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Ultrasonic-Accelerated Intermetallic Joint Formation with Composite Solder for High-Temperature Power Device Packaging

A novel and effective method of ultrasonic-assisted reflow is an effective solution to time-consuming problem of traditional reflow. In this study, three kinds of hybrid solder paste composed by different size of Ni particles were synthesized to obtain the high-melting-point joint for high temperature operation under ultrasonic-assisted reflow. The microstructure evolution, shear strength, and fracture morphology in joints before and after aging were systematically investigated. A high-melting-point and high-strength joint of sole IMCs with a few residual Ni was obtained at 250 °C in a short time (only 10 s) under lower ultrasonic power of 200 W, and the shear strength was up to 45.24 MPa in response to ordered arrangement that small Ni particles filled in the gap of large Ni particles. In addition, the microstructure, shear strength, and fracture morphology of joints formed by three hybrid solder pastes after aging treatment of 72 h, 170 h, and 360 h at 200 °C are distinct dramatically. Especially, the joint composed by mixing Ni particles remained higher shear strength of 49.75 MPa after 360 h aging, which ascribed to the dense joint without defects.