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High power white LED heat dissipation and life problem to improve the design

In many environmental protection light source application solutions, the LED is relative to other sources scheme more efficient, easy to assemble design of a light source technology, among them, in the applications of lighting light source, high power white LED using light emitting component is the most frequent, but although white LED the luminous efficiency, each single star power performance has a research and development progress, in fact white LED light-emitting uniformity, encapsulation material life, still exist problems, especially in the application of chip heat dissipation limit, the application for the development of the LED light source first must improve the problem.
High power white LED is applied to daily lighting purposes, actually after the environmental light source is becoming more and more attention, has become the primary choice by the development environmental protection light source. But actually white LED there are still many bottlenecks in the technology has yet to be overcome, there are related improvement plan, to strengthen the white LED the luminous uniformity, encapsulation material life, heat strengthening design bottlenecks, and so on various aspects to focus on the function and performance improvement.
Environmental protection demand high power white LED light source applications
The LED light source, a major cause of favor is products long life, light, electricity conversion efficiency is high, the material properties can be embedded in any plane. But in daily lighting source development, due to a "lighting" to achieve practical demand, the original cannot correspond directly to indicate that use of LED lighting applications, must be from chips, packaging, loading board, production technology and the external circuit to strengthen all aspects, to achieve required high power and high brightness illumination lighting USES utility.
As a observation of market demand, according to the market development of white LED lighting, can be said to be the future higher dosage of product project, but in order to use the utility, white LED must be for lighting applications to improve key function. One is LED chips for strengthening, for example, increase the light - electric conversion efficiency, or increasing the chip area, let a single LED light-emitting (flux) reached its design limits. Secondly, belongs to the design scheme of the compromise, if continues to increase under the premise of single chip LED chip area is more difficult, to switch to more pieces of LED chips encapsulation in the same light source module, and can be close to the method of practical technical scheme.
In chip packaging meet the requirements of low cost, high brightness
Examine the practical demand, in industry because of the production elasticity, design difficulty and control product yield/cost problems, LED chips will continue to increase cost and yield of design bottlenecks. Geared for increasing the design of the chip area may encounter difficulties, not technical and production technology can't do that, but on considerations of costs and benefits of large area of the LED chip cost is higher, and is designed to change in the actual manufacturing demand elasticity is low.
Instead is to use more of the integration of chip encapsulation way, let multichip LED small chips on the load board isometric array, using the line connecting the chip, with overall optical packaging materials packaging, forming a light source module products, and multichip packaging can after tested chip, using the secondary processing integrated into an equivalent large chips light source module, but in the production of elastic LED light source with a single chip design elements to be more flexible.
At the same time, the more pieces of the LED chip module solution, the production cost can also be because the chip cost greatly reduced, which is equal to the single chip design scheme under the same luminous flux, has a lower cost of development options.
Multichip integrated light source module, still need to consider the cost benefit maximization
Another development direction, is the LED chip area continues to increase, through large area to obtain high brightness, high flux output effect. But too much LED chip area is also the problem of design is better than expected, common improvement program to modify the structure of the compound crystal, make improvement on the chip surface; But the improving scheme is easy to influence the cooling efficiency of the chip itself, especially in the application of light LED module, most requirements under high power drive in order to obtain higher luminous flux, which can cause chip light-emitting chip junction in the process of assembling of the high fever is not easy to dissipate, elastic module of product applications and the main/passive cooling design scheme.
General design scheme, according to the analysis of the chip size 7 was adopted, its luminous efficiency is the best, but 7 was the big chip on the yield and the light performance is not easy to control, the cost is relatively high; Instead of using the laminated chip, such as 4 or 8 pieces of small power chip, current carrying plate with secondary processing in packaging material to form a LED light source module, can is the rapid development of the required brightness, power performance of the LED light source module design of the product.
Such as Philips, OSRAM, CREE and other lighting products manufacturers, with integration of 4, 8 or more small LED chips encapsulation of LED light source module products. But this kind of using multiple high brightness LED chip architecture components design also caused some problems, such as: the combined LED chips encapsulation is must match the built-in insulation materials, to avoid individual LED chip short-circuit phenomenon; Such process compared with the single chip design a lot of programs, so even if a monolithic solution to save cost, also because of the extra insulation materials processing and narrow the gap between the two kinds of plan cost.
Application of chip surface process improvement can also strengthen the LED light output
In addition to increasing the chip area or the number is the most direct method, there is another material properties of luminous efficiency improvement for chip itself. In LED sapphire substrate can be produced, for example, uneven surface structure, using the design of a bump irregular surface strengthening LED light output, is established in the chip surface Texture surface crystalline structure.
OSRAM namely have ThinGaN high brightness products, using this solution development in InGaN layer first forming metal film material, and then to stripping process, the surface can be obtained indirectly after stripping higher light output. OSRAM offers this technology makes it possible for the same chip 75% light extraction efficiency.
Japan OMRON, on the other hand, the development of thinking is quite different, the same is to squeeze out a chip of light extraction efficiency, OMRON try using plane light source technology, namely with LENS optical system for chips light reflex, guide and control, in view of the traditional shell type packaging structure LED products common light loss problem, and further improve its design, use of double reflection, in turn, control and strengthen the LED light out, but this kind of packaging technology is relatively more complex, high cost, so that most only for LCDTV backlight module design.
LED lighting applications must still be improve components droop and life problems
If looking forward to the LED light source import daily lighting application, its application to overcome problems will be more! Because everyday lighting light source, there will be a long time use of the situation, often open a continuous use for several hours, or even several hours, the long time to open the LED will because the luminous attenuation components caused by the heat of the chip and reduce the life phenomenon, components must submit a better scheme for heat treatment, so as to slow down the light premature failure problems occurred, affect product experience.
LED light source to import the daily application of another big problem is that as the traditional use of fluorescent lamps and lanterns, use more than dozens of hours can maintain the same luminous efficiency, but the LED is different. Because LED chips will lead to diminishing its luminous efficiency for element high fever, and the question whether in high power or low power LED, only low power LED for indicative purposes only, is fairly small effects on users; But if use LED as light source, its light output decline problems will be on to increase the brightness and strengthen the single element under the driving power of the shape, usually used in brightness down, after a few hours to heat dissipation design improvement to achieve a light application requirements.
LED packaging material improvement should be carried out according to high temperature, short wavelength light
In light source design schemes, tend to increase the drive current is used to exchange for the LED chip higher light output, but this makes the chip surface of the heat generated during light continues to increase, and the high temperature of the chip test packaging material durability, continuous operation under the condition of high temperature cause the packaging materials of the original with high durability degradation, light transmittance and material degradation or qualitative change will further decline, therefore, in the development of LED light source module must also consider to switch to high heat-resistant material for packaging materials.
Add a LED light source module component cooling method is quite a lot, can from the thermal conductivity of chips, packaging materials, module structure, PCB board design, and other key to improve. Between the chip and packaging materials, for example, if can strengthen heat conduction velocity, rapid will be the core of heat through the encapsulation material surface is also a kind of method of dissipation. Or by the contact between the chip and loading board, chip core heat directly to the direct conduction of heat through the material to the loading board, dissipation of the LED chip and hot key to improve. In addition, the PCB adopt metal material collocation and the LED chip is clingy assembly design, also can reduce the thermal resistance of heat transfer because it is over, achieve rapid degradation of luminous element design of central high fever.
Another in terms of packaging materials, in the past LED components most epoxy resin encapsulation, the heat resistance of the epoxy resin itself is not actually high, often also in the service life of the LED chip before the end of the epoxy resin has been because of long time high running and degradation, deterioration of discoloration occurs, the situation in the LED lighting application module design, because the chip high power drive and quicken the speed of encapsulation material degradation, and even affect the safety of the element.
Not only the hot issue, this kind of plastic material of epoxy resin, high sensitivity to light, especially the short wavelengths of light will make epoxy resin material appear damage phenomenon, and the high power LED light source module, the short wavelength light will more, on the material degradation speed also have intensified.
Design scheme for the LED light source applications, most companies tend to give up epoxy encapsulating materials mostly, switching to a more high temperature resistance, resistance to short wavelength light packaging materials, such as silicon resin which has relatively higher heat resistance of epoxy resin, and in terms of material properties, silicon resin can reach at 150 ~ 150 C environment still won't change color material advantage.
In addition, the silicon resin can be scattered blue light and ultraviolet ray, silicon resin can inhibit the encapsulation material due to high heat or shorter-wavelength light material degradation problems, slow encapsulation materials because of the bad cause a downturn of the light transmittance. And LED light source module, silicon resin also lengthen the service life of the LED element advantage, because the silicon resin itself high fever and shortwave and good light resistance, resistance in the LED packaging material can withstand long time use for heat and light, material life is relatively long many, also can make the service life of LED components, there are more than 40000 hours.


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