Patent Publication Number: US-6710276-B2

Title: Keyswitch for an electronic instrument

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a contact device for a keyswitch used in an electronic instrument such as portable telephone, and more particularly relates to a contact device in a key sheet module used in a keyswitch operated by a key top. 
     FIG. 10 is a plan view showing a conventional key sheet module, FIG. 11 is an enlarged sectional view taken along a line XI—XI of FIG. 10, and FIG. 12 is a plan view of fixed contacts. 
     The key sheet module  81  comprises a substrate  82 , and a plurality of keyswitches  83  provided on the substrate  82 . 
     Referring to FIGS. 11 and 12, the keyswitch  83  comprises a first circular fixed contact  86  secured on the substrate  82 , and a second annular fixed contact  87  provided around the first fixed contact  86 , and a movable contact  85  having a semispherical shape and mounted on the second fixed contact  87 . The first fixed contact  86  is connected to a circuit pattern  88  provided on the underside of the substrate  82  by a connecting pipe  82   a  secured to a wall of a through-hole formed in the substrate  82 . The second fixed contact  87  is connected to a circuit pattern  89  provided on the upper surface of the substrate  82 . An adhesive sheet  84  is adhered to the substrate  82  to hold the movable contact  85  each of the keyswitches  83 . 
     When the movable contact  85  is pressed by a key (not shown), the contact  85  contacts with the first fixed contact  86 . Thus, the first and second fixed contacts  86  and  87  are connected with each other. 
     In the conventional keyswitch, since circuit patterns  88  and  89  are provided on both surfaces of the substrate  82 , the manufacturing cost increases. Further, there are two different manufacturing steps comprising the soldering on the circuit patterns  88  and  89  and the adhering of the adhesive sheet  84 , which increases further the manufacturing cost. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a contact device which may be manufactured at a low cost. 
     According to the present invention, there is provided a keyswitch comprising a circuit substrate, a first fixed contact mounted on an upper surface of the circuit substrate, a second fixed contact mounted on the upper surface of the circuit substrate around the first fixed contact, a movable contact having a semicircular sectional shape and mounted on the second fixed contact, terminal electrodes provided on an underside of the circuit substrate and connected to the first and second fixed contacts respectively, a spacer mounted on the circuit substrate so as to surround the movable contact, and a cover mounted on the spacer to cover the movable contact. 
     The movable contact has a plurality of feet so as to hold the movable contact, and the second fixed contact has an opening. The first fixed contact is connected to the terminal electrode by a conductive pattern formed on the circuit substrate in the opening. 
    
    
     These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view showing a key sheet module for a present invention; 
     FIG. 2 is a plan view of a keyswitch of the present invention; 
     FIG. 3 is a sectional view taken along a line III—III of FIG. 2; 
     FIG. 4 is a plan view of fixed contacts; 
     FIG. 5 shows the underside of the keyswitch; 
     FIG. 6 is a plan view of a second embodiment of the present invention; 
     FIG. 7 is a sectional view taken along a line VII—VII of FIG. 6; 
     FIG. 8 is a plan view of fixed contacts; 
     FIG. 9 shows the underside of the keyswitch; 
     FIG. 10 is a plan view showing a conventional key sheet module; 
     FIG. 11 is an enlarged sectional view taken along a line XI—XI of FIG. 10; and 
     FIG. 12 is a plan view of fixed contacts. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a plan view showing a key sheet module for a present invention, FIG. 2 is a plan view of a keyswitch of the present invention, FIG. 3 is a sectional view taken along a line III—III of FIG. 2, and FIG. 4 is a plan view of fixed contacts. 
     The key sheet module  1  comprises a substrate  2 , and a plurality of keyswitches  3  provided on the substrate  2 . 
     Referring to FIGS. 2 and 3, the keyswitch  3  comprises a circuit substrate  5 , a first circular fixed contact  6  secured on the circuit substrate  5  and a second fixed contact  7  provided around the first fixed contact  6 , and a movable contact  11  having a semispherical shape and mounted on the second fixed contact  7 . The first fixed contact  6  is connected to a conductive pattern  10  provided on the underside of the substrate  5  by a connecting pipe  9  secured to a wall of a through-hole formed in the substrate  5 . 
     The conductive pattern  10  is connected to terminal electrodes  8   a  provided at two corners of the circuit substrate  5  as shown in FIG.  4 . The second fixed contact  7  is connected to terminal electrodes  8   b  provided on the underside of the circuit substrate  5  at other two corners. 
     The movable contact  11  is held by an annular spacer  12  secured to the upper surface of the circuit substrate  5 . The spacer  12  has a thickness approximately equal to the height of the movable contact  11 , and a cover  13  is secured on the spacer  12  to be contact with the surface of the movable contact  11 . 
     The circuit substrate  5  is mounted on the substrate  2  so that the terminal electrodes  8   a  and  8   b  are in contact with circuit patterns  4  on the substrate  2  and secured to the circuit patterns  4  by solders  15 . 
     When the movable contact  11  is pressed by a key (not shown), the contact  11  contacts with the first fixed contact  6 . Thus, the first and second fixed contacts  6  and  7  are connected with each other. 
     FIG. 6 is a plan view of a second embodiment of the present invention, FIG. 7 is a sectional view taken along a line VII—VII of FIG.  6 . 
     A keyswitch  23  comprises a first fixed contact  26 , a second fixed contact  27 , and a movable contact  31 . The movable contact  31  has four feet to form a cross. Accordingly, a spacer  32  has a cross hole  32   a  so as to hold the movable contact  31 . As shown in FIG. 8, the second fixed contact  27  has an opening  27   a  at a position between feet of the movable contact  31 . A conductive pattern  30  of the first fixed contact  26  is connected to the terminal electrodes  8   a  passing through the opening  27   a . The movable contact  31  has a gap  31   c  between the feet so as not to contact with conductive pattern  30  and the second fixed contact  27 . 
     Other parts are the same as the first embodiment and identified with the same reference numeral so that explanation thereof is omitted. 
     In accordance with the present invention, first and second fixed contacts provided on the upper surface of the circuit substrate are connected to terminal electrode provided on the underside of the circuit substrate. Therefore, a substrate on which the circuit substrate is mounted may provide a circuit pattern on only an upper surface. 
     Furthermore, adhesive manufacturing process is obviated. Thus, manufacturing cost can be largely reduced. 
     While the invention has been described in conjunction with preferred specific embodiment thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.