PDMS辅助热回流成型特点的仿真分析

Simulation Analysis of Characteristics of PDMS Assisted Thermal Reflow Forming

PDMS辅助热回流方法通过引入PDMS溶液,实现了高填充因子的球面和柱面等微结构阵列的加工。为了进一步拓展该方法的应用,需要借助仿真模型对该方法的成型特点进行分析。PDMS辅助热回流过程是一个在界面张力驱动下的流动过程,数值模型的建立主要基于流体动力学的基本方程。在此基础上,再利用CSF模型将界面张力引入到数值模型中,利用VOF模型仿真多相流动系统并计算两相的交界面,求解过程借助于商用流体动力学计算软件ANSYS-Fluent。基于仿真模型分析了高宽比和接触角对PDMS辅助热回流底部边缘特性的影响以及高宽比对该方法形状保持特性的影响。结果表明,该方法的底部边缘限制特性基本不受结构高宽比和接触角的影响,呈现出了很好的底部边缘限制特性;该方法对倾斜柱面结构的形状保持特性随着结构高宽比的增加逐渐变差,倾斜柱面结构出现了明显的回弹现象。

The PDMS-assisted thermal reflow method achieved the fabrication of spherical and cylindrical microstructure arrays with high fill factors by introducing PDMS solutions.In order to further expand the application of this method,it was necessary to analyze the forming characteristics of this method with the help of simulation models.The PDMS-assisted thermal reflow process was a flow process driven by interfacial tension,the numerical model was mainly established by the basic equations of fluid dynamics.Based on this,the CSF model was used to introduce the interfacial tension into the numerical model,the VOF model was used to simulate the multiphase flow system and calculate the interface between the two phases,the solution process was assisted by the commercial fluid dynamics calculation software ANSYS-Fluent.Based on the simulation model,the effects of aspect ratio and contact angle on the edge constraint characteristics of PDMS-assisted thermal reflow were analyzed and the influence of aspect ratio on the shape retention characteristics of the method were also analyzed.The results showed that the bottom edge constraint characteristic of this method was basically not affected by the aspect ratio and contact angle of the structure,and showed a good bottom edge constraint characteristic.The shape retention characteristic for tilted cylinder microstructures of PDMS-assisted thermal reflow was getting worse as the increasing of aspect ratio of the microstructure,and the tilted cylindrical structure had the obvious rebound phenomenon.