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The use of Diamond Composite Baseplates for Thermal Management of Power Electronic Modules
Keywords: IGBT module, metal matrix composite, diamond
One of the most important parameters of a power electronic module affecting thermal management is the thermal conductivity of its components, since the concentration of energy dissipation of the up-to-date modules tends to increase. Passive and active thermal cyclings during service life time, i.e. the changes in the ambient temperature and heating during operation, lead to thermally induced stresses in the module due to different coefficients of thermal expansion of the components. For instance, thermal fatigue of a soft solder layer enhanced by thermal cycling results in crack propagation that reduces the overall heat transfer in the module, thus worsening its electric efficiency and service life time. Therefore, Al matrix composites with a high volume fraction of SiC particles are used in IGBT modules instead of Cu. Low thermal expansion of the ceramic constituent reduces thermal expansion of the Al matrix depending on the volume fraction of the constituent in the composite. On the other hand, the thermal conductivity of AlSiC is typically 200 W/(m*K) which is nearly half of that of Cu that leads to an increased maximum IGBT junction temperature during operation. To overcome this disadvantage, diamond composites were chosen to provide a higher thermal conductivity in combination with a reduced CTE. The composites were produced by reinforcing of a metal matrix with diamonds by gas pressure infiltration or squeeze casting. With FEM simulation, the benefit of increased thermal conductivity together with the matched CTEs has been quantified in view of visco-plastic solder fatigue. These new materials show thermal conductivity up to 700 W/(m*K). The diamond composites in the form of small specimens were characterized on their mechanical and thermal properties, whereas those in the form of IGBT baseplates with a dimension of 137x127x5 mm3 were used for comparison with the standard baseplates from Cu and industrial AlSiC.
Svetlana Levchuk, Engineer
Siemens AG
Munich, Bavaria 81739,
Germany


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