Study on stress evolution in the cooling process of micro hot embossing

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