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摘要针对当前电子行业中普遍存在的无铅钎料焊点的可靠性问题，本论文以新型SnCuNi-xNd 无铅钎料为研究对象，分析了电子元器件在热循环试验条件的焊点可靠性问题，研究了不同的热循环次数对 SnCuNi-xNd焊点显微组织及力学性能的影响，并对焊点组织与性能之间的内在联系以及焊点在热循环试验条件下的失效原因及机制进行了初步探讨。 实验中使用的设备为 STR-1000 微焊点强度测试仪，使用该设备测试 SnCuNi-xNd 无铅钎料的焊点的力学性能。通过试验可知，向无铅钎料中添加 0.03-0.08%含量的稀土Nd元素时，力学性能有了较为明显的改善，其中最大拉伸力和剪切力分别可以提高约 4.8%和6.9%。分析了钎料基体以及焊点界面组织发现， Nd元素可对晶界迁移产生钉扎作用，阻碍晶界或相界迁移并细化晶粒，同时由于“协同作用”的影响，焊点强度有了较好的改善。但添加过量的Nd元素会因其过度氧化以及其所引起的应力场综合作用增大等原因导致自身活性作用降低。 钎料焊点的拉伸力会随着热循环试验的进行而减小。而进行了相同热循环次数时，添加了 Nd 元素 Sn0.7Cu0.05Ni 钎料焊点力学性能明显要优于未添加的钎料。在 800 次热循环之后，通过观察焊点断口形貌，我们发现 Ni 元素添加量为 0.05%时，焊点断口韧窝最细小，并存在明显的韧性断裂特征。因此我们推测焊点组织中细小均匀分布的 IMC 颗粒影响到了细小韧窝的。48081
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毕业论文关键词：无铅钎料，焊点强度，力学性能，热循环试验 Title The study on the effect of thermal cyclingon the Sn-Cu-Ni lead-free solder joint behavioral failure
Abstract This paper analyzes the joint reliability problems of electronic components in the thermal cycling test conditions and study the impact of the different number of thermal cycles on the microstructure and mechanical properties of SnCuNi-xNd solder according the lead-free solder join reliability problems in current electronics industry. The inter linkages between the organization and performance of the solder joints and the failure causes and mechanisms of the solder joints in thermal cycling test conditions were discussed. Through the STR-1000 micro joint strength test，the tensile and shear strength and other mechanical performances of the solder joint of SnCuNi-xNd were determined accurately. We can see that the mechanical properties of solder joint was improved badly when the suitable amount of Nd addition was 0.04-0.07%, among which the maximum tensile and shear force was enhanced in a degree of 6.0% to 7.7%. By the analysis of the matrix and the solder joint interface of solder joint, showing that Nd on grain boundary migration Producing the pinning effect, impeding the migration of grain boundary or phase boundary to grain refinement. The Nd controls the conduct of the interfacial reaction and the thickness of the interfacial compound layer effectively by the “synergy effect” of Ni. But excessive Nd could bring about more stress fields in the crystal lattice due to the polarization between different atoms, which retarded the diffusion of the atoms and reduced the activity of it. Under the different number of thermal cycles, the tensile strength of the brazing solder is gradually reduced, but in the same condition, the solder joint achieved good mechanical Properties when the addition of Nd was 0.03-0.08%. Further study of the fracture morphology of solder joint after 600 thermal cycles found that the SnCuNi-0.05Nd solder dimples was most small, showing that the more obvious characteristics of ductile fracture, suggesting a small dimple formation of the solder joint organization closely related to the fine and uniform distribution of IMC particles. Moreover, the SnCuNi-0.05Nd’s fracture surface occurred in the solder matrix while the one of SnCuNi and SnCuNi-0.15Nd were around the solder interface layer.
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