Patent Publication Number: US-7914305-B2

Title: Backplane connector with improved pin header

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the domestic benefit of U.S. Provisional Application Ser. No. 60/936,386, filed on Jun. 20, 2007, which disclosure is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to electrical connectors, and more particularly to electrical connectors which comprise differential signal pairs of electrical contacts that are designed for high speed electronic communication. 
     Electrical connectors provide signal connections between electronic devices using signal contacts. Often, the signal contacts are so closely spaced that undesirable interference or cross talk can occur between adjacent signal contacts. Cross talk occurs when one signal contact induces electrical interference in an adjacent contact due to the overlapping of electrical fields, thereby compromising signal integrity. With electronic device miniaturization and high speed electronic communication becoming more prevalent, the reduction of cross talk becomes a significant factor in connector design. 
     One commonly used technique for reducing cross talk is to position separate electrical shields, in the form of metallic plates, for example, between adjacent signal contacts. The shields act to block cross talk between the signal contacts by eliminating the overlapping electrical fields. Shields, however, take up valuable space within the connector that could otherwise be used to provide additional signal contacts, and thus limit contact density and connector size. Shields also increase the cost of manufacture of the connector. 
     While it is known to use air gaps between signal contacts to enhance electrical isolation of adjacent contacts, the utilization of air gaps can: compromise the structural integrity of the connector or complicate the design of the connector by requiring a multiplicity of terminal supporting frames or wafers, as well as increase the physical size of the connector. In pin headers of backplane connectors, for example, it is desirable that the connector housing have a one-piece plastic design that will withstand significant forces during insertion of a daughter card connector into engaging relation with the multiplicity of pin header contacts. There is a need to improve electrical signal integrity in such pin header connectors consistent with signal integrity achieved by daughter card connectors which employ a plurality of separate signal contact-carrying wafers. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrical connector which has a relatively simple design and in which differential signal pairs of electrical contacts are effectively isolated by an air dielectric medium from signal contacts of adjacent or nearby differential signal pairs. 
     Another object is to provide an electrical connector as characterized above in which the connector housing has a one-piece molded construction and the air dielectric isolation of signal contacts is achieved without materially affecting the structural integrity of the connector. 
     A further object is to provide a pin header electrical connector of the above kind which has uniformly spaced electrical contacts adapted for economical manufacture and versatile usage. 
     A still further object of the present invention is to provide a pin header for use in high speed data transfer systems in which the pin header has a base supporting a plurality of contact pins that are mateable to an opposing daughter card connector. The contact pins being disposed in spaced-apart rows or columns and the base including selected openings formed therein and disposed between selected adjacent signal pins residing in different rows or columns. 
     These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the course of this detailed description, reference will be frequently made to the attached drawings in which: 
         FIG. 1  is a perspective of an illustrative backplane connector in accordance with the invention, with a daughter card connector shown in inserted engaging relation with a pin header connector; 
         FIG. 2  is a perspective of the illustrated connector with the backplane removed; 
         FIG. 2A  is a plan view of a stamped lead frame for the signal and ground contacts for the individual wafers of the daughter card connector; 
         FIG. 3  is a perspective of illustrated the pin header connector in mounted relation on the backplane; 
         FIG. 4  is an enlarged perspective of one of the pin header connector contacts; 
         FIG. 5  is an enlarged plan view of the pin header connector as viewed from the mating side thereof; 
         FIG. 5A  is a fragmentary depiction of the contact arrangement of the illustrated pin header connector; 
         FIG. 5B  is a fragmentary depiction, similar to  FIG. 5A , of an alternative embodiment of the pin header connector; 
         FIG. 5C  is a fragmentary depiction of another alternative embodiment of a pin header connector; 
         FIG. 6  is a perspective, vertical section of the pin header connector shown in  FIG. 5 ; 
         FIGS. 7 and 7A  are enlarged fragmentary sections of the illustrated pin header connector, taken along planes of lines  7 - 7  and  7 A- 7 A, respectively in  FIG. 5 ; and 
         FIG. 8  is an enlarged fragmentary section of the illustrated pin header connector, taken parallel to the columns of contacts of the connector. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now more particularly to the drawings, there is shown an illustrative backplane connector  10  in accordance with the invention for electrically connecting a printed circuit board (PCB) board in the form of a backplane  11  and a daughter PCB card  12 . The backplane connector  10  includes a backplane pin header connector  14  mounted on the backplane  11  and a daughter card connector  15  mounted on the daughter card  12 , which, as illustrated, are plugged together. Because the backplane  11  and daughter card  12  are arranged at a right angle to each other, the backplane connector  10  is a right angle connector and the electrical paths through connector accordingly change direction or bend 90°. However, it will be understood that in other embodiments, the backplane and daughter card can be arranged at other angles to each other, or parallel to each other, and the electrical paths can be arranged accordingly. 
     The daughter card connector  15  in this case comprises a plurality of wafers  18  arranged in a side-by-side configuration. As shown best in  FIG. 2 , each wafer  18  includes a first wafer half or waflet  18   a  and an opposing second wafer half or waflet  18   b  that are joined together. The waflets  18   a ,  18   b  are constructed of an insulative support frame  19 , such as a thermoplastic material, disposed about a plurality of electrically conductive contacts  20 . Each waflet  18   a ,  18   b  in this case includes comprises a column of contacts, which can be stamped from a lead frame as depicted in  FIG. 2A , comprising pairs of edge-coupled differential signal contacts  24  located adjacent a ground contact  25 . For electrically isolating the differential signal pairs of contacts  24  of one wafer from the differential signal pairs of the other wafer, the ground contacts  25  in this case have a transverse width corresponding substantially to the width of the differential signal pair and the ground contacts  25  and signal contacts  24  of one wafer are offset from the other wafer such that the signal contacts  24  on one wafer are adjacent to a ground contact  25  of the adjacent wafer with an air gap therebetween established by the mating relation of the waflets  18   a ,  18   b.    
     The ground and signal contacts  24 ,  25  in each column extend roughly along parallel paths that transition generally 90° from a backplane face  130  of the daughter card connector to a mating face  132  of the daughter card connector. Each contact  24 ,  25  has a terminal end  26  in the form of a compliant pin for connection to the daughter board and a mating terminal end  28  for connection to the contacts of the pin header. The mating terminal ends  28  of the contacts in this case have a bifurcated dual beam design for redundant, more reliable connection with contacts of the pin header  14 , as disclosed in more detail in U.S. Provisional Application No. 60/936,387 (Molex Case No. A7-151US-PRO), filed Jun. 20, 2007, the disclosure of which is incorporated herein by reference. 
     To produce the waflets, it will be understood that the plastic frame  19  may be insert molded over the electrical contact lead frame which can be stamped and formed from a thin conductive sheet metal, such as copper. The plastic support frame  19  in this case includes a plurality of ribs or spokes  19   a  designed to support the contacts  24 ,  25  and transfer insertion loads from the top part of the wafer  18  to the compliant tails  26  during insertion of the daughter card connector  15  into engaging relation with the pin header connector  14 . The ribs  19   a  also serve as standoffs between two waflets  18   a ,  18   b , when married for defining a predetermined spacing between the contacts  24 ,  25  of adjacent columns. One waflet preferably has male pegs which mate in press fit relation in holes in the opposite waflet to secure the married wafer, or other suitable means for joining two elements together including slots, adhesives, welding and the like. When married, it will be seen that the ground terminals  25  in each waflet are edge-coupled to a signal contact  26  of adjacent differential signal pair while being broadside coupled to the signal contacts of a differential signal pair in an adjacent column. 
     The wafers  18  are mounted within respective slots of a front shroud or housing  30  in parallel relation to each other and are secured together by a cross stiffener strip  31 . The stiffener strip  31  preferably has slots that accept dovetails  32  on the back of each married wafer for maintaining proper spacing. The shroud or housing  30 , as is known in the art, has openings within which the mating terminals  28  of the daughter card connector wafers are protectively disposed. 
     Turning now to  FIG. 3 , the pin header connector  14  comprises a one-piece, preferably plastic molded, housing  35  having a base  36  and upstanding side and end walls  38 ,  39 , respectively. The base  36  is formed with a plurality of columns of slots each for receiving a respective column of electrical contacts  40 . Each column of contacts  14  comprise a plurality of edge coupled differential signal pairs of contacts and adjacent ground contacts, respectively, sometimes referred to herein as S and G respectively for clarity of description. For purposes herein, the term “column” refers to the direction in which contacts are aligned edge to edge, and the term “row” refers to a direction perpendicular to that column. 
     The ground and signal contacts  40  in this case are identically formed, each comprising, as depicted in  FIG. 4 , a stamped pin having a substantially coplanar flat shape with an elongated cross section oriented in aligned relation to the column within which the contact is located. Each contact  40 , in this case, has a compliant terminal portion  41  at one end for connection to the backplane  11  and a mating portion  42  at an opposite end thereof for mating engagement with the bifurcated contacts  28  of the daughter card connector  15 . Each contact  40  has a shoulder  44  intermediate the ends thereof for enabling the contacts to be installed into the housing with a simple press-in action, from a top or mating side of the connector  14 , as opposed to common practice of inserting contacts into the housing from a bottom or mounting side. The contact design also facilitates removal after assembly. 
     Upon engagement of the daughter card connector  15  with the pin header connector  14  as an incident to insertion of the daughter card connector into the pin header connector, it will be seen that the bifurcated terminals  28  of the daughter card connector  15  will progressively contact and be moved into engagement with the mating terminals  42  of the pin header contacts  40 . The pin header housing end walls  39  preferably are formed with offset recesses  41  to facilitate aligned engagement of the daughter card connector  15  with the pin header connector  14  upon mating, with the header housing recesses  41  providing a keying aspect for preventing improper mating. 
     The signal and ground contacts S, G of the pin header connector  14 , as best depicted in  FIGS. 5 and 5A , are disposed in a uniform arrangement of columns  45  (shown in vertical arrays) and rows  46  (shown in horizontal arrays). Each column  45  comprises edge coupled differential signal pairs of contacts S-S separated by a respective ground contact G. The signal contacts S-S of alternating columns in this case are offset by a pitch “p” of the rows  46 , such that one column  45 , in the order from top to bottom, begins with a ground contact G and the next adjacent column begins with a signal contact S. As viewed in  FIG. 5A , the first column on the left comprises, in order from top to bottom, a ground contact G, an edge coupled differential signal pair S-S, a ground contact G, a second differential signal pair S-S, a ground contact G etc. The adjacent column, beginning from the top, comprises a first differential signal pair S-S, a signal contact S, a second differential signal pair S-S, a ground contact G etc. By virtue of such arrangement, it can be seen that one signal contact S of each differential pair S-S is next to a signal contact S in the immediately adjacent column and the other signal contacts S of the differential pair is adjacent a ground contact G in the immediately adjacent column. 
     In accordance with an important aspect of the invention, and as shown in  FIG. 7 , the pin header connector housing base is formed with a predetermined pattern of core-outs  50  that define air passageways between the column of contacts that extend completely through the base for enhanced electrical isolation of the differential signal pairs without materially affecting the strength and rigidity of the connector housing and a series of partial core-outs that do not extend completely through the base  36  of the pin header connector  14 . To this end, the base  36  of the pin header connector housing  35  is formed with a pattern of elongated core-outs or air passageways  50  between the columns of contacts, with one passageway  50  being disposed between a signal contact S of each differential pair in one column and an adjacent signal contact S in the immediately adjacent column. It will be understood that since air has a lower dielectric constant than plastic, the air passageway enhances electrical isolation of the signal contact of one differential pair in one column from an adjacent signal contact of a differential signal pair in the adjacent column. Since the other signal contact of each differential pair in the illustrated embodiment is adjacent a ground contact, in that instance the ground contact provides a shielding effect. By virtue of the greater distance of signal contacts of differential signal pairs that are not in immediately adjacent relation to each other, together with the shielding effect of the air passageways  50  and ground contacts G, signal integrity also is not significantly affected by the more remotely located differential signal pairs. 
     Hence, the differential signal pairs in each column are effectively isolated from electrical noise of differential signal pairs in adjacent columns so as not to impede the integrity of high speed signal communications through the connector. It will be seen that since the air passageways  50  are relatively small in size, corresponding in length substantially to the cross-sectional length of the signal contacts S and the base  36  is devoid of any other gaps or openings that extend through the base between the columns of contacts, the air passageways  50  do not materially alter the structural strength and integrity of the pin header housing  35 , thereby not affecting its ability to withstand relatively high insertion forces that might be incurred upon mating insertion of a daughter card connector. Indeed, the air passageways  50  occupy a very small percentage of the area of the base, as established by the outer dimensions of the pin header connector housing  35 . 
     In accordance with a further aspect of the invention, as shown in  FIG. 7A , the pin header base  36  is formed with a plurality of partial core-outs or recesses  52 , which do not extend completely through the base  36 , but which further isolate the signal contacts S of differential signal pairs from the signal contacts S of adjacent and nearby differential signal pairs. In this case, such partial core-outs  52  are disposed between each signal contact S and an adjacent ground contact G in an adjacent column. The core-outs  52  again have a length corresponding substantially to the elongated cross-sectional length of the contact, but extend only midway through the base  36 , in this case from the mounting side of the base. The partial core-outs  52 , in conjunction with the adjacent ground contacts G, further electrically isolate the signal contact S of adjacent and nearby differential signal pairs. Since the partial core-outs  52  do not extend completely through the pin header base, they also do not materially affect the structural rigidity of the housing. The partial core-outs  52  may serve as the basis to the complete core-outs  50 , as shown in  FIGS. 7 and 7A , meaning that the partial core-outs  52  may be first formed in the connector housing base  36  and the remainder of the base drilled therethrough to define the complete core-out  50 . 
     Referring now to  FIG. 5B  of the drawings, there is shown an alternative embodiment of pin header connector in which pairs of air passageways  50 ,  50   a  are disposed on a common side of each differential signal pair of contacts S-S. Each air passageway  50  effects electrical isolation between the signal contact S in one column and the immediately adjacent signal contact S in an adjacent column, and the air passageway  50   a  is disposed between the other signal contact of each differential signal pair and the immediately adjacent ground contact for enhanced isolation of the signal contact from the other differential signal pairs. Again, since the air passageways are relatively small in size, they do not materially affect the structural integrity of the pin header housing. 
     Still a further alternative embodiment is depicted in  FIG. 5C , in which each column of contacts in this case starts with a ground contact and in which pairs of air passageways  50  are disposed on a common side of each differential signal pair of contacts for electrically isolating the contacts of that differential signal pair with the adjacent contacts of a differential signal pair in the adjacent column. Again, the base  36  of the pin header connector housing  35  is devoid of any other openings or gaps that extend through the base between the columns of contacts. 
     From the foregoing, it can be seen that a backplane connector is provided in which both the daughter card connector and pin header connector have differential signal pairs which are isolated by an air dielectric medium from adjacent contacts of adjacent differential signal pairs for enhanced signal integrity in high speed communications. The air dielectric isolation of signal contacts in the pin header is achieved while permitting utilization of a one-piece plastic housing for structural integrity. The pin header also may be designed with uniform closely-spaced columns and rows of contacts for economical manufacture and versatile usage.