Bi对Sn-0.7Cu无铅焊料微观组织和性能的影响

研究了Bi对Sn-0.7Cu焊料合金的微观组织、物理性能、润湿性能以及力学性能的影响.结果表明,在Sn-0.7Cu焊料合金中添加适量Bi后,合金的微观组织和性能有较明显的变化,Bi的加入能够降低焊料合金的熔点,提高润湿性能,同时对合金的力学性能也有很大影响,Bi能显著提高合金的抗拉强度,但合金的塑性会有所降低.     

Effects of Current Stressing on Shear Properties of Sn-3.8Ag-0.7Cu Solder Joints

Effects of electromigration on microstructure, shear strength, and fracture behavior of solder joints were investigated by single-ball shear samples of eutectic Sn-3.8Ag-0.7Cu (SAC) joined by Cu plates at two sides. The electromigration tests were conducted at a current density of about 1.1×103 A/cm2 and a working temperature of about 83℃. The results showed that the shear strength and flow stress decreased greatly after current stressing. Such a decrease was associated with no significant loss of the fract...     

Sn2.5Ag0.7CuxRE钎料时效焊点界面IMC研究

以Sn2.5Ag0.7CuxRE/Cu钎焊为研究对象,借助于扫描电镜和X衍射检测手段,研究了二硫化钼介质下时效焊点界面IMC组织结构特征及生长行为。实验结果表明:时效焊点界面Cu6Sn5IMC呈现由波浪状→扇贝状→层状的形态变化。焊点界面Cu6Sn5和Cu3Sn IMC的生长厚度与时效时间平方根呈线性关系,Cu6Sn5IMC具有较小的生长激活能、较大的生长系数。添加0.1%(质量分数)RE时,界面Cu6Sn5和Cu3Sn IMC的生长激活能最大,分别为81.74 kJ/mol和92.25 kJ/mol,对应焊点剪切强度最高。     

Effect of Bismuth on Intermetallic Compound Growth in Lead Free Solder/Cu Microelectronic Interconnect

The intermetallic compound (IMC) growth kinetics in pure Sn/Cu and Sn10 wt%Bi/Cu solder joints was studied, respectively, after they were aged at 160-210°C for different time. It was found that the total IMC in Sn10 wt%Bi/Cu joint developed faster than it did in pure Sn/Cu solder joint, when they were aged at the same temperature. And the activation energy Qa for total IMC in Sn10 wt%Bi/Cu joint was lower than that for pure Sn/Cu interconnect. The IMC growth process was discussed. The IMC Cu6Sn5 was enhanced in compensation of reduced IMC Cu3Sn growth. The work reveals that Bi element containing in lead free solder alloys with 10 wt% can enhance IMC growth in lead free solder/Cu joint during service.     

Wetting of microcrystalline and nanocrystalline Ni substrates by molten Sn-3.5Ag-0.7Cu alloy

Wetting behavior of molten Sn-3.5Ag-0.7Cu drops on Ni substrates with micrometer and nanometer grains was investigated using a modified sessile drop method. The wettability was poorer while the interfacial reactivity and atomic diffusivity were stronger for the nanocrystalline substrates compared with those for the microcrystalline substrates. The enhanced diffusion of the Ni atoms from the nanocrystallites greatly promoted the nucleation of the intermetallic compounds (IMCs), leading to a much thicker reaction layer and a more distinct regional distribution of the IMCs. On the other hand, the immediately roughened interface greatly decelerated the spreading of the triple line.     

热循环条件下SnAgCu/Cu焊点金属间化合物生长及焊点失效行为

研究了热循环过程中SnAgCu/Cu焊点界面金属间化合物的生长规律及焊点疲劳失效行为。提出了热循环条件下金属间化合物生长的等效方程以及焊点界面区不均匀体模型,并用有限元模拟的方法分析了热循环条件下焊点界面区的应力应变场分布及焊点失效模式。研究结果表明:低温极限较低的热循环,对应焊点的寿命较低。焊点的失效表现为钎料与金属间化合物的界面失效,且金属间化合物厚度越大,焊点中的累加塑性功密度越大,焊点越容易失效。     

Intermetallic compounds formed at the interface between Cu substrate and an Sn-9Zn-0.5Ag lead-free solder

The intermetallic compounds (IMCs) formed at the interface between Cu substrate and an Sn-9Zn-0.5Ag lead-free solder alloy have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED). The XRD patterns show that the main IMCs formed at the interface of Sn-9Zn-0.5Ag/Cu are γ-Cu₅Zn₈ and η′-Cu₆Sn₅. The Ag₃Sn IMC with orthorhombic structure was also observed at the Sn-9Zn-0.5Ag/Cu interface by TEM and ED analyses. The interfacial adhesion strength between the Cu substrate and Sn-9Zn-0.5Ag lead-free solder alloy is higher than that of the Sn-9Zn alloy due to the formation of Ag₃Sn IMC at the interface.     

Effect of High Magnetic Field on Growth Behavior of Compound Layers during Reactive Diffusion between Solid Cu and Liquid Al

The effect of magnetic field on the growth behavior of compound layer was examined at the interface between the solid Cu and liquid Al during reactive diffusion. It was found that the thickness of compound layer was reduced by the high magnetic field. The growth activation energy in β, γ1 and ε2 layers under a high magnetic field was larger than those in non magnetic circumstances, the increment percentage being 4.8%, 13.3% and 5.5%, respectively.     

Microstructure and interface evolution of Sn-2.5Bi-1.4In-1Zn-0.3Ag/Cu joint during isothermal aging

In this work, isothermal aging of Sn-2.5Bi-1.4In-1Zn-0.3Ag (in wt% hereafter) solder with Cu substrate for 0, 0.5, 2, 10, 100 and 200 h were conducted, and the variation of intermetallic compounds (IMCs) and microhardness were investigated. For the as-soldered sample, the Cu₆Sn₅ and Cu₅Zn₈ layers formed at the interface and Cu₆Sn₅, Cu₅Zn₈, Ag–Sn–In, Ag–Zn–In IMCs and Bi particles were observed in the solder matrix. During aging treatment, the Cu₅Zn₈ layer decomposed and finally disappeared at the interface, and a new Cu₃Sn layer appeared just below the Cu₆Sn₅ layer. Besides, in the solder matrix phase transformation from Cu₅Zn₈ into CuZn proceeded and the content of In in the Ag–Sn–In and Ag–Zn–In IMCs increased and Bi particles dispersed uniformly with the increasing aging time. Furthermore, the microhardness of the solder changed during aging owing to the observed phase evolution. These evolutions are always considered harmful to the reliability of the solder joints, especially the appearance and the growth of the Cu₃Sn layer.     

Sn-XAg-0.5Cu无铅钎料熔化特性、润湿性及力学性能研究

应用差示扫描量热(DSC)法、润湿平衡分析技术和拉伸试验,研究了Sn-XAg-0.5Cu(X=0.1~3.0)无铅钎料合金的熔化特性、润湿性能及力学性能。实验结果表明:所有钎料合金的开始熔化温度均为217.3℃;随合金中Ag含量增加,熔化温度区间变窄。钎料的润湿铺展面积和润湿力随Ag含量的增加而先显著增加,而后趋于稳定;对润湿铺展面积和润湿力(或润湿时间)产生显著影响的阈值Ag含量为1.0%(质量分数,下同)。Ag含量在0.5%~3.0%时,随着Ag含量的增加,钎料的断后伸长率逐渐下降,而抗拉强度和0.2%屈服强度均逐渐增加。     

Lateral features of Cu(In0.7Ga0.3)Se2-heterodiodes in the μm-scale by confocal luminescence and focused light beam induced currents

Polycrystalline Cu(In,Ga)Se₂ films (CIGSe) show substantial local variations of properties not only in regime of 10-100 nm but also in the scale length of few microns. We have analyzed optoelectronic properties of CIGSe heterodiodes by confocal luminescence and focused light beam induced currents (LBIC) versus temperature and excitation level with < 1 μm lateral resolution and we observe a strong dependence of the size of local patterns on excitation flux and a considerable dependence of the yield and the spectral shape of luminescence and of microscopic LBI currents on temperature. From experiments we derive activation energies for rates of non-radiative recombination of (2-7) meV and for minority carrier mobilities of about (60-70) meV. These energies are compared with local variations of band edges resulting from potential fluctuations which are formulated after an approach from literature and which has been fitted to experimental shifts of PL peaks and squeezing of PL spectra versus excitation flux. We estimate tunnel barriers for radiative transitions of trapped electrons of about (30-70) meV. Correlating our different results we attribute the activation energy for minority transport in CIGSe reflecting local variations of the conduction band edge mainly to spatial fluctuations of the optical band gap as a consequence of spatially varying elemental composition, and to variations of splitting of the quasi-Fermi levels introduced by spatially varying defect densities.     

Competitive Nucleation and Rapid Growth of Co-Si Intermetallic Compounds during Eutectic Solidification under Containerless Processing Condition

The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of ’lamellar-anomalous-divorced’ eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diflusion control. The calculated coupled zone demonstrates that (Co2Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi2) covers a composition range from 40.8% to 43.8% Si.     

Kinetic Aspects of the Nanocrystallization and Evolution of Microhardness in Al92-XNi8LaX Amorphous Alloys

Marginal glass forming Al-based alloys have attracted considerable attention due to the occurrence of a primary crystallization reaction that yields a microstructure consisting of uniformly dispersed Al-nanocrystals embedded in an amorphous matrix. Rapidly solidified Al-alloys ribbons containing 8 at.% Ni and 4-6 at.% La were prepared by single roller melt-spinning technique. As-melt-spun and annealed ribbons were investigated by means of differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and hardness measurements. XRD studies revealed that ribbons are fully amorphous in the as-melt-spun state. DSC studies showed that crystallization proceeds in two or three stages that are sensitively influenced by La content. Crystallizations kinetics were analysed by Kissinger and Johnson-Mehl-Avrami approaches. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding structural evolution.     

Creep Behavior of As-Cast Ti-48Al-2Cr Intermetallic Alloy for Aerospace and Automotive Applications

The creep properties of as-cast Ti-48Al-2Cr (at%) alloy which had been strengthen with addition of 2 at% Cr were investigated. Tensile creep experiments were performed in air at temperatures from 600-800°C and initial stresses ranging from 150 to 180 MPa. Stress exponent and activation energy were both measured. Data indicates that the alloy exhibits steady state creep behavior and the steady state creep rate is found to depend on the applied load and temperature. The measured power law stress exponent for steady state creep rate is found to be close to 3 and the apparent activation energy for creep is calculated to be 15.7 kJ/mol. The creep resistance of the present alloy was also compared with binary Ti-48Al (at%) to evaluate the effect of Cr addition on creep resistance of TiAl. It is concluded that addition of 2 at% of Cr does not have significant effect on the creep resistance of TiAl.     

The relation between the distribution of dihedral angles and the wetting angle during liquid phase sintering

This study presents a Monte Carlo method to simulate the effect of the wetting angle on a dihedral angle distribution and on a degree of the grain boundary penetration of a liquid phase during liquid phase sintering. For the high probability for wetting, the number of the grain boundary penetration of a liquid phase increased while the wetting angle decreased and a few bonded grains maintained a stable grain boundary with high dihedral angles. This finding contradicts the classical prediction that smaller values of mean dihedral angles produce superior wettability.