无铅焊料的选择与对策（未完待续）

通过大量的数据信息分析了各研究机构在无铅焊料方面的研究成果，在目前流行使用的无铅焊料的基础上，进一步研究并比较了其中的Sn-Cu系列与具有专利限制的SnAgCu系列焊料在消费类电子产品组装的波峰焊工艺中使用的可靠性，同时研究并比较Sn-Ag系列焊料与SnAgCu系列焊料在回流焊工艺使用的情况。结果表明，Sn-Cu共晶焊料在消费类电子产品组装的波峰焊工艺中完全可以取代Sn-Ag-Cu系列焊料，同时满足使用要求；而同样技术成熟的Sn-Ag共晶焊料也完全可以取代SnAgCu系列焊料在回流焊工艺使用，焊点的可靠性与成本可以媲美SnAgCu焊料。而且该二元合金在使用维护以及回收利用方面具有相当的优势。     

In situ investigation of SnAgCu solder alloy microstructure

In situ X-ray diffraction experiments, using synchrotron radiation, were employed to analyze microstructure evolution of the 96.5Sn3Ag0.5Cu (wt.%)—SAC305 lead-free solder alloy during heating (30-240 °C), isothermal dwell (240 °C) and cooling (240-30 °C). The special emphasis was placed on the study of the melting and solidification processes, explaining formation, distribution and the order of crystallization of the crystal phases (β-Sn, intermetallic compounds) in the solder alloy. Furthermore, thermal expansion behaviour of the main constituent phase β-Sn was analyzed prior to melting and after the consequent solidification.     

对于无铅化的理解和PCB相关考虑

从无铅化的定义、测定及相关典型无铅焊料的特性和焊接的要求,阐述其对PCB板的影响和克服方法,并提出要求用系统的观点来实现整机产品的可靠性---PCB板的基材材料、无铅焊料等材料选型,加工过程以及评价方法。     

Effects of limited cu supply on soldering reactions between SnAgCu and Ni

The volume difference between the various types of solder joints in electronic devices can be enormous. For example, the volume difference between a 760-μm ball grid array solder joint and a 75-μm flip-chip solder joint is as high as 1000 times. Such a big difference in volume produces a pronounced solder volume effect. This volume effect on the soldering reactions between the Sn3AgxCu (x=0.4, 0.5, or 0.6 wt.%) solders and Ni was investigated. Three different sizes of solder spheres (300, 500, and 760 μm in diameter) were soldered onto Ni soldering pads. Both the Cu concentration and the solder volume had a strong effect on the type of the reaction products formed. In addition, (Cu,Ni)₆Sn₅ massively spalled from the interface under certain conditions, including smaller joints and those with lower Cu concentration. We attributed the massive spalling of (Cu,Ni)₆Sn₅ to the decrease of the available Cu in the solders. The results of this study suggest that Cu-rich SnAgCu solders can be used to prevent this massive spalling.     

焊膏SnAgCu焊锡微粉在有机酸溶液中的腐蚀与防护

电子产品多用焊膏焊接,其黏度稳定性常受某些酸性物质的腐蚀而下降,进而导致可焊性下降.研究了SnAgCu无铅焊锡微粉在0.1 mol/L 乙二酸水溶液和0.1 mol/L 乙二酸乙醇溶液中的常温腐蚀行为,以及添加16 mmol/L 缓蚀剂苯并三唑(BTA)对其腐蚀行为的影响,并对微粉的腐蚀与缓蚀机制进行了分析.结果表明:焊锡微粉在乙二酸水溶液中的腐蚀程度比在同浓度的乙二酸乙醇溶液中更为严重,且在乙二酸水溶液中微粉表面出现大量均匀分布的腐蚀沟槽,而在乙二酸乙醇溶液中只有少量点蚀痕迹;微粉表面的富锡相易被腐蚀;焊膏中加入BTA对焊锡微粉有良好的缓蚀保护作用,由此使焊膏黏度的稳定性得到保证.     

回流时间对焊点质量的影响

讨论TSnAgCu305焊料和cu焊盘在不同回流时间下形成的金属间化合物的厚度和形貌,以及焊点内部的组织结构.通过剪切试验测得不同回流时间下得到的焊点强度.试验结果表明:回流时间较短时,IMC层的厚度随着时间的增大快速增长,随着时间推移最后IMC的厚度在5 μm左右趋于稳定.焊点内部的组织形貌随着时间变化由等轴晶到枝状...     

片式元件与基板间隙对SnAgCu系无铅焊点的应力分析

文章采用非线性有限元方法,重点讨论了片式元件与基板的间隙对Sn-2.5Ag-0.7Cu无铅钎料焊点的应力应变分析。研究表明,在实际中适当增大间隙高度有利于改善焊点的应力分布情况。当间隙高度为0.1mm~0.2mm时,元件底部拐角处、焊根的顶部和底部以及焊趾顶部的应力值普遍较低,应力分布得到了较好的改善,这一结果对于焊点的优化及设计具有指导意义。     

SnAgCu系钎料的合金组织和力学性能

研究了Cu含量对SnAgCu系钎料合金显微组织及其与化学镀Ni基板钎焊接头力学性能的影响。结果表明:高Cu含量SnAgCu合金会产生较多的(CuxNi1-x)6Sn5金属间化合物,从而减少镀Ni层的消耗,进一步提高钎焊接头的剪切强度。与Sn-3.0Ag-0.3Cu相比,Sn-3.0Ag-1.0Cu钎焊接头剪切强度提高了6.78%。经过150℃时效1000h后,界面Ni3(P,Sn)层的增长率从Sn-3.0Ag-0.3Cu合金的约66%降低到Sn-3.0Ag-1.0Cu合金的约40%。     

Interaction of intermetallic compound formation in Cu/SnAgCu/NiAu sandwich solder joints

The interaction between Cu/solder interface and solder/Ni interface at a Cu/SnAgCu/NiAu sandwich solder joint with various surface finishes and solder heights was investigated. The interfacial microstructure and composition of intermetallic compounds (IMCs) were characterized by a scanning electron microscope (SEM) equipped with energy-dispersive x-ray spectroscopy (EDX). The phase structure of IMC was identified by x-ray diffraction (XRD). It is found that ternary (Cu,Ni)₆Sn₅ IMCs form at both interfaces. The composition, thickness, and morphology of the ternary IMCs depend not only on the interface itself, but also on the opposite interface. That is to say, strong coupling effects exist between the two interfaces. Lattice parameters of (Cu,Ni)₆Sn₅ shrink with increasing Ni content, in agreement with Vegard’s law. The mechanism of ternary IMC formation and interface coupling effects are discussed in this paper.     

Controlling intermetallic compound growth in SnAgCu/Ni-P solder joints by nanosized Cu6Sn5 addition

Nanosized Cu₆Sn₅ dispersoids were incorporated into Sn and Ag powders and milled together to form Sn-3Ag-0.5Cu composite solders by a mechanical alloying process. The aim of this study was to investigate the interfacial reaction between SnAgCu composite solder and electroless Ni-P/Cu UBM after heating for 15 min. at 240°C. The growth of the IMCs formed at the composite solder/EN interface was retarded as compared to the commercial Sn3Ag0.5Cu solder joints. With the aid of the elemental distribution by x-ray color mapping in electron probe microanalysis (EPMA), it was revealed that the SnAgCu composite solder exhibited a refined structure. It is proposed that the Cu₆Sn₅ additives were pinned on the grain boundary of Sn after heat treatment, which thus retarded the movement of Cu toward the solder/EN interface to form interfacial compounds. In addition, wetting is an essential prerequisite for soldering to ensure good bonding between solder and substrate. It was demonstrated that the contact angles of composite solder paste was <25°, and good wettability was thus assured.