Patent ID: 7105070

Claim:
A method for producing a ceramic substrate, which comprises: (a) fabricating a green ceramic substrate comprising a laminate of ceramic green sheets and conductor layers, and surface conductors formed on a main surface of the laminate; (b) applying a ceramic paste to the green ceramic substrate so as to cover the surface conductors and the main surface of the laminate, the ceramic paste subsequently being integrated with the ceramic green sheets by cofiring; (c) laminating a restraint sheet on each of opposite sides of the green ceramic substrate to which the ceramic paste is applied, so as to restrain the green ceramic substrate, the restraint sheets containing a predominant amount of a sintering-resistant inorganic material, which is not sintered at a sintering temperature at which the green ceramic substrate is sintered; (d) firing the green ceramic substrate under restraint at a temperature at which the green ceramic substrate is sintered, whereas the restraint sheets are not sintered, to thereby yield a ceramic substrate restrained by means of the restraint sheets; and (e) removing, from the ceramic substrate restrained by means of the restraint sheets, the restraint sheets and a ceramic covering layer which is an upper portion of a ceramic layer formed from the ceramic paste applied in the covering step and which covers the surface conductors, to thereby expose the surface conductors, while leaving a lower portion of the ceramic layer formed from the ceramic paste applied in the covering step on the ceramic substrate.