化学镍金基板焊点的失效分析

硅麦克风在消费类电子产品中成功应用,近年来得到了迅猛发展。硅麦克风的封装工艺由于MEMS的特殊结构和封装材料的特殊性,与常见IC封装有许多不同点。其中引线键合工序由于所使用的PCB基板材料特殊的加工工艺,使得引线在PCB基板上的焊点失效成为研究硅麦克风封装成品率和可靠性的一个重要课题。文章重点探讨了硅麦克风封装过程中引线键合工序焊点失效问题,通过不同金线键合方式和金线键合参数的分析,确立了适合于硅麦克风封装的金线键合工艺。     

Comments on “General Fourier solution and causality inattenuating media” by R.E. Duren

For original paper, see IEEE Trans. Electromagn. Compat., vol.35, no.1, p.43-8 (1994). When applying mathematics to physical problems one must satisfy the mathematical axioms and in addition the physical laws. Neither the mathematical axioms nor the physical laws can be listed comprehensively, but one does not need to concern oneself too much with mathematical axioms as long as one does not make a mathematical mistake. The physical laws must be introduced into a mathematical model of a physical process, which implies that one must know which physical laws are important in any particular case and one must be sure to actually introduce them. Confusion is caused by the practice of using physical sounding terms in applied mathematics. For instance, R.E. Duren calls a function of time “causal” if it is zero for values of the time variable below a certain threshold. No law prevents one from doing so, but such “causal” functions have no evident connection with the causality law of physics and no results about physical causality should be derived from them. How does one know that the causality law is a physical law that has to be introduced and not a mathematical axiom that is satisfied as long as one calculates correctly? To answer this question the present author considers the causality law in the following form: every effect requires a sufficient cause that occurred a finite time earlier (Harmuth, 1993). The use of the term “time” shows that one is dealing with a physical concept. Pure mathematics has no time variable or spatial variable but it has complex variables     

NASA's master plan

This paper describes how the author's leadership team was asked to help identify NASA's core strengths and activities and think hard about how each of them supports their mission. The purpose of the exercise is focus-and also direction. If a program or activity doesn't support one of NASA's three key objectives, one has to ask why one is doing it, even if one may be doing it rather well. Once one has focused on the activities that do fit into NASA's mission, one must make sure one is managing them in the best way possible. The first task is to examine what NASA is doing and why it is doing it.     

贝塔斯瑞db系列远程有源定向强声扩声系统

对贝塔斯瑞db系列远程有源定向强声扩声系统进行了介绍,并对其系统进行了详细的测试,测试的目的一是验证是否满足立项需求;二是验证是否满足国标和欧盟安全标准;三是得出实际使用中的数据结果.测试结果表明,db系列产品的实测数据和功能符合立项与设计标准.     

高可靠小车红外光循迹设计原则

小车采用传统光循迹电路有两点不足：一是容易受环境光线的影响而造成误判;二是光衍射现象又容易被相邻的光敏管接收也造成误判。针对这两点不足,提出设计原则是采用低占空比强红外光调制发射能克服环境光线的干扰;再对光接收信号进行交流放大后解调能进一步克服环境干扰;采用逐个循环发射、接收能克服光衍射对相邻光敏管的干扰。最后对改进型的方案予以设计,给出电路结构框图及部分电路图。     

Generalization of active RC all-pass schemes

A generalization scheme of the active RC all-pass networks interconnecting one three-terminal network with another four-terminal one, constrained by a differential-input operational-amplifier, is presented. It is further shown that the scheme is, in fact, a completely general one for active filter realization.     

An effective multiuser receiver for DS/CDMA systems

Multiuser detection (MUD) is a key technique for combating multiple access interference (MAI) in CDMA systems. We propose a simple and effective multiuser receiver, which we refer to as the objective function based multiuser detector (OFMUD). This is a successive multistage joint detector based on the statistical optimization of an objective function. Two objective functions are considered in this paper. The first one is based on a maximum likelihood solution, and the second one is based on the least squared error solution. A key feature of the proposed detector is that among all the K user bits, we update the estimate of one and only one bit (the one that is most likely to be wrong) in every stage. Analytical and numerical results show that significant performance improvement can be achieved compared with the conventional DS/CDMA receiver. At the same time, the near-far problem is alleviated. In addition, it is shown that the proposed receiver can outperform the popular multiuser parallel interference cancellation receiver in most cases with a smaller computational cost     

Safety Assessment of Fuel Rods via Generalized Bernoulli Chains

The probabilistic safety assessed to$N$fuel rods assembled in one core of a nuclear reactor is commonly modelled by the sum of$N$independent Bernoulli random variables, i.e. 1 or 0, with individual safety probability$p_i$that the$i$-th rod shows no failure during one cycle, coded by 1. The requirement set by the German Reaktor-Sicherheitskommission (Reactor Safety Commission) demands that the expected number of unfailed rods in the core within one cycle is at least$N-1$, whereby a confidence level of 0.95 for the verification of this condition is demanded. There is an ongoing debate that this requirement based on an expected value might be a misleading probabilistic safety measure as it does not take into account the accumulated safety probabilities that at least$x$fuel rods show no failure during one cycle. In this paper we establish a bound for the accumulated safety probability under this safety condition, which implies that with probability greater than 0.98 at least$N-3$fuel rods show no failure during one cycle.     

On a compound redundant system with the particular switching devices

This paper considers a standby-redundant system consisting of 2 systems, in which one is main and the other is its standby-redundant system. These systems also consist of 2 subsystems connected in series, in which each one is composed of several identical units connected in parallel.A feature of this system is that the system has 2 switching devices connecting subsystems, in addition to one connecting main and standby systems, in order to utilize surviving units as many as possible. In this consideration it is assumed that all the units are not repairable.We shall obtain the system reliability and the mean time to system failure, and examine numerically the effects of this model to the usual one without particular switching devices.     

Synthesis of oscillator circuits employing only one unity-gain amplifier

A simple method to synthesise oscillator circuits employing only one unity-gain amplifier is presented. It is shown that any oscillator formed by one inverting infinite-gain ideal amplifier looped back by a perfect band-reject filter will automatically give rise, through a simple transformation, to an oscillator circuit employing only one unity-gain amplifier. It is further shown that the passive network must be at least a third-order band-reject filter.     

关于"八项质量管理原则"中前三项的一些思考

八项质量管理原则是2000版ISO9001和9004标准的理论基础。文章阐明了第一项原则的核心是“满足顾客要求”;第二项原则应是“领导作用关键”;第三项原则应是“人员充分参与”。     

A decision procedure for the unique decipherability of multivalued encodings (Corresp.)

It is shown that there exists an algorithm to determine whether or not a given multivalued variable-length encoding, that is, a variable-length code system in which more than one codeword may correspond to one source symbol, is uniquely decipherable. The proof is given in two steps. The problem is first reduced to a simpler one, that of determining the inclusion relation between two rather simple languages, a regular set and a language defined by two shortening homomorphisms. Then a concrete decision procedure is given for this simpler problem. Several further observations are made, including a conjectured decision method for the finite-delay property.     

Exploiting the attenuation of fiber-optic passive taps to createlarge high-capacity LANs and MANs

A local- or metropolitan-area network (LAN or MAN) that exploits the power losses of fiber-optic passive taps so that wavelengths can be reused in different portions of the network is proposed. This wavelength reuse makes it possible to design a large, high-capacity, multichannel network with many concurrent transmissions. An arbitrary number of nodes is supported by allowing packets to take multiple hops, when necessary, to reach their destinations. In one example configuration, there are two closed circular loops of fiber, one for transmissions in the clockwise direction and one for counterclockwise transmissions. Each node has one passive tap (per fiber), which is used for both a fixed-wavelength transmitter and a fixed-wavelength receiver     

一种硅衬底镂空结构的圆形射频微电感

利用MEMS工艺以及硅的湿法刻蚀工艺制作了一种硅衬底镂空结构的圆形射频微电感，并研究了硅衬底背面减薄对射频微电感性能的影响，结果表明：微电感硅衬底经过局部刻蚀减薄后其自谐振频率上升，电感量的频率稳定性提高，而其最大Q值下降。     

A note on the evaluation of footnotes and other devices forbackground information in popular scientific texts

Do readers of popular scientific texts appreciate references to the original sources? If they do, which reference system is most preferred? In order to answer these questions, we did two experiments. In the first one, four versions of a short popular science article were created: one without references and three with references-one incorporated references in running text, one in a separated text block at the end, and one between parentheses. The parentheses version was rated highest. In the second experiment, two versions of another popular science article were evaluated: one with references in parentheses and one with references in footnotes. This time, the footnote version was rated highest. We conclude that there is reason to doubt the received wisdom that common readers prefer omitting references or incorporating them in running text. Readers seem to favor the ancient and much-maligned mechanism of the footnote for providing background information     

A performance optimized architecture of deblocking filter for H.264/AVC

The in-loop deblocking filter is one of the complex parts in H.264/AVC. It has such a large amount of computation that almost all the pixels in all the frames are involved in the worst case. In this paper, a fast deblocking filter architecture is proposed, and it can effectively save the operating time. In the proposed architecture, two 1-D filters are introduced so that the vertical filtering and the horizontal filtering can be performed at the same time, Only 120 cycles are needed for a macroblock. Our architecture is also a memory efficient one, and only one 4×4 pixels register, one 4×4 transpose array and one 16×32 b two-port (SRAM) are used as buffers in the filtering process. The simulation and synthesis results show that, with almost the same or even smaller area than some 1-D filter based architectures before, the proposed one can save more than 40% processing time. The architecture is suitable for real-time applications and can easily achieve the requirement of processing real-time video in 1080HD (high definition format, 1 920×1 088@30 fps) at 100 MHz.     

Physical Analysis of Stress Testing for Failure of Electronic Components

Starting with an assumption concerning the type of physical process causing failure and an assumption concerning the random distribution of components with respect to a failure threshold. cumulative distribution functions in time, temperature, and voltage are derived. These cumulative distribution functions are identical to each other if the random variables are certain functions of time, temperature, or voltage, thus showing the equivalence of time, temperature, and voltage as stresses. The cumulative distribution function in time is the familiar log-normal function. If it is known that the assumed physical process is the only one causing failure, then one can rigorously replace time by temperature or voltage. However, it is demonstrated that in an accelerated test, i.e., one in which time is replaced by another stress such as temperature, one can never be sure that another process will not be predominant at longer times; thus, one can never make a certain extrapolation to longer times. One might be able to circumvent this difficulty by having a thorough knowledge of the physics, chemistry, and metallurgy of the possible failure processes in the component.     

Performance evaluation of single and multi-channel actor to actor communication for wireless sensor actor networks

The paper discusses two distributed actor to actor communication schemes (a single channel one and a multi-channel one) for wireless sensor actor networks (WSANs). The performance of these two schemes is evaluated through analysis and simulation. The simulation results show that the whole analysis is fairly accurate. It is further proven that the multi-channel scheme has better performance than the single channel one. The key feature of the multi-channel scheme is the separation of the single hop from the multi-hop traffic.     

On the error probability of coded frequency-hopped spread-spectrummultiple-access systems with more than one code symbol per dwellinterval

The multiple-access capability of an asynchronous, frequency-hopped spread-spectrum (FH-SS) communication system employing error correcting codes is reviewed. Many current FH-SS systems employ error correcting codes with more than one code symbol per dwell interval. A method of computing the codeword error probability induced in such spread-spectrum systems is presented. The codeword error probabilities induced in spread-spectrum systems utilizing more than one versus one code symbol per dwell interval are compared. It is concluded that FH-SS systems with one code symbol per dwell interval are more efficient in combating multiple-access interference than FH-SS systems with more than one code symbol per dwell interval     

复杂电磁环境与两个人体的相互作用研究

在复杂环境中单个人体的电磁场分布以及 SAR计算的比较多 ,而对多个人体的相互作用以及之间的相互影响研究较少。利用现有的方法 ,计算在一定条件下 ,两个人体的相互作用 ,将其计算的结果与单个人体存在的情况下的结果相比较 ,由比较可以得出结论 ,平面波入射情况下 ,两个人体存在时的分层 SAR与单个人体的分层 SAR相比差别较小 ,且比单个人体存在时要小一点。多个人体存在时的 SAR与入射波的极化有关。