Sn2.5Ag0.7Cu0.1RE/Cu Soldering Assisted With Ultrasonic Vibration And Electric Field And Its Aging Characteristics

Rapid development of electronic products puts forward higher demands for the quality and reliability of lead-free solder joints. SnAgCu system solder alloy, expecially SnAgCuRE lead-free solder alloy is considered as one of the best alternatives of SnPb solder alloy. However, wettability of SnAgCuRE solder alloy and reliability of the lead-free solder joints still require further improvements to meet the development of lead-free and halogen-free environment friendly soldering. Therefore, seeking new and effective wettability methods to improve the solderability of the solder alloy to meet the demands of micro-joining quality and reliability is the problem demanding prompt solution, which has been one of the research hotspots.In the study, orthogonal experimental design was applied to investigate the effects of ultrasonic vibration (USW) power and electric field (E) on microstructure, shear strength of solder joints and the fracture mechanism of the solder joint. The optimum USW and E parameters were determined. The study investigated the effects of aging parameters and application of USW and E on interfacial intermetallic compound (IMC) and shear strength of Sn2.5Ag0.7Cu0.1RE/Cu solder joints after aging. In addition, growth kinetic of interfacial IMC and fracture mechanism of the solder joints are analyzed.The soldering experimental results reveal that application of USW and E can realize the favourable soldering of Sn2.5Ag0.7Cu0.1RE/Cu with halogen-free flux. The maximum shear strength of28.7MPa is obtained from the joint soldered at USW power of88w, USW time of60s, and E of2kV/cm, which increases by68%comparing with that of the traditional soldering joint. USW has a greater effect on the solder joint than that of E, in which USW power has a remarkable influence. Compared with traditional soldering and soldering with USW assisted, application of USW and E can reduce the thickness and roughness of Cu6Sn5IMC layer, and enhance microhardness of soldering seam and shear strength of the solder joint. The fracture mechanisms of the solder joint translated from brittle fracture interior the IMC layer to mixed-fracture to ductile fracture in the soldering seam.The interfacial IMC layer of Sn2.5Ag0.7Cu0.1RE/Cu solder joint obtained with USW and E assisted after aging were comprised of Cu6Sn5and Cu3Sn, and cracks, voids were observed interior the IMC layers. With the aging time extension, the thickness of Cu6Sn5and Cu3Sn IMC layer increases. The morphology of Cu6Sn5changes from fine scalloped to thick and uneven scalloped. In addition, cracks, voids and other defects are observed in the interfacial IMC layer. Compared with traditional soldering and soldering with USW assisted, application of USW and E during soldering can increase the growing activation energy of Cu6Sn5and Cu3Sn IMC, suppress the growth of IMC during aging, thus enhancing the shear strength of the solder joints. The maximum value of activation energy of Cu6Sn5and Cu3Sn IMC were71.75kJ/mol and86.67kJ/mol, respectively. Thickness and morphology of interfacial IMC layer have large influence on the fracture path and mode of the solder joint. Application of USW and E during soldering can change the fracture path of the solder joint after aging and improve the fracture mode, which translated from failure based on brittle fracture to failure based on ductile fracture, and enhance shear strength of the solder joint, thus enhancing the realibity of the solder joint.In conclusion, application of USW and E can suppress the rapid growth of IMC layer during the soldering and aging process, improve the solderability and fracture mechanism of the solder joint, and can satisfy the high standards of the contemporary lead-free and halogen-free mirco-jointing of electronic products.