White LED light failure reasons of inquiry

( 1) Phosphor powder under the high temperature performance of recession

LED with phosphor by light excitation efficiency with temperature changes in the relationship, seems to have no relevant information. But there's the fact that the temperature rise, really affect the performance of phosphor and longevity.

is phosphor factory to do the test, when the temperature is 80 degrees, the excitation efficiency of phosphors was reduced by 2%, and recovered after cooling. And this is just to do a test of a very short time. Is that temperature, performance of phosphor. As for the performance of irreversible decline, it is a cumulative process, need a certain amount of time.

we often encounter such a thing, the aging of the white LED use or for a period of time, found that more bright LED, as shown in figure 1. At present, this kind of condition for small power LED, generally occurs within 1000 hours ( Here refers to the 1000 hours of luminous flux may be greater than the initial value, after the mid - 2008 products and SMT product can close to or reached 1000 hours) 。 For small power LED encapsulation, this situation is likely to remain to 2000 hours. This situation may be produced by the following situations

A phosphor powder and mix glue effect, reduce the performance of the phosphor powder, under the influence of initial temperature, the performance of the phosphor powder recovery;

B fluorescent powder and mix the glue, improve the performance of the phosphor powder.

C blue chip of the initial period of time performance is enhanced.

in the experiment found that in the initial period of time, the white LED the luminous flux of both rising from the start, there is also a decline in the first place. The situation in the same red chips have happened when different manufacturers packaging. Experiment is only in a short period of time, therefore, it is difficult to conclude that is a question of phosphors, or packaging materials and packaging technology.

but in small power blue LED the life of the trials found that common initial luminous flux rising phenomenon for a period of time, as shown in figure 2, the average flux rising at about 200 hours. And plug-in white light luminous flux rising is in commonly 100 hours. Can also be concluded from this, white LED should be the performance of the phosphor powder recession in the first place.

a small white LED power after the short-term period of the luminous flux of ascension, it is not very optimistic, began as a plane without wings, the result will be obvious. High power white LED, the flux is in commonly 100 hours rise, to 6000 hours after is in a state of not stable, over time, the luminous flux of certain goods is greatly rising and falling of the swing. 6000 hours later, basically start unswervingly all the way down. At present general high-power white light products in 1. Reached the end of your life (5 ~ 20000 hours Droop of 50%) 。

　　( 2) Blue LED their rapid decline

just chips in comparison, the blue LED is the worst, the life of a small power plug-in blue LED under 20 ma work, life, 7000 ~ 10000 hours. And small power plug-in red leds work under 50 ma 8000 hours even haven't droop! The same encapsulation, the consumption of red light power is a blue one. Eight times and performance is not worse. Yellow light, green life are far more than 10000 hours.

so, life is bad, blue chip itself congenital deficiency caused by less it constitute the life of white LED.

just chip material, blue and green LED chip, mainly epitaxial material doped with different substrate are generally not sapphire substrate heat conduction ability to the same. The extension part of the material structure, therefore, decided to their ability to tolerate temperatures. This should be improved the key chip.

in the chip of epitaxial material structure under the condition of no so fast to improve, only like this, through displacement substrate material to improve the ability of thermal conductivity.

　　( 3) LED encapsulation base ( Stents) Bad plug-in type of thermal conductivity of materials and other materials of small power LED, chip in scaffold materials is usually fixed iron, from the point of view of the heat dissipation, iron material is poor. At the same time, the support part of outward, cross-sectional area is small, it also increases the thermal resistance. Even piranha bracket, also exists the problem of the small cross-sectional area. Material and structure, determines the small power plug-in package heat conduction ability is poor.

white LED light decline problem, mainly caused by thermal, thermal path LED related materials are to be considered. Problem has been discussed above base, the rest is solid crystal glue, mix powder glue, plastic protection ( The lens) The problem.

there are data show that using silver slurry solid crystal last longer than with epoxy resin, but the initial luminous flux nearly a third lower than the epoxy resin.

with epoxy resin as side powder glue live shorter than with silica gel, but 25% higher compared to the initial luminous flux.

　　( 4) The influence of ultraviolet radiation on the LED

uv effect on the LED, mainly to the chip material, the influence of the phosphor and encapsulation colloid. The biggest impact is encapsulated colloid. General LED not to toward the sun, into the LED internal exposure to uv fluorescent powder and chips can be only some diffuse light, so the uv on chip and the role of the phosphor powder is not very strong.

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Xia Junfeng