有铅与无铅混用问题举例

首先，有铅工艺遇到无铅元器件。 有的SMT加工厂，虽然还没有启动无铅工艺，但是也遇到了无铅元器件、特别是BGA／CSP和LLP。有的元件厂已经不生产有铅的器件了，因此采购不到有铅器件，这种知道采购的器件是无铅的情况还不可怕，因为可以通过提高焊接温度，一般提高到230—235℃就可以。还有一种措施可以采用无铅焊料和无铅工艺，因为目前过渡阶段普遍情况是无铅焊料和有铅焊端混用，其可靠性还是可以被接受的。但是最糟糕的是无意中遇到了无铅元器件，生产前没有发现，生产中还是采用有铅焊料和有铅工艺，结果就非常糟糕，因为有铅焊料和无铅焊端混用效果最差。     

有铅和无铅混装工艺的探讨

对于高可靠性的产品通常还是采用有铅工艺,但是随着无铅化的深入,对于某些元器件,在市面上已买不到有铅元器件。这就出现了有铅制程下,有铅和无铅元器件混用的现象,那么如何才能同时保证有铅和无铅元器件的焊接质量呢?通过分析元器件引线框架或焊端镀层的成分,结合元器件封装形式来探讨有铅制程下有铅和无铅混装工艺的相关问题及应对措施。     

无铅焊接可靠性讨论及过渡阶段有铅、无铅混用应注意的问题（下）

目前正处于从有铅产品向无铅产品过渡的特殊阶段。由于对无铅焊点的长期可靠性等方面问题的研究还处在初期研究阶段,有铅和无铅混用时,可能会发生材料之间、工艺之间、设计之间不相容等问题而影响电子产品的可靠性。本文主要讨论过渡阶段有铅、无铅混用对可靠性的影响,以及通过对有铅誊无铅混用制程分析,介绍不同工艺（再流焊与波峰焊）、不同的元件（无引线或有引脚元件与BGA、CSP等球栅阵列元件）、不同混用情况对焊点可靠性的影响及过渡阶段有铅和无铅混用的应对措施与应注意的问题。文章中的观点供参考并与同行共同讨论。     

无铅焊接可靠性讨论及过渡阶段有铅、无铅混用应注意的问题

目前正处于从有铅产品向无铅产品过渡的特殊阶段。由于对无铅焊点的长期可靠性等方面问题的研究还处在初期研究阶段,有铅和无铅混用时,可能会发生材料之间、工艺之间、设计之间不相容等问题而影响电子产品的可靠性．本文主要讨论过渡阶段有铅、无铅混用对可靠性的影响,以及通过对有铅、无铅混用制程分析,介绍不同工艺（再流焊与波峰焊）、不同的元件（无引线或有引脚元件与BGA、CSP等球栅阵列元件）、不同混用情况对焊点可靠性的影响及过渡阶段有铅和无铅混用的应对措施与应注意的问题。文章中的观点供参考并与同行共同讨论。     

器件引线的无铅化进展

日本电子机器无铅化已成功地迈出第一步,在组装无铅焊接方面各厂家都有生产应用实例。现已进入第二步,在包括装配元器件在内的无铅化生产活动中遇到许多实际问题有待解决。实际上,电路板组装焊接(再流焊、波峰焊)无铅化和元器件引线端及其表面处理无铅化是紧密相关的。例如,为了确保电路板组装无铅焊接性能,元器件引线端及其表面处理,就不能再使用Sn-Pn焊料。日本夏普公司先行一步,一部分元器件引线端及其表面处理已开始实现无铅化(参阅图1)。     

过渡时期无铅焊接可靠性探讨

目前正处于从有铅产品向无铅产品过渡的特殊阶段。由于对铅焊点的长期可靠性等方面问题的研究还处在初期研究阶段,有铅和无铅混用时,可能会发生材料之间、工艺之间、设计之间不相容等问题而影响电子产品的可靠性。本刊将通过三期连载的形式分别讨论过渡阶段有铅、无铅混用对可靠性的影响,以及通过对有铅、无铅混用制程分析,介绍不同工艺（再流焊与波峰焊）、不同的元件（无引线或有引脚元件与BGA、CSP等球珊阵列元件）、不同混用情况对焊点可靠性的影响及过渡阶段有铅和无铅混用的应对措施与应注意的问题。     

无铅技术系列文章六：无铅器件

前言： 上两期我们谈论了无铅焊料合金以及PCB焊盘上的镀层材料。这次我们来看看形成焊点另外一端的器件焊端材料，以及器件封装材料在无铅技术中的问题和考虑等等。使用在PCBA上的器件种类繁多，我们只谈常用的无源器件以及半导体封装类的。     

有铅无铅高密度混装工艺技术研究

随着电子产品无铅化的不断推进,在高可靠电子产品组装中,采用有铅焊料焊接有铅无铅镀层器件并存的情况不可避免。因此混合焊接工艺和焊点的可靠性是研究的重点。本文提出了有铅无铅高密度混装工艺研究方法,针对有铅无铅镀层兼容性、高密度混装再流焊工艺、及有铅无铅高密度混装焊点可靠性开展技术研究工作,并与同行业者分享阶段性研究成果。     

无铅焊接的可靠性分析

目前,电子制造业正处于从有铅向无铅焊接过渡的特殊阶段,无铅材料、印制板、元器件、检测、可靠性等方面都没有标准,由于有铅和无铅混用时,特别是当无铅焊端的元器件采用有铅焊料和有铅工艺时会发生严重的可靠性问题。这些问题不仅是当前过渡阶段无铅焊接要注意,而且对于过渡阶段的有铅焊接也是要特别注意的问题。     

军用无铅器件组装可靠性分析及对策

无铅焊接技术已经广泛应用于消费类和通讯类电子产品中,但由于其发展时间较短,可靠性仍需进一步研究验证。军工企业出于可靠性的考虑仍旧采用有铅技术,但在实际生产中,不可避免地遇到越来越多的无铅器件。如何在采用有铅制程的情况下焊接无铅器件并保证其可靠性已成为军工单位迫切需要解决的问题。围绕混装工艺的可靠性,详细介绍适用于军工单位的有铅工艺制程焊接无铅元器件的工艺方法和可靠性分析,最终结合工作实际给出较为完整的应对策略。     

Effects of thermomechanical cycling on lead and lead-free (SnPb and SnAgCu) surface mount solder joints

Accelerated reliability tests have been performed on leadless and leaded lead-free and lead containing SMT component assemblies. Results so far have shown that lead-free reflow soldering is a viable alternative for conventional lead based reflow soldering. The selected ternary eutectic solder alloy SnAg3.8Cu0.7 requires higher processing temperatures which could restrict the use of certain board and component types, but other than that no major modifications seem necessary. Although better SnAg3.8Cu0.7 bulk mechanical properties were obtained compared to the near eutectic lead bearing bulk solder properties, reflowed solder joints did not reflect this difference. In general, quite similar reliability results were obtained as found for the lead based solders. Dependent on board and component metallisations and use environment, the reliability of the lead-free solders could perform better or worse than the lead based solders. Temperature dependent aspects such as solderability and mechanical behaviour of the lead-free assemblies could play a role in this. Although microstructural differences can be seen between the lead-free and lead bearing solder joints, similar joint failure mechanisms occur. Resistor solder joint cracks propagate from underneath the component through either transgranular (lead-free) grains or along intergranular (lead) grain boundaries between lead-rich and tin-rich areas and into coarsened regions near the component terminations. Gullwing lead cracks were seen propagating from the heel fillet along the lead/solder interfacial intermetallic mostly (some cracks started in the heel fillet and propagated through the solder body dispersed with coarsened spherical Ag₃Sn intermetallic particles). Package design and leadframe material seem to play a more important role in the fatigue mechanism than the change in microstructure of the solder joint.     

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。     

氮气保护在无铅化电子组装中的应用

无铅钎料的高熔点、差润湿性给SMT传统的焊接工艺带来了很大冲击,并且对焊点质量也产生了很大的影响。为了防止氧化,改善钎料与焊盘、元件引脚之间的润湿性,提高产品合格率,目前在电子纽装中普遍采用氮气保护。针对几种常用无铅钎料进行了氮气气氛中润湿性和焊点组织的分析,并初步研究了氮气保护对焊点质量和氧化渣的影响。结果表明：氮气保护可以改善无铅钎料润湿性,细化焊点组织,减少氧化渣量,而且对焊点外观和成品率也有一定的影响。     

Understanding the process window for printing lead-free solderpastes

Solder paste is primarily used as a bonding medium for surface mount assemblies (SMA) in the electronics industry, and is typically deposited using the stencil printing process. Stencil printing is a very important and critical stage in the reflow soldering of surface mount devices, and a high proportion of all SMA defects are related to this process. This is likely to continue with the drive toward the introduction of lead-free solder pastes. Work is continuing on the metallurgical properties of these lead-free solders, including solder joint strength and material compatibility. However, the initial challenge for the new Pb-free formulations is in achieving repeatable solder deposit from print to print and from pad to pad. To meet this challenge, new flux formulations are being developed. For a smooth transition to Pb-free soldering formulations, a proper understanding of the solder paste printing performance is necessary. The key parameters that affect solder paste printing have been identified and are the subject of numerous studies. In lead-free solder paste, the replacement of lead with other elements (including Bi, Cu) changes the density of this dense suspension. In this paper, we investigate the effects of printer parameters, i.e. squeegee speed and pressure (defined as the process window) on the printing performance of a variety of lead-free solder pastes. A three-level design of experiment on these factors was used. Comparisons are presented with lead-rich solder pastes. The metal content of the lead-free solders had a significant effect on the process window     

Modified Engelmaier’s model taking account of different stress levels

In this paper, the solder fatigue model created by Werner Engelmaier is modified so that it takes better into account the different stress levels the solder material experiences. This is accomplished by replacing the fatigue ductility constant by a correction term that is temperature- excursion- range-dependent. In order to obtain the correction term, the effect of the temperature cycling profile on lifetime is studied. The correction term obtained is package type specific. More compliant plastic packages with a small coefficient of expansion mismatch with the organic printed wiring board are handled separately, and stiff ceramic packages assembled on an organic board – resulting in a large CTE mismatch – are considered as another entity.

Correction terms for both lead-free and tin–lead solder materials are given. This is necessary as the creep characteristics of the solders are different. Comparing solder material specific correction terms makes it possible to determine which solder material performs best in a certain environment and a given assembly type. In the case of ceramic packages, the transition where a eutectic tin–lead solder becomes superior to a SnAgCu solder is expected to take place when temperature excursions are smaller than ca. 70 °C. This indicates that although in a highly accelerated stress test, lead-free solders may be inferior compared to tin–lead solders, in the real field environment, the situation may be reversed.     

Corrosion behavior of Sn-3.0Ag-0.5Cu lead-free solder joints

The aim of this study is to evaluate the corrosion behavior of Sn-3.0Ag-0.5Cu (SAC305) lead-free solder joint using salt spray test. The presence of Cu pad accelerates the dissolution of Sn from solder joints into corrosive medium because of galvanic corrosion mechanism. So, the solder joint was easily corroded in corrosive environment than SAC305 solder bar. During salt spray test, pitting corrosion begin from the solidification cracks in the solder joints, which will lead to a decrease of the reliability of solder joints and shorten the life of electronic devices.     

浅谈电子产品无铅化

鉴于铅对人体及自然环境的危害性,文章从电子产品无铅化的提出、焊料的无铅化、电子器件的无铅化、无铅化实施过程中存在的问题这几个方面阐述电子产品的无铅化。     

Reliability study of new SnZnAl lead-free solders used in CSP packages

We have implemented a company-wide effort to progressively reduce the use of Pb(lead) and eventually eliminate this environmental pollutant from its products. As part of this effort, it has developed a new lead-free solder that consisting of Sn(tin), Zn(zinc), and Al(aluminum) and yet offers superior productivity and joint reliability. The new lead-free solder has a melting point equivalent to that of a SnPb eutectic solder, and enables devices to be packaged at a lower temperature than with the increasingly popular Sn(tin), Ag(silver), Cu(copper) solder. Thus, the new lead-free solder accelerates the elimination of Pb from products. we have already used printed circuit boards containing the new lead-free solder in some products, and plans to extend its use to other products.We further mounted SnZnAl solder balls onto Cu/Ni(nickel)/Au(gold) plated polyimide substrate at a joining temperature of 215 °C for CSP applications. It was confirmed that the joint interface between soldered ball and substrate at the initial stage was made of 2-layered compounds, i.e., AuZnSn on soldered side and ZnSnNi on substrate side. After 1000 h aging at 150 °C, the two layers compounds become one layer of ZnSnNiAu compound. No strength deterioration of Cu/Ni/Au/SnZnAl after the 1300 h shelf test was detected in the ball shear strength compared with the initial value. This paper describes the characteristics of the new lead-free solder and the results of a study on its solder ball CSP package.     

电子封装无铅化趋势及瓶颈

欧盟通过法令限制电子用品中铅等有害物质的使用,含铅电子产品不久将退出市场,电子封装的无铅化已成必然趋势。焊料的无铅化是无铅封装的关键,目前无铅焊料的研究集中在Sn基焊料和导电胶粘剂两个方向。文中介绍了三种典型无铅焊料体系的不足之处,以及银导电胶研究中的三个难题。另外,关于无铅焊料还没有一个统一的标准。