无铅再流焊冷却速率研究应用现状

阐述了冷却速率对无铅再流焊质量影响的研究现状,总结了冷速对无铅钎料以及SMT焊点可靠性的影响。研究现状表明快速冷却有助于减少焊接缺陷,提高焊点可靠性。     

冷却速率对无铅钎料和焊点质量影响

阐述了再流焊冷却速率对无铅钎料和焊点质量的影响的研究现状.已有的研究结果表明:冷却速率对于无铅钎料的微观组织、拉伸性能、金属间化合物的形态和尺寸以及焊点中的凝固缺陷等都有显著的影响.选择合适的冷却速率可以提高焊点质量.     

冷却速率对无铅再流焊焊点质量的影响（待续）

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分...     

冷却速率对无铅再流焊焊点质量的影响

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。本文通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3～6℃／s。     

冷却速率对无铅再流焊焊点质量的影响（续完）

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3℃/s～6℃/s。     

冷却速率对无铅再流焊焊点质量的影响(待续)

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3℃/s～6℃/s。     

无铅焊点的可靠性问题

焊点的质量与可靠性很大程度决定了电子产品的质量。随着环境保护意识的增强,无铅焊料、无铅焊点成为了近年来的研究热点问题。无铅焊点由于焊料的差异和焊接工艺参数的调整,必不可少地会给焊点可靠性带来新的影响。本文从设计、材料及工艺角度分析了影响无铅焊点可靠性的因素,对无铅焊点可靠性测试方法做了介绍。     

无铅焊点的可靠性问题

焊点的质量与可靠性很大程度决定了电子产品的质量。随着环境保护意识的增强，无铅焊料、无铅焊点成为了近年来的研究热点问题。无铅焊点由于焊料的差异和焊接工艺参数的调整，必不可少的会给焊点可靠性带来新的影响。本文从设计、材料、及工艺角度分析了影响无铅焊点可靠性的因素，对无铅焊点可靠性测试方法做了介绍。     

有限元数值模拟在BGA/QFP/CCGA器件焊点可靠性研究中的应用

有限元数值模拟方法因其可以有效研究IC封装中无铅焊点的可靠性,被国内外专家学者所青睐,使得无铅焊点可靠性数值模拟成为IC封装领域的重要研究课题。综述了有限元法在球珊阵列封装(BGA)、方型扁平式封装(QFP)、陶瓷柱栅阵列封装(CCGA)3种电子器件无铅焊点可靠性方面的研究成果。浅析该领域国内外的研究现状,探究有限元方法在无铅焊点可靠性研究方面的不足及解决办法,展望无铅焊点可靠性有限元模拟的未来发展趋势,为IC封装领域无铅焊点可靠性的研究提供理论支撑。     

无铅焊点的可靠性研究

焊点的质量和可靠性很大程度上决定了电子产品的质量.随着环境保护意识的增强,无铅焊料、无铅焊点成为了近年来的研究热点.无铅焊点由于焊料的差异和焊接工艺参数的调整,其可靠性势必会受到新的影响.从设计、材料和工艺角度分析了影响无铅焊点的可靠性的因素,最后分析了焊点的常见的可靠性问题产生的原因,并给出了相应的解决办法.     

The effect of soldering process variables on the microstructure and mechanical properties of eutectic Sn-Ag/Cu solder joints

Fundamental understanding of the relationship among process, microstructure, and mechanical properties is essential to solder alloy design, soldering process development, and joint reliability prediction and optimization. This research focused on the process-structure-property relationship in eutectic Sn-Ag/Cu solder joints. As a Pb-free alternative, eutectic Sn-Ag solder offers enhanced mechanical properties, good wettability on Cu and Cu alloys, and the potential for a broader range of application compared to eutectic Sn-Pb solder. The relationship between soldering process parameters (soldering temperature, reflow time, and cooling rate) and joint microstructure was studied systemati-cally. Microhardness, tensile shear strength, and shear creep strength were measured and the relationship between the joint microstructures and mechani-cal properties was determined. Based on these results, low soldering tempera-tures, fast cooling rates, and short reflow times are suggested for producing joints with the best shear strength, ductility, and creep resistance.     

Characterization of small-sized eutectic Sn-Bi solder bumps fabricated using electroplating

We studied the effects of the cooling rate during the reflow process on the microstructure of eutectic Sn-Bi solder bumps of various sizes fabricated by electroplating. To fabricate eutectic Sn-Bi solder bumps of less than 50 μm in diameter, Sn-Bi alloys were electroplated on Cu pads and reflowed at various cooling rates using the rapid thermal annealing system. The interior microstructure of electroplated bumps showed a fine mixture of Sn-rich phases and Bi-rich phases regardless of the cooling rate. Such an interior microstructure of electroplated bumps was quite different from the reported microstructure of vacuum-evaporated bumps. Ball shear tests were performed to study the effects of the cooling rate on the shear strength of the solder bumps and showed that the shear strength of the bumps increased with increasing cooling rate probably due to the reduced grain size. Soft fractures inside the solder bump were observed during the ball shear test regardless of the cooling rate.     

Impact of board and component metallizations on microstructure and reliability of lead-free solder joints

Aging and accelerated thermal cycling (ATC) have been performed on 2512 chip resistors assembled with Sn3.8Ag0.7Cu (wt.%) solder. The boards were finished with immersion Ag (IAg), electroless nickel/immersion gold (ENIG), and hot air solder leveling Sn–Pb eutectic solder (HASL), and the components’ terminations were finished with 100% Sn and Sn8.0Pb (wt.%). The boards were reflowed with an average cooling rate of 1.6 °C/s. It was found that the microstructure and reliability of the solder joints depended on the board surface finish. The boards containing small amounts of Pb (from board/component terminations) were the most reliable. Solder joints to copper showed a significantly higher number of cycles to first failure than the joints on nickel. Better reliability of the Sn3.8Ag0.7Cu/Cu joints was attributed to an increased copper content in the bulk due to substrate dissolution.     

Aging studies of PBGA solder joints reflowed at different conveyorspeeds

In this paper, the shear cycle fatigue properties of plastic ball grid array (PBGA) assemblies' solder joints reflowed with three different profiles, and aged at 125°C for four, nine, 16, 25, and 36 days are studied. The profiles were devised to have the same "heating factor," which was defined as the integral of the measured temperature above the liquidus (183°C) with respect to dwell time in the reflow profile, but to have different conveyor speeds. The effects of conveyor speed on the solder joint (nonaged and aged) fatigue lifetimes were investigated. It was found hat with increasing the conveyor speed the solder joint shear fatigue lifetime could be improved substantially. Also, the shear fatigue lifetimes of aged solder joints decreased with increasing aging time and variation in fatigue lifetimes increased for faster conveyor speed. SEM and optical micrographs show that faster cooling rate caused a rougher interface of solder/IMC and less crystallization microstructure in solder joints. Rougher interface solder joints have a longer nonaged fatigue life. The thickness of IMC increases with increasing aging time and the growth rate for solder with faster cooling rate was larger. SEM cross section views reveal that cracks initiated at the acute position near the solder pad, then propagated along the interface of the bulk solder/IMC layer. Thicker IMC layers deteriorated fatigue life, so the fatigue lifetime variation of aged solder joints with fast cooling rate was larger     

Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements

Solder joint interconnects are mechanical means of structural support for bridging the various electronic components and providing electrical contacts and a thermal path for heat dissipation. The functionality of the electronic device often relies on the structural integrity of the solder. The dimensional stability of solder joints is numerically predicted based on their mechanical properties. Algorithms to model the kinetics of dissolution and subsequent growth of intermetallic from the complete knowledge of a single history of time-temperature-reflow profile, by considering equivalent isothermal time intervals, have been developed. The information for dissolution is derived during the heating cycle of reflow and for the growth process from cooling curve of reflow profile. A simple and quick analysis tool to derive tensile stress-strain maps as a function of the reflow temperature of solder and strain rate has been developed by numerical program. The tensile properties are used in modeling thermal strain, thermal fatigue and to predict the overall fatigue life of solder joints. The numerical analysis of the tensile properties as affected by their composition and rate of testing, has been compiled in this paper. A numerical model using constitutive equation has been developed to evaluate the interfacial fatigue crack growth rate. The model can assess the effect of cooling rate, which depends on the level of strain energy release rate. Increasing cooling rate from normalizing to water-quenching, enhanced the fatigue resistance to interfacial crack growth by up to 50% at low strain energy release rate. The increased cooling rates enhanced the fatigue crack growth resistance by surface roughening at the interface of solder joint. This paper highlights salient features of process modeling. Interfacial intermetallic microstructure is affected by cooling rate and thereby affects the mechanical properties.