Stacking of insulating substrates and a field plate to increase the PDIV for high voltage power modules

In this paper, two possibilities to decrease the stressing by the electric field strength in ceramic substrates (i.e., AMB, DBA, DBC, HTCC, LTCC) have been studied. First, the influence of a so-called field plate (a metal sheet protruding the metallization layout) attached on top of the metallization is shown to be advantageous to the field distribution of the DBC. Here, an increase of the partial discharge inception voltage (PDIV) by about 15 % can be achieved by placing a field plate on top of the substrate. Further, the effect of stacking two DBCs (0.3 mm Cu/0.38 mm Al2O3/0.3 mm Cu) was analyzed and compared with the influence of a thickness scaling of the ceramic. Stacking of substrates yields a higher gain than an increase of the ceramic thickness. The stacked substrates nearly double the PDIV. On the other hand the ceramic thickness would have to be enlarged by nearly three times to reach the same PDIV. Thinner ceramics which allow good heat dissipation as well as high stability regarding the partial discharge can be used. Phase resolved partial discharge (PRPD) measurements were carried out. The samples were DBCs with field plates, stacked DBCs as well as DBCs with varying ceramic thickness. In addition, a comparative simulation study on the distribution of the electric field strength is given. Therein, a detailed view on the effect of stacking is provided to understand its effect on the electric field strength distribution.