【作者】 陈熹；

【导师】 毛大立； 李明；

【作者基本信息】 上海交通大学 ， 材料物理化学， 2009， 博士

【摘要】 Sn-Zn共晶焊料因其熔点较低、接近Sn-Pb焊料，且力学性能优良、价格低廉、绿色环保，有望成为新一代无铅焊料。但是，Sn-Zn合金的抗氧化性、润湿性较差，阻碍了它的广泛应用。因此，Sn-Zn共晶焊料引起国内外众多研究者的关注，成为目前无铅焊料的重要研究课题之一。本论文以应用潜力巨大的Sn-9Zn合金为对象，以提高焊料抗氧化性为主要目标，并综合考虑合金的润湿性、熔点及力学性能，选择Cr、Al、Ti、La等代表性合金元素，对Sn-9Zn-M三元合金焊料的各种性能进行了系统研究。在此基础上，遴选出能够显著改善焊料抗氧化性和力学性能的Sn-9Zn-Cr合金，就其制备方法、不同Cr含量对各项性能的影响、焊点界面反应行为及其作用机理作了详细的研究。研究表明：在Sn-9Zn中添加微量Cr、Al、Ti、La元素，除La以外，其它三种元素对焊料的抗氧化性均有明显的改善，但作用机理各不相同。Al或Ti的加入，改变了氧化顺序，优先于Zn发生氧化，在焊料表面形成稳定致密的氧化膜，进而阻止焊料的进一步氧化，提高了Sn-9Zn焊料的抗氧化性。Sn-9Zn-Cr合金表面氧化膜仍以ZnO为主，但在Zn氧化膜与焊料交界的次表面形成Cr的偏聚层，好似一层“内阻挡层”，抑制了Zn氧化，从而大大降低了焊料的氧化速度。进一步研究发现： Cr、Al、Ti、La等四种合金元素的加入，总体上没有改变Sn-9Zn焊料的微观组织和固液相线。Al和Ti不同程度地降低了焊料的润湿性，在实际当中难以被采用，而Cr、La元素使Sn-9Zn焊料的润湿性略有提高。综合以上结果，Cr在不破坏润湿性、保持低熔点的同时，可大大提高Sn-9Zn合金的抗氧化性，Sn-9Zn-Cr合金焊料是一种具有应用前景、值得深入研究的新型焊料。考虑到今后的应用，为了解决低熔点Sn、Zn与高熔点Cr的合金化问题，研究中对采用不同中间合金的焊料制备技术进行了探讨。结果表明，采用中频感应炉、通过SnCr中间合金制备Sn-9Zn-Cr合金是最佳选择，并发现加入Cr对Sn-9Zn合金微观组织有明显的细化作用，加入0.1wt%左右的Cr效果最佳。研究还发现，Cr含量对Sn-9Zn-Cr焊料各项性能有重要的影响，存在一个最佳含量范围。当Cr含量达到0.1wt.%时，焊料具有最好的抗氧化能力和润湿性能，同时发现Sn-9Zn-0.1Cr合金比Sn-9Zn合金的延伸率提高约66%。焊点可靠性是评价焊料好坏的重要性能，因此本研究还考察了Sn-9Zn（-xCr）/Cu焊点界面反应情况。通过对界面金属间化合物层的形貌、厚度及生长动力学进行研究，结果显示：（1）在Sn-9Zn（-xCr）/Cu焊点中，界面处金属间化合物的成分为Cu₅Zn8；随时效时间的延长，金属间化合物层的厚度增加；（2）Sn-9Zn（-xCr）/Cu焊点界面反应受扩散控制。Sn-9Zn焊料中的Cr含量达到0.1wt.%时，其界面反应的扩散系数达到最低，表观激活能达到最高，对界面反应的抑制效果最佳。界面处金属间化合物层生长的减缓，笔者认为主要是因为Cr可与Zn反应形成～Zn₁₇Cr和/或～Zn₁₃Cr等金属间化合物，降低了焊料中Zn原子的活性、减缓了Zn原子的扩散速度。更多还原

【Abstract】 Because of low melting point, good mechanical property, low cost, andenvironment friendliness, Sn-9Zn eutectic solder is potential to be new kind of leadfree solder. However, bad oxidation resistance and wettability make it difficult to beused broadly. So Sn-9Zn eutectic solder attracts lots of attention, and the research onperformance improvement has become one of the most important issues.In this study, Cr, Al, Ti, La were selected as alloying elements for improvingperformance of Sn-9Zn solder. The aim was improving oxidation resistance, and otherperformance, such as wettability, melting point and mechanical property. And it isfound that Sn-9Zn-Cr alloy has good oxidation resistance and mechanical property.Furthermore, the preparation method, the effect of Cr content on performance, andinterfacial reaction behavior and mechanism were studied.The result shows that Cr, Al, Ti can improve oxidation resistance of Sn-9Zn alloyexcept La, and they have different mechanism. Because of preferential oxidization, Alor Ti addition forms compact and stable oxide film on the surface of Sn-9Zn solder,which inhibits further oxidation. Cr addition forms a barrier layer, which is so call“inner barrier layer”, in the sub-surface of Sn-9Zn solder to protect the solder fromfurther oxidation.Then influence of alloying element, Cr, Al, Ti, and La, on other properties ofSn-9Zn alloy was studied. In general, microstructure and melting point are notchanged by adding these alloying elements, neither are solidus/liquidus temperature,melting range. Although Al and Ti addition apparently decrease wettability of Sn-9Znsolder, Cr, and La improve it slightly. According to our research, Cr addition canimprove oxidation resistance while maintaining wettability and melting point. Sn-9Zn-Cr alloy is new kind of low temperature lead free solder with broadapplication prospect.For high quality of sample, exploration of preparation of Sn-9Zn-Cr solder wascarried out. Because of finer microstructure, the Sn-9Zn-Cr solder prepared by SnCrmaster alloy method with medium frequency induction furnace is the best choice. Andthe optimal content of Cr addition is0.1wt.%.Further research on the effect of Cr content on performance of Sn-9Zn solder isperformed. It seems that the best oxidation resistance and wettability were providedby the solder which has0.1wt.%Cr. And Sn-9Zn-0.1Cr alloy shows the bestelongation value, which is approximately66%more than that of Sn-9Zn alloy.Finally, morphology, thickness, and growth dynamics of intermetallic compoundlayer at Sn-9Zn-Cr/Cu interface were studied. The results show that:（1） Sn and Cr donot take part in the interfacial reaction at Sn-9Zn（-xCr）/Cu interface, and thecomposition of intermetallic compound layer is Cu₅Zn8. The thickness of theinterfacial IMC layers increases as the aging time is extended.（2） Interfacial reactionof Sn-9Zn solder with Cu plate is diffusion controlled. When Cr content is0.1wt.%,the diffusion coefficient shows the lowest value, while the activation energy is themaximum value. The reason of this phenomenon is that Cr addition reacts with Zn toform intermetallic compounds, such as～Zn₁₇Cr and/or～Zn₁₃Cr, which candecrease diffusion of Zn atom in the solder and make them more stable. So adding Crinto Sn-9Zn solder leads to slow down the growth of the interfacial IMC layer. Thestabilization effect of Cr addition on Zn atom is maximum when Cr content is0.1wt.%.更多还原