A plated material produced by providing a plating layer of, for example, tin (Sn) or a tin alloy, on an electroconductive base material, such as copper (Cu) or a copper alloy (hereinafter, appropriately referred to as base material), is known as a high performance conductor material having the excellent electroconductivity and mechanical strength of the base material, as well as the excellent electrical connectivity, corrosion resistance, and solderability of the plating layer. Thus, such plated materials are widely used in various terminals, connectors, and the like.
In recent years, since a fitting-type connector is multipolarized with advancement of electronic control, a considerable force is necessary for plugging a group of male terminals into/out of a group of female terminals. In particular, plugging-in/out such a connector is difficult in a narrow space such as the engine room of a vehicle, and it has been strongly demanded to reduce the force for plugging in/out such a connector.
In order to reduce the plugging-in/out force, the Sn plating layer on the surface of the connector terminal may be thinned to weaken contact pressure between the terminals. However, because the Sn plating layer is soft, a fretting phenomenon may occur between contact faces of the terminals, thereby causing inferior conduction between the terminals.
In the fretting phenomenon, the soft Sn plating layer on the surface of the terminal wears and is oxidized, becoming abrasion powder having large specific resistance, due to fine vibration between the contact faces of the terminals caused by vibration and changes in temperature. When this phenomenon occurs between the terminals, conduction between the terminals results in inferior. The lower the contact pressure between the terminals, the more the fretting phenomenon is apt to occur.
Patent Literature 1 describes an electrically conductive material for a connecting part, having a Cu—Sn alloy coating layer and a Sn coating layer, formed in this order, on the surface of a base material formed from a Cu strip, wherein the Cu—Sn alloy coating layer has the exposure area ratio at the material surface of 3 to 75%, the average thickness of 0.1 to 3.0 μm, and the Cu content of 20 to 70 at %; and the Sn or Sn alloy coating layer has the average thickness of 0.2 to 5.0 μm. It is also described that a Cu—Sn alloy coating layer is formed by performing a reflow treatment.
According to Patent Literature 1, when this electrically conductive material is used in, for example, a multipole connector in automobiles, a low insertion force upon fitting of male and female terminals is attained, and the assembly operation can be efficiently carried out; and the electrically conductive material is considered to be able to maintain electrical reliability (low contact resistance), even if maintained for a long period of time under a high temperature atmosphere, or even under a corrosive environment.    Patent Literature 1: JP-A-2006-77307 (“JP-A” means unexamined published Japanese patent application)