Overmoulding vs. Traditional Backshells — Which Is Right for Your Application?

by Chris Lowthorpe - Project Engineer

Choosing the Right Termination Protection

Protecting connector terminations from environmental exposure, mechanical stress and the rigours of operational use is one of the fundamental challenges in cable assembly design. For engineers working across defence, aerospace, marine and industrial applications, the choice between a traditional mechanical backshell and an overmoulded solution is a decision that warrants careful consideration. Both approaches have clear merits, and both have limitations. Understanding where each performs best is essential to specifying the right solution for your application.

Mechanical backshells: proven, flexible and maintainable in service

The mechanical backshell has been a staple of cable assembly design for decades, and for good reason. A backshell is a separately manufactured housing, typically aluminium, stainless steel or a composite material, that fits over the rear of a connector body to provide strain relief, EMC screening continuation and a degree of environmental protection. Backshells are available in an enormous range of configurations, covering the vast majority of common military and commercial connector families, and they can be specified with a variety of sealing options including environmental seals and potted variants for more demanding applications.

One of the most significant practical advantages of a mechanical backshell is that it can be removed. For platforms where inspection, repair or retermination of connectors is a defined maintenance activity, a removable backshell is often the only appropriate solution. It allows technicians in the field or in a maintenance facility to access the termination, carry out whatever work is required, and reassemble the connector to a known standard. In these applications, the slightly lower environmental sealing performance of a mechanical backshell is an acceptable trade off for the maintainability it provides.

Mechanical backshells also offer more flexibility at the design change stage. If a connector or cable specification changes during a programme, a different backshell can typically be accommodated without the need for new tooling. This makes them particularly well suited to development phases or low volume programmes where design iterations are likely.

What we mean by overmoulding

The word overmoulding is used to describe several quite different processes, so it is worth being precise about which one applies here.

In cable assembly, overmoulding means a moulded compound applied directly over a connector termination that has already been assembled, terminated and tested, encapsulating the interface in a single unified structure. It is not injection moulding of the connector housing itself, and it is not the fully moulded consumer style lead you find on a USB or audio cable, where the connector and the moulding are produced together as one item on high volume tooling. That is a different process and a different supply chain, and it is not something Cablescan offers.

Overmoulding: superior sealing and long term robustness

Rather than fitting a separate housing over the connector, overmoulding encapsulates the termination and the cable entry as one. The result is an assembly where there are no mechanical joints, no potential ingress points, and no reliance on compressed seals or potting compounds that may degrade or be disturbed in service.

The environmental sealing performance of a well designed overmould is significantly superior to that of a mechanical backshell. By applying a soft inner moulding directly around the contacts, screen terminations and cable entry, a fully watertight barrier is created that is an integral part of the assembly rather than an additional component fitted over it. This approach is capable of meeting the most demanding IP sealing and military environmental standards, and it does so reliably across the full service life of the assembly rather than being dependent on the ongoing integrity of discrete sealing components.

Beyond sealing, overmoulding provides a substantial improvement in the mechanical robustness of the interface between cable and connector. The overmould distributes mechanical loads, particularly bending, pulling and vibration, across a much greater length of cable than a conventional strain relief, significantly reducing the risk of conductor fatigue or termination failure in applications with high cycle counts or high vibration. The result is an assembly that is genuinely more durable over its operational life.

The slim profile of an overmoulded assembly is a further advantage where space or weight is constrained. Body worn systems, airborne equipment and compact vehicle mounted installations all benefit from the reduced envelope that overmoulding provides compared to a metal backshell. In these applications, pairing a low profile Amphenol connector that has an integrated backshell with an overmoulded termination can also offer a meaningful component cost saving by removing the need for a separate backshell entirely, depending on the connector family selected.

Cablescan's overmoulding capability

Cablescan works directly with customer engineering teams to optimise material selection, mould geometry and process parameters for each specific application. Where tooling already exists for common connector profiles, lead time and cost for standard configurations are reduced, and for bespoke or unusual connector arrangements we can develop methods using moulded parts to suit the assembly.

Material selection is a critical part of the process, and our engineers will advise on the appropriate compound based on the operating environment, flexibility requirements, temperature range, and any applicable standards or specifications. The balance between hardness and flexibility is particularly important. An overmould that is too rigid may transmit stress into the connector body under bending loads, while one that is too soft may not provide adequate mechanical protection in rugged applications. Getting this balance right from the outset is something our experience across military, aerospace and marine programmes has equipped us to do well.

If you are working on a new programme or reviewing the termination protection approach on an existing design, our team would be happy to discuss the options and advise on the most appropriate solution for your specific requirements.