九十年代计算机发展展望

<正>自从1946年第一台电子计算机ENIAC问世以来,计算机技术一直不停地发展着,特别是进入七十年代以后,随着微电子技术取得的显著成就,其发展更为迅速。目前计算机已跨入全面采用大规模集成电路的第四代,并开始向具有知识处理功能的第五代过渡。在过去的十年里,对第五代计算机的基础工作已做了不少,现在正在进入实现阶段。甚至在这种计算机尚未真正出现之前,人们又在开始探讨和研究模仿人脑思维机理的神经网络计算机了,已有人称之为第六代计算机。因此在未来的十年中,第四代计算机将     

空盒式遥测气压表的研制

本文介绍了遥测气压表空盒传感器的非线性补偿原理、结构多数的设计及保证精度的措施。     

计算机辅助高校行政管理的总体构想与初步实践

本文介绍计算机辅助高校行政管理系统的功能、组成和总体构想,并介绍我们在这方面所做的工作。这些工作包括建立了计算机辅助行政管理委员会,研制了一批数据库系统、一个综合电子邮件系统和一个简单的分布式数据库管理系统。     

HY6040数据采集板在交流接触器触头电参数采集中应用

介绍HY6040数据采集板在交流接触器触头电参数采集中的应用，分析参数采集的方法，简述参数采集的软件流程。     

改善预应力闸墩施工程序的有限元分析

分析了预应力闸墩在主要荷载(弧门水推力和锚束预应力)作用下应力分布的基础上,从改善传统的施工程序入手,提出了在浇筑混凝土锚块时于锚块中间预留施工缝,待锚束张拉完毕后,再将施工缝回填,以便增加锚束在闸墩表面产生的预压应力。文章采用有限元计算手段对该方案进行了分析研究。结果表明,预应力闸墩采用预留施工缝后,预应力锚束的预压效果显著提高。     

基于Bootstrap方法的独立分量分析可靠性研究

语音信号盲分离受到随机采样的数据所影响,产生统计可靠性问题,从而影响分离的效果.Bootstrap方法是以原始数据为基础的抽样统计推断法,可方便的应用于实际的数据处理之中,分析ICA的统计可靠性,但传统Bootstrap方法本身的计算特性限制了自助样本的生成范围,从而使得自助概率分布产生了一定的偏离,使之无法渐近于真实情形.本文通过对Bootstrap样本生成范围的拓展,改进了独立分量分析在语音信号应用的可靠性算法,获得了更加精确的可靠性参数.     

Materials behaviour and intermetallics characteristics in the reaction between SnAgCu and Sn–Pb solder alloys

The paper compares theoretical calculations with experimental data, to identify the metallurgical mechanisms with respect to the rework or repair that may be encountered in the transition period from Sn–Pb to Pb-free soldering. Thermodynamic calculations have been carried out to study material behaviour and possible formation of intermetallic precipitates during the reaction between Sn–Pb and Sn–Ag–Cu Pb-free alloys. Two Sn–Ag–Cu alloys that are relevant to current industrial interests, namely Sn–3.9Ag–0.6Cu* (known as ‘405 alloy’ in Europe and North America), and Sn–3.0Ag–0.5Cu (known as ‘305’ alloy in Asia), were reacted with different contamination levels of eutectic Sn–37Pb solder. The variables examined included those related to both the materials and processes, such as composition, temperature and cooling rate. Together these are the primary drivers with respect to the resultant solder microstructures, which were studied using scanning electron microscopy (SEM). Nanoindentation, which is suitable for the ultra-fine and complex microstructures, was also used to investigate the micromechanical properties, including hardness and elastic modulus, at both ambient and elevated temperatures. The results from this work provide guidance as to the consequence for microstructural evolution and hence mechanical integrity when small amounts of Pb exist in Pb-free alloys. The composition of alloys in this paper is in weight percentage (wt%)     

Microstructural considerations for ultrafine lead free solder joints

As solder joints become increasingly miniaturised to meet the challenging demands of future electronic packaging, it is vitally important to consider whether the solder joint size and geometry could become a reliability issue and thereby affect the implementation of the Pb-free solders. In this study, different bumping techniques, e.g., solder dipping, stencil printing followed by solder reflow, and electroplating of solders and subsequent reflow, were used to investigate the microstructure and interfacial interactions of molten Sn and Sn-based Pb-free solders on different metallizations, e.g., copper and electroless nickel immersion gold (ENIG). The resultant microstructures from a variety of pad sizes, ranging from 1 mm down to 25 μm, and representing different solder bump geometries have been investigated. In addition, thermodynamic and combined thermodynamic-kinetic modelling has been used in order to understand the microstructure of Pb-free solders, the kinetics of dissolution of the metallizations and the formation of interfacial intermetallic compounds (IMCs). Both the experimental results and theoretical predictions suggest that the solder bump size and geometry can influence the as-soldered microstructure. In the light of the increasing importance of the microstructural features of the ultrafine solder joint in determining its long term reliability, a novel computational interface between software for thermodynamic calculations, high-level scientific computing and multiphysics modelling, is introduced. This modelling methodology provides a potential platform for microstructure-based Finite Element (FE) reliability modelling of ultrafine interconnects for future microelectronic products.     

A Method for Quantification of the Effects of Size and Geometry on the Microstructure of Miniature Interconnects

Because the heterogeneity of microstructure has significant effects on the material properties of ultrafine interconnects, it should be quantified, to facilitate high-fidelity prediction of reliability. To address this challenge, a method based on autocorrelation and singular value decomposition is proposed for quantitative characterization of microstructure. The method was validated by developing a quantitative relationship between reported microstructure and tensile strength for SnAgCuRE solders reported in the literature. The method was used to study the effects of size and geometry in ultrafine Sn37Pb interconnects on microstructure and von Mises stress, which were obtained simultaneously by coupling a phase-field model with an elastic mechanical model. By use of this method the degree of heterogeneity of the microstructure in relation to preferred growth directions of the phases was quantified by use of a scalar microstructure index. It was found that microstructure heterogeneity increases with decreasing standoff height, and is higher for hourglass-shaped solder joints. The average von Mises stress was found to be positively related to the microstructure index. The strong correlation between microstructure index and average von Mises stress was confirmed by nonlinear regression analysis using an artificial neural network. This indicates that the mechanical behavior of ultrafine interconnects can be predicted more accurately on the basis of the microstructure index.     

Sensitivity matrix construction for electrical capacitance tomography based on the difference model

Image reconstruction for electrical capacitance tomography (ECT) is an inherently nonlinear and ill-posed inverse problem. Reconstruction methods based on a linear approximation widely are adopted. In this paper, that the gradient of the sensitivity function is related to the severity of nonlinearity between measured capacitances and permittivity distribution is explored, and the gradient magnitude of the sensitivity is used for the sensitivity normalization process to improve the fidelity of the linear approximation. Then, a new sensitivity normalization model — the difference normalization model is proposed, which combines both parallel and series normalization models with the central difference of the sensitivity to achieve better approximation. Given a comparison of sensitivities based on three normalization models, the features of sensitivity associated with the difference models are discussed. With the new method, the reconstruction performance of those conventional iterative algorithms using sensitivity maps, such as Landweber iteration method and iterative Tikhonov regularization (ITR), is improved significantly without increasing computational burden.