Zn元素的添加对Sn58Bi共晶焊料合金性能的影响

发布时间：2018-04-16 17:07

本文选题：Sn-Bi基焊料 + 界面反应　；参考：《天津大学》2016年博士论文

【摘要】：在电子封装领域中,低温焊接可降低由于不同材料间热膨胀失配性所引起的热破坏性。于是,具有低熔点、润湿性好的Sn-Bi基焊料成了低温焊接所需无铅焊料之一。本文系统、深入地研究了添加Zn元素的Sn-58Bi共晶焊料样品相关性能,即对CuZn大规模剥离现象,经回流焊接和液态时效后焊点的拉伸、蠕变性能,以及经电流和热应力共同作用后焊点机械性能等方面进行重点研究。CuZn的大规模剥离主要受Zn浓度的影响。在经过较长时间液态时效反应后,仅当焊料样品中Zn浓度大小达到0.67 wt.%时,这种剥离行为才可能发生。和Sn-58Bi-0.7Zn块状焊料相比,大规模剥离现象更容易在小体积焊料球样品中出现。焊料样品的相关微结构演化机制可通过向Cu-Sn-Zn等温相图中引入Zn的扩散路径进行分析和解释。此外,当时效温度大于Sn-58Bi-0.7Zn块状焊料液相线温度时,Cu6(Sn,Zn)5和CuZn层间Sn的浓度会大幅度增加。这时,CuZn的大规模剥离行为就发生了。通过热力学分析可以得出,这种大规模剥离行为的发生,在一定程度上归结于Cu6(Sn,Zn)5/CuZn界面处自由能的减少,而Sn浓度是影响这个自由能减小的主要原因。另一方面,与Sn-58Bi共晶焊料样品相比,Sn-58Bi-0.7Zn焊料样品的极限拉伸强度在回流焊接和液态时效后都分别得到提升。其中,Sn-58Bi-0.7Zn焊条样品分别提升6.05%和5.50%,而焊点样品则分别提升21.51%和29.27%。Cu/Sn-58Bi-xZn焊点增强的主要原因是由于Zn的添加让Bi晶粒得到细化,使断裂面从基底和界面金属间化合物之间转移到了界面金属间化合物和焊料之间。在经回流焊接和液态时效后的矩形焊料样品中,Sn-58Bi-0.7Zn矩形焊料的抗蠕变能力也都分别明显大于Sn-58Bi矩形焊料。此外,在拉伸试验期间,阳极界面位置处界面金属间化合物和富Bi层间连接性的大小会强烈影响电迁移和热时效耦合Cu/Sn-58Bi-0.7Zn焊点的极限拉伸强度。由于富Bi层的持续生长加速了孔洞和裂纹形成,而裂纹在界面中进一步传递将导致焊点拉伸强度降低。对于未加载电流应力而仅进行固态时效的焊点,在Cu-Sn-Zn/Cu-Zn界面处由Bi偏析所形成的空位及应力集聚对其极限拉伸强度会产生极大影响。耦合应力期间电流应力能造成孔洞形核,所以耦合焊点的极限拉伸强度要小于时效焊点的极限拉伸强度。对于耦合样品,通过有限元模型揭示了其阳极界面处生成的富Bi层可承担部分载荷,从而使焊点界面处的压入深度得到减小。因此,耦合样品的抗蠕变性要高于时效样品的抗蠕变性。
[Abstract]:In the field of electronic packaging, low temperature welding can reduce the thermal damage caused by thermal expansion mismatch between different materials.Therefore, Sn-Bi solder with low melting point and good wettability becomes one of the lead-free solders for low temperature welding.In this paper, the properties of Sn-58Bi eutectic solder samples with Zn addition have been studied systematically, that is, the tensile and creep properties of solder joints after reflux welding and liquid aging have been studied for CuZn stripping phenomenon, reflux welding and liquid aging.The mechanical properties of solder joints after the interaction of electric current and thermal stress were studied in detail. The effect of Zn concentration on the mass exfoliation of CuZn was studied.After a long time of liquid aging reaction, this kind of stripping behavior can occur only when the Zn concentration in the solder sample reaches 0.67 wt.%.Compared with Sn-58Bi-0.7Zn bulk solder, large scale peeling occurs more easily in small volume solder ball samples.The evolution mechanism of the microstructure of solder samples can be analyzed and explained by introducing Zn into the Cu-Sn-Zn isothermal phase diagram.In addition, when the aging temperature is higher than the liquid line temperature of Sn-58Bi-0.7Zn bulk solder, the concentration of Cu _ (6) O _ (2 +) Sn _ (5) and Sn between CuZn layers will increase greatly.In this case, the large-scale stripping of CuZn occurs.Through thermodynamic analysis, it can be concluded that the occurrence of this kind of large-scale stripping behavior is attributed to the decrease of free energy at the interface of Cu _ (6) O _ (6) SnN _ (5) Zn _ (5) / Cu _ (Zn), and the concentration of Sn is the main reason for the decrease of the free energy.On the other hand, compared with Sn-58Bi eutectic solder sample, the ultimate tensile strength of Sn-58Bi-0.7Zn solder sample is increased after reflux welding and liquid aging respectively.The main reason for the increase of Sn-58Bi-0.7Zn electrode sample was 6.05% and 5.50% respectively, while the solder joint sample increased 21.51% and 29.27%.Cu/Sn-58Bi-xZn solder joint enhancement was mainly due to the addition of Zn to refine the Bi grain.The fracture surface is transferred from substrate and interfacial intermetallic compound to interfacial intermetallic compound and solder.The creep resistance of Sn-58Bi-0.7Zn rectangular solder is obviously higher than that of Sn-58Bi rectangular solder after reflux welding and liquid aging.In addition, during tensile test, the intermetallic compounds and Bi-rich interlayer connectivity at the anode interface strongly affect the ultimate tensile strength of Cu/Sn-58Bi-0.7Zn solder joints coupled with electromigration and thermal aging.The continuous growth of Bi-rich layer accelerates the formation of pores and cracks, and the further propagation of cracks in the interface will result in the decrease of tensile strength of solder joints.For solder joints which are aged only by solid state without loading current stress, the vacancy formed by Bi segregation at the Cu-Sn-Zn/Cu-Zn interface and the stress concentration will have a great influence on the ultimate tensile strength of solder joints.During the coupling stress, the current stress can lead to the nucleation of holes, so the ultimate tensile strength of the coupling solder joint is smaller than the ultimate tensile strength of the aging solder joint.For the coupled samples, the Bi-rich layer formed at the anode interface is found to be partially loaded by the finite element model, thus reducing the depth of indentation at the interface of the solder joint.Therefore, the creep resistance of coupled samples is higher than that of aging samples.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG42

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