电子产品实施无铅化是一个系统工程

从六个方面内容进行了评述,并强调了电子产品实施无铅化是一个系统工程。企图从电子产品实施无铅化的提出、无铅化焊料的基本特性、无铅化焊料焊接时的特点与要求等出发,从而论述电子产品实施无铅化对电子元器(组)件、CCL基板材料、PCB基板的主要要求以及相关的测试与标准的制定等,其目的是使读者有一个较全面的了解,以利于电子产品(包含原材料、元器件、PCB、组装等)制造者、特别是相关的工程技术人员,从整体的关联或系统工程上来理解、研究和解决电子产品无铅化问题,使电子产品能顺利而迅速地从有铅化(锡-铅体系)时代过渡到无铅化(目前,最佳体系为锡-银-铜系列)时代。     

波峰焊接工艺技术的研究

作为一种传统焊接技术,目前波峰焊依然在电子制造领域发挥着积极作用。本文介绍了波峰焊接技术的原理,并分别从焊接前的质量控制、生产工艺材料及工艺参数这三个方面探讨了提高波峰焊质量的有效方法。     

Plastic constraint of large aspect ratio solder joints

The aspect ratio (joint area/joint thickness) of thin (0.001-0.006 in.) surface mount solder (60S-40Pb) joints plays an important role in determining the mechanical properties and fracture behavior of the joints. This study demon-strates that plastic constraint of a large aspect ratio 60Sn-40Pb solder joint can develop triaxial (hydrostatic) stresses several times greater than the average tensile strength of the bulk solder material. A four to sixfold increase in average joint stress and up to a tenfold increase in peak stress was measured on joints with aspect ratios ranging from 400 to 1000. Although a direct relationship of the aspect ratio to the average tensile stress is shown, as the Friction Hill model predicts, the observed stress increase is not nearly as high but proportional to the classical prediction. This is attributed to the existence of internal defects (oxide particles and micro-voids) and transverse grain boundaries which fail producing internal free surfaces. Thus, the actual aspect ratio is thickness/d², where d equals the distance between internal surfaces. The fracture of these constrained joints was brittle, with the separation occurring between a tin-rich copper tin intermetallic at the interface and the solder matrix. Voids within the solder joint are shown to relieve the plastic constraint and lower the average tensile stress of the joint. The Friction Hill model may play an important role in explaining the small percentage of atypical solder joint failures which sometimes occur on electronic assemblies. In particular, the sudden failure of a thin joint in a strain controlled environment may be attributed to the development of a large hydrostatic stress component. Therefore, a flaw free, plastically constrained joint which develops a high stress state will be a high risk candidate for failure.     

SnAgCu系无铅焊锡粉末特性的实验研究

实验研究了导液管内径对SnAgCu系无铅焊锡雾化粉末有效雾化率及粒度分布的影响。结果表明：在一定雾化条件下，导液管内径为3mm，雾化粉末具有较高的有效雾化率、粒度分布及最佳离散度；随着导液管内径的减小，粉末明显细化，有效雾化率略有增加，但粒度分布变差；随着导液管内径的增大，粉末有效雾化率急剧降低，粒度分布变差。     

On the advantages of using a hypoeutectic Sn-Zn as lead-free solder material

Hypoeutectic Sn-Zn may be a better choice than the eutectic Sn-9Zn as a lead-free solder. We checked the non-equilibrium melting behaviors of a series of Sn-Zn alloys (2.5-9 wt.% Zn) by differential thermal analysis, and found that at a heating rate of 5 °C/min, Sn-6.5Zn behaves the same way as the eutectic Sn-9Zn in melting. Dipping and spreading tests were carried out to characterize the wettability of Sn-Zn alloys on Cu. Both tests indicated that Sn-6.5Zn has significantly better wettability to Cu than Sn-9Zn does. The reaction layers formed during the spreading tests were examined. For all samples with 2.5-9 wt.% Zn, two reaction layers are formed at the interface, a thick and flat Cu₅Zn₈ layer adjacent to Cu and a thin and irregular Cu-Zn-Sn layer adjacent to the alloy. The total thickness of the reaction layers between the alloy and Cu was found to remarkably decrease with decrease of the Zn concentration.     

废退锡液处理方法进展

目前,废退锡液的处理方法有中和法、化学沉淀法、电解法,或用来制备三水合锡酸钡。而利用扩散渗析-离子膜电沉积组合工艺综合回收废退锡液中的硝酸、金属铜和锡是一种新型的处理方法。     

Effect of Homogenization on the Indentation Creep of Cast Lead-Free Sn-5%Sb Solder Alloy

Creep behavior of cast lead-free Sn-5%Sb solder in unhomogenized and homogenized conditions was investigated by long time Vickers indentation testing under a constant load of 15 N and at temperatures in the range 321–405 K. Based on the steady-state power law creep relationship, the stress exponents were found for both conditions of the material. The creep behavior in the unhomogenized condition can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring around 11.7 × 10⁻⁴ < (H _V /E) < 18 × 10⁻⁴. The low stress regime activation energy of 54.2 kJ mol⁻¹, which is close to 61.2 kJ mol⁻¹ for dislocation pipe diffusion in the Sn, and stress exponents in the range 5.0–3.5 suggest that the operative creep mechanism is dislocation viscous glide. This behavior is in contrast to the high stress regime in which the average values of n = 11.5 and Q = 112.1 kJ mol⁻¹ imply that dislocation creep is the dominant deformation mechanism. Homogenization of the cast material resulted in a rather coarse recrystallized microstructure with stress exponents in the range 12.5–5.7 and activation energy of 64.0 kJ mol⁻¹ over the whole ranges of temperature and stress studied, which are indicative of a dislocation creep mechanism.     

Fatigue crack initiation and growth in solder alloys

In modern electronic packaging, especially surface mount technology (SMT), thermal strain is usually induced between components during processing, and in service, by a mismatch in the thermal expansion coefficients. Since solder has a low melting temperature and is softer than other components in electronic packaging, most of the cyclic stresses and strains take place in the solder. Fatigue crack initiation and fatigue crack propagation are likely to occur in the solder even when the cyclic stress is below the yield stress. It is an objective of this research to study the behaviour of fatigue crack initiation and propagation in both lead‐containing solder (63Sn‐37Pb), and lead‐free solders (Sn‐3.5Ag). The effect of alloying (Cu and Bi addition), frequency, tensile hold time and temperature on low cycle fatigue (LCF) behaviour of the solders is discussed. Mechanisms of LCF crack initiation and propagation are proposed and LCF life prediction, based on the various models, is carried out.     

Re‐calibration of Engelmaier's Model for Leadless,Lead‐free Solder Attachments

In this paper, the solder attachment fatigue model created by Werner Engelmaier is re‐calibrated in order to make it applicable in conjunction with leadless, lead‐free solder attachments. Sn3.8Ag0.7Cu solder attached ball‐grid‐array components are addressed to three thermal cycling test profiles. Based on the results, both physical and statistical parameters are obtained and compared with the values relevant to tin–lead solder assemblies. The validity of the statistical distribution selection (two‐parameter Weibull) is studied. Acceleration factors correlating different test profiles are obtained, and they are found to be only weakly dependent on the test vehicle type. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of Ag addition on the corrosion properties of Sn‐based solder alloys

Corrosion properties of three different Sn‐Ag lead free solder alloys have been investigated in 0.3 wt% Na₂SO₄ solution as corrosive environment. As cast solder alloy was analyzed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Volume fractions of the Ag₃Sn in the solders were determined by image analysis technique. Pitting potential and corrosion potential for the alloys were determined by potentiodynamic tests. Electrochemical impedance spectroscopy (EIS) was carried out to measure the film and charge transfer resistance. Alloys with lower Ag content have been found as better corrosion resistance material.