Injection molding using high aspect ratio microstructures mold inserts produced by LIGA technique

The mu SET research group at LSU is developing the three-step LIGA process to inexpensively manufacture high aspect ratio microstructures (HARMs). The first two steps of the process (lithography and electroplating) produce a metallic mold insert that is used as a template for molding microstructures. This paper focuses on injection molding of thermoplastics to produce surfaces covered with HARMs hundreds of micrometers in height, tens of micrometers in width, and separated by gaps on the order of tens of micrometers. Injecting plastic into the narrow, high aspect ratio gaps existing in the HARMs mold inserts (micromolding) offers a set of challenges different from classical injection molding of larger scale parts. This paper provides results of a series of injection molding experiments using a commercially available injection molding machine. Replication of the HARMs was achieved by increasing the injection speed, elevating the tool temperature, and venting the mold cavity. Electron microscopy was used to investigate and assess the molding results.