Surface breakdown is investigated with substrates made either from standard glass/epoxy PCB board or Alumina
ceramic, and embedded in silicone gel or dibenzyltoluene (DBT) high temperature liquid. Depending on the substrate nature and gap distance, breakdown may occur either above the surface within the encapsulant material, or below within the solid substrate. In the case of ceramic substrate with liquid encapsulation, which could be tentatively used at high temperatures above 200°C, the weakest material is the ceramic, which shows irreversible degradation (cracks) after a single breakdown. Therefore, such insulating structure does not benefit from the self-healing character of liquids. Breakdown voltages also show a marked decrease at high temperature