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High-Temperature Die-Attach Technology for Power Devices Based on Thermocompression Bonding of Thin Ag Films

Wide-bandgap materials such as silicon carbide enable power electronics to face increasing demands for greater power density and high-temperature capability at the chip level. However, new packaging solutions have yet to be found to replace Pb solders in high-temperature applications. In this paper, the applicability of electrodeposited Ag thin film as a novel high-temperature die-attach material to connect power chips to direct-bonded copper substrates is investigated. Ag films were obtained by electrochemical deposition on the backmetallization of Si chips. The joint was then produced by thermocompression bonding at 350°C with a 40-N force applied for 10 min in air. A die shear strength of 1.70 MPa (twice the MIL standard) was achieved. The assembly demonstrated satisfactory resistance to thermomechanical fatigue when subjected to thermal aging and thermal cycling tests in high-temperature environments. The proposed bonding technology is thus a suitable solution for the provision of strong and reliable joints for power devices which have to operate in extreme temperature conditions (>200°C).