| Lead and its compound are poisonous, which is detrimental to environment and health. With enhancing people'conception of green environment, products including lead will be avoided by legislation in some countries. In 2003, the EU enacted"instruction of electronic and electric application abandoned (WEEE)"and"instruction of deleterious composition avoided in electric application (ROHS)", which had been implemented in July, 2006. Green products have become to be a trend in global market.《Measures supervised that preventing pollution for electric and informational products》has be enacted by the Ministry of China Information Industry, according to pressure of lead-free replacing conventional Sn-Pb solder. In developed countries, trade barrier is changing from tariff type into technology type in these years. The late time provided by the EU, which should be decided after environment-prevented technology being finishing. Under WTO principle, environment-prevented edict will affect directly export amount for every country, which is a limit of entering market in the same. But we will not enter market of the EU, according to environment-prevented state for electronic products in our country. So development of lead-free solder has become to be taken into account for domestic electron industry and academy field. For preventing environment of human, it is an inevitable trend that lead-free solder will be developed rapidly in future. It will be an advantage for holding lead-free technology in strengthening enterprise competition, which requires to removing lead in assembly process.For avoiding the pollution of Lead, the research of lead-free solder is required to replace Sn-Pb solder used widely. Nowadays, lots of companies and laboratories attach much importance to research of lead-free solder. Being forced by demands of environment-protected and market, the lead-free trend of electronic package has become an advanced problem of important science and technology and system engineering in academy and industry field. For obtaining the replacement of Sn-37Pb solder, a lot of lead-free solders were developed in these years. Most of them focused on binary or ternary Sn matrix solder such as Sn-Ag, Sn-Cu, Sn-Zn and Sn-Ag-Cu. Obviously, the aim of research was not only finding a replacement, but also making sure that they are not worse than Sn-37Pb for mechanical properties, weldability and reliability of lead-free solder. At present, properties of lead-free solder ware far from requirement of welding process, which was developed by domestic and overseas researchers. For example, wettabilty and low stress isothermal fatigue of Sn-3.5Ag solder are bad, which is developed by Indium Company. They are relatively bad for wettabilty and resistance to oxidability of Sn-Zn solder developed by IBM and ATT. Accordingly it is restricted in application. At present, it is very difficulty that lead-free solder is extensively used for electronic industry. And our country is changing into a big country in manufacture and consumption of electronic product and apart. We will get a problem what should make our products having stronger competition in domestic and overseas market, by developing lead-free solder actively. Therefore, it has a theoretical and actual significance by investigating microstructure, properties and interfacial reaction of Sn matrix lead-free solder.In this paper, effects of alloy composition on the microstructure, properties and interfacial reaction of Sn-Ag-Cu and Sn-Zn solder were investigated. At first, composition of Sn-Ag-Cu alloy was designed by thermodynamic calculation method. Sub-regular thermodynamics model was set up for Sn-Ag-Cu ternary alloy. And the THERMO-CALC software and its database were used. They were adopted for"Gibbs free energy minimum method"and"compositions having the same chemical potential in the equilibrium phase". Consequently, composition of alloy and eutectic temperature were calculated for Sn-(3.5～4.0)wt%Ag-(0.5～1.3)wt%Cu and 217℃, respectively. And they are almost consistent by comparing results of DSC measurements with molten temperature of thermodynamic calculation.With development of electronic product integration, it is taken increasingly into account for reliability of welded joint. That is mostly dependent on the reaction of interface. So it is very important that effects of interfacial reaction, diffusion and microstructure of interface are investigated on the reliability of welded joint during soldering operation and aging. The effects of Cu content on the morphology of intermetallic compound Cu6Sn5 formed in the Sn-3.8Ag-(x)Cu /Cu interface and solder joint shear strength ware mostly investigated. Morphology of Cu6Sn5 is scallop-like, which could be controlled by changing the Cu content and the large needle Cu6Sn5 could be avoided, giving rise to increasing the shear strength of the solder joint. The results of aging experimentation showed that under the aging condition of room temperature and 1000 h, morphology Cu6Sn5 was transformed into long and hollow hexagonal faceted needle in the Sn-3.8Ag-(x)Cu solder Owing to hollow of Cu6Sn5 present, it became the weak section for the interface of Sn-3.8Ag-(x)Cu and Cu,and resuted in decreasing the shear strength of welded joint . During aging, thickness of intermetallic compound layer is proportional to square aging time and its , growth manner is dependent on the diffusion mechanism. Dynamics of growth is according with the function of X (t )? X0=Kt1/2. The result shows that properties of Sn-3.8Ag-0.7Cu and Sn-3.8Ag-0.7Cu-5.0In- 5.0Bi alloy solder are better.In this paper, effects of alloy elements Bi and Ag ware studied on wettability, the resistance to oxidability of high - temperature and joint shear strength of Sn - 8Zn lead - free solder. At hightemperature, the changes of oxidation film shape and color were observed on the surface of liquid solder by oxidation weight increase△M value method. We analyzed oxidation film by X - ray diffraction analysis and studied hightemperature resistance to oxidability of solder. The reasons of increasing joint shear strength were analyzed by observations of solder microstructure and experiments of solder joint shear strength after heat treatment. The experimental results indicated that the appropriate compact oxidation film could enhance resistance to oxidability at hightemperature. To some extent, the effect of Ag is greater than Bi on the resistance to oxidability of Sn-8Zn solder. Effects of alloy elements( Bi and Ag) have a like trend on the wettability of solder and shear strength of welded joint. And both have optimum composition. Sn-8Zn-Bi solder are composed ofβ-Zn, Zn-rich and Bi precipitate phases. And Sn-8Zn-Ag is made up ofβ-Zn, Zn-rich and Ag3Sn compound. Properties of Sn-8Zn-1.25B and Sn-8Zn-0.5Ag are better than others. The experimental results indicated that the appropriate addition of alloy elements(Bi and Ag )could enhance resistance to oxidability at hightemperature and joint shear strength.
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