Reliable Flex Cables for Automotive and Industrial Vehicles

From passenger cars to construction and agricultural equipment, modern vehicles are packed with complex electronics, and all these systems require compact yet reliable interconnects. Electric vehicle (EV) battery packs are a prime example. As battery density increases, designers are under pressure to find interconnects that can save space and simplify assembly. That’s not easy because the connectors still need to maintain long-term reliability under harsh conditions.

Industrial and agricultural vehicles face similar demands. Consider satellite-guided, self-driving tractors: if a connector fails, the only safe response may be to halt the vehicle for inspection. However, crops and weather don’t wait for service technicians to arrive, and unplanned downtime can result in lost revenue or even total crop failure.

The challenge of wiring a modern vehicle

There is a common challenge across these applications: as vehicle electronics grow more complex, the number of interconnects increases. With more interconnects comes added bulk, additional points of failure, and new challenges for routing and installation.

To address these concerns, designers need interconnect systems that offer:

• A compact, easily integrated footprint to suit space-constrained designs
• Mechanically robust, vibration-resistant contacts to ensure reliability
• Safety-conscious handling features that help prevent shock and misconnection during service

In consumer-grade applications, flexible printed circuits (FPCs) and flexible flat cables (FFCs) have long been the go-to solutions for space-constrained, high-conductor-count interconnects. In automotive applications, these interconnects, colloquially known as ribbon cables, have been viewed with skepticism. Instead, designers of automotive systems tend to prefer traditional wiring harnesses, which have well-understood reliability characteristics.

Recognizing this, Hirose created the TB4 series of high-performance FPC/FFC-to-board connectors. These devices significantly enhance the robustness of flex cable interconnects, delivering the reliability of traditional wiring harnesses while being ultra-compact and easy to assemble.

An efficient approach to building vehicle interconnects

The TB4 series interconnect system (Figure 1) is a three-part assembly comprising a board-mounted receptacle, a center-locking plug that ensures a secure connection without the need for additional fasteners, and an orange retainer that locks the FPC or FFC cable in place. This design is remarkably space-efficient: the mated height of the horizontal connectors is just 4.5 millimeters (mm), and the 1 mm contact pitch minimizes overall width.

Figure 1: The TB4 series interconnect system features a simple three-part construction, providing robust vehicle interconnects with an ultra-low profile. (Image source: Hirose)

The TB4 series is rated for 1.0 amperes (A) and 100 volts, supporting a wide range of vehicle interconnect requirements. Beyond these electrical specifications, the design addresses key concerns associated with the use of flex cables in demanding environments. Features include:

• A two-point gold-plated contact mechanism within each receptacle for high signal integrity even under thermal cycling and vibration
• A single-way mating profile that prevents incorrect insertion and enhances safety during maintenance
• Protective guides that help shield from accidental finger contact, reducing the risk of shock
• A construction that meets RoHS3, halogen-free, and UL94V-0 flammability standards, and satisfies USCAR-2 requirements for automotive electrical connector systems
• Two key code types (black and gray) that help prevent misconnections when multiple TB4 assemblies are used in close proximity

This combination of features enables flex cable connections that match the reliability of traditional harnesses while offering a much smaller footprint.

Examining the TB4 series connectors

The TB4 series is available in a range of sizes and configurations to suit different applications. Where larger interconnects are required, the 26-TB4-30S-1H(800) (Figure 2) receptacle provides designers with 30 positions in a compact 8.75 × 37.9 mm footprint. This receptacle includes a small polarization mark that helps service technicians verify the correct mating orientation. The corresponding plug features a similar mark.

Figure 2 : All TB4 receptacles, including the 30-position 26-TB4-30S-1H(800), include a polarization mark to aid mating. (Image source: Hirose)

A component at the smaller end of the series is the 26-TB4-10P-1F(800) plug. This model provides 10 contact positions in a width of just 17.9 mm. Like all TB4 plugs, it also includes an integrated push tab for tool-free disconnection.

Figure 3: The 10-position 26-TB4-10P-1F(800) is the smallest plug in the TB4 family. (Image source: Hirose)

The final element of the TB4 system is a retainer that locks the ribbon cable in place. The 26-TB4-16RP-1(800) (Figure 4) retainer from the middle of the range serves the 16-position plug. The resulting assembly has a width of 23.9 mm.

Figure 4: The 26-TB4-16RP-1(800) retainer ensures a secure fit when inserting an FPC or FFC cable into the matching TB4 series plug. (Image source: Hirose)

Conclusion

Automotive, construction, and agricultural vehicles all depend on specialized interconnects to ensure reliable and safe operation within increasingly complex designs. The TB4 series from Hirose offers the space-saving benefits of FPC and FFC interconnects in these demanding environments, significantly reducing interconnect size while maintaining the critical standards required for vehicle system safety and reliability.