High-power LED thermal conductivity of the conduct...

LED packaging due to the complexity of the structure and process, and directly affect the performance and life of the LED, has been a research hotspot in recent years, especially high-power white LED package is a hot topic in the research hot spot. The LED package features include:Mechanical protection, in order to improve reliability;Enhance heat dissipation to reduce the chip junction temperature and improve the performance of the LED;Optical control and improve the light extraction efficiency, optimize the beam distribution;Supply management, including AC / DC change, and power control.     LED packaging methods, materials, structure and process of selection is decided by the chip architecture, optical / mechanical properties, specific applications and cost factors. After 40 years of development, LED packaging has undergone a frame type (Lamp LED), Chip SMD LED, power LED (Power LEDs) and other stages of development. As the chip power increases, especially in solid-state lighting technology development needs, proposed a new and higher requirements on the LED package, optical, thermal, electrical and mechanical structure. In order to effectively reduce the package thermal resistance, improve efficiency, and must adopt a new technology ideas to the package design.High thermal conductivity of a high-power LED Conductive Silver Paste            Uninwell-6886 series of conductive silver glue is a glue an integral part of the IED production package, conductive silver glue is conductive, better thermal conductivity, shear strength and bond strength is stronger. UNINWELL as the world's leading brand of high-end electronic adhesives, to "your side of the high-end electronic bonding protection expert to serve the purpose. Of Uninwell silver conductive glue, conductive silver paste, red plastic patch, underfill, TUFFY glue, LCM sealant, UV glue, anisotropic conductive adhesive of ACP, the solar cell conductive paste such as a series of electronic adhesives has the highest cost-effective, world five hundred of the more than 100 customers worldwide. Recently, UNINWELL often Cheung Industrial combination, to jointly develop high-end electronics adhesives markets.    UNINWELL conductive silver plastic with electrical conductivity, strong shear rheology is also very good, and low moisture absorption. Particularly suitable for high-power high-brightness LED package.     The company's specially developed BQ-6886 series of conductive silver glue, especially for high-power high-brightness LEDs, thermal conductivity: 25.8 shear strength: 14.7, highest in the industry. Two key technologies of high-power LED package     High-power LED package is mainly related to light, heat, electricity, structure and process, these factors are both independent of each other, but also influence each other. Which alone the purpose of the LED packaging, heat is the key, power, structure and technology is a means, while the performance of a concrete manifestation of the package level. Process compatibility and reduce production costs, the LED package design and chip design, chip design should take into account the package structure and process. Otherwise, the other chip manufacturing is completed, may be due to the needs of the package the chip architecture to adjust, thus extending the product development cycle and process cost, and sometimes even impossible. Specifically, the key technologies for high-power LED package include:(A) low thermal resistance packaging technology     LED luminous efficiency levels about 80% of the input electrical energy transformed into heat, and the small size of the LED chip, chip cooling the LED package that must be addressed key issues. Including the chip layout, the packaging material of choice (substrate materials, thermal interface material) and process, heat sink design.          The LED package thermal resistance is the main internal thermal resistance and the interfacial thermal resistance of the material (heat dissipation substrate and heat sink structure). Heat the substrate to absorb the heat generated by the chip, and conduction to the heat sink, heat exchange with the outside world. The heat dissipation substrate materials including silicon, metals (such as aluminum, copper), ceramic (eg, of Al2O3, AlN, SiC) and composite materials. Third-generation LEDs such as Nichia Corporation CuW do substrate, 1mm chip flip CuW substrate, reducing the package thermal resistance, and improved light-emitting power and efficiency; Lamina Ceramics has developed a low temperature co-fired ceramic-metal substrate, and the development of the LED packaging technology. The technology was first prepared by suitable for eutectic solder, high-power LED chips and the ceramic substrate, then the LED chip and the substrate directly welded together. Eutectic solder layer, the electrostatic protection circuit, drive circuit and control compensation circuit is not only a simple structure, but due to the high thermal conductivity thermal interface, greatly improving the thermal performance for high-power LED array package integrated on the substrate solutions.         LED process, the loss of radiative recombination to produce photons in the outward emission, including three aspects: the chip internal structural defects and the absorption of the material; photon in the outgoing interface index difference caused by the reflection losses; as well as The angle of incidence greater than the total reflection loss caused by the critical angle of total reflection. Therefore, a lot of light can not reach all parts of the chip out outside. Relatively high in the chip coated with a layer of refractive index transparent layer (Potting), because the adhesive layer between the chip and the air, thus effectively reduce the loss of photons at the interface and improve the light extraction efficiency. In addition, the role of the potting materials include mechanical protection on the chip, stress release, and as a light guide structure. Therefore, high transmittance, high refractive index, good thermal stability, good fluidity, easy to spray. In order to improve the reliability of the LED package, also called encapsulants with low moisture absorption, low-stress, anti-aging properties. Commonly used potting epoxy and silicone. Silica gel due to high transmittance, refractive index, good thermal stability, stress, moisture absorption and low, significantly better than the epoxy resins are widely used in LED packaging, but the cost is high. The study showed that higher silicone refractive index can effectively reduce the loss of photons by the refractive index of physical barriers and improve the external quantum efficiency, but the silica gel performance is influenced by ambient temperature. Increase with increasing temperature silicone internal thermal stress, resulting in lower refractive index of silica gel, thus affecting the efficiency of LED light and the light intensity distribution.