Patent Publication Number: US-10312034-B1

Title: Keyboard device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a keyboard device, and more particularly to a keyboard device with a membrane switch circuit member. 
     BACKGROUND OF THE INVENTION 
     Generally, the widely-used peripheral input device of a computer system includes for example a mouse device, a keyboard device, a trackball device, or the like. Via the keyboard device, characters or symbols can be directly inputted into the computer system. As a consequence, most users and most manufacturers of input devices pay much attention to the development of keyboard devices. 
     A keyboard device with scissors-type connecting elements will be described as follow.  FIG. 1  is a schematic cross-sectional view illustrating a conventional keyboard device. The conventional keyboard device  1  comprises plural keys  10 , a membrane switch circuit member  11  and a supporting plate  12 . Each key  10  comprises a keycap  101 , a scissors-type connecting element  102  and an elastic element  103 . In the key  10 , the keycap  101  is exposed outside the conventional keyboard device  1 . Consequently, the keycap  101  can be depressed by the user. The scissors-type connecting element  102  is used for connecting the keycap  101  and the supporting plate  12 . The elastic element  103  is penetrated through the scissors-type connecting element  102 . In addition, both ends of the elastic element  103  are contacted with the keycap  101  and the membrane switch circuit member  11 , respectively. The supporting plate  12  is located under the membrane switch circuit member  11 . The keycap  101 , the scissors-type connecting element  102 , the elastic element  103  and the membrane switch circuit member  11  are supported on the supporting plate  12 . 
     The membrane switch circuit member  11  comprises an upper wiring board  111 , a separation layer  112 , and a lower wiring board  113 . The upper wiring board  111  has plural upper contacts  1111 . The separation layer  112  is located under the upper wiring board  111 , and comprises plural perforations  1121  corresponding to the plural upper contacts  1111 . The lower wiring board  113  is located under the separation layer  112 , and comprises plural lower contacts  1131  corresponding to the plural upper contacts  1111 . The plural lower contacts  1131  and the plural upper contacts  1111  are collectively defined as plural key switches  114 . The elastic elements  103  are disposed on the membrane switch circuit member  11  and aligned with the corresponding key switches  114 . 
     The operations of the key  10  of the conventional keyboard device  1  in response to the depressing action of the user will be illustrated as follows. Please refer to  FIG. 1  again. When the keycap  101  is depressed, the keycap  101  is moved downwardly to push the scissors-type connecting element  102  in response to the depressing force. As the keycap  101  is moved downwardly relative to the supporting plate  12 , the keycap  101  pushes the corresponding elastic element  103 . At the same time, the elastic element  103  is subjected to deformation to push the membrane switch circuit member  11  and trigger the corresponding key switch  114  of the membrane switch circuit member  11 . Consequently, the membrane switch circuit member  11  generates a corresponding key signal. When the keycap  101  is no longer depressed by the user, no external force is applied to the keycap  101  and the elastic element  103  is no longer pushed by the keycap  101 . In response to the elasticity of the elastic element  103 , the elastic element  103  is restored to its original shape to provide an upward elastic restoring force. Consequently, the keycap  101  is returned to its original position where it is not depressed. The structures and the operations of the conventional keyboard device have been mentioned as above. 
     Conventionally, the keys of the keyboard device are arranged in a keyboard matrix. When one key is depressed, a keyboard controller realizes the information of the depressed key according to the column information and the row information and outputs the corresponding key signal. Generally, the intersection between each row and each column of the keyboard matrix represents a corresponding key intersection. When one keycap is triggered, the keyboard device starts to scan the keyboard matrix and recognizes which keycap is depressed. For example, the keyboard controller scans all columns of the keyboard matrix sequentially. If the corresponding signal is received from a specified row when a specified column is scanned by the keyboard controller, the keyboard controller can realize which key is depressed according to the received column information and row information. 
     The minimum matrix unit of the keyboard matrix is composed of four keys. When any of the four keys is depressed, the corresponding key signal can be successfully generated. When two of the four keys are arbitrarily depressed, the keyboard controller can realize which keys are triggered according to the column information and the row information. However, when three keys are simultaneously depressed, the information of two rows and the information of two columns are transmitted to the keyboard controller. Since four keys are defined by two rows and two columns, the keyboard controller cannot recognize the three depressed keys from the four keys according to the column information and the row information only. Under this circumstance, the fourth key is erroneously judged as the on-state key. That is, the fourth key is referred as a ghost key. 
     For avoiding the ghosting problem, some approaches have been disclosed. In accordance with a first approach, the keyboard device is further equipped with plural diodes near the corresponding key intersections. Since the current is allowed to pass through the membrane switch circuit member in one direction through the arrangement of the diodes, the erroneous judgement of the ghosting problem is avoided. However, the approach of installing diodes near the corresponding key intersection still has some drawbacks. Firstly, the diode is not cost-effective. Consequently, the cost of the keyboard device is increased. Secondly, the plural diodes on the membrane switch circuit member increase the thickness of the membrane switch circuit member. The increased thickness of the membrane switch circuit member is detrimental to the slimness of the keyboard device. Thirdly, the process of welding the diodes at the positions near the corresponding key intersections is very complicated. 
     In accordance with a second approach, the keyboard device is not equipped with the keyboard matrix. The output wire of each key is connected with a microprocessor of the keyboard device. Since this approach needs a great number of output wires, it is difficult to install the output circuits. For example, in case that the keyboard device contains 144 keys, the keyboard device comprises 144 output wires. Consequently, it is difficult to install so many output circuits. 
     Therefore, there is a need of providing a keyboard device with low cost and capable of avoiding the ghosting problem. 
     SUMMARY OF THE INVENTION 
     An object of the present invention provides a keyboard device with low cost and capable of avoiding the ghosting problem. 
     In accordance with an aspect of the present invention, there is provided a keyboard device. The keyboard device includes at least one key and a membrane switch circuit member. The at least one key is exposed outside the keyboard device. The membrane switch circuit member is located under the at least one key. When the membrane switch circuit member is pressed by the at least one key, at least one key signal is correspondingly generated. The membrane switch circuit member includes a first board, a second board, a third board and a fourth board. The first board is located under the at least one key, and includes at least one first contact. The second board is located under the first board, and includes at least one second contact and at least one first opening. The third board is located under the second board, and includes at least one third contact and at least one second opening. The fourth board is located under the third board, and includes at least one fourth contact. The at least one first contact, the at least one first opening and the at least one third contact are collaboratively defined as a first key matrix. The at least one second contact, the at least one second opening and the at least one fourth contact are collaboratively defined as a second key matrix. 
     In an embodiment, the at least one first contact, the at least one first opening, the at least one second opening and the at least one fourth contact are collaboratively defined as a third key matrix. 
     In accordance with another aspect of the present invention, there is provided a keyboard device. The keyboard device includes at least one key and a membrane switch circuit member. The at least one key is exposed outside the keyboard device. The membrane switch circuit member is located under the at least one key. When the membrane switch circuit member is pressed by the at least one key, at least one key signal is correspondingly generated. The membrane switch circuit member includes a first board, a second board, a third board and a fourth board. The first board is located under the at least one key, and includes at least one first contact. The second board is located under the first board, and includes at least one second contact and at least one first opening. The third board is located under the second board, and includes at least one third contact and at least one second opening. The fourth board is located under the third board, and includes at least one fourth contact. The at least one first contact, the at least one first opening and the at least one third contact are collaboratively defined as a first key matrix. The at least one first contact, the at least one first opening, the at least one second opening and the at least one fourth contact are collaboratively defined as a second key matrix. 
     In an embodiment, the at least one second contact, the at least one second opening and the at least one fourth contact are collaboratively defined as a third key matrix. 
     In accordance with a further aspect of the present invention, there is provided a keyboard device. The keyboard device includes at least one key and a membrane switch circuit member. The at least one key is exposed outside the keyboard device. The membrane switch circuit member is located under the at least one key. When the membrane switch circuit member is pressed by the at least one key, at least one key signal is correspondingly generated. The membrane switch circuit member includes a first board, a second board, a third board and a fourth board. The first board is located under the at least one key, and includes at least one first contact. The second board is located under the first board, and includes at least one second contact and at least one first opening. The third board is located under the second board, and includes at least one third contact and at least one second opening. The fourth board is located under the third board, and includes at least one fourth contact. The at least one second contact, the at least one second opening and the at least one fourth contact are collaboratively defined as a first key matrix. The at least one first contact, the at least one first opening, the at least one second opening and the at least one fourth contact are collaboratively defined as a second key matrix. 
     In an embodiment, the at least one first contact, the at least one first opening and the at least one third contact are collaboratively defined as a third key matrix. 
     From the above descriptions, the membrane switch circuit member of the keyboard device comprises at least four boards to install various key matrices. Consequently, the plural keys are constituted by various key matrices. Since the conducting lines of different key matrices are independent from each other, the ghosting problem can be overcome. In comparison with the first approach of the conventional technology, it is not necessary to install a great number of diodes in the keyboard device of the present invention. Consequently, the keyboard device of the present invention is cost-effective and capable of avoiding the ghosting problem. In comparison with the second approach of the conventional technology, the keyboard device of the present invention has less number of conducting lines. Consequently, the wiring method of the output circuit is simplified. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating a conventional keyboard device; 
         FIG. 2  is a schematic exploded view illustrating a portion of a keyboard device according to a first embodiment of the present invention; 
         FIG. 3  schematically illustrates some keys of the keyboard device according to the first embodiment of the present invention; 
         FIG. 4  is a schematic cross-sectional view illustrating a portion of a keyboard device according to a second embodiment of the present invention; 
         FIG. 5A  is a schematic cross-sectional view illustrating a portion of a keyboard device according to a third embodiment of the present invention; and 
         FIG. 5B  is a schematic cross-sectional view illustrating another portion of a keyboard device according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For solving the drawbacks of the conventional technologies, the present invention provides a keyboard device. 
     The structure of a keyboard device of the present invention will be described as follow.  FIG. 2  is a schematic exploded view illustrating a portion of a keyboard device according to a first embodiment of the present invention. The keyboard device  2  comprises plural keys  20 , a membrane switch circuit member  21  and a supporting plate  22 . The plural keys  20  are exposed to a top surface of the keyboard device  2  and connected with the supporting plate  22 . When one of the keys  20  is depressed, the key  20  is moved downwardly relative to the supporting plate  22 . Each key  20  comprises a keycap  201 , a connecting element  202  and an elastic element  203 . The keycap  201  is exposed outside the top surface of the keyboard device  2  so as to be depressed by the user. The connecting element  202  is arranged between the supporting plate  22  and the corresponding keycap  201 . The connecting element  202  is used for connecting the supporting plate  22  and the keycap  201  and allowing the keycap  201  to be moved upwardly or downwardly relative to the supporting plate  22 . The elastic element  203  is disposed under the corresponding keycap  201  and penetrated through the corresponding connecting element  202 . The elastic element  203  is used for providing an elastic force to the keycap  201 . In response to the elastic force, the keycap  201  is moved upwardly and returned to its original position. 
     The membrane switch circuit member  21  is arranged between the supporting plate  22  and the plural keys  20 . When the membrane switch circuit member  21  is pressed by one of the keys  20 , a corresponding key signal is generated. The supporting plate  22  is located under the membrane switch circuit member  21 . The plural keys  20  and the membrane switch circuit member  21  are supported by the supporting plate  22 . As shown in  FIG. 3 , the supporting plate  22  comprises plural hooks (not shown) corresponding to the keys  20 . The hooks are connected with the corresponding connecting elements  202 , so that the keycaps  201  are fixed on the supporting plate  22 . 
     In this embodiment, the keyboard device  2  is a keyboard device for a notebook computer. Moreover, the connecting element  202  is a scissors-type connecting element (also referred as a scissors member) that is swung with the movement of the keycap  201 . Moreover, the elastic element  203  is a rubbery elastomer. The examples of the above components are presented herein for purpose of illustration and description only. In another embodiment, the crater-shaped connecting elements for a desktop computer can be used to connect and move the keycaps. In a further embodiment, the keycaps are moved upwardly or downwardly in response to magnetic forces. 
     The structure of the membrane switch circuit member  21  will be described in more details as follows. As shown in  FIG. 2 , the membrane switch circuit member  21  comprises a first board  211 , a second board  212 , a third board  213  and a fourth board  214 . The first board  211  is located under the elastic elements  203  of the plural keys  20 . The first board  211  comprises plural first contacts  2111 . The plural first contacts  2111  are connected with each other through plural first conducting lines. For succinctness, the first conducting lines are not shown in  FIG. 2 . The plural first contacts  2111  and the plural keys  20  are not in a one-to-one arrangement. 
     The second board  212  is located under the first board  211 . The second board  212  comprises plural second contacts  2121  and plural first openings  2122 . The plural first openings  2122  are aligned with the corresponding first contacts  2111 , respectively. The plural second contacts  2121  are connected with each other through plural second conducting lines. For succinctness, the second conducting lines are not shown in  FIG. 2 . The plural second contacts  2121  (and the plural first openings  2122 ) and the plural keys  20  are not in a one-to-one arrangement. 
     The third board  213  is located under the second board  212 . The third board  213  comprises plural third contacts  2131  and plural second openings  2132 . The plural third contacts  2131  are aligned with the corresponding first contacts  2111  and the corresponding first openings  2122 , respectively. The plural second openings  2132  are aligned with the corresponding second contacts  2121 , respectively. The plural third contacts  2131  are connected with each other through plural third conducting lines. For succinctness, the third conducting lines are not shown in  FIG. 2 . The plural third contacts  2131  (and the plural second openings  2132 ) and the plural keys  20  are not in a one-to-one arrangement. 
     The fourth board  214  is located under the third board  213 . The fourth board  214  comprises plural fourth contacts  2141 . The plural fourth contacts  2141  are aligned with the corresponding second contacts  2121  and the corresponding second openings  2132 , respectively. The plural fourth contacts  2141  are connected with each other through plural fourth conducting lines. For succinctness, the fourth conducting lines are not shown in  FIG. 2 . The plural fourth contacts  2141  and the plural keys  20  are not in a one-to-one arrangement. 
     Moreover, one first contact  2111 , one first opening  2122  and one third contact  2131  of the switch circuit member  21  are collaboratively formed as a first key switch  23 . The plural first contacts  2111  of the first board  211 , the plural first openings  2122  of the second board  212  and the plural third contacts  2131  of the third board  213  are formed as plural first key switches  23 . These first key switches  23  are collaboratively formed as a first key matrix M 1  (see  FIG. 3 ). Similarly, one second contact  2121 , one second opening  2132  and one fourth contact  2141  are collaboratively formed as a second key switch  24 . The plural second contacts  2121  of the second board  212 , the plural second openings  2132  of the third board  213  and the plural fourth contacts  2141  of the fourth board  214  are formed as plural second key switches  24 . These second key switches  24  are collaboratively formed as a second key matrix M 2  (see  FIG. 3 ). 
     The keyboard device  2  of the present invention is capable of avoiding the ghosting problem. The principles of avoiding the ghosting problem will be illustrated with reference to  FIGS. 2 and 3 .  FIG. 3  schematically illustrates some keys of the keyboard device according to the first embodiment of the present invention. 
     Some keys  20  of the keyboard device  2  are shown in  FIG. 3 . For example, these keys  20  includes the key “Q”, the key “W”, the key “A” and the key “S”. The plural first key switches  23  of the key “Q”, the key “W” and the key “A” are defined by plural first conducting lines X 1 , X 2  and plural third conducting lines Y 1 , Y 2 . The plural first key switches  23  are constituted as a part of the first key matrix M 1 . The second key switch  24  of the key “S” is defined by a second conducting line X 2 ′ and a fourth conducting line Y 2 ′. The second key switch  24  is a part of the second key matrix M 2 . 
     When the key “Q” is depressed by the user, the components corresponding to the key “Q” are enabled to trigger the corresponding first key switch  23 . The operations of these components are similar to those of the conventional technology, and are not redundantly described herein. Since the first key switch  23  corresponding to the key “Q” is triggered, the first conducting line X 1  and the third conducting line Y 1  generate a corresponding key signal. In other words, the key signal corresponding to the first conducting line X 1  and the third conducting line Y 1  is outputted from the keyboard device  2  to a computer (not shown), which is in communication with the keyboard device  2 . According to the key signal corresponding to the first conducting line X 1  and the third conducting line Y 1 , the computer realizes that the depressed key  20  is the key “Q”. Consequently, a command corresponding to the key “Q” is executed by the computer. 
     When the key “W” is depressed by the user, the components corresponding to the key “W” are enabled to trigger the corresponding first key switch  23 . Since the first key switch  23  corresponding to the key “Q” is triggered, the first conducting line X 1  and the third conducting line Y 2  generate a corresponding key signal. In other words, the key signal corresponding to the first conducting line X 1  and the third conducting line Y 2  is outputted from the keyboard device  2  to the computer. According to the key signal corresponding to the first conducting line X 1  and the third conducting line Y 2 , the computer realizes that the depressed key  20  is the key “W”. Consequently, a command corresponding to the key “W” is executed by the computer. 
     When the key “A” is depressed by the user, the components corresponding to the key “A” are enabled to trigger the corresponding first key switch  23 . Since the first key switch  23  corresponding to the key “A” is triggered, the first conducting line X 2  and the third conducting line Y 1  generate a corresponding key signal. In other words, the key signal corresponding to the first conducting line X 2  and the third conducting line Y 1  is outputted from the keyboard device  2  to the computer. According to the key signal corresponding to the first conducting line X 2  and the third conducting line Y 1 , the computer realizes that the depressed key  20  is the key “A”. Consequently, a command corresponding to the key “A” is executed by the computer. 
     When the key “S” is depressed by the user, the components corresponding to the key “S” are enabled to trigger the corresponding second key switch  24 . Since the second key switch  24  corresponding to the key “S” is triggered, the second conducting line X 2 ′ and the fourth conducting line Y 2 ′ generate a corresponding key signal. In other words, the key signal corresponding to the second conducting line X 2 ′ and the fourth conducting line Y 2 ′ is outputted from the keyboard device  2  to the computer. According to the key signal corresponding to the second conducting line X 2 ′ and the fourth conducting line Y 2 ′, the computer realizes that the depressed key  20  is the key “S”. Consequently, a command corresponding to the key “S” is executed by the computer. 
     From the above descriptions, the plural keys  20  of the keyboard device  2  are constituted by the first key matrix M 1  and the second key matrix M 2 . When the plural first conducting lines X 1 , X 2  and the plural third conducting lines Y 1 , Y 2  are triggered, the first key switches  23  of the first key matrix M 1  are electrically conducted. When the plural second conducting lines X 1 ′, X 2 ′ and the plural fourth conducting lines Y 1 ′, Y 2 ′ are triggered, the second key switches  24  of the second key matrix M 2  are electrically conducted. Since the conducting lines of all keys  20  of the keyboard device  2  are not overlapped, the ghosting problem can be overcome. 
     The present invention further provides a second embodiment, which is distinguished from the first embodiment.  FIG. 4  is a schematic cross-sectional view illustrating a portion of a keyboard device according to a second embodiment of the present invention. The keyboard device  3  comprises plural keys  30 , a membrane switch circuit member  31  and a supporting plate  32 . Each key  30  comprises a keycap  301 , a connecting element  302  and an elastic element  303 . The membrane switch circuit member  31  comprises a first board  311 , a second board  312 , a third board  313  and a fourth board  314 . Except for the structure of the membrane switch circuit member  31 , the structures and functions of the other components are similar to those of the keyboard device  2  of the first embodiment. 
     The structure of the membrane switch circuit member  31  will be described in more details as follows. The first board  311  comprises plural first contacts  3111  and plural second contacts  3112 . The plural first contacts  3111  are connected with each other through plural first conducting lines. For succinctness, the first conducting lines are not shown in  FIG. 4 . The plural second contacts  3112  are connected with each other through plural second conducting lines. For succinctness, the second conducting lines are not shown in  FIG. 4 . 
     The second board  312  is located under the first board  311 . The second board  312  comprises plural third contacts  3121 , plural first openings  3122  and plural second openings  3123 . The plural first openings  3122  are aligned with the corresponding first contacts  3111 , respectively. The plural second openings  3123  are aligned with the corresponding second contacts  3112 , respectively. The plural third contacts  3121  are connected with each other through plural third conducting lines. For succinctness, the third conducting lines are not shown in  FIG. 4 . 
     The third board  313  is located under the second board  312 . The third board  313  comprises plural third openings  3131 , plural fourth contacts  3132  and plural fourth openings  3133 . The plural third openings  3131  are aligned with the corresponding third contacts  3121 , respectively. The plural fourth openings  3133  are aligned with the plural second contacts  3112 , respectively. The plural fourth contacts  3132  are aligned with the corresponding first contacts  3111  and the corresponding first openings  3122 , respectively. The plural fourth contacts  3132  are connected with each other through plural fourth conducting lines. For succinctness, the fourth conducting lines are not shown in  FIG. 4 . 
     The fourth board  314  is located under the third board  313 . The fourth board  314  comprises plural fifth contacts  3141  and plural sixth contacts  3142 . The plural fifth contacts  3141  are aligned with the corresponding third contacts  3121  and the corresponding third openings  3131 , respectively. The plural sixth contacts  3142  are aligned with the corresponding second contacts  3112 , the corresponding second openings  3123  and the corresponding fourth openings  3133 , respectively. The plural fifth contacts  3141  are connected with each other through plural fifth conducting lines. For succinctness, the fifth conducting lines are not shown in  FIG. 4 . The plural sixth contacts  3142  are connected with each other through plural sixth conducting lines. For succinctness, the sixth conducting lines are not shown in  FIG. 4 . 
     Moreover, one first contact  3111 , one first opening  3122  and one fourth contacts  3132  of the switch circuit member  31  are collaboratively formed as a first key switch  33 . The plural first contacts  3111  of the first board  311 , the plural first openings  3122  of the second board  312  and the plural fourth contacts  3132  of the third board  313  are formed as plural first key switches  33 . These first key switches  33  are collaboratively formed as a first key matrix (not shown). Similarly, one third contact  3121 , one third opening  3131  and one fifth contact  3141  are collaboratively formed as a second key switch  34 . The plural third contacts  3121  of the second board  312 , the plural third openings  3131  of the third board  313  and the plural fifth contacts  3141  of the fourth board  314  are formed as plural second key switches  34 . These second key switches  34  are collaboratively formed as a second key matrix (not shown). Similarly, one second contact  3112 , one second opening  3123 , one fourth opening  3133  and one sixth contact  3142  are collaboratively formed as a third key switch  35 . The plural second contacts  3112  of the first board  311 , the plural second openings  3123  of the second board  312 , the plural fourth openings  3133  and the plural sixth contacts  3142  are formed as plural third key switches  35 . These third key switches  35  are collaboratively formed as a third key matrix (not shown). 
     From the above descriptions, the plural keys  30  of the keyboard device  3  are constituted by the first key matrix, the second key matrix and the third matrix. When the first conducting lines and the fourth conducting lines are triggered, the first key switches  33  of the first key matrix are electrically conducted. When the third conducting lines and the fifth conducting lines are triggered, the second key switches  34  of the second key matrix are electrically conducted. When the second conducting lines and the sixth conducting lines are triggered, the third key switches  35  of the third key matrix are electrically conducted. In comparison with the keyboard device  2  of the above embodiment, the keyboard device  3  of this embodiment can be equipped with more keys  30  to avoid the ghosting problem. 
     The present invention further provides a third embodiment, which is distinguished from the above embodiments. Please refer to  FIGS. 5A and 5B .  FIG. 5A  is a schematic cross-sectional view illustrating a portion of a keyboard device according to a third embodiment of the present invention.  FIG. 5B  is a schematic cross-sectional view illustrating another portion of a keyboard device according to a third embodiment of the present invention. The keyboard device  4  comprises plural keys  40 , a membrane switch circuit member  41  and a supporting plate  42 . Each key  40  comprises a keycap  401 , a connecting element  402  and an elastic element  403 . The membrane switch circuit member  41  comprises a first board  411 , a second board  412 , a third board  413 , a fourth board  414  and a fifth board  415 . Except for the structure of the membrane switch circuit member  41 , the structures and functions of the other components are similar to those of the keyboard devices of the above embodiments. 
     The structure of the membrane switch circuit member  41  will be described in more details as follows. The first board  411  comprises plural first contacts  4111 , plural second contacts  4112  and plural third contacts  4113 . The plural first contacts  4111  are connected with each other through plural first conducting lines. For succinctness, the first conducting lines are not shown in the drawings. The plural second contacts  4112  are connected with each other through plural second conducting lines. For succinctness, the second conducting lines are not shown in the drawings. The plural third contacts  4113  are connected with each other through plural third conducting lines. For succinctness, the third conducting lines are not shown in the drawings. 
     The second board  412  is located under the first board  411 . The second board  412  comprises plural first openings  4121 , plural fourth contacts  4122 , plural second openings  4123  and plural third openings  4124 . The plural first openings  4121  are aligned with the corresponding first contacts  4111 , respectively. The plural second openings  4123  are aligned with the corresponding second contacts  4112 , respectively. The plural third openings  4124  are aligned with the corresponding third contacts  4113 . The plural fourth contacts  4122  are connected with each other through plural fourth conducting lines. For succinctness, the fourth conducting lines are not shown in the drawings. 
     The third board  413  is located under the second board  412 . The third board  413  comprises plural fifth contacts  4131 , plural fourth openings  4132 , plural fifth openings  4133 , plural sixth contacts  4134  and plural sixth openings  4135 . The plural fifth contacts  4131  are aligned with the corresponding first contacts  4111  and the corresponding first openings  4121 , respectively. The plural fourth openings  4132  are aligned with the corresponding fourth contacts  4122 , respectively. The plural fifth openings  4133  are aligned with the corresponding second contacts  4112  and the corresponding second openings  4123 , respectively. The plural sixth openings  4135  are aligned with the corresponding third contacts  4113  and the corresponding third openings  4124 , respectively. The plural fifth contacts  4131  are connected with each other through plural fifth conducting lines. For succinctness, the fifth conducting lines are not shown in the drawings. The plural sixth contacts  4134  are connected with each other through plural sixth conducting lines. For succinctness, the sixth conducting lines are not shown in the drawings. 
     The fourth board  414  is located under the third board  413 . The fourth board  414  comprises plural seventh contacts  4141 , plural eighth contacts  4142 , plural seventh openings  4143  and plural eighth openings  4144 . The plural seventh contacts  4141  are aligned with the corresponding fourth contacts  4122  and the corresponding fourth openings  4132 , respectively. The plural eighth contacts  4142  are aligned with the corresponding second contacts  4112 , the corresponding second openings  4123  and the plural fifth openings  4133 , respectively. The plural seventh openings  4143  are aligned with the corresponding sixth contacts  4134 , respectively. The plural eighth openings  4144  are aligned with the corresponding third contacts  4113 , the corresponding third openings  4124  and the corresponding sixth openings  4135 , respectively. The plural seventh contacts  4141  are connected with each other through plural seventh conducting lines. For succinctness, the seventh conducting lines are not shown in the drawings. The plural eighth contacts  4142  are connected with each other through plural eighth conducting lines. For succinctness, the eighth conducting lines are not shown in the drawings. 
     The fifth board  415  is located under the fourth board  414 . The fifth board  415  comprises plural ninth contacts  4151  and plural tenth contacts  4152 . The plural ninth contacts  4151  are aligned with the corresponding sixth contacts  4134  and the corresponding seventh openings  4143 . The plural tenth contacts  4152  are aligned with the corresponding third contacts  4113 , the corresponding third openings  4124 , the corresponding sixth openings  4135  and the corresponding eighth openings  4144 . The plural ninth contacts  4151  are connected with each other through plural ninth conducting lines. For succinctness, the ninth conducting lines are not shown in the drawings. The plural tenth contacts  4152  are connected with each other through plural tenth conducting lines. For succinctness, the tenth conducting lines are not shown in the drawings. 
     Moreover, one first contact  4111 , one first opening  4121  and one fifth contact  4131  are collaboratively formed as a first key switch  43 . The plural first contacts  4111  of the first board  411 , the plural first openings  4121  of the second board  412  and the plural fifth contacts  4131  of the third board  413  are formed as plural first key switches  43 . These first key switches  43  are collaboratively formed as a first key matrix (not shown). Similarly, one fourth contact  4122 , one fourth opening  4132  and one seventh contact  4141  are collaboratively formed as a second key switch  44 . The plural fourth contacts  4122  of the second board  412 , the plural fourth openings  4132  of the third board  413  and the plural seventh contacts  4141  of the fourth board  414  are formed as plural second key switches  44 . These second key switches  44  are collaboratively formed as a second key matrix (not shown). Similarly, one second contact  4112 , one second opening  4123 , one fifth opening  4133  and one eighth contact  4142  are collaboratively formed as a third key switch  45 . The plural second contacts  4112  of the first board  411 , the plural second openings  4123  of the second board  412 , the plural fifth openings  4133  of the third board  413  and the plural eighth contacts  4142  of the fourth board  414  are formed as plural third key switches  45 . These third key switches  45  are collaboratively formed as a third key matrix (not shown). 
     Similarly, one sixth contact  4134 , one seventh opening  4143  and one ninth contact  4151  are collaboratively formed as a fourth key switch  46 . The plural sixth contacts  4134  of the third board  413 , the plural seventh openings  4143  of the fourth board  414  and the plural ninth contacts  4151  of the fifth board  415  are formed as plural fourth key switches  46 . These fourth key switches  46  are collaboratively formed as a fourth key matrix (not shown). Similarly, one third contact  4113 , one third opening  4124 , one sixth opening  4135 , one eighth opening  4144  and one tenth contact  4152  are collaboratively formed as a fifth key switch  47 . The plural third contacts  4113  of the first board  411 , the plural third openings  4124  of the second board  412 , the plural sixth openings  4135  of the third board  413 , the plural eighth openings  4144  of the fourth board  414  and the plural tenth contacts  4152  of the fifth board  415  are formed as plural fifth key switches  47 . These fifth key switches  47  are collaboratively formed as a fifth key matrix (not shown). 
     From the above descriptions, the plural keys  40  of the keyboard device  4  are constituted by the first key matrix, the second key matrix, the third matrix, the fourth matrix and the fifth matrix. When the first conducting lines and the fifth conducting lines are triggered, the first key switches  43  of the first key matrix are electrically conducted. When the fourth conducting lines and the seventh conducting lines are triggered, the second key switches  44  of the second key matrix are electrically conducted. When the second conducting lines and the eighth conducting lines are triggered, the third key switches  45  of the third key matrix are electrically conducted. When the sixth conducting lines and the ninth conducting lines are triggered, the fourth key switches  46  of the fourth key matrix are electrically conducted. When the third conducting lines and the tenth conducting lines are triggered, the fifth key switches  47  of the fifth key matrix are electrically conducted. In comparison with the keyboard device  2  of the above embodiment, the keyboard device  4  of this embodiment further comprises the fourth key matrix and the fifth key matrix. The keyboard device  4  of this embodiment can be equipped with more keys  40  to avoid the ghosting problem. 
     The following two aspects should be specially described. Firstly, the supporting plate of the keyboard device is not restrictedly located under the membrane switch circuit member. For example, the supporting plate may be located over the membrane switch circuit member according to the practical requirements. However, the supporting plate comprises supporting plate openings corresponding to the elastic elements. The elastic elements are penetrated through the supporting plate openings. Consequently, the membrane switch circuit member can be triggered by the elastic elements. Secondly, the plural key matrices of the keyboard device are not overlapped with each other. It is noted that the examples of the key matrices are not restricted. That is, the example of the key matrices may be varied according to the practical requirements. 
     From the above descriptions, the membrane switch circuit member of the keyboard device comprises at least four boards to install various key matrices. Consequently, the plural keys are constituted by various key matrices. Since the conducting lines of different key matrices are independent from each other, the ghosting problem can be overcome. In comparison with the first approach of the conventional technology, it is not necessary to install a great number of diodes in the keyboard device of the present invention. Consequently, the keyboard device of the present invention is cost-effective and capable of avoiding the ghosting problem. In comparison with the second approach of the conventional technology, the keyboard device of the present invention has less number of conducting lines. Consequently, the wiring method of the output circuit is simplified. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.