Study On Free-form Gray-scale Mask Design And Microneedle Fabrication Process

With the rapid development of micro electro mechanical system (MEMS), the existing2D and quasi-3D process technology can’t meet the requirements of MEMS micro device types and performance, thus new3D micro-processing technology is urgent to develop. At present, there are a variety of micro machining technologies which can realize the fabrication of complex3D microstructures, such as micro-EDM, micro milling technology,3D laser micro technology,3D micro-molding and so on. But the processing methods mentioned above can only realize the single-piece production. Therefore, the study on3D micro-processing technology which can realize mass production has great significance in the field of MEMS research development and application. Gray-scale lithography and back-side exposure micro forming technology are the effective methods to fabricate3D micro structures. The design of gray-scale mask is an important part of the gray-scale lithography. Limited by the design of free-form surface gray-scale mask,3D micro-structure fabricated by using gray-scale lithography is currently restricted to structures with elementary analytic surfaces, such as cambered surface, spherical surface, and3D micro structures which contain free-form surface have not been realized yet. Back-side exposure diffraction method is one of the ways which can realize batch production of microneedles. However, due to the lack of specific theoretical research, the mechanism of the back-side exposure diffraction method is still unclear. Therefore, microneedles fabricated by this method still have some problems. For example, the microneedle tip is not small enough, and the tilt angle could be bigger. This paper studies the design algorithm of free-form surface gray-scale mask and back-side exposure diffraction microneedle forming technology.Based on the linear interpolation approximation tool path generation principle in Computer Aided Manufacturing (CAM), the coding principle of gray-scale lithography and the basic principles of the paving method, a novel algorithm which is suitable for free form surface gray-scale mask design is proposed in this paper. Pulse width and pulse density joint modulation are used in the design system, and combined with the modified paving method to generate the gray masks.The program of the algorithms is implemented by Visual C++and secondary development tool ObjectARX of AutoCAD development platform in Visual Studio2008(VS2008) development environment. Microsoft Foundation Classes(MFC) were used to complete operation interface design of gray-scale mask system. The operation interface can achieve the function of menu selection, data input and display, looking up operating steps, precautions and help documents.Four examples are given out to verify the mask design system. Analysis results show that the algorithm is an effective way to design free-form surface gray-scale mask. The research work in this paper provides technique accumulation for fabrication of3D micro structures with free-form surfaces.In this paper, a circular aperture diffraction simulation program is built by using the scalar angular spectrum theory, and the principle of back-side exposure diffraction method is perfected. According to the theory, a series of experiments are carried out to probe into the process parameters of back-side exposure diffraction method. The microneedles fabricated in this paper have a smaller tip and bigger tilt angle than the microneedles fabricated by other researchers using the same method. The research work in this paper accumulates experience for further development of back-side exposure microneedle molding technology.