电子系统封装器件的传热研究

开发了一个电子系统封装(SIP)典型器件的传热模型,用数值方法模拟了器件的热传递过程和温度分布状况,探讨了各种设计参数和物性参数对温度场的影响。计算结果表明:当t = 1 400 s,以LCP为基板时SIP器件传热过程达到稳定态,基板导热系数和对流换热系数是影响器件散热速率的关键参数,此外还计算了对于不同的环境对流换热系数和不同基板材料,不使芯片产生热失效所允许的输入功率耗散密度。这为研究高密度电子封装器件的热特性,进一步改善器件的热性能提供了理论依据。     

高功率双包层光纤激光器温度分布的有限元分析

高功率双包层光纤激光器的热效应严重制约光纤激光器的输出功率和光束质量。首先通过求解热传导方程得到简化情况下的温度解析解;然后，利用有限元方法对不同情况下的温度分布进行模拟计算。通过模拟计算得到：外包层聚合物材料的热传导系数对光纤的温度分布影响较小，因而在近似计算时可以认为纤芯及内、外包层热传导系数相等;外包层表面的对流换热系数对温度分布影响较大，增大对流换热系数，可以有效地降低光纤激光器的热效应;外包层光纤半径的大小对光纤激光器的温度分布也有影响。所得的结果为设计实现千瓦级光纤激光器提供了参考。     

基于AM-OLED基板的拓展多晶硅薄膜功能层的研究

在有源寻址有机发光二极管（active matrix organic light emitting diode, AM-OLED）显示基板中,将电学功能层--薄膜晶体管（thin film transistor, TFT) 有源层材料p型掺杂金属诱导晶化（metal induced crystallized, MIC）多晶硅（p+-MIC poly-Si）薄膜的版图适当延伸,来充当OLED的阳极,由于它具有低方块电阻、高功函数的电学特性和半反半透、低吸收率的光学特性,与OLED的金属铝阴极形成了微腔器件,成功地形成了显示基板上的多晶硅薄膜的光学功能层. 对这一功能层的厚度进行了优化,比较了不同厚度下TFT器件的电学特性和OLED的光学特性. 当其厚度为40nm时为最佳厚度,此时,TFT器件场迁移率、阈值电压、亚阈值幅摆、电流开关比和栅压诱导漏极漏电等性能为最佳,且红光微腔式OLED (microcavity-OLED, MOLED）的出光强度增大,光谱窄化,电流效率与功率效率均有所提高. 这不仅使器件的性能有所提高,而且大大地简化了AM-OLED基板的制备流程.     

基于ANSYS的功率VDMOS器件的热分析及优化设计

针对TO-220 AB封装形式的功率VDMOS器件,运用有限元法建立器件的三维模型,对功率耗散条件下器件的温度场进行热学模拟和分析,研究了基板厚度、粘结层材料及粘结层厚度对器件温度分布的影响.分析结果表明,由芯片至基板的热通路是器件的主要散热途径.基板最佳厚度介于1～1.2 mm之间,且枯结层的导热系数越大、厚度越薄,越有利于器件的散热.     

薄膜体声波谐振器的热学分析

采用有限元分析软件Comsol Multiphics构建谐振器三维模型,研究器件结构、材料对其热性能的影响。固态装配型谐振器(SMR)有更好的热传导能力与热应力稳定性。在SMR器件中增加一层SiO2,其最高稳态温度上升7℃。器件最高稳态温度随其谐振区面积的减小而迅速增大。当器件换用高热导率材料时,器件最高稳态温度及其随热耗散功率增加而增大的幅度明显降低。     

乐甫波器件温度特性实验研究

研究了基于ST-90°X石英基片和SU-8波导层的乐甫波器件的温度特性。采用电极宽度控制单向单相(EWC/SPUDT)结构和铝电极,设计制作了具有单一模式控制功能和低插入损耗的150 MHz剪切型声表面波(SH-SAW)延迟线器件,并在其表面涂覆不同膜厚的SU-8声波导层构成系列乐甫波器件。由于SU-8波导层与石英基片温度系数的相反极性特性,SU-8膜厚直接影响到了乐甫波器件的温度特性。实验发现,覆盖不同膜厚的SU-8的乐甫波器件的中心频率随温度呈非线性变化,且在60~80℃内,SU-8膜厚为0.95μm时,其频率温度系数约为0.830×10-6/℃。     

IPM中覆铜陶瓷基板的热传导性能研究北大核心CSCD

覆铜陶瓷(DBC)基板在功率模块的封装中应用广泛,其热传导性能对于功率模块的可靠性至关重要。基于智能功率模块(IPM)中覆铜陶瓷基板的图形化结构,制作不同材料及厚度的DBC基板样品并进行了热传导性能测试。通过仿真研究,进一步讨论DBC基板各层材料及厚度等因素的影响规律。实验与仿真结论一致,DBC基板的热传导性能随铜层厚度增加先增强后降低,随陶瓷层厚度增加而降低。在瞬态研究中发现,相同功率加载的初始10 s内,不同材料结构的DBC基板样品最高温度差高于55℃。因此,优化DBC基板的陶瓷层材料和尺寸设计对于提升功率模块的热可靠性有着重要的意义。     

微小流道冷板换热性能研究

为解决高热流密度、大功耗电子器件散热问题,设计了一种串、并联结合的微小流道集成模块冷板进行局部强化传热。结合热源温度、流体压降、均温性等因素,基于流体传热仿真的评估方法对冷板进行换热性能分析和优化。在微小通道区域,研究对比矩形长直型、圆形扰流柱、菱形扰流柱3种不同流道结构形式对冷板传热性能及流动特性的影响。研究结果表明：使用菱形扰流柱形式的微流道与矩形长直流道相比,最高温度降低23.8℃,均温性减小7.7℃,能满足冷板表面最高温度≤65℃的要求。菱形扰流柱可以大幅强化换热效果,散热效果提高了27%左右,取得了较好的工作温度和均温性。     

基于AM-OLED基板的拓展多晶硅薄膜功能层的研究

在有源寻址有机发光二极管(active matrix organic light emitting diode,AM-OLED)显示基板中,将电学功能层--薄膜晶体管(thin film transistor,TFT)有源层材料p型掺杂金属诱导晶化(metal induced crystallized,MIC)多品硅(p+-MIC poly-Si)薄膜的版图适当延伸,来充当OLED的阳极,由于它具有低方块电阻、高功函数的电学特性和半反半透、低吸收率的光学特性.与OLED的金属铝阴极形成了微腔器件,成功地形成了显示基板上的多晶硅薄膜的光学功能层.对这一功能层的厚度进行了优化,比较了不同厚度下TFT器件的电学特性和OLED的光学特性.当其厚度为40nm时为最佳厚度,此时,TFT器件场迁移率、阈值电压、亚阈值幅摆、电流开关比和栅压诱导漏极漏电等性能为最佳,且红光微腔式OLED(microcavity-OLED,MOLED)的出光强度增大,光谱窄化,电流效率与功率效率均有所提高.这不仅使器件的性能有所提高,而且大大地简化了AM-OLED基板的制备流程.     

硅基MOSFET功率放大器TO-3封装热性能研究

针对某款硅基MOSFET功率放大器TO-3封装散热问题,研究了其内部2个功率芯片在35 W下的热性能.通过建立该款功率放大器TO-3封装的有限元仿真模型,采用热仿真软件对这2个功率芯片的间距、焊片材料和厚度以及基板材料和厚度进行仿真优化,分析各个变量对芯片结温的影响.仿真结果表明在管基材料确定的情况下,氧化铍基板和金锡焊片对器件散热有较明显的效果.选用2.5 mm厚的10#钢和其他优化参数进行仿真,结果显示芯片位置处的温度最高,最高温度约为88℃.通过制备相应产品对比了优化前后该款功率放大器的温度变化,测试结果显示优化后器件热阻从2.015℃/W降低到1.535℃/W,产品散热效率提高了约23％.     

Passive cooling of large-area organic light-emitting diodes

The authors investigated passive cooling of large-area organic light-emitting diodes (OLEDs) with special focus on convective cooling. Electro-optical and thermal behaviour of large-area OLED devices are therefore modelled using finite element method (FEM) and computational fluid dynamics (CFD) simulations. Resulting temperature and luminance distributions are compared with measurement data at different driving conditions and test setups. The investigation yields that including laterally resolved convection coefficients from CFD simulations greatly improves model accuracy compared to simpler convection estimations. These findings are important for OLED and their heat spreader design especially for features like flexible, transparent, high-power and or large-area due to their specific limitations for heat spreading and or their high heat spreading requirements.     

Vertical natural convection models and their effect on failure analysis in electro-thermal simulation of large-surface OLEDs

Besides classical inorganic LEDs, intelligent light sources can be also based on organic LEDs. OLEDs function as surface light sources and manufacturing of large area light sources is feasible with OLED technologies. Despite their lower luminous efficacy their other properties make OLEDs still an attractive option especially in high end indoor applications. In natural convection environment the temperature difference in the same OLED panel can reach 20–30 °C which can result in up to 30–40% difference in current density and thus, in the luminance. This difference in temperature and current density leads to differential ageing of the organic materials. CFD simulation is the obvious way to investigate natural convection environments but integration of a CFD solver in an OLED simulator may be difficult and the solution times are high. As a possible workaround to this problem, in this paper the application of five natural convection models for vertical plates in an electro-thermal field solver based OLED simulator as thermal boundary condition are presented. Steady state and transient simulation results of a free-standing 50 × 50 mm² active surface OLED, surrounded by still air, are compared with measurement results. A typical failure type of OLEDs is thermal runaway caused by e.g. manufacturing problems, operational damages or overcurrent. The paper presents the effect of the natural convection model on the overcurrent caused thermal runaway simulation results.     

Hydrofluoroethers as heat-transfer fluids for OLEDs: Operational range, stability, and efficiency improvement

In this work we introduce a simple yet very efficient method of heat dissipation by immersing OLED device into hydrofluoroether (HFE) fluids. It is shown that due to highly fluorous nature of this class of fluids, HFE do not damage organic semiconductors which are comprised in the OLED stack and therefore can be used as encapsulation media. HFE also have high thermal conductivity, low viscosity and can efficiently dissipate the heat by means of natural convection with laminar flow. By employing HFE we were able to significantly improve the OLED operating dynamic range. Lifetimes of OLEDs operating in HFE at high currents can be improved by about a factor of 8. Furthermore, HFE fluid significantly improves the light outcoupling by a factor of 70% due to higher than air refractive index (n = 1.3).     

Microlens arrays for light extraction enhancement in organic light-emitting diodes: A facile approach

The commonly studied architecture of organic light-emitting diodes (OLEDs) faces the obstacle of limited light outcoupling from the planar glass substrate, which greatly affects the device external efficiency. Introduction of microstructures is considered as an effective approach to extract photons trapped within the device. To reach this end, a two-steps fabrication technique based on breath figure patterns and replica molding is here presented. Through this approach elastomeric microlens arrays having different morphological features are obtainable in a fast and simple way. We show how the mere application of these patches on the external face of a conventional OLED leads to a neat efficiency enhancement up to 34%. An increase of light intensity at viewing angle between 30 and 60° is also demonstrated. These results are a proof of principle that improving the performance of an OLED by a non-lithographic surface modification strategy and without altering its functioning, is feasible.     

布喇格光纤激光器的光纤温度分布特性研究

为了分析布喇格光纤激光器中光纤的温度分布特性,提出了布喇格光纤激光器中光纤的稳定热模型,通过热传输方程分析了其中的温度分布,并采用数值有限元法对布喇格光纤的温度分布和由此产生的热应力进行了数值研究,然后对热功率密度、光纤包层数和环境对流传热系数对光纤温度分布的影响进行了模拟计算.结果表明,表层温度远低于覆层材料的临界值...     

A General Model for the Electric Power and Energy Efficiency of a Solar Thermoelectric Generator

A general model for the electric power and energy efficiency of a solar thermoelectric generator is discussed, considering the influences of the input energy, the thermal conductivity, the absorptivity and emissivity of the heat collector, and the cooling water. The influences of these factors on the performance of the thermoelectric device are discussed, considering the thermoelectric generator as a whole, including the heat collector, the thermoelectric device, and the cooling. Results show that high input energy, and high absorptivity and low emissivity of the heat collector, are helpful for obtaining a high-performance thermoelectric generator. A high thermal transfer coefficient of the cooling water can increase the temperature difference across the thermoelectric device but results in greater accessory power requirements if increased further.     

掺镱大功率光子晶体光纤激光器热效应分析

数值模拟分析了大功率光子晶体光纤(PCF)激光器的温度场和热应力场.通过引入等效热传导率对光子晶体光纤结构进行简化,建立了光子晶体光纤激光器的三维温度场模型.利用有限元方法数值模拟得到了自然对流换热时光子晶体光纤中的温度场及光纤端面的热应力场,并对强制对流换热时光子晶体光纤的冷却效果进行了数值模拟分析.结果表明,对于选取的PCF,通过采取强制对流换热措施可以承受1000 W的抽运功率而不会产生热效应损伤,如果需要通过提高抽运功率以获得更大功率的激光运转,则需要改变光纤的结构.     

Effects of surface treatment of ITO anode layer patterned with shadow mask technology on characteristics of organic light-emitting diodes

We investigated the effects of various surface treatments of indium tin oxide (ITO) on the electrical and optical characteristics of organic light-emitting diodes (OLEDs). A 150-nm-thick ITO anode layer was patterned directly with a shadow mask during the sputtering process without the use of a conventional photolithography patterning method. The sputtered ITO layer was subjected to thermal and oxygen plasma treatments to reduce the sheet resistance and improve surface roughness. The thermal treatment was performed for 1 h at temperatures of 250 and 380 °C, which were chosen so that the glass substrates would not deform from thermal damage. The measured sheet resistance decreased from 30.86 Ω/sq for the as-sputtered samples to 8.76 Ω/sq for the samples thermally treated at 380 °C for 1 h followed by oxygen plasma treatment. The root-mean-square surface roughness measured by atomic force microscopy considerably decreased to 3.88 nm with oxygen plasma treatment. The thermal treatment considerably decreased the sheet resistance of the ITO anode layer patterned with the shadow mask. The spike-like structures that are often formed and observed in shadow mask-patterned ITO anode layers were almost all removed by the oxygen plasma treatment. Therefore, a smooth surface for shadow mask-patterned ITO layers with low sheet resistance can be obtained by combining thermal and oxygen plasma treatments. A smooth surface and low sheet resistance improves the electrical and optical characteristics of OLEDs. The surface-treated ITO layer was used to fabricate and characterize green phosphorescent OLED devices. The typical characteristics of OLED devices based on surface-treated shadow mask-patterned ITO layers were compared with those fabricated on untreated and photolithography-patterned ITO layers to investigate the surface treatment effects. The OLED devices fabricated by thermal treatment at 380 °C for 1 h followed by oxygen plasma treatment for 180 s showed the highest luminance and current density. Furthermore, the leakage current that might be induced by the rough ITO surface was dramatically reduced to 0.112 mA/cm². Our study showed that the shadow mask-patterned ITO anode layer treated by heat and plasma and having a low sheet resistance and surface roughness yielded excellent electrical and optical properties for OLEDs compared to those based on an untreated ITO layer. The fabricated OLED devices using the surface-treated shadow mask-patterned ITO layer exhibited comparable characteristics to those obtained from a conventional photolithography-patterned ITO anode.     

基于纳米压印PET基底的高效柔性有机电致发光器件

为了克服现有的以玻璃为基底、ITO为电极的有机电致发光器件（OLED）的韧性差、对裂纹缺陷敏感等固有缺点,对现有的OLED器件结构进行优化。本文提出了以PET为基底,旋涂高导PEDOT：PSS作为阳极的高效柔性OLED器件结构。并在此基础上,通过纳米压印蛾眼模板将光耦合结构引入器件,提高器件的光取出效率。此绿光FOLED器件在亮度为1 000 cd·m^-2时,功率效率为36.10 lm·W^-1。在此基础上,通过纳米压印引入光耦合结构的柔性OLED器件表现出良好的光电性质,在亮度为1 000 cd·m^-2时,功率效率可达到80.46 lm·W^-1。并且这种绿光柔性OLED器件在以器件半边长为曲率半径180°弯折200次后亮度衰减很少。此种高导PEDOT：PSS电极和柔性PET基底可以成为较好的ITO透明电极和刚性玻璃基底的替代物,为生产可穿戴式设备提供了可能。     

非均匀温度场下红外热成像仪温控系统设计

为降低外界环境温度和内部发热元件形成的非均匀温度场对红外热成像仪的成像性能影响。通过Proe和Ansys ICEPARK建立红外热成像仪的有限元模型,在红外镜头表面进行黑色阳极氧化、喷砂处理增强辐射换热,以及安装风扇增强对流换热保证高温环境时的散热,低温环境时采用热电阻进行温升设计,并仿真分析红外热成像仪在不同温度环境下整机内部温度分布和红外镜头温度分布情况,并利用在高低温箱的红外热成像仪来观察平行光管中的靶标图的成像质量,验证温控设计的高效性。结果表明:所采用温度控制电路板对风扇与热电阻能进行温度控制,当环境温度下降至0℃和升高至30℃时,启动温控系统使红外热成像仪光学系统温度正常,保证红外热成像仪的成像质量。