Microstructure and properties of Sn2.5Ag0.7Cu0.1RE lead-free soldering joints with ultrasonic assisted

Sn2.5Ag0.7Cu0.1RE/Cu solder joints were obtained with ultrasonic vibration assisted. Microstructure and properties of the joints were studied. Experimental results show that reliable soldering of Sn2.5Ag0.7Cu0.1RE/Cu can be achieved under condition of ultrasonic power of 88 W and low-halogen flux. The maximum shear strength of 26.0 MPa is obtained from the joint soldered at ultrasonic vibration time of 60 s, which increased by 35%. Compared with that of the solder joint obtained without external energy assisted, the application of ultrasonic vibration during soldering can decrease thickness and roughness of the interfacial Cu6Sn5 intermetallic compound, and the fracture mechanisms of the solder joints transforms from brittle fracture to mixed fracture, which is dominated as ductile fracture.