Influence of manufacturing parameters on the PD-behaviour of AlN-substrates

Metallized aluminiumnitride-substrates (AlN) for power semiconductor modules are examined in regard to their partial discharge behaviour. The samples used differ in the size of the metallization and in the duration of the structuring etching process, which has an effect on the vertical geometry of the edges. Other examined samples were metallized by sputtering a thin layer of copper onto the surface of a blank AlN-plate instead of the usual bond technology. These samples differ in size and shape of the metallization. It is found out that the duration of the etching process has a decreasing influence on the appearance of partial discharges of high apparent charge. This is because a longer etching process makes the edges of the metallization become steeper and some thin copper on the surface of the ceramic along the edges disappear. As in these examinations sets of samples with different sizes of the metallization are regarded the desired effect can be seen in each set of samples. When comparing the sets to each other, an influence of the size of the metallization on the PD-behaviour with bigger samples showing more PD can be recognized. This is proved by PD-measurements of the samples with sputtered metallization. In regard to the shapes of the metallization the influence of the angles of a corner is examined. It can be seen that smaller angles cause more partial discharge because of higher field strength at the tip.