Mixer slit plates fabricated by direct-LIGA

Direct-LIGA services combining X-ray based micro-fabrication and electroplating are routinely provided to customers worldwide on a “best effort” basis by several LIGA centers. In a publicly founded project in collaboration between BESSY and Ehrfeld Mikrotechnik BTS GmbH the direct-LIGA process was adapted and optimised for fabricating mixer slit plates for micro-reactors. The application of SU-8 as a resist in deep X-ray lithography opens new opportunities for a direct and cost-effective mass fabrication of LIGA metal micro-parts. This joint paper will report on efforts from BESSY, Micro Resist Technology, and Ehrfeld BTS in fabrication of mixer slit plates by direct-LIGA for use in modular micro-reaction technology. The high demands regarding precision and yield of the micro-slit plates need certain improvements in the LIGA processing chain. Our approach consists of X-ray patterned SU-8 resist molds with a layer thickness of up to 350 μm and an aspect ratio of up to 30:1. Furthermore, the pattern-transfer into the SU-8 resist was done by a low-cost X-ray mask based on a graphite membrane. Other processing steps like NiFe electroplating and SU-8 removal will be discussed in this paper.