Abstract:
A contact comprises a plate, a positioning section connected to the plate via a first flexible neck and adapted to be mounted by an external solder ball, a contacting section located above and connected to the positioning section via a second flexible neck. The first flexible neck is deformable to absorb a tension originated from the plate. The second flexible neck is deformable to force the contacting section to abut against an external electrical device when the external electrical device urges the contacting section to electrically connect to the solder ball via the contact.

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 a ball grid array technique for simultaneously connecting to the CPU by urging and connecting to the printed circuit board by solder balls. 
     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 onabottom 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.  10 . 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 formedbetween the contact noses  17 ,  18  when the package  2  is urged against the connector  30 . 
     With the conventional LGA connector, 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. 
     Moreover, the contact noses  17 ,  18  each have a relatively small contacting surface abutting against the interface  40 ,  99  thereby causing a relatively high contacting resistance and affecting the transmission of signals. 
     It is requisite to provide a new LGA connector for solving the above problems. 
     SUMMARY OF THE INVENTION 
     The primary purpose of the present invention is to provide a new LGA contact which has a positioning section for connection to a printed circuit board via a solder ball in advance and a resilient contacting section for connection to a CPU via urging. 
     Another purpose of the present invention is to provide a new LGA connector which has new LGA contacts each of which may be partially surface mounted to a printed circuit board via a solder ball and partially connected to a CPU by urging. 
     Still another purpose of the present invention is to provide a new LGA connector having solder balls mounted thereon and having special structure for preventing wicking problem during a soldering procedure. 
     Further a purpose of the present invention is to provide a new LGA connector which has a special structure for decreasing contacting resistance associated with an external electrical device which urges the LGA connector. 
     In accordance with one aspect of the present invention, a contact comprises a plate, a positioning section connected to the plate via a first flexible neck and adapted to be mounted by an external solder ball, a contacting section located above and connected to the positioning section via a second flexible neck. The first flexible neck is deformable to absorb a tension originated from the plate. The second flexible neck is deformable to force the contacting section to abut against an external electrical device such as a CPU package when the external electrical device urges the contacting section to electrically connect to the solder ball via the contact. 
     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 in a vertical manner, a first positioning section connected to the engagement plate via a first neck and maintained in a horizontal position, a second positioning section connected to the first positioning section via an intermediate section and maintained parallel to the first positioning section, and a contacting section connected to the second positioning section via a second neck. The contacting section is located beyond the passageway and a solder ball may be selectively mounted onto either one of the first positioning section and the second positioning section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a 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  44  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 an IC package; 
     FIG. 7 is a schematic view showing that the connector has been urged by an IC package; 
     FIG. 8 is a schematic view similar to FIG. 6 except that the solder ball is positioned in different place of the connector; 
     FIG. 9 is a schematic view showing that the connector has been urged by an IC package; and 
     FIG. 10 is a schematic view of a conventional contact received in an LGA connector and sandwiched between an IC 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 T-shape in cross-section and comprises a longitudinal hole  601  and a lateral hole  602  communicating with and perpendicular to the longitudinal hole  601 . The longitudinal hole  601  is wider than the lateral hole  602 . 
     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 a U-shaped engagement plate  51 , a first curved neck  52  extending from the U-shaped engagement plate  51 , a first positioning section  53  connected to the first curved neck  52 , a slope section  54  connected to the first positioning section  53 , a second positioning section  55  connected to the slope section  54 , a second curved neck  56  connected to the second positioning section  55 , and a contacting section  57  connected to the second curved neck  56 . The first curved neck  52  and the second curved neck  56  are made relatively narrow for increasing their flexibility. The contacting section  57  is located in the highest position of the contact  5  extending beyond a very upper portion of the passageway  60  and the second positioning section  55  is located in the lowest position of the contact  5  substantially registering with a very lower portion of the passageway  60 . A reception space  601 A is defined between the U-shaped engagement plate  51 , the first positioning section  53 , and the slope section  54 . 
     The U-shaped engagement plate  51  has two vertical sections  511  connected by a horizontal section  512 . Each vertical section  511  has a tapered head  514  for facilitating loading of the contact into the passageway  60  from a bottom direction. Each vertical section  511  has two protrusions  513  formed by stamping and projecting outward for engagement with an inner wall  602 A adjacent the lateral hole  602  by interference. The first curved neck  52  extends upward from the center of the horizontal section  512  and then bent for substantially 90 degrees. The first positioning section  53 , the second positioning section  55 , and the contacting section  57  retain parallel to each other and the first positioning section  53  is located in a horizontal position between the horizontal positions of the contacting section  57  and the second positioning section  55 . 
     A solder ball  90  is soldered onto the first positioning section  53  in advance and then soldered onto a solder pad  99  of the 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  602 A can accommodate most portions of the solder ball  90 . Normally, the solder ball  90  may be damaged due to different coefficients of thermal expansion (CTE)between the plastic materials of the connector and the printed circuit board  9 . When the connector experiences a soldering procedure, a relatively high temperature will cause the plastic material of the connector to expand which in turn generates tension passing to the first curved neck  52  via the engagement plate  51 . Similarly, the printed circuit board  9  expands in response to the relatively high temperature. Since the CTEs of the connector and the printed circuit board  9  are different, a torsion will be generated between the connector and the printed circuit board  9  and damage the solder ball  90 . Therefore, the first curved neck  52  especially the bent portion thereof may deform to absorb some of the torsion due to different CTEs between the connector and the printed circuit board  9 . 
     Referring to FIG. 7, the CPU package  7  having a plurality of contact pads  77  (only one is shown) is urged to the contacting sections  57  of the connector in a direction  100  and each second curved neck  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  via the contact  5 . 
     If low profile is not a critical consideration, the solder ball  90  may be soldered onto the second positioning section  55  (FIG. 8) and then the CPU package  7  may be urged to the connector (FIG.  9 ). If the solder ball  90  is soldered onto the second positioning section  55 , the well known CTE problem may be more effectively solved by deformation on the bent portion of the first curved neck  52  and the interconnections of the slope section  54  to the first positioning section  53  and the second positioning section  55 . Moreover, it is easier to surface mount the solder ball  90  onto the second positioning section  55  rather than mount it onto the first positioning section  53  because the second positioning section  55  directly exposes to external from the passageway  60  while the first positioning section  53  is located inside the passageway  60 . The second curved neck  56  is a substantially L-shaped structure which may prevent wicking problem from occurring on the contacting section  57  because its L-shaped structure and length prohibit melted solder portion from passing to the contacting section  57  thereby. The contacting section  57  is made particularly wider than the second curved neck  56 . 
     Alternatively, the contact  5  may be loaded into the passageway  60  in such a way that the second positioning section  55  extends beyond the very lower portion of the passageway  60  for directly positioning on the contact pad  99  of the printed circuit board  9  via surface mount without the interconnection of the solder ball  90 . The related drawing is omitted herein because it is quite similar to that of FIG.  8  and any skilled can appreciate from the description. 
     It should be deemed as a feature that the contact  5  of the present invention provides selective mounting positions  53 ,  55  for the solder ball  90 . The user may select one of the positioning sections  53 ,  55  for mounting the solder ball  90  according to his demand. For example, to achieve low profile requirement, the user had better choose the first positioning section  53  for surface mounting the solder ball  90  thereon, while to solve the CTE problem more effectively, the user had better choose the second positioning section  55  for surface mounting the solder ball  90 . 
     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.