The hottest micro mold processing technology

Micro mold processing technology

application technology and market prospect of micro parts and micro molds

with the progress of micro and nano technology, products continue to develop in the direction of miniaturization, and micro electromechanical systems with characteristic dimensions of micrometers have been highly valued by people. Micro electro mechanical systems (MEMS) technology is a micro electromechanical system integrating micro sensors, actuators, signal processing and control circuits, interface circuits, communication and power supply

in recent years, MEMS has been successively applied to precision machinery, photoelectric communication, image transmission, biochemical medicine, information storage and other fields, such as micro gears, plug-in optical fiber connectors, micro pumps for medicine, light guide plates, microlenses, endoscope parts, microfluidic chips, micro containers for cell culture, and diffraction gratings in rotating sensors (Figure 1). Its wide application is expected

Figure 1 product with microstructure A is micro gear, B is micro lens, C is light guide plate

at present, the concept of micro product has not been accurately defined. From the perspective of micro injection molding, the meaning of micro product is given, that is, micro product should have the following characteristics: the overall structure is small, and its single piece weight is usually only a few milligrams; It has a surface micro structure, that is, the overall size of the product is still ordinary, but the scale of its local micro structure is in the order of microns; Micro precision parts refer to products with arbitrary size but with micron size accuracy. If the size and manufacturing accuracy are limited, the micro mold has the following characteristics: the volume of the formed part reaches 1 cubic millimeter; The micro size ranges from a few microns to hundreds of microns; The surface roughness of the die is 0.1 μ Below m; Mold manufacturing accuracy from 1 μ M to 0.1 μ m。

it is expected that the growth rate of China's MEMS market will accelerate from 2010, and the growth rate is expected to reach 29.2% in 2011

micro mold processing difficulties

micro mold does not necessarily refer to small volume. The traditional mold with large volume but microstructure characteristics is also called micro mold. The manufacturing difficulty of micro mold lies in the processing of micro cavity or micro convex concave structure, while the manufacturing of other structural parts of the mold is basically the same as that of ordinary mold. The forming of micro cavity can be processed on a small metal block, and then the metal block is embedded into the template as an insert and assembled as a whole, which is not only convenient for the micro machining of micro cavity and the replacement of insert, but also can improve the overall life of the mold

the traditional mechanical processing method cannot process the micro mold with too small size or microstructure size, and the dimensional accuracy and surface roughness cannot meet the design requirements of the micro mold. Although the developed lithography technology can meet the requirements of small size and high precision, its wide application is limited by its high manufacturing cost, long processing cycle, complex process flow and other defects

micro mold processing technology has developed rapidly, and there are many kinds

micro mold processing technology has developed rapidly in recent years, and there are many kinds. According to the different processing principles, it can be divided into three categories: optical fabrication technology, such as LIGA technology, UV-LIGA technology, electron beam lithography technology, laser processing technology; Corrosion technology, such as etching technology; Micro machining technology, such as micro turning, micro milling, micro grinding, micro EDM and other traditional machining methods

optical fabrication technology is mainly applied to the processing of parts with micron microstructure, and the processing accuracy is less than 10nm; Micromachining technology is applied to the machining of parts with millimeter microstructure, and the machining accuracy is less than 100nm

ga technology

liga technology is a new optical fabrication technology developed in recent years. Its name comes from German, which means the perfect combination of deep X-ray etching, electroforming and plastic molding. The main process flow is as follows

deep X-ray etching: use synchrotron radiation X-rays to etch photoresist patterns with a large aspect ratio on photoresist hundreds of microns thick, and the aspect ratio generally reaches 100

electroforming and molding: deposit the metal from the electrode into the gap of the photoresist pattern of the base plate until the metal fills the gap of the photoresist pattern. In fact, this process is to convert photoresist patterns into metal patterns with opposite structures. This metal structure can be used as the final product or as a mold for batch replication

injection mold replication: attach the metal mold shell with the substrate and photoresist removed to the metal plate with the injection hole, inject plastic into the cavity from the injection hole, and remove the mold shell after cooling. A plastic structure is left on the metal plate as a micro product

compared with other traditional micro machining technologies, LIGA technology has many advantages: high precision, which can reach sub micron level; High aspect ratio structure can be obtained, which is more than hundreds; The straightness and perpendicularity along the height direction are very good; Suitable for a variety of materials, such as metals, ceramics and polymers. Its disadvantages are: it needs to use expensive synchrotron radiation X-rays, and the cost is high; The obtained shape is cylindrical, which is difficult to machine curved and inclined micro devices; Cannot produce a cavity with a small mouth and a large belly

-liga technology

expensive synchrotron radiation X-rays limit the application of LIGA technology. The quasi LIGA technology, which uses similar process principles to explore low-cost and high aspect ratio, came into being, and derived UV-LIGA technology, laser LIGA technology and DEM technology

UV-LIGA technology suitable for medium thickness photoresist has been widely used. The essence of its technology is to replace the synchrotron radiation X-ray deep exposure of LIGA technology with deep UV deep exposure. Compared with X-ray, the exposure depth of deep ultraviolet ray is much lower, when the PMMA photoresist with thick exposure (greater than 4 μ m) It needs to adopt the method of multiple exposure and multiple development. Now IBM has developed a new negative deep UV photoresist SU-8, which can reduce the number of exposures and get better exposure results. The following is the main process flow of this technology

deep UV exposure: UV is used to etch photoresist patterns on SU-8 photoresist

electroforming and molding: deposit the metal from the electrode into the gap of the photoresist pattern on the bottom plate until the metal fills the gap of the photoresist pattern. This metal structure is used as a mold for batch replication

injection molding replication: Plastic microstructure products opposite to metal microstructure are copied on the metal structure by injection molding. Table 1 Comparison between LIGA technology and UV-LIGA technology

according to table 1, UV-LIGA technology has the advantages of low processing cost and short cycle compared with LIGA technology, but there are deficiencies in processing depth, depth width ratio, side wall perpendicularity and other parameters. When the requirements for the verticality and aspect ratio of the side wall of the cavity are not very high, it can completely replace LIGA technology

at present, the depth of UV LIGA technology in the cavity is less than 100 μ M has been successfully applied in mold making, gradually replacing the traditional machining methods

3. Electron beam lithography

electron beam lithography is a processing technology that uses electron beam to form micro nano structures on photoresist

it requires an exposure machine that generates electron beams. At present, there are mainly two types of exposure machines: direct writing and projection. The direct writing exposure machine directly hits the concentrated electron beam on the substrate with photoresist on the surface, which does not need the expensive mask in the optical lithography process. With the miniaturization of direct writing electron beam lithography machine, direct writing lithography technology will be more and more widely used in scientific research. However, its limitation is that the electron beam is scanning imaging type, and the productivity is very low, which is far from the chip/hour productivity that optical lithography can achieve, so it is difficult to apply to mass production. Because of this, electron beam lithography is generally used to make high-precision masks

4. Etching technology

the so-called etching technology is the process of selectively removing unnecessary materials from the substrate surface by chemical or physical methods. It can be divided into wet method and dry method in mechanism. Wet etching is to soak the silicon wafer in a solution that can react with the etched film, and chemically remove the unwanted film

dry etching is to place the processed substrate in the plasma, and under the bombardment of corrosive and energetic particles, react to generate gaseous substances to remove the etched film. This method is generally anisotropic

5. Micro turning

micro turning is an effective method for machining rotating parts. When machining micro parts, it is required to have a reasonable miniaturized lathe, condition monitoring system, high-speed and high-precision spindle, high-resolution servo feed system, and a turning tool with a small enough blade and high enough hardness. Compared with ordinary turning, micro turning lathes and tools are smaller, and of course, the workpiece is smaller

the Industrial Technology Institute of the Ministry of industry of Japan developed the world's first micro lathe in 1996. The lathe is 32mm long, 25mm wide, 30.5mm high and weighs only 100g; The rated power of the spindle motor is 1.5W and the speed is 10000rpm. It is used to cut brass, and the surface roughness in the feed direction is rz1.5 μ m. Roundness of processed workpiece 2.5 μ m. The minimum processed outer circle diameter is 60 μ m。

a set of micro turning system developed by Kanazawa University in Japan, including micro lathe, control unit, optical micro system and monitor. The machine is 200mm long, the spindle power is 0.5W, and the speed rpm is continuously adjustable; Radial runout 1 μ Within m; Clamping workpiece diameter 0.3mm; The feed resolution of XYZ axis is 4nm; The cutting force is monitored by a mechanical sensor with three directions to improve the feed accuracy of the base course

use the diamond probe tip on the atomic force microscope as a turning tool to machine a diameter of 10 on a brass wire blank with a diameter of 0.3mm μ The cylindrical surface of M is also machined with a length of 120 μ m. Pitch 12.5 μ M

Figure 2 micro lathe

6 Micro milling

micro milling technology mainly uses micro end mills with diameters ranging from tens of microns to one millimeter to carry out micro machining on conventional ultra precision machine tools

because these machine tools are mainly used to process non micro geometric parts with high accuracy, they usually need expensive design and manufacturing processes to achieve the desired accuracy, while for micro parts, they lack the necessary flexibility, high cost and low efficiency. It is urgent to develop and manufacture a miniaturized milling equipment, which has the advantages of space saving, energy saving, easy reorganization and low cost

at present, domestic research on micro milling mainly focuses on machining surface quality, milling force, wear and life of milling cutter, milling state and processing ability of micro parts

the Precision Engineering Research Institute of Harbin Institute of technology has developed the first miniature sleeper in China