Probe pin and an IC socket with the same

1. A probe pin comprising a plunger formed of a sheet metal, and a coil spring unit formed of a metal wire and configured to hold the plunger thereon, wherein:

in a developed state, the plunger includes a first portion and a second portion each of which has an upper contact strip, a wide portion, and a lower contact strip, and which are connected to each other via the wide portions formed in the first and second portions;

the plunger is formed in a united manner by folding together the first and second portions along a boundary of the wide portions formed in the first and second portions to thereby bring at least the wide portions formed in the first and second portions into tight contact with each other;

a resilient deformation portion is formed at a lower portion of each of the lower contact strips formed in the first and second portions; and

when the first and second portions are folded together to form the plunger, the lower contact strips formed in the first and second portions are brought to come into tight contact with each other except for the resilient deformation portions and form a unitary body whereas the resilient deformation portions form paired resilient deformation portions that are resiliently deformable with respect to each other.

2. A probe pin as claimed in claim 1 , wherein:

a contact point portion having a contact point is formed at an upper portion of each of the upper contact strips formed in the first and second portions; and

when the first and second portions are folded together to form the plunger, the upper contact strips formed in the first and second portions are brought to tight contact with each other except for the contact point portions and form a unitary body whereas the contact point portions form contact point portions on which a plurality of the contact points are so spread in a plane.

3. A probe pin as claimed in claim 1 , wherein:

a contact point portion having a contact point is formed at an upper portion of each of the upper contact strips formed in the first and second portions; and

when the first and second portions are folded together to form the plunger, the upper contact strips formed in the first and second portions are brought to tight contact with each other and form a unitary body and the contact point portions form a single contact point.

4. A probe pin as claimed in claim 1 , wherein:

a protrusion is formed on any one of the first and second portions, and an opening or recess is formed in the other of the first and second portions, the protrusion being fitted into the opening or recess when the first and second portions are folded together to form the plunger.

5. An IC socket for electrically connecting a semiconductor device as a first contact object, and a second contact object, comprising at least:

a base member including a placing recess to house the semiconductor device, and a plurality of through-holes; and

a plurality of the probe pins as claimed in claim 1 , which are held in probe-pin housing spaces defined by the plurality of through-holes, respectively, wherein:

the upper contact strips of the plungers of the plurality of probe pins come into contact respectively with external contact points of the first contact object; and

contact points provided to the coil spring units constituting the probe pins come into contact respectively with external contact points of the second contact object.