Zhenghong Wang

Electrochemical behavior of Sn-xZn lead-free solders in aerated NaCl solution

Electrochemical corrosion behavior of Sn-xZn solder alloys (i.e. hypoeutectic Sn-6.5Zn, eutectic Sn-9Zn and hypereutectic Sn-12Zn, in wt.%) in aerated 0.5 M NaCl solution was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques, aiming to assess the effect of Zn content on the corrosion behavior of Sn-Zn alloys. Scanning electron microscopy (SEM) equipped with EDX, X-ray diffraction (XRD) were performed to characterize the surface morphology and to identify the chemical composition of the corrosion products, respectively. It is found that increasing Zn contents lead to an increase in corrosion current density and the corrosion potential shifted towards more negative values, revealing that the corrosion rates increase in the order of: Sn-6.5Zn <; Sn-9Zn <; Sn-12Zn. The acquired electrochemical impedances were successfully fitted with an equivalent circuit model. Fitted results reveal that total impedance decreased with increasing Zn content, indicating that Sn-6.5Zn alloy exhibits the highest corrosion resistance. The results are further confirmed by surface morphology characterization of the corrosion products, which shows a more homogeneous product film for lower Zn content. Analysis of the corrosion products indicates that oxide hydroxychlorides are the dominant corrosion products. Based on the obtained results, it is suggested that Sn-Zn alloy with lower Zn content appears to be more attractive in terms of superior corrosion resistance.

Corrosion process study of Zn-30Sn high-temperature lead-free solder

The corrosion process of Zn-30Sn high-temperature solder alloy was investigated in neutral 0.5 M NaCl solution at room temperature (25 ± 0.5 °C) by Scanning Electron Microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface observation by SEM indicates that the surface morphology of Zn-30Sn evolves from the dense particle structure to porous structure, and finally converts to platelet-like structure. Energy Dispersive X-ray Analysis (EDXA) shows that Zn phase is corroded preferentially due to no Sn compound was observed. The outer surface of corrosion product was confirmed as Zn(OH)<inf>2</inf> by XPS. Dominant corrosion products were characterized as a mixture of ZnO, Zn(OH)<inf>2</inf> and Zn<inf>5</inf>(OH)<inf>8</inf>Cl<inf>2</inf>·H<inf>2</inf>O. The corrosion process was further discussed in detail.

Constitutive behavior and Anand model of novel lead-free solder Sn-Zn-Bi-In-P

The Anand constitutive model has emerged as a popular method to describe the inelastic deformation behavior of Sn-Pb solders and, more recently, to describe the behavior of lead-free solders in electronic assemblies, mainly due to its effective description of constitutive behavior and high compatibility with finite element modes. Heretofore, although plenty of experimental and theoretical works have been conducted on building constitutive models for lead-free solders, e.g. Sn-Ag, Sn-Ag-Cu, Sn-Cu based solders, insufficient works have been conducted on modeling Sn-Zn based lead-free solder alloys. In this paper, a series of compression tests were conducted for a novel lead-free solder Sn-9Zn-2.5Bi-0.5In-0.05P and Sn-8Zn-3Bi solder at three constant strain rates (10-3/s, 10-2/s, 10-1/s) and different temperatures (20°C, 60°C, 100°C). Anand constitutive model was applied to describe the inelastic behavior as well as saturation stress of both solder alloys. Comparison of the experimental results and Anand model predictions were evaluated with the material parameters extracted from compression tests and non-linear least squares fitting of the constitutive relation. The results reveal that, for both two solder alloys, the Anand model predictions are in good agreement with experimental data of stress-strain responses at various strain rates and temperatures applied in the present work. In addition, the stress-strain responses of both solder alloys are also discussed on the basis of experimental data.