Research On Properties Of Low Temperature SnBi Solder Alloy

As the electronic packaging technology develops, the study and exploitation of lead-free solder has been the one of the major issues in the field of electronic packaging. The new low-temperature solders which have high reliability and usability will rise at a rapid speed. The solders are the fundamental one and also the top priority in the electronic assembly industry.Firstly,the effect of Ag and Cu addition on Sn-Bi is observed.The Sn-Bi solder contains the Sn-50Bi?Sn-57 Bi and Sn-65 Bi. Sencondly, the Sn-xBi(x=5,10,15) solder are choosed in consideration of the solid solution and low strength property of Sn-Bi. Three kinds of Sn-xBi solders are choosed and every solder are got in three cooling method-cooling in water, cooling in air and cooling in furnace. In this paper,the study of microstructure characteristic and mechanical property of Sn-xBi are put on the focus.The results above show that the microstructure of Sn-Bi alloy is significantly refined and Ag3 Sn particulates are deposited when 1% Ag is added. On the other hand, Bi is refined to some degree and Cu6Sn5 particulates are deposited as well when 0.5% Cu is added. Secondly, we find that 1% Ag addition has a great influence on Sn-Bi alloy's mechanical properties—tensile strength, plasticity at normal temperature, toughness are significantly enhanced while plasticity at 100? is reduced, but little on modulus of elasticity. And tensile strength is enhanced, while plasticity and toughness are reduced when 0.5% Cu is added, but modulus of elasticity is barely effected. At last, intermetallic reactions in Sn-Bi joints are observed. The results show that Ag or Cu addition has little effect on the morphology of Cu/solder/Cu interface and the distribution of intermetallic compounds(IMC), but we observed significant growth of IMC layer.The study of Sn-xBi shows tha as the content of Bi increases, the solidus temperature of Sn-xBi solder alloy get decreased. Through the spreading area method to evaluate the wetting property. The result shows that the Bi element has the surface-active action, the addition of Bi can reduce the surface tension of solder and then the wetting property is improved. The microstructrues of Sn-xBi show that the Bi distributes in the Sn matrix as solid solution. And with different cooling method, the solid solubility of Bi in Sn matrix is different. Owing to the solid solution strengthening of Bi phase, as the content of Bi get increased,the tensile strength of Sn-Bi increases. The tensile strength of Sn-5Bi,Sn-10 Bi,Sn-15 Bi solder cooling in water is 60.2MPa,78.6MPa and 81.6MPa. After aging treatment,the tensile strengths get increased to 67.8MPa, 82.4MPa and 82.9MPa. Then the nano-indentation test is conducted. The creep resistance property shows as follows, Sn-15 Bi cooling in water>Sn-10 Bi cooling in water>Sn-15 Bi cooling in air>Sn-10 Bi cooling in air>Sn-15 Bicooling in furnace>Sn-10 Bi cooling in furnace.The Sn-10 Bi and Sn-15 Bi cooling in water and cooling air belong to the dislocation creep mechanism. The Sn-10 Bi and Sn-15 Bi cooling in furnace belong to atomic diffusion mechanism.