回流焊接过程中焊料成球的原因

通孔波峰焊接和表面贴装（锡膏回流焊接）是电子组装互连的两种主要基本方式。其中表面贴装技术具备高可靠性、高产量以及低成本的特点，在近20年内受到广泛的欢迎和得到飞速的发展。但是，不恰当的回流曲线设置，不合理的材料选择，以及较差的焊接环境等因素可能导致很多的焊接缺陷，最终可能导致长期的可靠性问题。常见的主要焊接缺陷包括：较差的润湿性（缺焊，冷焊，空焊），焊料球、锡珠、立碑、元器件开裂、过度的金属间化合物生长，焊点空洞等等1。因此，通过了解各种缺陷的基本原因，从而进行合理的材料工艺组合和优化，可以提高组装焊接的质量和确保其长期可靠性。     

SMT波峰焊接的工艺研究

对ＳＭＴ焊接中的焊点内在质量，焊点显微组织，以焊接工艺参数对焊接显微组织与焊接强度的影响进行了初步的研究与探讨；同时对ＳＭＴ混装波峰焊接最佳工艺流进行了较为深入地工艺试验，提出了焊接整体质量与最佳ＳＭＴ混装波峰焊接的实用工艺。     

Sn-3.0Ag-0.5Cu/Cu焊点可靠性研究

采用铺展面积法研究了Sn-3.0Ag-0.5Cu无铅钎料在不同温度下的润湿性能,同时探讨了150℃等温时效对Sn-3.0Ag-0.5Cu/Cu焊点界面组织及力学性能的影响。结果表明,随着钎焊温度的升高,Sn-3.0Ag-0.5Cu钎料的润湿性能明显增加。焊后钎料/Cu界面处对应的金属间化合物为Cu6Sn5相,经150℃时效,界面层的形貌由原来的齿状逐渐转化为层状,且厚度随着时效时间的增加而增加。发现界面层金属间化合物厚度与时效时间的二次方根成线性关系。对焊点在时效过程中的力学性能进行分析,发现Sn3.0Ag0.5Cu/Cu焊点的力学性能随着时效时间的增加逐渐降低,时效初期,焊点的力学性能下降较快,后期趋于平缓。     

应用光束技术的焊接工艺

自非接触性微焊接方法（局部焊接方法）开发至今已有约十年的历史了,由于这种焊接方法优于其它焊接方法（即：焊烙铁、热风等）一直受到高度重视,而且被广泛应用于工业电子领域。该技术已被用于全球范围的许多工厂的生产线中,包括美国、日本、欧洲和墨西哥。本主要针对下面几方面的技术进行论述：1）点焊方法,这种方法在生产线中使用的最多;（2）连续焊接方法,主要应用于一般间距的表面贴装元件和通孔元件的焊接;（3）向上焊接方法,这种方法是用光束照射产品的底部,使用这些方法不需翻转印制电路板（在下中简称PCB板）就可对待焊接的元件进行焊接。本还将列举一些实例和对最佳的电路板设计做进一步的说明及对焊接质量进行评估。     

SMT无铅焊接缺陷及工艺分析

本文详细介绍SMT无铅焊接钎料及其工艺特点，对无铅再流焊的相关典型缺陷进行了分析，并提出了有效的预防措施以及进行无铅焊接返工的几个关键问题。     

时效对Sn3.0Cu0.15Ni/Cu界面组织的影响

研究了150℃时效0,200,500h对Sn3.0Cu0.15Ni/Cu界面组织结构的影响.结果表明:界面金属间化合物层由Cu6Sn5层和Cu3Sn层组成,质量分数为0.15％的Ni的加入会使IMC层最初变厚,但在时效过程中,热稳定性强的界面化合物(Cu,Ni)6Sn5的生成,会抑制Cu3Sn化合物层的生长;同时Ni的加入会降低Cu6Sn5颗粒的长大速度,并且随着时效时间的延长,Cu6Sn5颗粒的形貌呈多面体结构.     

SMT用印制板与无铅焊接

一、前言 微电子技术的飞速发展和电子产品小型化、轻量化及高可靠的要求，使表面贴装元器件在电子产品中的应用日益广泛，表面安装技术因此也成为电子装联工艺的主流。作为表面贴装元器件的安装、连结和支撑的载体——SMT用印制板也有了相应的发展和进步，对表面安装元器件与印制板焊接连接用的焊料，也逐步由传统的锡铅合金焊料逐步向无铅焊料过渡。[第一段]     

几种SMT焊接缺陷及其解决措施

主要针对采用了表面组装技术 (SMT)生产的印制电路组件中出现的焊料球、立片、桥接等几种焊接缺陷现象进行分析 ,并将有效的解决措施进行了经验性总结。     

Sn-58Bi-0.5Ce/Cu界面金属间化合物的性能研究

研究了Sn-58Bi-0.5Ce/Cu钎焊接头在120℃时效过程中界面组织形貌及金属间化合物层(IMC)的厚度变化。结果表明:在Sn-58Bi-0.5Ce/Cu钎焊接头界面处形成了较为平坦的双层金属间化合物,靠近钎料的上层为Cu6Sn5相,邻近Cu基板的下层为Cu3Sn相。等温时效处理后,IMC层逐渐凸起,且随着时效时间的增加,IMC层不断增厚。通过对实验数据进行拟合,得到钎焊接头界面IMC层的生长速度常数为5.77×10–17m2/s。     

Sn-37Pb焊球与Ni/NiP UBM界面反应特性研究

通过对共晶锡铅焊球与Ni/NiP UBM层扫描电镜界面微观组织观察和成分分析,研究了Sn-37Pb/Ni和Sn-37Pb/NiPUBM焊点界面反应特性。研究表明芯片侧界面IMC由Ni层到焊料的顺序为:靠近Ni层界面化合物为(Ni,Cu)_3Sn,靠近焊料侧化合物为(Cu,Ni)_6Sn_5;PCB板侧界面IMC包括靠近NiP层的NiSnP化合物和靠近焊料侧的(Cu,Ni)_6Sn_5化合物,NiSnP是由于Ni的扩散形成。PCB板侧NiP镀层中存在微裂纹缺陷,此裂纹缺陷会导致金属间化合物中产生裂纹,从而对焊点力学性能和可靠性产生不良的影响。     

SMT再流焊接工艺预测与仿真技术研究现状

综述了电子电路表面组装技术（ＳＭＴ）再流焊焊接工艺仿真与预测研究的必要性、重要意义及其研究现状，并对其应用现状及其发展趋势进行了评述。     

关于SMT电路板焊装维修工艺的讨论（待续）

以ＯＫ集团表面贴装工艺电路板焊装维修设备为工作环境，介绍表面贴装电板的焊装修工艺。     

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.     

电子组装用焊锡粉雾化制备技术现状与发展

焊锡粉是焊锡膏的主要成分,其质量的好坏对焊锡膏的印刷质量起着至关重要的作用.概述了焊锡粉的分类、性能及应用,并重点介绍了当前雾化法制备焊锡粉的技术与特点.结合制粉技术的发展,对球形焊锡粉新型制备技术进行了展望.     

Effect of cooling rate on microstructure and shear strength of pure Sn,Sn-0.7Cu,Sn-3.5Ag,and Sn-37Pb solders

The microstructure and shear strength characteristics of pure Sn and the eutectic compositions of Sn-37Pb, Sn-0.7Cu, and Sn-3.5Ag prepared under identical reflow conditions but subjected to two different cooling conditions were evaluated at room temperature. For the four solders, the ultimate shear strength increased with increasing strain rate from 10⁻⁵ s⁻¹ to 10⁻¹ s⁻¹. Decreasing the cooling rate tended to decrease the ultimate shear strength for both the Sn-0.7Cu and Sn-3.5Ag solders. The effects of work hardening resulting from increased strain rate were more prevalent in quench-cooled (QC) samples.     

Effect of Interfacial Reaction on the Tensile Strength of Sn-3.5Ag/Ni-P and Sn-37Pb/Ni-P Solder Joints

This work investigates the effect of interfacial reaction on the mechanical strength of two types of solder joints, Sn-3.5Ag/Ni-P and Sn-37Pb/Ni-P. The tensile strength and fracture behavior of the joints under different thermal aging conditions have been studied. It is observed that the tensile strength decreases with increasing aging temperature and duration. Associated with the tensile strength decrease is the transition of failure modes from within the bulk solder in the as-soldered condition toward failures at the interface between the solder and the intermetallic compounds (IMCs). For the same aging treatment, the strength of the Sn-3.5Ag/Ni-P joint degrades faster than that of Sn-37Pb/Ni-P. The difference between the two types of joints can be explained by the difference in their interfacial reaction and growth kinetics. An empirical relation is established between the solder joint strength and the Ni₃Sn₄ intermetallic compound thickness.     

Effect of Zn Addition on Interfacial Reactions Between Sn-4Ag Solder and Ag Substrates

In this study, the effect of Zn (Zn = 1 wt.%, 3 wt.%, and 7 wt.%) additions to Sn-4Ag solder reacting with Ag substrates was investigated under solid-state and liquid-state conditions. The composition and microstructure of the intermetallic compounds (IMCs) significantly changed due to the introduction of different Zn contents. In the case of Sn-4Ag solder with 1 wt.% Zn, a continuous Ag-Sn IMC layer formed on the Ag substrates; discontinuous Ag-Zn layers and Sn-rich regions formed on the Ag substrates under liquid-state conditions when the Sn-4Ag solders contained 3 wt.% and 7 wt.% Zn. If 3 wt.% Zn was added to Sn-4Ag solder, the Ag-Sn IMC would be transformed into a Ag-Zn IMC with increasing aging time. Rough interfaces between the IMCs and the Ag substrates were observed in Sn-4Ag-7Zn/Ag joints after reflowing at 260°C for 15 min; however, the interfaces between the IMCs and the Ag substrates became smooth for Sn-4Ag-1Zn/Ag and Sn-4Ag-3Zn/Ag joints. The nonparabolic growth mechanism of IMCs was probed in the Sn-4Ag-3Zn/Ag joints during liquid-state reaction, and can be attributed to the detachment of IMCs. On the other hand, the effect of gravity was also taken into account to explain the formation of IMCs at the three different interfaces (bottom, top, and vertical) during the reflow procedure.     

印制电路板铜面保护层对无铅焊点结构影响

采用扫描电镜与能谱测试,研究了两种不同印刷电路板铜面保护层,即有机保护层(Organic Solderability Preservatives,OSP)与浸银层(Immersion Ag,I—Ag),对无铅焊点结构的影响。结果显示,采用有机保护层的焊接界面金属间化合物层厚度明显超过了浸银层;在两种不同保护层中的焊点中,均出现薄片状或树枝状Ag3Sn金属间化合物,但在浸银层焊点中,薄片状Ag3sn主要在焊接界面层处非均匀形核长大,而有机保护层焊点中,薄片状Ag3Sn较少出现,代之以树枝状Ag3Sn近似均匀地分布在焊点中。断口分析显示,采用有机保护层的焊点中出现了较多的气孔,而且气孔主要出现在靠近铜面焊点中,这明显降低了焊点的强度。     

Kinetics of Intermetallic Compound Formation at the Interface Between Sn-3.0Ag-0.5Cu Solder and Cu-Zn Alloy Substrates

The growth kinetics of an intermetallic compound (IMC) layer formed between Sn-3.5Ag-0.5Cu (SAC) solders and Cu-Zn alloy substrates was investigated for samples aged at different temperatures. Scallop-shaped Cu₆Sn₅ formed after soldering by dipping Cu or Cu-10 wt.%Zn wires into the molten solder at 260°C. Isothermal aging was performed at 120°C, 150°C, and 180°C for up to 2000 h. During the aging process, the morphology of Cu₆Sn₅ changed to a planar type in both specimens. Typical bilayer of Cu₆Sn₅ and Cu₃Sn and numerous microvoids were formed at the SAC/Cu interfaces after aging, while Cu₃Sn and microvoids were not observed at the SAC/Cu-Zn interfaces. IMC growth on the Cu substrate was controlled by volume diffusion in all conditions. In contrast, IMC growth on Cu-Zn specimens was controlled by interfacial reaction for a short aging time and volume diffusion kinetics for a long aging time. The growth rate of IMCs on Cu-Zn substrates was much slower due to the larger activation energy and the lower layer growth coefficient for the growth of Cu-Sn IMCs. This effect was more prominent at higher aging temperatures.     

无铅波峰焊钎料抗氧化影响的研究

研究了目前常用的Sn-0.7Cu无铅钎料在手浸锡炉和模拟波峰炉中的抗氧化情况.主要研究了微量P元素的加入对钎料抗氧化性的影响.通过钎料在液态下表面颜色变化和锡渣的产生量的比较可以发现微量P元素的加入可以提高钎料的抗氧化性能.通过比色分析发现微量P元素在钎料表面或亚表面富集,形成"阻挡层",抑制了钎料的进一步氧化.通过实验得出P的最佳质量分数为0.011%.