Ultrasonic-assisted soldering of Si and Cu joint with SnAgTi solder in air

Abstract

The reliable connection of single crystal Si and Cu at low temperature is widely utilized and plays a crucial role in the field of electronic packaging. In this study, Sn–Ag–Ti active filler is ultrasonically coated onto the Si surface to facilitate the subsequent ultrasonic soldering process to realize the bonding of Cu to pre-metallized Si. Furthermore, a detailed analysis was conducted on the influence of ultrasonic time on both the bonding mechanism and mechanical properties of the joint. The results revealed that Ti–Sn compound within the solder decomposed with ultrasonic action duration time of 20 s, resulting that Ti elements enriched at the Si/solder interface and reacted with SiO2 to form a mixture comprising TiO2 and SiTi phase. It contributed to higher strength (43.9 MPa) at the Si/solder interface. Additionally, it has been found that microstructure and property at the Cu/solder interface were directly affected by ultrasonic time. Specifically, when subjected to 3 s of ultrasonic action, poor load-bearing capacity exhibited by thin infiltration layers caused fracture at the Cu/solder interface; When the ultrasonic action time is 6 s, the joint strength reaches its maximum value of 41.3 MPa, leading to fracture occurring within the Si material. However, when the ultrasonic holding time is extended to 20 s, the joint strength decreases to 20.3 MPa. This phenomenon arises from impaired plasticity of Cu6Sn5 near the Cu–Sn layer, which is attributed to the presence of attached dendritic Cu6Sn5 phases and shed bulk Cu6Sn5 that are prone to crack initiation. This research presents a promising approach for ceramic/metal heterogeneous joining.