WO2001061972A1

WO2001061972A1 - Mobile telephone with lcd module and emi shielding

Info

Publication number: WO2001061972A1
Application number: PCT/GB2001/000663
Authority: WO
Inventors: David Wuilmot
Original assignee: Vtech Mobile Limited
Priority date: 2000-02-18
Filing date: 2001-02-16
Publication date: 2001-08-23
Also published as: AU2001232129A1; GB2364158B; GB2364158A; GB0003948D0

Abstract

A mobile telephone comprises a display, a light guide positioned behind the display to allow the display to be backlit, and is characterised in the light guide including a metallic layer providing EMI shielding. The metallic layer may be a thin layer of metallised plastic applied to a rear surface of the light guide.

Description

MOBILE TELEPHONE WITH LCD MODULE AND EMI SHIELDING

Field of the Invention

This invention relates to a mobile telephone and in particular to a mobile telephone with EMI (Electro- Magnetic Interference) shielding. The term 'mobile telephone' used in this patent specification should be expansively construed to cover any kind of mobile device with communications capabilities and includes radio telephones, smart phones, communicators, and wireless information devices. It includes devices able to communicate using not only mobile radio such as GSM or UMTS, but also any other kind of wireless communications system, such as Bluetooth.

Description of the Prior Art

Many of the components m a mobile telephone emit electro-magnetic waves which may interfere with electronic devices. Consequently, mobile telephones include quite elaborate EMI (Electro-Magnetic Interference) shielding to prevent the leakage out of unwanted electro-magnetic energy. For example, the LCD display of a typical GSM mobile telephone overlies several printed circuit board components which emit electro-magnetic waves. Consequently, some kind of shielding has to be provided to prevent the propagation of these electro-magnetic waves through the display or through the radio section of the phone. Normally this is achieved by placing a metallic shield, or a plastic part coated with metallic paint, over these printed circuit board components. Over the shield or metallised plastic part is then placed a light guide and over the light guide is placed the display itself. At one or more sides of the light guide are placed LEDs : the light guide diffuses the light from the LEDs so that the display is uniformly backlit. This conventional structure works well in terms of shielding and backlighting.

Statement of the Invention

In accorαance with a first aspect of the present invention, a mobile telephone comprises a display, a light guide positioned behind the display to allow the display to be backlit, and is characterised m the light guide including a metallic layer providing EMI shielding.

Hence, the present invention contemplates combining or integrating the EMI shielding function into the light guide. This can be achieved m various ways. For example, the metallic layer may be a thin layer of metallised plastic applied to a rear surface of the light guide, the light guide having a front surface adjacent to the display and a rear surface whose external side faces away from tne display. Typically a 20 - 50 micron layer is adequate.

The metallic layer may also be integral with the light guide; for example, the light guide may be made wholly or partly of material which provides EMI shielding.

In a second aspect, there is provided a light guide positionable behind a display in a mobile telephone, characterised in the light guide includes a metallic layer providing EMI shielding.

This approach has three considerable advantages over the prior art. First, eliminating the need for a separate EMI shield behind the display saves typically 1.55mm in thickness; as mobile telephones become ever thinner and smaller, this is a very considerable saving. Secondly, eliminating the need for a separate EMI shield saves assembly time, and thereby reduces assembly costs. Thirdly, eliminating the need for a separate EMI shield reduces component costs.

Brief Description of the Drawings

The invention will be further described with reference to the accompanying drawing in which Figure 1 is a schematic cross-section through a light guide LCD panel structure in accordance with the present invention and Figures 2 and 3 which are perspective drawings of a light guide LCD panel structure.

Detailed Description

Referring now to Figure 1, a LCD 1 overlies a conventional plastic light guide 2. The light guide 2 includes light diffusing surface 3, so that light from LEDS 4 are scattered from the light diffusing surface 3 up through LCD 1 to backlight the LCD 1.

The rearward face of the light guide 2 is coated with a thin, 20 -50 micron, layer 5 of metallic paint. The metallic paint layer 5 operates as an EMI shield, preventing the electro-magnetic waves propagating from the PCB and related components indicated generally at 6 from passing out through the display 1. The metallic paint is of conventional constitution and applied using conventional techniques, which will be familiar to the skilled implementer.

Figure 2 shows the underside of the light guide 2, indicating the area of metallic shielding 5. The shielded area pattern is carefully designed to ensure that full shielding takes place and that a shielding loop is set up. In the illustrated light guide, a large rectangular area is metallised; this area is bounded by four walls of approximate 1mm - 2mm height; the internal faces of each wall is metallised as is its top face. Metallised surface 7 on the light guide 2 defines the top faces of the four walls and contacts shielding tracks 8 on the PCB 6 to complete a shielding loop when the light guide is fixed onto the PCB 6.

Figure 3 shows the PCB 6 (without components) for a GSM mobile telephone; light guide 2 is located onto the PCB 6, with the metallised surface portions 7 of the light guide (not shown in Figure 3, but visible in Figure 2) contacting PCB shielding tracks 8 in the PCB 6. The display 1 is shown located onto light guide 2. Light guide 2 can be rapidly secured to PCB 6 using five screws as shown. The entire light guide assembly 2 is approximately 3mm to 4 mm thick.

Claims

1. A mobile telephone comprises a display, a light guide positioned behind the display to allow the display to be backlit, characterised in the light guide includes a metallic layer providing EMI shielding.

2. The mobile telephone of Claim 1 in which the metallic layer is a thin layer of metallised plastic applied to a rear surface of the light guide, the light guide having a front surface adjacent to the display and a rear surface whose external side faces away from the display.

3. The mobile telephone of Claim 1 in which the metallic layer is integral with the light guide.

4. The mobile telephone of Claim 3 in which the light guide is made wholly or partly of material which provides EMI shielding.

5. A light guide positionable behind a display in a mobile telephone, characterised in that the light guide includes a metallic layer providing EMI shielding.

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