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。     

热循环对Sn-58Bi-xCNTs/Cu钎焊接头微观组织与力学性能的影响

研究了热循环对Cu/Sn-58Bi/Cu和Cu/Sn-58Bi-0.03CNTs/Cu接头的微观组织、界面金属间化合物(Intermetallic Compound,IMC)形貌、厚度变化及焊点抗拉强度和拉伸断口形貌的影响规律。结果表明,随着热循环周次的增加,钎料微观组织均出现了粗化现象,且在同一热循环条件下,Cu/Sn-58Bi-0.03CNTs/Cu接头组织较为细小;焊点界面IMC层厚度均随热循环周次的增加而出现不断增厚的趋势,且石墨化多壁碳纳米管(CNTs)颗粒增强Sn-58Bi复合钎料焊点界面IMC层长大的趋势较为缓慢;热循环周次增加,接头的抗拉强度均呈现下降趋势;热循环处理后的Cu/Sn-58Bi/Cu焊点和Sn-58Bi-0.03CNTs/Cu焊点拉伸断口形貌主要由韧窝和少量解理面组成,Cu/Sn-58Bi/Cu焊点的断裂机制从韧性断裂转变为韧-脆混合断裂模式,Sn-58Bi-0.03CNTs/Cu焊点的断裂机制均为韧性断裂。     

时效时间对Sn-58Bi-xCe/Cu焊点组织及显微硬度的影响

研究了时效时间对Sn-58Bi/Cu和Sn-58Bi-0.5Ce/Cu焊点组织和显微硬度的影响。结果表明:随着时效时间增加,Sn-58Bi/Cu和Sn-58Bi-0.5Ce/Cu焊点组织逐渐粗化,界面IMC厚度不断增加;同一时效时间下,Sn-58Bi-0.5Ce/Cu焊点的晶粒尺寸和界面IMC层厚度均低于Sn-58Bi/Cu焊点。焊点的显微硬度均随时效时间增加先增大后降低,且Sn-58Bi-0.5Ce/Cu焊点的显微硬度均高于Sn-58Bi/Cu焊点。Ce颗粒的添加可有效抑制时效过程中焊点组织的粗化及界面IMC层厚度的增加,从而获得较高的显微硬度。     

微连接Cu/SAC305/Cu界面元素扩散与几何尺寸效应

通过对不同钎料层厚度(15~50μm)的Cu/SAC305/Cu三明治结构焊缝进行高温时效处理,研究在高温时效过程中钎料层厚度对IMC生长行为的影响.结果表明,钎料层厚度对高温时效过程中的界面元素固态扩散的影响显著.钎料层厚度越小,在时效过程中界面处越有利于Cu₃Sn的生长,160℃时效相同时间后Cu₆Sn₅层与Cu₃Sn层的厚度比越小;时效过程中IMC层(Cu₆Sn₅层+Cu₃Sn层)的生长速率随着钎料层厚度的减小也呈现减小的趋势;扩散系数受钎料层尺寸的影响,扩散系数与钎料层厚度之间近似满足抛物线关系.     

时效温度对Sn-58Bi-xMo复合钎料焊点组织和性能的影响

研究了时效温度对Sn-58Bi-xMo(x=0,0.25)钎料基体显微组织、焊点界面IMC形貌及力学性能的影响规律。研究结果表明:随着时效温度的升高,钎料基体的显微组织逐渐粗大,焊点界面IMC的厚度也逐渐增大,IMC形貌由扇贝状转变为表面较为平缓的层状;相同时效条件下,Cu/Sn-58Bi-0.25Mo/Cu焊点的显微组织及IMC厚度较小;焊点的抗拉强度及剪切强度均随时效温度的提高呈下降趋势,且Mo颗粒的添加大大减缓了焊点时效过程中剪切强度的下降趋势。在同一时效温度下, Sn-58Bi-0.25Mo复合钎料焊点的抗拉强度及剪切强度均高于Sn-58Bi钎料焊点的。     

硼酸铝晶须对Sn-58Bi/Cu界面金属间化合物 层演变及剪切行为的影响

研究了硼酸铝晶须对Sn-58Bi/Cu界面金属间化合物(IMC)层组织演变的影响.结合钎焊接头显微组织、剪切性能以及断口形貌,分析了Sn-58Bi-1.2%Al₁₈B₄O₃₃钎焊接头的断裂机理.结果表明,硼酸铝晶须的加入可以细化钎料组织,抑制大块富铋相的出现;钎料/基板界面IMC层厚度和晶粒粒径均随着重熔次数的增加而增大,但硼酸铝晶须的加入能够阻碍界面IMC层的增厚和晶粒粗化,提高钎焊接头的性能;不同重熔次数下Sn-58Bi-1.2% Al₁₈B₄O₃₃/Cu钎焊焊点比Sn-58Bi/Cu钎料焊点能承受更高的剪切载荷,且经过多次重熔后接头强度保持稳定.     

Cu/Sn-58Bi-0.5Ce/Cu钎焊接头的热时效行为

对比研究了不同时效温度下Sn-58Bi和Sn-58Bi-0.5Ce钎焊接头的组织、界面IMC形态、厚度及接头拉伸性能和断口形貌。结果表明:Ce颗粒的添加细化了Sn-58Bi钎料的组织,抑制了Sn-58Bi钎料接头时效过程中组织的粗化、IMC形貌变化及厚度的增大。随时效温度的升高,Cu/Sn-58Bi-0.5Ce/Cu钎焊接头IMC形貌从扇贝状逐渐趋于平整,厚度逐渐增大,抗拉强度逐渐降低,拉伸断口由韧性断裂转变为脆性断裂。     

电迁移对Cu/Sn-58Bi-0.01CNTs/Cu焊点组织及可靠性的影响

选用直流稳压电源对Cu/Sn-58Bi-x CNTs/Cu(x=0,0.01)焊点的抗电迁移性能进行了测量,研究了不同通电时间下焊点的组织、界面IMC形貌及蠕变性能。结果表明:随着通电时间的增加,钎料焊点的显微组织均呈粗化的趋势,焊点界面IMC形貌均由扇贝状趋于平坦,厚度呈上升的趋势,钎料焊点的蠕变断裂寿命均降低。与同一通电时间的焊点阳极对比,焊点阴极附近的组织更为细小,界面IMC更薄;相较于同一通电时间的Sn-58Bi钎料焊点,Sn-58Bi-0.01CNTs复合钎料的焊点显微组织更为细小,界面IMC更薄,焊点的蠕变性能更优。     

纳米锑掺杂对回流焊Sn-3.0Ag-0.5Cu-xSb焊点界面IMC生长的影响机理

研究了纳米锑掺杂对回流焊过程中Sn-3.0Ag-0.5Cu-xSb(x=0,0.2%,1.0%和2.0%)焊点界面金属间化合物(IMC)生长动力学的影响.借助扫描电镜(SEM)观察了焊点的微观结构,利用X射线能谱分析(EDX)及X射线衍射谱仪(XRD)确定了IMC的相和成分.结果表明,部分纳米锑颗粒溶解在富锡相中形成SnSb二元相,部分纳米锑颗粒溶解在Ag₃Sn相中形成Ag₃Sb相,剩余部分沉降在界面Cu₆Sn₅金属间化合物层表面.随着纳米锑含量的增加,IMC厚度减小.当纳米锑的含量为1.0%时,IMC厚度最小.通过曲线拟合,确定出界面IMC层生长指数和扩散系数.结果表明,IMC层生长指数和扩散系数均随着纳米锑含量的增加而减小.当纳米锑的含量为1.0%,IMC层生长指数和扩散系数均有最小值,分别为0.326和10.31×10^-10 cm²/s.由热力学相图和吸附理论可知,Sn,Sb元素之间易形成SnSb化合物,引起Sn元素的活性、Cu-Sn金属间化合物形成的驱动力和界面自由能下降,从而导致Cu₆Sn₅金属间化合物生长速率下降,抑制IMC生长.     

微量Nd对Sn-6.5Zn合金及钎料/Cu界面结构的影响

研究了微量稀土元素Nd的添加对Sn-6.5Zn合金组织及钎料/Cu焊点界面金属间化合物(IMC)特征的影响.结果表明:微量Nd元素在Sn-6.5Zn钎料中的添加能够显著细化合金组织和形成均匀细密界面IMC层;添加0.1 wt％Nd元素即能促进钎料/Cu焊点界面反应及界面区域成分的均匀性.     

Cu基板退火处理的Cu/Sn58Bi/Cu钎焊接头界面微结构

研究了铜基板退火处理对Cu/Sn58Bi界面微结构的影响. 结果表明,在回流以及时效24 h后Cu/Sn58Bi/Cu界面只观察到Cu₆Sn₅. 随着时效时间的增加,在界面形成了Cu₆Sn₅和Cu₃Sn的双金属间化合物(IMC)层,并且IMC层厚度也随之增加. 长时间时效过程中,在未退火处理的铜基板界面产生了较多铋偏析,而在退火处理的铜基板界面较少产生铋偏析. 比较退火处理以及未退火处理的铜基板与钎料界面IMC层生长速率常数,发现铜基板退火处理能减缓IMC层生长,主要归因于对铜基板进行退火处理能够有效的消除铜基板的内应力与组织缺陷,从而减缓Cu原子的扩散,起到减缓IMC生长的作用.     

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.     

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.     

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.     

Ni-CNTs增强颗粒对Sn58Bi-0.1Er焊点组织与力学性能的影响

采用真空熔炼方法制备了不同Ni-CNTs含量的Sn58Bi-0.1Er钎料合金,研究不同Ni-CNTs含量对Sn58Bi-0.1Er复合钎料在Cu 基板上的润湿性能的影响,并对不同Ni-CNTs含量下接头界面处金属间化合物的组织形貌及接头的剪切性能进行了分析. 结果表明,当Ni-CNTs 增强颗粒的添加为0.01% ~ 0.05%(质量分数)时,复合钎料合金在铜板上的润湿性得到了提高,随着Ni-CNTs含量的进一步增加,复合钎料在铜板上的润湿性开始呈下降趋势;随着Ni-CNTs的加入,Sn58Bi/Cu界面金属间化合物由锯齿状的Cu₆Sn₅转变成薄层状的(Cu, Ni)₆Sn₅, Ni-CNTs增强颗粒的加入可以有效减小界面金属间化合物层的厚度;Ni-CNTs增强颗粒的加入提高了Sn58Bi/Cu接头的剪切力,当Ni-CNTs的添加量为0.1%时,接头的剪切力最高为432.86 N,较Sn58Bi-0.1Er钎料接头的剪切力提升了两倍以上. Ni-CNTs增强颗粒的添加有效地改善了Sn58Bi-0.1Er接头的力学性能.     

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.     

Ni segregation in the interfacial (Cu,Ni)6Sn5 intermetallic layer of Sn-0.7Cu-0.05Ni/Cu ball grid array (BGA) joints

Ni segregation in the interfacial (Cu,Ni)₆Sn₅ intermetallic layer of Sn-0.7Cu-0.05Ni/Cu BGA solder joints was investigated by using synchrotron micro X-ray fluorescence (XRF) analysis and synchrotron X-ray diffraction (XRD). Compared to Sn-0.7Cu/Cu BGA joints, Ni containing solder show suppressed Cu₃Sn growth in both reflow and annealed conditions. In as-reflowed Sn-0.7Cu-0.05Ni/Cu BGA joints, Ni was relatively homogenously distributed within interfacial (Cu,Ni)₆Sn₅. During subsequent annealing, the diffusion of Ni in Cu₆Sn₅ was limited and it remained concentrated adjacent the Cu substrate where it contributes to the suppression of Cu₃Sn formation at the interface between the Cu substrate and Cu₆Sn₅ intermetallics.     

Dissolution and interfacial reactions of thin-film Ti/Ni/Ag metallizations in solder joints

The dissolution and interfacial reactions involving thin-film Ti/Ni/Ag metallizations on two semiconductor devices, diode and metal-oxide-semiconductor field-effect transistor (MOSFET), a Sn–3.0Ag–0.7Cu solder, and a Au-layer on the substrates are studied. To simulate the dissolution kinetics of the Ag-layer in liquid solder during the reflow process, the computational thermodynamics (Thermo-Calc) and kinetics (DICTRA: DIffusion Controlled TRAnsformations) tools are employed in conjunction with the assessed thermochemical and mobility data. The simulated results are found to be consistent with the observed as-reflowed microstructures and the measured Ag contents in the solder. In the as-reflowed joints two different intermetallic compounds (IMC) are found near the diode/solder interface. Both are in the form of particles of different morphologies, not a continuous layer, and are referred to as IMC-I and IMC-II. The former corresponds to Ni₃Sn₄ with Cu atoms residing in the Ni sublattice. It is uncertain whether IMC-II is Cu₆Sn₅ phase with Ni atoms residing in the Cu sublattice or a Cu–Ni–Sn ternary phase. Near the as-reflowed MOSFET/solder interface, both particles and a skeleton-like layer of Ni₃Sn₄ are observed. The primary microstructural dynamics during solid state aging are the coarsening of IMC particles and the reactions involving the unconsumed (after reflow) Ni- and the Ti-layer with Sn and Au. While the reaction with the Ni-layer yields only Ni₃Sn₄ intermetallic, the reaction involving the Ti-layer suggests the formation of Ti–Sn and Au–Sn–Ti intermetallics. The latter is due to the diffusion of Au from the substrate side to the die side. It is postulated that the kinetics of Au–Sn–Ti layer is primarily governed by the diffusion of Au through the Ni₃Sn₄ layer by a grain boundary mechanism.