摘  要Sn-Bi合金作为低温无铅钎料，在温度要求较低的封装中具有很大的优势，但是Bi本身脆性很大，对钎料的力学性能带来不利影响。本文主要研究添加合金元素Ag、Cu对Sn-Bi钎料合金力学性能的影响。文中从钎料合金的微观组织、力学性能及焊接接头的界面特性等几个方面来进行比较分析。86382

第一步，本文对钎料合金的室温组织进行观察，分析发现添加1%的Ag后，合金组织中的Sn相和Bi相均明显细化，并析出弥散分布的颗粒状金属间化合物Ag3Sn；而添加0。5%的Cu后，合金组织中的Bi相虽然细化，但不明显，并出现弥散分布的颗粒状金属间化合物Cu6Sn5。第二步，本文采用万能拉伸试验机对钎料合金在室温、100℃、125℃三个温度下的力学性能进行了测试和分析，实验结果表明添加1%的Ag后，钎料合金的强度和韧性明显增加，室温塑性上升、高温塑性降低，而对弹性模量影响不大。而添加0。5%的Cu后，钎料合金的强度明显增加，塑性和韧性都明显降低而对弹性模量影响不大。第三步，对焊接接头的界面特性进行观察，发现添加1%的Ag或0。5%的Cu后，界面形貌和金属间化合物的分布特点都没有改变，但接头界面处金属间化合物层的厚度明显增加。

综上所述，通过添加合金元素Ag、Cu有利于改善Sn-Bi钎料合金的微观组织和力学性能。

毕业论文关键字：无铅钎料；Sn-Bi合金；Ag；Cu；力学性能

Abstract When lower temperature is demanded in electronic packaging, Sn-Bi alloy, as a kind of low-melting lead free solder, has s great advantage。 But Bi itself is very brittle, which has a negative effect on mechanical properties of Sn-Bi alloy。 So in this paper, we mainly research on the effects of Ag and Cu addition on mechanical properties of Sn-Bi lead free solder。 The microstructure, mechanical properties of Sn-Bi solder and intermetallic reactions of joints are analyzed。

Firstly, the microstructure of Sn-Bi alloy is observed。 The results showed that the microstructure of Sn-Bi alloy is significantly refined and Ag3Sn particulates are deposited when 1% Ag is added。 The other hand, Bi is refined to some degree and Cu6Sn5 particulates are deposited as well when 0。5% Cu is added。 Secondly, we conducted stretching tests on Sn-Bi alloy at normal temperature, 100℃ and 125℃。 The results showed that 1% Ag addition has a great influence on Sn-Bi alloy’s mechanical properties----tensile strength, plasticity at normal temperature, toughness are significantly enhanced while plasticity at 100℃ is reduced, but little on modulus of elasticity。 And tensile strength is enhanced, while plasticity and toughness are reduced when 0。5% Cu is added, but modulus of elasticity is barely effected。 At the last, intermetallic reactions in Sn-Bi joints are observed。 The results show that Ag or Cu addition has little effect on the morphology of Cu/solder/Cu interface and the distribution of intermetallic compounds (IMC), but we observed significant growth of IMC layer。

In conclusion, we can refine the microstructure and improve mechanical properties of Sn-Bi alloy by Ag or Cu addition。

Keywords: lead free solder; Sn-Bi alloy; Ag; Cu; mechanical properties

目  录

第一章  绪论 1

1。1 钎料无铅化的发展 1

1。1。1 研究无铅钎料的现实意义 1

1。1。2 无铅钎料存在的问题 2

1。1。3 无铅钎料的研究现状及发展趋势 2

1。2 Sn-Bi无铅钎料合金的研究现状 3

1。2。1 Sn-Bi钎料的优势及用途