Partial Discharge Control In A Power Electronic Module

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Many industrial applications make use of high voltage power electronic devices. Examples include traction, marine power and power system based power electronics. Further developments are currently taking place within the aerospace sector that will mean the market for such devices will continue to grow. Most of the applications that power electronic devices are used in demand reliable operation. In turn this means that care must be taken in the design of the insulation system. Modules that operate at voltages over 5kV are currently available and there will always be a drive to improve the power density of the module by raising voltages or by miniaturisation. To do this, weak points in the dielectric system must be progressively improved. A power electronic module is typically composed of a metallized substrate soldered onto a baseplate. Different techniques are used to achieve this such as directly bonded copper or active metal brazing. The high voltage silicon IGBTs / diodes are typically soldered this substrate that is itself made from aluminum nitride (AlN), a ceramic with a good insulation strength. Wire bonds are then used to make connections between the individual IGBT / diode terminals and external connections for gate drives / busbars. The whole assembly is immersed in a soft dielectric, typically silicone gel, in order to provide the dielectric strength along the surfaces of the substrate, between the busbars and any other parts of the module subject to high electric fields. An epoxy layer may then be placed over the top of the entire dielectric system. The critical area in which the insulation system of a power module is extremely weak is at the edge of the metallisation of the substrate. The performance of the silicon gel is particularly critical in this location not just in terms of preventing discharge within the gel itself but also in terms of preventing discharge at the gel-substrate interface in close proximity to the metallisation.The invention being developed by the University of Manchester relates to the modification of the dielectric system of a module thus reducing the probability of electric discharge at this interface. The use of the technology being developedwould help to reduce the high levels of failure rates that can currently occur on low volume production runs of high value power electronic modules. It would also significantly improve the reliability of power electronic modules as insulation defects that did not show up in initial testing but which exist and have the ability to cause cumulative damage would be reduced in severity by the technology.The funding of this project through the follow on fund mechanism will allow the technical case for the technology to be enhances through a more thorough understanding of the ability of technology to enhance the dielectric system and through the understanding of the relationship between the manufacturing process and the electrical performance. In parallel, the commercial activities that are discussed will allow the commercial case for the technology to be strengthened through the completion of a cost benefit analysis, the appraisal of the technology to be used in the next generation of power electronic modules and the identification of prospective partners.The close association with the University of Manchester Intellectual Property team will also allow the mechanism for long term promotion and development of this technology to be identified as well as understanding the ways in which the technology can be used in other technical areas.