AN ELECTROLUMINESCENT LIGHT

Abstract: The generation of noise due the excitation of electronic circuits on a printed circuit board disposed in close proximity to the rear face of an EL as a result of a high voltage alternating current is prevented by the formation of a shield layer on the rear face of the EL.

Description: The present invention relates to an electro-luminescent light for use in the illumination and display of an electronic device. Background to the Invention Electro-luminescent lights (hereafter EL) are used in the illumination of the key button from its rear side and the illumination of the display which carries out all kinds of display operations. Since Els represent a thin and relatively bright light source, they have often been used in recent years particularly in electronic devices where small size and thinness is desirable. However it is necessary to provide a solution to the noise and vibration generated by those Els which emit light due to the supply of a high voltage alternating current at the level of 600HZ and 150V. Up until the present time, an interference material has been provided in the EL as a solution to vibration problems. However as regards noise, due to the fact that it was rare for the electronic circuits to be in close proximity to the EL, no particular problem arose and no solution has been advanced. However as shown by JP-A-SHO-62-15713 and JP-A-HEI-9-93324, in an electronic device in which small size and thinness are desirable, as the electronic components are installed in high density, the printed circuit board is sometimes in close proximity to the EL. Hence the high voltage alternating current supplied to the EL excites the electronic circuits on the printed circuit board and the problem arose that noise was generated. In particular when the EL illuminates the key button, there is the problem that noise is superimposed on the on-off signal of the key button and an error signal may be generated. JP-A-5 093 909 discloses an electro-luminescent light according to the preamble of claim 1. JP-A-9 266 068 discloses a similar electro-luminescent light wherein a shield is provided, and furthermore the provision of a conductive adhesive on the peripheral region of the shield layer is mentioned. The present invention is proposed in order to solve the above problems and has the purpose of providing an EL which prevents the generation of noise in a circuit of a printed circuit board which is disposed in close proximity to the EL and which can easily be assembled. Disclosure of the Invention The structure of the shield of the electro-luminescent light of the present invention comprises a printed circuit board on which is mounted the electronic components, an electro-luminescent light which is placed in close proximity to the printed circuit board and illuminates due to the application of a high voltage alternating current, and a shield member which is provided between the electro-luminescent light and the printed circuit board and shields the high voltage alternating current which is applied to the electro-luminescent light. In this way, it is possible to prevent the generation of noise in the electronic circuit on the printed circuit board. The structure of the shield of the electro-luminescent light of the present invention comprises a click board on top of the printed circuit board for placing the contact points of the switches in the on-off position by the depression of a plurality of key buttons arranged in parallel and a shield member placed between the electro-luminescent light and the click board and between the electro-luminescent light and the printed circuit board. In such a way it is possible to prevent the generation of noise in the electronic circuits on the printed circuit board, particularly noise in the on-off signals generated by the operation of the key buttons. The structure of the shield of the electro-luminescent light of the present invention comprises a shield member constructed by a shield layer printed into the bracing seat used for fixing the click board to the printed circuit board. Hence this structure has the advantage that it is easy to assemble a device with a shield layer. The structure of the shield of the electro-luminescent light of the present invention preferably comprises a shield layer printed in carbon ink. Hence it is possible to prevent the generation of noise in the electronic circuits on the printed circuit board at a low cost. The structure of the shield of the electro-luminescent light of the present invention further preferably comprises a shield member electrically connected to the shield line wired printed onto the printed circuit board. Hence it is possible to again improve the effects of the shield. The structure of the shield of the electro-luminescent light of the present invention is, further preferably, electrically connected by crimping an electrically conductive adhesive, which is printed onto the shield member, to the shield line on the printed circuit board. Hence it is possible to easily perform connecting operations. Simple Explanation of the Drawings Figure 1 is a cross section of an EL according to a first example, not fully in accordance with the present invention. Figure 2 is a cross section showing the structure of a shield of an EL according to the first example. Figure 3 is an enlarged cross section of the connecting part of the EL and the printed circuit board of the first example. Figure 4 is an enlarged cross section of the connecting part of the printed circuit board and the EL according to a second example, not fully in accordance with the present invention. Figure 5 is a cross section of the structure of a shield of an EL according to a preferred embodiment of the present invention. Figure 6 is a cross section of the structure of the shield of an EL according to a further example, not fully in accordance with the present invention. Figure 7 is an enlarged cross section of the structure of the shield of an EL according to this example. Figure 8 is a diagram showing the flexible printed board and the crystal display element used in a further example, not fully in accordance with the present invention. Figure 9 is a cross section showing the structure of a shield of an EL according to this example. Figure 1 is a cross section showing the EL according to a first example. Reference numeral 1 denotes a base film, 2 is a transference electrode laminated on the base film 1, 3 is a luminant layer, 4 is a dielectric layer, 5 is a back plate, 6 is an insulating layer. The elements 1-6 form the EL. 7 is the rear face of the insulating layer, that is to say, it is a shield layer which is laminated onto the shield member on the rear surface of the EL by a process of printing or deposition. 8 is an insulating layer, 9 is an interference material adhered to the rear surface of the insulating layer and formed from non-woven fabric. In other words, the EL is formed from the laminating of each layer shown by the reference numerals 1-6 by a means such as printing. Light is created by excitation of the electrical field by passing a high voltage alternating current between the transference electrode and the back plate which results in the collision of electrons with the luminant layer 3. The shield layer 7 is provided to shield the EL. The interference material 9 is for the purpose of preventing the EL from generating vibration. Figure 2 is a cross section showing the structure of the shield of the EL according to the first example, which uses the EL shown in Figure 1 as a source of light to illuminate the key button. Figure 3 is an enlarged cross section showing the connecting part of the EL with the printed circuit board. The EL is represented by the reference numeral 10 in Figs. 2 and 3 and as shown in Figure 1 has a multi-layered structure on its rear face comprising shield layer 7, insulation layer 8, and interference layer 9. 11 is the case of the electrical device and 12 are the key buttons provided in a plurality of parallel rows on the case 11 of which Figure 3 only shows three. 13 is a click board corresponding to the protruding parts on the rear face of the key buttons 12. The click board is formed by the depression of the key buttons 12 and places the contact points of the switch (not shown) in the on/off position. 14 is a printed circuit board on which is mounted the wiring pattern or the electrical components comprising the electrical circuit containing the switch circuit of the click board 13. 15 is a conductive adhesive printed onto the shield layer 7 and is shown in Figure 3 as applied with pressure and heat fused with the shield line on the top of the printed circuit board 14 and electrically connecting the shield layer 7 and the shield line. In this way, the peripheral edge of the EL 10 as shown in Figure 2 is on top of the click board 13 on those parts of the click board 13 which are on top of the printed circuit board 14. However as shown in Figure 3, in those partial regions on which there is no click board 13, the edge of the EL is sealed to the top of the shield line on top of the printed circuit board 14. The operation of this device will now be explained. When a high voltage alternating current is passed between the transference electrode 2 and the back plate 5, the EL 10 illuminates and light is emitted from the rear of the key button 12. At this time, if a shield layer 7 is not provided, the high voltage alternating current in the EL 10 will excite electrical components and the switch circuit of the click board 13 mounted on the printed circuit board 14 and result in the generation of noise. The excitation of the high voltage alternating current in the switch circuit will cause the on/off signals to be reversed and the opposite operation signal to be sent. However in example 1, as there is a shield layer 7 printed on the rear face of the EL 10, the high voltage alternating current applied to the EL 10 is prevented from exciting the electrical components and the switch circuits on the click board 13 on top of the printed circuit board 14 and the generation of noise is prevented. Since each of the layers 2-6 are normally printed on the base film 1 when the when the EL is fabricated, after the printing of the insulation layer 6, performance is improved by the printing of the shield layer 7. Performance is further improved by the printing of a conductive adhesive 15 at fixed regions on the peripheral edge of the shield layer 7. Furthermore according to example 1, since the shield layer 7 and the shield line on top of the printed circuit board 14 are in electrical connection due to the conductive adhesive 15, the effect of the shield is improved. In other words, the shield will obviously function even if the shield line on top of the printed circuit board 14 and the shield layer 7 are not in electrical contact. It is sufficient to place the shield layer 7 and the shield line on top of the printed circuit board 14 or another shield line in electrical contact to obtain the desired result. It is possible to use silver paste (ink) or a silver and carbon composite paste as a material for printing the shield layer. As a result of much experimentation, it has been found that carbon paste (ink) obtains a sufficient result for the shield layer. On a comparison of the two pastes above, the use of the carbon paste enables a lower cost and marginally reduced weight. According to example 1 above, the printing of a shield layer 7 on the rear face of the EL 10 prevents the generation of noise in the electronic circuits and the switch circuits of the click board 13 on top of the printed circuit board 14 which is positioned on the rear face of the EL 10. It also improves performance. Figure 4 is an enlarged cross section showing the connecting part between the EL and the printed circuit board according to a second example. In the figure, the same of similar elements are represented by the same numerals as in Figure 3. In example 2, the luminant layer 3, the dielectric layer 4 and the back plate 5 which comprise the EL 10 are arranged so as not to overlap in the partial region connecting the shield line of the printed circuit board 14 and the shield layer 7. In other words, when the shield line of the printed circuit board 14 and the shield layer 7 are placed in contact, heat is applied while pressure is applied from above the base film 1 to the conductive adhesive 15. In such a case, the EL 10 can bend and distort due to the pressure and cracks can form in the luminant layer 3, the dielectric layer 4 and the back plate 5. In order to prevent the formation of such cracks, the device is adapted so that these layers do not overlap in the partial region connecting the shield line on the printed circuit board 14 and the shield layer 7. In particular since the adhesion of the transference electrode 2 and the luminant layer 3 is poor and cracks often form in the luminant layer 3, it is sufficient if only the luminant layer 3 does not overlap. The same materials used in example 1 to printed the shield layer may be used. As shown above according to example 2, it is possible to prevent the generation of noise by printing a shield layer 7 on the rear face of the EL 10. Furthermore the formation of cracks in the luminant layer 3, the dielectric layer 4 and the back plate 5. can be prevented by ensuring that these layers do not overlap in the partial region connecting the shield line on the printed circuit board 14 and the shield layer 7. Figure 3 is a cross section showing the structure of the shield of an EL according to a preferred embodiment of the present invention. In embodiments 1 and 2 above, the shield layer 7 is provided on the rear face of the EL 10. However in this embodiment, as shown in Figure 5, the shield layer is provided between the EL 10 and the printed circuit board 14 and between the EL 10 and the click board 13. Normally the click board 13 is adhered onto the printed circuit board 14. As it has a fixed position and since the bracing seat can be provided in the same way as the shield layer 7, the shield layer 7 can printed on top of the bracing seat. According to the embodiment above, noise can be prevented by the provision of the shield layer 7 between the EL 10 and the printed circuit board 14 and the EL 10 and the click board 13. Furthermore assembly including the shield layer 7 is simplified by the printing of the shield layer 7 on top of the bracing seat. Figure 6 is a cross section showing the structure of a shield of an EL according to a further example which is adapted for use in an EL which illuminates a crystal display element. Figure 7 is an enlarged cross section of Figure 6. In Figures 6 and 7, reference numeral 16 denotes a case, 17 is a display window provided on the face of the case 16, 18 is a crystal display element which is positioned so that the face on the crystal screen side is opposite the display window 17. 19 is transparent plastic which acts as a positional determination member adhered to the upper face of the EL 10. 10 is an EL which acts as a source of light illuminating the crystal display element 18 from its rear face through the transparent plastic. The EL is comprised from the base film 1, the transference electrode 2, the illuminant layer 3, the dielectric layer 4, the back plate 5 and the insulation layer 6 as shown in Figure 1. 20 is a flexible body made from a rubber seat and interposed between the case 16 and the peripheral edge of the crystal display element 18. 21 is a holder which supports the crystal display element 18 through the transparent plastic 19 and the EL 10. Its rear face is formed on the shield member. 14 is a printed circuit board disposed on the lower part of the holder 21 and on which the electrical components which comprise the motive circuits and the like of the crystal display element 18 are mounted. 22 is a pawl provided in the case 16. 23 is a pawl provided in the holder 21 which is engaged with the pawl 22 in the case 16. The method of assembling the crystal display element will now be explained. The EL 10, the transparent plastic 19 and the crystal display element 18 are stacked in layers on top of the holder 21. On the very top of these layers is disposed a rubber seat 20. When the holder is pushed into the case 16 in this state, as shown in Figure 6, the pawl 23 of the holder 21 engages with the pawl 22 of the case 16 and supports the crystal display element 18 in a determined position. In other words, in this example, the holder 21 acts as a shield member. Hence the generation of noise due to the high voltage alternating current applied to the EL 10, which excites the printed circuit board 14 is prevented by the shield member formed on the face of the holder 21. In this example, the transparent plastic 19 provided as a unit on the EL 10 protrudes from the end face of the EL 10 towards the rib 21a on the end face of the holder 21. Therefore the end face of the EL 10 is formed so as not to contact with the face of the holder 21. Normally since the EL 10 is fabricated in a plurality of flat respective layers and cut to a suitable size for use, the end face of the EL 10 shows each EL layer as exposed. Hence if the end face of the EL 10 is in contact with the surface of the holder 21, the transferance electrode will be short circuited. In embodiment 4, the transparent plastic 19 determines the position of the EL 10 so that the end face of the EL 10 does not come into contact with the holder 21. As shown above according to this example of the present invention, the generation of noise due to the application of a high voltage alternating current to the EL 10 can be prevented by the provision of a shield member on the face of the holder 21 provided on the printed circuit board 14 and the EL 10. Figure 8 is a figure showing the flexible printed board and the crystal display element used in a still further example. Figure 9 is a cross section showing the structure of the shield of the EL according to this example. Further Figure 8(a) is a plan view of the flexible printed board on which is mounted the crystal display element . and the motive circuits therefor. Figure 8(b) is a side view and Figure 8(c) is a rear view. In Figure 8, reference numeral 18 is a crystal display element, 24 is a flexible printed board one end of which is engaged with the end of the crystal display element 18 and on the surface of which is mounted the motive circuits and the like for the crystal display element 18. 25 is a driver IC comprising the motive circuits mounted on the flexible printed board 24, 26 is a connector, 27 is a shield member formed on the rear surface of the flexible printed board 24 and which for example may be formed by aluminum deposition on the rear face of the flexible printed board 24, Figure 9 shows the crystal display element 18 and the flexible printed board 24, shown in Figure 8, as assembled in the case with the EL 10. In the figure, 14 is a printed circuit board, 16 is a case, 17 is a display window, 28 is a holder with an aperture formed on its lower face, and which abuts with and supports the EL 10, the crystal display element 18 and the flexible printed board 24 in its interior. The flexible printed board 24 as shown in the figure, is disposed presses against the EL 10 and is bent around the rear face of the crystal display element 18. The shield member 27 on the rear face of the flexible printed board 24 faces the rear face of the EL 10. The upper face of the flexible printed board 2 on which is mounted the driver IC 25, the connector 26 and the like faces the printed circuit board 14 through the aperture in the lower surface of the holder 28. 29 is a connector provided on the top of the printed circuit board 14, and is connected to the connector 26 on top of the flexible printed board 24. As shown above in accordance the latter example, noise due to the excitation of the electrical circuits such as the motive circuits on the face of the flexible printed board 24 and the electrical circuits on the printed circuit board 14 as a result of the application of a high voltage alternating current in the EL 10 can be prevented by the formation of a shield member 27 on the rear face of the flexible printed board 24. The configuration as shown in Figure 9 provides a flexible printed board 24 and a printed circuit board 14. However all the electrical components can be mounted on the flexible printed board 24 and the printed circuit board 14 can be dispensed with. Industrial Applicability As shown above, the EL in accordance with the present invention and the shield structure therefor are adapted to prevent the generation of noise in electronic devices such as mobile telephones due to the application of a high voltage alternating current in the EL.

Claims: An electro-luminescent light which comprises a printed circuit board on which is mounted electronic circuit components, an electro-luminescent light which is disposed in close contact with the printed circuit board and which generates light due to the application of a high voltage alternating current, and a shield member which is disposed between electro-luminescent light and the printed circuit board and which shields the high voltage alternating current applied to the electro-luminescent light further comprising a click board on the printed circuit board, said click board placing the switch contact point in the on/off position in response to the depression of a plurality of rows of key buttons, wherein the shield member is disposed between the electro-luminescent light and the click board and between the electro-luminescent light and the printed circuit board characterized in that the shield member is constructed by a shield layer printed onto the bracing seat which fixes the click board to the printed circuit board. An electro-luminescent light according to claim 1, wherein the shield layer is printed in carbon ink. An electro-luminescent light according to claim 1, wherein the shield member is electrically connected to the shield line wire printed onto the printed circuit board. An electro-luminescent light according to claim 3, wherein the conductive adhesive which is printed onto the top of the shield member is electrically connected to the shield line on the printed circuit board by crimping.

Inventors: INOUE TSUTOMU, INUBUSHI TOSHIYA, INOUE, TSUTOMU, INUBUSHI, TOSHIYA, INOUE, Tsutomu, Mitsubishi Denki Kabushiki K., INUBUSHI, Toshiya, Mitsubishi Denki Kabushiki K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1998
Main classification: H05B33
IPC codes: H05K1, H05B33