Key Interconnection Points for Connectors: Contact Portion

What is a connector? Hirose Electric, a long-established connector manufacturer, answers the simple questions like "What is a connector?” and provides more technical information including important points for mounted products in our Connector Basics You’ll Want to Know Series.

In this article, we will be discussing the third and final connection key point for the correct transmission of electricity: the contact area. During the final assembly, the connectors are fitted together in a process called "Mating”. This article explains what points are involved in the mating process to ensure that electricity is transmitted correctly and stably.

The Contact Resistance Value Matters

Connector mating, the process of fitting two connectors with complementing shapes together, is a task that requires specialized skills and knowledge. In many cases, assembly is done not by the connector, cable, or board mounting manufacturers, but by a specialized assembly manufacturer or a dedicated connector mating department when handled internally.

While the role of the contact area is very important when mating connectors, the quality of the contact area is determined based on the stability of the resistance value at the contact area of the conductors. The resistance value of the contact is always listed as "contact resistance" in connector catalogs and specification sheets.

Stabilizing the Contact Resistance Value

If the contact resistance is unstable, electricity cannot be transmitted correctly. For this reason, connector manufacturers have incorporated various design innovations in their connectors in order to stabilize contact resistance.

[Preventing Film Resistance]
Increase Contact Pressure

Terminal contact areas come in a variety of shapes and sizes, but they are all made of metal, so an oxide film can form on the surface. Increasing the contact force enables the terminal contact area to break through the oxide film and transmit electricity correctly.

[Corrosion Prevention]
Plating on the Contact Portion

The metal surface of the terminal will oxidize and corrode, becoming non-conductive overtime. To prevent this, suitable plating is applied to the terminal contact area and the solder area to mitigate loss of conductivity and maintain stable contact resistance over a long period of time.

[Vibration Countermeasure]
Securing the Contact Point

Various types of equipment, including automotive and industrial equipment, generate vibration. Vibration wears down the terminal contact area and causes connector malfunction. However, the impact of the vibration can be reduced by securing the connector contact points.

[Dust and Dirt Adhesion Prevention]
Multi-point Contacts

Some devices are used in environments with dust and dirt. Connectors with a multi-point contact design can be adopted for devices with such usage environments in order to maintain the contact resistance even when contamination to the connector occurs.

How to Select The Type of Plating Applied to The Terminals

Plating is applied to the contact area in order to stabilize contact resistance, but we often receive questions on how to select the plating material. When in doubt, please select the plating based on the operating environment of the equipment and the circuit current. If you use gold plating for all of your products, the contact resistance will be stable. However you can reduce costs by selecting tin plating instead of gold when appropriate.

Refer to the following operating conditions as a guide when selecting between tin and gold plating.

Plating Specifications	Tin Plating	Gold Plating
Mating Durability (Cycles) *1	Less than 30 times	Less than 50 times
Vibration *2	None	Present
Environmental Stress *3	None	Present
Current Used	100μA or more	100μA or less

*1: The mating durability differs depending on the Hirose product series. For details, please refer to the series catalog.
*2: Constant or intermittent exposure to vibration and shock.
*3: Examples of environmental stress: Hydrogen chloride, salt water, sulfur participation, outdoor environment, continuous high-load cycling, etc.

In the next article, we will explain connectors based on the following components: shielded cable, FPC/FFC, coaxial cable, and optical fiber.

Previous Article> (Part 3) Key Interconnection Points for Connectors: Board Mounting
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