Polymer Stencil Printing for High-Throughput Fabrication of Metamaterials

Abstract

In this thesis report, the potential for high-throughput fabrication of micromechanical metamaterials is studied. Metamaterials are structures typically consisting of repetitive micrometre-sized features that introduce new and extraordinary ‘material’ properties. However, up to now these structures are predominantly fabricated with slow 3D-print fabrication techniques. In this work, a range of micromechanical metamaterial designs are closely studied for their design aspects, alongside an investigation towards the high-throughput opportunities of mechanical contact-based fabrication techniques like nano imprint lithography and microtransfer moulding. What is missing from current research, is the connection between the design attributes of micromechanical metamaterials and the capabilities of high-throughput micrometre-level fabrication techniques.

Here I showthat micromechanical metamaterials can be broken down into geometric elements and eventually elementary material transformations that can be directly linked to fabrication techniques with high-throughput potential. These material transformations can be used to form several fabrication process flows. During this breakdown, stencil printing emerged as a compelling fabrication technique for high-throughput fabrication of thin intricate 2½D features. At this moment little is known about the prospects for stencil printing with polymeric materials because stencil printing has its origins in printed circuit board (PCB) fabrication. By performing experiments on the most influential parameters of ordinary PCB stencil printing found in literature and applying these parameters to polymer stencil printing, an understanding of the operating mechanisms is obtained. It is exhibited that by tweaking parameters such as viscosity, wettability,
stencil design and substrate temperature, stencil printing with polymers like polydimethylsiloxane (PDMS) can be transformed from an ill-defined mess to a successful replication of the designed laser-cut stencil. The achieved stencil print shows good replication with a mean line width of 638 &m with a standard deviation of 20.8 &m against a 585 &m line width of the laser-cut stencil. The key to this rewarding transformation is the mixing of polytetrafluoroethylene (PTFE) into the PDMS matrix in a 50/50 wt% mixing ratio.