Abstract: A screen-printing paste containing Cu.sub.2 O or NiO and preferably aluminum oxide or, more preferably, an aluminum compound such as aluminum acetylacetonate which forms aluminum oxide under calcination heat, is printed over an entire surface of a substrate consisting of aluminum oxide ceramic, after which it is calcined in air at from 800.degree. to 1350.degree. C. to produce an adhesion-promoting spinel layer. That layer is then metallized by plating in an electroless bath for deposition of copper or nickel, as the case may be, after which the metal layer thus deposited is reinforced galvanically.