两种高温老化方式对功率白光LED光热参数的影响

测试和比较了大功率白光LED在高温耐电(HTCD)和高温存储(HTS)两种老化条件的光热性能变化。结果表明,在HTCD老化下,光通量衰减达到40～60%;而HTS下的衰减只有10～14%。这说明,电流应力对LED的寿命影响比较大。利用热阻瞬态响应法测试和结构函数理论分析两种高温老化条件下LED的热特性,结果表明,在HTCD老化下LED热阻的变化较HTS更为明显,并且热阻变化大多体现在导热Ag胶层。这主要是由于高温条件下电流应力引起Ag颗粒的空间分布不均,使粘结界面产生空隙导致热阻发生不同程度的改变。     

LED静电损伤在老化过程中的变化趋势

针对发光二极管(LED)的可靠性问题,将抗静电测试与高温老化实验结合,将蓝绿色发光材料制成的二极管分组,测试其经过老化过程后的光色参数变化。实验数据表明,蓝绿色LED裸片与封装样品老化过程中的衰减趋势有一定差异,老化程度与封装材料和发光材料的搭配方式有关。对于未被静电损伤的芯片,经过老化过程后,并没有出现静电损伤被放大导致功能性失效的现象,静电对其参数衰减无明显影响,与单一的老化实验趋势相似。对于经过静电击打后出现异常,无法正常发光的芯片,高温老化实验产生了使其迅速损坏和复原的情况。     

加固液晶显示模块高温工作特性研究

加固液晶显示模块需要通过高温环境试验, 以保证环境温度较高时仍能工作。建立了加固液晶显示模块的有限元分析模型, 测试了常温下的温度分布, 通过将仿真结果和实际测试数据相比较, 对模型进行了优化, 保证了仿真结果的精度。在此基础上, 仿真分析了不同环境温度、不同驱动电流下液晶屏和LED背光板上的温度分布。仿真结果表明: 当环境温度升高到65 ℃时, 必须将LED驱动电流降低到150 mA, 才能保证液晶屏温度不超过清亮点, LED结温不超过最大限制值。     

高温老化条件下LED模组封装材料失效研究

为了获得高温条件下封装材料对LED模组可靠性的影响,在125℃环境温度下,使用高温试验箱同时对四种不同的样品进行恒定温度的老化试验。结果表明:在高温试验条件下,没有使用硅胶和荧光粉的LED模组具有很高的可靠性;而硅胶的碳化以及随之产生的气体、阻碍散热的荧光粉都会使光照度加速衰减,同时使用硅胶及荧光粉会使光照度迅速衰减导致模组失效。     

温度和湿度对LED可靠性的影响及其机制分析

LED要实现大规模应用必须解决可靠性问题,温度和湿度是影响LED可靠性的两个关键因素.文章对某公司的LED模块进行了显微解剖,依据相关数据对其进行了热湿方面的仿真分析,得到了该模块的热、湿扩散情况、热应力及湿应力分布情况.结果表明:温度场在短时间内达到平衡,而湿度场的平衡时间则长达几十天;湿应力大小为103Pa,热应力大小为108Pa,即LED使用过程中的湿应力远远小于热应力.该结论为进一步研究热湿耦合对LED器件的影响提供了基础,同时为LED模块的封装可靠性设计提供了依据.     

YAG:Ce3 荧光粉对白光LED衰减的影响

对封装的蓝光和白光LED进行了光衰对比试验,结果表明,白光LED初期衰减明显比蓝光LED快.因此,又对自制的YAG:Ce3 荧光粉进行了光照、温度测试,结果发现,荧光粉在光照作用下,荧光强度出现先降后升然后稳定的现象,跟白光LED的衰减相吻合,结合色坐标的偏移,蓝光LED本身的衰减仍是白光LED衰减的主要原因.     

蓝光LED投光灯具高温老化光电性能研究

为了实际工程对灯具进行快速筛选和评价的需要,研究大功率LED投光灯具的老化光电特性,应用高温老化和光电性能测试的方法,对大功率蓝光LED投光灯具进行了高温老化试验并做了光电性能测试,分析其光电参数在老化过程中的变化情况。实验结果显示,光通量参数值在老化过程中有不同变化,其中一种灯具光通量值有上升的情况。结果表明:在灯具光源选取一致的情况下,散热结构与驱动电源是影响灯具性能的两个主要方面。     

铝铜合金对LED芯片电极可靠性的影响

发光二极管(LED)芯片反射电极中铝的稳定性对芯片的可靠性至关重要,少量铜的加入可改善铝的耐电流性.理论计算了电子柬蒸镀沉积时,镀源和镀膜中铜质量分数的对应关系.对纯铝和不同铜质量分数的铝铜合金进行了金属线耐电流测试和薄膜反射率测试,并对纯铝或铝铜合金电极的LED芯片进行了老化测试.结果表明,相对于纯铝电极结构,铜质量分数为2％的铝铜合金电极在几乎不影响反射率的前提下,可显著提高电极的耐电流性能.以铝铜合金为电极的LED芯片在老化过程中,可有效阻止铝的电迁移,从而显著提升了LED芯片的可靠性.     

静电对GaN基白光LED可靠性的影响

对GaN基白光二极管(LED)分别施加-1 600、-1 200、-800、-400、400、800、1 200和1 600V静电打击,每次静电打击后,测量LED电学参数和光学参数的变化。从理论上分析了静电对LED可靠性的影响。实验表明:LED样品的I-V特性曲线及光学参数,受反向静电打击的影响比较大,而受正向静电打击的影响不明显。LED样品在被反向静电打击后,芯片内部产生二次缺陷和熔融通道,导致其I-V曲线变形,光通量减小,老化性能衰减速率加快。在1 600V范围内,LED可靠性受正向静电影响不明显。     

硅酸盐型LED荧光粉的表面处理及其性能

采用硅溶胶对Sr2–xBaxSiO4∶Eu2+LED荧光粉进行表面处理,以改善其稳定性、在树脂中的分散性及封装应用的老化效果。考察了硅溶胶用量、处理温度和时间对荧光粉性能影响,分析了表面处理对荧光粉的晶体形貌和发光性能的影响,并对其应用老化性能进行了研究。结果表明,表面处理使硅酸盐荧光粉的初始发光强度提高约2%,可靠性也有所提高,可使封装后的LED的光衰减少6%。     

The establishment of reliability model for LED lamps

In order to verify which of the distributions and established methods of reliability model are more suitable for the analysis of the accelerated aging of LED lamp, three established methods (approximate method, analytical method and two-stage method) of reliability model are used to analyze the experimental data under the condition of the Weibull distribution and Lognormal distribution, in this paper. Ten LED lamps are selected for the accelerated aging experiment and the luminous fluxes are measured at an accelerated aging temperature. AIC information criterion is adopted in the evaluation of the models. The results show that the accuracies of the analytical method and the two-stage method are higher than that of the approximation method, with the widths of confidence intervals of unknown parameters of the reliability model being the smallest for the two-stage method. In a comparison between the two types of distributions, the accuracies are nearly identical.     

Overdriving reliability of chip scale packaged LEDs: Quantitatively analyzing the impact of component

The objective of this study is to quantitatively evaluate the impacts of LED components on the overdriving reliability of high power white LED chip scale packages (CSPs). The reliability tests under room temperature are conducted over 1000 h in this study on CSP LEDs with overdriving currents. A novel method is proposed to investigate the impact of various components, including blue die, phosphor layer, and substrate, on the lumen depreciation of CSP LEDs after aging test. The electro-optical measurement results show that the overdriving current can lead to both massive light output degradation and significant color shift of CSP LEDs. The quantitative analysis results show that the phosphor layer is the major contributor to the failure in early period aging test. For the long-term reliability, the degradations of phosphor and reflectivity of substrate contribute significantly on lumen depreciation. The proposed reliability assessment method with overdriving loadings can be usefully implemented for LED manufacturers to make a cost- and effective-decision before mass production.     

Reliability test and failure analysis of high power LED packages

A new type application specific light emitting diode(LED) package(ASLP) with freeform polycarbonate lens for street lighting is developed,whose manufacturing processes are compatible with a typical LED packaging process.The reliability test methods and failure criterions from different vendors are reviewed and compared.It is found that test methods and failure criterions are quite different.The rapid reliability assessment standards are urgently needed for the LED industry.85℃/85 RH with 700 mA is used to test our LED modules with three other vendors for 1000 h,showing no visible degradation in optical performance for our modules,with two other vendors showing significant degradation.Some failure analysis methods such as C-SAM,Nano X-ray CT and optical microscope are used for LED packages.Some failure mechanisms such as delaminations and cracks are detected in the LED packages after the accelerated reliability testing.The finite element simulation method is helpful for the failure analysis and design of the reliability of the LED packaging.One example is used to show one currently used module in industry is vulnerable and may not easily pass the harsh thermal cycle testing.     

Semi‐quantitative temperature accelerated life test (ALT) for the reliability qualification of concentrator solar cells and cell on carriers

An adequate qualification of concentrator photovoltaic solar cells and cell‐on‐carriers is essential to increase their industrial development. The lack of qualification tests for measuring their reliability together with the fact that conventional accelerated life tests are laborious and time consuming are open issues. Accordingly, in this paper, we propose a semi‐quantitative temperature‐accelerated life test to qualify solar cells and cell‐on‐carriers that can assure a minimum life when failure mechanisms are accelerated by temperature under emulated nominal working conditions with an activation energy >0.9 eV. A properly designed semi‐quantitative accelerated life test should be able to determine if the device under test will satisfy its reliability requirements with an acceptable uncertainty level. The applicability, procedure, and design of the proposed test are detailed in the paper. Copyright © 2015 John Wiley & Sons, Ltd.     

GaAs红外发光二极管加速寿命试验研究

本文采用步进应力的试验方法设计了一个针对GaAs红外发光二极管的可靠性加速寿命的研究方案.这种方法主要是把步进应力和恒定应力两种方法相结合,用此来评估GaAs红外发光二极管的可靠度;然后总结除了GaAs红外发光二极管这种光电器件的寿命分布形式和失效模式.     

大功率集成LED光转换光源的研制

介绍了一种应用远程激发技术的大功率集成LED光转换光源,通过使用固晶区无绝缘层的镜面铝基板进行集成封装蓝光LED光源,即COB光源。所制蓝光光源与远程激发荧光粉模块结合制成LED光转换光源。利用镜面铝基板的高导热系数,解决多种LED封装形式下芯片点亮温度过高、光源衰减快的问题。采用LED荧光高分子模块与蓝光芯片分离结合的远程激发技术制成白光光源,解决荧光粉分布不均、热老化、色偏移问题。通过与传统粉胶封装方式制得的大功率集成LED器件比较测试,该种光源具有防眩光、光色均匀度高、长寿命、节能和环保的优点,从而具有更广泛的用途。     

层压封装平面LED光源的耐候实验

研究了层压封装的平面LED光源在高温高湿与水下环境的可靠性。平面LED光源采用标准层压工艺封装,对封装后的LED模组进行高温高湿耐候试验与水下环境试验,并与未封装的LED模组进行对比实验。实验结果表明,在环境温度为80℃、相对湿度为80%,模组工作电流为300 mA,连续33天高温高湿条件下,层压封装的平面LED模组的照度变化和温度均高于未封装的LED模组。在40℃水下环境下连续工作400 h,层压封装的平面LED模组的照度略有变化,且光衰小于1%。因此,层压封装能有效阻断外界高温高湿环境对LED模组可靠性的影响,更适合在常温水下照明应用。     

Qualification of plastic encapsulated microcircuits (PEM) for avionicsBased on ``Plastic Encapsulated Microcircuits (PEM) Qualification Testing'''', by J. A. Scalise, which appeared in the Proceedings of the 46th Electronic Components and Technology Conference, Orlando, FL, U.S.A., 28–31 May 1996, pp. 392–397. © 1996 IEEE.

Microcircuit package qualification testing is used to establish the reliability of integrated circuit processes and devices as they relate to part packaging. This paper presents the results of package qualification tests conducted on plastic encapsulated microcircuits (PEMs) and plastic discrete devices (diodes, transistors) used in avionics applications. Highly accelerated stress test (HAST) and temperature cycle (TC) test results, including part failure mechanisms and associated failure rates, are provided. A variety of plastic package styles and integrated circuit functions have been tested. Examples of package styles tested include small outline (SO), plastic leaded chip carrier (PLCC), thin small outline package (TSOP), plastic quad flat package (PQFP) and plastic dual-in-line (PDIP).Manufacturers' devices have been evaluated and various plastic compounds have been compared to determine which provide optimum reliability. The testing showed that package qualification performance of PEMs is affected by type of compound, passivation (including die coat) and die size. HAST failures are caused by moisture penetration of the package while temperature cycle failures result from coefficient of thermal expansion (CTE) mismatch effects.     

Experimental power cycling on insulated TRIAC package: Reliability interpretation thanks to an innovative failure analysis flow

This paper presents the insulated TO-220AB TRIAC package aging when these devices are subjected to experimental power cycling test with various case temperature swings (ΔT_case). This study includes reliability tests set-up, results and failure analysis. An innovative failure analysis flow is proposed to identify the failure mechanism implied. This new failure analysis process flow is necessary due to the complex stack of these devices. Finally, thanks to the reliability tests and the complete failure analysis results, the thermal resistance (R_th) change is correlated to the physical defect modification. This whole study gives the first data collection that is required to propose a lifetime prediction model for insulated TO-220AB TRIAC package during power cycling accelerated aging tests.