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News > Dynamic industry > Perfect solution for high-brightness LED lighting applications, and thermal design

Perfect solution for high-brightness LED lighting applications, and thermal design

LED lighting applications, to meet the requirements of the existing alternative sources close to the brightness usually take in "quantity" to win the design approach, namely in the area of design of a large number of units of LED elements, or take to enhance the luminous efficiency of a single element for design, But this, which caused a planar or point-like element temperature need treatment, while cooling means are available to take active or passive design, particularly in the active cooling design is more complex, and how to achieve optimal thermal design Avoid bad light affect the life of the LED elements is an important key to the development of high-brightness LED lighting.
LED (LightEmittingDiode) solid-state lighting is great potential in recent years, is considered the future of the industry, as consumers and industry caught looking, you can take advantage of LED solid-state lighting to solve a lot of energy wasted on inefficient illumination problem, because LED with volume small, high luminous efficiency, energy saving and other advantages, therefore, the majority of people on the future development of LED solid-state lighting high hopes. LED solid-state lighting for traditional light sources emitting technologies, it is more environmentally friendly, energy-saving aspects of a number of advantages, the first observation of a common everyday lighting, nothing more than incandescent and fluorescent, incandescent basically luminous efficiency performance That tends to be a disadvantage, even with low-cost and other advantages habits have been established, but the rise of the concept of environmental protection under the social atmosphere, has become an environmentally friendly, non-efficient lighting products. In the fluorescent lamp, although mining high-frequency gas discharge optical technology to achieve power efficiency, but in fact can not be avoided fluorescent control process environmentally harmful mercury, environmental demands on the light source is not the best choice.
Back to the development of LED solid state light source, the early multi-LED light source for indicating that the signal, an indicator light medium / low brightness, low power driving the light source applications, therefore no heat aspect considerations, on the one hand is indicated by a light source currently used only to identify the status of the device, the switching status prompt, not for lighting purposes, because the drive power is not high and no significant natural cooling problems to be solved. But the question is, the intended use of high brightness LED, mostly geared towards alternative green light and developed, so the design approach will cause a lot of impact.
When the LED solid-state light source toward the direction of thinking everyday lighting applications, there will be bright enough problems, we must try to take advantage of improving power increased luminous efficiency of the LED elements, or the use of a greater number of high-brightness LED conduct modular design, so the light source includes lighting applications "high brightness" requirement.
Play a high-performance, environmentally friendly lighting efficiency thermal design is a key
LED core design element that is imposed by the use of a voltage LED die to produce luminescence results, similar to the silicon wafer with the general, LED chips will be because of the prolonged use and produce bad light phenomenon, most of the design elements in order to enhance brightness, multi-use bias increase crystals that enhance energy imposed on the LED power, so wafers can stimulate a higher brightness, this way, to strengthen the power LED light failure problems will make the crystals, accelerated life issues appearance, high temperature and even strengthen the brightness due to the component itself generated will cause shortening of product life.
When a single LED die with brightness enhancement, single LED wattage consumption will increase from 0.1W to 1,3, or even more than 5W, while the LED light source module measurement analysis majority, there will be encapsulated module thermal resistance due to increased luminous efficacy and enhance the general will continue to increase by 250K / W to 350K / W upper and lower margin.
While viewing the test results will be found, LED will have with the "power" to increase, "life" is declining, this may make the plateau has 20,000 hours life LED light source element, because the heat affected and reduced to remaining service life of 1,000 hours. Especially when the element is at the operating temperature of 50 degrees Celsius, capable of maintaining an optimum life of 20,000 hours, but when the LED elements operating in an environment of 70 degrees Celsius, the average life expectancy is reduced to 10,000 hours, if continued in running at 100 degrees Celsius environment, life will be remaining 5,000 hours.
LED module design thermal impedance status
In addition to the key components LED susceptible to temperature, the light has taken most of the modular design concept development, or even to replace the traditional light sources, so that the light emitting element can be integrated with electronic circuits in a very small space, because the LED driving element for DC Direct the majority of fixtures connected to AC power supply AC power mainly to simplify the LED light source facilities for the complexity of the current mainstream approach is to directly power rectifier, transformer module with integrated LED light-emitting element, but the question is, since available under a lot of relatively small circuit space, convection in the device space is relatively small, and naturally can not get better cooling effect, only through active countermeasures forced cooling, heat dissipation module processing .
If the module is observed by the thermal impedance of the heat produced by the model, to predict the temperature LED die junction, the junction semiconductor pn junction points mean, the definition of thermal resistance R corresponding to a temperature difference between the ratio of the power dissipation, and thermal resistance The formation of a considerable number of factors, but the way the heat flow through the review model, we can more clearly confirmed that the dissipation of heat treatment, which is a key issue because it reduces the efficiency of heat dissipation can go from components, assembly methods, substrate material, structure improvement works. General LED solid-state light flux model can be from a few key point to view.
For example, LED light-emitting element can be disassembled for LED die, die and wire-pin, plastic packaging, and then observe the expansion and LED light source modules, LED components that will be joining the metal pin, MetalCorePCB ( MCPCB) board, and finally cooling aluminum extrusion heat sink, etc., while the heat flux model can be observed that there are several series impedance, such as binding sites, and other pieces of metal grains journeys, the board and the environment, and then view series impedance of thermal loop, trying to find the cooling inefficiencies sticking point.
And from model to further observation, can be found from the junction to the heat grains throughout the external environment, in fact, is made up of several ways to increase the total heat from, for example, grain and take the load of the material properties of the metal sheet, optical resin material in contact with the circuit board thermal resistance package LED die material, the surface of the LED element or contact with the aluminum cooling fins between extrusion glue, and even combinations of air between the cooling device and, constitute the entire Heat thermal process. Operational temperature of LED solid-state light sources how dissipation, it will affect the effectiveness of the entire light source lighting applications, the key to the effectiveness of the use of energy, life and other devices, and to improve the way the heat can be customized wafer-level technology, packaging technology LED die, board level of technology to make improvements.
In the heat of the wafer-level processing means, due to the traditional wafer manufacturing method, and many more as a sapphire substrate design, and thermal conductivity of the sapphire substrate is close to 20W / mK, in fact, it is difficult to produce a rapid heat LED epitaxial shed, the current mainstream practice, the enhancement processing for the wafer level LED heat, especially for high-power, LED element aspects high brightness, using flip-chip (Flip-Chip) form, effective use of flip-chip epitaxial heat conduction out.
There is also another kind of way, is the adoption of "vertical" approach to the production of electrode LED components, LED components due to upper and lower ends are equipped with metal electrodes, which may be greater benefit in the heat of the problem. For example, using a GaN substrate as the material, due to the GaN substrate that is a conductive material, and therefore the electrodes can be located below the substrate to connect, quick dissipation efficiency can be obtained by epitaxy temperature, but this practice because of higher material costs, also sapphire substrate than traditional approaches cost a lot more expensive, will increase the production cost components.
As for the heat level to strengthen the practice of the package is quite a bit, here are a few common practice. In general, LED production process, will use an optical grade epoxy resin to wrap the entire LED, thereby to cause the LED element can be in terms of better performance in mechanical strength, can be protected even within the associated line element, but the ring Although the practice of the epoxy resin component can improve the strength, but at the same time limiting the operating temperature range element, when used as optical grade epoxy resin at high temperatures, because of the high temperature or light, so that deterioration of the optical characteristics of the epoxy resin even the material itself can also cause deterioration.
Common ways to improve the current package, only in most medium / low power LED components only with traditional shells packaging technology, LED components in terms of high brightness, high power, and most use LumiledsLuxeon series packaging method, the thermal path concentrated in the bottom of the metal, the interior package switch optical characteristics and high temperature, the performance was excellent in light-resistant silicone resin to be packaged, this packaging method obtain better performance in mechanical strength, while its internal high temperature, ultraviolet radiation , high-intensity blue LED has a more powerful tolerance.
In the heat to improve the circuit board level, the more general approach that is taken FR4 (PCB) production, the thermal conductivity of the show will take the metal base PCB, such as MCPCB, IntegratedMetalSubstrate (IMS) processing, advanced high-performance heat transfer capacity will take the ceramic substrate (Ceramic) to production.
General FR4 (PCB) with a low-cost advantage, but the thermal efficiency of the relatively poor, mostly for low-power LED loading areas. Metal-based PCB (MCPCB, IMS) due to the high operating temperatures, e.g., MCPCB structure consists of copper foil, an insulating (dielectric) layer, an aluminum plate, generally copper foil layer (circuit) is 1.0 to 4.0 ounces, an insulating (dielectric) layer 7.5um ~ 150um, aluminum plate (metal core) layer of a thickness of about 1mm ~ 3.2mm, available in 140 degrees Celsius environment, but the production costs for the high price. Higher ceramic substrate (Ceramic) unit price and cost, because the thermal expansion coefficient of the ceramic's performance is good, can make journeys more closely match wafer, but can not be used in a large area of the circuit, the LED light source applications, mostly only used to carry Block circuit LED elements used to enhance the heat transfer efficiency.
In addition to the aforementioned common carrier multiplication circuit board, but in fact there are a variety of relatively better heat conduction technology, substrate technology, such as a ceramic substrate (alumina), aluminum-magnesium alloys, soft printed circuit boards, direct steel bonding substrate (DBC) metal matrix composite substrate technology, but there are still some technical process, loading or cost considerations, must be depending on the actual magnitude of the heat flux model limitations and improve the final product is worth replacing the carrier board may be.
Exterior casing, configuration limitations and modular circuit design
LED solid-state light source, due to the actual needs of the application, because there will be no on-site installation of DC power, but mostly alternative to traditional light sources set the environment and only an AC power source, in order to allow LED solid-state light source can be installed to replace a convenient way to reach the relevant Design must be towards the development of integrated power conversion circuit ACLED direction or design, but in fact, the development of cost ACLED still high, and the status of related products remains to be seen, therefore, at this stage towards the integration of the power converter design approach more feasible.
Most of the installation environment, if for replacing incandescent plateau design approach, then there will be a considerable technical challenge! Because of the small volume of incandescent, LED driver circuit must be integrated solid state light source, power conversion circuits, temperature sensing circuit and active cooling circuit, this way, in the limited space of the product is relatively dense circuit configuration, the first to face is the thermal design.
Currently LED solid-state light bulb-type design, the circuit much more expensive than modular design, in order to simplify the circuit design, is also related to the power chip makers have launched an integrated circuit design LED bulbs exclusive power, temperature control, power conversion, active cooling resolve driver circuit program, are yet single-chip solution, but has already complicated circuits and diverse discrete digital / analog components integrated into several pieces to solve the integrated circuit, the LED solid-state light bulb shaped design will not be limited by space or compromise must take let lose alternative to traditional lighting products design constraints.
With bulb-type design, for example, take the bulb holder a lot of mining aluminum extrusion configuration mechanism design, a move that allows the internal circuitry of the heat generated by the LED, heat dissipation through the aluminum extrusion body bulb body, taken with modular chip solution that allows substantial simplification of the internal circuits, but also reduces the internal temperature of the thermal conductivity of the problem, with active cooling mechanism uses miniaturized fan forced air cooling heat treatment, solve miniaturized LED bulb design and development needs.
Another common Recessed Lighting, LED solid-state light source is rushing into the product line, because the embedded lamps (Downlights), common design is the use of halogen bulbs as the light source, this is high fever, low efficiency, high cost of inefficiency light, but in order based landscaping and decorating needs, but also the many interior design is quite common application source, although it has taken fluorescent downlight design style, but there will be larger fluorescent type problems, some indoor environment create an atmosphere of light, and will not use this type of light source. Back LED solid-state light source to replace this type of room lights embedded design applications, and bulb-type LED solid-state light sources, Downlights configuration design challenges more demanding, because the majority of demand for Downlights soft light, LED spot light sources light way, you must use an optical lens to improve the properties of the light source, this will cause an increase in volume on a limited extent, although some products to take advantage of packaging technology to improve the light type, but in general can trim light patterns.
In addition, the volume Downlights more limited, with mostly set in decorating the ceiling, mezzanine, wooden among Downlights for higher cooling requirements, in order to get better application security. Recessed Lighting LED light source design, due to the installation of lighting to match the decor of the main, but can be done in the design of the functional design of distributed, for example, the power supply circuit with embedded lamp body separate development, which allows the power conversion circuit is not will become a model for thermal heat lamp module embedded inside a ring, so that the light source itself is only set up the drive circuit associated with active cooling circuit, which can effectively reduce product size, or increase the installation space cooling chassis, cooling components and upgrade the entire source The thermal efficiency, or to trim the optical lens type spatial light increases, the use of products to enhance satisfaction.
This LED semiconductor components, since its inception, mostly as indicator display panel uses, in order to develop the current everyday lighting applications, have gradually developed a high power, high brightness LED component technology, along with the response to improve the brightness and efficiency of energy use demand, the development of peripheral technologies also continued to improve, for example, high-performance AC-DC converters, LED driver circuit, temperature control circuit, and improve the overall thermal efficiency of the assembly configuration and design, have pushed the LED solid-state light source You can replace the traditional light sources technical standards! LED is now available as a light source, not only can achieve high efficiency electrical energy directly into light, and with up to tens of thousands of hours of life, maintaining a relatively low cost, but also have beyond strong features of traditional bulbs fragile, also has environmental protection, no mercury, small size, rich color gamut advantages.

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