Abstract:
A contact is provided for use in a land grid array (LGA) socket. The contact includes a support body defining a support body plane. The support body is configured to be held in a hole in an LGA socket and has opposed side edges. The contact also includes a contact beam having a base portion projecting from one of the side edges. The base portion extends along a base axis and has an upper end joined at a deflectable bend with an outer portion of the contact beam. The outer portion is configured to have surface mounted thereon an adjoining contact, and the outer portion projects from the bend at a first angle with respect to the base axis and at a second angle with respect to the support body plane.

Description:
BACKGROUND OF THE INVENTION 
     Certain embodiments of the present invention generally relate to a contact configured to deflect across a defined vertical range while electrically connecting a circuit board to a processor. 
     Many large electronic devices, such as computers, use sockets to connect different electronic components. For example, pin grid array (PGA) sockets are used to electrically connect electronic packages, such as processors, to printed circuit boards. PGA sockets facilitate electrical communication between a large number of pins on the processor and contacts on the circuit board. PGA sockets may utilize a cover that is slidably movable on a base between open and closed positions. The sliding movement may be actuated, for example, by a lever. The cover has a hole array configured to match a pin array on the processor. Similarly, the base has an array of pin receiving chambers configured to accept the pin array of the processor. The processor is mated to the socket by first placing the processor such that its pins slide into the holes of the cover. With the cover in the open position, the processor pins pass through the holes of the cover into the pin receiving chambers of the base, but are not electrically connected to the pin receiving chambers of the base. 
     When the cover is slid to the closed position, the processor pins electrically connect to contacts in the pin receiving chambers in the base. The contacts have fingers that flexible receive the processor pins therebetween. This PGA base and cover arrangement, however, requires use of a mechanism, such as a lever assembly, thereby introducing excess parts and manufacturing cost. The PGA base and cover arrangement also requires additional space for the contacts as the fingers on the contacts must flex outward away from each other to receive the processor pins. These drawbacks are especially troublesome in applications where space is at a premium, such as on motherboards for desktop and laptop computers. 
     Consequently, land grid array (LGA) sockets have been developed which require only vertical compression to allow a processor and circuit board to electrically communicate. The LGA sockets do not require the lever mechanism, and can be used in applications with more stringent space requirements. LGA sockets, however, require a vertical compression force to be continuously applied to the processor to maintain proper communication between the processor and the circuit board. 
     One LGA socket has been proposed in an application, entitled “Surface Mount Technology Land Grid Array Socket,” filed on Aug. 5, 2002, and afforded Ser. No. 10/212,414.  FIGS. 1 and 2  illustrate the above-noted electrical system  10  including a surface mount land grid array (LGA) socket  11 . The electrical system  10  also includes a circuit board  12  to which the socket  11  is mounted and a processor  18  mounted to the socket  11 . The socket  11  includes a frame  14 , a housing  16  (see FIG.  2 ), and bias spring arms  20 . The frame  14  includes an array of holes  86  therein that hold socket contacts in a pattern that corresponds to a pattern of contacts provided on the bottom of the processor  18 . The bias spring arms  20  locate and position the processor  18  with respect to the socket  11  such that the processor contacts align and engage socket contacts to facilitate electrical communication between the processor  18  and the circuit board  12 . When the housing  16  is positioned in the frame  14  and the processor  18  is positioned on the housing  16 , the processor and socket contacts are placed under a desired vertical load between the circuit board and the processor. 
     However, existing LGA socket contacts have experienced certain limitations, such as an unduly limited range of deflection. More specifically, after the processor is positioned on top of the socket contact, the processor applies a normal vertical force that deflects the socket contact between first and second contact positions. The range of deflection determines certain tolerances of the individual components, such as the socket, processor, and circuit board. Conventional LGA socket contacts have an unduly limited range of deflection which places undesirably narrow limits on the component tolerances. Additionally, conventional socket contacts may not return to their unbiased first position upon removal of the processor while affording the desired deflection range. 
     A need exists for an LGA socket contact that addresses the above noted problems and others experienced heretofore. 
     BRIEF SUMMARY OF THE INVENTION 
     Certain embodiments include an electrical contact for use in a land grid array (LGA) socket. The contact includes a support body defining a support body plane. The support body is configured to be held in a hole in an LGA socket and has opposed side edges. The contact also includes a contact beam having a base portion projecting from one of the side edges. The base portion extends along a base axis and has an upper end joined at a deflectable bend with an outer portion of the contact beam. The outer portion is configured to have surface mounted thereon an adjoining contact, and the outer portion projects from the bend at a first angle with respect to the base axis and at a second angle with respect to the support body plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an isometric view of an electrical socket system using contacts formed in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates an isometric view of a frame holding contacts formed in accordance with and embodiment of the present invention. 
         FIG. 3  illustrates a front view of a contact formed according to an embodiment of the present invention. 
         FIG. 4  illustrates a bottom view of a contact formed according to an embodiment of the present invention. 
         FIG. 5  illustrates a side view of the contact of FIG.  4 . 
         FIG. 6  illustrates an isometric view of a contact formed according to an embodiment of the present invention. 
         FIG. 7  illustrates a sectional view of a housing showing contacts inside of holes. 
         FIG. 8  illustrates a sectional view of a housing and frame formed in accordance with an embodiment of the present invention. 
         FIG. 9  illustrates a sectional view of a housing and frame formed in accordance with an embodiment of the present invention. 
     
    
    
     The foregoing summary, as well as the following detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, embodiments which are presently preferred. It should be understood, however, that the present invention is not limited to the precise arrangements and instrumentality shown in the attached drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  illustrates a front view of a contact  90  formed in accordance with an embodiment of the present invention. The contact  90  is metal and has a generally rectangular support body  94  with parallel first and second sides  114  and  116  and parallel top and bottom ends  118  and  122 . A curved foot  110  is formed with, and extends from, the bottom end  122  to join a cylindrical solder ball pad  98  with the support body  94  and the solder ball pad  98  oriented perpendicular to each other. The solder ball pad  98  is configured to receive a spherical solder ball  154 . In operation, the solder ball  154  is used for mounting the housing  16  ( FIGS. 2 and 7 ) to the circuit board  12  ( FIG. 1 ) and to allow electrical communication between the contact  90  and the circuit board  12 . The solder ball  154 , for example, may be selected to accommodate either SnPb or Pb free processing. After solder reflow, the solder ball  154  is more oval in shape than shown in FIG.  3 . The solder ball pad  98  is flexible to accommodate differences in contraction and expansion between the contact  90  and the circuit board  12 . 
     The rectangular support body  94  has two gaps  102  notched in the first side  114 . A curved arm  104  extends laterally from the support body  94  between the gaps  102  and joins a base portion  106 . The arm  104  connects the support body  94  and the base portion  106  such that the support body  94  and the base portion  106  are oriented to each other at an angle slightly greater than ninety degrees. By way of example only, the base portion  106  may form a 91-98 degree angle with the support body  94 . The base portion  106  extends slightly beyond the top end  118  of the support body  94 . A contact beam  112  is formed with, and extends from, the base portion  106  at a bend  200  at a generally forty-five degree angle to the top end  118  of the support body  94  along a horizontal axis  170 . In operation, the contact beam  112  extends out of the hole  86  ( FIGS. 2 and 7 ) and is deflected by the processor  18  (FIG.  1 ). 
     The support body  94  also has retention bumps  158  formed opposite each other on the first and second sides  114  and  116  and extending outward away from each other. In operation, when the contact  90  is inserted into a hole  86  (FIGS.  2  and  7 ), the retention bumps  158  resistibly engage walls of the hole  86  to retain the contact  90  within the hole  86 . The retention bumps  158  are evenly spaced apart along the first and second sides  114  and  116  and opposite each other on the first and second sides  114  and  116  to evenly distribute the stress imparted on the contact  90  by the walls of the hole  86  and by contact with the circuit board  12  ( FIG. 1 ) and processor  18  (FIG.  1 ). Thus, the retention bumps  158  prevent the support body  94  from bowing. 
       FIG. 4  illustrates a bottom view of the contact  90  of  FIG. 3  without the solder ball  154 .  FIG. 4  better shows the angled orientation of the support body  94  to the base portion  106 . During assembly, the contact  90  is inserted into a hole  86  ( FIGS. 2 and 7 ) in the housing  16  ( FIGS. 2 and 7 ) such that the support body  94  and the base portion  106  are retained in the hole  86 . Because the hole  86  is generally defined by right angles, the walls of the hole  86  resistibly deflect the support body  94  proximate the second side  116  inward in the direction of arrow F such that the support body  94  and the base portion  106  are oriented at an angle closer to ninety degrees. Thus, the contact  90  is resistibly nested within the hole  86 . 
     Additionally, because the support body  94  and the base portion  106  are oriented at an obtuse angle, the contact  90  takes up less space and can be fitted into a smaller hole  86  (FIGS.  2  and  7 ). Thus, more holes  86  and more contacts  90  can be fitted into the housing  16  (FIGS.  2  and  7 ). 
     The contact beam  112  includes a first segment  126  with an outer side wall  138 . The outer side wall  138  is aligned in a plane with an end  130  of the base portion  106 . A second segment  134  having an outer side wall  142  extends from the first segment  126  in a direction away from the support body  94 . The outer side wall  142  of the second segment  134  forms an obtuse angle with the outer side wall  138  of the first segment  126  along a transverse axis  174 . A rectangular contact tip  146  extends from the second segment  134  having an outer side wall  150  that is generally parallel with the outer side wall  138  of the first segment  126 . 
     In operation, the processor  18  ( FIG. 1 ) applies a vertical normal force on the contact tip  146 . The vertical normal force deflects the contact beam  112  downward toward the solder ball pad  98  such that the contact beam  112  absorbs a cantilever force where the first segment  126  engages the base portion  106 . The vertical normal force also deflects the contact beam  112  such that the contact tip  146  extends forward away from the base portion  106  in the direction of arrow C. However, because of the obtuse angle between the first and second segments  126  and  134 , the vertical normal force also applies a torsional force to the second segment  126  in the direction of arrow E such that the contact tip  146  and the second segment  126  are deflected in the direction of arrow B away from the support body  94 . 
     Since the contacts  90  are all retained in an array of rows in the housing  16  ( FIGS. 2 and 7 ) the contact beams  112 , if long enough and deflectable only downward and in the direction of arrow C, can be deflected such that adjacent contacts  90  in a row touch each other. Thus, having contact beams  112  that deflect only downward and in the direction of arrow C limits the length of the contact beams  112 . However, because the second segment  134  and the contact tip  146  are partially deflected in the direction of arrow B, a longer contact beam  112  can be used to engage the processor  18  ( FIG. 1 ) without the contact beams  112  in adjacent rows touching each other. For example, the contact beam  112  may be as long as the support body  94 . The added length of the contact beam  112  makes for a stronger contact beam  112  that can be deflected over a greater vertical range. The added length of the contact beam  112  also makes the contact beam  112  stronger such that the contact beam  112  can reflect back to its original unbiased position when the vertical normal force is removed from the contact beam  112 . 
     Additionally, because the contact beam  112  absorbs a torsional force as well as a cantilever force, the contact beam  112  stores more energy upon deflection than if it absorbed only a cantilever force. By storing additional energy, the contact beam  112  can be deflected along a larger vertical range and, upon being released from the vertical normal force, can release more energy and thus reflect back to its original unbiased position. 
       FIG. 5  illustrates a side view of the contact  90  of FIG.  4  and  FIG. 6  illustrates an isometric view of the contact  90  of FIG.  4 . As shown, the first and second segments  126  and  134  of the contact beam  112  share a common upper surface  162  aligned along a plane. In operation, when the processor  18  ( FIG. 1 ) is positioned on top of the contact  90 , the vertical normal force applied by the processor  18  on the contact tip  146  deflects the contact beam  112  downward in the direction of arrow D, outward in the direction of arrow B, and forward in the direction of arrow C. 
       FIG. 7  illustrates the contacts  90  when positioned in the holes  86 . Each hole  86  accepts a contact and is sized to properly align, secure, and position the contact  90  in the desired location. The processor  18  ( FIG. 1 ) has not yet been positioned on top of the housing  16 . Therefore, the contacts  90  are in a non-biased first contact position. When the processor  18  is lowered on top of the housing  16 , the processor  18  deflects the contacts beams  112  in the direction of arrow A to a second contact position. 
     The contact beams  112  extend from a top surface  82  of the housing  16 . When the contacts  90  are in the first contact position as shown, the each contact  90  has an unloaded contact height  96  measured from the end of the solder ball  154  to the contact tip  146 . When the contacts  90  are deflected to the second contact position, the contacts  90  have a loaded contact height (not shown) that is less than the unloaded contact height  96 . At the loaded contact height, the resilient biasing of the contact beams  112  results in a contact force between the contacts  90  and the processor  18 . The contacts  90  are selected to provide geometry to meet the impedance, inductance, and capacitance requirements of a specified application. 
       FIG. 8  illustrates a sectional view of the socket  11  before the housing  16  is soldered to the circuit board  12  (FIG.  1 ). As shown, the housing  16  is lowered into the frame  14  such that the solder balls  154  extend beneath a bottom surface  30  of the frame  14  by a predefined clearance to facilitate soldering the solder balls  154  to the circuit board  12 . The contact beams  112  extend upward by the unloaded contact height  96 . After the socket  11 , with the frame  14  and housing  16  positioned as above described, is oriented and placed on the circuit board  12 , the housing  16  may be soldered to the circuit board  12 . 
     Next, the processor  18  may be placed in the frame  14  as illustrated in FIG.  9 . Once the processor  18  is placed within the frame  14 , a clamping mechanism (not shown) may be used to force the processor  18  down into the proper position and provide the desired biasing force on the contact beams  112 . The clamping mechanism may also include a heat sink. Thus, the clamping mechanism pushes the processor  18  against the contact beams  112  until the processor  18  comes to rest on a shelf  44  of the frame  14 . As the processor  18  engages the contact beams  112 , the processor  18  delivers the vertical normal force against the contact beams  112  and deflects the contact beams  112 . The contacts  90  thus engage both the processor  18  and the circuit board  12  ( FIG. 1 ) and electrically connect the processor  18  and the circuit board  12 . 
     A further applied clamping force will further deflect the contact beams  112  into the second contact position and simultaneously push the frame  14  downward until the bottom surface  30  of the frame  14  abuts against the circuit board  12  (FIG.  1 ). Any clamping force applied to the processor  18  after the frame  14  is against the circuit board  12  will not result in any further biasing of the contact beams  112  beyond the second contact position. Rather, the force will be transferred to the frame  14  and circuit board  12 . Thus, the force seen by the solder balls  154  is controlled and limited to a predetermined level. 
     The shelf  44  has a shelf height  46  that is sized to allow the contact beams  112  to be biased to the second contact position and no more. This is accomplished by setting the shelf height  46  equal to the vertical distance from the bottom of the solder balls  154  (after reflow) to the contact tips  146  ( FIG. 4 ) when the contact beams  112  are deflected to the second contact position. By way of example, the force used to bias all of the contact beams  112  of the illustrated embodiment may be 65 pounds. 
     The electrical system  10  of  FIG. 1  requires a large vertical range of deflection to accommodate the different tolerances of many different components. Because the contact beams  112  are generally as long as the support body  94  ( FIG. 4 ) and store torsional energy as well as cantilever energy, the contact beams  112  can be deflected across the large vertical range of deflection required by the electrical system  10 . Additionally, the length and energy storing capabilities of the contact beams  112  allow the contact beams  112  to reflect back to their original unbiased position. Thus, the contacts  90  ( FIG. 4 ) can be used several times over a long period of time. Finally, the non-perpendicular orientation of the support body  94  and the base portion  106  ( FIG. 3 ) of each contact  90  allows for the contact  90  to be inserted into a smaller hole  86  (FIG.  7 ). Thus, more contacts  90  can be used in the electrical system  10 . 
     While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. For example, a different surface other than the bottom surface of the processor may be used to contact the frame, thereby changing the location of the shelf, or using a different contacting surface on the frame to be contacted by the processor. It is therefore contemplated by the appended claims to cover such modifications as incorporate those features which come within the spirit and scope of the invention.