Abstract
High voltage power modules are used in numerous applications to build high power converters. Technically, these modules are made of different materials and among them, dielectric materials are organic and inorganic. Organic insulators (gels) are used to avoid corona discharges in the vicinity of connecting wires and high voltage dies (diodes and transistors) and to protect them from moisture and contaminants. Inorganic insulators (ceramic substrates) are used to insulate the high voltage which dies from the grounded elements and to transfer heat to the heat sink. Despite being used since the late 90s, there is a lack of fundamental knowledge about the electrical properties of these substrates. Consequently, manufacturers tend to assure the reliability by over sizing them. As there are no clear rules for how to do that, failures occur, leading to the converter shutdown. The aim of this study is to bring new information about the understanding of the dielectric strength of ceramic materials used in these modules. We have focused our work on the correlation between the mechanical and the dielectric properties of ceramics by using relevant experiments. We provide new information about the impact of existing cracks on the ceramic dielectric failure, according to the electromechanical breakdown model. Our conclusions bring crucial information about the precautions to be taken during manufacturing and implementation of these substrates in power modules to reduce the likelihood of the particular causes of failure.
Highlights
The aim of this study is to bring new information about the understanding of the dielectric strength of ceramic materials used in these modules
We have focused our work on the correlation between the mechanical and the dielectric properties of ceramics by using relevant experiments
We provide new information about the impact of existing cracks on the ceramic dielectric failure, according to the electromechanical breakdown model
Summary
Inside this assembly, one finds different materials, whose functions are to assure the interconnection, the insulation and the heat exchange between the semiconductor and its environment. One of its main functions is to warrant the electrical insulation between the semiconductors and their environment It must ensure the evacuation of the heat generated by the semiconductors. With the development of the new wide bandgap semiconductors, such as SiC or GaN, higher voltages along with higher current densities could potentially increase the insulating requirements imposed on the ceramic materials inside the substrates [2]
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