Formation mechanism and mechanical performance of ultrasonic-assisted soldered joints of SiCp/2024Al composites at low temperature

Reliable joining of SiC particle–reinforced aluminium metal matrix composites (SiC p /Al MMCs) at a lower temperature is an important requirement in the application of advanced electronic packaging. Therefore, ultrasonic-assisted soldering of SiC p /Al MMCs at 250 ℃ was required and investigated. The joint forming process and mechanical properties were the focus of this paper. A liquid solder of Sn-9Zn alloy was forced to flow into the gap of the joints at a speed of 50~60 mm/s due to the effect of ultrasound during the soldering process. Acoustic flow arising in the liquid solder was beneficial in transferring the bubbles out of the joint, and the porosity in the joint decreased from 12% to 0 within 5 s. The periodic change of sound pressure resulted in the flowing quickly of liquid solder into the gap. During the soldering, the oxide film on the surface of the Al matrix was broken gradually, exhibiting obvious asynchronism. The oxide film of the Al matrix was completely removed within 5 s, and SiC particles began to appear in the bond. The Al matrix dissolved by the solder precipitated in the bond to form α-Al phases at 10 s. The typical microstructure of the soldered joint was Al MMCs/β-Sn + Sn–Zn eutectic structure + SiC particles + η-Zn + α-Al/Al MMCs. The maximum shear strength of the joints reached 70 MPa, which was approximately 2.5 times the reported shear strength of soldered SiC p /Al MMCs with a Ni coating. This lays a foundation to the application of SiC p /Al MMCs in the field of electronic packaging.