Our company has increased the research and development of white LEDs, and developed low-attenuation white light products by changing the packaging process and material matching, which is a slight force for the LED lighting industry. The following are five points of experience summarized in the LED packaging process, and exchanged with colleagues in the industry, in order to contribute to the improvement of white LED packaging technology.
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Five aspects of white LED
1. Effect of wafer on light attenuation of white LED
From the results of the current experiments, the effects of wafers on light decay fall into two broad categories: the first is that the material of the wafer is different, resulting in different attenuation. Currently, the commonly used blue wafer substrate is made of silicon carbide and sapphire, and the general structural design of silicon carbide. For a single electrode, the heat conduction effect is better. The sapphire is generally designed as a double electrode, the heat is difficult to be exported, and the heat conduction effect is poor. The second is the size of the wafer. When the wafer material is the same, the attenuation difference of the size is different.
2. Effect of solid crystal primer on light decay of white LED
The solid crystal glue commonly used in the white LED packaging industry is epoxy resin, silicone resin, and silver glue. Each of the three has its own advantages and disadvantages, and should be considered comprehensively when selecting. Epoxy resin insulation has poor thermal conductivity, but high brightness; silicone resin has better thermal conductivity than epoxy resin, and has high brightness. However, due to the proportion of silicon component, the silicone resin and the ring in the fluorescent rubber remain on the side of the solid wafer. When the oxygen resin is combined, the interlayer phenomenon will occur. After the thermal shock, the peeling will cause the dead lamp; the thermal conductivity of the silver glue is better than the former two, which can prolong the life of the LED chip, but the absorption of light by the silver paste is compared. Large, resulting in low brightness. For the two-electrode blue chip, when the crystal is fixed with silver glue, the control of the amount of glue is also very strict, otherwise it is easy to generate a short circuit, which directly affects the yield of the product.
3. Effect of phosphor on the light decay of white LED
There are many ways to realize white LEDs. The most common and most mature one is to mix blue and yellow light into white light by applying a yellow phosphor on the blue light wafer. Therefore, the material of the phosphor is attenuated by white LEDs. 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 the effect of accelerating aging white LEDs, and phosphors from different manufacturers The degree of influence of fading is also different, which is closely related to the raw material composition of the phosphor. Lehman Optoelectronics uses the best material white phosphor, which makes the white LEDs have a great improvement in attenuation control compared with their peers.
4. The effect of fluorescent glue on the light decay of white LED
Traditionally packaged white LEDs, fluorescent glues are generally epoxy or silica gel. The results of light decay experiments show that the life of white LEDs with silica gel is significantly longer than that of epoxy resin. One of the reasons is that the above two methods are used to package the finished LED. The silica gel has stronger UV resistance than the epoxy resin and the heat dissipation effect of the silica gel is better than that of the epoxy resin. However, under the same conditions, the initial brightness of the silica gel is higher than that of the epoxy. The resin powder is low, the most important reason is that the refractive index of silica gel (1.3-1.4) is lower than that of epoxy resin (1.5 or more), so the initial light effect is not as high as that of epoxy resin.
5. Influence of the bracket on the light decay of white LED
LED brackets mainly include copper brackets and iron brackets. The copper bracket has good thermal conductivity, good electrical conductivity and high price. The heat conduction and electrical conductivity of the iron bracket are relatively poor, and it is more likely to rust, but the price is cheap.
Most of the LEDs on the market use iron brackets. Brackets of different materials have different effects on the performance of LEDs, especially for light fading. 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, and the thickness of the plating layer of the stent. Also closely related. When selecting the bracket, it is also necessary to pay attention to whether the size of the cup of the bracket matches the light-emitting chip and the mold particle, and the quality of the matching quality directly affects the optical effect of the white LED, otherwise the shape of the spot is asymmetrical and has a yellow circle, and Black spots, etc., directly affect the quality of the product.