LED packaging must be designed in a reasonable way to be put into use

LED gradually replaces traditional incandescent lamps and moves towards backlight and lighting market applications. Compared with traditional incandescent light sources, LED has many advantages. LED has long service life, high efficiency, not easy to damage, does not contain mercury, does not produce toxic gases, low power consumption, etc. For the environment we live in, LED is nothing more than the best light source alternative. At the same time, LED is hailed as a new light source in the 21st century.

In the LED process, packaging is a very important part. The function of packaging is to connect the external lead to the electrode of the LED chip , which not only protects the LED chip, but also improves the luminous efficiency . Therefore , LED packaging is not only to complete the output of electrical signals, but more importantly, to protect the normal operation of the tube core and output visible light. However, no matter what kind of LED, it needs to design a reasonable packaging form for different types before it can be put into practical application.

With the different application methods of LED, the heat dissipation solution and luminous effect as well as the appearance and size will also change. According to the LED packaging form, it can be roughly divided into 6 categories: Lamp-LED, TOP-LED, Side-LED, SMD-LED, High-Power-LED, Flip Chip-LED, etc.

In the entire LED industry chain, packaging is a linking part. Traditional low-level LEDs are mostly used for outdoor display billboards or indicator lights, and their packaging materials are liquid epoxy resin. As LEDs turn to indoor lighting and backlight applications, high power and high brightness become the focus of LED development. High-power LEDs must reduce shielding, increase light transmittance, and enhance the utilization of light refraction and reflection. After the bare crystal overcomes the brightness problem and enters the packaging, it is very important to maintain the highest light transmittance and minimize light attenuation in the packaging process. In

the past, the most commonly used packaging material for LEDs was epoxy resin. The epoxy resin packaging process is relatively simple and low-cost, so it currently has a high market share in LED packaging materials. However, its disadvantages are low impact damage resistance, poor toughness, and heat resistance of less than 170oC. After aging, it will gradually turn yellow due to the benzene ring component, which will affect the color of the light. In particular, the lower the wavelength, the faster the aging. In particular, some white light-emitting diodes use near ultraviolet light (Near ultraviolet) to emit light, which has a lower wavelength than other visible light and ages faster. Therefore, in order to deal with the aging problem caused by the heat energy generated by high-power LEDs, silicone with higher heat resistance should be considered as the packaging material when selecting packaging materials.

Using silicone to replace epoxy resin has a higher lumen retention rate (transmittance, light transmittance, penetration, expressed in percentage units). For example, the Luxeon series LEDs of Lumileds in the United States are silicone encapsulated. Other companies also have silicone encapsulation solutions, such as Momentive's InvisiSi1, Dow Corning Toray, and Shin-Etsu Chemical's KER-2500AB, which are also silicone packaging solutions for LEDs.

In addition to having better resistance to low wavelengths in the wavelength range of 300~350nm and being less prone to aging, silicone also has better light transmittance, refractive index, and heat resistance than epoxy resin. Currently, the light refractive index of silicone can reach between 1.4 and 1.5, and the future development target for silicone is a refractive index of 1.6 or above. Silicone

is a packaging solution for high-power LEDs and LED backlight TV light sources. Silicone packaging is applicable to various packaging forms, but the more suitable material still needs to be selected according to the size and power of the package body. Because methyl silicone can withstand heat of up to 200 oC for long-term use, it has advantages over epoxy resin in terms of UV resistance, weather resistance, and even service life. As for LED backlight packaging, materials with low moisture and oxygen permeability are required, which are also the development applications that many silicone manufacturers are rushing to enter. The only problem is that the price cost is high, and the adhesion of silicone is still not ideal after high temperature and high humidity tests with silver-plated layers, PPA, and ceramic substrates. The solution is to improve the adhesion and matching between silicone and the adherend, and then extend the baking time to improve the current adhesion problem.

Industry insiders said: Currently, the price cost issue is the biggest consideration for the industry to adopt silicone packaging, but because silicone has excellent heat resistance, seasonal resistance, UV resistance, electrical insulation, chemical stability, release and many other reasons, it will definitely gradually replace epoxy resin as the main LED packaging material. When the economic scale of the market reaches tens or hundreds of tons, the price will be expected to have a larger space. It is estimated that there will be a chance to happen with the increase in the penetration rate of the backlight and lighting markets.