GB2361810A

GB2361810A - A gasket for an electromagnetic shield

Info

Publication number: GB2361810A
Application number: GB0010042A
Authority: GB
Inventors: Nigel David Tout
Original assignee: Nokia Mobile Phones Ltd
Current assignee: Nokia Oyj
Priority date: 2000-04-26
Filing date: 2000-04-26
Publication date: 2001-10-31
Anticipated expiration: 2020-04-26
Also published as: GB2361810B; GB0010042D0

Abstract

Means to form an electro-magnetic shield comprising:<BR> ```forming a gasket on one of an electro-magnetic shield member or a printed circuit board, said gasket being of a material that gasses at temperature and being complimentary in shape to a perimeter of the electro-magnetic shield member,<BR> ```placing the electro-magnetic shield member and the printed circuit board in contact, such that the gasket is sandwiched between the two, and<BR> ```subjecting the gasket to heat such that the material of the gasket gasses to form a seal between the shield member and the printed circuit board.

Description

2361810 1 This invention relates to electro-magnetic (EM) shielding and in

particular to an elect ro-mag netic shield that includes a material which gasses at temperature. This material expands under applied heating to form a compressible part on the wall section of the shield to ensure a good contact is made between the walls and the PCB (printed circuit board).

Generally EM shielding is provided in devices by a metal box-like structure which is positioned over EM sensitive components on a PC13. The walls of the box are grounded to the PC13. A gasket is used to ensure a good connection between this conductive wall of the box and the PC13.

In accordance with the invention at least a portion of a walled section of an electro-magnetic shield is provided with a material that gasses at temperature.

The invention enables EM shields with very thin walls to be produced with accurate gaskets. The forming of gas in the material provides a gasket with a good connection between the EM shield and the PC13. The blistered material makes for a compression bead on the wall section which is compressible thus ensuring a good contact is made between the wall and the PC13.

The invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 shows a PCB with a plurality of EM shields; Figure 2 shows a detailed View of the material applied to the wall; and Figure 3 shows a detailed view of blistering on the surface of a wall of an EM shield.

Figure 1 shows a PCB 2 on which a plurality of EM shields 4 are located. The EM shields are generally of rectangular shape having one open side which is 2 placed on the PC13. A gasket 6 is provided around the edge of the EM shield 4.

As shown in Figure 2 the gasket 6 comprises a metal layer 62 which is placed on the telephone chassis or the PC1B, a layer 64 which gasses at temperature is placed on top of the metal layer 62. A further metal layer 66 is placed on top of the material that gasses 64. A non-reflective, laser absorbing material 68 may be placed on top of the metal layer 66 to ensure local heating.

An example of a material that gasses at temperature is a conductive foam such as Gortex. This may be used without the metal layers 62, 66 or the nonreflective layer 68. Alternatively a non-conductive material such as a foam or rubber spray elastomer may be used. A very fine layer of material may be extruded onto the PCB, so meaning that very fine walls can be placed accurately.

In use a gasket 6 (comprising layers 62, 64, 66, 68) is formed either on the PCB (or housing of a device) or on the open edges of the EM shield (i. e. those edges which will, in use, contact the PCB or housing). The EM shield (4) and the PCB (2) (or housing) are then placed in contact, with the edges of the EM shield (4) being placed on the gasket (6) as shown in figure 1. The gasket is then heating, preferably with a laser, to cause the material (64) to gas. This results in a good seal being made between the wall of the EM shield and the PCT (or housing).

As shown in figure 3, after heating the gasket expands to form a compressible seal between the EM shield 4 and the PCB 2.

3

Claims

A gasket for an EM shield, the gasket comprising a material which gasses at temperature.
2. A gasket as claimed in claim 1 wherein said material which gasses at temperature is sandwiched between two layers of metal.
3. A gasket as claimed in claim 2, wherein a non-reflective, laser absorbing material is provided on a metal layer.
4. An electro-magnetic shielding device for shielding electronic components from EM radiation, the shielding device comprising a metal section having at least one edge defining an open face of the metal section and a gasket as claimed in claim 1, 2 or 3, wherein the gasket is provided on the edge of the metal section.
5. A printed circuit board comprising a plurality of electronic components, some of which require electro-magnetic shielding and some of which do not, wherein a gasket of material which gasses at temperature is provided around those components that require electro-magnetic shielding for the purpose of forming a seal with an electro-magnetic shielding member subsequently mounted on the gasket.
6. A method of forming an electro-magnetic shield, said method comprising:

forming a gasket on one of an electro-magnetic shield member or a printed circuit board, said gasket being of a material that gasses at temperature and being complimentary in shape to a perimeter of the electro-magnetic shield member, placing the electro-magnetic shield member and the printed circuit board in contact, such that the gasket is sandwiched between the two, and subjecting the gasket to heat such that the material of the gasket gasses to form a seal between the shield member and the printed circuit board.