Datasheet

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EMI ESSENTIALS
Fabric-Over-Foam and Conductive Foam Wire Mesh Tape
Applications • Shielding or grounding of computer and
telecommunication equipment seams
and apertures
• Covers opened infrequently for servicing
(6-12 times per year)
• Long lasting resiliency is ideal for highly
sensitive components in permanent or
semi-permanent enclosures
• Consistent point-to-point contact for high
shielding effectiveness over the life of the
gasket
• Design exibility provides grounding and
shielding solutions for I/O shielding panels,
disk drive insulators, ground planes or circuit
boards, electromedical devices, keyboard
devices
• Mask-and-peel tape for painted electronic
enclosures
• Cable and wire harness wrapping
Features and Benets
Product Highlights
• UL 94VO and HB ame retardant
• Ideal for applications requiring low
pressure force
• Self-terminating cut-to lengths
• High conductivity and shielding attenuation
• Galvanically-compatible with most mating
surfaces
• High abrasion and shear resistance
• Most economical gasket for low-cycling
applications
• High shielding effectiveness over broad
frequency range
• Available in wide variety of sizes and shapes
• Knit construction for long lasting resiliency
• Versatile mounting options
• Available with elastomer gasket for moisture
and dust sealing
• Simple installation
• Ideally suited for thin or low-prole
applications
• Conductive foil tape with release mask for
painted enclosures
• Tin copper cloth and nickel copper cloth
versions provide easy-to-handle alternatives
to foils
Electrical Shielding
Effectiveness
Transfer Impedance (500 MHz)
>85 dB 90 - 105 dB —
H-eld (200 MHz)
Modied Mil 285
30 - 45 dB 55 - 65 dB —
Plane Wave (2 GHz)
Modied Mil 285
90 - 100 dB 80 - 115 dB 85 - 95 dB
Surface Resistivity <0.07 ohms/square N/A Low surface resistivity based on material selection
Volume Resistivity N/A 0.0004 - 0.114 ohm-cm N/A
Mechanical
Available Size Range
Height: 0.015 - 0.945 (0,038 - 24,0) Height: 0.062 - 0.500 (1,57 - 12,7) Width: 0.025 - 2.00 (6,4 - 50,8)
Thickness: 0.003 - 0.007 (0,08 - 0,18)
Deection Operating Range 20 - 75% deection 20 - 70% deection N/A
Compression Force
(based on shape selection)
3 - 10 Ibs/in. ft. (4,5 - 15,0 Kg/m)
@ 20% deection (dependent on foam
selection and shape)
From 6 - 50 Ibs/in. ft.
(8,8 - 74 Kg/m) round
N/A
Compression Set <4 - 20% @ 50% deection 10% @ 20% compression N/A
Joint Unevenness
Accommodation
0.020 - 0.050 (0,51 - 1,27) 0.010 - 0.300 (0,25 - 7,6) N/A
Compound/Material
Availability
Cover: Flame retardant metallized Ni/Cu,
Tin/Cu and silver woven or non-woven textile.
Core: Flame retardant urethane, TPE
BeCu, Monel, aluminum, tin-plated steel,
tin-plated brass, Enviroseal version with
neoprene or silicone
Tin-plated copper, copper foil, nickel copper
cloth tape
Temperature Range -40 - 158°F (-40 - 70°C) Enviroseal -103 - 500°F (-75 - 260°C) 50 - 500°F (10 - 260°C) based on material
selection
Available Proles Round, rectangular, square “D”, “C”, “J”, “P”,
“U”, clip-on, knife edge
Round, rectangular, square, single-round with
n, double-round with n
Rolls
Mounting Methods Groove, PSA, clip-on, dart Groove, pressure-sensitive adhesive,
mechanical fasteners, channel mount
Pressure-sensitive adhesive, conductive or
non-conductive
Custom Shapes Available Cut-to lengths, mitered and spliced corners,
kiss-cut, other proles
Cut-to lengths, mitered corners, at tape, and
EMI washers
Die-cut shapes
Environmental
Fluid Seal
N/A Enviroseal product only: moisture, rain N/A
Air/Dust Provides barrier against dust Enviroseal product only N/A
Galvanic Compatibility Compatible with a wide variety of mating
surfaces—zinc, aluminum, stainless steel, etc.
Variety of platings to ensure galvanic
compatibility with mating surface
Wide variety of materials available to meet
galvanic compatibility requirements
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Overview of EMC/RFI Issues
The phenomenon of electromagnetic interference (EMI) is familiar to virtually everyone, even if they do not
understand the underlying principles. Most people have witnessed rsthand the effects of interference.
To control EMI, government organizations, such as the FCC, CSA, and EEC, mandate that manufacturers may
not design, produce or sell electronic equipment that jams the public broadcast services. In other instances,
however, EMI can constitute more than a mere nuisance. The military and medical communities, for example,
require trouble-free operation of their electronic equipment in adverse electromagnetic environments since
malfunctions could jeopardize missions and personnel. The European Union’s EMC directive also mandates
that “the apparatus has an adequate level of intrinsic immunity to electromagnetic disturbance to enable it
to operate as intended”.
EMC Design of High Speed Systems
The interference and susceptibility (immunity) effects of electronic apparatus are created by time-variant
electromagnetic elds which may be propagated along a conducting medium or by radiation through space.
Because the source of the conducted and radiated interference energy levels may be related, a coordinated
systems design effort is required to reduce these effects.
A design program for an equipment item that must meet both an emission and an immunity requirement
consists of:
• Suppression: Reducing the interference at its source.
• Isolation: Isolating the offending circuits by ltering, grounding and shielding.
• Desensitization: Increasing the immunity of any susceptible circuits.
These three steps should be carried on throughout the entire equipment design and implemented as early
as possible within the design program.
Effects of Logic Speed
The trend in today’s electronic devices is faster, smaller, and digital rather than analog. Most equipment
(95%) of today contains digital circuits. Today’s digital designer must create a circuit board that has the
lowest possible EMI, combined with the highest possible operating/processing speeds. Design of the PCB
is the most critical EMC inuencing factor for any system, since virtually all active devices are located on
the board. It is the changing current (accelerated electron movement) produced by the active devices that
result in EMI.
Design Approaches
There are two approaches that can be used to reduce the emission from the PC board. The rst approach is
to operate the circuit at the slowest speeds consistent with the functionality of the system, lay out the PCB
with the smallest possible loop areas (especially the high speed devices), and insert suppression components
such as lters, ferrite beads, and bypass capacitors into the circuit to reduce its bandwidth. These techniques
will result in a desired decrease in the high frequency harmonic amplitudes and circuit bandwidth and a
corresponding undesired decrease in both the operating speed and system reliability. The use of slower
speeds with reduced bandwidth will help to desensitize the circuit to external susceptibility elds.
The second is to use shielding. Shielding is the only non-invasive suppression technique. Since the shielding
is not inserted into the circuit, it does not affect the high frequency operating speed of the system, nor does
it affect the operation of the system should changes be made to the design in the future. In addition,
shielding does not create timing problems and waveform distortion; it does not decrease system reliability;
and it reduces crosstalk. Plus, shielding works for both emission suppression as well as susceptibility
(immunity) problems.
Even with the overall advantages of shielding, the most cost-effective approach is to use a combination
of circuit suppression/hardening and shielding.
EMI INTRODUCTION