Rapid tooling using SU-8 for injection molding microfluidic components

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Abstract
In this work we present an injection molding tool fabricated using current micromachining techniques. The process was used to fabricate micro fluidic channels in a plastic substrate with depths of approximately 27 micrometers . The process can easily be altered to form channels of varying depths ranging from a few microns to approximately 100 micrometers . The tool was made using a photosensitive epoxy (SU-8) on silicon. Complex two-dimensional micro channel / chamber shapes and intersections are also achievable because the process for defining SU-8 is lithography. Two polymers were successfully used for injection molding the channels, clear rigid polycarbonate and opaque flexible polypropylene. Plastic replications of the inverse pattern of the SU-8 tool were made with the described process. Fabrication time of the tool was approximately 30 minutes and survived without failure, 22 shots for polypropylene and eight shots for polycarbonate (Lexan). Some deformities of the channels were observed and were more pronounced in the PP channels. Channel height was increased by 2-3 micrometers due to a ridge that was formed due to shear forces generated during the release stage of the process. The channel width shrunk approximately 7.9% maximum for polypropylene after release from the mold.

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