Technical Information

Linear Encoders for Vacuum Environments
A vacuum is an empty space devoid of air or any other gas. Depending on their quality, vacuums are classified as rough, fine, high,or ultra-high.
Vacuum technology plays a critical role in numerous production processes and research applications. Procedures that use vacuum
technology have become indispensable in fields such as electronics, thin-film technology, new materials research, biotechnology,
medical technology, and analysis technology.
The components used in vacuum environments, including the encoders needed for positioning tasks, must meet high standards.
HEIDENHAIN linear encoders for high and ultra-high vacuum environments meet these requirements thanks to special design features:• Vacuum-compatible circuit boards, adhesives, and coatings for reduced outgassing• Vented hollow spaces for shorter pumping time
• Temperature resilience for high bake-out temperatures• Use of non-ferromagnetic materials for high process reliability• Clean-area production• Pre-packaging bake-out for exceptional cleanness

Vacuum classes
When air is pumped out of a space, thepressure drops and a vacuum is created.
The less air that remains, the higher thevacuum class. There are four classes ofvacuum. Pressures of down to 1 mbar
constitute a rough vacuum, and lower
pressures, a fine vacuum. Under
0.001 mbar, a high vacuum is attained,
and below 0.000 000 1 mbar, an ultra-highvacuum.

Vacuum applications
Vacuum environments are needed wherever
the presence of foreign particles wouldinterfere. Certain types of measurements
must be carried out directly within a vacuum,
such as the examination of structures atthe sub-micron level. Common vacuum

06/2024

VacuumPressurein mbar

Height in km Mean free path in m Time in s
above sea
without collision offor covering a surface
level
two gas moleculeswith particles

Rough10+3 to 1

< 50

< 10–5< 10–5Fine

1 to 10–3

50 to 100

10–5 to 10–1

10–5 to 10–2

High

10–3 to 10–7

100 to 500

10–1 to 10+3

10–2 to 10+2

Ultra-high< 10–7> 500> 10+3> 100

applications for linear and angle encoders
include electron microscopes, manipulators,
multiple actuators, XY tables, wafer
inspection in the semiconductor industry,and spectrometer axes for measuring
synchrotron radiation.

High temperature resilience
Achieving a high vacuum class requires
heating the chamber to 100 °C or 120 °C,
thus vaporizing any water molecules stillclinging to the encoder’s housing. This
enables faster pumping. As a consequence,vacuum-compatible encoders must be
designed for temperatures of up to 100 °C
or 120 °C.

Requirements for vacuum-compatible
encoders
Standard encoders from HEIDENHAIN
suffice for applications in rough and finevacuum environments with a limited
temperature range. But encoders for highand ultra-high vacuums must meet special
requirements.
Low outgassing
In order to prevent a dramatic pressure
increase within the vacuum chamber,vacuum-compatible encoders must notrelease gases in large quantities. In an
ultra-high vacuum, every component iscritical. Some plastics, for example, outgas
solvents. Plastics like these are commonly
contained in circuit boards, adhesives, orcoatings but should be completely omitted
from devices deployed in ultra-highvacuums. That’s why HEIDENHAIN
uses vacuum-compatible circuit boards,adhesives, and coatings. In an ultra-highvacuum environment, the number ofcomponents must be reduced to aminimum. Signal converters, for example,
should be kept outside of the vacuum
chamber, which is why HEIDENHAIN
offers vacuum-compatible encoders
featuring external signal converters. Thesedevices can also be placed within thevacuum chamber in applications requiring
merely a high vacuum.

Ventilation of hollow spaces
Generating a vacuum requires pumping theair out of a space. The time required for
attaining the desired pressure, known as
the pumping time, should be kept to aminimum for fast deployment of thevacuum system. Pumping times can beshortened when air is able to escapequickly from all hollow spaces. For thisreason, HEIDENHAIN encoder housingsare equipped with additional air vents,
second openings for threaded holes, andholes drilled into empty cavities.

High cleanness
Encoders used in a vacuum chamber
require special cleaning for minimalcontamination. Most greases, oils, andfingerprints will outgas within a vacuum
environment and are therefore prohibited.
If fine particles or dust are released within
the vacuum chamber, they could destroy
the microelectronic circuits under inspection
or falsify experimental results. Production,cleaning, and packaging are therefore
subject to special requirements.
Prior to packaging (double packaging),
the devices are baked out at 100 °C for
24 hours, thereby releasing residual
atmospheric contamination from thesurface and pumping it away.
Electrical connection
HEIDENHAIN encoders are equipped withconnectors that can be used with vacuumcompatible feedthroughs.

Avoidance of ferromagnetic materials
Depending on the processes within thevacuum chamber, certain materials cannot
be used. Ferromagnetic materials, forexample, cannot be used in electron
microscopes for inspecting microelectronic
circuits. The measuring standards andscanning heads of vacuum-compatible
encoders from HEIDENHAIN are made ofnon-magnetizable materials. Because its
signal converters contain ferromagneticmaterials, HEIDENHAIN offers encoders
that permit external installation of thesignal converter.

The linear encoders of the LIF series requiresignal converters for signal conversion to
1 VPP. These signal converters are housedin the D-sub connector. In high-vacuum
applications, the signal converters can be
attached directly to the encoder or be
installed outside of the vacuum chamber,but in ultra-high vacuum applications, thesignal converters must be installed outsideof the vacuum chamber. The cable between
the scanning head and signal converter can
be up to 3 meters in length.

Vacuum-compatible feedthroughs

Vacuum-compatible encoders

The vacuum-compatible encoders fromHEIDENHAIN are based on modified
standard encoders. The original scanningprinciple, along with any optoelectronic andoptical components, are preserved, but thehousing, circuit boards, and adhesives havebeen modified to meet the requirementsof the given vacuum rating.

HEIDENHAIN vacuum-compatible encoders
employ the following special measures:• No magnetizable materials• Laser inscription instead of labels• Air vents• Specialized cleaning and packaging• Cable with PTFE insulation and tin-plated
copper braiding

LIF 481 V

For high vacuum environments of down to 10–7 mbar

For ultra-high vacuum
environments of down
to 10–11 mbar

LIC 4113V/LIC 4193V

LIF 481V

Measuring methods

Absolute

Incremental

Measuring lengths*

240 mm to 3040 mm

70 mm to 1640 mm

Accuracy grade*±1 μm (Robax);±3 μm; ±5 μm±3 μm

Interpolation error±20 nm±12 nmInterface

EnDat 2.2; Fanuc i; Mitsubishi; » 1 VPPPanasonic; Yaskawa

Signal period–4 µm

Graduation-carriermaterial*• Robax glass ceramic–6 –1
therm ≈ (0 ±0.5) · 10 K–6 –1• Glass therm ≈ 8 · 10 K

• Zerodur glass ceramic therm ≈ 0 K–1 (0 ±0.1) · 10–6 K–1• Glass therm ≈ 8 · 10–6 K–11)

LIF 471V

LIF 481 U

 TTL» 1 VPP

Bake-out temperature 100 °CCables, connectors• 15-pin D-sub high-vacuumcompatible connector (male)

120 °C• 16-pin high-vacuum-compatible round connector(APE in atmosphere) with feedthrough• Signal converter integrated into connector(APE in vacuum)

UHV-compatible plugconnector without
feedthrough (APE inatmosphere)* Please select when ordering1)
Robax glass ceramic, available in measuring lengths of up to 1640 mm
Robax is a registered trademark of Schott-Glaswerke, Mainz, Germany

More information:
DR. JOHANNES HEIDENHAIN GmbHDr.-Johannes-Heidenhain-Straße 583301 Traunreut, Germany +49 8669 31-0
 +49 8669 32-5061
info@heidenhain.dewww.heidenhain.com
627568 · 06 · A · 02 · 06/2024 · PDF• Brochure: Exposed Linear Encoders• Product Information: LIF 481V/LIF 471 V/LIF 481 U• Product Information: LIC 4113 V/LIC 4193 V