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Thermal management, the key to improve the service life of UVC LED
"More heat is generated than light". This sentence summarizes the "heat challenge" faced by the growing market of UVC led. Good product thermal management is a key step to improve the service life of UVC led.
1、 Thermal management overview
Thermal management refers to the use of reasonable cooling and heat dissipation technology and structural optimization design for the heat consuming components and systems in the package to control their internal temperature, so as to ensure the normal reliability of electronic devices and systems. The purpose is to derive these heat through various methods to maintain the temperature of the package within the allowable range.
2、 Thermal management is the key to improve the life of UVC LED
Like any electronic component, UVC LED is sensitive to heat. UVC LED has low external quantum efficiency. In the input power, less than 5% of the power is generally converted into light (at present, it is said that the efficiency of industrialized products of relevant manufacturers has exceeded 5%), and the remaining more than 95% of the power is converted into heat. This leads to abnormal heating of UVC LED chip. At this time, if the heat is not removed quickly and the LED chip is kept below its maximum operating temperature, the service life and reliability of UVC LED will be directly affected and even can not be used.
Due to the small volume of UVC led, most of the heat cannot be dissipated from the front, so the back of LED becomes the only way to effectively dissipate heat. The task of improving heat dissipation is transferred to the downstream packaging and modules. At this point, how to do a good job of thermal management in the packaging process is particularly important.
3、 The thermal management of packaging links is inseparable from the two aspects of materials and processes
1. materials. After years of development, there is little difference in the packaging materials and solid crystal process of UVC led on the market. The main solution of UVC led on the market is flip chip with high thermal conductivity aluminum nitride substrate. Because aluminum nitride (AIN) has excellent thermal conductivity (140w/mk-170w/ MK), it can resist the aging of the ultraviolet light source itself. This scheme not only meets the needs of UVC LED high heat management, but also facilitates the quality control of UVC led.
2. packaging process is the influencing factor of thermal management. The packaging process is mainly reflected in the solid crystal technology, including silver paste welding, solder paste welding and Gold Tin eutectic welding.
Although silver paste welding has good adhesion, it is easy to cause silver migration and device failure.
For solder paste welding, the melting point of solder paste is only about 220 degrees. Therefore, after the device is pasted, it will melt again after passing through the furnace again. The chip is easy to fall off and fail, affecting the reliability of UVC led.
Gold Tin eutectic welding mainly uses flux for eutectic welding, which can effectively improve the bonding strength and thermal conductivity between the chip and the substrate. In contrast, it has higher reliability and is conducive to the quality control of UVC led.
Therefore, Gold Tin eutectic welding is widely used in the market. Compared with the first two solid crystal methods, it mainly uses flux for eutectic welding, which can effectively improve the bonding strength and thermal conductivity between the chip and the substrate, and is more reliable, which is conducive to the quality control of UVC led.
4、 If the material and process are the same, the thermal management effect may still vary greatly
1. the key to good thermal management is to reduce the welding void rate
In the welding process, the problem of welding void rate is mainly involved. Welding cavity refers to the defect formed during the welding process between LED chip and substrate, which is in the form of cavity in appearance, and is an important index affecting heat dissipation. Through relevant experiments, it is concluded that the lower the welding cavity rate, the better the heat dissipation effect, the longer the product life and the better the quality.
2. heat dissipation of light source module is also one of the keys.
For multi chip integrated UVC LEDs, the more integrated chips, the more severe the heat dissipation problem. Although the manufacturer will improve the heat dissipation effect by reducing the welding void rate, the aluminum substrate is not the final radiator.
After the heat generated by the LED lamp beads is transferred to the aluminum plate, the aluminum substrate needs to efficiently transfer the heat to the radiator through the thermal conductive interface material to dissipate heat, so as to ensure the stability and safety of the LED lamp beads for long-term use. The thermal conductive interface material can provide an effective thermal conductive path for the gap and rough surface texture between the aluminum substrate and the heat sink, and then improve the heat dissipation efficiency of the module. There are a variety of thermal conductive interface materials, which are highly compressible and super soft. The thermal conductive silica gel sheet can be used as a vibration absorber and can also be used in UV LED.
With the further expansion of the UVC LED market, manufacturers need to consider new ways to meet this challenge. At present, the problem is still how to deal with the high heat demand of UV LED, while ensuring that the components remain cost-effective, durable and resistant to the wear and tear of the UV light source itself. UVC disinfection technology realized by LED can bring real transformation effect. It is necessary to ensure that the thermal challenges faced by UV LED can be overcome in the industrial development.