【作者】 贺永；

【导师】 陈子辰； 傅建中；

【作者基本信息】 浙江大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 聚合物微热压成型技术作为一种成本低、效率高、质量优的微细加工方法，已成为微纳机电系统加工技术中的一种重要方法也是目前的研究热点。本学位论文结合国家863计划项目“面向微流控芯片的微模具制造装备研究”(No.2002AA421150)及教育部博士点基金“聚合物三维微流体芯片制造新方法及工艺研究”(No.20030335091)对微热压成型过程理论及其装备技术进行了研究。针对项目的研究任务和国内外研究现状，本论文积极吸收相关学科的新思想、新技术，采用理论研究、计算机仿真与实验研究相结合的方法，以微热压技术中亟需解决的问题为研究对象，通过对聚合物微热压成型的机理及微热压装备关键技术的研究，建立了压印过程模型、揭示了微压印过程中聚合物流变特性与压印质量及压印效率间的内在关系、提出了模具拓扑优化策略、优化了压印工艺、研发了热压装备。论文的主要工作如下：第一章，阐述了本学位论文的研究背景与意义，详细介绍了国内外在热压成型技术机理、工艺及成型装备等领域的研究现状。在此基础之上，提出了论文的主要研究内容。第二章，阐述微热压中聚合物从宏观力学表征到微观结构变化的变形机理，引入了聚合物微加工中宏观力学表征的三种现象，时间依赖性、温度依赖性及时温等效转换性。基于聚合物的网络理论及分子理论，从微观角度解释了聚合物压印过程的流变行为及聚合物分子运动机理，为后续章节的理论、仿真及实验研究奠定理论基础。第三章，通过对微流控芯片热压过程进行受力分析，建立了基于流变理论的微流控芯片热压过程模型。为了更好地表征压印过程的粘弹性力学行为，将聚合物的材料常数n修正为时间的函数。基于流体NS方程对压印过程进行了推导，所得结论和基于流变理论的结果吻合，从另一方面验证了模型的正确性。在微流控芯片热压过程模型的基础上，对常规微热压过程进行了建模研究，通过对两组流动进行耦合建立了微热压过程模型，获得了压印完成所需时间及聚合物微结构高度和时间的变化关系。第四章，对模具拓扑结构与聚合物流动特性间的关系进行了系统的研究。采用DEFORM软件分析了热压过程聚合物流动的影响要素，揭示了模具占空比、模具深宽比、模具宽厚比、模具位姿变化时所呈现出不同的流动形貌及流动特性。解释了不等温压印过程和等温压印过程流动行为不同的原因。针对压印过程易出现的填充效率不佳以及热压过程本质上是一个模腔非封闭的聚合物流动问题，提出了模具结构拓扑优化策略，通过在模具边缘布置一些流动坝，达到降低边界处聚合物流动率、促进聚合物有效填充的目的。仿真结果表明优化策略对促进聚合物填充具有很好的效果。第五章，系统的分析了热压成型过程缺陷产生原因，使用ANSYS软件对冷却及脱模阶段聚合物的受力状况进行了有限元模拟分析。分析结果显示冷却阶段一直保持的压印力会造成模具及聚合物微结构应力集中，是形成模具断裂、微结构破损等现象的一个重要原因。首次研究了脱模方向对脱模质量的影响，由于微小的脱模方向偏差就可能引入很大的切向力而导致微结构的破坏。为了确保正确的脱模方向，设计了新型的自动脱模机构。提出了压印过程优化工艺，通过在冷却过程中缓慢减少压印力，直至冷却到脱模温度时释放完毕。该优化工艺不但可以有效的降低压印力造成的应力集中，还可以避免由于过早释放压印力而导致结构回弹及变形。第六章，在理论及仿真研究的基础上，针对现有压印装备中存在的一些问题，自行设计了基于帕尔帖效应的聚合物微热压装备。采用半导体制冷片进行升降温，在降温时辅助以水流带走半导体制冷片表面热量，设计了精密温控的模糊PID控制器，使得热压装备的温度控制精度达到0.2℃，升降温速率达1℃／s，能大幅度提高压印效率。使用液压方式施加压强，降低了压印过程的压力不均匀分布，提高了压印品质。第七章，为了验证自行设计的微热压装备的性能，进行了温度、压力及真空度控制精度的实验研究，实验结果表明热压装备能较好的满足设计要求。选择两种典型的微结构，微流控芯片及液晶导光板进行了压印实验研究，分析了各个工艺参数对成型后质量的影响。通过分析微流控芯片尺寸误差，得出在低温下压印所产生的回弹是微流道尺寸误差的主要原因。采用正交表分析了导光板热压时工艺参数对压印质量的影响，获得了优化的压印参数。第八章，对论文的主要研究工作和创新点作了总结，并对未来的研究工作进行了展望。更多还原

【Abstract】 Fabrication of micro structures with hot embossing is an important technology due to its numerousadvantages such as low cost, high efficiency and parallel operation. Supported by the National Hi-TechResearch and Development Program (863) of China—"Research on the manufacturing device of the micromold used in microfluidic chips" (No. 2002AA421150) and the Research Foundation of DoctorialProject—"Study of new methods and process of manufacturing of 3D polymer microfluidic chips"(RFDP20030335091), actively absorbed the original thoughts, new theories and technologies of correlativesubjects, the model in embossing process was established, the rheological character of polymer with respectto the imprint quality and the imprint efficiency was expounded, the strategy of mold topology optimizationof structures was proposed and hot embossing process was optimized with theoretical analysis, numericalsimulation and experiments.In chapter 1, the background and significance of the research are introduced, the development trend andthe current research situations of hot embossing mechanism, hot embossing process and the device of hotembossing were expatiated, and then the study contents of this dissertation were proposed.In chapter 2, the flow mechanism of the polymer in hot embossing was described from the mechanicalbehavior in macroscopy to the evolvement of structure in microscopy. Three phenomena in macroscopy,dependency of time, dependency of temperature and time temperature equivalence principle were imported.Based on the polymer network theories and the molecule theories, the rheological behavior of polymer and itsmolecule movement were explained, which established the theoretical base of the theorical analysis,numerical simulation and experiment study in the following chapters.In chapter 3, the mechanical model of microfluidic chip in hot embossing based on the rhologicalanalysis was established with theoretical analysis and numerical simulation. For better describing theviscoelastic behavior in hot embossing process, the rule of the polymer material’s constant n changing withtime was acquired. The result deducted from the Navier-Stokes (NS) equation accords with that of rhologicalanalysis, which proves the right of this model on the other hand. Based on the hot embossing model ofmicrofluidic chips, normal hot embossing process was modeled with the coupling of two flow fields. Thetime required for completely filling and the time development of micro pattern height were got.In chapter 4, the change of mold structures with respect to flow behavior in the embossing step wasstudied systematically. The factors influencing the polymer flow were analyzed with the DEFORM code. Thedifferent flow profile and flow character with the different mold duty ratio, aspect ratio, width to thicknessratio and the mold attitude were expounded. The difference of flow character between isothermal hotembossing process and non-isothermal hot embossing process was investigated and the reason was analyzed.The strategy of topology optimization of mold structures was proposed to improve the filling efficiency in hot embossing process. With the arrangement of some flow barriers at the mold boundary, the flow speed at theboundary can be decreased and the filling efficiency can be accelerated. Numerical simulation results showthat this strategy has better effect on the accelerating filling speed.In chapter 5, the reason that caused the defects in hot embossing was studied systemically. The finiteelement method (FEM) was used to analyze the cooling step and the demolding step. The numericalsimulation results show that profile precision is largely influenced by the topology of mold structures duringthe embossing step. Inadequate holding time will result in low pattern fidelity. Inapposite demoldingtemperature could induce large thermal stress at the bottom of the micro pattern, while keeping imprintpressure during the cooling step will aggravate this phenomenon. The demolding direction with respect to theproduct quality was studied in the first time, and the large lateral stress will be induced by the little error ofthe demolding direction, then the fracture and other defects would happen. To keep the right demoldingdirection, a new pneumatic demolding device was designed. The optimization process of hot embossing wasproposed with the decreasing the imprint pressure in the cooling step until rearching the demoldingtemperature. This optimized process can not only reduce the stress concentration, but also avoid the recoveryand the distortion of micro structures induce by releasing the imprint pressure too early.In chapter 6, a hot embossing system based on the Peltier effect was designed to improve some problemsthat existing in the current hot embossing device with the help of theoretical analysis and numericalsimulation. Thermoelectric cooler is used for heating/cooling and the heat of the cooler surface is taken awayby the flowing water when cooling. A fuzzy-PID control was designed for the precision control oftemperature. The temperature control precision can reach 0.2℃and temperature increasing/decreasing speedis larger than 1℃/s. The imprint pressure is applied with hydraulic pressure system, which can decrease thenon-uniform distribution of pressure in the embossing step and can improve the imprint quality.In chapter 7, the control precision of the temperature, the pressure and the vacuum was tested to verifythe performance of self-designed hot embossing device. The experiment results show the device accords wellwith the design specification. Two types of micro structures, microfluidic chips and the light guide plate werechosen as the experimential object and the process parameters with respect to the imprint quality wereanalyzed. By analyzing the error of channel sizes, the main reason of the error was assumed as the recoveryof polymer. Orthogonal method was used in the analysis of relationship between the process parameters andthe imprint quality. Then the optimized process parameters were got.In chapter 8, the study contents and conclusions of the dissertation have been summarized and thefurther research works have been forecast.更多还原