Papers by Author: Meng Ju Lin

Abstract: A novel micromachining technology is investigated in this work. Precision machining of micrometer sizes can be achieved by a tool scraping on CNC machine. The knife for scraping with small knife nose with radius of fifty micrometer can scrape surfaces of designed function by path planning of CNC machine. To investigate performance, micro channels are scraped on workpieces by micro shaping. For tool path planning, feeding rate and scraping depth have significant effect on machining performance and depth-to-width ratio. Poly-methyl methacrylate (PMMA) and aluminum alloy are materials for scraping. From the results of experiments, aluminum alloy has better machining performance and smoother scraping surface than PMMA. Smaller scraping depth would induce better performance and size precision. For feeding rate, 800 mm/min is better for PMMA and 500 mm/min is better for aluminum alloy.

Abstract: Cantilever plate structure deposited metal layer is widely used MEMS. Due to mismatch of thermal expansion coefficients between structure and metal layers, residual gradient stress would be induced and deform structure as devices cooling down from process high temperature to room temperature. In this work, constraints effect is investigated. There are three constraints discussed and could be fabricated by back etching, isotropic wet etching, and anisotropic dry etching. For detail analysis, finite element method is used to analyze. Different width and length of structure sizes are used to discuss constraint effect. From the results, it is found different constraint would affect deformation. Under the same structure sizes, flat surface constraint has the largest deformation. And ICP etching constraint has the smallest deformation. Due to mechanics behavior of plate being much different comparing to beam, deformation of plate is no long parabolic shape in length direction. There are complex deformations in width direction. It is also found the deformation is determined by mechanics behavior on constraints. Width and constraint types have no significant on deformation when length is large at free end and middle section. And length has no significant effect on deformation for ICP and backside etching at clamped end. Temperature would induce increasing deformation linearly at free end and middle section.

Abstract: Pulse heated reflow soldering is widely used as junction methods of electronic devices such as ACF, HSC, FPC, PCB, TCP, and FFC. Hot bars are the devices used in pulsed heated reflow method to heat and melt the solder materials between devices and wire becoming a junction. Therefore the performance is determined by the welding properties. The welding time, temperature and induced pressure are important factors affecting welding property. And the temperature has the significant effect due to electricity and mechanical property of solder being determined by welding temperature. However, the consistency of temperature is hard to achieve due to complex coupling of driving current, materials property, heat generation, heat conduction and hot bar shape. In this work, different shapes of hot bat are designed to obtain the temperature consistency. Due to the welding requirement, the heating process is a two steps process. And the hot bar is heated by electric current from power supply with feedback control. For assembly purpose, the hot bar is designed as a rectangular plate with circular holes near the other side respect to the heating edge to fasten the hot bar on the welding machine. And the hot bar with polygon hole in the center part would induce the uniform temperature distribution. Four dimensions of the hot bar determine the shape and investigate the temperature consistency: polygon’s sizes and its positions. Some experiments are made to measure the temperature distribution. The results show the shape has significant effect on temperature consistency. Changing the polygon hole positions will alter the temperature distribution. The central part of heating edge will hotter than both ending part initially. And in some cases, during the heating process, the both ending part will have cooler, hotter, and cooler temperature that central part with respect to heating time. The polygon hole sizes have also significant effect on the temperature distribution. They have the similar temperature distribution phenomena as positions effect. Therefore, from the experiments and analysis, the hot bar could have more uniform temperature distribution by shape design. And it is also found the temperature distribution would induce thermal residual stress and deform the hot bar.

Abstract: There are two kinds of microsprings often used: box microsprings and zig-zag (serpentine) microsprings. Box microsprings are considered with larger spring constant k and more symmetric structure keeping balance than zig-zag microspring. Density of spring number, N, is defined as the numbers of turns within a constant total spring length to investigate performance of box microspring. With applying the same force, the relation between spring constants and microspring sizes are discussed. Under different size parameters of box microsprings: B, W, T, and L, the spring constants decrease like exponential decay and approach a limit value as density of spring number increasing. The results show density of spring number has significant effect on spring constant. Rate of change on spring constant, Kt, is defined as the ratio of spring constant between N=1 and N=10. It means normalization of spring constant that increase density of spring number from minimum to maximum. The results show Kt decreases when B and W increase and increase as T and L increasing. Therefore, the spring constant is coupled affected by different size parameters due to different tendency as results shown. Such that the results can apply in microspring design by adjusting these size parameters to obtain the spring constant.

Abstract: As depositing layers with different thermal expansion coefficients, the residual gradient stress will cause the structure deformed. The deformation of structure in the free ending, middle section, and clamped end are detail investigated. It is found the clamped end often has complex deformation shape. The warpage due to buckling is found. The results show if the thickness of structure is much larger than above deposing layer, warpage will hardly happen and the free ending will have more flat region. As the thickness of structure layer being not much larger than above deposing layer, the warpage happens and the free ending is parabolic shape. In the clamped end, the complex deformation even is concave shape in the center part but protruding shape in the side region. The larger temperature difference will be more easily warpage and be no more flat. The results also show that as the ratio of length to width decreasing, seriously warpage and complex deformation happens. The free ending may be a little protruding shape. However, if the ratio of length to width is larger, the free ending will have concave shape.

Abstract: Deformable focusing micromirror is one of the important optical MEMS devices. The focusing length is determined by the profile of the micromirror surface. For uniform deformation, based on bulk microfabrication of isotropic etching and wafer bonding, a novel micro electrostatic deformable focusing mirror actuated by hemispherical electrode is designed and analyzed. Due to the coupling between elastic and electrostatic force, numerical method of finite element using ANASYS software is used to analyze the deformations and stresses of different structure sizes. The phenomenon that structures deform abruptly fast due to nonlinear increasing electrostatic force called pull-in is also discussed. Using the least square method, the profile of micro focusing mirror can be curve fitting as a parabola. And the focal length can be obtained. The results show deformation increases nonlinearly as applying voltages increasing. The stresses increase linearly when thickness also increase but nonlinearly when radius of mirror increases. The maximum stress happens in the region of bounded. The focal length decreases quasi-linearly as applying voltage increases. The mirror sizes and gaps have effect on pull-in voltages. Larger gap and smaller mirror radius will cause larger pull-in voltage.

Abstract: During depositing a thin film as a structure layer, residual stress from thermal treatment of depositing process will cause deformation after release. Thus the yield ratio and deformation of the devices may be lowered. This work investigates the effect of sacrificial layer on deformation by residual stress causing when depositing a thin film as structure layer. A model is established by using theory of plates-and-shells to investigate the deformation caused by residual stress when the structure layers of the devices are center-anchored circular plate. Theoretically, it is found that the deformation would happen when depositing structure layer under higher temperature. And from the analysis, the thicker structure plate will cause less deformation. When the thickness of the structure layer is larger than 3μm , the maximum deformation will reduce to the order of μm. Furthermore, four cases of different sacrificial layer types and temperature distribution with effect on deformation are discussed. If the thickness of the structure layer is above 5μm, the deformation caused by residual stress is not so important. And it is found that if the thickness of structure layer is 10μm order or above, the residual stress effect on deformation can be neglected. It is found the sacrificial layer will affect the deformation. But it is found that with the same structure layer thickness, as the sacrificial layer thickness increasing, the four cases have different effect on deformation. The in-plane dimension effect is also considered. When the in-plane dimension of sacrificial layer is above 20 times of outer radius, the in-plane dimension effect is neglected and can considered as an infinite dimension.