Abstract:
In an electrical connector having a strip line arrangement of a plurality of signal contacts flanked by ground planes, the improvement comprising the signal contacts having an elongated cross-section defined by minor surfaces and major surfaces, with the major surfaces extending transversely between the ground planes. An electrical connector for reducing cross-talk and controlling impedance, comprising: an insulative housing; a ground plane; and a plurality of contacts. Each contact has having an elongated cross-section and a mating portion for engaging a contact of a mating connector. The elongated cross-section, at least in the mating portion, extends transverse to the ground plane. An electrical connector for reducing cross-talk and controlling impedance, comprising: an insulative housing; a ground plane; and a plurality of contacts. Each contact has an elongated cross-section and a mating portion for engaging a contact of a mating connector. The contacts maintain a generally uniform angle to the ground plane substantially along the length of the contact.

Description:
This application is a 371 of PCT/US96/10210 filed Jun. 11, 1996, and CIP of 08/452,020 filed Jun. 12, 1995 and CIP of 08/452,021, filed Jun. 12, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical connectors and more particularly to electrical connectors including means for controlling electrical cross talk and impedance. 
     2. Brief Description of Prior Developments 
     As the density of interconnects increases and the pitch between contacts approaches 0.025 inches or 0.5 mm, the close proximity of the contacts increases the likelihood of strong electrical cross talk coupling between the contacts. In addition, maintaining design control over the electrical characteristic impedance of the contacts becomes increasingly difficult. In most interconnects, the mated plug/receptacle contact is surrounded by structural plastic with air spaces to provide mechanical clearances for the contact beam. As is disclosed in U.S. Pat. No. 5,046,960 to Fedder, these air spaces can be used to provide some control over the characteristic impedance of the mated contact. Heretofore, however, these air spaces have not been used, in conjunction with the plastic geometry, to control both impedance and, more importantly, cross talk. 
     SUMMARY OF THE INVENTION 
     In the connector of the present invention there is a first member and a second member each of which comprises a metallic contact means and a dielectric base means. On each member the metallic contact means extends perpendicularly from the dielectric base means. The two metallic contact means connect to form what is referred to herein as a generally “I-beam” shaped geometry. The concept behind the I-beam geometry is the use of strong dielectric loading through the structural dielectric to ground on the top and bottom of the mated contact edges and a relatively light loading through air on the mated contact sides. These different dielectric loadings are balanced in such a way as to maintain a controlled impedance and yet minimize coupling (and cross talk) between adjacent contacts. In this way, all lines of the interconnect can be dedicated to signals while maintaining a controlled impedance and a relatively low rise time-cross talk product of less than 1 nano-second percent. Typical rise time-cross talk values for existing 0.05 to 0.025 inch pitch controlled impedance interconnects range from 2.5 to 4 nano-second percent. 
     The I-beam geometry of this invention may also be advantageously used in an electrical cable assembly. In such an assembly a control support dielectrical web element is perpendicularly interposed between opposed flange elements. Each of the flange elements extend perpendicularly away from the terminal ends of the web element. On both of the opposed sides of the web there is a metalized signal line. The opposed end surfaces of the flanges are metalized to form a ground plane. Two or more such cable assemblies may be used together such that the flanges are in end to end abutting relation and the longitudinal axes of the conductive elements are parallel. An insulative jacket may also be positioned around the entire assembly. 
     For both connectors and cable assemblies having the I-beam geometry of this invention, it is believed that rise time cross-talk product will be independent of signal density for signal to ground ratios greater than 1:1. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is further described with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic illustration of one preferred embodiment of the connector of the present invention; 
     FIG. 1 a  is a schematic illustration of another preferred embodiment of the connector of the present invention; 
     FIG. 2 is a schematic illustration of another preferred embodiment of the connector of the present invention; 
     FIG. 3 is another schematic illustration of the connector illustrated in FIG. 2; 
     FIG. 4 is a side elevational view of another preferred embodiment of the connector of the present invention; 
     FIG. 5 is an end view of the connector shown in FIG. 4; 
     FIG. 6 is a perspective view of the connector shown in FIG. 4; 
     FIG. 7 is an end view of the receptacle element of the connector shown in FIG. 4; 
     FIG. 8 is a bottom plan view of the receptacle element shown in FIG. 7; 
     FIG. 9 is a cross sectional view taken through IX—IX in FIG. 7; 
     Fig. 1O is an end view of the receptacle element of the preferred embodiment of the present invention shown in FIG. 4; 
     FIG. 11 is a bottom plan view of the receptacle element shown in FIG. 10; 
     FIG. 12 is a cross sectional view taken through XII—XII in FIG. 10; 
     FIG. 13 is a perspective view of the receptacle element shown in FIG. 10; 
     FIG. 14 is a cross sectional view of the plug and receptacle elements of the connector shown in FIG. 4 prior to engagement; 
     FIG. 15 is a cross sectional view taken through XV—XV in FIG. 4; 
     FIG. 16 is a cross sectional view corresponding to FIG. 13 of another preferred embodiment of the connector of the present invention; 
     FIGS. 17 and 18 are graphs illustrating the results of comparative tests described hereafter; 
     FIG. 19 is a perspective view of a preferred embodiment of a cable assembly of the present invention; 
     FIG. 20 is a detailed view of the area within circle XVIII in FIG. 17; 
     FIG. 21 is a cross sectional view of another preferred embodiment of a cable assembly of the present invention; 
     FIG. 22 is a side elevational view of the cable assembly shown in FIG. 17 in use with a receptacle; 
     FIG. 23 is a cross sectional view taken through XXIII—XXIII in FIG.  20 . 
     FIG. 24 is a top plan view of a plug section of another preferred embodiment of the connector of the present invention; 
     FIG. 25 is a bottom plan view of the plug section shown in FIG. 24; 
     FIG. 26 is an end view of the plug section shown in FIG. 24; 
     FIG. 27 is a side elevational view of the plug section shown in FIG. 24; 
     FIG. 28 is a top plan view of a receptacle section which is engageable with the plug section of a preferred embodiment of the present invention shown in FIG. 24; 
     FIG. 29 is a bottom plan view of the receptacle shown in FIG. 28; 
     FIG. 30 is an end view of the receptacle shown in FIG. 28; 
     FIG. 31 is a side elevational view of the receptacle shown in FIG. 28; 
     FIG. 32 is a fragmented cross sectional view as taken through lines XXXII—XXXII in FIGS. 24 and 28 showing those portions of the plug and receptacle shown in those drawings in an unengaged position; and 
     FIG. 33 is a fragmented cross sectional view as would be shown as taken through lines XXXIII—XXXIII in FIGS. 24 and 28 if those elements were engaged. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Theoretical Model 
     The basic I-beam transmission line geometry is shown in FIG.  1 . The description of this transmission line geometry as an I-beam comes from the vertical arrangement of the signal conductor shown generally at numeral  10  between the two horizontal dielectric layers  12  and  14  having a dielectric constant εand ground planes  13  and  15  symmetrically placed at the top and bottom edges of the conductor. The sides  20  and  22  of the conductor are open to the air  24  having an air dielectric constant ε 0 . In a connector application the conductor would be comprised of two sections  26  and  28  which abut end to end or face to face. The thickness, t 1  and t 2  of the dielectric layers  12  and  14 , to first order, controls the characteristic impedance of the transmission line and the aspect ratio of the overall height h to dielectric width w d  controls the electric and magnetic field penetration to an adjacent contact. The aspect ratio to minimize coupling beyond A and B is approximately unity as illustrated in FIG.  1 . The lines  30 ,  32 ,  34 ,  36  and  38  in FIG. 1 are equipotentials of voltage in the air-dielectric space. Taking an equipotential line close to one of the ground planes and following it out towards the boundaries A and B, it will be seen that both boundary A are very close to the ground potential. This means that at both boundary A and boundary B we have virtual ground surfaces and if two or more I-beam modules are placed side by side, a virtual ground surface exists between the modules and there will be no coupling between the modules. In general, the conductor width w c  and dielectric thickness should be small compared to the dielectric width or module pitch. 
     Given the mechanical constraints on a practical connector design, the proportioning of the signal conductor (blade/beam contact) width and dielectric thicknesses will, of necessity, deviate somewhat from the preferred ratios and some minimal coupling will exist between adjacent signal conductors. However, designs using the basic I-beam guidelines will have lower cross talk than more conventional approaches. Referring to FIG. l a , an alternate embodiment is shown in which the dielectric is shown at  12 ′ and  14 ′ with their respective ground planes at  13 ′ and  15 ′. In this embodiment the conductor  26 ′ and  28 ′ extend respectively from dielectric layers  12 ′ and  14 ′, but the conductors  26 ′ and  28 ′ abut side to side rather than edge to edge. An example of a practical electrical and mechanical I-beam design for a 0.025 inch pitch connector uses 8×8 mil beams 26″and 8×8 mil blades 28″, which when mated, form an 8×16 mil signal contact and the contact cross-section is shown in FIG.  2 . The dielectric thickness, t, is 12 mils. The voltage equipotentials for this geometry are shown in FIG. 3 where virtual grounds are at the adjacent contact locations and some coupling will now exist between adjacent contacts. 
     Referring to FIG. 2, the I-beam transmission geometry is shown as being adapted to a less than ideally proportioned multi-conductor system. Signal conductors  40 ,  42 ,  44 ,  46  and  48  extend perpendicularly between two dielectric and horizontal ground planes  50  mounted on base  51  and  52  mounted on base  53  which have a dielectric ε. To the sides of the conductors are air spaces  54 ,  56 ,  58 ,  60 ,  62  and  64 . 
     Referring to FIG. 3, another multi-conductor connector is shown wherein there are parallel conductors  66 ,  68  and  70  which extend perpendicularly between two dielectric and horizontal ground planes  72  mounted on base  73  and  74 .(Mounted on base  75 ) to the sides of the conductors are air spaces  76 ,  78 ,  80  and  82  and equipotential line shown as at  84  and  86   
     Electrical Connector 
     Referring particularly to FIGS. 4 to  12  it will be seen that the connector of the present invention is generally comprised of a plug shown generally at numeral  90  and a receptacle shown generally at numeral  92 . The plug consists of a preferably metallic plug housing  94  which has a narrow front section  96  and a wide rear section  98 . The front section has a top side  100  and a bottom side  102 . The wide rear section has a top side  104  and a bottom side  106 . The plug also has end surfaces  108  and  110 . On the top side of both the front and rear sections there are longitudinal grooves  112 ,  114 ,  116  and  118  and  119 . In these grooves there are also apertures  120 ,  122 ,  124 ,  126  and  128 . Similarly on the bottom sides of both the front and rear section there are longitudinal grooves as at  129  which each have apertures as at  130 . On the top sides there is also a top transverse groove  132 , while on the bottom side there is a similarly positioned bottom transverse groove  134 . The plug also has rear standoffs  136  and  138 . Referring particularly to FIG. 9 it will be seen that the plug includes a dielectric element  140  which has a rear upward extension  142  and a rear downward extension  144  as well as a major forward extension  146  and a minor forward extension  148 . The housing also includes opposed downwardly extending projection  150  and upwardly extending projection  152  which assist in retaining the dielectric in its position. In the longitudinal grooves on the top side of the plug there are top axial ground springs  154 ,  156 ,  158 ,  160  and  162 . In the transverse groove there is also a top transverse ground spring  164 . This transverse ground spring is fixed to the housing by means of ground spring fasteners  166 ,  168 ,  170  and  172 . At the rearward terminal ends of the longitudinal ground springs there are top grounding contacts  176 ,  178 ,  180 ,  182  and  184 . Similarly the grooves on the bottom side of the plug there are bottom longitudinal ground springs  186 ,  188 ,  190 ,  192  and  194 . In the bottom transverse groove there is a bottom transverse ground spring  196  as with the top transverse ground spring, this spring is fixed in the housing by means of ground spring fasteners  198 ,  200 ,  202 ,  204  and  206 . At the rear terminal ends of the ground springs there are bottom ground contacts  208 ,  210 ,  212 ,  214  and  216 . The plug also includes a metallic contact section shown generally at  218  which includes a front recessed section  220 , a medial contact section  222  and a rearward signal pin  224 . An adjacent signal pin is shown at  226 . Other signal pins are shown, for example, in FIG. 7 at  228 ,  230 ,  232 ,  234  and  236 . These pins pass through slots in the dielectric as at  238 ,  240 ,  242 ,  244 ,  246 ,  248  and  250 . The dielectric is locked in place by means of locks  252 ,  254 ,  256  and  258  which extend from the metal housing. Referring again particularly to FIG. 9 the plug includes a front plug opening  260  and top and bottom interior plug walls  262  and  264 . It will also be seen from FIG. 9 that a convex section of the ground springs as at  266  and  268  extend through the apertures in the longitudinal grooves. Referring particularly to FIGS. 10 through 12, it will be seen that the receptacle includes a preferably metallic receptacle housing  270  with a narrow front section  272  and a wider rear section  274 . The front section has a topside  276  and a bottom side  278  and the rear section has a topside  280  and  282 . The receptacle also has opposed ends  284  and  286 . On the top sides of the receptacle there are longitudinal grooves  288 ,  290  and  292 . Similarly on the bottom surface there are longitudinal grooves as at  294 ,  296  and  298 . On the top surface there are also apertures as at  300 ,  302  and  304 . On the bottom surface there are several apertures as at  306 ,  308  and  310 . The receptacle also includes rear standoffs  312  and  314 . Referring particularly to FIG. 12, the receptacle includes a dielectric element shown generally at numeral  316  which has a rear upward extension  318 , a rear downward extension  320 , a major forward extension  322  and a minor forward extension  324 . The dielectric is retained in position by means of downward housing projection  326  and upward interior housing projection  328  along with rear retaining plate  330 . Retained within each of the apertures there is a ground spring as at  332  which connects to a top ground post  334 . Other top ground posts as at  336  and  338  are similarly positioned. Bottom ground springs as at  340  are connected to ground posts as at  342  while other ground posts as at  344  and  346  are positioned adjacent to similar ground springs. Referring particularly to FIG. 12, the receptacle also includes a metallic contact section shown generally at numeral  348  which has a front recess section  350 , a medial contact section  352  and a rearward signal pin  354 . An adjacent pin is shown at  356 . These pins extend rearwardly through slots as at  358  and  360 . The dielectric is further retained in the housing by dielectric locks as at  362  and  364 . The receptacle also includes a front opening  365  and an interior housing surface  366 . Referring particularly to FIG. 13, this perspective view of the receptacle shows the structure of the metallic contact section  350  in greater detail to reveal a plurality of alternating longitudinal ridges as at  367  and grooves  368  as at which engage similar structures on metallic contact  218  of the receptacle. 
     Referring particularly to FIGS. 14 and 15, the plug and receptacle are shown respectively in a disengaged and in an engaged configuration. It will be observed that the major forward extension  146  of the dielectric section of the plug abuts the minor forward extension of the dielectric section of the receptacle end to end. The major forward extension of the dielectric section of the receptacle abuts the minor forward extension of the dielectric section of the plug end to end. It will also be observed on the metallic section of the plug the terminal recess receives the metallic element of the receptacle in side by side abutting relation. The terminal recess of the metallic contact element of the receptacle receives the metallic contactelement of the plug in side by side abutting relation. The front end of the terminal housing abuts the inner wall of the plug. The ground springs of the plug also abut and make electrical contact with the approved front side walls of the receptacle. It will be noted that when the connector shown in FIG. 15 where the plug and receptacle housings are axially engaged, the plug metallic contact and receptacle metallic contact extend axially inwardly respectively from the plug dielectric element and the receptacle dielectric element to abut each other. It will also be noted that the plug and receptacle dielectric elements extend radially outwardly respectfully from the plug and receptacle metallic contact elements. 
     Referring to FIG. 16, it will be seen that an alternate embodiment the connector of the present invention is generally comprised of a plug shown generally at numerals  590  and a receptacle shown generally at numerals  592 . The plug consists of a plug housing  594 . There is also a plug ground contact  596 , plug ground spring  598 , plug signal pins  600  and  602 , plug contact  606  and dielectric insert  608 . The receptacle consists of receptacle housing  610 , receptacle ground contact  612 , receptacle ground springs  614  and receptacle contact  616 . An alignment frame  618  and receptacle signal pins  620  and  622  are also provided. It will be appreciated that this arrangement affords the same I-beam geometry as was described above. 
     Comparative Test 
     The measured near end (NEXT) and far end (FEXT) cross talk at the rise time of 35 p sec, for a 0.05″ pitch scaled up model of a connector made according to the foregoing first described embodiment are shown in FIG.  17 . The valley in the NEXT wave form of approximately 7% is the near end cross talk arising in the I-beam section of the connector. The leading and trailing peaks come from cross talk at the input and output sections of the connector where the I-beam geometry cannot be maintained because of mechanical constraints. 
     The cross talk performance for a range of risetimes greater than twice the delay through the connector of the connector relative to other connector systems is best illustrated by a plot of the measured rise time-cross talk product (nanoseconds percent) versus signal density (signals/inch). The different signal densities correspond to different signal to ground ratio connections in the connector. The measured rise time-cross talk product of the scaled up 0.05″ pitch model I-beam connector is shown in FIG. 18 for three signal to ground ratios; 1:1, 2:1, and all signals. Since the cross talk of the scaled up model is twice that of the 0.025 inch design, the performance of the 0.025 inch pitch, single row design is easily extrapolated to twice the density and one half the model cross talk. For the two row design, the density is four times that of the model and the cross talk is again one half. The extrapolated performance of the one row and two row 0.025 inch pitch connectors are also shown in FIG. 18 relative to that of a number of conventional connectors as are identified in that figure. The rise time cross talk product of the 0.025 inch pitch I-beam connector for all signals is .75 and is much less than that of the other interconnects at correspondingly high signal to ground ratios. Referring particularly to the 0.05 inch pitch model curve in FIG. 18, it will be observed that the rise time cross-talk product is independent of signal density for signal to ground ratios greater than 1:1. 
     Electrical Cable Assembly 
     Referring to FIGS. 19 and 20, it will be seen that the beneficial results achieved with the connector of the present invention may also be achieved in a cable assembly. That is, a dielectric may be extruded in an I-beam shape and a conductor may be positioned on that I-beam on the web and the horizontal flanges so as to achieve low cross talk as was described above. I-beam dielectric extrusions are shown at numerals  369  and  370 . Each of these extensions has a web  371  which is perpendicularly interposed at its upper and lower edges between flanges as at  372  and  373 . The flanges have inwardly facing interior surfaces and outwardly facing exterior surfaces which have metallized top ground planes sections  374  and  376  and metallized bottom ground plane sections respectively at  378  and  380 . The webs also have conductive layers on their lateral sides. I-beam extrusion  370  has vertical signal lines  382  and  384  and I-beam extrusion  374  has vertical signal lines  386  and  388 . These vertical signal lines and ground plane sections will preferably be metallized as for example, metal tape. It will be understood that the pair of vertical metallized sections on each extrusion will form one signal line. The property of the I-beam geometry as it relates to impedance and cross talk control will be generally the same as is discussed above in connection with the connector of the present invention. Referring particularly to FIG. 20, it will be seen that the I-beam extrusions have interlocking steps as at  390  and  392  to maintain alignment of each I-beam element in the assembly. Referring to FIG. 21, I-beam elements shown generally at  394 ,  396  and  398  are metallized (not shown) as described above and may be wrapped in a foil and elastic insulative jacket shown generally at numeral  400 . Because of the regular Alignment of the I-beam element in a collinear array, the I-beam cable assembly can be directly plugged to a receptacle without any fixturing of the cable except for removing the outer jacket of foil at the pluggable end. The receptacle can have contact beams which mate with blade elements made up of the ground and signal metallizations. Referring particularly to FIG. 23, it will be seen, for example, that the receptacle is shown generally at numeral  402  having signal contacts  404  and  406  received respectively vertical sections of I-beam elements  408  and  410 . Referring to FIG. 22, the receptacle also includes ground contacts  412  and  414  which contact respectively the metallized top ground plane sections  416  and  418 . It is believed that for the cable assembly described above rise time cross-talk product will be independent of signal density for signal to ground ratios greater than 1:1. 
     Ball Grid Array Connector 
     The arrangement of dielectric and conductor elements in the I-beam geometry described herein may also be adapted for use in a ball grid array type electrical connector. A plug for use in such a connector is shown in FIGS. 24-27. Referring to these figures, the plug is shown generally at numeral  420 . This plug includes a dielectric base section  422 , a dielectric peripheral wall  424 , metallic signal pins as at  426 ,  428 ,  430 ,  432  and  434  are arranged in a plurality of rows and extend perpendicularly upwardly from the base section. Longitudinally extending metallic grounding or power elements  436 ,  438 ,  440 ,  442 ,  444  and  446  are positioned between the rows of signal pins and extend perpendicularly from the base section. The plug also includes alignment and mounting pins  448  and  450 . On its bottom side the plug also includes a plurality of rows of solder conductive tabs as at  452  and  454 . 
     Referring to FIGS. 28-31, a receptacle which mates with the plug  420  is shown generally at numeral  456 . This receptacle includes a base section dielectric  458 , a peripheral recess  460  and rows of metallic pin receiving recesses as at  462 ,  464 ,  466 ,  468  and  470 . Metallic grounding or power elements receiving structures  472 ,  474 ,  476 ,  478 ,  480  and  482  are interposed between the rows of pin receiving recesses. On its bottom side the receptacle also includes alignment and mounting pins  484  and  486   
     It will be appreciated that electrical connector has been described which by virtue of its I-beam shaped geometry allows for low cross talk and impedance control. 
     It will also be appreciated that an electrical cable has also been described which affords low cross talk and impedance control by reason of this same geometry. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.