SnAgCuCe/Er无铅钎料表面锡晶须的形态及特性

在Sn-3.8Ag-0.7Cu无铅钎料中添加1%(质量分数)的稀土铈或铒会在其内部形成尺寸较大的稀土相CeSn3和ErSn3.暴露于空气中的CeSn<,3和ErSn3将发生氧化,同时在其表面会出现锡晶须的快速生长现象.文中研究了稀土相CeSn3与ErSn3表面锡晶须的生长行为.结果表明,在CeSn3与ErSn3表面形成了大量的传统圆柱状锡晶须,同时,在其表面还出现了一些特殊形态的锡晶须,如带纹状的锡晶须、扭曲状的锡晶须、变截面的锡晶须、锡晶须的分枝、合并及搭接现象等.     

稀土相RE-Sn表面Sn晶须的生长规律

将稀土相CeSn3、LaSn3、(La0.4Ce0.6)Sn3及ErSn3暴露于空气中,研究在时效处理过程中其表面Sn晶须的生长规律。结果表明:室温时效过程中,在稀土相的表面均出现了Sn晶须的生长现象,且稀土相LaSn3的表面倾向于形成包状和扭结状的Sn晶须,稀土相CeSn3和(La0.4Ce0.6)Sn3的表面倾向于形成针状和扭结状的Sn晶须,而稀土相ErSn3的表面倾向于形成大尺寸的杆状和棒状Sn晶须。150℃时效过程中,稀土相CeSn3、LaSn3和(La0.4Ce0.6)Sn3的表面没有出现Sn晶须的生长现象,而稀土相ErSn3的表面出现了大量的小尺寸线状Sn晶须。综上所述,稀土相的氧化倾向决定了其表面Sn晶须的生长规律。     

Sn-3.8Ag-0.7Cu-1.0Er无铅钎料中Sn晶须变截面生长现象

在Sn-3.8Ag-0.7Cu无铅钎料中添加质量分数为1%的稀土Er会在其内部形成尺寸较大的稀土相ErSna.暴露于空气中ErSn3将发生氧化,同时在其表面会出现Sn晶须的快速生长现象.室温时效条件下,在氧化的ErSn3表面会生长出少量的杆状Sn晶须,Sn晶须的截面尺寸会发生连续变化;高温时效条件下,在氧化的ErSn3表面会生长出大量的针状Sn晶须,Sn晶须的截面尺寸会发生阶梯式变化.提出了ErSn3氧化过程中体积应变能是一个变量的模型,可以解释观察到的现象.     

稀土Ce加速Sn晶须生长的研究

稀土被认为是金属中的"维他命",在钎料中添加微量的稀土Ce可以显著地改善钎料合金的综合性能.然而,当钎料中添加过量的稀土时,将会发现Sn晶须的快速生长现象.结果表明,如果将Sn3.8Ag0.7Cu1.0Ce钎料内部的稀土相暴露于空气中,稀土相将发生氧化而产生体积膨胀,钎料基体对体积膨胀的抑制作用将使稀土相内部产生巨大的压应力从而加速Sn晶须的生长.     

Sn晶须形态的研究

添加微量稀土可以有效地改善钎料的综合性能.然而当钎料中添加过量的稀土时,钎料内部会形成体积较大的稀土相.如果将稀土相暴露于空气中,其将发生氧化,氧化产生的压应力将加速稀土相表面Sn晶须的生长.研究了CeSn3与YSn3与ErSr3稀土相表面Sn晶须的生长情况.研究结果表明,稀土相表面出现了Sn晶须的快速生长现象,且试验中发现了一些特殊形态的Sn晶须.     

Sn晶须的形态机制

将稀土相CeSn3与ErSn3暴露于空气中,研究在时效处理过程中稀土相表面Sn晶须的形态机制.结果表明:时效过程中在稀土相表面出现的绝大多数Sn晶须均是具有恒定截面的规则Sn晶须;同时也发现少数特殊形态的不规则Sn晶须,如卷曲状的Sn晶须、变截面的Sn晶须、分枝及搭接的Sn晶须等;由于稀土相的氧化所产生的体积膨胀提供Sn晶须生长的驱动力,而稀土相的氧化极不均匀,因此,认为Sn晶须在生长过程中其根部受力状态的改变是导致特殊形态Sn晶须出现的根本原因.     

稀土相ErSn3表面Sn晶须的快速生长

将稀土相ErSn3分别暴露于空气与真空环境中,研究在时效处理过程中ErSn3表面Sn晶须的生长情况。结果表明：大气环境中,在稀土相ErSn3的表面出现了Sn晶须的生长现象,且室温条件下Sn晶须的分布不均,生长速度慢,而高温条件下Sn晶须的分布均匀,生长速度快;真空环境中,在稀土相ErSn3的表面未出现Sn晶须的生长现象。由于在大气环境中稀土相ErSn3发生了氧化,氧原子向ErSn3晶格内部的扩散引起的体积膨胀提供了Sn晶须生长的驱动力,因此,大气环境中在ErSn3的表面会出现Sn晶须的生长现象,而真空环境中则不会出现     

SnAgCuEr系稀土无铅钎料的显微组织

系统研究了添加微量稀土Er对Sn3.8Ag0.7Cu无铅钎料合金显微组织和性能的影响.试验发现,微量Er的添加,使Sn3.8Ag0.7Cu钎料合金的熔化温度稍有降低,铺展面积有所增加,抗剪强度有所提高.通过显微组织观察,加Er后网状共晶物体积百分比增大,初晶金属间化合物(IMC)的尺寸变小.微量Er抑制了时效过程钎料与铜基体界面IMC层(IML)的增厚,时效400 h后差别更明显,有利于提高钎料接头的可靠性.指出含微量稀土的SnAgCuEr合金是性能优良的无铅钎料合金.     

CROSS SECTION CHANGING GROWTH PHENOMENON OF Sn WHISKER IN Sn–3.8Ag–0.7Cu–1.0Er LEAD–FREE SOLDER

在Sn--3.8Ag--0.7Cu无铅钎料中添加质量分数为1%的稀土Er会在其内部形成尺寸较大的稀土相ErSn₃. 暴露于空气中ErSn₃将发生氧化, 同时在其表面会出现Sn晶须的快速生长现象. 室温时效条件下, 在氧化的ErSn₃表面会生长出少量的杆状Sn晶须, Sn晶须的截面尺寸会发生连续变化; 高温时效条件下, 在氧化的ErSn₃表面会生长出大量的针状Sn晶须, Sn晶须的截面尺寸会发生阶梯式变化. 提出了ErSn₃氧化过程中体积应变能是一个变量的模型, 可以解释观察到的现象.     

等温时效中稀土Er对Sn-3.8Ag-0.7Cu无铅钎料显微组织演化的影响

系统研究了等温时效中添加微量稀土Er对Sn-3.8Ag-0.7Cu钎料合金显微组织演化规律的影响.结果表明,Er对Sn-3.8Ag-0.7Cu钎料显微组织及等温时效过程中显微组织的演化产生了重要影响.在钎焊过程中,Er有效地细化了钎料组织,改变了钎料内部Cu-Sn金属间化合物的形态、尺寸及分布情况.在等温时效过程中,钎料内部生成的ErSn3金属间化合物为组织的再结晶过程提供了大量的形核质点,有效避免了再结晶组织的粗化及裂纹的产生和扩展.     

Nd对Sn-3.8Ag-0.7Cu/Cu焊点高温可靠性的影响

通过研究150 ℃时效条件下Sn-3.8Ag-0.7Cu-0.05Nd/Cu焊点剪切力变化和界面微观结构演变,探讨稀土元素Nd对焊点高温可靠性的影响及其影响机制. 结果表明,不同时效时间后Sn-3.8Ag-0.7Cu-0.05Nd/Cu焊点剪切力明显高于Sn-3.8Ag-0.7Cu/Cu焊点,且时效过程中Sn-3.8Ag-0.7Cu-0.05Nd/Cu焊点剪切力的下降速率低于原焊点. 这是由于0.05%Nd可将界面原子扩散系数由1.88 × 10?10 cm2/h降低至1.10 × 10?10 cm2/h,即通过抑制界面金属间化合物的粗化来提高焊点的高温可靠性.     

The Inhibition of Tin Whiskers on the Surface of Sn-8Zn-3Bi-0.5Ce Solders

Through the refinement of the (Ce, Zn)Sn₃ intermetallic phase, the formation of tin whiskers, previously observed on the surface of a Sn-3Ag-0.5Cu-0.5Ce solder, was prevented in a Sn-9Zn-0.5Ce alloy. However, whisker growth can still occur on the surface of Sn-8Zn-3Bi-0.5Ce solder after air storage at room temperature and at 150 °C due to the formation of large (Ce, Zn)Sn₃ intermetallic clusters. Further experiments showed that decreasing the Bi-content in this Sn-8Zn-0.5Ce alloy to 1 and 2 wt.% can recover the beneficial effects of Zn additions on the refinement of the (Ce, Zn)Sn₃ phase and obviously reduce the appearance of tin whiskers. In addition, alloying the Sn-8Zn-3Bi-0.5Ce solder with 0.5 wt.% Ge, which increases the oxidation resistance of the (Ce, Zn)Sn₃ intermetallic clusters, can also effectively inhibit tin whisker growth.     

Sn-0.3Ag-0.7Cu-xNd钎料显微组织及性能

研究了稀土元素Nd的添加量对超低银无铅钎料Sn-0.3Ag-0.7Cu的润湿性能、显微组织和力学性能的影响.结果表明,微量Nd元素的加入可以显著改善Sn-0.3Ag-0.7Cu超低银无铅钎料的润湿性能和焊点的力学性能,并且能够起到细化基体组织的作用.当钎料中Nd元素的质量分数达到0.1%时,钎料的综合性能最佳,基体组织最为均匀细化.虽然Ag元素含量的降低使钎料的性能有所下降,但是加入适量Nd元素后钎料的润湿性能已接近传统Sn-3.8Ag-0.7Cu钎料.     

BGA单板结构与板级结构焊点剪切力学行为分析

采用试验方法研究BGA封装结构中焊点的剪切力学行为. 分析并比较了Sn-3Ag-0.5Cu,Sn-0.3Ag-0.7Cu,Sn-0.3Ag-0.7Cu-0.07La和Sn-0.3Ag-0.7Cu-0.07La-0.05Ce四种钎料焊点在单板结构与板级结构中的力学性能. 结果表明, 单板结构中焊点的抗剪强度高于板级结构中焊点的抗剪强度. 在单板结构中,高银焊点的抗剪强度最大,加入稀土元素的低银焊点只是得到了一定程度上的改善,然而对于板级结构,加入稀土元素的低银焊点剪切力学性能基本与高银焊点相当. 在同等拘束条件下,低银焊点的延展性优于高银焊点. 此外,对于同一种钎料而言,单板结构中的焊点断裂在体钎料上,而板级结构则断裂在IMC/体钎料界面处.     

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.     

Bi对Sn-0.3Ag-0.7Cu无铅钎料熔点及润湿性能的影响

研究了添加适量的Bi元素对低银型Sn-0．3Ag-0．7Cu无铅钎料合金性能的影响,应用差示扫描量热仪和SAT-5100型润湿平衡仪对Sn-0．3Ag-0．7Cu&#183;xBi（x=0.1,3,4．5）钎料的熔点、润湿性能作了对比试验分析。结果表明,一定量Bi元素的加入可以降低Sn-0．3Ag-0．7Cu钎料合金的熔点,并改善其润湿性能。但过多的Bi元素会导致钎料的液固相线温度差增大,塑性下降,造成焊点剥离缺陷。综合考虑得到Sn-0．3Ag-0．7Cu-3．0Bi无铅钎料具有最佳的综合性能。     

Pb-free solders for flip-chip interconnects

A variety of lead-free solder alloys were studied for use as flip-chip interconnects including Sn-3.5Ag, Sn-0.7Cu, Sn-3.8Ag-0.7Cu, and eutectic Sn-37Pb as a baseline. The reaction behavior and reliability of these solders were determined in a flip-chip configuration using a variety of under-bump metallurgies (TiW/Cu, electrolytic nickel, and electroless Ni-P/Au). The solder micro-structure and intermetallic reaction products and kinetics were determined. The Sn-0.7Cu solder has a large grain structure and the Sn-3.5Ag and Sn-3.8Ag-0.7Cu have a fine lamellar two-phase structure of tin and Ag₃Sn. The intermetallic compounds were similar for all the lead-free alloys. On Ni, Ni₃Sn₄ formed and on copper, Cu₆Sn₅Cu₃Sn formed. During reflow, the intermetallic growth rate was faster for the lead-free alloys, compared to eutectic tin-lead. In solidstate aging, however, the interfacial intermetallic compounds grew faster with the tinlead solder than for the lead-free alloys. The reliability tests performed included shear strength and thermomechanical fatigue. The lower strength Sn-0.7Cu alloy also had the best thermomechanical fatigue behavior. Failures occurred near the solder/intermetallic interface for all the alloys except Sn-0.7Cu, which deformed by grain sliding and failed in the center of the joint. Based on this study, the optimal solder alloy for flip-chip applications is identified as eutectic Sn-0.7Cu. Editor’s Note: A hypertext-enhanced version of this article can be found at www.tms.org/pubs/journals/JOM/0106/Frear-0106.html For more information, contact D.R. Frear, Interconnect Systems Laboratories, Motorola, Tempe, AZ 85284; (480) 413-6655; fax (480) 413-4511; e-mail darrel.frear@motorola.com.     

Kinetics of intermetallic phase formation at the interface of Sn-Ag-Cu-X (X = Bi, In) solders with Cu substrate

The effects of Bi and In additions on intermetallic phase formation in lead-free solder joints of Sn-3.7Ag-0.7Cu; Sn-1.0Ag-0.5Cu-1.0Bi and Sn-1.5Ag-0.7Cu-9.5In (composition given in weight %) with copper substrate are studied. Soldering of copper plate was conducted at 250 °C for 5 s. The joints were subsequently aged at temperatures of 130-170 °C for 2-16 days in a convection oven. The aged interfaces were analyzed by optical microscopy and energy dispersive X-ray spectroscopy (EDX) microanalysis. Two intermetallic layers are observed at the interface - Cu₃Sn and Cu₆Sn₅. Cu₆Sn₅ is formed during soldering. Cu₃Sn is formed during solid state ageing. Bi and In decrease the growth rate of Cu₃Sn since they appear to inhibit tin diffusion through the grain boundaries. Furthermore, indium was found to produce a new phase - Cu₆(Sn,In)₅ instead of Cu₆Sn₅, with a higher rate constant. The mechanism of the Cu₆(Sn,In)₅ layer growth is discussed and the conclusions for the optimal solder chemical composition are presented.