WO2002026010A1

WO2002026010A1 - Method for manufacturing of housings

Info

Publication number: WO2002026010A1
Application number: PCT/SE2001/002027
Authority: WO
Inventors: Jan Erik Lans
Original assignee: Nolato Silikonteknik Ab
Priority date: 2000-09-25
Filing date: 2001-09-21
Publication date: 2002-03-28
Also published as: AU2001288200A1; SE0003416L; SE0003416D0; SE517854C2

Abstract

The invention relates to a method for manufacturing housings (1) for electromagnetic shielding. These housings (1) have a body (3), which substantially encloses an inner space (5) and which, on a surface (9) facing said space (5), is coated with an electrically conductive layer. The method comprises the steps of forming (100) a plurality of contours (15) for the bodies (3) of the housings (1) in one continuous piece (13), coating (104) the formed contours (15) in the continuous piece (13) with the electrically conductive layer by casting, and finally punching (108) the continuous piece (13) to separate the housings (1) and give them their right outer contours.

Description

METHOD FOR MANUFACTURING OF HOUSINGS

Field of the Invention

The present invention refers to a method for manufacturing housings for electromagnetic shielding. Background Art

As more and more electronic components are being used in various contexts, shielding of electromagnetic radiation is becoming increasingly important. The purpose of the shielding is to protect electronic circuits from interference in the form of electromagnetic radiation. The shielding is based on the principle of the Faraday cage, i.e. the electronic circuit is shielded from the surrounding electric fields by means of an electrically conductive casing which encloses the circuit. Thus, no interference can penetrate the material of the conductive casing. Electromagnetic shielding of electric and electronic components is required, for example, in devices transmitting and/or receiving radio signals.

In most cases, shielding devices comprising polymer materials have a body and an electrically conductive layer applied onto the body. The body is designed to enclose the circuit to be shielded and the electrically conductive layer is applied onto the body's inner surface, which faces the circuit. During manufacture, the electrically conductive layer is applied onto the body by casting, so that the shape and thickness of the layer can be controlled with a high degree of accuracy. During application of the electrically conductive layer, a flash of excess material forms as the material spreads along the edges of the mould in connection with the casting.

This flash has to be trimmed, which implies an additional step in the manufacturing process. In most cases, the trimming is done manually, which is a time-consuming and, thus, costly procedure. In some cases, however, the flash is punched off in an automated step, but this nevertheless constitutes an additional step in the manufacturing process .

The body often comprises one or more holes. These holes have been arranged to allow ventilation to the shielded circuit, or allow fixing screws or tall components to pass. The holes could also be arranged to allow wires to be drawn through the device to the shielded circuit . A skin of the electrically conductive material may form across these holes as the electrically conductive layer is applied. This skin also has to be removed manually.

The body is treated with a primer, usually before the electrically conductive layer is cast onto the body. The primer treatment consists in the body being coated with a primer layer, which improves the adherence between the body and the electrically conductive layer. In the primer treatment, there is a risk of some of the .primer being sprayed onto the outer face of the body. This has to be avoided at all costs, since in many cases great demands have to be met concerning the appearance of the outer face, which is often visible in the final product in which the housing is used, for example a mobile_, telephone . Summary of the Invention

The object of the invention is to improve the handling of flash from a conductive layer during manufacture of housings for electromagnetic shielding. A further object of the invention is to achieve the handling of flash without adding an extra step to the manufacturing process. A particular object of the invention is to avoid manual handling of flash.

According to the invention, the objects are achieved by means of a method for manufacturing housings for elec- tromagnetic shielding as defined in claim 1. Advantageous embodiments of the invention are defined in claims 2-8. The invention thus provides a method for manufacturing housings for electromagnetic shielding, said housings having a body, which substantially encloses an inner space and which, on a surface facing said space, is coated with an electrically conductive layer, comprising the steps of forming a plurality of contours for the bodies of the housings in one continuous piece, coating the formed contours in the continuous piece with the electrically conductive layer by means of casting, and, finally, punching the continuous piece to separate the housings and give them their right outer contours .

During coating of the electrically conductive layer by casting, flash may form on the continuous piece between the formed contours . In connection with the final punching of the continuous piece, the flash is automatically trimmed since it is removed together with the material around the contours. This allows automatic handling and thus no manual work is needed. A further advantage of the invention is that no individual handling of the hous- ings is needed, since several housings are handled at a time. This results in a more efficient and easily handled process .

The step of coating by casting preferably comprises the step of coating the contours with an electrically conductive polymer layer to form at least part of the electrically conductive layer. A polymer has a good workability, which allows easy application of the layer while achieving satisfactory electromagnetic shielding.

The step of coating by casting suitably comprises the step of coating the contours with a silicone material mixed with an electrically conductive material to form at least part of the electrically conductive layer. Silicone has the advantage of being strong and temperature resistant . The method suitably comprises the step of punching holes in the body in connection with the final punching. In many cases, a hole may be needed in the housing, for instance, to allow ventilation. By punching the hole in connection with the final punching, the problem of skin forming across the hole is avoided and no manual removal of such skin is needed. The step of coating the formed contours by casting is preferably carried out in a casting machine, which has a moulding tool comprising several cavities that are located in such manner that each cavity corresponds to a formed contour in the continuous piece. This means that all the bodies in the continuous piece can be coated with the electrically conductive layer in a simple manner. A faster process and a higher manufacturing rate are thereby achieved.

In one embodiment, the method comprises the step of performing an incomplete shaping of the housings before the step of casting coating is carried out .

In certain embodiments, housings of special shape may be needed. In this case, it may be advantageous to shape part of the housing at an earlier stage, for ex- ample if the housing is to be provided with a hook.

The method preferably comprises the step of treating the formed contours in the continuous piece with a primer before the step of casting coating is carried out.

The primer treatment is carried out in order to im- prove the adherence of the electrically conductive layer to the body. The handling of the housings in one continuous piece implies that the risk of overspraying the outer face of the body with primer is avoided. This is due to the fact that the formed contours are treated with primer and, thus, any overspray will end up on the continuous piece around the contours and will not reach the outer face.

The method suitably comprises the step of after- hardening the continuous piece coated with the electri- cally conductive layers by means of casting before the step of punching is carried out . The after-hardening consists in the polymer layer being heat-treated to ensure that it is crosslinked and that a stable state is obtained. In this way, the electrically conductive layer has been securely attached to the body before the final punching is carried out. Brief Description of the Drawings

A currently preferred embodiment of the invention will be described below by way of example and with reference to the accompanying drawings . Fig. 1 is a perspective view of a housing for electromagnetic shielding.

Fig. 2 is a block diagram schematically illustrating an inventive method for manufacturing housings for electromagnetic shielding. Fig. 3 is a plan view of a sheet having a plurality of formed housing contours. Detailed Description of a Currently Preferred Embodiment

Fig. 1 is a perspective view of a housing 1 for electromagnetic radiation shielding. The housing 1 has a body 3, which on the inside defines a space 5. The body 3 also defines an opening, which is adapted to face a base (not shown) , such as a circuit board, so that the housing 1 and the base together enclose the space 5 in all directions. An electrically conductive layer is arranged on the inner face 9 of the body 3.

The body 3 consists of a material with a high draw ratio, such as sheet metal or plastic. This allows the material to be stretched or drawn from a plane piece to the desired shape without rupturing. The electrically conductive layer is mouldable and resilient. The layer consists at least partly of silicone rubber mixed with silver, which provides electric conductibility. The body 3 may be coated with a primer layer to ensure improved adherence of the electrically conductive layer to the body 3. Fig. 2 illustrates a preferred embodiment of the inventive method for manufacturing housings 1 for electromagnetic shielding of the kind shown in Fig. 1.

In a first step 100, a plurality of contours for a housing are formed in one continuous sheet . The contours are made in a regular formation so as to form a matrix of, for example, 2x2 or 2x4 contours. The further working of the sheet is adapted to this formation. The contours can be formed in a number of ways. They can be deep- drawn, punched or folded in the sheet. It is also possible to make the contours in a plastic sheet by injection moulding or vacuum moulding. Fig. 3 shows a sheet 13 with formed contours 15. The contours 15 will serve as housing bodies once the manufacture has been completed. In some cases, the bodies are partly shaped before any further processing is carried out . Such incomplete shaping is done to produce special shapes or elements on the bodies, for example a hook.

The sheet is further worked in step 104. In this step, the contours of the continuous sheet are coated with a layer of electrically conductive silicone rubber. The coating takes place in a casting machine, which has a mould comprising one cavity for each contour in the sheet. These cavities are located in such manner that they correspond to the contour formation of the sheet so that all the contours can be coated simultaneously. During coating, a flash often forms from excess silicone rubber at the edges of the mould. This flash sticks to the sheet on the outside of the formed contours . To improve the adherence of the silicone rubber to the body, the latter may be treated with a primer in step 102. During primer treatment there is no risk of over- spraying the primer onto the outer face of the body since the housings are made from one sheet. Instead, the primer will stick to the sheet outside the contours. The sheet may then be after-hardened in a step 106 so that the binding between the electrically conductive layer and the body is strengthened.

In a final step 108, the contours are punched in the sheet to separate the housings and give them their final shape. Any holes in the bodies of the housings are also punched in this step. During the final punching, any flash is automatically trimmed in connection with the removal of sheet material around the contours. Since the holes are punched in the final step 108, the problem of skin covering the holes is avoided. When the sheet has been divided into several individual housings, the manufacturing process is complete and the housings are ready for use . It will be appreciated that a number of modifications can be made to the embodiment described above, within the scope of the invention as defined in the claims. The electrically conductive layer may, for example, consist of another mouldable, resilient polymer than silicone rubber. The electrically conductive layer may also partly consist of other materials.

Claims

1. A method for manufacturing housings (1) for elec- tromagnetic shielding, said housings (1) having a body

(3) , which substantially encloses an inner space (5) and which, on a surface (9) facing said space (5) , is coated with an electrically conductive layer, comprising the steps of forming (100) a plurality of contours (15) for the bodies (3) of the housings (1) in one continuous piece (13) , coating (104) the formed contours (15) in the continuous piece (13) with the electrically conductive layer by casting, and finally punching (108) the continuous piece (13) to separate the housings (1) and give them their right outer contours .

2. A method according to claim 1, in which the step of coating (104) comprises the step of coating the contours with an electrically conductive polymer layer to form at least part of the electrically conductive layer.

3. A method according to claim 2, in which the step of coating (104) comprises the step of coating the con- tours (15) with a silicone material mixed with an electrically conductive material to form at least part of the electrically conductive layer.

4. A method according to any one of the preceding claims, further comprising the step of punching holes in the body (3) in connection with the final punching.

5. A method according to any one of the preceding claims, in which the step of coating the formed contours

(15) is carried out in a casting machine, which has a mould comprising several cavities that are located in such manner that each cavity corresponds to a formed contour (15) in the continuous piece (13) .

6. A method according to any one of the preceding claims, further comprising the step of performing an incomplete shaping of the housings (1) before the step of coating (104) is carried out.

7. A method according to any one of the preceding claims, further comprising the step of treating the formed contours (15) with a primer before the step of coating (104) is carried out.

8. A method according to any one of the preceding claims, further comprising the step of after-hardening

(106) the continuous piece (13) coated with the electrically conductive layers by casting before the step of final punching (108) is carried out.