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LED Packaging: Reasonable Design

Sep 03, 2020

Only reasonable design of LED package can be put into application. According to experts, LEDs are gradually replacing traditional incandescent lamps to the backlight and lighting market applications. Compared with traditional incandescent light sources, LEDs have many advantages. LEDs have long service life, high efficiency, not easy to damage, no mercury, and no toxic gas. , Low power consumption... and other characteristics, for our environment, LED is nothing more than the best light source alternative. At the same time, LED is hailed as a new type of light source in the 21st century. In the LED manufacturing process, packaging is a very important part. The function of packaging is to connect the outer leads to the electrodes of the LED chip, which not only protects the LED chip, but also improves the luminous efficiency. Therefore, the LED package is not only to complete the output of electrical signals, but more importantly, to protect the normal operation of the die to output visible light. But no matter what kind of LED, it needs to be designed with a reasonable packaging form for different types before it can be put into practical application. With the different LED application methods, the heat dissipation scheme and luminous effect, as well as the appearance and size will also change. According to the LED package form, it can be roughly divided into Lamp-LED, TOP-LED, Side-LED, SMD-LED, High- Power-LED, FlipChip-LED... and other 6 categories. In the entire LED industry chain, packaging is the link between the previous and the next. Traditional low-end LEDs are mostly used for outdoor display billboards or indicators. The packaging material is liquid epoxy resin. As LEDs turn to indoor lighting and backlight applications, high-power, high-power Brightness has become the focus of LED development. High-power LEDs must reduce shading, increase light transmittance, and strengthen the utilization of light refraction and reflection. After the bare crystal overcomes the brightness problem and enters the package, how to maintain the highest light transmittance during the packaging process? Attenuation to the minimum is critical.

In the past, the most commonly used packaging material for LEDs was epoxy. The epoxy resin packaging process is relatively simple and low in cost. Therefore, the current market share of LED packaging materials is high, but the disadvantages are low impact damage resistance, poor toughness and The heat resistance is less than 170oC. After aging, the benzene ring component will gradually turn yellow and affect the bright color, especially the lower the wavelength, the faster the aging, especially some white light-emitting diodes use near ultraviolet (Nearultraviolet) to emit light, compared with other visible light Its wavelength is lower and aging faster. Therefore, in order to cope with the aging problem caused by the heat generated by high-power LEDs, silicone with higher heat resistance should be considered as the packaging material in the selection of packaging materials. Using silicone to replace epoxy resin has a higher lumen retention rate (Transmittance, light transmittance, transmittance, expressed in percentage units). For example, the Luxeon series of LEDs from Lumileds in the United States are changed to silicone sealant, and other companies also There are silicone sealing solutions, such as InvisiSi1 Toray from Momentive. Dow Corning (DowCoringToray), Japan's Shin-Etsu Chemical's KER-2500AB, etc. are also silicone packaging solutions for LEDs. In addition to silicone has better resistance to low wavelengths in the range of 300-350nm, and is less prone to aging, silicone has better light transmittance, refractive index, and heat resistance than epoxy. At present, the refractive index of silicone light can reach between 1.4 and 1.5, and the future refractive index of 1.6 or more is the goal of silicone development.

Silicone is a packaging solution for high-power LEDs and LED backlight TV light sources. Silicone packaging is suitable for various packaging forms, but it is still necessary to choose more suitable materials according to the size and power of the package. Because methyl silicone has a long-term use of heat resistance up to 200oC, it has advantages over epoxy resin in UV resistance, weather resistance, and even service life. As for the LED backlight package, materials with lower moisture and oxygen permeability are required, which are also the development and application of many silicone manufacturers. However, the current problem is that the price is relatively high, and after the high temperature and high humidity test after packaging with silver plating, PPA, and ceramic substrates, the adhesiveness of silicone is still not ideal. The solution is to improve the silicone and the bonded body. Adhesion and matchability, coupled with extending the baking time, to improve the current adhesion problems. Experts said: The current price and cost issue is the biggest consideration for the industry when using silicone packaging, but because silicone has excellent heat resistance, seasonal resistance, UV resistance, electrical insulation, chemical stability, release properties and many other reasons, it must be It can gradually replace epoxy resin and become the main show of LED packaging materials. When the economic scale of the market reaches tens of hundreds of tons or more, the price will have a larger space. It is estimated that the market penetration of backlight and lighting will increase. , There will be a chance.