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One major problem in the lighting industry is the thermal management of the devices. Handling of thermal resistance from solder point to the ambiance of the light-emitting diode (LED) package is linked to the external thermal management that includes a selection of the cooling mode, design of heatsink/substrate and thermal interface material (TIM). Among the significant factors that increase the light output of the of the LED system are efficient substrate and TIM. In this work, the influence of TIM on the luminous flux performance of commercial indium gallium aluminium phosphide (InGaAlP) low-power (LP) LEDs was investigated.

One batch of LEDs was mounted directly onto substrates which were glass-reinforced epoxy (FR4) and aluminium-based metal-core printed circuit boards (MCPCBs) with a dielectric layer of different thermal conductivities. Another batch of LEDs was prepared in a similar way, but a layer of TIM was embedded between the LED package and substrate. The TIMs were thermally conductive epoxy (TCE) and thermally conductive adhesive (TCA). The LED parameters were measured by using the integrated system of thermal transient tester (T3Ster) and thermal-radiometric characterization of LEDs at various input currents.

With the employment of TIM, the authors found that the LED’s maximum luminous flux was significantly higher than the value mentioned in the LED datasheet, and that a significant reduction in thermal resistance and junction temperature was revealed. The results showed that for a system with low thermal resistance, the maximum luminous flux appeared to occur at a higher power level. It was found that the maximum luminous flux was 24.10, 28.40 and 36.00 lm for the LEDs mounted on the FR4 and two MCPCBs, respectively. After TCA application on the LEDs, the maximum luminous flux values were 32.70, 36.60 and 37.60 lm for the FR4 and MCPCBs, respectively. Moreover, the findings demonstrated that the performance of the LED mounted on the FR4 substrate was more affected by the employment of the TIM than that of MCPCBs.

One of the major problems in the lighting industry is the thermal management of the device. In many low-power LED applications, the air gap between the two solder pads is not filled up. Heat flow is restricted by the air gap leading to thermal build-up and higher thermal resistance resulting in lower maximum luminous flux. Among the significant factors that increase the light output of the LED system are efficient substrate and TIM.

The findings in this work can be used as a method to improve thermal management of LP LEDs by applying thermal interface materials that can offer more efficient and brighter LP LEDs. Using aluminium-based substrates can also offer similar benefits.

Users of LP LEDs can benefit from the findings in this work. Brighter automotive lighting (signalling and backlighting) can be achieved, and better automotive lighting can offer better safety for the people on the street, especially during raining and foggy weather. User can also use a lower LED power rating to achieve similar brightness level with LED with higher power rating.

Better thermal management of commercial LP LEDs was achieved with the employment of thermal interface materials resulting in lower thermal resistance, lower junction temperature and brighter LEDs.

The purpose of this study is to design a more flexible and larger range of the dimming circuit that achieves the independence of multiple LED strings drive and can time-multiplex the power circuit.

The state-space method is used to model the BUCK circuit working in Pseudo continuous conduction mode, analyze the frequency characteristics of the system transfer function and design the compensation network. Build a simulation platform on the Orcad PSPICE platform and verify the function of the designed circuit through the simulation results. Use Altium Designer 16 to draw the printed circuit board, complete the welding of various components and use the oscilloscope, direct current (DC) power supply and a signal generator to verify the circuit function.

A prototype of the proposed LED driver is fabricated and tested. The measurement results show that the switching frequency can be increased to 1 MHz, Power inductance is 2.2 µH, which is smaller than current research. The dimming ratio can be set from 10% to 100%. The proposed LED driver can output more than 48 W and achieve a peak conversion efficiency of 91%.

The proposed LED driver adopts pulse width modulation (PWM) dimming at a lower dimming ratio and adopts DC dimming at a larger dimming ratio to realize switching PWM dimming to analog dimming. The control strategy can be more precise and have a wide range of dimming.

The aim of this paper is to evaluate using statistical methods how two soldering techniques – the convection reflow and vapour phase reflow with vacuum – influence reduction of voids in lead-free solder joints under Light Emitted Diodes (LEDs) and Ball Grid Arrays (BGAs).

Distribution of voids in solder joints under thermal and electrical pads of LEDs and in solder balls of BGAs assembled with convection reflow and vapour phase reflow with vacuum has been investigated in terms of coverage or void contents, void diameters and number of voids. For each soldering technology, 80 LEDs and 32 solder balls in BGAs were examined. Soldering processes were carried out in the industrial or semi-industrial environment. The OM340 solder paste of Innolot type was used for LED soldering. Voidings in solder joints were inspected with a 2D X-ray transmission system. OriginLab was used for statistical analysis.

Investigations supported by statistical analysis showed that the vapour phase reflow with vacuum decreases significantly void contents and number and diameters of voids in solder joints under LED and BGA packages when compared to convection reflow.

Voiding distribution data were collected on the basis of 2D X-ray images for test samples manufactured during the mass production processes. Statistical analysis enabled to appraise soldering technologies used in these processes in respect of void formation.

This study investigates the impact of three parameters such as: number of LED chips, pitch and LED power on the junction temperature of LEDs using a best heat sink configuration selected according to a lower temperature. This study provides valuable insights into how to design LED arrays with lower junction temperatures.

To determine the best configuration of a heat sink, a numerical study was conducted in Comsol Multiphysics on 10 different configurations. The configuration with the lowest junction temperature was selected for further analysis. The number of LED chips, pitch and LED power were then varied to determine the optimal configuration for this heat sink. A general equation for the average LED temperature as a function of these three factors was derived using Minitab software.

Among 10 configurations of the rectangular heat sink, we deduce that the best configuration corresponds to the first design having 1 mm of width, 0.5 mm of height and 45 mm of length. The average temperature for this design is 50.5 C. For the power of LED equal to 50 W–200 W, the average temperature of this LED drops when the number of LED chips reduces and the pitch size decreases. Indeed, the best array-LED corresponds to 64 LED chips and a pitch size of 0.5 mm. In addition, a generalization equation for average temperature is determined as a function of the number of LED chips, pitch and power of LED which are key factors for reducing the Junction temperature.

The study is original in its focus on three factors that have not been studied together in previous research. A numerical simulation method is used to investigate the impact of the three factors, which is more accurate and reliable than experimental methods. The study considers a wide range of values for the three factors, which allows for a more comprehensive understanding of their impact. It derives a general equation for the average temperature of the LED, which can be used to design LED arrays with desired junction temperatures.

This paper aims to identify antecedents for, and consequences of, low-intensity inter-unit conflict in multinational corporations (MNCs). Inter-unit conflict in MNCs is an important and well-researched theme. However, while most studies have focused on open conflict acknowledged by both parties, much less research has dealt with low-intensity conflicts. Still, low-intensity conflicts can be highly damaging – not least because they are rarely resolved.

The authors used a qualitative approach to understanding low-intensity conflict relying on 170 interviews in four Danish MNCs.

They describe consequences of low-intensity conflict and identify three types of actions by headquarters’ representatives that could lead to the development of low-intensity conflicts, namely, ignoring, bypassing and educating.

Very few studies have dealt with low-intensity conflict – not least in international business research. The authors argue that the study of low-intensity conflict in MNCs can provide relevant, novel knowledge of MNC functioning.

The purpose of this paper is to ensure adequate thermal management to remove and dissipate the heat produced by a light-emitting diode (LED) and to guarantee reliable and safe operation.

A three-dimensional (3-D) computational fluid dynamics (CFD) model was used to analyze the distribution of fluid velocities among microchannels at four different aspect ratios.

The results showed that at the same inlet flow rate, the larger the aspect ratio of the microchannels, the better the uniformity of the internal fluid velocity and thus better the heat dissipation performance on the surface of the high-power LED chip. In addition, the thermal performance of a high-power LED water cooling system with four different aspect ratios’ microchannel structures is further studied experimentally. Specifically, the coupling effect between the fluid velocity distribution in the microchannels and the heat dissipation performance of a high-power LED water cooling system is qualitatively analyzed and compared with the simulation results of the fluid velocity distribution. The results fully demonstrated that a larger aspect ratio of the microchannels results in better heat dissipation performance on the surface of the high-power LED chip.

Optimizing the structural parameters to facilitate a relatively uniform velocity distribution to improve the water cooling system performance may be a key factor to be considered.

The purpose of this paper is to investigate the thermal behaviors of high power LED packages to enhance the thermal performances of low temperature co‐fired ceramic chip on board (LTCC‐COB) package. Thermal analysis demonstrated an improved LTCC‐COB package design that is comparable to a metal lead frame package with low thermal resistance.

The LED device developed in this study is a LTCC package mounted directly on the metal PCB. A numerical simulation was performed to investigate the thermal characteristics of the LED module using the finite volume method, which is embedded in commercial software (Fluent V.6.3). Thermal resistance and temperature measurement validate the simulated results.

The effect of the thickness of the die attach material on the thermal resistance was dominant due to low thermal conductivity, and the junction temperature decreased significantly with slight increases in thermal conductivity, especially when the value was less than 5 W/mK. The results reveal that the thermal resistance of MCPCB is about 49 per cent‐58 per cent of the junction to board thermal resistance. The thermal model results showed good agreement with experimental results.

The developed model overcomes the large thermal resistance of a conventional LTCC package for high power LED module. The extensive results have demonstrated an improved thermal design, optimal dimensions of each component and boundary conditions for high power LTCC‐COB type package.

This paper seeks to describe the development of an inexpensive stereolithography (SL) system with high power ultraviolet light‐emitting diode (UV‐LED) curing light source. The advantages of UV‐LED light source will be investigated and the results presented.

The working principle of the UV‐LED light‐based SL system (LED‐SL) and its characteristics were explicated; the effect of beam divergence angle on the shape of a single cured line was analyzed; and the effects of the shapes of single cured lines shone by different light sources on the fabrication accuracy were compared.

LED‐SL has significantly higher part fabrication efficiency and accuracy than UV lamplight‐based prototyping systems. Furthermore, the UV‐LED energy consumption is much lower than laser and UV lamp sources, which conforms to the requirement of Green Manufacturing.

In increasing the scanning speed, the vibration of the focusing lens set has an obvious effect on the scanning accuracy; therefore, further research is needed.

This research verified the feasibility of adopting high power UV‐LED as the light source for a rapid prototyping system and enhanced the versatility of conventional UV‐SL technology.