Contact printing is one of the major fabrication methods in printed electronics fabrication due to its low cost, large fabrication area and minimal material waste. However, effective ink transfer in contact printing is essential in printed electronics fabrication. Due to high printing quality requirement of printed electronics, controllable ink transfer in contact printing is critical. Two typical contact printing processes used in printed electronics were conducted by soft PDMS stamp and hard silicon stamp by custom made contact printing machine. Problems are addressed from those printing experiments and surface energy is found to be one of the key factors in controlling ink transfer between stamp and substrate. To enhance the ink transfer efficiency during contact printing, a strategy...[ Read more ]

Contact printing is one of the major fabrication methods in printed electronics fabrication due to its low cost, large fabrication area and minimal material waste. However, effective ink transfer in contact printing is essential in printed electronics fabrication. Due to high printing quality requirement of printed electronics, controllable ink transfer in contact printing is critical. Two typical contact printing processes used in printed electronics were conducted by soft PDMS stamp and hard silicon stamp by custom made contact printing machine. Problems are addressed from those printing experiments and surface energy is found to be one of the key factors in controlling ink transfer between stamp and substrate. To enhance the ink transfer efficiency during contact printing, a strategy based on stimuli responsive material coating was investigated. The stimuli responsive material modifies the stamp surface such that ink can be picked up and transferred in a more efficient fashion based on surface energy change triggers by different stimuli. Photo-responsive and electrical-responsive materials were selected for investigation because of fast response, reversible change in contact angle, ease of application and compatibility with contact printing process. In this thesis, these two types of materials were tested out for their ability as effective surface coating on printing stamp surface to facilitate the ink transfer process. Free-radical initiators & azobenzene material were selected as photo-responsive coating candidates. Different variation of photo-responsive materials were synthesized and tested for wettability change under UV irradiation. Low and irreversible contact angle change was found on these material coated surfaces. The key issue with poor contact angle modulation is most likely the energy field is too weak to give the photo-responsive material a significant change in wetting. The conversion into surface energy is not efficient. Poor contact angle modulation results limit their application on contact printing stamp as stimuli responsive coating. On the other hand, electrowetting provides a large reversible contact angle change which is adequate for contact printing process. Using barium strontium titanate (Ba_0.5Sr_0.5TiO₃) as dielectric provided a reversible 30° contact angle change under 60V. A simple printing setup using electrowetting printing stamp can show 100% material transfer and it confirms surface energy plays an important role in contact printing.