Replication of polymer microstructure using thermal-assisted ultrasonic embossing

A thermal-assisted ultrasonic embossing method was proposed based on silicon molds to replicate thermoplastic substrates in a low cost and high efficiency. The ultrasonic vibration was applied to the mold-polymer interface to heat the polymer rapidly to the embossing temperature. To reduce the risk of damaging the mold, the die was preheated to a temperature which is 35-50°C below the glass transition temperature (Tg) of the polymer. Then, the influences of the ultrasonic amplitude, ultrasonic force, ultrasonic time, and the thermal-assisted temperature were studied by orthogonal array experiments to reveal the mechanism of ultrasonic embossing. The influence of the substrate thickness was also investigated. The experimental results show that the most important parameter for replication is the thermal-assisted temperature, follows by the ultrasonic amplitude. Moreover, the ultrasonic force is the most important parameter for replication uniformity, while the thinner polymer sheets are more conducive to be replicated under the same circumstances. With the optimized parameters, the replication accuracy has reached 99% on a Polymethyl Methacrylate (PMMA) substrate, and the cycle time is less than 50 s. All theses studied show that thermal assisted ultrasonic embossing has high replication efficiency and is a potential way to mass formation of polymer microstructures.