微量Bi、Sb对Sn-3.5Ag-0.5Cu无铅钎料组织与性能的影响

【作者】 罗飞；

【导师】 芦笙；

【作者基本信息】 江苏科技大学 ， 材料加工工程， 2010， 硕士

【摘要】 近年来,无铅钎料的研究一直是热点课题,但是完全实现无铅钎料的商业化生产与应用,仍有许多问题需要深入研究。本文以无铅钎料Sn-3.5Ag-0.5Cu为主要研究对象,在其中添加Bi、Sb元素,借助SEM、EDS、XRD、DTA和可焊性测试仪等手段,系统地研究了微量Bi,Sb对Sn-3.5Ag-0.5Cu无铅钎料的显微组织、熔化特性、可焊性及电导率和显微硬度等性能的影响。对钎料熔点的研究结果表明:添加微量的Bi元素可以大幅降低Sn-Ag-Cu钎料的熔点,使熔化温度区间增宽,而Sb元素的添加对熔点的影响不大,同样增大了合金的熔化温度区间, Sn-3.5Ag-0.5Cu熔点为216.4℃,熔程为6.3℃,而Sn-3.5Ag-0.5Cu-1.2Bi-0.8Sb无铅钎料的熔点可下降到209.8℃,熔程增宽至13.4℃,完全满足NCMS对于无铅钎料的评估标准。对钎料润湿性的研究结果表明:与Sn-3.5Ag-0.5Cu无铅钎料相比,添加适量的Bi、Sb都有助于钎料合金在母材上铺展,Sn-3.5Ag-0.5Cu-0.8Bi-1.2Sb钎料在240℃下的润湿时间由前者的1.95s降为0.78s,减少了60%,并且此成分的钎料合金的最大润湿力也达到0.58mN,具有最佳的润湿性能。对钎料热稳定性的研究结果表明:添加适量的Bi、Sb有助于在钎料合金表面形成致密的氧化膜阻挡钎料的二次氧化及烧损,但合金元素Bi的添加量应小于0.8wt%。对钎料的电导率的研究结果表明:Bi添加量小于1.0wt%时,因其净化作用减少了合金缺陷使导电率升高,而Sb元素的添加引起的点阵畸变增加了电子的散射几率,并且各组元间化学相互作用的加强也使有效电子数减少,因此Sb元素的添加明显降低了钎料的导电率。对钎料的显微硬度的研究结果则表明:在基体合金中单独添加Bi及复合添加Bi、Sb,由于Bi、Sb的固溶强化效应及弥散分布的Cu6(Sn, Sb)5三元金属间化合物的作用,使显微硬度值得以提高,尤其Sb的增强效果明显。对钎料的显微组织进行观察得知:Sn-3.5Ag-0.5Cu-yBi-zSb(0.4≤y,z≤1.2)的组织也是由大量β-Sn初生相与少量Cu6Sn5、Ag3Sn共晶产物组成,Bi、Sb添加量各小于0.8wt%时,均以固溶形式存在于β-Sn初生相中,随着Bi含量的提高,钎料组织中的Ag3Sn相得到了一定程度的细化,长条状的化合物变成针状;而随着Sb含量的增加,初晶晶粒变得粗大,金属间化合物呈发散漩涡状分布,出现很多弥散分布的颗粒相,经EDS及XRD分析可知,新产生的金属间化合物应为Cu6(Sn, Sb)5。综合来看,Sn-3.5Ag-0.5Cu-0.8Bi-1.2Sb综合性能优良,具有深入开发的价值。更多还原

【Abstract】 The research in lead-free solder alloy has been a popular topic in recent years. However, a lot of problems in full commercial production and application of lead-free solders must be studied in detail. Based on Sn-3.5Ag-0.5Cu lead-free solder and by means of SEM、EDS、XRD、DTA and weldability test, effects of Bi, Sb elements on microstructure, wettability, melting characteristic and such physical properties were studied and the solder alloy component of favorable combination property was gotten.The results of melting characteristic experiments show that trace addition of Bi element has positive effects on depressing the melting temperature and broadening the melting range. However, the addition of Sb has little effect on melting temperature but broadens the melting range. The melting point of lead-free solder Sn-3.5Ag-0.5Cu is 216.4℃and the melting range is 6.3℃. The melting point of Sn-3.5Ag-0.5Cu-1.2Bi-0.8Sb lead-free solder reduces to 209.8℃, and the melting range increases to 13.4℃. The melting characteristics may meet the evaluation standard required by NCMS. The results of wettability experiments show that Sn-3.5Ag-0.5Cu lead-free solder has poor wettability. Adding suitable amount of Bi,Sb elements into the solder alloy may help the liquid solder spread on the surface of base metal. Compared to the specimen Sn-3.5Ag-0.5Cu, the wetting time of Sn-3.5Ag-0.5Cu-0.8Bi-1.2Sb under the condition of 240℃reduces from 1.95s to 0.78s, representing a decline of 60%. In addition, the maximum wetting force of this componential solder also reaches 0.58mN, which leads to the best wetting performance. The results of heat stability experiments show that with proper addition of Bi and Sb elements, the compact oxide film may form on the surface of the solder alloy to prevent reoxidation and melting loss. However, the adding amount of Bi should be no more than 0.8%. In addition, the results of electrical conductivity test show that trace addition of Bi(≤1.0wt%) enhances the electrical conductivity because of its purifying effect. But the addition of Sb leads to the lattice distortion so as to increase the scattering probability of electrons, and the enhancement of the chemical interaction among each component reduces effective mass of electrons. As a result, the electrical conductivity may decline obviously when adding Sb element. The results of microhardness test show that accompanied the solution strengthening and the effects of new formed dispersed Cu6(Sn, Sb)5 ternary inter-metallic compound, the addition of both Bi, Sb elements may enhance the microhardness of the solder alloy, especially obvious for the strengthening effect of Sb.By observing the microstructure of solder alloys, it can be concluded that the structure of Sn-3.5Ag-0.5Cu-yBi-zSb(0.4≤y,z≤1.2)consists of a mass ofβ-Sn primary phases and little amount of eutectic phases composed by Cu6Sn5 and Ag3Sn. It is approved that elements Bi and Sb are solid-soluted in the matrix ofβ-Sn primary phases when the addition level is less than 0.8wt% respectively. The inter-metallic Ag3Sn phases in the alloy system have been refined in a certain degree, and the strip-like IMCs turn to be acicular ones while raising Bi content. Furthermore, to increase the content of Sb, the primary phases may become coarse, and the IMCs turn to be dispersively distributed in a whorl-like formation. A lot of new particle phases are present dispersively in the matrix, and by means of EDS and XRD analysis, it can be approved that new IMCs are Cu6(Sn, Sb)5 ternary compounds.By analyzing the data gathered from the experiments, a new solder alloy was optimized for the further study. The compositions are Sn-3.5Ag-0.5Cu-0.8Bi-1.2Sb.更多还原