Publikationsserver der RWTH Aachen University
Fabrication of polymer micro devices by ultrasonic hot embossing
Abstract
dc:descriptionIn this thesis ultrasonic micro hot embossing is shown to be suitable for the fabrication of polymer micro structures and entire devices. Micro structures are generated in a couple of seconds. Similar as in hot embossing, a polymer film is softened by heating and a micro pattern is molded from a metal tool. Heating is achieved with an ultrasonic welding machine generating mechanical vibrations with up to several 10 µm amplitude at a frequency between 20 and 70 kHz. These vibrations are applied to the polymer film by pressing it with the horn of the ultrasonic machine onto the tool. The cyclical deformations of the polymer film generate local heating and melting of the polymer where it is in contact to protruding micro structures on the tool. After turning off the vibrations and cooling of the polymer within a few seconds the micro structure can be de-molded. Micro structures with feature sizes of down to 2 µm were produced this way at 35 kHz. With the same machine a micro channel was sealed by ultrasonic welding with a specially designed tool. The following parameters turned out to control the process significantly: frequency, amplitude, time, pressure, and polymer type. Process limits were observed with respect to the achievable aspect ratio, overall pattern size, and minimum and maximum structure height. The fabrication process is demonstrated by manufacturing micro fluidic devices, such as micro mixers and micro thermal flow sensors, and, corrugated membranes. Ridges on the mixing channel were used to enhance a mixing of two liquids. The micro structure of the ridges was molded onto the mixing channel 20 µm high, 250 µm wide, and orientated at an angle of 45° with respect to the channel walls. The mixing channel was designed 25 mm long, 100 µm high, and 500 µm wide with a Tjunction inlet and an outlet. Testing results show that the ridges decreased the mixing time by a factor of 4. The micro thermal flow sensor consists of a 100 µm high, 500 µm wide, and 1 cm long channel from polypropylene which is crossed by a gold wire with a diameter of 50 µm. The measurement results support theory. The reaction times of the sensor were measured to be 24 ms after switching on and 20 ms after switching off the piezo-actuated micro diaphragm pump at 0.5 Hz. Furthermore, it was shown that this technique can be applied to generate molded interconnect devices (MID) also. A pattern of an electrically conducting metal was generated on a polymer substrate by welding a polymer layer with the metal on top onto the substrate where there were protruding micro structures on the tool. Sharp edges around the protruding structures cut the metal and ensure electrical insulation. The on-welded areas are mechanically removed after this process. A coil from a 10 µm thick aluminum layer was generated this way on a 250 µm thick polypropylene sheet. The coil was combined with a capacitor to a transponder which was excited with a primary coil to resonance oscillations at 1.5 to 2.5 MHz.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2008
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Khuntontong, Puttachat
- Contributors dc:contributor
-
- Schomburg, Werner Karl
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng