The luminous efficiency of deep UV LED is mainly determined by the external quantum efficiency, which is affected by the internal quantum efficiency and light extraction efficiency. With the continuous improvement (>80%) of the internal quantum efficiency of deep UV LED, the light extraction efficiency of deep UV LED has become a key factor limiting the improvement of the light efficiency of deep UV LED, and the light extraction efficiency of deep UV LED is greatly affected by the packaging technology. The deep UV LED packaging technology is different from the current white LED packaging technology. White LED is mainly packaged with organic materials (epoxy resin, silica gel, etc.), but due to the length of deep UV light wave and high energy, organic materials will undergo UV degradation under long-time deep UV radiation, which seriously affects the light efficiency and reliability of deep UV LED. Therefore, deep UV LED packaging is particularly important for the selection of materials.

LED packaging materials mainly include light emitting materials, heat dissipation substrate materials and welding bonding materials. The light emitting material is used for chip luminescence extraction, light regulation, mechanical protection, etc; Heat dissipation substrate is used for chip electrical interconnection, heat dissipation and mechanical support; Welding bonding materials are used for chip solidification, lens bonding, etc.

1. light emitting material: the LED light emitting structure generally adopts transparent materials to realize light output and adjustment, while protecting the chip and circuit layer. Due to the poor heat resistance and low thermal conductivity of organic materials, the heat generated by the deep UV LED chip will cause the temperature of the organic packaging layer to rise, and the organic materials will undergo thermal degradation, thermal aging and even irreversible carbonization under high temperature for a long time; In addition, under high-energy ultraviolet radiation, the organic packaging layer will have irreversible changes such as decreased transmittance and microcracks. With the continuous increase of deep UV energy, these problems become more serious, making it difficult for traditional organic materials to meet the needs of deep UV LED packaging. In general, although some organic materials have been reported to be able to withstand ultraviolet light, due to the poor heat resistance and non airtightness of organic materials, organic materials are still limited in deep UV LED packaging. Therefore, researchers are constantly trying to use inorganic transparent materials such as quartz glass and sapphire to package deep UV LED.

2. heat dissipation substrate materials: at present, LED heat dissipation substrate materials mainly include resin, metal and ceramic. Both resin and metal substrates contain organic resin insulation layer, which will reduce the thermal conductivity of the heat dissipation substrate and affect the heat dissipation performance of the substrate; Ceramic substrates mainly include high / low temperature co fired ceramic substrates (HTCC /ltcc), thick film ceramic substrates (TPC), copper-clad ceramic substrates (DBC) and electroplated ceramic substrates (DPC). Ceramic substrates have many advantages, such as high mechanical strength, good insulation, high thermal conductivity, good heat resistance, low coefficient of thermal expansion and so on. They are widely used in power device packaging, especially high-power LED packaging. Due to the low light efficiency of deep UV LED, most of the input electric energy is converted into heat. In order to avoid high-temperature damage to the chip caused by excessive heat, the heat generated by the chip needs to be dissipated into the surrounding environment in time. However, the deep UV LED mainly relies on the heat dissipation substrate as the heat conduction path. Therefore, the high thermal conductivity ceramic substrate is a good choice for the heat dissipation substrate for deep UV LED packaging.

3. welding bonding materials: deep UV LED welding materials include chip solid crystal materials and substrate welding materials, which are respectively used to realize the welding between chip, glass cover (lens) and ceramic substrate. For flip chip, Gold Tin eutectic method is often used to realize chip solidification. For horizontal and vertical chips, conductive silver glue and lead-free solder paste can be used to complete chip solidification. Compared with silver glue and lead-free solder paste, the Gold Tin eutectic bonding strength is high, the interface quality is good, and the thermal conductivity of the bonding layer is high, which reduces the LED thermal resistance. The glass cover plate is welded after the chip solidification, so the welding temperature is limited by the resistance temperature of the chip solidification layer, mainly including direct bonding and solder bonding. Direct bonding does not require intermediate bonding materials. The high temperature and high pressure method is used to directly complete the welding between the glass cover plate and the ceramic substrate. The bonding interface is flat and has high strength, but has high requirements for equipment and process control; Solder bonding uses low-temperature tin based solder as the intermediate layer. Under the condition of heating and pressure, the bonding is completed by the mutual diffusion of atoms between the solder layer and the metal layer. The process temperature is low and the operation is simple. At present, solder bonding is often used to realize reliable bonding between glass cover plate and ceramic substrate. However, metal layers need to be prepared on the surface of glass cover plate and ceramic substrate at the same time to meet the requirements of metal welding, and solder selection, solder coating, solder overflow and welding temperature need to be considered in the bonding process.

In recent years, researchers at home and abroad have conducted in-depth research on deep UV LED packaging materials, which has improved the luminous efficiency and reliability of deep UV LED from the perspective of packaging material technology, and effectively promoted the development of deep UV LED technology.