Contacting Device for Protecting Electronic Components Against Electromagnetic Radiation

The present invention relates to a contacting device. The device is intended to achieve good contact between removable casing parts and to meet the requirements made with respect to electromagnetic interference and radio frequency interference.

In electronic units, such as display screen terminals, the casing usually comprises walls manufactured from conductive material, e.g. aluminium. The electronic components from which the terminal data circuits are built up are thus protected not only from dust and dirt, but also from other external effects in the form of electromagnetic or radio frequency interference fields from other apparatus. Is is also of importance to be able effectively to screen the terminal circuits from their environment because of the electromagnetic or radio frequency radiation coming from one terminal that can interfere with other terminals in the surroundings.

For this screening is required that the walls of the casing are in good electrical contact, so that no wave traps are created in the gaps between two walls, which would thus enable the occurrence of interfering radio waves.

It is previously known to achieve good contact between two adjacent walls in such a display screen terminal by screwing or adhering spring elements of metallic material, e.g. according to the U.S. Pat. No. 3,504,095, on one of the engagement surfaces between two meeting walls in the casing. There is thus obtained good screening of the terminal against its environment, but fitting the spring elements can be detailed and time-consuming.

The object of the present invention is to achieve a contacting device between the walls in a casing which screens electronic components or units from interference fields in its environment.

According to the inventive concept, resilient contact surfaces are created on one or both sides of the casing walls by placing a metallic strip or wire along the edges of the wall so that good contact is obtained between them.

The invention will now be described in detail with reference to the accompanying drawing, wherein:

FIG. 1 is a side view of a portion of a casing wall provided with a contacting device in accordance with the invention;

FIG. 2 illustrates the same part in a view from above;

FIGS. 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b schematically illustrate various embodiments of the contacting device in accordance with the invention.

FIG. 1 illustrates a portion of a casing wall 1 of metallic material, e.g. aluminium, included in a casing for electronic components which is to be shielded. Together with three other walls and a bottom plate, the wall 1 may form an open box for the components, the box being covered by a lid or cover. The bottom plate and the four side walls can be connected together so that an effective contact is obtained for shielding. The problem is, however, to obtain good contact between the removable lid and the box as well. For this purpose perforations 3 are punched out along the upper edge 1a of the wall 1, and a strip 2 of metallic material is arranged in the perforations 3 so that the strip serpentines its way through the sheet material of the wall. FIG. 2 illustrates more closely how the strip 2, by the way it is placed, has obtained a wave configuration through the sheet and good contact is obtained at the engagement areas of the strip against the edges of the perforations 3. In the embodiment illustrated in FIGS. 1 and 2 the perforation 3 has been formed as a cut-out at right-angles to the edge surface 1a, with a narrower upper and a wider lower part 3a and 3b, respectively. Other implementations of the perforations 3 are of course conceivable for achieving the illustrated wave configuration of the strip 2. The desired wave configuration can be obtained by varying the distances d.sub.1, d.sub.2 between consecutive perforations 3, 4, 5. Resilient contact surfaces A are thus obtained, which can engage against a further casing wall or lid.

FIGS. 3a, 3b illustrate an embodiment of the contacting device in a side view and from above, respectively. A lid 8 has been placed on the casing wall 1, the resilient contact surfaces A engaging with good contact against the inner surface of the lid 8.

In the same views, FIGS. 4a, 4b illustrate a lid with resilient contact between the inner surface of the casing wall 1 and the outer surface of the lid flange.

In the same views, FIGS. 5a, 5b illustrate a combination of cover-lid according to FIGS. 3a, 3b and 4a, 4b. In this case a further contact strip 21 has been placed in the perforations, and will thus lie above (or underneath) the strip 2 in the wider portion 3b of FIG. 1. It is thus possible to obtain contact surfaces on either side of the casing wall 1 in this way.

FIGS. 6a, 6b finally illustrate how a further loose casing wall 13 can be joined to the wall 1, achieving good contact effect at the same time. In this case the perforations 3 can either be stamped out in the wall 1 or in the wall 13 along the respective edge.

The simplicity of the contacting device in accordance with the invention makes it cheap in manufacture and easy to adjust to different contact requirements. The strip or wire 2 may have a circular, quadratic or other cross section. Different properties can be achieved by altering the following parameters:

Cross-sectional dimensions

The wire material

The distances d.sub.1, d.sub.2 between the perforations (3)

The widths of the perforations 3

Use of more than one wire or strip (2, 21) in the same perforation

Allowing or not allowing strips to intersect at the perforation

The advantages attained with the inventive contacting device are mainly as follows:

It permits movement in the engaging surfaces in all directions

It is easy and quick to fit

The strip is self-cleaning

It is easy to modify the spring bias

It is easy to obtain different amounts of deflection in resilient surfaces

It permits different material and material thicknesses

It is durable and without sharp edges

Does not scratch engagement surfaces

The wire or strip does not require any bending or punching

The wire or strip can be taken directly from the manufacturer's reel during fitting

There will now be obvious to those skilled in the art many modifications and variations of the above structure. These modifications and variations will not depart from the scope of the invention if defined by the following claims.