Patent Publication Number: US-8123563-B2

Title: Electrical connector incorporating passive circuit elements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation of Ser. No. 12/463,118, now U.S. Pat. No. 7,887,371 filed May 8, 2009, which is a Continuation of Ser. No. 11/902,551, now U.S. Pat No. 7,540,781 filed Sep. 24, 2007, which is a Continuation of Ser. No. 10/874,837, now U.S. Pat. No. 7,285,018 filed Jun. 23, 2004, the entire disclosures of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to an electrical connector incorporating passive circuit elements and methods of manufacturing such an electrical connector. 
     Modem electronic circuitry is often built on printed circuit boards. The printed circuit boards are then interconnected to create an electronic system, such as a server or a router for a communications network. Electrical connectors are generally used to make these interconnections between the printed circuit boards. Typically, connectors are made of two pieces, with one piece on one printed circuit board and the other piece on another printed circuit board. The two pieces of the connector assembly mate to provide signal paths between the printed circuit boards. 
     A desirable electrical connector should generally have a combination of several properties. For example, it should provide signal paths with appropriate electrical properties such that the signals are not unduly distorted as they move between the printed circuit boards. In addition, the connector should ensure that the two pieces mate easily and reliably. Furthermore, the connector should be rugged so that it is not easily damaged by handling of the printed circuit boards. For many applications, it is also important that the connector have high density, meaning that the connector can carry a large number of electrical signals per unit length. 
     Examples of electrical connectors possessing these desirable properties include VHDM®, VHDM®-HSD and GbX® connectors manufactured and sold by the assignee of the present invention, Teradyne, Inc. 
     One of the disadvantages of present electronic systems is the need, often times, to populate the surfaces of the interconnected printed circuit boards with passive circuit elements. These passive circuit elements, such as capacitors, inductors and resistors, are necessary, for example: (i) to block or at least reduce the flow of direct current (“DC”) caused by potential differences between various electronic components on the interconnected printed circuit boards; (ii) to provide desired filtering characteristics; and/or (iii) to reduce data transmission losses. However, these passive circuit elements take up precious space on the board surface (thus reducing the space available for signal paths). In addition, where these passive circuit elements on the board surface are connected to conductive vias, there could be undesirable signal reflections at certain frequencies due to impedance discontinuity and resonant stub effects. 
     What is desired, therefore, is an electrical connector and methods of manufacturing such an electrical connector that generally possesses the desirable properties of the existing connectors described above, but also provides passive circuit elements in the connector to deliver the desired qualities provided by the passive circuit elements described above. And it is further desired that such an electrical connector provide the passive circuit elements cost effectively. 
     SUMMARY OF THE INVENTION 
     The objects of the invention are achieved in the preferred embodiment by an electrical connector that electrically connects a first printed circuit board and a second printed circuit board, where the electrical connector includes: (a) an insulative housing; (b) a plurality of signal conductors, with at least a portion of each of the plurality of signal conductors disposed within the insulative housing; (c) each of the plurality of signal conductors having a first contact end, a second contact end and an intermediate portion therebetween; and (d) a passive circuit element electrically connected to the intermediate portion of each of the plurality of signal conductors, where the passive circuit element is housed in an insulative package and includes at least a capacitor or an inductor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features of this invention, as well as the invention itself, may be more fully understood from the following description of the drawings in which: 
         FIG. 1  shows a perspective view of a prior art electrical connector assembly illustrated as  FIG. 1  in U.S. Pat. No. 6,409,543, where the electrical connector assembly includes a daughtercard connector and a backplane connector; 
         FIG. 2  shows a perspective view of a wafer of a daughtercard connector in accordance with the preferred embodiment of the present invention; 
         FIG. 3  shows a perspective view of the wafer of  FIG. 2 , with a portion of an insulative housing removed from the drawing to better illustrate attachment of passive circuit elements to signal conductors of the wafer; 
         FIG. 4  shows a perspective view of the wafer of  FIG. 3 , with some of the passive circuit elements removed from the drawing to better illustrate portions of the signal conductors to which the passive circuit elements are attached; 
         FIG. 5  shows a perspective view of a wafer of a daughtercard connector in accordance with another embodiment of the present invention; and 
         FIG. 6  shows a flowchart of a preferred manufacturing process for the connector in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a perspective view of a prior art electrical connector assembly  10  illustrated as  FIG. 1  in U.S. Pat. No. 6,409,543. The &#39;543 patent, which is directed to the GbX® connector, is assigned to the assignee of the present invention and is incorporated by reference herein. The electrical connector assembly  10  includes a daughtercard connector  20  that is connectable to a first printed circuit board (not shown) and a backplane connector  50  that is connectable to a second printed circuit board (not shown). The daughtercard connector  20  has a plurality of modules or wafers  22  which are preferably held together by a stiffener  24 . 
     Each wafer  22  includes a plurality of signal conductors  30 , a shield plate (not visible in  FIG. 1 ), and a dielectric housing  26  that is formed around at least a portion of each of the plurality of signal conductors  30  and the shield plate. Each of the signal conductors  30  has a first contact end  32  connectable to the first printed circuit board and a second contact end  34  mateable to the backplane connector  50 . Each shield plate has a first contact end  42  connectable to the first printed circuit board and a second contact end  44  mateable to the backplane connector  50 . 
     The backplane connector  50  includes an insulative housing  52  and a plurality of signal conductors  54  held by the insulative housing  52 . The plurality of signal conductors  30 ,  54  are arranged in an array of differential signal pairs. The backplane connector  50  also includes a plurality of shield plates  56  that are located between rows of differential signal pairs. Each of the signal conductors  54  has a first contact end  62  connectable to the second printed circuit board and a second contact end  64  mateable to the second contact end  34  of the corresponding signal conductor  30  of the daughtercard connector  20 . Each shield plate  56  has a first contact end  72  connectable to the second printed circuit board and a second contact end  74  mateable to the second contact end  44  of the corresponding shield plate of the daughtercard connector  20 . 
     As discussed in the Background Of The Invention section, the electrical connector assembly  10  of  FIG. 1  does not have passive circuit elements that would provide desirable characteristics, such as DC flow minimization, desired filtering characteristics or data transmission loss reduction. 
     Referring now to  FIG. 2 , there is shown a wafer  100  of a daughtercard connector (not shown) in accordance with the preferred embodiment of the present invention. The wafer  100  may be one of a plurality of such wafers that are held together by a stiffener, such as the stiffener  24  of  FIG. 1 . The wafer  100  includes a plurality of signal conductors  110  and an insulative housing  102 . The signal conductors  110  are more clearly shown in  FIG. 3 , which illustrates the wafer  100  of  FIG. 2  with a portion of the insulative housing  102  removed from the drawing. Note that the signal conductors  110  are arranged as differential signal pairs, with a first distance between signal conductors of a differential pair smaller than a second distance between signal conductors of adjacent differential pairs. However, it should be apparent to one of ordinary skill in the art reading this specification that the present invention and its concepts can be applied equally as well to single-ended signal connectors. 
     Each signal conductor  110  has a first contact end  112 , a second contact end  114  and an intermediate portion  116  therebetween. The intermediate portion  116  of the signal conductor  110  is disposed within the insulative housing  102 . Preferably, the wafer  100  also includes a ground conductor member or a shield plate having a first contact end  122  and a second contact end  124 . The configuration of the shield plate may be similar to the shield plate of  FIG. 1 . The first contact ends  112 ,  122 , which are illustrated as press-fit “eye of the needle” contact ends, are connectable to a first printed circuit board (not shown). The second contact ends  114 ,  124  are connectable to a mating connector (not shown), such as the backplane connector  50  of  FIG. 1 . 
     Attached to the intermediate portion  116  of each signal conductor  110  is a passive circuit element  140 . Preferably, the passive circuit element  140  includes at least a capacitor or an inductor housed in an insulative package and is a commercially available off-the-shelf component. For example, if the passive circuit element  140  is desired to function as a direct current blocking circuit, then may be one of the ceramic or tantalum chip capacitors that are sold by KEMET Electronics Corporation-of-Greenville, South Carolina can be utilized. The technical information for these ceramic or tantalum chip capacitors are available from KEMET (www.kemet.com) and are incorporated by reference herein. If the passive circuit element  140  is desired to function as a high frequency passive equalization circuit, then one of the resistor/inductor/capacitor packages that are sold by Maxim Integrated Products, Inc. of Sunnyvale, Calif. can be utilized. The technical information for these packages are available from Maxim (www.maxim-ic.com) and are incorporated by reference herein. It should be noted that while the preferred embodiment is directed to a two-piece (daughtercard connector and backplane connector), shielded, differential pair connector assembly, the concepts of the invention are applicable to a one-piece connector, an unshielded connector, a single-ended connector or any other type of electrical connector. 
     Referring now to  FIG. 6 , there is shown a flowchart  200  of a preferred manufacturing process for a connector in accordance with the present invention. This flowchart  200  illustrates the process steps for modifying and adapting an existing connector, such as the daughtercard connector  20  of  FIG. 1 , to provide the desirable passive circuit elements. It should be apparent to one of ordinary skill in the art that as the various process steps of the flowchart  200  are described, some of the steps need not be included in order to manufacture a connector in accordance with the present invention. Furthermore, the sequence of some of the steps may be varied. 
     Step  210  describes providing a wafer, such as a wafer  22  of  FIG. 1 , where during the molding of the insulative housing around the plurality of signal conductors, openings are defined through which an exposed area of each of the signal conductors is accessible. Preferably, the openings are provided adjacent the intermediate portions  116  of the signal conductors  110 . Note that the plurality of signal conductors are preferably stamped from a lead frame, as is known in the art. Typically, the signal conductors  110  are made of a solder wettable material, such as beryllium-copper or the like, and intermediate portions  116  of the signal conductors  110  may be coated with nickel or other non-solder wetting material. In this case, the exposed area of the signal conductors is provided with solder wettable material, such as tin-lead coating. 
     Step  214  describes cutting and removing a portion of the exposed area of the signal conductors such that only a portion of the exposed area remains.  FIG. 4 , which is a perspective view of the wafer  100  of  FIG. 3  with some of the passive circuit elements  140  removed from the drawing, shows the remaining portion  116   a,    116   b  of the exposed area of the signal conductors  110 . Step  216  describes cleaning and inspecting the signal conductors  110  after the cutting and removing step  214 . This step can be performed manually or automatically, and can be bypassed if desired. 
     Step  218  describes applying solder paste or conductive adhesive to the remaining. portion  116   a,    116   b  of the exposed area of the signal conductors  110 . Step  220  then describes picking and placing passive circuit elements  140  onto the remaining portions  116   a,    116   b  of the exposed area of the signal conductors  110 . Note that the openings in the insulative housing described in step  210  are sized to receive the passive circuit elements  140 . And step  222  describes conventional SMT reflow to securely attach the passive circuit elements  140  to the remaining portions  116   a,    116   b  of the exposed area of the signal conductors  110 . While the preferred method of step  218  is to apply the solder paste or conductive adhesive to the remaining portion  116   a,    116   b  of the exposed area of the signal conductors  110 , it should be apparent to one of ordinary skill in the art that the solder paste/conductive adhesive may instead be applied to the passive circuit elements  140  or to both the remaining portion  116   a,    116   b  of the exposed area of the signal conductors  110  and the passive circuit elements  140  as desired. 
     Steps  224  and  226  respectively describe. inspecting-and-cleaning the attachment area around the passive circuit elements  140  and the remaining portions  116   a,    116   b  of the exposed area of the signal conductors  110 . Steps  228  and  230  respectively describe testing for electrical continuity across the attachment area and potting/visual or mechanical inspection as required. Finally, step  232  describes assembling a plurality of wafers  100  to form a connector in accordance with the preferred embodiment of the present invention. 
     While the flowchart  200  illustrates cutting and removing a portion of the exposed area of the signal conductors  110  (step  214 ) after the insulative housing has been molded around the plurality of signal conductors, it is certainly possible, and in some cases even preferable, to cut and remove the portion of the exposed area of the signal conductors before the insulative housing has been molded around the plurality of signal conductors. The molded insulative housing will define openings through which the remaining portion of the exposed area of the signal conductors will be accessible. 
     In an alternative manufacturing-process (not shown) for a connector in accordance with the present invention, a passive circuit element (preferably a capacitive element) may be provided as follows: (i) providing a first lead frame which includes a plurality of first signal conductors, with each of the plurality of first signal conductors having a first contact end and an intermediate portion; (ii) providing a second lead frame which includes a plurality of second signal conductors, with each of the plurality of second signal conductors having a second contact end and an intermediate portion; (iii) positioning the plurality of first signal conductors and the plurality of second signal conductors adjacent one another such that for each first signal conductor there is a corresponding second signal conductor adjacent thereto; (iv) attaching at least a segment of the intermediate portion of each first signal conductor to at least a segment of the intermediate portion of the corresponding second-signal conductor with a dielectric material provided therebetween so as to provide a capacitive element; and (v) providing an insulative housing around at least a portion of each of the plurality of first and second signal conductors. In this process, the attached intermediate portions of the first signal conductor and the second signal conductor serve as capacitive plates to provide the desired capacitive characteristics. Other applicable steps from  FIG. 6  can then be utilized as needed. 
     Referring now to  FIG. 5 , there is shown a perspective view of a wafer  150  of a daughtercard connector (not shown) in accordance with another embodiment of the present invention. The wafer  150  may be one of a plurality of such wafers that are held together by a stiffener, such as the stiffener  24  of  FIG. 1 . The wafer  150  of  FIG. 5  is similar to the wafer  100  of  FIG. 2 , with the substantive difference being the presence of additional passive circuit elements  140  along the intermediate portions  116  of the signal conductors  110 . Note that in the wafer  150  illustrated in  FIG. 5 , all but two signal conductors that are shortest in length are provided with two passive circuit elements  140  each. In some simulations, it has been shown that having additional passive circuit elements  140  provides better desired qualities, such as high frequency passive equalization. It should be noted that the desirable number of passive circuit elements  140  is not limited to one or two per signal conductor, but rather depends on various other factors, including the structure and electrical characteristics of the connector. 
     Having described the preferred embodiment of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. 
     It is felt therefore that these embodiments should not be limited to disclosed embodiments but rather should-be-limited only-by the spirit and scope of the appended claims. 
     All publications and references cited herein are expressly incorporated herein by reference in their entirety.