Direct patterning of micro-features on a polymer substrate using ultrasonic vibration

Micro-molding of thermoplastic polymer is a popular fabrication method for micro-devices. Most micromolding techniques use heated molds to plasticize the thermoplastic polymer, which requires an increased cycle time and additional heating/cooling equipment. In this study, a novel micro-molding process using ultrasonic vibration energy is developed to locally melt the polymer surface by converting the ultrasonic vibration energy into thermal energy, from which the micro-patterns engraved on a sonotrode tip can be rapidly replicated on a polymer substrate. In order to replicate the micro-patterns with high accuracy, the sonotrode should be designed to allow longitudinal vibration only, not transverse or twisting vibrations. In this paper, the sonotrode design was investigated through finite element analyses, from which the resulting natural frequency of the sonotrode can be adjusted to be within the desirable range. Experimental investigations of the ultrasonic patterning were then performed using the sonotrode with the micro-patterns. The effects of various processing parameters on the replication characteristics are also discussed and analyzed statistically in order to find the optimal processing conditions.