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Low power surface-mounted (SMD) LEDs are paid much attention in research and development due to their portability and miniaturization. Optical characteristics of SMD LEDs have to maintain more accurate specifications in signaling applications such as traffic lights or railway. Current and temperature stabilization is important for attaining constant spectral properties of SMD LEDs. In this manuscript, the effect of change in ambient temperature and injection current on SMD LED intensity and wavelength shift is reported. Measurements were carried out using a spectrometer to record the LED optical parameters at various operating conditions. Detailed analyses show that the ambient temperature has a significant influence on optical characteristics of low-power SMD LED. The investigation of LED optical behaviors helps in choosing the appropriate working condition at the optimum level.

Die crack is a potentially serious issue affecting reliability and performance in Semiconductor industry. As a result, customers, particularly in the automotive industry, are concerned about the consequences of this failure mode and expect zero defect. In view of this an investigation was carried out with a focus to eliminate die crack occurrence in the AlInGaP die used in certain LED packages. Crack are only observed in AlInGaP die, other die such InGaN material system were found not exhibit cracks under similar conditions of design and process. Using a process mapping approach, it was observed that cracks only occur on one particular die attach (DA) equipment model. The lower elastic modulus of GaAs combined with the crystal orientation creates condition where external forces during LED assembly, in particularly in DA process, can exceed the mechanical strength of the die causing cracking. It is known that in situation where a crack does not extend into the epitaxial layer, the die will perform well. This makes it impossible to detect at electrical testing. In a controlled experiment, dice were intentionally subjected to large stresses at DA to induce partial cracks. These LEDs were biased with high current and reverse voltage in cyclic mode to induce further stress and initiate crack propagation. It was found that with further crack propagation, these crack dice we able to be segregated. Combined with correct bond force, which will not mechanically overstress the die during assembly and stress test, shown to eliminate this failure mode in mass production and prevent failure in customer application.

The optical performance of high-power multichip Chip-on-Board (COB) white light-emitting diodes (WLEDs) with different phosphor layer thicknesses ranging from 1.5mm to 3.5mm were investigated in this paper. This investigation reports that the optical performance in terms of phosphor conversion efficiency, Correlated Color Temperature (CCT) and Color Rendering Index (CRI) readings of WLEDs are significantly dependent on the phosphor layer thickness (or phosphor-dispersed epoxy weight). WLED packages with thicker phosphor layer have lesser phosphor conversion efficiency, and functions with an excessive yellow-to-blue ratio that shifts white light output to a yellowish color, lowering both CCT and CRI values.

A detailed thermal simulation of the performance of FR-4 PCBs having various "via configuration" is made in this study. The results indicate the thermal resistance from the simulation is significantly affected by compact thermal via configurations. Thermal resistance can be improved by increasing via number and also with copper filled via. For further explanation of the significant drop of thermal resistance at PCBs with thermal via, the detailed thermal resistance distribution at the thermal module are further examined. The significant drop in thermal resistance mainly occur in FR-4 PCBs with the help of thermal via. However, there is observed a maximum number of via which contribute to optimized thermal resistance across the PCB.

The optical properties of high power Warm-White Light Emitting Diodes (WW-LEDs) in Chip-on-Board (COB) package of Dam-and-Fill encapsulation with three different phosphor packaging configurations were investigated in this paper. The phosphor configurations studied were remote phosphor, double phosphor layers and normal phosphor configuration. Analysis of experimental data shows that LED samples in COB package with normal phosphor configuration had the highest efficiency compared to the other two phosphor configurations, differing from usual results obtained in other comparison studies of phosphor configurations in LED packages. This investigation also shows that LED samples with remote phosphor configuration has the highest relative intensity at red-yellow emission region, while LED samples with normal phosphor configuration has the highest relative intensity at blue emission region.

This paper presents the thermal analysis and validation of high power LED system with simulation and experimental methods. A 3W high power LED package is mounted on MCPCB and heat sink, which is tested inside a (300 × 300 × 300mm) still air chamber with three different forward currents. Experimental measurement with Thermal Transient Tester (T3Ster) is performed to capture the thermal transient characteristic of the LED system. The simulation is conducted with FloEFD 12.1 CFD software, using two-resistor model the LED package is defined with thermal resistance at different forward current. From the validation the simulation result closely match the experimental result, with highest percentage error at 4.75%. The surrounding air temperature of the system is also studied in the simulation. Following the verification, LED system with and without rectangular fixture are simulated and compared. The model without fixture shows better thermal results. The flow trajectory plot shows the difference in air convection with and without fixture. The simulation shows fixture disrupts the natural convection in the chamber.

The junction temperature of an light emitting diode package (LED) is a parameter of consequence as electrical and optical characteristics of the packages progressive decline with increment in the junction temperature. This paper is to compare the temperature rise in p-n junction of a four-chip cool white high power light emitting diode (HPLED) by using thermal transient tester (T3ster) and thermal imaging camera (TIC) under open air condition. The measured electrical thermal resistance of the HPLED package through cumulative structure function is 3.753K/W. The optical power of the cool white HPLED package is 1.30W and is used to calculate the real thermal resistance of the package. The obtained junction temperature rise of the package by using thermal transient testing is compatible with the thermal imaging method. The measured temperature rise in the p-n junction is 16.270C while the recorded junction temperature rise by using the camera is 16.500C.

This work signifies the importance of optical power in determining the real thermal resistance value for high power infrared (IR) emitter. Thermal transient measurement and optical test have been employed to study the influence of optical power on thermal resistance determination. For measurement, the IR emitter is driven at constant current of 1.0A with ambient temperature of 24.6oC under still air condition. From the findings, real junction-to-board thermal resistance Rth JBR obtained from the structure function with optical power consideration is 7.52±0.01 K/W. However, the electrical junction-to-board thermal resistance Rth JBE value (4.87±0.01 K/W) is much lower when optical power is not taken into consideration. It is found that structure function considering optical power offers higher values of real thermal resistance compared to that without optical power consideration.

Die cracking is the occurrence of fracture(s) in or on any part of the die of a semiconductor device. Failure caused by die cracking is one of the major concerns in packaging design and reliability. In this paper, fracture is inflicted onto the chip of a few units of p-Ge infrared emitting diode (IRED) package. Failure analysis such as curve tracing, decapsulation and visual inspection as well as SEM and EDX was performed on the units to characterize the fracture pattern and size. The results show dependence of the current-voltage (I-V) characteristic on the severity of the fracture inflicted onto the chip.

In this paper, comparison on wall-plug efficiency for the infrared (IR) emitter, warm-white LED and multi-chips LED has been studied. The main objective of this work is to provide a specific reference on wall-plug efficiency between various types of LED. Optical measurement is carried out at constant current of 1.0A under ambient temperature of 26.0 ± 1.0oC. It is found that IR emitter offers the highest wall-plug efficiency (34.5%) compared to warm-white LED (18.4%) and multi-chips LED (29.3%). In addition, influence of forward current on optical power for all the LEDs has also been discussed. As a result, optical power increases with increasing of forward current.

This paper deals with the simultaneous study of thermal and optical behaviors of light-emitting diode (LED) through various measuring conditions. The conditions such as different types of thermal interface materials (TIMs) and increases of driving current have been selected for detailed investigation. The results revealed that the measuring conditions led to a greater impact on thermal properties than optical properties of the LED. The determined junction-to-ambient thermal resistance and junction temperature were enhanced about 1.35% and 0.78%, respectively by replacing alumina to silver thermal compound. This indicates that the application of silver thermal compound provided a slightly weaker heat transfer from the packaged LED to ambient. On the other hand, it was only 0.5% deviation on the overall optical performance was found between both the TIMs. Despite, it was observed that the increase of driving current caused an augment in optical power, and adversely decreased the efficiency of the LED. Finally, the study of real thermal resistance of the LED was performed as to improve the accuracy of the measurement.

This paper is focused on thermal and optical properties of four-chip HPLED package with different thermal interface materials. The package is attached to MCPCB via solder paste and thermal compound. Through cumulative structure function, solder point of HPLED package is determined as 2.955K/W. The photometric properties of these two HBLED packages are evaluated by using TERALED. The total thermal resistance of the HPLED-S and HPLED-C is 10.68K/W and 13.00K/W respectively. Results show that the junction temperatures of HPLED with solder paste is lower than HPLED with thermal compound. Optical power, wall plug efficiency and luminous flux of both packages under various ambient temperature and forward current are discussed in this study. The HPLED-C produces more luminance than HPLED-S, but high thermal resistance of the HPLED-C induces the rise in junction temperature therefore increases the degradation rate of wall plug efficiency of the package.

This paper mainly discusses the thermal characterization of high power Light Emitting Diodes (LEDs). The Metal Core Printed Circuit Board (MCPCB) was designed with the aid of the recommended solder pad given in the product datasheet. Aluminium Nitride (AlN) was employed as the dielectric layer. Industrial grade aluminium (grade 5052) was utilized as the substrate material of the MCPCBs. The samples under test were varied in terms of substrate thickness on which the LEDs were mounted. The temperature rise at the junction and junction to ambient thermal resistance of the LEDs was investigated. The device performances were investigated with various substrate thicknesses under different ambient temperature at a fixed current input. The experimental results show that the increase in the substrate thickness greatly improved the thermal and optical performance of the LED packages. There were increments in the percentage of decrease in junction temperature rise and the percentage of decrease in the total thermal resistance which is from 19.8 % to 21.2 % and 15.2 % to 17.2 % respectively. The decreases in wall plug efficiency were reduced from 0.9% to 0.2%. Transient dual interface method was employed to determine the junction to board thermal resistance of the sample.

The junction temperature and the thermal resistance are vital characteristics that will determine the overall performance of LED packages. The influence of two different electrical connections of multi-chip LED packages on the thermal and optical characteristics is discussed in this paper. The thermal and optical characteristics of the LED package are investigated. Measurements are carried out on LED packages with series and parallel connections in sequence. The objective of this study is to compare the thermal and optical performance of the LED packages with different electrical connections. Experimental results revealed that there is a slight variation of 3 to 5% in R thJA and ΔT J values between both connections. For both thermal and optical measurements, the results for parallel connection are observed to be better than that for series connection.

Phosphor converted light emitting diodes (LEDs) are emerging are the most promising solid state lighting source since the past few decades and with no doubt in few years to come, this technology would conveniently replace the current lighting industries. This paper elucidates the significance of thermal and optical performance difference between cool and warm white LEDs. The analyses were carried out in terms of effects of phosphor concentration on the rise in junction temperature, thermal resistance as well as the optical properties of the samples. It was observed that the cool white samples achieved 6.68% less junction temperature compared to warm white LED recorded at room temperature of 25.1°C and the average efficiency of the cool white LED was found to be higher in magnitude compared to warm white LEDs. The effects of phosphor concentration on degradation of LED performances were discussed in terms of photon scattering, light trapping and thermal loading phenomena.

Generally, the effect of thermal interface material on thermal behavior of system-level light-emitting diode was presented. Application of thermal tape and thermal paste were selected to be applied on the contacting surfaces between package and heat sink. Thermal Transient Tester and T3Ster-Master software were adopted for thermal transient recording and evaluation. From the studies, it was observed that the selection of thermal interface material had a great impact on thermal management of light-emitting diode. Employing thermal paste as boundary condition revealed a reduction of about 6% in junction to ambient thermal resistance compared to thermal tape. In this paper, the thermal responses of the light-emitting diode with corresponding boundary conditions have been clearly discussed in terms of materials properties such as thermal conductivity, thickness and viscosity of the selected thermal interface materials.

Study on thermal behaviour for a Light-Emitting Diode (LED) package under different ambient temperatures was presented in this paper. Thermal transient measurements were carried out by using the Thermal Transient Tester (T3Ster) at each ambient temperature of 30°C, 50°C, 70°C, and 90°C T3Ster-Master evaluation software was adopted to analyze the recorded thermal transient structure function. Experimental results show that as the ambient temperature increases, the junction-to-ambient thermal resistance, R thJA an LED package will increase.

In this paper, thermal characterization of a high power infrared emitter as a function of input current is reported. Thermal behavior of the high power infrared emitter is investigated by employing thermal transient method. For measurement, input current is varied from 0.2A to 1.0A at constant ambient temperature of 27°C under still-air environment. It is found that junction-to-interface thermal resistance, Rth JI of the high power infrared emitter increases from 2.50 KfW to 3.17 K/W with the increase of input current from 0.2A to 1.0A at an ambient temperature of 27°C. From the findings, increase of junction-to-interface thermal resistance, Rth JI for the high power infrared emitter as a function of input current is due to the variation of optical efficiency with input current as presented in this paper.

This work reports on the effect of employing different thermal interface materials on transient dual interface methodology for light emitting diode (LED) packages. The measurements were carried out by setting two different boundary conditions with and without thermal interface materials which were thermal paste and mylar sheets. Analysis based on structure function evaluation reveals that the exact point of separation between junction and board of an LED package can be identified using transient dual interface method. It was also observed that the total junction to ambient thermal resistance for thermal paste was less compared to mylar sheet or without any interface. For an optimum driving current of 350mA, with thermal paste as interface, the total thermal resistance and junction temperature values obtained were 12.36/W and 62.23°C respectively.

This paper focuses on thermal characterization of high power infrared (IR) emitter. Thermal transient method is used to measure the junction temperature and calculate the thermal resistance (R th ). The emphasis is placed upon the investigation of thermal resistance value of units from different production lots at room temperature (25°C ± 0.5°C) for a limited range of input current (500mA, 800mA and 1A) with the air velocity kept constant throughout the experiment All investigations are based on the transient junction temperature measurements performed during the cooling process. The presented results include the cumulative structure functions and differential structure functions. It was found that the thermal resistance value of each unit differs from each other but the differences are minimal, proving the units are very consistent.

Junction temperature and thermal resistance are important factors in determining the overall performance of LED packages. Thermal transient measurements of multi-chip high brightness LED package with two specified positions under various ambient temperatures are discussed in this paper. Case 1 and case 2 are introduced as the inclined angle of the package at 0° and 90°. The main goal is to study the thermal characteristics of the LED package at different degree of inclinations using thermal transient tester (T3ster). Experimental results on junction temperature and thermal resistance for both cases at different ambient temperature are presented. From the obtained structure functions, results shows that the position of an LED package would influence the heat transfer of the whole LED package.

This paper is about the optical studies on two types of warm-white light emitting diode (LED) packages (ceramic and pre-molded package) at the influences of biasing current. Spectroradiometer measurement set and application software were adopted in this study. Experiments were carried out with increasing biasing current from 300mA to 700mA, in 100mA steps, at the same ambient temperature of 25°C. Experimental results showed that luminous intensity of LED was increased and dominant wavelength was slightly shifted as the biasing current increases.

This paper focuses on the thermal characterization of high power white light LED of 1W and 3W. Thermal transient method is used to measure the junction temperature and calculate the thermal resistance. The emphasis is placed upon the investigation of junction temperature in both the 1W and 3W LEDs for a limited range of drive-in current (500mA up to 1A) with the air velocity kept constant throughout the experiment. All investigations are based on the transient junction temperature measurements performed during the cooling process. The presented results include the cumulative structure functions and differential structure functions. It was found that the measured junction temperatures and thermal capacitances of both the LEDs increased with the input power (drive-in current). However, the thermal resistance decreased with the increase of drivein current.