Present situation and Prospect of deep UV LED packaging technology
发布时间：2021-12-16 11:07
来源：萤光创新
Deep ultraviolet light emitting diode Deep ultraviolet light emitting diode (duv-led) has many advantages such as environmental protection, mercury free, long service life, low power consumption, fast response, light structure and so on. In recent years, deep ultraviolet LED technology has made rapid development, mainly reflected in the continuous improvement of light efficiency and reliability. On the one hand, it is due to the progress of nitride material epitaxy and doping technology in the process of chip manufacturing, on the other hand, it is due to It is applicable to the development of deep UV LED packaging technology.
Dr. Peng Yang, Huazhong University of science and technology Professor Chen Mingxiang and Professor Luo Xiaobing published "current situation and Prospect of deep UV LED packaging technology" in Journal of luminescence (EI, core journals) Review articles. This review focuses on the systematic analysis of the key technologies of deep UV LED packaging, including packaging material selection, packaging structure design, packaging process optimization, reflected light loss suppression and effective thermal management. The follow-up technology development is prospected.
Deep UV LED has important application value in sterilization, biochemical detection, medical health, secret communication and other fields. Especially in the field of sterilization, deep ultraviolet LED mainly uses high-energy ultraviolet to irradiate microorganisms and destroy nucleic acid structure, so as to achieve the purpose of microbial inactivation. Compared with traditional sterilization and disinfection technology, deep UV LED has the advantages of high sterilization efficiency, strong applicability, no chemical pollutants and simple operation. It can be widely used in air, water and object surface disinfection. With the worldwide spread of New Coronavirus (COVID-19), deep ultraviolet LED disinfection is considered to be an effective way to eliminate New Coronavirus. It has been used in public places, transportation vehicles, personal protection and other fields, and provides technological support to curb COVID-19's spread.
Figure 1 Application of deep UV LED disinfection: (a) public elevator; (b) Aircraft cabin; (c) Personal protection.
Key technologies of deep UV LED packaging
(1) Packaging material selection
Light emitting material: the LED light emitting structure generally adopts transparent materials to realize light output and adjustment, and protect the chip and circuit layer at the same time. Traditional organic materials have poor heat resistance, low thermal conductivity and UV degradation, which are difficult to meet the needs of deep UV LED packaging. Quartz glass has stable physical and chemical properties, high transmittance (> 90%) in deep UV band, high mechanical strength, good heat resistance, UV resistance and high air tightness. It has become an effective choice for lens materials for deep UV LED packaging.
Heat dissipation substrate material: ceramic substrate has many advantages, such as high mechanical strength, good insulation, high thermal conductivity, good heat resistance and low coefficient of thermal expansion. It is a good choice for heat dissipation substrate for deep UV LED packaging.
Welding bonding materials: deep UV LED welding materials include chip solid crystal materials and substrate welding materials, which are used to realize chip Glass cover Welding between (lens) and ceramic substrate. Flip chip often adopts Gold Tin eutectic to realize chip crystal fixation, with high strength, good interface quality, and high thermal conductivity of bonding layer, which reduces led thermal resistance. Solder is often used between glass cover plate and ceramic substrate to realize reliable bonding, but metal layer needs to be prepared on the surface of glass cover plate and ceramic substrate at the same time to meet the requirements of metal welding.
(2) Packaging structure design
Harmful gases such as water vapor in the environment are easy to damage the deep UV LED chip and circuit layer, affecting its service life and reliability. Therefore, the packaging structure with cavity is often used for deep UV LED packaging, mainly including to packaging and surface mount packaging structure with three-dimensional glass cover plate or three-dimensional ceramic substrate.
(3) Packaging process optimization
Deep UV LED packaging process mainly includes solid crystal Wiring (or flip eutectic) and glass cover plate welding (bonding). Among them, glass cover plate bonding is the key link of the whole packaging process. Since the chip has been pasted in the substrate cavity, it is necessary to adopt low-temperature welding process to realize reliable bonding between glass cover plate and three-dimensional ceramic substrate. At present, there are mainly two methods: low melting point solder bonding and low-temperature bonding.
(4) Reflected light loss suppression
There are Fresnel reflection loss on the upper and lower surfaces of the glass, and Fresnel reflection loss and total reflection loss on the upper and side of the chip. In order to improve the light efficiency of deep UV LED, it is necessary to adopt some methods to suppress the reflection loss, including thin film coating and nanostructure for suppressing Fresnel reflection, hemispherical lens for suppressing total reflection, surface coarsening, nano particle doped packaging layer, etc.
(5) Junction temperature and heat management
The light efficiency of deep UV LED is relatively low. In order to meet the application requirements, multi chip integrated packaging is often used to obtain high-power deep UV LED modules. However, while pursuing high optical power density, the heat flux per unit area is greater, and the heat accumulation causes the junction temperature of deep UV led to increase. Therefore, the total thermal resistance of deep UV LED can be reduced through packaging structure optimization and effective thermal management, including eutectic bonding, aluminum nitride ceramic substrate, high thermal conductivity solid crystal materials, passive heat dissipation (heat dissipation fins, etc.) and active heat dissipation (air cooling, water cooling, etc.), so as to improve the heat dissipation performance and reliability of deep UV LED.
Prospect
At present, deep UV LED technology has made great progress, but compared with near UV and blue LED, deep UV LED still faces the problems of low light efficiency, poor reliability and high cost, which is still difficult to meet the needs of large-scale applications. In order to further improve the light efficiency and reliability of deep UV LED, there are still many research directions of deep UV LED packaging technology, including but not limited to:
(1) Exploration of new packaging materials and packaging structures. Research and develop packaging materials with UV resistance, high UV transmittance and low temperature curing, welding materials with high thermal conductivity, high strength, low temperature bonding and high temperature service, and develop deep UV LED packaging structures with high light extraction and high heat dissipation by means of packaging structure design and optimization, so as to improve the photothermal performance of deep UV LED devices.
(2) Development of high integrated deep UV LED packaging process. In the future, deep UV LED will inevitably develop towards large-scale, multi chip, integration and low cost. It is necessary to develop highly integrated deep UV LED packaging processes to meet the development needs of deep UV LED, including chip to wafer (c2w), wafer to wafer (W2W) and other board level packaging processes.
(3) Enhanced collaborative design of deep UV LED packaging. At present, each link of deep UV LED technology is independent of each other, resulting in the disconnection between chip design, packaging technology and device application, which makes it difficult for the final deep UV led to meet the requirements of optical performance and reliability in the application process.
The original text is reproduced in [China Optics]
Qingdao fluorescent Innovation Technology Co., Ltd. has a professional postdoctoral team, focusing on the research of ultraviolet sterilization application. After years of deep cultivation in the ultraviolet industry, the company has obtained a number of national invention and utility model patents. At present, a number of sterilization module products have been put into the market. For more details, please visit the company's website at www.qdyingguang.com Com contact the company for the official account of WeChat.
Keywords: UVC, UVC led, deep ultraviolet, ultraviolet sterilization, ultraviolet disinfection, deep ultraviolet LED, water sterilization, water disinfection, air sterilization, air purification, flowing water sterilization, static water sterilization
