What is affecting the efficiency of light pick-up in LED packaging

- Feb 12, 2019-

1. Heat Dissipation Technology

For light-emitting diodes (LEDs) composed of PN junctions, when the forward current flows through the PN junction, the PN junction has heat loss. The heat is radiated into the air through bonding, encapsulating materials, heat sinks, etc. In this process, each part of the material has a thermal impedance, that is, thermal resistance, which is a fixed value determined by the size, structure and material of the device.

2. Selection of Filling Adhesive

According to the law of refraction, when light is incident from a dense medium to a sparse medium, when the incident angle reaches a certain value, that is, when the incident angle is greater than or equal to the critical angle, the total emission will occur. For GaN blue chip, the refractive index of GaN material is 2.3. According to the law of refraction, the critical angle is 0=sin-1 (n2/n1) when light rays are emitted from the crystal to air.

3. Reflection Processing

Reflection processing has two main aspects: one is the reflection processing inside the chip, the other is the reflection of packaging materials to light. Through the reflection processing inside and outside the chip, the ratio of light flux emitted from the chip can be increased, the absorption inside the chip can be reduced, and the luminous efficiency of power LED products can be improved. From the packaging point of view, power-type LED usually assembles power-type chips on metal brackets or substrates with reflective chambers. The bracket-type reflective chambers generally adopt electroplating to improve the reflective effect, while the substrate-type reflective chambers usually adopt polishing method and electroplating treatment when conditions permit. However, the above two methods are affected by the accuracy of the die and the process, and the reflected after treatment. The cavity has some reflective effect, but it is not ideal. At present, because of the poor polishing accuracy or the oxidation of metal coating, the reflective effect of the reflective cavity made in our country is poor, which causes many light rays to be absorbed after they are irradiated into the reflective region and can not be reflected to the light surface according to the anticipated target, thus resulting in the low efficiency of light extraction after final packaging.