| The green manufacture of electronic products with miniaturization, lightweight and more functional makes Sn Ag Cu system solder alloy, expecially Chinacharacterized Sn AgCu RE system solder alloy be considered as one of the the best alternative of Sn Pb solder alloy. Carrying out the research about the quality and the engineering application of lead-free solder joint is the hot issues to be resolved in the field of electronics packaging and assembly. For the problem of the insufficient wettability and quality of lead-free solder in electronics packaging and assembly of halogen-free or less halogen flux, this paper takes Sn AgCu system solder alloy and C194 for lead frame in actual electronics packaging and assembly as object, study the wetting, soldering, and aging characteristics of Sn2.5Ag0.7Cu0.1RE/C194 cooper alloy, with the purpose of expanding the application of SnAgCu system solder alloy and providing an experimental and theoretical basis for lead-free electronics packaging and assembly.By orthogonal test and single factor experiment design, this paper studies the effect of soldering flux, wetting temperature and USW condition(ultrasonic vibration power and time) on the wettability of Sn2.5Ag0.7Cu0.1RE/C194 copper alloy, and the optimum technological parameters were determined. The soldering experiment, the microstructure, the property and the fracture mechanism of Sn2.5Ag0.7Cu0.1RE/C194 copper alloy solder joint under the action of ultrasonic vibration were carried out. In the end, this paper discuss the growth of interfacial IMC and fracture mechanism of Sn2.5 Ag0.7 Cu0.1 RE/C194 copper alloy solder joint assisted with USW in the process of aging.The results show that the application of USW can realize the favorable wetting and soldering of Sn2.5Ag0.7Cu0.1RE/C194 copper alloy. The maximum spreading area of 52.7mm2 and minimum angle 24.2? is obtained at the USW power of 88 w and ultrasonic vibration time 50 s, which increased by 60.% and decreases by 47% compared with that of without the USW assisted, the shear strength is 24.3 MPa, which increased by 49%.Compared with no USW assisted, the propotion of β-Sn in Sn2.5Ag0.7Cu0.1RE/C194 copper alloy solder seam increases, eutectic organization becomes loose, Ag3 Sn changes from granular or needle to sheet with large space, the hardness of soldering seam increases; the thickness and roughness of the interfacial IMC decreases, the thickness of the IMC is 3.2μm, and the minimum roughness is 2.1μm decreased by 22% and 64%, respectively. The fracture pattern translated from brittle fracture interior the IMC layer to mixed-fracture which was dominated by ductile fracture, in the soldering seam and interior IMC.There have been Cu3 Sn in Sn2.5Ag0.7Cu0.1RE/C194 copper alloy solder joint in the aging process. Compared with no USW assisted, the growth rate of Cu6Sn5, Cu3 Sn in solder joint with USW assisted was lower, the thickness of IMC was thinner, and the shear strength was higher. At the aging time of 450 h, the shear strength of the solder joint was 17.6MPa, increased by 38%. With the extension of aging time, Cu6Sn5, Cu3 Sn thickness increased, the shape of Cu6Sn5 changed from scalloped to lamellar gradually, the shear strength of the solder joint decreased. The shear fracture changed from mixed fracture of mainly ductile fracture in the soldering seam and interior IMC to brittle fracture interior IMC.In conclusion, USW can improve the wettability and the shear strength of Sn2.5 Ag0.7Cu0.1RE/C194 copper alloy, restrain the growth of the IMC layer, change the mode of fracture, improve the reliability of the Sn2.5 Ag0.7 Cu0.1RE/C194 copper alloy solder joint, and is an effective assistant way of realizing reliable connection under the condition of halogen-free or less halogen flux. |
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