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UV LED has the advantages of energy saving, long life, high efficiency, single and adjustable wavelength, etc., and has become an ideal substitute for UV mercury lamps containing harmful mercury elements. However, a single UV LED chip or lamp bead can hardly meet the demand for high UV energy density in UV applications. It must be packaged in the form of multi-chip or multi-lamp bead modules to increase the packaging density and provide higher light energy output. Chip on Board (COB) is a mature packaging technology that can directly mount multiple chips on a substrate to increase the packaging density. However, with the increase in the number of chips, the packaging density also increases. Among them, heat dissipation problems based on thermal management and optical design, reliability problems, and light spot and irradiance uniformity are more prominent. In addition, the electrical power of a single UV LED is often greater, and the quantum efficiency is often much lower than that of visible light. Many materials also absorb UV light, which makes these problems more prominent. Therefore, it is urgent to conduct systematic research on it. While the academic community has made great progress in the packaging technology of visible light LEDs, there are relatively few studies on packaging technology in the field of ultraviolet LEDs. Some studies are often focused on epitaxial chips, which to a certain extent restricts the development of the ultraviolet LED industry. It is necessary to conduct a comprehensive and systematic study on ultraviolet LED packaging technology. This paper first uses the COB packaging of flip-chip ultraviolet LEDs as a carrier, and uses the finite element simulation method to study the thermal properties of three common COB packaging substrates, and discusses how to increase the packaging density of the device as much as possible under the premise of ensuring reliability. Under the premise of ensuring reliability and substrate size of 13×13×1 mm, aluminum substrates are not suitable for packaging densities greater than 0.38 W/mm~2; according to the trend, it can be inferred that alumina ceramic substrates cannot meet the packaging density of more than 0.94 W/mm~2; while aluminum nitride ceramic substrates can meet the packaging requirements of higher packaging density, but its high price is an important factor that needs to be considered for its large-scale application. These conclusions provide an important reference for further research. Then, taking into account factors such as cost and process, based on metal substrate, the effects of different factors such as chip spacing and packaging structure, substrate and adhesive materials, adhesive packaging area and porosity on the heat dissipation of UV LED COB module were comprehensively and systematically studied through the combination of finite element simulation, optical design analysis and experiment. The packaging structure of UV LED COB module with high performance, high reliability and low thermal resistance was obtained.
The study shows that in the packaging structure, the selection of the optimal chip spacing of about 2.5 mm can obtain lower junction temperature and higher irradiance; the introduction of high thermal conductivity aluminum partition to optimize the packaging structure is an effective way to improve the heat dissipation effect. In the selection of packaging materials, although materials with higher thermal conductivity can promote heat dissipation, when the thermal conductivity of the substrate and adhesive is greater than 240 W/(m K) and 60 W/(m K), respectively, the increase in the thermal conductivity of the substrate and adhesive has almost negligible effect on the heat dissipation of UV LED COB module. In addition, in the packaging process, when the area ratio (Sa/Sc) of the adhesive area (Sa) and the chip area (Sc) is 0.9, it can not only achieve excellent heat dissipation, but also minimize the use of adhesive materials, while avoiding the adhesive materials blocking light and causing leakage; the dispersed holes have better heat dissipation performance, because the dispersed holes have a larger contact surface area, which increases the heat dissipation path in all directions; through multiple experimental explorations, the more optimized reflow soldering process parameters were obtained, that is, when the eight temperature zones of the reflow soldering process are 100, 130, 160, 190, 230, 255, 255, and 215°C, respectively, and the reflow soldering speed is 0.65 m/min, better solid crystal welding quality can be obtained; it is worth mentioning that this paper also compared the simulation results obtained through sample preparation tests, and found that the error was about 3.2%, which confirmed the reliability and effectiveness of the research methods and research ideas used in this paper. This paper has achieved certain results in the research on ultraviolet LED packaging technology to achieve high performance, high reliability and low thermal resistance, which has a relatively positive significance for promoting the development of ultraviolet LED packaging technology.