title: Study of SU-8 to make a Ni master-mold: Adhesion, sidewall profile, and removal.
abstract: For disposable microfluidic devices, easy and inexpensive fabrication is essential. Consequently, replication of microfluidic devices, using injection molding or hot embossing, from a master-mold is widely used. However, the conventional master-mold fabrication technique is unsatisfactory in terms of time and costs. In this regard, direct Ni growth (electroplating) from a back plate is promising when the photoresist is well-defined. Here, we demonstrate the use of SU-8 as a photoresist to define the Ni-growth region. We accomplish this application by focusing on the adhesion, the sidewall profile, and the removal of SU-8: the adhesion is enhanced by controlling the exposure dose, the soft-baking time, and by choosing the adhesion-promoting layer; the sidewall profile is regulated by selecting the intensity of each exposed wavelength, showing an aspect ratio of up to 20.9; and, easy removal is achieved by choosing a proper photoresist-stripper. Using the master-mold fabricated by this method, we test the mechanical stability of the features according to the aspect ratio and length; in the hot embossing process, the features are stable in the aspect ratio of up to 5.8 at a length of 200 microm. In addition, the plastic devices fabricated from this method are applied to the passive stop valves, showing a capillary pressure (-0.2 to -7.2 kPa).
authors.affiliation: Biosensor Group, Electronics and Telecommunications Research Institute (ETRI), Daejeon, Korea. yahokim@umich.edu
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Haesik
authors.initials: H
authors.lastname: Yang
authors.forename: Kyuwon
authors.initials: K
authors.lastname: Kim
authors.forename: Yong Taik
authors.initials: YT
authors.lastname: Lim
authors.forename: Hyeon-Bong
authors.initials: HB
authors.lastname: Pyo
mesh_terms: D000268:Adhesiveness; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D009532:Nickel / Q000737:chemistry*
chemical_list: D009532:Nickel