A brief discussion on LED epoxy packaging technology

Epoxy resins used in the production process of LEDs are one of the key points in the LED industry when making products. Epoxy resins refer to organic polymer compounds containing two or more epoxy groups in the molecule. Except for a few, their relative molecular quality is not high. The molecular structure of epoxy resins is characterized by the presence of active epoxy groups in the molecular chain. The epoxy groups can be located at the end, in the middle or in a ring structure of the molecular chain. Due to the presence of active epoxy groups in the molecular structure, they can undergo cross-linking reactions with various types of curing agents to form insoluble, infusible polymers with a three-dimensional network structure.

In order to maintain the airtightness of LED ICs, protect the core from external erosion, prevent moisture from invading from the outside, mechanically support the wires, effectively discharge the heat generated inside, and prevent electronic components from being damaged by mechanical vibration and impact, which may cause changes in component characteristics. Different shapes and material properties (with or without dispersion agents) are used to function as lenses or diffuse lenses, providing a shape that can be held in the hand.

1. Curing temperature and time of LED encapsulation resin

1. The hardener of general LED sealing resin is anhydrous acid, and its curing temperature is about 120~130℃.
2. The curing time is shortened after the addition of accelerator.

2. Curing time and distortion phenomenon and curing rate
1. The thermal conductivity of the resin is low, and the internal curing heat accumulates, which affects the curing rate. (Reaction rate)
2. High heat inside (curing heat) and outside (oven) Disply case is easy to deform.

3. The ratio and characteristics of resin and hardener
1. The amount of hardener used depends on the required characteristics.
2. Generally, when the hardener ratio is small, the hardened material is hard and yellow.
3. When the hardener ratio is large, the hardened material becomes brittle and has less color.

4. Tg (glass transition point) and HDT (heat deformation temperature)
1. Test method: TMA, DSC.b: The temperature difference between the two is 2~3 ℃.
2. Tg becomes higher after adding fillers.
3. The low electrical properties (insulation resistance and dielectric loss rate) of epoxy resin are mostly consistent with the heat deformation temperature.
The epoxy resin used to form the tube shell must have moisture resistance, insulation, mechanical strength, and high refractive index and transmittance of the light emitted by the LED. When selecting packaging materials with different refractive indices, the impact of packaging geometry on photon escape efficiency is different, and the angular distribution of luminous intensity is also related to the tube core structure, light output method, and the material and shape of the packaging lens. If a pointed resin lens is used, the light can be concentrated in the axial direction of the LED, and the corresponding viewing angle is smaller; if the top resin lens is round or flat, the corresponding viewing angle will increase.