White LEDs are usually formed using two methods. The first is the use of "blue light technology" in combination with phosphors to form white light; the second is a variety of monochromatic light mixing methods. Both methods have succeeded in producing white light devices. China's urban traffic management lights are also using white LEDs to replace the early traffic lights. The following discussion with the development of photoelectric to discuss the impact of LED packaging materials on white LED lamp beads.


Wafer effects
 
Judging from the experimental results, the impact of wafers on light attenuation falls into two categories: The first is that the material of the wafer causes different attenuation. The commonly used blue wafer substrates are silicon carbide and sapphire. The general structure of silicon carbide is designed to be single. Electrodes have good heat conduction effects. Sapphire is generally designed as a two-electrode electrode. It is difficult to derive heat and has poor thermal conductivity. The second is the size of the wafer. When the wafer material is the same, the difference in size is different.
 
Effect of solid crystal
 
Solid-state adhesives commonly used in the white LED packaging industry include epoxy insulating adhesives, silicone insulating adhesives, and silver adhesives. Each has its own advantages and disadvantages. It must be considered comprehensively when it is selected. Epoxy insulating adhesive has poor thermal conductivity but high brightness; silicone insulating adhesive has slightly better thermal conductivity than epoxy resin and has high brightness, but due to a certain proportion of silicon components, the silicon resin and the fluorescent adhesive ring remain on the side of the solid wafer. Oxygen resin will produce interlayer phenomenon, after the cold and heat shock will cause peeling and cause dead light; the thermal conductivity of silver paste is better than the former two, it can prolong the life of the LED chip, but the silver glue absorbs light. Large, resulting in low brightness. For double-electrode blue wafers, the control of the amount of glue is very strict when using silver glue to crystallize, otherwise it is easy to produce a short circuit, which directly affects the product yield.
 
Effect of phosphor
 
There are many ways to realize white LEDs. One of the most commonly used and most mature methods is to use a layer of yellow phosphor on a blue wafer to mix blue and yellow light into white light, so the phosphor material will attenuate the white LED. great influence. The most popular phosphors in the market are YAG yttrium aluminum garnet phosphors, silicate phosphors, and nitride phosphors. Compared with blue LED chips, phosphors have accelerated aging of white LEDs, and phosphors from different manufacturers The degree of influence of decay is also different, which is closely related to the raw material composition of the phosphor. Source Lei technology choose the best material white phosphor, so that the white LED made in the attenuation control compared to their counterparts have greatly improved.
 
Fluorescent glue effect
 
Traditional encapsulated white LEDs, fluorescent plastics generally use epoxy resin or silica gel, after the light decay experiment results, the white LED with silica gel powder life is significantly longer than the epoxy resin. One of the reasons is that the above two methods are used to encapsulate the finished LED. Silicone is more resistant to UV than epoxy resin and the heat dissipation effect of silicone is better than that of epoxy resin; but under the same conditions, the initial brightness of silicone powder is higher than that of epoxy. The lower the resin blending is, the most important is that the refractive index (1.3-1.4) of silica gel is lower than that of epoxy resin (1.5 or higher), so the initial luminous efficacy is not as high as that of the epoxy resin.
 
Impact of stents
 
LED brackets mainly include copper brackets and iron brackets. Copper brackets have good thermal conductivity, good electrical conductivity, and high prices. The iron stent has relatively poor thermal and electrical conductivity and is more susceptible to rust, but at a lower price. Most of the LEDs on the market use iron brackets. Different material supports have different effects on the performance of the LED, especially the light attenuation. This is mainly due to the fact that 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, and the plating thickness of the bracket. Also closely related. When selecting the bracket, it is necessary to pay attention to whether the size of the cup of the bracket is matched with the light emitting chip and the die. The quality of the matching quality directly affects the optical effect of the white LED, otherwise the uneven shape of the light spot and the yellow circle are easily caused. Black spots, etc., directly affect the quality of the product.