Analysis of the demolding forces during hot embossing

Hot embossing is one of the main processing techniques for polymer microfabrication, which helps the LIGA (UV-LIGA) technology to achieve low cost mass production. When hot embossing of high aspect ratio microstructures, the deformation of microstructures usually occurs due to the demolding forces between the sidewall of mold inserts and the thermoplastic (PMMA). The study of the demolding process plays a key role in commercial manufacturing of polymer replicas. In this paper, the demolding behavior was analyzed by Finite element method using ABAQUS/Standard. Simulation identified the friction force caused by interface adhesion and thermal stress due to shrinkage between the mold and the polymer as the main sources of the demolding forces. Simulation also showed that the friction force made a greater contribution to the deformation than thermal stress, which is explained in the accompanying theoretical analysis. To minimize the friction force the optimized experiment was performed using PTFE (Teflon) as anti-adhesive films and using Ni-PTFE compound material mold inserts. Both lowered the surface adhesion energy and friction coefficient. Typical defects like pull-up and damaged edges can be reduced.