无铅喷锡(HASL)润湿不良问题及对策

针对东莞康佳电子有限公司生产无铅喷锡(HASL)PCB板时所遇到的焊盘润湿不良问题,采用了正常PCB板材与异常PCB板材对比,对smt生产制程条件进行内检等方法措施,以及最终对焊盘异常的PCB送国家级实验室5所分析结论确认焊盘润湿不良问题的主要表现为锡膏对PCB焊盘润湿不良,造成不良的主要原因与PCB焊盘HASL表面不平整以及焊盘已发生合金化降低其可焊性有关。并在批量生产中采取烘烤箱使用105±5℃,烘烤4小时烘烤PCB和使用酒精擦洗PCB焊盘来减少润湿不良的方法措施保证生产。     

PCB设计中一些考虑因素

从整机角度出发，提出电子产品PCB设计过程中对基材、元器件的要求，并对设计过程中的热、焊盘、焊点质量、阻焊、测试等进行了分析。     

QFN器件组装工艺缺陷分析及预防措施

QFN器件在组装过程中容易出现信号焊盘桥连、散热焊盘空洞和侧面焊点爬锡高度不足等工艺缺陷。分析了缺陷形成机理,并从PCB焊盘设计、焊膏印刷模板设计提出了有效预防措施。     

QFN封装元件的板级组装和可靠性研究

近两年来，QFN封装(Quad flat No—lead方形扁平无引脚封装)由于其良好的电和热性能，得到了快速的推广和应用。采用微型引线框架的QFN封装称为MLF封装(Micro Lead Frame——微引线框架)。全球最大微电子制造商之一的Amkor公司，已经销售MLF封装的IC超过1亿只。因此人们迫切希望了解有关QFN的焊盘设计、装配工艺以及板级可靠性设计和工艺等方面的技术问题。由于QFN封装没有焊球，元件与PCB的电气连接是通过印刷焊膏到PCB上，然后贴片和进行回流焊完成的。为了形成可靠的焊点，需要特别注意焊盘的设计，同样．由于这种元件底部有大面积焊盘，其表面贴装工艺很复杂，要求进行合适的模板设计、焊膏印刷，以及回流焊曲线设置。本文对上述各方面要求和影响进行探讨，对PCB焊盘设计、表面组装工艺以及板级组装的可靠性作了详细地介绍。     

PCB设计对焊点强度及坑裂失效的影响

采用正交试验设计的方法,讨论了PCB基材的树脂禽餐、焊盘类型,以及焊盘大小对焊点强度和坑裂失效的影响。结果表明：在3个方面的因素中,PCB基材的树脂含量对焊点强度的影响程度最大。有阻焊膜限定的焊盘类型（SMD）要比无阻焊膜限定的焊盘类型（NSMD）的焊点强度要高,且不容易发生坑裂失效。     

QFN元件的贴装及返修工艺

QFN封装（Quard Flat No—lead方形扁平无引脚封装）具有良好的电性能和热性能、体积小、重量轻，其应用正在快速增长。QFN的封装和CSP有些相似，但元件底部没有焊球，与PCB的电气和机械连接是通过PCB焊盘上印刷焊膏、过回流焊后形成的焊点来实现，对PCB焊盘设计和表面贴装工艺提出了一些新的要求。印刷网板设计、焊后检查、返修等都是表面贴装过程中应该特别关注的。     

论述PCB顿阻焊的曝光、显影

PCB板制程中阻焊曝光、显影工序，是将丝网印刷后有阻焊的PCB板。用重氮菲林将PCB板上的焊盘覆盖，使其在曝光过程中不受紫外线的照射，而阻焊保护层经过紫外光照射更加结实的附着在PCB板面上，焊盘因没有受到紫外光照射，可以露出铜焊盘，以便在热风整平时上铅锡。     

QFN元件的贴装及返修工艺

QFN封装（Quard Flat No—lead方形扁平无引脚封装）具有良好的电性能和热性能、体积小、重量轻，其应用正在快速增长。QFN的封装和CSP有些相似，但元件底部没有焊球，与PCB的电气和机械连接是通过PCB焊盘上印刷焊膏、过回流焊形成的焊点来实现的，对PCB焊盘设计和表面贴装工艺提出了一些新的要求。印嗣网板设计、焊后检查、返侈等都是表面贴装过程中所应该关注的。     

基于DOB工艺的卫星导航抗干扰专用裸芯片测试板设计

针对卫星导航抗干扰专用芯片,为了在裸芯片封装前能够更快速地进行芯片功能测试,采用DOB工艺,将芯片裸片分别装联到常规矩形排列的PCB焊盘和优化后交错排列的PCB焊盘上,通过破坏性拉力实验对比发现,键合强度存在较大差异,经过优化的PCB焊盘设计更能满足DOB工艺需求,此外通过对比焊盘优化后承载裸芯片的PCB和承载封装后芯片的PCB电性能参数,验证了基于DOB工艺裸芯片测试的可行性,提高芯片测试效率,为芯片优化和上市节约时间,降低成本。     

PCB排板布局焊盘及导线的可制造性设计

电子产品PCB Layout 需注意可制造性。器件的排板布局、焊盘及导线的合理设计是其可制造性的基本要求。文中总结了实际生产中的经验,论述了PCB Layout过程中排板布局、焊盘及导线的设计原则、要求和方法。基本的可制造性设计是产品生产高效率、高质量和低成本的关键,而把可制造性与高等教育的PCB设计教学紧密结合具有重要现实意义。     

An All Digital Implementation of Constant Envelope: Bandwidth Efficient GMSK Modem using Advanced Digital Signal Processing Techniques

Gaussian Minimum Shift Keying (GMSK) has been the most common modulation format belonging to the class of partial response Continuous Phase Modulation (CPM) scheme. It is primarily adopted in the GSM standards (B=0.3) for land mobile radio communication systems because of its high bandwidth efficiency and constant envelope modulation characteristics. The focus of this paper is the design of the demodulator wherein we demonstrate an all digital implementation of sub-optimal synchronization techniques for a GMSK modem based on two Laurent Amplitude modulation pulse (AMP) streams approximation representing the matched filter. In this all digital implementation, we perform a joint estimation of the symbol timing and carrier offset wherein the symbol timing is performed using interpolation techniques.     

The Overlapping Problem and Performance Degradation of Mobile Digital Communication Systems

The expansion in the use of land mobile communications have led to a state of congestion in that portion of the radio spectrum allocated to the land mobile service. Digital communication is one of the methods that can be applied to improve spectrum utilization. In a typical digital communication system, messages are not queued and all overlapped messages have to be retransmitted. That overlapping phenomenon has a negative impact on the performance of the system. The behavior of various determinants of system performance (like probability distribution of waiting time and the load that saturates the channel capacity) are studied in detail. A simulation model was developed to simulate four basic design approaches. It was found that a combination of randomizer (for automatic retransmission) and an inhibit signal has no significant payoff and that each one of these features is superior to a commonly used method of automatic retransmission with constant delay. The relative merits of each design is studied as a function of the load on the channel.     

阴影环境下陆地移动卫星信道的模型研究

陆地移动卫星信道通常用全阴影模型和部分阴影模型进行分析。本文利用全阴影模型的研究结论,就实际陆地移动卫星信道部分阴影模型的仿真问题,拟合了模型参数与卫星仰角之间的关系。通过统计特性的数值计算,验证了部分阴影模型与全阴影模型的一致性。     

Clutter losses and environmental noise characteristics associatedwith various LULC categories

To enhance the accuracy of propagation predictions for broadcasting and land mobile applications, a more accurate characterization of clutter loss and of environmental noise has been needed. A series of tests was performed to quantify the environmental RF noise levels associated with various types of ground clutter and to quantify the effects of ground clutter on RF propagation path loss. Tests were performed at 162, 460, and 860 MHz in four different localities in the United States. Each had very different land clutter, as characterized by the land use land cover (LULC) categories used in the United States. It was found that the numbers currently in use by industry for clutter loss are, in general, slightly less than the observed values. Both the clutter loss and noise results can be applied to system design     

Improved design of a helical resonator filter for 450-500 MHZ band land mobile communication

The improved design procedure and experimental results for a practical helical resonator filter to be used at the output of a low power UHF land mobile transmitter are described. The adequate attenuation at more than three times the operating frequency of the filter has been achieved by the transmitter's final matching network.     

VB+MapInfo在土地利用信息系统中的应用

集成化开发已成为地理信息系统应用软件开发的主要方式，具有效率高、功能完善的特点。根据现代化土地经营管理的需求，阐述了基于Visual Basic与MapInfo集成技术的土地利用信息系统的设计方法，介绍了系统体系结构，并对系统功能及一些关键技术进行了论述。     

Tracking and ground cover ratio

Energy yield and occupation of land are two parameters that must be optimized when designing a large PV plant. This paper presents the results of simulating the energy yield of flat panels for some locations and different tracking strategies as a function of the ground cover ratio. Some interesting results for design purposes, such as the optimal solar trackers depending on the land availability or the energy gains of every tracking strategy, are shown. For example, the energy gains associated to one north–south axis tracking, referenced to static surfaces, ranges from 18 to 25%, and from 37 to 45% for the two‐axes tracker for reasonable ground cover ratios. To achieve these results, a simulation tool with appropriate models to calculate the energy yield for different solar trackers has been developed. Copyright © 2008 John Wiley & Sons, Ltd.     

平板Bootlace波导透镜阵设计

本文对一种变形Bootlace透镜阵天线平板Bootlace波导透镜阵天线进行了讨论。该天线能适应陆地平台的特殊环境与使用要求,具有很强的防弹/防撞能力。给出了完整的设计方法及公式,用它可直接完成工程设计。     

A review of floating photovoltaic installations: 2007–2013

The paper gives a review of the various projects that have been realised in throughout the years. These have all been in enclosed water bodies such as reservoirs, ponds and small lakes. The main motivation for the floating photovoltaic (PV) panels was the land premium, especially for agricultural sites were the land was more valuable for growth of the crops (in these cases, grapes because the sites were wineries). The PV panels of the existing projects are mounted on a rigid pontoon structure and vary between horizontal and tilted installations. Future concepts proposed for marine and large lacusterine sites are envisaged to incorporate laminated thin film PV, which would allow the structure to be flexible and able to yield with the oncoming waves, and submergible arrays, which would be submerged in harsh weather conditions. Interest and research has been developing in this niche field throughout the years and has currently reached the megawatt scale with even bigger plans for the future. Copyright © 2014 John Wiley & Sons, Ltd.     

基于FPGA的曼彻斯特编解码器设计

自上世纪80年代以来,MIL-STD-1553B总线标准已广泛应用于海陆空三军,但是其核心编解码芯片多为国外生产,为实现自主研发,设计出基于FPGA的曼彻斯特编解码器是影响整个总线系统通信质量的关键。本设计采用硬件描述语言(Verilog)设计电路,ISE完成综合和布局布线的工作,并用modelSim进行仿真验证。在深入分析曼彻斯特码型特点的基础上,对编解码器的工作过程和逻辑结构进行详细介绍。