In short:Semiconductor, electronics assembly and inspection machines earn their money in move-and-settle time, so use direct-drive linear and rotary motors with fine optical encoders and stiff mechanics. Then control heat, because a few watts in the wrong place moves the stage more than the motor does, and choose materials that suit the cleanroom or vacuum.
Typical requirements
| Linear encoder resolution | About 10 nm and finer (optical); interpolation down to 1 nm on published systems |
|---|---|
| Linear encoder accuracy | Better than ±1 µm/m (optical); about ±3 µm over 1 m (magnetic) |
| Settling window | Within one encoder count achievable on direct-drive linear motors |
| Ironless linear motor force | About 3 N to 2 kN continuous (one published U-channel range) |
| Voice coil stroke | Up to about 20–40 mm, zero cogging |
| Coil temperature limit (rule of thumb) | Keep below about 100 °C; much lower near metrology |
| Vacuum | High vacuum to about 10⁻⁷ hPa; UHV below 10⁻⁹ hPa after bakeout (published stages) |
| Voltage sag immunity (SEMI F47) | Ride through 50% for 200 ms, 70% for 0.5 s, 80% for 1 s |
Machinery we specify motion for
- Wafer-handling robots
- Lithography and wafer inspection stages
- SMT and PCB pick-and-place machines
- Die bonders and back-end assembly
- Flat-panel display (FPD) production
- PV cell and module lines
- Flying-probe and electronic test equipment
- Precision XY and air-bearing stages
What this market needs from motion
Wafer handling and inspection, die bonding, pick-and-place, PCB inspection, laser processing and display metrology all share the same economics. Throughput is set by how quickly an axis moves to the next point and settles inside its window, and quality is set by how stable it stays while the camera, probe or laser works. Everything else, including the motor, encoder, drive, bearings and frame, is chosen to shorten move-and-settle and protect stability.
Three constraints stand out:
- Dynamic performance: high acceleration, short settling, smooth constant-velocity scans.
- Thermal stability: heat from motors and drives distorts the stage and the metrology loop.
- Cleanliness: particles in cleanrooms, outgassing in vacuum, and ESD around devices.
Linear motors and direct drive
Direct drive removes the screw or belt between motor and load, so there is no backlash, wind-up or belt stretch to ring at the end of a move. Aerotech’s linear motors application guide notes that direct-drive linear motors give the shortest settling times, within an encoder count, while belt-driven systems ring because of belt compliance.
| Motor type | Strengths | Trade-offs | Typical axis |
|---|---|---|---|
| Ironless (U-channel) linear | No cogging, no attraction force, smooth scanning | Lower force per size, heat in a thin coil | Inspection scans, fine XY |
| Iron-core linear | Highest force, attraction can preload air bearings | Cogging, strong attraction loads bearings | Long-travel gantries, heavy bridges |
| Voice coil | Very short stroke, very fast, no commutation | Stroke limited to tens of mm | Focus, Z-height, bonding force |
| Ironless or direct-drive rotary | Zero cogging, large centre hole | Torque limited for size | Wafer theta, rotary inspection tables |
| Linear motor module (tubular) | Simple, sealed, fast pick-and-place | Moving mass of slider | Placement heads, test handlers |
Examples from our catalogue:
- The Akribis AUM ironless U-channel range covers about 3 N to nearly 2 kN continuous for fast-settling stages; the Akribis AJM iron-core motor gives up to about 447 N continuous and 1.4 kN peak in a compact package.
- Flat Akribis AVA voice coils (20 mm stroke) build into low-profile stages; cylindrical AVM coils reach 40 mm stroke.
- For rotary axes, the ironless Akribis ACD and flat ACW direct-drive motors have zero cogging and large centre holes.
- Tubular motors such as the LinMot P01-23 suit compact pick-and-place and test handling axes.
Browse frameless torque motors and servo and stepper motors for the wider range.
How to size a linear motor axis: a worked example
Aerotech’s sizing method adds acceleration, friction and gravity forces for peak force, then takes an RMS over the cycle for continuous force. Apply it to an XY inspection stage stepping 20 mm in 60 ms, then dwelling 40 ms for an image, with 8 kg moving mass on the axis.
- Acceleration: with a triangular profile, a = 4 × 0.020 / 0.060² = 22 m/s² (about 2.3 g). Peak velocity is 0.67 m/s.
- Peak force: 8 × 22 = 178 N, plus a little bearing friction and cable drag.
- RMS force: the motor is pushing for 60 ms of every 100 ms, so F_rms = 178 × √(60 / 100) = 138 N.
- Coil temperature: Aerotech gives the rise as R_th × (F_rms / K_m)², with K_m the motor constant in N/√W. A motor with K_m = 20 N/√W dissipates about 48 W here; at 0.5 K/W thermal resistance the coil runs about 24 K above ambient.
- Encoder: for a ±0.5 µm settling window, choose 50 nm resolution as a minimum and preferably 10 nm or finer.
Then ask where those 48 W go. If 1 K of it reaches a 300 mm aluminium carriage, the carriage grows by about 7 µm, which is far more than the settling window. A motor with a higher motor constant, water cooling or a longer duty cycle may be the cheaper fix than a cleverer controller. Aerotech recommends keeping coil temperatures below about 100 °C; near metrology you will want far less.
High-resolution encoders
Choose encoders on resolution, accuracy, speed at that resolution, sub-divisional error and environment. Aerotech’s guide puts magnetic linear encoders at about ±3 µm over 1 m and optical encoders at better than ±1 µm/m with resolution to about 10 nm and finer.
- The Renishaw TONiC and VIONiC incremental systems interpolate down to 1 nm and 2.5 nm on 20 µm scales.
- The miniature Renishaw ATOM fits space-constrained axes on placement heads and small stages.
- Renishaw RESOLUTE is true absolute, so wafer and gantry axes know their position at power-up without homing.
Mount the scale as close to the work point as you can to reduce Abbe error, and map residual errors with an interferometer into the controller. Read absolute vs incremental encoders and browse encoders.
Drives and controllers
Linear motor and voice coil axes need drives with fast current loops, low noise and high-resolution encoder inputs. Dedicated linear motor drives such as the Kinco DD2S accept pulse inputs up to 4 MHz or EtherCAT. Multi-axis gantries with dual-drive bridges (two motors on one beam) need a controller that handles gantry coupling, error mapping and position-synchronised output for camera or laser triggering. See servo drives and motion controllers.
Cleanroom and vacuum compatibility
Cleanrooms. Fab and back-end tools are specified to an ISO 14644-1 class. Class 5 allows 3,520 particles/m³ at 0.5 µm and above, and front-end tools often sit in cleaner mini-environments. Cable chains, brushes, ball screws and greased guides shed particles. Use cleanroom cable and lubricants, cover or bellows exposed guides, and route exhaust away from the wafer.
Vacuum. PI’s guidance for vacuum positioning is a good checklist:
- Avoid brass and other copper-zinc alloys and high vapour pressure metals such as zinc, lead and cadmium.
- Replace PVC cable with PTFE or polyimide, keep cables short, and use crimped or welded rather than soldered contacts.
- Replace standard plastics with PEEK, ceramics or metal for UHV, and vent screws and blind holes to avoid virtual leaks.
- Use vacuum grease, or none on UHV stages. Hydrocarbons can deposit on optics.
- Run motors gently: in vacuum they lose convective cooling. Keep drives and controllers outside the chamber.
- Check bakeout limits. PI rates HV stages to 80 °C and UHV stages up to 120 °C with a scale fitted, 150 °C without. Its test HV stage reached about 10⁻⁷ hPa after two days of pumping, and UHV stages fell below 10⁻⁹ hPa after bakeout.
ESD. Around exposed devices, follow the customer’s ESD control programme, commonly built on IEC 61340-5-1: conductive or dissipative materials and grounded moving parts.
SEMI standards that touch motion components
- SEMI S2 is the EHS guideline for semiconductor manufacturing equipment. Tool makers assess the whole tool, so ask for component safety data such as STO, guarding and electrical safety, rather than an “S2-certified motor”.
- SEMI F47 sets voltage sag immunity. According to Advanced Energy, equipment must ride through sags to 50% for 200 ms, 70% for 0.5 s and 80% for 1 s, and power supplies as components are expected to meet it. Ask drive and power supply makers how their products behave in a sag, and whether DC bus hold-up keeps axes in position.
- SEMI E10 defines reliability, availability and maintainability metrics. Tool makers use it to report MTBF and uptime, so component failure rate data feeds directly into their figures.
Typical pitfalls
- Sizing on peak force only and finding the coil hot, the stage drifting and the settling window missed.
- Mounting motors next to scales or metrology frames.
- Specifying encoder resolution without accuracy, speed limit or sub-divisional error.
- Using standard cable and grease in vacuum, then chasing outgassing and long pump-down.
- Ignoring voltage sags until the tool loses position during a site power dip.
Send us your move profile, accuracy and environment, and our specialist engineering and supply partners can propose motors, encoders and drives for each axis.
Linear motors for pick-and-place machines
Linear motors and voice coils drive the fastest axes in placement, bonding and inspection machines. Size them on peak force for acceleration and RMS force over the real move-and-dwell cycle, then check coil temperature rise, because heat in the coil reaches the carriage and the scale. A higher motor constant means less heat for the same force. Ironless motors scan smoothly with no attraction force; iron-core motors give more force for gantries; voice coils handle short-stroke focus and bond-force axes. Do not forget cable chain drag and moving cable mass on a light axis, and ask for vacuum-compatible materials and cabling if the stage goes into a chamber.
- SMT pick-and-place: high-acceleration gantry axes
- Wafer inspection: smooth constant-velocity scanning stages
- Die bonders: bond head Z and bond force control
- Long-stroke FPD and PV axes: multi-metre linear travel
- Wire bonders: fast, compact linear modules
Available through our supply network
All linear actuators →Specify linear actuators for semiconductor and electronics →
Encoders for wafer stages and inspection axes
The encoder decides how well a precision stage can settle and how accurately it reports position. As a rule of thumb, choose resolution five to ten times finer than the settling window, then check accuracy, sub-divisional error and the maximum speed at that resolution. Mount scales close to the work point to cut Abbe error and keep them away from motor coils. For rotary theta stages, high-accuracy absolute ring encoders remove homing at power-up. Magnetic scales tolerate dust and fluids on back-end and PV equipment where nanometre optics are overkill. In vacuum, confirm cable, adhesive and bakeout limits, and in cleanrooms ask what the readhead and scale shed.
- Wafer stages: fine linear feedback for move-and-settle
- Theta and rotary inspection tables: absolute ring encoders
- Back-end assembly: robust magnetic linear scales
- Metrology axes: high-accuracy rotary feedback
Available through our supply network
All encoders and feedback →Specify encoders and feedback for semiconductor and electronics →
Direct-drive rotary stages for wafer and inspection tools
Direct-drive rotary motors give wafer theta stages, rotary inspection tables and optical stages zero backlash and a large centre hole for vacuum lines, optics or cables. For scanning and alignment, choose ironless or low-cogging designs and check torque ripple at the slowest speed you run, because ripple shows up as velocity error under the camera. Size continuous torque on the RMS of the move profile and keep coil losses low near metrology frames. Specify flatness and wobble requirements, which depend on the bearing and mounting, not only the motor. For limited-angle axes on large stages, curved ironless motor segments can replace a full ring at lower mass.
- Wafer theta stages: smooth, backlash-free alignment
- Rotary inspection tables: low speed-ripple scanning
- Optical stages: direct drive with a clear aperture
- Large-diameter stages: limited-arc curved motor segments
Available through our supply network
All frameless and torque motors →Specify frameless and torque motors for semiconductor and electronics →
Servo drives for linear motors and wafer handling
Precision stages need drives with fast current loops, low current noise and encoder inputs that keep up with fine resolution at full speed. Linear motor drives must commutate from the scale, so check phasing options at power-up and whether Hall sensors are needed. For gantries with two motors on one beam, the controller and drives must support gantry coupling so the bridge does not twist. Ask how the drive behaves in a voltage sag, since SEMI F47 requires equipment to ride through dips to 50% for 200 ms; DC bus hold-up or a controlled stop may be needed. Low-voltage DC drives suit wafer robots and compact handling axes.
- Linear motor stages: high-bandwidth current control
- Dual-drive gantries: coordinated motors on one bridge
- Wafer-handling robots: compact low-voltage joint drives
- Electronics assembly: high-speed point-to-point axes
Available through our supply network
All servo drives →Specify servo drives for semiconductor and electronics →
Servo and stepper motors for electronics assembly and handling
Not every axis in an electronics or semiconductor tool needs a linear motor. Conveyor widths, magazine lifts, feeders, nozzle rotation and wafer cassette handling run well on compact servo motors or steppers with screws and belts. Five-phase steppers give finer full steps and smoother running than two-phase types for low-cost positioning, and closed-loop steppers avoid lost steps. Low-voltage servo motors suit battery-free mobile handling units and compact tool modules. Specify the move profile, positioning accuracy, holding behaviour and audible noise, and check the motor is not a heat source next to sensitive optics. In cleanrooms, ask about bearing grease and sealed shafts.
- SMT machines: feeder, conveyor and nozzle rotation axes
- Wafer cassette handling: lift and transfer axes
- Test handlers: compact positioning axes
- Inspection machines: focus and filter mechanisms
Available through our supply network
All servo and stepper motors →Specify servo and stepper motors for semiconductor and electronics →
Motion control for semiconductor equipment
Semiconductor and electronics tools need a controller that coordinates many axes on a deterministic network, usually EtherCAT, and links motion to cameras, lasers and probes. Check how many synchronised axes it handles at your cycle time, whether it supports gantry coupling for dual-drive bridges, and whether it can apply an error map from interferometer calibration. Position-synchronised outputs that fire a camera or laser at a set position, rather than on a timer, make a large difference on scanning tools; confirm whether the controller or the drives provide them. An industrial PC or PLC-based controller with a standard programming environment eases long-term support and SEMI E10 uptime reporting.
- Pick-and-place machines: multi-axis gantry coordination
- Inspection tools: camera triggering on position
- Dispensing and bonding: coordinated path motion
- Test equipment: synchronised handling axes
Available through our supply network
All controllers and plcs →Specify controllers and plcs for semiconductor and electronics →
Low-backlash gearing for wafer-handling robots
Wafer-handling robots and aligners use compact, low-backlash gearing in each joint so the end effector places wafers repeatably without vibration. Strain-wave gear sets suit the joints of SCARA-style and articulated handlers, and their hollow shafts carry vacuum lines and cables. Hollow-shaft harmonic actuators package motor, gear and encoder, which saves space in tool modules. Specify repeatability at the end effector, the payload including the end effector, joint speed, and the lubricant: in cleanrooms ask for low-outgassing grease and sealed housings, and in vacuum robots confirm whether the gear can run in vacuum at all or must sit behind a seal or magnetic coupling.
- Wafer-handling robots: zero-backlash joint reduction
- Aligners and pre-aligners: precise rotary indexing
- Equipment front-end modules: compact geared axes
- Rotary tables in test handlers: low-backlash indexing
Available through our supply network
All gearboxes and harmonic drives →Specify gearboxes and harmonic drives for semiconductor and electronics →
Standards to have in view
- SEMI S2 (environmental, health and safety guideline for semiconductor manufacturing equipment)
- SEMI F47 (voltage sag immunity for semiconductor processing equipment)
- SEMI E10 (equipment reliability, availability and maintainability metrics)
- ISO 14644-1 (cleanroom air cleanliness classes)
- IEC 61340-5-1 (protection of electronic devices from electrostatic phenomena)
- ISO 230-2 (accuracy and repeatability of positioning of numerically controlled axes)
Which standards apply depends on the end product and its market. Your engineer will confirm what the component itself needs to meet.
Frequently asked questions
Ironless or iron-core linear motor for an inspection stage?
Ironless motors have no cogging and no magnetic attraction to the track, so they give the smoothest constant-velocity scans and the cleanest settling. They produce less force for their size. Iron-core motors give much more force and their attraction can preload an air bearing, but cogging and attraction make them harder to use for nanometre-level stability. Many machines use ironless for scanning axes and iron-core for heavy long-travel gantries.
When should I use a voice coil instead of a linear motor?
Use a voice coil for short strokes, typically a few millimetres up to about 40 mm, where you need fast, smooth, cog-free force control: focus axes, Z-height on placement heads, probing, bonding force and fine stages stacked on a coarse axis. Linear motors take over where travel is longer. Voice coils have very low moving mass and no commutation, so they are simple to drive.
How fine an encoder do I need?
As a rule of thumb, choose a resolution five to ten times finer than the smallest step or settling window you must hold, and an accuracy that fits your error budget after mapping. For a ±0.5 µm settling window, 50 nm resolution is a minimum and 10 nm or finer is better. Also check the encoder's speed limit at that resolution and its sub-divisional error, which shows up as velocity ripple.
Why does heat matter so much in precision stages?
Copper loss in the motor heats the coil, the stage and the scale. Aluminium grows by about 23 µm per metre per kelvin, so a 1 K rise across a 300 mm aluminium carriage moves features by about 7 µm. Size motors on RMS force with margin so coils run cool, keep motors away from encoder scales and metrology frames, and consider water cooling or low-expansion materials.
What changes for motion inside a vacuum chamber?
Standard plastics, PVC cables, brass, soldered joints and ordinary grease all outgas or contaminate. Vacuum stages use PEEK, ceramics, PTFE or polyimide cable, vacuum grease or none at all, and vented screws to prevent virtual leaks. Motors cannot cool by convection, so run them gently and monitor temperature. Keep drives and controllers outside the chamber, and check bakeout temperature limits for encoders.
What should I send for a precision stage enquiry?
Send axis travel, moving mass, move profile (step size, move time and settling window), duty cycle, required accuracy, repeatability, straightness and flatness, encoder interface, environment (cleanroom class, vacuum level, temperature control), allowed heat into the machine, mains supply and SEMI requirements such as S2 or F47, and the motion controller or drive platform you use.
Sources
- Aerotech: Linear motors application guide
- Control Engineering (PI): Designing motion control and precision positioning equipment for high-vacuum applications
- Advanced Energy: SEMI F47 compliance and voltage sag immunity
- Beckman Coulter: ISO 14644-1 classification table
Figures are summarised from the sources above and from manufacturers' published data on the date shown. Always confirm against the current datasheet for your exact part.