低银无铅焊料的研制动态

分析了低银无铅焊料(w(Ag)≤1.0％)在成本、抗跌落性能、Ag3Sn化合物的形成等方面与高银焊料相比的优势,综述了低银焊料在应用过程中面临的问题,如高熔点与氧化、热疲劳性能、返修缺陷等,并列举了实例,提出了一些有针对性的解决方案.最后展望了低银无铅焊料的发展趋势.     

低银无铅焊料润湿及可靠性能研究

利用润湿测量法研究了低银无铅焊料SAC0307、SAC0507和SAC0807的润湿性能,发现上述低银焊料润湿性能几乎相同.通过波峰焊接实验鉴定了其溶解铜焊盘性能,发现所做短时间溶铜实验中上述低银焊料的低银焊料的溶铜速度几乎相同.温度循环实验后检测了金属间化合物生长及裂纹发生情况,确定低银无铅焊料SAC0807裂纹萌生率最低.所作实验研究中皆采用共晶锡银焊料SAC305作为参照焊料.     

微量Co对第二代低银SAC焊料合金改性机理研究

目前电子制造业界把低成本的低Ag无铅焊料合金定义为第二代无铅焊料合金。在目前已公开的第二代无铅低Ag焊料合金类型中,又以掺入微量Co改性的应用性能和可靠性表现最优秀而受到了关注。重点对该类型焊料合金掺Co改性的机理展开了研究试验。在研究试验结论的基础上,分析了其推广应用的良好前景。     

低银系无铅焊料

概述了低银系无铅焊料的开发和特性。     

无铅焊料的新发展

传统焊接技术使用锡铅焊料,对环境造成严重伤害。该文从环保角度出发,阐述了应用无铅焊料的必然性,并介绍了无铅焊料近几年的发展,指出现阶段无铅焊料离市场要求还有一定差距。     

无铅焊料的开发与应用

工业垃圾对环境的污染已成公害，一些国家和地区已明确提出禁止和削减使用有害物质，包括含铅焊料。本介绍对环保有利的无铅焊料，重点说明无铅焊料的技术现状和有效的使用方法及再利用问题等。     

无铅焊料的新发展

传统焊接技术使用锡铅焊料,对环境造成严重伤害。文章从环保角度出发,阐述了应用无铅焊料的必然性,并介绍了无铅焊料近几年的发展,指出现阶段无铅焊料离市场要求还有一定差距, 需进一步加强研究与开发。     

对无铅焊料影响环境的评价

通过分析与计算无铅焊料工艺中能源消耗和再利用过程的能量损失，以及毒性释放程度和节能办法，综合评价无铅焊料对环境的影响。     

纳米无铅焊料的研究进展

电子封装互连过程中,无铅锡基焊料是常用的连接材料。然而,由于其较高的熔点(210~240℃),在电子器件连接过程中需施加较高的回流温度,这不仅增加了电子组装过程中的能耗,也大大降低了器件的可靠性。纳米无铅焊料具有热力学尺寸效应,其熔点较块体材料有大幅度的降低,从而受到了越来越广泛的关注。综述了近年来国内外纳米无铅焊料的发展动态,介绍了常用的纳米无铅焊料的制备方法及影响纳米颗粒尺寸的因素,总结了纳米无铅焊料在应用和存放过程中所产生的问题,同时也对纳米无铅焊料未来产业化的实现提出了建议。     

Effect of microelements addition on the interfacial reaction between Sn-Ag-Cu solders and the Cu substrate

Three kinds of Sn-Ag-based lead-free solders, Sn-3.5Ag-0.7Cu, Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge, and Sn-3.5Ag-0.07Ni (in wt.%), were selected to explore the effect of microelements (Ni and Ge) on the interfacial reaction between the solder and the Cu substrate. The thickness of the interfacial intermetallics formed with the Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge and Sn-3.5Ag-0.07Ni solders is several times that of the Sn-3.5Ag-0.7Cu solder. The added microelements converted the feature of interfacial intermetallics from pebble shape to worm shape. However, the results of x-ray diffraction (XRD) analysis suggest that the interfacial intermetallics formed with both solders have the same crystal structure. The results of energy dispersive spectroscopy (EDS) analysis show that the major interfacial intermetallic formed with the Sn-3.5Ag-0.7Cu solder is Cu₆Sn₅, while it is (Cu_x,Ni_1−x)₆Sn₅ with Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge. Ni influences the interfacial intermetallics and plays the influential role on the difference of interfacial reaction rate between liquid solder and solid Cu and the morphology of interfacial intermetallics. Additionally, the growth kinetics of the interfacial intermetallic compounds (IMCs) formed in the systems of Cu/Sn-3.5Ag-0.7Cu and Cu/Sn-3.5Ag-0.07Ni at high-temperature storage was also explored.     

微量Ce对SnAgCu焊料与铜基界面IMC的影响

配制了w(Ce)为0.1%和不加Ce的两种Sn-3.5Ag-0.7Cu焊料。在443K恒温时效,研究Ce对焊料与铜基板界面金属间化合物(IMC)的形成与生长行为的影响。结果发现,焊点最初形成的界面IMC为Cu6Sn5,时效5d后,两种焊料界面均发现有Cu3Sn形成。随着时效时间的增加,界面化合物的厚度也不断增加。焊料中添加w为0.1%的Ce后,能抑制等温时效过程中界面IMC的形成与生长,生长速率降低近1/2。并且,界面IMC的形成与生长均由扩散机制控制。     

Effects of Co addition in eutectic Sn-3.5Ag solder on shear strength and microstructural development

In this study, the approach of composite solder using eutectic Sn-3.5Ag solder and Co was tried. Co particles and Sn-3.5Ag solder paste were mechanically mixed at Co weight fractions from 0.1% to 2.0%. For the Co-mixed Sn-3.5Ag solder pastes, their melting temperatures and spreading areas were measured. The solder pastes were stencil printed on test substrates and reflowed to form solder bumps. Ball shear test was performed to examine shear strength of Co-reinforced Sn-3.5Ag solder bumps. As a result, Co addition up to 2 wt.% did not alter the melting temperature under heating but reduced undercooling. The maximum shear strength of Co-reinforced Sn-3.5Ag solder bumps increased by 28% compared to normal ones. The increase in shear strength can be attributed to the (Cu,Co)₃Sn₂ intermetallic compounds.     

Effect of soldering and aging time on interfacial microstructure and growth of intermetallic compounds between Sn-3.5Ag solder alloy and Cu substrate

The formation and the growth of the intermetallic compound (IMC, hereafter) at the interface between the Sn-3.5Ag (numbers are all in wt.% unless otherwise specified) solder alloy and the Cu substrate were investigated. Solder joints were prepared by changing the soldering time at 250°C from 30 sec to 10 h and the morphological change of IMCs with soldering time was observed. It resulted from the competition between the growth of IMC and the dissolution of Cu from the substrate and IMCs. They were further aged at 130°C up to 800 h. During aging, the columnar morphology of IMCs changed to a more planar type while the scallop morphology remained unchanged. It was observed that the growth behavior of IMCs was closely related with the initial soldering condition.     

基板稀土微合金化对Sn3Ag0.5Cu/Cu钎焊界面反应的影响

研究了在Cu基板中加入质量分数1%的稀土元素Ce、Er后,与Sn3Ag0.5Cu(SAC305)无铅钎料进行钎焊并时效处理后的界面反应及其化合物(IMC)生长行为。结果表明:钎焊完成后,在SAC305/Cu钎焊界面只观察到Cu_6Sn_5,而SAC305/Cu-1Ce及SAC305/Cu-1Er界面还有Cu_3Sn形成;在时效处理过程中,纯Cu基板上的金属间化合物生长速率最快,Cu-1Ce基板次之,Cu-1Er基板最慢,且形成的IMC厚度也是依次递减;加入质量分数1%的Ce、Er元素对IMC生长均有抑制作用,且Er的抑制作用较Ce强。     

Effect of Cr additions on interfacial reaction between the Sn-Zn-Bi solder and Cu/electroplated Ni substrates

Intermetallic compounds (IMCs) growth on the Sn-8Zn-3Bi (-Cr) solder joints with Cu and electroplated Ni substrates was investigated after aging at 150 °C. It was found that the IMCs were the Cu₅Zn₈ and Ni₅Zn₂₁ at the solder/Cu and solder/Ni interface, respectively. The IMCs growth rate at the Sn-8Zn-3Bi-Cr/Cu and Ni interface was slower than that at Sn-8Zn-3Bi/Cu interface (about 1/2 times) and Sn-8Zn-3Bi/Ni interface (about 1/4 times) during aging. The reason may be that Cr reacts with Zn and forms the Sn-Zn-Cr phase which block the diffusion of Zn atom to the interface and slow down the IMCs growth rate.     

Interfacial reaction between Sn-0.7Cu (-Ni) solder and Cu substrate

The interfacial reaction between Sn-0.7mass%Cu-(Ni) solders and a Cu substrate was investigated to reveal the effect of the addition of Ni to Sn-Cu solder on the formation of intermetallic compounds (IMCs). Sn-0.7Cu-xNi solders (x=0, 0.05, 0.1, 0.2 mass%) were prepared. For the reflow process, specimens were heated in a radiation furnace at 523 K for 60 sec, 300 sec, and 720 sec to estimate the interfacial reaction between the molten solder and Cu substrate. Then, for the aging process, some specimens were heat-treated in an oil bath at 423 K for 168 h and 504 h. The cross sections of soldered specimens were observed to measure the dissolution thickness of the Cu substrate and the thickness of the IMC and to investigate the microstructures of IMC. The results showed that, just after the reflow process, the dissolution thickness of the Cu substrate increased with the increase of Ni content in the Sn-0.7Cu-xNi solder and the thickness of the IMC between the solder and Cu substrate was the minimum in the Sn-0.7Cu-0.05Ni solder. After the aging process, the IMC grew with the increase of aging time. In the case of 0.05% Ni, the IMC thickness was the thinnest regardless of aging time. It is clear that 0.05% Ni addition to Sn-0.7Cu solder very effectively inhibits the formation and growth of the IMC between solder and Cu substrate. Electron probe microanalysis of the IMC showed that the IMC layer in the Sn-0.7Cu-Ni solder contained Ni, and the IMC was expressed as (Cu_1−y ,Ni _y )₆Sn₅.     

Reliability investigation and interfacial reaction of ball-grid-array packages using the lead-free Sn-Cu solder

The interfacial reactions between two Sn-Cu (Sn-0.7Cu and Sn-3Cu, wt.%) ball-grid-array (BGA) solders and the Au/Ni/Cu substrate by solid-state isothermal aging were examined at temperatures between 70°C and 170°C for 0 to 100 days. For the Sn-0.7Cu solder, a (Cu,Ni)₆Sn₅ layer was observed in the samples aged at 70–150°C. After isothermal aging at 170°C for 50 days, the solder/Ni interface exhibited a duplex structure of (Cu,Ni)₆Sn₅ and (Ni,Cu)₃Sn₄. For the Sn-3Cu solder, only the (Cu,Ni)₆Sn₅ layer was formed in all aged samples. Compared to these two Sn-Cu solders, the Cu content in the (Cu,Ni)₆Sn₅ layer formed at the interface increased with the Cu concentration in the Sn-xCu solders. And, the shear strength was measured to evaluate the effect of the interfacial reactions on the mechanical reliability as a function of aging conditions. The shear strength significantly decreased after aging for 1 day and then remained nearly unchanged by further prolonged aging. In all the samples, the fracture always occurred in the bulk solder. Also, we studied the electrical property of Cu/Sn-3Cu/Cu BGA packages with the number of reflows. The electrical resistivity increased with the number of reflows because of an increase of intermetallic compound (IMC) thickness.     

Effects of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys

The materials used in the present research are pure Sn metal and Sn-0.5% Cu, Sn-3.5%Ag, Sn-0.3%Sb, and Sn-3.5%Ag-0.5%Cu alloys. Effects of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys have been investigated. Creep tests are performed at the stress and temperature range of 3 to 12 MPa and 378 to 403 K, respectively. A 3.5% addition of Ag had the largest contribution to the creep-rupture strength of Sn metal among the single addition of 0.5%Cu, 3.5%Ag, and 0.3%Sb. The combined addition of 3.5%Ag and 0.5%Cu makes the largest creep-rupture strength. The effects of these elements on the microstructure of the lead-free alloys are also investigated with optical microscope (OM) and transmission electron microscope (TEM) observations.     

微量Ag、Bi、Ni对无铅微焊点固-液界面扩散的影响

为了获得微量元素Ag、Bi、Ni对无铅微焊点固-液界面扩散行为的影响规律,以低银无铅微焊点Cu/SAC0705+Bi+Ni/Cu为主要研究对象,并与Cu/SAC0705/Cu及高银钎料Cu/SAC305/Cu进行对比。研究了三种成分焊点固-液扩散后界面IMC的生长演变行为,并分析了Ag、Bi、Ni对微焊点固-液扩散的影响。研究结果表明:钎料中微量元素Ag、Bi、Ni添加可细化界面IMC晶粒,对提高界面强度有利。长时间的固-液时效过程中,界面IMC的生长速率主要取决于界面IMC的晶粒尺寸。Cu/SAC0705+Bi+Ni/Cu焊点界面IMC晶粒尺寸最小,界面IMC生长速率最大,为11.74μm/h。Cu/SAC0705/Cu焊点界面IMC晶粒尺寸最大,界面IMC生长速率最慢,其数值为1.24μm/h。