Abstract:
A keypad for a mobile phone includes a circuit board having a fixed contact point; a dome switch disposed on the circuit board; a base pad member having a projection for pressing the dome switch to generate signal; an upper pad member having a key top, the upper pad member being integrally formed with the base pad member, and an EL element disposed surface-contacting between the base pad member and the upper pad member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (a) Field of the Invention  
           [0002]    The present invention relates to a keypad for a mobile phone and, more particularly, to a keypad that has an EL element formed in a thin sheet and integrated therein, thereby minimizing noise and vibration generated by the EL element.  
           [0003]    (b) Description of the Related Art  
           [0004]    Generally, a keypad for a mobile phone is an input device consisting of a separate grid of numerical and function keys arranged for efficient data entry. The keys are fitted into holes formed on a front housing of the mobile phones and jutted out so that users can conveniently input the data.  
           [0005]    Light source formed of a luminous element is installed on the bottoms of the key so that the user can identify the numerical numbers and letters printed on the keys in a dark place. When the light source is turned On, the light is emitted to the letters and numerical numbers printed on the keys by the backlight effect, thereby making the users identify them.  
           [0006]    [0006]FIG. 7 shows one of keys constituting a conventional keypad for a mobile phone.  
           [0007]    A key  50  generally comprises a base  52 , a key top  54  elevated from the base  52 , and a projection  56  formed on a bottom center of the key top  54 .  
           [0008]    The base  52  and the key top  54  are integrally formed by a connecting portion  58 . The connecting portion  58  is designed to be thiner than the base  52  for the effective operation of the key  50 . A printing layer of letters and numerical numbers is formed on a top surface of the key top  54  through a silkscreen printing or a laser marking.  
           [0009]    The base  52  is provided at its bottom surface with a groove  62  in which a light source formed of an LED lamp is installed.  
           [0010]    A dome switch  68  is located under the projection  56 , and a fixed contact point  70  formed on a printed circuit board  64  is located under the dome switch  68 .  
           [0011]    When using the mobile phone, the light source  66  is applied with electric power to provide backlight to the keypad, making it possible to see the printing layer  60  with the letters and numerical numbers formed on the key top  54  even in the dark place.  
           [0012]    When pushing the key  50 , the projection  56  formed on the bottom of the key  50  overcomes the elastic formed of the dome switch  68  and pushes the dome switch  68  so that the dome switch  68  contacts the fixed contact point  70 , thereby generating a signal.  
           [0013]    When releasing the pushing force applied to the key  50 , the key  50  is returned to its initial position by the self-elastic force of the connecting portion  58  and the dome switch.  
           [0014]    However, in the conventional keypad, since a groove is formed on the bottom surface of the base  52  and the light source formed of the LED lamp is installed in the groove, the thickness of the keypad is increased as many as the thickness of the light source.  
           [0015]    Furthermore, since the key  50 , the dome switch  68 , and the printed circuit board  64  are disposed in the front housing of the mobile phone, and a part of the key  50  is exposed out of the front housing, it is time consuming to assemble all of the members, thereby deteriorating the productivity.  
           [0016]    To solve the above-described problem, a keypad for a communication device, which is provided with a sheet-type luminous element (an EL element) that is designed such that a spacer having opposite adhesive surfaces is attached on a circuit board and a backlight is provided on the spacer, has been proposed. However, a special assembling process for attaching the spacer is required, and the thickness of the keypad is increased as many as the thickness of the spacer.  
           [0017]    Furthermore, a dome switch, a moving contact point, and a fixed contact point that are constituting the luminous element are not sealed, this causes the mobile phone&#39;s life to be reduce and also causes a shielding process for preventing the noise and vibration caused by current applied to the luminous element to be required.  
         SUMMARY OF THE INVENTION  
         [0018]    The present invention has been made in an effort to solve the above-described problems of the conventional art.  
           [0019]    It is an objective of the present invention to provide a keypad that is designed to be produced with less expense and to minimize the thickness thereof by integrating a thin film EL element thereinto.  
           [0020]    It is another objective of the present invention to provide a keypad that can enhance the reliability and increase its life by preventing the noise and vibration generated by an EL element.  
           [0021]    To achieve the above objectives, the present invention provides a keypad for a mobile phone, comprising a circuit board having a fixed contact point; a dome switch disposed on the circuit board; a base pad member having a projection for pressing the dome switch to generate signal; an upper pad member having a key top, the upper pad member being integrally formed with the base pad member; and an EL element disposed surface-contacting between the base pad member and the upper pad member.  
           [0022]    According to a preferred embodiment of the present invention, a diffusing layer is formed on the EL element and a printed film is located on the EL element.  
           [0023]    According to another preferred embodiment, the EL element is integrally formed with the base pad member, and the key top is attached on the EL element.  
           [0024]    Preferably, the base pad member and the key top are formed of a material selected from at least one of silicon rubber and synthetic resin. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a sectional view of a keypad for a mobile phone according to a first embodiment of the present invention;  
         [0026]    [0026]FIG. 2 is a sectional view for illustrating a diffusing layer printed on a keypad of FIG. 1;  
         [0027]    [0027]FIG. 3 is a sectional view for illustrating a printing film installed in a keypad of FIG. 1;  
         [0028]    [0028]FIG. 4 is a sectional view of a keypad for a mobile phone according to a second embodiment of the present invention;  
         [0029]    [0029]FIG. 5 is a sectional view for illustrating a light guide layer printed on a keypad of FIG. 4;  
         [0030]    [0030]FIG. 6 is a sectional view of a keypad for a mobile phone according to a third embodiment of the present invention; and  
         [0031]    [0031]FIG. 7 is a sectional view of a conventional keypad for a mobile phone.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    Preferred embodiments of the present invention will be described more in detail hereinafter in conjunction with the accompanying drawings.  
         [0033]    [0033]FIGS. 1 and 2 show a keypad according to a first embodiment of the present invention. A keypad of this embodiment may be formed of silicon rubber.  
         [0034]    A keypad of this embodiment comprises an upper pad member  2  having plural key tops  8  pressed or touched by a user and a base pad member  6  disposed opposing the upper pad member  2 , and an EL element  14  integrally disposed between the upper and base pad members  2  and  6 .  
         [0035]    The key tops  8  of the upper pad member  2  are arranged to maintain their space at a predetermined distance and elevated upward passing over a front cover and spaced away from each other at a predetermined distance. The base pad member  6  is provided with plural projections  4  corresponding to the key tops  8 .  
         [0036]    The projections  4  are located such that they can press corresponding dome switch S provided on a circuit board P by the user pressing the key tops  8 .  
         [0037]    The base pad member  6  is further provided with groove portions  10  for providing the elastic force and the restitutive force to the key top  8 .  
         [0038]    A printed layer  12  with numerical numbers or letters is formed on the key tops  8 . The printed layer  12  is formed by a spray printing method, a laser marking method, or a silk screen-printing method.  
         [0039]    A think film EL element for the backlighting is disposed between the upper and base pad members  2  and  6 .  
         [0040]    When electric field is applied to the EL element  14 , the electrons and electron holes are coupled to emit light front the surface. Since the EL element  14  is capable of being driven even by low voltage as well as providing the wide view angle, it can be widely applied. Furthermore, since the EL element  14  is formed of a thin sheet, the occupying space in the mobile phone can be minimized when compared with the conventionally used LED lamp, thereby making it possible to make the phone compact.  
         [0041]    Describing the method for inserting the EL element  14  to integrate with the keypad, the base pad member  6  is first formed using a low mold (not shown), and then the EL element  14  that is shorter than the pad member  6  is disposed on the pad member  6 . Next, silicon rubber liquid is poured on the EL element  14  and pressed by a mold in the shape of the base pad member  6 , thereby forming the base pad member  6 .  
         [0042]    Next, the silicon rubber liquid is pressed by a mold in the shape of the key top, thereby forming the key top and attaching the base pad member  6  to the upper pad member  2 . As a result, the EL element  14  tightly surface contact between the base pad member  6  and the upper pad member  2 .  
         [0043]    The EL element is an alternating current planar light source driven a predetermined driving voltage and frequency, inevitably generating the noise and vibration. However, in the present invention, the EL element  14  is tightly disposed contacting between the base pad member  6  and the upper pad member  2 , thereby alleviating the noise and the vibration.  
         [0044]    In addition, as shown in FIG. 2, a diffusing layer  16  may be formed on the EL element to allow the light emitted from the EL element  14  to be diffused, thereby enhancing the backlighting effect.  
         [0045]    In the first embodiment, the printing layer  12  is printed on the key tops  8 . However, as shown in FIG. 3, a printing film  18  with letters and numerical numbers may be integrated on the EL element  14 .  
         [0046]    By integrating the printing film  18  on the EL element  14 , the letters and numerical numbers can be more clearly shown.  
         [0047]    [0047]FIGS. 4 and 5 show a second embodiment of the present invention.  
         [0048]    The keypad of the second embodiment is identical to that of the first embodiment except that the key tops are formed of a different material from that of the pad members.  
         [0049]    That is, the key pad of this second embodiment comprises a base pad member  6   a  formed of silicon rubber, an upper pad member  6   b  integrally formed with the base pad member  6   a,  and key tops  20  formed of synthetic resin, the key tops  20  being attached on the upper pad member  6   b  by adhesive  22 .  
         [0050]    In this embodiment, the EL element  14  is also surface-contacted with the pad members.  
         [0051]    [0051]FIG. 6 shows a keypad according to a third embodiment of the present invention.  
         [0052]    In third embodiment, the EL element  14  having a length identical to that of a base pad member  6  formed of silicon rubber is integrally surface-contacted with the EL element  14 . A key tops  20  formed of synthetic resin is attached on the EL element by adhesive  22 .  
         [0053]    As described above, as the thin EL element is integrally inserted into the keypad, the thickness of the keypad can be minimized while simplifying the assembling and manufacturing process, thereby improving the productivity.  
         [0054]    In addition, since the EL element is tightly disposed contacting between the base and upper pad members, the noise and vibration caused by the EL element can be suppressed, thereby improving the reliability and endurance of the element.