GB2285181A

GB2285181A - Electromagnetic radiation shielding for printed circuit boards

Info

Publication number: GB2285181A
Application number: GB9326371A
Authority: GB
Inventors: Christopher Louis Benini; Stephen John Graham Taylor
Original assignee: HITEC SHEET METAL Ltd
Current assignee: HITEC SHEET METAL Ltd
Priority date: 1993-12-23
Filing date: 1993-12-23
Publication date: 1995-06-28
Also published as: GB9326371D0

Abstract

A radiation shielding device is constructed from conductive sheet material with a substantially rigid open frame (10, Fig. 1) and a cover 18 for attaching over the frame. The frame has downwardly directed spaced apart fingers (12) to engage correspondingly spaced apertures in a printed circuit board. The fingers protruding through the circuit board can be secured by soldering. The upper peripheral edge of the frame wall (14) may be folded inwards to form a flat horizontal shelf which provides additional support for the cover. The downturned peripheral edge of the cover is slotted at intervals to form a plurality of flanges 20 to enable the cover to push-fit onto the frame. The flanges may be formed in a shallow 'V' to enhance the spring action required to clamp the cover to the frame. The frame is provided with at least one horizontal strut (16) to provide additional rigidity. The frame and cover surround and enclose components on an electrical printed circuit board to shield the components from stray electromagnetic radiation. <IMAGE>

Description

Title: Electromagnetic Radiation Shielding for Printed Circuit Boards Field of invention This invention concerns electromagnetic shielding for devices such as printed circuit boards.

Background to the invention It is known that sensitive electronic devices can be shielded from the effects of magnetic, electrostatic and electromagnetic fields by encasing such devices in a suitable housing, usually formed from conductive sheet material having an ability to concentrate high levels of magnetic flux. The metal casing reduces the strength of any magnetic, electric or electromagnetic fields and hence the circuitry is shielded from undesirable stray field effects. The same shields can be employed to reduce unwanted radiation from devices such as transmitters local oscillators and the like.

It is an object of the present invention to provide an improved form of metallic casing for screening electronic circuits and devices mounted on printed circuit boards.

Summary of the invention According to the present invention radiation shielding means constructed from conductive sheet material comprises a substantially rigid open frame adapted for attachment to a circuit board, so as to surround a component mounted thereon which requires shielding and a cover therefor constructed from the same or similar conductive sheet material having a downturned peripheral edge which is adapted to grip the upper peripheral edge of the frame when fitted thereover to secure the cover thereto.

The frame and cover provide a continuous conductive framework around the component.

In a preferred embodiment the metallic frame includes downwardly directed spaced apart fingers for engaging correspondingly spaced apertures in the printed circuit board.

Where the fingers protrude through the board they can be secured as by soldering to an earthing track or the like on the underside of the board.

The upper peripheral edge of the frame wall is preferably folded inwards to form a flat horizontal shelf which provides additional support for the cover and increases the structural rigidity of the frame.

The downturned peripheral edge of the cover is preferably slotted at intervals so as to form a plurality of resiliently deformable flanges to enable the cover to be push fitted onto the frame. The otherwise rigid nature of the cover not only ensures when fitted, the shielding for the enclosed components but also provides a degree of protection against damage.

The resilient flanges are preferably folded to form a shallow 'V' so as to enhance the spring action required to clamp the cover to the frame.

If the flanges are bent so as to be splayed outwardly this eases the attachment of the cover to the frame.

The frame may be provided with at least one horizontal strut so as to provide additional rigidity. This is particularly desirable for larger sizes of frame.

Although only described with relation to the screening of a single component, the invention includes within its scope frames and covers adapted to surround and enclose a plurality of components.

Description of embodiment The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a view of the frame with additional supporting strut.

Figure 2 is a view of the cover.

Figure 3 is a view of the frame on a printed circuit board with a smaller frame and cover enclosed by said frame.

Referring to Figure 1, the metallic frame (10) made out of conducting metal sheets which may include mu-metal but more typically comprises 24 gauge CR4 mild steel, has downwardly projecting equally spaced apart fingers (12) formed along the lower wall edge so as to interconnect with a printed circuit board. The conducting metal sheet is preferably tinplated to allow for soldering to the board and to improve conductivity. The upper walls (14) are folded inwardly along their upper edges so as to provide additional support for the cover (18) and to improve the rigidity of the frame.

A strut (16) is shown which acts to improve the strength of the frame.

In Figure 2 a cover (18) constructed from similar conducting material is shown. The cover does not have to be soldered to form a contact and so can be protected against corrosion by the cheaper process of zinc plating and clear passivating. As with the frame, mu-metal may alternatively be employed. Resilient flanges (20) are formed in a shallow 'V' shape so as to provide a spring action when clamping the cover onto the frame. The resilient engagement of the cover flanges ensure a good low resistance electrical connection between the lid and the frame.

The cover is provided with one or more holes (22) in the flat surface (24) so that removal of the cover is aided by insertion of a releasing device. Similar holes may be provided for the insertion of turning or adjustment devices such as non-metallic screwdrivers and the like.

In Figure 3 a smaller frame (26) and cover (28) is shown over one area of the printed circuit board (32), with the larger frame (30) encompassing a larger area of the board, surrounding it. Flux leakage from a particular component, which is within an area protected by a larger frame and cover, can thus be contained by a smaller version of the invention.

Claims

Claims:

l. A radiation shielding means constructed from conductive sheet material, comprising a substantially rigid open frame, adapted for attachment to a circuit board and a cover therefor also constructed from conductive sheet material and having a downturned peripheral edge which is adapted to grip the upper peripheral edge of the frame when fitted thereover to secure it thereto, such that in use the frame and cover surround a component mounted on a circuit board which requires radiation shielding.

2. A shielding means according to claim 1, wherein the frame includes downwardly directed spaced apart fingers for engaging correspondingly spaced apertures in a circuit board are provided.

3. A shielding means according to claim 1 or 2, wherein the upper peripheral edge of the frame wall is folded inwards to form a flat horizontal shelf which provides additional support for the cover and increases the structural rigidity of the frame.

4. A shielding means according to claim 1, wherein the downturned peripheral edge of the cover is slotted at intervals so as to form a plurality of resiliently deformable flanges to enable the cover to be push-fitted onto the frame.

5. A shielding means according to claim 4, wherein the resilient flanges are folded to form a shallow 'V' so as to enhance the spring action required to clamp the cover to the frame.

6. A shielding means according to any one of claims 1 to 3, wherein the frame is provided with at least one horizontal strut so as to provide additional rigidity.

Amendments to the claims have been filed as follows Claims: 1. A radiation shielding means constructed from conductive sheet material, comprising a substantially rigid open frame, adapted for attachment to a circuit board and a cover therefor also constructed from conductive sheet material and having a downturned peripheral edge which is adapted to grip the upper peripheral edge of the frame when fitted thereover to secure it thereto, such that in use the frame and cover surround a component mounted on a circuit board which requires radiation shielding.
2. A shielding means according to claim 1, wherein the frame includes downwardly directed spaced apart fingers for engaging correspondingly spaced apertures in a circuit board are provided.
3. A shielding means according to claim 1 or 2, wherein the upper peripheral edge of the frame wall is folded inwards to form a flat horizontal shelf which provides additional support for the cover and increases the structural rigidity of the frame.
4. A shielding means according to claim 1, wherein the downturned peripheral edge of the cover is slotted at intervals so as to form a plurality of resiliently deformable flanges to enable the cover to be push-fitted onto the frame.
5. A shielding means according to claim 4, wherein the resilient flanges are folded to form a shallow 'V' so as to enhance the spring action required to clamp the cover to the frame.
6. A shielding means according to any one of claims 1 to 3, wherein the frame is provided with at least one horizontal strut so as to provide additional rigidity.

6. A shielding means according to any one of claims 1 to 3, wherein the frame is provided with at least one horizontal strut so as to provide additional rigidity.

7. A shielding means constructed and arranged substantially as described herein and with reference to the accompanying drawings.

Forchbr Amendments to the claims have been filed as follows 1. A radiation shielding means constructed from conductive sheet material, comprising a substantially rigid open frame, adapted for attachment to a circuit board and a cover therefor also constructed from conductive sheet material and having a downturned peripheral edge which is adapted to grip the upper peripheral edge of the frame when fitted thereover to secure it thereto, such that in use the frame and cover surround a component mounted on a circuit board which requires radiation shielding.

2. A shielding means according to claim 1, wherein the frame includes a substantial plurality of downwardly directed spaced apart fingers for engaging correspondingly spaced apertures in circuit board.

3. A shielding means according to claim 1 or 2, wherein the upper peripheral edge of the frame wall is folded inwards to form a flat horizontal shelf which provides additional support for the cover and increases the structural rigidity of the frame.

4. A shielding means according to claim 1, wherein the downturned peripheral edge of the cover is slotted at intervals so as to form a plurality of resiliently deformable flanges to enable the cover to be push-fitted onto the frame.

5. A shielding means according to claim 4, wherein the resilient flanges are folded to form a shallow 'V' so as to enhance the spring action required to clamp the cover to the frame.