Application prospect of TES ceramic substrate in LED

[Source: "High-tech LED - Technology and Applications" November issue]

High-power LED lighting technology has been developed for more than five years, and the reliability of the product has always been doubtful. Although the industry is all aiming at "heat dissipation", the annoying problem remains unresolved. At present, the luminous efficiency of LED is only 30% to 45%, and most of the remaining energy is converted into thermal energy. A large amount of thermal energy needs to be emitted in time, otherwise the junction temperature of the LED will rise. Long-term exposure of LEDs to high temperatures can degrade packaging materials, resulting in reduced lifetime or even permanent failure of LEDs. Therefore, while LEDs are developing rapidly, people are constantly researching new technologies for LED heat dissipation.

Although heat dissipation is a major bottleneck for LED luminaires, the excessive stress of electricity is the main reason for forcing the LED and its power supply system to be destroyed. At present, the public's eyes are too concerned about heat dissipation, and the antistatic ability of the lamps is ignored.

At present, the material of the radiator is mainly metal materials such as aluminum and copper, and the metal material has good thermal conductivity but good electrical conductivity. With the improvement of people's safety performance, the conductivity becomes a fatal scar of the lamp, and the poorly conductive Al2O3 ceramic substrate is less able to meet the outdoor lighting due to the lower thermal conductivity, antistatic ability and surge resistance. Need.

For outdoor lighting, surge, static electricity, lightning strikes, electromagnetic wave pulses, etc. will cause the capacitor to burn, which is also the main cause of LED lamp failure. The heat dissipation design mode of traditional high-power LED lamps adopts copper substrate + temperature equalization plate + heat dissipation material. In order to enhance the heat dissipation effect, the Heat Sink is designed as a fin type. The more fins, the more antennas there are, and the more static electricity is absorbed outdoors.

The insulating layer between the copper substrate and the aluminum substrate is the core technology of the heat dissipation substrate. The composition of the insulating layer is organic material. When the mechanism absorbs static electricity, when the insulating material is penetrated by static electricity, it is easy to burn carbonization, which leads to leakage and light decay, and the power capacitor is burnt and the LED fails. This is why many outdoor lighting fixtures do not meet the expected life expectancy.

In order to solve the damage caused by static electricity and electromagnetic pulse to LED, a new type of thermoelectric substrate (T he rma l & E lectricit y Substrate, TES) material - polycrystalline semiconductor ceramic substrate began to emerge. It is superior to existing conventional thermal conductive materials in terms of expansion coefficient, antistatic ability, and surge resistance.

The basic pathways for heat exchange are: conduction, convection and radiation. In order to effectively dissipate heat, people often achieve this by reducing the thermal resistance of the heat flow path and strengthening the convection coefficient, often ignoring the heat radiation. LED luminaires generally use natural convection heat dissipation. The heat sink quickly transfers the heat generated by the LEDs to the surface of the radiator. Due to the low convection coefficient, the heat cannot be dissipated into the surrounding air in time, causing the surface temperature to rise and the working environment of the LED to deteriorate. .

Increasing the emissivity can effectively remove the heat from the surface of the radiator through the form of heat radiation. Generally, the aluminum radiator is anodized to increase the surface emissivity. The TES ceramic material itself can have high emissivity characteristics without complicated follow-up. deal with.

For more details, please refer to the November issue of "High-tech LED-Technology and Applications"

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