GUEST EDITORIAL Materials Development – New Competencies Required for the Development of <strong>Power</strong> Modules By Dr.-Ing. Frank Osterwald, Senior Director Research & Development, Danfoss Silicon <strong>Power</strong> The development of power modules and their components is a multi-disciplinary task. <strong>Power</strong> module developers have to be trained in thermal,mechanical, electrical and materials engineering. Furthermore, they must understand requirements coming from applications, in order to proactively drive power module development in the right direction. Typically, “right direction” means to achieve a targeted quality, reliability and cost/performance ratio. The first step in power module development is to find out what the application requires in terms of power and in terms of mission profile. After that, many other requirements must be taken into account - all of them influencing the outline, arrangement, and the material of the ingredients and joints in a power module in order to obtain the desired properties. To get to lower cost, one could try just leaving out some costly components or parts. However this is not possible in general – but an approach like this might work if another component or part is able to take over the function of the missing component or part. Usually, this leads to multifunctional components or materials. In the past, for example, for the double function of good electrical conductivity and thermal properties, an engineer would have chosen a suitable material like copper. If more functions were required, such as corrosion resistance, a nickel-layer would be added to ensure that copper surface properties are properly modified, without significantly changing good electrical and thermal properties. Nowadays, there are many examples of multifunctional materials in power modules, and more are in development to adapt to even more functions. Some current multifunction examples are; • frame material that fulfil many roles, • silicone gel that is multi-talented, • base plates designed to obtain certain properties in conjunction with soldered DBC’s, or substrates already including the functionality of base plates, • solder that fulfils with good electrical and thermal properties, while being flexible enough to withstand thermo-mechanical stresses, • mould compounds that protect the power semiconductors against bad environments (not just rains and storms) while being easily processed and without increasing CTE mismatch, • AlSiC base plates tailored to perfectly adapt to the CTE of the substrates that are soldered to them, while keeping reasonable thermal conductivity and solderability, • pressure sinter materials with lowered sintering temperatures achieved by applying nano-technologies in the joining materials leading to better manufacturability and extended performance of the power modules. From my point of view, the development of power modules is currently undergoing a shift towards more intense material development. Whenever a discussion targets new concepts or joining methods for power modules, we ask the question: “How can this or that property or behaviour of a certain material be modified?” We discuss modification of surface properties using extra layers, or we look for a change in the properties or behaviour of the bulk material itself through adding or removing ingredients (as little as a few “ppm”), or to subject the bulk material to heat treatments or other processes. Whatever intention we might have as power module developers will not be achieved without close cooperation with our materials suppliers. And since materials development requires target specifications, our material suppliers need to be involved in our projects from the very beginning, as specialized equipment manufacturers will have to be. To be able to really achieve a better cost/performance ratio, together we must keep a close focus on cost. However, in this case, the total cost of ownership is to be considered, rather than just the materials price per kilo by itself. In this light it is highly appreciated that more and more materials specialists decide to become members of our ECPE family. In the framework of ECPE research work, materials suppliers together with other specialists for engineered materials can help power module developers hit their targets, not simply to provide “green” materials. New doped or alloyed wires, solder or sinter pastes, adhesives, layer materials and deposition techniques, as well as completely engineered base plates, substrates and housing materials will play a big role in the future, as we progress to more cost efficient and more reliable power modules. Thus, materials science will be the enabler for energy efficiency. Hopefully, this movement of power electronics development towards materials science will make our profession even more attractive to young talents. We can offer many challenges for physicists, chemists and materials scientists, to augment mechanical and electrical engineering in our research and development departments. We envision new multidisciplinary teams for joint development projects and new breakthroughs that will continue our record of progress in the development of power modules. siliconpower.danfoss.com 16 Bodo´s <strong>Power</strong> Systems ® August 2009 www.bodospower.com
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