This article examines how modern backshell technologies contribute to high-performance interconnects’ electrical and mechanical integrity and some key factors to consider during the specification phase.
Today’s aerospace, defense, and medical applications demand connectors that offer high-speed and compact interconnections, withstand vibrations and shocks, and maintain immunity against electromagnetic and RF interference (EMI/RFI). Achieving this requires integrating connector and cable assemblies with robust mechanical and electrical protections.
In any high-performance environment, be it a satellite or an MRI scanner, reliable and robust connectors are paramount. These applications often operate under extreme conditions, including vibration, shock, and exposure to electromagnetic interference.
Understanding the operational context of the connector is crucial in ensuring it performs as it should over the system’s lifetime. This is demonstrated well in the differing environmental stresses that an industrial robot undergoes — which faces continuous exposure to mechanical stress and potential contaminants — versus those for a cube satellite — which is exposed to extreme temperature variations, strong gravitational forces, and high radiation levels. However, while there is no one-size-fits-all connector, there are two critical functional requirements that any connector should meet: mechanical and electrical integrity.
Mechanically, connectors must resist deformation or disconnection under stress, ensuring a stable and continuous connection. This is vital in environments where vibrations or impacts are common, as any movement can lead to wear or accidental disconnections.
Electrically, connectors must provide consistent conductivity and be shielded from external electromagnetic sources to prevent interference that can degrade signal quality and/or cause malfunctions.
A failure in either of these factors will affect the system’s longevity and reliability, meaning backshells (protective enclosures for connectors) can be essential in the design process.
How backshell connectors provide protection… and considerations for specification
If we look first at mechanical integrity, the backshell provides crucial strain relief in the system. By securing the cable and connector, they prevent movement and vibration that would otherwise enable cables to rub and fret against areas of the chassis or the airframe, which would, therefore, lead to wear or disconnection. In addition, backshells offer physical protection against impacts or rough handling, shielding the connector from potential damage. In harsh environments, where mechanical failure can have serious consequences, the role of the backshell is indispensable in reducing or eliminating the risk of short circuits from exposed conductors.
The electrical integrity of a connector in a harsh environment is equally crucial; backshells contribute significantly to this by offering effective cable management and comprehensive shielding. Proper cable management within the backshell — including a braid that is, in turn, fixed to the backshell — minimizes the risk of electrical noise and interference from adjacent cables or devices, preserving signal clarity.
Advanced backshell designs will feature 360° EMC shielding, which provides a conductive barrier around the connection point. This shielding is essential in environments with high levels of electronic noise, as it prevents electromagnetic interference (EMI) from disrupting signal transmission and protects any surrounding components that might be prone to signals that come from within the cable bundle. A well-designed backshell will also ensure it is possible to reliably ground the shield to dissipate unwanted electrical noise and maintain signal integrity.
Backshell materials
Choosing the right material for the backshell is a critical decision that impacts their performance and suitability for the application or the specific environmental conditions and mechanical stresses the connector will face. There is a range of options when it comes to the materials used to construct the backshells; for example, stainless steel and composite materials have been used, but for many high-performance applications, aluminum is the preferred option — especially in aerospace, military, and other applications where weight and durability are crucial.
The metal’s high strength-to-weight ratio makes it an excellent lightweight protective covering. Due to its high conductivity, it also benefits from good shielding properties and its high levels of thermal conductivity aid heat dissipation.
Backshell technologies
In addition to the material used in their construction, backshells have evolved to incorporate multiple technologies and the following should be considered when meeting the demands of a given application.
EMI/RFI shielding backshells minimize electromagnetic and RF interference. They are crucial in environments with high levels of electronic noise and typically incorporate a metal barrier braid that covers the full cable assembly. However, it’s vital to note that this shielding should be integrated as an end-to-end solution, not just on the cables and braid but also on the PCB side.
Angled backshells provide a solution for space-constrained applications by directing cables at 90o, reducing the required clearance space. These angled backshells can also be used in conjunction with EMI/RFI shielding to allow horizontal PCB-to-cable connection even in these operating environments.
Design flexibility
A project’s required technical specifications naturally change throughout the design cycle. A measure to mitigate vibration might not be as effective as planned, or an EMI issue might occur late in the design cycle.
Designs and layouts can be modified to incorporate a new component, but several backshells are now being manufactured using a two-part construction method. This enables, for example, a last-minute upgrade to add EMI shielding. By taking this approach, this upgrade can be implemented not only at any point during the design phase but also when issues arise in the field.
Summary
Connector backshells are indispensable for ensuring mechanical and electrical integrity in high-performance interconnects. They provide critical functions such as strain relief, vibration resistance, and comprehensive EMI shielding, which are essential for maintaining connector reliability and performance in demanding environments.
However, the application’s operational environment, be it a robot, a military surveillance drone, or a medical scanner, needs to be considered early in the design process to ensure correct functioning over the system’s lifetime. While there is no one-size-fits-all connector, specification considerations should first examine the required mechanical and electrical shielding level.
Following this, the considerations should switch to the backshell’s material, required functionality, and the likelihood of changes being made late in the design. These considerations will enable the highest level of signal integrity, even in the harshest environments.
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