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High heat-density SiC heater chip for thermal characterization of high temperature packaging
Keywords: SiC, thermal characterization, reliability
Using wide-bandgap semiconductors capable a higher electric density and high operating temperature, next-generation power devices are expected to achieve further downsizing with reducing or even eliminating cooling systems. However, the reliability of such a power module critically depends on the thermal management, and thus the packaging materials and design are intensively focused in the field of high temperature electronics. Optimal power module design hence needs detailed thermal properties of all the packaging materials, particularly heat conductive circuit board thermally connected to cooling systems like a heatsink. High voltage power modules applied in train or electric vehicle systems often employ metal bonded ceramic substrate as heat conductive circuit board that might be only the choice to ensure both the electric insulation and high heat conductivity. These ceramic circuit boards are designed based on the electrical, thermal, and mechanical requirements, and the demands for thermal performance is recently focused due to the reasons described above. Higher thermal performance, i.e. lower thermal resistance of ceramic circuit board can be reached by improving the thermal conductivity of the ceramic material, or simply by thinning the ceramic sacrificing the mechanical properties. In these developments for better thermal performance, the precise measurement technique of the heat resistance is urgently needed because the heat resistance of the ceramic circuit board is rather small. The measurements are especially difficult when the target material is used in the form of a packaged structure. The heat in a power module is usually generated at a device chip surface, and flows through various heat conducting path. The thermal flow path through the ceramic substrate plays the critical role where the heat resistance is controlled by the temperature gradient in the thin ceramic board. Thus the testing method in simulating actual packaging form, including die-attach, is necessary for thermal design of high power modules. In the present study, we introduce a heater dummy chip equipped with temperature sensor, with extremely high capability of high heat-density using SiC wafer. As often used in high voltage/temperature SiC devices exhibit their advantage of high thermal stability and heat conductivity. Our testing heater chip (thermal test engineering group, TEG) consist of insulated SiC and Pt thin-film heater and temperature sensor realizes extreme heat density of 250 W/mm2 with reliability above 300°C of high temperature. The TEG chip was the n-doped 4H SiC chip,which is used generally for SiC devices, coated with an alumina insulation film and molded the Pt heater and sensor by lithography technique. Using the TEG chip, we demonstrate simple but accurate heat resistant measurements of several types of metal bonded ceramic substrates. The combination of SiC TEG chip and heat resistance measurement system is also applied to power cycle testing, avoiding numerous problems arising from using actual working device chips. Therefore, this study systematically was carried out the thermal measurement technology of SiC with repetitive power cycle by TEG chip as new concept heat system. Through this progress, the technologies developed in the study may have further applications in evaluation and testing of various packaging materials targeted for high temperature/wattage power modules.
Naoki Wakasugi,
Yamato Scientific Co.,Ltd. and Osaka University
Ibaraki city, Osaka prefecture

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