Connection terminal

A connection terminal comprising:

• an elastic piece configured to provide urging force toward a connecting part of a counterpart terminal;
• and
• a contacting section protruding from the elastic piece toward the connecting part of the counterpart terminal and configured to come in contact with a surface of the connecting part of the counterpart terminal by the urging force of the elastic piece, wherein
• the contacting section includes
• a hollow portion located at a center of the contacting section, having a recess in a direction away from the connecting part of the counterpart terminal, having no contact with the surface of the connecting part of the counterpart terminal, and formed on a surface of the elastic piece facing the connecting part of the counterpart terminal, and
• a contact portion located to sandwich the hollow portion in a plan view of the elastic piece and configured to come in contact with the surface of the connecting part of the counterpart terminal,
• the contacting section has a hemispherical shape,
• the hollow portion has a circular shape in the plan view of the elastic piece,
• the contact portion has an annular shape located on an outer periphery of the hollow portion in the plan view,
• an outer diameter of the contact portion is set such that current flow between the contact portion and the connecting part of the counterpart terminal is enhanced without increasing a size of the contacting section, and
• the outer diameter of the contact portion is increased to increase an apparent contact surface diameter and decrease a contact resistance of the contact portion according to the expression:
• Rc=(ρ/D)+(μ/2na);
• where Rc is the contact resistance, ρ is a volume resistivity of a metal of the contact portion, D is the apparent contact surface diameter, 2a is an actual contact surface diameter and n is a number of actual contact surfaces.