Thickness dependence of dielectric breakdown strength for silicon nitride substrate

Silicon nitride ceramics have attracted increasing attention as insulated heat-dissipating substrates for power modules due to their high thermal conductivity and mechanical strength. However, there are very few reports on their dielectric breakdown strength, which was only evaluated for the substrates with thicknesses between 250 and 640 µm, though thinner substrates are preferable for attaining better performance of the module. In this work, dielectric breakdown of sintered silicon nitride substrates with thicknesses ranging from 285 to 15 µm was evaluated for the first time. Average breakdown strength increased from 36.38 to 103.80 kV/mm with decreasing thickness from 285 to 15 µm. It should be noted that the silicon nitride specimen had very high dielectric breakdown voltage of 1.5 kV even with a thickness as small as 15 µm.