Cu/Al引线键合界面金属间化合物生长过程的原位实验研究

铜引线键合由于在价格、电导率和热导率等方面的优势有望取代传统的金引线键合, 然而Cu/Al引线键合界面的金属间化合物(intermetallic compounds, IMC)的过量生长将增大接触电阻和降低键合强度, 从而影响器件的性能和可靠性. 针对以上问题, 本文基于原位高分辨透射电子显微镜技术, 研究了在50–220 ℃退火温度下, Cu/Al引线键合界面IMC的生长问题, 实时观测到了Cu/Al IMC的动态生长及结构演变过程. 实验结果表明, 退火前颗粒状的Cu/Al IMC 分布在键合界面, 主要成分为Cu₉Al₄, 少量成分为CuAl₂. 退火后Cu/Al IMC的成分是: 靠近Cu一端为Cu₉Al₄, 远离Cu的一端为CuAl₂. 同时基于原位观测Cu/Al IMC的动态生长过程, 计算得到了Cu/Al IMC 不同温度下的反应速率和激活能, 给出了基于原位实验结果的Cu/Al IMC的生长公式, 为优化Cu/Al引线键合工艺和提高Cu/Al引线键合的可靠性提供了指导.     

Wetting and reaction promoted by ultrasound between sapphire and liquid Al–12Si alloy

Ultrasonic-assisted wetting between sapphire bulks and liquid Al–12Si alloy in an atmospheric environment at 620 °C is carried out in this study. Complete, rather than partial, wetting and joining can be achieved with the aid of ultrasound. Growth of epitaxial alumina on sapphire bulks is promoted dramatically during ultrasonic-assisted wetting comparing to that during hot-dipping without ultrasound. XRD results show that the epitaxial alumina is non-crystalline. This indicates that the temperature on the surface of the sapphire substrate is not more than 1200 °C even though the collapse of acoustic cavitation bubbles could theoretically produce extremely high temperature. The bonding force at the interface between the Al–Si alloy and sapphire is strengthened because of the epitaxial alumina. The interfacial shear strength of sapphire/Al–Si alloy can reach as high as 60–65 MPa. The fracture morphology shows that cracks initiated at the interface between Si grains and the epitaxial alumina on sapphire. This result is especially useful for the joining of metals and ceramics.     

Interdiffusion of Al-Ni system enhanced by ultrasonic vibration at ambient temperature

At ambient temperature, Al–1%Si wire of 25 μm diameter was bonded successfully onto the Au/Ni/Cu pad by ultrasonic wedge bonding technology. Physical process of the bond formation and the interface joining essence were investigated. It is found that the wire was softened by ultrasonic vibration, at the same time, pressure was loaded on the wire and plastic flow was generated in the bonding wire, which promoted the diffusion for Ni into Al. Ultrasonic vibration enhanced the interdiffusion that resulted from the inner defects such as dislocations, vacancies, voids and so on, which ascribed to short circuit diffusion.     

Preparation of CuO nanoparticles by metal salt-base reaction in aqueous solution and their metallic bonding property

This article describes a method for preparing CuO nanoparticles in aqueous solution, and a demonstration of feasibility of metallic bonding with the use of the CuO particles. Colloid solution of CuO nanoparticles was prepared from Cu(NO₃)₂ aqueous solution (0.01 M) and NaOH aqueous solution (0.019 M) at 5–80 °C. Leaf-like aggregates with an average size of 567 nm composed of CuO nanoparticles were produced at 20 °C. The size of leaf-like aggregates decreased with increasing reaction temperature. Metallic copper discs could be bonded using the CuO nanoparticles under annealing at 400 °C and pressurizing at 1.2 MPa for 5 min in H₂ gas. A shear strength required for separating the bonded discs was 25.4 MPa for the CuO nanoparticles prepared at 20 °C, whose aggregates were the largest among the CuO particles examined. These results indicated that the formation of leaf-like aggregates of CuO nanoparticles led to efficient metallic bonding.     

Simulation of the trajectory of a punted rugby ball taking into account the asymmetrical pressure distribution caused by the seams

Abstract  

This paper describes the effect of the seams of a rugby ball on the side force and the flight trajectory of the punted kick. Measurement of the aerodynamic force on a non-spinning rugby ball reveals that the side force coefficient depends on the position of the seam as well as the angle of attack. It was found from pressure-sensitive paint measurements that the seam of the ball is the trigger for initiating low pressure when the seam is situated around 60° from the stagnation point. The flight trajectory of the fluctuating ball can be obtained by numerically integrating the six degree-of-freedom non-linear equations of motion. It was shown that a slower spinning ball fluctuates from side to side during flight because of the asymmetrical pressure distribution on the sides of the ball.     

A convenient method to determine the bulk modulus of nanowires and its temperature dependence based on X-ray diffraction measurement

The bulk modulus of nanowires (NWs) and its temperature dependence were determined by a simple and convenient method based on temperature-dependent X-ray diffraction (XRD) measurement. It was found that the bulk moduli for Ni, Cu, and Ag NWs were much higher than that for their counterpart bulk materials in the temperature range from 25 °C to 800 °C and the influence of temperature on the bulk modulus for NWs was stronger than that for their counterpart bulk materials. A surface bond contraction model and the force–interatomic-distance curves were introduced to explain the experimental results.     

Effects of Interface Structures on the Application Properties of Ni/Al Clad Composite

The Ni/Al clad metal composite can be applied for the ultrasonic welding of nickel and aluminum structures for lithium-ion cell packaging. The roll bonding Ni/Al clad sheets with 0.15 mm thickness were produced and the effects of interface microstructures and phase transformation on the application properties of such composites are studied in this investigation. The results show that the interface of Ni and Al forms a jagged, interlocking pattern at the rolling state but not a metallurgical bonding. During the annealing process, the first formed Al₃Ni phase in the interface of Ni and Al is beneficial to their bonding together but the sequently formed Al₃Ni₂ phase results in the formation of cracks and the separation of the Ni/Al layers. The bonding mechanism changes to metallurgical bonding with the formation of such phases. The Ni/Al clad sheet acquires good bending endurance, stable welding strength and suitable electrical resistivity with annealing from 425 to 475°C for 1 h.     

Oxidation behaviour of SiC coatings

Amorphous silicon carbide (SiC) films were deposited on silicon substrates by radio-frequency magnetron sputtering. The films were oxidized in air in the temperature range 400–900 °C and for times from 1 to 16 h. Neutron reflectivity measurements provided information on the thickness, density and roughness of the SiC and on the formed SiO₂ layers. Fourier transform infrared spectroscopy was used to determine the bond structure of the formed SiO₂ and changes in the bonding of SiC after exposure at the oxidation temperature. The surface morphology of the oxidized films was characterized by atomic force microscopy measurements. The oxidation kinetics is initially fast and as the SiO₂ layer is formed it slows down. The SiC consumption varies linearly with time at all oxidation temperatures. Exposure of the SiC at the oxidation temperature affects its density and to some degree its bond structure, while the formed SiO₂ has density and bond structure as that formed by oxidation of Si under the same conditions. PACS  66.30.Ny; 68.47.Gh; 68.55.J-     

Ultrasonic-promoted rapid TLP bonding of fine-grained 7034 high strength aluminum alloys

High strength aluminum alloys are extremely sensitive to the thermal cycle of welding. An ultrasonic-promoted rapid TLP bonding with an interlayer of pure Zn was developed to join fine-grained 7034 aluminum alloys at the temperature of lower 400 °C. The oxide film could be successfully removed with the ultrasonic vibration, and the Al-Zn eutectic liquid phase generated once Al and Zn contacted with each other. Longer ultrasonic time can promote the diffusion of Zn into the base metal, which would shorten the holding time to complete isothermal solidification. The joints with the full solid solution of α-Al can be realized with the ultrasonic action time of 60 s and holding time of only 3 min at 400 °C, and the shear strength of joints could reach 223 MPa. The joint formation mechanism and effects of ultrasounds were discussed in details.     

电迁移对Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P倒装焊点界面反应的影响

本文研究了150 ℃, 1.0× 10⁴ A/cm²条件下电迁移对Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P倒装焊点界面反应的影响. 回流后在solder/Ni和solder/Ni-P的界面上均形成(Cu,Ni)₆Sn₅类型金属间化合物. 时效过程中两端界面化合物都随时间延长而增厚, 且化合物类型都由(Cu,Ni)₆Sn₅转变为(Ni,Cu)₃Sn₄. 电迁移过程中电子的流动方向对Ni-P层的消耗起着决定性作用. 当电子从基板端流向芯片端时, 电迁移促进了Ni-P层的消耗, 600 h后阴极端Ni-P层全部转变为Ni₂SnP层. 阴极界面处由于Ni₂SnP层的存在, 使界面Cu-Sn-Ni三元金属间化合物发生电迁移脱落溶解, 而且由于Ni₂SnP层与Cu焊盘的结合力较差, 在Ni₂SnP/Cu界面处会形成裂纹. 当电子从芯片端流向基板端时, 阳极端Ni-P层并没有发生明显的消耗. 电流拥挤效应导致了阴极芯片端Ni层和Cu焊盘均发生了局部快速溶解, 溶解到钎料中的Cu和Ni原子沿电子运动的方向往阳极运动并在钎料中形成了大量的化合物颗粒. 电迁移过程中(Au,Pd,Ni)Sn₄的聚集具有方向性, 即(Au,Pd,Ni)Sn₄因电流作用而在阳极界面处聚集.     

Influence of heat treatment on microstructure and mechanical properties of the interface in an EN AW-6082/1.4310 composite extrusion

The presented paper deals with a unidirectional steel wire reinforced aluminum matrix composite manufactured by composite extrusion. The main objective of this work was to determine the effect of heat treatment, and the influence of long solution annealing times on the composites interface regarding microstructural changes and the resulting interface strength. For evaluation of the microstructure high resolution transmission electron microscope (TEM) investigations accompanied with electron dispersive X-ray spectroscopy (EDX) were performed. It could be shown that diffusion from the steel wire into the aluminum matrix occurs and that the diffusion paths as well as particle formation is influenced by the preceded heat treatment. Diffusion paths in the range of 40–150 nm could be observed for Al, Fe, Cr and Ni. After annealing times over 5 h an extensive growth of an intermetallic reaction layer was found. The mechanical properties of the interface were determined by push-out-tests and tensile tests radial to the interface, which provided the debonding shear strength σ_deb and for the latter experiment the interfacial radial strength σ_IR. It has become apparent that debonding shear strength is highly influenced by matrix properties. In radial tensile tests the failure is predominantly controlled by the chemical bond of the interface. It was shown that interface strength of specimen with small reaction zones of about 3 μm were beneficial for the mechanical behavior in both loading conditions. Longer annealing times showed a drastic decrease of interface shear strength. It was concluded from EDX measurements and in comparison with literature that the reaction zone is dominated by the growth of Al₅Fe₂ (η-phase).     

Effect of ultrasonic vibration time on the Cu/Sn-Ag-Cu/Cu joint soldered by low-power-high-frequency ultrasonic-assisted reflow soldering

Techniques to improve solder joint reliability have been the recent research focus in the electronic packaging industry. In this study, Cu/SAC305/Cu solder joints were fabricated using a low-power high-frequency ultrasonic-assisted reflow soldering approach where non-ultrasonic-treated samples were served as control sample. The effect of ultrasonic vibration (USV) time (within 6 s) on the solder joint properties was characterized systematically. Results showed that the solder matrix microstructure was refined at 1.5 s of USV, but coarsen when the USV time reached 3 s and above. The solder matrix hardness increased when the solder matrix was refined, but decreased when the solder matrix coarsened. The interfacial intermetallic compound (IMC) layer thickness was found to decrease with increasing USV time, except for the USV-treated sample with 1.5 s. This is attributed to the insufficient USV time during the reflow stage and consequently accelerated the Cu dissolution at the joint interface during the post-ultrasonic reflow stage. All the USV-treated samples possessed higher shear strength than the control sample due to the USV-induced-degassing effect. The shear strength of the USV-treated sample with 6 s was the lowest among the USV-treated samples due to the formation of plate-like Ag₃Sn that may act as the crack initiation site.     

Novel pad structures for the improvement of wire bonding strength in DXD panel

New pad structures are suggested to improve the wire bonding strength in the TFT panels suitable for the flat panel X-ray detector application. Several candidates of bonding pad structure are tested and one of them is chosen which shows the strongest and the most stable bonding with aluminum wire. Some morphological consideration was adopted to the surface of AlNd (Nd 2 at.%) pads whose thickness are 4000 Å. To avoid the defect of signal lines such as hillocks due to increased thickness of AlNd, we selectively increased the thickness of AlNd on the bonding area only.     

Application of laser in seam welding of dissimilar steel to aluminium joints for thick structural components

Laser welding-brazing technique, using a continuous wave (CW) fibre laser with 8000 W of maximum power, was applied in conduction mode to join 2 mm thick steel (XF350) to 6 mm thick aluminium (AA5083-H22), in a lap joint configuration with steel on the top. The steel surface was irradiated by the laser and the heat was conducted through the steel plate to the steel-aluminium interface, where the aluminium melts and wets the steel surface. The welded samples were defect free and the weld micrographs revealed presence of a brittle intermetallic compounds (IMC) layer resulting from reaction of Fe and Al atoms. Energy Dispersive Spectroscopy (EDS) analysis indicated the stoichiometry of the IMC as Fe₂Al₅ and FeAl₃, the former with maximum microhardness measured of 1145 HV 0.025/10. The IMC layer thickness varied between 4 to 21 μm depending upon the laser processing parameters. The IMC layer showed an exponential growth pattern with the applied specific point energy (E_sp) at a constant power density (PD). Higher PD values accelerate the IMC layer growth. The mechanical shear strength showed a narrow band of variation in all the samples (with the maximum value registered at 31.3 kN), with a marginal increase in the applied E_sp. This could be explained by the fact that increasing the E_sp results into an increase in the wetting and thereby the bonded area in the steel-aluminium interface.     

One-step fastest method of nanocrystalline CuAlS<Subscript>2</Subscript> chalcopyrite synthesis,and its nanostructure characterization

Nanocrystalline CuAlS₂ chalcopyrite has been mechanosynthesized at room temperature for the first time by ball milling the stoichiometric mixture of elemental of Cu, Al, and S powders under argon atmosphere. Initially, the CuAlS₂ phase is formed by solid state reaction of elemental powders within 15 min of milling and in the course of milling crystallite size decreases slowly to ~5 nm within 10 h of milling. Microstructure characterization and phase transformation kinetics of the elemental powders toward the chalcopyrite phase formation has been made by employing the Rietveld analysis using X-ray diffraction data of unmilled and ball-milled samples.     

Study of shear transfer in Al/epoxy joint by digital photoelasticity

An improved six-step phase-shifting method is proposed for calculating full-field shear stress based on a four-step color phase-shifting method in digital photoelasticity. The method was verified using a disk under diametral compression and then applied to an aluminum alloy/epoxy joint for studying the shear transfer behavior. Experimental results revealed that the isochromatic fringe order and shear stress at the bonding interface are distributed continuously and increased with compression. In particular, an antisymmetric thermal residual shear stress appears at the bonding interface, because of the difference in the thermal expansion coefficients of Al and the resin. This indicates that the thermal residual shear stress at the bonding interface is self-balanced and reaches a peak at the edges of the bonding interface. The load transfer is realized by the shear band from the bonding interface to the bottom support. Basically, the bonding interfacial shear stress is balanced with the load.     

A peculiarity of silver-based corona wire heating on ozone generation

The effect of corona wire temperature on the ozone generation in the positive dc corona electrostatic precipitator is studied experimentally. The external heating of the corona wire can suppress the ozone generation. In this study, nichrome and two kinds of silver-based wires 0.1 mm diameter were tested as discharges electrodes. The nichrome corona wire heating shows a well-known monotonic decreasing the rate of ozone production. In the case of the tested silver-based wires the rate of ozone production decreases nonlinearly and passes through a local minimum in the range from 35 to 55 °C with increasing the wire temperature. At the wire temperature about 46 °C ozone generation by positive dc corona discharge is decreased by 53% with Ag:Mn = 0.85:0.15 wire and by 25% with Ag:Ni = 0.7:0.3 wire as compared to the same wire at 26 °C. Under these conditions the corona wire heating increases slightly the corona current and speed of airflow.     

Vibration and stability of sandwich beams with elastic bonding

This paper is a study of the vibration and stability of symmetrical sandwich cantilevers with elastic bonding. The horizontal displacements of the face layer and the core are discontinuous due to the elasticity of the interface bond. The shear traction at the interface is assumed to be proportional to the relative horizontal displacement of the layers. The core layer is subjected to a horizontal (conservative) or tangential (non-conservative) axial force at its free end. It is shown that a symmetrical sandwich beam with elastic bonding has two kinds of vibration modes: i.e., bending modes and longitudinal modes. Numerical results are given for a beam composed of FRP face layers and a syntactic-foam core layer. It is shown that the divergence and the flutter type instability loads, as well as the natural frequency, are affected considerably by the stiffness of the interface bond.     

Microstructural evolution of SiC joints soldered using Zn–Al filler metals with the assistance of ultrasound

SiC ceramics were successfully soldered with the assistance of ultrasound. Two kinds of filler metals, namely non-eutectic Zn–5Al–3Cu and eutectic Zn–5Al alloys, were used. The effects of ultrasonic action on the microstructure and mechanical properties of the soldered joints were investigated. The results showed that ultrasound could promote the wetting and bonding between the SiC ceramic and filler metals within tens of seconds. For the Zn–5Al–3Cu solder, a fully grain-refined structure in the bond layer was obtained as the ultrasonic action time increased. This may lead to a substantial enhancement in the strength of the soldered joints. For the Zn–5Al solder, the shear strength of the soldered joints was only ∼102 MPa when the ultrasonic action time was shorter, and fractures occurred in the brittle lamellar eutectic phases in the center of the bond layer. With increasing ultrasonic action time, the lamellar eutectic phase in the bond layer of SiC joints could be completely transformed to a fine non-lamellar eutectic structure. Meanwhile, the grains in the bond layer were obviously refined. Those results led to the remarkable enhancement of the shear strength of the joints (∼138 MPa) using the Zn–5Al solder, which had approached that enhancement using the Zn–5Al–3Cu solder. The enhanced mechanical properties of the joints were attributed to the significant refinement of the grains and the change in the eutectic structure in the bond layer. Prolonged enhanced heterogeneous nucleation triggered by ultrasonic cavitation is the predominant refinement mechanism of the bond metals of the SiC joints.     

Metal bonding strength in low‐temperature processed titanium using atomic force microscopy with single‐wall carbon nanotube tip

We report the development of a Ti–Ti bonding process at a low bonding temperature below 200 °C using chemically surface‐activated Ti thin films and a reliable evaluation method for measuring the Ti–Ti bond strength by means of atomic force microscopy (AFM). Using Ti as an interlayer enables void‐free bonding because Ti exhibits fast diffusion and oxide solubility. On the other hand, wafer bonding is an important processing step for 3D circuit integration that requires a high reliability of the process. However, the reliability of bonding‐strength values obtained by employing conventional measurement devices is limited by comparably large measurement errors and restricted the availability of suitable sample material. In this study, the use of AFM to measure the bonding strength is proposed. The interfacial bonding properties depend on the Ti deposition parameters. A bonding temperature of 200 °C was found to be appropriate for the development of a low bonding temperature wafer‐bonding process. The pretreatment methods like plasma activation and chemical activation at 200 °C result in a Ti bonding strength of approximately 8.22 J/m², sufficient for applications in 3D circuit integration. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)