新型纳米结构颗粒增强无铅复合钎料性能

为了解决传统复合钎料制备中强化颗粒容易粗化的问题,提高无铅复合钎料的性能,选用共晶Sn-3.5Ag、Sn-3.0Ag-0.5Cu钎料作为基体,3种不同类型具有纳米结构的有机-无机笼型硅氧烷齐聚物(POSS) 颗粒作为增强相而制成复合钎料。研究了复合钎料的铺展性能、钎焊接头的力学性能和抗蠕变性能。结果表明,复合钎料的润湿性能均优于基体钎料的润湿性能,复合钎料钎焊接头的剪切强度和蠕变断裂寿命均明显提高。在相同条件下,Sn-Ag-Cu基复合钎料钎焊接头的性能优于Sn-Ag基复合钎料钎焊接头。      

等温时效对新型Sn-Ag基复合钎料显微组织和力学性能的影响

研究了等温时效对Sn-3.5Ag共晶钎料及其复合钎料的力学性能和显微组织变化的影响。为了弥补传统复合钎料制备和服役中强化颗粒容易粗化的问题, 制备了不同种类最佳配比的具有纳米结构的有机无机笼型硅氧烷齐聚物(POSS)颗粒增强的Sn-Ag基复合钎料。对钎焊接头在不同温度（125、150、175℃）下进行时效,通过SEM和EDAX分析了钎料与基板间金属间化合物层(IMC)的生长情况。结果表明, 经过不同温度时效,复合钎料钎焊接头界面处金属间化合物的生长速率比Sn3.5Ag共晶钎料慢, 复合钎料的IMC生长的激活能分别为80、97和77kJ/mol,均高于Sn3.5Ag共晶钎料。经过150℃时效1000h后,复合钎料钎焊接头的剪切强度分别下降了22%、13%和18%,下降幅度相当或明显小于Sn-3.5Ag钎料钎焊接头。      

纳米结构强化的新型Sn-Ag基无铅复合钎料

通过外加法向Sn-3.5Ag钎料中加入质量分数为1%,2%和3%的纳米级多面齐聚倍半硅氧烷(polyhedral oligomeric silsesquioxanes,POSS)颗粒制备无铅复合钎料.系统研究POSS颗粒的显微组织,钎料的熔化特性、润湿性能和力学性能.结果表明:POSS颗粒的加入并没有改变Sn-Ag基复合钎料熔化温度.复合钎料的铺展面积均有所增加,润湿角有所下降,表现了良好的润湿性.POSS颗粒的加入显著提高钎料钎焊接头的剪切强度.     

Ag颗粒含量对SnCu基复合钎料性能的影响

利用颗粒增强原理研制了新型Ag颗粒增强SnCu基复合钎料,研究了Ag颗粒不同含量对复合钎料性能影响.结果表明:当Ag含量(体积分数)为5%时,复合钎料铺展面积最大,润湿角最小,钎焊接头蠕变寿命最长,比基体钎料提高23倍.     

硅氧烷齐聚物颗粒增强Sn-Ag基复合钎料的熔化特性

具有纳米结构的有机-无机笼型硅氧烷齐聚物（POSS）作为强化相的POSS/Sn-3.5Ag复合钎料可有效地改善基体钎料钎焊接头的力学可靠性。在前期试验的基础上,采用差热分析试验的方法分析了POSS 质量分数为3%的POSS/Sn-Ag复合钎料中POSS颗粒的熔化特性。结果表明,3% POSS/Sn-Ag复合钎料的熔化温度与Sn-3.5Ag共晶钎料相近,POSS颗粒的加入对其熔化温度影响不大,说明复合钎料在熔化特性上可以满足工艺性能的要求。此外,差热分析计算表明,3% POSS/Sn-Ag复合钎料在冷却过程中具有更高的表观活化能值,说明POSS强化相可能主要存在于Sn晶粒的晶界处。     

Ag颗粒增强复合钎料钎焊接头蠕变断裂及强化机理研究

测定了不同应力和温度下Ag颗粒增强复合钎料及基体钎料63Sn37Pb钎焊接头蠕变寿命,分析了Ag颗粒增强复合钎料及基体钎料钎焊接头蠕变断裂机理.表明:Ag颗粒增强复合钎料钎焊接头蠕变寿命优于基体钎料;Ag颗粒表面Ag-Sn金属间化合物形成及Ag颗粒对富Pb层阻碍作用是复合钎料钎焊接头蠕变性能提高的主要因素;钎焊接头Cu基板上一薄层富Pb相区形成是蠕变裂纹主要原因.     

应力对Ag颗粒增强SnCu基复合钎料蠕变性能的影响

使用搭接面积为1mm2的单搭接钎焊接头,研究了恒定温度下应力对Ag颗粒增强SnCu基复合钎料钎焊接头蠕变寿命的影响,结果表明:Ag颗粒增强SnCu基复合钎料的蠕变抗力优于99.3Sn0.7Cu基体钎料;随着应力的增大,复合钎料及其基体钎料钎焊接头的蠕变寿命均呈下降趋势,且应力对复合钎料钎焊接头蠕变寿命的影响比基体钎料明显.     

温度对Cu颗粒增强复合钎料蠕变性能的影响

蠕变性能是影响钎焊接头可靠性的重要指标之一.采用搭接面积为1 mm2的单搭接钎焊接头,在恒定载荷下,测定了Cu颗粒增强锡铅基复合钎料钎焊接头的蠕变寿命,分析并讨论了温度对该复合钎料蠕变寿命的影响.结果表明:Cu颗粒增强的锡铅基复合钎料的蠕变抗力优于传统63Sn37Pb共晶钎料;钎焊接头蠕变寿命随温度的升高而降低,并且温度对复合钎料钎焊接头蠕变寿命的影响较传统63Sn37Pb钎料明显.     

液态Sn-Ag-Cu钎料润湿性能的优化

采用钎料改性工艺制备了Sn-3.5Ag0.6Cu合金,用润湿平衡法测试了液态Sn-3.5Ag0.6Cu钎料在铜基体表面的润湿性,研究了钎料制备工艺、钎剂卤素含量、浸渍温度和时间等因素对润湿性能的影响.结果表明:采用改性工艺可增强钎料的润湿性能,当钎剂卤素含量为0.4wt%、在270℃下浸渍2～3s时,液态Sn-3.5Ag0.6Cu钎料对铜表面的润湿性可以达到最佳状态.指出降低钎料的熔点和液态表面张力是提高润湿性的关键.     

关于液态Sn—Ag—Cu钎料润湿性能的实验研究

采用钎料改性工艺制备了Sn-3．5Ag0．6Cu合金，用润湿平衡法测试了液态Sn-3．5Ag0．6Cu钎料在铜基体表面的润湿性，研究了钎料制备工艺、钎剂卤素含量、浸渍温度和时间等因素对润湿性能的影响。结果表明：采用改性工艺可增强钎料的润湿性能，当钎剂卤素含量为0．4％（质量分数）、在270℃下浸渍2～3s时，液态Sn-3．5Ag0．6Cu钎料对铜表面的润湿性可以达到最佳状态。指出降低钎料的熔点和液态表面张力是提高润湿性的关键。     

Investigation of microstructures and tensile properties of a Sn-Cu lead-free solder alloy

In recent years, the pollution of environment from lead (Pb) and Pb-containing compounds in microelectronic devices attracts more and more attentions in academia and industry, the lead-free solder alloys begin to replace the lead-based solders in packaging process of some devices and components. In this work, microstructures and mechanical properties of the lead-free solder alloy Sn99.3Cu0.7(Ni) are investigated. This paper will compare the mechanical properties of the lead-based with lead-free solder alloys (Sn99.3Cu0.7(Ni) and 63Sn37Pb). The tensile tests of lead-based and lead-free solder alloys (Sn99.3Cu0.7(Ni) and Sn63Pb37) were conducted at room and elevated temperature at constant strain rate; the relevant tensile properties of Sn99.3Cu0.7(Ni) and Sn63Pb37 were obtained. Specifically, the tensile strength of this lead-free solder- Sn99.3Cu0.7(Ni) in 25^∘C, 50^∘C, 75^∘C, 100^∘C, 125^∘C was investigated; and it was found that tensile strength of the lead-free solder decreased with the increasing test temperature at constant strain rate, showing strong temperature dependence. The lead-free solder alloy Sn99.3Cu0.7(Ni) was found to have favorable mechanical properties and it may be able to replace the lead-based solder alloy such as Sn63Pb37 in the packaging processes in microelectronic industry.     

Composite lead-free electronic solders

Composite approaches have been developed in lead-free solder research in an effort to improve the service temperature capabilities and thermal stability of the solder joints. This article overviews the background for composite lead-free solder development, the roles of reinforcements and their requirements, composite solder processing techniques, as well as current status of composite solder research. Examples of several representative lead-free composite solders produced with various methods and reinforcement types are presented. The effects of reinforcement addition on processing and mechanical properties are analyzed. Difficulties and problems that exist in composite solder research are proposed and tentative solutions are attempted with examples of newly emerging novel lead-free composite solders.     

Development of a microwave sintered TiO2 reinforced Sn–0.7wt%Cu–0.05wt%Ni alloy

The use of reinforcing nano-size ceramic particulates is a promising method to improve the mechanical and thermal properties of lead-free solder materials. In addition, advanced fabrication processes routes such as microwave sintering powder metallurgy (PM) enhance properties in the fabrication of composite solders. To elucidate the mechanisms underlying the improvements in mechanical and thermal properties, Sn–Cu–Ni with TiO₂ nano-composite additions, fabricated via a microwave sintering PM method, were investigated using state-of-the-art characterization techniques. Synchrotron micro-X-ray fluorescence (XRF) results detected trace Ti in the solder matrix. This was consistent with X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) results which indicated that nano crystals were within the Sn matrix. It is possible these nano crystal form due to the migration of Ti during the rapid high energy microwave heating. A hypothesis of improved thermal and mechanical properties of nano-composite solders is discussed based on the results and the microwave sintering PM route was discussed as a promising method for next generation lead-free solder processing.     

Sn-Cu系无铅钎料微合金化研究进展

电子产品绿色化的需求促进了电子组装中钎料合金的无铅化发展。目前,Sn-Cu系钎料以优良的综合性能和较低的成本成为最具使用前景的无铅钎料之一。但是Sn-Cu系钎料的熔点较高,在Cu基上的铺展性和钎焊性也较Sn-Pb钎料差,这在很大程度上限制了其应用。通过添加多种合金元素可改善Sn-Cu合金的微观组织和焊接性能。本文首先系统地综述了合金元素对Sn-Cu系无铅钎料微观组织、润湿性、力学性能等的影响,然后指出Sn-Cu系无铅钎料存在的问题。最后,对Sn-Cu系无铅钎料的发展方向和前景进行了展望。     

Critical studies to improve service reliability of Sn–Ag–Cu solder joints by thermal treatments

Lead-free electronic packages intended for use in applications such as aerospace, military, and other highly demanding service conditions, necessitate exceptional mechanical reliability of lead-free electronic solder joints under realistic service conditions. Most current design strategies employed for improving the reliability of lead-free electronic solder joints are aimed at developing suitable alloying additions and reinforcements to the solder itself. At present there exists no suitable methodology to minimize the effects of service conditions while the solder joint is in service. Since thermomechanical fatigue reliability of electronic solder joints is closely related to the crack nucleation that occurs during very early stages of repeated thermal excursions, this study is based on subjecting solder joints to a limited number of thermal shock (TS) cycles in a chosen temperature regime to nucleate cracks, then evaluating their effectiveness in improving reliability when the solder joints are subjected to additional TS cycles in a different temperature regime. This study is a preliminary investigation, aimed at developing suitable methodology to minimize the effects of damage to lead-free solder joint specimens subjected to repeated thermal excursions during service, by imposing appropriate thermal treatments. These thermal treatments can be automatically implemented at programmed intervals during the service life of the electronic packages. Methods employed in these studies may also be useful to enhance long-term service reliability and to obtain a conservative estimate of long-term service reliability.     

Effects of Nano-TiO2 additions on thermal analysis, microstructure and tensile properties of Sn3.5Ag0.25Cu solder

For development of a lead-free composite solder for advance electrical components, a series of Sn3.5Ag0.25Cu (SAC) solders containing TiO₂ nanopowders have been studied. The results showed that the addition of 0.25–1 wt.% TiO₂ nanopowders into the lead-free SAC solder caused its liquidus temperature to increase by about 3.5–5.9 °C. Metallographic observations of the lead-free SAC composite solders revealed a reduction in the grain size of β-Sn, Ag₃Sn phase and Ag₃Sn phase located between the spacing lamellae. In terms of mechanical behavior, the addition of larger weight fractions of TiO₂ nanopowders in lead-free SAC solder matrix led to an improvement in microhardness, 0.2%YS and UTS. However, ductility of the lead-free SAC composite solders was observed to decrease.     

Influence of nanoparticle addition on the formation and growth of intermetallic compounds (IMCs) in Cu/Sn–Ag–Cu/Cu solder joint during different thermal conditions

Abstract

Nanocomposite lead-free solders are gaining prominence as replacements for conventional lead-free solders such as Sn–Ag–Cu solder in the electronic packaging industry. They are fabricated by adding nanoparticles such as metallic and ceramic particles into conventional lead-free solder. It is reported that the addition of such nanoparticles could strengthen the solder matrix, refine the intermetallic compounds (IMCs) formed and suppress the growth of IMCs when the joint is subjected to different thermal conditions such as thermal aging and thermal cycling. In this paper, we first review the fundamental studies on the formation and growth of IMCs in lead-free solder joints. Subsequently, we discuss the effect of the addition of nanoparticles on IMC formation and their growth under several thermal conditions. Finally, an outlook on the future growth of research in the fabrication of nanocomposite solder is provided.     

Thermal property,wettability and interfacial characterization of novel Sn–Zn–Bi–In alloys as low-temperature lead-free solders

The effect of indium (In) addition on thermal property, microstructure, wettability and interfacial reactions of Sn–8Zn–3Bi lead-free solder alloys has been investigated. Results showed that addition of In could lower both solidus and liquidus temperatures of the solder alloys with wettabilty significantly improved. The spreading area of Sn–8Zn–3Bi–1.0In was increased by 34% compared to that of Sn–8Zn–3Bi. With the increase of In content, Zn-rich precipitates were smaller in size and distributed more uniformly, which might be beneficial for mechanical properties and corrosion resistance of the solders. The intermetallic compounds (IMCs) formed between Sn–8Zn–3Bi–xIn solder/Cu substrate was identified as Cu–Zn with a scallop layer adjacent to the solder and a flat layer to the substrate. The addition of In slightly influenced the thickness of the IMCs. The newly developed Sn–Zn–Bi–In solder system has great potential to replace the Sn–Pb solders as low-temperature lead-free solders.     

The ‘IMC rings’ growth mechanism in Sn–Ag–Cu solder ball and NiAu-plated BGA ball pad

Due to environmental pollution concerns, the law says the lead (Pb) inside electronics devices must be eliminated. Lots of lead-free materials have been introduced and been used for electronic products and Sn–Ag–Cu (SAC) is one of most popular lead-free representatives and has been used in high-volume production. The most popular IC packages, BGA packages which have higher I/O counts, and better thermal and electrical performance than lead-frame type packages, use solder balls of SAC for lead-free applications to connect with printed circuit boards. A particular phenomenon, so-called ‘IMC rings’, is only observed on BGA solder ball pad surfaces after the SAC solder balls are mounted on BGA ball pads which are plated with NiAu. It has not been found in either eutectic solder or Sn–Ag solder welding on plated NiAu pads. No significant evidence exists to show that ‘IMC rings’ degrade the strength of solder joints or cause earlier failures in mechanical tests. ‘IMC rings’ appear to be an inevitable outcome after the SAC is soldered onto a plated NiAu ball pad. This study is to find the growth mechanism of ‘IMC rings’ on the ball pad which is created between SAC ball and plated NiAu pad during solder ball temperature reflow. The design of the experiment and data have been discussed.