Research On MEMS Self-Assembly Powered By Surface Tension And Its Precision Control Technology

As a cross synthesis of front technology of multi-subjects, the development ofMicro-Electro-Mechanical-System (MEMS) technique is in?uenced by some factorssuch as: micro machining,micro assembly,material science and packaging reliabilityand so on. Microstructure which manufactured through micro machining technologyoften need to be assembled to construct a system.Further development of MEMS islimited by the defects of low assembly e?ciency and low precision of traditional microassembly methods to some degree. MEMS solder self-assembly powered by surfacetension brought forward in the project shows prominent predominance such as highassembly e?ciency and high precision, which meet the requirement of mass productionof MEMS, so it can provide some application value. This dissertation studies the self-assembly technology from three aspects including self-assembly mechanism research,dynamic self-assembly model development and precision control through finite elementmethod.Firstly, studying the theory foundation related to the MSMS solder self-assembly,such as: surface tension, Laplace pressure, wetting theory, self-alignment and minimalenergy principle and so on, meanwhile, the feasibility and rationality of self-assemblypowered by surface tension is introduced. Combined with the relation between Laplacepressure, surface tension and movement of microstructure, the two and three dimensionself-assembly geometric model developed previously is deduced and the relationshipbetween solder volume, ration of length to width of pad and self-assembly angle isobtained.Secondly, aiming at the limitation of low precision of simulation results of twoand three dimension geometric model and three dimension static model for MEMSself-assembly developed previously, the dynamic self-assembly model is developed bySurface Evolver in this dissertation for the first time. The self-assembly angle is setas an optimization parameter in this model, as a result, the assembly angle is changedduring the iteration process till reaching the minimal system energy state which canimprove the calculation speed and simulation precision e?ectively. Then the relation-ship between solder volume, ration of length to width of pad and self-assembly angleis studied exhaustively. The study shows that: the ratio of length to width of padis a key parameter which a?ect the solder configuration and self-assembly precisiongreatly. The relationship curve between the self-assembly angle and the increasingsolder volume is easy to"jump"when the ratio is more than 0.8, which can bring insome assembly angle no easy to be obtained. While the self-assembly angle increaseas the increase of solder volume steadily and no"jump"phenomena existed when the ratio are equal to 0.6 and 0.4, which is good for MEMS self-assembly technology.At last, according to the shortage of thermal distortion and thermal stress distri-bution analysis of microstructure can not be executed in Surface Evolver, the solderconfiguration data are extracted by"C"language and then the model is reconstructedin ANSYS. In order to improve the self-assembly precision, the"hinge"and"self-lock"structure are designed, and then the distortion and stress distribution are ob-tained under the di?erent conditions of"hinge"and"self-lock"boundary conditionthrough the thermal/structure couple analysis. The study shows that:"hinge"and"self-lock"structure can improve the assembly precision e?ectively; what is more, theself-assembly model can provide better synthesis performance when the"hinge"locatedat the end of the movable structure, but the"hinge"and"self-lock"structure canresult in stress concentration and microstructure distortion.High precision, mass assembly technology is required for the development ofMEMS technique, and self-assembly may be a choice in the future. The study re-sult including dynamic self-assembly model, ration of length to width of pad, extractmethod for model data and precision control method in this dissertation may providevaluable reference for the further research in the MEMS self-assembly field.