Abstract:
An electrical connector includes an insulative housing ( 2 ) attachable to a first board and having a receiving recess ( 8 ) for receiving a second board in a first direction; and a plurality of terminals ( 3 ) arranged in the receiving recess in a second direction perpendicular to the first direction. Each terminal ( 3 ) has a pair of contact sections ( 14, 15 ) to be brought into spring contact with a pair of connection lands ( 5 ) provided on front and back edge sections ( 20 ) on front and back surfaces of a second board. The pair of connection lands ( 5 ) on the front and back edge sections are short-circuited and offset in the second direction. The pair of contact sections are offset in the second direction.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electrical connector having terminals with contact sections in spring contact with the connection sections provided on front and back sides of a board and such a board. 
   2. Description of the Related Art 
   JP 2001-143786 discloses two connectors connected by an interconnection board. The interconnection board has a plurality of connection lands arranged on opposite edges of front and back sides thereof. The connection lands in corresponding pairs on the front and back sides are short-circuited with conductive through-holes. 
   The connector has a plurality of terminals each with a pair of contact sections to be brought into spring contact with the connection lands provided on the front and back sides of the interconnection board. 
   However, the capacitance of the connection sections is so large as to cause impedance mismatch in high-speed signal transmissions. The area of the connection land is made large to assure stable contact with the contact section of the terminal. The connection lands are disposed on the front and back sides of the interconnection board to make perfect pairs across the interconnection board to form large capacitance. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the invention to provide an electrical connector and a circuit board capable of minimizing the capacitance produced between the corresponding connection lands of the circuit board. 
   According to the invention there is provided an electrical connector which includes an insulative housing attachable to a first board and having a receiving recess for receiving a second board in a first direction; and a plurality of terminals arranged in the receiving recess in a second direction perpendicular to the first direction. Each terminal has a pair of contact sections to be brought into spring contact with a pair of connection lands provided on front and back edge areas on front and back surfaces of a second board. The pair of connection lands on the front and back edge areas are short-circuited and offset in the second direction. The pair of contact sections are offset in the second direction. 
   Since the corresponding connection lands are offset in the second direction, the overlap area of the corresponding connection lands is reduced, thereby minimizing the capacitance produced between the corresponding connection lands. 
   The contact sections of the terminal may be offset in the first direction so that the second board is plugged at two stages, resulting in the reduced plugging force. It is preferred that the contact sections of terminals are staggered in the first direction, thereby preventing the second board from tilting in the third direction. The second board may be an arranging board of a second connector or an interconnection board having connection lands on another edge area to be connected to a second connector. 
   The terminal is made by processing a sheet of metal in a third direction perpendicular to the first and second direction and having a connection section projecting from the housing and a retention section held by the housing except that a portion thereof may be spaced from the housing to prevent a molten flux from moving upward by capillary action to the contact section. 
   According to the invention there is also provided a circuit board having a plurality of connection lands on the edge area on either side of the circuit board, with the corresponding connection lands on both the sides being short-circuited and offset in the second direction. It may work as an interconnection board having a plurality of connection lands on each of a plurality of edge areas, with the corresponding connection lands on both the sides being short-circuited, to which a connector is connected. The connection lands include signal connection lands and ground connection lands, with both contact sections are staggered, and the ground connection lands on at least one side communicate with each other to form a ground layer. 
   As has been described above, according to the invention, the connection lands provided on both sides of a second board and short circuited in corresponding pairs are offset in the second direction so that the capacitance between the pairs of connection lands is minimized, making a good high-speed signal transmission path between the terminal and the connection lands. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an electrical connector according to an embodiment of the invention; 
       FIG. 2  is a perspective of a terminal for the electrical connector; 
       FIG. 3  is a schematic diagram of contact sections of the terminal; 
       FIG. 4  is a perspective view of an arrangement of the terminals; 
       FIGS. 5(A)  and (B) are sectional views taken along a plane perpendicular to the direction in which the terminals are arranged; 
       FIG. 6  is a perspective view of a retention section of the terminal; and 
       FIGS. 7(A)  and (B) are plan views of front and back sides of a substrate. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the invention will now be described with reference to  FIGS. 1–6 . 
   In  FIG. 1 , a connector  1  is attached to a printed circuit (PC) board P for example. The circuit section to which a terminal of the connector  1  is to be connected is omitted from the drawing. The connector  1  includes a housing  2  made of an insulative material and a plurality of terminals  3  that are made by stamping and bending a sheet of metal and arranged in the housing  2 . 
   The housing  2  has a rectangular shape and a plurality of rows of receiving recesses  8  extending downward from the top face for receiving in the plugging direction a connection section  5  including signal connection lands  6  and ground connection lands  7  of a daughter board  4 . A pair of terminal grooves  9  ( 9 A,  9 B) for receiving a pair of opposed contact sections of each terminal  3  are provided in opposed walls of the receiving recess  8 . The opposed terminal grooves  9 A and  9 B are offset by p/2 in the terminal arranging direction wherein p is the terminal arranging pitch. The terminal grooves  9 A and  9 B extend to the bottom of the receiving recess  8 . A plurality of apertures  10  are provided in the housing  2  such that the lower connection section of the terminal  3  fitted in the terminal grooves  9 A and  9 B projects from the housing  2 . 
   In  FIG. 2 , the terminal  3  is made by stamping and bending a sheet of metal so as to have a retention section  11  to be held by the housing  3  and a pair of branches  12  and  13  extending upward from the retention section  11  such that their center lines are spaced by p/2 in the terminal arranging direction as described above. The branch  12  extends upward substantially along a plane of the retention section  11  and has a V-shaped upper end forming a contact section  14 . The other branch  13  has a substantially right-angle section  13 A near the retention section  11  and a V-shaped contact section  15  opposed to the contact section  14 . 
   In  FIG. 3 , the contact section  15  is disposed at a position lower than that of the contact section  14  by the quantity of q. The distance d between the contact sections  14  and  15  in the direction of the sheet thickness is made a little less than the thickness of the daughter board  4  so that the contact sections  14  and  15  of the branches  12  and  13  are brought into spring contact with the connection lands  6 B and  6 A of the daughter board  4 . The terminal  3  has a connection section  16  extending downward from the retention section  11  and having a solder ball  17  thereon. 
   In  FIG. 4 , the terminals  3  are alternately arranged such that the contact sections  14  and  15  are staggered. Consequently, the daughter board  4  is brought into contact with the contact sections  14  and  15  that are offset alternately in height as shown in  FIG. 5(A) . Alternatively, the terminals  3  are arranged in the same row as shown in  FIG. 5(B)  so that the daughter board  4  tends to tilt to the right in the figure. 
   In  FIG. 6 , the terminal  3  is inserted into the terminal grooves  9 A and  9 B in the opposed walls of the receiving recess  8  and held at the bottom of the housing  2 . A retention groove  18  is provided in the bottom of the housing  2  so as to have a width a little smaller than the thickness of the retention section  11  so that the opposed retention walls  18 A holds the press-fitted retention section  11  of the terminal  3 . An indented section  19  is provided between the retention walls  18 A so that the retention section  11  is spaced from the retention walls  18 A. The depth of the indented section  19  is sufficiently large that the molten flux for soldering does not come up by capillary action. The aperture  10  on the other side of the retention section  11  allows the contact section  15  of the terminal  3  to project downward. This aperture  10  also form an indented section from the retention walls  18 A. Alternatively, the terminal may be made by stamping and twisting with respect to the plane of the receiving recess  8 . 
   The daughter board  4  has a lower edge or arranging section  20  on which a plurality of connection lands are arranged and inserted into the receiving recess  8  of the housing  8 . The lower edge section  20  has a size suitable for insertion into the receiving recess  8 . A circuit section  21  above the lower edge section  20  has an extended portion  22  projecting laterally from the lower edge section  20  and having a lower edge or stopper  22 A. When the lower edge section  20  of the daughter board  4  is inserted into the receiving recess  8 , the stopper  22 A abuts against the top surface of the housing  2  to stop the insertion at a predetermined position. 
   The connection lands  5  include signal connection lands  6  and ground connection lands  7  arranged alternately on the lower edge section  20 . The signal connection lands  6  on a side of the daughter board  4  ( FIG. 1 ) are provided within the lower edge section  20  while the ground connection lands  7  extend to the circuit section  21  and join with a single ground layer  7 A. On the other side of the daughter board  4  ( FIG. 2 ), the signal and ground connection lands  6  and  7  extend upward for connection with the corresponding circuit trances. The surface of the ground layer may be treated with resist. 
   Similarly to the contact sections  14  and  15 , the portion of a signal connection land  6 A below the through-hole  6 C is offset by p/2 from the signal connection land  6 B. This holds for the ground connection land  7 , too. Consequently, the overlapping area of the opposed connection lands  5  on the opposite sides of the daughter board  4  is minimized to reduce the capacitance between them, thereby allowing high-speed signal transmission. 
   Since the contact sections  14  and  15  are offset in the plugging direction, when the daughter board  4  is inserted into the receiving recess  8  such that the connection section  5  is inserted between the contact sections  14  and  15 , the insertion force works at two stages and can be minimized. As shown in  FIG. 4 , the contact sections  14  and  15  are staggered, the daughter board  4  is held at positions distributed uniformly in both the terminal arranging direction and the plugging direction so that it does not tilt in the terminal thickness direction. If this tilt is tolerated or corrected by other means, such terminal arrangement as shown in  FIG. 5(B)  can be employed. 
   When the terminal  3  is soldered to the PC board P with the solder ball  17 , the indented section  19  prevents the upward movement by capillary action of the molten flux along a gap between the terminal and the housing. The overlap area of opposed connection sections can be set by changing the offsetting in the terminal arranging direction. The maximum offset is defined by the fact that there is no overlap between them. The through-hole may be replaced with a conductor running around the lower edge of the daughter board. 
   In  FIGS. 7(A)  and (B), another connection section is provided in an area other than the lower edge section, and the corresponding lands are connected with a circuit of the circuit section. Another connector is connected to the other connection section so that the daughter board can be used as an interconnection board. The daughter board may be a terminal arranging plate of another connector or a flexible board. The indented section for preventing the upward movement of the molten flux may be distributed to a plurality of locations.