An investigation of the detrimental impact of trapped air in thermoplastic micro-embossing

Abstract

In hot micro-embossing, a thermally softened polymer is forced into the cavities of a patterned stamp. If embossing is performed in normal atmospheric surroundings, it is possible for air to become trapped inside the cavities of the stamp, impeding pattern replication. We present a fast simulation technique that captures the impact of trapped air in the micro-embossing process. The technique can predict the extent of stamp cavity filling for any given stamp design and linear viscoelastic polymer properties, under the assumption that air, once trapped inside a cavity, is unable to escape. We find that the smaller the effective stiffness of the softened polymer relative to the surrounding atmospheric pressure, the more severe the impact of trapped air. Moreover, the trapping of air becomes more detrimental as the widths of stamp cavities become a larger proportion of their lateral spacing. The results of embossing experiments with two widely used thermoplastic polymers, Zeonor 1060R and polymethylmethacrylate, agree with simulation results and indicate that there is little permeation of trapped air in these materials during a typical embossing process of up to 15 min duration, carried out at between 5 and 45 °C above their glass-transition temperatures.