Ultrasound-assisted soldering of Cu alloy using a Ni-foam reinforced Sn composite solder

Ultrasound-assisted soldering of Cu/Cu was conducted with a self-developed Ni-Sn composite solder. The microstructure and mechanical properties of Cu/Ni-Sn/Cu joints were investigated in terms of ultrasonic vibration time. Results indicated that, in the joint ultrasonically soldered for 5 s, (Ni,Cu)
₃
Sn
₄
was formed along the Ni metal foam and got contact with each other in local area while (Cu,Ni)
₆
Sn
₅
was fabricated at the interface of Cu substrate and Ni-Sn composite solder. Ni metal foam distributed randomly and a large amount of Sn remained in solder seam. Increasing the ultrasonic vibration time to 20 s, the amount of (Ni,Cu)
₃
Sn
₄
increased and a stripe layered structure composed of (Ni,Cu)
₃
Sn
₄
and Ni metal foam was obtained. The thickness of (Cu,Ni)
₆
Sn
₅
increased slightly and the amount of Sn decreased a little. Further increasing the ultrasonic vibration time to 30 s leaded to the volume increase of the stripe layered structure, which is composed of (Ni,Cu)
₃
Sn
₄
and Ni metal foam. The thickness change of (Cu,Ni)
₆
Sn
₅
was not obvious compared with its counterpart fabricated in 20 s while there still remained a small amount of Sn in solder seam. The joint ultrasonically soldered for 30 s exhibited the highest shear strength of 64 MPa and the fracture occurred in the solder seam near the (Cu,Ni)
₆
Sn
₅
intermetallic compound layer.