Studies of Polymer Deformation and Recovery in Hot Embossing

In large area micro hot embossing, process temperature plays a critical role in both the local fidelity of microstructure formation and global uniformity. Micro embossing at the lowest temperature with acceptable fidelity can improve the global flatness after demolding. This paper focuses on polymer deformation and recovery in micro embossing when the process temperatures are below its glass transition temperature (Tg). In this study, PMMA (Polymethyl Methacrylate) substrates (Tg =105 °C) were employed as the process material, and the process temperature ranged from 25 °C to Tg. It was found that at temperature below Tg-55 °C, significant recovery occurred after processing, but it was still possible to form permanent structures with sufficiently high loading stress. With an increase in temperature, plastic deformation increased and was the dominate polymer deformation for permanent cavities formation. However, the formation of protrusive structures was not complete since there was little polymer flow. The polymer will lose its storage modulus at a raised temperature and microstructures could be formed with high fidelity. A compromise between the local fidelity and global flatness has to be reached in micro hot embossing.