Abstract:
A contact comprises an engagement plate, a first curved neck and a second curved neck respectively extending from different positions of the engagement plate. A surface mount section is connected to the first curved neck and retained horizontal for mounting a solder ball thereon. A contacting section is connected to the second curved neck via a resilient arm. The resilient arm is deformable in response to an external urge to the contacting section, and a tension resulted from the deformed resilient arm is fully absorbed by the engagement plate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a land grid array (LGA) connector for electrically connecting a CPU to a printed circuit board, especially an LGA connector combined with land grid array and ball grid array techniques and having a strain relief structure preventing solder balls from being damaged by an urging force which is required in the LGA technique. 
     2. The Prior Art 
     Land grid array (LGA) connectors are commonly used with IC packages and do not require soldering procedures during engagement between the LGA connector and a related printed circuit board (PCB). Normally, an LGA assembly includes an IC package having a plurality of flat contact pads formed on a bottom surface thereof, a connector having an insulative housing and defining a plurality of passageways therethrough, and a plurality of conductive contacts received in the passageways of the connector. Fastening means comprises a top plate positioned on a top surface of the IC package, a bottom plate positioned on a bottom surface of the PCB, and a plurality of sets of aligned holes defined through the PCB. The fastening means is used to configure the assembly. Each set of aligned holes receives a screw therein which engages with a washer and a nut thereby sandwiching the LGA assembly between the top and bottom plates of the fastening means. 
     U.S. Pat. No. 5,653,598 discloses an electrical contact for use in a connector  30  between mutually opposed electrical interfaces  40 ,  99  such as contact pads respectively formed on an IC package  2  and a printed circuit board  9 , as shown in FIG.  8 . The conventional contact comprises a generally planar contact body  10  having first and second major faces  110 ,  120 . The body includes a pair of spaced apart spring arms  140 ,  150  connected by a resilient bight portion  160 . The spring arms  140 ,  150  each have a free end with an outwardly facing edge forming a contact nose  17 ,  18  for engaging with the corresponding interface  40 ,  99 . Shorting sections  19 ,  20  generally extend toward each other from the free ends and are offset such that, upon deflection of the spring arms  140 ,  150  toward each other, the shorting sections  19 ,  20  overlap and the first major face  110  engages the second major face  120 . Thus, a shortened electrical path is formed between the contact noses  17 ,  18  when the package  2  is urged against the connector  30 . 
     The shorting sections  19 ,  20  may not properly contact each other due to unwanted lateral deflection thereof when the bight of the contact is deformed. Although the inner wall of the passageway receiving the contact may be used to limit the lateral deflection of the shorting sections  19 ,  20 , unwanted scraping of the shorting sections  19 ,  20  against the inner wall of the passageway may occur thereby adversely affecting the proper overlap of the two shorting sections  19 ,  20 . Proper overlap and engagement of the two shorting sections  19 ,  20  is difficult to achieve with this structure. Moreover, an additional contact resistance exists between the shorting sections  19 ,  20  thereby adversely affecting the signal transmission. 
     Additionally, the conventional LGA connector is in advance fixed in a motherboard via screws in a pre-assembly procedure. In a final assembly procedure, the screws have to be released first and then fastened for urging the CPU to the LGA connector. Therefore, in the total assembly procedure, the screws have to be fastened, released, and fastened again. This is cumbersome and not accepted by most mother board manufacturers. 
     U.S. patent application Ser. No. 09/434,593 invented by Bob McHugh, Nick Lin, Hanchen Tan, and Jwomin Wang, filed on Nov. 5, 1999 (Serial number unknown) which belongs to the same assignee with the present application, has disclosed a connector having a combined LGA/BGA structure for solving the above problems of the prior art. Such a connector comprises an insulative housing having a plurality of passageways for receiving corresponding number of contacts therein. Each contact has a contacting section for contacting with a corresponding contact pad of a CPU package which urges the connector, a surface mount section for mounting a solder ball thereon thereby connecting to a printed circuit board via the solder ball, and a resilient neck connected between the contacting section and the surface mount section for providing a tension forcing the contacting section to electrically abut against the CPU package when the contacting section is urged by the CPU package. Although this structure works well in solving the problems of the prior art, it may encounter a problem of damaging the connection of solder ball to either the connector or the printed circuit board due to the urging of the CPU package to the connector. Specifically, the solder ball is in advance soldered on the surface mount section of the contact and then experiences a reflow procedure in order to further connect to the printed circuit board. The solder ball may be forced to disconnect from either the connector or the printed circuit board thus causing malfunction when the CPU package urges the connector. It is requisite to provide a new structure to solve the problem. 
     SUMMARY OF THE INVENTION 
     The primary purpose of the present invention is to provide a combined LGA/BGA contact which includes a strain relief structure for protecting an existed soldered connection from being damaged when an external urge is applied on the contact. 
     Another purpose of the present invention is to provide a combined LGA/BGA connector which includes a strain relief structure in the contact thereof for protecting an existed soldered connection from being damaged when the connector is urged. 
     In accordance with one aspect of the present invention, a contact comprises an engagement plate, a first curved neck and a second curved neck respectively extending from different positions of the engagement plate. A surface mount section is connected to the first curved neck and retained horizontal for mounting a solder ball thereon. A contacting section is connected to the second curved neck via a resilient arm. The resilient arm is deformable in response to an external urge to the contacting section, and a tension resulted from the deformed resilient arm is fully absorbed by the engagement plate. 
     In accordance with another aspect of the present invention, a connector comprises an insulative housing in which a plurality of passageways are defined. A plurality of contacts are received in the passageways. Each contact comprises an engagement plate firmly retained in the passageway, a first curved neck and a second curved neck respectively extending from different positions of the engagement plate, a surface mount section connected to the first curved neck and retained horizontal for mounting a solder ball thereon, and a contacting section connected to the second curved neck via a resilient arm and extending out of the passageway. The resilient arm is deformable in response to an external urge to the contacting section, and a tension resulted from the deformed resilient arm is fully absorbed by the engagement plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a combined LGA/BGA connector in accordance with the present invention for receiving a CPU package; 
     FIG. 2 is a perspective view of the LGA socket of FIG. 1 taken from an opposite direction; 
     FIG. 3 is an enlarged top view of several passageways of FIG. 1; 
     FIG. 4 is a cross-sectional view taken from line  4 — 4  of FIG. 3; 
     FIG. 5 is an enlarged perspective view of the contact shown in FIG. 1; 
     FIG. 6 is a schematic view showing that the connector of the present invention has been mounted on a printed circuit board while not yet surged by a CPU package; 
     FIG. 7 is a schematic view showing that the connector has been urged by a CPU package; and 
     FIG. 8 is a schematic view of a conventional contact received in an LGA connector and sandwiched between a CPU package and a printed circuit board. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a connector in accordance with the present invention comprises an insulative housing  6  defining a plurality of passageways  60  therein for receiving contacts  5 . The housing  6  is substantially a body having four raised sides  61  and a central cavity  63  defined between the four raised sides  61  and sized to receive an IC package such as a CPU package  7 . The passageways  60  are defined through a bottom surface of the central cavity  63 . The contact  5  is received in each of the passageways  60 . A first resilient arm  611  is formed in one of the four raised sides  61  and capable of deformation in a first space  610  defined in the raised side  61 . Two second resilient arms  612  are formed in another raised side  61  adjacent to the one in which the first resilient arm  611  is formed. The second resilient arm  612  is capable of deformation in a second space  620  defined in the raised side  61 . The first resilient arm  611  and the second resilient arms  612  each have a chamfer surface  611 A,  612 A respectively formed in an upper edge thereof for guiding insertion of the CPU package  7  to the central cavity  63 . The CPU package  7  is fixed in the cavity  63  by normal force originated from the deformation of the resilient arms  611 ,  612 . Three ears  62  extend from opposite raised sides  61  near three corner of the housing  6  and each ear  62  has a post  621  extending downward for engagement within openings (not shown) of a printed circuit board  9  (see FIG.  6 ). Similarly, an additional post  622  extending from the bottom of the housing  6  near another corner thereof for engagement within another opening (not shown) of the printed circuit board  9 . 
     Referring to FIGS. 3 and 4, each passageway  60  has a cross-shape in a cross-sectional view and comprises a longitudinal hole  601  and a lateral hole  602  communicating with and perpendicular to the longitudinal wide hole  601 . The longitudinal hole  601  is much wider than the lateral hole  602 . Two end walls  602 A are defined in two ends of the lateral hole  602  for engagement purpose which will be explained later. 
     Referring to FIGS. 5 and 6, the CPU package  7  has a plurality of contact pads  77  (only one is shown for simplicity) and the printed circuit board  9  also has a plurality of contact pads  99  (only one is shown) and each pair of contact pads  77 ,  99  are arranged to register with each other when the CPU package  7  and the printed circuit board  9  sandwich the connector. The contact  5  comprises an H-shaped engagement plate  51  including two vertical sections  511  connected by a horizontal section  512 , a first curved neck  52  and a second curved neck  54  respectively extending from an upper edge and a lower edge of the horizontal section  512 , a surface mount section  53  connected to the first curved neck  52 , a hook-shaped resilient section  56  connected to the second curved neck  54  by its lower horizontally extending section  55 , and a contacting section  57  connected to an upper extending section of the hook-shaped resilient section  56 . The hook-shaped resilient section  56  and the second curved neck  54  are made much narrower than the contacting section  57  for increasing their flexibility when the contacting section  57  is urged by external force. The contacting section  57  is located in the highest position of the contact  5 . A reception space  601 A is defined between the surface mount section  53 , the curved necks  52 ,  54  of the contact  5 , and three adjacent inner walls (not labeled) of the longitudinal wide hole  601 . Each vertical section  511  has a tapered head  514  for facilitating loading of the contact  5  into the passageway  60  from a bottom direction. Each vertical section  511  has two barbs  513  formed in each side thereof for engagement with the end wall  602 A (see FIG. 3) of the lateral hole  602  by interference. The surface mount section  53  is much wider than the first curved neck  52  and retains horizontal inside the longitudinal hole  601 . A solder ball  90  is soldered onto the surface mount section  53  in advance and then soldered onto a solder pad  99  of a printed circuit board  9  as shown in FIG.  6 . With this structure, the connector can be fixed on the printed circuit board  9  in advance via the solder balls  90 . The connector together with the solder balls  90  may be maintained in a relatively low profile because the reception space  601 A can accommodate most portions of the solder ball  90 . 
     Referring to FIG. 7, a CPU package  7  having contact pads  77  are urged to the contacting sections  57  of the connector in a direction  100  and each hook-shaped resilient section  56  is deformed to force the contacting section  57  to abut against the contact pad  77  of the CPU package  7  so that each contact pad  77  of the CPU package  7  is electrically connected to a corresponding one of the solder pads  99  of the printed circuit board  9 . When the contacting section  57  is urged, a tension resulted from the deformation of the resilient section  56  and the second curved neck  54  will be fully absorbed by the H-shaped engagement plate  51  and the end walls  602 A of the lateral hole  602 . The H-shaped engagement plate  51  works well as a strain relief structure for protecting the solder ball  90  from being damaged when the connector is urged. Therefore, the connection of the solder ball  90  to either the surface mount section  53  or the solder pad  99  of the printed circuit board  9  will not be damaged when the connector is urged by the CPU package  7 . 
     While the present invention has been described with reference to a specific embodiment, the description is illustrative of the invention and is not to be construed as limiting the invention. Therefore, various modifications to the present invention can be made to the preferred embodiment by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.