Sn-37Pb焊球与Ni/NiP UBM界面反应特性研究

通过对共晶锡铅焊球与Ni/NiP UBM层扫描电镜界面微观组织观察和成分分析,研究了Sn-37Pb/Ni和Sn-37Pb/NiPUBM焊点界面反应特性。研究表明芯片侧界面IMC由Ni层到焊料的顺序为:靠近Ni层界面化合物为(Ni,Cu)_3Sn,靠近焊料侧化合物为(Cu,Ni)_6Sn_5;PCB板侧界面IMC包括靠近NiP层的NiSnP化合物和靠近焊料侧的(Cu,Ni)_6Sn_5化合物,NiSnP是由于Ni的扩散形成。PCB板侧NiP镀层中存在微裂纹缺陷,此裂纹缺陷会导致金属间化合物中产生裂纹,从而对焊点力学性能和可靠性产生不良的影响。     

Sn3.8Ag0.7Cu和Sn37Pb焊点界面显微结构研究

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）研究了Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点在时效过程中的界面金属间化合物（IMC）形貌和成份。结果表明：150℃高温时效50、100、200、500h后,Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点界面IMC尺寸和厚度增加明显,IMC颗粒间的沟槽越来越小。50h时效后界面出现双层IMC结构,靠近焊料的上层为Cu6Sn5,邻近基板的下层为Cu3Sn。之后利用透射电镜观察了Sn37Pb/Ni和Sn3.8Ag0.7Cu/Ni样品焊点界面,结果显示,焊点界面清晰,IMC晶粒明显。     

电迁移对Ni/Sn63Pb37/Cu焊点界面反应的影响

研究了在125℃,1×103 A/cm2条件下电迁移对Ni/Sn63Pb37/Cu BGA焊点界面反应的影响.回流后,在焊料/Ni界面处形成Ni3Sn4、在焊料/Cu界面处形成Cu6Sn5的金属间化合物.随着电迁移时间增加,芯片侧金属间化合物转变为(Cu,Ni)6Sn5类型化合物,印制板侧Cu6Sn5金属间化合物类型保...     

等温时效对SnSb4.5CuNi/Cu焊接接头力学性能的影响

SnSb4.5CuNi/Cu焊点在175℃进行等温时效,分析了不同时效时间的SnSb4.5CuNi/Cu焊点中金属间化合物(IMC)组织形貌演变,通过纳米压痕法测量SnSb4.5CuNi/Cu焊点界面IMC的硬度和弹性模量,对焊接接头进行拉伸强度和低周疲劳测试。结果表明,时效48 h的焊缝中Cu6Sn5呈曲率半径均匀的半圆扇贝状特征,IMC的弹性模量与铜基板很接近,在恒幅对称应变条件下焊点的抗低周疲劳的性能最佳,焊点的抗拉强度高;当时效时间大于48 h,焊接接口的抗疲劳性能和抗拉伸强度逐渐变差。     

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。     

微量Ni对Sn-3.0Ag-0.5Cu钎料及焊点界面的影响

研究了Ni的含量对无铅钎料Sn-3.0Ag-0.5Cu润湿性、熔点、重熔及老化条件下界面化合物(IMC)的影响。结果表明:微量Ni的加入使SnAgCu润湿力增加6%;使合金熔点略升高约3℃;重熔时在界面形成了(Cu,Ni)6Sn5IMC层,且IMC厚度远高于SnAgCu/Cu的Cu6Sn5IMC厚度。在150℃老化过程中,SnAgCuNi/Cu重熔焊点IMC随着时间的增加,其增幅小于SnAgCu/Cu的增幅,此时Ni对IMC的增长有一定抑制作用。     

Sn-Ag-Cu焊料中金属间化合物对焊接性能的影响

讨论了Sn-Ag-Cu焊料与Cu焊盘间在回流焊过程中形成的金属间化合物(IMC)的种类、形态,Ag含量和Cu含量对IMC的影响,IMC在老化过程中的生长演变及其对焊接性能的影响。结果表明:Sn-Ag-Cu焊料与Cu焊盘之间的金属间化合物主要是Cu6Sn5和长针状的Ag3Sn,Ag和Cu的添加对组织有明显细化作用,但过量添加会影响IMC的性能。IMC的演变主要是与老化温度、老化时间有关,较厚的IMC不利于焊接性能的提高。     

添加Sb和LaB6对Sn3.0Ag0.5Cu/Cu界面IMC生长的影响

研究了Sb和稀土化合物的添加对Sn3.0Ag0.5Cu无铅焊料焊接界面金属间化合物层生长的影响。研究结果表明,固态反应阶段界面化合物层的生长快慢排序如下:v(SAC0.4Sb0.1LaB6/Cu)v(SAC0.4Sb/Cu)v(SAC0.1LaB6/Cu)v(SAC/Cu)。计算各种界面IMC生长的激活能Q结果表明,Sn3.0Ag0.5Cu/Cu界面IMC生长的激活能最高,为92.789 kJ,其他焊料合金Sn3.0Ag0.5Cu0.4Sb0.1LaB6/Cu,Sn3.0Ag0.5Cu0.1LaB6/Cu和Sn3.0Ag0.5Cu0.4Sb/Cu界面IMC生长的激活能分别为85.14,84.91和75.57 kJ。在老化温度范围内(≤190℃),Sn3.0Ag0.5Cu0.4Sb0.1LaB6/Cu的扩散系数(D)最小,因而其界面化合物的生长速率最慢。     

微量Ni,Ge元素改善Sn-0.7Cu无铅合金焊料性能的机理研究

本文简单概述了Sn-Cu系无铅钎料的国内外研究现状。在无铅焊料互连结构中,反应界面化合物层（IMC）的形貌及厚度是决定焊点可靠性的一个重要因素。本文通过研究Sn-0.7Cu共晶焊料中添加Ni微量元素对Sn-0.7Cu与Cu界面反应的影响。结果表明:对于Sn-0.7Cu/Cu界面,液态反应初始生成相为Cu₆Sn₅,在随后的5次回流焊之后形成新的Cu₃Sn相,IMC厚度快速增长从而严重影响焊接的可靠性;添加Ni元素的Sn-0.7Cu/Cu界面初生相为（Cu,Ni）₆Sn₅,但在回流焊和热老化试验之后,Ni的添加延缓了IMC的增长,IMC的生长受到抑制,且界面无其它相生成。再者,初步探讨了Ge元素的添加对该体系焊料抗氧化性能的影响。     

Sn基焊料/Cu界面IMC形成机理的研究进展

锡基无铅焊料和Cu基材界面间容易形成Cu<,6>Sn<,5>、Cu<,3>Sn及其他金属间化合物(IMC),而IMC将剧烈地影响焊接接头的性能,故对其的研究有助于了解IMC形成的本质,从而控制其形成和长大,以改善接头性能.综述了近期的研究结果,指出Cu<,6>Sn<,5>易形成扇贝状,而Cu<,3>Sn常常为薄层状;其...     

Interfacial reaction and shear strength of SnAgCu-xNi/Ni solder joints during aging at 150 °C

The interfacial microstructure and shear strength of Sn3.8Ag0.7Cu-xNi (SAC-xNi, x = 0.5, 1, and 2) composite solders on Ni/Au finished Cu pads were investigated in detail after aging at 150 °C for up to 1000 h. The interfacial characteristics of composite solder joints were affected significantly by the weight percentages of added Ni micro-particles and aging time. After aging for 200 h, the solder joints of SAC, SAC-0.5Ni and -1Ni presented duplex intermetallic compound (IMC) layers regardless of the initial interfacial structure on as-reflowed joints, whose upper and lower IMC layers were comprised of (CuNi)₆Sn₅ and (NiCu)₃Sn₄, respectively. Only a single (NiCu)₃Sn₄ IMC layer was ever observed at the SAC-2Ni/Ni interface on whole aging process. Based on the compositional analysis, the amount of Ni within the IMC regions increased as the proportion of Ni addition increased. The IMC (NiCu)₃Sn₄ layer thickness on the interface of SAC and SAC-0.5Ni grew more slowly when compared to that of SAC-1Ni and -2Ni, while for the (CuNi)₆Sn₅ layer the reverse is true. Except the IMCs sizes are increased with increased aging time, the interfacial IMCs tended to transfer their morphologies to polyhedra. In all composite joints testing, the shear strengths were approximately equal to non-composite joints. The fracturing observed during shear testing of composite joints occurred in the bulk solder, indicating that the SAC-xNi/Ni solder joints had a desirable joint reliability.     

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.     

Morphology and growth kinetics of intermetallic compounds in solid-state interfacial reaction of electroless Ni-P with Sn-based lead-free solders

A comparative study of solid/solid interfacial reactions of electroless Ni-P (15 at.% P) with lead-free solders, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, and pure Sn, was carried out by performing thermal aging at 150°C up to 1000 h. For pure Sn and Sn-3.5Ag solder, three distinctive layers, Ni₃Sn₄, SnNiP, and Ni₃P, were observed in between the solder and electroless Ni-P; while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders, two distinctive layers, (CuNi)₆Sn₅ and Ni₃P, were observed. The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated, as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers. With increasing aging time, the coarsening of interfacial Ni₃Sn₄ IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)₆Sn₅ IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders. Furthermore, the Ni content in interfacial (CuNi)₆Sn₅ phase slightly increased during aging. A small addition of Cu (0.7 wt.%) resulted in differences in the type, morphology, and growth kinetics of interfacial IMCs. By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers, the role of initial Cu and Ag in lead-free solders is better understood.     

Reactions of lead-free solders with CuNi metallizations

We have done experimental research on the dissolution rate and intermetallic growth on Cu, Ni, and CuNi-alloy substrates as a function of time and Cu/Ni ratio of the substrate. Reactions that occur when CuNi metallizations are soldered with lead-free solders were investigated. The experiments were performed using Sn-3.5Ag and Sn-3.8Ag-0.7Cu solders and different CuNi alloys. To determine the rate of dissolution of the substrate material into the solder, CuNi foils of different concentrations were immersed in Sn-3.5Ag and Sn-3.8Ag-0.7Cu solder baths for soldering times ranging from 15 sec to 5 min at 250°C. In addition, reflows of solder balls were made on top of bulk substrates to study the reaction when there is a practically infinite amount of CuNi available compared to the amount of solder. Thin film experiments were also done, where Ni containing under bump metallizations (UBMs) were fabricated and reflowed with eutectic SnAg solder balls. The nickel slows down the dissolution of the UBM into the solder and the formation of intermetallics during reflow compared to Cu metallizations. The solder/UBM interfaces were analyzed with SEM to find out how Ni concentration affects the reaction, and how much Ni is needed to obtain a sufficiently slow reaction rate.     

Effect of silver content on thermal fatigue life of Sn-xAg-0.5Cu flip-chip interconnects

The thermal fatigue properties of Sn-xAg-0.5Cu (x=1, 2, 3, and 4 in mass%) flip-chip interconnects were investigated to study the effect of silver content on thermal fatigue endurance. The solder joints with lower silver context (x=1 and 2) had a greater failure rate compared to those with higher silver content (x=3 and 4) in thermal fatigue testing. Cracks developed in the solders near the solder/chip interface for all joints tested. This crack propagation may be mainly governed by the nature of the solders themselves because the strain-concentrated area was similar for tested alloys independent of the silver content. From the microstructural observation, the fracture was a mixed mode, transgranular and intergranular, independent of the silver content. Higher silver content alloys (x=3 and 4) had finer Sn grains before thermal cycling according to the dispersion of the Ag₃Sn intermetallic compound, and even after the cycling, they suppressed microstructural coarsening, which degrades the fatigue resistance. The fatigue endurance of the solder joints was strongly correlated to the silver content, and solder joints with higher silver content had better fatigue resistance.     

Mechanical response of solder joints in flip-chip type structures

The mechanical response of PbSn solder joints of two different solder alloys (37 wt.% Pb - 63 wt.% Sn and 95 wt.% Pb - 5 wt.% Sn) used as flip-chip type interconnects is measured through mechanical testing (in tension and in shear). The influence of solder pad composition (Au and Ni) upon the behaviour of the solder joints is examined. Fatigue testing performed upon flipchip samples demonstrates the difference in mechanical comportment between Pb37Sn63 and Pb95Sn5 solders. A model for predicting fatigue life is put forward.     

Effects of Metallic Nanoparticles on Interfacial Intermetallic Compounds in Tin-Based Solders for Microelectronic Packaging

Tin (Sn)-based solders have established themselves as the main alternative to the traditional lead (Pb)-based solders in many applications. However, the reliability of the Sn-based solders continues to be a concern. In order to make Sn-based solders microstructurally more stable and hence more reliable, researchers are showing great interest in investigating the effects of the incorporation of different nanoparticles into them. This paper gives an overview of the influence of metallic nanoparticles on the characteristics of interfacial intermetallic compounds (IMCs) in Sn-based solder joints on copper substrates during reflow and thermal aging. Nanocomposite solders were prepared by mechanically blending nanoparticles of nickel (Ni), cobalt (Co), zinc (Zn), molybdenum (Mo), manganese (Mn) and titanium (Ti) with Sn-3.8Ag-0.7Cu and Sn-3.5Ag solder pastes. The composite solders were then reflowed and their wetting characteristics and interfacial microstructural evolution were investigated. Through the paste mixing route, Ni, Co, Zn and Mo nanoparticles alter the morphology and thickness of the IMCs in beneficial ways for the performance of solder joints. The thickness of Cu₃Sn IMC is decreased with the addition of Ni, Co and Zn nanoparticles. The thickness of total IMC layer is decreased with the addition of Zn and Mo nanoparticles in the solder. The metallic nanoparticles can be divided into two groups. Ni, Co, and Zn nanoparticles undergo reactive dissolution during solder reflow, causing in situ alloying and therefore offering an alternative route of alloy additions to solders. Mo nanoparticles remain intact during reflow and impart their influence as discrete particles. Mechanisms of interactions between different types of metallic nanoparticles and solder are discussed.     

Processing and aging characteristics of eutectic Sn-3.5Ag solder reinforced with mechanically incorporated Ni particles

Composite solders offer improved properties compared to non-composite solders. Ni reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic Sn-3.5Ag solder paste. The average size of the Ni particle reinforcements was approximately 5 microns. The morphology, size and distribution of the reinforcing phase were characterized metallographically. Solid-state isothermal aging study was performed on small realistic size solder joints to study the formation and growth of the intermetallic (IM) layers at Ni reinforcement/solder and Cu substrate/solder interfaces. Effects of reflow on microstructure and solderability, were studied using Cu substrates. Regarding solderability, the wetting angle of multiple reflowed Ni reinforced composite solder was compared to the solder matrix alloy, eutectic Sn-3.5Ag. General findings of this study revealed that Ni particle reinforced composite solder has comparable wetting characteristics to eutectic Sn-3.5Ag solder. Significant IM layers growth was observed in the Ni composite solder joint under isothermal aging at 150 C. Microstructural evolution was insignificant when aging temperature was lower than 100 C. Multiple reflow did not significantly change the microstructure in Ni composite solder joint.     

Interfacial reactions and shear strengths between Sn-Ag-based Pb-free solder balls and Au/EN/Cu metallization

The morphological and compositional evolutions of intermetallic compounds (IMCs) formed at three Pb-free solder/electroless Ni-P interface were investigated with respect to the solder compositions and reflow times. The three Pb-free solder alloys were Sn3.5Ag, Sn3.5Ag0.75Cu, and Sn3Ag6Bi2In (in wt.%). After reflow reaction, three distinctive layers, Ni₃Sn₄ (or Ni-Cu-Sn for Sn3.5Ag0.75Cu solder), NiSnP, and Ni₃P, were formed on the electroless Ni-P layer in all the solder alloys. For the Sn3.5Ag0.75Cu solder, with increasing reflow time, the interfacial intermetallics switched from (Cu,Ni)₆Sn₅ to (Cu,Ni)₆Sn₅+(Ni,Cu)₃Sn₄, and then to (Ni,Cu)₃Sn₄ IMCs. The degree of IMC spalling for the Sn3.5Ag0.75Cu solder joint was more than that of other solders. In the cases of the Sn3.5Ag and Sn3Ag6Bi2In solder joints, the growth rate of the Ni₃P layer was similar because these two type solder joints had a similar interfacial reaction. On the other hand, for the Sn3.5Ag0.75Cu solder, the thickness of the Ni₃P and Ni-Sn-P layers depended on the degree of IMC spalling. Also, the shear strength showed various characteristics depending on the solder alloys and reflow times. The fractures mainly occurred at the interfaces of Ni₃Sn₄/Ni-Sn-P and solder/Ni₃Sn₄.     

回流焊对SnAgCu焊点IMC及剪切强度的影响

研究了回流焊次数对Sn-0.3Ag-0.7Cu-xNi/Cu(x=0,0.05)焊点的界面反应及其剪切强度的影响。结果表明:随着回流焊次数的增加,界面金属间化合物(IMC)Cu6Sn5和(Cu1-xNix)6Sn5的厚度均增加。在钎料中添加w(Ni)为0.05%,可有效抑制IMC的生长,与回流焊次数无关。回流焊次数对Sn-0.3Ag-0.7Cu/Cu和Sn-0.3Ag-0.7Cu-0.05Ni/Cu的剪切强度影响都不大,五次回流焊后剪切强度略有下降,剪切强度分别为21MPa和25MPa。发现断裂面部分在钎料中,部分在钎料和IMC之间。