A Study of Micro-Mechanical Punching for the Interconnection of Polymer Microfluidic Devices
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The design of a microfluidic device can become encumbered when there is a desire to include multiple functional features. To avoid these complications one alternative is the modular design where independent devices are assembled into a system. To achieve this design structures that interconnect the modules are needed such as a micro- through-hole. Through-holes have been conventionally fabricated at the macroscale with mechanical punching. There has been a significant focus on the micro- mechanically punching of metallic foils and attention to polymeric foils is limited. In this study the generation of micro-through-holes was investigated with experiments and numerical modeling. The micro- mechanical punching process was integrated with double-sided hot embossing. A pair of mold inserts were designed with features for the fabrication of through-hole, and features for a passive alignment step. Features for mechanical punching were designed to provide five levels of punch to die clearances, and a set of pins with an aspect ratio of 1:1. The mold inserts were applied to fabricate through-holes on a sheet of thermoplastic polymer. The resulting through-holes were characterized to observe the effect of the selected clearances. The results of the experiments and the simulations showed that clearance has a significant effect on the micro-punching process. As clearance was increased it allowed more substrate material to flow into the die. When more material flowed into the die it would affect the ability to generate a fracture and its propagation through the substrate. This would have a significant influence on the success of generating a through-hole and its subsequent dimensions and the topography of the sidewalls.