摘要
随着公众环保意识的增强，人们已经认识到含铅钎料对环境和人体健康的威胁，表面组装技术的开展，使得研制新型、实用的无铅软钎料以替代传统的Sn-Pb系钎料合金成为近年来研究的热点。本文便是基于这一出发点，研制在一定程度上能满足实用要求的无铅钎料。
对钎料的研制是按照从实用化的角度出发，兼顾成本和钎焊性能，运用合金化原则和数学设计方法(均匀设计)，基于现存的Sn-Zn二元钎料近共晶成分进行多元钎料合金设计和性能改善。并通过实验加以验证、逐步优化合金成分。实验中采用溶剂覆盖法制备钎料试样合金，并从理论上讨论了溶剂对熔融液态金属的覆盖、分离、精炼性能，指出了这些工艺性能与溶剂表面性能的关系，摸索并实践了制备无铅钎料的工艺。
论文从制备的钎料合金的润湿性能、超电势问题、钎料电阻、熔点和钎料断裂等方面，对钎料的性能进行分析，进而优化钎料的成分。钎料的钎焊性能在很大程度上决定于钎料的润湿性，文中采用铺展面积法来测定钎料的润湿性能，通过测定钎料润湿性能随温度变化的曲线来预测钎料实用化焊接的可行性工艺温度范围。研究中发现Sn-Zn系钎料在富氧环境中的钎焊性能劣于传统钎料，但是通过改善钎剂表面性能可以使钎料钎焊性能大幅度改善。研究中发现Bi的加入可很大程度地降低钎料的熔点，同时Bi还可以改善钎料的润湿性能，Bi质量百分含量在5％左右时，Sn-Zn-Bi系润湿性能较好。在酸性溶液中，阴极Sn-Zn系钎料的超电势比传统钎料超电势低，合金元素Bi的添加会适当提高钎料的超电势，Bi含量在＜5％(wt)时Sn-Zn-Bi系钎料的超电势随Bi含量增加而
四川人学硕上毕业论文
升高，同时随zn含量的增加，也会使超电势有一定程度升高。通过对钎料密
度的测定，粗算无铅钎料的使用成本，同时测定出无铅钎料的电阻率比传统钎
料低。通过对钎料接头断口形貌的初步研究，推测钎焊接头的主要断裂形式。
最后，通过对实验数据的分析，对实验的钎料合金成分进行了优化，提出
了具有良好实用前景的Sn一Zn基多元合金钎料，其合金成分范围为含Zn:4一
6.5%，Bi:1~3%，Ag:0.5一1.0%，或Cu:0.3%，余量为Sn。
In viewing of increasing environmental and health concerns of lead and lead containing solders, especially the recent development of surface mount technology(SMT), the lead-free alternatives need to be considered and become the focus of research. This scientific research and development project bases on this starting point, develops the novel lead-free solders, which can meet the requirements of practicability.
The development is aimed at the practicability, giving some consideration to the cost and solderability. With the method of uniform and experiment design, the solder component essential design is on the basis of binary eutectic and near-eutectic Sn-Zn solder alloy systems. The properties of the lead-free solders are predicted and improved by the means of alloying method and experiments, then the solder components get optimized. The sample solder alloys are prepared and refined by the flux to the molten metals on the covering, separation and purify are also discussed in the paper. It also points out the relationship between the flux processing properties and the flux surface properties.
The component design and optimization proceeds from the respects of wettability, overpotential, resistance, melting point, melting range and so on. It shows that the solderability is up to the wettability to a certain degree, and it also analyses the feasibility of applying the method of spreading area to the wettability. Besides, it explains the relationship between the wetting angle and the spreading area. The wettability of Sn-Pb solders is better than that of Sn-Zn family solder alloys, and
reduces surface tension solder to improve the wettability. The additive Bi can decreas the melting point of the solders, and improve the wettability, and it will get the best wettability when the weight percentage of Bi reaches to 5%. The over-potential of the Sn-Zn solders is much lower than the Sn-Pb solder alloys. The additive Bi will change the over-potential of the solders, near the weight percentage of 5%, the over-potential has maximum value. And value the cost of solders through the density.
From the analysis of experimental data, the Sn-(4~6.5)Zn- (1~3) Bi-(0.5~ 1.0)Ag/0.3Cu solder system has been proposed.
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