Roll-to-roll hot embossing of microstructures
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In this paper we present a new roll-to-roll embossing process allowing the replication of micro patterns with feature sizes down to 0.5 μm. The embossing process can be run in ‘continuous mode’ as well as in ‘discontinuous mode’. Continuous hot embossing is suitable for the continuous output of micro patterned structures. Discontinuous hot embossing has the advantage that it is not accompanied by waste produced during the initial hot embossing phase. This is because in ‘discontinuous mode’, embossing does not start before the foil has reached the target temperature. The foil rests between two parallel heating plates and foil movement and embossing starts only after the part of the foil resting between the heating plates has reached a thermal steady state. A new type of embossing master is used which is based on flexible silicon substrates. The embossing pattern with sub-μm topographic resolution is prepared on silicon wafers by state of the art lithography and dry etching techniques. The wafers are thinned down to a thickness of 40 μm, which guarantees the mechanical flexibility of the embossing masters. Up to 20 individual chips with a size of 20 × 20 mm² were assembled on a roller. Embossing experiments with COC foils showed a good replication of the silicon master structures in the foil. The maximum depth of the embossed holes was about 70% of the master height.
KeywordsChip Thickness Cyclic Olefin Copolymer Emboss Process Silicon Master Master Structure
The work presented was funded by the Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. The authors would like to thank Kai Mrosk for embossing experiments, Anna Ohlander for stamp embossing tests and Daniel Sauer and Thorsten Knoll for providing the AFM micrographs and the confocal microscope measurements, respectively.
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