Light-emitting diodes (LED) chip scale packages (CSPs) have been promoted as a new light source with many advantages in smaller package size, lower material and process cost, and better heat dissipation effect. However, as it is exposed in harsh environments such as high temperature, high humidity, and high blue light irradiation, silicone material used in LED CSPs always suffers deterioration, which will seriously affect the LED's reliability and working life. Thus, the preparation of high reliable silicone has practical significance to promote the application of LED CSPs in lighting. In this research, titanium was introduced into the molecular chain of phenyl silicone by using the hydrolysis condensation method. A high temperature aging test was then performed to the prepared silicone before and after modification, and their optical, thermomechanical, and dielectric properties were characterized to evaluate their reliabilities. The results show that: (1) the Arrhenius function with the dielectric property as an aging characterization can be used as a temperature accelerated life model to predict the service life of the prepared silicone and (2) the titanium modified silicone can advance the high temperature stability on optical properties, thermomechanical, and dielectric properties and enhance the life expectancy. The major contributions of this study are to support the improvement of the novel LED CSP packaging materials and processes, and also to provide the technical guidance on the fast, accurate, and cost-effective reliability assessment for high-quality LED light sources.

Better mechanical, thermal properties and longer lifetimes are needed for the die attach layer in high-power electronic packaging. As traditional Sn-Ag-Cu (SAC) solders have many limitations, the sintered nanosilver materials are becoming one of the substitutes for high-power electronic packaging. However, the high performance of sintered nanosilver materials is only achieved when its fine sintering densification is formed. This article investigates the sintering densification process of nanosilver particles based on the design of orthogonal experiments and sintering kinetics modeling in which both the macroproperties and micromorphology are linked and analyzed. The results lead to several conclusions, such as: 1) the orthogonal experiments consider the effects of sintering temperature, dwell time, and sample preparation pressure on the sintering relative shrinkage and relative density - the results show that the most critical impact factor on sintering densification is the sintering temperature. (2) In the sintering kinetic experiments, the sintering densification rates obtained by fitting the relative density versus dwell time curves during 175 °C-250 °C follow the Arrhenius model, and the apparent activation energy of sintering kinetics is calculated to be 36 kJ/mol, while it is calculated from the particle size is 38.1 kJ/mol. 3) Through modeling the relationship between particle size, line shrinkage, and porosity, the line shrinkage and porosity first increase at the initial stage, while the particle size increases, and the macroscopic volume decreases at the end of sintering, the porosity decreases.

With the popularity and widespread application of high-power light-emitting diode (LED) in lighting industry, its reliability has gradually become one of research focuses.The failure of gold bonding wires in the traditional LED package has been a critical bottleneck that restricts its reliability. In this paper, the failure mechanism of LED under cyclically electrical loading is firstly identified through both gold bonding wire mechanical simulation and power cycling test experiment, which is the fatigue fracture of gold bonding wire. Then, two lifetime prediction methods, the acceleration factor extraction method based on current acceleration model and the strain-based Coffin-Manson analytical method, are established and verified with experimental results. The results show that the lifetime prediction accuracy of the proposed methods is high and they can achieve a fast and accurate reliability assessment for high-power LEDs with wire-bonding packaging technology.

The inherent luminous characteristics and stability of LED packages during the operation period are highly dependent on their junction temperatures and driving currents. In this paper, the luminous flux of LED packages operated under a wide range of driving currents and junction temperatures are investigated to develop a luminous flux response surface model. The coefficients of the proposed model are further extracted to compare the luminous efficacy decay mechanisms of LED packages with different packaging structures. Furthermore, a spectral power distribution (SPD) method modeled by the Gaussian function is proposed to analyze the long-term degradation mechanisms of all selected LED packages. The results of this study show that: (1) The luminous flux of phosphor converted white LED decreases to accompany with the increase of junction temperature, while that of bare blue LED die keeps relatively stable; (2) The proposed general luminous flux response surface model can be used to predict the luminous flux of LEDs with different packaging technologies accurately, and it can be known from the proposed model that the influences of driving current and temperature on LED chip and phosphor vary with different packaging structures; and (3) The driving current and temperature dependent sensitivities and degradation mechanisms of LED packages can be investigated by using both the luminous flux response surface model and the spectral power distribution method.

with the increasing requirements on guaranteeing the color uniformity and improving the luminous efficacy and manufacturing efficiency, a wafer level chip scale packaging (WLCSP) technology has been developed by thermally impressing a thin multiple phosphor film on a LED wafer, then being segmented into individual LED chips. In this paper, a high power white LED Chip-on-Board (COB) module with high color rendering index (CRI, Ra > 93) and tunable correlated color temperatures (CCTs) is prepared by the flip chip technology. In this COB module, the tunable color temperatures are achieved by using two types of white LED CSPs with different target CCTs of 3000 K and 5000 K. The thermal and photochromatic properties and the photochromatic stability of the COB module are studied through both experiments and simulations. The results show that: 1) The measured spectral power distribution (SPD) intensity of the prepared COB module is smaller than the arithmetic sum of SPD intensities of its each series connected CSPs, which may be attribute to the light absorption happened among CSPs; 2) The junction temperature and driven current have the different effects on the photochromatic properties of COB module (i.e. luminous flux, CCT and CRI); 3) The nonlinearity of luminous flux as a function of driven current and junction temperature should be considered in its modeling.

High-power light-emitting diode (LED) chip-scale packages (CSPs) prepared by the flip-chip technology have become one of the most promising light sources. The die attach solder layer always plays an important role in heat dissipation, mechanical support, and electronic conductivity. Among different types of solder materials, Sn-3.0Ag-0.5Cu (SAC305) solder alloy shows its great competitiveness on solderability and mechanical properties for the interconnection of high-power LED CSPs. However, reliability problems caused by voids in the SAC305 solder limit its wide application in the high-power LED chip-scale packaging process. Existence of the voids has been considered as one of the major issues causing chip-on-substrate level reliability problems in microelectronic and optoelectronic devices. In this paper, mechanical and thermal properties of SAC305 solder layers with arbitrary voids used in high-power LED CSPs are studied with both finite-element simulations and experiments. The results show that void size and void position within the solder layer are the two most critical issues on the shear strength of interconnection and the chip-on-substrate level thermal distribution in high-power LED CSPs.

In this paper, the heat transfer performance of the multi-chip (MC) LED module is investigated numerically by using a general analytical solution. The configuration of the module is optimized with genetic algorithm (GA) combined with a response surface methodology. The space between chips, the thickness of the metal core printed circuit board (MCPCB), and the thickness of the base plate are considered as three optimal parameters, while the total thermal resistance (R_tot) is considered as a single objective function. After optimizing objectives with GA, the optimal design parameters of three types of MC LED modules are determined. The results show that the thickness of MCPCB has a stronger influence on the total thermal resistance than other parameters. In addition, the sensitivity analysis is performed based on the optimum data. It reveals thatR_tot increases with the increased thickness of MCPCB, and reduces as the space between chips increases. The effect of the thickness of base plate is far less than that of the thickness of MCPCB. After optimization, three types of MC LED modules obtain lower T_j andR_tot. Moreover, the optimized modules can emit large luminous energy under high-power input conditions. Therefore, the optimization results are of great significance in the selection of configuration parameters to improve the performance of the MC LED module.

In this paper, an integrated LED lamp with an electrolytic capacitor-free driver is considered to study the coupling effects of both LED and driver's degradations on lamp's lifetime. An electrolytic capacitor-less buck-boost driver is used. The physics of failure (PoF) based electronic thermal simulation is carried out to simulate the lamp's lifetime in three different scenarios: Scenario 1 considers LED degradation only, Scenario 2 considers the driver degradation only, and Scenario 3 considers both degradations from LED and driver simultaneously. When these two degradations are both considered, the lamp's lifetime is reduced by about 22% compared to the initial target of 25,000 h. The results of Scenario 1 and 3 are close to each other. Scenario 2 gives erroneous results in terms of luminous flux as the LED's degradation over time is not taken into consideration. This implies that LED's degradation must be taken into considerations when LED and driver's lifetimes are comparable.

In this work, a physics-of-failure (PoF) reliability prediction methodology is combined with statistical models to consider the interaction between the lumen depreciation and catastrophic failures of LEDs. The current in each LED may redistribute when the catastrophic failure occurs in one of LEDs in an array, thus affecting the operation conditions of the entire LED array. A physics-of-failure based reliability prediction methodology is combined with statistical models to consider the interaction between the lumen depreciation and the catastrophic failure. Electronic-thermal simulations are utilized to obtain operation conditions, including temperature and current. Meanwhile, statistical models are applied to calculate possibilities of the catastrophic failure in different operation conditions.

The spectral power distribution (SPD) is considered as the figureprint of a light emitting diode (LED). Based on the analysis on its SPD, a method to predict both lumen depreciation and color shift for the phosphor converted white LEDs (pc-LEDs) is proposed in this paper. First, the entire SPD of a pc-LED is predicted by superimposing two asymmetric double sigmoidal (Asym2sig) models, which represent the decomposed blue light and phosphor converted light peaks, respectively. For a better understanding of how the SPD model affects the photometric and colorimetric characteristics of a pc-LED, a sensitivity study of the SPD parameters is then performed on its luminous flux Φ, color coordinates CIE1976( u′, v′). Second, the evolutionary process of the SPD is predicted for a pc-LED with the color temperature as 3000 K under degradation testing. And based on these predicted SPDs, the drift curves of Φ, u′, v′, and du′ v′are further predicted. Finally, lifetimes of the pc-LED due to lumen depreciation and color shift are estimated simultaneously from the predicted Φ and du′ v′ drift curves.

In this study, an electro-optical simulation method is developed to predict the light intensity distribution and luminous flux of an in-house fabricated GaN based blue LED chip. The entire modeling process links an electrical simulation with ANSYS and optical simulation with LightTools, by assuming a proportional relation between the distributed current density and light emission energy on the multiple quantum well (MQW) layer. Experimental results show that the proposed simulation method can give a good prediction on the light intensity distribution for a semi-packaged GaN based blue LED chip. Further analysis on the simulation results reveals that an increase of at most 8% of the luminous flux can be achieved when the current density is controlled to evenly distribute on the MQW layer whereas the chip structure and electro pattern remains the same.