This invention relates to a contacting structure with respect to a spherical bump represented by a BGA type package.
As shown in FIGS. 1(A), 1(B) and 1(C), the BGA type IC package has a plurality of spherical bumps 2 disposed on a lower surface of an IC package body 1. Each of the spherical bumps 2 exhibits either a semi-spherical shape as shown in FIG. 1(A) or a spherical shape as shown in FIG. 1(B). The spherical bumps are made of a metal having a low melting point such as a soldering material or the like. According to a method often employed, the spherical bumps are loaded directly on a wiring board and a lower dead point portion (i.e. bottom-most portion) of each spherical bump is welded to a wiring pattern.
Since the BGA type IC package is mounted by welding the lower dead point portions of the spherical bumps to a wiring pattern or the like as previously described, it is required that a socket for use of aging tests be such as to not subject the lower dead point portions of the spherical bumps to damage.
To fulfill this requirement, Japanese Laid-Open Patent Application Hei 6-203926 proposes a contacting structure in which contact pins, which are disposed on a socket body, are each provided with a resilient support element and a distal end portion at a distal end of the resilient support element such that the contacting portion is placed opposite a lower spherical surface of the spherical bump. The contacting portion is provided with an escape portion in non-contact relation with the lower-most point portion of the spherical bump. Further, the contact pin includes a contacting end which is to be contacted with an external area of the lower-most dead point of the spherical bump around the escape portion.
In the above conventional device, since the contact pin can provide an electrical contact either at a plurality of points or in an annular fashion about the lower dead point portion of the spherical bump around the escape portion while effectively preventing an occurrence of damage to the lower dead point portion by the escape portion on the distal end of the resilient support element providing a non-contacting state with the lower dead point portion of the spherical bump, the problem of damaging the lower-most point of the spherical bump can be solved effectively.
However, the conventional device has such shortcomings that, since the spherical bump is softened because the aging test is usually carried out at a comparatively high temperature or because the aging test is sometimes carried out for a long time, the contacting end of the contact pin, which contacts the spherical bump under pressure, tends to overly pierce into the bump, thereby to leave a grave piecing trace in the bump. As a consequence, merchandise value is badly jeopardized.
The present invention has been accomplished in view of the above problems. It is, therefore, an object of the present invention to provide a contacting structure with respect to a spherical bump, in which an occurrence of damage to a spherical bump can be minimized while ensuring a reliable electrical contact between an IC package and a contact pin of a socket.
To achieve the above object, from one aspect of the present invention, there is essentially provided a contacting structure with respect to a spherical bump in which the spherical bump is to be contacted with a contact pin, the contact pin includes a contacting portion supported by a resilient support element, and the contacting portion is arranged in opposite relation to that part of a spherical surface of the spherical bump other than a lower-most point portion. The contacting portion has a projection capable of biting (or pressing) into the spherical surface of the spherical bump, and also has a pressure receiving surface for setting a biting amount of the projection (i.e. an amount by which the projection can press into the spherical surface).
From another aspect of the present invention, there is also provided contacting structure with respect to a spherical bump in which the spherical bump is to be contacted with a contact pin, the contact pin includes a plurality of contacting portions supported by a resilient support element, and the contacting portions are arranged in opposite relation to that part of a spherical surface of the spherical bump other than a lower-most point portion. The contacting portions each have a projection capable of biting (or pressing) into the spherical surface of the spherical bump, and also has a pressure receiving surface for setting a biting amount of the projection.
The above and other objects and attendant advantages of the present invention will be apparent to those skilled in the art from a reading of the following description and claims in conjunction with the accompanying drawings which constitute part of this disclosure.