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Precise chip joint method with sub-micron Au particle for high-density SiC power module operating at high temperature
Keywords: Precise chip joint, Sub-micron Au particle, High-density SiC power module
In this work, a novel precise chip joint method using sub-micron Au particle for high-density SiC power module operating at high temperature is proposed. A module structure of SiC power devices are sandwiched topside and bottom side is obtained. The precise flip-chip joint between top side (gate/source or anode pad side) of power device and circuit electrodes without wire bonding makes minimize a chip mounting space. So this study focused on the Au/Au junction using a sub-micron Au particle with low temperature sintering. To obtain Au/Au junction, Al electrodes on SiC power devices were deposited with Au coating by means of zincate treatment method and electroless Ni plating and immersion Au plating. The cluster structure of the sintered Au particle heated at 250°C can be made without compression. To make a precise position and height control of the chip bonding, base structures of Au particle are made on the circuit electrodes. The SiC chips are bonded on these base structure without compression. The accuracy of the bonding position of chips were less than 10 µm and also the accuracy of the height after bonding chips were less than 20 µm. Mechanical shear fatigue tests for flip-chip bonded SiC-SBD (Schottky barrier diode) were carried out. As a result, initial shear strength of the joint were over 40 MPa. The shear strength of 25 MPa after thermal cycle stress of 500 cycles between -40°C and 250°C is obtained. We also jointed SiC-JFET (Junction Field Effect Transistor) for realizing a SiC power module. The gate and source joints to each circuit electrodes are formed using sub-micron Au particle in one-time process. The flip-chip bonding of SiC-JFET is successfully achieved on the substrate without short or open failure in electrically. Finally we joint the backside of the SiC-JFET (drain side) and the SiC-SBD (cathode side) to each circuit electrodes in one-time by means of reflow process with AuGe solder. The SiC power module was successfully packaged. The forward and reverse characteristics electrical testing were performed. Resulting of these test, the characteristics of SiC-JFET and SiC-SBD were not changed before and after the packaging process. It is confirmed that the high-density SiC power module can be made by proposal method.
Fumiki Kato,
National Institute of Advanced Industrial Science and Technology
Tsukuba, Ibaraki

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