Aluminum nitride sintered body having a metallized coating layer on its surface

An article of manufacture comprising an aluminum nitride sintered body and a metallized layer on a surface of said sintered body, said metallized layer consisting of 0.4 to 10% by weight aluminum oxide, 3 to 15% by weight calcium oxide, and the remainder being tungsten, wherein said metallized layer has a thermal resistance not greater than 1.9.degree. C./W;

• said thermal resistance being defined as the thermal resistance measured by forming a sample of said metallized layer to a thickness of approximately 15 .mu.m on an area of 2 mm.times.2 mm on a sample of said aluminum nitride sintered body, forming an Ni coat layer to a thickness of 2 to 3 .mu.m on the sample metallized layer, forming an Au coat layer to a thickness of 2 to 3 .mu.m on the Ni coat layer, die-bonding on the Au coat layer a transistor having a bonding area of 1.4 mm.times.1.4 mm and a chip resistance .theta..sub.chip =0.8.degree. C./W using an Au-Si solder having a eutectic crystal composition and a thickness of about 30 .mu.m, packaging the transistor in a driveable state, applying an electrical pulse with an applied power of P=30W for 50 ms to the packaged transistor so that heat is generated in the transistor, and measuring the thermal resistance by the V.sub.Be transient thermal resistance method.