ceramic substrate 10 at 835 u00b0 c in a vacuum furnace in order to verify the thickness of the brazing filler metal 12 the sample thus bonded was cut to measure the thickness of the brazing filler metal 12 as a result the thickness of the brazing filler metal 12 was about 20 u03bcm as the ceramic substrate 10 an s grade aln substrate produced by atg company was used thereafter the sample thus bonded was taken out of the vacuum furnace then as shown in fig2 a through 2c ultraviolet curing alkali peeling resists 16 having a desired circuit pattern and a thickness of 10 to 15 u03bcm were applied on both faces of the bonded copper plates 14 fig2 a and undesired portions of the copper plates 14 were removed with an etchant comprising copper chloride aqueous hydrogen peroxide and hydrochloric acid fig2 b thereafter the resists 16 were removed with an aqueous solution of 3 5 sodium hydroxide fig2 c in the etching at this time larger masks than usual masks by 50 u03bcm were used as the resists 16 in view of correction carried out by etching and conditions such as the conveyer speed of the etching machine and the spray pressure of the etchant were controlled so as to provide a difference of 20 u03bcm or less between the top and bottom portions of the copper plate and so as to meet the dimensional precision at this time the design value of a chip mounting portion was 11 mm u00d7 11 mm the bottom face of the copper plate then in order to remove undesired portions of the brazing filler metal between circuit patterns and on the edge faces of the substrate the sample was dipped in a mixed solution containing 1.