Thermodynamic Assessments of the Ag-Ni Binary and Ag-Cu-Ni Ternary Systems

The phase diagram of the Ag-Ni binary system has been evaluated by using the calculation of phase diagrams (CALPHAD) method based on experimental data of the phase equilibria and thermodynamic properties. Gibbs free energies of the liquid and fcc phases were described by the subregular solution model with the Redlich–Kister equation. On the basis of the thermodynamic parameters of the Ag-Ni, Ag-Cu, and Cu-Ni systems, and experimental information of the phase equilibria in the Ag-Cu-Ni system, the thermodynamic assessment in the Ag-Cu-Ni system was carried out. The calculated results in both the Ag-Ni and Ag-Cu-Ni systems are in reasonable agreement with experimental data.     

Bondability analysis of bond pads by thermoelectric temperature measurements

To reduce cost and enhance reliability for microelectronics applications, a complete understanding of the thermosonic bonding process is required. In particular, the question of whether melting, diffusion, or significant heating occurs along the interface during friction has often been raised. We present results obtained with a new device based on thermoelectric temperature measurements to determine the temperature at the bond interface. In addition to the temperature information, the data characterizes the bonding process in real time on a micrometer scale. The basic principle of the developed apparatus is temperature measurement by an Au-Ni thermocouple fixed within the inside chamfer of a bonding capillary. Different bond substrates with high and low bond contact quality have been investigated. The thermoelectric temperature measurements very precisely determines the bonding behavior of the bond pads. A few nanometers surface contamination on a bond pad significantly reduces the temperature rise at the bond interface and therefore impairs bondability of the substrate. These results demonstrate the sensitivity and accuracy of the measurement principle. The apparatus is a powerful tool to measure the tribology of the bond system and to characterize the bondability of different bond pads.     

基于薄膜HIC金铝键合失效的工艺研究

介绍了薄膜混合集成电路(HIC)中金铝键合失效机理,提出了一种解决金铝键合失效的新工艺。分析失效机理发现,铝丝和薄膜金导带形成的金铝界面因原子扩散而形成内部空洞,出现键合根部的键合丝断裂的现象。通过改变键合区金属层结构,实现了单一金属化系统,有效避免了金属间化合物的形成。该项研究结果对陶瓷基薄膜HIC的工艺应用范围的拓宽具有参考价值。     

Thermodynamic Assessment of the Ni-Bi Binary System and Phase Equilibria of the Sn-Bi-Ni Ternary System

As a basis to understand the interfacial reaction between the Sn-Bi solder and the Ni substrate in electronic packaging, thermodynamic calculations of phase equilibria have been carried out on the binary Ni-Bi system. The Gibbs free energy of the NiBi phase has been approximated, using a three-sublattice model, and thermodynamic parameters have been evaluated, using available experimental information on phase boundaries and other related thermodynamic properties. The calculated phase diagram and thermodynamic quantities of the Ni-Bi binary system showed good agreement with the experimental data. The Sn-Bi-Ni ternary system was calculated using the thermodynamic parameters of the Sn-Bi, Sn-Ni, and Ni-Bi binary systems, and it was compared with experimental measurements.     

Anomalous B penetration through ultrathin gate oxides during rapidthermal annealing

We have observed accelerated diffusion of B in ultrathin gate oxides during rapid thermal annealing (RTA) of the gate stack. Enhanced diffusion by 10-100 times over standard furnace annealing has been measured in SiO₂. The activation energy for B diffusion in SiO₂ during RTA is decreased by about 0.5 eV when compared to furnace annealing results. We propose a model that involves the capture of optically generated holes by diffusion defects which results in reduced B migration enthalpy through the modified defect, whose bonding has been weakened by the presence of captured positive charge. No similar optical radiation effect was observed when F was present in the oxide     

Studies of the Ag-In phase diagram and surface tension measurements

The phase boundaries of the Ag-In binary system were determined by the diffusion couple method, differential scanning calorimetry (DSC) and metallographic techniques. The results show that the region of the (hcp) phase is narrower than that reported previously. Thermodynamic calculation of the Ag-In system is presented by taking into account the experimental results obtained by the present and previous works, including the data on the phase equilibria and thermochemical properties. The Gibbs energies of liquid and solid solution phases are described on the basis of the sub-regular solution model, and that of the intermetallic compounds are based on the two-sublattices model. A consistent set of thermodynamic parameters has been optimized for describing the Gibbs energy of each phase, which leads to a good fit between calculated and experimental results. The maximum bubble pressure method has been used to measure the surface tension and densities of liquid In, Ag, and five binary alloys in the temperature range from 227°C to about 1170°C. ON the basis of the thermodynamic parameters of the liquid phase obtained by the present optimization, the surface tensions are calculated using Butler’s model. It is shown that the calculated values of the surface tensions are in fair agreement with the experimental data.     

Increasing bondability and bonding strength of gold stud bumps onto copper pads with a deposited titanium barrier layer

A flip-chip assembly is an attractive scheme for use in high performance and miniaturized microelectronics packaging. Wafer bumping is essential before chips can be flip-bonded to a substrate. Wafer bumping can be used for mechanical-single point stud bump bonding (SBB), and is based on conventional thermosonic wire bonding. This work proposes depositing a titanium barrier layer between the copper film and the silver bonding layer to achieve perfect bondability and sufficiently strong thermosonic bonding between a stud bump and the copper pad.A titanium layer was deposited on the copper pads to prevent copper atoms from out-diffusing during thermosonic stud bump bonding. A silver film was then deposited on the surface of the titanium film as a bonding layer to increase the bondability and bonding strength for stud bumps onto copper pads. The integration of the silver bonding layer with a diffusion barrier layer of titanium on the copper pads yielded 100% bondability between the stud bump and pads. The strength of bonding between the gold bumps on the copper pads significantly exceeds the minimum average values in JEDEC specifications. The diffusion barrier layer of titanium effectively prevents copper atoms from out-diffusing to the silver bonding layer surface during thermosonic bonding, which fact can be interpreted with reference to the experimental results of energy dispersive spectrometry (EDS) and analyses of Auger depth profiles. This diffusion barrier layer of titanium efficiently provides perfect bondability and sufficiently strong bonding between a stud bump and copper pads with a silver bonding layer.     

Structural,mechanical and electronic properties of sodium based fluoroperovskites NaXF3 (X=Mg,Zn) from first-principle calculations

The structural stability, mechanical, electronic and thermodynamic properties of the cubic sodium based fluoro-perovskite NaXF₃ (X=Mg, Zn) have been studied using density functional theory (DFT). The generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE) is used for modeling exchange-correlation effects. In addition, the alternative form of the GGA proposed by Engel and Vosko (GGA-EV) is also used to improve the electronic band structure calculations. The results show that both compounds are stable in the cubic Pm3m structure. From Poisson׳s ratio, it is inferred that cubic anti-perovskite NaXF₃ are ductile in nature and that bonding is predominantly of ionic in nature. The electronic band structure calculations and bonding properties show that anti-perovskites have an indirect energy band gap (M–Г) with a dominated ionic character. The thermal effects on thermal expansion coefficient, Debye temperature and Grüneisen parameter were predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The calculations are found to be in good agreement with other results.     

Thermodynamic Calculation of Phase Equilibria in the Sn-Ag-Cu-Ni-Au System

Sn-Ag-Cu base solders are the most promising candidates to substitute for Sn-Pb eutectic solder. Gold (Au) coatings are used to protect conductor surfaces from oxidation and thereby to promote solderability, and Ni is often used as a diffusion barrier layer between lead-free solders and substrates to restrict the growth of intermetallic compound layers. In the present work, thermodynamic calculations of phase equilibria in the Sn-Ag-Cu-Ni-Au system, which is of importance for developing lead-free solders, are carried out using the calculation of phase diagrams (CALPHAD) method. Substitutional solution and sublattice models are used to describe the solution and intermediate phases, respectively. Some examples of thermodynamic calculation are presented, and it is shown that the phase diagrams, liquidus projection, and thermodynamic properties can be predicted based on the present calculations.     

Design of tone-dependent color-error diffusion halftoning systems.

Grayscale error diffusion introduces nonlinear distortion (directional artifacts and false textures), linear distortion (sharpening), and additive noise. Tone-dependent error diffusion (TDED) reduces these artifacts by controlling the diffusion of quantization errors based on the input graylevel. We present an extension of TDED to color. In color-error diffusion, which color to render becomes a major concern in addition to finding optimal dot patterns. We propose a visually meaningful scheme to train input-level (or tone-) dependent color-error filters. Our design approach employs a Neugebauer printer model and a color human visual system model that takes into account spatial considerations in color reproduction. The resulting halftones overcome several traditional error-diffusion artifacts and achieve significantly greater accuracy in color rendition.     

Dislocation assisted diffusion: A mechanism for growth of intermetallic compounds in copper ball bonds

A combination of Finite Element Analysis (FEA), Molecular Dynamics (MD) simulation and analytical formulation is employed to predict the thickness of Intermetallic Compounds (IMCs) right after ball bonding of copper wire to an aluminum pad. The IMCs growth is related to the enhanced diffusion through the dislocations that are generated in the aluminum pad during the bonding process. Dislocation density and diffusional constants are estimated from the results of the FEA and MD simulation and used to calculate the thickness of IMCs that can form through dislocation-assisted diffusion. It is shown that dislocations have a strong effect on controlling diffusional processes that lead to IMC growth. Results are compared with independently acquired experimental data in the literature. The good agreement between the computed and experimental results supports the validity of the proposed mechanism.     

Effect of Ni on the Formation of ${hbox {Cu}}_{6}{hbox {Sn}}_{5}$ and ${hbox {Cu}}_{3}{hbox {Sn}}$ Intermetallics

In this paper, the effect of Ni on the formation of Cu₆Sn₅ and Cu₃Sn intermetallics between tin and (Cu,Ni) substrates has been studied by making use of the thermodynamic assessment of the Sn-Cu-Ni system. The driving forces for the diffusion of the elements in the intermetallic layers were calculated as a function of Ni content. Assuming constant mobilities of component atoms, the results suggest that the diffusion fluxes of all the components in the (Cu, Ni)₆Sn₅ layer increase with increasing content of dissolved Ni, while the Cu and Sn fluxes in the (Cu, Ni)₃Sn layer decrease. Therefore, the dissolution of Ni retards the growth of (Cu, Ni)₃Sn. When the Ni content of the (Cu,Ni) substrate is high enough, the intermetallic compound growth in the reaction zones is dominated by (Cu, Ni)₆Sn₅, and the (Cu, Ni)₃Sn layer disappears gradually. The small thickness of (Cu, Ni)₃Sn is associated with large difference between Sn and Cu fluxes in (Cu, Ni)₃Sn that encourages also the "Kirk-endall void" formation. In addition, the calculated driving forces suggest that the growth rate of (Cu, Ni)₆Sn₅ should further increase if (Cu, Ni)₃Sn disappears, resulting in an unusually thick (Cu, Ni)₆Sn₅ layer. The results of thermodynamic calculations supplemented with diffusion kinetic considerations are in good agreements with recent experimental observations.     

Design of CMOS Ternary Latches

This paper describes the design methodology of latches with three stable operating points. Open-loop analysis is used to obtain insight into how a conventional binary latch structure can be modified to yield a ternary latch. Four novel ternary latch structures, compatible with a standard CMOS process, are presented. Properties of each latch, including robustness of the ternary behavior, speed, and power dissipation, are described. Measurement results of four RS ternary flip-flops based on the proposed latch structures, fabricated in a standard 0.18-mum CMOS process, are presented. Maximum operating frequency and skew tolerance are reported for each of the four latches     

Enhancing perceived quality of compressed images and video with anisotropic diffusion and fuzzy filtering

Fuzzy filtering has recently been applied and optimized for reducing distortion in compressed images and video. In this paper, we present a method combining the powerful anisotropic diffusion equations with fuzzy filtering for removing blocking and ringing artifacts. Due to the directional nature of these artifacts, we have applied directional anisotropic diffusion. In order to improve the performance of the algorithm, we select the threshold parameter for the diffusion coefficient adaptively. Two different methods based on this approach are presented: one designed for still images and the other for YUV video sequences. For the video sequences, different filters are applied to luminance (Y) and chrominance (U,V) components. The performance of the proposed method has been compared against several other methods by using different objective quality metrics and a subjective comparison study. Both objective and subjective results on JPEG compressed images, as well as MJPEG and H.264/AVC compressed video, indicate that the proposed algorithms employing directional and spatial fuzzy filters achieve better artifact reduction than other methods. In particular, robust improvements with H.264/AVC video have been gained with several different content types.     

Au-In-based Hermetic Sealing for MEMS Packaging for Down-Hole Application

Hermetic sealing of micro-electro mechanical systems (MEMS) sensors for down-hole application requires high-quality void-free bonds, with metallic hermetic sealing being widely used for this purpose. As most of the MEMS sensors cannot withstand high temperatures, transient liquid phase (TLP) bonding is promising for metallic sealing applications, since the re-melting temperature of the bond is much higher than the bonding temperature. In this paper, major issues involving TLP bonding, including non-uniform diffusion kinetics across the interface and the formation of intermetallic compounds prior to bonding for fast reactive metallic systems like Au-In, have been addressed by using diffusion barriers. The performance of various diffusion barriers that include Ti, Ni, and Pt has been evaluated. Ni has been determined to be a prospective candidate, since it averts diffusion to a certain extent prior to TLP bonding. The mechanical strength and hermeticity of the Au-In joints have also been characterized after aging at 300 °C up to 500 h. No major changes in the thermo-mechanical properties of the AuIn and AuIn₂ phases were observed and, hence, these phases are concluded to be thermally stable at this temperature regime. Improvements in hermeticity were confirmed when subjected to high-temperature thermal aging.     

功率型LED封装中的热阻分析

芯片固晶过程是影响功率型LED封装热阻的重要方面.分析了银胶、共晶合金等不同导热率的固晶材料产生的固晶热阻的大小,并基于正向电压测结温法首次提出了一种测量LED固晶热阻的方法,得到了很好的测量结果,能有效分析封装结构中各部分引入的热阻的大小.

Abstract：

The LED chip bonding is an essential technology to reduce the thermal resistance of LED. Thermal performance of bonding materials such as Ag-epoxy resin was analyzed using heat transfer tools. For the sake of assessing the bonding technology, a method of measuring the thermal resistance induced by bonding process was proposed for the first time based on the forward working voltage method. It is shown that the theoretical simulation results agreed well with the measured results.     

一种基于基片集成波导技术的引线键合结构

当前微波毫米波芯片的引线键合主要是在芯片焊盘和微带线之间实施,当工作频率达到毫米波频段,引线键合的性能对键合线属性及微带线加工精度的敏感度越来越高,键合操作中键合线长度的差异或微带线加工的误差都可能导致键合性能的快速恶化。文章提出了一种基于基片集成波导(SIW)的引线键合结构,该结构直接使用SIW与芯片焊盘或其他电路进行键合,对比现有微带键合方案,使用本文提出的基于SIW的键合方案,可以显著减小加工精度的敏感度,同时减少对介质基片的限制等。文章分别设计了无源和有源SIW键合结构,仿真和测试结果表明:基于SIW的键合结构拥有良好的键合性能,相比微带键合结构,降低了传输损耗、降低了对结构尺寸的灵敏度、改善了键合性能。     

硅片直接键合杂质分布的模型与模拟

根据键合过程和半导体中杂质扩散的规律建立了硅片直接键合工艺的数学模型,得到了键合后硅片中杂质的浓度分布.并利用MATLAB软件,编写了键合工艺模拟程序,计算结果与实验进行了比较.该模型可以为相关器件的研究提供参考.