Ni颗粒增强无铅复合钎料中IMC形态之演变

通过改变钎焊工艺曲线来控制热输入量。研究了Ni颗粒周围金属间化合物(IMC)以及钎料/基板界面处IMC的形态演变。结果表明,随着热输入量由低变高,Ni颗粒周围IMC形态从向日葵状向多边形状发展,最终成为遍布整个钎料层的细碎的IMC形态;而钎料/基板界面层,因Ni颗粒的加入,出现大量的三维孔洞状IMC。从而形成了Cu元素扩散的通道,使得界面层厚度增加且呈线性增长趋势。     

颗粒增强Sn-Ag基无铅复合钎料显微组织与性能

通过外加法向Sn-3.5Ag焊料中加入体积分数为10%的微米级Cu、Ni颗粒制备了无铅复合钎料,对钎料的显微组织、拉剪及润湿性能进行了研究。结果表明,颗粒周围以及基板界面处的显微组织中生成了金属间化合物,其形态及大小因加入颗粒而不同。颗粒的加入提高了钎料钎焊接头的剪切强度,其中Cu颗粒增强的接头的剪切强度提高了33%,Ni颗粒的提高了20%。两种复合钎料的铺展面积均下降了约15%,其中Cu颗粒增强复合钎料润湿角由11°增加到18°。     

混合稀土对Sn-0.70Cu-0.05Ni钎料组织与性能的影响

向Sn-0.70Cu-0.05Ni无铅钎料中添加微量混合稀土元素RE(主要是La和Ce),研究了RE添加量对该钎料合金显微组织及性能的影响.结果表明,添加微量的RE能显著细化该钎料合金组织,抑制金属间化合物的生长,改善合金的组织分布,提高钎料的润湿性及力学性能.当w(RE)为0.10%时,钎料的润湿力,拉伸强度分别为3...     

基于纳米压痕法的SnBi-xNi钎料的塑性比较

借助纳米压痕的方法,采用压痕形成过程中塑性应变与总应变的比值来表征钎料塑性。对Sn Bi-x Ni(x=0,0.05,0.1,0.15和0.2)成分钎料的硬度、弹性模量及塑性进行了对比。结果表明:Sn58Bi钎料合金加入Ni元素后,钎料硬度和弹性模量升高。当Sn58Bi-x Ni钎料中Ni含量的质量分数为0.1%时,其硬度及弹性模量最大。当Ni质量分数超过0.1%时,钎料的硬度与弹性模量有所下降。当添加Ni元素质量分数为0.05%~0.1%时,钎料合金的组织得到了细化,钎料合金的塑性提高;当Ni质量分数大于0.15%时,钎料的塑性降低。     

微量锗对Sn-0.7Cu-0.05Ni钎料微观组织与性能的影响

为改善Sn-0.7Cu-0.05Ni钎料抗氧化性差及溶铜速率快的问题,向Sn-0.7Cu-0.05Ni钎料中添加微量锗,研究了不同锗添加量(质量分数0.01%~0.10%)对SnCuNi钎料合金显微组织及性能的影响。结果表明,微量的锗能显著细化Sn-0.7Cu-0.05Ni钎料合金组织,抑制金属间化合物的生长,改善合金的组织分布,提高钎料的润湿性及力学性能。此外,锗的添加还能显著提高钎料的抗氧化性并降低溶铜速率,当锗的质量分数从0增至0.10%时,溶铜速率从0.117 m/s降至0.110 m/s。     

Sn-Zn系无铅钎料最新进展

Sn-Zn系钎料熔点与传统Sn-37Pb钎料十分接近,成本低廉,被研究者所推崇。由于Zn的存在导致Sn-Zn钎料润湿性差及抗氧化性不足,阻碍了该钎料的发展。添加合金元素和纳米颗粒是改善Sn-Zn钎料组织和性能行之有效的方法之一,为国内外研究者所推崇。结合国内外Sn-Zn系无铅钎料最新研究成果,探讨添加微量的合金元素In、Ni、Cr、Ga、Bi、Cu、Al、Ag、稀土元素及纳米颗粒对钎料润湿性、抗氧化性、力学性能、显微组织和界面组织的影响,同时简述有关钎剂对Sn-Zn的影响,并对Sn-Zn系钎料的发展趋势进行分析与展望。     

镍磷锗对SnAgCuCe系钎料性能及组织的影响

为改善Sn3.0Ag0.5CuCe(SAC305Ce)无铅钎料的性能,向其添加了微量Ni、P及Ge并进行了研究。结果表明,同时添加质量分数为0.10%Ni、0.01%P和0.05%Ge,150℃时效168h后,钎料综合性能最佳。钎料合金组织中共晶组织的分布较为密集,IMC厚度有轻微增加,润湿力约0.48mN,剪切强度约62MPa。     

Y2O3增强Sn-3Ag-0.5Cu复合无铅钎料

研究了稀土氧化物颗粒增强复合无铅钎料Sn-3Ag-0.5Cu-Y2O3的钎焊接头的显微组织形貌、性能特点及有关影响机制.结果表明:Y2O3增强颗粒均匀分布于Sn-3Ag-0.5Cu钎料基体中,不仅细化了钎焊接头中共晶相Ag3Sn和Cu6Sn5相颗粒尺寸,而且也显著提高了钎焊接头的剪切强度.另外适量Y2O3颗粒的添加对钎料润湿性影响不大.     

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。     

低银焊料超声雾化制粉及焊膏性能研究

在Sn-0.7Cu-0.1Ag低银焊料基础上进行微合金化,研究了Ag和Ni对钎料润湿性以及元素X对钎料润湿抗氧化性的影响,比较了超声波雾化法与气体雾化法制备焊锡粉的区别.结果表明:随着Ag含量增加,钎料合金的润湿力提高并且润湿时间减少.添加Ni元素,钎料润湿力并没有明显变化,润湿时间略有减小.高活性焊剂可以显著提高钎料润湿力,同时缩短润湿时间.在低银钎料中添加微量元素X,质量分数超过0.003%时,可以显著改善钎料抗氧化性能.采用超声波雾化法较气体雾化法制得的低银焊锡粉,异形粉比例明显下降.     

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.     

Creep properties of eutectic Sn-3.5Ag solder joints reinforced with mechanically incorporated Ni particles

The creep deformation behavior of eutectic Sn-3.5Ag based Ni particle rein forced composite solder joints was investigated. The Ni particle reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic Sn-3.5Ag solder paste. Static-loading creep tests were carried out on solder joint specimens at 25 C, 65 C, and 105 C, representing homologous temperatures ranging from 0.6 to 0.78. A novel-design, miniature creep-testing frame was utilized in this study. Various creep parameters such as the global and localized creep strain, steady-state creep rate, onset of tertiary creep and the activation energy for creep were quantified by mapping the distorted laser ablation pattern imprinted on the solder joint prior to testing. The Ni-reinforced composite solder joint showed improved creep resistance compared to the results previously reported for eutectic Sn-3.5Ag solder, Sn-4.0Ag-0.5Cu solder alloys, and for eutectic Sn-3.5Ag solder reinforced with Cu or Ag particle reinforcements. The activation energy for creep was ∼0.52 eV for Sn-3.5Ag and Sn-4Ag-0.5Cu solder alloys. The activation energies ranged from 0.55–0.64 eV for Cu, Ag, and Ni reinforced composite solder joints, respectively. Most often, creep fracture occurred closer to one side of the solder joint within the solder matrix.     

Reliability of composite solder bumps produced by an in-situ process

In an attempt to develop a thermally stable solder system, an in-situ Pb-Sn solder composite reinforced with Cu₆Sn₅ dispersoids was investigated for its thermal stability. The stability was evaluated mainly by measuring the growth rate of intermetallics at in-situ composite solder/BLM interface as a function of the number of reflow soldering cycles and aging time. The rates were compared with those of the eutectic Pb-Sn and Sn-Ag solders. After the thermal treatments, the solder joints were tested for their shear strengths. The results indicated that the in-situ composite solder has a higher shear strength and better thermal stability than the eutectic Pb-Sn solder. Jointly appointed by CAAM at POSTECH     

Formation and growth of intermetallics around metallic particles in eutectic Sn-Ag solder

Incorporation of metallic particulate reinforcements in eutectic Sn-Ag solder results in the formation of intermetallic compounds (IMCs) along particulate/solder interfaces with different morphologies. For instance, “sunflower” and “blocky faceted” IMC shapes have been observed around Ni particle reinforcements incorporated in the eutectic Sn-Ag solder matrix. The time and temperature above solder liquidus during the heating stage of the reflow process has been found to play a significant role in determining the IMC morphology in these Ni particulate-reinforced solders. Similar studies were carried out with Cu and Ag particulate reinforcements using the same solder matrix. The amount of heat input caused no significant change in morphology of the IMCs formed around Cu and Ag particulate reinforcements. Also, the IMC morphology around Ni particles was sensitive to the Cu content in the solder, whether the Cu came from the substrate during reflow or it was already present within the solder.     

A reliability comparison of electroplated and stencil printed flip-chip solder bumps based on UBM related intermetallic compound growth properties

The effects of under bump metallurgy (UBM) microstructures on the intermetallic compound (IMC) growth of electroplated and stencil printed eutectic Sn-Pb solder bumps were investigated. The process parameters and their effects on UBM surface morphology and UBM shear strength were studied. For the electroplating process, the plating current density was the dominant factor to control the Cu UBM microstructure. For the stencil printing process, the zincation process has the most significant effect on the Ni UBM surface roughness and Ni grain sizes. In both processes, the good adhesion of UBM to aluminum can be obtained under suitable UBM processing conditions. Samples with different UBM microstructures were prepared using the two processes. The resulting samples were thermal aged at 85/spl deg/C, 120/spl deg/C, and 150/spl deg/C. It was observed that the Cu UBM surface roughness had larger effect on the IMC growth and solder ball shear strength than the Ni UBM surface roughness. The thickness of Cu/sub 3/Sn and Cu/sub 6/Sn/sub 5/ IMC depended strongly on the UBM microstructure. However, for Ni/Au UBM, no significant dependence was observed. More likely, the thickness of Au-Ni-Sn IMC near the IMC/solder interface was controlled by the amount of gold and the gold diffusion rate in the solder. Shear tests were performed after thermal aging tests and thermal/humidity tests. Different failure modes of different sample groups were analyzed. Electroless Ni UBM has been developed because it is a mask-less, low-cost process compared to electroplated Cu UBM. This study demonstrated that the process control was much easier for Ni UBM due to its lower reactivity with Sn material. These properties made Ni UBM a promising candidate for the lead-free solder applications.     

Eutectic Sn-Ag solder bump process for ULSI flip chip technology

A novel eutectic Pb-free solder bump process, which provides several advantages over conventional solder bump process schemes, has been developed. A thick plating mask can be fabricated for steep wall bumps using a nega-type resist with a thickness of more than 50 μm by single-step spin coating. This improves productivity for mass production. The two-step electroplating is performed using two separate plating reactors for Ag and Sn. The Sn layer is electroplated on the Ag layer. Eutectic Sn-Ag alloy bumps can be easily obtained by annealing the Ag/Sn metal stack. This electroplating process does not need strict control of the Ag to Sn content ratio in alloy plating solutions. The uniformity of the reflowed bump height within a 6-in wafer was less than 10%. The Ag composition range within a 6-in wafer was less than ±0.3 wt.% Ag at the eutectic Sn-Ag alloy, analyzed by ICP spectrometry. SEM observations of the Cu/barrier layer/Sn-Ag solder interface and shear strength measurements of the solder bumps were performed after 5 times reflow at 260°C in N₂ ambient. For the Ti(100 nm)/Ni(300 nm)/Pd(50 nm) barrier layer, the shear strength decreased to 70% due to the formation of Sn-Cu intermetallic compounds. Thicker Ti in the barrier metal stack improved the shear strength. The thermal stability of the Cu/barrier layer/Sn-Ag solder metal stack was examined using Auger electron spectrometry analysis. After annealing at 150°C for 1000 h in N₂ ambient, Sn did not diffuse into the Cu layer for Ti(500 nm)/Ni(300 nm)/Pd(50 nm) and Nb(360 nm)/Ti(100 nm)/Ni(300 nm)/Pd(50 nm) barrier metal stacks. These results suggest that the Ti/Ni/Pd barrier metal stack available to Sn-Pb solder bumps and Au bumps on Al pads is viable for Sn-Ag solder bumps on Cu pads in upcoming ULSIs     

Isothermal aging effects on the microstructure and solder bump shear strength of eutectic Sn37Pb and Sn3.5Ag solders

The reliability of the eutectic Sn37Pb (63%Sn37%Pb) and Sn3.5Ag (96.5%Sn3.5%Ag) solder bumps with an under bump metallization (UBM) consisting of an electroless Ni(P) plus a thin layer of Au was evaluated following isothermal aging at 150 °C. All the solder bumps remained intact after 1500 h aging at 150 °C. Solder bump microstructure evolution and interface structure change during isothermal aging were observed and correlated with the solder bump shear strength and failure modes. Cohesive solder failure was the only failure mode for the eutectic Sn37Pb solder bump, while partial cohesive solder failure and partial Ni(P) UBM/Al metallization interfacial delamination was the main failure mode for eutectic Sn3.5Ag solder bump.     

一种低成本倒装芯片用印刷凸焊点技术的研究

利用化学镀底部金属化层结合丝网印刷制作凸焊点的技术,通过剪切实验得到了凸焊点的剪切强度,用电子显微镜对失效表面进行了分析研究,应用SEM及EDAX分析了凸焊点的组织结构与成分变化,对热老炼后凸焊点的强度变化进行了研究。结果表明凸焊点内部组织结构的变化是剪切失效的主要原因。经X光及扫描声学显微镜检测,表明组装及填充工艺很成功。对已完成及未进行填充的两种FCOB样品进行热疲劳实验对比,发现未进行填充加固的样品在115周循环后出现失效,而经填充加固后的样品通过了1 000周循环,表明下填料明显延长了倒装焊封装的热疲劳寿命。     

Effect of dwell times on thermomechanical fatigue behavior of Sn-Ag-based solder joints

Thermomechanical fatigue (TMF) caused by the mismatch in the coefficient of thermal expansion (CTE) between solder and substrate gradually degrades the mechanical properties of solder joints during service. Solder joints fabricated with eutectic Sn-Ag and Sn-Ag solder with Cu or Ni were subjected to TMF between −15°C and +150°C with dwell times of 115 min at high-temperature extreme and 20 min at low-temperature extreme. Characterization of surface damage and residual-mechanical strength of these solder joints were carried out after 0, 250, 500, and 1,000 TMF cycles. Results obtained from this study were compared with those obtained with longer dwell time at lower temperature extreme. The solder joints that experienced longer dwell times at high-temperature extreme exhibited less surface-damage accumulation and less decrease in simple-shear strength as compared to those that experienced longer dwell times at low-temperature extreme. Quaternary alloys containing small amounts of Cu and Ni exhibit better TMF performance than binary and ternary alloys under TMF cycling with longer dwell times at high-temperature extreme.