Patent Publication Number: US-6670565-B2

Title: Illuminated button switch

Description:
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP02/04683. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a illumination type push button switch used in an electronic apparatus, such as a portable telephone or a personal computer. 
     BACKGROUND ART 
     Recently, electronic apparatuses including a portable telephone and a personal computer have better functions and cover a broader spectrum. Push button switches used in an operating part of the apparatuses are required to light a push button for illuminating to enable an operation even in dark. 
     The conventional illumination type push button switch will be described with reference to FIG.  5 . 
     FIG. 5 is a sectional view of the conventional illumination type push button switch. Dark-colored push button  1  made of insulating resin includes, at its top surface, display part  1 A which is, for example, semitransparent or milk-white and is exposed in the form of a letter, a mark, a design or the like. Switch contact  2  disposed below button  1  includes wiring board  3 , flexible insulating film  4 , insulating spacers  5  each having both surfaces coated with adhesive for bonding wiring board  3  and insulating film  4  together, plural fixed contacts  3 A on a top surface of wiring board  3 , and plural movable contacts  4 A on a bottom surface of insulating film  4 . Fixed and movable contacts  3 A and  4 A face each other at a predetermined space. Switch contact  2  thus functions as a membrane switch. Light-emitting diode (LED)  6  is mounted on the top surface of wiring board  3  near fixed contact  3 A. Insulating film  4  and insulating spacer  5  have respective holes through which LED  6  is inserted. Board  7  is mounted on a bottom surface of wiring board  3 . Case  8  made of insulating resin covers these elements and has, at its top side, a hole through which button  1  projects vertically movably. The illumination type push button switch is thus configured. 
     When specified push button  1  is pressed downward, insulating film  4  is pressed by push part  1 B and sags, thereby allowing corresponding movable contact  4 A on the bottom surface of this film  4  to contact with corresponding fixed contact  3 A on the top surface of wiring board  3 . This action allows switch contact  2  to establish electrical connection and disconnection. 
     When LED  6  on the top surface of wiring board  3  emits light, display part  1 A of push button  1  over LED  6  illuminates from behind with the light, which thus facilitates the identification of button  1  even in dark. 
     In the conventional push button switch described above, since LED  6  has light emission directivity, the light emitted by LED  6  lights display part  1 A of push button  1  weak if display part  1 A is in a position out of alignment with LED  6 . Further, if many push buttons  1  are arranged, the number of LEDs  6  must be equal to the number of buttons  1 . This increases the number of components, and further, it takes time, for example, to make the holes in insulating film  4  and insulating spacers  5  and to mount LEDs  6  to wiring board  3 . This makes the conventional push button switch expensive accordingly. 
     SUMMARY OF THE INVENTION 
     A push button switch includes a push button, a switch contact for establishing electrical connection and disconnection when the push button is pressed and released, a board mounted to the switch contact to face the push button across the switching contact, and an EL element mounted to a substrate to face the switch contact across the substrate. The board has a through-hole formed therein near the switch contact. The EL element includes a light-emitting part including a light-transmitting electrode layer, a luminescent layer, and a back electrode layer overlaid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a illumination type push button switch in accordance with an exemplary embodiment of the present invention. 
     FIG. 2 is a sectional view of an EL element of the illumination type push button switch in accordance with the embodiment. 
     FIG. 3 is a sectional view of another EL element of the illumination type push button switch in accordance with the embodiment. 
     FIG. 4 is a sectional view of another illumination type push button switch in accordance with the embodiment. 
     FIG. 5 is a sectional view of a conventional illumination type push button switch. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment of the present invention will be described with reference to FIGS. 1 to  4 . It is to be noted that elements similar to those in the prior art are denoted by the same reference numerals and will not be described in detail. 
     FIG. 1 is a sectional view of a illumination type push button switch in accordance with the exemplary embodiment of the present invention. Dark-colored push buttons  11  and  12  made of insulating resin, such as ABS resin, polycarbonate, or acrylic resin, include display parts  11 A,  12 A which are, for example, semitransparent or milk-white at their top surfaces, respectively, and are exposed in the form of a letter, a mark, a design or the like. Switch contact  2  below push button  11  includes wiring board  3 , flexible insulating film  4 , and insulating spacers  5  each having both surfaces coated with adhesive for bonding wiring board  3  and insulating film  4  together. Plural fixed contacts  3 A on a top surface of wiring board  3  and plural movable contacts  4 A on a bottom surface of insulating film  4  face each other at a predetermined space. This arrangement allows switch contact  2  to function as a membrane switch. Board  17  made of aluminum, insulating resin, or the like is mounted to a bottom surface of wiring board  3  and has plural through-holes  17 A and  17 B formed therein around and between fixed contacts  3 A. EL element  20  is mounted to a bottom surface of board  17 . 
     In EL element  20 , a bottom surface of light-transmitting substrate  21  formed of a film, glass, resin or the like is overlaid with light-transmitting electrode layer  22  formed by sputtering or a method using an electron beam, or by printing light-transmitting synthetic resin. The resin includes indium tin oxide or the like dispersed therein. Electrode layer  22  ends before an outer periphery of substrate  21 . Electrode layer  22  is overlaid by printing with luminescent layer  23  made of synthetic resin including light-emitting material, such as zinc sulfide dispersed therein, dielectric layer  24  made of synthetic resin including barium titanate or the like dispersed therein, and back electrode layer  25  made of resin including silver or carbon. Luminescent layer  23 , dielectric layer  24 , and back electrode layer  25  are covered with insulating layer  26  made of epoxy resin, polyester resin or the like. 
     Case  8  made of insulating resin covers EL element  20 , switch contact  2 , board  17 , and others. Case  8  has, at its top side, a hole through which push button  11  projects vertically movably. 
     When specified push button  11  or  12  is pressed downward, insulating film  4  is pressed by push part  11 B or  12 B and sags, thereby allowing corresponding movable contact  4 A on the bottom surface of film  4  to contact with corresponding fixed contact  3 A on the top surface of wiring board  3 . This action allows switch contact  2  to establish electrical connection and disconnection. 
     Upon a voltage being applied between light-transmitting electrode layer  22  and back electrode layer  25  of EL element  20 , luminescent layer  23  between layers  22  and  25  emits light. The light passes through through-holes  17 A,  17 B and back-lights the push buttons  11  and  12 , thus facilitating the identification of buttons  11 ,  12  even in dark. 
     EL element  20  may be positioned between push buttons  11 ,  12  and switching contact  2  or between switching contact  2  and board  17 . An alternating-current voltage of several tens of voltages is preferably applied to EL element  20 , while switch contact  2  operates with a DC voltage of several voltages. For this reason, upon being located over or below switch contact  2 , EL element  20  must be distanced from switch contact  2  or must be shielded for preventing the contact from noise or the like. 
     In case that EL element  20  is mounted to the bottom surface of board  17  according to the present embodiment, although board  17  has through-holes  17 A and  17 B for permitting the light to pass, almost portion of EL element  20  which do not correspond to through-holes  17 A or  17 B are separated by board  17 . This ensures a distance corresponding to the thickness of board  17  at through-holes  17 A and  17 B. 
     According to the present embodiment described above, EL element  20  capable of lighting the push buttons simultaneously with surface-light emission unlike an LED is mounted to the bottom surface of board  17  and emits the light via through-holes  17 A and  17 B of board  17  to push buttons  11  and  12 . Thus, the push buttons illuminate clearly, and the illumination type push button switch employs a small number of components and is inexpensive. 
     The switching contact including fixed contacts  3 A on the top surface of wiring board  3 , movable contacts  4 A on the bottom surface of insulating film  4  may be made of, for example, transparent resin including silver, carbon, or the like dispersed therein so as to transmit the light. This allows push buttons  11  and  12  to illuminate more brightly. 
     As shown in FIG. 2, the EL element may includes plural partial light-emitting parts  27 A and  27 B including plural partial back electrode layers  25 A,  25 B which are formed at parts, respectively, instead of being formed over the whole surface. This arrangement allows the switch of the present embodiment to perform various lighting, for example, to light a specified push button and to light all the push buttons simultaneously. 
     Instead of partial back electrode layers  25 A and  25 B, the switch may partly include plural partial light-transmitting electrode layers  22  or partial luminescent layers which emit light in different colors. 
     As shown in FIG. 3, plural partial back electrode layers  25 A and  25 B may transmit light and may be overlaid with luminescent layer  28  which emits light in color different from respective colors of luminescent layer  23 , dielectric layer  29 , and back electrode layers  30 A and  30 B. Upon a voltage being applied between light-transmitting electrode layer  22  and any one of partial back electrode layers  25 A and  25 B, a corresponding part of luminescent layer  23  emits light. Upon voltage being applied between any one of partial back electrode layers  25 A,  25 B and corresponding one of partial back electrode layers  30 A,  30 B, a corresponding part of luminescent layer  28  emits light. 
     Upon a voltage being applied between all these electrode layers, luminescent layers  23  and  28  emit light in different colors, and then, push buttons  11  and  12  can illuminate with a combination of these lights of different colors. 
     As described above, the EL element, which emits light in different colors, increases variety of lighting. For example, the light to be emitted can be changed between the different colors, and thus, the push button can illuminate with the combination of the lights of different colors. 
     In the above description, board  17  is mounted to the bottom surface of the membrane switch including wiring board  3  and insulating film  4  that are put together. As shown in a sectional view of FIG. 4, board  31  made of paper phenol, epoxy including glass therein or the like may have plural fixed contacts  31 A on its top surface and have through-holes  31 B formed therein near fixed contacts  31 A. Board  31  may be affixed to insulating film  4 , which has movable contacts  4 A formed on its bottom surface via insulating spacers  5 . 
     Instead of the membrane switch, the switching contact may be, for example, a switch including movable contacts that are made of resilient metallic foil and have center portions protruding like a dome, and fixed contacts on the wiring board. In this switch, the movable contact is turned inside out with the push button for connection with and disconnection from the fixed contact. The switch contact may include dome-like movable contacts made of rubber or elastomer for connection with and disconnection from respective fixed contacts. The contact may be a single push switch. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, an inexpensive illumination type push button switch including a small number of components and lighting a push button clearly is provided.