WO2004103049A1

WO2004103049A1 - Rfi/emi shield integrated with display

Info

Publication number: WO2004103049A1
Application number: PCT/FI2004/050060
Authority: WO
Inventors: Aimo Vainio; Eero Karhunen; Ville Kampman
Original assignee: Myorigo S.A.R.L.
Priority date: 2003-05-13
Filing date: 2004-05-07
Publication date: 2004-11-25
Also published as: FI20030708A; EP1625779A1; FI20030708A0

Abstract

An electromagnetic shield and an arrangement for shielding electric components against RF/EM interference. In the arrangement a frame is placed on top of a printer circuit board (PCB) and a display is placed on top of the frame. The interior surfaces of the display, the frame, and the PCB comprise an RFI/EMI shield. Thus the lids know in the art are omitted from the shield according to the invention. This saves space inside a mobile phone or other devices in which the shield is assembled.

Description

RFI/EMI shield integrated with display

Field of the invention

[001] The present invention generally relates to shields protecting electronic components from radio frequency and/or electromagnetic interferences Background of the invention

[002] All electronic devices functioning with high frequency clock signals cause electromagnetic noise, which harms the operation of sensitive components and/or devices For example, a pππted circuit board (PCB) may interfere with the operation of an antenna One manufacturing challenge is to eliminate electromagnetic interference radiating from the PCB or from the electric components assembled on it The known solution for interference elimination is to use a shield protecting components situated inside the shield and/or components situated outside the shield from radio frequency interference (RFI) and/or electromagnetic interference (EMI) [003] US6180876 describes an apparatus and a method for shielding discrete areas of a PCB from electromagnetic interference This apparatus includes a frame and separate shielding lids The frame is soldered onto the solder tracks of the PCB The frame provides fencing dividing the PCB into discrete areas The shielding lids are placed on top of the frame so that each lid shields a separate discrete area The lids are of different heights depending on the height of the components contained in the respective discrete areas of the PCB

[004] FIG 1 shows two prior art EMI shields accordant to US6180876 A frame 101 is placed on the top of a PCB 102 and lids 103 and 104 are placed on top of the frame 101 The fences of the frame define two discrete areas 105 and 106 covered by the lids The PCB, the frame, and the two lids form the two EMI shields The lids can be considered as boxes which are open towards the frame The interior surfaces of the lid 103, the frame 101 , and the PCB 102 comprise one of the EMI shields shown in the figure [005] When devices become smaller and smaller and at the same time the displays of the devices become larger, it is difficult to eliminate RF/EM interference using common solutions More specifically, there is a lack of space for a RFI/EMI shield located outside of the display area Correspondingly, if the RFI/EMI shield is placed under a display of a device, the device may become too thick The first drawback of the pnor art RFI/EMI shields is their relatively large size

[006] In addition, the shields are usually composed of several components such as shielding lids, which complicates assembling Thus, the second drawback of the pnor art RFI/EMI shields is that they are relatively costly to assemble

Summary of the invention [007] One objective of the invention is to solve the drawbacks of RFI/EMI shields in the prior art Another objective of the invention is to provide a RFI/EMI shield especially suitable for a mobile phone and other small-sized devices equipped with a display [008] The objectives of the invention are achieved by placing a frame on the top of a printer circuit board (PCB) and a display on top of the frame so that the intenor surfaces of the display, the frame, and the PCB compπse an RFI/EMI shield Thus, lids are omitted from the RFI/EMI shield according to the invention This saves space inside the device in which the shield is assembled [009] The invention compnses the RFI/EMI shield and the arrangement for protecting electric components from RFI/EMI

Brief description of the drawings

[010] The invention is described more closely with reference to the accompanying drawings, in which

FIG 1 shows two of the prior art EMI shields,

FIG 2 shows the EMI shield according to the invention,

FIG 3 shows the electromagnetic shielding arrangement in a device having at least one display, FIG 4 shows a display partly covering a frame

Detailed description of the invention

[011] Radio frequency interference (RFI) can be considered a certain type of electromagnetic interference (EMI) The term "electromagnetic shield" or simply "shield" refer to the shield that is intended to protect a device and its components from EMI and/or RFI.

[012] FIG. 2 shows the electromagnetic shield in accordance with the invention. The shield is especially intended for mobile phones and other small- sized devices that include at least one display. The shield is composed of: a frame 201 , a printed circuit board 202, and a display 203. The frame has fencing that divides the area of the PCB 202 into two discrete areas 204 and 205. The continuous fencing 206 extends in an outward direction from the surface of the PCB and surrounds the discrete area 204 of the PCB. The dis- play 203 of a device is assembled on the frame 201. Naturally, the back plane of the display is assembled on the frame so that the face of the display 207 is usable. The frame 201 , the PCB 202, and the display 203 encapsulate the discrete area 204 of the PCB. [013] There are certain basic demands concerning all kinds of RFI/EMI shields. Encapsulation covering a radiation source must have good conductive capacity. It should be well grounded, and there should be no large apertures or gaps in it. If these demands are not fulfilled, an RFI/EMI shield fails to work. Thus the frame 201 shown in FIG. 2 is grounded to the PCB 202, and the display 203 is grounded to the frame 201. [014] FIG. 3 shows the electromagnetic shielding arrangement according to the invention. This figure is a cross-section of the electromagnetic shielding. The arrangement comprises: a frame 301 , a printed circuit board 302, and a display 303 having continuous fencing surrounding a discrete area of the PCB. A plurality of electric components 304-306 is situated in the discrete area of the PCB 302. The frame 301 is grounded to the PCB 302, for example, by soldering, screwing, or gluing, or by using clips. Correspondingly, the display 303 is grounded to the frame, for example, by soldering, screwing, or gluing, or by using clips. The grounding between the display and the frame can be achieved by using metal springs, conductive adhesive, or some other conductive elastomer. The back plane of the display is preferably made of conductive material such as metal or metalized plastic. As shown in FIG. 3, the plurality of electric components 304-306 is encapsulated inside the display 303, the frame 301 , and the PCB 302. This encapsulation 307 is illustrated with a dashed line. The encapsulation operates as electromagnetic shielding. The encapsulation/shielding 307 protects the components of the PCB 302 from the RFI/EMI originating outside of the encapsulation. The component 304 situated inside the encapsulation is a radiation source The encapsulation/shielding also protects electπc components situated outside of the encapsulation For example, the antenna of a mobile phone needs to be protected against RFI [015] Thus in the arrangement according to the invention an appropriate display is assembled to a frame so that the display, the frame, and a certain area of the PCB surrounded by the frame encapsulate at least one component situated in the said area of the PCB The arrangement saves space in inside a device in which the shield is assembled In addition to this, the ar- rangement and the shield according to the invention offer the following benefits First, the arrangement makes it easier to pre-test the display with the shield Secondly, it makes it easier to maintain a device containing the PCB, especially when the display is assembled on the frame by screwing or by using clips Thirdly, the display efficiently attenuates RFI and thus protects the operation of electπc components

[016] A person skilled in the art realizes that there are many alternatives for implementing a shield according to the invention For example, a frame does not need to surround the whole surface of a PCB Correspondingly, the surface of the display, i e the back plane of the display, may be larger than the area of the PCB surrounded by the frame, because also in this case the display operates as a part of the RFI/EMI shield

[017] FIG 4 shows a display partly covenng a frame This figure is a cross- section of the electromagnetic shielding The shielding comprises the frame 401 , the PCB 402, and the display 403 The display 403 only partly covers the frame 401 and the PCB 402 under it The shape of the frame 401 is such that the frame covers the component 406 The other components 404 and 405 situated on the PCB are covered by the display 403 Also in this case the components 404-406 are encapsulated 407 by the shielding [018] In addition, it is possible that a frame is a part of the outer covering of a device Plastic or metalized plastic is especially useful material for this purpose The outer covenng of a mobile phone is usually composed of two pieces a piece which is situated on the same side as the display and another piece which is situated on the opposite side For example, the piece situated on the opposite side of the display may be formed so that it contains the frame that is a part of an RFI/EMI shield

Claims

1. An electromagnetic shield to be used in a device having at least one display, characterized in that said shield is composed of:

- a printed circuit board, - a frame having continuous fencing which extends in an outward direction from the surface of the printed circuit board and surrounds a discrete area of the printed circuit board, said discrete area to contain a plurality of electric components, and

- a display of the device assembled to said frame, wherein a back plane of the display is made of conductive material.

2. The shield as defined in claim 1, characterized in that the display is assembled to the frame by a set of fixtures enabling the detaching and reassembling of the display.

3. The shield as defined in claim ^ characterized in that the frame is a part of the outer covering of a device.

4. The shield as defined in claim 1, characterized in that the device is a mobile communication device.

5. An electromagnetic shielding arrangement, characterized in that said arrangement comprises: - a printed circuit board,

- a frame having continuous fencing which surrounds a discrete area of the printed circuit board, said discrete area to contain a plurality of electric components, and

- a display assembled to said frame and a back plane of the display is made of conductive material, wherein the display, the frame, and said discrete area of the printed circuit board encapsulate the plurality of electric components.

6. The arrangement as defined in claim 1, characterized in that the display is detachable from the frame and thus enable access to the printed circuit board.

7. The arrangement as defined in claim 1, characterized in that the display covers the frame at least partly.

8. The arrangement as defined in claim 1, characterized in that the arrangement is used in a mobile communication device.