Investigation of localized heating characteristics in selective ultrasonic imprinting

Ultrasonic imprinting is a patterning technology in which ultrasonic vibration energy is used to soften the surface of thermoplastic polymer to allow the formation of micropatterns. Compared with other patterning technologies, ultrasonic imprinting has the advantages of short cycle time and low energy consumption. This study deals with the selective ultrasonic imprinting process, which provides higher flexibility in developing versatile micropatterns. Selective ultrasonic imprinting uses a profiled mask film by which ultrasonic waves are transferred from an ultrasonic horn to a target polymer film. The target polymer film is locally softened in the regions in contact with the mask film, so that micropatterns can be selectively replicated in these regions. In this study, this localized heating mechanism is numerically investigated through structural-thermal-coupled finite element analysis, by effectively connecting transient structural and heat transfer analyses. This coupled simulation was performed to investigate the localized heating mechanism of the selective imprinting using an E-shaped mask, and then compared with experimental findings. Micropattern replication was then performed using an arbitrarily shaped logo, with which differentiation of optical transparency could be obtained.