大功率LED纳米银烧结界面热阻和发光性能

利用纳米银烧结工艺制备大功率LED,重点探究了纳米银键合层的界面热阻及器件发光性能。通过将纳米银膏在不同温度下烧结,系统地研究了烧结温度对纳米银烧结后电阻率及接头剪切强度的影响,并分析了烧结后银膏的晶体结构及接头断口微观形貌。结果表明,接头键合强度和银膜导电率均随纳米银烧结温度的升高而增大。实验中还对比分析了纳米银烧结LED和传统锡银铜（SAC305）焊膏封装LED的界面热阻、结温以及发光性能。与纳米银烧结LED样品相比,传统焊膏封装LED的界面热阻和结温分别提高了8.9%和29.6%,说明纳米银键合层拥有更好的导热性并可及时为芯片散热降温。此外,通过高温老化实验,深入探讨了不同焊膏烧结LED的界面热阻及发光效率变化。实验表明,经过100℃下点亮500 h,纳米银和传统焊膏烧结LED样品的总热阻分别增大了0.03 K/W和4.28 K/W,但纳米银键合层界面热阻比老化前有所降低,同时纳米银烧结LED样品在不同电流下的发光效率始终高于传统焊膏封装LED样品。     

纳米银焊膏烧结大功率LED模块的高温可靠性研究

介绍了一种加速老化试验模型对LED模块进行寿命预测。分别采用纳米银焊膏、锡银铜焊料、导电银胶作为芯片粘结材料。控制环境温度和正向电流,在特定的时间测量光输出。比较了不同粘接材料及环境温度对LED老化过程的影响,并针对老化过程进行分析推导,建立老化数学模型,对其进行寿命预测。试验结果表明,纳米银焊膏粘接的模块对温度的抗性最好,纳米银焊膏有潜力在未来固态照明、投影和其他高功率器件领域得到应用。     

照明用大功率发光二极管封装材料的优化设计

根据传热理论,建立了大功率发光二极管的有限元模型.选择了4种键合材料（高导热导电银胶、纳米银焊膏,大功率芯片键合胶、Sn70Pb30）,4种基板材料（Al2O3、AlN、Al-SiC、铜钼合金）.采用ANSYS有限元热分析软件进行了温度场仿真,得到了大功率发光二极管封装材料的最优选择.研究了基板厚度、芯片输出功率及外接热沉时对发光二极管结温的影响.结果表明:纳米银焊膏-AlN组合具有最优的散热效果|增加散热基板厚度提高散热能力的作用不大|单个发光二极管输出功率有限,应优化封装结构并采用多芯片阵列来满足照明级的需要|外接铝热沉能达到理想的散热效果.     

照明用大功率发光二极管封装材料的优化设计

根据传热理论,建立了大功率发光二极管的有限元模型.选择了4种键合材料(高导热导电银胶、纳米银焊膏,大功率芯片键合胶、Sn70Pb30),4种基板材料(Al2O3、AlN、Al-SiC、铜钼合金).采用ANSYS有限元热分析软件进行了温度场仿真,得到了大功率发光二极管封装材料的最优选择.研究了基板厚度、芯片输出功率及外接...     

金锡共晶互连对HP-LED光热性能的改善

随着功率型LED(HP-LED)对散热的要求越来越高,传统导电银胶越来越难以满足LED的高散热要求。虽然共晶互连工艺是微电子领域中的一种有效的散热互连方法,但是由于LED的特殊性,该工艺在LED互连封装中的性能改善研究还比较少。本文对金锡共晶互连、锡膏互连和银胶互连的3种LED器件分别进行了光学、热学以及剪切力等方面的测试分析研究,结果表明:底部与顶部同时加热的金锡共晶工艺互连的LED器件可以有效地改善仅底部加热共晶互连层中的空洞缺陷,在1 000 mA电流条件下,相对于锡膏、银胶互连的LED器件具有较低的热阻、较稳定的峰值波长偏移、较强的互连层剪切力等性能。金锡共晶互连工艺是一种可以有效改善大功率LED散热及互连强度的方法。     

辐射与发光

发光与发光器件TN312.82007032029大功率白光LED封装设计与研究进展=Advances inpackaging design and research on high-power white LED[刊,中]/陈明祥(华中科技大学微系统研究中心.湖北,武汉(430074)),罗小兵…//半导体光电.?2006,27(6).?653-658从光学、热学、电学、机械、可靠性等方面,详细评述了大功率白光LED封装的设计和研究进展,并对封装材料和工艺进行了具体介绍。提出LED的封装设计应与芯片设计同时进行,并且需要对光、热、电、结构等性能统一考虑。在封装过程中,虽然材料(散热基板、荧光粉、灌封胶)选择很重要,但封装工艺…     

大功率发光二极管可靠性和寿命评价试验方法

介绍了发光二极管（LED）的发展简史。提出可能影响LED可靠性的几种因素,主要有封装中的散热问题和LED本身材料缺陷。对于LED可靠性,主要方法是通过测试其寿命来分析其可靠性,一般采取加速实验的方法来测试推导LED寿命。介绍了根据加速应力(主要分为单一加速应力和复合加速应力2种)评价LED寿命的测试方法。在不同加速试验应力条件下测试了大功率LED可靠性,并建立了LED寿命的几种数学模型。最后根据具体实例,通过选择加速应力和试验方法,给出具体推导LED寿命的数学公式。     

铝/氧化铝复合基板封装的LED光源的光热特性

为获得具有高出光效率、高导热性能的发光二极管(LED)封装基板,采用直接敷铝(Al)工艺制备了铝/氧化铝(Al_2O_3)复合陶瓷基板并对其表面进行化学机械抛光处理。运用光学模拟软件Tracepro和热学模拟软件ANSYS对该陶瓷基板封装的LED光源的光学性能和热学性能进行了模拟计算,并和传统氧化铝陶瓷基板封装的LED光源进行了对比分析,最后将所制备的铝/氧化铝陶瓷基板封装成板上芯片直装(COB)型LED光源进行测试。模拟和实验测试结果均表明:直接敷铝工艺制备的铝/氧化铝陶瓷基板热传递速度更快,导热性能更加优异,更适合用于大功率LED光源的封装;铝/氧化铝陶瓷基板封装的的LED光源比基于传统氧化铝陶瓷基板的LED光源的光通量大,出光效率更高。     

LED感应局部加热封装试验研究

采用感应局部加热技术,对大功率发光二极管(LED)封装进行了试验研究。结果表明,由于感应加热对材料和结构具有选择性,封装过程中仅Cu-Sn合金焊料层加热,实现了芯片和覆铜陶瓷基板间的热键合。封装后的LED性能测试表明,该封装技术不仅降低了热阻,使LED在高电流下(4倍电流)仍能保持较低的工作温度,而且降低了热应力和整体高温对芯片结构的损坏,提高了器件性能和可靠性。     

照明用大功率LED回路热管散热器的研究

分析了照明用大功率LED封装的散热特性,提出了一种用于大功率LED系统散热的回路热管;研究了热负荷、倾角、加热方式等对热管的起动性、均温性、热阻等的影响。试验结果表明,所设计的热管散热器的热阻在0.19K/W~3.1K/W之间,蒸发器的均温性被控制在1.5℃以内,满足大功率LED封装的均温性要求,在热负荷为100W时,蒸发器的温度被控制在100℃以下,满足大功率LED结点温度的控制要求。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.