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Analysis of Light Efficient of LED Packaging(II)
- May 20, 2017 -

2. The choice of filler

According to the law of refraction, when the light is incident from the optical density medium to the optical sparse medium, the total emission occurs when the incident angle reaches a certain value, that is, greater than or equal to the critical angle. The refractive index of the GaN material is 2.3, and the critical angle θ0 = sin-1 (n2 / n1) is given when the light is emitted from the inside of the crystal to the air.

Where n2 is equal to 1, i.e., the refractive index of air, and n1 is the refractive index of GaN, whereby the critical angle? 0 is calculated to be about 25.8 degrees. In this case, the light emitted by the incident light is less than 25.8 degrees in the space of the solid angle of the light, it is reported that the current external quantum efficiency of GaN chips in the 30% -40%, therefore, due to the internal absorption of chip crystals , Can be injected into the crystal outside the proportion of light is very small. It is reported that the current GaN chip external quantum efficiency of 30% -40%. Similarly, the light emitted by the chip through the packaging material, sent to the space, but also consider the impact of material on the efficiency of light extraction.

Therefore, in order to improve the efficiency of LED products to take light, you must improve the value of n2, that is, to improve the refractive index of the packaging material to improve the critical angle of the product, thereby enhancing the product packaging luminous efficiency. At the same time, the packaging material to light absorption is small. In order to increase the proportion of light emitted, the outline of the package is preferably arched or hemispherical, so that light from the package material to the air, almost perpendicular to the interface, and thus no longer produce total reflection.

3. Reflective treatment

There are two main aspects of the reflection process, one is the reflection of the internal processing of the chip, the second is the reflection of the material on the light, through the internal and external reflection processing, to improve the proportion of the light emitted from the chip within the chip to reduce the absorption, Improve the luminous efficiency of power LED products. From the package, the power LED is usually the power chip assembled with a reflective cavity on the metal bracket or substrate, the bracket-type reflective cavity is generally taken to improve the reflective effect of plating, and the substrate-type reflective cavity is generally used to polish Way, the conditions will also be electroplating, but the above two kinds of processing methods by the mold accuracy and process effects, after treatment of the reflective cavity has a certain reflection effect, but not ideal. At present, the domestic production of substrate-based reflective cavity, due to lack of precision polishing or metal coating oxidation, reflection effect is poor, which led to a lot of light in the refraction area after being absorbed, can not reflect the desired target to the smooth surface, resulting in the final After the package to take light efficiency is low.

We have studied and tested a variety of self-intellectual property using the organic material coating of the reflective treatment process, through this process, so that reflected in the carrier cavity of the light absorption is very small, can most of the The light above it is reflected to the smooth surface. The efficiency of the treated product after this treatment can be increased by 30% to 50% compared with that before treatment. Our current 1W white power LED luminous efficiency up to 40-50lm / W (in the distant PMS-50 spectral analysis test instrument test results), get a good package effect.

4. Phosphor selection and coating

For white power LED, the improvement of luminous efficiency is also related to the choice of phosphor and process. In order to improve the efficiency of the phosphor to stimulate the blue chip, the first choice of phosphor to be appropriate, including the excitation wavelength, particle size, excitation efficiency, etc., need a comprehensive assessment, taking into account the various performance. Secondly, the coating of the phosphor should be uniform, and it is preferable that the thickness of the adhesive layer of each light-emitting surface is uniform, so that the local light can not be emitted due to uneven thickness, and the quality of the spot can be improved.

Second, the conclusion

Good thermal design to improve the power LED products luminous efficiency has a significant role, but also to ensure product life and reliability of the premise. And the design of a good light channel, where the focus refers to the reflective cavity, filled with plastic and other structural design, material selection and process, can effectively improve the power LED light extraction efficiency. For power-type white LED, the choice of phosphor and process design, the improvement of light and luminous efficiency is also essential.

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