【作者】 邹长东；

【导师】 翟启杰； 高玉来；

【作者基本信息】 上海大学 ， 钢铁冶金， 2010， 博士

【摘要】 随着对铅(Pb)及含铅合金毒性认识的加深,许多国家和地区都禁止或限制铅在电子产品中的应用,取而代之的是无铅焊料。目前已经开发出来的无铅焊料主要以Sn基无铅焊料为主,但其熔化温度远高于传统的Sn-Pb共晶合金,导致无铅焊料在应用过程中存在诸多问题。因此,如何降低Sn基无铅焊料合金的熔化温度成为电子工业界关注的焦点。本文围绕无铅焊料熔化温度过高的问题,开展了应用纳米尺寸效应降低Sn基无铅焊料合金熔化温度的研究,以期解决目前无铅焊料熔化温度过高带来的封装缺陷。围绕此主题,本文研究了具有不同尺寸大小和分布的Sn基无铅焊料合金纳米粒子的制备,并对Sn基无铅焊料合金纳米粒子熔化温度的尺寸效应进行了研究。在此基础上,进一步研究如何获得尺寸更小、分布范围更窄的Sn3.0Ag0.5Cu无铅焊料合金纳米粒子,以获得熔化温度大幅度降低的Sn基无铅焊料合金。最后对Sn基无铅焊料合金纳米粒子的凝固过程进行研究,为Sn基无铅焊料合金纳米粒子的实际应用提供借鉴。论文主要内容归纳如下:1)研究了不同尺寸Sn基无铅焊料合金纳米粒子的合成,尤其是表面剂浓度对纯Sn、Sn3.5Ag(wt.%)和Sn3.0Ag0.5Cu(wt.%)纳米粒子尺寸大小及分布的影响。结果表明,纳米粒子的尺寸大小及分布范围随着表面剂浓度的增加而减小,从表面剂与纳米粒子的络合作用阐述了表面剂的作用;研究了还原剂加入速率对Sn3.5Ag纳米粒子的尺寸大小和分布的影响,从一次粒子和二次粒子的竞争生长角度阐述了还原剂加入速率对尺寸大小和分布的影响;研究了反应物浓度对Sn3.0Ag0.5Cu纳米粒子的尺寸大小及分布的影响,从液相中晶核的形核及晶核的碰撞角度阐述了反应物浓度的影响作用;最后研究了Sn3.5Ag和Sn3.0Ag0.5Cu纳米粒子的形成过程,结果表明纳米粒子中首先形成金属间化合物相,而β-Sn相则是缓慢形成的。2)揭示了Sn基无铅焊料合金纳米粒子熔化温度的变化规律。研究结果表明,随着尺寸的减小,纯Sn纳米粒子的熔化温度和熔化潜热均随之降低,表现出明显的尺寸依赖性。Sn3.5Ag纳米粒子的熔化温度也表现出明显的尺寸效应,熔化温度随着尺寸的减小而降低。平均尺寸约为30nm的Sn3.5Ag纳米粒子的熔化温度为210℃,显著低于Sn3.5Ag大块合金的熔化温度。Sn3.0Ag0.5Cu纳米粒子的熔化温度随尺寸的变化规律与前二者类似,纳米粒子的熔化温度随着尺寸的减小而显著降低。平均尺寸为30nm左右的Sn3.0Ag0.5Cu纳米粒子的熔化温度为201℃,比母合金熔化温度低了16℃,显著降低了Sn3.0Ag0.5Cu无铅焊料合金的熔化温度。理论分析结果表明,当Sn3.0Ag0.5Cu纳米粒子的尺寸小于10nm时,其熔化温度与SnPb共晶合金的熔化温度相当。3)成功实现了大幅度降低Sn3.0Ag0.5Cu无铅焊料合金熔化温度的研究目的。研究了尺寸更小、分布范围更窄的Sn3.0Ag0.5Cu纳米粒子的制备及表征,并对其熔化温度进行研究,获得了熔化温度大幅度降低的Sn3.0Ag0.5Cu无铅焊料合金。20A电流下、液体石蜡保护介质下制备的Sn3.0Ag0.5Cu无铅焊料合金纳米粒子的熔化温度可以降低到190℃左右;50A电流下、液体石蜡保护介质下制备的Sn3.0Ag0.5Cu无铅焊料合金纳米粒子的熔化温度降到了180℃左右,与Sn-Pb共晶合金的熔化温度相当。因此,自耗电极直流电弧法为大幅度降低Sn基无铅焊料合金的熔化温度奠定了技术基础。4)研究了Sn基无铅焊料合金纳米粒子凝固过冷度的变化规律。采用DSC方法研究了Sn基无铅焊料合金纳米粒子的凝固过冷度,研究结果表明,Sn3.5Ag纳米粒子和Sn3.0Ag0.5Cu纳米粒子的凝固过冷度均随着冷却速率的增加而增大;同时,过冷度随着纳米粒子尺寸的减小而增大。对比研究发现,在相同的冷却速率下,Sn3.0Ag0.5Cu纳米粒子的凝固过冷度远大于微米粒子及母合金的过冷度。过冷度的提高会带来焊点凝固组织的细化,从而提高焊点的力学性能。更多还原

【Abstract】 Due to the toxicity of lead (Pb), Pb-containing solder alloys are being phased out from the electronic industry, which has promoted the development and implementation of lead-free solders. These lead-free solder alloys possess, however, some weaknesses, mainly root in their higher melting temperature compared to the Sn-Pb eutectic solders. To solve this issue, researchers have tried to decrease the melting temperatures of the lead-free solders. A feasible approach to decrease the melting temperatures of a solder alloys is to decrease the particle size of the solder alloys down to the nanometer range.In this dissertation, we focus on the research to decrease the melting temperature of the lead-free solder alloy by decreasing their particle size down to nanometer range. The Sn-based lead free solder alloy nanoparticles with different sizes and size distribution were synthesized by chemical reduction method. The size-dependent melting temperature of these synthesized nanoparticles was studied by differential scanning calorimetry (DSC) and theoretical calculation. Based on these researches, the approach to prepare smaller nanoparticles of Sn3.0Ag0.5Cu lead-free solder alloy was studied, and nanoparticles of Sn3.0Ag0.5Cu lead-free solder alloy with equivalent melting temperature to SnPb solder alloy was obtained. Moreover, the undercooling of the Sn-based lead solder alloy nanopaticles was studied by DSC at different cooling rates. The major contents of this dissertation are epitomized as follows:1. Synthesis of Sn-based lead free solder alloy nanoparicles with different particle sizes and size distribution. The effect of surfactant on the nanoparticles size and size distribution was studied. It was found that the larger ratio of the weight of the surfactant to the precursor resulted in smaller particle size. Due to the capping effect caused by the surfactant molecules coordinating with the nanoclusters, a larger amount of surfactant would restrict the growth of the nanoparticles. Meanwhile, the effect of the reduction adding rate on the particle size and size distribution of Sn3.5Ag nanoparticles was studied. The results showed that the particle size increased and then decreased as decreasing the reduction adding rate, which can be explained by the competitive growth of the primary particles and second particles. The effect of the precursor concentration on the particle size and size distribution of Sn3.0Ag0.5Cu nanoparticles was also studied. The results showed that the particle size of Sn3.0Ag0.5Cu nanoparticles increased as increasing the precursor concentration. Finally, the formation of Sn3.5Ag and Sn3.0Ag0.5Cu nanoparticles was correspoindingly analyzed.2. The size-dependent melting temperature of Sn-based lead free solder alloy. The melting temperatures of Sn nanoparticles showed strong size-dependent tendency. The size-dependent melting properties of tin nanoparticles were comparatively analyzed by employing different size-dependent theoretical melting models and the differences among these models were discussed. The Sn3.5Ag and Sn3.0Ag0.5Cu nanoparticles also showed size-dependent melting temperature tendency. The melting temperature of Sn3.5Ag nanoparticles with average particle size of 30nm was about 210℃, 11℃lower than that of the bulk alloy. The melting temperature of Sn3.0Ag0.5Cu nanoparticles with average particle size of 30nm was 201℃, much lower than that of the bulk alloy. Theoretical analysis showed that the melting temperature can be as low as that of eutectic Sn-Pb solder alloy when the particle size was decreased to 10nm.3. The research on the Sn3.0Ag0.5Cu nanoparticles with large melting temperature depression. The Sn3.0Ag0.5Cu nanoparticles with smaller particles size and narrower size distribution were prepared by the self-developed consumable electrode direct current arc (CDCA) technique. The prepared nanoparticles were characterized by various methods such as X-ray diffraction (XRD), field emission scanning electronic microscope (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). The melting temperatures of the Sn3.0Ag0.5Cu nanoparticles were measured by DSC, and the results showed that the calorimetric melting onset temperature of the nanoparticles of SnAgCu solder alloy could be as low as 180℃, which was equivalent to that of the traditionally used SnPb eutectic alloy (183℃). The CDCA technique showed promising prospect in manufacturing large amount of nanoparticles with controlled shape, small size, narrow particle size distribution and nearly oxide-free composition. This undoubtedly puts forward a novel feasible approach to manufacture high quality lead-free solders for electronic packaging.4. The research on the undercooling of the Sn-based lead-free solder alloy. The solidification properties of the Sn3.5Ag and Sn3.0Ag0.5Cu nanoparticles were studied by DSC at different cooling rates. The undercooling of these nanoparticles showed strong cooling rate dependent tendency. The undercooling of the Sn3.5Ag and Sn3.0Ag0.5Cu nanoparticles was in the range of 85.0~91.0℃and 82.0~88.5℃, respectively. In addition, the undercooling of Sn3.0Ag0.5Cu nanoparticles was much larger than that of the Sn3.0Ag0.5Cu micro-sized particles, hopefully producing better mechanical properties of the solder joints.更多还原