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Microstructures, interface reaction, melting characteristics, tensile property, thermal fatigue behavior and wettability of Sn58Bi, Sn35Bi0.3Ag and Sn35Bi1.0Ag solders were investigated. Only Sn phase and Bi phase like net-type distribute uniformly in the Sn58Bi matrix, Sn35Bi0.3Ag and Sn35Bi1.0Ag solder show the AgSn particles in the Sn matrix around net-like Bi phase, at the solder/Cu solder joints, only CuSn intermetallic compound was observed. The liquid phase line temperature of Sn35Bi0.3Ag and Sn35Bi1.0Ag is higher than that of SnBi solder. Sn35Bi1.0Ag solder joints show superiority in mechanical property and fatigue life, which can attribute to the strengthening effect of AgSn particles. Moreover, the wettability of Sn35Bi1.0Ag solder was best of all, and the N atmosphere and RMA flux can enhance the wettability obviously, which can provide the reference support of the research of SnBi base solders. [ABSTRACT FROM AUTHOR]

With the addition of Zn, Co and Fe, the microstructures and properties of SnAgCu solders can be improved obviously, the constitutive response of SnAgCu solder bearing 0.8%Zn, 0.8%Co and 0.8%Fe was studied under uniaxial tension. Anand model was used to represent the inelastic deformation behavior of the lead-free solders. The material parameters of the constitutive relations for SnAgCu(Zn,Co, Fe) solders were determined from separated constitutive relations and experimental results. Combining the model, finite element analysis (FEA) was used to study the thermally induced inelastic deformation and the stress-strain response of the solder joints in wafer-level chip scale packages (WLCSP) mounted on printed circuit boards (PCB). And it is found that the addition of Zn, Co and Fe can enhance the fatigue life of SnAgCu solder joint, the superiority can be found for the addition of Fe among the three elements. [ABSTRACT FROM AUTHOR]

Growth kinetics of intermetallic compound (IMC) layers formed between SnAgCu solder for reflow soldering and Cu substrate by solid state isothermal aging were investigated at temperatures between 100 and 140 °C. For the aged samples, two distinct layers of IMCs of the type CuSn and CuSn were identified with the later adjacent to the copper substrate. In the as-soldered samples, only a single layer of interfacial CuSn type IMC was formed. Moreover, the apparent activation energies were 96.75 kJ/mol (total IMC), 85.98 kJ/mol (CuSn IMC) and 105.92 kJ/mol (CuSn IMC), respectively. [ABSTRACT FROM AUTHOR]

The microstructures, wettabilities and mechanical properties of SnAgCu-xZn (x = 0, 0.5, 0.8, 1.0, 1.2, 2.0, 2.5, 3.0) solders were investigated, respectively. The results indicated that adding small amount of Zn can evidently improve the wettability, mechanical properties and refine the microstructure of SnAgCu lead-free solder. However, there existed an effective range for the Zn addition, the best Zn content was found to be 0.8 % in the current study. Moreover, the presence of Zn in the solders plays a major role in inhibiting the growth of Cu-Sn intermetallic layer in the solder/Cu interface. Based on thermal-cycling tests, it is demonstrated that the addition of Zn can enhance the thermal-fatigue properties of SnAgCu solder joints. [ABSTRACT FROM AUTHOR]

In this paper, SiC nanowires (NWs) were added to the SAC105 solder as an enhancement agent. By mechanical stirring, the Sn1.0Ag0.5Cu (SAC105)- x SiC (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) solders were prepared and served as samples to investigate the thermal properties, wettability, microstructure, interfacial microstructure, and mechanical properties. It was found that the addition of 0.4% SiC NWs allowed a substantial increase in the spreading area. The Cu 6 Sn 5 IMC and Ag 3 Sn IMC, and β-Sn grains were significantly refined within the SAC105-0.6SiC solder matrix. Meanwhile, the interfacial morphology became much flatter, and the thickness was minimized. Due to the refinement of Ag 3 Sn IMC and the reduction of the interfacial thickness, the mechanical properties of the composite solder were unsurprisingly improved. These were well demonstrated by the deeper and smaller dimples derived from the fracture surface. In addition, the mechanisms of microstructure refinement and enhancement of mechanical properties were revealed from the aspects of dispersion, adsorption, and pinning effect of SiC NWs. The deterioration of solder properties due to the agglomeration of SiC NWs was also well discussed. • The melting behavior, wettability, microstructure, and mechanical properties of SAC105-SiC(nanowires) solder were revealed. • The addition of 0.6 wt% SiC nanowires to SAC105 solder can significantly refine the microstructure and interfacial IMC. • The agglomerated SiC nanowires at the interface were found to seriously deteriorate the shear strength. [ABSTRACT FROM AUTHOR]

Highlights: [•] New lead-free solders were designed with different Yb. [•] The enhancement of properties of solders were analyzed. [•] Rare earth Yb can refine the microstructure of solders. [Copyright &y& Elsevier]

In order to enhance the joint performance, the Cu/Sn58Bi-0.6B 4 C/Cu 3D structure was obtained by ultrasonic-assisted connection. The influence of ultrasound on the solder and its wettability, as well as the microstructure, interfacial IMC structure, and mechanical properties, was investigated. It is indicated that ultrasonic cavitation improves the crystal structure of the solder alloy by refining grain size and making the microstructure more uniform. The ultrasound also changes the preferred orientation of β-Sn and Bi phases, and increases the low-angle grain boundaries and local orientation differences for improved alloy strength. Additionally, the ultrasound promotes the molten solder spreading on the Cu substrate. The microstructure of the filler metal layer is improved by ultrasonic, and the Cu 6 Sn 5 compounds floating in the solder matrix act as the strengthening phase. Cavitation bubbles erosion increases the contact area between the solder and Cu substrate. The audiogenic high temperature reduces the IMC thickness difference at both ends of the joint caused by the temperature gradient. Besides, the grain size in the solder matrix and interfacial IMC is refined with increased supercooling. The ultrasound strengthens joint shear strength significantly and improves the potential path for crack propagation. The appearance of dimples in the fracture alters its mode from being typically brittle to a mixed ductile and brittle fracture. The above enhancement will be further improved with the appropriate extension of ultrasonic time. We hope to strengthen joint performance by ultrasound, and provide reference for future research and application combining soldering with ultrasonic technology. [ABSTRACT FROM AUTHOR]