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Cooling of an embossed part has been recognized as one of the critical steps in the hot embossing of polymer microdevices. Numerical analysis was performed to study the stress developed in an embossed microstructure during the cooling process of hot embossing. A hemisphere-tipped post was selected as an example structure to demonstrate the stress evolution. The posts are located at 5, 10, 15, and 20 mm from the center of the embossed part. The results of the analysis showed that stresses of the posts increased as the radial locations of the post increased. In addition, the stress rapidly increased until the cooling time reached about 100.0 s. The maximum stresses of 28.9, 30.2, 32.3, and 34.5 MPa were estimated at the post locations of 5, 10, 15, and 20 mm from the center of the part, respectively. Experiments were performed to verify the numerical models. Undercut at the bottom of a post was observed as it was predicted in the numerical analysis.

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A cost effective alignment and positioning system was developed for double-sided hot embossing processes using kinematic principles. Alignment tooling located and transferred the top mold insert location to the proper location for the complementary mold insert and hot embossing was performed. The samples were checked for alignment accuracy and consistency. Adjustments were made and sampling repeated and measured. Results showed the alignment system can improve the locating and positioning of the complementary mold insert in relation to the top in a repeatable and cost effective manner.

Thermal stress and shrinkage were investigated to analyze pattern defects during the cooling and demolding steps in hot embossing. Hot embossing is one of the most popular fabrication methods that replicate polymer microdevices in fields such as micro-fluidics and micro-optics. Numerical models were developed to study the effect of thermal stress and adhesion force on a molded microstructure during the cooling and demolding steps of micro hot embossing. The alignment microstructure, a hemisphere-tipped post, was located at four radial locations of 5, 10, 15, and 20 mm from the center of the polymer substrate to determine the effect of thermal stress and adhesion forces, relative to pattern location, leading to pattern deformation. Results showed that thermal stress increased as the microstructure was moved further away from the center of the polymer substrate due to an increase in shrinkage velocity. Process parameters could be designed to improve replication fidelity by analyzing the stress distribution of a molded microstructure during cooling and demolding.