Abstract:
An intercoupling component for receiving an array of contacts includes a non-conductive substrate having a plurality of holes disposed on its upper surface and arranged in a predetermined footprint corresponding to the array of contacts. Contacts are disposed within the holes and a cavities, which may be open to air or filled with some other dielectric material, are disposed in the substrate between adjacent contacts.

Description:
This application is a continuation of U.S. application Ser. No. 10,178,957, filed Jun. 24, 2002, now U.S. Pat. No. 6,743,049. 

   TECHNICAL FIELD 
   This description relates to interconnection devices, and more particularly to interconnection devices which connect an array of contacts within a digital or analog transmission system. 
   BACKGROUND 
   High speed communication between two printed circuit cards over an interconnection device with a dense array of contacts may result in cross-talk between communication channels within the interconnection device and a resulting degradation of signal integrity. In addition to cross-talk between communication channels, high speed communication across an interconnection device may generate undesirable levels of noise. Reduction of cross-talk and noise while at the same time maintaining a dense array of contacts within an interconnection device is often a design goal. 
   SUMMARY 
   In an aspect, the invention features an intercoupling component for receiving an array of contacts within a digital or analog transmission system having an electrical ground circuit and a chassis ground circuit. A plurality of electrically conductive contacts are disposed within holes formed on a segment formed of insulative material. One or more electrically conductive shields are disposed within the segment and are configured to connect to the chassis ground circuit of the system. 
   Embodiments may include one or more of the following. At least some of the plurality of the electrically conductive contacts disposed within the holes on the segment may be configured to electrically connect with the electrical ground circuit of the system. 
   A frame formed of electrically conductive material may surround the segment and be in electrical contact with both the shield member and the electrical ground circuit of the system. The frame may be molded around the segments. 
   One or more ground planes which are configured to electrically connect with the electrical ground circuit of the system may be disposed within the segment. One or more cavities filled with air may be disposed on the segment. 
   The intercoupling component may further include a retention member configured to releasably retain an array mating of contacts with the plurality of electrically conductive contacts. 
   In another aspect, the invention features an intercoupling component for receiving an array of contacts within a digital or analog transmission system having an electrical ground circuit and a chassis ground circuit. A plurality of electrically conductive contacts are disposed within holes formed on a plurality of segments, each formed of insulative material. One or more electrically conductive shields are disposed within gaps between adjacent segments and are connected to the chassis ground circuit of the system. 
   In another aspect, the invention features an intercoupling component for receiving an array of contacts within a digital or analog transmission system having one or more segments formed of electrically insulative material and having an upper and lower surface, the segment including a plurality of holes disposed on its upper surface and arranged in a predetermined footprint corresponding to the array of a contacts and a plurality of electrically conductive contacts each disposed within each hole on the upper surface of the segment. The plurality of contacts are arranged in a plurality of multi-contact groupings, with at least one multi-contact grouping including a first electrically conductive contact and a reference contact. The reference contact is located at a distance D from the first electrically conductive contact and is configured to electrically connect to the electrical ground circuit of the system. 
   Embodiments may include one or more of the following. The first electrically conductive contact and reference may be configured to form a transmission line electrically equivalent to a co-axial transmission line. The first electrically conductive contact may be configured to transmit single-ended signals. Additionally, each multi-contact grouping may be located a distance of ≧D from adjacent multi-contact groupings. 
   The intercoupling component may also include a second electrically conductive contact member located at a distance D 2  from the first electrically conductive contact. The first and second electrically conductive contacts may form a transmission line electrically equivalent to a twin-axial differential transmission line. The first and second electrically conductive contacts within each multi-contact grouping may be configured to transmit disparate single-ended signals or low-voltage differential signals. Additionally, each multi-contact grouping may be located a distance ≧D 2  from adjacent multi-contact groupings. 
   The first and second electrically conductive contacts may have substantially the same cross-section, initial characteristic impedance, capacitance, and inductance. 
   The intercoupling component may also include one or more shield members formed of electrically conductive material disposed within the segment and configured to connect to the chassis ground circuit of the system. Additionally, the intercoupling component may include a frame disposed around the one or more segments. 
   In another aspect of the invention, a circuit card for use in a digital or analog transmission system having an electrical ground circuit and a chassis ground circuit, the circuit card includes a printed circuit board having a plurality of contact pads arranged in a predetermined footprint; and an interconnection device. The interconnection device includes one or more segments having an upper and lower surface, the upper surface of the segment having a plurality of holes arranged in a predetermined footprint to match the predetermined footprint of the plurality of surface mount pads, a plurality of electrically conductive contact member disposed within each of the holes and electrically connected to their respective surface mount pad, and one or more a shield members formed of electrically conductive material disposed within the segment. Additionally, a frame formed of electrically conductive material surrounds the one or more segments and the frame is electrically connected the shield member and to the chassis ground circuit of the system. 
   Additional embodiments include one or more of the following features. The plurality of contacts may be arranged in a plurality of multi-contact groupings which includes a first electrically conductive contact; and a reference contact located at a distance D from the first electrically conductive contact and connected to the electrical ground circuit of the system. 
   The plurality of multi-contact groupings may also include a second electrically conductive contact located a distance D 2  from the first electrically conductive contact. 
   The first and second electrically conductive contacts have substantially the same cross-section, capacitance and inductance. The first and second electrically conductive contacts may be configured to transmit low voltage differential signals or disparate single ended signals. 
   In another aspect of the invention, an intercoupling component for receiving an array of contacts within a digital or analog transmission system having an electrical ground circuit, the intercoupling component includes a segment formed of a material having a dielectric constant Er 1 . The segment has an upper and lower surface and a plurality of holes are disposed on the upper surface of the segment. A first signal contact disposed within a first hole on the segment and a second signal contact disposed within a second hole on the segment adjacent to the first hole in which the first signal contact is disposed. The segment also includes a cavity formed between the first and second signal contacts. 
   Additional embodiments include one or more of the following features. The cavity may be formed on the upper surface, lower surface or within the segment and may be is open to air. An insert formed of a material having a dielectric constant of Er 2  may be disposed within the cavity. 
   The intercoupling component may include a plurality of first signal contacts disposed within a plurality of holes and a plurality of second signal contacts each disposed within a hole that is adjacent to a hole containing a first signal contact. The segment may include a cavity disposed between each pair of first and second signal contacts. The intercoupling component may also include ground contacts disposed within holes on the segment or a ground plane. 
   In another aspect of the invention, a method for adjusting the differential impedance of a pair of differential transmission lines in a interconnection device for receiving an array of contacts within a digital or analog transmission system having an electrical ground circuit, the intercoupling component. The method includes providing a segment having a dielectric constant Er 1  and having an upper and lower surface and including a plurality of holes disposed on its upper surface. Providing a pair of signal contacts disposed within two adjacent holes on the segment, the pair of signal contacts configured to transmit differential signals. Spacing the pair of signal contacts such that they create a certain differential impedance of the two contacts in the pair of signal contacts. Providing a cavity in the segment between the two signal contacts in the pair of signal contacts to adjust the differential impedance between the pair of signal contacts. 
   Additional embodiments include one or more of the following steps. Inserting a material having a dielectric constant of Er 2  in the cavity in the segment. 
   Providing a plurality of pairs of signal contacts disposed with a plurality of adjacent holes on the segment, the plurality of pairs of signal contacts forming an array of pairs of signal contacts disposed in the segment. Providing a plurality of cavities disposed in the segment between the two signal contacts in each pair of signal contacts to adjust the differential impedance of the two signal contacts in each pair of signal contacts. 
   Providing a plurality of ground contacts disposed within a plurality of holes on the segment and within the array of pairs of signal contacts, the plurality of ground contacts electrically connected to the electrical ground circuit of the system. 
   Providing a ground plane disposed within the segment and within the array of pairs of signal contacts, the ground plane configured to electrically connect with the electrical ground of the system. 
   Embodiments of the invention may have one or more of the following advantages. 
   One or more contacts disposed within the array of contacts and are configured to connect to the electrical ground of the system may help to reduce cross-talk between two or more contacts during signal transmission. Additionally, the use of a electrically conductive shield member connected to the chassis ground of the system and disposed within or between one or more segments may help to reduce undesired electromagnetic fields generated by high-speed electron flow over the contact array during operation. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a is a perspective view, partially exploded, of an plug on a secondary circuit board and a matching socket on a primary circuit board within an digital or analog signal transmission system. 
       FIG. 2A  is a perspective view of a plug. 
       FIG. 2B  is a side view of a plug, partially cut away. 
       FIG. 3A  is a perspective view of a plug shield. 
       FIG. 3B  is a perspective view of a plug segment. 
       FIG. 3C  is a bottom view of a plug. 
       FIG. 4A  is a perspective view of a socket, partially exploded. 
       FIG. 4B  is a side view a socket, partially cut away, partially exploded. 
       FIG. 5A  is a perspective view of socket shield. 
       FIG. 5B  is a perspective view of a socket segment. 
       FIG. 5C  is a bottom view of a socket. 
       FIG. 6  is a schematic of an interconnection device in operation. 
       FIG. 7  is a partial view of three contact groupings within a socket. 
       FIGS. 8-8A  are a top and perspective view, respectively, of three contact groupings within a socket and air cavities disposed on the socket. 
       FIG. 8B  is a cross-sectional view of a socket having a cavity filled with air-filled glass balls between contacts. 
       FIG. 9  is a partial view of three contact groupings and a continuous ground plane disposed within another interconnection device. 
       FIG. 10  is a partial view of three contact groupings and a number of ground planes disposed within another interconnection device. 
       FIG. 11  is a partial view of three contact groupings and a number of ground planes disposed within another interconnection device. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , in a digital or analog signal transmission system  10 , a plug  12  and matching socket  14  releasably connect two printed circuit boards, a primary circuit board  18  and a secondary circuit board  16 . 
   Digital or analog transmission system  10  may be any system which transmits digital or analog signals over one or more transmission lines, such as a computer system (as illustrated in FIG.  1 ), a telephony switch, a multiplexor/demultiplexor (MUX/DMUX), or a LAN/WAN cross-connect/router. 
   Secondary circuit board  16  may include a central processing unit (CPU), application specific integrated circuit (ASIC), memory, or similar active or passive devices and components. In this example, secondary circuit board  16  includes an ASIC device  24 , and primary circuit board  18  is a daughter board connected to a motherboard  20  by a card slot connector  22 . In another embodiment, the primary circuit board may be a self-contained system or board, not connecting to any other system or motherboard, as in the case of a single board computer. 
   The socket  14  includes a frame  30  formed of electrically conductive material that surrounds a number of segments  32 . The segments  32  are formed of electrically insulative material. A shield (not shown in  FIG. 1 ) formed of electrically conductive material is located between each of the segments  32  and is in electrical contact with the frame  30 , thus forming an electrically conductive “cage” around the perimeter of each segment  32 . As will be explained in greater detail below, the frame  30  is electrically connected to the chassis ground circuit (shown in  FIG. 6 ) of the system  10 . 
   The socket  14  has an array of holes arranged in a series of three-hole groupings  35  on each segment  32 . A female socket assembly  34  (not shown in  FIG. 1 ) is located within each of the holes  33   a - 33   c  and is configured to releasably receive a male pin. As will be explained in greater detail below, the three-contact grouping  35  includes a first signal contact (disposed within hole  33   a ), a second signal contact (disposed within hole  33   b ) and a reference contact (disposed within hole  33   c ). The reference contact is electrically connected to the electrical ground circuit (Vcc) (shown in  FIG. 6 ) of the system  10 . 
   Plug  12 , which mates with socket  14 , also includes a frame  40  formed of electrically conductive material that surrounds a number of segments  42 . Like the socket segments  32 , the plug segments  42  are formed of electrically insulative material. A shield (not shown in  FIG. 1 ) formed of electrically conductive material is located between each of the segments  42  and is in electrical contact with the frame  40 , thus forming an electrically conductive “cage” around the perimeter of each segment  42  within the plug  12 . As will be explained more below, the frame  40  is electrically connected to the chassis ground circuit (shown in  FIG. 6 ) of the system  10 . 
   The plug  12  has an array of male pins  44  arranged in a series of three-pin groupings  45  on each segment  42 . Each three-pin grouping  45  includes a first signal pin  44   a , a second signal pin  44   b  and a reference pin  44   c . As will be explained in greater detail below, these three pins mate with their respective sockets to form a twin-axial communication channel and a reference ground return between the plug  12  and socket  14 . 
   Each of the male pins  44  protrude from the upper surface of the segments  42  and are received by the matching array of female sockets (not shown) disposed within each of the holes  34  on the socket  14 . Each male pin and female socket attach to a solder ball (not shown in  FIG. 1 ) that protrudes from the bottom surface of the plug  12  and socket  14 , respectively, and is mounted via a solder reflow process to contact pads on the respective printed circuit boards,  16 ,  18 . Thus, when the plug  12  is inserted into the socket  14 , an electrical connection is formed between the secondary circuit board  16  and primary circuit board  18 . In separate embodiments, the male pins  44  and female sockets  34  may not be terminated by a solder reflow process using solder balls, but may employ other methods for mounting the pins or sockets to a printed circuit card, such as through-hole soldering, surface mount soldering, through-hole compliant pin, or surface pad pressure mounting. 
   The plug frame  40  includes three guide notches  46   a ,  46   b ,  46   c  which mate with the three guide tabs  36   a ,  36   b ,  36   c  on the socket frame  30  in order to ensure proper orientation of the plug  12  and the socket  14  when mated together. 
   Referring to  FIGS. 2A-B , each male pin  44  extends from the lower surface of the plug  12  and protrudes from the upper surface of the segments  42 . A solder ball  50  is attached (e.g., by soldering) to the terminal end of each male pin  44  and protrudes from the bottom surface of the plug. The array of solder balls  50  attached to the terminal end of each male pin  44  may be mounted (e.g., by a solder reflow process) to contact pads located on the secondary circuit board  16 . 
   The plug frame  40  is formed of electrically conductive material and includes solder balls  52  are attached (e.g., by a solder reflow process) to the bottom surface of the plug frame  40 . When the plug  14  is mounted to the secondary circuit board  16 , the solder balls  52  attached to the plug frame  40  are electrically connected to the chassis ground circuit of the system  10 . 
   Referring to  FIGS. 3A-C , a shield (FIG.  3 A), a segment ( FIG. 3B ) and the bottom surface of the plug ( FIG. 3C ) is shown. A shield  60  formed of electrically conductive material is located between each of the segments  42 . Each shield  60  is generally U-shaped and includes two short sides  61 ,  62  on each side of a longer middle portion  63 . When assembled into the plug, the two short sides  61 ,  62  of each shield  60  are in electrical contact with the frame  40 , while the middle portion  63  of each shield  60  is located between each of the segments  42 . Thus, the frame  40  and shields  60  form a electrically conductive “cage” around the perimeter of each segment  42 . This electrically conductive “cage” is connected to the chassis ground circuit (shown in  FIG. 6 ) of the system  10  via solder balls  52  on the bottom of the frame  40 . The chassis ground circuit is a circuit within system  10  which connects to the metal structure on or in which the components of the system are mounted. 
   In this example, each shield  60  has four notches: two on the short sides of the shield  64 ,  65  and two on the middle portion of the shield  66 ,  67 . When the shields  60  are assembled into the plug  12 , the two notches on the short sides of each shield  64 ,  65  mate with the two dog-eared tabs  71 ,  72  on each corresponding segment  42 . Similarly, the two notches located on the middle portion  66 ,  67  of each shield  60  mate with two corresponding tabs (not shown) on each segment  42 . Each shield  60  also has three tabs  68  on it&#39;s middle portion  63  which are pressed in opposite directions by adjacent segments  42  after the plug  12  assembled and helps to secure the shields  60  in place. 
   Each segment  42  includes two dog-eared tabs  71 ,  72  located at each end of the segment  42 . The two dog-eared tabs  71 ,  72  fit into two matching grooves  81 ,  82  formed on the bottom surface of the frame  40 . The two triangular bump-outs  73 ,  74  on each of the segments  42  press against adjacent shields  60  and segments  42  in order to secure the segments  42  and the shields  60  within the frame  40 . It should be noted that there are many ways to secure the segments  42  and shields within the frame  40  such as by glue, adhesive, cement, screws, clips, bolts, lamination or the like. The frame  40  may also be constructed by partially encapsulating the segments  42  with an electrically conductive resin or other material. 
   Referring to  FIGS. 4A-B , the socket  14  has an array of holes (e.g.,  33   a ,  33   b ,  33   c ) disposed on the segments  32 . A female socket contact  34  is disposed within each of the holes and is configured to releasably receive a corresponding male pin  44 . A solder ball contact  90  is attached (e.g., by soldering) to the terminal end of each female socket contact  34  and protrudes from the bottom surface of the socket  12 . The array of solder balls  90  attached to the terminal end of each female socket contact  34  may be mounted (e.g., by soldering) to contact pads located on the primary circuit board  18 . 
   Like the plug frame  40 , the socket frame  30  is formed of electrically conductive material and includes solder balls  92  attached (e.g., by soldering) to the bottom surface of the socket frame  30 . When the socket  14  is mounted to the primary circuit board  18 , the solder ball contacts  92  attached to the socket frame  30  are electrically connected to contact pads which are connected to the chassis ground circuit of the system  10 . Additionally, when the plug  12  is inserted into the socket  14 , the plug frame  40  and socket frame  30  are electrically connected to each other and are in turn, electrically connected to the chassis ground circuit of the system  10 . 
   As shown in  FIGS. 5A-C , the assembly of the socket  14  is similar to the assembly of the plug  12  depicted in  FIGS. 3A-C . Dog-eared tabs  102 ,  103  located on the socket segments  32  fit into corresponding notches  104 ,  105  disposed oh the socket frame  30 . A shield  100  is located between each of the segments and electrically contacts the socket frame  30 , thus forming an electrically conductive “cage” around the perimeter of each socket segment  32 . 
   The male pins  44  on the plug  12  and corresponding female socket contacts  34  disposed within the socket  14  may be any mating pair of interconnection contacts and not restricted to pin-and-socket technology. For example, other embodiments may use fork and blade, beam-on-beam, beam-on-pad, or pad-on-pad interconnection contacts. As will be explained in greater detail below, the choice of contact may effect the differential impedance of the signal channels. 
   Referring to  FIG. 6 , in digital or analog signal transmission system  10 , differential signal communication over a single three-contact grouping between secondary circuit board  16  and primary circuit board  18  is illustrated. The plug  12  mounted to the secondary circuit board  16  is plugged into the socket  14  mounted to the primary circuit board  18 , forming an electrical connection between the primary and secondary circuit boards,  16 ,  18 . Within the three-contact grouping, three male pins (not shown in  FIG. 6 ) of the plug  12  and three corresponding female socket contacts of socket  14  couple to form a first signal channel  108 , a second signal channel  110 , and a reference channel  112 . The first and second signal channels  108 ,  110  are coupled with a resistor  118  to form a symmetric differential pair transmission line. The reference channel  112  is electrically connected to the electrical ground circuit (Vcc)  114  of the system  10 . The electrical ground circuit (Vcc)  114  is a circuit within system  10  that is electrically connected to the power supply (not shown) of system  10  and provides the reference ground for system  10 . Additionally, the plug frame  40  and socket frame  50  are in electrical contact with each another and with the chassis ground circuit  120  of the system  10 . 
   In this example, an ASIC chip  24  mounted to the secondary circuit board  18  includes a driver  100  which sends signals over the first and second signal channels,  108 ,  110 . The primary circuit board  18  includes a receiver  116  which receives the signals generated by the driver  100 . The receiver  116  may be incorporated within a memory device, a central processing unit (CPU), an ASIC, or another active or passive device. The receiver  116  includes a resistor  118  between the first signal channel  108  and the second signal channel  110 . In order to avoid signal reflection due to mismatched impedance, the differential impedance of the first and second signal channels,  108 ,  110  should be such that it approximately matches the value of the resistor  118 . 
   The driver  100  includes a current source  102  and four driver gates  104   a - 104   b ,  106   a - 106   b  and drives the differential pair line (i.e., first and second signal channels  108 ,  110 ). The receiver  116  has a high DC input impedance, so the majority of driver  100  current flows across the resistor  118 , generating a voltage across the receiver  116  inputs. When driver gates  106   a - 106   b  are closed (i.e., able to conduct current) and driver gates  104   a - 104   b  are open (i.e., not able to conduct current), a positive voltage is generated across the receiver  116  inputs which may be associated with a valid “one” logic state. When the driver switches and driver gates  104   a - 104   b  are closed and driver gates  106   a - 106   b  are open, a negative voltage is generated across the receiver inputs which may be associated with a valid “zero” logic state. 
   The use of differential signaling creates two balanced signals propagating in opposite directions over the first and second signal channels,  108 ,  110 . The electromagnetic field generated by current flow of the signal propagating over the first signal channel  108  is partially cancelled by the electromagnetic field generated by the current flow of the signal propagating over the second signal channel  110  once the differential signals become co-incidental or “in-line” with one another. Thus, the differential signaling reduces cross-talk between the first and second signal channels and between adjacent contact groupings. 
   The addition of the reference channel  112  in close proximity to the first and second channels  108 ,  110  functions to help bleed off the parasitic electromagnetic field to circuit ground  114 , which may further reduce cross-talk between signal channels and between contact groupings. 
   The driver  100  may also be configured to operate in an “even” mode where two signals propagate across the first and second channel at the same time in the same direction. In this mode, current travels in the same direction over the first and second signal channels,  108  and  110 , and, therefore the electromagnetic fields generated by the current flow would largely add. However, the reference channel  112  would still operate to bleed off the electromagnetic field and reduce cross-talk between adjacent contacts and contact groupings. 
   The socket  12  and plug  14  also feature electrically conductive “cages” formed by the frame and the shields around the perimeter of the segments,  34 ,  44 . The plug frame  40  and socket frame  30  are in electrical contact with each other and with the chassis ground  120  of the system  10 . When high speed communication takes place over an interconnection device, electromagnetic fields substantially parallel to the board are created due to the electron flow at high frequencies. The frames  30 ,  40  and the shields  32 ,  42 , act as “cages” to contain the electromagnetic fields generated by the electron flow across the device, which may reduce the amount of noise emitted by the interconnection device. Additionally, the “cages” act to absorb electromagnetic fields which might otherwise be introduced into the socket  12  and plug  14 , and which may adversely affect the primary or secondary circuit boards  18 ,  16  and any associated active or passive devices and components mounted thereto. 
   Referring again to  FIG. 6 , when a pair of interconnection devices are mated, the differential impedance for the first and second signal channels should be approximately equal to the value of resistor  118  in order to avoid reflection of the signal. In a Low Voltage Differential Signaling (LVDS) application, the value of the resistor  118  is typically 100 ohms. Thus, in a pair of interconnection devices for use in an LVDS application, the first and second signal channels should be designed such the differential impedance is approximately 100 ohms. The differential impedance of the first and second channel signal is a complex calculation that will depend on a number of variables including the characteristic impedance of the contacts, the dielectric constant of the medium surrounding the contacts, and the spatial orientation of the signal contacts and the reference ground contacts. One simplified analytical approach to determining the differential impedance, might be as follows: 
   (1) First determine the self inductance and self capacitance for each of the signal channels with respect to the reference channel within a unit given a selected conductor cross section and spatial relationship. 
   (2) Determine the differential mutual inductance and capacitance between the two signal channels within a unit given the selected conductor cross section and spatial relationship; and 
   (3) Combine the self impedance (i.e., the self inductance plus self capacitance) and differential mutual impedance (i.e., the differential mutual inductance plus differential mutual capacitance) to approximate the differential impedance of the two signal channels. 
   A similar analytical approach may be used to orient the units with respect to one another. It should be noted, however, that these analytical approaches are idealized and does not account for parasitics produced in real-world transmission lines. Due to the complexity of the calculations for real-world transmission lines, computer modeling and simulations using different parameters is often an efficient way to arrange the contacts for a particular application. 
   Referring to  FIG. 7 , the spacing between the three groups of three-contact arrays  35   a - 35   c  within a segment  32  on socket  14  is shown. In this embodiment, the interconnection device  14  is adapted to be used in an LVDS application. Each contact array  35   a - 35   c  includes a pair of signal contacts,  34   a - 34   b ,  34   d - 34   e ,  34   g - 34   h , and a reference contact  34   c ,  34   f ,  34   i . Each of the signal contacts,  34   a - 34   b ,  34   d - 34   e ,  34   g - 34   h , and the corresponding male pins (not shown) are formed of copper alloy and have an initial characteristic impedance of approximately 50 ohms (single-ended). The segment  32  is formed of polyphenylene sulfide (PPS) having a dielectric constant of approximately 3.2. Two shield members  60   a ,  60   b  are located adjacent to the top and bottom edge of the segment  32 . Table I provides the spatial orientation between contacts within a group as well as between adjacent groups in order to produce a differential impedance in the first and second signal channels of a mated pair of interconnection devices of approximately 100 ohms. 
   
     
       
             
             
             
           
         
             
                 
               TABLE I 
             
             
                 
                 
             
             
                 
               Dimension 
               Value 
             
             
                 
                 
             
           
           
             
                 
               A 
               .070″ 
             
             
                 
               B 
               .063″ 
             
             
                 
               C 
               .037″ 
             
             
                 
               D 
               .050″ 
             
             
                 
               E 
               .048″ 
             
             
                 
               F 
               .083″ 
             
             
                 
               G 
               .150″ 
             
             
                 
               H 
               .004″ 
             
             
                 
                 
             
           
        
       
     
   
   The spatial orientation for the mating plug to socket  14  shown in  FIG. 7  would have similar spacing in order to properly plug into socket  14 . 
   The differential impedance of the differential signal channels may be adjusted by inserting material with a different dielectric constant than the segment between the differential signal contacts. For example, an air cavity (air having a dielectric constant of approximately 1) or a Teflon® insert may be inserted between the differential signal contacts in the segment in order to create a composite dielectric having a dielectric constant that is greater or less than the dielectric constant of the segment itself. This will have the effect of lowering or raising the resulting differential impedance between the differential signal contacts on the interconnection device. 
   The absolute value of a materials dielectric constant (Er) between adjacent conductors is inversely proportional to the resulting differential impedance between those conductors. Thus, the lower the resulting dielectric constant (Er) of a composite dielectric material between signal contacts, the higher the resulting differential impedance between the contacts. Similarly, the higher the resulting dielectric constant (Er) of a composite dielectric material between signal contacts, the lower the resulting differential impedance between the contacts. 
   As shown in  FIGS. 8 and 8A , a socket  14  includes a segment  32  with three contact groupings  35   a ,  35   b ,  35   c . Each contact grouping includes a first signal contact  34   a ,  34   d ,  34   g , a second signal contact  34   b ,  34   e ,  34   h , and a reference contact  34   c ,  34   f ,  34   i . A cavity  130   a - 130   c  is formed on the segment  32  centered between the first and second signal contact of each grouping. The cavities are open to air and extend from the top surface to approximately 0.113″ within the segment  32 . Table II provides the dimensions of the air cavities shown in  FIGS. 8-8A , given the same parameters specified in the description of FIG.  7 . 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE II 
             
             
                 
                 
             
             
                 
               Dimension 
               Value 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               A 
               .021″ 
             
             
                 
               B 
               .021″ 
             
             
                 
               C 
               .011″ 
             
             
                 
               D 
               .0753″ 
             
             
                 
                 
             
           
        
       
     
   
   By adding this air cavity between the signal contacts in the plug  14 , the differential impedance of the differential signal channels on the female side of the interconnection device is increased. The size and shape of the air cavity will depend on the desired value for the differential impedance of the differential signal channels. In an LVDS application, the desired differential impedance for the first and second signal channels formed by a mating pair of male and female contacts should be 100 Ohms, +/−5 Ohms. Thus, the female side alone may have a differential impedance of more or less than 100 Ohms and the male side may have a differential impedance of more or less than 100 Ohms, but the pair when mated have an average differential impedance of 100 Ohms (+/−5 Ohms). Male and female differential impedance values should be equal to eliminate any impedance mismatch (dissimilar impedance values) between the two. Any impedance mismatch usually results in an increased signal reflection of the applied energy back towards the signal source thereby reducing the amount of energy being transmitted through the mated connectors. The introduction of a composite dielectric as described herein can minimize the differential impedance mismatch between male and female connectors, thus minimizing reflection of the applied energy back towards the signal source, thereby increasing the amount of energy being transmitted through the mated connectors. 
   While an air cavity between differential signals is depicted in  FIGS. 8-8A , any material having a differential dielectric constant than the segment may be inserted between the signal contacts on either the male or female side. For example, as shown in  FIG. 8B , a cavity  159  located between signal contacts  34   a  and  34   b  is filled with air-filled glass balls  160 , which has a different dielectric constant than the material of the segment and thus creates a composite dielectric between the signal contacts. In other implementation, a Teflon® insert or other material having a lower dielectric constant than the material of the segment (e.g., PPS resin) may be disposed between the signal contacts in order to create a composite dielectric which reduces the resulting dielectric constant of the segment between signal contacts. Similarly, material with a higher dielectric constant may be added between the signal contacts in order to create a composite dielectric which will raise the dielectric constant of the segment between contacts. 
   As shown in  FIG. 9 , another interconnection device  140  includes a segment  32  with three contact grouping  35   a - 35   c  is shown. Each contact grouping includes a pair of differential signal contacts,  34   a  and  34   b ,  34   d  and  34   e ,  34   g  and  34   h , and a ground reference contact  34   c ,  34   f ,  34   i . A continuous ground plane  150  is disposed within segment  32  and is in contact with each of the reference ground contacts,  34   c ,  34   f ,  34   i . The ground plane  150  separates the differential signal contacts from each other and will have the effect of raising the differential impedance of each pair of differential signal contacts. Additionally, the ground plane  150  will further reduce cross talk between pairs of differential signal contacts by bleeding off remnant electromagnetic fields generated by electron flow across the differential signal contacts. 
   As shown in  FIG. 10 , another interconnection devices  142  include a number of ground planes  152   a - 152   h  disposed within the segment  32 . Each of the ground planes  152   a - 152   h  is configured to electrically connect with the reference ground (Vcc) of the system. Similarly, as shown in  FIG. 11 , another interconnection device  144  includes a number of ground planes  154   a - 154   d  which are configured to electrically connect with the reference ground of the system. Like the continuous ground plane shown in  FIG. 9 , the multiple ground planes illustrated in  FIGS. 10-11  will effect the differential impedance of the differential signal contacts as well as further reduce cross talk between pairs of differential signal contacts. 
   The illustrations shown in  FIGS. 1-11  show a twin-axial arrangement of differential pair contacts within a system using differential signaling. However, the technique for reducing cross-talk using a reference pin connected to ground in close proximity to one or more signal channels is not limited to systems using differential signaling, but could be used in systems using other communication techniques. For example, in a system in which individual disparate electrical signals are transmitted (e.g., single ended or point-to-point signaling), a signal contact and reference contact may be arranged in a pseudo co-axial arrangement where a signal contact and a reference contact form a contact-grouping and do not physically share a common longitudinal axis (as would a traditional co-axial transmission line), but electrically performs like a traditional co-axial transmission line. In a pseudo co-axial arrangement, the signal contact and reference contact are physically arranged such that the signal contact and the reference contact are substantially parallel to each other but do not share a common longitudinal axis. The reference contacts within the field of contacts will help to absorb electromagnetic fields generated by the signal contacts and may reduce cross-talk between single-ended transmission lines. 
   The examples illustrated in  FIGS. 1-11  show contact groupings consisting of three contacts, a first signal contact, second signal contact and reference contact. However, contact groupings in other embodiments may include more or less than three contacts. For example, a contact grouping may include a first signal contact and second signal contact (forming differential transmission line), a third and fourth signal contact (forming second differential transmission line) and a reference contact. Additionally, in a system which uses point-to-point or single-ended signaling, a contact grouping may include one or more signal contacts and a reference contact within the contact grouping. 
   In whatever transmission arrangement is used (e.g., differential or single-ended), the spatial orientation of the contacts within a contact grouping can be selected such that the contacts are electrically equivalent to traditional twin-axial or coaxial wire or cable with respect to cross-sectional construction and electrical signal transmission capabilities. Additionally, the spatial relationship between adjacent contact groupings should be selected to approximate electrical isolation and preserve signal fidelity within a grouping via the reduction of electromagnetic coupling. 
   The arrays of twin-axial contact grouping depicted in  FIGS. 1-5  and  FIGS. 7-11 , are intended to match the multi-layer circuit board routing processes in order to permit the interconnection device,  12 ,  14 , to be mounted to contact pads of printed circuit board without the need for routing with multiple Z-axis escapes as the case with traditional “uniform grid” or “interstitial grid” connector footprints. Thus, the orientation of the contacts on plug  12  and socket  14  permit it to be mounted and interconnected with the internal circuitry of a multi-layer circuit board using less layers within the circuit board than traditional connectors. 
   A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. 
   For example, the interconnection device does not need to be formed of multiple segments with shield members located between adjacent segments as illustrated in  FIGS. 1-5  and  7 - 11 . A single segment may be created around one or more shield members by forming (e.g., by injection molding) non-conductive resin or other material around one or more shield members. The frame may then be formed around the segment and the shield(s) by forming (e.g., by injection molding) a conductive resin or other material around the perimeter of the segment. 
   Additionally, the shield member and frame do not need to be two separate pieces. The shield and frame may consist of a one-piece construction with the segment molded or inserted within the single-piece shield-frame member. 
   In the illustration shown in  FIG. 1 , the plug and socket are releasably retained to each other by the mating array of pins and sockets and the mating of the plug and socket frames. A clip, pin, screw, bolt, or other means may be used to further secure the plug and socket to each other. 
   The interconnection device described herein may be used to connect any array of transmission lines in a digital or analog transmission system, such as an array of transmission lines on a printed circuit board (as illustrated in FIG.  1 ), an active or passive device or a cable bundle. 
   Accordingly, other embodiments are within the scope of the following claims.