Abstract:
A first aspect of the invention is an electrical connector that includes a housing formed to include first and second opposing ends and an elongated slot between the ends. The slot receives a connective edge of a printed circuit card. Closely spaced contacts located in the slot engage conductive pads on the printed circuit card. A first alignment member is formed integrally at the first end of the housing, to engage a non-polarized keyway during insertion of the printed circuit card into the elongated slot, aligning the printed circuit card relative to the contacts. A second aspect of the invention is the keying of the printed circuit card along a connective edge. The connective edge includes two connective regions which define a polarized keyway between the two connective regions. A third, non-connective, region located at one end of the connective regions defines a non-polarized keyway between the connective regions and the non-connective region. The polarized keyway is the dimensional datum point for fabrication of the printed circuit card and the non-polarized keyway is located precisely with reference to the polarized keyway. A third aspect of the invention is that different types of the printed circuit card, differentiated by the location of the polarized keyway, and the electrical connector form a system in which the connector may receive any of the types of the printed circuit card.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrical connector that receives a printed circuit card and couples the printed circuit card electrically to a mother printed circuit board. More particularly, the present invention relates to an electrical connector having an alignment member for aligning the printed circuit card relative to the connector during insertion of the printed circuit card into the connector to align conductive pads on the printed circuit card with electrical contacts of the connector. 
     2. Background Information 
     It is well known to provide card-edge electrical connector sockets for electrically coupling a printed circuit card board to a main mother printed circuit board. As electrical components get smaller and smaller, spacing between contacts of the electrical connector and between the conductive pads on the printed circuit card is reduced. Tighter positional tolerances are required on the connector in order to ensure proper engagement between the contacts of the connector and the pads of the printed circuit card. It is known to replace some generally centralized pad positions in the printed circuit card with a slot or keyway that mates with an alignment post or key formed in the connector socket to provide polarization and alignment between the printed circuit card and the socket. The selected clearance gap between the keyway and the key, plus the manufacturing tolerances of both the keyway and the key, aligns the conductive pads of the printed circuit card with the contacts of the electrical connector closely enough to make a proper connection. 
     An exemplary add-in printed circuit card is the Accelerated Graphics Port (AGP) add-in card described in the  Accelerated Graphics Port Interface Specification. Revision  2.0, Intel Corporation, May 4, 1998. (Available on the Worldwide Web at http://www.intel.com/pc-supp/platform/agfxport/index.htm) FIG. 1 is an exploded view showing a typical assembly of an AGP add-in card  20  to a mother board  10 . The electrical connection between the printed circuit board and the mother board is provided by a connector  30 . An AGP card has conductive pads along a portion of one edge for connection to the AGP bus through the connector. The connector has a pitch of 1.00 mm between centers of adjacent contacts allowing the overall length of the connector to be less than 75 mm. The fine pitch of the contacts requires that the use of a keyway to locate the pads relative to the connector contacts with great accuracy. The keyway  26  for the AGP add-in card is specified to have a width of 1.88+/−0.05 mm. The key formed on the socket connector is specified to have a width of 1.78+/−0.03 mm. Therefore, the clearance between the keyway formed in the add-in card and the key in the socket is 0.10 mm+/−0.08 mm due to manufacturing tolerances. The keyway is the datum point for location of the pads when the printed circuit card in manufactured. The key is the datum point for the location of the contacts when the connector is manufactured. The mating of the keyway to the key aligns these two manufacturing datum points to within 0.18 mm. 
     Two types of AGP cards have been defined, a 3.3 volt card and a 1.5 volt card. The 3.3 volt card uses 3.3 volt signaling and operates at a bus speed of either 66 MHz or 133 MHz. The 1.5 volt card uses primarily 1.5 volt signaling, although clock and reset are 3.3 volts, and operates at a bus speed of 266 MHz. To prevent connection of a 3.3 volt AGP card to a 1.5 volt AGP bus or connection of a 1.5 volt AGP card to a 3.3 volt AGP bus, the alignment keys for the two cards are in different locations. FIG. 2 shows the connecting edge of a 3.3 volt card  20  and FIG. 4 shows the connecting edge of a 1.5 volt card  60 . The specifications for both cards allow the same connector to be used for both cards by making the 1.5 volt card connector edge a 180° rotation of the 3.3 volt card connector edge. In particular, the keyway  26  for the 3.3 volt card is located between pads  41  and  43  counting from the left of the component side; the 1.5 volt card keyway  66  is located between pads  41  and  43  counting from the right of the component side (pads  81  and  83  from the left). 
     The AGP architecture allows a motherboard to be constructed with a 3.3 volt AGP bus using a keyed connector so that only 3.3 volt AGP cards can be inserted into the connector. Likewise, a 1.5 volt AGP bus can be provided that accepts only 1.5 volt AGP cards using the same keyed connector installed with the opposite orientation. Thus, the keying provides polarization to prevent installation of printed circuit cards that are incompatible with the bus in addition to providing alignment of the manufacturing datum points. It is known to produce an AGP card that is compatible with both the 3.3 volt AGP bus and the 1.5 volt AGP bus where the card has two polarized keyways so that it may be inserted in either a 3.3 volt AGP connector or a 1.5 volt AGP connector. 
     An AGP bus can be designed that can electrically accommodate either a 3.3 volt only card or a 1.5 volt only card. However, the keying of the prior art prevents a single installed connector from accepting both types of cards. Accordingly, there is a need for a connector that can accept printed circuit cards with a variety of polarized keyings and still provide highly accurate positioning of the printed circuit card pads relative to the connector contacts. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention is an electrical connector that includes a housing formed to include first and second opposing ends and an elongated slot between the ends. The slot receives a connective edge of a printed circuit card. Closely spaced contacts located in the slot engage conductive pads on the printed circuit card. A first alignment member is formed integrally at the first end of the housing, to engage a non-polarized keyway during insertion of the printed circuit card into the elongated slot, aligning the printed circuit card relative to the contacts. A second aspect of the invention is the keying of the printed circuit card along a connective edge. The connective edge includes two connective regions which define a polarized keyway between the two connective regions. A third, non-connective, region located at one end of the connective regions defines a non-polarized keyway between the connective regions and the non-connective region. The polarized keyway is the dimensional datum point for fabrication of the printed circuit card and the non-polarized keyway is located precisely with reference to the polarized keyway. A third aspect of the invention is that different types of the printed circuit card, differentiated by the location of the polarized keyway, and the electrical connector form a system in which the connector may receive any of the types of the printed circuit card. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of a printed circuit card being inserted into a connector according to the present invention. 
     FIG. 2 is a printed circuit card that embodies the present invention inserted into a conventional connector. 
     FIG. 3 is the printed circuit card of FIG. 2 inserted into a connector that embodies the present invention. 
     FIG. 4 is a second printed circuit card that embodies the present invention inserted into a conventional connector. 
     FIG. 5 is the printed circuit card of FIG. 4 inserted into a connector that embodies the present invention. 
     FIG. 6 is the printed circuit card of FIG. 4 with insertion being prevented by a connector that embodies the present invention. 
     FIG. 7 is another connector that embodies the present invention. 
     FIGS. 8 and 8A are details of the connector of FIG.  7  and the printed circuit card of FIG. 5 showing a positional relationship. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an embodiment of the present invention which provides a card and a connector system for cards having closely spaced connector pads, such as connector pads with a nominal center spacing of 1 mm or less. The connective edges of the cards  20  are formed in a manner that provides a polarized keyway  26  and a non-polarized keyway  28 . Both keyways serve the purpose of providing alignment to a mating connector  30  on a motherboard  10 . Only one of the two keyways is engaged by any particular connector. The system permits a family of related cards to be produced where each card in the family places the polarized keyway in a different position. These cards can be inserted into conventional connectors with cooperative alignment keys, such that the alignment key properly aligns the connector and the card and prevents incompatible cards from being inserted into the connector. 
     The connector portion of the system is a universal connector  30  that provides a non-polarized key  38  that engages the non-polarized keyway  28  of the cards  20  embodying the present invention to properly align the connector and the card. The universal connector is able to receive all the related cards of the family. In this way, a family of cards, each requiring a different connection, can be produced for use in a corresponding family of conventional polarized connectors  20  that provide the specific electrical connection required by a specific card. The universal connector makes it possible to provide a single connector that can mechanically receive any of the cards in the family when a connection is provided that is electrically adaptive to provide the specific electrical connection required by a specific card. For example, a connector can be provided according to the present invention to receive either a 3.3 volt Accelerated Graphics Port (AGP) card  20  (FIG. 2) that has a keyway  26  between pad positions  42  and  43  or a 1.5 volt AGP card  60  (FIG. 4) that has a keyway  66  between pad positions  81  and  83 . 
     FIG. 2 illustrates a printed circuit card  20  that embodies the present invention. The connective edge of the card includes two regions  50 ,  52  containing connective pads and a third region  54  without connective pads. The adjacent edges of the first two regions define a polarized keyway  26 . The adjacent edges of the second and third regions define a non polarized keyway  28 . The polarized keyway typically serves as the positional datum for fabrication of the printed circuit board as indicated by reference line  56 . 
     FIG. 2 shows a first printed circuit board  20  of the present invention inserted in a conventional connector  40  having a polarized key  46  that engages the polarized keyway  26  of the printed circuit board. The non-polarized keyway  28  has a dimension that provides clearance around the end of the conventional connector  40  so that the non-polarized keyway does not engage the connector. 
     FIG. 3 shows the first printed circuit board  20  of the present invention inserted in a universal connector  30  of the present invention having a non-polarized key  38  that engages the non-polarized keyway  28  of the printed circuit board. The non-polarized key is formed by increasing the thickness of the end of the connector to form an aligning member that will properly align the connector and the printed circuit board. It should be observed that the printed circuit card aligns a conventional connector at the primary datum  56  while aligning a universal connector at a secondary datum  58 . The relationship between the primary and secondary datum of the printed circuit card must be properly controlled to successfully implement the present invention. 
     FIG. 4 shows a second printed circuit board  60  of the present invention inserted in a conventional connector  40  having a polarized key  46 . FIG. 5 shows the second printed circuit board  60  inserted in the universal connector  30  of the present invention. The second printed circuit board  60  is another member of the family that includes the first printed circuit board  20 . It will be observed that all members of a board family have connective edges that differ only in the position of the polarized keyway  26 ,  66 . Pad positions are, of course, omitted from a board in the vicinity of the polarized connector. The electrical connection is designed in such a way that pads which are omitted for the polarized keyways are at positions with redundant signals. 
     It may be noted that in the example shown in FIGS. 2 and 4, which is illustrative of two AGP family boards, the polarization has been designed so that the same conventional connector  40  can be used for both applications by reversing the orientation of the connector. This does not create a universal connector however, because, as seen in FIG. 1, the mechanical orientation of the board  20  is fixed relative to the motherboard by the mechanical connection  22  that secures the board in position. The reversibility of the conventional connector is merely an inventory convenience that permits use of the same connector part to provide a specific polarized connector of either type. 
     It may be observed in FIG. 5 that the embodiment of the connector  30  shown provides an aligning member to serve as a non-polarized key  38  at only one end. The aligning member end is characterized by having a width that closely matches the non-polarized keyway  68 . The close fit of the aligning member to the keyway causes the secondary datum  78  of the card to be substantially coincident with the datum of the connector  72 . 
     The opposing end  36  is narrower than the aligning member end in this embodiment. It will be appreciated that this embodiment of the connector requires that the connector be installed with a specific orientation so that the aligning member end is correctly oriented with respect to the motherboard. The connector includes hold-down clips  32 ,  34  for holding the connector in position during assembly of the motherboard. In the embodiment shown, the hold down clip  34  at one end is larger than the hold down clip  32  at the opposite end. By providing closely matching holes in the motherboard to receive the hold down clips, the connector can be restricted to assembly in the proper orientation. 
     FIG. 6 shows another embodiment of a connector  80  of the present invention. In this embodiment, the non-aligning end  86  is wider than the aligning member  88  to prevent insertion of the printed circuit board  60  with the incorrect orientation. This is useful in applications where the printed circuit board is not otherwise limited to a single orientation. This embodiment also shows the use of dissimilar hold down clips  82 ,  84  to orient the connector during assembly to the motherboard. 
     FIG. 7 shows another embodiment of a connector  90  of the present invention. In this embodiment, one end  98  is the primary aligning member. However the opposite end  96  is also dimensioned and located so that it serves as a secondary aligning member. The primary aligning member is distinguished from the secondary aligning member only in that the primary aligning member serves as the positional datum for the fabrication of the connector. Line  72  represents the primary datum for the connector. Nominally, the connector is completely symmetrical with a 2-fold axis of symmetry. That is, the connector appears the same when rotated end for end by 180 degrees. It will be appreciated that when the secondary alignment member engages the non-polarized keyway, a secondary datum  74  is being used to align the connector to the card. This creates a stacking tolerance that will be described below. 
     Since the embodiment of the universal connector  80  shown in FIG. 7 is symmetrical, the hold-down clips  92  are substantially similar in size to permit assembly of the universal connector in either orientation. By making these hold-down clips substantially similar in size to the hold-down clips  42  of the conventional polarized connector  40  (FIG.  4 ), the universal connector can be assembled on a motherboard designed to hold a conventional connector. It may be noted in this regard, that the conventional connector must be assembled in a specific orientation. The conventional connector  40  includes a third hold down clip  44  which is offset between the first two hold down clips  42 , generally in alignment with the polarized key. This embodiment of the universal connector  80  simply omits the third hold down clip because the it is not necessary to orient the symmetrical universal connector. 
     FIG. 7 illustrate another feature that is particularly important when interchangeable assembly with conventional connectors is desired. The contact pins are omitted in the positions  56 ,  76  of the polarized keyways for all cards that are intended to be received by the universal connector. These contacts must be omitted if the connector is to be assembled to a motherboard designed to receive a conventional connector because the conventional connector has a hold-down clip rather than contact pins in the vicinity of the polarized key. Omitting these contacts is also beneficial because the polarized keyways might interfere with contacts in those positions during insertion of the printed circuitcard. For this reason, it can also be beneficial to omit contacts from non-symmetrical embodiments of the universal connector similar to the embodiments previously described. 
     It may be seen in FIGS. 2 through 5, that the connector pads are staggered so that adjacent pads engage the connector at two alternating depths. Pad  1  engages the connector further from the edge than does adjacent pad  3 . It should also be noted that the opposing pads are also staggered so that pad  2  (not shown), which is on the opposite side of the card directly behind pad  1 , engages the connector closer to the edge than does opposing pad  1 . The connector pad has a width of about 1.09+/−0.05 mm in the area were it engages the connector contact. The space between adjacent traces in the connector edge is about 0.25+/−0.05 mm. 
     The fine pitch of the connector pads requires that the keyway locate the pads relative to the connector contacts with great accuracy. The non-polarized keyway  28  for an AGP add-in card employing the present invention is specified to have a width of 3.40+/−0.05 mm. The aligning member of the universal connector is specified to have a width of 3.30+/−0.03 mm. Therefore, the clearance between the keyway formed in the add-in card and the key in the socket is 0.10 mm+/−0.08 mm due to manufacturing tolerances. 
     FIG. 8 illustrates how the positional relationship between a connector contact  95  and a pad  62  on the printed circuit card is established when the secondary keyway  68  is used to align the printed circuit card  60  (FIG. 5) to the secondary connector key  96  of a symmetrical universal connector  90  (FIG.  7 ). The misalignment of parts in FIG.  8  and detail FIG. 8A has been exaggerated so that the effect of the permissible tolerances can be seen more clearly. FIG. 8 will be explained with reference to the dimensions of an AGP add-in card and connector that embody the present invention. 
     If a secondary keyway  68  is used to align the printed circuit card to a universal connector using the secondary keying end  96  to align the connector and the card, several tolerances are stacked to arrive at the final connector contact  95  to pad  62  tolerance. 
     The printed circuit card  60  is fabricated using the primary keyway  66  as the positional datum  76  for all features of the board. The connector pads  62  have a positional tolerance of +/−0.05 mm relative to the primary keyway. This means that the centerline  61  of a pad may be offset by as much as 0.05 mm from the nominal position. The secondary keyway  68  also has a positional of tolerance of +/0.05 mm and the secondary datum  78  established by the secondary keyway is therefore less precise than the positional datum of the primary key. The centerline of a pad may therefore be offset by as much as 0.10 mm relative to the secondary keyway. 
     The universal connector  90  is fabricated using the primary keying end  98  (FIG. 7) as the positional datum  72  for all features of the connector. The secondary keying end  96  and the connector contacts  95  have a positional tolerance of +/0.05 mm. The secondary datum  74  established by the secondary key is therefore less precise than the positional datum of the primary key. Thus the connector contacts have a positional tolerance of +/0.10 mm relative to the secondary keying end. 
     The secondary keyway has a dimensional tolerance of +/−0.05 mm for the width of the keyway. The universal connector has a dimensional tolerance of +/0.03 mm for the width of the end section that engages the secondary keyway. There is a nominal clearance of 0.10 mm between the keyway and the keying end. In a worst case, where the secondary keying end is undersized, the secondary keyway is oversize, and the secondary keyway is engaged with all the clearance on one side, the datum  74  of the secondary keying end  96  may be offset from the datum  78  of the secondary keyway  68  by as much as 0.09 mm, one-half the maximum clearance between the keying end and the keyway. 
     In the worst case of the pad  62  being offset 0.10 mm toward the secondary keyway  68  (distance  100  is long and distance  102  is short), the contact  95  being offset 0.09 mm toward the pad from the secondary keyway (distance  104  is long and distance  106  is short), and the contact being offset 0.10 away from the secondary keying end (distance  108  is long), the centerline  93  of the contact may be offset by as much as 0.29 mm relative to the centerline of the pad  61 . 
     The effect of a misalignment between the contact  95  and the pad  62  is seen in FIG. 8A which is an enlargement of circled area A in FIG.  8 . FIG. 8A shows the parts rotated 90° counter-clockwise from their orientation in FIG.  8 . 
     The contact  95  will be considered as having a square cross-section although it actually is somewhat rounded because of the plating process that deposits the greatest thickness away from the edges of the contact. The contact is formed so that a small area  97  makes contacts with the pad  62 . 
     The pad  62  has a width of 1.09+/−0.05 mm. In the worst case of an undersized pad, the edge  63  of the pad is 0.52 mm from the centerline  61  of the pad. Since the worst case contact to pad misalignment is 0.29 mm relative to the centerline of the pad, the centerline  93  of the contact will always be on the pad. 
     The contact  95  has a width of 0.74+0.10/−0.05 mm. In the worst case of an oversized contact, the edge  99  of the contact is 0.42 mm from the centerline of the contact. The contact may extend beyond the pad by as much as 0.13 mm. Adjacent pads are offset and connected by traces  64  that run between pads. The trace has a width of 0.41+/−0.05 mm. Adjacent traces have centerlines spaced at 1.00+/−0.05 mm. In the worst case, the edge  65  of the adjacent trace may be as close as 0.72 mm from the centerline  61  of the adjacent pad. Thus, even in the worst case, there will be 0.30 mm clearance between a contact and the adjacent trace. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.