Cu@Sn@Ag core–shell particles preform for power device packaging under harsh environments

This paper presents a novel die attach material for power device packaging based on transient liquid phase (TLP) bonding. Through two-step electroless plating, the Cu@Sn@Ag particles were prepared, and realize interconnection with Cu Substrates after being compressed into preform. Due to the large specific surface area of the core–shell particles, the reflow time can be reduced to 15 min at a low temperature of 250 °C under a pressure of 3 MPa to form high-remelting-point intermetallic compounds (IMCs), which can withstand a high temperature of at least 475 °C. Due to the protection of the Ag coating, the Cu@Sn@Ag particles exhibited excellent oxidation resistance, and the bonding process can be carried out in the atmosphere. Then, the service reliability of the bondlines was evaluated in harsh environments, such as high temperature and humidity, high temperature storing, and thermal shock. The average resistivity of the bondlines was increased from 4.6 ± 1.4 to 8.5 ± 3.8 µΩ cm after being stored at high temperature (85 °C) and high humidity (85% RH) environment for 14 days. After storing at 300 °C for 15 days, the porosity of bondline increased from 6.8 to 10.8%, and the average shear strength decreased from 30.5 ± 6.3 to 22.3 ± 5.6 MPa. After thermal shock between − 40 and 125 °C for 500 cycles, the bonding rate decreased from 99.9 to 84.2%. Moreover, the short-circuit time of electrochemical migration under 60 V voltage was extended to 145 s. The bondline based on the novel core–shell particles exhibited excellent performance as a die attach material under harsh environments.