无铅选择性焊接：波峰焊接的将来

正在草拟中的法规和向着无铅电子组装发展的市场趋势带来了几个问题，包括提高电子元件的热容差的需求。无铅焊料合金，如象：熔点为217℃的锡-银-铜(SnAgCu)，要求的工艺温度比传统的锡-铅(SnPb)合金的工艺温度高，因此，在焊接过程中，降低工艺窗口，并注重于对热工艺的严格控制的需求上。无铅合金的较高熔点和电子元件的热临界值之间的这种奇论是无铅领域展开激烈挑战的原由。元件热容差的提高将会给电子制造厂家带来较重的经济负担，因为这些厂家将面临着更高的总热工艺成本。有关热工艺成本的提高将推动着电子组装厂家最大限度地提高其热工艺的效率。当焊接复杂的混合技术印制电路板(PCB)上的通孔(TH)元件时尤其是这样，这类组装板，对现有的焊接方法，如象：波峰焊接，的工艺能力的热量需求较大。对这一问题的可能采用的解决方法是使用现场专用的选择性焊接，以便形成无铅组装的TH互连。本论述了用于替代TH互连的无铅焊接的波峰焊接的一种切实可行的焊接技术：选择性焊接。本概述了TH选择性焊接为改善无铅制造成本的效果方面在质量和成本上的优点。     

无铅波峰焊接工艺的优化

全球电子电气工业膨勃发展，锡铅焊接逐步向无铅焊接转化，波峰焊接越来越多的向回流焊接发展，但新的“无铅波峰焊接技术”仍是业界研究的一个焦点。在美国由几家公司组成的社团收集了很多无铅波峰焊接过程中的相关数据，并对这些数据进行分析，研究，试图找到适用于无铅波峰焊接的工艺参数。但是对于高可靠性的电子产品，如网络设备，到目前为止还达不到实际所需的高可靠性要求，需通过大量工艺优化来实现无铅波峰焊接的高可靠性。该篇文章聚焦无铅波峰焊接工艺窗口及多层板的选择性波峰焊接，愿我的工作对你的应用有所帮助! 研究工作使用了可以承受无铅焊接温度的新型PCB材质，厚度为0．125英寸，该PCB为18层板，其中8层为接地层，10层为信号层，PCB焊盘镀层分别为浸银（1mm-Ag）和高温防氧化有机涂层（OSP）二种，焊接材料选用SnPb和SAC305，PCB为典型的通讯用线路板，布线设计复杂程度高，特制的波峰焊接夹具可以使该PCB在无铅波峰焊炉上实施选择性波峰焊接，焊后2D X-RAY和3D X-RAY检测系统观察焊点可靠性，焊点形状及焊接缺陷。一套可靠的，具有破坏性的试验分析工具（DPA）用来评估焊点质量，并与共晶焊料Sn／Pb装配结果做质量对比分析，与此同时，详细记录焊接温度，使用的元器件，以及对应的焊点质量。与共晶Sn／Pb焊料焊接结果相比，首先发现镀通孔润湿性差，通孔内焊锡量不足，桥接增多，焊点内有大量空洞。无铅波峰焊接工艺窗口变窄，要想获得理想的焊锡量，就要不断优化焊接曲线。试验结果发现，浸银的PCB在镀通孔填充率和可焊性方面均优于OSP、PCB。     

现代波峰焊接工艺

本简要描述了波峰焊接工艺的原理和趋势,重点论述了混装波峰的材料选择,工艺优化,并分析了波形,DFM及无铅焊接对波峰焊接工艺的影响。     

无铅焊接技术的特点及其应用难点

无铅焊料和无铅焊接工艺与传统的锡铅及其焊接工艺有相当差别，充分了解其特点，掌握其应用中的难点、焦点和发展方向，是实施无铅的重要内容。     

电子组件的波峰焊接工艺

在电子组件的组装过程中，焊接发挥了相当重要的作用。它涉及到产品的性能、可靠性和质量等方面，甚至影响到其后的每一个工艺步骤。此外，由于电子组件朝着轻、薄、小的方向快速发展，为焊接工艺提出了一系列的难题，因此，电了制造业的各个厂家围绕SMT的焊接工艺展开了激烈的竞争，旨在进一步提高焊接质量，克服焊接中存在的短路、桥接、焊球和漏焊等缺陷，从而提高产品质量，满足市场需求。     

无铅焊接技术在手工焊接中的应用

随着世界环保意识的逐渐增强,无铅、无毒化成为新世纪电子工业制造中的热门话题,世界各国纷纷展开了关于无铅焊接材料、无铅焊接设备、无铅焊接技术的研制与开发。手工焊接作为一种最基础的焊接方法,在当今的电子组装中仍然起着不可缺少的作用。仅就无铅焊接技术在手工焊接中的应用作一分析和讨论。     

开发高性能无铅波峰焊料合金的重点

在开发高性能无铅焊料合金时，研究人员必须评估四项主要特性：工艺良率、铜浸出率、浮渣形成和热／机械可靠性。     

推进无铅焊接应用

虽然国际国内都在不同程度地应用无铅技术，但目前还处于过渡和起步阶段，从理论到应用都还不成熟，没有统一的标准，对无铅焊接的焊点可靠性还没有统一的认识，因此无论国际国内无铅应用技术都非常混乱，大多企业虽然焊接材料无铅化了，但元器件焊端仍然有铅。究竟哪一种无铅焊料更好，哪一种PCB焊盘镀层对无铅焊更有利，哪一种元器件焊端材料对无铅焊接焊点可靠性更有利，什么样的温度曲线最合理、     

无铅波峰焊工艺与设备的技术特点探讨

(上接2004年第5期第201页) 3.2 锡炉的腐蚀性问题 波峰焊接PCB上的插装电子元器件,当采用无铅焊料时,由于无铅焊料的焊接温度比Sn-Pb合金焊料高约30 ℃～50 ℃,另外无铅焊料中Sn的含量大幅度提高,一般都在95 %以上,造成了波峰焊时无铅焊料对锡炉和喷口的腐蚀性加强.国内一般锡炉采用的材料是SUS304和SUS316型不锈钢.实验表明,不锈钢材料在高温条件下6个月就被高Sn无铅焊料明显腐蚀.最容易受到腐蚀的是与流动焊料接触的部位,如泵的叶轮、输送管和喷口.     

Development of lead-free wave soldering process

Lead-free wave soldering was studied in this work using a 95.5Sn/3.8Ag/0.7Cu alloy. A process DOE was developed, with three variables (solder bath temperature, conveyor speed, and soldering atmosphere), using a dual wave system. Four no-clean flux systems, including alcohol- and water-based types, were included in the evaluation. A specially designed "Lead-Free Solder Test Vehicle", which has various types of components, was used in the experiments. Both organic solderability preservative (OSP) and electroless nickel/immersion gold (Ni/Au, or ENIG) surface finishes were studied. Soldering performance (bridging, wetting and hole filling) was used as the responses for the DOE. In addition, dross formation was measured at different solder bath temperatures and atmospheres. Dross formation with Sn/Ag/Cu bath was compared to that with eutectic Sn/Pb bath. Regarding the connector-type component, a pad design giving the best soldering performance was evaluated based on the DOE results. Finally, a confirmation run with the optimum flux and process parameters was carried out using the Sn/Ag/Cu solder, and a comparative run was made with the Sn/Pb solder alloy and a no-clean flux used in production. The soldering results between the two runs indicate that with optimum flux and process parameters, it is possible to achieve acceptable process performance with the Sn/Ag/Cu alloy.     

无VOC助焊剂的无铅波峰焊工艺探讨

概述了一种新型绿色助焊剂——无挥发性有机化合物(VOC)助焊剂。该助焊剂有无松香、无卤素、免清洗、无污染、方便储存和运输等优点,已经成为助焊剂领域的发展方向。讨论了此助焊剂在无铅波峰焊中应用时需要注意的问题。结果表明,当电路板的预热温度控制在110～120℃,轨道倾角控制在5°～7°,印制板引线脚与焊料的接触时间3～5 s,焊接温度260℃并采用喷雾涂敷方法时,可达到理想的焊接效果。     

Interfaces in lead-free soldering

Structural integrity of circuits is greatly dependent on interfacial microstructure. In this paper, the status of the current understanding of various interfaces appearing in lead-free soldering is reviewed, and recent data on interfaces in electronic interconnections, primarily analyzed by transmission electron microscopy (TEM), is presented. The compound Cu₆Sn₅ is formed, as localized precipitates attach to the interface of a Cu substrate with Sn plating, even in an as-received condition. After long-time exposure at room temperature, it grows into a Cu₆Sn₅ layer along the interface. When the temperature is raised slightly or Sn in a plating layer is consumed by the reaction, a Cu₃Sn layer can grow between a Cu₆Sn₅ layer and a Cu substrate. In soldering, most Sn alloys involving pure Sn, Sn-Ag, or their ternary alloys form two intermetallic compounds, e.g., Cu₆Sn₅ and Cu₃Sn, on a Cu substrate, with the former much thicker than the latter. The Ni plating forms Ni₃Sn₄/Ni₃Sn₂ double layers at the interface with Sn alloys in soldering with the latter layer very much thinner. In contrast, Fe-42Ni alloy forms (Fe,Ni)Sn₂ double layers by the reaction with Sn and Sn-Ag(-Cu). When Zn becomes one of the elements of the solder, Zn first reacts with a substrate. Thus, the Sn-Zn alloy forms different intermetallic compounds at an interface with Cu, i.e., the CuZn/Cu₅Zn₈ double layers. The Sn-Zn alloy also forms a thin AuZn layer when thin Au plating is on a substrate.     

SnAgCu无铅焊点的电迁移行为研究

电迁移引发的焊点失效已经成为当今高集成度电子封装中的最严重的可靠性问题之一。应用SnAgCu无铅焊膏焊接微米级铜线,进行电迁移实验。结果表明:焊点形貌从原来的光滑平整变得凹凸不平,阴极处出现了裂纹和孔洞,并且在铜基板和Cu6Sn5金属间化合物(IMC)之间出现薄薄的一层Cu3Sn金属间化合物,由ImageJ软件测量其平均厚度约为2.11μm;而在阳极附近没有明显的Cu3Sn金属间化合物形成。     

浅谈电子元器件生产中的无铅手工焊

无铅焊接存在润湿性较差、温度较高、氧化速度快等缺点。在工艺上需严格控制焊接温度和时间,才能保证焊接质量。     

Thermal and mechanical stability of soldering QFP with Sn-Bi-Ag lead-free alloy

Thermal stability of the circuit boards with a quad flat package (QFP) soldered with Sn-58wt%Bi-(0, 0.5 and 1.0) wt% Ag and their microstructural features were evaluated. The addition of 1.0 wt% Ag causes the formation of large primary Ag/sub 3/Sn precipitates in the solder while no primary Ag/sub 3/Sn is found in Sn-57Bi-0.5Ag. Thermo-Calc calculation indicates that the lowest limit content for the formation of primary Ag/sub 3/Sn is about 0.8 wt%. Heat-exposure below 100/spl deg/C has no serious degradation on the joint structure for all solders. Heat-exposure at 125/spl deg/C caused serious degradation in joint strength for all alloys. The contamination of Pb from Sn-Pb surface plating on the components reduces the interface tolerance by forming ternary Sn-Pb-Bi phase melting at low temperature. Thermal fatigue between -20 and 80/spl deg/C does not have any significant influence on joint structure.     

无铅回流焊后跨线碳膜裂纹的探讨

针对PCB在过无铅回流焊后跨线位碳膜出现裂纹问题进行分析探讨,通过从调整碳膜参数、不同碳膜厚度对比、不同碳膜性能对比的结果,得出结论:碳膜开裂与油墨性能和设计有直接的关系。最终调整碳膜工艺参数和更改线路设计等方案,能有效改善碳膜裂纹的问题。     

Impact of lead-free soldering processes on the performance of signal relay contacts

Various legislations, rules and regulations in Europe [Restrictions of the use of certain hazardous substances in electrical and electronic equipment (ROHS)] and Japan (Recycling Law for Home Electric Appliances) have either targeted restrictions or a full ban on the use of lead, to be enforced from 2001, 2005, and 2006 onwards. Next to these regulations, marketing arguments are becoming more and more important for so called "GREEN" products. Up to now, mainly tin-lead alloys have been used in electronics. The process temperatures usually applied have been in the range of 230/spl deg/C. All currently discussed lead-free alternatives for professional electronics need process temperatures which are at least 30/spl deg/C higher. In addition, the process duration is significantly longer. The combination of higher process temperatures and longer duration together results in a significant thermal stress on the precision mechanics of the relay. In order to guarantee proper functioning of the relay after the solder process with maximum process temperatures of 255/spl deg/C, the dimensional changes of the plastic parts must be less than a few micrometers in order to guarantee stable contact forces. The outgassing of the used insulating and sealing materials must be minimal in order not to pollute or contaminate the contacts. With the lead-free version of the IM relay, an identical performance and the same reliability during electrical and climatic endurance tests can be expected, even though relays were processed with typical lead-free soldering processes with temperatures up to 255/spl deg/C.