LIGA

LIGA is a manufacturing sequence that produces metal microstructures with aspect ratios routinely exceeding 100:1, making it essential for microfluidic devices, medical implants, and precision mechanical components. The acronym comes from the German terms for lithography, electroplating, and molding. Unlike conventional micromachining, which subtracts material, LIGA builds structures through additive processes that preserve dimensional accuracy at micrometer scales.

The process begins with X-ray lithography on a thick resist layer, typically polymethyl methacrylate (PMMA) between 100 and 500 micrometers deep. Synchrotron radiation exposes the resist through a patterned mask, and development leaves behind a three-dimensional mold cavity. The high-energy X-rays penetrate deep without significant scattering, enabling vertical sidewalls and uniform exposure across the full depth. This precision at depth is what sets LIGA apart from optical lithography, which struggles with thick resists.

Electroplating fills the resist mold with metal, most commonly nickel, though copper and alloys are used for specific applications. The metal deposits uniformly into the cavity, building up the inverse of the mold shape. Once the plating reaches the desired thickness, the structure is separated from the resist, yielding a metal master or insert. This metal mold then enters the injection molding or hot embossing phase, where thermoplastic or thermosetting polymers are formed against the metal cavity to produce multiple copies.

LIGA's expense stems from synchrotron access and the precision tooling required. Equipment and facility time make it economical only when part geometry cannot be achieved any other way or when production volumes justify the upfront investment. Typical applications include fuel injection nozzles, micro-reactor components, and biomedical devices where aspect ratios exceed 20:1 and tolerances are in the single micrometer range. For lower aspect ratios, UV lithography or etching are faster and cheaper alternatives.

The process is sensitive to resist adhesion, electroplating current distribution, and mold demolding forces. Poor adhesion causes resist to lift during plating; uneven plating produces tapered walls. Thermal cycling during molding can cause dimensional shift if the metal master and polymer mold have mismatched expansion rates. Successful LIGA production demands tight control of chemistry, temperature, and timing at every stage.