β-Sn晶粒取向及温度对Cu/SAC305/Cu微焊点时效界面反应的影响

为了探究不同等温时效温度下β-Sn晶粒取向及晶界特征对界面反应的影响,采用准原位观测手段对不同Sn取向的Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu)微焊点进行研究. 结果表明,在不同温度下时效时,微焊点两侧界面IMC(Cu₆Sn₅ + Cu₃Sn两相)自始至终呈现对称性生长,表明时效过程中β-Sn晶粒取向及晶界的存在不会影响界面反应. 但是随着时效温度的升高,界面IMC的形貌和厚度发生明显变化. 在100 ℃时效后,界面处生成扇贝状的Cu₆Sn₅和较薄的不连续的Cu₃Sn层;在125 ℃时效后,界面处生成扇贝状的Cu₆Sn₅和较薄的连续的Cu₃Sn层;而在150 ℃时效后,界面IMC由层状Cu₆Sn₅和层状Cu₃Sn双层结构组成. 时效温度的升高促使Cu和Sn原子扩散加快,促进了扇贝状Cu₆Sn₅向层状转变并造成Cu₃Sn的快速生长. 同时,基于界面IMC厚度随时效时间的演变规律,获得了不同时效温度下微焊点界面IMC生长曲线,可为Sn基微焊点的可靠性评价提供依据.     

电迁移对Ni/Sn3.0Ag0.5Cu/Cu焊点界面反应的影响

研究了温度为150℃,电流密度为5.0×10³A/cm²的条件下电迁移对Ni/Sn3.0Ag0.5Cu/Cu焊点界面反应的影响.回流焊后在Sn3.0Ag0.5Cu/Ni和Sn3.0Ag0.5Cu/Cu的界面上均形成了（Cu,Ni）₆Sn₅型化合物.时效过程中界面化合物随时效时间增加而增厚,时效800 h后两端的化合物并没有发生转变,仍为（Cu,Ni）₆Sn₅型.电流方向对Cu基板的消耗起着决定作用.当电子从基板端流向芯片端时,电流导致基板端Cu焊盘发生局部快速溶解,并导致裂纹在Sn3.0Ag0.5Cu/（Cu,Ni）₆Sn₅界面产生,溶解到钎料中的Cu原子在钎料中沿着电子运动的方向向阳极扩散,并与钎料中的Sn原子发生反应生成大量的Cu₆Sn₅化合物颗粒.当电子从芯片端流向基板端时,芯片端Ni UBM层没有发生明显的溶解,在靠近阳极界面处的钎料中有少量的Cu₆Sn₅化合物颗粒生成,电迁移800 h后焊点仍保持完好.电迁移过程中无论电子的运动方向如何,均促进了阳极界面处（Cu,Ni）₆Sn₅的生长,阳极界面IMC厚度明显大于阴极界面IMC的厚度.与Ni相比,当Cu作为阴极时焊点更容易在电迁移作用下失效.     

Sn5Sb1Cu0.1Ni0.1Ag/Cu(Ni)焊点的抗时效性能

采用扫描电镜(SEM)研究在150 ℃等温时效下Cu/Sn5Sb1Cu0.1Ni0.1Ag/Cu与Ni/Sn5Sb1Cu0.1Ni0.1Ag/Ni焊点的界面扩散行为. 结果表明，在时效过程中，随着时效时间的增加，Cu/Sn5Sb1Cu0.1Ni0.1Ag/Cu焊点界面金属间化合物(intermetallic compound，IMC)形貌由开始的细针状生长为棒状，IMC层厚度增加，界面IMC主要成分为(Cu,Ni)₆Sn₅. Ni/Sn5Sb1Cu0.1Ni0.1Ag/Ni焊点的界面IMC形貌由细小突起状转变为较为密集颗粒状，且IMC层厚度增加，界面IMC主要成分为(Cu,Ni)₃Sn₄. 经过线性拟合，两种焊点的界面IMC层生长厚度与时效时间t1/2呈线性关系，Sn5Sb1Cu0.1Ni0.1Ag/Cu界面间IMC的生长速率为7.39 × 10?2 μm2/h，Sn5Sb1Cu0.1Ni0.1Ag/Ni界面间IMC的生长速率为2.06 × 10?2 μm2/h. 镀镍层的加入可以显著改变界面IMC的形貌，也可降低界面IMC的生长速率，抑制界面IMC的生长，显著提高抗时效性能.     

基于原位观察Sn-3.0Ag-0.5Cu/Cu钎焊接头110℃时效过程中的显微结构

基于自制原位观察装置,研究了Sn-3.0Ag-0.5Cu/Cu焊点在110℃恒温时效下,0~168 h不同时效时间界面金属间化合物(IMC)的微观形貌和生长变化规律.结果表明,随着时效时间的延长,界面IMC(Cu₆Sn₅和Cu₃Sn)的厚度在不断增加;同时IMC的生长具有三维特性;随着时效时间的延长,Cu₆Sn₅在纵向方向上变化比较明显,高度是逐渐降低的;而在横向方向上变化较慢.SEM研究发现,时效过程中界面IMC的形貌由扇贝状转变成较为平整的层状,并出现分层现象.     

Sn3.0Ag0.5Cu/Cu回流焊点界面化合物尺寸分布特征及生长机制

在电子封装过程中,钎料与基体之间形成金属间化合物层,其主要成分为Cu₆Sn₅,Cu₆Sn₅晶粒的尺寸和形貌特征能够显著影响焊点的服役性能. 采用回流焊的方法制备了一系列Sn3.0Ag0.5Cu/Cu焊点,使用Image-Pro Plus软件对焊接界面化合物Cu₆Sn₅晶粒的尺寸分布和化合物层的厚度进行了统计分析. 结果表明,Cu₆Sn₅的平均粒径正比于t0.38(t为回流时间), 界面化合物层的平均厚度正比于t0.32. 随着回流时间的增加,界面化合物生长速度变慢,Cu₆Sn₅晶粒的尺寸分布更加均匀. 回流时间较长的样品中Cu₆Sn₅的粒径尺寸分布与FRD模型的理论曲线基本相符,而对于回流时间短的样品,晶粒尺寸分布与FRD理论偏离较大. 统计结果显示,出现频次最高的晶粒尺寸小于平均值. 最后讨论了界面Cu₆Sn₅晶粒的生长机制,分析了回流时间对界面Cu₆Sn₅晶粒生长方式的影响.     

锡在Cu6Sn5金属间化合物表面的润湿行为

利用改良座滴法研究了高真空条件下熔融纯Sn在350 ~ 450 ℃下分别与Cu₆Sn₅和T2纯铜的润湿行为. 结果表明，表面镀金的金属间化合物基板在各试验温度下的润湿性均优于纯铜基板；金属基板表面氧化膜对润湿性的影响不容忽视；离子溅射后表面形成的金膜可以作为一种改善润湿性及控制界面IMC厚度的有效方法；润湿性改善的机制为Sn与氧化膜的化学反应，界面析出IMC或者IMC的溶解过程并非限制铺展的主要因素；铺展过程表现出线性铺展规律，可用反应产物控制模型对其进行描述，计算得到Sn/Cu₆Sn₅和Sn/Cu两体系的铺展激活能分别为20.469 kJ/mol和22.270 kJ/mol.     

焊接时间及焊接温度对Sn35Bi0.3Ag/Cu焊接接头性能的影响

分别在不同焊接时间和不同焊接温度下制备了Sn35Bi0.3Ag/Cu焊接接头,采用扫描电子显微镜(SEM)、万能拉伸试验机、超声波成像无损探伤检测仪等测试手段,研究了焊接时间(1～9 min)和焊接温度(210～290℃)对Sn35Bi0.3Ag/Cu焊接接头微观结构和力学性能的影响.结果表明,在焊接过程中,Cu元素扩散到焊接界面处,形成了(Cu₆Sn₅,Cu₃Sn)界面层,同时发现生成的Ag3Sn相能够抑制界面层的生长.随着焊接时间的延长或焊接温度的升高,反应层变厚,抗剪强度先增大后减小.对焊接接头断口形貌分析发现,焊接接头的断裂由Bi相颗粒及Cu₆Sn₅颗粒共同作用.焊接接头的断裂发生在IMC/焊料一侧,Bi相颗粒及Cu6Sn5颗粒共同影响着接头的抗剪强度.此外,当焊接时间为3 min、焊接温度为230℃时,接头的钎着率最大,为99.14%,抗剪强度达到最大值,为51.8 MPa.     

BGA结构Sn-3.0Ag-0.5Cu/Cu焊点低温回流时界面反应和IMC生长行为

采用差示扫描量热法将焊点的熔化行为表征与焊点回流焊工艺相结合,研究了球栅阵列（BGA）结构单界面Sn-3.0Ag-0.5Cu/Cu微焊点在钎料熔化温度附近等温时效形成局部熔化焊点时的界面反应及界面金属间化合物（IMC）的生长行为.结果表明,在钎料熔点217℃时效时,焊点中钎料基体仅发生界面局部熔化;而在稍高于熔点的218℃时效时,焊点钎料基体中全部共晶相和部分-Sn相发生熔化,且Cu基底层的消耗量显著增大,绝大部分Cu基底直接溶蚀进入钎料基体并导致界面IMC净生长厚度相对217℃时效时减小;等温时效温度升高至230℃时,焊点中钎料基体全部熔化,界面IMC厚度达到最大值.界面IMC的生长动力学研究结果表明,界面Cu₆Sn₅和Cu₃Sn层的生长分别受晶界扩散和体积扩散控制,但界面IMC层的晶界凹槽、晶粒粗化和溶蚀等因素对其生长行为也有明显影响.     

热循环对Sn58Bi-0.1Ti/Cu焊点界面与性能影响

为了改善Sn58Bi低温钎料的性能,通过在Sn58Bi低温钎料中添加质量分数为0.1%的纳米Ti颗粒制备了Sn58Bi-0.1Ti纳米增强复合钎料。研究了纳米Ti颗粒的添加对-55～125℃热循环过程中Sn58Bi/Cu焊点的界面金属间化合物(IMC)生长行为的影响。结果表明:回流焊后,在Sn58Bi/Cu焊点和Sn58Bi-0.1Ti/Cu焊点的界面处都形成一层扇贝状的Cu6Sn5IMC层。在热循环300次后,在Cu_6Sn_5/Cu界面处形成了一层Cu_3Sn IMC。Sn58Bi/Cu焊点和Sn58Bi-0.1Ti/Cu焊点的IMC层厚度均和热循环时间的平方根呈线性关系。但是,Sn58Bi-0.1Ti/Cu焊点的IMC层厚度明显低于Sn58Bi/Cu焊点,这表明纳米Ti颗粒的添加能有效抑制热循环过程中界面IMC的过度生长。另外计算了这2种焊点的IMC层扩散系数,结果发现Sn58Bi-0.1Ti/Cu焊点的IMC层扩散系数(整体IMC、Cu_6Sn_5和Cu_3Sn IMC)明显比Sn58Bi/Cu焊点小,这在一定程度上解释了Ti纳米颗粒对界面IMC层生长的抑制作用。     

基于纳米压痕法分析无铅焊点内Cu6Sn5金属化合物的力学性能

采用纳米压痕技术对微电子封装中无铅焊点内界面化合物（IMC）Cu₆Sn₅的弹性模量和硬度进行了测试。根据实际工业工艺流程和服役工况,制备接近真实服役状态下的微电子封装中无铅焊点界面化合物试样;采用扫描电镜（SEM）和能量色散X射线荧光光谱仪（EDX）确定IMC的形貌和化学成分;利用连续刚度测量（CSM）技术,采用不同的加载速率对无铅焊点（Sn3.0Ag0.5Cu、Sn0.7Cu和Sn3.5Ag）内的界面化合物Cu₆Sn₅进行测量,得到载荷、硬度和弹性模量-位移曲线。根据纳米压痕结果确定Cu₆Sn₅的蠕变应力指数。     

热循环对Sn58Bi(纳米Ti)/Cu焊点界面与性能影响

为了改善Sn-58Bi低温钎料的性能,通过在Sn-58Bi低温钎料中添加质量分数为0.1%的纳米Ti颗粒制备了Sn-58Bi-0.1Ti纳米增强复合钎料。在本文中,研究了纳米Ti颗粒的添加对-55～125 _^oC热循环过程中Sn-58Bi/Cu焊点的界面金属间化合物(IMC)生长行为的影响。研究结果表明：回流焊后,在Sn-58Bi/Cu焊点和Sn-58Bi-0.1Ti/Cu焊点的界面处都形成一层扇贝状的Cu₆Sn₅ IMC层。在热循环300次后,在Cu₆Sn₅/Cu界面处形成了一层Cu₃Sn IMC。Sn-58Bi/Cu焊点和Sn-58Bi-0.1Ti/Cu焊点的IMC层厚度均和热循环时间的平方根呈线性关系。但是,Sn-58Bi-0.1Ti/Cu焊点的IMC层厚度明显低于Sn-58B/Cu焊点,这表明纳米Ti颗粒的添加能有效抑制热循环过程中界面IMC的过度生长。另外计算了这两种焊点的IMC层扩散系数,结果发现Sn-58Bi-0.1Ti/Cu焊点的IMC层扩散系数(整体IMC、Cu₆Sn₅和Cu₃Sn IMC)明显比Sn-58Bi/Cu焊点小,这在一定程度上解释了Ti纳米颗粒对界面IMC层的抑制作用。     

Bismuth segregation enhances intermetallic compound growth in SnBi/Cu microelectronic interconnect

There was a sudden increase of intermetallic compound (IMC) Cu₆Sn₅ growth rate in the eutectic Sn58wt. %Bi/Cu joint during aging process. With aging time increasing, Bi accumulated at the Cu₃Sn/Cu interface and gradually induced the fracture mode of the joint to change from ductile to brittle one along this interface. Bi segregation enhanced IMC Cu₆Sn₅ growth by means of promoting the interfacial reaction at Cu₃Sn/Cu interface, which was concluded from IMCs (Cu₆Sn₅ and Cu₃Sn) growth behavior for pure Sn/Cu and Sn10wt. %Bi/Cu interconnects at the same temperature.     

Effect of bismuth on the growth kinetics of intermetallic compounds in Sn-3.5Ag solder joints: A growth kinetic model

The effect on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints, caused by adding Bi to eutectic Sn-3.5Ag solder alloy, was examined at the aging temperatures of 150°C and 180°C. The Cu₆Sn₅ layer growth was significantly enhanced, but the Cu₃Sn layer growth was slightly retarded by the addition of Bi, resulting in significant growth enhancement of the total (Cu₆Sn₅+Cu₃Sn) IMC layer with increasing Bi addition. The IMC layer growth in the Bi-containing solder joints was accompanied by the accumulation of Bi ahead of the Cu₆Sn₅ layer that resulted in the formation of a liquid layer at the Cu₆Sn₅/solder interface. A kinetic model was developed for the planar growth of the Cu₆Sn₅ and Cu₃Sn layers in the solder joints, accounting for the existence of interfacial reaction barriers. Predictions from the kinetic model showed that the experimental results could be well explained by the hypothesis that the formation of a Bi-rich liquid layer at the Cu₆Sn₅/solder interface reduces the interfacial reaction barrier at the interface.     

Effect of rare earth metal Ce addition to Sn-Ag solder on interfacial reactions with Cu substrate

The effect of adding a small amount of rare earth cerium (Ce) element to low Ag containing Sn-1wt%Ag Pb-free solder on its interfacial reactions with Cu substrate was investigated. The growth of intermetallic compounds (IMCs) between three Sn-1Ag-xCe solders with different Ce contents and a Cu substrate was studied and the results were compared to those obtained for the Ce-free Sn-1Ag/Cu systems. In the solid-state reactions of the Sn-1Ag(-xCe)/Cu solder joints, the two IMC layers, Cu₆Sn₅ and Cu₃Sn, grew as aging time increased. Compared to the Sn-1Ag/Cu joint, the growth of the Cu₆Sn₅ and Cu₃Sn layers was depressed for the Ce-containing Sn-1Ag-xCe/Cu joint. The addition of Ce to the Sn-Ag solder reduced the growth of the interfacial Cu-Sn IMCs and prevented the IMCs from spalling from the interface. The evenly-distributed Ce elements in the solder region blocked the diffusion of Sn atoms to the interface and retarded the growth of the interfacial IMC layer.     

Suppressing effect of 0.5 wt.% nano-TiO2 addition into Sn-3.5Ag-0.5Cu solder alloy on the intermetallic growth with Cu substrate during isothermal aging

This study investigated the effects of adding 0.5 wt.% nano-TiO₂ particles into Sn3.5Ag0.5Cu (SAC) lead-free solder alloys on the growth of intermetallic compounds (IMC) with Cu substrates during solid-state isothermal aging at temperatures of 100, 125, 150, and 175 °C for up to 7 days. The results indicate that the morphology of the Cu₆Sn₅ phase transformed from scallop-type to layer-type in both SAC solder/Cu joints and Sn3.5Ag0.5Cu-0.5 wt.% TiO₂ (SAC) composite solder/Cu joints. In the SAC solder/Cu joints, a few coarse Ag₃Sn particles were embedded in the Cu₆Sn₅ surface and grew with prolonged aging time. However, in the SAC composite solder/Cu aging, a great number of nano-Ag₃Sn particles were absorbed in the Cu₆Sn₅ surface. The morphology of adsorption of nano-Ag₃Sn particles changed dramatically from adsorption-type to moss-type, and the size of the particles increased.The apparent activation energies for the growth of overall IMC layers were calculated as 42.48 kJ/mol for SAC solder and 60.31 kJ/mol for SAC composite solder. The reduced diffusion coefficient was confirmed for the SAC composite solder/Cu joints.     

Microstructural evolution of intermetallic compounds in Sn–3.5Ag–X (X = 0, 0.75Ni, 1.0Zn and 1.5In)/Cu solder joints during liquid aging

In this paper, the microstructural evolution of IMCs in Sn–3.5Ag–X (X = 0, 0.75Ni, 1.0Zn, 1.5In)/Cu solder joints and their growth mechanisms during liquid aging were investigated by microstructural observations and phase analysis. The results show that two-phase (Ni₃Sn₄ and Cu₆Sn) IMC layers formed in Sn–3.5Ag–0.75Ni/Cu solder joints during their initial liquid aging stage (in the first 8 min). While after a long period of liquid aging, due to the phase transformation of the IMC layer (from Ni₃Sn₄ and Cu₆Sn phases to a (Cu, Ni)₆Sn₅ phase), the rate of growth of the IMC layer in Sn–3.5Ag–0.75Ni/Cu solder joints decreased. The two Cu₆Sn₅ and Cu₅Zn₈ phases formed in Sn–3.5Ag–1.0Zn/Cu solder joints during the initial liquid aging stage and the rate of growth of the IMC layers is close to that of the IMC layer in Sn–3.5Ag/Cu solder joints. However, the phase transformation of the two phases into a Cu–Zn–Sn phase speeded up the growth of the IMC layer. The addition of In to Sn–3.5Ag solder alloy resulted in Cu₆(Sn_x,In_1?x)₅ phase which speeded up the growth of the IMC layer in Sn–3.5Ag–1.5In/Cu solder joint.     

Reliability studies of Sn–9Zn/Cu solder joints with aging treatment

Sn–9Zn (in wt.%) solder ball was bonded to Cu pad, and the effect of aging on shear reliability was investigated. After reflow, the intermetallic compound (IMC) phase formed at the interface was Cu₅Zn₈, and the as-reflowed Sn–9Zn/Cu joint had sufficient shear strength. In the isothermal aging test, only Cu₅Zn₈ IMC was observed in the samples aged at temperatures between 70 and 120 °C. On the other hand, after aging at 150 °C for 250 h, Cu₆Sn₅ phase was observed at the interface between the interfacial Cu₅Zn₈ IMC layer and the Cu substrate. And, the layer-type Cu₅Zn₈ IMC layer was disrupted locally at the interface. In the ball shear test conducted after aging treatment, the shear strength significantly decreased after aging at all temperatures for initial 100 h, and then remained constant by further prolonged aging. The fracture mainly occurred at the interface between the solder and Cu₅Zn₈ IMC layer. The aged Sn–9Zn/Cu solder joint had an inferior joint reliability.     

Intermetallic compound growth suppression at high temperature in SAC solders with Zn addition on Cu and Ni-P substrates

The effect of adding 0.5-1.5 wt.% Zn to Sn-3.8Ag-0.7Cu (SAC) solder alloy during reflow and solid state ageing has been investigated. In particular, the role of the Zn addition in suppressing interfacial Intermetallic Compound (IMC) growth on Cu and Ni-P substrates has been determined. Solder-substrate couples were aged at 150 °C and 185 °C for 1000 h. In the case of 0.5-1.0 wt.% Zn on Cu substrate, Cu₃Sn IMC was significantly suppressed and the morphology of Cu₆Sn₅ grains was changed, leading to suppressed Cu₆Sn₅ growth. In the SAC-1.5Zn/Cu substrate system a Cu₅Zn₈ IMC layer nucleated at the interface followed by massive spalling of the layer into the solder, forming a barrier layer limiting Cu₆Sn₅ growth. On Ni-P substrates the (Cu,Ni)₆Sn₅ IMC growth rate was suppressed, the lowest growth rate being found in the SAC-1.5Zn/Ni-P system. In all cases the added Zn segregated to the interfacial IMCs so that Cu₆Sn₅ became (Cu,Zn)₆Sn₅ and (Cu,Ni)₆Sn₅ became (Ni,Cu,Zn)₆Sn₅. The effect of Zn concentration on undercooling, wetting angles and IMC composition changes during ageing are also tabulated, and a method of incorporating Zn into the solder during reflow without compromising solder paste reflow described.     

Microstructure evolution in Cu pillar/eutectic SnPb solder system during isothermal annealing

The reaction between Cu pillar and eutectic SnPb solder during isothermal annealing was studied systematically. Intermetallic compounds (IMCs), such as Cu₆Sn₅ and Cu₃Sn, were formed in between Cu and SnThe parabolic rate law was observed on IMC formation, which indicated that the growth of IMCs was controlled by atomic diffusion (a diffusion-limited process). Annealing at 165 °C for 160 h decreased the growth rate of Cu₆Sn₅, and at the same time increased the growth rate of Cu₃Sn. This was when Sn in solder was exhausted completely. The activation energies for the growth of Cu₃Sn and Cu₆Sn₅ were measured to be 1.77 eV and 0.72 eV, respectively. The Kirkendall void that formed at the interface between Cu pillar and solder obeyed the parabolic rate law. The growth rate of the Kirkendall void increased when the Sn in solder was consumed in its entirety.     

Growth Behavior of Intermetallic Compounds at SnAgCu/Ni and Cu Interfaces

The growth behavior of reaction-formed intermetallic compounds (IMCs) at Sn3.5Ag0.5Cu/Ni and Cu interfaces under thermal-shear cycling conditions was investigated. The results show that the morphology of (Cu _x Ni_1–x )₆Sn₅ and Cu₆Sn₅ IMCs formed both at Sn3.5Ag0.5Cu/Ni and Cu interfaces gradually changed from scallop-like to chunk-like, and different IMC thicknesses developed with increasing thermal-shear cycling time. Furthermore, Cu₆Sn₅ IMC growth rate at the Sn3.5Ag0.5Cu/Cu interface was higher than that of (Cu _x Ni_1–x )₆Sn₅ IMC under thermal-shear cycling. Compared to isothermal aging, thermal-shear cycling led to only one Cu₆Sn₅ layer at the interface between SnAgCu solder and Cu substrate after 720 cycles. Moreover, Ag₃Sn IMC was dispersed uniformly in the solder after reflow. The planar Ag₃Sn formed near the interface changed remarkably and merged together to large platelets with increasing cycles. The mechanism of formation of Cu₆Sn₅, (Cu _x Ni_1–x )₆Sn₅ and Ag₃Sn IMCs during thermal-shear cycling process was investigated.