Abstract:
An IC socket includes an insulative housing having an IC package receiving recess, in which an IC package is received. Contacts are disposed within cavities, which are provided in the IC package receiving recess in a matrix arrangement. Each contact includes a base which is installed into a cavity, an upwardly extending contact arm, which is offset above a cavity and a downwardly extending terminal portion, for electrically connecting with a circuit board. The insulative housing includes first partition walls which are provided between rows of cavities adjacent to each other in the first direction and second partition walls which are provided between rows of cavities adjacent to each other in a second direction perpendicular to the first direction, the first partition walls having greater heights than those of the second partition walls.

Description:
FIELD OF THE INVENTION 
     The invention relates to an IC (integrated circuit) socket, on which an LGA (land grid array) or a BGA (ball grid array) package is mounted. 
     BACKGROUND OF THE INVENTION 
     BGA or LGA IC sockets commonly have a large number of electrical contacts (hereinafter, simply referred to as “contacts”), arranged in a matrix along a bottom surface of an IC package receiving recess for electrically connecting with an IC package. 
     An example of such an IC socket is known a burn in socket. One such burn in socket is disclosed in Japanese Unexamined Utility Model Publication No. 5(1993)-90378 ( FIG. 2 ). The burn in socket comprises a large number of contacts, which are located within an IC package receiving recess and arranged in a matrix. The contacts comprise transition sections that extend diagonally in a stepwise manner. Contact sections are formed at the free ends of the transition sections. The contact sections protrude into and are exposed within the IC package receiving recess of a housing. 
     Another conventional IC socket is disclosed in U.S. Pat. No. 4,761,140 ( FIG. 2  and  FIG. 3 ). This IC socket comprises rectangular contacts, which are provided along the four inner walls of an IC package receiving recess. The edges of free ends of the contacts are housed in the contact cavities, and do not protrude into the IC package receiving recess. 
     In the burn in socket disclosed in Japanese Unexamined Utility Model Publication No. 5(1993)-90378, the contact sections of the contacts protrude upwardly within the IC package receiving recess. Therefore, external objects, such as fingers and the like, may strike the exposed contact sections during mounting or dismounting of an IC package to or from the IC socket. This is particularly problematic in applications where the burn in socket is utilized to diagnose a CPU (central processing unit) of the IC package because the mounting and dismounting of the IC package is generally performed manually. When a finger strikes the contact sections of the contacts, there is a risk that the contact sections will plastically deform, thereby causing poor electrical contact between them and the IC package, when the IC package is mounted. 
     In the IC socket of U.S. Pat. No. 4,761,140, deformation of the contacts is prevented, because the edges of the free ends of the contacts are not engaged by a finger, even if a finger strikes the contacts. However, the size of the cavities, for housing the contacts, is relatively large, thereby causing a problem that the contacts cannot be arranged in a high density. 
     SUMMARY OF THE INVENTION 
     The invention has been developed in view of the circumstances described above. It is an object of the invention to provide an IC socket having high density contacts while reducing the risk of plastic deformation of the contacts caused by external objects. 
     The IC socket of the present invention is an IC socket to be mounted on a circuit board. The socket has an insulative housing and a plurality of contact disposed therein. The insulative housing has a plurality of cavities arranged in a matrix within an IC package receiving recess, a plurality of electrical contacts, disposed in the plurality of cavities and fixing sections for fixing an IC package in the IC package receiving recess. First partition walls are provided in the housing between rows of cavities adjacent to each other in a first direction and second housing partition walls are provided between rows of cavities adjacent to each other in a second direction perpendicular to the first direction. The first partition walls have greater heights than those of the second partition walls. The electrical contacts each have a base which is installed within a cavity, a contact arm which extends in a first direction from the upper side of the base in an offset manner above an adjacent cavity for electrically contacting the IC package and a terminal portion which is provided at the lower side of the base for electrically connecting the electrical contact to the circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying figures of which: 
         FIG. 1  is a sectional view of an IC socket according to the invention. 
         FIG. 2A  is an enlarged plan view of an insulative housing of the IC socket illustrated in  FIG. 1 . 
         FIG. 2B  is an enlarged front view of the insulative housing of the IC socket illustrated in  FIG. 1 . 
         FIG. 3  is a left side view of the insulative housing illustrated in  FIGS. 2A and 2B . 
         FIG. 4A  is a rear view of an electrical contact, which is utilized in the IC socket of the invention. 
         FIG. 4B  is a left side view of the electrical contact, which is utilized in the IC socket of the invention. 
         FIG. 4C  is a front view of the electrical contact, which is utilized in the IC socket of the invention. 
         FIG. 4D  is a right side view of the electrical contact, which is utilized in the IC socket of the invention. 
         FIG. 5A  is a plan view of the electrical contact illustrated in  FIGS. 4A ,  4 B,  4 C, and  4 D. 
         FIG. 5B  is a bottom view of the electrical contact illustrated in  FIGS. 4A ,  4 B,  4 C, and  4 D. 
         FIG. 6A  is a partial sectional view of the insulative housing, in a state in which the contacts are installed in the insulative housing. 
         FIG. 6B  is a partial plan view showing the arrangement of the contacts, in the state in which the contacts  8  are installed in the insulative housing. 
         FIG. 7A  is a partial sectional view of the insulative housing that illustrates the shapes of the contacts, in a state in which an IC package is mounted on the IC socket. 
         FIG. 7B  corresponds to  FIG. 6B , and is a partial plan view showing the arrangement of the contacts, in the state in which the IC package is mounted on the IC socket. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a preferred embodiment of the invention will be described in detail with reference to the attached drawings. Referring first to  FIG. 1 , the IC socket  1  comprises an insulative housing  2  (hereinafter, simply referred to as “housing”), a metallic reinforcing plate  4 , and a metallic cover member  6 . The housing  2  is mountable on a circuit board  20 . The reinforcing plate  4  is located at the bottom surface  74  of the housing  2 . The cover member  6  is rotatably supported by the reinforcing plate  4 . 
     An IC package receiving recess  14  is formed in the housing  2 . A plurality of contacts  8  are located in the IC package receiving recess  14 . The cover member  6 , which covers the upper portion of the housing  2 , is rotatably supported by a shaft  12  of the reinforcing plate  4  being inserted through bearings  10  of the cover member  6 . An IC package  76  (refer to  FIG. 7 ) is secured in the housing  2  by first pressing the cover member  6  downward so that the IC package  76  is urged against the contacts  8 , then engaging a lever  18  with an engaging piece  16  at the foot of the cover member  6 . The reinforcing plate  4 , the cover member  6 , and the lever  18  will collectively be referred to as a fixing mechanism. Note that the IC package  76  is omitted from  FIG. 1 . This construction is similar to that disclosed in Japanese Patent Application 2002-379635 (filed on Dec. 27, 2002). 
     Next, the housing  2 , which is utilized in the IC socket  1 , will be described with reference to  FIG. 2A ,  FIG. 2B , and  FIG. 3 . The housing  2  is generally rectangular and is molded from an insulative material. The IC package receiving recess  14  is also rectangular as defined by outer peripheral walls  24  ( 24   a ,  24   b ,  24   c , and  24   d ). A rectangular opening  28  is formed in the bottom surface  26  of the IC package receiving recess  14 . Contact receiving cavities  30  are formed and arranged in a matrix in the bottom surface  26  at regions around the opening  28 . Note that in  FIG. 2A , only a portion of the contact receiving cavities  30  and the contacts  8  are illustrated, and the rest are omitted. A respective contact  8  is housed in each cavity  30 . 
     Next, the contacts  8  will be described with reference to  FIGS. 4A ,  4 B,  4 C,  4 D,  5 A, and  5 B. The contact  8  comprises a base  40 , a contact arm  44  and a terminal section  48 . The base  40  is long in the vertical direction. The contact arm  44  is integrally bent from the base at a side edge  42  thereof. The terminal section  48  extends downward from the base  40  and is bent toward the same side as the contact arm  44  through a step portion  46 . 
     Barbs  52  ( 52   a ,  52   b ,  52   c , and  52   d ) are formed on the side edges  42  and  50  of the base  40  to engage the inner walls of a cavity  30  when the contact  8  is installed therein. The contact arm  44  comprises a bent back portion  58  which is bent back from the base  40 , an extension portion  60  which extends upward from the bent back portion  58 , an offset portion  62  which extends diagonally upward from the extension portion  60  and a free end  64  which curves and extends from the offset portion  62 . The upper surface of the free end  64  is curved. The upper surface of the free end  64  is the electrical contact point between the contact  8  and the IC package  76 . Cutouts  54  and  56  are formed in the side edge  42  of the base  40 , to impart elasticity to the bent back portion  58  of the contact arm  44 . 
     The foot  68  of the terminal section  48  is formed as a recessed circular member. A solder ball  66  (refer to  FIG. 6A ), for connecting with the circuit board  20  is attached to the lower surface of the foot  68 . 
     Installation of the contacts  8  into the housing  2  will now be described in detail with reference to  FIGS. 6A ,  6 B,  7 A, and  7 B. As illustrated in  FIG. 6A , a plurality of contact receiving cavities  30  pass through the housing  2  from the bottom surface  26  of the IC package receiving recess  14 . The contact receiving cavities  30  are defined in a matrix arrangement by first partition walls  70  and second partition walls  72 , which are perpendicular to each other. 
     When the contacts  8  are inserted into the contact receiving cavities  30 , the bases  40  frictionally engage the inner walls of the contact receiving cavities  30 , as described above, to secure the contacts  8  therein. The solder balls  66  on the terminal sections  48  slightly protrude from the bottom surface  74  of the housing  2 . The free ends  64  of the contact arms  44  protrude above the bottom surface  26  of the IC package receiving recess  14 . The top sections  70   a  of the first partition walls  70  are formed to be approximately the same height as the bottom surface  26 . The top sections  70   a  may be set to be slightly lower than the bottom surface  26  to allow space for burrs that form during molding. The top sections  72   a  of the second partition walls  72  are formed to be shorter than or lower than the top sections  70   a  of the first partition walls  70 . 
     Recesses  80  are formed in a step portion  78  between the first partition walls  70 . The step portion  78  is of the same height as the top sections  72   a . The recesses  80  are formed at positions and depths so that when the free ends  64  of the contacts  8  move downward, that is, flex, the foot  64   a  thereof does not strike the step  78  but instead is received in the recesses  80 .  FIGS. 6A and 6B  clearly illustrate that the offset free ends  64  extend over and overlap respective adjacent contact receiving cavities  30 . By this configuration, the contact arms  44  are sufficiently elastic and at the same time arranged in a high density arrangement. In addition, the free ends  64  do not interfere with the contact arms  44  of adjacent contacts  8 , due to the configuration of the offset portion  62 . 
     The IC socket  1  having the IC package  76  secured therein will be described with reference to  FIG. 7A  and  FIG. 7B . Note that in the figures, the outline of the IC package  76  is illustrated by broken lines. The exemplary IC package  76  illustrated in  FIG. 7A  and  FIG. 7B  is of the LGA type. When the IC package  76  is mounted on the IC socket  1 , the contact arms  44  flex downward against the lands (not shown) of the IC package  76 . The contact arms  44  flex into spaces  30   a  of the contact receiving cavities  30 , in which adjacent contacts  8  are installed, without interference with the second partition walls  72 , which are of a relatively low height. 
     During mounting or dismounting of the IC package, a finger (not shown) may inadvertently touch or press the contact arms  44 . However, downward movement of the finger is restricted by the first partition walls  70  thus preventing excessive force on the contact arms  44 . The contact arms  44  remain within their ranges of elastic deformation as the finger contacts the first partition walls  70 . Therefore, plastic deformation of the contact arms  44  is prevented. 
     As described above, the IC socket  1  of the present invention obtains the desired advantageous effects by the cooperative actions of the first and second partition walls  70  and  72 , which define the contact receiving cavities  30  of the housing  2 , and the shapes of the contacts  8 . Accordingly, the present invention is not limited to the embodiment described above, and various modifications are possible as long as the shapes and the positional relationships are maintained. In addition, the IC package  76 , which was utilized in illustrating the above embodiment was of the LGA type. However, a BGA type IC package may alternatively be accommodated. In the case that a BGA type IC package is utilized, the degree of flexure of the free ends  64  of the contacts  8  will increase. However, the flexure is accommodated by the spaces  30   a  of the contact receiving cavities  30 , and the recesses  80 . 
     In addition, the foot  64   a  of the contact arms  44  may extend further downward than those illustrated in  FIGS. 6A ,  6 B,  7 A, and  7 B, as long as they are of lengths which can be accommodated within the contact receiving cavities  30  and the recesses  80 . In this case, the risk of fingers and the like engaging the feet of the contact arms is further reduced. Therefore, deformation of the contacts can be further effectively prevented.