LIGA

UV LIGA utilizes an inexpensive ultraviolet light source, like a mercury lamp, to expose a polymer photoresist, typically SU-8.

However, UV LIGA is not as effective at producing precision molds and is thus used when cost must be kept low and very high aspect ratios are not required.

X-ray masks are composed of a transparent low-Z carrier, a patterned high-Z absorber, and a metallic ring for alignment and heat removal.

The applied photoresist is then milled down to the precise height by a fly cutter prior to pattern transfer by X-ray exposure.

Further, the cutting of the PMMA sheet by the fly cutter requires specific operating conditions and tools to avoid introducing any stress and crazing of the photoresist.

[citation needed] A key enabling technology of LIGA is the synchrotron, capable of emitting high-power, highly-collimated X-rays.

This high collimation permits relatively large distances between the mask and the substrate without the penumbral blurring that occurs from other X-ray sources.

During exposure, secondary radiation effects such as Fresnel diffraction, mask and substrate fluorescence, and the generation of Auger electrons and photoelectrons can lead to overexposure.

At this stage, the PMMA structures can be released as the final product (e.g., optical components) or can be used as molds for subsequent metal deposition.

In the electroplating step, nickel, copper, or gold is plated upward from the metalized substrate into the voids left by the removed photoresist.

Taking place in an electrolytic cell, the current density, temperature, and solution are carefully controlled to ensure proper plating.

In the 1990s, LIGA was a cutting-edge MEMS fabrication technology, resulting in the design of components showcasing the technique's unique versatility.

Currently, only two companies, HTmicro and microworks, continue their work in LIGA, benefiting from limitations of other competing fabrication technologies.

UV LIGA, due to its lower production cost, is employed more broadly by several companies, such as Veco, Tecan, Temicon, and Mimotec in Switzerland, who supply the Swiss watch market with metal parts made of nickel and nickel-phosphorus.