Effect of process parameters on filling behavior of PMMA in hot embossing

This study aims to evaluate the effects of process parameters and feature size on filling behavior of polymethyl methacrylate (PMMA) in rapid hot embossing. The filling behavior of PMMA was characterized by analyzing the surface topography of microlenses that were formed on the surface of PMMA after a series of hot embossing experiments, which were conducted by using a universal testing machine that is equipped with a rapid heating module. Experimental results indicated that increasing embossing temperature, embossing force, maintain force and embossing time led to higher average heights of microlenses, and thus improved the filling capacity of PMMA. Furthermore, embossing temperature has the most significant enhancement effect. Whereas, soaking time and demolding temperature shew very slight influence on the filling height of microlens. Therefore, cancelling soaking treatment and increasing demolding temperature are efficient strategies for shortening the cycle time of non-isothermal hot embossing without weakening the filling capacity of PMMA. Moreover, enlarging microhole diameter results in the increase of curvature radius and average height of microlens. Finally, a 5 × 5 microlens array was hot embossed on the PMMA substrate by using a 5 × 5 microhole array SiC mold. It is found that microlens at the center has the maximum height, while microlenses away from the center of PMMA substrate have smaller heights, which is attributed to the decreased contact pressure along the radial direction.