| It is urgent for the electronic material industry to develop lead-free solders at present. Sn-Zn based solders have low melting temperature and can achieve reliable joints and mechanical properties, The raw materials of Sn-Zn solders are abundant and cheap. But Sn-Zn based solders still have not been used widely because they are easily to be oxidated and corroded.There are many alloys system have been exploited so far, mainly including Sn-Ag, Sn-Cu, Sn-Bi, Sn-Zn binary system and Sn-Ag-Cu, Sn-Ag-Bi, Sn-Zn-Bi, Sn-Zn-Ag ternary system. Among them, the Sn-Zn system Pb-free solder is a kind of new alloy system developed in recent years, with low price, nontoxic. Compared with other solders, the eutectic temperture is close to Sn-Pb, and the solder has good adhension property, creep resistance and heat fatigue property, so it has become the focus of the lead-free solder. The solder is easily to be oxidated and has poor wettability because of Zn existing, it can not be widely used so far. The solder is instantaneously oxidated durning the welding process, and the oxidation of Zn leads flux to be drossed; Futhermore, durning the welding process, the solder is easily to be oxidated, so it exists the problem of welding and reduce the credibility. The poor oxidation resistance becomes one factor of the development restrict of the Sn-Zn system lead-free solder. So the paper aims at Sn-Zn alloy system, studies many performance of it and the influence of adding other metal elements. Adding Ag, Bi, RE, analyse the influences of the elements on mechanical property by measuring shearing strength, elongation and fracture surface; study the influences of the elements on wettability by measuring the wetting strength and the wetting area; analyse the influences of the elements on oxidation resistance by the increasing oxidated mass, observing oxid film form ,shaping form and analyzing of X-ray diffraction.The shearing strength of solder joint decrease accompanied with enhance of elongation and corrosion resistance when adding Ag element. The structure of Sn-Zn-Ag system Pb-free solder consist of Sn-rich, Zn rich phase and the compound. The intermetallic compounds at the interface between Sn-Zn-Ag solder and Cu substrate is flat comparatively. With adding appropriate amount of Bi, the melting temperature of the Sn-Zn system declines, the wettability increases and the joint shearing strength enhances accompanied by elongation declines. The structure of Sn-Zn-Bi system Pb-free solder consists of Sn-rich, Zn rich phase and the extraction of Bi, besides, adding more RE improves structures of the solder distinctly and increases the fine crystal grains. The shearing strength of solder joint decrease accompanied with the enhance of elongation and corrosion resistance when adding RE element.For the purpose of evaluate multi performance at the same time, set the percent of alloy elements as factors and the mechanical property and the wettability of solder as targets, then conduct the extreme vertices design with multi-factor and multi-target. The regression equations related the shearing strength and the wettability of solder to elements were established. After considering the effects of solder's ingredients to melting temperature, pasty range, elongation, oughness, fusion, element losing for burning etc.The contribution of Sn-Zn-Ag-Bi-RE lead-free solder has been optimized, the obtained performances are: Ag:1.78wt.%,Bi:2.71wt.%,RE:0.18wt.%,Zn:8.59wt.% and Sn:86.74wt.%.
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