The UV-LED single chip has a small area and is easy to design flexibly; however, the radiant power of a single chip is also low, and it is difficult to meet the requirements of high radiant power density in many applications, which is currently difficult to replace in many fields. One of the important reasons for UV discharge lamps. Therefore, with the development of UV-LED, its packaging and system design has also become the focus of attention.
Germany
Schneider et al. of KIT of Germany proposed a high power density UV-LED module, which densely encapsulates 98 395 nm LED chips on a ceramic substrate to achieve higher radiation power density. The first 98 LED chips were encapsulated on an alumina ceramic substrate by silver paste as shown. The single LED chip has an input power of 1.65 W, an operating current of 500 mA, a junction temperature of 25 ° C, and an output radiated power of 375 mW. 98 chips are connected in series. The maximum input power of the whole module is 162 W, ​​the package area is 2.11 cm2, and the thermal power density reaches 59.2 W/cm2.
The characteristic test results under air-cooled conditions show that the module emits an ultraviolet wavelength of 397 nm and a radiation power density of 13.1 W/cm2 at an input power of 120 W and an operating current of 400 mA. The thermal simulation results show that if the heat dissipation characteristics of the module are improved, the radiation power density is expected to reach 20.8 W/cm2. To this end, a surface micro heat sink was designed as shown.
The heat sink is based on the principle of short heat transfer microchannels under laminar flow conditions, and many short microchannels are connected in parallel to increase the heat conduction area and use water as the coolant. The heat sink of this structure made of plastic has a heat flux of 500 W/cm2. When a material with lower thermal resistance such as aluminum or alumina ceramic is used, the heat flux of the heat sink is expected to reach 800 W/cm2. Can effectively improve the heat dissipation performance of the LED module. Subsequently, a thick film printed aluminum substrate was used instead of the ceramic substrate, and it was confirmed that the improved module had better heat dissipation performance, and the maximum irradiance could reach 31.6 W/cm 2 .
Taiwan
Horng et al. of Zhongxing University in Taiwan used a composite electroplating process to prepare a diamond-doped copper (DAC) heat sink and applied it to the heat dissipation of the UV-LED package. The laser ray method measured the thermal diffusivity of the DAC heat sink to be 0.7179 cm2/s. The experimental results show that the UV-LED thermal resistance of the DAC heat sink is only 18.4 K/W, which is lower than that of pure copper of 24.8 K/W, and its heat dissipation characteristics and optical performance are improved. When the injection current is 350 mA, the surface temperature of the UV-LED using the DAC heat sink is 45.3 °C, while the surface temperature of the UV-LED of the pure copper heat sink is 50.1 °C under the same conditions, and the surface temperature of the sapphire substrate is only 62.5 °C. . Under this condition, the radiation output power and radiation efficiency of the UV-LED increased to 71.8 mW and 4.3%, respectively.
Fudan University
The Fudan University research group developed a high-power UV LED light curing system of kW or higher based on the high power density package of the sandwich structure of copper plate and AlN board. As an insulating layer between the positive and negative electrodes of the copper plate and between the copper plate electrode and the heat sink, the AlN plate can achieve good insulation effect and ensure efficient heat dissipation of the chip, thereby improving the heat dissipation characteristics of the LED module; The connection increases the driving current of the LED module and increases the package power per unit area to 20~500 W/cm2. The mobile UV curing system shown in the figure has an input power density of 200 W/cm2 and a total power of 14 kW. It can be applied to the curing of various floor coatings and has been applied to wear-resistant paper coating. Layer and wood paint curing.
Guangdong Ocean University
Zhou et al. of Guangdong Ocean University designed a special fan-shaped UV-LED array to meet the special requirements of high-speed rotary curing such as disc curing, and used the TracePro optical simulation software to illuminate the irradiance distribution of the source. simulation. The array structure is shown in Figure (a). A number of high-power UV-LED fan arrays are mounted on the aluminum substrate, and each layer of UV-LEDs is equally spaced on an arc centered on O. The number of LED chips in the radial direction gradually increases linearly, so that the irradiance gradually increases in the radial direction. As can be seen from the cross section of Figure (b), the UV-LED array is distributed on a parabolic cylinder. A collimating lens is mounted directly in front of each LED to generate approximately parallel light having a divergence angle of less than 3°, and then the exiting light of the UV-LED array is concentrated in a small rectangular area to form a high power density irradiation surface.
Nanjing University of Information Science and Technology
Xiao Yurong and others of Nanjing University of Information Science and Technology designed a circular UV-LED array illumination for the uniform illumination ultraviolet light source required in the construction of fingerprint fluorescence detection. Firstly, the radiation angle distribution of a single LED is measured, and the approximate light intensity distribution equation of a single LED is fitted; then, 8 LEDs are evenly placed on a ring with a radius of 10 mm, placed on a central axis 5 mm above the ring. 1 LED; under the illumination error of a given viewing screen, according to the Sparrow rule, the distance between the observation screen and the annular array is determined, thereby achieving uniform illumination distribution of the LED ring array. The experimental results show that when the distance from the observation screen to the ring is 11.0 cm, the relative error of the illuminance is less than 1.27% in a circle with a radius of 10.0 mm. The LED array illuminance uniformization method has high reliability and the design method is simple and easy. However, due to the certain dispersion of the radiation of each LED, there is still a certain difference between the homogenization effect and the ideal effect.
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