Improve the design of high-power white LED heat dissipation and life issues

In the the numerous green light applications, LED relative to other light source solutions more energy-efficient, easy to the assembly design a light source technology, which in lighting source applications, high-power white LED compared with the most frequent light-emitting components, but the white LED luminous efficiency, single power performance has R & D progress actually white LED luminous uniformity, packaging material life still exists, especially in the application of the chip cooling limit is the development of the LED light source applications first and foremost must be improve the problem ...

High power white LED used in the day-to-day lighting purposes, in fact, received increasing attention in the green light, has become the first choice of the development of environmentally friendly light source. But in fact the white LED are still many technical bottlenecks to be overcome, there are related improvement program to strengthen the focus on features and performance of white LED luminous uniformity, the life of the packaging material, heat strengthening all aspects of design bottleneck improvement.

The green light increased demand for high-power white LED applications qualify

LED light source to be the main cause of all ages, is nothing more than the product of long life, light - high power conversion efficiency, material properties can be fitted in any plane. In the development of the day-to-day lighting source, due to the need to achieve practical lighting needs, the original to indicate that the use of LED lighting applications will not be able to correspond directly from the chip, package, carrier board, production technology and an external circuit must be strengthened, in order to achieve the high power required for lighting purposes, high brightness lighting utility.

Observed on the level of market demand for white LED lighting applications market development, it can be said future higher dosage of the project, but to use utility, white LED lighting applications must focus on functional improvement. One is to strengthen for the LED chip, e.g., to increase their optical - electrical conversion efficiency, or to increase the chip area, to allow a single LED light emission amount (flux) reaches its design limit. Second, is a compromise design program, the more difficult to continue to increase the area of monolithic LED chip under the premise switch to multi-chip LED chip is packaged in a light source module, but also the practical technical solutions can be achieved close to the aforementioned method .

In a multi-chip package to meet the requirements of the low-cost, high-brightness design

Industry practice needs to view, because of the flexibility of the production, difficult to design and control product yield / cost issues, LED chips continue to increase encounter cost and yield design bottleneck. Reimbursing increased chip area design difficulties that may be encountered, not the technical and production technology can not do, but on the cost and benefit considerations, the higher cost of LED chips in a large area, but the actual manufacturing needs change The lower design flexibility.

The contrary, is the use of multi-chip integrated package, equally spaced multi-chip LED small chip carrier board, wire to connect the chip, with the overall package of the optical package material, the formation of a light source module products, while the number of The chip package during chip testing, the use of secondary processing integrated into an equivalent light source module of the large chip, but in the production of elasticity compared to the LED light source elements of the monolithic design to be more elastic.

The same time, the multi-chip LED chip module solutions, its production costs can also be significantly reduced because of the cost of the chip, is equal to the same luminous flux of the monolithic design, the development of a lower cost of ownership option.

Maximize the cost-effectiveness of multi-chip integrated light source modules still need to consider the

Another direction of development, is the area of the LED chip continues to increase, through a large area for high brightness, high luminous flux output effect. But too large LED chip area will appear inferior design expected the common improvement program to modify the structure of polycrystalline produced improvement in the chip surface; related improvement programs easily affect the cooling efficiency of the chip itself, especially in the light source LED module applications, most of them require high power drive to get higher luminous flux, this will cause the chip light-emitting process the chip junction that brings together the fever does not easily dissipate impact module application flexibility and Active / Passive thermal design program.

7mm2 chip size adopted the general design of the program, according to analysts, the luminous efficiency is the best, but 7mm2 large chip is less likely to yield and optical performance control, the cost is relatively high; instead use multi-chip-chip, such as the 4 tablets or eight low-power chips, the formation of a LED light source module carrier board with packaging materials for secondary processing, and design products more quickly to the development of the required brightness performance power LED light source module.

Light products manufacturers such as Philips, OSRAM, CREE, launch integration 4,8 pieces or more small LED chip package LED light source module products. But this type of multi-chip LED chip high brightness components of the architecture program also raises a number of design issues, such as: multiple LED chip combination package that must be used with the built-in insulation material, to avoid individual LED chip short circuit; such a process relative to the monolithic design many programs, cost savings even more monolithic programs, also due to the additional insulating material process to narrow the gap between the two programs cost.

The application of the surface of the chip manufacturing process improvements can enhance the LED light output

In addition to increasing the number of chip area or is the most direct way, another to improve the performance of the chip itself luminous material properties. The uneven surface structure, for example, can be produced in the LED sapphire substrate using an uneven irregular design surface strengthening amount of the LED light output, namely, the chip surface to create the Texture surface crystal framework.

OSRAM that is developed to exploit this program Thin GaN high brightness products, first forming a metal film material in the InGaN layer, and then the peeling process, so that after peeling the surface of a higher amount of light output can be obtained indirectly. OSRAM called this technique allows the same chip to get 75% of the light extraction efficiency.

Japanese OMRON development thinking, on the other hand, is quite different, as efforts to squeeze the chip light extraction efficiency, OMRON that try to take advantage of the flat light source technology, with LENS optical system chip light source reflection, guidance and control for traditional artillery shells type package structure of the LED products common loss of light, and further to improve its design structure and strengthening thereby control the LED's light extraction amount, using the double-reflection effect, but this encapsulation technology is relatively more complex, high cost, so most only in the LCD TV backlight module design.

LED lighting applications still need to improve the the element light fades and life issues

If you look forward to the LED light source into everyday lighting applications, applications need to overcome the problem will be more! Because the situational the daily lighting source will be used for a long time, often an open continuously, to spend a few hours, or even tens of hours, that is a long time to turn on the LED will be because of the high heat of the component chips decay, reduced life phenomenon The components must come up with better solutions for the heat treatment, in order to slow down the light fades prematurely, affecting product experience.

Another big problem of the LED light source into the day-to-day applications, such as the traditional use of fluorescent lamps, use can maintain the same luminous efficiency of more than several tens of hours, but the LED is different. LED light-emitting chip will result in diminishing the luminous efficiency because components fever, and this regardless of the high-power or low-power LED on their faces, only low-power LED for indicative purposes only multi fairly small impact on the user ; However, if the LED as a light source, diminishing its light output will be strengthened to improve the brightness and the driving power of the single components more exacerbated, generally used a few hours after the brightness decline, the need for improved thermal design in order to achieve a light source application requirements.

LED packaging materials need to improve response to high-temperature, short-wavelength light

Light source design, they tend to take advantage of the increased drive current exchange for higher light output of the LED chip, but it makes the surface of the chip in the emission process heat continued to increase, the high temperature of the chip to test the durability of the packaging materials, continuous running high temperature state, so that the original packaging materials degradation have high thermal durability and material degradation or qualitative change will further contributed to the decline in light transmission in the development of the LED light source module packaging material considerations must also switch to high The heat-resistant material.

LED light source module component cooling methods to increase more from chips, packaging materials, the thermal conductivity of the structure of the module, PCB carrier board design focus on improving. For example, the chip-to-package materials, if we strengthen the heat conduction velocity core heat source through encapsulation material surface fugitive is also a way to fast. Or by the contact between the chip and the carrier board, directly to the chip core fever direct conduction heat source through the material to the carrier board oven, the focus of improvement of the LED chip fever. PCB adopted a metal material with LED chip close to the assembly design, and also reduce the thermal resistance of the heat conduction, to achieve the design goal of rapid dissipation of the light emitting element core high fever.

Other packaging materials, LED components in the past the majority of mining epoxy encapsulation, in fact, the heat resistance of the epoxy itself is not often the LED chip is still not the end of its useful life, epoxy resin has been prolonged fever running the emergence degradation, deterioration of the discoloration, this situation in lighting applications, LED module design, chip high power drive accelerated speed of leaving the package material degradation, and even affect the security element.

Not only fever, epoxy type of plastic material, high sensitivity to light, particularly short wavelength light causes the epoxy material damage phenomena, and the high power LED light source module, the short wavelength light will be more, the rate of deterioration of materials will be exacerbated by the phenomenon.

Application design for LED light source, the majority of companies are inclined to give up the epoxy encapsulation material, switch to more high temperature resistance, short-wavelength light packaging materials, such as silicon resin that with epoxy resin and higher heat resistance, and in the material properties, silicone can be reached at 150 ~ 180 ° C environment still does not change color material advantage.

In addition, the silicone can also be dispersed blue light and ultraviolet rays, silicone can inhibit the encapsulation material issues of material degradation due to heat or short-wavelength light, slow packaging materials deterioration and lead to a decline in transmittance problem. LED light source module, the silicone the extended LED component life advantages because the silicone itself anti-fever and anti-light advantage of short-wavelength LED packaging materials can withstand prolonged use produce sustained high fever and light irradiation, the material relatively long life of many, but also allows the LED components have a service life of over 40,000 hours.(More information please visit www.greendyled.com)