FLAT CABLE CONNECTORS

Abstract: An electrical connector for a flat cable (10) having alternate signal and ground conductors comprises a movable part (2) in which an array of sockets (20) having rearwardly extending contact pins (8) is mounted in an insulating housing (19) and surrounded by upper and lower conductive shells (18,20), the signal conductors (14) of the cable being fixed to the pins (8) and the ground conductors (12) being fixed to the shells. A fixed part (3) comprises mating contacts (32) and springy fingers (34) fixed within housing (30) for engagement of contacts (32) in sockets (20) of the movable part (2) and engagement of springy fingers (34) with the conductive shells (18,20)

Description: This invention relates to an electrical connector for flat cables according to the pre-characterizing part of claim 1. In particular the invention is concerned with connectors having minute spacings between conductors and where alternate conductors are used as signal conductors and ground conductors thus allowing use of higher density cables for high speed electronic signals. Ground conductors are attached to the housing of the connector. Miniaturisation in the electronics industry, in addition to increasing the number of elements which can be placed on a circuit chip has generated a need for interconnection techniques that are also miniaturised. In addition to the miniaturisation and increased quantity of elements to be interconnected, higher speed circuits require improved electrical properties of the interconnecting means. To satisfy these needs, precision spaced conductors in flat cables and miniaturised coaxial cables have been developed. A connector in the simplest terms is a device used to provide rapid, efficient, connect-disconnect service for electrical wire and cable termination. Improvements to create higher quality cables for higher speed electronics have focused on coaxial cables in which the spacing between conductors has been reduced from (0.1 inch) 0.25cm to about (0.05 inch) 0.13cm. Existing technology provides coaxial cable having an individual ground associated with each signal conductor that is generally terminated in a manner in which shield integrity is maintained throughout the connector. - In accordance with the pre-characterizing part of claim 1, FR-A 2 066 671 discloses an electrical connector for flat cables, in which two rows of conductors are provided, the upper row including signal conductors, the other row including ground conductors. The socket assembly includs a plurality of leaf spring contact elements, each socket being comprised of two leaf springs, one of which being connected to a signal conductor, the other of which being connected to a ground conductor. The ends of the leaf springs facing away from the flat cable are formed such that they can receive a contact pin therebetween. US-A 4 662 700 discloses an electrical connector for flat cables in which a socket assembly comprises an array of signal contact sockets and a backshell for termination with a ribbon cable. A cable shielding and a housing are positioned over the backshells' rear. There is no ground connection between the ground conductors of the cable and the shell. GB-A 2 098 412 discloses a plug having an electrically conductive shell, an insulating body, pins and strips of resilient electrically conductive material having mounting portions and a contact portion. When the co-operating socket is coupled with the plug, a contacting portion is urged against the shell wall and provides an electrical connection between the shell and a conductive shell of the socket so to obtain the desired RF shielding. It is the problem underlying the present invention to provide an electrical connector for flat cables in which a great number of signal contacts are provided that can be used within a limited region without compromising the electrical property. In an electrical connector for flat cables of the above-mentioned type, this problem is solved in accordance with the characterizing features of claim 1. An important feature of the invention resides in the fact that the signal conductors of the cable are attached to signal contact pins of the socket assembly (which is commercially available), while the ground conductors of the cable are bent away from the cable and affixed to the grounding shell. The invention will now be particularly described by way of example with reference to the accompany drawings in which: Figure 1 shows an exploded view of a flat cable connector according to the invention; Figure 2 shows the front face of a socket assembly forming part of the connector of Figure 1; Figure 3 shows a side view of a signal conductor attached to a signal contact pin of the connector; Figure 4 shows a perspective view of the fixed connector half and the movable connector half of the connector; Figure 5a shows a side view of the fixed connector half with a single springy finger; Figure 5b shows a side view of the fixed connector half with two springy fingers; Figure 6 shows a cross-sectional view of the mating contacts of the connector joined within the sockets of the movable connector half; Figure 7 shows cross talk data traces, and Figure 8 shows a time domain reflectometer trace. This invention relates to wire and cable connector assemblies which have prearranged regular spacing configurations and ground conductor attachment to housing shells thus allowing for the use of high density cables for high speed electronics. The spacing arrangements allow for miniaturisation and the ability to increase the number of elements to be interconnected without compromising electrical properties. The embodiments of the invention to be described below are particularly intended for use on flat ribbon cable 10 as shown in Figure 1 and comprise a plurality of conductors in side by side parallel relationship in which alternate conductors are used as signal conductors 14 and ground conductors 12. The connectors of this embodiment are comprised of two halves, one identified as a movable connector half 1 and the other identified as either the fixed half of the connector or the header 3. The movable connector half 1 is further comprised of a socket assembly 2, grounding shells 16 and 18 and flat ribbon cable 10 affixed to the socket assembly 2 and shell 16 in a prearranged spacing configuration described below. The flat ribbon cable 10 is comprised of a plurality of isolated signal conductors 14 positioned so that there is at least one ground conductor 12 between two adjacent signal conductors 14. In order to prepare the end of the ribbon cable for connection to the movable half 1, the insulation is stripped away, alternate signal conductors 14 are bent in one direction to an offset position for engagement with contact pins of one row and intermediate signal conductors 14 are bent in the opposite direction to an offset position for engagement with the contact pins of a second row parallel spaced from the first row. The ground conductors 12, which lie intermediate signal conductors 14, are folded back along the cable and the ends of the ground conductors are bent outwardly from the cable, preferably all on one side of the cable. In a preferred cable, all of the conductors of the cable 10 are on (0.0125' inch) 0.032cm centre lines. The signal conductors 14, in their assembled position therefore have at least a space of (0.025 inch) 0.064cm between them. The socket assembly 2 is commercially available from E. I. DuPont de Nemours, Inc., AMP, Inc., or ITT Cannon. The socket assembly 2 comprises a plastic housing 19 having a front face 4 and a rear face 6. An array of conductive sockets 20 secured within the housing 19 are accessible from the front face 4 and a corresponding array of signal contact pins 8 each integral with a socket 20 protrude from the rear face 6. Preferably the signal contact pins 8 have (0.050 inch) 0.127cm spacing between each other and between adjacent rows of pins which corresponds to the spacing of the signal conductors discussed above. Figure 2 shows the preferred spacing arrangement as designated by the letter "a". Figure 3 shows the signal conductors 14 as attached to the signal contact pins 8 preferably by means of soldering. They may also be attached by a metal filled adhesive or other materials so that electrical conductivity and mechanical integrity are maintained. Insulation covering the conductors of the flat ribbon cable 10 is minimized and is preferably kept to a thickness of approximately (0.01 inch) 0.025cm. The outwardly bent ground conductors 12 of the ribbon cable 10 are affixed directly to the grounding shell upper half 16 which surrounds the region of attachment between the socket assembly 2 and the flat ribbon cable 10. The use of this grounding configuration allows the socket 20 to be used solely for the signal conductors 14 thus increasing the overall signal capacity of the connector. An additional feature of this configuration is the improved electrical signal transmission. The ground conductors 12 are preferably attached to the grounding shell 16 by soldering. Other means for attaching the ground conductors 12 to the grounding shell 16 include spot welding and the use of a conductive adhesive such as metal-filled epoxy. A lower grounding shell 18 covers the lower half of the movable connector 1, thus enclosing the signal conductors 14 and contact pins 8 and providing increased strain relief to the connector. Both grounding shells 16 and 18 are formed from thin sheet metal and are designed to fit closely around the socket assembly 2 and terminating area of the flat ribbon cable 10 as shown in Figure 1. The grounding shells 16 and 18 may either fit snuggly together or have ends that overlap to prevent separation of the shells and to provide electrical continuity between the two shells. Other means for attaching the shells together include the use of an adhesive. The enclosure formed by the shells may optionally be filled with a material such as plastic to provide environmental protection. Figure 4 is a perspective view of the movable connector part 1, fully assembled, and the fixed connector part 3. The lower ground shell 18 meets with the upper shell 16 to fully surround the socket assembly 2 and the region of the ribbon cable comprising the signal conductor-contact joint. Figure 3 also shows the sockets 20 of the socket assembly 2 which are used to mate with mating contacts 32 of the header 3. Figure 1 also shows the exploded view of the fixed half of the connector also identified as the header 3. Header 3 comprises an insulated housing 30 within which are located an array of two parallel rows of mating contacts 32. The mating contacts 32 are spaced to fit within the sockets 20 of the movable connector part 1 when the connector is fully assembled. Figures 1 and 6 show a row of springy fingers 34 contained within the insulated housing 30 and located above the array of mating contacts 32. The single row of springy fingers 34 and array of mating contacts 32 are preferably arranged so that there is a 50 mil space between each row. The springy fingers serve the purpose of electrically and mechanically contacting the ground shells 16 and 18. Figure 5a shows a cross-sectional view of a single springy finger 34 (part of a row of springy fingers) shown above the mating contacts 32 within the housing 30. The insulated housing 30 shown in Figure 1 and 3 is preferably constructed from a thermoplastic and has an overall width of approximately (0.2 inch) 0.5cm. Combined with the preferable spacing of (0.050 inch) 0.127cm for each of the two signal contact rows, a capability of 40 signal positions per (inch) 2.54 cm is achieved. A cable assembly is thereby provided having 200 signal contacts for each (square inch) 6.45 square cms of area used on the substrate to which the fixed half 3 of the connector is mounted. An alternative embodiment to the single row of springy fingers 34 provides a second row of springy fingers 36 also within the insulated housing 30 and located below the array of mating contacts as seen in Figure 5b. Alternate designs where spacing may not be critical can also be used. Figure 6 is a cross-sectional view of the mated joining of the header 3 and the movable connector half 1 in which the mating contacts 32 of the header 3 fit within the sockets 20 of the movable connector half thus making electrical contact with the contact pins 8. The following example is given of a connector and its method of use. This is intended to be illustrative only and not to limit the scope of the present invention in any way. EXAMPLE 1 A connector was made in accordance with the invention using a cable having conductors with (0.008 inch) 0.02cm diameters. There were 40 signal conductors and 41 ground conductors in the cable wherein each signal conductor was positioned between two ground conductors. Conductor spacing was (0.0125 inch) 0.032cm centre to centre. The 40 signal conductors were terminated to 40 signal contacts. The 40 signal contacts were then connected to 40 mating socket contacts thus providing a total of about 200 signal contacts per (square inch) 6.45 square cms as the fixed connector part measured about (0.2 inch) 0.5cm by (1.0 inch) 2.54cms. Nine springy fingers were used to connect with the ground conductors. This connector asssembly was tested by first putting a 150 pico-second rise time signal through the system. The discontinuity at the connector interface was approximately 150 millirho. A second electrical test on the same conductor was performed by sending a signal with a 1.25 nanosecond rise time through the entire assembly. This signal had a 250 millivolt level. One signal line was driven and the adjacent line was sensed for cross talk with near end cross talk measuring approximately 12 millivolts and far end cross talk approximately 10 millivolts. Figure 7 show results of the cross talk at the near end and far end. Figure 8 shows the time domain reflectometer traces.

Claims: An electrical connector for flat cable (10) with a plurality of signal and ground conductors (14, 12) which comprises: (a) a movable connector part (1), including a socket assembly (2) with a front and rear face (4, 6) having at least one row of spaced signal contact sockets (20) accessible from the front face (4) and a corresponding array of signal contact pins (8) extending rearwardly from the sockets (20) the plurality of signal conductors (14) and ground conductors (12) having a spacing configuration in which said signal conductors (14) are affixed respectively to said sockets (20) by engagement with the associated signal contact pins (8); (b) characterized by upper and lower conductive shells (16, 18) to at least one of which are affixed said ground conductors (12), which are bent away from the cable (10) said shells (16, 18) extending around said movable connector (1), and (c) a second connector part (3) including an insulated housing (30) containing an array of mating contacts (32) and at least one row of springy fingers (34), said second connector part (3) being engageable with said movable connector part (1) by engagement of said mating contacts (32) in said sockets (20) and engagement of said one shell (16) with said springy fingers (34). An electrical connector according to claim 1 wherein one ground conductor (12) is positioned adjacent each signal conductor (14). An electrical connector according to claim 1 wherein said ground conductors (12) are affixed to said one shell (16) by soldering or by an electrically conductive adhesive. An electrical connector according to any preceding claim wherein said signal conductors (14) are affixed to said signal contacts (8) by soldering, or by an electrically conductive adhesive. An electrical connector according to claim 1 wherein said second connector part (30) has a second row of springy fingers (36) engageable with the other of said shells (18). An electrical connector according to claim 1 wherein space between said shells (16, 18) enclosing said movable connector part (1) is filled with a material to provide environmental protection. An electrical connector according to claim 6 wherein the material filled between said shells is plastic. An electrical connector according to claim 1 wherein the socket assembly (2) comprises two parallel-spaced rows of regularly spaced sockets (20). An electrical connector according to claim 8 wherein the spacing between said sockets (20) is about (0.05 inch) 0.127cm both in the rows and between the rows. An electrical connector according to claim 9 wherein the overall dimensions of the second connector part (3) are about (0.2 inch) 0.5cm by (1.0 inch) 2.54cms.

Inventors: HANSELL, GEORGE A. III
Applicants: W.L. GORE & ASSOCIATES, INC.
Application year: 1988
Main classification: H01R23
IPC codes: H01R12