Connector

Abstract

The detachable connector disclosed herein facilitates the coupling of high frequency signals from coaxial or other paired signal paths to so-called microstrip signal paths or the like. These microstrip signal paths comprise conductor strips on a circuit board having a ground plane on the opposite side of a dielectric substrate from the signal conductor strips. In the connector the transformation of the signal path from coaxial to microstrip form is provided at a point different from the releasable connection which permits the circuit board to be disconnected from the connector. A section of circuit board material is included within the connector to provide signal paths having matching characteristic impedances on the opposite sides of the line of separation. Conductive areas which match the impedance characteristics of the conductor strips on the circuit board are provided by the method of etching a metallic foil on the circuit board section in the connector.

Parent Case Text

This application is a continuation of copending application Ser. No. 712,196 filed Mar. 11, 1968, which earlier application was assigned to the assignee of the present invention and has now been abandoned.

Description

This invention relates to edge connectors for circuit boards and more particularly to detachable connectors which facilitate the coupling of signals from coaxial signal paths to microstrip signal paths.

The increased use of integrated circuits in computer circuitry has led to the development of circuit boards of increasing complexity in which a plurality of functions are provided in a single board and in which high frequency pulse signals are coupled to and from the circuit components along so-called microstrip or stripline R.F. transmission lines. In circuit boards employing microstrip lines for R.F. signal transmission, for example, the signals are transmitted along conductor strips on one side of a flat dielectric substrate, such as fiberglass reinforced teflon, and a so-called ground plane is provided on the opposite side of the substrate. However, in transmitting signals between different circuit boards and between different equipment assemblies it is preferred that coaxial cables be used to minimize cross coupling and interference. Heretofore, it has been common practice to mount coaxial connectors on the circuit boards themselves for coupling signals from coaxial signal paths to the respective signal conductor strips on the board. However, this practice greatly increases the cost and bulk of the board and requires the use of relatively expensive coaxial connectors. Further, impedance mismatches are produced which cause reflections of high frequency signals.

Among the several objects of the present invention may be noted the provision of a detachable connector for releasably coupling a plurality of coaxially shielded signal paths to respective signal conductor strips on a circuit board; the provision of such a connector which minimizes impedance mismatching; the provision of such a connector which provides good signal isolation; the provision of such a connector which is compact; and the provision of such a connector which may be relatively easily and inexpensively constructed to precise tolerances. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, a detachable connector according to this invention is adapted to couple a plurality of coaxially shielded signal paths to respective signal conductor strips on a circuit board of the type having a ground plane on the side of a dielectric substrate opposite the signal conductor strips. The connector includes a flat dielectric spacer having one edge adapted to abut an edge of the circuit board. A metallic member is provided one portion of which is in contact with one face of the spacer and another portion of which extends beyond the one edge and provides a contact engageable with the ground plane of the circuit board. A plurality of metallic contact fingers are mounted on the face of the spacer which is opposite the member. These fingers extend beyond the one edge of the spacer for engagement with respective ones of the conductor strips on the circuit board. Each of the contact fingers is provided with an elongate area of conductive material in contact with the dielectric spacer, the areas being of widths which provide characteristic impedances with respect to the metallic member which are substantially equal to the characteristic impedances of the respective conductor strips on the board. The outer conductors of a plurality of coaxial cables are commonly connected to the metallic member and the center conductors of the cables are connected to the respective ones of the contact fingers.

The invention accordingly comprises the constructions and methods hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings in which several of various possible embodiments of the invention are illustrated:

FIG. 1 is a side view in section of a connector of this invention;

FIG. 2 is a view in perspective of the connector of FIG. 1 connected to a circuit board;

FIG. 3 is an exploded view of the connector of FIG. 1;

FIG. 4 is a plan view of a connector construction providing additional isolation between circuits;

FIG. 5 is a plan view of a connector of this invention providing still further isolation between circuits;

FIG. 6 is a perspective view of the connector of FIG. 5; and

FIG. 7 is a side view in section of another embodiment of the connector according to this invention in which a coaxial lead is attached to the connector at right angles thereto.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring now to FIGS. 1- 3, the connector illustrated there is adapted for making connections to a circuit board 11 of the type comprising a dielectric substrate 13 completely covered on one side (bottom) by a continuous metal foil 15 which constitutes a ground plane and having disposed on the other side a plurality of signal conductor strips 17. The strips 17 are typically formed by selectively etching away a continuous metal foil similar to that indicated at 15 by known printed circuit board techniques. The connector, which is designated generally at 21, employs a dielectric spacer 23 which preferably comprises a section of circuit board material which is substantially identical to that comprising the circuit board 11. The spacer 23 is mounted on a metallic member 25 having an L-shaped cross-section by soldering the lower foil layer 26 thereof to the metallic member. Preferably, a metallic shim 27 is interposed between the spacer 23 and the member 25. The spacer 23 and shim 27 are mounted on a portion 31 of member 25 which constitutes the longer leg of the L-shaped cross-section and is generally adjacent to a portion 33 constituting the shorter leg of the L-shaped cross-section. A portion 35 of the longer leg 31 projects beyond the front edge 36 of spacer 23 and, as is described in greater detail hereinafter, provides a contact adapted to engage the ground plane foil 15 of the circuit board 11.

The metal foil originally covering the upper face of the section of circuit board material comprising the dielectric spacer 23 is selectively etched away, by known printed circuit techniques, to provide a series of elongate metallic pads or lands 37 which are electrically isolated from one another and which extend transversely to the front edge 36 of the spacer 23. As it is possible to achieve great dimensional accuracy with known printed circuit techniques, the dimensions of the pads or lands 37 may be precisely controlled. In particular, the widths of the lands 37 are held to values which provide characteristic impedances with respect to the metallic member 25 which are substantially equal to the characteristic impedances of the respective conductor strips 17 on circuit board 11.

A plurality of contact fingers 39 are mounted on the lands 37, e.g. by means of soldering or welding. The contact fingers 39 are preferably slightly narrower than the lands 37 so that the impedance characteristics of each combined conductive element are determined principally by the dimensions of the land rather than by those of the contact fingers. In other words, the lands 37 provide predetermined areas of contact with the dielectric material of the spacer 23 for the contact fingers 39. The contact fingers 39 extend beyond the front edge 36 of the spacer 23 and provide resilient contact members adapted to engage and electrically contact respective conductor strips 17 on the circuit board 11.

The shorter leg 33 of the L-shaped section comprising member 25 is apertured at spaced intervals across the connector and ferrules 43 are swaged or staked in these apertures. The insulated center conductors 45 of a plurality of coaxial cables 47 extend through the ferrules 43 and the center conductors are electrically connected, e.g. by soldering or welding as indicated at 48, to respective ones of the contact fingers 39. The outer conductors or coaxial shields 49 of the cables 45 are soldered to the ferrules 43. Crimp connectors may be used as an alternative. Where ribbon cable, twisted from transmission lines or other conductors is to be connected to the member 25 and contact fingers 39, other appropriate means can be substituted for the ferrules 43 and for the solder connections to the fingers 39 as will be understood.

The connector 21 preferably includes a protective surrounding plastic shell or housing as indicated at 51 and the L-shaped member 25 preferably includes a plurality of bendable tabs 53 which may be bent over a ridge 55 molded along one edge of the housing 51 for securing the assembly. As illustrated in FIG. 1, the housing 51 includes an entrance slot 61 for receiving an edge of a circuit board such as 11 and for aligning the board with respect to the contact portion 35 of L-shaped member 25 and the resilient contact fingers 39. When thus inserted into the connector, the leading edge of the board 11 abuts the front edge 36 of the dielectric spacer 23. The metallic shim 27 provides a desirable height of the base of the contact fingers 39 above the thickness of the circuit board 11 which facilitates the operation of the resilient contact fingers 39 and contact portion 35 while retaining the desired impedance matched characteristics between the circuit board terminal strips 17 and the lands 37 upon which the signal carrying fingers 39 are mounted. As the function of providing a detachable connection is provided between two elements having matched impedance characteristics, impedance discontinuities are substantially reduced and reflections of signals being coupled are correspondingly minimized. Further, since the transition from coaxial to strip type circuit path is performed at a different point than the point of separation or detachment, it is not necessary that expensive coaxial couplings be employed and impedance discontinuities at the point of transition are reduced.

In the embodiment of FIGS. 1- 3, the top foil of the section of circuit board material which comprises spacer 23 is etched away to leave only the contact finger mounting lands 37. Based on 0.250 inch contact spring, isolation between signal paths in such a construction is about 32 db at 500 MH.sub. Z. Improved isolation, e.g. about 45 db at 500 MH.sub. Z between the different circuits or signal paths may be obtained if the top foil layer is etched away as illustrated in FIG. 4 to leave not only contact finger mounting lands 37 but also a comb-like pattern 71. Pattern 71 includes a plurality of finger-like extensions 73 which are interposed between adjacent lands 37. This comb-like foil structure 71 is grounded by connection to the ground plane at any convenient point and provides shielding between adjacent channels or signal paths so that better isolation is obtained.

Isolation may be further improved, as illustrated in FIGS. 5 and 6, by providing similar isolating strips 75 on a circuit board 11A between adjacent signal conductor strips 17A. Contact fingers 77 are then soldered to the shielding extensions 73 on the comb-like element 71 to form bridging ground connections between the connector and the shielding strips 75 on the circuit board. This construction yields an isolation value of about 50 db or better at 500 MH.sub. Z and contact spacing of 0.250 inch. Further isolation can be achieved by slitting the member leg 35 to form ground contacts corresponding to the signal contact fingers 39. Greater redundancy can be expected from this contact configuration.

In the embodiment shown in FIG. 7 a coaxial cable 81, which may for example comprise a semi-rigid line of the type having a solid tubular outer shield 83, is attached to the connector substantially at right angles to the signal paths on the circuit board. In this embodiment, the L-shaped metal member, here designated 25A, and the shim 27A are apertured through the longer leg of the L-shaped cross-section as indicated at 85 and the dielectric spacer 23 A is bored half way through, as indicated at 87, to accept the full diameter of the coaxial line. The outer conductor 83 is soldered to the bottom foil or ground plane 26A of the circuit board section constituting spacer 23A. The center conductor 89 of coaxial line 81 extends completely through the dielectric substrate of spacer 23A and is connected, e.g. by soldering, to the respective contact finger 39A. The contact fingers 39A are mounted on lands 37A formed by etching away the top foil of the circuit board section comprising spacer 23A as in the previous embodiments. As is understood by those skilled in the art, this method of interconnecting coaxial and strip type signal paths produces a relatively low level of discontinuity or mismatch at the junction. Thus, by performing the transition from coaxial to strip type signal path in this manner and by separately providing for the easy detachment of the connector from the circuit board between impedance matched elements as described previously, an overall low level of impedance mismatch may be achieved.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. It will also be seen that although use of the connector of this invention has been described with reference to connections to printed circuit boards of microstrip construction, it will be understood that the connector can also be used for connection to the signal paths and to a ground plane of a strip line circuit board construction, single or multilayer, by appropriate alteration of the mating edge of the strip line circuit board. The connector can also be used for joining round conductor or flat conductor ribbon cable ends.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A connector comprising a flat dielectric spacer having a pair of opposite flat faces and having an edge extending along said spacer between said faces, a plurality of metallic, electrically conductive contact finger means mounted in spaced relation to each other in engagement with one of said spacer faces, and metallic electrically conductive ground plane contact means mounted in engagement with the other of said spacer faces at a location adjoining said spacer edge extending along said other face opposite said contact finger means, said contact finger means each having a length of metallic, electrically conductive material of selected width engaged with said one spacer face at a location adjoining said spacer edge and extending transversely of said spacer face away from said edge for providing each of said contact finger means with a characteristic impedance with respect to said ground plane contact means, said contact finger means and ground plane contact means each having a portion extending from said spacer beyond said spacer edge to cooperate with said spacer edge in defining a space to accommodate an edge portion of a circuit board between said contact finger means and said ground plane contact means in abutting relation to said spacer edge, whereby, when a circuit board which has a plurality of signal conductor strips separated from a ground plane by a dielectric substrate to provide said respective strips with said characteristic impedances with respect to said ground plane and which has said strips terminating at a location adjoining an edge of said circuit board is inserted in said space with said contact finger means engaged with respective strips, with said ground plane contact means engaged with said ground plane and with said circuit board edge engaged with said spacer edge, said circuit board impedances are matchable with said connector impedances substantially free of impedance

2. A connector as set forth in claim 1 wherein said ground plane contact means comprises a metallic member of L-shaped cross-section and said spacer lies against a portion of the longer side of said L-shaped cross-section which portion is adjacent the shorter side of said L-shaped

3. A connector comprising a flat dielectric spacer having a pair of opposite flat faces and having an edge extending along said spacer between said faces, a plurality of metallic, electrically conductive contact finger means mounted in spaced relation to each other in engagement with one of said spacer faces, and metallic electrically conductive ground plane contact means mounted in engagement with the other of said spacer faces adjacent said spacer edge extending along said other face opposite said contact finger means, said contact finger means each having a length of metallic, electrically conductive material of selected width engaged with said one spacer face adjacent said spacer edge and extending transversely of said spacer face away from said edge for providing each of said contact finger means with a characteristic impedance with respect to said ground plane contact means, said contact finger means and ground plane contact means each having a portion extending from said spacer beyond said spacer edge to cooperate with said spacer edge in defining a space to accommodate an edge portion of a circuit board between said contact finger means and said ground plane contact means in abutting relation to said spacer edge, said ground plane contact means comprising a metallic member of L-shaped cross-section having said spacer lying against a portion of the longer side of said L-shaped cross-section adjacent the shorter side of said L-shaped cross-section, said ground plane contact means further including a conductive shim interposed between said spacer and said metallic member, whereby, when a circuit board which has a plurality of signal conductor strips separated from a ground plane by a dielectric substrate to provide said respective strips with said characteristic impedances with respect to said ground plane and which has said strips terminating adjacent an edge of said circuit board is inserted in said space with said contact finger means engaged with respective strips, with said ground plane contact means engaged with said ground plane and with said circuit board edge engaged with said spacer edge, said circuit board impedances are matchable with said connector impedances

4. A connector as set forth in claim 3 wherein said spacer has a metallic foil adhered to said other spacer face thereof and conductively attached

5. A connector comprising a flat dielectric spacer having a pair of opposite flat faces and having an edge extending along said spacer between said faces, a plurality of metallic, electrically conductive contact finger means mounted in spaced relation to each other in engagement with one of said spacer faces, and metallic, electrically conductive ground plane contact means mounted in engagement with the other said spacer faces adjacent said spacer edge extending along said other face opposite said contact finger means, said contact finger means each having a section of a metallic foil of selected width adhered to said one spacer face adjacent said spacer edge and extending transversely of said spacer face away from said edge for providing each of said contact finger means with a characteristic impedance with respect to said ground plane contact means, said contact finger means and ground plane contact means each having a portion extending from said spacer beyond said spacer edge to cooperate with said spacer edge in defining a space to accommodate an edge portion of a circuit board between said contact finger means and said ground plane contact means in abutting relation to said spacer edge, whereby, when a circuit board which has a plurality of signal conductor strips separated from a ground plane by a dielectric substrate to provide said respective strips with said characteristic impedances with respect to said ground plane and which has said strips terminating adjacent an edge of said circuit board is inserted in said space with said contact finger means engaged with respective strips, with said ground plane contact means engaged with said ground plane and with said circuit board edge engaged with said spacer edge, said circuit board impedances are matchable with said connector impedances substantially free of impedance discontinuities

6. A connector as set forth in claim 5 including an insulating shell around said spacer, ground plane contact means and contact finger means, said shell having a slot therein for permitting one edge of said circuit board to be inserted between said extending portion of said metallic ground

7. A connector as set forth in claim 6 wherein said shell includes a ridge running substantially along one edge thereof and wherein said ground plane contact means comprises a metallic member having a plurality of bendable tabs which are engaged with said ridge to retain said metallic member

8. A connector comprising a flat dielectric spacer having a pair of opposite flat faces and having an edge extending along said spacer between said faces, a plurality of metallic, electrically conductive contact finger means mounted in spaced relation to each other in engagement with one of said spacer faces, and metallic electrically conductive ground plane contact means mounted in engagement with the other of said spacer faces adjacent said spacer edge extending along said other face opposite said contact finger means, said contact finger means each having a length of metallic, electrically conductive material of selected width engaged with said one spacer face adjacent said spacer edge and extending transversely of said spacer face away from said edge for providing each of said contact finger means with a characteristic impedance with respect to said ground plane contact means, said contact finger means and ground plane contact means each having a portion extending from said spacer beyond said spacer edge to cooperate with said spacer edge in defining a space to accommodate an edge portion of a circuit board between said contact finger means and said ground plane contact means in abutting relation to said spacer edge, whereby, when a circuit board which has a plurality of signal conductor strips separated from a ground plane by a dielectric substrate to provide said respective strips with said characteristic impedances with respect to said ground plane and which has said strips terminating adjacent an edge of said circuit board is inserted in said space with said contact finger means engaging with respective strips, with said ground plane contact means engaged with said ground plane and with said circuit board edge engaged with said spacer edge, said circuit board impedances are matchable with said connector impedances substantially free of impedance discontinuities therebetween, said connector having a comb-like conductive element on said one face of said spacer, said comb-like element having portions interleaved with said contact finger means for electrically isolating said contact finger means

9. A connector as set forth in claim 8 for attachment to a circuit board having isolating strips interleaved between said signal conductor strips wherein said connector includes further contact finger means extending from said comb-like element to engage said respective isolating strips on

10. A detachable connector for coupling a plurality of coaxially shielded signal paths with a circuit board which has a plurality of signal conductor strips and a ground plane separated by a dielectric substrate and in which said signal conductor strips have characteristic impedances on said board, said connector comprising: a metallic member of L-shaped cross-section, said member being apertured at spaced intervals along the portion thereof forming the shorter leg of said L-shaped cross-section; a plurality of coaxial cables having insulated center conductors passing through the apertures in said member and having outer conductors connected to said member around the respective apertures; a flat dielectric spacer lying against a portion of the longer leg of said L-shaped cross-section adjacent the shorter leg thereof with a portion of said longer leg projecting beyond one edge of said spacer to engage said ground plane of said circuit board, said one edge of said spacer being disposed to abut an edge of said circuit board; a plurality of elongate metallic lands adhered to said spacer adjacent said one edge and extending transversely thereto, the width of each land being selected to provide a characteristic impedance with respect to said member for matching the characteristic impedance of a respective signal conductor strip on said board; and a plurality of contact fingers each of which is mounted on and extends beyond a respective one of said lands over said one spacer edge to engage a respective one of said signal conductor strips on said board, the center conductors of said coaxial cables being connected to respective ones of

11. A detachable connector for coupling a plurality of coaxially shielded signal paths to respective signal conductor strips on a circuit board of the type having a ground plane on the side of a dielectric substrate opposite said signal conductor strips, said connector comprising: a metallic member of L-shaped cross-section, said member being apertured at spaced intervals along the portion thereof forming the longer leg of said L-shaped cross-section; a flat dielectric spacer lying against a portion of the longer leg of said L-shaped cross-section adjacent the shorter leg thereof with a portion of said longer leg projecting beyond one edge of said spacer thereby to provide a contact engageable with the ground plane of said circuit board, said one edge of said spacer being adapted to abut an edge of said circuit board; a plurality of elongate metallic lands adhered to said spacer adjacent said one edge and extending transversely thereto, the width of each land providing a characteristic impedance with respect to said member which is substantially equal to the characteristic impedance of the respective conductor strip on said board; a plurality of contact fingers each of which is mounted on and extends beyond a respective one of said lands over said one edge for engagement with a respective one of the conductor strips on said board; and a plurality of coaxial cables having outer conductors which pass through the apertures in the longer leg of said L-shaped cross-section and partially through said spacer and having center conductors which pass

12. A detachable connector system comprising: a circuit board having a plurality of signal conductor strips and a ground plane conductor and having a dielectric substrate between said strips and ground plane conductors, said signal conductor strips terminating adjacent one edge of said board and having characteristic impedances on said board; a flat dielectric spacer having a pair of opposite flat faces and having one edge engaged with said edge of said circuit board; metallic ground plane contact means one portion of which is in contact with one face of said spacer and another portion of which extends beyond said one edge of said spacer and engages said ground plane conductor of said circuit board; a plurality of metallic contact finger means mounted on the face of said spacer opposite said ground plane contact means extending beyond said one edge of said spacer and engaging respective signal conductor strips on said board, each of said contact finger means having an area of conductive material in contact with said dielectric spacer to provide said contact finger means with characteristic impedances with respect to said ground plane contact means which are substantially equal to the characteristic impedances of the respective signal conductor strips on said board; and a plurality of pairs of conductors having one conductor of each of said pairs connected to respective contact finger means on said spacer and having the other conductors of said pairs commonly connected to said

13. A connector system as set forth in claim 12 wherein said spacer embodies a section of said dielectric material of said circuit board

14. A connector system as set forth in claim 13 wherein said ground plane contact means comprises a metallic member of L-shaped cross-section and said spacer lies against a portion of the longer side of said L-shaped cross-section, which portion is adjacent the shorter side of said L-shaped

15. A connector system as set forth in claim 13 wherein said ground plane contact means further includes a conductive shim interposed between said

16. A connector system as set forth in claim 15 wherein said section of dielectric material embodied in said substrate has a metallic foil adhered

17. A connector system as set forth in claim 12 wherein said areas of conductive material of said contact finger means in contact with said dielectric spacer comprise sections of a metallic foil adhered to said

18. A connector system as set forth in claim 12 including an insulating shell around said spacer, ground plane contact means and contact finger means, said shell having a slot receiving one edge of said circuit board therein for engaging said circuit board edge between said extending portion of said metallic ground plane contact means and contact finger

19. A connector system as set forth in claim 18 wherein said shell includes a ridge running substantially along one edge thereof and wherein said ground plane contact means comprises a metallic member having a plurality of bendable tabs engaged with said ridge to retain said metallic member

20. A connector system as set forth in claim 12 including a comb-like conductive element on said opposite face of said spacer, said comb-like conductive element having portions interleaved with said contact finger means for electrically isolating said contact finger means from one

21. A connector system as set forth in claim 20 wherein said circuit board has isolating strips thereon interleaved between said signal conductor strips and wherein said additional contact finger means extend from said portions of said comb-like element on said spacer to engage said

22. A detachable connector system comprising: a circuit board having a plurality of signal conductor strips and a ground plane conductor and having a dielectric substrate between said strip and ground plane conductors, said signal conductor strips terminating adjacent one edge of said board and having characteristic impedances on said board; a flat dielectric spacer having a pair of opposite flat faces and having one edge engaged with said one circuit board edge; metallic ground plane contact means one portion of which is in contact with one face of said spacer and another portion of which extends beyond said one edge of said spacer and engages said ground plane conductor of said circuit board; a plurality of metallic contact finger means mounted on the face of said spacer opposite said ground plane contact means extending beyond said one edge of said spacer and engaging respective signal conductor strips on said board adjacent said one board edge, each of said contact finger means having an area of conductive material in contact with said dielectric spacer to provide said contact finger means with characteristic impedances with respect to said ground plane contact means which are substantially equal to the characteristic impedances of the respective signal conductor strips on said board; and a plurality of coaxial cables having center conductors connected to respective contact finger means on said spacer and having outer conductors commonly connected to said ground plane contact means.