Characterization of manufacturability of microstructures for micro-injection moulding of micro devices using star patterns

The replication accuracy of micro features plays a very important role in polymeric micro devices, such as microfluidic and micro optics. However, there is no effective way at the moment for the assessment of manufacturability of such microstructures. This study develops a new method of using a star pattern with a continuous change of width and aspect ratio to characterize the manufacturability of microstructures. The designed patterns have a width from 20 microns to 320 microns with an aspect ratio from 2.5 to 0.156. Concentric markers are designed on the star patterns for the easy identification of achievable feature accuracy under various processes. It is found that the dry etching and electroforming cause a depth error of less than 5%, while the maximum error from injection moulding is 2.8% where the channel aspect ratio is less than 1. However, when the aspect ratio of protrusion microstructures is higher than 1 with a width of 50 µ m, insufficient filling occurs under nominal injection moulding conditions with relative error more than 10%. The designed star patterns are proved to be an easy and fast way to determine achievable feature accuracy for polymer micro replication processes, including injection moulding and hot embossing.