Microstructure Evolution and Mechanical Properties of Cu-Sn Solder Joints Soldered by Ultrasound-TLP

The ultrasonic-assisted transient liquid phase soldering（ultrasound-TLP） was used to solder Cu/Sn/Cu sandwich structure. The frequency and power of the ultrasound were 600 W and 20 kHz respectively, the heating temperature was 280 ℃ during soldering, and the pressure was 0.06 MPa. Full Cu₃Sn solder joints were obtained after applying ultrasound for 20 s. Compared with that of traditional TLP soldering, the welding efficiency is greatly improved. During the soldering process, Cu₃Sn shows saw-toothed, Cu₆Sn₅in the joint shows rod-like or strip-like and eventually turns into full Cu₃Sn, and the Cu₃Sn grains show equiaxed crystal. Full IMC solder joints soldered by ultrasound-TLP have uniform mechanical properties.The Young’s modulus and hardness of Cu₃Sn are 129.183, 4.861 GPa, respectively, and the Young’s modulus and hardness of Cu₆Sn₅ are 127.586, 6.110 GPa, respectively. The shear strength of solder joints obtained at 2, 8 and 20 s is 31.80, 39.03 and 70.58 MPa, respectively. The shear strength of the solder joints increases as the proportion of intermetallic compounds in the weld increases.