Electrical connectors are designed to transfer power or signal between two interfaces. When joined or “mated,” the two interfaces should support a consistent flow of power or signal despite vibration or mechanical stress. Likewise, they must be capable of separation for maintenance without damage. In most cases, the connector manufacturer performs mating force calculations during the product qualification process to ensure that mating and unmating can occur without damage and to determine how many times (also known as the mating cycle). In addition to validating quality products, it’s important for design teams to use this data to control or avoid binding (over-compression of connector pins) or bottoming out and to determine if inject/eject hardware is required.
Let’s break down the factors that influence mating force calculations to better understand the significance of this data for product engineers. Do your connectors add up?
Mating Force Resistance
All connectors are susceptible to resistance, which decreases the transfer of energy within a circuit, resulting in some power or signal loss. The two types of resistance that affect connectors are:
- Bulk Resistance
Bulk resistance is caused by the material along the current’s path and depends on the shape and material of the contact pins. - Contact Resistance
Contact resistance is caused by the mechanical connection of the two connector ends and depends on the contact force between pins and sockets, which can vary significantly depending on the connector type and pitch.
When the contact force is high, it means that the greatest amount of surface area on contact pins and sockets is touching. The more surface area contact, the larger the pathway for energy to travel, thus making it easier to transmit signal or power from one connector to the other — even if a film is present. In other words, high contact force results in a more stable current that is less vulnerable to factors that can cause resistance. If the contact force decreases, the amount of surface area touching between contacts also decreases, thus creating a smaller pathway for the current to travel, which makes it more difficult to transfer signal or power from one connector to the other. Low-force contacts are less stable and more susceptible to factors like the buildup of film, which can cause contact resistance and may eventually prevent any power or signal from passing through the connection.
To ensure the best possible connection, design teams must select the most conductive material that simultaneously provides the highest “normal force,” which is the optimal force generated by contacts as they are mated. Before calculating mating force, it’s important to understand the two phases involved in the mechanical act of mating or unmating a connector.
Phase 1: Contacts spread open as connector ends are mated. Because pressure is required to spread contacts open, two forces are at play: insertion force and friction force.
Phase 2: Contacts slide apart as the connector ends are unmated. Because contacts inherently revert to their original stature, this action only involves friction force.
As these two phases illustrate, the mating force of an electrical connector is normally higher than the unmating force due to the forces involved. Other factors that influence mating force calculations include:
- Geometric properties
- Contact spring rate
- Normal force
- Friction
Because mating force has everything to do with the quality and reliability of a connector, it’s important to work with a manufacturing partner that designs and tests connectors for maximum contact retention. Poor-quality connectors may not have contact retention features built into the design. Over time, repeated mating and unmating will cause contact force and, by default, the stability of the connection to decline. In addition to accurate mating force data, design teams should also look for manufacturers with in-house testing and certification capabilities and a manufacturing process focused on efficiency, value and transparency.
Learn more about top-rated off-the-shelf and customized connector solutions by iCONN Systems.
