Micro-Feature Replication via Polymer Molding at Ambient Pressure

The study focuses on the ability of a polymer to replicate micro-features when processed at an elevated mold temperature without externally applied pressure. Replication is performed using four different polymers—High Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), and Poly (Methyl Methacrylate) (PMMA) on a silicon mold containing surface features as small as 500nm. Feature replication is assessed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to compare feature dimensions of the mold to those of the replicated parts. Shrinkage in dimensions is observed to be anisotropic in the molded parts and its extent of varies among the different polymers. Crystalline HDPE shows a higher degree of shrinkage relative to amorphous polymers such as PS and PMMA. These results verify the theoretical value of shrinkage calculated from the coefficient of volumetric shrinkage values and density. By increasing the mold temperature well above the melting point of the polymer, a depth ratio of 70–80% can be achieved in parts having aspect ratios of around 0.5. The result is comparable to the values achieved by similar studies. Varying aspect ratios are fully replicated by all four polymers at elevated mold temperature. This clearly shows that increasing mold temperature results in significant improvement in depth ratios for micro-featured parts. The amorphous materials provide better feature replication and lower surface roughness than the semi-crystalline polymer.