Four Trends of Power White LED Packaging Technique
Posted: 12/18/2015 01:12:49   Edited: 12/18/2015 01:12:49  Clicks: 1141
This article introduces four development trends of power-type white LED packaging technique.

Trend 1: The exploitation of new fluorescent powder
YAG: Ce3 + is the earliest widely used fluorescent powder in the white light LED technology, but due to its inadequate red components in the emission spectrum, it is difficult to obtain high color rendering index and low color temperature of white LED; on the other hand, the sustainable development of semiconductor lighting pushes people to develop higher conversion efficiency of phosphors. Early, people add (Ca, Sr) S: Eu2 +, (Ca, Sr) Ga2S4: Eu2 + red and green phosphor to YAG: Ce3 + to implement the requirements of high color rendering index and low color temperature, but because this kind of alkaline earth metal sulfide chemical and physical properties is not stable and has easily deliquescence, volatile and corrosive problem, it cannot satisfy the needs of LED lighting industry. Recently, people have developed a kind of red phosphors with excellent thermal stability and chemical stability, which can completely replace alkaline earth metal sulfide and realize high color rendering index or low color temperature white LED. Because of its silicon nitrogen (oxygen) tetrahedron structure, known as nitric oxide, it has a higher efficiency.
Trend 2: The establishment and development of white LED optical model
Phosphor used in white LED still need to consider the specific requirements of LED, such as particle size of phosphor. Study of phosphors are mainly concentrated in the influence of optical properties to white LED encapsulation, for example, extraction efficiency, color spatial distribution and quality of the light color. These studies adopt the method of monte carlo ray tracing which uses optical software to simulate LED encapsulation structure, process the phosphor layer into Mie scattering material, so it can be acquired excitation and emission characteristics of white LED by optical simulation. However, the simulation doesn't take into account the scattering characteristics of phosphor powder concrete, so it is lack of experimental verification.
Trend 3: Coating methods of new fluorescent powder
Traditional way of phosphor powder coating is point powder pattern, namely a mixture of the phosphors with colloid filling to the chip stents bowl, then heat curing. This way the quantity of coating fluorescent powder is difficult to control, and because the excitation light everywhere, which makes it easier for the white LED appear a spot of macular or blue light and other phenomenon. Some companies presented a conformal coating of a phosphor coating way, and they cover a fluorescent powder layer in inverted LED chip surface, which enhances the stability of the light color of white LED. There are also firms that adopt the method of depositing a layer of fluorescent powder in the chip surface. These methods above are all the ones that make the chip directly touch fluorescent powder. Optical simulation results of some researchers show that this kind of phosphor powder and chips contact near field excitation method increases the excitation light back scattering loss and reduces light efficiency of the device. Sommer in Australia uses numerical simulation method to simulate phosphors conformal coating structure, and the result shows that the coating procedure does not provide a better angle uniformity. Phosphors along with the development of the white LED optical simulation of far field excitation scheme shows more advantages.
Trend 4: Large current injection and heat radiation structure
In order to meet the needs of general lighting high flux, people improve the driving power of the single chip. In the past 1w high power chip is injected into the 3w, 5w, or even higher power chip. This makes the thermal dissipation of the white LED is more and more serious, so people adopt various cooling technology, such as micro heat pipe, heat pipe, water cooling, air cooling and other methods to dissipates LED heat.

Four Trends of Power White LED Packaging Technique

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