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Lesson 13.7Micro & nanoChapter 13 · Micro- and nanofabrication

LIGA

Draws deep slots with X-rays or UV, fills them with nickel, then molds copies

LIGA makes tiny metal parts with tall, perfectly straight walls, such as the gears and springs inside some mechanical watches. Its name abbreviates the German words for lithography (drawing a pattern with light), electroplating and molding, the three steps it chains together. It reaches shapes too small and too deep for any cutting tool.

LIGA: a real photo
Photo: Forschungszentrum Karlsruhe, CC BY-SA 3.0, via Wikimedia Commons
Draw with X-rays, fill with nickel, then copy by moldingLIGA in six states · cross-sections, not to scale1Coat thick resistthick resist (PMMA)metal base plateup to millimeters thick2Expose to X-raysX-rays from a synchrotronmaskrays pass only through the gaps3Developdeep slotsexposed resist washes away4Electroform nickelplating bathnickel grows up from the base5Lap flat, strip resistnickel partsfree-standing metal parts6Mold plastic copiesnickel insertplastic copythe nickel becomes a moldPlastic (resist, copy)Metal (base, mask, nickel)X-raysPlating bath
LIGA · six cross-sections from resist to molded copyRead the six panels left to right, top row first; circled numbers match the steps below.

How it works

  1. Coat a thick resist. A layer of resist, a plastic that light can change chemically, is bonded to a metal base plate. Common resists are PMMA (acrylic) and SU-8 (an epoxy), up to millimeters thick.

  2. Expose. Parallel X-rays from a synchrotron (a ring-shaped particle accelerator that emits intense light), or UV light in the cheaper UV-LIGA, shine through a mask. Gold patches on the mask block the rays; where they pass, the resist changes all the way down, which can take hours.

  3. Develop. A chemical bath dissolves the exposed resist. Deep slots remain, with near-vertical, mirror-smooth walls.

  4. Electroform. In a plating bath, electric current deposits nickel onto the bare base plate at the bottom of each slot. The metal grows upward and fills the slots atom by atom, often over many hours.

  5. Lap and strip. The top is lapped (ground flat with fine abrasive), then the leftover resist is dissolved. Free-standing metal parts remain, or a metal mold insert if they stay joined.

  6. Mold copies (optional). The nickel insert serves as a mold for injection molding or hot embossing (pressing it into softened plastic). It can make thousands of cheap plastic replicas.

Key facts

Materials
Resist: PMMA or SU-8; metal: nickel, nickel alloys, copper, gold; copies in plastics or ceramics
Typical parts
Watch gears and springs, micro-gears, nozzles, comb drives for MEMS, molds for microfluidic chips
Part size
Features of a few microns; heights from tens of microns to millimeters; parts usually millimeters across
Precision
Sub-micron accuracy side to side; height-to-width ratios up to about 100:1 with X-rays
Surface finish
Very smooth, near-vertical, mirror-like side walls
Batch size it suits
Metal parts in small to medium series; molded plastic copies in large series
Tooling and machine cost
X-ray LIGA needs rare, costly synchrotron time; UV-LIGA uses ordinary UV lamps and is far cheaper; plus masks and plating baths
Speed
Slow: exposure and plating each take hours, but one plate carries many parts at once

Strengths and limits

Strengths

  • Very tall, thin walls that stay near-vertical and smooth
  • Sub-micron precision on parts millimeters tall
  • Solid metal parts, not just thin coatings
  • A metal mold makes cheap plastic copies

Limits

  • The X-ray version needs a synchrotron: rare and expensive
  • Long exposure and plating times
  • Only 2.5D shapes (a flat outline extruded straight up), no undercuts
  • UV-LIGA is cheaper but less tall and less precise

Where it's used

  • WatchmakingEscape wheels, anchors, springs, hands (UV-LIGA nickel parts)
  • MEMS (micro-electro-mechanical systems, tiny machines on chips)Micro-gears, actuators, comb drives, optical switches
  • MedicalMicro-needles, molds for microfluidic test cards, hearing-aid parts
  • Optics and X-rayX-ray lenses, micro-spectrometer molds, gratings
  • ElectronicsMicro-connectors, probe needles for testing chips
  • Energy (historic)Separation nozzles for uranium enrichment, the 1980s origin of LIGA

How to recognize it

  • You will rarely see LIGA parts: they sit hidden inside mechanical watches, chip-testing probe cards and microfluidic devices.
  • A tiny metal gear or spring with walls so straight and shiny they look polished, thinner than a hair in places.
  • The same outline from top to bottom, with sharp inside corners and no draft (the slight taper most molded parts need).
  • Molded LIGA copies: clear plastic chips with micro-channels or tiny pillars, visible only under a magnifier.

Compare with

Photolithography13.2the same draw-with-light step, but in thin resist for flat chip patterns; LIGA goes deep and adds metal.Electroforming11.7grows metal parts by plating onto a pattern; LIGA is electroforming inside a lithographic micro-mold.Femtosecond laser machining13.6also makes micro-parts, but by removing material from a solid sheet; LIGA grows them, with straighter, taller walls.

Watch it

Support Center for Microsystems Education · An animated walk through each LIGA step

sylmandcls · A real X-ray lithography beamline at a synchrotron

Mimotec SA · How a Swiss maker produces UV-LIGA watch parts

Tech Ed · Where LIGA fits among other ways to make micro-machines

See real photos

Remember

  • LIGA: draw deep slots with X-rays or UV, fill them with nickel, then optionally mold copies.
  • It makes tall, straight-walled micro-parts that no cutting tool can reach.
  • X-ray LIGA is the most precise but needs a synchrotron; UV-LIGA is the cheaper workhorse of watchmaking.

More in Micro- and nanofabrication

All 100 processes
13.1Czochralski crystal growth (silicon wafers)Pulls a giant single crystal of silicon slowly out of a meltOpen the lesson13.2PhotolithographyProjects a pattern with light onto a light-sensitive coating, then etches itOpen the lesson13.3Molecular beam epitaxy (MBE)Grows a crystal one atomic layer at a time from beams in ultra-high vacuumOpen the lesson13.4Atomic layer deposition (ALD)Coats a surface one atomic layer per cycle with alternating gasesOpen the lesson13.5Focused ion beam (FIB)Mills or adds material with a beam of ions under a microscopeOpen the lesson13.6Femtosecond laser machiningRemoves material with ultrashort laser pulses, without meltingOpen the lesson13.8Two-photon polymerizationHardens resin only at a laser focus to print 3D micro-partsOpen the lesson13.9ElectrospinningPulls a polymer jet into nanofibers with high voltageOpen the lesson

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