A method for rejecting unreliable ceramic capacitor blanks

The possibility of assessing the degree of baking of ceramic capacitor blanks according to changes in their electrophysical properties (tan δ and E _br) after moistening is considered. The method of vacuum moistening involving measurements of dielectric losses or the electric strength is proposed for nondestructive random (at the baking stage) or total (at the stage of burning-in of Mo-Mn electrodes) testing of blanks for capacitors. This method allows rejection of up to 25–30% of unreliable capacitor blanks.     

基于三层悬臂梁结构的电容式风速传感器设计

为解决传统电容式测风传感器的输出非线性,设计了一种基于MEMS微机械加工技术的电容式风速传感器.传感器的敏感结构创新性地采用了一个三层结构的悬臂梁,这种三层结构的悬臂梁构成了一个平行板电容器.风力作用于传感器敏感结构引起电容器的极板面积、极板间距以及绝缘层介电常数的变化,从而引起电容器输出电容的变化,通过测量传感器输出电容的变化值可以实现风速的测量.基于流体力学原理和多层悬臂梁理论对传感器进行了理论分析,并为传感器设计了制作工艺流程.     

预埋芯片混合集成基板制造技术研究

文中基于多层共烧陶瓷基板开展预埋芯片混合集成基板技术的研究。通过对混合集成基板的内应力进行仿真分析,得到了预埋芯片基板工艺中芯片和腔体结构的最佳匹配关系。在多层共烧陶瓷基板腔体中埋置芯片并通过金凸点垂直互连实现电连接。在腔体中填充苯并环丁烯（benzocyclobutene, BCB）介质并将BCB 与多层共烧陶瓷基板表面异质抛光形成平面结构,用于后续薄膜电路工艺的实施。文中详细研究和优化了金凸点芯片垂直互连工艺以及多层共烧陶瓷基板/BCB/Au 异质界面的抛光工艺,制作出了适合后续薄膜工艺的预埋芯片混合集成基板。     

Embedded components in printed circuit boards: a processing technology review

It is evident that embedded passive components (EPCs) allow packaging substrate miniaturization and have the potential to reduce costs. Moreover, they exhibit superior electrical behaviour with respect to the minimization of parasitic effects. However, as for most emerging technologies, there is no well-established process or method for EPCs that lead to the desired result, but many have been and are still being investigated. This article attempts to review the state of the art of resistor and capacitor EPCs, including an assessment of the pros and cons of the various technologies pursued.In the review, it is found that compared to discrete surface mount devices, EPCs provide (in order of current importance): space reduction of 30% or more, better HF signal integrity and potential cost reduction. Embedded resistors in thin-film technology are, in general, restricted to small resistance values up to a few k. Embedded resistors in ceramic thick-film technology require a high temperature curing process and much care during lamination, but they can be combined with embedded capacitors and exhibit high stability. Whereas embedded resistors in polymer thick-film technology require a low curing temperature and can be combined with capacitors, they exhibit poorer electrical properties and stability. Moreover, tolerances of embedded resistors after manufacturing are exceeded by 15%, independent of the manufacturing technology, which means that laser trimming is required.Embedded capacitors are based mostly on barium-titanite with a dielectric constant of only approximately 20, which limits the capacitance density to a few nF/in². Ferroelectric material with a dielectric constant up to 2000 for embedded capacitors has been investigated but not yet established. Besides the traditional screen print technology for the deposition of pastes and inks, the ink-jet technology becomes more promising. Much higher flexibility with respect to material composition, layer thickness and even active components like LEDs have already been produced by ink-jetting.     

Experimental and finite element investigation on wrinkling of circular single layer and two-layer sheet metals in deep drawing process

This paper deals with the comparison of wrinkling behavior of both single and two-layer sheets in the deep drawing process. Unfortunately, due to the significant difference in the material properties of the two layers, it is very challenging for the finite element method to predict the location and relative possibility of wrinkling in the multilayer sheets. Blank holder force (BHF) has a significant effect on the failure mode of sheet metals. By decreasing BHF, wrinkling turns out as the principal failure mode, whereas its increase results in splitting and fracture. Thus, this paper investigates the effect of blank holder forces on wrinkling and fractures in drawing process of single and two layers. Moreover, the effect of material and arrangement of layers on wrinkling, fracture, and required deformation forces in the cylindrical deep drawing will be discussed. Results show that the optimum blank holder force for two-layer sheets is affected by the material and arrangements of lay-ups.     

Influence of dielectric and machining parameters on the process performance for electric discharge milling of SiC ceramic

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD).     

Deformation mechanisms in composite nano-layered metallic and nanowire structures

Using molecular dynamics simulations, the deformation behavior of two types of nanocomposite metallic materials (nano-layered thin films and composite nanowires) is investigated and compared with that of the bulk materials. The first structure is a hybrid nano-layered metallic composite formed by alternating layers of Cu, Ni, Cu, and Nb layers. The nanocomposite has a pre-existing dislocation structure inside it, generated by initially loading a perfect structure to a high strain to nucleate dislocations, then completely unloading it, and loading it again. Four different structures are considered all having the same Cu and Ni layers thickness and varying Nb thickness. Comparison of the deformation behavior between the different structures revealed that the addition of Nb layer makes the material stronger. However, this behavior has a critical limit below which the strength of the material decreases. This is attributed to the extended shearing of the interface that results from the accumulation of dislocations in the Cu/Nb interface. The second structure discussed is a composite nanowire made of a Ni layer sandwiched between two Cu layers. We show that the natural development of coherency stresses at the interfaces between the two layers increases the ability of the wire to deform by a twinning process under tensile loading. This process results in the reorientation of the composite nanowire that, under unloading, forces the nanowire to completely recover the straining, leading to a pronounced pseudoelastic behavior.     

Experimental research on machining characteristics of SiC ceramic with end electric discharge milling

Silicon carbide (SiC) ceramic has been widely used in modern industry. However, the beneficial properties of SiC ceramic make machining difficult and costly by conventional machining methods. This paper proposes a new process of machining SiC ceramic using end electric discharge (ED) milling. The process is able to effectively machine a large surface area on SiC ceramic at low cost and no environmental pollution. The effects of emulsion concentration, emulsion flux, milling depth, copper electrode number, and copper electrode diameter on the process performance such as the material removal rate, electrode wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface is examined with a scanning electron microscope, and the material removal mechanism of SiC ceramic during end ED milling is obtained.     

Orientation rotation behavior during in situ tensile deformation of polycrystalline 1050 aluminum alloy

Microstructural evolutions and orientation rotation behavior taking place during uniaxial tensile deformation at room temperature are studied in polycrystalline 1050 aluminum alloy. Specimens are elongated in an in situ deformation stage equipped in a high-resolution electron backscattered diffraction (HR-EBSD) system. Variations in grain boundary characteristics, such as misorientation and grain boundary distribution, during in situ tensile deformation are analyzed statistically using HR-EBSD. Orientation rotation behavior in individual grains is traced during the whole deformation process. A large number of grains in polycrystalline 1050 aluminum alloy rotate during deformation and are divided into subgrains due to multiple slip. The plane normal directions of individual grains show no remarkable tendency of the orientation rotation during in situ tensile deformation, while the orientation rotation of the tensile direction is found to be strongly dependent on the initial orientation of each grain prior to deformation.     

Finite element modeling of heat transfer in single and multilayered deposits of Ni-WC produced by the laser-based powder deposition process

The localized high-energy input and high-cooling rate inherent in the laser-based powder deposition (LBPD) process yield deposits with superior mechanical and metallurgical properties. However, these characteristics induce thermal stresses within the deposited material that subsequently lead to cracks. This tendency is predominant in the LBPD of metal–ceramic composite materials such as nickel (Ni) and tungsten carbide (WC). In this study, the thermal behavior of single and multilayered compositionally graded Ni-WC composite material during LBPD is studied using an experimentally verified three-dimensional finite element model. The model incorporates both directional- and temperature-dependent material properties. The effect of the mass fraction of the reinforcement, laser power, scanning speed, powder flow rate, and preheating temperature on temperature, temperature gradient, cooling rate, and molten pool evolution are investigated. The distribution and dissolution of WC in Ni-WC deposits are analyzed in the light of the scanning electron microscope, energy-dispersive spectroscopy, and microhardness distribution. The dissolution of WC in the molten Ni varies based on the mass fractions of the Ni and WC and the prevailing thermal conditions such as molten pool temperature and cooling rate. Experimental and numerical results confirm that the desired composition gradient can be achieved in a multilayered Ni-WC composite material deposit by adjusting the laser power. The developed heat transfer analysis may be used to select the suitable process variables needed to achieve the desired properties in the LBPD of single and multilayered Ni-WC composite material.     

高阻尼多层U形波纹管轴向等效刚度的有限元分析

运用ADINA有限元软件对高阻尼多层u形波纹管的轴向等效刚度进行了分析。考虑几何非线性、材料非线性、层间接触非线性以及夹层阻尼材料特性对波纹管轴向等效刚度的影响,其分析结果对含夹层阻尼波纹管的设计与研究有一定的参考意义。     

Post-collapse characteristics of ductile circular honeycombs under in-plane compression

The post-collapse behaviour of a circular honeycomb material under in-plane compression is analysed in order to estimate the effect of the structural topology on the material strength. A structural approach using the limit analysis and the concept of an equivalent structure is employed to describe the large plastic deformations during post-collapse process. Based on some published experimental results (International Journal of Solids Structures 36 (1999) 4367–996) and our numerical simulations, certain deformation patterns are constructed depending on the direction of loading, and the corresponding post-collapse load-carrying capacities during large deformation until densification of cells are presented.The present analysis shows that the post-collapse stress associated with an equi-biaxial compression is not excessively larger than the corresponding uniaxial stresses, in contrast to those of hexagonal honeycombs in response to biaxial loading. This behaviour is attributed to the different deformation mechanism as the curvature of a cell wall invokes bending without stretching.The influence of the size of the connecting segment between two neighbouring cells is studied, showing that the “shape” of the limit surface varies significantly depending on this connection.     

微波多层板共晶烧结翘曲变形数值计算

针对微波多层板叠层复合材料共晶烧结翘曲变形问题,对共晶烧结升温、降温阶段的数值计算方法进行了研究。采用ANSYS Workbench 协同仿真平台,在 ACP(ANSYS Composite Pre)模块中建立了微波多层板的叠层结构,采用顺序耦合方法计算了共晶烧结升温及降温阶段的变形累积效果。计算结果表明:微波多层板与铝壳体共晶烧结完成后,形成以焊接面为中心的向上翘曲变形,在壳体烧结面尺寸 120 mm × 40 mm下,Z向最大变形量为0.181 mm。 仿真计算结果与实测数据吻合良好,验证了微波 多层板共晶烧结过程翘曲变形数值计算的正确性,为微波多层板共晶烧结翘曲变形分析及优化设计提供了参考。     

层高对陶瓷浆料微流挤出成形质量的影响研究

为了确定微流挤出成形陶瓷浆料的最佳层高以及能够成形的最大高度,针对氧化锆陶瓷浆料,分析了丝体从喷头挤出后喷头与沉积丝体之间的5种高度关系,探讨了层高对打印质量的影响机理,并根据浆料特性建立了层间压缩形变模型;通过不同喷头直径和不同层高的3D打印工艺实验,采用数码显微镜扫描、尺寸测量及力学实验等方法对打印试样的表面形貌、成形精度及力学性能等进行了测量与表征,验证了所建模型的正确性。结果表明,当层高与喷头直径的比值分别为0.96、0.92、0.86、1、1.2时,打印质量从优到劣依次递减,因此,合理的层高设置可以减少陶瓷零件的打印缺陷,提高打印质量,为基于材料挤出工艺的参数选择提供一定的理论指导。     

Surface characterization and material migration during surface modification of die steels with silicon, graphite and tungsten powder in EDM process

The present study reports the results of an experimental work carried out to evaluate the improvement in machined surface properties of die steels machined using powder mixed electric discharge machining (PMEDM) process. Two surface responses, surface finish and microhardness were analyzed for changes when machined with Si, W and graphite powders mixed in dielectric fluid. The machined surfaces were subsequently analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to study the element migration from powder, dielectric and the tool. The powder mixed with dielectric and its concentration, current and pulse on time were identified as the significant factors affecting surface finish. Brass electrode and tungsten powder resulted in good surface finish. Amongst the dielectrics used, kerosene provided a better cooling effect whereas EDM oil resulted in better surface finish. The microhardness of the machined surface was also affected by powder and its concentration, current, pulse on time and electrode material. W-Cu electrode and W powder resulted in a higher microhardness. The SEM and EDS analysis showed significant migration of material from the suspended powder, electrode and dielectric to the machined surface.     

陶瓷表面加弧辉光离子镀钛改性及其钎焊性

针对常规钎料难以润湿陶瓷表面的问题，利用加弧辉光离子镀膜技术在Si3N4陶瓷表面预沉积了一层高活性的Ti膜。为充分发挥Ti的活性作用，在活性镀Ti层表面进行了二次电镀Ni。试验表明，在钎焊过程中二次镀Ni层可有效保护Ti膜不被氧化，镀膜陶瓷与金属钎焊接头的剪切强度也显著提高。采用BAg72Cu-V钎料时，镀膜Si3N4陶瓷与金属钎焊接头的剪切强度可达205MPa。     

Modelling of MHS cellular solid in large strains

The stress–strain characteristics of metal hollow sphere (MHS) material are obtained in relatively large strains under uniaxial compression in two characteristic loading directions. Based on the hypothesis of periodic repeatability of a representative block, large deformations of the material are modelled when assuming point connections between the spheres. The elastic deformations are neglected and a rigid perfectly plastic model is assumed for the base material. A structural approach using the limit analysis and the concept of an equivalent structure are then employed to describe the large plastic deformations during post-collapse process of metal hollow spheres, which undergo mainly a snap-through deformation. Stress vs. material density relationships are proposed for different strain levels in each direction of loading. The obtained results can be used to estimate the energy absorbing capacity of MHS materials under quasi-static loading. The theoretical predictions are compared with some test results and reasonable agreement is shown.     

点焊过程力学特征的有限元分析

电阻点焊过程中的力学特征对焊点性能和焊接结构的质量有重要影响。文中基于ANSYS有限元系统，建立二维轴对称热弹塑性有限元模型，对点焊过程中的力学特征进行分析。分析中将预先得到的点焊瞬态温度场作为节点温度载荷施加于模型上，同时考虑随温度变化的材料性能及其塑性行为。通过分析得到结合面和电极一工件界面上的接触压力、点焊接头中的应力、应变、变形以及电极位移等力学特征的分布及变化情况。同时参考分析结果进行粘接点焊的试验研究，表明粘接点焊可以显著提高结构的强度和疲劳寿命。     

电火花沉积电极材料过渡机制及规律

利用旋转电极电火花沉积装置,在Q235钢表面逐层沉积1至6层铜合金涂层,计算分析了每层沉积厚度、过渡形态、表面和截面形貌,探讨了电火花沉积电极材料的过渡机制、形态和规律。结果表明：工件和电极的质量变化曲线相似,随着沉积层数的增加,质量变化量减少直至趋于稳定;沉积层以熔融物质团（液态、半固态）的形态过渡沉积生成,电极与工件材料在沉积层与基体界面处互相渗透,生成厚约20~30 μm的过渡层;工件材料对沉积层的稀释作用主要发生在过渡物质团结合处,对其内部影响极小,且随着沉积层数的增加而减小,沉积层由多层电极材料覆盖叠压构成;随着沉积层数的增大,放电能量利用率降低,单次沉积厚度降低,电极对沉积表面的磨削涂覆作用增大,电极材料沉积率有所下降。     

Determination of the flow stress and thermal properties of ceramic powder feedstock in ceramic injection molding

To simulate numerically the material behavior of a ceramic powder feedstock that consist of a two-phase mixture of zirconia powder and polymer binder, a material model is needed that incorporates the change in volume fraction and temperature dependency of viscosity. Heat transfer occurs between the feedstock and the mold during ceramic injection molding (CIM). The feedstock is heavily influenced by thermal properties such as thermal conductivity and specific heat. In this study, three models are proposed to explain the material and thermal properties: a rigid-plastic flow stress model that is dependent on volume fraction and viscosity, a thermal conductivity model, and a specific heat model as a function of temperature. The material parameters in each model are obtained by using the optimization method. Error functions are defined as the differences between the experimental measurements and numerical simulation results. The parameters are determined by minimizing the error functions. The confirmation simulation for each model is conducted by applying cases that are not directly used in the optimization. The results of the confirmation simulation tend to follow the experimental results well, with correlation coefficients exceeding 0.92. The numerical simulation of the CIM process with the determined parameters is compared with the flow behavior of an actual CIM process. Simulation results, such as flow pattern and direction, are in good agreement with the measured feedstock behavior. Therefore, the method for determining the material parameters of the proposed models is feasible.