Dr. Bob on Electrical/Electronic Connector Contact Spring Materials
A functional description of the performance requirements for an electrical/electronic connector is that it must transfer an electronic signal or electrical power between two sub-units of an electrical/electronic system without unacceptable power loss or degradation in signal integrity. Also, it must maintain this capability consistently over multiple mating cycles (separability). In practice, meeting these requirements is accomplished by creating a metallic contact interface between the two halves of the connector, usually a plug and receptacle.
The resistance of a contact interface depends on the area of the interface and the conductivity of the materials in contact. A simplified expression of this relationship, for a circular unplated contact area, is:
RContact = r ( H / FNormal)1/2
where RContact is the resistance of the contact interface, r is the resistivity of the contact material, H is the hardness of the contact material, and FNormal is the contact normal force—that is, the force perpendicular to the contact interface. The general form of this equation applies to contact interfaces of geometries other than circular.
Note that the contact material is referenced directly in both r and H. The contact material is also implicit in the FNormal term, because it is the deflection of the contact springs during the mating of the connector which generates the contact normal force.
For electrical/electronic connectors, minimizing resistance—both bulk and contact—is important. Thus a low-resistivity, high-conductivity metal is desirable. The resistivity of metals varies significantly depending on the material and its processing, both mechanical and chemical. For example, copper, aluminum, and iron have resistivities (in microohm-centimeters) of 1.67, 2.65, and 9.71, respectively. Mechanical processing, drawing, rolling, and forming can slightly increase the resistivity of a metal. Alloying is more significant when chemistry is altered. For example, copper alloy C26000, a car