Original design of field grading materials for high voltage power module applications

One of the main goals in aeronautic industry is to increase the total electrical power in on-board systems. The first approach is to increase the voltage while reducing the volume of converters. However, this approach induces very high electrical constraints on the insulating materials used for power module. These local high electric fields can cause premature failure, by partial discharge activity and insulation breakdown. In order to efficiently reduce the electrical stresses in high voltage power modules, the design of new stress-control encapsulating composite materials with graded properties has been developed using the particles electrophoresis auto assembling technique. It is a promising solution since it does not impact the volume of the power module and has a negligible impact on the overall mass. The aim of this paper is to evaluate different strategies to achieve such field grading encapsulating composite with local high relative permittivity ($\varepsilon_{r} \gt 10)$, tailored around critical areas where the electric field is high. The present paper mainly proposes two processes to enable the electrodeposition of a field grading layer within a composite encapsulation to cover multiple electrodes of a direct bonded copper (DBC) substrate with a complex layout. The first approach consists in adding a new and fixed electrode on the layout of DBC substrate that will not be polarized or used during normal operation of the module. The second method consists in adding a removable top electrode above the substrate. Results show that the latter approach is potentially the best choice to enable the electrodeposition of a homogenous thickness of field graded layer on a complex DBC layout with multiple adjacent copper tracks.