Abstract:
A connector assembly ( 100 ) includes an insulative housing ( 10 ) defining a central slot ( 14 ) with two rows of passageways ( 16 ) by two sides thereof and two rows of contacts ( 20 ) disposed in the corresponding passageways, respectively. An electronic card ( 9 ) is received in the central slot and has a number of circuit pads ( 91 ) on a bottom portion thereof to engage the corresponding contacts, respective. Each of the contacts defines a contact section ( 22 ) extending into the central slot, and such contact section is of a downward bellows type with an overlapped region. The inner arm of the overlapped region provides a contact apex contacting the corresponding circuit pad. A height of the overlapped region is similar to a lengthwise dimension of the corresponding circuit pad when the printed circuit board is fully inserted into the slot.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/740,459 filed Nov. 28, 2005. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to card edge connectors, and particularly to high-speed card edge connectors. 
   2. Description of Related Art 
   In today&#39;s high speed electronic systems, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. High-speed card edge connectors are popular type of electrical connector that require passing fast rise time signals without distorting or degrading that rise time. Such high-speed card edge connectors are generally employed in computer and telecommunication equipments. 
   A conventional card edge connector commonly has an elongated housing defining an elongated slot for receiving a mating edge of a daughter printed circuit board or a card. A plurality of terminals are spaced along one or both sides of the slot for engaging contact pads adjacent the mating edge of the daughter printed circuit board to thereby establish electrical interconnection between the daughter card and a mother backplane printed circuit board on which the card edge connector is mounted. Such card edge connectors typically utilize preload features in the contacts in order to achieve a suitable contact force between the contacts and the inserted card. 
   U.S. Pat. Nos. 5,062,292 and 5,051,099 both disclose typical card edge connectors. Signal contact members of those card edge connectors are loaded from a mounting face of the housing and are inserted so that free tips thereof rest behind a plastic wall that exists between the card and the tips. Outwardly extending flanges of an intermediate portion of each signal contact member engage a corresponding flange receiving surface within the housing to lock the signal contact members within the housing. Noticeably, such a preloaded contact tip requires a long portion of the contact to extend above the contact-card interface. This length is required not only for providing a preload feature but also for allowing a sufficient lead-in portion on the contact. This tip design adds significant capacitance because the tip consists of a long extension that does not lie within the current path. This capacitance is detrimental to signal integrity. In common industry language, this tip design can be described as having a large electrical stub. In addition, the surface pads on the plug-in card are usually enlarged to provide sufficient surface area for the mating of the contacts. The increased surface area at the mating location increases the residual capacitance on the plug-in card, therefore further degrading signal integrity. 
   U.S. Pat. No. 5,919,049 discloses another conventional card edge connector. Similarly, the connector has preloaded contacts secured in the housing. It can be readily seen that the contacts as disclosed in these prior arts have tips pointing towards the inserted card. Clearly, it adds the risk of the card mechanically stubbing on the sheared tips of the contacts. Moreover, it is not easy to reduce the connector height for such a tip design. 
   U.S. Pat. No. 6,926,565 discloses another type of high speed card edge connector. The &#39;565 patent suggests a modified geometry of the retention mechanism that holds the contact into the housing. In prior art for lower speed signals, the retention mechanism consists of a solid tab. The solid tab adds a discrete capacitance element between adjacent signal lines. Discrete capacitance elements within a connector&#39;s construction will degrade signal transmission. The &#39;565 patent invention makes the solid tab a U shape geometry, forcing the current to flow around the outside perimeter defined by the retention mechanism. This geometry reduces capacitance and adds inductance. This balancing of capacitance and inductance provides better signal transmission. However, the &#39;565 patent simply removes capacitance from a retention mechanism of the contact. 
   Hence, an improved high-speed card edge connector is highly desired. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide improved contacts for reducing the capacitance of a high speed card edge connector which is adapted for receiving a daughter card. 
   Another object of the present invention is to provide an electrical connector having improved contacts for eliminating risk of the mechanically stubbing when a daughter card is inserted into the connector. 
   In order to achieve the above-mentioned objects, a connector assembly in accordance with the present invention includes an insulative housing defining a central slot with two rows of passageways by two sides thereof and two rows of contacts disposed in the corresponding passageways, respectively. An electronic card is received in the central slot and has a number of circuit pads on a bottom portion thereof to engage the corresponding contacts, respective. Each of the contacts defines a contact section extending into the central slot, and such contact section is of a downward bellows type with an overlapped region. The inner arm of the overlapped region provides a contact apex contacting the corresponding circuit pad. A height of the overlapped region is similar to a lengthwise dimension of the corresponding circuit pad. 
   Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of the present embodiment when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a card edge connector in accordance with the present invention; 
       FIG. 2  is an exploded view of the connector shown in  FIG. 1 ; 
       FIG. 3  is a perspective view, partly in section, of the connector shown in  FIG. 1 ; 
       FIG. 4  is a perspective view of contacts; 
       FIG. 5  is a perspective view of the contacts mounted on a printed circuit board; and 
       FIG. 6  is a top plan view of two side-by-side arranged connectors of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made to the drawing figures to describe the present invention in detail. 
   With reference to  FIGS. 1–2 , a card edge connector  100  in accordance with the present invention, which is adapted for mounting on a mother board (not shown) and receiving a daughter card  9  ( FIG. 5 ), comprises a dielectric housing  10 , a plurality of conductive contacts  20 , and a pair of overmold members  30  assembled in the housing  10 . 
   The dielectric housing  10  has a base wall  11 , two side walls  12  extending upwardly from opposite longitudinal edges of the base wall  11 , and two end walls  13  connecting distal edges of the two side walls  12 . An elongated central slot  14  is surrounded by the walls  12 ,  13  above a top of the base wall  11 . A pair of receiving openings  15  extend along a lengthwise direction beneath corresponding side walls  12  for receiving corresponding overmold members  30 . Two rows of passageways  16  are disposed by two sides of the central slot  14  and extend through the side walls  12  for insertion of corresponding contacts  20 . A plurality of spaced latches  17  are formed on outsides of the housing  10  with a latch hole  170  defined for locking the two overmold members  30  on the housing  10 . 
   In the preferred embodiment, the contacts  20  are inserted molded within the overmold members  30  which can share the same mold tooling (not shown) with a simple changeover key feature (not labeled) at the end of the mold. It should be noted here that one integral overmold  30  can be also applicable if desired. Attention is directed to  FIGS. 3 and 4  wherein exemplary contacts  20  are illustrated in detail. Each contact  20  comprises an elongated body  21  insert molded in the overmold member  30 , a contact section  22  formed on a top, and a tail  23  extending opposite to the contact section for electrically and mechanically connecting to the mother board. A neck portion  24  slantedly extends between the contact section  22  and the body  21  so that to provide a spring force to the contact  20  when the contact  20  is assembled into the housing  10 . The contact section  22  includes a preloading stop portion  220  extending upwardly from the neck portion  24  and a letter “C”-like contacting portion  221  extending into the central slot  14  a predetermined distance. During the insertion of the daughter card  9 , the neck portion  24  is deflected to the extent that the card can be substantially received in the central slot  14 . As the neck portion  24  deflects, the “C”-like contacting portion  221  may compress some and move toward the preloading stop portion  220 . However, the neck portion  24  is designed to provide the majority of the required deflection. If desired, the contact tip  222  may be designed to compress against the preloading stop portion  220  prior to the onset of permanent deformation of the “C”-like portion  221 . In this way, the “C”-like portion will be supported by the preloading stop portion  220  and permanent deformation of the “C”-like portion will be prevented in the event that the contact experiences excessive forces or deflection. This will be referred to as a tip compression safety feature. A contact tip  222  is formed at a free end of the contact  20  and projects towards the preloading portion  220  away from the daughter card  9  when the card is inserted into the central slot  14 . As can be readily seen in  FIGS. 3 and 4 , each passageway  16  has a pair of protrusions  160  formed on a top portion thereof and protruding inwardly so that a width of the top portion of the passageway  16  is narrower than the width of the rest portion. The preloading stop portion  220  of each contact  20  has projections  223  protruded on opposite edges thereof. The projections  223  are stopped by the protrusions  160  and abut thereagainst when the contact  20  is assembled to the passageway  60  so that a preloaded feature of the contact section  22  is achieved under the spring tension of the slantedly extended neck portion  24 . Compared with some conventional card edge connector contacts, the contact of the present invention eliminates any risk of the daughter card  9  mechanically stubbing on the sheared tip of the contact. The contact tip  222  is pointing away from the daughter card  9  as the card  9  is inserted into the connector  100 , while, in the prior arts, the tip is pointing towards the insertion of the card. Moreover, the “C”-like contacting portion  221  provides a lead-in feature as well known to the art. 
   In other words, the contact section  22  of the contact  20  is of downward bellows type with an overlapped region. An inner arm of the overlapped region provides a contact apex contacting the corresponding circuit pad. A height of the overlapped region is similar to a lengthwise dimension of the corresponding circuit pad. 
   Turn to  FIG. 5 , it should be noted here that the present contact provides an additional inductance component in a series of longitudinal planes formed by each of the contact sections, which are perpendicular to contact pads  91  of the mated plug-in daughter card  9 . When the contact of the present invention and the plug-in card are considered simultaneously, the contact inductance cancels out the plug-in card capacitance. Therefore, the detrimental effect of the card capacitance is minimized. Also, in the present contact design, the entire lead-in feature and preload feature exist within the electrical current path. Only a very small portion of the contact, such as a portion between a point (not labeled) contact with the contact pad  91  and the corresponding contact tip, extends beyond the electrical current path. Therefore, the contact exhibits reduced capacitance by virtue of the reduction in electrical “stub” length. Thus, the signal integrity is improved. If the previously described tip compression safety feature is not required, then it&#39;s possible to shorten the electrical stub length to virtually nothing. The tip stub needs only to be designed long enough to form a sufficient contact interface radius. 
   The tail portion  23  of the contact  20  is configured as an eye of needle type press-fit tail  21  for insertion into holes of the mother board. However, other types of the tail portion are also applicable if desired. Note that the tail portions  23  of each row of contacts  20  are staggeredly arranged one by one. The contacts  20  with inner and outer arranged tails  23  have equal electrical length. In the preferred embodiment, for high-speed signal transmission requirement, differential pair of contacts are employed to transmit signals. Each differential pair are alternately arranged with ground contacts (not labeled). 
   Additionally, due to the “C”-like design of the contacting portion  221 , the overall connector height can be reduced since the conventional contact design needs a relatively long portion to achieve the preload feature. It should be noted here that, although the preferred embodiment shows a preloaded contact configuration, the present invention can be also applied to a non-preloaded card edge connector. 
   Turn to  FIG. 2  in conjunction with  FIG. 3 , the overmold member  30  are provided with a plurality of ribs  31  on inner side thereof. These ribs  31  ensure that the contacts  20  are touching the housing wall for proper force-deflection response. Opposite to the ribs  31 , a plurality of spaced bars  32  are formed for engagement with the holes  170  of corresponding latches  17  to thereby lock the overmold members  30  on the housing  10 . The two overmold members  30  have different keying features to prevent an improper assembly. 
   Referring to  FIG. 6 , a pair of connectors  100  of the present invention are arranged side-by-side on a mother board (not shown). It can be readily seen that notches  18  defined between adjacent two latches  17  of each connector  100  cooperates with the notches  18  on the other connector and together define an opening  19  therebetween. These openings  19  allow for the extraction tooling (not shown) to reach between the connectors. The tooling will grab the overmold members  30  during the exaction process. 
   It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.