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good metal conductivity as well as insulation thickness is important for best cable
shielding and back-shell technology.
Military-Specification connectors and
cabled interconnections used in missioncritical and high-reliability modules for
military avionics, autonomous vehicles,
satellites, and soldier-worn systems are
especially vulnerable to Cybersecurity issues. Surprisingly, internal-signal noise
management is also a key element in
controlling signal integrity within one's
own system.
Standard noise and EMI control methods include isolation, grounding, filtering,
balancing, shielding, signal separation,
impedance control, cable design, and
managing the signal/time domain. To
help protect signal integrity, connector
and cable harness designers are also adding back-shells and cable shields for EMI
protection, as well as providing mechanical strain reliefs.
Many of the smallest cables require
shielding inside and out to isolate mixed
signals within the interconnection system. Do not overlook the need to directly
connect cable shielding to metal shell
connectors. It is important that there is
a firm and direct connector ground on
the board and/or the metal shell of the
circuit package.

Connector sizes and metals
Micro- and nano-sized connectors are
often used with metal shells connected
to braided-cable shields. The metal frequently used is Aluminum 6061 with T6
treatment for the advantages of strength
and lower weight, as well as the EMI
sealing. Metal shells are usually treated
with electroless nickel plated at .0005inch thickness, and some novel designs
use stainless steel for the metal housing, and occasionally see gold plating on
shells used in environmentally-hazardous
environments.
Connector shells can also use a separate metallic, back-shell covering that
screws on, or is an integral portion of the
connector shell. The back-shell is then attached to the outside shielded braid of
the cable harness to finish the assembly.
To ensure signal purity, miniature connectors often use beryllium-tempered

Circular connections provide
rugged, high-reliability,
watertight (IP67) links for
continuous signal integrity in
harsh environments
Courtesy of Omnetics

spring-pin contacts, as small as 13 onethousands of an inch in diameter, to provide constant connection through high
vibration and physical shock.
Preventing poor pin-to-socket connections during vibration is critical, as
they can cause signal noise and be interruptive to very high-speed digital signal
transmission. Shielding within both the
connectors and cable is vital to prevent
EMI problems. As designers focus on
higher densities and increase the number of functions, the space available for
internal wire-routing of signals is getting
smaller and more critical. Custom designs
are more frequently employed for cabling
to specifically fit within each new instrument, to reduce overall size and weight.

Circular connectors
A Micro circular connector designed to
work well for EMI reduction includes the
triple-thread ratcheting metal mechanism made of lightweight aluminum and
provides rugged, high-reliability, watertight (IP67) connections for continuous
signal integrity in harsh-environment
military, aerospace, security, and petroleum applications subject to high shock
and vibration.
Such circular connectors are built
with integrated back shells for EMI, and
feature alignment keys and insulators
that enable quick, secure couplings and
over-molded strain reliefs on the back of
each connector that conform to the cabling, improving the overall reliability.
These connectors come in multiple pin

counts, and are offered in various shell
and plating materials to meet specific environmental challenges. They are rated
for 3A per contact, 250VAC, and standard
operating temperatures spanning -55ºC
to 125ºC.

Rectangular connectors
Standard Micro and Nano-D connector
models should be qualified to military
QPL reliability and performance specifications, and connectors with 360 degrees of sealing assure high levels of RF
and Conducted interference attenuation.
For example, Omnetics offers metal-onpolymer EMI shielding gaskets for special
designs. Such Micro-D or Nano-D backshells are designed to protect the back end
of the connector shell and provide strain
relief, preventing mechanical stress for
the crimped contacts, for high-reliability
applications.
Backshells provide additional EMI protection when they are used as a grounding point for the cable shield, a ground
wire, or when braiding is added over the
wires. Additionally, customized backshells are designed to specific shapes
and functions to aid in meeting the key
design requirements or challenges. Many
design formats are available for Micro-D
and Nano-D connectors, including twopiece solutions, straight, 45°, 90°, oval or
round wire/cable exit, and with two distinct wire/cable exits.
Higher signal speeds and mixed-signal
cable make for a noisy electrical environment, as the combination of electric and
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