Heat Dissipation Of Light-emitting Diodes Research Articles

Heat dissipation promotion of LED chips by c-BN film

The light-emitting diodes (LEDs) are now the most important lighting devices due to their excellent wall-plug efficiency (WPE). However, their unique structure means that heat dissipation from the chip can only be achieved by conduction. The insulating thermal conductivity layer becomes a bottleneck in the heat transfer of the chip, seriously affecting its lifetime and reliability. Cubic boron nitride (c-BN) has good thermal stability, electrical insulation and high thermal conductivity, making it a potential insulating and heat dissipating material. In this study, we investigate the application of c-BN films to promote heat dissipation in LEDs based on c-BN films grown by physical vapor deposition (PVD) sputtering. In our study, we highlighted the performance variations between c-BN and Si substrates under different driving powers, ranging from 9 W to 12 W. By incorporating the c-BN film onto the Si substrate, we observed a distinct improvement in the temperature distribution of the LED array. Specifically, with a driving power of 9 W, the temperature was reduced by approximately 4.1 °C, and with 12 W, the reduction reached 16.8 °C. This enhanced thermal management not only augments the stability and lifespan of the components but also boosts the optical output power of the LED chip array, with an increase ranging from 21.3% to 27.9%. We find that c-BN films can effectively enhance chip heat dissipation, significantly improve WPE, and suppress light decay, as demonstrated by temperature distribution and luminescence power measurements. The experimental and simulation results demonstrate that c-BN films can reduce the temperature of LED beads by approximately 5–17 °C compared to Si substrates. This c-BN thin film substrate shows promise for use in commercial device heat dissipation structures.

Enhanced Heat Dissipation in Gallium Nitride-Based Light-Emitting Diodes by Piezo-phototronic Effect.

As a new generation of light sources, GaN-based light-emitting diodes (LEDs) have wide applications in lighting and display. Heat dissipation in LEDs is a fundamental issue that leads to a decrease in light output, a shortened lifespan, and the risk of catastrophic failure. Here, the temperature spatial distribution of the LEDs is revealed by using high-resolution infrared thermography, and the piezo-phototronic effect is proved to restrain efficaciously the temperature increment for the first time. We observe the temperature field and current density distribution of the LED array under external strain compensation. Specifically, the temperature rise caused by the self-heating effect is reduced by 47.62% under 0.1% external strain, which is attributed to the enhanced competitiveness of radiative recombination against nonradiative recombination due to the piezo-phototronic effect. This work not only deepens the understanding of the piezo-phototronic effect in LEDs but also provides a novel, easy-to-implement, and economical method to effectively enhance thermal management.

Finite Element Simulation of the Machining Process of Boiling Structures in a Novel Radial Heat Sink for High-Power LEDs.

A phase change heat sink has higher heat transfer efficiency compared to a traditional metal solid heat sink, and is thus more preferred for the heat dissipation of high-power light-emitting diodes (LEDs) with very high heat flux. The boiling structure at the evaporation surface is the biggest factor that affects heat sink resistance. It is necessary to investigate the plastic deformation law during the machining process of boiling structures. In this study, a novel phase change radial heat sink was developed for high-power LED heat dissipation. First, a working principle and a fabrication process for the heat sink were introduced. Subsequently, to achieve an excellent heat dissipation performance, the machining process of boiling structures was numerically simulated and investigated. To be specific, plastic deformation generated during the formation was analyzed, and key parameters related to the morphology of the boiling structures were discussed including feeding angles and machining depths. Moreover, the finite element (FE) simulation results were compared with those of experiments. Last but not least, the heat transfer performance of the fabricated heat sink was tested. Results showed that the developed heat sink was well suited for a high-power LED application.

Thermal boundary conductance between high thermal conductivity boron arsenide and silicon

Thermal boundary conductance (TBC) is important for heat dissipation in light-emitting diodes (LEDs). In this study, we predicted the TBC between the high thermal conductivity boron arsenide (BAs) and silicon (Si) by nonequilibrium molecular dynamics (MD) simulations. From the thermal conductivity accumulation function with respect to phonon frequency, the dominant phonon frequencies for heat conduction in BAs are extremely different from those in Si. However, our nonequilibrium MD simulations indicated that the TBC of the BAs/Si interface was still high compared to most other interfaces, even though there was a major frequency mismatch in the thermal conductivity accumulation function between BAs and Si. The primary reason for the high TBC is the overlap of phonon density of states between BAs and Si in the frequency range of 5–8 THz. The range of predicted TBC of the BAs/Si interface was between 200 and 300 MW/m2 K in the temperature range of 300–700 K, and the values of the TBC were not sensitive to the temperature. We also found that the TBCs in Si/BAs and Si/Ge interfaces were close to each other considering the simulation uncertainty. This work indicates BAs as an excellent material for heat dissipation across the interfaces.

Synergistic Effect of Aligned Graphene Nanosheets in Graphene Foam for High‐Performance Thermally Conductive Composites

Graphene shows a great potential for high-performance thermally conductive composite applications because of its extremely high thermal conductivity. However, the graphene-based polymer composites reported so far only have a limited thermal conductivity, with the highest thermal conductivity enhancement (TCE) per 1 vol% graphene less than 900%. Here, a continuous network of graphene foam (GF), filled with aligned graphene nanosheets (GNs), is shown to be an ideal filler structure for thermally conductive composite materials. Compared to previous reports, a clear thermal percolation is observed at a low graphene loading fraction. The GNs/GF/natural rubber composite shows the highest TCE of 8100% (6.2 vol% graphene loading) ever reported at room temperature, which gives a record-high TCE per 1 vol% graphene of 1300%. Further analyses reveal a significant synergistic effect between the aligned GNs and 3D interconnected GF, which plays a key role in the formation of a thermal percolation network to remarkably improve the thermal conductivity of the composites. Additionally, the use of this composite for efficient heat dissipation of light-emitting diode (LED) lamps is demonstrated. These findings provide valuable guidance to design high-performance graphene-based thermally conductive materials, and open up the possibility for the use of graphene in high-power electronic devices.

Analysis of thermal and optical characteristics of light-emitting diode on various heat sinks

ABSTRACT Light-emitting diodes (LED) are widely used in today’s world due to its less power consumption and its high luminance capacity. Around 20–30% of energy is converted to light energy and 70–80% of energy is dissipated as heat. The excessive increase in temperature causes failure of LED. An effective thermal management is required for the proper heat dissipation in LED. In this study, the heat dissipation and the optical characteristics of the 16 W LED are studied using different types of aluminium heat sinks. The variation of case and junction temperature and the optical characteristic of LED is measured for different heat sinks. It was observed that heat sink with higher surface area shows the best result in terms of lower case and junction temperature. The higher luminous intensity was observed for the parallel fin type 1 heat sink due to the higher surface area.

Enhancement of Heat Dissipation in LED Using Graphene and Carbon Nanotubes

Enhanced heat dissipation in light emitting diodes (LED) increases its stability and lifetime. Although multilayer graphenes (MGPs) or multi-walled carbon nanotubes (MWCNTs) can enhance the heat dissipation to some extent, better results are obtained when both are used together. Due to the strong π-π bond interaction and van der Waals interaction between the layers, MGPs are prone to stacking and agglomeration, which limits their effective thermal conductivity. The addition of MWCNTs can increase the area of contact between the heat-dissipating coating and the air, and the effect of the MWCNTs on the heat-dissipating coating of the rear of LED is studied by changing the ratio of MGPs to MWCNTs. The ability of two different anionic surfactants to disperse MGPs and MWCNTs for facilitating heat removal was also evaluated. The concentration of the surfactants and the pH value were varied and based on the results, an optimal heat-dissipating coating for LED with excellent thermal conductivity is proposed.

Graphene-Carbon-Metal Composite Film for a Flexible Heat Sink.

The heat generated from electronic devices such as light emitting diodes (LEDs), batteries, and highly integrated transistors is one of the major causes obstructing the improvement of their performance and reliability. Herein, we report a comprehensive method to dissipate the generated heat to a vast area by using the new type of graphene-carbon-metal composite film as a heat sink. The unique porous graphene-carbon-metal composite film that consists of an electrospun carbon nanofiber with arc-graphene (Arc-G) fillers and an electrochemically deposited copper (Cu) layer showed not only high electrical and thermal conductivity but also high mechanical stability. Accordingly, superior thermal management of LED devices to that of conventional Cu plates and excellent resistance stability during the repeated 10 000 bending cycles has been achieved. The heat dissipation of LEDs has been enhanced by the high heat conduction in the composite film, heat convection in the air flow, and thermal radiation at low temperature in the porous carbon structure. This result reveals that the graphene-carbon-metal composite film is one of the most promising materials for a heat sink of electronic devices in modern electronics.

Thermal Conductivity and Mechanical Properties of Low-Density Silicone Rubber Filled With Al2O3 and Graphene Nanoplatelets

A simple approach is developed to obtain a multiscale network of heat conducting by filling spherical alumina (S-Al2O3) and graphene nanoplatelets (GnPs) into silicone rubber (SR). This unique structure effectively minimizes the thermal contact resistance between fillers and matrix. The physical properties of the composites are characterized by thermal conductivity, density, and tensile strength. A high thermal conductivity of 3.37 Wm−1 K−1 has been achieved, which is 47.1% higher than the single filler at the same loading. A strong and obvious synergistic effect has been observed as S-Al2O3 and GnPs filled into silicone rubber matrix. It is interesting that the composites with GnPs have the lower density (2.62 g/cm3, reduced by 6%) and the superior tensile performance, compared to silicone rubber composite with neat S-Al2O3. The composites have the potential applications in heat dissipation of light-emitting diode.

Effect of composite surface treatment on heat dissipation of LEDs

A three-layered structure comprising two layers of substrates with an adhesive layer at the center is introduced to improve heat dissipation of light-emitting diodes (LEDs). The adhesive layer is a type of treated composite composed of three components: hexagonal boron nitride (H-BN), epoxy resin (EP), and silane coupling agent. EP can be better positioned as a filler agent by using H-BN, thereby increasing adhesion. Introducing the silane coupling agent builds a heat conducting path from H-BN to EP, which effectively increases the thermal conductivity of the adhesive layer. In addition, the substrate surface treatment acts as an attraction agent and a catalyst that increases the interstitial between the composite and treated substrate surface. When the weight fraction of H-BN is 75%, the thermal conductivity of the treated composites at the center reaches 11.536W·m−1K−1, which is 38.57% higher than that of untreated H-BN/EP composites and 49 times that of EP. The thermal conductivity and adhesion strength of surface-treated three-layered structure are 9.571W·m−1K−1 and 56.60MPa, respectively. Analysis of the thermal stability of the three-layered structure shows that surface-treated structures are more durable than surface-untreated structures.

The Design of Freeform Surface Fresnel Lens Used for LED Uniform Illumination

This paper presents a new kind of light emitting diode(LED) secondary light distribution lens which adopts the type of Fresnel lens surface. The research purpose of this paper is to improve the LED heat dissipation efficiency of the secondary light distribution lens and the light efficiency, so as to prolong the service life of the LED. In this paper, we use the numerical method for solving the partial differential equation to establish a freeform surface lens which could produce uniform illumination, then the innovative method of combine the Fresnel lens structure with freeform surface lens was proposed. The design of freeform surface Fresnel lens allows dramatically cut the thickness of the lens (as well as the weight and volume) , it can solve the problem of difficulty in heat dissipation. By comparing the ray tracing simulation results of original freeform surface lens and freeform surface Fresnel lens in optical simulation software, experiments show that the latter not only shows the same degree of illumination uniformity, but also greatly reduced the thickness of the lens.

Copper Aluminum Nano Junction Normal Temperature Processes and Methods Applied to the LED High Heat Transfer Performance

High-power light-emitting diodes (LED) have extremely broad applications. However, with the job requirements of high- brightness and high color temperature from light-emitting diodes, it must be followed to enlarge the operating current, thus heating up more rapidly. If its heat dissipation problem cannot be effectively solved, operation will be prone to bring about color shift, and it may even considerably shorten its life. Moreover, application value will therefore be greatly reduced. So in order to enhance the high-power LED luminous brightness and life to cope with the future development needs of high-power LED components, it is necessary to replace the use of conductive silver paste to stick thermally conductive Cu slug fixing grain and lead frame heat dissipation aluminum sheet. This is done by directly bonding thermally conductive Cu slug with pure aluminum, the formation of highly efficient direct heat conduction cooling structure. Therefore the topic points at the crux of the LED heat dissipation difficulty, puts forward of copper and aluminum bonding technology in the ordinary temperature and pressure, method to effectively improve thermal conductivity performance between LED die bond Cu slug and joining aluminum cooling module. This will ultimately make the LED's operation and applications perfect.

Self-Driven Electronic Cooling Based on Thermosyphon Effect of Room Temperature Liquid Metal

Thermal management has been a critical issue for the safe running of an electronic device. Driving liquid metal with low melting point to extract heat from the thermal source is highly efficient because of its superior thermophysical properties over conventional coolant such as water or the like. In this paper, utilizing thermosyphon effect to drive room temperature liquid metal for electronic cooling was proposed for the first time with its technical feasibility demonstrated. This may lead to a self supported cooling which just utilizes the waste heat produced by the hot chip to drive the flow of liquid metal. And the device thus fabricated will be the one without any external pump and moving elements inside. A series of conceptual experiments under different operational conditions were performed to evaluate the cooling performance of the new method. Meanwhile, the results were also compared with that of water cooling by ways of thermal infrared graph and temperatures acquired by thermocouples. According to the measurements, it was found that the cooling performance of liquid metal was much stronger than that of water, and this will become even better with the increase of heat load, and height difference between the cooler and heater. A theoretical thermal resistance model was established and convective heat transfer coefficient was calculated to interpret the phenomenon with uncertainty analyzed. With further improvement of the present system and liquid metal coolant, this method is expected to be flexibly useful for heat dissipation of light-emitting diode (LED) street lamp, desk computer and radio remote unit (RRU), where confined space, efficient cooling, low energy consumption, dust-proof and water-proof are critically requested.

Analysis of heat dissipation in LED with various adhesives

Light-emitting diodes (LEDs) are semiconducting, light producing units, with the advantages of small size, long life, low voltage, reduced energy consumption, and high vibration resistance. Unfortunately, most LED output power is converted into heat, with little converted into optical energy. If the heat is not transferred outward from the unit, the LED will overheat and its light emission efficiency, stability, and lifespan will be reduced. Improving LED heat dissipation has become a hot topic. This paper used the finite element method to discuss the temperature change in LED heat sources, using epoxy and Al2O3 adhesives with varying heat transfer coefficients.