Titanium nitride-molybdenum metallizing method for aluminium nitride

A paste containing molybdenum (Mo) and titanium nitride (TiN) powders was printed on aluminium nitride (AlN) substrates and fired. The adhesive strength of substrates metallized with Ni/Au plate was about 25 kg/2.5 mm² and was unchanged after a thermal cycle test. TiN-Mo does not adhere to the grain boundary phase of the AlN substrate nor to the surface oxide layer but to the AlN grain itself. This method, therefore, seems to be applicable to any kind of AlN substrate, which can have different grain boundary oxide phases and thermal conductivities. This TiN-Mo metallized AlN substrate replaced a beryllium oxide (BeO) heat sink, which has been used for RF power transistors. There was no trouble in assembling the AlN heat sinks into transistors. Thermal resistance and electrical properties of transistors with AlN heat sinks were almost equal to those of transistors with BeO heat sinks