GB2140227A

GB2140227A - Method and apparatus for shielding electrical connections

Info

Publication number: GB2140227A
Application number: GB08411701A
Authority: GB
Inventors: Ronald W Brewer
Original assignee: Instrument Specialties Co Inc
Current assignee: Laird Technologies Inc
Priority date: 1983-05-10
Filing date: 1984-05-08
Publication date: 1984-11-21
Also published as: GB8411701D0; GB2140227B; DE3417402A1; JPS6035480A

Abstract

A shield for shielding an electrical connection includes a base portion having at least two end walls 27 and a side wall 25 which are configured to receive an electrical connector, and an arrangement for grounding the shield to a circuit board 55 including a pair of flanges extending downwardly from a lower edge of the end walls 27, each flange including a plurality of resilient fingers 37 for contacting a grounding pad 65 on a circuit board 55. A clamp is operatively connected to the base portion and is adapted for releasably electrically connecting shielding 61 on a cable 51 to the arrangement for grounding the shield to the circuit board. The clamp portion includes a first segment 39 which is secured to an upper edge of the side wall 25 of the base portion and a second segment 45, and an arrangement 49 for releasably securing the segments 39, 45 together. <IMAGE>

Description

SPECIFICATION Method and apparatus for shielding electrical connections The present invention relates generally to electromagnetic shields. More particular, the present invention relates to a connector shield for an electrical connection and a method of shielding an electrical connection.

A particular problem in electronic equipment is the effect of electrostatic and/or electromagnetic waves on interconnecting cables particularly at the termination of the cables where connections between pieces of electronic equipment occur. At such terminations, the cables are often connected through a connector to printed circuit boards and the like. Accordingly, in order to eliminate the effects of the radiation on sensitive circuitry, a shielding device interconnecting shielding ordinarily provided on the cable and ground is highly desirable to effectively isolate the radiation.

One known arrangement for connecting the shielding on the cable to ground is to form a pigtail from the cable shielding and then solder the pigtail to a grounding pad provided on a printed circuit board. Such an arrangement is cumbersome to utilize and does not provide a completely satisfactory shielding. In particular, since the ratio of the length of the pigtail to the width of the pigtail is high, the shielding effectiveness of this arrangement is reduced.

Further, the pigtail itself acts as a radiating element for unwanted radiation.

Another proposal includes folding a continuous metal foil on a ribbon cable and crimping a metallic clip over the folded foil. The metallic clip is attached to a card edge-type connector with double-backed foam tape. The metallic clip forms an electrical contact between a metal bump on an edge card connector and the folded section of the metal cable foil. Such an arrangement is uniquely adapted for an edge card connector and is not readily adaptable for use with other types of connectors such IDC connectors (insulation displacement connector).

Accordingly, it is an object of the present invention to provide an improved shielding method and apparatus for an electrical connector, particularly of the IDC type.

A further object of the present invention is to provide a shielding apparatus which is relatively simple in construction and relatively easy to install. In particular, it is an object of the present invention to provide a shielding apparatus which may be installed without the use of special tools and may be readily retrofit to existing assemblies without requiring replacement of any parts of existing cables or printed circuit boards.

Still a further object of the present invention is to provide a shielding apparatus which permits disconnection of the halves of the connector without the use of tools when necessary. An additional object of the present invention is to provide a shielding method and apparatus which ensures proper shielding against electromagnetic waves and does not serve as a substantial radiating element itself.

These objects and others are accomplished by a connector shield and a method of shielding an electrical connection according to the present invention. A connector shield according to the invention, for an electrical connection between a termination of a cable and a circuit board, comprises a base portion including means for receiving an electrical connector and means for grounding the shield to a circuit board, and a clamp portion operatively connected to the base portion and adapted for releasably electrically connecting shielding on the cable to the means for grounding the shield to the printed circuit board.

In a preferred embodiment, the base portion has at least two end walls and a side wall. A first segment of the clamp portion is secured to an upper edge of the side wall while flanges extend from a lower edge of each of the end walls. A second segment of the clamp portion is provided and an arrangement for releasably securing the first and second segments together is arranged on one of the segments. Further in the preferred embodiment, the flanges and each of the clamp segments contain a plurality of resilient fingers for ensuring good electrical contact. Still further in the preferred embodiment, the height of the walls of the shield is small compared to the length of the clamp portion to minimize the shield's inductance.

The invention also comprehends a method of shielding an electrical connection between a termination of a cable and a circuit board, comprising arranging an electrical connector within a base portion of a shield, connecting a cable having shielding thereon to the connector, at least a portion of the shielding of the cable being exposed, clamping a clamp portion of the shield about the cable and the shielding on the cable, and connecting the connector with a circuit board such that portions of the shield contact grounding pads on the circuit board.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein like members bear like reference numerals and in which: Figure 1 is an exploded perspective view of a connector shield according to the present invention as the shield is arranged about a circuit board, an electrical connector and a cable, Figure 2 is bottom perspective view of the shield according to the present invention, Figure 3 is a side view of the shield according to the present invention in a completed installation, and Figure 4 is a front view of the installation of Figure 3.

With reference to Figure 2, the shield according to the present invention includes a base portion 21 and a clamp portion comprised of two parts 23a, 23b (hereinafter coliectively referred to by reference numeral 23). The base portion 21 includes a side wall 25 and a pair of end walls 27 generally perpendicular to the side wall 25. Side wall segments 29 are connected to the end walls 27. The side wall segments 29 are arranged generally perpendicular to the end walls 27 and generally parallel to the side wall 25. The side wall segments 29 extend only a small portion of the length of the side of the base portion 21 opposite the side wall 25. In this way, a semi-closed generally C-shaped opening 31 is defined by the side wall 25, the end walls 27 and the side wall segments 29.The opening 31 is dimensioned and configured to snugly receive a standard electrical connector, preferably an IDC connector (insulation displacement connector).

The end walls 27 each include a flange 33 extending from a lower edge of the base portion 21, i.e., beyond the lower edge of the side wall 25 and the side wall segments 29. The free end of the flanges 33 is serrated to define a plurality of resilient fingers 37. The free ends of the resilient fingers 37 are bent outwardly generally 900 with respect to the plane of the end walls 27. The flanges 33, and more particularly the resilient fingers 37, are adapted to contact respective grounding pads on a printed circuit board as will be described in greater detail subsequently.

In the preferred embodiment, the clamp portion 23 of the shield includes a first segment 39 secured to an upper edge of the side wall 25 of the base portion 21. The first segment 39 extends over the entire length of the side wall 25 generally perpendicular thereto. The first segment 39 includes a downwardly turned flange 41 ata free edge for limiting flexure of the segment 39 along its length. The first segment 39 of the clamp portion 23 also includes a plurality of resilient fingers 43 formed along substantially the entire length of the segment 39. The fingers 43 are preferably formed by cutting through the segment material on three sides of the fingers 43 and bending the fingers slightly away from the surface of the segment 39 about the attached end.The resilient fingers 43 are connected to the segment 39 near the side wall 25 with a free end of the fingers 43 being closely adjacent the downwardly extending flange 41.

In the preferred embodiment, the entire base portion 21 and the first segment 39 of the clamp portion 23 are formed from a single piece of electrically conductive material. One material found to be particularly suitable for formation into the desired configuration is a beryllium copper alloy. Such an alloy can be formed to the desired shape and the necessary cuts can be made for forming the serrations in the flanges 33 and for forming the resilient fingers 43 of the first clamp segment 39 while the material is in a soft condition. Thereafter, the alloy can be heat treated for improving the strength properties of the formed part.

The clamp portion 23 further includes a second segment 45 having substantially the same length and width as the first segment 39. The second segment 45 includes an upwardly formed flange 46 on each longitudinal edge to improve rigidity.

The second segment 45 is also formed with a plurality of resilient fingers 47 similar to the resilient fingers 43 on the first segment 39. Each end of the second segment 45 includes a clamping arrangement 49 for releasably securing the second segment 45 to the first segment 39 of the clamp portion 23. It should be noted that the clamping arrangements 49 can be arranged on the first segment 39 if desired. It should be noted that the first and second clamp segments may be formed from a single strip of material with a continuous material hinge arranged between one end of the first and second segments. In such an arrangement, only a single clamping arrangement 49 is required to secure the first and second segments together.

In the illustrated embodiment, each of the clamping arrangements 49 comprises a resilient hook formed by bending portions of the material utilized for forming the second segment 45. Each clamping arrangement 49 includes a downwardly extending portion 50 and an upwardly turned portion 52 whose edge is adapted to engage an underside of the first segment 39 to securely clamp the segments 39,45 together. In the preferred embodiment, the entire second segment 45 with the clamping arrangements 49 at each end is formed from a single piece of electrically conductive material, such as a beryllium copper alloy.

Other types of clamping arrangements 49 may be employed in lieu of the resilient hooks of the illustrated embodiment. For example, the clamping arrangement 49 may comprise a flange depending from the second segment 45 having a slightly increased width at a free end with a slot arranged centrally therein. Such a flange would be adapted to compressively fit within a slot provided in the first segment 39 and to spring outwardly after passing through the slot such that the enlarged free end engages a lower surface of the first segment 39 to releasably secure the first and second clamp segments together.

The shield is adapted to cooperate with a flat ribbon-type cable 51, a standard electrical connector 53, such as an IDC connector, and a printed circuit board 55 of a known construction (Figure 1). The cable 51 includes a plurality of conductors 57 embedded in insulation 56. The conductors 57 make electrical contact within openings 59 provided between halves 53a and 53b of the electrical connector 53 in a known manner. An electrically conductive shielding foil 61 and suitable insulation 58 surround the conductors 57 and their insulation along the length of the cable. At the end of the cable 51,the conductors 57 extend outwardly and a portion of the cable shielding 61 is exposed.

In order to utilize the shield, the electrical connector 53 is arranged within the opening 31 of the base portion 21 such that the electrical connector 53 is partially surrounded by the wall 25, the end walls 27 and the partial side wall segments 29. Also, the base portion 21 is arranged such that the first segment 39 of the clamp portion 23 is just below the openings 59 in the connector 53. Thereafter, the conductors 57 of the cable 51 are inserted within the openings 59 in the electrical connector 53 up to the exposed shielding 61 of the cable 51 such that the shielding lies upon the first clamp segment 39.

The second segment 45 of the clamp portion 23 is placed on top of the exposed cable shielding 61 directly over the first clamp segment 39. The clamping arrangements 49 are then resiliently flexed outwardly, preferably by hand, and hooked beneath the ends of the first segment 39 against a lower surface thereof. Preferably, the second segment 45 is arranged on the exposed shielding 61 of the cable 51 such that the resilient fingers 47 contact the shielding 61 and have a free end extending away from the electrical connector 53.

Upon clamping of the clamping arrangements 49 and with the aid of the resilient fingers 43, 47, the exposed shielding 61 of the cable 51 is held in secure electrical contact with the first and second segments of the clamp portion 23.

The electrical connector 53 is then inserted in a known manner along a plurality of pins 63 (only a portion of which are shown) arranged on the circuit board 55. As the electrical connector 53 is pressed downwardly along the pins 63, the resilient fingers 37 of the flanges 33 contact grounding pads 65 (shown in exaggerated height in the drawings for clarity) arranged on the printed circuit board 55 at the ends of the rows of connector pins 63.

In the installed condition (Figures 3 and 4), an electrical circuit is completed between the exposed shielding 61 and the grounding pads 65 through the clamp segments 39, 45, the side wall 25, the end walls 27 and the resilient fingers 37. It should be noted that the distance from the first clamp portion 39 to the lower end of the flanges 33 is greater than the distance from the cable connection on the connector 53 to the bottom of the connector 53. Accordingly, since the clamp portion 23 is secured to the cable 51 which is secured within the connector 53, downward movement of the connector 53 along the pins 63 causes the ends of the fingers 37 to resiliently flex upwardly upon initial contact with the grounding pads 65.In this way, good electrical contact between the fingers 37 and the grounding pads 65 and an effective shielding of the electrical connection between the cable 51 and the circuit board 55 is accomplished.

The ratio of the distance of the clamp portion 23 from the circuit board 55 to the overall length of the shield in the direction transverse to the cable 51 is very small. In other words, the height of the side wall 25 compared to the length of the side wall 25, and consequently the length of the clamp portion 23, is very small. In this way, the inductance within the shield is minimized. Further, the shield according to the present invention, when compared to the pigtail arrangement of the prior art, does not act as a substantial radiating element itself. Accordingly, better shielding is provided throughout the electromagnetic spectrum by the shield according to the present invention.

As can be appreciated, the present invention provides a relatively simple yet highly efficient shield for an electrical connection. Further, the shield according to the present invention readily retro-fits existing assemblies without requiring replacement of any parts of the cable or the printed circuit board hardware. Further, the shield does not require any tools to connect or disconnect. A simple flexure of the clamping arrangements 49 secures the first and second segments of the clamp portion 23 together. Still further, the shield is dimensioned such that the inductance produced by the shield is minimized further enhancing the shielding effect.

Claims

1. A connector shield for an electrical connection between a termination of a cable and a circuit board, comprising a base portion including means for receiving an electrical connector and means for grounding the shield to a circuit board, and a clamp portion operatively connected to the base portion and adapted for releasably electrically connecting shielding on the cable to the means for grounding the shield to the printed circuit board.

2. A connector shield as claimed in Claim 1, wherein the clamp portion includes a first segment secured to the base portion and a second segment, the first and second segments being adapted to receive the cable therebetween, and means for releasably securing the first and second segments together.

3. A connector shield as claimed in Claim 1 or Claim 2, wherein the means for grounding the shield comprise at least one resilient flange extending downwardly from a lower surface of an end wall of the base portion.

4. A connector shield as claimed in Claim 3, wherein the base portion has two end walls and a side wall and a flange is provided on each end wall of the base portion, each flange including a plurality of resilient fingers.

5. A connector shield as claimed in any one of Claims 1 to 4, wherein the base portion comprises a material strip formed to engage at least three sides of the electrical connector.

6. A connector shield as claimed in Claim 2, further comprising a plurality of resilient fingers arranged on the first and second segments for ensuring electrical contact between the segments and the shielding of the cable.

7. A connector shield as claimed in Claim 2, wherein the means for releasably securing the first and second segments together comprise a resilient hook arranged at each end of one of the first and second segments.

8. A connector shield as claimed in any one of Claims 1 to 7. wherein the entire shield is formed from an electrically conductive material.

9. A connector shield as claimed in Claim 8, wherein the entire shield is comprised of an electrically conductive metal.

10. A connector shield as claimed in Claim 9, wherein the metal is a beryllium copper alloy.

11. A connector shield as claimed in any one of Claims 1 to 10, wherein the ratio of the distance of the clamp portion from the circuit board to the width of the shield is small.

12. A connector shield as claimed in Claim 2, wherein the first and second segments are elongated and present an elongated slot between the segments when the segments are secured to one another.

13. A connector shield as claimed in Claim 4, wherein a height of the walls is small compared to a length of the clamp portion.

14. A connector shield as claimed in any one of the preceding claims, wherein the electrical connector is an insulation displacement connector.

1 5. A method of shielding an electrical connection between a termination of a cable and a circuit board, comprising arranging an electrical connector within a base portion of a shield, connecting a cable having shielding thereon to the connector, at least a portion of the shielding of the cable being exposed, clamping a clamp portion of the shield about the cable and the shielding on the cable, and connecting the connector with a circuit board such that portions of the shield contact grounding pads on the circuit board.

16. A method as claimed in Claim 15, further comprising resiliently contacting the cable shielding and the grounding pads with a plurality of fingers.

17. A connector shield for an electrical connection between a termination of a cable and a circuit board, substantially as herein described with reference to the accompanying drawings.

1 8. A method of shielding an electrical connection between a termination of a cable and a circuit board, substantially as herein described with reference to the accompanying drawings.