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How to Improve the Reliability of LED Lighting?


With the development of blue and white light emitting diodes (LEDs) in 1990, whether full-color display using LEDs or high attention paid to energy-saving issues by the public in recent years, more and more products such as smartphones, personal computers (PC), TV backlights, lighting, white household appliances or traffic signs have been applied. More and more. In order to meet the market demand, the industry has devoted considerable research and development resources to a variety of product lines, including LED for lighting with high performance and reliability, small thin LED with PICOLED as the representative product, and customized color LED for vehicles.

The output value of white LED for lighting is growing rapidly

Due to the trend of energy saving in the world and the rising awareness of energy saving caused by the earthquake in Northeast Japan, the demand for white LED for lighting in Japanese market has increased dramatically, and the output value of LED lighting market is growing rapidly. However, there are still some problems to be solved urgently in terms of product characteristics if the lighting source is to be completely transformed from traditional incandescent bulb lighting to LED lighting. The focus of research and development in the industry is especially on the high performance and reliability of LED lamps. The following will share the technology of high Ra value and luminous efficiency with the employee respectively.

Consideration of High Ra Value and Luminescence Efficiency

Average chromogenicity evaluation index (Ra) is an index that light source can make the object show or reproduce the true color. The higher the index, the better the color reproducibility (Ra of sunlight is 100). White LED for lighting is expected to have both high luminous efficiency and high performance chromogenicity (Ra > 80). However, there is a trade-off between luminous efficiency and Ra value. Because of the higher demand for luminous efficiency in the market, most of the high luminous efficiency LEDs in the market are Ra_70.

Generally, the packaging structure of white LED lamp is to install blue LED wafer on the substrate, and then encapsulate it with resin containing fluorescent substance. When the luminous color (blue) of the LED element is mixed with the luminous color (yellow, red or green) of the fluorescent body, a white light will be formed.

From the point of view of luminous efficiency, most of them use blue and yellow light to form white light, but this will cause poor repeatability of red light, so it is not suitable for lighting purposes. The general solution is to increase the composition of red light, thereby improving the repeatability of red light, but this will lead to the problem of unsatisfactory luminescence efficiency.

In order to give consideration to both high luminous efficiency and high Ra value, the manufacturer configures the fluorescent body in the packaging effectively, and takes the technology of both sides as the solution, successfully develops products with Ra (> 80) and high luminous efficiency. Compared with other products with the same Ra value, the R9 value of this series of products is higher and the repeatability of red is better. With the breakthrough of this technology, the LED lamp can not only reduce the uneven chroma, but also respond to more detailed chroma grade.

High reliability

In recent years, the market demand for reliability has also become increasingly high. Especially because of the high reflectivity of LED packaging, most of them adopt silver plating, but silver will cause the deterioration of LED beam due to sulfur (a phenomenon which is blackened by reaction with sulfur). This phenomenon causes serious problems for outdoor LED lamps. Therefore, various manufacturers have proposed various silver plating solutions, but at present this problem can not be completely improved.

In view of this, the industry abandons silver plating and adopts nickel/gold plating instead. After changing the silver plating to nickel/gold plating, the cost of LED packaging will increase and the luminous efficiency will be poor due to the decrease of reflectivity. However, these problems have been successfully overcome by improving the packaging structure.

The new packaging structure can not only maintain high luminescence efficiency, but also achieve high reliability of LED luminescence performance. This series of products show excellent performance even in vulcanization test, which can completely avoid the phenomenon of beam degradation.

LED Miniaturization/Thinning

With the small size of mobile devices, there is a strong demand for small spacing products in the market year by year. Parts are also facing more requirements of reducing height and size. In addition, because outdoor full-color display devices mostly use LED, in order to improve performance, full-color LED packaging is also moving towards higher density.

Casting technology

In order to ensure the strength of the product, the manufacturer proposes a method of resin sealing for semiconductor components. Transfer Mold method is used in resin sealing process, but the cavity thickness of casting die will be thinner and thinner (0.10 mm), so the fluidity of resin must be ensured. In addition, in order to ensure the optical characteristics of LED, it is impossible to add filler materials to ensure the strength of parts. In this way, the mechanical strength of products will be reduced, but the above problems have been solved.

Assembly technology

In the production of LED wafers, the LED components must be welded in the sealing resin with thickness t=0.10mm. Therefore, the manufacturer successfully uses the self-developed wire welder to narrow the distance and reduce the circuit.

At present, the world's smallest super-miniature LED is only 1006 size and 0.2 mm thick. This product is not limited by space. It uses high-brightness LED elements to emit light through the LED, so that light can penetrate the interior of the mobile phone shell.

In addition, the miniature LED can also be applied to point matrix displays. Traditional 1608 size products have a minimum spacing of 2 mm, while ultra-small LED can be installed with a minimum spacing of 1.5 mm in high density, so it can show a more detailed performance.

In other features, because the package size of this scheme is very small, it can be used in seven-segment display and dot matrix display module, and omit the process of Die-bonding, welding wire and resin bonding which are necessary for chip direct packaging (COB) technology.

Automotive LED Lighting Attracts Attention

With the rapid popularization of LED bulbs and lighting applications, automotive LED lighting is more popular than ever in the market. In the use of vehicle interior, whether it is the main backlight of automobile audio, automobile navigation system or air conditioning panel, at present, almost all of the LED light sources have been used. Next, indoor lights and warning lights, which still use traditional light bulbs, as well as instrument panel backlights with cold cathode tubes, will gradually face the fate of being replaced.

In recent years, traditional bulbs such as taillights, steering lights and positioning lights have been gradually replaced in vehicle outfits. Even headlights have been replaced by traditional halogen lamps, high brightness discharge (HID) lamps and LED lamps. From the point of view of environmental identification, the trend of using LED lights as daytime Running Lamps (DRL) deserves more attention.

In order to meet the diversified automotive demand, the industry will focus on the following two aspects in the research and development of automotive LED technology.

Customized requirements for chroma and brightness

In terms of automobile interior, the light source around dashboard such as air conditioning panel is mostly specified by the car factory. Aluminum gallium indium phosphide component type LED series products, which are introduced by the manufacturer, can be customized according to customers'requirements, regardless of color and luminosity, with the advantage of self-made components.

Others, such as white and pink LED series successfully created by InGaN and resins containing fluorescent materials, can also provide customized color functions. High-frequency keys, such as the backlight of the main button, can highlight the difference between them and the adjacent keys by subtle color differences, thus arousing users'attention. This kind of Al-Ga-In phosphide element adopts the technology of suppressing the wavelength difference in the Epitaxial Growth stage, so it can meet the strict specifications of customers.

R&D of vulcanization resistance countermeasures/expansion of new products

On the other hand, the market for taillights and other vehicle exterior applications of LED lamp is the greatest requirement of heat resistance and weather tolerance, but because the traditional LED packaging conductor frame is silver-plated material, vulcanization and beam degradation problems are easy to occur, this issue has also begun to receive attention.

In view of this, nickel plating/palladium plating/gold plating has been used as wire rack material to successfully solve the problem of beam degradation caused by sulfuration. In addition, for the photometric reduction caused by nickel/palladium/gold plating, the manufacturer has developed a new series of products, which can be solved by improving the output efficiency of the components themselves, showing no less than the beam intensity of the silver plated products. In the future, nickel plating, palladium plating and gold plating will be adopted as improvement measures for package vulcanization, and new product lines will be actively expanded to meet the diverse needs of customers.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.