Tapered LIGA HARMs

Abstract

The standard LIGA process takes advantage of the use of x-ray lithography to produce mold inserts with nearly vertical sidewall; the typical slope of patterns produced by x-ray lithography of polymethylmethacrylate is 0.1%. This lack of significant taper (draft angle) greatly increases the difficulty associated with ejecting parts during demolding. In this paper, a procedure is described to fabricate a mold insert with tapered features having a height of approximately 1 mm and lateral dimensions of approximately 300 μm. A set of six oblique exposures of a thick layer of SU-8 (an EPON epoxy based negative tone resist) is used to create hexagonal posts with a 3° draft angle. An electroforming process is used to fabricate a nickel mold insert with the tapered features. This mold insert is used to injection mold tapered polymer high aspect ratio microstructures. The dimensions of the SU-8 tapered structures (as well as the mold insert) are within 4 μm of desired/predicted values.