This paper presents ultrasonic embossing using silicon molds to replicate microstructures on Polymethyl Methacrylate (PMMA) substrates. The pattern of the silicon mold consists of micro grooves with different sizes. The molds were fabricated by wet etching, and both concave and convex types were fabricated. The effects of the processing parameters on replication quality, including average microstructure depth, uniformity and the location-related replication depth were investigated via orthogonal experiments. The results show that the ultrasonic amplitude is the most important parameter for replication depth. The ultrasonic time benefits the accumulation of the heat, so it also influences replication depth. As for ultrasonic force, it has less influence on replication depth but significant influence on replication uniformity. The width of the grooves of the high density patterning molds ranged from 10 to 30 μm, and the center distance between the two microstructures from 20 to 50 μm in our experiments. The concave molds were intended to reach higher replication depth than that of convex molds with the same micro grooves. The average replication depth reached 98 %, and the uniformity on one chip reached 99 % with an area of 11 × 11 mm. All experiments were finished in 60 s, which is more efficient than the hot embossing technique, thus this paper provides a potential method for medium-sized bulk production and rapid fabrication for polymer microcomponents.

A thermal assisted ultrasonic bonding method for poly(methyl methacrylate) (PMMA) microfluidic devices has been presented. The substrates were preheated to 20–30 °C lower than glass transition temperature (Tg) of the polymer. Then low amplitude ultrasonic vibration was employed to generate facial heat at the interface of PMMA substrates. PMMA microfluidic chips were successfully bonded with bulk temperature well below Tg of the material and with pressure two orders lower than conventional thermal bonding, which was of great benefit to reduce the deformation of microstructures. The bonding process was optimized by Taguchi method. This bonding technique showed numerous superiorities including high bonding strength (0.95 MPa), low dimension loss (0.3–0.8%) and short bonding time. Finally, a micromixer was successfully bonded by this method and its performance was demonstrated.

Bonding is a bottleneck for mass-production of polymer microfluidic devices. A novel ultrasonic bonding method for rapid and deformation-free bonding of polymethyl methacrylate (PMMA) microfluidic chips is presented in this paper. Convex structures, usually named energy director in ultrasonic welding, were designed and fabricated around micro-channels and reservoirs on the substrates. Under low amplitude ultrasonic vibration, localized heating was generated only on the interface between energy director and cover plate, with peak temperature lower than Tg (glass transition temperature) of PMMA. With the increasing of temperature, solution of PMMA in isopropanol (IPA) increases and bonding was realized between the contacting surfaces of energy director and cover plate while no solution occurs on the surfaces of other part as their lower temperature. PMMA microfluidic chips with micro-channels of 80 μm × 80 μm were successfully bonded with high strength and low dimension loss using this method.

Hot embossing method was studied for the fabrication of microfluidic microchannels on COP (cyclo-olefin polymer) chip. The ending temperature of heating stage, i.e. embossing reference temperature (Tr), was determined by the viscoelastic property of the COP, according to variable temperature quasi-creep experiments. Taguchi method was used to decide the processing parameters in cooling and demolding stage. The optimized parameters of hot embossing are: embossing reference temperature 143 °C, temperature and pressure holding time 2 min, pressure at cooling and demolding stage 1.6 MPa, the demolding temperature in the lower heating plate 80 °C and temperature difference between the upper and lower heating plate 10 °C. Experiment shows that microchannel fabricated with the above parameters has high repeatability and low substrate deformation, average repeatability is 97.6% in width and 94.3% in depth. Experiments on background fluorescence, electrophoresis, and DNA separation and detection were carried out on COP and PMMA (polymethylmethacrylate) chips, respectively. Compared to the PMMA chip, the COP chip has higher signal to noise ratio, higher electrophoresis efficiency, and lower peak area relative standard deviation (R.S.D.). In separation 6 μg/ml ϕ X174 RF DNA Hinc II, 11 DNA fragments have been identified in less than 2 min on the COP chip, thus it has large application potential in biochemical analysis.