Analyze how to improve the reliability of LED lighting

With the large-scale display of blue and white light-emitting diodes (LEDs) in 1990, whether it is the full-color display using LEDs, or the high attention paid by the public in recent years to energy-saving issues, LED The diversified product applications such as smartphones, personal computers (PCs), TV backlights, lighting, white goods, or traffic signs have become more widespread. In order to meet the market demand, the industry has devoted a wide range of product lines, including LEDs for lighting with high color rendering and high reliability, small thin LEDs with PICOLED as products, and customized LEDs for vehicles. Research and development resources.

The output value of white LED for lighting is growing rapidly

Affected by the world's energy-saving trend and the awareness of energy conservation caused by the earthquake in the Tohoku region of Japan, the demand for white LEDs for lighting has increased sharply in the Japanese market, prompting the LED lighting market to continue to grow rapidly. However, to make the lighting source completely from the traditional The conversion of incandescent bulb lighting to LED lighting still has some problems to be solved in terms of product characteristics. Among them, the industry's research and development focus is especially on the high color rendering and high reliability of LED lamps. Share with the technology of luminous efficiency.

Consider both high Ra value and luminous efficiency

The average color rendering index (Ra) is an index of the light source that causes the object to express or reproduce the true color. The higher the index, the better the color reproducibility (the solar Ra is 100), and the market expects white light for illumination. LEDs have both high luminous efficiency and high color rendering (Ra ≧ 80), but there is a trade-off characteristic between luminous efficiency and Ra value. Due to the higher requirements for luminous efficiency in the market, the current market is mostly Ra≒70 high luminous efficiency LED.

Generally, the package structure of the white LED lamp is to mount the blue LED chip on the substrate and then package the resin containing the phosphor. When the luminescent color (blue) of the LED element is mixed with the luminescent color (yellow, red, green, etc.) of the phosphor, white light is formed.

From the viewpoint of luminous efficiency, white light is generally formed by blue light + yellow light, but this causes poor red light reproducibility and is therefore not suitable for lighting purposes. The general solution adopted is to increase the composition of red light, thereby improving the reproducibility of red light, but this may cause problems in that the luminous efficiency is not ideal.

In order to achieve high luminous efficiency and high Ra value, the company has efficiently placed the phosphor inside the package and solved the countermeasures with the best of both worlds. It has successfully developed Ra≧80 and has extremely high luminous efficiency. This series of products has performed very well on the Ra or R9 (red) index. Compared with other brand products with the same Ra value, the series has higher R9 value and better red reproducibility. . With the breakthrough of this technology, LED lights can not only reduce the chromaticity unevenness, but also respond to more detailed color gradation.

High reliability

In recent years, the demand for reliability in the market has also become increasingly high. In particular, due to the high reflectivity of the LED package, silver plating is generally used, but silver will cause LED beam degradation due to vulcanization (a phenomenon of blackening due to reaction with sulfur), which is caused by outdoor LED lights. Serious problems, so each manufacturer does not propose countermeasures for various silver plating solutions, but this problem cannot be completely improved.

In view of this, the industry abandoned the silver plating method and switched to nickel plating/gold plating. After the silver plating of the LED package is changed to nickel plating/gold plating, although the cost is increased and the luminous efficiency is not good due to the decrease of the reflectance, these problems have been successfully overcome after the improvement of the package structure.

The new package structure not only maintains high luminous efficiency, but also achieves high-reliability LED illumination performance. This series of products exhibits excellent performance even in the vulcanization test, and can completely avoid beam degradation.

LED small / thin

With the compactness and shortness of mobile devices, the demand for small-pitch products on the market is increasing year by year, and parts are also facing more requirements for lowering the height and reducing the size. In addition, since most of the outdoor full-color display devices use LEDs, in order to improve the performance, the full-color LED package is also moving toward higher density.

Component technology

In order to make the package smaller and thinner, the internal LED components must also be small and thin. Therefore, the manufacturer has successfully developed the component size of the aluminum gallium indium phosphide (AlGaInP) light-emitting LED to a corner of 0.13 mm (mm) from the formation of the light-emitting layer on the wafer to the wafer formation using a self-developed process technology. The thickness t = 50 micrometers (μm), achieving the goal of miniaturization in one fell swoop.

Molding technology

In order to ensure the strength of the product, the manufacturer has proposed a processing method for resin sealing of a semiconductor element. The resin sealing process employs a transfer molding method, but the mold cavity of the mold is increasingly thinner (the cavity thickness is 0.10 mm), so the fluidity of the resin must be ensured. In addition, in order to ensure the optical characteristics of the LED, it is impossible to add a filler material for ensuring the strength of the component, and as a result, the mechanical strength of the product is lowered, but the above problems have been solved.

Assembly technology

In the fabrication of LED wafers, the LED components must be soldered in a sealing resin having a thickness of t = 0.10 mm. Therefore, the manufacturer has successfully developed a wire bonding machine to successfully reduce the pitch and reduce the loop.

At present, the world's smallest ultra-small LED is only 1006 in size and only 0.2 mm thick. This product is not limited by the installation space, and uses high-brightness LED components to transmit light through the inside of the outer casing of the mobile phone. Translucent.

Not only that, ultra-small LEDs are also suitable for point matrix displays. The traditional 1608 size product has a minimum pitch of 2 mm, while the ultra-small LEDs can be mounted at a high density of 1.5 mm at a minimum pitch, thus providing a more detailed performance.

In other features, the package size of the solution is extremely small, so it can be used on seven-segment display and dot matrix display modules, and omits the die attach necessary for direct package (COB) technology (Die-bonding). ), wire bonding, resin bonding (Bonding) and other processes.

LED lighting for vehicles is attracting attention

With the rapid popularization of LED bulbs and lighting applications, automotive LED lighting has been favored by the market more than ever. In the interior of the vehicle, whether it is a major backlight such as car audio, car navigation system or air conditioning panel, LED light source has been almost fully adopted. Next, indoor lights and warning lights, such as the traditional bulbs, and the backlight of the instrument panel using cold cathode tubes will gradually face the fate of replacement.

In the exterior of vehicles, traditional light bulbs such as taillights, turn signals, and positioning lights have been gradually replaced in recent years. Even the headlights have been turned into LED lights by traditional halogen lamps and high-intensity discharge (HID) lamps. Replaced. From the point of view of environmental recognition, the trend of using LED lights as Daytime Running Lamps (DRL) is even more worthy of attention.

In order to respond to diversified vehicle demand, the industry will focus on R&D in the development of automotive LED technology.

Customization requirements for chromaticity and brightness

In the interior of automobiles, most of the light sources around the instrument panel such as air-conditioning panels are specified by the car manufacturer. The aluminum phosphide indium component LED series products introduced by the industry have the advantages of self-made components. Both color and luminosity can be customized according to customer requirements.

Others, such as the white light and pink LED series successfully created by using InGaN and phosphor-containing resins, can also provide color customization. For example, the backlight of the main button, such as the backlight, can be used to arouse the user's attention by subtly distinguishing the color difference between the button and the adjacent button. The aluminum gallium arsenide component is a technique for suppressing the difference in wavelength at the stage of epitaxial growth, and thus can meet the strict specifications of customers.

Research and development of anti-sulfurization measures / expansion of new products

On the other hand, the market's maximum requirements for LED lamps for exterior applications such as taillights are heat resistance and resistance to harsh weather. However, since the lead frame of the conventional LED package is silver-plated, it is easy to produce vulcanization and light beams. Deterioration problems, this issue has begun to receive attention.

In view of this, the industry has changed the nickel/palladium plating/gold plating as the lead frame material, and successfully solved the problem of beam degradation caused by vulcanization. In addition, for the shortcomings of luminosity reduction caused by nickel plating/palladium plating/gold plating, the company has also developed a series of new products, which are solved by improving the output efficiency of the components themselves, showing the beam intensity no less than that of silver plating products. . In the future, the industry will adopt nickel plating/palladium plating/gold plating as a countermeasure for package vulcanization improvement, and actively expand new product lines to meet the diverse needs of customers.

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