In recent years, various micromachining techniques have been applied to the production of mechanical products such as surface micromachining, microfabrication, excimer laser etching, LIGA, and precision machining. There are many ways to achieve surface micro-machining, or to improve from traditional precision machining (such as diamond lathes, micro-drilling machines, micro-grinders, etc.), or from special processing technologies (such as laser processing, ion beam processing, etc.), but More based on semiconductor manufacturing technology; silicon substrate microfabrication generally uses etching (etching) methods, including chemical etching, plasma etching and reactive sputtering etching; LIGA technology is based on X-ray lithography Three-dimensional microstructure manufacturing process, including: deep etching X-ray lithography, electroforming and injection molding replication; excimer laser etching is a new technology emerging in the world in recent years, used to make high aspect ratio polymerization The micro-mechanical structure of the material, the microstructure made by this technology has the advantages of large aspect ratio, high precision and neat edges; precision machining technology uses the tool to change the shape of the material or destroy the surface layer of the material, and remove it in the form of chips to achieve Required shapes, such as turning and milling of single crystal diamond tools, micro-drilling techniques for micro-twist drills and micro-grinding techniques Since all of the above micromachining technologies have their own advantages and disadvantages, and the form, function and application of the microstructures to be manufactured are different, it is necessary to analyze and compare them in specific production practices in order to select the best. Processing Technology. 2 principle and characteristics of micro heat pump The micro heat pump is based on the working principle of the traditional heat pump, using MEMS micromachining technology to produce the various components of the heat pump system, and integrating these components and their sensors, controllers, power supplies, etc. into a tiny machine in a small volume range. The miniaturization technology of the micro heat pump is based on the enhanced heat and mass transfer caused by the flow of liquid in the microchannel. Compared with the conventional heat pump device, the micro heat pump uses many parallel microchannels, so that the volume and weight of the heat pump device can be fundamentally Get zoomed out. The main characteristics of micro heat exchangers are as follows: (1) The performance of the micro heat pump is significantly improved due to the good heat and mass transfer performance of the liquid flowing in the microchannel. We can simply see from the definition of heat transfer coefficient, a = C / d, C is generally Changshu in laminar flow, so the smaller the feature size d, the greater the heat transfer coefficient. The relationship between the water velocity (mass flow rate) of the flow channel and the heating power in the micro heat exchangers with different diameters of the three hydraulic channels, the heat transfer power between the fluids increases as the hydraulic diameter of the channel decreases. (2) Micro heat pumps make distributed air conditioning possible and easier to adjust. This reduces the loss of piping and circulation. (3) Micro heat pump processing is difficult, and the processing precision is extremely high. However, with the development of current MEMS technology, the production of micro heat pumps has become possible. 3Micro heat pump system based on MEMS technology The micro-steam compression heat pump system mainly includes the following components: a micro compressor, a micro heat exchanger and a throttling device. Microcapillaries can be used for the throttling device. Therefore, the manufacture of the micro heat pump is mainly the manufacture of micro compressors and micro heat exchangers. 3.1 Micro Compressor Micro compressors mostly use rotary compressors. The rotary compressor has no reciprocating transmission mechanism, does not require an inhalation valve, has few components, is simple in structure, easy to manufacture, has low cost, and is easy to operate, has a long maintenance cycle, and is easy to automate. In order to meet the volume and weight requirements, ASPEN manufactures a micro-rotor compressor for their micro heat pump system using precision machining technology. As shown in Figure 2, the compressor can produce 300W of cooling capacity in a 38 environment. About 2 inches, 27 inches long, 13 pounds, refrigerant: R134a, voltage: 24V or 12VDC. Beijing University of Technology uses micro-EDM technology to manufacture micro rotary compressors. The compressor is made of cast iron and aluminum alloy and weighs 400g. It can generate 300W cooling capacity in 400 environment. Refrigerant: R22, voltage: 24V or 12VDC. 3.2 micro heat exchanger The micro-evaporator developed by the Pacific Northwest National Laboratory (PNNL) includes a copper underlayer, a patterned silicon layer and a top layer of borosilicate glass. The silicon layer is processed by etching, including fins and microchannels to improve heat transfer. Efficiency, microchannel width is about 50~80m, fin height is about 30m. The Royal Norwegian Academy of Sciences (SINTEF) has developed a miniature condenser using MEMS technology. The channel of the condenser is made of silicon. The thermal conductivity and density of silicon are close to that of aluminum, and its tensile strength is stronger than that of steel. The microchannel is made by photolithography. When it is prepared, the mask is covered on the silicon wafer as needed, and tetramethylammonium hydroxide is used as an etchant. The upper and lower surfaces of the silicon layer are bonded to the borosilicate glass plate. The size of the water channel is shown in the enlarged view of C in Fig. 5, the upper side is 1017m, the bottom side is 500m, and the height is 140m. 3.3 Micro heat pump system ASPEN developed a vapor compression miniature heat pump for the US military. The system can generate 300W of cooling capacity in a 38 environment, the total refrigeration system is about 6 pounds, and the cooling system size is 241mm1778mm9398mm. 4 Conclusions and prospects At present, the micro heat pump is still in the laboratory development stage, and the processing method of the core component micro compressor is mostly limited to the precision machining technology, but the microchannel heat exchanger of micron order has been processed by the etching technology. With the development of MEMS technology and its continuous application in mechanical products, the manufacture of micro heat pumps will be more perfect. Due to its high efficiency and light weight performance advantages, micro heat pumps in military, aerospace, medical and other fields will be displayed. Broad application prospects, in addition, the application of MEMS technology in mechanical products will certainly drive the continuous advancement of MEMS technology, making it more suitable for the development needs of modern industry.
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Application Analysis of MEMS Technology
1 Comparison of several micro-manufacturing technologies