Research on Heat Dissipation Methods of High Power Semiconductor Laser
Semiconductor lasers were first studied from abroad. The earliest technology originated from the United States and Japan, and was mainly used in the military. With the iterative development of technology, it began to be applied to the civilian market and applied in industries such as optoelectronics and communications. With the development of my country's national defense industry and optoelectronic manufacturing industry, the industry has begun to increase the demand for high-power lasers, and people have also begun to conduct research on high-power semiconductor laser devices. During the research, it was discovered that the light quality of traditional semiconductor lasers could no longer meet the needs of people. In order to increase the output power of semiconductor lasers, people began to continuously improve and analyze. During the research, it was found that half of the electric energy of the semiconductor laser is converted into heat energy when it is in use. If the semiconductor laser itself does not dissipate heat well, it will directly affect the life and use of the semiconductor laser. Therefore, the heat dissipation problem is urgently needed to be solved by researchers now. One of the problems.
Classification of laser heat dissipation methods
At present, the main heat dissipation methods of lasers are divided into traditional heat dissipation methods and new heat dissipation methods. Traditional heat dissipation methods include: air cooling, semiconductor refrigeration, natural convection heat dissipation, etc., and new heat dissipation methods include: flip chip heat dissipation and microchannel heat dissipation.
The heat dissipation mechanism of semiconductor laser packaging is mainly composed of laser chip, welding layer, heat sink, metal layer and so on. The welding layer in the heat dissipation structure of the semiconductor laser is mainly used to connect the chip and the heat sink by welding. In order to achieve the purpose of reducing thermal resistance when high-power semiconductor lasers are used, some materials with relatively high thermal conductivity, such as gold-tin solder, are often used during soldering. During the entire packaging process, there will be many levels, these levels mainly include: chip, solder layer, heat sink, metal layer, using the heat transfer effect of the heat sink and metal layer to conduct the thermal energy of the laser chip, and finally make the semiconductor laser Form a good heat dissipation to extend the service life of the laser.
The heat dissipation performance of high-power semiconductor lasers is mainly evaluated by thermal resistance and heat flux. In the evaluation, attention should be paid to the heat flux at the limited temperature. If the temperature difference between the two is found to be relatively large during the heat dissipation analysis, condensation will appear on the surface of the laser chip. After this problem occurs, in addition to affecting the optical output power, it will also affect the locking of the wavelength, and even due to the junction. Exposure problems damage the photoelectric performance of the circuit and ultimately affect the reliability. At present, a common method to reduce thermal resistance is to use thermal conductivity materials. The emergence of thermal conductivity materials provides more optimization space for lasers to lower the temperature.
Natural convection heat sink cooling and heat dissipation method Natural convection heat sink cooling and heat dissipation is to use some materials with high thermal conductivity to take away the heat generated, and then dissipate the heat through natural convection.During the research, the scientific and technical personnel also found that the fins can also help dissipate heat, and can maximize the heat transfer rate in the heat dissipation system when dissipating heat. When the temperature is the same, the fin pitch will decrease as the fin height increases. When using the substrate to place the heat sink vertically, the height needs to be appropriately increased, and the heat dissipation effect is improved by increasing the height. Such a heat dissipation method will reduce a lot of costs when used. In actual work, copper or aluminum nitride is often used as a heat sink, but the heat sink method cannot fully meet the heat dissipation needs of high-power semiconductor lasers.
Large channel water cooling method
If you want to lower the temperature of the heat sink, you need to build a channel in the heat sink. If you want to achieve the cooling effect, you need to add a certain water source to this channel, so as not to delay the work of the laser. In response to this, researchers found during their research that the heat dissipation effect of the spoiler structure is better than that of the traditional cavity structure, but the pressure increase in the channel will also occur. Research has found that although large channels are widely used, because of the continuous increase in laser output power, large channels of water cooling can no longer meet the heat dissipation requirements of high-power semiconductor lasers.
Spray cooling method
Spray cooling is to spray the cooling liquid to the heat transfer surface by means of atomization with the help of pressure to achieve the purpose of cooling. The main characteristics of spray cooling are large heat transfer coefficient and low coolant flow. Researchers have found that when using water as the medium and using solid cone nozzles for experiments, the microstructured surface can increase the heat exchange effect. During the study, it was found that the cooling performance of spray cooling is related to the spray flow rate. In addition, the researchers also discovered a spray phase change cooler. During the experiment, the nozzle height in the spray cooling device and the heat dissipation effect are also very closely related.
Concluding remarks
All in all, the two most critical factors to improve the heat dissipation effect are to reduce the thermal resistance of the heat dissipation system and increase the heat flux. When reducing thermal resistance, materials with high thermal conductivity can be used to reduce it; when increasing heat flux, it can be helped by increasing the heat transfer coefficient of the heat dissipation terminal. As the performance indicators of high-power lasers become higher and higher, many methods can no longer meet the application requirements. More researchers need to make continuous efforts to study, so as to find more suitable heat dissipation methods for high-power semiconductor lasers.
