Abstract
A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive synchrotron source needed to expose the photoresist layer in X-ray LIGA. SU-8 photoresist appeared to be well-suited for LIGA templates, but also as a permanent material. Based on UV-LIGA and SU-8, Mimotec SA has developed processes to manufacture mold inserts and metallic components for various market fields. From one to three-level parts, from Ni to other materials, from simple to complicated parts with integrated functionalities, UV-LIGA has established itself as a manufacturing technology of importance for prototyping, as well as for mass-fabrication. This paper reviews some of the developments that led to commercial success in this field.
Highlights
Developed in the early 1980s by a team under the leadership of Becker and Ehrfeld [1], X-ray lithography demonstrated the fabrication of highly 2.5-dimensional structures with aspect ratios as high as 100:1
X-ray LIGA is well suited for fabricating very high aspect ratio structures, very precise shape definition, high straightness and planarity of sidewalls, this approach has not made its way into large-scale industrial applications, Micromachines 2014, 5 mainly because of the expensive synchrotron source needed to expose the photoresist layer and the rather small patterned area
In the early 1990s, Frazier and Allen used UV light and polyimide photoresist to fabricate microstructures [3], but real advances in so-called UV-LIGA started with the use of a near-ultraviolet-sensitive epoxy-based material called EPON® SU-8, first developed as a mask for reactive ion etching (RIE) at IBM Yorktown [4]
Summary
Developed in the early 1980s by a team under the leadership of Becker and Ehrfeld [1], X-ray lithography demonstrated the fabrication of highly 2.5-dimensional structures with aspect ratios as high as 100:1. Combined with electroplating and known under the acronym X-ray LIGA (Lithographie, Galvanoformung and Abformung), this technique has been used in many research projects, but only on a limited scale for industrial applications. X-ray LIGA is well suited for fabricating very high aspect ratio structures, very precise shape definition, high straightness and planarity of sidewalls, this approach has not made its way into large-scale industrial applications, Micromachines 2014, 5 mainly because of the expensive synchrotron source needed to expose the photoresist layer and the rather small patterned area. Real LIGA is combined with injection molding (Abformung) In most cases, this latter step is omitted, and the electroplated layer is the final part. Beside bulk and surface micromachining techniques originally used for micromachining in the late 90s, LIGA can be considered a forerunner to additive manufacturing and a facilitator for the fabrication of micromechanical structures with a high degree of three dimensionality, or HARMS (high aspect ratio microstructures), desired for many applications
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