The distribution and number of a-spots provides a highly redundant network of resistances in parallel at the contact interface, a very important factor in the stability of contact interface resistance. It must be noted that permanent connection interfaces are also created in the same manner, and differ only in the amount of deformation, cold welding and the total contact area that is created.
A summary of the effects of the a-spot surface structure of contact interfaces follows:
• On the microscale of the contact interface all surfaces are rough.
• Surface roughness leads to the creation of small individual contact areas, called a-spots, at the contact interface.
• The number of a-spots created depends on two factors: the contact force and the surface roughness. The contact force determines the total a-spot contact area and the surface roughness determines how many a-spots will be included in that area.
• The geometry of the apparent contact area containing the a-spots is determined by the geometries of the plug and receptacle contact surfaces as they come together during mating.
• Current flow across the contact interface is constricted to flow through the a-spot distribution a geometric effect leading to an increase in resistance, constriction resistance, at the contact interface.