WO2002076168A1

WO2002076168A1 - Device for electronic shielding and method for manufacturing the same

Info

Publication number: WO2002076168A1
Application number: PCT/SE2002/000384
Authority: WO
Inventors: Tore Nilsson
Original assignee: Nolato Silikonteknik Ab
Priority date: 2001-03-12
Filing date: 2002-03-06
Publication date: 2002-09-26
Also published as: SE0100855D0; EP1374656A1; SE517060C2; SE0100855L

Abstract

A device for electromagnetic shielding, comprising a body (4) and, arranged thereon, a shielding surface (9) which is circumferentially defined by an elastic and electrically conductive sealing means (6). The body (4) is made of a material without any essential electric conductivity and supports an element with (5) electrical conductivity. The element (5) has a first surface (7) facing the environment. The sealing means (6) circumferentially defines a portion of said first surface (7), which portion forms said shielding surface (9). The present invention also relates to a method for manufacturing such a device, and a mobile telephone comprising such a device.

Description

DEVICE FOR ELECTRONIC SHIELDING AND METHOD FOR MANUFACTURING THE SAME

Field of the Invention

The present invention relates to a device and a method for electromagnetic shielding, and a mobile telephone comprising such a device. More specifically, the present invention relates to such a device comprising a body and, arranged thereon, a shielding surface, which is circumferentially defined by an elastic and electrically conductive sealing means .

Background Art

Electromagnetic shielding of electronic components is based on the principle of Faraday cage, i.e. the components are screened off from electric fields in the environment, such as radio-frequency interference, by means of an electrically conductive case. Thus the interference cannot penetrate the material of the conductive case .

Electromagnetic shielding of electric and electronic components is required, inter alia, in apparatus for transmitting and/or receiving radio signals. Especially in portable apparatus, such as mobile telephones, it is necessary to provide efficient shielding without the construction being unnecessarily heavy and unwieldy.

Shielding devices are frequently in the form of what is referred to as shield cages which are mounted over the component to be shielded. The component is usually carried by a printed circuit board, in which the shield cage is secured in a suitable manner.

Mounting such shield cages, however, is time-consum- ing and therefore other types of shielding devices have been developed.

Such a device is of the kind described by way of introduction. An electrically conductive shielding sur- face is provided on a body and is enclosed by an elastic and an electrically conductive seal . The body may consists of, for instance, a rear piece of a mobile telephone. These prior-art devices are conventionally manu- factured with a body of magnesium or of metallised plastic. The body thus has an electrically conductive surface. On this surface a seal is dispensed, which encloses a partial surface forming said shielding surface.

In mounting, the printed circuit board is arranged on the seal with the electronic components facing the shielding surface. The shielding surface defines, together with the seal and the printed circuit board, a space forming a Faraday cage, whereby the necessary shielding of the components is provided immediately in conjunction with the mounting of the printed circuit board on the body.

Thus the time-consuming step of mounting shield cages on printed circuit boards is eliminated.

There are, however, a number of problems associated with the type of shielding devices described by way of introduction, having a body and a shielding surface. To manufacture a body of metallised plastic, a moulding is usually injection moulded from a common plastic melt. A metallic layer is then applied to the mould- ing in a suitable fashion, for instance by chemical coating, vacuum vaporisation or applying a metallic paint. Thus metallisation is a surface treatment, which requires expert knowledge. It is therefore a common procedure that external suppliers perform the metallisation of the body, which results in logistic additional costs and increased lead times.

Also the bodies made of magnesium must be finished. The finishing results in anti-scaling which ensures that the strength and appearance of the body are maintained and that the contact with the electrically conductive seal remains satisfactory. Also in this case, logistic additional costs and increased lead times will arise. The thus finished bodies are also rather sensitive and must therefore be handled carefully. In particular, it is important to ensure no cracks arise in the surface layer since the existence of cracks would jeopardise the shielding capacity of the device. In the case of magnesium bodies, cracking causes a risk of oxidation, resulting in reduced strength and a negative effect on the appearance of the body.

The requirement for careful handling means, in turn, that the electrically conductive seal can only be applied by dispensing. This results in a number of limitations to the geometric configuration of the seal .

Finally, bodies of the type described above are relatively expensive. There is thus a need for a device of the type described by way of introduction, which can be manufactured in a logistically more efficient manner and which does not require careful handling.

Summary of the Invention

In view of that stated above, an object of the present invention is to provide an improved device for electromagnetic shielding of the type described by way of introduction and a method for manufacturing such a device.

The device should be easy, quick and inexpensive to manufacture .

Moreover the device should not require careful handling. One more object of the present invention is to provide a mobile telephone which comprises such a device.

To achieve these objects and also other objects that will be evident from the following description, a device having the features stated in claim 1, a method having the features stated in claim 15 and a mobile telephone having the features stated in claim 21 are thus provided. Advantageous embodiments of the device are evident from claims 2-14, preferred embodiments of the method are evident from claims 16-20, and preferred embodiments of the mobile telephone are evident from claims 22-23.

More specifically, according to the present inven- tion a device for electromagnetic shielding is provided, comprising a body and, arranged thereon, a shielding surface which is circumferentially defined by an elastic and electrically conductive sealing means, said device being characterised in that the body is made of a material without any essential electrical conductivity, the body supports an element with electrical conductivity, the element having a first surface facing the environment, and the sealing means circumferentially defines a portion of said first surface, which portion forms said shielding surface.

This results in a device which can be manufactured in a simple, quick and inexpensive manner and which does not require careful handling. This is achieved, more specifically, by means of the element supported by the body and forming the shielding surface. This element can in a suitable manner be integrated in the body immediately in conjunction with its manufacture or immediately afterwards. Thus, no complicated finishing procedure is necessary. Moreover, the element can be given such a rigidity that it does not tend to crack. This results in a device, whose shielding capacity is ensured also if the device would be handled carelessly. Moreover, a higher degree of freedom is achieved in the application of the sealing means. It goes without saying that the sealing means can be applied by dispensing, but the fact that the element can be made relatively insensitive to careless handling implies that the sealing means can also be applied by an injection moulding process. This makes it possible to manufacture devices of this type at a low cost and in large volumes of production. It will also be possible to give the sealing means a desirable geometric appearance. In particular, it will be possible to provide thin sealing means which require only low compression forces. Furthermore the element forms, together with the body, a sandwich construction, which implies that the body achieves advantageously high rigidity. The element is preferably made of stainless steel, electroplated nickel silver or aluminium and preferably has an essentially flat extension.

According to a preferred embodiment of the inventive device, said element is made of a piece of metal sheet. This piece of metal sheet can thus be put in a mould and then integrated in the body during injection moulding thereof.

The element preferably has zones which are moulded into the body, and said shielding surface advantageously covers essentially the whole of said first surface.

According to one more preferred embodiment of the inventive device, the sealing means comprises an elastic and electrically conductive material, which preferably consists of an electrically conductive silicone rubber. According to another preferred embodiment of the inventive device, the sealing means comprises a core formed integrally with the body and, applied thereto, a layer of an elastic and electrically conductive material which makes contact with said shielding surface. This makes it possible to reduce the amount of the relatively expensive elastic and electrically conductive layer included in the sealing means.

According to yet another preferred embodiment of the inventive device, the sealing means is adapted to divide said shielding surface into separate subportions. As a result, the inventive device can act to shield separate groups of electronic components.

According to another preferred embodiment of the inventive device, it comprises a rib means extended over the shielding surface. The rib means forms a stiffening which further contributes to increasing the rigidity of the body. The element may have at least one hole, the rib means being integrally formed with the body and connected therewith through said hole. The hole also implies that the rib means can be formed in connection with the injection moulding of the body. Preferably, a layer of an elastic and an electrically conductive material which makes contact with the shielding surface is applied to said rib means, whereby the rib means and the layer applied thereto form a part of the sealing means which thus divides the shielding surface into separate subpor- tions.

According to another preferred embodiment of inventive device, at least one hole is formed in said element, through which hole extends a projection which is formed integrally with the body and outside of which is applied a layer of an elastic and an electrically conductive material which makes contact with the shielding surface. This allows a so-called screw tower to be provided in a simple manner, which does not affect the shielding capacity of the device and which can be used for mounting of, for instance, a printed circuit board on the device.

Moreover, according to the present invention a method is provided for manufacturing a device for electromagnetic shielding, said device comprising a body and, arranged thereon, a shielding surface which is circumfe- rentially defined by an elastic and electrically conductive sealing means, said method being characterised by the steps of manufacturing the body by injection moulding of a material without any essential electrical conductivity, integrating an element with electrical conductivity in the body in conjunction with the injection moulding thereof, and arranging the sealing means so as to circumferentially define a portion of a first surface, facing the environment, of the element, said portion forming said shielding surface. As a result, a method is provided which allows efficient and quick manufacture of the device. By the element being integrated in the body during manufacture thereof, the need for subsequent finishing steps is eliminated. The eliminated need for finishing further implies that the body does not obtain a sensitive surface, which in turn means that the body does not have to be handled with great care. Thus, methods other than dispensing can be used for application of the sealing means. Finally, the integration of an element in the body means that the body achieves advantageously high rigidity.

According to a preferred embodiment of the inventive method, the step of arranging the sealing means comprises applying, along an edge of the shielding surface, an elastic and electrically conductive material which makes contact with said shielding surface. Preferably, said material is applied by injection moulding. This results in a high degree of freedom in the geometric configuration of the sealing means. In particular, manufacture of thin sealing means is allowed, which results in advantageously low compression forces. Alternatively, the sealing means may be applied by dispensing. According to one more preferred embodiment of the inventive device, the sealing means is adapted to divide said shielding surface into separate subportions. The sealing means advantageously comprises an elastic and electrically conductive material, which is applied by injection moulding or dispensing along an edge of the respective subportions and in contact therewith.

Finally, according to the present invention a mobile telephone is provided, comprising a device as described above . According to a preferred embodiment of the inventive mobile telephone, the body of the device forms an insert introduced into a case of the mobile telephone.

According to yet another preferred embodiment of the inventive mobile telephone, the body of the device forms a front piece or a rear piece of the mobile telephone. A preferred embodiment of the inventive device will now be described by way of example and with reference to the accompanying drawings .

Brief Description of the Drawings

Fig. 1 is a schematic sectional side view of a device according to the present invention.

Fig. 2 is a top plan view of a preferred embodiment of an inventive device for electromagnetic shielding. Fig. 3 is a cross-sectional view along line A-A in Fig. 2.

Fig. 4 is a cross-sectional view along line B-B in Fig. 2.

Fig. 5 is a top plan view of an element of the device illustrated in Fig. 2.

Description of Embodiments

In the following description, components having a similar function have been given the same reference nume- rals.

Fig. 1 illustrates schematically an inventive device for electromagnetic shielding of electronic components 1 which are supported by a carrier 2 in the form of a printed circuit board 3. The device comprises a body 4, which is made of a material without any essential electrical conductivity, and, supported thereby, an element 5 which is made of material with electrical conductivity. The element 5 has a first surface 7 facing the environment and a second surface 8 facing the body 4. An electrically conductive sealing means 6 encloses circumferentially the first surface 7, facing the environment, of the element 5, said first surface 7 thus forming an electrically conductive shielding surface 9. It will be appreciated, however, that the body can also be designed so as to only grasp selected zones 10, such as the edges of the element, whereby also the second surface 8 will be facing the environment. By arranging one more sealing means on the second surface 8, it will be possible to form a second shielding surface.

For shielding of the components 1, the printed cir- cuit board 3 is arranged on the sealing means 6 with the components 1 facing the shielding surface 9. The components 1 will thus be arranged in a space 11, which is defined by the printed circuit board 3 , the shielding surface 9 and the sealing means 6 and which forms a Faraday cage.

Thus, the desired electromagnetic shielding of the components 1 is achieved immediately in conjunction with the mounting of the printed circuit board 3 on the body 4, whereby the current time-consuming and complicated work with the mounting of shield cages on printed circuit boards is eliminated.

Furthermore the shielding surface 9 is made of the first surface 7 of the element 5. Shielding surfaces of conventional devices of the corresponding type have pre- viously required finishing of the body. Finishing is a relatively complicated process which is normally carried out by external suppliers. The eliminated need for such finishing thus means that the shielding device can be manufactured in a quicker, and thus also less expensive, manner.

By using an element 5 which has high torsional rigidity, it will be possible to provide a shielding surface 9 having a rigid and strong structure compared with the conventional shielding surfaces which comprise a surface coating.

The conventional shielding surfaces must be handled with care to prevent cracking. When arranging a sealing means round such a prior-art shielding surface, only the use of a dispensing technology is therefore allowed, in which the sealing means is produced by means of a nozzle, through which a sealing material is dispensed while the nozzle is being moved along the extent of the intended sealing means. This dispensing technology gives an extremely low degree of freedom in the geometric configuration of the sealing means.

The element 5 can thus be given such a torsional rigidity that the tendency of the shielding surface 9 to crack is eliminated or, in any case, significantly reduced. The inventive device can thus be made to have a reliable shielding capacity also when handled carelessly. The relatively rigid and strong structure of the shielding surface 9 of the inventive device allows in particular the use of other procedures than dispensing for the application of the sealing means 6. For example, it would be possible to apply the sealing means 6 by an injection moulding process. It will be appreciated that the degree of freedom in the geometric configuration of the sealing means 6 then increases significantly.

For instance manufacture of thin, tapering sealing means 6, as shown in Fig. 1, is allowed. Such a thin and tapering sealing means 6 results in a good electrically conductive contact between the sealing means 6 and the printed circuit board 3 even at low compression forces. Such low compression forces are advantageous in many applications, for example in mobile telephones. According to today's requirements, mobile telephones must be made thin and light. Too high compression forces in this context may cause deformation of the case of the mobile telephone. It is also common practice to mount the printed circuit board on the body by means of self- tapping screws. The low compression forces counteract unintentional release of these screws.

If the body is designed so that both surfaces 7, 8 of the element are exposed to the environment, it is possible to apply the sealing means to each surface 7, 8 in one step by injection moulding. In the conventional type of shielding devices, it is necessary, as mentioned above, to utilise dispensing for application of said sealing means. It is then only possible to apply a sealing means to one surface at a time.

As is evident, the element 5 supported by the body 4 is partly moulded into the body 4. The element 5 has more precisely zones 10 which are moulded into the body 4 in the manufacture thereof. The body 4 is advantageously manufactured in an injection moulding process.

The element 5 forms, together with the body 4, a sandwich construction which results in advantageously high rigidity of the inventive device.

For manufacturing the inventive device, it is thus possible to manufacture the body 4 and the element 5 integrated therein in a first injection moulding step and, in a second injection moulding step, apply the seal- ing means 6 so as to circumferentially enclose a shielding surface 9 of the element 5. The torsional rigidity of the element 5 causes the tendency of the shielding surface 9 to cracking when handled carelessly to be eliminated or, in any case, reduced. It is thus the torsional rigidity of the element 5 that renders the second injection moulding step possible. The same torsional rigidity also means that the body 4, together with the element 5, forms a sandwich construction which gives the device advantageously high rigidity. The inventive device is extremely advantageous for electromagnetic shielding of electronic components in mobile telephones.

In this context, the device may form an insert which is introduced into a case of a mobile telephone. It is particularly advantageous, however, to let the inventive device form a rear piece or a front piece of a mobile telephone. The body 4 of the inventive device consequently consists of said rear or front piece and the element 5 is moulded into the body 4 in the injection moulding of the same. An embodiment of the inventive device for electromagnetic shielding will now be described in more detail with reference to Figs 2-4.

The device comprises a body 4 and an element 5 sup- ported by the same .

The body 4 is advantageously made by a conventional injection moulding process of a plastic material which has no essential electrical conductivity.

The element 5 is made of a torsionally rigid mate- rial with electrical conductivity, such as stainless steel, electroplated nickel silver or aluminium, and consists, according to the embodiment shown, of a torsionally rigid piece of metal sheet 12 which is integrated into the body 4. The piece of metal sheet 12 can be arranged in a mould of an injection moulding apparatus before the injection moulding of the body 4, after which zones 10 of the piece of metal sheet 12 are moulded into the body 4 in connection with the injection moulding thereof. However, it will be appreciated that it is also possible to connect the piece of metal sheet 12 with the body 4 in other manners .

A sealing means 6 is arranged along an edge of a portion of said first surface 7. In the embodiment shown, this portion covers essentially the whole of the first surface 7. Said portion forms a shielding surface 9 which is consequently defined circumferentially by said sealing means 6.

The structure of the sealing means 6 is clearly to be seen from one of the enlargements of a detail in Fig. 3 and comprises a core 13 formed integrally with the body 4 and, applied thereto, a layer 14 of an elastic and electrically conductive material, such as an electrically conductive silicone rubber. The layer 14 is arranged so as to make contact with the shielding surface 9 formed of said portion.

The piece of metal sheet 12 included in the inventive device is shown in more detail in Fig. 5, to which reference is now also made. Two sets of through holes 15 are formed in the piece of metal sheet 12. Each set of holes 15 allows the forming of a rib means 16 in connection with the injection moulding of the body 4, which rib means 16 thus, through said holes 15, are formed integrally with the body 4 and extend across the shielding surface 9, which as a result is divided into three subportions 17. A layer 18 of an elastic and electrically conductive material is applied to each of these rib means 16 in such a manner that the material makes contact with said subportions 17, which is clearly to be seen from the other enlargement of a detail in Fig. 3. The rib means 16 and the layers of material 18 arranged thereon thus form a part of said sealing means 6. Furthermore six holes 19 are formed in the piece of metal sheet 12. Through each of these holes 19 extends a hollow projection 20 which is integrally formed with the body 4. On this projection there is arranged a layer 21 of an elastic and electrically conductive material which makes contact with the shielding surface 9.

Finally, the body 4 has a number of stiffening means 22 of a conventional kind. It will be appreciated that the piece of metal sheet 12, together with the body 4, forms a sandwich construction with advantageously high rigidity. By selecting a suitable degree of torsional rigidity of the element 5, it will thus be possible to reduce the number of necessary stiffening means 22, which of course reduces the amount of material that is required for the manuf cture of the body 4. The body 4 as illustrated forms a chassis for a mobile telephone, which chassis can be inserted into a case of a mobile telephone (not shown) . As mentioned above, it is, however, also possible to let said body form a rear or front piece of a mobile telephone. For shielding an electronic component (not shown) supported by a carrier, such as a printed circuit board, the carrier is arranged on the sealing means 6, the com- ponent facing the shielding surface 9. The carrier can be fixed in this position by using the above-described projections 20 which form so-called screw towers.

When said carrier is arranged in the manner mention- ed above, three defined spaces of the type designated 11 in Fig. 1 will be formed, each of which forms a Faraday cage. Electronic components that are arranged in separate spaces will thus also be mutually shielded. The design of the projections 20 ensures that the screw towers formed thereof will not have a detrimental effect on the shielding capacity of the device.

Not only do the rib means 16 define subportions 17 of the shielding surface, they also increase the rigidity of the device. As mentioned above, the sealing means 6 comprises a core 13 along that part of the extension of the sealing means 6 which circumferentially encloses the shielding surface 9, and rib means 16 along that part of the extension of the sealing means which acts to divide the shielding surface 9 into subportions 17. Both the core

13 and the rib means 16 can be formed integrally with the body 4 and thus consist of the same material as the body 4. On this core 13 and these rib means 16 a layer

14 of an elastic and electrically conductive material is arranged, which material advantageously consists of electrically conductive silicone rubber. As a result, the consumption of material as regards the relatively seen more expensive elastic and electrically conductive material is reduced in the manufacture of the sealing means 6.

According to the present invention, the elastic and electrically conductive material of the layers 14, 18 of the sealing means 6 is advantageously applied by an injection moulding process, thereby allowing manufacture of sealing means 6 of a relatively complex geometric configuration. For instance, manufacture of thin sealing means 6 requiring low compression forces is allowed. Also the elastic and electrically conductive material of the layer 21 of the projections 20 is advantageously applied by an injection moulding process.

It will be appreciated that the present invention is not limited to the embodiments illustrated.

The element 5 supported by the body 4 has been illustrated, for instance, in the form of a flat piece 12 of metal sheet. It is conceivable to give the element 5 a more complex geometric configuration. For example, it is possible to provide the element with projecting portions which contribute to defining the shielding spaces in the lateral direction. To allow easy manufacture of the body 4 and the element 5 integrated therein by an injection moulding process, it is however preferred to give the element 5 an essentially plane configuration.

It will also be appreciated that the invention may comprise other means than the above-described screw tower to allow mounting of carriers in the form of printed circuit boards. To this end, the device may comprise, for example, suitably designed snap catches.

Several modifications and variations are thus conceivable, and therefore the scope of the present invention is exclusively defined by the appended claims.

Claims

1. A device for electromagnetic shielding, compris- ing a body (4) and, arranged thereon, a shielding surface (9) which is circumferentially defined by an elastic and electrically conductive sealing means (6) , c ha rac t e r i s e d in that the body (4) is made of a material without any essential electrical conductivity, the body (4) supports an element (5) with electrical conductivity, the element (5) having a first surface (7) facing the environment, and the sealing means (6) circumferentially defines a portion of said first surface (7) , which portion forms said shielding surface (9) .

2. A device as claimed in claim 1, in which said element (5) is made of stainless steel, electroplated nickel silver or aluminium.

3. A device as claimed in claim 1 or 2 , in which the element (5) is made of a torsionally rigid material.

4. A device as claimed in any one of claims 1-3, in which the extension of the element (5) is essentially flat .

5. A device as claimed in any one of the preceding claims, in which a piece of metal sheet (12) forms said element (5) .

6. A device as claimed in any one of the preceding claims, in which the element (5) has zones (10) which are moulded into the body (4) .

7. A device as claimed in any one of the preceding claims, in which said shielding surface (9) covers essentially the whole of said first surface (7) .

8. A device as claimed in any one of the preceding claims, in which the sealing means (6) comprises an elastic and electrically conductive material.

9. A device as claimed in claim 8, in which the material is an electrically conductive silicone rubber.

10. A device as claimed in any one of the preceding claims, in which the sealing means (6) comprises a core (13) formed integrally with the body and, applied thereto, a layer (14) of an elastic and electrically conductive material which makes contact with said shielding surface (9) .

11. A device as claimed in any one of the preceding claims, in which the sealing means (6) is adapted to divide said shielding surface (9) into separate subportions (17) .

12. A device as claimed in any one of the preceding claims, further comprising a rib means (16) extended over the shielding surface (9) .

13. A device as claimed in claim 12, in which the element (5) has at least one hole (15) , the rib means (16) being integrally formed with the body (4) and connected therewith through said hole (15) .

14. A device as claimed in claim 12 or 13, in which a layer (18) of an elastic and electrically conductive material which makes contact with the shielding surface (9) is applied to said rib means (16) , whereby the rib means (16) forms a part of the sealing means (6) which thus divides the shielding surface (9) into separate subportions (17) .

15. A device as claimed in any one of the preceding claims, in which at least one hole (19) is formed in said element (5) , through which hole (19) extends a projection (20) which is formed integrally with the body (5) and outside of which is applied a layer (21) of an elastic and electrically conductive material which makes contact with the shielding surface (9) .

16. A method for manufacturing a device for electro- magnetic shielding, said device comprising a body (4) and, arranged thereon, a shielding surface (9) which is circumferentially defined by an elastic and electrically conductive sealing means (6) , c h a r a c t e r i s e d by the steps of manufacturing the body (4) by injection moulding of a material without any essential electrical conductivity, integrating a torsionally rigid element (5) with electrical conductivity in the body (4) in conjunction with the injection moulding thereof, and arranging the sealing means (6) so as to circumfe- rentially define a portion of a first surface (7) , facing the environment, of the element (5), said portion forming said shielding surface (9) .

17. A method as claimed in claim 16, in which the step of arranging the sealing means (6) comprises apply- ing, along an edge of the shielding surface (9) , an elastic and electrically conductive material which makes contact with said shielding surface (9) .

18. A method as claimed in claim 17, in which said material is applied by injection moulding.

19. A method as claimed in claim 18, in which said material is applied by dispensing.

20. A method as claimed in any one of claims 16-19, in which the sealing means (6) is adapted to divide said shielding surface (9) into separate subportions (17) .

21. A method as claimed in claim 20, in which the sealing means (6) comprises an elastic and electrically conductive material which is applied by injection moulding or dispensing along an edge of the respective subportions (17) and in contact therewith.

22. A mobile telephone, comprising a device as claimed in any one of claims 1-15.

23. A mobile telephone as claimed in claim 22, in which the body (4) of the device forms an insert introduced into a case of the mobile telephone.

24. A mobile telephone as claimed in claim 22, in which the body (4) of the device forms a front piece or a rear piece of the mobile telephone.