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Overmolding of an M8 connector onto a flat cable:
How Fillio replaced an internal potting step for a customer

How can an electronic component supplied with a flat cable be connected to a 4-pin M8 connector in a watertight manner without adding to the workload of the customer’s internal assembly line? For this project, our team replaced a manual potting process with low-pressure polyamide (PA) overmolding, incorporating a small, custom-designed adapter PCB. The result: a ready-to-install component, controlled tooling costs, and a robust, watertight connection—exactly the kind of solution Fillio was designed for.

Overmolded round cable with flat cable

THE CUSTOMER'S CHALLENGE

The electronic component supplied by the customer came with a flat cable, which was convenient for internal integration into their product but difficult to interface directly with a standard M8-type cylindrical industrial connector. Several challenges had to be addressed simultaneously:

 

  • Establish a reliable electrical connection between a flat cable and a standard round cable.

  • Ensure a level of water resistance compatible with the operating environment (typically IP67/IP68).

  • Avoid any time-consuming or manual assembly steps on the customer’s side.

  • Control tooling costs and time-to-production, a key challenge for an SME that rapidly iterates on its product.

 

The initial solution, based on two-component potting performed in-house at the customer’s facility, worked but had several limitations: long cycle times, variability in sealing quality depending on the operator, handling of resins (HSE, storage), and space requirements in the workshop.

OUR SOLUTION

We have designed an overmolded part that combines three components engineered to work together.

A standard M8 cable, carefully selected

Rather than molding the M8 connector, we started with an off-the-shelf pre-assembled cable equipped with a 4-pin M8 connector molded onto one end. The other end is stripped to expose the conductors. This approach leverages a proven, standardized, and readily available component—and avoids the investment in dedicated tooling for M8 injection molding. A choice aligned with our philosophy: move fast, keep costs low, and focus engineering where it creates the most value.

An adapter PCB designed for the process

The two cables connect to a small adapter PCB designed specifically for this project. It serves three purposes:

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  • Electrical interface: The conductors from the M8 cable and the flat cable are soldered on either side, with a layout that eliminates any risk of short circuits.

  • Mechanical support: the PCB stiffens the junction area, which facilitates positioning in the mold and protects the solder joints from stress during injection.

  • Repeatability: a dimensionally controlled, mass-produced part replaces a variable manual process.

 

This is exactly the kind of co-design we appreciate: a small, well-designed PCB can radically simplify the rest of the process.

Low-pressure polyamide overmolding

The assembly—consisting of the stripped end of the M8 cable, the PCB, and the end of the flat cable—is then encapsulated using a low-pressure polyamide (PA) overmolding process, which is Fillio’s core expertise. This process, which injects the material at pressures of only a few dozen bars, is particularly well-suited for electronics:

 

  • Moderate pressures and temperatures, compatible with solder joints and components.

  • Excellent adhesion of the PA to the cable jackets and the PCB substrate, ensuring a watertight seal at the interface.

  • Aluminum tooling that is lighter and significantly less expensive than a high-pressure injection mold—a real advantage for small- or medium-volume production runs.

  • Short cycle times and an automatable process.

 

The overmolded body creates a clean tapered transition between the flat cable and the round cable, while also acting as a strain relief at both ends: no mechanical stress is transmitted to the solder joints.

HOW THIS HAS CHANGED THINGS FOR THE CUSTOMER

The switch from in-house potting to this overmolded part at Fillio has had several tangible benefits:

 

  • Elimination of an in-house assembly step. The part arrives ready for integration, with no potting required, no curing time, and no need to re-test for leaks in the workshop.

  • No more resin to handle in-house. HSE constraints related to two-component systems are eliminated, as are storage requirements. (At Fillio, excess resins are recycled or reused internally—a commitment we uphold in all our projects.)

  • Repeatable sealing. The controlled industrial process guarantees consistent results, independent of the operator, with rigorous quality control on every batch and traceability available upon request.

  • Low tooling costs. The low-pressure aluminum mold and the use of a standard M8 cable eliminate the heavy investments typical of conventional injection molding.

  • Rapid time-to-market. From proof of concept to launch, we maintain tight timelines with few iterations—exactly what innovative SMEs prioritize.

FOR WHAT KIND OF PROJECTS?

This approach—off-the-shelf cable + adapter PCB + low-pressure overmolding—is applicable far beyond this specific case. It is particularly relevant whenever it is necessary to:

 

  • Interface an electronic component with a standard waterproof connector (M8, M12, etc.).

  • Convert a flat, ribbon, or FFC cable to an industrial round cable.

  • Eliminate a manual potting or bonding operation on the customer’s end.

  • Achieve an IP67/IP68 rating without an added gasket.

  • Launch a product in small or medium production runs without investing in high-pressure tooling.

 

The same principle can be applied with other engineering resins and connector geometries, depending on the environmental and mechanical requirements of the application. This is exactly the kind of challenge we love to tackle with our customers, through co-creation, in our workshop in Quebec.

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