Injection molding of polymeric LIGA HARMs

The primary goal of an ongoing research effort at LSU is to develop 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 can be used as a template for molding microstructures. The final step of LIGA is molding. This paper focuses on injection molding of thermoplastics to produce surfaces covered with HARMs. The resulting microstructures are hundreds of micrometers in height, tens of micrometers in width, and separated by gaps on the order of tens of micrometers. Injection molding experiments using high density polyethylene were performed using a commercially available injection molding machine. Experimental variables included injection speed, the tool temperature, and air pressure in the mold cavity. Elevating the tool temperature above the melting point ensured that the polymer completely filled the mold, producing microstructures with the desired geometry. As the temperature of the mold was reduced, higher injection speeds did not necessarily ensure filling of the mold cavity. The cycle time is shorter than the values previously reported in the literature [Madou (1996)].