大功率LED封装的热管理

建立了一种大功率LED照明灯具的实际封装结构,采用ANSYS有限元软件对其进行热分析,得出了其稳态的温度场分布,并通过实际测量与计算得出了原始模型LED的实际节温,在此基础上提出了几种优化方案,分别采用不同的LED封装材料以及不同的铝热沉结构尺寸,并且进行了模拟对比,对其中一种可行性方案进行了参数优化,在经济和效果之间达到了较好的平衡,获得了较好的优化效果.     

Thermal simulation and optimization design on a high-power LED spot lamp

In this paper, thermal characteristics of the high-power LED spot lamp are reported. The emphasis is placed upon optimizing design of the heat sink of LED spot lamp using the optimization module and the orthogonal-experiment method. Results demonstrate that the weight of the heat sink is decreased to 46.1% of that for the initial structure, and the influence of each factor on junction temperature and weight of the heat sink is acquired by range analysis. Finally, the influence of ambient temperature and natural convection coefficient on the LED maximum temperature is analyzed. The results and the optimizing methodology are of great importance to the thermal design of LED lamps.     

Thermal analysis of high power LED package with heat pipe heat sink

The goal of this study is to improve the thermal characteristics of high power LED (light-emitting diode) package using a flat heat pipe (FHP). The heat-release characteristics of high power LED package are analyzed and a novel flat heat pipe (FHP) cooling device for high power LED is developed. The thermal capabilities, including startup performance, temperature uniformity and thermal resistance of high power LED package with flat heat pipe heat sink have been investigated experimentally. The obtained results indicate that the junction temperature of LED is about 52 °C for the input power of 3 W, and correspondingly the total thermal resistance of LED system is 8.8 K/W. The impact of the different filling rates and inclination angles of the heat pipe to the heat transfer performance of the heat pipe should be evaluated before such a structure of heat pipe cooling system is used to cool high power LED system.     

Heat dissipation design and analysis of high power LED array using the finite element method

High-power Light Emitting Diode (LED) technology has developed rapidly in recent years from illumination to display applications. However, the rate of heat generation increases with the LED illumination intensity. The LED chip temperature has an inverse proportion with the LED lifetime. High-power LED arrays with good thermal management can have improved lifetime. Therefore, for better optical quality and longer LED lifetime it is important to solve the LED thermal problems of all components. In particular, Metal Core Printed Circuit Board (MCPCB) substrate heat sink design and thermal interface materials are key issues for thermal management. This paper presents an integrated multi-fin heat sink design with a fan on MCPCB substrate for a high-power LED array using the finite element method (FEM). The multi-fin heat sink design and simulation results provide useful information for LED heat dissipation and chip temperature estimation.     

一种高功率LED射灯的散热设计与实验研究

以一款MR16 LED射灯为模型,采用ANSYS有限元软件进行热分析。以散热器翅片保持60℃为标准,通过实验与仿真相结合的方法,分析了LED射灯的热流功率、散热器基座厚度、LED芯片间距、对流面积对整个系统散热性能的影响。结果表明,散热器对流面积是影响灯具散热性能的最重要因素;对一定的散热器,存在一个有效的最大芯片输入功率。现有MR16 LED射灯的散热器最大散热功率只能达到2.5 W左右,要使散热功率增大并且发挥散热器最佳性能,必须增加散热器的对流面积。对该结构散热器散热性能的定量研究对今后高功率LED灯具的生产具有一定的指导意义。     

基于Ansys优化模块的热设计应用

发热量大的电子器件温度会比较高,过高的温度会影响到器件的正常工作,因此需要用到热仿真软件去进行有效的热设计。优化设计是有限元分析软件(Ansys)的特有模块,利用该模块应用于两种典型的热设计实例,分别是处理器CPU散热器结构和电路板器件分布的优化设计,仿真分析出来的结果显示,CPU散热器的散热性能得到明显的提高,电路板上各器件的温度均得到降低,获得良好的优化效果。     

The influence of the phosphor layer as heat source and up-stream thermal masses on the thermal characterization by transient thermal analysis of modern wafer level high power LEDs

In the last years Waver Level LED Packages (WLP-LEDs) were developed. They are thin film flip chips where the sapphire substrate remains attached on top of the epitaxial light emitting layer (EPI) which can be assembled directly on a printed circuit board. The thermal resistance and the thermal path of WLP-LED packages are measured by transient thermal analysis and transient finite element simulation. This study investigates the impact of the upstream thermal masses, i.e. the sapphire (SP), phosphor layer (PL) and the side coating (SC) on the transient thermal impedance curve and the cumulative structure function. It is shown that the standard approach to extract thermal properties by features (steps) within the structure function is misleading for thermal networks with upstream thermal load and distributed heat source (EPI and PL) because they influence the shape of the structure function. By transient thermal measurements and finite element (FE) simulation the transient thermal measurements are analysed to extract information about the thermal parameters and the thermal path. Starting from the analysis of the blue flip chip LED (FC-LED, no PL and no SC) the FE-model is set up. Stepwise the FE model is extended and the influence of the PL and the SC on the transient thermal measurement is investigated. A FE model is validated and calibrated which allows simulating the transient thermal curves of these modern LEDs. Using the model the impact of structural changes in the LED package on the transient thermal curves can be identified for reliability analysis.     

Thermal design for the high-power LED lamp

This paper summarizes different kinds of heat sinks on the market for high power LED lamps. Analysis is made on the thermal model of LED, PCB and heat sink separately with a simplified mode provided. Two examples of simulation are illustrated as a demonstration for the thermal simulation as guidance for LED lamp design.     

Thermal design for the high-power LED lamp

This paper summarizes different kinds of heat sinks on the market for high power LED lamps.Analysis is made on the thermal model of LED,PCB and heat sink separately with a simplified mode provided.Two examples of simulation are illustrated as a demonstration for the thermal simulation as guidance for LED lamp design.     

Development of a thermal resistance model for chip-on-board packaging of high power LED arrays

The performance of high power LEDs strongly depends on the junction temperature. Operating at high junction temperature causes degradation of light intensity and lifetime. Therefore, proper thermal management is critical for LED packaging. While the design of the heat sink is a major contributor to lowering the overall thermal resistance of the packaged luminaire, another area of concern arises from the need to address the large heat fluxes that exist beneath the die. In this study we conduct a thermal analysis of high power LED packages implementing chip-on-board (COB) architecture combined with power electronic substrate focusing on heat spreading effect. An analytical thermal resistance model is presented for the LED array and validated by comparing it with finite element analysis (FEA) results. By using the analytical expression of thermal resistance, it is possible to understand the impact of design parameters (e.g., material properties, LED spacing, substrate thickness, etc.) on the package thermal resistance, bypassing the need for detailed computational simulations using FEA.     

LED导热胶片性能研究与评估

大功率LED器件的基座与散热基板之间的接触热阻会阻碍其芯片PN结与散热基板之间的热传导,从而影响到器件的光、色、电性能及寿命。导热胶片用于填充材料界面之间接合或接触时产生的微空隙及表面凹凸不平的孔洞,是减小接触热阻、降低芯片PN结温度的有效手段。文章主要通过测定热阻值来开展对导热胶片在实际应用中导热性能的研究。通过阻容...     

A novel nanoscale SOI MOSFET with Si embedded layer as an effective heat sink

A novel structure such as nanoscale silicon-on-insulator (SOI) MOSFET with silicon embedded layer (SEL-SOI) is proposed to reduce self-heating effects (SHEs) successfully. The SEL as a useful heat sink with high thermal conductivity is inserted inside the buried oxide. The SEL acts like a heat sink and is therefore easily able to distribute the lattice heat throughout the device. We noticed excellent improvement in the thermal performance of the device using two-dimensional and two-carrier device simulation. Our simulation results show that SHE has been dramatically reduced in the proposed structure. In regard to the simulated results, the SEL-SOI structure has shown good performance in comparison with the conventional SOI (C-SOI) structure when utilised in the high temperature applications.     

改善大功率LED散热的关键问题

考虑热导率与散热方式的影响,使用大型有限元软件ANSYS10．0模拟并分析了大功率LED热分布。通过分析不同封装、热沉材料及散热方式对LED热分布与最大散热能力的影响,指出解决LED散热问题的关键不是寻找高热导率的材料,而是改变LED的散热结构或者散热方式。     

照射角度对大功率LED筒灯散热性能影响的分析

为了满足照明需求,有时需要将LED灯具设计成照射角度可调的结构,采用有限元软件分析了三款搭配常见散热器的大功率LED筒灯在不同照射角度下的散热性能,结果发现搭配辐射状散热器的LED筒灯在低于30°照射角下散热效果较佳;搭配平板状散热器的LED筒灯绕不同方向转动照射时散热效果不同,在绕文中所示X轴方向转动时散热效果较好,适合多角度照射;搭配柱状散热器的LED筒灯在多角度照射情况下都具有较好的散热效果。研究结果为以后的筒灯设计提供了参考依据。     

基于脉冲式U-I 特性的高功率型LED 热学特性测试

热学特性是影响功率型LED光学和电学特性的主要因素之一,设计了一套基于脉冲式U-I特性的功率型LED热学特性测试系统,可以测试在不同结温下LED工作电流与正向电压的关系,从而获得LED的热学特性参数。该系统通过产生窄脉冲电流来驱动LED,对其峰值时的电压电流进行采样,同时控制和采集LED的热沉温度,从而获得不同温度下LED的U-I特性曲线。与其他U-I测试系统相比,文中采用了窄脉冲(1 s)工作电流,LED器件PN结区处于发热与散热的交替过程,不会造成大的热积累,大大提高了测量精度。实验中,对某功率型LED进行了测试,获得了该器件的电压、电流和结温特性曲线,并利用B样条建立该器件的U-I-T模型,进而实现了对其结温的实时在线检测。     

基于倒装焊芯片的功率型LED热特性分析

对LED的导散热理论进行了研究,推导出了倒装焊LED芯片结温与封装材料热传导系数之间的关系。通过分析倒装焊LED的焊球材料、衬底粘结材料和芯片内部热沉材料对芯片结温的影响,表明衬底粘结材料对LED的结温影响最大,并且封装材料热传导系数的变化率与封装结构的传热厚度成反比,与传热面积成正比。该研究为倒装焊LED封装结构和材料的设计提供了理论支持。     

大功率LED照明灯有限元热设计与高效系统开发

随着LED亮度要求的不断提高,LED的温度分布和采用的散热手段对LED的可靠性有很大影响。利用ANSYS软件对LED照明的散热问题进行了详细的模拟计算。基于100 WLED实验和模拟结果的一致性,分析比较了不同结构和加载方式对200 WLED温度分布的影响。采用增加散热片个数及其长度、Al锭厚度、灯头的直径等因素,对LED的散热进行了优化设计,结合基于VC++的二次开发系统,较好实现了LED热模拟分析。研究发现LED照明灯的传热方向主要是轴向,轴向散热设计可提高LED开发效率;点阵排列LED灯的温度分布呈现一定的温度梯度;在基于实验验证的模拟可以较好实现不同功率的LED灯散热设计。模拟分析为LED的散热方案优化设计提供了有效的参考依据和手段。     

Multiple heat path dynamic thermal compact modeling for silicone encapsulated LEDs

A new multiple heat path dynamic compact model extraction method for LED packages with silicone domes is proposed. The method enables separate characterization of the LEDs dome and the main heat path. It is based on thermal transient analysis of LED configurations with and without the dome. The heat paths de-embedding procedure proposed significantly increases accuracy of the LED thermal characterization compared to a typical singular heat path approach.The method is demonstrated with a representative mid-power LED. The results are validated with steady-state FEA. Suppressed estimation errors of the heat path evaluation are indicated.     

A survey of the thermal stability of an active heat sink

In cases where forced convective cooling alone is inadequate, or where the size of the housing limits the heat sink's dimensions, ICs can be cooled using an active heat sink. Compared to a classical finned heat sink, it can benefit from a substantial size reduction or from an important enhancement of the heat transport from the IC to its surroundings. The active heat sink's function is based upon a Peltier-effect cooling system. The active heat sink controls the IC's thermal resistance to its surroundings. The Peltier-effect heat pump is a non-linear system. Therefore, surveys of the system's stability are far from evident. Thermo-electric models for both the Peltier-effect heat pump and a NTCR (Negative Temperature Coefficient Resistance) temperature sensor are presented. These are linked to thermal models for the IC packaging and a finned heat sink on one hand and to electronic models for the controlling circuit on the other hand. Simulation show non-linear thermal behaviour and system instabilities according to the power load on the IC, to the forward amplification of the circuit, but also to the ambient temperature change. The latter phenomenon occurs after power-on of the whole device of which the IC is a part. The theoretical results were confirmed by infrared thermographic measurements on a self constructed active heat sink.     

Experimental study on high-power LEDs integrated with micro heat pipe

Micro heat pipe (MHP) is applied to implement the efficient heat transfer of light emitting diode (LED) device. The fabrication of MHP is based on micro-electro-mechanical-system (MEMS) technique, 15 micro grooves were etched on one side of silicon (Si) substrate, which was then packaged with aluminum heat sink to form an MHP. On the other side of Si substrate, three LED chips were fixed by die bonding. Then experiments were performed to study the thermal performance of this LED device. The results show that the LED device with higher filling ratio is better when the input power is 1.0 W; with the increase of input power, the optimum filling ratio changes from 30% to 48%, and the time reaching stable state is reduced; when the input power is equal to 2.5 W, only the LED device with filling ratio of 48% can work normally. So integrating MHP into high-power LED device can implement the effective control of junction temperature.