Suitable Flux And Interface Microstructure Study Of Lead-free Sn-Zn Solder

As the materials containing lead harm to the humans and the environment, the lead-free solder has become the inevitable development of the electronic packaging connected materials. There are many new types of lead-free solder applied to the industrial production, but the performance is insufficient, particularly the poor wettability of the Sn-Zn solder. In this paper, the flux applied to Sn-9Zn solder was studied, and the interface microstructure of Sn-Zn solder and the copper substrate formed after soldering was investigated trying to do some exploration in the wettability of Sn-9Zn/Cu.Based on the characteristics of traditional rosin-based flux, by analysis the action mechanism of flux components, the three flux groups were designed. Rosin, zinc chloride, ammonium chloride and ethanol are based components, the glycol, oleic acid, lactic acid is added to them separately. Then in view of uniform design method, arrange the experiment points by it, greatly reducing the number of experiments, compared with the traditional method arranging experiments. Each group flux has four independent variables (ethanol doesn't) and they were divided into 12 levels. The wetting spreading area was taken as function. Using computer program UST4.0, the data has been processed with mathematical statistic regress analysis. For 3 groups gain three polynomial equations between independent variables and function or the influencing trend figures of wetting spreading area of flux components. Analyses of variance show that three polynomial equations have notable significance or more notable significance. In three soldering flux group, it is obvious that ZnCl₂ has an effect on wetting spreading area of soldering. The content of ZnCl₂ has a positive correlation with wetting spreading area of soldering in ethylene glycol; the content of has a linear relation with wetting spreading area of soldering: wetting spreading area reduces with NH₄Cl increasing. In oleic acid group, the content of oleic acid has a parabolic relation with wetting spreading area; the interaction of ZnCl₂ and NH₄Cl has an effect on wetting spreading area also. In lactic acid, the content of ZnCl₂ has a linear relation with spreading wetting area: the wetting spreading area increases with ZnCl₂ content increasing.The interface microstructure of Sn-Zn solder and the copper substrate formed after soldering was analyzed using OM, SEM, EDX and so on in this paper. The conclusions: the thickness of IMCs of the soldering interface was large between the eutectic composition of Sn-Zn solder and the Cu substrate; the thickness of IMCs of the soldering interface was little between the hypoeutectic composition of Sn-Zn solder and the Cu substrate. The interface compound was Cu₅Zn₈ in the soldering process.