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Zhang J.,Technical University of Delft | Zhang J.,State Key Laboratory of Solid State Lighting | Zhang G.,Technical University of Delft | Zhang G.,State Key Laboratory of Solid State Lighting
Conference Proceedings - 2016 13th China International Forum on Solid State Lighting, SSLCHINA 2016 | Year: 2016

In this paper, the effects of newly defined solder geometric factors in a 2-pad LED lighting assembly on the reliability of Land Grid Array solder joints are investigated by adopting the methodology that we derived from our previous work. This has been done by conducting a series of FEM simulations to establish a response surface model for LED package geometric parameters to predict solder joint reliability. It shows that the LED carrier size (A) and solder coverage (SC) are the most influential factors. Decreasing the package size and increasing the solder coverage area can prolong the lifetime. Besides, it shows that the area ratio between two solder joints (AR) also affects the reliability greatly at large carrier size and solder coverage. It is found that in order to minimize the fatigue damage accumulation in the joints, a package design with a small carrier size, large solder coverage and equal pad size is preferable. Given the fact that the effect of SC is marginal in smaller packages, from a cost reduction point of view, intermediate solder coverage level is suggested. © 2016 IEEE.


Ye H.,Materials Innovation Institute M2i | Ye H.,Technical University of Delft | Ye H.,Applied Scientific Research | Koh S.W.,Technical University of Delft | And 6 more authors.
Applied Thermal Engineering | Year: 2014

The drive of increased electrical currents to achieve high luminous output for phosphor-converted white light-emitting diodes (PW-LED) has led to a series of thermal problems. The light performance of PW-LED is affected by the heat generated by the two major sources in a package/module: chip(s) and phosphors. In this work, spectral shift and consequent color properties change due to the increased temperature during operation were studied by a group of experiments. An electrical-thermal-luminous-chromatic (E-T-L-C) model was then developed to predict the light performance with thermal management under in-situ temperature. The model was then validated by integrated analyses of common LED packages. Besides, the model can also be used to analyze the thermal performance and light quality due to thickness and particle density variation of phosphors. The proposed dynamic E-T-L-C model can definitely benefit the design of future HB LEDs for better light quality. © 2013 Elsevier Ltd. All rights reserved.


Huang J.,Beijing University of Technology | Golubovic D.S.,Lumileds | Koh S.,Huawei | Yang D.,Guilin University of Electronic Technology | And 4 more authors.
Optics Express | Year: 2015

The IES standard TM-21-11 provides a guideline for lifetime prediction of LED devices. As it uses average normalized lumen maintenance data and performs non-linear regression for lifetime modeling, it cannot capture dynamic and random variation of the degradation process of LED devices. In addition, this method cannot capture the failure distribution, although it is much more relevant in reliability analysis. Furthermore, the TM-21-11 only considers lumen maintenance for lifetime prediction. Color shift, as another important performance characteristic of LED devices, may also render significant degradation during service life, even though the lumen maintenance has not reached the critical threshold. In this study, a modified Wiener process has been employed for the modeling of the degradation of LED devices. By using this method, dynamic and random variations, as well as the non-linear degradation behavior of LED devices, can be easily accounted for. With a mild assumption, the parameter estimation accuracy has been improved by including more information into the likelihood function while neglecting the dependency between the random variables. As a consequence, the mean time to failure (MTTF) has been obtained and shows comparable result with IES TM-21-11 predictions, indicating the feasibility of the proposed method. Finally, the cumulative failure distribution was presented corresponding to different combinations of lumen maintenance and color shift. The results demonstrate that a joint failure distribution of LED devices could be modeled by simply considering their lumen maintenance and color shift as two independent variables. © 2015 Optical Society of America.


Dong M.,Beijing University of Technology | Wei J.,Technical University of Delft | Ye H.,Technical University of Delft | Yuan C.,State Key Laboratory of Solid State Lighting | And 2 more authors.
Journal of Semiconductors | Year: 2013

Phosphor plays an important role in LED packages by converting the wavelength of light and achieving specific color. The property and degradation of phosphor are strongly affected by the temperature. Some structural factors have been investigated in this paper and their effects are evaluated. Remote phosphor is an effective approach to improve the performance and reliability of LED modules and products. It is a trade-off that the final product design depends on both the thermal performance and the cost. © 2013 Chinese Institute of Electronics.


Gao Y.,State Key Laboratory of Solid State Lighting | Wu H.,State Key Laboratory of Solid State Lighting | Dong J.,State Key Laboratory of Solid State Lighting | Zhang G.Q.,Technical University of Delft
2015 12th China International Forum on Solid State Lighting, SSLCHINA 2015 | Year: 2015

Color temperature is one of the most significant characteristics for light sources due to its influence on human visual perception, circadian rhythm, emotion, work efficiency, and etc. Currently, it is common for LED light sources to render or tune color temperatures by mixing various color LEDs with different intensity. Existing methods can hardly take into consideration all the lighting requirements, including power consumption, luminous flux, spectrum components, and etc. In this paper, we first make a brief introduction on the significance of color temperature and emphasize the hazard of excess blue light. Then an optimization algorithm of light chromaticity is proposed for the design and control of LED light sources based on linear programming. Objective functions and constraints are described in details. In the optimal color rendering design, we simultaneously restrain the luminous flux, color temperature and the spectrum components of blue light. An example of LED light source design is taken to verify our approach. Results show that the proposed algorithm is able to fulfill the requirement of color temperature, while maintaining satisfied photometric and electrical performance comparing with conventional methods. The optimization algorithm is suitable for both color temperature control and rendering color light with targeted spectral components. © 2015 IEEE.


Tang H.,State Key Laboratory of Solid State Lighting
2013 10th China International Forum on Solid State Lighting, ChinaSSL 2013 | Year: 2013

In this paper analyzes the thermal characteristics of light emitting diode (LED) streetlight module which has serious problems of heat dissipation. Firstly, Finite Element Method (FEM) combined with the heat transfer theory was utilized to calculate the thermal performance of an LED streetlight module by the ANSYS. Then, the thermal behavior of LED streetlight module is investigated by experimental measurements which are used for verifying the feasibility of the simulation. Finally, the structure of the heat sink module was optimized by the Taguchi experimental design method, and some suggestions were proposed. © 2013 IEEE.


Liu Y.,Harbin University of Science and Technology | Zhao J.,State Key Laboratory of Solid State Lighting | Yuan C.C.-A.,CAS Institute of Semiconductors | Zhang G.Q.,Technical University of Delft | Sun F.,Harbin University of Science and Technology
IEEE Transactions on Components, Packaging and Manufacturing Technology | Year: 2014

This paper presents a new chip-on-flexible (COF) packaging structure for flip-chip (FC) light-emitting diode (LED). Two bonding methods, AuSn and Sn-Ag-Cu (SAC) soldering, were compared from thermal, mechanical, and optical performances of the packages. Compared with the package by AuSn soldering method, the package by SAC soldering method showed lower chip temperature due to the avoiding of the large unbounded area. In addition, the SAC soldering package showed a much lower residue stress than the AuSn soldering package. Thus, the possibility for the defects, such as the crack on the reflecting layer and the warping of the pads formation decreased significantly. The reflectivity of the flexible substrate showed a sharp decrease because of the high temperature of AuSn soldering process. Based on the comprehensive evaluation of the thermal properties, residue stress, and optical performances of the LED packages, SAC soldering method is suggested to be more suitable for high-power LED packaging on COF substrates. © 2011-2012 IEEE.


Chen L.,Lamar University | Adams J.,Lamar University | Chu H.-W.,Lamar University | Fan X.,Lamar University | Fan X.,State Key Laboratory of Solid State Lighting
Journal of Materials Science: Materials in Electronics | Year: 2016

Die-attach film failure during soldering reflow is of particular concern for reliability of 3D ultra-thin stacked-die chip scale packages (CSPs), as extremely high vapor pressure can be generated from vaporized moisture to cause severe damages. Under rapid heating, pressure-driven moisture vapor flow could become as significant as concentration-driven diffusion, and should be included in moisture transport models. In this study, a convection–diffusion (CD) model is presented for analyzing vapor pressure and moisture behavior of soft die-attach films for 3D CSPs, with both vapor flow and the effect of temperature on saturated moisture content considered. By using a 1D model according to experimental observations, the over-saturation phenomenon in the thin film and vapor pressure evolution are investigated. It is found that the reflow profiles and substrate thickness could have great impact on the magnitude of vapor pressure, which agrees well with the experimental results. Sensitivity analyses show that a high vapor permeability and a large porosity could lead to low vapor pressure. Being a vapor pressure-based model, the CD model is suitable to study multiple-material systems without discontinuity issue at the material boundary. It is concluded that the CD model could serve as an effective method for predicting vapor pressure and moisture behaviors during soldering reflow for 3D stacked-die CSPs. © 2015, Springer Science+Business Media New York.


Shen H.,McMaster University | Li B.,McMaster University | Li B.,State Key Laboratory of Solid State Lighting | Hao-Ling Yu L.,McMaster University | Kitai A.,McMaster University
Journal of the American Ceramic Society | Year: 2014

As a substrate candidate for low-cost III-nitride thin film growth, 3C-SiC whiskers are employed and manipulated in this work. The alignment of the whiskers is achieved on a patterned 3M Vikuiti™ Brightness Enhancement Film surface. The degree of whisker alignment using this approach is higher than the whiskers lined up by extrusion methods according to X-ray diffraction (XRD) analysis. The aligned whiskers are transferred from the 3M film and embedded into an alumina matrix by tape casting. A self-regulating sintering technique for SiC whiskers is used to protect the whiskers from being oxidized in air during sintering at 1600°C. The aligned whiskers are rigidly embedded in the alumina matrix as shown in scanning electron microscopy (SEM) images and energy-dispersive X-ray spectrometry energy mapping images. GaN thin films grown by a low-cost sputtering process on Alumina/SiC as well as Si and SiC as reference materials are characterized by XRD and SEM. © 2014 The American Ceramic Society.


Fan X.,Lamar University | Fan X.,State Key Laboratory of Solid State Lighting | Yuan C.,State Key Laboratory of Solid State Lighting | Yuan C.,CAS Institute of Semiconductors
Proceedings - Electronic Components and Technology Conference | Year: 2013

High power electronic devices create hot spots, which give rise to the junction temperature significantly higher than the ambient temperature. This induces a situation that the moisture diffusion from environment to device is in the direction against temperature gradient direction. In addition, far field relative humidity is different from the environment surrounding the packaged devices. In this paper, two mechanisms of moisture transport are studied. First, the localized relative humidity related to the far field ambient environment is investigated. Second, moisture diffusion in the presence of temperature gradient inside package is studied. Several scenarios are investigated with the use of an LED package as example. © 2013 IEEE.

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