Different methods for the fabrication of UV-LIGA molds using SU-8 with tapered de-molding angles

De-molding is one of the most crucial steps for successful mass production of high aspect ratio microstructures in microreplication technologies of LIGA process. With a proper taper angle in mold structure, normal contact pressure on the structure will be abated; this will facilitate the de-molding procedure and at the same time prevent the microstructures of mold from being damaged. However, in the case of UV lithography, the top area of the patterned SU-8 resist is observed to be larger than the bottom area especially in cases of thick layer and high aspect ratio structures. In order to obtain an applicable metal mold for hot-embossing process, we purpose here several novel methods with backside exposure which can fabricate different taper angles with proper direction on the mold structures easily. In this paper, we described the technology concept, process details and related experimental results both in mold structures and molded PMMA replicas. In addition, various interesting 3D microstructures can be produced by combining these exposure methods. On-chip microneedle arrays were selected to demonstrate this ability.