Low and Stable Electrical Resistance

As vehicle markets move toward safer and transformational energy products, vehicle manufacturers are responding to four related trends that will dominate the future of the transportation industry: the rise of autonomous vehicles, powertrain electrification, enriched connectivity and shared mobility.

These trends, however, rest on the ability of manufacturers to leverage connectors that offer the winning combination of high circuit counts and miniaturization so they can fit into the limited space available in dense, feature-rich vehicle architectures. At the same time, these connectors must exhibit low and stable electrical resistance over an extended period – especially if they are to perform reliably for the lifespans envisioned for the far-off promise shared mobility.

A vast number of innovations are helping vehicle manufacturers respond to transportation industry trends. These include powertrain electrification, bandwidth and connectivity enhancements, automatic updating, driver-assist capabilities, autonomous-driving platforms with sophisticated safety systems as well as an array of sensor-driven control units and new digital features. All of them, however, require additional devices, new cabling and innovative connectors to bring them together. 

That last item – connectors – is where space and weight limitations converge with the shift to shared vehicles (shared mobility). Shared vehicles must offer a vastly extended service life to live up to their definition. As they serve one user after another, operating for long periods day after day, reliability becomes an overriding concern. With demand growing for reliable performance over increasingly long service lives, manufacturers already face the challenge of sourcing miniaturized connectors that offer stable long-term reliability and low electrical resistance. 

As vehicles rely on increasingly complex systems and build in new functions, the number of circuits rises. To accommodate these circuits without increasing the weight or size of vehicles, miniaturization plays an outsized role. But there’s a catch. 

Smaller terminals tend to have lower normal forces, especially at end-of-life, which can negatively impact electrical contact resistance. These terminals can also be subjected to repeated insertion, decoupling, and operational micro-motion (fretting). As a result, the layer of Tin on the terminal blade is worn down, exposing the underling metals to corrosive effects. This, in turn, increases electrical resistance in the circuit, compromising its performance. After multiple insertion and decoupling cycles, as the top Tin plating gradually wears away, it typically piles up at the end of the wear track on the blade. The gradual wearing down of the surface changes the physical characteristics of the interface, which can negatively impact the mate force and electrical contact resistance.

Mate force plays a key ergonomic role in the connector industry. Automotive line workers will struggle to repeatedly mate anything above 75 N. This limit puts constraints on the number of terminals that can be designed into a connector without mate assistance. Consequently, it becomes imperative to reduce the friction at each individual terminal interface to lower mate force on high-circuit count hand-mate connectors.

In general, friction and electrical contact resistance have an inverse relationship. So, the challenge is to strike the right balance and maintain both low mate force and low and stable electrical resistance over time. Consider the growing number of miniaturized electrical systems in vehicles, and it's easy to appreciate the scope of the challenge.

Material Strength. To combat the intrinsic weakness of miniaturized terminals, Molex terminals incorporate a two-piece design that increases the strength of the terminal. First, the design encloses the exterior portion of the terminal in metal for added rigidity. The interior portion of the connector uses a Copper Alloy. This, in turn, is encapsulated by Nickel and Tin plating to prevent corrosion of the underlying Copper Alloy. The two-piece design enables increased end-of-life normal force that helps maintain stable electrical contact resistance throughout the life cycle of the terminal.

Reduced Pitch. This design element enables Molex to take miniaturization to a new level. By reducing the pitch compared to industry-standard cavities, Molex can incorporate more circuits into a smaller connector housing. As a result, Molex can significantly increase the circuit count of each connector while maintaining the same footprint or reduce the footprint for the same number of circuits, exceeding industry standard cavities.

Low-Friction Design. ZeroWear Technology is a Molex innovation that addresses the challenges miniaturization presents to the electronic terminal interfaces used in automotive connectors. It is a technology that prevents the complete wearing through of the top plating, such as Tin or Silver. This technology is designed to enhance both the service life and performance of these devices under the full range of operating conditions. 

Molex engineers have developed a lower-friction interface that strikes a fine balance between mate force and electrical resistance. By reducing the level of mate force (friction), ZeroWear terminals can still achieve the goal of low electrical resistance on a circuit and retain it longer.  After repeated cycles of insertion and decoupling, ZeroWear’s lower mate force terminals exhibit less wear and more free Tin remaining at the interface than industry-standard connectors. This increases their life cycle and improves performance. 

Taken together with other Molex innovations, ZeroWear packs more circuits into each miniaturized connector. Moreover, the lower mate-force design enables Molex to offer higher circuit counts even on hand-mate connectors. Since hand-mate connectors are smaller than connectors that require a mechanical lever for insertion, manufacturers now have more opportunities to benefit from miniaturization without sacrificing the long-term performance goal of low and stable circuit resistance.

Don’t miss an explanation of Reliability and Validation of Automotive Connectors.

See how zonal architecture will change automotive design. It reduces the complexity of cable harnesses in vehicles in both the number of wires and the distance they travel. Zonal Architecture: Making the Car of the Future Possible.