LED拓扑结构对可见光通信性能影响的分析

在室内可见光通信的研究中,发光二极管的拓扑结构通常被忽略,大多将其视为一固定参数。针对其拓扑结构问题,提出了对不同的LED拓扑结构进行仿真分析,通过matlab建立了室内可见光通信系统模型,并对室内可见光通信中的发光二极管拓扑结构进行仿真测试,得到了不同发光二极管拓扑结构下的室内接收信噪比分布,进而分析不同的LED拓扑结构对信号传输的影响。仿真结果表明,发光二极管对室内接收信噪比分布的影响主要由其结构分布的均匀程度和发光二极管的照射强度是否均衡决定,且优化后的发光二极管拓扑结构具有更良好的室内信噪比分布,更适合室内可见光通信。     

基于硅基集成工艺的基板堆叠传输结构设计

随着电子产品向小型化、轻量化方向发展,堆叠基板的垂直互连成为高密度电路集成的关键技术。垂直互连结构会影响跨层传输的信号质量,进而影响电路的射频性能。基于该互连结构的主要传输原理,采用多层硅基板进行堆叠,通过焊球实现上下层的信号传输,利用HFSS仿真软件建立垂直互连结构模型,分析了关键结构参数对传输性能的影响。仿真结果表明优化后的垂直互连结构在DC～20 GHz的频段内回波损耗优于15 dB,传输损耗优于0.5 dB,能够实现良好的微波传输性能。     

机载红外系统主反射镜的拓扑优化设计

反射镜轻量化设计一直是光机结构设计领域的一项挑战性课题。针对某机载红外光学系统的主反射镜,提出了一种基于SIMP拓扑优化方法的反射镜轻量化设计流程,建立了反射镜拓扑优化的数学模型,以最小化镜体自重和抛光载荷作用下的镜面矢高位移RMS值为优化目标,同时考虑对称约束和拔模约束,对反射镜进行了拓扑优化设计。根据拓扑优化结果设计了新的反射镜轻量化结构,并将其与传统结构进行了对比。采用拓扑优化方法设计的反射镜具有更高的轻量化率,同时能够获得较高的面形精度。     

星敏感器支撑结构多目标拓扑优化设计与试验

针对微小卫星对星敏感器的特殊要求,结合星敏感器特殊的工作性能和环境,采用拓扑方法对星敏感器支撑结构进行多目标优化设计并进行有限元分析和试验。首先,对模态分析和随机振动响应的基本理论进行介绍,推导出多目标拓扑优化的表达公式;其次,以支撑结构的体积最小和星敏感器在支撑结构上的四个安装点RMS值最小为目标,以最低自振频率为约束,建立支撑结构的拓扑优化模型,利用OptiStruct软件对其进行拓扑优化设计;然后利用MSC.PatranNastran有限元分析软件对优化后的支撑结构进行模态分析和随机振动响应分析,得到基频为327 Hz ,安装点RMS值的放大率最大为1.55;最后,对支撑结构进行振动试验,试验结果和有限元分析结果的相对误差最大为6.68%,二者吻合较好,该星敏感器支撑结构满足微小卫星对其性能指标的要求。     

功率型LED模组基板横/纵向散热性能研究

为了研究LED模组的散热性能,对其基板的横向和纵向散热性能进行了对比研究。首先建立加快基板横向和纵向散热性能的有限元模型,即在基板上覆盖高导热层和基板内添加高热导率热沉结构。并运用有限元(FEM)分析方法对两种基板的散热效果以及基板和LED芯片温度分布的均匀性进行了对比分析。最后,对于基板上覆盖高导热层的结构,结合实际工艺和散热性能的考虑,进一步优化了高导热层的厚度。     

工件台方镜轻量化结构的拓扑优化设计

为满足工件台方镜的高模态及高轻量化的要求,在设计过程中充分考虑其材料的选择,并重点引入拓扑优化方法。依据变密度法建立SIMP模型,在方镜的特定约束工况下,以结构第1阶模态为设计约束,最小体积为设计目标进行迭代,得到了较好的轻量化结构。并对拓扑优化后的结构与常规结构进行了分析对比,结果表明:拓扑优化的结构第1阶模态为710.5 Hz,提高+4.5%。同时,在轻量化率上提高了+8.2%。因此,拓扑优化的结果要优于常规结构方式,体现出了拓扑优化方法在工件台结构设计过程中具有重要的实际应用价值。     

双向横向热执行器结构设计

在传统非对称冷热梁结构横向热执行器的基础上,提出了一种能实现双向横向运动的热执行器.采用对称结构设计,主要由折叠柔性梁、直柔性梁、宽梁和连接梁构成,通过选择加热臂,可以控制结构的偏转方向,实现双向推挽运动.在典型尺寸下,仿真结果显示,在20 mW驱动作用下,产生的末端位移9.55 μm,驱动力9.4μN,其性能与单向横向执行器相当.同时还进行了结构优化分析.     

空间微型光学载荷主结构优化设计

针对某空间微型光学载荷主结构质量过重、地面重力变形过大以及基频太低的问题,提出以质量最小、随机加速度响应RMS值为目标,基频、变形为约束条件,推导出多目标拓扑优化的表达公式,建立优化数学模型,并对光学载荷主结构进行拓扑优化设计。对优化后的主结构进行工程分析,结果表明,优化后的主结构质量较小,基频较高,变形和随机振动响应较小。最后对主结构和其上端安装的光学载荷进行了力学试验,并对试验后的设备进行了性能检测,结果满足总体指标,证明了所设计的主结构具有良好的性能,同时该主结构优化方法有效可行。     

基于拓扑结构的计算机网络稳定性分析

本文将依据网络拓扑结构按照其传输结点连接度将网络进行分类和建模，并采用克拉索夫斯基稳定性分析方法对网络拓扑结构是否对其稳定性产生影响进行了理论分析，理论分析结果表明，均质拓扑结构的网络传输结点连接度对其稳定性没有影响，而非均质拓扑结构的网络传输结点连接度直接影响其稳定性．     

红外光电系统机械固定件的拓扑优化设计

红外光电系统机械件复杂度高,在满足稳定性要求的前提下,对结构的轻量化有着更急迫的需求。本文采用ANSYS拓扑优化方法对某红外光电系统进行拓扑优化设计,并以电源固定件为例,以结构柔度最小为设计目标,单元密度为设计变量,实现30%的体积约束,并对拓扑优化的结果进行模型重构。与初始经验设计方案对比,优化重构后的固定件减重37.8%,且结构的刚度和强度均得到了提升。进而表明,拓扑优化方法可以为红外光电系统结构的轻量化设计提供有利的借鉴。     

一种非谐振式MEMS电磁能量收集器

介绍了一种新型非谐振式微电子机械系统(MEMS)电磁振动能量采集器的设计、微加工和表征测试。该能量收集器由MEMS结构、线圈、小型化NdFeB磁体和陶瓷基板组成。建立结构模型对结构固有频率、位移和应力进行仿真。利用MEMS技术制备能量收集器结构和Al线圈等关键部件,并结合嵌有永磁体的陶瓷基板进行组装,在组装过程中使用Cu/Sn倒装焊键合技术将陶瓷与芯片互连,成功制备出能量收集器原理样机。利用振动台对样机性能进行测试,测试结果表明,实际加工能量收集器的谐振频率为5241Hz,在1m/s²固定加速度以及7Hz振动频率条件下,经电路100倍放大测得该能量收集器最大输出电压为257mV。     

激光淬火基体对镀铬层界面剪切强度的影响

为了揭示激光淬火预处理基体提高镀铬身管寿命的机理,采用多裂纹拉伸技术分别对激光淬火处理和激光未处理基体上的镀铬层界面剪切强度进行了测量,发现激光淬火基体可以提高镀铬层界面剪切强度77.7%,并从基体与铬层的界面材料结构和力学两个方面进行了分析。结果表明,激光预处理的界面是连续过渡的,而原始基体的界面存在一个过渡;激光淬火基体表面残余压应力的存在提高了铬层的断裂应力;基体表面硬度的提高减小了最大裂纹间距。     

Interfacial adhesion of spin-coated thin adhesive film on silicon substrate for the fabrication of polymer optical waveguide

An investigation was carried out to study the interfacial adhesion of spin-coated polymeric adhesive thin film on a silicon substrate for fabrication of a polymeric optical waveguide. An adhesive shear button was made on a silicon substrate by using a photolithography process, and interfacial adhesion was measured with a Dage D2400 shear tester. Different adhesion strengths were found at different portions of the same sample. Higher adhesion strength was observed at the center of the substrate than at other locations of spin-coated adhesive films. Adhesion strength was also measured after heat exposure of the deposited and cured adhesive layer to evaluate the heat resistance of the adhesive film. After heat exposure, adhesion strength decreased substantially from all locations of the substrate due to the thermal degradation. Again, the adhesion was measured for different plasma-treated substrate conditions. The surface morphology of plasma-treated and untreated silicon substrates before deposition were characterized by atomic force microscopy. Lower adhesion strength was unexpectedly observed for all plasma-treated substrates, even for higher surface roughness. The fracture surfaces after shear testing were also characterized by optical microscopy. The complete study provides important indications for the fabrication of better-performing polymeric optical waveguides for photonic devices.     

Effect of bonding duration and substrate temperature in copper ball bonding on aluminium pads: A TEM study of interfacial evolution

The effect of bonding duration and substrate temperature on the nano-scale interfacial structure for bonding strength were investigated using high resolution transmission electron microscopy. It shows that intermetallic compound crystallization correlates with bonding duration, as a longer duration is applied, alumina fragmentation becomes pervasive, resulting in continuous alloy interfaces and robust bonds. In addition, a substrate temperature (i.e. 175 °C) promotes the fracture of alumina, and simultaneously contributes to the interfacial temperature, accelerating interdiffusion and facilitating the formation of intermetallic compounds, therefore increasing bonding strength. The compound formed during bonding is CuAl₂, regardless of the bonding parameters applied.     

高出光率LED模组基板结构研究

针对带有常规的第一类反光杯的基板结构因受限于封装引线键合工艺而反光杯尺寸较小的情况,通过光学理论分析了其存在反射光线不完全的问题,提出在LED模组芯片间开设第二类反光结构的解决方案。并基于光学分析软件Tracepro的仿真研究,验证了其有效性。在此基础上设计了新型包含两类反光杯的基板结构,最高可使LED模组出光效率和中心光强与没有开反光杯的情况相比提升近23%和38%。     

Fabrication of 70 nm narrow metal nanowire structure on flexible PET film by nanoimprint lithography

As a promising substrate for various kinds of devices, polyethylene-terephthalate (PET) film has many advantages in terms of transparency, flexibility, chemical stability, thermal resistance, mechanical strength and low fabrication cost. In order to build actual device structure on PET substrate, micro to nanometer scale patterns of functional material have to be formed. In this work, 70 nm sized resist patterns with near zero residual layer were made on PET film, using nanoimprint lithography process, based on ‘partial filling effect’. After brief oxygen plasma treatment and e-beam evaporation of functional materials such as Cr metal, resist patterns were lifted-off with acetone solution and 70 nm sized Cr nanowire structure was uniformly formed on flexible PET substrate.     

A testing method for assessing solder joint reliability of FCBGA packages

A brittle solder joint at the interface between a solder ball and a substrate metal pad could result in an open joint failure after the solder ball is attached to a motherboard. Existing metrologies, such as ball shear, do not always detect the weak solder joint strength. A peel test for solder joint strength evaluation of substrate was developed. Several problems were observed during the initial stages of the development for this metrology. These included solder bridging and inconsistency of the test results. Solder bridging was reduced by changing the stencil design to have stencil openings that match the solder ball layout and using a jig to align the coupon and substrate while assembling the peel test samples. The paste printing and peeling methods were modified and the coupon quality was carefully monitored to make the sample preparation and testing more consistent. The impact of the physical aging and reflow on the solder joint strength was investigated. It showed that the peel strength did not decrease with physical aging, but did decrease with an increased number of reflows. The peel test results correlated with the performance of the substrates. The substrate with low peel strength had weak solder joints and failed under use conditions. The substrates with high peel strength demonstrated stronger solder joints and performed well under use conditions. The metrology provides a gross check about the presence of brittle solder joints on flip chip ball grid array substrates and is successfully used in monitoring the solder joint strength.     

Advanced BCD technology with vertical DMOS based on a semi-insulation structure

A new semi-insulation structure in which one isolated island is connected to the substrate was proposed. Based on this semi-insulation structure, an advanced BCD technology which can integrate a vertical device without extra internal interconnection structure was presented. The manufacturing of the new semi-insulation structure employed multi-epitaxy and selectively multi-doping. Isolated islands are insulated with the substrate by reverse-biased PN junctions. Adjacent isolated islands are insulated by isolation wall or deep dielectric trenches. The proposed semi-insulation structure and devices fixed in it were simulated through two-dimensional numerical computer simulators. Based on the new BCD technology, a smart power integrated circuit was designed and fabricated. The simulated and tested results of Vertical DMOS, MOSFETs, BJTs, resistors and diodes indicated that the proposed semi-insulation structure is reasonable and the advanced BCD technology is validated.     

光子晶体微带天线的设计与仿真

以传统的介质型光子晶体结构为基础,提出了一款新型的光子晶体微带天线,其介质板中空气孔洞按三角形点阵形式周期排列于介质板上下两层,其高度为原有高度的一半,研究该结构对天线性能的影响。结果表明:该结构的引入使天线的回波损耗降低到–44 dB,天线具有更好的阻抗特性和辐射效率,天线全向性增强,达到了改善天线性能的目的。此外,由于该结构的特殊性,讨论了天线加入缺陷结构后的禁带特性。     

Ni基钎料激光钎焊金刚石磨粒界面显微结构及形成机理

采用Ni基合金钎料,在Ar气保护条件下,对金刚石磨粒进行了激光钎焊试验研究.采用扫描电镜(SEM)和能谱仪(EDS)及X射线衍射仪(XRD)分析金刚石磨粒与Ni基钎料结合界面的组织结构与物相组成,并探讨了钎料与金刚石界面处碳化物的形成机理.测试结果表明,激光钎焊过程中在金刚石表面附近形成的富cr层与金刚石表面的C元素反应生成碳化物Cr3C2,通过反应热力学与动力学分析显示界面反应产物可以依靠置换反应形成,使金刚石磨粒与钎料实现了牢固结合.