1. Field of the Invention
The present invention relates to a socket for electrical parts for detachably holding and accommodating electrical parts such as a semiconductor device (which is called herein as an xe2x80x9cIC packagexe2x80x9d) or the like, to conduct electrical performance test and examination of the electrical parts, and more particularly, making improvements in the contact stability between the socket for electrical parts and the electrical part.
2. Prior Art of the Invention
In a known art, there has been provided an IC socket, as xe2x80x9csocket for an electrical partxe2x80x9d for detachably holding and accommodating an IC package as an xe2x80x9celectrical partxe2x80x9d.
Such IC package includes BGA (Ball Grid Array) type, in which a number of spherical solder balls (terminals) are arranged to the lower surface of the rectangular package body projecting downward in a matrix arrangement.
On the other hand, aforementioned IC package is positioned to be accommodated on the accommodation surface portion of a socket body of the IC socket at a predetermined position, and the solder balls of this IC package each make contact with the contact point of a tab film, a sheet like base plate to establish electrical connection when the performance test of such IC package is being conducted.
Further more, an elastic member is provided on the lower surface of the tab film to prevent the solder balls from being damaged and to enhance the contact stability between the solder ball and the contact point of the tab film. (Please refer to the Japanese laid open patent publication No. Hei 11-242977)
FIG. 10 is a sectional view showing a contact state of the solder ball 2a of the IC package 2 accommodated on the accommodation surface portion of the IC socket and the tab film 5 in a conventional IC socket. The tab film 5 is formed with a contact point 5a to which solder ball 2a contacts at a position corresponding to the solder ball 2a. To the lower side of the tab film 5, an elastic member 4, a plate shape body having elasticity made of silicon rubber is disposed.
In such IC socket, after the IC package 2 is mounted on the tab film 5, the package body 2b is pressed downward the amount as prescribed, accordingly the elastic member 4 is elastically deformed through the solder ball 2a and the tab film 5. By reaction force from this elastic deformation, a predetermined contacting pressure is produced between the solder ball 2a and the contact point 5a on the tab film 5, to ensure electrical contact between the solder ball 2a and the contact point 5a. 
However, in the conventional structure of such IC socket, the projection amount (height) from the lower surface of the package body 2b to the lowermost point of each solder ball 2a happens to vary with in the range of n xcexcm to 10 nxcexcm (n:1-9 integer) due to the curving of the package body 2b, due to the difference in the diameter of the solder ball 2a, and due to the variation occurring when mounting the solder ball 2a to the package body 2b or the like.
When IC package 2 having such variation in the projection amount of the solder ball 2a is to be mounted on to the conventional IC socket, solder balls 2a each having approximately same amount of projection from the lower surface of the package body 2b to the lower most point of the solder ball 2a, establish electrical contact with the contact points 5a of the tab film 5 at a predetermined contacting pressure as shown in FIG. 10, respectively, by pushing the package body 2b downward the amount as prescribed. At this time, the elastic member 4 is elastically deformed predetermined amount through the solder ball 2a and the tab film 5.
In this state, the elastic member 4 is formed to have a plate like body (one sheet with plane surface). And in the vicinity of the contact point 5b of the tab film 5 corresponding to the solder ball 2c having smaller projection amount from the package body 2b than that of the solder ball 2a, the elastic member 4 is pressed downward (elastically deformed) as shown in FIG. 10 by the solder ball 2a adjacent to the solder ball 2c, unable to make contact between the solder ball 2c and the contact point 5b. Or else, even if the solder ball 2c and the contact point 5b are able to be contacted, the elastic member 4 is unable to be pressed (elastically deformed) the amount prescribed therefore stability of the electrical contact between the solder ball 2c and the contact point 5b can not be maintained.
In order to ensure electrical contact even in the IC package 2 having solder ball 2c with small amount of projection, it is necessary to make larger the pushing amount for pressing downward the IC package 2 in response to the solder ball 2c with small amount of projection. In this, operating force of the member for pressing downward the IC package may become larger and the solder ball 2a with large amount of projection may be damaged and destroyed.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the related art mentioned above and to provide a socket for electrical parts capable of maintaining the contact stability even when there is a variation in the amount of the downward projection of the solder ball (terminal) of the IC package, and reducing the operating force toward the member for pressing downward the IC package and, preventing the solder ball from being damaged and destroyed.
This and other objects can be achieved according to the present invention by providing a socket for electrical parts comprising;
a base member;
an elastic member disposed on the base member; and
a base plate, in the form of deformable sheet, disposed on the elastic member, and provided with a plurality of contact points to which a plurality of terminals of an electrical part is to be contacted, disposed on the upper surface of the base plate in a predetermined distance;
when a position corresponding to each contact point of the elastic member is compressed by the pressing force from the terminal of the electrical part, an escaping space is provided for elastic deformation portion pushed away by the compression and is disposed at a position corresponding in between each terminal.
Another aspect of the present invention is characterized by that the elastic member is formed with a protrusion projecting toward the base plate at a position corresponding to each contact point, and in between such protrusions, the escaping space is formed.
Still another aspect of the present invention is characterized by that the elastic member is formed with a protrusion projecting toward the base member at a position corresponding to each contact point, and in between such protrusions, the escaping space is formed.
Another aspect of the present invention is characterized by that the base member is formed with a protrusion projecting toward the elastic member at a position corresponding to each contact point, and in between such protrusions, the escaping space is formed.
According to the present invention of the characteristics and structures mentioned above, when the position corresponding to each contact point of the elastic member is compressed by the pressing force from the terminal of the electrical part, an escaping space is provided for the elastic deformation portion which is pushed away by the compression to be escaped at a position corresponding to a position in between each terminal, so that the portion corresponding to the terminal of the elastic member can be elastically deformed independently without being affected by the surrounding deformation. Accordingly, this portion corresponding to the terminal will also be deformed following the deformation of the terminal and the base plate even when there is a variation in the projection amount of the terminal, thereby ensuring the contact stability and preventing the contact pressure of the terminals from varying, and also preventing the terminal from being deformed or destroyed by excessive pressure.
Furthermore, an elastic member is formed with a protrusion at a position corresponding to each contact point and an escaping space is formed in between each protrusion. Therefore, compared to the conventional one, region (protrusion) where the terminals are to be contacted can be easily deformed so that the operating force against the cover member for applying predetermined contact pressure between the terminal and the contact point can be reduced.
Still furthermore, a base member is formed with a protrusion projecting toward the elastic member at a position corresponding to each contact point and an escaping space is formed in between each protrusion so that protrusion can be easily formed in the base member having predetermined strength.