Sn-Ag-Cu焊点IMC生长规律及可靠性研究

Sn-Ag-Cu焊料目前是最有希望替代Pb-Sn合金的焊料.在回流焊过程和电子产品服役过程中,Sn-Ag-Cu焊料与基体金属间形成的金属间化合物(IMC)及其演变是影响焊点可靠性的主要因素之一.本文针对Sn-Ag-Cu焊料与Cu和Au/Ni/Cu界面形成的IMC,分析其回流和时效过程中IMC的变化规律.     

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。     

不同金属黏附层对无铅焊料SAC305剪切强度的影响

<正>无铅焊料是不含铅或含铅量极少的一种焊料的统称,以Sn为主要的组成成分,向其中加入Ag,Cu等金属元素。在无铅材料中,Sn-Ag-Cu无铅焊料是公认的最优秀的无铅焊料,无铅焊料中铅元素的质量分数极低,基本在0.02%-0.1%之间共晶Sn-Ag-Cu系无铅焊料在凝固过程中产生粗大的Ag_3Sn、Cu_6Sn_5金属间化合物(IMC)。由于在金属间化合物生长的过程中,界面附近的原子会发生穿过界面的互扩散,而不同原子扩散速度不同,     

Sn3．5Ag0．75Cu钎料与Au／Ni／Cu焊盘接头老化过程中IMC组织的演变

通过SEM（Scanning Electron Microscope）背散射照片和EDX（Energy Dispersive X-Ray Spectroscopy）成分分析研究了无铅钎料Sn3．5Ag0．75Cu与Au／Ni／Cu焊盘接头在老化过程中其界面金属间化合物（IMC）的生长演变过程；在175℃温度条件下老化72h后发现Cu可以穿过Ni层参与形成界面金属间化合物（Au，Ni，Cu）Sn4和（Au，Ni，Cu）6Sn5；基于金属间化合物生长动力学理论计自得该焊点结构中AuSn4生长的活化能为53．78KJ／mol。[第一段]     

回流次数对Sn3.8Ag0.7Cu-xNi/Ni焊点的影响

研究了复合无铅焊料Sn3.8Ag0.7Cu-xNi(x=0.5,1.0,2.0)与Au/Ni/Cu焊盘在不同回流次数下形成的焊点的性能.结果表明,Ni颗粒增强的复合焊料具有良好的润湿性能,熔点小于222℃;X为0.5的焊料界面IMC由针状(CuNi)6Sn5演化为双层IMC,即多面体状化合物(CuNi)6Sn5和回飞棒...     

Sn-3Ag-0.5Cu/Ni微焊点多次回流焊后IMC厚度及组织分析

采用Sn-Ag-Cu焊球(直径200,300,400和500μm),镀Ni盘,研究1,3,5次回流焊条件下焊点的IMC厚度及显微组织与焊球尺寸间的关系。结果表明:对于同一尺寸的焊球,随着回流焊次数的增加,IMC的厚度增大,形状由平直状逐渐过渡为体钎料一侧凹凸不平;在同一回流焊次数下,随着焊球尺寸的增大,IMC厚度减小,形貌相对没有明显差别。IMC的组成成分随着Ni向体钎料方向的不断扩散而从Sn、Ag、Cu合金变成Sn、Ag、Cu、Ni合金,其主要组成部分为(Cu,Ni)6Sn5。     

IMC生长对焊盘润湿性能的影响

无铅热风整平(又称:无铅喷锡)是适应市场无铅化要求的一种表面处理,近年来得到发展。热风整平工艺在完成后,焊盘Cu基与焊料已然形成金属间化合物(IMC),此界面对于后续焊接性能及焊点物理属性都有非常重要影响。业界对热风整平基板焊盘上IMC生长的研究报道较少。本文对此表面处理形成IMC层的影响及及生长模式进行了研究,发现IMC过度生长对焊盘在贴装过程中的润湿性能影响巨大,并对工艺中如何控制IMC生长做了进一步的探讨,以为业界同行参考。     

SnAgCu焊点电迁移诱发IMC阴极异常堆积

为了研究电迁移过程中焊点与焊盘界面金属问化合物(IMC)的变化,在28℃下,对无铅Sn3.0Ag0.5Cu焊点进行了6.5A直流电下的电迁移实验.结果发现,通电144h后,阳极侧IMC层变厚,平均达到10.12 μm;阴极侧IMC层大部分区域变薄至0.86μm,局部出现Cu焊盘的溶解消失,但在界面边缘处出现Cu3Sn5...     

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。     

镧对Sn3.5Ag0.5Cu钎料组织性能影响

运用莱卡显微镜、扫描电镜和能谱分析等手段,研究了稀土元素La的添加量对Sn3.5Ag0.5Cu钎料及其与Cu基体焊接后微观组织及性能的影响。结果表明:添加不同含量的稀土La均能使钎料及其与Cu基体焊接后组织与性能得到改善,其中以w(La)达到0.05%时为最优,显微硬度及剪切强度分别提高14%和10.7%。键参数函数计算结果表明La具有"亲Sn"倾向,可细化钎料组织,降低IMC(界面金属间化合物)的长大驱动力。     

The effect of Ag content on the formation of Ag3Sn plates in Sn-Ag-Cu lead-free solder

The formation of Ag₃Sn plates in the Sn-Ag-Cu lead-free solder joints for two different Ag content solder balls was investigated in wafer level chip scale packages (WLCSPs). After an appropriate surface mount technology reflow process on a printed circuit board, samples were subjected to 150°C high-temperature storage (HTS), 1,000 h aging, or 1,000 cycles thermal cycling test (TCT). Sequentially, the cross-sectional analysis was scrutinized using a scanning electron microscope/energy dispersive spectrometer (SEM/EDX) to observe the metallurgical evolution of the amount of the Ag₃Sn plates at the interface and the solder bulk itself. Pull and shear tests were also performed on samples. It was found that the interfacial intermetallic compound (IMC) thickness, the overall IMC area, and the numbers of Ag₃Sn plates increase with increasing HTS and TCT cycles. The amount of large Ag₃Sn plates found in the Sn-4.0Ag-0.5 Cu solder balls is much greater than that found in the Sn-2.6Ag-0.5Cu solder balls; however, no significant difference was found in the joint strength between two different Ag content solder joints.     

Spreading Behavior and Evolution of IMCs During Reactive Wetting of SAC Solders on Smooth and Rough Copper Substrates

The effect of surface roughness of copper substrate on the reactive wetting of Sn-Ag-Cu solder alloys and morphology of intermetallic compounds (IMCs) was investigated. The spreading behavior of solder alloys on smooth and rough Cu substrates was categorized into capillary, diffusion/reaction, and contact angle stabilization zones. The increase in substrate surface roughness improved the wetting of solder alloys, being attributed to the presence of thick Cu₃Sn IMC at the interface. The morphology of IMCs transformed from long needle shaped to short protruded type with an increase in the substrate surface roughness for the Sn-0.3Ag-0.7Cu and Sn-3Ag-0.5Cu solder alloys. However, for the Sn-2.5Ag-0.5Cu solder alloy the needle-shaped IMCs transformed to the completely scallop type with increase in the substrate surface roughness. The effect of Ag content on wetting behavior was not significant.     

Sn-Ag-Cu系无铅焊锡成分的优化研究

通过正交实验法对Sn-Ag-Cu系无铅焊锡合金的成分进行了优化研究。用光学显微镜、电导仪、热分析仪等对合金的微观组织、电导率、熔点、铺展性能进行了分析,并与Sn37Pb进行了对比。结果表明,Ag、Cu对Sn-Ag-Cu系焊锡合金的熔点、铺展性和电导率都有影响,当Ag质量分数为3%,Cu为2.8%,焊锡合金具有最佳的综合性能,且与铜基板的扩散层厚度大于Sn37Pb。     

Properties of Sn3.8Ag0.7Cu Solder Alloy with Trace Rare Earth Element Y Additions

In the current research, trace rare earth (RE) element Y was incorporated into a promising lead-free solder, Sn3.8Ag0.7Cu, in an effort to improve the comprehensive properties of Sn3.8Ag0.7Cu solder. The range of Y content in Sn3.8Ag0.7Cu solder alloys varied from 0 wt.% to 1.0 wt.%. As an illustration of the advantage of Y doping, the melting temperature, wettability, mechanical properties, and microstructures of Sn3.8Ag0.7CuY solder were studied. Trace Y additions had little influence on the melting behavior, but the solder showed better wettability and mechanical properties, as well as finer microstructures, than found in Y-free Sn3.8Ag0.7Cu solder. The Sn3.8Ag0.7Cu0.15Y solder alloy exhibited the best comprehensive properties compared to other solders with different Y content. Furthermore, interfacial and microstructural studies were conducted on Sn3.8Ag0.7Cu0.15Y solder alloys, and notable changes in microstructure were found compared to the Y-free alloy. The thickness of an intermetallic compound layer (IML) was decreased during soldering, and the growth of the IML was suppressed during aging. At the same time, the growth of intermetallic compounds (IMCs) inside the solder was reduced. In particular, some bigger IMC plates were replaced by fine, granular IMCs.     

感应自加热重熔无铅焊料凸台的剪切失效模式

通过两次高频感应重熔制备了Cu焊盘上S n3．5Ag焊料和Sn3．0Ag0．5Cu焊料凸台,并进行了120℃下的老化试验以及老化试件的剪切强度试验,分析了不同老化时间下两种无铅焊料凸台的剪切断裂模式。焊料凸台的剪切载荷-位移曲线的特征以及对焊料凸台剪切断口的扫描电镜形貌分析结果表明,不同老化时间下无铅焊料凸台的剪切断裂表现为塑性、韧性和脆性三种断裂模式。对凸台焊料合金的组织以及界面观察结果表明,随老化时间不断生长的脆性金属间化合物层以及焊料组织粗大是致使断裂失效模式转变的根本原因。     

Effect of Ag Content and the Minor Alloying Element Fe on the Mechanical Properties and Microstructural Stability of Sn-Ag-Cu Solder Alloy Under High-Temperature Annealing

This study compares the high-Ag-content Sn-3Ag-0.5Cu with the low- Ag-content Sn-1Ag-0.5Cu solder alloy and the three quaternary solder alloys Sn-1Ag-0.5Cu-0.1Fe, Sn-1Ag-0.5Cu-0.3Fe, and Sn-1Ag-0.5Cu-0.5Fe to understand the beneficial effects of Fe on the microstructural stability, mechanical properties, and thermal behavior of the low-Ag-content Sn-1Ag-0.5Cu solder alloy. The results indicate that the Sn-3Ag-0.5Cu solder alloy possesses small primary β-Sn dendrites and wide interdendritic regions consisting of a large number of fine Ag₃Sn intermetallic compound (IMC) particles. However, the Sn-1Ag-0.5Cu solder alloy possesses large primary β-Sn dendrites and narrow interdendritic regions of sparsely distributed Ag₃Sn IMC particles. The Fe-bearing SAC105 solder alloys possess large primary β-Sn dendrites and narrow interdendritic regions of sparsely distributed Ag₃Sn IMC particles containing a small amount of Fe. Moreover, the addition of Fe leads to the formation of large circular FeSn₂ IMC particles located in the interdendritic regions. On the one hand, tensile tests indicate that the elastic modulus, yield strength, and ultimate tensile strength (UTS) increase with increasing Ag content. On the other hand, increasing the Ag content reduces the total elongation. The addition of Fe decreases the elastic modulus, yield strength, and UTS, while the total elongation is still maintained at the Sn-1Ag-0.5Cu level. The effect of aging on the mechanical behavior was studied. After 720 h and 24 h of aging at 100°C and 180°C, respectively, the Sn-1Ag-0.5Cu solder alloy experienced a large degradation in its mechanical properties after both of the aging conditions, whereas the mechanical properties of the Sn-3Ag-0.5Cu solder alloy degraded more dramatically after 24 h of aging at 180°C. However, the Fe-bearing SAC105 solder alloys exhibited only slight changes in their mechanical properties after both aging procedures. The inclusion of Fe in the Ag₃Sn IMC particles suppresses their IMC coarsening, which stabilizes the mechanical properties of the Fe-bearing SAC105 solder alloys after aging. The results from differential scanning calorimetry (DSC) tests indicate that the addition of Fe has a negligible effect on the melting behavior. However, the addition of Fe significantly reduces the solidification onset temperature and consequently increases the degree of undercooling. In addition, fracture surface analysis indicates that the addition of Fe to the Sn-1Ag-0.5Cu alloy does not affect the mode of fracture, and all tested alloys exhibited large ductile dimples on the fracture surface.     

Comparison of Sn-Ag-Cu Solder Alloy Intermetallic Compound Growth Under Different Thermal Excursions for Fine-Pitch Flip-Chip Assemblies

The intermetallic compound (IMC) evolution in Cu pad/Sn-Ag-Cu solder interface and Sn-Ag-Cu solder/Ni pad interface was investigated using thermal shock experiments with 100-μm-pitch flip-chip assemblies. The experiments show that low standoff height of solder joints and high thermomechanical stress play a great role in the interfacial IMC microstructure evolution under thermal shock, and strong cross-reaction of pad metallurgies is evident in the intermetallic growth. Furthermore, by comparing the IMC growth during thermal aging and thermal shock, it was found that thermal shock accelerates IMC growth and that kinetic models based on thermal aging experiments underpredict IMC growth in thermal shock experiments. Therefore, new diffusion kinetic parameters were determined for the growth of (Cu,Ni)₆Sn₅ using thermal shock experiments, and the Cu diffusion coefficient through the IMC layer was calculated to be 0.2028 μm²/h under thermal shock. Finite-element models also show that the solder stresses are higher under thermal shock, which could explain why the IMC growth is faster and greater under thermal shock cycling as opposed to thermal aging.     

Depressing effect of 0.2wt.%Zn addition into Sn-3.0Ag-0.5Cu solder alloy on the intermetallic growth with Cu substrate during isothermal aging

The formation and growth of intermetallic compounds (IMCs) in lead-free solder joints, during soldering or subsequent aging, have a significant effect on the thermal and mechanical behavior of solder joints. In this study, the effects of a 0.2wt.%Zn addition into Sn-3.0Ag-0.5Cu (SAC) lead-free solder alloys on the growth of IMCs with Cu substrates during soldering and subsequent isothermal aging were investigated. During soldering, it was found that a 0.2wt.%Zn addition did not contribute to forming the IMC, which was verified as the same phase structure as the IMC for Sn-3.0Ag-0.5Cu/Cu. However, during solid-state isothermal aging, the IMC growth was remarkably depressed by the 0.2 wt.% Zn addition in the SAC solder matrix, and this effect tended to be more prominent at higher aging temperature. The activation energy for the overall IMC growth was determined as 61.460 and 106.903 kJ/mol for Sn-Ag-Cu/Cu and Sn-Ag-Cu-0.2Zn/Cu, respectively. The reduced diffusion coefficient was confirmed for the 0.2Zn-containing solder/Cu system. Also, thermodynamic analysis showed the reduced driving force for the Cu₆Sn₅ IMC with the addition of Zn. These may provide the evidence to demonstrate the depressing effect of IMC growth due to the 0.2wt.%Zn addition in the Sn-Ag-Cu solder matrix.     

Reaction of Liquid Sn-Ag-Cu-Ce Solders with Solid Copper

Small amounts of the rare-earth element Ce were added to the Sn-rich lead-free eutectic solders Sn-3.5Ag-0.7Cu, Sn-0.7Cu, and Sn-3.5Ag to improve their properties. The microstructures of the solders without Ce and with different amounts (0.1 wt.%, 0.2 wt.%, and 0.5 wt.%) of Ce were compared. The microstructure of the solders became finer with increasing Ce content. Deviation from this rule was observed for the Sn-Ag-Cu solder with 0.2 wt.% Ce, and for the Sn-0.7Cu eutectic alloy, which showed the finest microstructure without Ce. The melting temperatures of the solders were not affected. The morphology of intermetallic compounds (IMC) formed at the interface between the liquid solders and a Cu substrate at temperatures about 40°C above the melting point of the solder for dipping times from 2 s to 256 s was studied for the basic solder and for solder with 0.5 wt.% Ce addition. The morphology of the Cu₆Sn₅ IMC layer developed at the interface between the solders and the substrate exhibited the typical scallop-type shape without significant difference between solders with and without Ce for the shortest dipping time. Addition of Ce decreased the thickness of the Cu₆Sn₅ IMC layer only at the Cu/Sn-Ag-Cu solder interface for the 2-s dipping. A different morphology of the IMC layer was observed for the 256-s dipping time: The layers were less continuous and exhibited a broken relief. Massive scallops were not observed. For longer dipping times, Cu₃Sn IMC layers located near the Cu substrate were also observed.