White light LED attenuation and material analysis-EEWORLD

Collect

　With the advent of blue LED, white LED can be easily obtained by combining phosphor and blue LED, which is the most mature white light packaging method in the industry. At present, white LED has become a lighting source, and general household lighting has become a reality. However, during use, many white light products have large attenuation and are not suitable for the lighting market. In response to the needs of the high-end lighting market, Leman Optoelectronics has increased its research and development of white light, and developed low-attenuation white light products by changing the packaging process and material matching, making a small contribution to the LED lighting industry. The following are five experiences summarized by our company in the packaging process, which are shared with colleagues in the industry, in order to contribute to the improvement of white light LED packaging technology. 　1. The influence of the chip on the light decay of white light LEDs. 　　According to the current experimental results, the influence of the chip on the light decay can be divided into two categories: the first is that the different materials of the chip lead to different attenuation. The commonly used blue light chip substrate materials are silicon carbide and sapphire. The general structure of silicon carbide is designed as a single electrode, and its thermal conductivity is relatively good. Sapphire is generally designed as a double electrode, and the heat is difficult to be discharged, and the thermal conductivity is poor; the second is the size of the chip. When the chip material is the same, the attenuation difference is different for different sizes. 2. The influence of the bottom adhesive on the light decay of white light LEDs 　　. The commonly used adhesives in the white light LED packaging industry are epoxy resin insulation glue, silicone resin insulation glue, and silver glue. Each of the three has its advantages and disadvantages, and comprehensive considerations should be made when selecting. Epoxy resin insulation glue has poor thermal conductivity, but high brightness; silicone resin insulation glue has slightly better thermal conductivity than epoxy resin and high brightness, but because the silicon component accounts for a certain proportion, the residual silicone resin next to the chip will combine with the epoxy resin in the fluorescent glue to produce a layer phenomenon, which will peel off after the cold and hot shock, resulting in dead light; silver glue has better thermal conductivity than the previous two, which can extend the life of the LED chip, but silver glue absorbs light more, resulting in low brightness. For dual-electrode blue light chips, when using silver glue to fix the crystal, the amount of glue must be strictly controlled, otherwise it is easy to cause a short circuit, which directly affects the yield rate of the product. 　3. The influence of phosphor on the light decay of white light LED 　　There are many ways to realize white light LED. The most common and mature one is to apply a layer of yellow phosphor on the blue light chip to mix blue light and yellow light into white light, so the material of the phosphor has a great influence on the decay of white light LED. The most mainstream phosphors in the market are YAG yttrium aluminum garnet phosphors, silicate phosphors, and nitride phosphors. Compared with blue light LED chips, phosphors have the effect of accelerating the aging of white light LEDs. Moreover, the degree of influence of phosphors from different manufacturers on light decay is also different, which is closely related to the raw material composition of the phosphors. Leman Optoelectronics uses white light phosphors with the best materials, which greatly improves the attenuation control of white light LEDs compared with its peers. 　4. The influence of fluorescent glue on the light decay of white light LEDs 　　In traditionally packaged white light LEDs, fluorescent glue generally uses epoxy resin or silicone. The results of light decay experiments show that the life of white light LEDs with silicone powder is significantly longer than that of epoxy resin. One of the reasons is that when the above two methods are used to encapsulate finished LEDs, silicone has stronger UV resistance than epoxy resin and better heat dissipation effect than epoxy resin; but under the same conditions, the initial brightness of silicone powder is lower than that of epoxy resin powder. The main reason is that the refractive index of silicone (1.3-1.4) is lower than that of epoxy resin (above 1.5), so the initial light efficiency is not as high as that of epoxy resin. 5. The influence of brackets on the light decay of white light LEDs 　　LED brackets mainly include copper brackets and iron brackets. Copper brackets have good thermal and electrical conductivity and are expensive. Iron brackets have relatively poor thermal and electrical conductivity and are more prone to rust, but are cheap. Most LEDs on the market use iron brackets. Brackets made of different materials have different effects on the performance of LEDs, especially on light decay. This is mainly because the thermal conductivity of copper is much better than that of iron. The thermal conductivity of copper is 398W (mk), while the thermal conductivity of iron is only about 50W (mk), which is only 1/8 of the former. The thickness of the electroplating layer of the bracket is also closely related. When selecting a bracket, you should also pay attention to whether the size of the bracket's bowl matches the light-emitting chip and die. The quality of the match directly affects the optical effect of the white light LED. Otherwise, it is easy to cause asymmetric spot shape, yellow circles, and black spots, which directly affect the quality of the product.

　

　　

　

　

　　

Keywords：LED Reference address：White light LED attenuation and material analysis

Previous article：LED display asynchronous graphic control technology detailed graphic explanation
Next article：Mao Yuhai: Advantages and Disadvantages of High Voltage LEDs

Popular Resources
Popular amplifiers