Preface
"It generates more heat than light", this sentence sums up the "heat challenge" faced by the growing market of UVC LEDs. Good product thermal management is a key step to improve the life of UVC LEDs.
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 use various methods Dissipate these heat to maintain the temperature of the package within the allowable range.
2. Thermal management is the key to improving the life of UVC LEDs
Like any electronic components, UVC LEDs are sensitive to heat. UVC LED has low external quantum efficiency. In the input power, generally only less than 5% of the power is converted into light (currently, it is said that the efficiency of industrial products of related manufacturers has exceeded 5%), and the remaining more than 95% Power is converted into heat. This causes the UVC LED chip to generate abnormally severe heat. At this time, if the heat is not quickly removed and the LED chip is kept below its maximum operating temperature, the life and reliability of the UVC LED will be directly affected, and it may even be unusable.
Due to the small size of the UVC LED itself, most of the heat cannot be dissipated from the front, so the back of the LED becomes the only way to effectively dissipate heat. The task of improving heat dissipation is transferred to downstream packages and modules. At this time, how to do a good job of thermal management in the packaging process is particularly important.
3. The thermal management of the packaging process is inseparable from the two aspects of materials and processes
1. Material aspects. After years of development, the current UVC LED packaging materials and die bonding processes on the market are not much different. UVC LEDs on the market are basically based on flip-chip and high thermal conductivity aluminum nitride substrates. As aluminum nitride (AIN) has excellent thermal conductivity (140W/mK-170W/mK), it can withstand the aging of the ultraviolet light source itself. This solution not only satisfies the need for high thermal management of UVC LEDs, but also benefits the quality control of UVC LEDs.
2. Packaging process is an influencing factor of thermal management. The packaging process is mainly embodied in die-bonding technology, including three methods: silver paste soldering, solder paste soldering and Au-Sn eutectic soldering.
Although the bonding force of silver paste soldering is good, it is easy to cause silver migration and cause device failure.
For solder paste soldering, since the melting point of the solder paste is only about 220 degrees, after the device is mounted, re-melting will occur after the device is placed in the furnace again, and the chip is likely to fall off and fail, which affects the reliability of the UVC LED.
Au-Sn eutectic welding is mainly carried out by flux, which can effectively improve the bonding strength and thermal conductivity of the chip and the substrate. In contrast, it has higher reliability and is beneficial to the quality control of UVC LEDs.
Therefore, the gold-tin eutectic welding method is mostly used in the market. Compared with the first two die bonding methods, eutectic welding is mainly performed by flux, which can effectively improve the bonding strength and thermal conductivity of the chip and the substrate, and is more reliable, which is conducive to the quality control of UVC LEDs.
4. With the same materials and processes, the thermal management effect may still be quite different
1. To do a good job of thermal management, the key is to reduce the welding void rate
In the welding process, the problem of welding void rate is mainly involved. Welding voids refer to defects formed during the welding of LED chips and substrates. They appear as voids in appearance. They are an important indicator that affects heat dissipation. According to related experiments, the lower the welding void rate, the better the heat dissipation effect and the longer the product life. , The better the quality.
2. The heat dissipation of the light source module is also one of the key points.
For multi-chip integrated UVC LEDs, the more integrated chips, the more severe the heat dissipation problem. Although manufacturers will reduce the solder void rate to improve the heat dissipation effect, the aluminum substrate is not the final heat sink.
After the heat generated by the LED lamp bead is conducted to the aluminum plate, the aluminum substrate needs to efficiently conduct the heat to the radiator through the thermal interface material to dissipate heat, so as to ensure the stability and safety of the LED lamp bead for long-term use. The thermal interface material can provide an effective heat conduction path for the gap between the aluminum substrate and the heat sink and the rough surface texture, thereby improving the heat dissipation efficiency of the module. There are various types of thermal interface materials, high compressibility, and super softness. Thermally conductive silicone sheets that can be used as vibration absorbers can also be used in UV LEDs.
5. Summary
As the UVC LED market further expands, manufacturers need to consider new methods to meet this challenge. Now, the question remains how to deal with the high thermal demands of UV LEDs while ensuring that the components remain cost-effective, durable, and resistant to the wear of the UV light source itself. The UVC disinfection technology implemented by LEDs can bring real transformative effects. In the development of the industry, it is necessary to ensure that the thermal challenges faced by UV LEDs can be overcome.
