Heat dissipation issues continue to plague high-axis power white LED applications. Experts from the China Epoxy Resin Industry Association said that it seems that it is only because of the expectation of achieving heat dissipation, but to complicate a simple matter. Is this in line with the concept of cost and progress? It is difficult to do at today's application level. Judging, but there are actually some companies who are considering this aspect. For example, Citizen’s product published in 2004 is capable of dissipating heat from a heat sink with a thickness of 2 to 3 mm on the package, providing applications for use by the manufacturer. High-power white LEDs with heat sinks allow the thermal design of the PCB to be utilized.
The change of packaging materials improves the life of white LEDs by 4 times. Of course, the problem of heat is not only affecting the brightness performance, but also the life of the LED itself. Therefore, in this part, LEDs continue to develop packaging materials to respond to the continuous increase in the brightness of the LEDs. Impact. In the past, epoxy resins used as encapsulating materials have poor heat resistance, and it may happen that the epoxy resin has been discolored before the life of the LED chip itself is reached, so in order to improve heat dissipation, It is necessary to get more current to be released. This architecture is quite important.
In addition to this, not only the thermal phenomenon will affect the epoxy resin, but even the short wavelength will cause some problems for the epoxy resin. This is because the white LED light spectrum also contains short-wavelength light, and epoxy. Resin is quite easy to be destroyed by short-wavelength light in white LEDs, even low-power white LEDs will cause damage to epoxy resin, not to mention the high-power white LEDs contain more short-wavelength light, so deteriorate Naturally, it accelerates, and even some products have a service life of less than 5,000 hours after continuous lighting. According to experts from China Epoxy Resin Industry Association, it is better to overcome the discoloration caused by the old packaging material--epoxy resin. It is better to develop a new generation of packaging materials.
At present, in solving the problem of life, many LED packagers are turning to epoxy resin and adopting silicone resin and ceramics as packaging materials. According to statistics, because the packaging materials are changed, the LED life can be improved. . As far as the data is concerned, instead of the epoxy resin encapsulating material - silicone resin, it has high heat resistance. According to the test, even if it is at a high temperature of 150 to 180 degrees Celsius, it will not change color. It seems to be a Good packaging material.
Since silicone can disperse blue and near-ultraviolet light, silicone can suppress the degradation of light transmittance due to the deterioration of the material due to current and short-wavelength light compared to epoxy resin. According to experts, according to the current application, almost all high-power white LED products have been modified with silicone resin as the material of the package, for example, because of the influence of short-wavelength light, relative to the wavelength of 400-450 nm. The light, the epoxy resin is about a few percent of the single digit, but the silicone absorbs less than one percent of the light from 400 to 450 nm. This difference makes the silicone resin perform better in terms of short wavelength resistance. . OSRAM (Thin GaN) is a metal film formed on an InGaN layer, and then sapphire is peeled off.
Thus, the metal film produces a mapping effect and a light extraction efficiency of 75% can be obtained. Therefore, in terms of lifetime performance, silicone can achieve the goal of extending the life of white LEDs, and can even reach a life of more than 40,000 hours, but it is still really suitable for lighting applications, because silicon Resin is a soft material with elasticity, so in the process of packaging, special attention should be paid to the application method to design the most appropriate application technology.
For future applications, improving the light output efficiency of white LEDs will be the key to success. The production technology of white LEDs has developed the goal of simulating white light from the combination of blue LEDs and yellow YAG phosphors in the past. By using three-color mixing or using GaN materials, white LEDs have been developed for applications. The out will expand in a wider direction.
Experts said that the luminous efficiency of white LEDs has been well developed in these years. The goal of the Japan LED Lighting Promotion Association is to expect to achieve a luminous efficiency of 100 lm/w in 2009, and in fact there are quite a few The industry is developing in this direction, so it is expected that within a few years, 100 lm/w luminous efficiency can be practically applied. Many LED package manufacturers are turning to epoxy resin, and have changed the use of silicone and ceramics as packaging materials to improve the service life of LEDs. With the diversified application market potential , Nichia has actively developed white semiconductor lasers. Due to the expectation that the LEDs will achieve white light with high color purity and high brightness requirements, the industry will continue to improve from each field to achieve this goal, but in the speed of progress, it still looks quite slow. .
Some players have begun to consider other technologies to achieve the current industry's brightness requirements for similar white LEDs. Nichia Chemical in the field of high-brightness blue and white LEDs is trying to develop a part of the research and development direction toward the development of white lasers. According to experts, Nichia is developing a semiconductor light source using the same GaN-based materials as white LEDs. In terms of current performance, the brightness has reached 10 cd/mm. Today's white LEDs If it is desired to achieve this luminance value, it is quite difficult to increase the current, even if the current is increased, but this will cause the temperature of the junction to rise, and the result will not only reduce the overall luminous efficiency, but also waste a considerable amount. Unnecessary power. The white semiconductor laser developed by Nichia Chemical Co., Ltd. no longer uses the phosphor material at the chip end, but separates the portion generated by the illuminating portion and the white light. The laser semiconductor of Nichia is using a 200 mw blue-violet semiconductor thunder. Shooting, emitting 405nm wavelength light, connecting the blue or blue-violet semiconductor laser to the surface of the fiber, and emitting white light from the other side of the fiber coated with the phosphor material, and the white light diameter generated in the module Only 1.25mm, each area is only 1/20 of the same amount of white LED, and because the required power consumption is less than 0.1W, so the heat dissipation part does not need to be too annoyed.
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