Ce对Sn-Ag-Cu系焊料合金的组织与性能影响

通过添加稀土Ce研究了Sn-3.0Ag-2.8Cu系焊料合金的显微组织和性能。用光学显微镜、SEM、EDX对其显微组织进行分析,并且对其导电性,润湿性,硬度等重要性能进行测试。结果表明,添加稀土w(Ce)为1%焊料合金的导电性明显提高;而润湿角明显减小,润湿性增强;同时焊料合金的硬度也有所增加。     

Effect of Ni-Coated Carbon Nanotubes on the Corrosion Behavior of Sn-Ag-Cu Solder

In this study, the effect of Ni-coated carbon nanotubes (Ni-CNTs) on the corrosion resistance of 95.8Sn-3.5Ag-0.7Cu (SAC) solder at ambient temperature in 3.5 wt.% NaCl solution was investigated using the potentiodynamic polarization method. The corrosion products were analyzed by field-emission scanning electron microscopy (S4800), energy-dispersive spectroscopy, and x-ray diffraction. The results showed that addition of Ni-CNTs enhanced the corrosion resistance of the SAC solder and that increasing the content of Ni-CNTs made the effect more evident. The mechanism of the corrosion resistance improvement is the formation of a compact corrosion layer of Ni-CNTs that provides an inert physical barrier to the initiation and development of corrosion. Furthermore, in the corrosion microcell produced by the Ni-CNTs dispersed in the SAC solder, the Ni-CNTs act as a third phase (electrode) which contributes to reducing the galvanic corrosion between Sn anode and Ag₃Sn cathode. Hence, the corrosion resistance of the composite solders was improved.     

Specific Heat Capacities of Sn-Zn-Based Solders and Sn-Ag-Cu Solders Measured Using Differential Scanning Calorimetry

The specific heat capacities (C _p) of Sn-Zn-based solders and Sn-Ag-Cu solders have been studied using differential scanning calorimetry. The procedure of measuring the specific heat capacity followed the standard test method designed by the American Society for Testing and Materials (ASTM) E1269-05. The results of this work are lists of specific heat capacities of Sn-9Zn, Sn-9Zn-xAg (x = 0.1, 0.5, 1, 2, and 3), Sn-9Zn-0.5Ag-yAl (y = 0.1, 0.2, and 0.5), Sn-9Zn-0.5Ag-yGa (y = 0.1, 0.2, and 0.5), Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga, and Sn-zAg-0.5Cu (z = 1.0, 2.0, 3.0, and 3.5). The study also found that C _p increased with increasing heating temperature. Furthermore, the lead-free solders investigated have a higher specific heat capacity than the traditional Sn-37Pb solder. Among the studied lead-free solders, Sn-3.5Ag-0.5Cu has the lowest C _p and Sn-9Zn-0.1Ag has the highest C _p. Increased silver content in the Sn-9Zn-xAg and Sn-xAg-0.5Cu solder alloys was also found to effectively lower their C _p.     

Effects of Minor Additions of Zn on Interfacial Reactions of Sn-Ag-Cu and Sn-Cu Solders with Various Cu Substrates during Thermal Aging

The effects of Zn additions to Sn-0.7Cu and Sn-3.8Ag-0.7Cu (all in wt.% unless specified otherwise) Pb-free solders on the interfacial reactions with Cu substrates were investigated. The study was focused on the intermetallic compound (IMC) growth, Cu consumption and void formation as a function of thermal aging and solder composition. Four different kinds of Cu substrates (high-purity Cu, oxygen-free Cu, vacuum-sputtered Cu, and electroplated Cu) were prepared to compare their interfacial reaction behaviors with Zn-added solders. Thermal aging was performed at 150°C for up to 1000 h to accelerate the interfacial reactions between solders and Cu substrates. Growth of IMCs (Cu₆Sn₅ and Cu₃Sn) in Zn-added solders was slower than those without Zn additions. The growth of the Cu₃Sn phase, in particular, was drastically reduced in the Zn-added solders on all four Cu substrates. On an electroplated Cu substrate, numerous voids were observed in the Cu₃Sn phase for Sn-Cu and Sn-Ag-Cu solders aged at 150°C for 1000 h. However, these voids were largely eliminated in the Zn-added solders. On the other three Cu substrates, the conditions which produce a high density of voids were not found after aging both solders with and without Zn. The Cu consumption with Zn-added solders was also significantly lower. The beneficial effects of Zn additions on interfacial reaction behaviors are reported, and the corresponding mechanisms in suppressing void formation and Cu consumption due to Zn additions will be discussed.     

Sn-Ag-Cu无铅焊料的可靠性研究

欧盟对电子产品的RoHS法令的实施加快了电子封装钎焊无铅化的步伐。Sn-Ag-Cu焊料以其优良的机械性能和可焊性,逐渐得到了国际社会的认可。文章对无铅焊料的发展过程,Sn-Ag-Cu合金的性能进行了综述,重点介绍了Sn-Ag-Cu焊点的可靠性,包括试验法和有限元法。最后对Sn-Ag-Cu焊料的应用前景进行了展望。     

Multiscale Modeling of the Effect of Micro-alloying Mn and Sb on the Viscoplastic Response of SAC105 Solder

This study investigates the time-dependent viscoplastic response of two relatively new SAC105-X solders—SAC105-05Mn (Sn_1.0Ag_0.5Cu (SAC105) doped with 0.05 wt.% Mn), and SAC105-55Sb (SAC105 doped with 0.55 wt.% Sb). The results showed that the addition of Mn or Sb increases the creep resistance of SAC105 solder by one to two orders of magnitude at the tested stress levels of 2–20 MPa. The addition of Mn as a fourth alloying element promotes homogeneous distribution of micron-scale Cu₆Sn₅ intermetallic compounds (IMCs), thereby reducing their interparticle spacing as compared to that of SAC105. On the other hand, addition of Sb does not change the spacing of the Cu₆Sn₅ particle, but promotes the formation of uniformly sized Sn dendritic lobes, homogeneously distributed in the whole solder joint. Moreover, Sb also forms a solid solution with Sn and strengthens the Sn matrix in SAC105-55Sb itself. The effects of these microstructural changes (obtained using image processing) on the secondary creep constitutive response of SAC105 solder interconnects were then modeled using a mechanistic multiscale creep model. The mechanistic model was able to accurately capture the trends in the secondary creep constitutive response of the alloys and to explain the improvement in creep resistance of SAC105 due to the addition of Mn and Sb.     

Impact of Thermal Cycling on Sn-Ag-Cu Solder Joints and Board-Level Drop Reliability

The electronic packaging industry uses electroless nickel immersion gold (ENIG) or Cu-organic solderability preservative (Cu-OSP) as a bonding pad surface finish for solder joints. In portable electronic products, drop impact tests induce solder joint failures via the interfacial intermetallic, which is a serious reliability concern. The intermetallic compound (IMC) is subjected to thermal cycling, which negatively affects the drop impact reliability. In this work, the reliability of lead-free Sn-3.0Ag-0.5Cu (SAC) soldered fine-pitch ball grid array assemblies were investigated after being subjected to a combination of thermal cycling followed by board level drop tests. Drop impact tests conducted before and after thermal aging cycles (500, 1000, and 1500 thermal cycles) show a transition of failure modes and a significant reduction in drop durability for both SAC/ENIG and SAC/Cu-OSP soldered assemblies. Without thermal cycling aging, the boards with the Cu-OSP surface finish exhibit better drop impact reliability than those with ENIG. However, the reverse is true if thermal cycle (TC) aging is performed. For SAC/Cu-OSP soldered assemblies, a large number of Kirkendall voids were observed at the interface between the intermetallic and Cu pad after thermal cycling aging. The void formation resulted in weak bonding between the solder and Cu, leading to brittle interface fracture in the drop impact test, which resulted in significantly lower drop test lifetimes. For SAC/ENIG soldered assemblies, the consumption of Ni in the formation of NiCuSn intermetallics induced vertical voids in the Ni(P) layer.     

激光快速成形过程的热行为及其影响

建立了激光快速成形(LRF)过程熔池的比色测温系统，分别采用实时跟踪和定点测量两种方式实现了熔池温度和熔池后沿冷却速率(温度梯度)的测量。结果表明，随着激光功率和送粉率的增大，熔池温度升高，熔池后沿冷却速率减小;随着激光扫描速度的增加，熔池温度下降，熔池后沿冷却速率增大。单道多层熔覆和多道搭接熔覆过程温度检测结果发现，随着沉积层数和沉积道数的增加，成形过程呈现热累积效应，即熔池温度逐渐升高，而熔池后沿的冷却速率则呈现完全相反的趋势。     

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。     

Influence of Surface Segregation on Wetting of Sn-Ag-Cu (SAC) Series and Pb-Containing Solder Alloys

Wetting of Sn-Ag-Cu (SAC) series solder alloys to solid substrates is strongly influenced by surface segregation of low-level bulk impurities in the alloys. We report in situ and real-time Auger electron spectroscopy measurements of SAC alloy surface compositions as a function of temperature as the alloys are taken through the melting point. A dramatic increase in the amount of surface C (and frequently O) is observed with temperature, and in some cases the alloy surface is nearly 80 at.% C at the melting point. The C originates from low-level impurities incorporated during alloy synthesis and inhibits wetting because C acts as a blocking layer to reaction between the alloy and substrate. A similar phenomenon has been observed over a wide range of (SAC and non-SAC) alloys synthesized by a variety of techniques. That solder alloy surfaces at melting have a radically different composition from the bulk uncovers a key variable that helps to explain the wide variability in contact angles reported in previous studies of wetting and adhesion.     

基于TASPCB的PCB热分析、热设计技术探讨

简要地介绍了电子产品热分析、热设计的重要性及其方法的发展。重点介绍基于TASPCB环境下的电子元器件热模型的建立方法和电子元器件热功耗评估技术,并给出典型PCB热设计的实例,提出电子产品PCB设计的热设计优化措施。     

Effect of Cu concentration on the reactions between Sn-Ag-Cu solders and Ni

The reaction between the Sn-Ag-Cu solders and Ni at 250°C for 10 min and 25 h was studied. Nine different Sn-Ag-Cu solders, with the Ag concentration fixed at 3.9 wt.% and Cu concentrations varied between 0.0–3.0 wt.%, were used. When the reaction time was 10 min, the reactions strongly depended on the Cu concentration. At low-Cu concentrations (≦0.2 wt.%), only a continuous (Ni_1−xCu_x)₃Sn₄ layer formed at the interface. When the Cu concentration increased to 0.4 wt.%, a continuous (Ni_1−xCu_x)₃Sn₄ layer and a small amount of discontinuous (Cu_1−yNi_y)₆Sn₅ particles formed at the interface. When the Cu concentration increased to 0.5 wt.%, the amount of (Cu_1−yNi_y)₆Sn₅ increased and (Cu_1−yNi₆)₆Sn₅ became a continuous layer. Beneath this (Cu_1−yNi_y)₆Sn₅ layer was a very thin but continuous layer of (Ni_1−xCu_x)₃Sn₄. At higher Cu concentrations (0.6–3.0 wt.%), (Ni_1−xCu_x)₃Sn₄ disappeared, and only (Cu_1−yNi_y)₆Sn₅ was present. The reactions at 25 h also depended strongly on the Cu concentration, proving that the strong concentration dependence was not a transient phenomenon limited to a short reaction time. The findings of this study were rationalized using the Cu-Ni-Sn isotherm. This study shows that precise control over the Cu concentration in solders is needed to produce consistent results.     

The Effect of Sb Addition on Sn-Based Alloys for High-Temperature Lead-Free Solders: an Investigation of the Ag-Sb-Sn System

Today there is renewed interest in alloys belonging to the Sb-Sn-X (X = Cu, Ag, Bi) ternary systems and their phase equilibria, phase transformations, and thermodynamic properties because of their possible use as high-temperature lead-free solders in the electronics industry. The integral mixing enthalpy of Ag-Sb-Sn liquid alloys has been measured along five different sections (Ag_0.25Sn_0.75, Ag_0.50Sn_0.50, Sb_0.30Sn_0.70, Sb_0.50Sn_0.50, and Sb_0.70Sn_0.30) at 530°C, 600°C, and 630°C, using a high-temperature Calvet calorimeter by dropping pure elements (Ag or Sb) in the binary alloy liquid bath. The ternary extrapolation models of Muggianu and Toop were used to calculate the integral enthalpy of mixing and to compare measured and extrapolated values. Selected ternary alloys have been prepared for thermal investigation by using a differential scanning calorimeter at different heating/cooling rates in order to clarify the temperature of the invariant reactions and the crystallization path.     

Effects of Sb,Zn doping on structural,electrical and optical properties of SnO2 thin films

Highly transparent, low resistive pure and Sb, Zn doped nanostructured SnO₂ thin films have been successfully prepared on glass substrates at 400° C by spray pyrolysis method. Structural, electrical and optical properties of pure and Sb, Zn doped SnO₂ thin films are studied in detail. Powder X-ray diffraction confirms the phase purity, increase in crystallinity, size of the grains (90–45 nm), polycrystalline nature and tetragonal rutile structure of thin films. The scanning electron microscopy reveals the continuous change in surface morphology of thin films and size of the grains decrease due to Sb, Zn doping in to SnO₂. The optical transmission spectra of SnO₂ films as a function of wavelength confirm that the optical transmission increases with Sb, Zn doping remarkably. The optical band gap of undoped film is found to be 4.27 eV and decreases with Sb, Zn doping to 4.19 eV, 4.07 eV respectively. The results of electrical measurements indicate that the sheet resistance of the deposited films improves with Sb, Zn doping. The Hall measurements confirm that the films are degenerate n-type semiconductors.     

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。     

Influence of High-G Mechanical Shock and Thermal Cycling on Localized Recrystallization in Sn-Ag-Cu Solder Interconnects

The impact of isothermal aging and recrystallized grain structure distribution on mechanical shock and thermal cycling performance of solder joints with 1% and 3% silver content Sn-Ag-Cu interconnects were investigated. Localized recrystallized grain structure distributions were analyzed to identify correlations between the microstructure evolution and shock performance. The results reveal that the shock tolerance depends on the amount of shock energy that can be absorbed during each shock cycle, which depends on microstructural features. Based on the recrystallized grain distribution, additional isothermal aging in 1% silver Sn-Ag-Cu interconnects shows improved shock performance, whereas degraded shock performance was observed in 3% Sn-Ag-Cu interconnects. Using the same grain boundary distribution analysis on thermally cycled samples, relationships between the particle size distribution, localized recrystallized grain structure development, shock, and thermomechanical performance were identified: finer particle spacing is beneficial for thermal cycling as it resists grain boundary generation, while conversely, wider particle spacing facilitates recrystallization and grain boundary mobility that allows Sn to absorb shock energy.     

空间目标热分析建模研究

讨论了空间目标热分析的主要研究方法,建立了空间目标的整体模型,分析了目标在空间背景下的热平衡方程,并通过热网络法和有限元对目标与环境间的热交换进行了计算,讨论了不同角系数情况下空间目标的静态温度场分布.     

微电子封装中Sn—Aq—Cu焊点剪切强度研究

提出了一种对微电子封装器件中焊点剪切强度进行测试的方法，可有效降低测试误差。利用该方法，对Sn—Ag—Cu无铅焊料分别在Cu基板和Ni-P基板上形成的焊点，经不同的热时效后的剪切强度进行了测量，并对断裂面的微观结构进行了研究。结果表明，新的剪切测试方法误差小，易于实施，焊点剪切强度、断裂面位置与焊料在不同基板界面上金属间化合物的形貌、成分有关。