FI103936B - The RF shield - Google Patents

Description

103936

The present invention relates to a radio frequency shield comprising a cover-like part which at least partially surrounds the electrical parts mounted on the switching board of the radio device.

It is known to use a metal or metallized, earthed enclosure for the shielding of devices containing electronic components, which, on the one hand, eliminates interference from external electrical or magnetic fields on the device and, on the other hand, prevents interference generated by the device. In particular, devices or parts of devices containing radio transmitters or those operating in the vicinity of a strong radio transmitter shall be protected against electromagnetic interference from radio frequency signals which could damage the most sensitive electrical components of the devices or cause malfunctions in the device.

The enclosures of many consumer electrical appliances are made today of plastic or similar insulating material. The manufacture of a plastic casing is advantageous, the plastic material is lightweight and does not place any restrictions on the shape of the casing. Devices susceptible to radio frequency interference, such as handsets, may be subjected to radio frequency (RF) protection, for example, by applying a conductive coating to the inner surface of the plastic housing. Another commonly used braiding method is to insulate the interfering parts of the device and the interfering parts from each other with a separate conductive coated rf sheath, which is placed to protect the components mounted on the circuit board. The rf protective cover, separate from the device casing, may be of appropriate design and simple • ·: .1 · ·. The use of a separate protective cover is particularly advantageous if the device is manufactured in a plurality of different versions. The same type of rf cover is applicable to different versions of the device: 1 · 1:

Such a conductive protective sheath, which acts as an rf shield, is usually made of plastic, for example by injection molding, and coated with a conductive coating, for example: electrolytically, by vacuum evaporation or by coating with a conductive paint. Typically, the coating covers both the inner and outer surfaces of the protective casing. Protective cover. · · ·. designed to cover the device susceptible to interfering or interfering electronics] · '. Input devices associated with the device, such as 103936 2 monitors, keyboards, microphones, or loudspeakers, as well as light sources, usually LEDs, are usually placed on, or made for, a separate circuit board outside the RF enclosure. openings.

In hand-held phones, the switching plate outside the rf cover is a flexible, thin film which is affixed to the outer surface of the cover and is required only for said input media and light sources. A significant portion of the circuit board film is covered by a display, which is usually a liquid crystal display (LCD). The LCD requires separate backlighting to distinguish characters printed on the screen even in low light. The lighting is implemented with LEDs mounted in connection with the display element 10. The backlighting can be enhanced by a reflector which can be placed, for example, on the underside of a transparent plate which acts as a light guide under the display element. The light emitting diodes are then mounted on the sides of the transparent plate, whereby light is directed through the light guide to the underside of the display element, both directly and reflected from the reflector.

A cross-section of such a backlit LCD structure is shown in Figure 1. As shown, the LCD element 11 has a transparent plate 12 serving as a light guide. The light-emitting diodes 13 illuminating the display 11 are disposed on a film-like switching board 14 on the sides of the light guide 12. The connection plate 14 has an opening the size of a screen 11 and a light guide 20 12 so that the conductive surface (the line reinforced in the figure) of the rf shield 15 can serve as a reflector. The reflector may also be a reflective,, for example, white tape, which at the same time affixes the light guide 12 to the underside of the rf shield 15. In Figure 1, the rf shield 15 and the coupling plate 14 and the light guide 12 are separated from one another. 25 for the sake of convenience. The housing of the device is depicted by a dashed line 16. The figure also indicates the location of the connection plate 17 on the inside of the rf guard 15.

Such a multi-overlapping structure, particularly for the S · «'display, is bulky and also imposes restrictions on the appearance of the housing of the device.

In practice, the cases of modern, ultra-compact handsets have a '· 30 for this reason a formatting protrusion on the screen. Particularly problematic • · · v: Creates a transparent disk below the screen that acts as a light guide. alignment and attachment to the RF enclosure. Usually on the mounts «. ···. use tape.

The present invention enables the device to provide a smaller size LCD display and solves the problems associated with the combination of an rf protective cover and a transparent sheet which acts as a light guide. The solution according to the invention is set forth in claim 1.

In the invention, the rf sheath is made of a transparent material, for example plastic, and leaves one or more uncoated areas which act as a light guide on the conductive coating thereto. The invention combines the rf shield and the light guide into a single component and thereby eliminates the need for separate light guide plates. The manufacture of the rf protective cover according to the invention is simple and well controlled. Areas intended for photoconductors may be masked with, for example, adhesive tape or protective varnish before being coated with a conductive coating. The mask is removed after coating, except for a colorless protective varnish which does not necessarily need to be removed. The masking prevents the coating from sticking to areas intended for photoconductors.

In a preferred embodiment, the LCD element is disposed on the outer surface of a photoconductor included in the rf shield according to the invention, and the light-emitting diodes of the display backlight are disposed on a switching board inside the shield. Correspondingly, the keypad elements can also be illuminated. The design allows the display to be executed in a smaller space than pie-20 and, on the other hand, can also increase the packing density of the circuit board inside the rf cover.

In a preferred embodiment, the LCD element is disposed in a recess formed in the rf screen. In the recess area, the rf sheath is a light *: *: conductor with a reflective coating on the underside. On the sides of the recess are light-emitting diodes, which act as the backlights of the screen, as shown in Fig. 1. in a state of the art. The reflective coating can be implemented with the same material as the conductive coating. This design allows the display to be embedded in a • • · housing enclosure so that the device that contains the display can be built highly. . flat.

The invention will now be described in more detail with reference to the accompanying drawing,. 1 »: Figure 1 illustrates a prior art method of arranging liquid crystal displays. ·. ·. for work backlight, • · «· •« · 4 103936

Fig. 2 is a cross-sectional view of an rf protective cover of the invention, the uncoated portion of which serves as a light guide for a light source illuminating a display or keyboard,

Figure 3 illustrates an embodiment in which a liquid crystal display is embedded in a molded recess in an rf protective casing; Figure 4 shows a first surface of an rf protective casing according to the invention,

Figure 5 shows another surface of an rf protective cover according to the invention, and

Figure 6 is a side elevation view of the location of the rf shield according to the invention in the radiotelephone.

The known structure shown in Figure 1 has been previously described in this text. Fig. 10 2 shows a conductive coated rf shield 21 according to the invention having a transparent area on both its inner and outer surfaces which acts as a light guide 22. The light guide 22 acts like a window which naturally passes in both directions and from the light source outside the cover. I make light coming from the outer surface 23, from the light source 15 inside the sheath, through the inner surface 24 of the light guide. In Figure 2, the component 25 placed on the outer surface 23 of the light guide 22 may be either a display, a key on the keyboard, or some other component of the device which requires backlighting. The light source 26 is disposed on a connecting plate 27 inside the protective cover 21.

The backlighting implemented in accordance with the principle of Figure 2 significantly reduces the number of components to be installed on the ulf: 20 side of the rf shield, for example for the keypad: since each key typically requires its own light source, T: according to prior art. In addition, a light source illuminating the key can be placed to illuminate • ·; optimally, for example directly below the key. This is not ♦ · · ·, * j *. 25 may not be possible if the key and light source are located on the same switching board. The invention also gives greater freedom to use different and. . light sources of different sizes. In principle, one powerful light source can illuminate multiple keys when positioned correctly. Such a structure is difficult to accomplish if the light source has to be placed on the same level, on the same switchboard, with: '·': 30 objects. Of course, similar advantages are achieved by illuminating a liquid crystal display or possibly another object in accordance with the invention.

The light output to the target can be increased by a reflector which is easy to implement, for example in Figure 2, to the surface of the connecting plate 27 inside the rf protective cover 21. The light-emitting diodes 26 serving as the light source 26 may be on the reflecting surface or in uncoated portions thereof provided that the surface is conductive.

The light guide associated with the rf sheath according to the invention can also be used as a screen shield, whereby the screen is placed inside the shield in place of the light source 26 of Figure 2. Such a solution is possible for displays that do not require separate backlighting, but can be thought of as the light source itself.

Figure 3 shows a preferred embodiment of the invention, according to which a liquid crystal display with reflectors and light sources can be implemented in a very small space. According to this cross-sectional view, the rf sheath 31 is formed with a recess 33 sized for the LCD element 32, the bottom of which has an uncoated outer surface 34 but an inner surface 35 with a conductive coating similar to the other parts of the shell. The coating is marked with a solid line in the picture. The coupling plate 36 contained in the Rf sheath is located in the immediate vicinity of the inner surface 35 of said recess 33. The light-emitting diodes 37 illuminating the LCD element 32 may be disposed on a switching board 36 on the sides of the recess 33 to function similarly to the prior art solution of Figure 1 by illuminating the underside of the screen 32 both directly through the light guide and As described above. . according to the embodiment, the display based on the LCD element can be implemented in a very flat form.

T: Referring to Figures 4 and 5, an RF protection 51 is shown which may be used in a radiotelephone or other suitable electronic device.

The Rf shield 51 comprises a substantially planar substrate 52 made as a precursor of translucent plastic. The two main surfaces of the substrate 52 are shown in Figures 4 and 5, respectively. The portion of the substrate 52 has a cut-out portion formed by a rectangular aperture 53 that can be viewed in a radial direction. 30 diopter displays.

«» *. 4, as shown in Fig. 4, the first main surface of the substrate has an electrically conductive coating deposited in the form of a lattice 54. Due to the lattice shape t. ·. ·. visible light can pass through openings 55 of conductive lattice 54 and further through 9 · »« ♦ «·

M1 6 103936 to a substrate 52. The size and density of the apertures 55 is determined such that interference with radio frequency electromagnetic radiation is substantially attenuated. The ideal dimensions of the apertures 55 depend on the wavelength of radiation to be prevented, such that the dimensions are of the order of magnitude 5 or, preferably, smaller. For example, for protection against radio frequency radiation in the 900 MHz range, the corresponding wavelength would be about 33 cm. Thus, any aperture having a aperture substantially less than 33 cm would be suitable for attenuating such radiation.

Figure 5 shows another main surface of the substrate serving as a keyboard circuit board 10. Electrical contacts 56 are deposited on the surface of the substrate, which can be activated by suitable keys. The conductive grooves 57 extend from the electrical contacts 56 and pass through the substrate 52 to the terminals 58 on the first main surface thereof (see Figure 4). The substrate may also be provided with grooves and contacts for other components such as headphone carriers, buzzer or microphones 15.

Referring to Fig. 6, a circuit diagram of an RF shield 51 in a radiotelephone is shown. The Rf shield 51 is disposed on the radiotelephone over the main circuit board 59 with the rectangular aperture 53 over the display 61, and the remainder of the rf shield 51 over the circuits 60 of the main circuit board 59. The Rf shield 51 can be secured to the main circuit board 20 59 using screws or rivets. Through the rectangular opening 53 of the rf guard 51, the screen 61 is visible through the rf guard 51. The first main surface of the substrate is adjacent to the main circuit board 59, and the electrically conductive gate 54 operates such that it · · •. · I prevents radio frequency radiation from circuits 60 on main circuit board 59 from spreading.

:;: Grounding of the conductive gate is achieved by various spring contacts which connect the ground conductors of the main circuit board 59 to the conductive gate 54. A radio keypad 63 is arranged on the other main surface of the substrate 52. The keys 63 have electrically conductive actuators · . ·: ·. provide an electrical connection for the RF contacts 51 for the electrical contacts 56 in the part used in the keyboard circuit board. Connection of electrical contacts 56. 30 to the main circuit board 59 first occurs through the grooves 57 and then from the terminals 58 on the first side of the substrate first through the spring contacts 59 to the main circuit board 59.

Circuits 60 on main circuit board 59 include light emitting diodes 62 (LEDs) for illuminating the keypad *: 1 63 through the rf shield 51. The light emitted by the LEDs 62 passes through the apertures 55 of the conductive lattice 54 to the translucent substrate 52 of the rf shield 51. As it passes through the translucent substrate 52, the light is slightly dispersed and emits the substrate 52 evenly illuminated.

The color of the display backlight can be influenced by the material of the reflective coating ma-5. When used as both conductive and reflective coatings, different metals such as aluminum, copper or silver provide the desired color tone for the backlight. Another way to influence the color of the backlight is to make the rf cover made of transparent colored plastic, leaving the uncoated areas colored.

The invention allows the implementation of a simple rf protective casing 10, which has no additional apertures but still serves as a light guide.

The uncoated portions of the skin acting as a light guide are easily accomplished by masking them prior to conductive coating and removing masking after coating. For masking, for example, tape or protective varnish may be used. No need to remove the colorless protective varnish after coating.

The invention eliminates the need for an additional transparent sheet serving as a light guide for a liquid crystal display, which reduces the volume required by the display of the device and simplifies the configuration of the device. Also, by placing the light sources acting as backlights on the switching board inside the rf cover, the packing density of the switching board can be increased and possibly the outer dimensions of the device reduced. In some cases, the invention may completely eliminate the need for a connection plate outside the rf cover, whereby the rf cover may serve as a housing for the device.

The invention is not limited to the above examples but it is possible to apply it to the extent permitted by the appended claims.

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Claims (11)

An Rf shield comprising a cover-like part having at least a part surrounding the electrical parts mounted on the switchboard of the radio device, having an inner and outer surface, at least one of which being electrically conductive, characterized in that the cover part (21) is made of transparent material the conductive coating having at least one uncoated region serving as a light guide (22). An rf shield according to claim 1, characterized in that the light coming through the inner surface (24) of the photoconductor illuminates an object (25) on the outer surface (23) of the photoconductor. The rf screen according to claim 2, characterized in that the subject is a liquid crystal display. An rf guard according to claim 2, characterized in that the target is located on a key. The rf shield according to claim 2, characterized in that at least a portion of the light emitted through the inner surface (24) is generated by a light-emitting diode (26) mounted on the switching plate (27). The rf shield according to claim 2 or 5, characterized in that at least a portion of the light transmitted through the inner surface (24) is reflected by a reflector disposed between the inner surface of the light guide and the coupling plate. The rf shield according to claim 6, characterized in that the reflector is formed by a reflective coating on the surface of the coupling plate (27). * · • * «• · · The rf shield according to claim 6, characterized in that the reflector • · · 25 is formed by a reflective coating on the inner surface (35) of the light guide. An rf shield according to claim 8, characterized in that the reflective surface; : wax is the same coating material as the conductive coating. a · • · 103936 An RF shield according to any one of claims 2 to 8, characterized in that the light guide has a recess (33) in which the object (32) to be illuminated is placed. The rf shield according to claim 1, characterized in that the light guide 5 acts as a shield for the light source on the connection plate.