Abstract:
An LGA socket used for connecting a chip module and a print circuit board includes an insulative housing and a number of terminals received in the housing. The housing has a top surface and a bottom surface opposite to each other. Each of the terminals includes an upper arm extending beyond the top surface of the housing and a lower arm extending beyond the bottom surface of the housing. The upper arms and the lower arms of the terminals extend from the base portion with different lengths so as to form different pitches at top and bottom surfaces of the housing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrical socket, and more particularly to a land grid array (LGA) socket having contact terminals having contact engaging portion with uniformed pitch, and tail portion with variable pitches different to the contact engaging portion. 
     2. Description of Related Art 
     Electrical sockets includes land grid array (LGA) sockets, ball grid array (BGA) sockets and pin grid array (PGA) sockets in accordance with the contacting between terminals and a central processing unit (CPU) or a printed circuit board (PCB). 
     A CPU socket disclosed in U.S. Pat. No. 7,074,048 issued to Cheng on Jul. 11th, 2006 includes an insulative housing having a plurality of passageways equidistantly arrayed thereon and a plurality of conductive terminals received in the passageways of the housing, respectively. Each terminal includes a base portion, an elastic arm and a solder portion extending from opposite sides of the base portion, and a contacting portion located at a free end of the elastic arm. The solder portion has a solder ball attached thereon. The pitch of the contacting portions is equal to the pitch of the solder portions after the terminals are assembled in the housing. The socket achieves the electrical connecting between the CPU and the PCB by soldering the solder portions of the terminals to pads of the PCB and the contacting between the contacting portions and pads of the CPU. 
     With the trend toward miniaturization in computer technology, the LGA socket becomes more smaller while more and more contact terminals are arranged within a single socket. Due to the difference between the CPU technology and the PCB technology, new processes can obtain small pitches of the pads on the CPU. However, manufacturing the PCB having the same pad pitches with the CPU needs higher costs, and the yield of the finished products is low. The LGA socket which can only electrically connect the CPU and the PCB with the same pitches limits the development of the CPU having fine pitch pads. Additionally, using solder balls to electrically connecting with the PCB also increases the height of the CPU socket. 
     In view of the above, an improved CPU socket for electrically connecting the CPU with the PCB with different pitches is needed. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an LGA socket for electrically connecting a CPU and a PCB having pads with different pitches and reducing the overall height thereof. 
     According to one aspect of the present invention, an LGA socket comprises an insulative housing having a top surface and a bottom surface opposite to each other and defining a plurality of passageways arranged with two different pitches; and a plurality of terminals received in said passageways. Each terminal has a base portion, an upper arm and a lower arm extending from opposite ends of the base portion and to a same side thereof. The upper arm extends beyond the top surface of the housing and the lower arm extends beyond the bottom surface of the housing. The upper arm and the lower arm of the terminals extend from the base portion with different lengths whereby make the upper arms and lower arms of terminals form different pitches at the top and bottom surfaces of the insulative housing, respectively. 
     Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an LGA socket in accordance with a preferred embodiment of the present invention; 
         FIG. 2  is an exploded, perspective view of the LGA socket shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of the terminals in the same row shown in 
         FIG. 1 ; 
         FIG. 4  is a front view of the terminals shown in  FIG. 3 ; and 
         FIG. 5  is a sketch view showing the LGA socket establishing electrical connection between a CPU and a PCB. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made to the drawings to describe the present invention in detail. 
       FIGS. 1-5  illustrate an LGA socket  100  in accordance to a preferred embodiment of the present invention, which is generally used for connecting a CPU  3  to a PCB  4 . The LGA socket  100  includes an insulative housing  1  having a plurality of terminals  2  received therein. The CPU  3  and the PCB  4  both define a plurality of pads  30 ,  40 . 
     Referring to  FIGS. 1 and 2 , the insulative housing  1  made of insulative material and having a planar structure. The insulative housing  1  includes a top surface  10 , a bottom surface  11  opposite thereto and defines a plurality of passageways  12  extending from the top surface  10  to the bottom surface  11  and arranged in rows. Each passageway  12  has a receiving hole  120  and a retaining slot  121  communicating with the receiving hole  120  and located at one side of the receiving hole  120 . The retaining slot  121  is used to retain the terminals  2  in the insulative housing  1  and has a plurality of inclined guiding surface  122  for guiding the terminal  2  attached to the insulative housing  1 . The passageways  12  located in the longitudinal row are designated as a passageway group (not labeled) which includes seven passageways  12  which are marked with T 1  to T 7  one by one. The housing  1  is divided into two areas respectively marked with A and B. 
     The passageways T 1  to T 3  of a passageway group belongs to area A, and the passageways T 4  to T 7  belongs to area B. The guiding surface  122  of the passageways T 1  to T 3  in area A are located at the top surface  10  for guiding the terminals  2  attached to the insulative housing  1  in an up to down direction. While the guiding surface  122  of the passageways T 4  to T 7  in area B are located at the bottom surface  11  of the insulative housing  1  for guiding the terminals  2  into the insulative housing  1  in a down to up direction. The pitch P 1  of the retaining slot  121  in area A is larger than the pitch P 2  of the retaining slot  121   s  in area B. The distance between the retaining slot  121  of the passageway T 3  in area A and the retaining slot  121  of the passageway T 4  in area B is equal to the pitch P 1 . 
     Referring to  FIG. 3  to  FIG. 5 , the terminal  2  stamped from metallic material includes a base portion  20 , a pair of elastic arms bending from a middle portion of the base portion  20 , a holding portion  23  and a guiding portion  24  respectively extending from opposite ends of the base portion  20  in a vertical direction. The pair of elastic arms includes an upper arm  25  extending upwardly from the base portion  20  and a lower arm  26  extending downwardly from the base portion  20 . The upper arm  25  has a first arm portion  250  extending upwardly from the base portion  20  and a first extending portion  251  extending obliquely from an end of the first arm portion  250 . The first extending portion  251  extends beyond the top surface  10  of the insulative housing  1 . The lower arm  26  has a lower arm portion  260  extending downwardly from the base portion  20  and a second extending portion  261  extending obliquely from an end of the lower arm portion  260  and beyond the bottom surface  11  of the insulative housing  1 . The length of the first arm portion  250  is the same with that of the second first arm portion  260 . A first contacting portion  220  is arc shaped and formed at free end of the first extending portion  251  for contacting with the pad  30  of the CPU  3 . A second contacting portion  221  is also arc shaped and formed at free end of the second extending portion  261  for contacting with the pad  40  of the PCB  4 . The holding portion  23  extending vertically from two sides of the base portion  20  can match with the retaining slot  121  of the insulative housing  1  to retain the terminal  2  therein. The base portion  20 , the holding portion  23  and the guiding portion  24  are disposed in a same vertical plane. 
     The terminals  2  received in the insulative housing  1  are also arranged in different rows either in the transversal direction or in the longitudinal. The terminals in the longitudinal row are designated as a terminal group and include two types of terminals  2  which are arranged side by side and have an identical structure. Each group has seven terminals numbered one by one with S 1  to S 7  from left to right. The terminals S 1  to S 7  can be divided into two types according to the assembling direction thereof. The terminals S 1  to S 3  are received in the passageways T 1  to T 3  in area A one by one and attached to the insulative housing  1  from a top surface  10 . The terminals S 4  to S 7  received in the passageways T 4  to T 7  one by one and attached to the insulative housing  11  from the bottom surface  11 . The holding portions  23  of the terminals S 1  to S 3  extend upwardly from the base portions  20 , and the guiding portions  24  of the terminals S 1  to S 3  extend downwardly from the base portions  20  for guiding the terminals S 1  to S 3  into the passageways T 1  to T 3 . The length of the first extending portion  251  of the terminals S 1  to S 3  is longer than the length of the second extending portion  261  of the same terminal  2 . The lengths of the first extending portions  251  of the terminals S 1  to S 3  are reduced gradually one by one from left to right. The lengths of the second extending portions  261  of terminals S 1  to S 3  are the same from left to right. Because the pitch P 1  of area A is the same, a pitch P 4  between the first contacting portions  220  of the adjacent terminals  2  in the left portion is the same, a pitch P 3  between the second contacting portions  221  of the adjacent terminals  2  in the left portion is also the same. The pitch P 4  is smaller than the pitch P 3 , and the difference between the pitch P 3  and the pitch P 4  is equal to the difference between the pitch P 1  and the pitch P 2 . That is to say that P 3  minus P 4  equal to P 1  minus P 2 . 
     While the holding portions  23  of the terminals S 4  to S 7  all extend downwardly from the base portions  20 . The guiding portions  24  of the terminals S 4  to S 7  extend upwardly from the base portions  20  for guiding the terminals S 4  to S 7  into the passageways T 4  to T 7  from the bottom surface  11 . The lengths of the first extending portion  251  and the second extending portion  261  of the terminal S 4  are equal. The length of the first extending portion  251  of the terminals S 5  to S 7  is shorter than the length of the second extending portion  261  of the same terminals S 5  to S 7 . The lengths of the first extending portions  251  of the terminals S 4  to S 7  are the same, and the lengths of the second extending portions  261  of the terminals S 4  to S 7  are increased one by one from left to right. Because the pitch P 2  of the passageways  12  in B area is the same, the pitch between the adjacent first contacting portions  220  of the terminals S 4  to S 7  is the same, and the pitch between the adjacent second contacting portions  221  of the terminals S 4  to S 7  is also the same. 
     In addition, the lengths of the first extending portions  251  of the terminals S 1  to S 4  are respectively equal to the lengths of the second extending portions  261  of the terminals S 7  to S 4 . The lengths of the second extending portions  261  of the terminals S 1  to S 4  are respectively equal to the lengths of the first extending portions  251  of the terminals S 7  to S 4 . So that the lengths of the first extending portions  251  of the terminals S 1  to S 4  in the same terminal group are reduced one by one from left to right, the lengths of the second extending portions  261  of the terminals S 4  to S 7  in the same terminal group are increased one by one from left to right. 
     Because the pitch P 2  between the retaining slot  121  of the passageways T 4  to T 7  is shorter than the pitch P 1  between the retaining slot  121  of the passageways T 1  to T 4 , the first contacting portions  220  of the terminals S 4  to S 1  are gradually and closely arranged and the second contacting portions  221  of the terminals S 4  to S 7  are gradually diffusely after the terminals S 1 -S 7  secured to the insulative housing  1 . By the pitch compensation of the passageways T 4  to T 7 , the pitch of the first contacting portions  220  of the terminals S 4  to S 7  and the pitch of the second contacting portions  221  of the terminals S 4  to S 7  are respectively equal to the pitch P 4  and the pitch P 3 , which is also described as P 4 =P 3 +P 2 −P 1 . So the pitches of the first contacting portions  220  of all the terminals S 1  to S 7  are the same and equal to the pitch P 4 , and the pitches of the second contacting portions  221  of the terminals S 1  to S 7  are also the same and equals to the pitch P 3 . Then, the LGA socket  100  can electrically connect the CPU  3  and the PCB  4  with different pad pitches. 
     The LGA socket  100  can electrically connect the CPU  3  having fine pad pitches and the PCB  4  having coarse pad pitches. In addition, the LGA socket  100  achieves the electrical connection between the CPU  3  and the PCB  4  through the first contacting portions  220  abutting against the pads  30  of the CPU  3  and the second contacting portions  221  abutting against the pads  40  of the PCB  4  rather than solder balls also reducing the height of the LGA socket  100 . 
     It is also can be seen that the top and lower arms  250 ,  260  of the central terminals S 4  of the terminals S 1 -S 7  extend from the base portion  20  with the same length, and the top and lower arms  250 ,  260  of the terminals S 1 , S 2 , S 3 , S 5 , S 6 , S 7  extend from the base portion  20  with different lengths. Furthermore, the terminals S 1 , S 2 , S 3  are essentially similar to the terminals S 7 , S 6 , S 5 , respectively. Therefore, the manufacture process of the terminals is also facilitated. 
     While the preferred embodiments in accordance with the present invention has been shown and described, equivalent modifications and changes known to persons skilled in the art according to the spirit of the present invention are considered within the scope of the present invention as defined in the appended claims.