to the ceramic material.

In an embodiment a method for producing a substrate includes forming a green sheet stack including first green sheets and second green sheets, wherein each of the first green sheets and the second green sheets contains a ceramic material as a main component, and wherein the second green sheets further contain a sintering aid in addition to the ceramic material.

In a power-module substrate unit, a circuit layer is structured by a plurality of small circuit layers; a ceramic substrate layer is structured by at least one plate; the small circuit layers are formed to have a layered structure having a first aluminum layer bonded on one surface of the ceramic substrate layer and a first copper layer bonded on the first aluminum layer by solid diffusion; a radiation plate is made of copper or copper alloy; the metal layer and the radiation plate are bonded by solid diffusion.

In a power-module substrate unit, a circuit layer is structured by a plurality of small circuit layers; a ceramic substrate layer is structured by at least one plate; the small circuit layers are formed to have a layered structure having a first aluminum layer bonded on one surface of the ceramic substrate layer and a first copper layer bonded on the first aluminum layer by solid diffusion; a radiation plate is made of copper or copper alloy; the metal layer and the radiation plate are bonded by solid diffusion.