El-combined sheet switch

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to an EL-combined sheet switch to be used, for example, in an inputting device for portable telephones, electronic pocket-books, etc.

2. Description of the Related Art:

Known are portable appliances such as portable telephones, electronic pocket-books, notebook-type personal computers, etc., in which an additional backlight is provided in the switch key area so as to facilitate the key operation even in the dark.

For example, in a portable telephone, a thin EL device is disposed in the side of the back surface of a switch key board, as the backlight source, and through-holes arc provided in the site of the EL device that correspond to switch keys. In that constitution, when the switch key is pressed at its front surface, it is electrically connected with the EL device at the contact therebetween through the through-hole, and after the pressure is released, the electric connection is cut off. In this, therefore, the part of each through-hole does not emit light by itself, but the switch keys arc lightened through light emission around the through-holes, and could be differentiated even in the dark.

Ordinary EL devices emit light in the electric field of an alternating current, and generate electromagnetic noise. Therefore, electronic appliances equipped with an EL-combined sheet switch will often malfunction because of the electromagnetic noise to be generated by the EL device therein.

US-A-5,664,667 discloses a pushbutton switch with a printed wiring board, partially covered by a plastic dome sheet including the contact electrodes, and a keypad arranged above the printed board, wherein the keypad has a portion which is made of translucent material, and a light source, as e.g. light emitting diodes, mounted on the printed board. Another portion of the keypad provides at its inner surface an electrically conductive and light-reflecting layer. This layer is grounded and serves to shield external electrostatic influences on the internal contact electrodes. The light of the emitting diodes converges toward the keypad and results in illuminating due to the cooperation of this light-reflecting layer with another electrically conductive and light-reflecting layer, formed over the entire upper surface of the plastic dome sheet, which acts as a convex mirror. Illumination of the keypad illumination is accomplished with a small number of diodes.

SUMMARY OF THE INVENTION

The problems noted above are solved by the features of claim 1. Preferred embodiments are addressed in the subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

• Fig. 1 is a cross-sectional view showing the constitution of one embodiment of the invention.
• Fig. 2 is a cross-sectional view showing the constitution of another embodiment of the invention.
• Fig. 3 is a cross-sectional view showing the constitution of still another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The EL-combined sheet switch of the invention comprises a circuit board with a driving circuit mounted thereon, a flexible contact sheet, and an EL sheet as laminated in that order. The circuit board is provided with a switch pattern as formed on its surface that faces the contact sheet; and the contact sheet is provided with a counter electrode that faces the switch pattern. The counter electrode can be detachably contacted with the switch pattern. Between the contact sheet and the EL sheet, provided is a shield layer capable of shielding the contact sheet from the electromagnetic noise to be made by the EL sheet.

Preferably, the shield layer is connected with the ground electrode formed on the circuit board.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The EL-combined sheet switch of the invention is used for the ten keys in portable electronic appliances such as portable telephones, electronic pocket-books, etc., and it comprises an EL sheet 7 by which the letters and the symbols on the key tops are visible even in the dark.

Fig. 1 shows the constitution of one embodiment of the invention. In this, the circuit board 1 is of a thin insulating board, and a driving circuit for a portable electronic appliance is mounted on the back surface (lower side in Fig. 1) of the circuit board 1 while a contact sheet 3 is provided on the front surface (upper side in Fig. 1) thereof via an adhesive layer 2 therebetween.

On the front surface of the circuit board 1, formed is a switch pattern 1a. The switch pattern 1a acts as a contact point for switching, and is formed through printing with an ink that comprises carbon, silver or any other metal with high conductivity. The driving circuit formed on the back surface of the circuit board 1 is electrically connected with the switch pattern 1a formed on the front surface of the circuit board 1 via a conductive through-hole (not shown).

The adhesive layer 2 is of a non-conductive, polyethyl acetate or polyvinyl acetate-based adhesive, via which the circuit board 1 and the contact sheet 3 are bonded to each other. The contact sheet 3 is of a PET (polyethylene terephthalate) sheet, and has a dome part 3a that swells toward the front surface to be in a semi-spherical form, at the position corresponding to the switch pattern 1a. The dome part 3a is elastic. Therefore, when its top is pushed down from its outside, the dome part 3a is elastically deformed, and its inner surface reaches the circuit board 1. After the pushing force is released, the dome part 3a is then restored to its original position.

At the ceiling of the dome part 3a, formed is a counter electrode 4 that faces the switch pattern 1a. The counter electrode 4 is formed through printing with the same ink as that for the switch pattern 1a. A pair of the counter electrode 4 and the switch pattern 1a form a switch mechanism. When the top of the dome part 3a is pushed down from its outside and deformed downward, then the counter electrode 4 is contacted with the switch pattern 1a, whereby the circuit for the switch pattern is electrically put on and gives an input signal to the electronic appliance having this. Next, when the pressure to the dome part 3 is released, then the switch pattern 1a is detached from the counter electrode 4. In that manner, the switch pattern 1a and the counter electrode 4 arc detachably provided relative to each other.

On the front surface of the contact sheet 3, formed is a shield layer 5 through metal vapor deposition with aluminium or the like. As the case may be, the shield layer 5 may be formed through spraying or printing with an ink as prepared by mixing and kneading a conductive substance such as carbon, silver or the like with a binder.

To the front surface of the shield layer 5, attached is an EL sheet 7 via an adhesive layer 6 therebetween. The adhesive layer 6 may be made of the same material as that for the adhesive layer 2. In the EL sheet 7, formed is a through-hole 7a in the site corresponding to the dome part 3a, and the cross-sectional area of the through-hole 7a shall be larger in some degree than the projected area of the dome part 3a. Through the through-hole 7a, the swollen part of the dome part 3a is exposed out above the front surface of the EL sheet 7.

To the front surface of the EL sheet 7, fitted is a switch key board 8. The switch key board 8 is of a molding of a rubber-based flexible elastic material, in which is formed a pushing part 8a in the area that faces the through-hole 7a of the EL sheet 7. The pushing part 8a protrudes toward the front surface. On the front surface of the pushing part 8a, provided are any of numerals, letters, symbols, etc. These numerals and others are semi-transparent relative to the black background around them, and are seen through light irradiation from the back side, while being differentiated from the black background around them. At the center of the ceiling inside the pushing part 8a, formed is a pushing projection 8b that protrudes downward. When the pushing part 8a is pushed from the outside, the pushing projection 8b pushes the top of the dome part 3a whereby the switch pattern 1a is contacted with the counter electrode 4. When the pressure to the pushing part 8a is released, the pushing projection 8b is restored to its original position.

The shield layer 5 is described in more detail. In Fig. 1, the shield layer 5 as formed on the upper surface of the contact sheet 3 runs to detour around one side (right side in Fig. 1) of the contact sheet 3, and extends to a predetermined site on the back surface of the contact sheet 3 to form a back conductive part 5a. Between the back surface of the contact sheet 3, on which the back conductive part 5a is positioned, and the ground electrode 1b formed on the front surface of the circuit board 1, the adhesive layer 2 is removed, and the back conductive part 5a is electrically connected with the ground electrode 1b via a conductive adhesive 9 provided therebetween. The ground electrode 1b is grounded with a lead wire (not shown), and the electromagnetic noise having entered the shield layer 5 is let away through the back conductive part 5a and the ground electrode 1b. As the case may be, the electric connection of the back conductive part 5a with the ground electrode 1b may be made by a hot melt, in place of the conductive adhesive 9.

Another embodiment of the invention is described with reference to Fig. 2. As in Fig. 2, the basic structure of this embodiment is the same as that of the embodiment illustrated in Fig. 1. In Fig. 2, therefore, the same parts as those in Fig. 1 are designated by the same numeral references as in Fig. 1. In this embodiment, the shield layer 5 does not run to the back surface of the contact sheet 3. In this, a conductive member 11 is provided to run between the front surface of the shield layer 5 and the back surface of the circuit board 1, by which the device is grounded. Precisely, the conductive member 11 is of a metallic screw of copper, silver or the like, via which the shield layer 5 is electrically connected with the ground electrode 1c formed on the front surface of the circuit board 1. With that constitution, the shield layer 5 is grounded via the ground electrode 1c. In this embodiment, the shield layer 5 is not needed to be prolonged to ihc back surface of the contact sheet 3, and, in addition, no conductive adhesive is needed between the contact sheet 3 and the ground electrode 1c. Therefore, this embodiment is advantageous in that the grounding structure therein is simplified and the production costs for it arc reduced.

Fig. 3 shows the constitution of still another embodiment of the invention. As illustrated, a contact sheet 33 is provided on the front surface of a circuit board 31, on which is mounted a driving circuit for a portable electronic appliance, via an adhesive-coated spacer 32 between those 33 and 31. In the position of the front surface of the circuit board 31, in which the spacer 32 is not provided, a switch pattern 31a is provided. In the position of the back surface of the contact sheet 33, in which the spacer 32 is not provided, a counter electrode 34 is so provided that it faces the switch pattern 31a.

On the front surface of the contact sheet 33, formed is a shield layer 35, and on the front surface of the shield layer 35, provided is an EL sheet 37 via an adhesive layer 36 therebetween. The EL sheet 37 does not have a through-hole for switching operation. In this embodiment, therefore, the production of the EL sheet is easy.

To the front surface of the EL sheet 37, attached is a switch sheet 40 via an adhesive layer 39 therebetween. The switch sheet 40 has the same constitution as that of the contact sheet 3 in the embodiments previously described hereinabove (see Figs. 1 and 2), and is provided with a dome part 40a.

On the front surface of the switch sheet 40, provided is a switch key board 38. As in the constitution of Fig. 1, the shield layer 35 detours around the contact sheet 33 to run to the back surface of the contact sheet 33, and this is connected with the ground electrode 31b via a conductive adhesive 31c therebetween. The details of the other constitution in Fig. 3 are the same as those in Fig. 1.

As has been described in detail hereinabove, in the EL-combined sheet switch of the invention, provided is a shield layer between the contact sheet and the EL sheet, and the electromagnetic noise from the EL sheet is blocked by the shield layer. Therefore, electronic appliances provided with the EL-combined sheet switch of the invention are prevented from malfunctioning. Where the shield layer is connected with the ground electrode formed on the circuit board, the constitution of the EL-combined sheet switch can be simplified.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.