shown in fig5 was formed under the similar manner as in the comparative example 1 except that the material of the base plate was changed from aluminum to a cupper molybdenum alloy of 5 mm in thickness a thermal cycle test was performed to evaluate the power module as like as the examples after the thermal cycle of 3000 times cracks were recognized in the brazing material layer on the boundary surface between the ceramic substrate layer 2 and the base plate 7 a following sample was prepared for comparison a molten aluminum as shown in the example 1 was contacted directly to both surfaces of a ceramic substrate board of aluminum nitride cooled and solidified to form aluminum layers then in order to form a circuit portion on one of the both surfaces of the ceramic substrate board an etching resist was printed on the one surface by using a screen printer uv dried and subjected to etching using a ferric chloride solution to form a desired circuit pattern the ceramic substrate board with the circuit pattern was subjected to an electroless nickel plating three sheets of the ceramic substrate board thus obtained were fixed by brazing on an aluminum base plate subjected to an electroless nickel plating and having a thickness of 5 mm and a purity of 99 99 further a semiconductor tip was provided on each of the substrate boards to form a power module as shown in.