Patent Publication Number: US-7591655-B2

Title: Electrical connector having improved electrical characteristics

Description:
RELATED APPLICATIONS 
     The present patent document is a continuation-in-part of application Ser. No. 11/462,012, filed Aug. 2, 2006, now U.S. Pat. No. 7,413,484, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electrical terminals of the type to be inserted into apertures of an electrical panel member and electrical connectors containing such terminals. 
     BACKGROUND OF THE INVENTION 
     Due to the increasing complexity of electronic components, it is desirable to fit more components in less space on a circuit board or other substrate. Consequently, the spacing between electrical terminals within connectors has been reduced, while the number of electrical terminals housed in the connectors has increased, thereby increasing the need in the electrical arts for electrical connectors that are capable of handling higher and higher speeds and to do so with greater and greater pin densities. It is desirable for such connectors to have not only reasonably constant impedance levels, but also acceptable levels of impedance and cross-talk, as well as other acceptable electrical and mechanical characteristics. 
     Previous attempts to design such high speed electrical connectors have focused on the mating ends of the electrical terminals in the connector to achieve desired levels of impedance and cross-talk, pin densities, and other desired electrical and mechanical characteristics, but these attempts have largely ignored the mounting ends of the electrical terminals within the connector. For example, previous attempts to reduce the cross-talk within a connector and obtain desired impedance levels involved the use of edge coupling or edge-to-edge positioning of the mating ends of the electrical terminals within a connector, without any suggestion that modifying the mounting ends of the electrical terminals would have any desirable mechanical or electrical effects within the connector. In contrast, various embodiments of the present invention focus on the mounting ends of the electrical terminals within a connector, which, surprisingly, can be configured to achieve the desired electrical performance of a high speed, high density electrical connector, while maintaining the physical characteristics necessary to readily insert the connector into a panel member aperture without damage to the terminals of the connector or the panel member apertures. 
     SUMMARY OF THE INVENTION 
     In some embodiments of the present invention, the electrical terminals have a mounting end that is substantially smaller than the mating end, resulting in mechanical and electrical advantages. Moreover, unlike known electrical terminals, various embodiments of the terminals of the present invention also are configured to provide the mechanical and electrical characteristics necessary to function within an aperture of substantially reduced size, or a micro via. For example, the configuration of the mounting portion of certain embodiments of the present invention results in improved electrical performance and impedance levels, reduced capacitance/impedance discontinuities, reduced electrical degradation, reduced capacitive coupling, and/or reduced insertion forces in micro via applications, while maintaining the structural integrity necessary for high density electrical terminals and connectors. 
     The electrical terminal of the present invention may include a base, an insertion portion, or mounting end, that extends from the base to a first end, and a slit formed through the insertion portion and extending from or between the base and the first end, where the slit separates a first leg and a second leg that comprise a compliant portion. In some embodiments, the insertion portion of the electrical terminal may be configured for insertion into a panel member aperture having a diameter of less than about 0.014 inch (0.36 millimeter) or less than about 0.016 inch (0.41 millimeter). A segment of the first leg may be deformed in one direction away from the slit, and a segment of the second leg may be deformed in a second direction away from the slit opposite the first leg. In certain embodiments, the center of one or more of the leg segments is offset from the center of the slit. In some embodiments, the insertion portion has a first tapered segment adjacent the first end and a second tapered segment extending from or between the first tapered segment and the base. A secondary taper from the base to the end of the leg segments may also be included. 
     In certain embodiments of the present invention, the electrical terminals of the connector are configured so that the insertion force associated with mounting the connector in a panel member is reduced, as compared with prior art connectors, and the insertion force is substantially constant over the length of travel of the mounting hardware in a panel member aperture. The electrical terminals of the present invention may have an end portion that facilitates insertion into and alignment with a panel member aperture by providing tactile feedback to a user. 
     Electrical connections with a panel member and electrical performance of the electrical connections between panel members and associated components may be improved by certain embodiments of the present invention. Some embodiments of the present invention also have the advantage that the mounting ends of the electrical terminals are configured to permit an increased number of electrical terminals per unit area (pin density) and to increase the possibilities for routing electrical traces between terminals. 
     In some embodiments of the present invention, a connector is provided for insertion into a panel member having apertures with a first diameter and apertures with a second diameter, where the first diameter is different from the second diameter. The dimensions of the electrical terminals to be inserted into the apertures may also vary from one terminal to the next within the connector. For example, a connector may include a first array of electrical terminals containing differential signal pairs separated by one or more grounds and a second array of electrical terminals containing differential signal pairs separated by one or more grounds, where the electrical terminals of the differential signal pairs have a first size and the ground terminals have a second size that is greater than the first size. The cross-talk between the differential signal pairs in adjacent linear arrays may be reduced by offsetting the differential signal pairs in one linear array from those of the adjacent linear array(s). 
     Other features and advantages of the present invention will be apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of an electrical terminal of the present invention; 
         FIG. 1A  is an enlarged perspective view of the portion of  FIG. 1  within enclosure A; 
         FIG. 2  is a side elevational view of the electrical terminal of  FIG. 1 ; 
         FIG. 2A  is an enlarged perspective view of the portion of  FIG. 2  within enclosure A; 
         FIG. 3  is a top view of the electrical terminal of  FIG. 1 ; 
         FIG. 3A  is an enlarged perspective view of the portion of  FIG. 3  within enclosure A; 
         FIG. 4  is a perspective view showing the dimensions of one embodiment of the electrical terminal of the present invention, as compared with three existing electrical terminals; 
         FIG. 5  is a perspective view of one embodiment of a connector of the present invention; 
         FIG. 5A  is an enlarged perspective view of the portion of  FIG. 5  within enclosure A; 
         FIG. 5B  is a partial perspective view of one embodiment of a connector of the present invention having terminals positioned broadside-to-broadside within a housing; 
         FIG. 5C  is a partial perspective view similar to  FIG. 5B  with the housing removed; 
         FIG. 6  is a pin configuration for one embodiment of a connector of the present invention; 
         FIG. 6A  is a pin configuration for another embodiment of a connector of the present invention; 
         FIG. 7  is a graph illustrating a substantially constant insertion force profile as obtained in one embodiment of the present invention; 
         FIG. 8  is a top view of a panel member having four electrical traces routed between adjacent electrical terminals according to one embodiment of the present invention; 
         FIG. 9  is an exploded perspective view of one embodiment of a connector of the present invention; 
         FIG. 10  is a perspective view of an assembled connector containing electrical terminals of one embodiment of the present invention; and 
         FIG. 11  is an enlarged partial perspective view of a pair of aligned mating connectors, where each connector is secured to a respective panel member. 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     DETAILED DESCRIPTION 
     Various embodiments of the present invention include electrical terminals and electrical connectors having desirable electrical and mechanical characteristics, such as desirable impedance levels, impedance profiles, insertion losses, cross-talk levels, pin densities, and/or insertion force profiles, for example. In some embodiments, such desirable characteristics are achieved by an electrical terminal having a mounting end that is substantially smaller than its mating end. In other embodiments, an electrical connector, such as a press-fit connector, has a plurality of electrical terminals with mounting ends that are configured to provide improved characteristics. These and other embodiments are described in more detail below. 
     One embodiment of the present invention is directed to an electrical terminal  10 , also referred to as a contact or pin, as depicted in  FIGS. 1 to 3 . In this embodiment, the electrical terminal  10  includes a base  12  with an insertion portion  14 , or mounting end, that extends from the base  12  to an end  28 . The electrical terminal  10  is configured for insertion into an aperture in a panel member or circuit board (not shown), also referred to as a substrate. 
     The insertion portion  14  of the electrical terminal  10  shown in  FIGS. 1 and 1A  includes a compliant portion  18  and a tip or end portion  26 , which has an upper surface  34  and a lower surface  35 . The compliant portion  18  includes a slit  20 , also referred to as a shear or elongated opening, formed in insertion portion  14 , where the slit  20  is defined by two flexible leg members  22 ,  24 , the base  12 , and the end portion  26 . The end portion  26  is disposed between the compliant portion  18  and the end  28  and includes a plurality of tapers  30 ,  32  formed adjacent to the end  28 . The leg members  22 ,  24  of the compliant portion  18  may have a constant thickness or a variable thickness. 
     In the embodiment of  FIGS. 1 to 3 , the base  12  is connected to a first end of each of the leg members, and the end portion  26  is connected to a second end of each of the leg members. The base  12  may be any suitable shape. Four exemplary types of bases  12  are shown in  FIG. 4 . 
     In the embodiment of  FIGS. 1 to 3 , a beam portion  16 , or mating end, is configured to extend into a connector  70 , such as the connector shown in  FIGS. 5 and 5A , and to extend from the base  12  in a direction opposite the direction in which the insertion portion  14  extends from the base  12 . The embodiment of  FIG. 5 , which is shown in more detail in  FIG. 5A , is a connector containing a plurality of lead frames  72 ,  73  in which the individual terminals  10  are housed. The connector may contain shields or it may be shieldless. 
     The embodiment shown in  FIGS. 1A and 2A  includes a lead-in ramp  38  that is adjacent to the end of the leg  22  which is adjacent to the end  28 . This ramped portion  38  extends to an intermediate segment  40  which further extends to a lead-out ramp  42 . Proceeding from the end of the lead-in ramp  38  that is adjacent to the end  28 , toward the base  12 , the perpendicular distance between the lead-in ramp  38  and a central plane  44  increases, where the plane  44  is a substantially central plane  44  that extends from an end  68  to an end  69  of the slit  20 , as shown in  FIG. 1A . Continuing along the intermediate segment  40  from the end of the segment  40  that is adjacent to the lead-in ramp  38 , toward the base  12 , the distance between the intermediate segment  40  and the central plane  44  continues to increase for at least a portion of the length of the intermediate segment  40 , reaching a maximum distance  45 , and then decreasing for the remaining portion of the length of the segment  40 . Further proceeding along the lead-out ramp  42  from an end of the intermediate segment  40  that is adjacent to the base  12 , toward the base  12 , the distance between the lead-out ramp  42  and the central plane  44  continues to decrease. 
     The description of one leg  22  may also apply to the other leg  24  of the compliant portion  18 . In one embodiment, in which the upper and lower surfaces  34 , are parallel, the second leg  24  is a mirror image of the first leg  22  with respect to a mid-plane  66  that bisects the thickness of the terminal between the upper and lower surfaces  34 ,  35 , as shown in  FIGS. 2 and 2A . 
     While the legs  22 ,  24  may have a profile defined by a plurality of linear segments (such as a trapezoidal profile) formed away from the upper surface  34  and defined by the lead-in ramps  38 , intermediate segments  40 , and lead-out ramps  42 , the profile is not intended to be so limited. For example, any combination of the lead-in ramp  38 , intermediate segment  40 , and lead-out ramp  42  could define a curved or substantially arcuate profile. 
     In some embodiments, the legs  22 ,  24  are substantially symmetric with each other. In other words, in embodiments having parallel upper and lower surfaces  34 ,  35 , the legs  22 ,  24  are of substantially equal size and have lead-in ramps  38 , intermediate segments  40 , and lead-out ramps  42  defining substantially similar profiles, albeit in opposite directions with respect to the mid-plane  66 . In certain embodiments, each of the legs  22 ,  24  has a substantially rectangular cross sectional profile, but other profiles also may be used, including any combination and magnitude of curved or rounded edges. 
     The electrical terminals  10  of the present invention may be made of any suitable material. Suitable materials include, but are not limited to, metals and/or alloys or other materials having sufficient electrical conductance, formability and ability to hold a formed profile. In one embodiment, the terminals are formed from a sheet material having a thickness of about 0.006 inch (0.15 millimeter) to about 0.008 inch (0.2 millimeter), or of about 0.006 inch (0.15 millimeter) or less, and having an upper surface  34  and a lower surface  35 . The electrical terminals  10  may be cut out, e.g., by stamping, or otherwise removed from the sheet of material, but, for purposes of discussion, the electrical terminal retains its upper and lower surfaces  34 ,  35 . In one embodiment, the slit  20  is formed substantially perpendicular to the upper surface  34  and bisects the legs  22 ,  24 , which may have substantially equal cross sectional areas. The formation of the slit  20  may, but does not necessarily, entail the removal of material from the compliant portion  18 , depending upon the manufacturing techniques employed. Although the slit  20  may be primarily formed through the insertion portion  14 , the slit  20  may extend from or between the base  12  and the end portion  26  of insertion portion  14 . In other words, the slit  20  may extend into a portion of the base  12 . 
     Upon formation of the slit  20 , and possibly simultaneously with the formation of the slit  20 , respective segments or portions of the legs  22 ,  24  may be deformed in substantially opposite directions. In their undeformed state, the legs  22 ,  24  define a plane, and upon deforming the legs, at least portions of the legs extend outside the plane, providing the interference between the legs and a corresponding aperture formed in a panel member when the insertion portion  14  of the terminal  10  is inserted into the panel member aperture. 
     In the embodiment shown in  FIGS. 3 and 3A , the compliant portion  18  includes a taper  36 . More specifically, a first width  46  of the compliant portion  18  (i.e., the combined width of the legs  22 ,  24  as measured along the end of the compliant portion  18  adjacent to the end portion  26 ) is less than a second width  48  of the compliant portion  18  as measured along the end of the compliant portion  18  adjacent to the base  12 . For clarity, the width is measured along a line extending between the side edges of the legs that is substantially perpendicular to the central plane  44  extending from the base  12  to the end  28 . In one embodiment, the total amount of the taper  36  is between about zero and about 0.6 degrees, and in another embodiment, the total amount of the taper  36  is between about 0.1 and about 0.3 degrees. For example, for a compliant portion  18  that is about 0.05 inch (1.27 millimeter) in length, a taper of about 0.6 degrees applied to only one side of the compliant portion equates to an increase in width of about 0.001 inch (0.025 millimeter). Similarly, proportionally reduced tapers can be calculated for compliant portions having other dimensions. 
     In one embodiment, the taper  36  is formed on each of the opposite sides of the compliant portion  18  substantially perpendicular to the upper and lower surfaces  34 ,  35 , each taper being about zero to about 0.6 degrees. The thickness of the legs  22 ,  24  (i.e., the distance between upper and lower surfaces  34 ,  35 ) may remain substantially constant, or a secondary taper may be formed in the legs  22 ,  24 . More specifically, the distance between the upper and lower surfaces  34 ,  35  may be varied between the end  28  and the base  12  to form a second taper that decreases in a direction from the base  12  toward the end  28 , to supplement the effect of the taper  36 . 
     In the embodiment of  FIGS. 3 and 3A , the slit  20  has a center  21 , or centerline, while legs  22 ,  24 , or leg segments, may have vertically aligned centers of curvature  23  or deformation, in instances where the deformation of the legs is considered to be nonlinear. In some embodiments of the present invention, the slit centerline  21  and at least one, and preferably each, center of curvature  23  of the legs  22 ,  24  are noncoincident. Stated another way, the midpoint of one or both of the deformed legs  22 ,  24  is offset from the midpoint or center  21  of the slit  20 , where the slit extends a first distance from an axis intersecting the midpoint of the leg(s) toward the tip end  28 , and a second distance from the axis toward the base  12 , and where the first distance is less than the second distance. By virtue of at least this offset, or the combination of this offset, the taper  36  in compliant portion  18 , the tapers  30 ,  32  in end portion  26 , and/or the secondary taper, the insertion force of the insertion portion  14  into a panel member aperture may be reduced and may be substantially uniform over substantially the entire length of insertion into the panel member aperture, or at least over a certain portion of terminal travel within the aperture. 
     In some embodiments of the present invention, the slit  20  and leg members  22 ,  24  are configured to cooperate to achieve a desired insertion force profile, such as a profile that is substantially uniform along at least about 40%, at least about 50%, or at least about 60% of the distance traversed by an electrical terminal during insertion into a panel member aperture. One such embodiment is shown in  FIG. 7 . In certain embodiments, the compliant portion of an electrical terminal has a size and shape sufficient to achieve an insertion force profile that varies less than about 20%, less than about 15%, or less than about 10%, for example, over at least a certain portion of terminal travel, where the percent variance is the variation in force over that portion of terminal travel as a percentage of the total force required to fully seat the terminal within the panel member aperture. In other embodiments, the insertion force profile varies less than about 5% or less than about 1%. In still other embodiments, the insertion force varies less than about 1 pound per pin, less than about 0.5 pounds per pin, or less than about 0.25 pounds per pin along the measured distance of travel. 
     In some embodiments, the force required to fully insert the electrical terminal into a panel member aperture (insertion force) is less than about 6 pounds per terminal, less than about 5 pounds per terminal, or less than about 4 pounds per terminal, for example. In some embodiments, the insertion force is between about 5 pounds per terminal and about 10 pounds per terminal or between about 3 pounds per terminal and about 6 pounds per terminal. In certain embodiments of the present invention, the terminal is configured to withstand an insertion force of at least about 4 pounds. 
     Surprisingly, various embodiments of the present invention in which the mounting end of the electrical terminal has a surface area of no more than about 1.3 square millimeters or no more than about 2.5 square millimeters, or a width of no more than about 0.24 millimeters or no more than about 0.36 millimeters require a force of at least about 1 pound, at least about 2.5 pounds, or at least about 3 pounds to remove the electrical terminal from a panel member aperture (retention force). The retention force of an electrical terminal having a compliant section is a measure of the retention of the compliant section within an aperture or plated through-hole. Thus, some embodiments have a retention force per unit area of about 0.77 pounds per square millimeter to about 1.1 pounds per square millimeter. In other embodiments, the terminal is configured to substantially maintain its position within a panel member aperture up to a withdrawal force of about 1 to 2 pounds, about 4 pounds, or about 5 pounds, for example. Such retention forces insure that there is adequate contact between the mounting end of the terminal and the panel member aperture so that acceptable electrical characteristics are obtained. 
     In addition to contributing to reduced insertion forces and substantially more uniform insertion force profiles, the taper  36  in some embodiments of the electrical terminal  10  of the present invention provides improved electrical performance. For example, in some embodiments, an increased amount of surface area of the legs  22 ,  24  in physical contact with a panel member aperture, also referred to as a sleeve or barrel, improves electrical performance. The sleeve may be a plated through-hole. The references herein to a diameter of an aperture refer to the inner diameter of such a plated through-hole. The increased surface area may provide improved electrical performance despite a decrease in radial interference between the legs  22 ,  24  and the panel member aperture. Moreover, by virtue of the legs  22 ,  24  of the insertion portion  14  being offset from the center  21  of slit  20 , the legs  22 ,  24  may be disposed a lesser distance from the end  28  of the end portion  26 . This shorter distance between the regions of contact of the legs  22 ,  24  and the panel member aperture and end  28  improves electrical performance by reducing the time frame required to reflect electrical energy pulses that travel from the regions of contact of the legs  22 ,  24  toward the end  28  before propagating back through the legs  22 ,  24  toward the beam portion  16  of electrical terminal  10  to the path of electrical connection. 
     In some embodiments of the present invention, the end portion  26  of the electrical terminal  10  is disposed between the end  28  and the compliant portion  18 , and a first taper  32  is formed adjacent to the end  28  along opposite sides of end portion  26 . In addition, a second taper  30  also may be formed adjacent to the end  28  along the upper and lower surfaces  34 ,  35  of the end portion  26 . That is, the second taper  30  may be oriented about 90 degrees from the first taper  32 . In one embodiment, the tapers  30 ,  32  are of equal magnitude. Such a double tapered, substantially pointed end portion  26  improves alignment with apertures in a panel member and reduces sliding resistance between the end portion  26  and the panel member aperture. 
     In some embodiments of the present invention, the end portion  26 , which also may be referred to as a tactile feedback tip or alignment tip, of an electrical terminal  10  includes a resting ledge  31 , as shown in  FIG. 1A , and a tapered lateral engagement section  33  that is smaller in the radial dimension than an aperture of a pattern of apertures in a substrate  64 , such as a panel member or circuit board. The apertures may have any suitable shape and size and may be arranged in any pattern suitable for obtaining a desired pin density. For example, one or more of the apertures may have a diameter of less than about 0.02 inch (0.51 millimeter), less than about 0.016 inch (0.41 millimeter), or less than about 0.012 inch (0.3 millimeter) so as to achieve a pin density of at least about 120 pins per square inch, at least about 195 pins per square inch, at least about 200 pins per square inch, at least about 225 pins per square inch, or at least about 255 pins per square inch. The apertures may comprise a plating, if desired, and the combined surface area of the first leg member  22  and the second leg member  24  of the compliant portion  18  in contact with the plating may be at least about 0.09 square millimeters. 
     In the embodiment of  FIG. 1A , the resting ledge  31  is configured to cooperate with the substrate to maintain the compliant portion  18  of the electrical terminal  10 , which when uncompressed may be larger in the radial dimension than the aperture, above the substrate under the weight of a connector housing capable of holding a plurality of electrical terminals  10  for registration with the pattern of apertures. The resting ledge  31  of the alignment tip  26  also allows for lateral movement of the connector sufficient to allow the lateral engagement section  33  to cooperate with or engage the substrate and provide tactile feedback to a user to facilitate alignment of the tip with an aperture in a panel member. 
     In some embodiments of the present invention, a tactile feedback tip of an electrical connector includes a plurality of tapered segments, as shown in  FIGS. 1A ,  2 A, and  3 A. In one embodiment, the tactile feedback tip  26  includes a first portion  30  having a first taper, the first portion  30  being positioned adjacent to an upper surface  34  (along the width of the tip), and a second portion  32  having a second taper, the second portion being positioned between the upper surface  34  and the lower surface  35  (along the thickness of the tip). The first taper and the second taper may have the same magnitude or different magnitudes. In some embodiments, the tip  26  contains a tip end  28 , a longitudinal axis that passes through the tip end  28 , a first tapered segment  30  positioned adjacent the tip end  28 , a second tapered segment  32  positioned adjacent the tip end  28  and adjacent the first tapered segment  30 , and a third segment  34 , or upper surface, positioned adjacent the first tapered segment  30 , adjacent the second tapered segment  32 , and adjacent a slit opening  20 . The tip may be configured to permit the use of tactile feedback to align the tip with an aperture in a panel member. In some embodiments, the first tapered segment (along the width of the tip) has a taper angle of about 20 degrees to about 30 degrees, or about 0 degrees to about 20 degrees; and the second tapered segment (along the thickness of the tip) has a taper angle of about 12 degrees to about 18 degrees, or about 20 degrees to about 25 degrees. 
     Certain embodiments of the present invention are electrical connectors that have various pin densities, configurations, arrangements, and assignments, while maintaining acceptable mechanical and electrical performance criteria. For example, the electrical terminals  10 , or pins, of the connector may be arranged in linear arrays (i.e., arrays that are generally linear) and may be assigned to ground, single-ended signals, differential signals, or power, while maintaining acceptable levels of cross-talk, insertion loss, and impedance. In some embodiments, each array includes a plurality of differential signal pairs separated by one or more ground terminals. The differential signal pairs in adjacent arrays may be offset, for example by a row pitch or less (as shown in  FIGS. 6 and 6A ), or by two row pitches, to minimize the cross talk between the differential signal pairs within the connector. Other cross-talk minimizing configurations may also be used, such as the configurations disclosed in U.S. Pat. No. 7,207,807, which is incorporated herein by reference in its entirety. The adjacent linear arrays may have any suitable column spacing distance, such as about 1.5 millimeters, about 1.6 millimeters, about 1.8 millimeters, or less than about 2 millimeters. In some configurations, the distance between the centerlines of two electrical terminals that make up a differential signal pair is less than the distance between any one of those centerlines and the centerline of a ground terminal. 
     In the embodiment shown in  FIGS. 5 and 5A , the electrical connector  70  includes a housing  76 , a first plurality of electrical terminals in a first lead frame  72 , and a second plurality of electrical terminals in a second lead frame  73 , where the second lead frame  73  is positioned adjacent to the first lead frame  72 , and where a first electrical terminal  10  of the first plurality of electrical terminals has a mounting end having a first maximum width, a second electrical terminal  74  positioned adjacent to the first electrical terminal  10  in the first lead frame  72  has a mounting end having a second maximum width, a third electrical terminal of the second plurality of electrical terminals has a mounting end having approximately the first maximum width, and a fourth electrical terminal positioned adjacent to the third electrical terminal in the second lead frame  73  has a mounting end having the second maximum width, wherein the first maximum width is not equal to the second maximum width. In the embodiment of  FIGS. 5 and 5A , the first maximum width is less than the second maximum width, and the mounting ends of the terminals are positioned edge-to-edge. In some embodiments, the first and third terminals may comprise signal contacts (single-ended or differential) and the second and fourth terminals may comprise ground contacts. In certain embodiments, the terminals are stitched into openings within a housing, rather than being positioned within lead frames. The signal contacts may be offset from each other, as shown in  FIGS. 6 and 6A , for example, so that cross-talk within the connector is minimized 
     In other embodiments, the mounting ends  14  of the terminals  10  are positioned broadside-to-broadside within a linear array  88 , as shown in  FIGS. 5B  and  5 C. Such electrical terminals  10  may be positioned within lead frames or may be stitched into openings within a housing  89 . 
     In some embodiments of the present invention, such as the embodiment shown in  FIG. 1 , the beam portion  16 , or mating end, of the electrical terminal  10  is the portion of the terminal that mates with another terminal, and the insertion portion  14 , or mounting end, of the electrical terminal  10  is the portion of the terminal that is configured for mounting in a panel member or similar structure. Each of the mating end  16  and the mounting end  14  of an electrical terminal  10  may have a cross-section that defines an edge and a broadside, where the broadside is longer than the edge. The edge of one electrical terminal of a connector of the present invention may be positioned adjacent to the edge of an adjacent electrical terminal within an array of electrical terminals, as shown in  FIGS. 5 and 5A , or the broadside of one terminal may be positioned adjacent the broadside of an adjacent terminal within an array, as shown in  FIGS. 5B and 5C . Such edge-to-edge positioning and broadside-to-broadside positioning refers only to the geometric arrangement of the terminals and does not necessarily refer to any electrical coupling of the terminals. In some embodiments, the edge of the mating end of one differential signal is positioned adjacent to the edge of the mating end of another differential signal in the same linear array. Similarly, in other embodiments, the edge of the mounting end of one differential signal is positioned adjacent to the edge of the mounting end of another differential signal in the same linear array. In still other embodiments, the mounting ends of the electrical terminals are positioned broadside-to-broadside, or the mounting ends of some terminals are positioned broadside-to-broadside, whereas the mounting ends of other terminals are positioned edge-to-edge. 
     In some embodiments of the present invention, an electrical connector contains electrical terminals having different shapes and sizes, and/or panel member apertures having different shapes or sizes. One embodiment of an electrical terminal of the present invention  10  is shown in  FIG. 4 , as compared with three other electrical terminals  78 ,  80 ,  82 , any of which may be used in conjunction with the electrical terminal  10  in a single connector. As shown in  FIG. 4 , in certain embodiments, the electrical terminal of the present invention  10  is substantially smaller than other electrical terminals that may be used in the same connector. 
     In certain embodiments, the electrical terminals of a first differential signal pair are configured to be inserted into a panel member aperture having a first width, and a first ground terminal is configured to be inserted into a panel member aperture having a second width, where the first width is less than the second width. The apertures may be of any suitable shape and size. For example, the apertures may be of a generally circular shape and may have a first width that is a diameter of less than about 0.016 inch (0.41 millimeter) or less than about 0.014 inch (0.36 millimeter), and a second width that is a diameter of greater than about 0.03 inch (0.76 millimeter) or greater than about 0016 inch (0.41 millimeter); or the first width may be a diameter of less than about 80%, 70%, 60%, 50%, or 40% of the second diameter. In certain embodiments of the present invention, the insertion of an electrical terminal into a panel member aperture results in radial deformation of the aperture, where the deformation of the aperture may facilitate retention of the terminal within the aperture, but does not exceed a predetermined amount. In some embodiments, the electrical terminals of a differential signal pair each have a width (or volume) that is less than the width (or volume) of a ground terminal in the same connector. For example, the volume of each of the electrical terminals of a differential signal pair may be less than about 80%, 70%, 60%, 50%, or 40% of the volume of the ground terminal. 
     One embodiment of a connector of the present invention includes electrical terminals  10  of a differential signal pair, where each terminal has a compliant portion with a first length, and a ground terminal  74  with a compliant portion having a second length that is greater than the first length. The connector may include a plurality of adjacent linear arrays in which each terminal of a differential pair has a compliant portion with the first length, and each ground terminal has a compliant portion with the second length. In some embodiments, the differential signal pairs  84  within a linear array  88  are separated by one or more ground terminals  86  in the linear array  88 , as shown in  FIGS. 6 and 6A . 
     In some embodiments of the present invention, the insertion portion  14  of the electrical terminal  10  may be configured for insertion into a panel member aperture of less than about 0.016 inch (0.41 millimeter), which aperture may be of any suitable shape, such as a generally circular shape. For example, a panel member may have a thickness of about 0.02 inch (0.51 millimeter) and an aperture diameter of about 0.009 inch (0.23 millimeter), and the electrical terminal  10  may have an insertion portion  14  that has a maximum width of less than about 0.016 inch (0.41 millimeter) in a flexed position. In other embodiments of the present invention, the compliant section  18  has a width sized to cooperate with an aperture having a diameter of less than about 0.012 inch (0.3 millimeter). 
     In various embodiments, the present invention has desirable electrical characteristics at the mating end of the terminal, the mounting end of the terminal, or both ends of the terminal. For example, in certain embodiments, a connector containing a plurality of electrical terminals arranged in linear arrays in a housing has a substantially constant impedance profile (with a variance of less than about 10 percent, for example) and a worst case multi-aggressor asynchronous differential cross-talk of less than about six percent at an initial rise time of about 40 picoseconds. In other embodiments, the connector has less than about three percent or less than about two percent cross talk at an initial rise time of about 40 picoseconds. In still other embodiments, the connector has less than about six percent, three percent, or two percent worst case multi-aggressor asynchronous differential cross talk at an initial rise time of about 40 picoseconds. 
     In certain embodiments of the present invention, an electrical connector having a pin density of at least about 195 pins per square inch or at least about 200 pins per square inch is provided. In other embodiments, the connector has a pin density of at least about 225 pins per square inch or at least about 255 pins per square inch. In still other embodiments, the connector has a signal pin density of at least about 70 signal pins per square inch or at least about 80 signal pins per square inch. The electrical terminals of a connector of the present invention may contain the electrical terminals described herein, electrical terminals in the prior art, or a combination of both, to obtain a connector with a desired pin density and acceptable mechanical and electrical properties. 
     In some embodiments, the connector has a pin density of at least about 200 pins per square inch or at least about 225 pins per square inch, and a differential impedance of between about 85 ohms and about 115 ohms. Some embodiments have an insertion loss of less than about 2 dB at 5 GHz. Other embodiments have an insertion loss of less than about 3 dB at 10 GHz. 
     In certain embodiments of the present invention, desirable electrical and mechanical characteristics are achieved by an electrical terminal  10  having a mounting end  14  that is substantially smaller than its mating end  16 . More specifically, in some embodiments, the mounting end defines a length and/or width that is less than about 50% of the length and/or width of the mating end. Alternatively, the mounting end  14  may define a length and/or width that is less than about 60%, 40%, or 30%, for example, of the width of the mating end  16 . In other embodiments, the mounting end  14  defines a cross sectional area that is less than about 60% of the cross sectional area of the mating end  16 . Alternatively, the mounting end  14  may define a cross sectional area that is less than about 70%, 50%, 40%, or 30%, for example, of the cross sectional area of the mating end  16 .  FIG. 4  shows the relative dimensions of one embodiment of the electrical terminal of the present invention. This figure also shows a comparison of one embodiment of the electrical terminal  10  of the present invention with three existing electrical terminals  78 ,  80 ,  82 . These existing electrical terminals  78 ,  80 ,  82  are examples of terminals that may be used in conjunction with, or that may be replaced by, the electrical terminal  10  of the present invention within a connector. 
     In one embodiment of an electrical connector of the present invention, the mounting ends of the electrical terminals of the connector extend from the connector housing a first distance, and the mating ends of the terminals extend from the housing a second distance. In another embodiment, such as the embodiment shown in  FIG. 5A , the mounting end of a first electrical terminal  10  of the connector  70  extends from the housing or lead frame  72  a first distance d 1 , and the mounting end of a second terminal  74  in the same connector  70  extends from the housing or lead frame  72  a second distance d 2 . In either embodiment, the first distance may or may not be equal to the second distance. In certain embodiments, the first distance is less than about 80% of the second distance. In other embodiments, the first distance is less than about 50%, less than about 40%, or less than about 30%, of the second distance. 
     The mounting ends of two adjacent electrical terminals, such as the electrical terminals of an edge-to-edge positioned differential signal pair, may extend from the connector housing a first distance (which may be less than about 2 millimeters or less than about 1.6 millimeters, for example), and the mounting ends of at least one of the ground terminals of the connector may extend from the housing a second distance (which may be about 2 to 3 millimeters, for example), where the first distance is less than the second distance, and the worst case multi-aggressor asynchronous differential cross-talk of the connector is less than about five percent at an initial rise time of approximately 40 picoseconds. In some embodiments, the two adjacent electrical terminals each define a width (which may be about 0.2 to 0.25 millimeter, for example) that is smaller than the width of at least one of the ground terminals in the connector (which may be about 0.3 to 0.35 millimeter, for example). In other embodiments, the two adjacent electrical terminals each define a length that is smaller than the length of at least one of the ground terminals in the connector. In still other embodiments, the two adjacent electrical terminals each define a volume that is less than the volume of at least one of the ground terminals in the connector. For example, the volume of the mounting end of each of the two adjacent electrical terminals may be less than about 50% of the volume of the mounting end of the ground contact. In some embodiments, such as embodiments intended for use in daughtercard applications, the mounting end of the electrical terminal has a length of less than about 50% or less than about 40% of the thickness of a panel member. In other embodiments, such as embodiments intended for use in backplane applications, the mounting end of the electrical terminal has a length of less than about 25% or less than about 20% of the thickness of a panel member. 
     The electrical terminals of the present invention may be arranged in such a way as to route a plurality of electrical traces between two of the electrical terminals. In certain embodiments, at least two or at least three electrical traces may be routed between the terminals of a first linear array and a second linear array positioned adjacent to the first linear array, where each array includes terminals (such as signal contacts, for example) sized and shaped to fit within a panel member aperture having a diameter of about 0.016 inch (0.41 millimeter) or less. In other embodiments, such as the embodiment shown in  FIG. 8 , at least four electrical traces may be routed between electrical terminals, where each of the traces has a width of about 0.004 inches (0.1 millimeter) and where the traces are separated from each other by a distance of at least about 0.005 inches (0.13 millimeter). In certain embodiments, each of four electrical traces comprises a differential signal trace having a width, where each trace is separated from an adjacent trace by a distance of at least about two times the width of the trace. In some embodiments, the distance between centerlines of adjacent linear arrays is less than about 1.4 millimeters, for example. 
     One embodiment of the present invention provides a method for routing a plurality of electrical traces between adjacent electrical terminals of an electrical connector. In some embodiments, the method includes: providing a panel member with a first aperture and a second aperture positioned adjacent to the first aperture, where each aperture has a width or diameter of less than about 0.012 inch (0.3 millimeter), for example; inserting a first electrical terminal into the first aperture and a second electrical terminal into the second aperture; and routing at least three electrical traces between the first electrical terminal and the second electrical terminal, while maintaining an acceptable level of cross-talk (such as near-end cross-talk or far-end cross-talk). The panel member also may include apertures having a width or diameter greater than the width or diameter of the first and second apertures. The electrical traces may have any suitable width, such as a width of at least about 0.004 inch (0.1 millimeter), and may be routed between any of the terminals (such as signal contacts and/or ground contacts) in the connector. For example, in the embodiment illustrated in  FIG. 8 , at least four electrical traces may be routed between a first terminal  90  or array of terminals and a second terminal  92  or array of terminals. In some embodiments, the first terminal is positioned within a first lead frame, and the second terminal is positioned within a second lead frame. 
       FIGS. 9 to 11  show examples of connectors  50 ,  60 ,  62  that are usable with various embodiments of the electrical terminal  10  of the present invention to connect panel members  64 . In the embodiment of  FIG. 9 , the connector  50  includes a connector portion  52  that is configured to receive a plurality of electrical terminals  10 . The connector portion  52  also includes a plurality of alignment pins  58  (four) having corresponding apertures (not shown) to receive the alignment pins. Once the alignment pins  58  are received in the corresponding panel member apertures, alignment also may be achieved between the electrical terminals and their corresponding apertures in the panel member. As shown in  FIG. 9 , a connector portion  54  also is configured to receive a plurality of electrical terminals  10  and a plurality of alignment pins  58 . The connector portions  52 ,  54  may be secured together to form the connector  50  and further include a plurality of interconnecting members  56  installed prior to assembly of the connector portions  52 ,  54  to provide electrical connectivity between the electrical terminals  10  in the connector portions. The connector  50  may be used to connect a plurality of panel members  64  of any type. 
     As shown in  FIG. 11 , some connectors  60 ,  62  are used to connect two or more panel members  64 . In this embodiment, the connectors  60 ,  62  each include at least one side similar to connector  50  so that each of the connectors is connected to a corresponding panel member  64 . As further shown in  FIG. 11 , the panel members  64  are assembled substantially perpendicularly to each other. However, the connectors  60 ,  62  may be configured so that the corresponding panel members  64  may be disposed end to end or at any angle from each other. 
     While the invention has been described with reference to particular embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.