Abstract:
An electrical contact is provided that includes a body configured to be held on a circuit board. The body of the contact is movable relative to the circuit board along at least a first axis of motion. The contact includes a contact portion joined with the body that is configured to engage an electrical component. The contact portion may include one or more contact beams. The contact further includes a termination lead joined to the body and having an outer end that is configured to be soldered to the circuit board. The termination lead extends from the body at an acute or right angle to the first axis of motion. The termination lead flexes about an arcuate path as the body of the contact shifts along the first axis of motion with respect to the circuit board.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to a contact configured to be joined to a conductive member while being held in a housing. For example the contact may be carried in an electrical socket and soldered to a circuit board. More particularly, the present invention relates to a contact having termination leads that flex to accommodate movement between the contact, a conductive member and a housing holding the contact.  
         [0002]     An example of an application in which contacts are held in a housing and joined to a conductive member is in electrical sockets that are generally used to connect processors to circuit boards. The typical socket includes a body having an array of cavities that carry contacts. One type of socket is a pin grid array (PGA) socket which holds contacts that each have a flexible planar body joined to a solder ball at one end and a semicircular collar at another end. The solder ball extends out of the socket cavity below a bottom surface of the socket and is soldered to an electrical trace on the circuit board. The collar is located proximate, but below, a top surface of the body and receives and engages a pin extending from the processor in order to electrically connect the processor to the circuit board.  
         [0003]     Another type of socket is a land grid array (LGA) socket, which holds contacts that each have a flexible body formed with a contact beam at one end and a solder ball at another end. The contact beams extend upward beyond the top surface of the socket cavities, while solder balls extend downward beyond the bottom surface of the socket. The solder balls join the contacts to electrical traces on a circuit board. The processor has several contact pads on its bottom surface that are positioned on the socket with the contact pads engaging the contact beams. The processor vertically compresses the contact beams downward in order to electrically connect the processor contact pads to the circuit board.  
         [0004]     Conventional socket contacts suffer from several drawbacks. The contacts, socket and the circuit board are different sizes and are made of different materials, and thus have differing coefficients of thermal expansion. The coefficient of thermal expansion determines the amount that a material expands and contracts as the material is heated and cooled. Hence, the contacts, the socket and the circuit board expand and contract at different rates as the surrounding temperature changes such as when the electronic device is first turned on and begins to warm up.  
         [0005]     Also, during assembly, once the socket is placed on a circuit board, but before the processor is inserted, the solder balls must be liquefied sufficiently to solder each contact to a corresponding trace on the circuit board. This is achieved through a reflow solder process during which the socket and circuit board are passed through an oven and heated to a relatively high temperature. Upon completion of reflow soldering the solder balls are formed directly to the bodies of the contacts and the contacts in turn are held rigidly in the cavities of the socket. The solder balls rigidly join the contacts and traces on the circuit board. Thus, as the circuit board, contacts and socket expand at a different rates, the solder joints between the contacts and the circuit board are strained. When these strains become substantial, the solder joints may fracture.  
         [0006]     The impact of the mismatch in the coefficients of thermal expansion is magnified by the use of large sockets carrying a large array of contacts. The socket expands and contracts evenly in all directions. Thus, cavities near the center of the socket move or shift laterally less than cavities near the outer perimeter of the socket. Also, for sockets with an opening through the center, cavities in the central portion of each side of the socket move or shift less than cavities near the ends or corners of each side. Hence, while the solder joints near the center of a large socket may only be slightly affected by differences in coefficients of thermal expansion, solder joints near the edge or corner are greatly impacted by the differences in coefficients of thermal expansion. Therefore, the most strain occurs at the solder joints near the perimeter of the socket and near the corners. The inability to accommodate for differences in coefficients of thermal expansion between the contacts, socket and the circuit board limits the use of large sockets.  
         [0007]     A need exists for a socket and contact that address the above noted problems and others experienced heretofore.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0008]     An electrical contact is provided that includes a body configured to be held on a circuit board. The body of the contact is movable relative to the circuit board along at least a first direction of motion. The contact includes a contact portion joined with the body that is configured to engage an electrical component. The contact portion may include one or more contact beams. The contact further includes a termination lead joined to the body and having an outer end that is configured to be fixedly secured to the circuit board. The termination lead extends from the body at a non-parallel angle to the first direction of motion, along which the contact moves relative to the circuit board. The termination lead flexes about an arcuate path as the body of the contact shifts along the first direction of motion with respect to the circuit board. The termination lead may also flex to permit relative motion between the circuit board and the body of the contact along a second direction of motion that is oriented at an angle to the first direction of motion.  
         [0009]     Optionally, the body may be provided with a central beam that defines and extends along a longitudinal axis of the body. The termination lead extends laterally from the central beam at one of acute and right angles with respect to the longitudinal axis. A plurality of termination leads may be provided on the body and distributed such that a pair of termination leads are located near the center of the central beam and extend laterally outward therefrom. Optionally, termination leads may be provided at one end or at opposite ends of the central beam and also oriented to extend laterally outward therefrom.  
         [0010]     In accordance with at least one alternative embodiment, an electrical socket is provided having a housing that is configured to be placed on a circuit board and to receive an electronic package, such as a processor or the like. The socket includes a contact having a body that is securely held in the housing where the body joints a termination lead. The termination lead has an outer end that is configured to be fixedly secured to the circuit board. The termination lead flexes when the housing of the socket shifts with respect to the circuit board. The housing may hold a plurality of contacts about the perimeter of the housing or evenly distributed across the housing. The contacts are shifted by different amounts with respect to the circuit board as the housing expands and contracts with changes in temperature. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  illustrates a side isometric view of a contact formed in accordance with one embodiment of the present invention.  
         [0012]      FIG. 2  illustrates a top isometric view of the contact of  FIG. 1 .  
         [0013]      FIG. 3  illustrates an isometric view of a socket containing a plurality of contacts in accordance with an embodiment of the present invention.  
         [0014]      FIG. 4  illustrates an exploded, partial enlarged view of a section of the socket of  FIG. 3  with a contact removed from a cavity in the housing in accordance with an embodiment of the present invention.  
         [0015]      FIG. 5  illustrates a contact formed in accordance with an alternative embodiment.  
     
    
       [0016]     The foregoing summary, as well as the following detailed description of certain 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, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]      FIG. 1  illustrates an isometric view of a contact  10  formed according to an embodiment of the present invention. The contact  10  includes rectangular end walls  14  on opposite ends thereof and is generally made of a conductive material such as a copper alloy. The end walls  14  each include legs  18  divided by a gap  22 . The end walls  14  have rounded retention barbs  26  on opposed outer surfaces  30 . Each end wall  14  has at least on flexible contact beam  34  that projects from a top edge  38  of the end wall  14 . The contact beams  34  are bent to extend toward the opposite end wall  14 . As shown in  FIG. 1 , the contact beams  34  are oriented parallel to one another along a longitudinal axis  78  of the contact  10 . Each contact beam  34  has an elbow  46  at one end that is formed with the end wall and has a contact arch  42  at an opposite end. Each contact beam  34  may be flexed about the elbow  46  in the directions of arrows A and B. The contact beams  34  extend from opposite end walls  14  and are interleaved with each other such that a contact beam  34  extending from one end wall is located between contact beams  34  extending from the other end wall  34 , and vice versa.  
         [0018]     Optionally, the contact  10  may include only a single contact beam  34  and a single end wall  14 . Alternatively, more than two contact beams  34  may be formed with each end wall  14 . Alternatively, an uneven number of contact beams  34  may be used (e.g., one contact beam  34  on one end wall  14  and two or three contact beams  34  on the opposite end wall  14 ). Each end wall  14  has a curved arm  50  extending from a bottom end  52  between the legs  18 . The curved arms  50  are formed with a thin center beam  54 . The center beam  54  extends parallel to the longitudinal axis  78  between the end walls  14 . The center beam  54  includes a slot  56  cut in the center thereof to form thin side walls  60  on opposite sides of the slot  56 . The center beam  54  includes center termination leads  58  and  59  extending perpendicularly from opposite sides of the center beam  54  along a transverse axis  82 . The center termination leads  58  and  59  are formed with circular pads  62  on outer ends thereof that carry solder balls  66  (only one of which is shown in  FIG. 1 ). End termination leads  70  and  71  are provided on opposite ends of the center beam  54  proximate the end walls  14 . The end termination leads  70  and  71  extend laterally from the center beam  54  at an acute angle, such as a generally 45 degree angle, to the longitudinal axis  78  and toward the nearest end wall  14 . The end termination leads  70  and  71  also are formed with circular pads  62  that carry the solder balls  66  ( FIG. 2 ). Thus, the contact  10  retains several solder balls  66  for the purpose of forming solder joints with a common pad or trace on the printed circuit board  74  (not shown when reflow soldered). The center termination leads  58  and  59  and the end termination leads  70  and  71  retain the solder balls  66  remote from the center beam  54  and the end walls  14 .  
         [0019]      FIG. 2  further illustrates the contact  10  of  FIG. 1  at a different orientation to better show the relative alignment of the contact beams  34 . As shown in  FIG. 2 , each contact beam  34  is tapered with a wide base portion proximate elbows  46  and a narrow end portion proximate contact arches  42 . The contact beams  34  are arranged in contact pairs  35  and  37  facing in opposite directions.  
         [0020]      FIG. 3  illustrates an isometric view of an electrical socket  80  having an opening  82  through the center thereof. The socket  80  includes a housing  84  which is comprised of side portions  86 . Each side portion  86  includes at least one row of cavities  88  that are arranged side by side and oriented to extend toward the opening  82  proximate the center of the socket  80 . Each cavity  88  receives a corresponding contact  10 .  
         [0021]      FIG. 4  illustrates an enlarged portion of the socket  80  to better show a cavity  88  and a contact  10  once loaded into the cavity  88 . Each cavity  88  is oriented perpendicular to the edge  90  of the socket  80 . The cavity  88  includes side walls  92  that have notches  94  cut therein. The notches  94  are arranged in pairs and aligned across from one another. The notches  94  are positioned proximate opposite ends  96  and  98  of the cavity  88 . The notches  94  are arranged in pairs and aligned across from one another. The notches  94  are positioned proximate opposite ends  96  and  98  of the cavity  88 . The notches  94  are configured to receive the retention barbs  26  ( FIG. 1 ) formed along the opposite outer surfaces  30  of the end walls  14  of the contact  10 . The retention barbs  26  securely engage the notches  94  to retain the contacts  10  in place.  
         [0022]     Once the contacts  10  are inserted into the cavities  88  in the housing  84  of the socket  80 , the socket  80  is then positioned on a circuit board and the solder balls  66  ( FIG. 2 .) are soldered to electrical traces on the circuit board. A processor (not shown) is then positioned on the socket  80  such that contact pads on the processor are aligned with, and engage, the contact arches  42 .  
         [0023]     Returning to  FIG. 1 , the compression of the processor on the contact arches  42  in the direction of arrow A flexes the contact beams  34  about the elbows  46 . The processor and circuit board are thus indirectly electrically connected as the electrical signals travel from the contact arches  42  along the contact beams  34  to the end walls  14 , and through the center beam  54 , center and end termination leads  58 ,  59 ,  70  and  71 , and solder balls  66 .  
         [0024]     Because the socket  80  and circuit board are made of insulating materials such as plastic and the contact  10  is made of a conductive material such as copper, the socket  80 , the circuit board and the contact  10  have different coefficients of thermal expansion. As the surrounding temperature changes, the contacts  10 , the socket  80  and the circuit board expand or contract at different rates and by different amounts. Thus, the contacts  10  shift with respect to the circuit board along the longitudinal and transverse axes  78  and  82  ( FIG. 1 ).  
         [0025]     With reference to  FIG. 2 , the center termination leads  58  and  59  function as cantilever beams that flex in the direction of arrow D with movement or shifts between the contact  10  and the circuit board in either direction along the longitudinal axis  78 . The slot  56  permits the side walls  60  to bow or flex in the directions denoted by arrow G. The center termination leads  58  and  59  are thus permitted to translate or shift along their lengths in the direction of arrow G as the side walls  60  bow, thereby permitting transverse or lateral movement or shifting to occur between the circuit board and the pads  62  on the center termination leads  58  and  59 . Therefore, as the contact  10 , socket  80  and circuit board expand or contract by different amounts along the longitudinal axis  78  and/or transverse axis  82 , less strain is applied to the solder joints at the pads  62 . The end termination leads  70  and  71  function as cantilever beams that flex in the directions of arrows E and F with longitudinal and transverse movement or shifts between the contact  10  and the circuit board. The end termination leads  70  and  71  are oriented at an acute angle to the center beam  54  and thus permit movement between the contact  10  and circuit board along the longitudinal axis  78 , as well as along the transverse axis  82 .  
         [0026]     Optionally, the center termination leads  58  and  59  may be modified to extend at an acute angle from the center beam  54  with the slot  56  retained or removed. Alternatively, the end termination leads  70  and  71  may be oriented at a perpendicular angle to the center beam  54 , with a slot (similar to slot  56 ) provided within the center beam  54  to permit transverse movement or shifting at the end termination leads  70  and  71 .  
         [0027]     Optionally, the center and end termination leads  58  and  59  and  70  and  71  may be formed at alternative angles or in varied combinations (e.g., less than 6 leads or more than 6 leads). Alternatively, an uneven number of termination leads may be provided. Alternatively, termination leads may be provided at different positions along the length of the center beam  54 .  
         [0028]      FIG. 5  illustrates a contact  110  formed in accordance with an alternative embodiment. The contact  110  includes end walls  114  that are joined by a center beam  154 . The end walls  114  also include contact beams  134  that extend from the top ends  138  of the end walls  114  and are bent toward one another and offset to overlap in an interleaved manner. Each contact beam  134  includes a contact arch  142  proximate the outer end thereof. The center beam  154  includes termination leads  158  and  159  extending laterally from opposite sides of the center beam  154 . The termination leads  158  and  159  are located at intermediate points along the length of the center beam  154  and are slightly offset from one another and are bent in an L-shape to face in opposite directions parallel to a longitudinal axis  178  of the contact  110 . Termination leads  170  and  171  are also provided at opposite ends of the center beam  154  and extend outward laterally from either side of the center beam  154 . The termination leads  170  and  171  are bent in an L-shape and are oriented to face the end walls  114 .  
         [0029]     In the embodiment of  FIG. 5 , the termination leads  158 ,  159 ,  170  and  171  are formed in an L-shape with the base of the L-shaped portion joining the sides of the center beam  154 . Outer ends of the L-shaped portion of the termination leads  158 ,  159 ,  170  and  171  include circular pads  162  that are configured to retain solder balls (not shown) in a manner similar to that explained above in connection with the contact of  FIG. 1 . By forming each termination lead  158 ,  159 ,  170  and  171  in an L-shape, they are able to flex in two directions (namely in the transverse and longitudinal directions denoted by arrows H and I) to permit shifting between the circuit board (not shown) and the contact  110  in the direction of the longitudinal axis  178  and the transverse axis  182 .  
         [0030]     It is to be understood that the contacts  10  and  110  may be used with many other conductive members besides circuit boards, sockets and processors.  
         [0031]     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.