微热压印成型过程缺陷研究

Defects in micro hot embossing process

为了获得更好的压印质量,对聚合物微热压印成品缺陷产生的原因进行了研究.采用有限元法(FEM)模拟冷却阶段和脱模阶段产生的缺陷,分析结果显示,由于聚合物和模具间不同的热膨胀系数,在冷却阶段极易产生很大的热应力集中,而一直保持压印力将会加剧应力集中效应,导致微结构在底部出现断裂.在脱模阶段由于模具和聚合物表面黏附作用的影响,高深宽比结构脱模时容易产生断裂、颈缩现象.手动脱模时容易造成微结构产生倾斜,而常规的脱模装置会造成微结构产生翘曲变形,影响成品质量。根据分析结果设计了气动自动脱模装置,并对压印工艺进行了优化,在随后的实验中成功制得了高质量的高深宽比微结构.

The reason causing the structure defects induced in micro hot embossing process was investigated to get better product quality. The defects in the cooling and demolding step were analyzed with finite element method （FEM）. The simulation results showed that large thermal stress concentration can be found in the cooling step due to the different coefficients of thermal expansion between the polymer and the mold, while keeping imprint pressure will aggravate the phenomenon and result in damage at the bottom of micro patterns. Fracture and necking can be easily induced by the adhesion between the polymer and the mold when demolding high aspect ratio patterns. Incline structures can be found when using manual demolding and wrap structure can be caused when using common demolding device. Hot embossing process was optimized and a new pneumatic demolding device was designed. Successful fabrication of fine patterns with high aspect ratio verified the improvements.