An insulated gate bipolar transistor (IGBT) die attachment technique using pressureless silver nanopowder sintering on direct bonded copper (DBC) for liquid cooled heat sink is studied. Henkel (Loctite Ablestik SSP 2020-EN) silver paste is used, and its sintering process is optimized at 200°C for 60 min with no pressure on the nickel and gold electroplated DBC substrate. A porosity of 29% is obtained. Irregular shaped particles of micro-meter scale and nano-meter scale sizes are observed via scanning electron microscope (SEM). Differential scanning calorimeter (DSC)/thermogravimetry analysis (TGA)/simultaneous thermal analysis (STA) results indicate that the solvent starts to evaporate at 114°C and reaches its peak at 133°C. The temperature for sintering is set at 200°C to minimize the thermal budget on the fabricated IGBT dies. The isothermal test indicates that a minimum sintering time of 40 min is required to promote sufficient diffusion of atoms. A sintering time of 60 min is found to provide reliable die attachments.
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