The Effect of Wetting Gravity Regime on Shear Strength of SAC and Sn-Pb Solder Lap Joints

The failure of solder joints due to imposed stresses in an electronic assembly is governed by shear bond strength. In the present study, the effect of wetting gravity regime on single-lap shear strength of Sn-0.3Ag-0.7Cu and Sn-2.5Ag-0.5Cu solder alloys reflowed between bare copper substrates as well as Ni-coated Cu substrates was investigated. Samples were reflowed for 10 s, T _gz (time corresponding to the end of gravity regime) and 100 s individually and tested for single-lap shear strength. The single-lap shear test was also carried out on eutectic Sn-Pb/Cu- and Sn-Pb/Ni-coated Cu specimens to compare the shear strength values obtained with those of lead-free alloys. The eutectic Sn-Pb showed significantly higher ultimate shear strength on bare Cu substrates when compared to Sn-Ag-Cu alloys. However, SAC alloys reflowed on nickel-coated copper substrate exhibited higher shear strength when compared to eutectic Sn-Pb/Ni-coated Cu specimens. All the substrate/solder/substrate lap joint specimens that were reflowed for the time corresponding to the end of gravity regime exhibited maximum ultimate shear strength.     

Joining of Cu,Ni, and Ti Using Au-Ge-Based High-Temperature Solder Alloys

Au-Ge-based solder alloys are promising alternatives to lead containing solders due to the fact that they offer a combination of interesting properties such as good thermal and electrical conductivity and high corrosion resistance in addition to a relatively low melting temperature (361 °C for eutectic Au-28Ge at.%). By adding a third element to the eutectic Au-28Ge alloy not only the Au content could be reduced but also the melting temperatures could be further decreased. In this study, in addition to the eutectic Au-28Ge (at.%) two ternary alloys were chosen from the Au-Ge-Sb and Au-Ge-Sn system, respectively. The soldering behavior of these alloys in combination with the frequently used metals Cu, Ni, and Ti was investigated. The interface reactions and microstructures of the joints were characterized in detail by SEM and EDX analysis. For the determination of the mechanical properties, shear tests were conducted. Mean shear strength values up to 104 MPa could be achieved.     

Ag<Subscript>3</Subscript>Sn plate formation in the solidification of near-ternary eutectic Sn-Ag-Cu

Near-ternary eutectic Sn-Ag-Cu alloys are leading lead-free candidate solders for various applications. These alloys yield three phases upon solidification: β-Sn,Ag₃Sn, and Cu₆Sn₅. Large, plate-like, pro-eutectic Ag₃Sn structures can grow rapidly within the liquid phase, potentially adversely affecting the mechanical behavior and reducing the fatigue life of solder joints. This article reports on the formation of such plates in Sn-Ag-Cu solder balls and joints and demonstrates how large Ag₃Sn plate formation can be minimized. For more information, contact S.K. Kang, IBM T.J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York 10598; (914) 945-3932; fax (914) 945-2141; e-mail kang@us.ibm.com.     

The influence of temperature on creep behavior of Cu particle enhanced SnPb based composite soldered joints

Creep property of solder alloys is one of the important factors to affect the reliability of soldered joints in SMT(surface mount technology). Particle-enhancement is a way to improve the properties of solder alloys and has caused much more attention than before. Temperatures applied to soldered joints are one of the primary factors of affecting creep properties of particle enhancement composite soldered joints. In this paper single shear lap creep specimens with a 1 mm2 cross-sectional area were fabricated using Cu particle enhancement 63Sn37Pb based composite soldered joints and 63Sn37Pb eutectic soldered joints to examine the influence of temperature on creep behavior of soldered joints. Results indicated that the creep resistance of soldered joints of Cu particle enhancement 63Sn37Pb based composite soldered joint was generally superior to that of the conventional 63Sn37Pb soldered joint. At the same time, creep rupture life of the composite soldered joint was declined with increasing temperature and drop faster than that of the conventional 63Sn37Pb eutectic soldered joint.     

BGA封装器件焊点抗剪强度的试验

采用微焊点强度测试仪研究了Sn-Pb共晶钎料BGA（球栅阵列封装技术）封装器件焊点的抗剪强度，并对不同直径的BGA球焊点的抗剪强度进行了比较。研究结果表明，在相同条件下，BGA球直径越大，抗剪强度越小，共晶钎料BGA球焊点的抗剪强度比锡铅合金钎糕点自身的抗剪强度大。     

Development of high strength Sn-0.7Cu solders with the addition of small amount of Ag and In

Nowadays, a major concern of Sn-Cu based solder alloys is focused on continuously improving the comprehensive properties of solder joints formed between the solders and substrates. In this study, the influence of Ag and/or In doping on the microstructures and tensile properties of eutectic Sn-0.7Cu lead free solder alloy have been investigated. Also, the effects of temperature and strain rate on the mechanical performance of Sn-0.7Cu, Sn-0.7Cu-2Ag, Sn-0.7Cu-2In and Sn-0.7Cu-2Ag-2In solders were investigated. The tensile tests showed that while the ultimate tensile strength (UTS) and yield stress (YS) increased with increasing strain rate, they decreased with increasing temperature, showing strong strain rate and temperature dependence. The results also revealed that with the addition of Ag and In into Sn-0.7Cu, significant improvement in YS (∼255%) and UTS (∼215%) is realized when compared with the other commercially available Sn-0.7 wt. % Cu solder alloys. Furthermore, the Sn-0.7Cu-2Ag-2In solder material developed here also exhibits higher ductility and well-behaved mechanical performance than that of eutectic Sn-0.7Cu commercial solder. Microstructural analysis revealed that the origin of change in mechanical properties is attributed to smaller β-Sn dendrite grain dimensions and formation of new inter-metallic compounds (IMCs) in the ternary and quaternary alloys.     

铝/铜异种材料等离子弧熔钎焊搭接接头工艺分析

采用LHM-200等离子弧焊机和Zn-Al钎料对T2紫铜与LF6防锈铝异种材料进行了等离子弧熔钎焊,通过扫描电镜(SEM)和能谱分析仪(EDS)观察分析其接头显微组织和界面元素组成.结果表明,通过合理设置工艺可以得到较为理想的焊接接头,焊缝表面无裂纹、气孔等现象,搭接接头抗剪强度可达175.5 MPa;控制等离子弧焊工艺可以有效控制钎缝成形,提高接头性能,最佳参数范围为等离子气体的流量0.2,0.75 L/min,焊接电流45~55 A,焊接速度1.41~3.03 cm/s;在铜母材与钎料界面处是Al₂Cu和CuZn₂金属间化合物层;而在铝母材与钎料界面处为Al-Zn共晶组织;焊缝中心的是黑白相间的条纹组织,黑区为富铝区,白区为富锌区.     

Characterization of Solder Joint Reliability Using Cyclic Mechanical Fatigue Testing

This article summarizes the mechanics of two mechanical fatigue methods, cyclic bending fatigue and shear fatigue, in inducing failure in solder joints in package assemblies, and it presents the characteristics of fatigue failures resulting from these methods using example cases of Sn-Pb eutectic and Sn-rich Pb-free solder alloys. Numerical simulation suggests that both testing configurations induce fatigue failure by the crack-opening mode. In the case of bending fatigue, the strain induced by the bending displacement is found to be sensitive to chip geometry, and it induces fatigue cracks mainly at the solder matrix adjacent to the printed circuit board interface. In case of shear fatigue, the failure location is firmly fixed at the solder neck, created by solder mask, where an abrupt change in the solder geometry occurs. Both methods conclude that the Coffin–Manson model is the most appropriate model for the isothermal mechanical fatigue of solder alloys. An analysis of fatigue characteristics using the frame of the Coffin–Manson model produces several insightful results, such as the reason why Pb-free alloys show higher fatigue resistance than Sn-Pb alloys even if they are generally more brittle. Our analysis suggests that it is related to higher work hardening. All these results indicate that mechanical fatigue can be an extremely useful method for fast screening of defective package structures and also in gaining a better understanding of fatigue failure mechanism and prediction of reliability in solder joints.     

电迁移对低银无铅微尺度焊点力学行为的影响

研究了电迁移条件下不同电流密度(0.63~1.0×104 A/cm2)和通电时间(0~48 h)对低银无铅Sn-Ag-Cu微尺度焊点的拉伸力学行为的影响. 结果表明,电迁移导致了低银无铅微尺度焊点的抗拉强度显著降低,并且随着电流密度的增加或通电时间的延长,焊点的抗拉强度均呈下降趋势;同时电迁移还导致焊点的拉伸断裂模式发生明显变化,在经历高电流密度或长时间通电的电迁移后,焊点在服役条件下会发生由韧性断裂向脆性断裂的转变. 此外含银量高的微尺度焊点的抗电迁移性能更强.     

纳米颗粒增强SAC0307锡膏焊点的分析

研究了纳米颗粒添加对低银SAC0307锡膏焊点显微组织和力学性能的影响.结果表明,添加纳米铜颗粒的焊点钎料共晶区中岛状Cu₆Sn₅相尺寸大、且难于弥散分布,添加量超过0.3%时,Cu₆Sn₅相极易在液/气界面聚集、合并和长大,导致钎料流动性变差、锡膏中助焊剂气体难于逸出而形成气孔.而添加0.1~5.0%纳米银颗粒的焊点均无气孔产生,其焊点钎料中的Ag₃Sn相尺寸小易于弥散分布,且β-Sn初晶相细化明显.随纳米银添加量的增加,焊点抗剪强度先增加后降低,0.5%添加量时抗剪强度最大、较相同条件下的SAC0307焊点提高了30.8%.     

通孔元件焊点的抗热疲劳性能预测Ⅰ.焊点抗热疲劳能力的实验研究

针对通孔焊点进行了热冲击的可靠性测试，以非破坏性和破坏性的实验方法，对比分析了波峰焊点和再流焊点的抗热疲劳能力．结果表明，CTE(热膨胀系数)失配是焊点产生裂纹的主要原因，而焊点形态的差异又使得再流焊点内部断裂程度不同于波峰焊点．再流焊点裂纹产生在钎料内部；而波峰焊点由于具有饱满的圆角过渡形态，裂纹产生在镀铜孔与线路板的连接拐角处．裂纹的产生导致了两种焊点强度的降低，对其电性能的影响却甚微。     

Ag—Pb和Ni对元铅钎料焊点形状、微结构及剪切强度的影响

研究了器件端头两种不同的金属化层（Ag-Pd和Ni/Ag-Pd）对Sn-Sb钎料表面粘装焊点的形状、微结构及剪切强度的影响,并与常用的Sn-Pb-Ag钎料焊点进行了比较,结果表明：Sn-Sb/Ag-Pd焊点由于Sn-Sb钎料与Ag-Pd／陶瓷界面;Sn-Sb/Ni/Ag-Pd焊点中Ni有效地阻止了Ag-Pd在钎料中的溶解,焊点形状理想,强度很高;而对于Sn-Pb-Ag钎料、器件金属化层对焊点形状和强度影响不大,剪切测试后,断裂发生在钎料内部。     

电子封装微互连焊点力学行为的尺寸效应

研究了微互连模拟焊点在不同直径(d=200-575μm)和长度(l=75-525 μm)匹配条件下准静态微拉伸的力学行为.研究结果表明,焊点几何尺度因子d/l对焊点内的力学拘束及接头强度有重要影响;d/l增大时导致焊点中力学拘束和应力三轴度的提高,但接头强度并不完全符合Orowan近似公式的预测结果,保持l恒定而增加d时会出现强度变小的尺寸效应.研究结果还表明,无论无铅还是含铅钎料,其焊点拉伸强度与焊点体积(d2l)之间的变化关系符合反比例函数,即σF-Joint=1/Ad2l+B,焊点的强度随焊点体积的减小而显著增大,显示了焊点"越小越强"的"体积"尺寸效应.     

Effect of mechanical properties using different filler metals on wide-clearance activated-diffusion-brazed Ni-based superalloy

The investigation of mechanical properties and failure mechanism of activated-diffusion-brazed (ADB) joints in IN-738 plate were conducted. Joints of this type, which had wide clearance, were formed using the brazing alloys Nicrobraz 150 and DF4B. The microstructural characterization showed that chromium borides with a blocky morphology were present in joints associated with the two brazing alloys. A major difference in matrix phase chemistry was observed, however, for the two brazing alloys, e.g., an Ni-B eutectic phase was observed in Nicrobraz 150, but DF4B exhibited a coarsened gamma prime (γ) phase and an absence of a nickel boride matrix phase. Results of tensile test showed that ADB specimens using DF4B brazing alloy exhibited 95% nominal tensile strength of IN-738 base materials. Fracture cracks in the joint area were initiated and confined to dispersed chromium boride sites. However, tensile test of ADB specimens using Nicrobraz 150 showed poor tensile properties at all testing temperatures, and their fractures were initiated at a brittle nickel boride site and propagated along the weak-bonded interface between the Ni-B eutectic phase and base materials.     

Cu和Sb元素添加对Sn-Bi共晶合金性能的影响

向Sn-Bi共晶合金中同时添加Cu和Sb元素设计额定温度为142℃的易熔合金,并对合金的熔点、相组成、准静态拉伸性能、焊接接头力学性能进行了研究.结果表明,Cu与Sb元素的添加使合金的熔点上升,但是合金的过冷度和熔化潜热下降.添加Cu和Sb元素后,在合金基体内形成了块状的SnSb相和长条状的Cu6Sn5、Cu3Sn相,...     

Residual stresses in welded joints in 1460 aluminium alloy

In order to obtain high-strength aluminium butt joints with corrosion resistance, ultrasonic soldering of A1070 rods was conducted using quasi-melting Sn–xZn (x = 23, 40, 82 mass%) hypereutectic alloy. Ultrasonic vibrations were applied at soldering temperatures ranging 220–300°C through A1070 rods without a solder bath.

The tensile strength of the solder joints with Sn–23Zn or 40Zn alloy were higher than that of the joint soldered with Sn–9Zn eutectic alloy. The joints soldered with Sn–23Zn or 40Zn alloy showed the same strength as A1070 rods which employed the same heat treatment as the ultrasonic soldering process. The thickness of the hypereutectic solder layer in the joints was thicker than that of the Sn–9Zn solder layer because unmelted α-Zn solid solution should have prevented the solder from being pressed out of the joint gap by the applied pressure during soldering. Tensile tests of the joints after immersion in NaCl aqueous solution revealed that the corrosion resistance of the joints soldered with hypereutectic alloy was higher than that of the joint soldered with Sn–9Zn alloy. It is considered that the improvement was achieved by the thick hypereutectic solder layer which should have reduced the notch effect in the joints.     

Dispersion strengthening for dimensional stability in low-melting-point solders

An improved solder structure with an ultrafine grain size of ∼200–500 nm and significantly enhanced mechanical properties has been created by incorporating nanosized, nonreacting, noncoarsening oxide dispersoids into solder alloys. These solders display up to three orders of magnitude reduction in the steady-state creep rate, 4–5 times higher tensile strength at low strain rates, and improved ductility under highstrain-rate deformation. With a dispersion of TiO₂ particles, the Pb-Sn eutectic solder with a low-melting point of 183°C can be made more creep resistant than the Au-20Sn eutectic solder with a much higher melting point of 278°C. This technique can be extended to other solder systems, such as the emerging lead-free solder alloys, and used to achieve enhanced dimensional stability. For more information, contact H. Mavoori, Bell Laboratories, Lucent Technologies, 1A-102 Bell Labs, 600 Mountain Avenue, Murray Hill, New Jersey 07974; e-mail hareesh@lucent.com.     

铋对SAC305−xBi/Cu焊接接头显微组织、热性能、力学性能和界面行为的影响

通过添加1％ 和2％(质量分数)的Bi提高SAC305焊接接头的性能,并研究Bi掺杂对SAC305?xBi/Cu焊接接头显微组织、热性能和力学性能的影响.Bi掺杂通过细化初始β-Sn和共晶相改善焊接接头的显微组织.当Bi含量低于2％ 时,Bi溶解到β-Sn基体中形成固溶体;而当Bi含量等于或高于2％时,β-Sn基体中形...     

Al-Si过共晶钎料的制备及其对核用SiC陶瓷的焊接研究

SiC是核聚变反应堆流道插件及结构材料的优秀候选材料。为了获得大尺寸的SiC部件,通过钎焊方法连接SiC,选择50Al-50Si合金作为钎料,研究50Al-50Si合金钎料的显微组织、力学性能及在真空1100℃×10min条件下对SiC陶瓷的钎焊性能。并在此钎料基体上加入不同含量(2%,6%,10%,14%)的Ti,研究Ti的加入对钎料显微组织性能及SiC陶瓷接头力学性能的影响。结果表明,Al-Si-Ti钎料能完成SiC陶瓷的连接而获得性能优异的接头。在Ti含量增加到6%时,接头剪切强度升高至138.98MPa,随着Ti含量增多,接头剪切强度又下降。     

QFP结构微焊点强度的试验

采用微焊点强度测试仪（STR-1000型）测试了方形扁平式封装器件（QFP）的抗拉强度,并对不同间距、不同钎料成分的QFP和SOP结构焊点进行了比较。研究结果表明,在相同的钎料成分下,焊脚问距越大,所需的抗拉力越大,抗拉强度越高;共晶钎料QFP焊点的抗拉强度比纯铅的抗拉强度低,QFP焊点的结合强度比钎料自身的抗拉强度高。