无铅软钎料的新进展

从环保角度出发,阐述了无铅钎料使用的必然性。介绍了国外无铅钎料的开发情况,尤其是近几年的进展。指出了现阶段研制的无铅钎料与市场要求的差距,提出相应对策。     

无铅钎料发展现状

无铅钎料是绿色电子产品的一个重要组成部分。本文综述了近年来国际上无铅钎料的发展动态，并为国内企业如何适应这一趋势提出了建议。     

Sn-Ag系电子无铅软钎料的超电势研究

随着微电子表面组装技术（SMT）的迅速发展和公众环境意识的增强，无铅软钎料成为近年来研究的焦点。主要研究了Sn-Ag系合金钎料的超电势电化学性能，并且与传统的Sn-Pb近共晶合金进行了对比。试验证明在酸、碱两种不同的溶液环境中，无铅软钎料在Sn-Pb合金的超电势有明显的差异。并指出含铋的钎料的超电势随着铋的含量的增加而降低，从而提出了在无铅软钎料研究中应当考虑因超电势变化而引起的问题。     

微电子组装中Sn-Zn系无铅钎料的研究与开发

无铅钎料的研究开发是我国电子材料行业目前面临的紧迫课题.其中Sn-Zn系无铅钎料具有低的熔点,优良的力学性能,能获得可靠的钎焊接头,且其原材料丰富、价格便宜,有望替代Sn-Pb钎料.但该系钎料易氧化,抗腐蚀性较差,目前还未得到广泛的采用.介绍了开发新型无铅钎料应满足的要求,及几种有潜力的Sn-Zn系无铅钎料.     

无铅钎料开发研究现状

综述了国内外无铅钎料开发的新进展和部分钎料的应用情况,重点介绍了合金元素对Sn-Zn和Sn-Ag两种合金系的性能影响。结合目前的研究成果,详细介绍了无铅钎料开发的现状及前景。     

绿色高性能无铅钎料的研究与发展

铅和铅的化合物破坏环境，有害人体健康，国际上无铅的呼声日益高涨，美国，欧洲、日本等发达国家纷纷立法，电子产品无铅化的安排已经提到议事日程，各大公司纷纷展开无铅钎料的研究，并相继试验推出无铅产品，电子组装无铅化是一个系统工程，需要各个环节和全社会的配合，中国在激烈的国际竞争中要赢得市场，必须拥有自主知识产权的无铅钎料及产品，这需要全社会特别是相关企业的重视和全力配合。     

锡基无铅钎料的性能研究与新进展

介绍了现阶段锡基无铅钎料的使用和生产情况,归纳了钎料合金的特点,综述了不同系列无铅钎料的熔化特性、焊后的剪切强度及可焊性等,总结了目前无铅钎料研究所取得的新成果、新进展以及存在的问题。从锡晶须,虚焊等方面指出了无铅钎料可靠性的不足,并提出部分解决方案,指出了无铅钎料的发展趋势和应用前景。     

Sn-Cu-Ni系无铅钎料的研究现状

综合分析了Sn-Cu-Ni系无铅钎料的国内外研究现状,概述了Sn-Cu-Ni系无铅钎料的润湿性、微观组织、界面反应、力学性能、焊点可靠性、物理性能等性能特点。从钎焊工艺、添加微量元素等方面阐述了Sn-Cu-Ni系钎料各项性能的影响因素,并对Sn-Cu-Ni系钎料的应用前景和研究方向进行了展望。     

表面封装用无铅软钎料的接头强度及熔点范围的研究

研究了Bi的添加量,对电子表面封装(SMT)用Sn-Ag近共晶无铅软钎料钎焊接头抗拉强度和熔点及熔点范围的影响。随着Bi含量的增加,钎焊接头抗拉强度也随着增加,同时钎料的液固相线温度均降低。当Bi的含量达到5%时,抗拉强度增加快;Bi的添加量大于5%时,抗拉强度上升缓慢。在Bi的含量增加时,熔点温度范围也逐渐变宽,使得凝固时间变长,这对于表面组装中的电子元件与器件的焊接是非常不利的。故在Sn-Ag近共晶无铅软钎料中Bi的添加量,应加以适当的控制。     

无铅钎料Sn-0.7Cu机械合金化研究

利用扫描电子显微镜和差热分析仪,研究了Sn-0.7Cu粉末的机械合金化过程;同时将机械合金化获得的粉末制成焊膏,进行铺展实验,并对金相组织进行了分析.研究结果表明,机械合金化是一种制备钎料粉体的方法;粉末的最终颗粒尺寸可通过合适的工艺参数来控制;用机械合金化获得的钎料粉体制成的焊膏,其铺展面积及润湿角方面与传统的熔炼法获得的钎料差别不大,铺展试样的金相组织由富Sn相、Cu6Sn5和少量Cu3Sn相组成.     

无铅可焊性镀层及其在电子工业中的应用

在电子工业中 ,为消除铅的污染 ,探讨了各种替代Sn-Pb合金的无铅可焊性镀层。论述了电镀Sn -Zn、Sn-Ag、Sn-Bi合金的方法及其镀层的可焊性能。     

Microstructure and Creep Deformation of Sn-Ag-Cu-Bi/Cu Solder Joints

Sn-Ag-Cu solder is one of the candidate alternatives to Sn-Pb-based solders. In order to improve its performance, different materials have been added to Sn-Ag-Cu-based solders. Several studies on Sn-Ag-Cu-based solders with Bi additions have shown Sn-Ag-Cu-Bi to be a class of solders with good wetting behavior and good performance that show great promise for use in the electronics assembly and packaging industry. To investigate the mechanical reliability of the Sn-Ag-Cu-Bi solders further, single-lap shear creep characteristics have been studied in this work. Dog-bone-type solder joint specimens were formed using five types of solder alloys, Sn-3.0Ag-0.5Cu and Sn-3.0 Ag-0.5Cu-xBi (x = 1 wt.% to 4 wt.%) with Cu substrates, and creep tests were performed at temperatures of 120°C and 150°C under stresses of 5 MPa to 10 MPa. Results indicate that the rupture times for Sn-3.0Ag-0.5Cu-xBi solder joints up to 4 wt.% of Bi are longer than the rupture time for Sn-3.0Ag-0.5Cu. Stress exponents ranged from 3 to 7 for temperatures of 150°C and 120°C with stresses under 10 MPa. Microstructural analyses using scanning electron microscopy (SEM) were performed and related to the creep behavior of the solder joints.     

Damage Produced in Solder Alloys during Thermal Cycling

The anisotropy of tin is associated with significant variations in its coefficient of thermal expansion and elastic modulus, with crystallographic direction. Under pure thermal cycling (with no externally applied stress or strain), substantial strains, in excess of 100%, may develop locally, and for very small structures, such as soldered interconnections comprising a few grains, structural integrity may be adversely affected. To examine this possibility, freestanding samples of tin, Sn-3.5wt.%Ag, Sn-0.5wt.%Cu, and Sn-3.8wt.%Ag-0.7wt.%Cu, have been subjected to thermal cycling. Temperature cycles from 30°C to 125°C or from −40°C to 55°C initially caused surface cracking, with openings up to several tens of microns after 3,000 cycles. Subsequently, the surface cracks grew into the interior of the specimens, with the maximum penetration ranging from a few microns after 100 cycles to more than 200 μm after 3,000 cycles. The cracks initiated from damage accumulated along grain boundaries. For the same temperature range, less damage resulted after the lower maximum (or mean) temperature cycle, and there appears to be a thermally activated component of cracking. The microstructure produced by rapid cooling (water quenching) was slightly more resistant than that formed by air, or furnace, cooling. Apart from microstructural coarsening, no damage accrues from isothermal exposure alone.     

Evaluation of Lead- Free Solder Joints in Electronic Assemblies

The feasibility of printed circuit board assembly with lead-free solder alloys was investigated. Studies were conducted with two baseline eutectic binary alloys, SnBi and SnAg, and three new lead-free solder formulations: (1) 91.8Sn-4.8Bi-3.4Ag (wt%) developed at Sandia Laboratories, (2) 77.2Sn-20In-2.8Ag developed at Indium Corp. of America, and (3) 96.2Sn-2.5Ag-0.8Cu-0.5Sb provided by AIM Inc. The basic physical properties (melting temperature, wetting, mechanical strength) pertinent to each of the newly developed alloys are described. The feasibility of 0.4 mm pitch assembly was established with each of the lead-free solder alloys investigated, although the processing windows were generally found to be narrower. All solder joints exhibited good fillets, in accordance with the workmanship standards. Wetting of the lead-free solders was significantly improved on immersion tin vs imidazole finished circuit boards. The laminates did not suffer thermal degradation effects, such as warpage, delamination, or severe discoloration (reflow was performed under an inert atmosphere). It is thus concluded that the manufacturability performance of the new solder formulations is adequate for surface mount applications.     

Tensile and Fatigue Behaviors of Aged Cu/Sn-4Ag Solder Joints

Tensile properties and stress-controlled fatigue fracture behaviors of Cu/Sn-4Ag solder joints aged at 180°C for different times were systematically investigated. It was found that the tensile strength of the solder joints decreased with increasing aging time and that the fracture mode changed from ductile to brittle. The fatigue life of the solder joints also decreased with increasing aging time. For most of the solder joints, fatigue cracks tended to initiate around the Cu/Cu₆Sn₅ interfaces due to the strain incompatibility and local strain concentration on a micro-scale, and they then propagated within the solder proximately along the Cu/Cu₆Sn₅ interfaces. The samples aged for␣different times or tested under different stress amplitudes had similar fractography morphologies, which consisted mainly of a propagation region, covered by solder, and a final fracture region. Based on the experimental observations above, the corresponding interfacial fatigue failure mechanisms were discussed in terms of different influencing factors.     

Effect of Strain Rate and Temperature on the Tensile Properties of Tin-Based Lead-Free Solder Alloys

The tensile properties of Sn-3Ag-0.5Cu, Sn-3.5Ag, and Sn-0.7Cu lead-free solders were investigated on small-scale specimens and compared with those of Sn-37Pb eutectic solder at various strain rates from 1 × 10⁻⁴ s⁻¹ to 1 × 10⁻² s⁻¹ and over a wide temperature range from 25°C to 150°C. The tests were under true strain-rate-controlled conditions. The ductility of each lead-free solder is relatively constant while that for Sn-Pb eutectic solder strongly depends on strain rate and temperature. The strain rate sensitivity index m for lead-free solders is relatively stable and showed little dependence on temperature, whereas the values of m for Sn-37Pb increased linearly with increasing temperature.     

氮气保护对无铅再流焊QFP焊点拉伸强度的影响

无铅钎料差的润湿性给传统电子组装工艺带来了巨大的挑战,氮气保护有利于改善无铅钎料的润湿性,提高焊点质量.主要研究了不同氧含量对QFP引脚焊点拉伸强度的影响,得到一个最佳的氧含量范围.     

无铅焊膏用松香型助焊剂活化点的研究

论述了无铅焊膏用松香型助焊剂活化点研究的重要性,探讨了活化点的物理意义及其影响因素.实验结果表明,无铅焊膏用松香型助焊剂的活化点就是松香树脂酸在有机溶剂中电离溶解平衡常数的升温曲线的拐点,松香种类对其活化点没有影响,决定其活化点的影响因素是松香本身的物理化学性质、溶剂以及有机酸的电离常数.     

微电子封装无铅钎焊的可靠性研究

本文阐述了微电子封装聚用无铅钎料的必要性。概述了无钎铅料的研究现状,最后着重分析讨论了微电子封装无铅钎焊的可靠性问题。