Studies of Polymer Deformation and Recovery in Hot Embossing

TL;DR

This study investigates how process temperature affects polymer deformation and recovery in micro hot embossing of PMMA, highlighting the transition from elastic to plastic deformation near Tg and implications for process optimization.

Contribution

It provides experimental insights into deformation mechanisms at various temperatures, emphasizing low-temperature embossing for improved flatness and microstructure fidelity.

Findings

Elastic deformation dominates below Tg-55°C with significant relaxation.

Plastic deformation dominates near Tg, enabling permanent microstructures.

Lower process temperatures reduce required load pressure for microstructure formation.

Abstract

In large area micro hot embossing, the process temperature plays a critical role to both the local fidelity of microstructure formation and global uniformity. The significance of low temperature hot embossing is to improve global flatness of embossed devices. This paper reports on experimental studies of polymer deformation and relaxation in micro embossing when the process temperatures are below or near its glass transition temperature (Tg). In this investigation, an indentation system and a micro embosser were used to investigate the relationship of microstructure formation versus process temperature and load pressure. The depth of indentation was controlled and the load force at a certain indentation depth was measured. Experiments were carried out using 1 mm thick PMMA films with the process temperature ranging from Tg-55 degrees C to Tg +20 degrees C. The embossed structures included a single micro cavity and groups of micro cavity arrays. It was found that at temperature of Tg-55 degrees C, elastic deformation dominated the formation of microstructures and significant relaxation happened after embossing. From Tg-20 degrees C to Tg, plastic deformation dominated polymer deformation, and permanent cavities could be formed on PMMA substrates without obvious relaxation. However, the formation of protrusive structures as micro pillars was not complete since there was little polymer flow. With an increase in process temperature, microstructure could be formed under lower loading pressure. Considering the fidelity of a single microstructure and global flatness of embossed substrates, micro hot embossing at a low process temperature, but with good fidelity, should be preferred.