High Power LED Research Articles

Effects of Bonding Materials on Optical-Thermal Performances and High-Temperature Reliability of High-Power LED.

The die-bonding layer between chips and substrate determinates the heat conduction efficiency of high-power LED. Sn-based solder, AuSn20 eutectic, and nano-Ag paste were widely applied to LED interconnection. In this paper, the optical–thermal performances and high-temperature reliability of LED with these bonding materials have systematically compared and studied. The thermal conductivity, electrical resistivity, and mechanical property of these bonding materials were characterized. The LED module packaged with nano-Ag has a minimum working temperature of 21.5 °C. The total thermal resistance of LED packaged with nano-Ag, Au80Sn20, and SAC305 is 4.82, 7.84, and 8.75 K/W, respectively, which is 4.72, 6.14, and 7.84 K/W higher after aging for 500 h. Meanwhile, the junction temperature change of these LEDs increases from 2.33, 3.76, and 4.25 °C to 4.34, 4.81, and 6.41 °C after aging, respectively. The thermal resistance of the nano-Ag, Au80Sn20 and SAC305 layer after aging is 1.5%, 65.7%, and 151.5% higher than before aging, respectively. After aging, the LED bonded with nano-Ag has the better optical performances in spectral intensity and light output power, which indicates its excellent heat dissipation can improve the light efficiency. These results demonstrate the nano-Ag bonding material could enhance the optical-thermal performances and high-temperature reliability of high-power LED.

High Power LED Fish Collector Heat Sink

High-power LED fish collector lamps are small in size and work with high heat flow density, LED chips emit more and more heat, and heat dissipation problems have gradually become a bottleneck limiting the development of LED. In this paper, for a typical power LED, it mainly discusses the LED packaging technology, the heat sink structure and characteristics of the impact on the heat dissipation conditions.

Investigation of wound healing potential of photo-active curcumin-ZnO-nanoconjugates in excisional wound model

Wound healing, being a dynamic process consisting of hemostasis, inflammation, proliferation, and remodeling, involves the complicated interplay of various growth mediators and the cells associated repair system. Current wound healing therapies usually fail to completely regain skin integrity and functionality. Traditionally, curcumin is considered a potent natural wound healing agent as it possesses antibacterial, antioxidant, and anti-inflammatory properties. It is also known that zinc oxide (ZnO) nanoparticles (NPs) have photocatalytic properties, including the generation of reactive oxygen species. ZnO nanoaprticles are also Food and Drug Administration (FDA) approved as safe substances. While ZnO oxide requires illumination with ultraviolet light to become photocatalytically active, dye-sensitized ZnO can be activated by illumination with visible light. In the present study, we explored the wound healing potential of ZnO nanoparticles sensitized with curcumin (Cu+ZnO Nps) and illuminated with visible (blue) light generated by an array of high power LEDs. We studied the antibacterial effect of our conjugates by percentage reduction in bacterial growth and biofilm formation. The wound healing potential was analyzed by percentage wound contraction, biochemical parameters, and histopathological analysis of the wounded site. Additionally, angiogenesis and wound associated cytokines was evaluated by immunohistochemistry of CD31 and gene expression analysis of IL-1β, TNF-α, and MMP-9 after 16 days of post-wound treatment, respectively. Our study suggests that the therapeutic effect of Cu+ZnO NPs with LED illumination increases its wound healing potential by producing an antibacterial and anti-inflammatory effect. Moreover, the treatment strategy of using a nano formulation in combination with LED illumination further increases its efficacy. It was concluded that the anti-inflammatory and bactericidal effects of the LED illuminated Cu+ZnO Np showed accelerated wound healing with increased wound contraction, collagen deposition, angiogenesis, and re-epithelialization.

Selectively Metalizable Low-Temperature Cofired Ceramic for Three-Dimensional Electronics via Hybrid Additive Manufacturing.

With increasing interest in the rapid development of customized ceramic electronics, hybrid additive manufacturing (HAM) technology has become a competent alternative to traditional solutions such as printed circuit boards and cofired ceramic technology. Herein, the novel HAM technology is proposed by combining a dispensing three-dimensional (3D) printing process and selectively laser-activated electroless plating for fabricating 3D fully functional ceramic electronic products. An appropriative 3D-printable and metalizable low-temperature cofired ceramic slurry is developed to build the green body of ceramic electronics. After the debinding and sintering process, the 3D ceramic structure can be selectively laser-activated and then electrolessly plated to achieve electronic functionality. The thickness of the plated copper layer approaches 10 μm after 4 h of plating, and the electrical conductivity is 5.5 × 107 S m-1, which is close to pure copper (5.8 × 107 S m-1). To reduce the surface roughness of the laser-activated ceramic surface and thereby enhance the conductivity of the copper layer, the laser parameters are optimized as a 1250 mm s-1 scan speed, a 0.4 W laser power, and a 20 kHz laser-spot frequency. A high-power 3D light-emitting diode circuit board with an internal cooling channel is successfully developed to prove the feasibility of this HAM technology for customizing fully functional 3D conformal ceramic electronics.

A magnetic nanofluid device for excellent passive cooling of light emitting diodes

Efficient thermal management is an urgent unmet need for a plethora of energy-generating and consuming devices and systems. An improved cooling of high-power light-emitting diodes (LED) used in modern lighting will enhance energy savings, lifetime, and maintain high luminosity for a longer time. However, current passive techs are unable to address this challenge. We have performed detailed experimental and simulation investigations to address this challenge, resulting in the magnetic nanofluid cooling (MNFC) device providing the highest passive cooling of a high-power LED. For a versatile MNFC device suitable for cooling in a broad range of heat flux and temperatures of a heat load, the role of hydrodynamic and magnetic properties on the MNFC device performance was quantified. Several types of ferrofluid coolants with a range of viscosity and magnetic property values were studied. The MNFC device performance was compared with other passive devices by normalized cooling to applied heat flux and found that our device provided the highest reported temperature drop of 197 °C and the most efficient normalized cooling of 29 °C⋅kW−1⋅m2. The simulation model was modified significantly and included practical device parameters of temperature-dependent viscosity and electrical heating of the heat load, obtaining an excellent quantitative agreement with experiments obtaining dominant parameters for superior MNFC and relevant nondimensional numbers. We developed a material selection map by combining experimental and simulation findings, which were utilized to develop an efficient MNFC device demonstrating an excellent passive cooling of a high-power LED by ≈100 °C. The developed device and green, passive cooling methodology are useful to enhance the efficiency and lifetime, ensuring continuous high performance of a target device by removing generated waste heat.

Investigations on High-Power LEDs and Solder Interconnects in Automotive Application: Part I—Initial Characterization

Thermo-mechanical reliability is one major issue in solid-state lighting. Mismatches in the coefficients of thermal expansion (CTE) between high-power LED packages and substrates paired with temperature changes induce mechanical stress. This leads to a thermal degradation of LED modules by crack formation in the solder interconnect and/or delamination in the substrate, which in turn increases junction temperature and thus decreases light output and reduces lifetime. To investigate degradation and understand influence of LED package design and solder material, a reliability study with a total of 1800 samples − segmented in nine LED types and five solder pastes − is performed. First of all, in this paper a state-of-the-art review of high-power LED packages is performed by analyzing and categorizing the packaging technologies. Second, the quality inspection after assembly is realized by transient thermal analysis (TTA), scanning acoustic microscopy (SAM) and X-ray. For TTA, a new method is introduced to separate the thermal resistance of the LED package from solder interconnect and substrate by applying the transient dual interface method (TDI) on samples with different solder interconnect void ratios. Further measurement effort is not required. The datasheet values for thermal resistance are verified and the different LED package types are benchmarked. The void ratio of the solder interconnects is determined by X-ray inspection combined with an algorithm to suppress disruptive internal LED package structures. TTA and TDI revealed that initial thermal performance is independent of solder paste type and that voiding is more critical to smaller LED packages. In addition, lower silver proportion in the paste is found to increase voiding. SAM is less sensitive for initial void detection than X-ray, but it’s applied to monitor crack propagation while aging in combination with TTA. The results of the reliability study, i.e., the crack growth under temperature shock test for the different SAC solders, will be presented in a second independent paper.

Optical system design method for the concentration of radiation from a high-power LED

An optical system is considered that ensures the concentration of radiation from an LED emitting within a hemisphere onto a near-field illuminated area. The system is proposed to consider such a system as a composition of two zones — the central zone, which is a lens, and the zone responsible for capturing radiation from the LED within an angle of 40 to 90 degrees. Variants with a central zone in the form of bi-aspherical and sphero-elliptical lenses of finite thickness are analyzed. The alternative variant of the concentrating system composed from a collimating TIR lens and additional focusing lens is also analyzed. The expressions are given that allow analyzing possible concentration efficiency and the light spot size, and examples of systems are given designed with taking into account theoretical analysis results. Factors are discussed that define the choice of the required configuration. The results have shown the good agreement between the theoretical approach and practical design results. The optical elements designed as examples showed the high optical efficiency (near 90 %), thus such approach can be used for designing the LED optical systems for efficient light flux concentration, for example operating with fiber bundle as needed in some optical — electronic devices.

Testing and modeling of selected heat dissipation systems for high power LED light sources

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Research on thermal resistance Measurement method of high power LED

Due to the special packaging and working conditions of high-power LEDs, it is a huge challenge to accurately measure the junction-to-case thermal resistance. The traditional transient dual interface and structure function methods have been successfully applied to measure the thermal resistance of high-power LEDs. In this paper, a different interface condition is designed to change the contact thermal resistance between the DUT and the heat sink, making the Z th curve separation point clearer. More importantly, the structural thermal resistance between multiple layers on the heat flow path of the device is obtained by converting the Z th curve. Finally, the effectiveness of the method is verified by comparative analysis of experimental data.

Preparation and Optical Properties of Compound Nanopowder Art Ceramics.

The fluorescent glass of white LEDs has high physical and chemical stabilities, good heat dissipation performance, and can maintain an excellent performance of fluorescent powder itself. In order to realize luminescent materials such as white LED lighting, laser lighting, and long-term lighting, this study proposes the preparation of a compound nanopowder art ceramic and its optical properties. In order to play the role of nanoparticles in optoelectronic or photonic devices, it is necessary to explore the preparation process and performance research of dielectric ceramics. This study uses high-purity aluminate (MgAl2O4) powder for transparent ceramics, doped with yellow nanophosphor as raw materials, through a sintering process in oxygen atmosphere, sintering combined with heat treatment, and isostatic pressing to prepare transparent ceramics. The ceramic sample is placed in a high-temperature and high-pressure environment for heat and other static pressure, and fluorescent samples are obtained. The results show that under 350 mA driving current, high-power white LEDs in the fluorescent ceramic package have almost no attenuation after 700 h, and the average attenuation of the LED package of the phosphor package is about 10%. The use of fluorescent ceramics can be packaged not only to improve the LED device's light efficiency but also to increase the life of the white LED device.

Development of Radiator with Thermoplastic Polymer and Insert-Molded Aluminum Alloy Parts for Light-Emitting Diode Headlights

The increasing popularity of electric vehicles has increased the demand for lightweight auto parts. However, the excessive weight of traditional metal heat sinks has remained a concern. Metal has excellent thermal conductivity but low radiation efficiency. Conversely, thermoplastic polymers have excellent heat radiation efficiency but poor thermal conductivity. In this study, we propose a radiator constructed using thermoplastic polymer and insert-molded aluminum alloy parts to maintain the low junction temperature of light-emitting diodes (LEDs); the radiator’s weight is reduced through a combination of aluminum alloy and a thermally conductive polymer designed for automotive headlights. At an LED thermal load of 11.48 W, the measured temperature on the LED pad is 60.8 °C. The weight of the proposed radiator is 23.37% lighter than that of a pure metal radiator. When the lightweight radiator is used in high-power LED headlights, it effectively dissipates heat within a limited space.

Ice-templated graphene in-situ loaded boron nitride aerogels for polymer nanocomposites with high thermal management capability

Efficient heat dissipation is essential for further improving the integration of high-power electronic packaging equipment. Through-plane direction aligned three-dimensional boron nitride nanosheets/graphene(3D-BNNS/Gr) aerogels are designed as heat transferring skeletons for epoxy nanocomposites. Graphene was in-situ synthesized on BNNS by a combustion synthesis method to ensure good contact, and subsequent aligning of BNNS/Gr nanofillers by a self-assembly ice-templating strategy to reduce contact resistance between individual BNNS. At a relatively low 3D-BNNS/Gr loading of 11.2 vol%, the composites exhibit superior through-plane thermal conductivities of 2.23 and 1.09 W m−1 K−1, demonstrating a 1073% and 1069% thermal conductivity enhancement at room temperature (RT) and liquid nitrogen temperature (77 K) compared with pure epoxy resin. Meanwhile, the mechanical properties of the composites at RT and 77 K were synchronously enhanced. Furthermore, the 3D-BNNS/Gr-epoxy nanocomposite film then acts as a heat spreader for heat dissipation of high-power LED modules and exhibits superior cooling efficiency.

DESIGN AND IMPLEMENTATION OF AUTO INTENSITY CONTROLLING SYSTEM FOR HOME AUTOMATION APPLICATIONS USING IOT

Machine vision framework is generally utilized in the cutting-edge on-line location industry. Its light source framework is the one of the key parts. As another kind of green light asset, High-power LED enjoys many benefits, for example, energy saving, climate insurance, against seismic, and high radiant effectiveness, which make them generally applied in many fields, for example, modern lighting. Nonetheless, the picture nature of the tried article has a incredible connection with the security of the light source.

Performance and analysis of an ultraviolet C-band light emitting diode with an emission wavelength of 268 nm

We report a high-power ultraviolet C-band light-emitting diode (LED) with peak wavelength at 268 nm delivering 199 mW optical power at 350 mA direct current. The peak wall-plug and external quantum efficiencies are greater than 10% and 13%, respectively. We developed an approach to determine light-extraction efficiency (LEE) and internal quantum efficiency (IQE) based on the carrier recombination rate equation and used it to analyze the junction-temperature-dependent optical power behavior. For this LED, we obtained a LEE of ∼16% and a peak IQE of ∼83%. The efficiency droop percentage was quantified to be ∼20% at 350 mA, owing to Auger and other higher order carrier losses.

LED-Based Photo-CIDNP Hyperpolarization Enables 19F MR Imaging and 19F NMR Spectroscopy of 3-Fluoro-DL-tyrosine at 0.6 T

Although 19F has high potential to serve as a background-free molecular marker in bioimaging, the molar amount of marker substance is often too small to enable 19F MR imaging or 19F NMR spectroscopy with a sufficiently high signal-to-noise ratio (SNR). Hyperpolarization methods such as parahydrogen-based hyperpolarization or dynamic nuclear polarization (DNP) can significantly improve the SNR, but require expensive and complex sample preparation and the removal of toxic catalysts and solvents. Therefore, we used the biologically compatible model of the fluorinated amino acid 3-Fluoro-DL-tyrosine with riboflavin 5ʹ-monophosphate (FMN) as a chromophore dissolved in D2O with 3.4% H2Odest., allowing to transform light energy into hyperpolarization of the 19F nucleus via photo-chemically induced dynamic nuclear polarization (photo-CIDNP). We used a low-cost high-power blue LED to illuminate the sample replacing traditionally used laser excitation, which is both potentially harmful and costly. For the first time, we present results of hyperpolarized 19F MRI and 19F NMR performed with a low-cost 0.6 T benchtop MRI system. The device allowed simultaneous dual-channel 1H/19F NMR. 19F imaging was performed with a (0.94 mm)2 in-plane resolution. This enabled the spatial resolution of different degrees of hyperpolarization within the sample. We estimated the photo-CIDNP-based 19F signal enhancement at 0.6 T to be approximately 465. FMN did not bleach out even after multiple excitations, so that the signal-to-noise ratio could be further improved by averaging hyperpolarized signals. The results show that the easy-to-use experimental setup has a high potential to serve as an efficient preclinical tool for hyperpolarization studies in bioimaging.

Blue LED-pumped intense short-wave infrared luminescence based on Cr3+-Yb3+-co-doped phosphors

The growing demand for spectroscopy applications in the areas of agriculture, retail and healthcare has led to extensive research on infrared light sources. The ability of phosphors to absorb blue light from commercial LED and convert the excitation energy into long-wavelength infrared luminescence is crucial for the design of cost-effective and high-performance phosphor-converted infrared LEDs. However, the lack of ideal blue-pumped short-wave infrared (SWIR) phosphors with an emission peak longer than 900 nm greatly limits the development of SWIR LEDs using light converter technology. Here we have developed a series of SWIR-emitting materials with high luminescence efficiency and excellent thermal stability by co-doping Cr3+-Yb3+ ion pairs into Lu0.2Sc0.8BO3 host materials. Benefitting from strong light absorption of Cr3+ in the blue waveband and very efficient Cr3+→Yb3+ energy transfer, the as-synthesized Lu0.2Sc0.8BO3:Cr3+,Yb3+ phosphor emits intense SWIR light in the 900–1200 nm from Yb3+ under excitation with blue light at ~460 nm. The optimized phosphor presents an internal quantum yield of 73.6% and the SWIR luminescence intensity at 100 °C can still keep 88.4% of the starting value at 25 °C. SWIR LED prototype device based on Lu0.2Sc0.8BO3:Cr3+,Yb3+ phosphor exhibits exceptional luminescence performance, delivering SWIR radiant power of 18.4 mW with 9.3% of blue-to-SWIR power conversion efficiency and 5.0% of electricity-to-SWIR light energy conversion efficiency at 120 mA driving current. Moreover, under the illumination of high-power SWIR LED, covert information identification and night vision lighting have been realized, demonstrating a very bright prospect for practical applications.

Borylated Cymantrenes and Tromancenium Salts with Unusual Reactivity.

In continuation of our study of the chemistry of cationic (cycloheptatrienyl)(cyclopentadienyl)manganese(I) sandwich complexes, so-called “tromancenium” salts, we report here on their boron-substituted derivatives focusing on useful boron-mediated synthetic applications. Transmetalation of lithiated tricarbonyl(cyclopentadienyl)manganese (“cymantrene”) with boric or diboronic esters affords monoborylated cymantrenes that are converted by advanced high-power LED photosynthesis followed by oxidation with tritylium to their 8-boron-substituted tromancenium complexes. These new functionalized tromancenium salts are fully characterized by 1H/11B/13C/19F/55Mn NMR, IR, UV–vis, HRMS spectroscopy, single-crystal structure analysis (XRD) and cyclic voltammetry (CV). IR spectra were thoroughly analyzed by density functional theory (DFT) on the harmonic approximation in qualitative agreement of calculated vibrations with experimental values. Uncommon chemical reactivity of these borylated tromancenium salts is observed, due to the strongly electron-withdrawing cationic tromancenium moiety. No Suzuki-type cross-coupling reactions proved so far achievable, but unusual copper-promoted amination with sodium azide under microwave irradiation is possible. Diazoniation of aminotromancenium affords an extremely reactive dicationic tromanceniumdiazonium salt, which is too labile for standard Sandmeyer reactions, in contrast to analogous chemistry of cobaltocenium salts. Overall, borylated tromancenium salts display unexpected and intriguing chemical properties with the potential for novel synthetic applications in future work.

Ultrafast GGAG:Ce X-ray scintillation ceramics with Ca2+ and Mg2+ co-dopants

Among the aluminate garnet materials, cerium-doped gadolinium gallium aluminum garnet ceramics (GGAG:Ce) show fast scintillation properties, which suggests that they have promising applications in medical imaging, high-energy ray detection and high-power LED lighting. In this study, Gd3Ga3Al2O12:Ce scintillation ceramics co-doped with Me2+ (Me = Mg, Ca) are fabricated using a two-steps route: a solid-state reaction followed by annealing in air. The optical and scintillation properties, including the absorption, radio luminescence (RL), light yield, and decay time, of these co-doped ceramics are studied in detail. Doping with Mg2+ and Ca2+ leads to the oxidation of Ce3+ to Ce4+, which accelerates the scintillation process and decreases the light yield. Co-doping with Ca2+ and Mg2+ shows a synergistic effect on this phenomenon. Compared with 0.2 at% Ca2+ or 0.2 at% Mg2+ single-doped GGAG:Ce, the GGAG:Ce co-doped with 0.1 at% Ca2+ and 0.1 at% Mg2+ has the fastest decay time (∼31 ns) and maintains a relatively high light yield (∼27400 ± 1600 ph/MeV, 77% of undoped GGAG:Ce). These findings shed new light on designing Ce-activated garnet scintillator materials with ultra-fast decay time for applications in time-of-flight (TOF) PET technology.

On-Demand Programming of Liquid Metal-Composite Microstructures through Direct Ink Write 3D Printing.

Soft, elastically deformable composites with liquid metal (LM) droplets can enable new generations of soft electronics, robotics, and reconfigurable structures. However, techniques to control local composite microstructure, which ultimately governs material properties and performance, is lacking. Here a direct ink writing technique is developed to program the LMmicrostructure (i.e., shape, orientation, and connectivity) on demand throughout elastomer composites. In contrast to inks with rigid particles that have fixed shape and size, it is shown that emulsion inks with LMfillers enable in situ control of microstructure. This enables filaments, films, and 3D structures with unique LM microstructures that are generated on demand and locked in during printing. This includes smooth and discrete transitions from spherical to needle-like droplets, curvilinear microstructures, geometrically complex embedded inclusion patterns, and connected LM networks. The printed materials are soft (modulus < 200 kPa), highly deformable (>600 % strain), and can be made locally insulating or electrically conductive using a single ink by controlling the process conditions. These capabilities are demonstrated by embedding elongated LM droplets in asoft heat sink, which rapidly dissipates heat from high-power LEDs. Theseprogrammable microstructures can enable new composite paradigms for emerging technologies that demand mechanical compliance with multifunctional response.

Heat Transfer Performance and Structural Optimization of a Novel Micro-channel Heat Sink

With the advent of the 5G era, the design of electronic equipment is developing towards thinness, intelligence and multi-function, which requires higher cooling performance of the equipment. Micro-channel heat sink is promising for the heat dissipation of super-thin electronic equipment. In this study, thermal resistance theoretical model of the micro-channel heat sink was first established. Then, fabrication process of the micro-channel heat sink was introduced. Subsequently, heat transfer performance of the fabricated micro-channel heat sink was tested through the developed testing platform. Results show that the developed micro-channel heat sink has more superior heat dissipation performance over conventional metal solid heat sink and it is well suited for high power LEDs application. Moreover, the micro-channel structures in the heat sink were optimized by orthogonal test. Based on the orthogonal optimization, heat dissipation performance of the micro-channel radiator was further improved.