Patent Publication Number: US-9837220-B2

Title: Keyswitch structure

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to a keyswitch structure. Particularly, the invention relates to a keyswitch structure of low noise design. 
     2. Description of the Prior Art 
     Keyboard devices generally have regular-sized keys and larger-sized keys, such as Space key, Enter key, Caps Lock key, Shift key. The larger-sized keys usually have one or more linking bars to enhance the strength of the keycap. Moreover, by means of the linking bar, when the user presses the keycap on the non-center portion, the larger-sized key is prevented from slanting during the pressing operation. The linking bar is generally connected to the engaging portion that protrudes from the lower surface of the keycap. When the user presses the keycap, the engaging portion protruding from the keycap will hit the baseplate and generate loud noise, impairing the operation smoothness and comfortability. 
     Therefore, how to effectively reduce the noise generated by the keycap hitting the baseplate is one of the major considerations for keyswitch design. 
     SUMMARY OF THE INVENTION 
     In view of the prior arts, it is an object of the invention to provide a keyswitch structure to effectively reduce the operation noise. 
     It is another object of the invention to provide a keyswitch structure of low noise design that can provide a buffer effect to eliminate or reduce noise generated by direct collision of key elements during operation. 
     It is yet another object of the invention to provide a keyswitch structure having a buffer design that utilizes the multi-layered membrane switch layer to effectively reduce noise without increasing the material cost. 
     In an embodiment, the invention provides a keyswitch structure including a keycap having a lower surface and an engaging portion protruding from the lower surface, the keycap moving to a lower position when the keycap is pressed, a linking bar coupled with the engaging portion, a distal end of the engaging portion being lower than the linking bar when the keycap moves to the lower position, a baseplate disposed below the keycap, the baseplate having a recessed space corresponding to the engaging portion, and a buffer film disposed on the baseplate, the buffer film substantially extending over the recessed space and having a deformable portion corresponding to the recessed space, wherein when the keycap moves toward the baseplate to the lower position, the distal end of the engaging portion pushes the deformable portion to make the deformable portion extend into the recessed space. 
     In an embodiment, the recessed space is a through hole or a groove formed on the baseplate. 
     In an embodiment, the buffer film is a membrane switch layer including at least one first type layer and at least one second type layer; the first type layer has an opening formed at location corresponding to the recessed space, and the second type layer extends over the recessed space to constitute the deformable portion. 
     In an embodiment, the deformable portion has a recessed groove; the recessed groove opens toward the keycap or the baseplate. 
     In an embodiment, the deformable portion has two recessed grooves, and the two recessed grooves open toward the keycap and the baseplate, respectively. 
     In an embodiment, the membrane switch layer includes multiple second type layers extending over the opening, and the total thickness of the second type layers is equal to or less than 0.075 mm. 
     In an embodiment, the buffer film includes a membrane switch layer and a sheet, wherein the membrane switch layer has a through hole corresponding to the engaging portion. The sheet extends over the through hole to serve as the deformable portion. When the keycap moves toward the baseplate, the engaging portion presses the sheet through the through hole to make the sheet extend into the recessed space. 
     In an embodiment, the sheet is a polyester sheet or a rubber sheet, and the thickness of the sheet is smaller than the thickness of the membrane switch layer. 
     In an embodiment, the linking bar includes a first linking bar and a second linking bar. The engaging portion includes at least one first engaging portion and a second engaging portion connected to the first linking bar and the second linking bar, respectively. The second linking bar is neighboring to the edge of the keycap, the first linking bar is neighboring to the center of the keycap, and the length of the first engaging portion is larger than or equal to the length of the second engaging portion. 
     In an embodiment, the keycap has a longitudinal axis; the linking bar has a middle section and two end sections extending from two ends of the middle section, respectively. The two end sections are neighboring to the opposite ends of the longitudinal axis and the middle section is neighboring to the center of the longitudinal axis, and the length of the first engaging portion connected to the middle section is larger than the length of the first engaging portion connected to the end section. 
     In an embodiment, the two end sections are positioned higher than the middle section, so the cross-section of the linking bar is curved as U-shaped. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are an exploded view and a partial assembled view of the keyswitch structure according to an embodiment of the invention; 
         FIGS. 1C and 1D  are schematic views of  FIG. 1A  before and after the keyswitch structure is pressed, respectively; 
         FIGS. 2A and 2B  are schematic views of the engaging portion according to different embodiments of the invention; 
         FIG. 3  is schematic view of the baseplate according to another embodiment of the invention; 
         FIGS. 4A to 4E  are schematic views of the membrane switch layer serving as the buffer film according to different embodiments of the invention; 
         FIGS. 5A and 5B  are schematic views of the buffer film according to different embodiments of the invention; 
         FIGS. 6A and 6B  are an exploded view and a partial assembled view of the keyswitch structure according to another embodiment of the invention; 
         FIGS. 6C and 6D  are schematic views of  FIG. 6A  before and after the keyswitch structure is pressed, respectively; 
         FIGS. 7A and 7B  are an exploded view and a partial assembled view of the keyswitch structure according to another embodiment of the invention; 
         FIGS. 7C and 7D  are schematic views of  FIG. 7A  before and after the keyswitch structure is pressed, respectively; 
         FIGS. 8A and 8B  are schematic views of the engaging portion according to different embodiments of the invention; and 
         FIG. 9  is a schematic view of the keyboard device according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention provides a keyswitch structure of low noise design and a keyboard having the keyswitch structure. Particularly, the keyswitch structure of the invention can be a keyswitch of the computer keyboard, but not limited thereto. The keyswitch structure of the invention can be a button, a numeral key, etc. of other electronic devices. The keyswitch structure of the invention can be any suitable keyswitch structure having an engaging portion, particularly a keyswitch structure having the engaging portion connected to the linking bar, such as larger-sized key of the keyboard, but not limited thereto. Hereafter, a computer keyboard is illustrated as an example to explain the details of the keyswitch structure of the invention. 
     As shown in  FIGS. 1A and 6A , in an embodiment, the keyswitch structure  100 / 200  of the invention includes a keycap  110 , a linking bar  122 / 124 , a baseplate  130 , and a buffer film  140 . The keycap  110  is disposed over the baseplate  130  and is downward/upward movable relative to the baseplate  130 . The linking bar  122  is connected to the keycap  110 , wherein the linking bar  122 / 124  generally has the following functions: (1) as shown in  FIG. 1A , to enhance the structural strength of the keycap  110 , or (2) as shown in  FIG. 6A , to improve the linking effect of the keycap  110 , so that when the user presses the keycap on the right side, the whole keycap including the left side can descend simultaneously to prevent the keycap  110  from exhibiting a slant state with the left side higher and the right side lower. The buffer film  140  is disposed on the baseplate  130  to provide the impact absorption effect when the keycap  110  moves toward the baseplate  130  (as described later). It is noted that the keyswitch structure  100 / 200  may further include other components, such as a support mechanism (e.g. scissors-like support, a butterfly-like support) to support the keycap  110  moving relative to the baseplate  130  and a restoring unit including elastic restoring unit such as rubber dome or magnetic restoring unit such as magnets to provide the restoring force, making the keycap  110  return to its original position after being pressed, which are not shown in the drawings. 
     In the embodiment of  FIG. 1A , the linking bar  122  is only connected to the keycap  110  to increase the structural strength of the keycap  110 . The linking bar  122  is preferably a frame-like linking bar defining a non-closed loop. For example, the linking bar  122  can have a rectangular shape and an opening  122   a  is formed between two ends of the linking bar  122  to increase the deformability of the linking bar  122  and improve the assembly convenience as the linking bar  122  is to be connected to the keycap  110 . Moreover, the linking bar  122  preferably has a circular cross section for the bar body and can be formed by bending a metal line, but not limited thereto. In other embodiments, the bar body of the linking bar  122  may have an oval or square-shaped cross section, and the linking bar  122  can be made from any suitable materials to enhance the strength of the keycap  110  according to the design requirements. 
     The keycap  110  has an engaging portion  112  for coupling with the linking bar  122 . In this embodiment, the keycap  110  has a plurality of engaging portions  112 , wherein the plurality of engaging portions  122  are disposed on the lower surface  110   a  of the keycap  110  and correspond to the frame-shaped linking bar  122  to respectively couple with the corresponding portions of the linking bar  122 . In other words, the plurality of engaging portions  112  are distributed in a frame shape on the lower surface  110   a  of the keycap  110 . Moreover, the engaging portion  112  protrudes from the lower surface  110   a  of the keycap  110 . As shown in  FIG. 2A , the keycap  110  includes a key top  111   a  and a key skirt  111   b  encirclingly connected to the key top  111   a . The engaging portion  112  protrudes from the lower surface  110   a  of the key top  111   a  and extends downwardly beyond the bottom surface of the key skirt  111   b . As such, a distal end of the engaging portion  112  protrudes beyond the bottom surface of the key skirt  111   b . That is, the distal end of the engaging portion  112  is the end of the engaging portion  112  that is far away from the lower surface  110   a  of the keycap  110 . 
     In an embodiment, as shown in  FIG. 2A , the engaging portion  112  is a hook-like structure having an engaging groove  112   a , and the engaging groove  112   a  has a groove opening  112   b  at the distal end (i.e. the end that is far away from the lower surface  110   a ) of the hook-like structure. The groove opening  112   b  allows the bar body of the linking bar  122  to enter the engaging groove  112   a  to couple with the engaging portion  112 . When the linking bar  122  enters the engaging groove  112   a  from the groove opening  112   b  to engage with the engaging groove  112   a , the distal end of the engaging portion  112  is lower than the bottom of the linking bar  122 . In other words, in this embodiment, the depth of the engaging groove  112   a  (i.e. the distance from the distal end of the engaging portion to the bottom of the engaging groove) is larger than the diameter or thickness of the linking bar  122 , which is measured along the direction parallel to a virtual straight line running through the keycap  110  to the baseplate  130 , i.e. the vertical direction, so that the bar body of the linking bar  122  can be substantially fully received in the engaging groove  112   a . That is, the portion of the linking bar  122  that couples with the engaging portion  122  substantially does not protrude out of the engaging groove  112   a , so that the distal end of the engaging portion  112  is lower than the portion of the linking bar  122  that couples with the engaging portion  122 . In this embodiment, the width of the groove opening  112   b  is preferably smaller than the diameter of the bar body of the linking bar  122 , which is measured along the horizontal direction. Consequently, when the linking bar  122  enters the engaging groove  112   a  and couples with the engaging portion  112 , the movement of the linking bar  122  out of the engaging opening  112   b  can be restricted to prevent the detachment of the linking bar  122  from the engaging portion  112 . Moreover, the sidewall of the engaging portion  112  that defines the engaging groove  112   a  preferably has an appropriate thickness to provide the deformability and promote the convenience of connecting the linking bar  122  to the engaging portion  112 . In other words, when the linking bar  122  enters the engaging groove  112   a  from the groove opening  112   b , the sidewall of the engaging portion  112  that defines the engaging groove  112   a  can elastically expand outward to facilitate the entrance of the linking bar  122  into the engaging groove  112   a.    
     It is noted that  FIG. 2A  illustrates the linking bar  122  entering the engaging groove  112   a  from the distal end of the engaging portion  112  (i.e. from the bottom surface of the engaging portion  112 ) to couple with the engaging portion  112 , but not limited thereto. In another embodiment, as show in  FIG. 2B , the groove opening  112   b ′ can be formed on the side surface of the engaging portion  112 ′, so that the linking bar  122  can enter the engaging groove  112   a ′ from the side of the engaging portion  112 ′ to couple with the engaging portion  112 ′. 
     Furthermore, the baseplate  130  is disposed below the keycap  110 , and the baseplate  130  has a recessed space  132  corresponding to the engaging portion  112  of the keycap  110 . In this embodiment, the recessed space  132  is preferably a through hole formed on the baseplate  130  (as shown in  FIG. 1C ), but not limited thereto. In another embodiment, as shown in  FIG. 3 , the recessed space  132 ′ can be a groove or blind hole formed on the baseplate  130 . When the keycap  110  moves toward the baseplate  130 , the recessed space  132  provides an escaping room for the engaging portion  112 , so that the engaging portion  112  can move into the recessed space  132 . In this embodiment, the baseplate  130  is preferably a metal plate, but not limited thereto. 
     As shown in  FIGS. 1A and 1C , the buffer film  140  is disposed on the baseplate  130 , wherein the buffer film  140  substantially extends over the recessed space  132 , and the buffer film  140  has a deformable portion  142  corresponding to the recessed space  132 . That is, the deformable portion  142  substantially covers the recessed space  132  as the buffer film  140  is disposed on the baseplate  130 . In general, the deformable portion  142  can be formed by modifying the thickness, material, or shape thereof to have a greater deformability relative to other portions of the buffer film  140 . For example, the deformable portion  142  can be (a) a portion of the buffer film  140  that has a relatively thinner thickness, (b) a portion of the buffer film  140  that has a relatively softer material formed by ejection molding or adhering, or (c) a portion of the buffer film  140  that has a shape susceptible to deformation, such as a tongue-like portion with only one end connected to the buffer film  140 . 
     In a preferred embodiment, the deformable portion  142  of the buffer film  140  is a portion having a relatively thinner thickness, so that the deformable portion  142  has a greater elastic deformability compared to the other portions of the buffer film  140 . With the deformable portion  142 , the buffer film  140  can be designed to have a thicker thickness at most portions other than the deformable portion  142 , so that the buffer film  140  is less breakable to increase the manufacturability. In this embodiment, the thickness of the deformable portion  142  is preferably equal to or less than 0.075 mm, but not limited thereto. The deformable portion  142  of the buffer film  140  preferably covers on the recessed space  132 , and the rest of the buffer film  140  (i.e. the portions of the buffer film  140  other than the deformable portion  142 ) covers on the surface of the baseplate  130  around the recessed space  132 . Accordingly, when the engaging portion  112  of the keycap  110  moves downwardly, the deformable portion  142  can deform to provide the buffering effect to reduce the impact noise. As shown in  FIG. 1D , when the keycap  110  is pressed, the keycap  110  will move to a lower position. That is, when the keycap  110  moves toward the baseplate  130  to the lower position, the distal end of the engaging portion  112  is lower than the linking bar  122  and pushes the deformable portion  142  to make the deformable portion  142  extend into the recessed space  132 . Particularly, when the keycap  110  moves toward the baseplate  130 , the engaging portion  112  protruding the bottom surface of the key skirt  111   b  of the keycap  110  will hit the deformable portion  142  of the buffer film  140  first, and the deformable portion  142  then deforms downwardly and extends into the recessed space  132  of the baseplate  130 . By such a design, without increasing the key height, the keyswitch structure  100  provides the engaging portion  112  of the keycap  110  with enough space for moving downward, and the deformable portion  142  of the buffer film  140  serves like a bouncing pad to absorb the impact noise generated by the engaging portion  112 . 
     In a preferred embodiment, the buffer film  140  is a membrane switch layer, wherein a portion of the membrane switch layer is partially hollowed out to form a blind hole and serves as the deformable portion  142 . Particularly, the membrane switch layer consists of multiple layers, wherein at least one layer of the membrane switch layer is formed with an opening corresponding to the recessed space  132 , and at least another layer of the membrane switch layer substantially extends over the opening to constitute the deformable portion  142 . In other words, the membrane switch layer includes at least one first type layer and at least one second type layer, wherein the first type layer has the opening formed at location corresponding to the recessed space  132 , and the second type layer extends over the recessed space to constitute the deformable portion  142 . The total thickness of the portion of the second type layer extending over the opening (i.e. the deformable portion) is preferably equal to or less than 0.075 mm. 
     For example, as shown in  FIG. 4A , in an embodiment, the membrane switch layer  140   a  is a three-layered structure, wherein the first layer  144  and the third layer  148  are circuit layers, and the second layer  146  disposed between the first layer  144  and the third layer  148  is a spacer layer to isolate both circuit layers  144  and  148 . When the keycap  110  moves toward the baseplate  130  to trigger the membrane switch layer  140   a , the conductor pads formed on the first layer  144  and the third layer  148  contact each other to output the trigger signal. In this embodiment, the first layer  144  and the second layer  146  are the first type layer and have openings  144   a  and  146   a  formed right above the recessed space  132 , respectively. That is, the openings  144   a  and  146   a  are formed at location corresponding to the recessed space  132 . The openings  144   a  and  146   a  are aligned and communicate with each other. The third layer  148  is the second type layer that extends beneath the opening  146   a  to constitute the deformable portion  142 , i.e. the third layer  148  covers the opening  146   a  from the bottom side, wherein the membrane switch layer  140   a  has a recessed groove on the top side, and the recessed groove opens toward the keycap  110  (i.e. a downward concave portion). In other words, the portion of the third layer  148  that corresponds to the openings  144   a ,  146   a  is the deformable portion  142 , which receives the engaging portion  112  and provides the buffering effect. The thickness of the deformable portion  142  equals to the thickness of the third layer  148 . 
     It is noted that when the buffer film is a membrane switch layer, the deformable portion  142  may have different configurations by manipulating the multiple-layered structure of the membrane switch layer, not limited to the embodiment of  FIG. 4A . In another embodiment, as shown in  FIG. 4B , the first layer  144  and the third layer  148  of the membrane switch layer  140   b  are the first type layer and respectively have openings  144   a  and  148   a  formed at location corresponding to (i.e. right above) the recessed space  132 . The openings  144   a  and  148   a  do not communicate with each other and are separated by the second layer  146 . That is, the second layer  146  is the second type layer that extends between the openings  144   a  and the  148   a  to constitute the deformable portion  142 . The membrane switch layer  140   b  has two recessed grooves on the top side and the bottom side, respectively. The upper recessed groove constituted by the opening  144   a  and positioned above the second layer  146  opens toward the keycap  110  (i.e. a downward concave groove), and the recessed groove constituted by the opening  148   a  and the positioned below the second layer  146  opens toward the baseplate  130  (i.e. an upward concave groove). In this embodiment, the portion of the second layer  146  that corresponds to the openings  144   a ,  148   a  is the deformable portion  142 , which receives the engaging portion  112  and provides the buffering effect. The thickness of the deformable portion  142  equals to the thickness of the second layer  146   
     In another embodiment, as shown in  FIG. 4C , the second layer  146  and the third layer  148  of the membrane switch layer  140   c  are the first type layer and have openings  146   a  and  148   a  formed right above the recessed space  132 , respectively. That is, the openings  146   a  and  148   a  are formed at location corresponding to the recessed space  132 . The openings  146   a  and  148   a  are aligned and communicate with each other. The first layer  144  is the second type layer that extends over the opening  146   a  to constitute the deformable portion  142 , i.e. the first layer  144  covers the opening  146   a  from the top side, wherein the membrane switch layer  140   c  has a recessed groove on the bottom side, and the recessed groove opens toward the baseplate  130  (i.e. an upward concave portion). In other words, the portion of the first layer  144  that corresponds to the openings  146   a ,  148   a  is the deformable portion  142 , which receives the engaging portion  112  and provides the buffering effect. The thickness of the deformable portion  142  equals to the thickness of the first layer  144 . 
     In another embodiment, as shown in  FIG. 4D , the first layer  144  of the membrane switch layer  140   d  is the first type layer and has an opening  144   a  formed at location corresponding to the recessed space  132  (i.e. right above the recessed space  132 ). The second layer  146  and the third layer  148  are the second type layers that extend beneath the opening  144   a  to constitute the deformable portion  142 , wherein the membrane switch layer  140   d  has a recessed groove on the top side, and the recessed groove opens toward the keycap  110 . In other words, the portions of the second layer  146  and the third layer  148  that correspond to the opening  144   a  are the deformable portion  142 , which receives the engaging portion  112  and provides the buffering effect. The thickness of the deformable portion  142  equals to the total thickness of the second layer  146  and the third layer  148  (i.e. the total thickness of the second type layers) and preferably equals to or less than 0.075 mm. 
     In another embodiment, as shown in  FIG. 4E , the third layer  148  of the membrane switch layer  140   e  is the first type layer and has an opening  148   a  formed at location corresponding to the recessed space  132  (i.e. right above the recessed space  132 ). The first layer  144  and the second layer  146  are the second type layers that extend over the opening  148   a  to constitute the deformable portion  142 , i.e. that cover the opening  148   a  from the top side, wherein the membrane switch layer  140   e  has a recessed groove on the bottom side, and the recessed groove opens toward the baseplate  130 . In other words, the portions of the first layer  144  and the second layer  146  that correspond to the opening  148   a  are the deformable portion  142 , which receives the engaging portion  112  and provides the buffering effect. The thickness of the deformable portion  142  equals to the total thickness of the first layer  144  and the second layer  146  (i.e. the second type layers) and preferably equals to or less than 0.075 mm. 
     In another embodiment, as shown in  FIGS. 5A and 5B , the buffer film  140  includes a membrane switch layer  140   f  and a sheet  141 . The membrane switch layer  140   f  has a through hole  149  corresponding to the engaging portion  112 , and the sheet  141  extends beneath or over the through hole  149  from one side to serve as the deformable portion  142 . When the keycap  110  moves toward the baseplate  130 , the engaging portion  112  presses the sheet  141  through the through hole  149  to make the sheet  141  extend into the recessed space  132 . Particularly, in the embodiment of  FIG. 5A , the sheet  141  extends beneath the through hole  149  to serve as the deformable portion  142 , i.e. the sheet  141  covers the through hole  149  from the bottom side. When the keycap  110  moves toward the baseplate  130 , the engaging portion  112  passes through the through hole  149  to push the sheet  141  toward the recessed space  132  and make the sheet  141  deform and extend into the recessed space  132  (similar to  FIG. 1D ). The membrane switch layer  140   f  may have a multiple-layered structure as described above; the first layer  144 , the second layer  146 , and the third layer  148  have openings  144   a ,  146   a , and  148   a , respectively. The openings  144   a ,  146   a , and  148   a  are aligned and communicate with each other to form the through hole  149  at location corresponding to the recessed space  132 . In the embodiment of  FIG. 5A , the sheet  141  extends beneath the through hole  149  (i.e. covers the third layer  148  from the bottom side), and the portion of the sheet  141  that is located beneath the through hole  149  (i.e. the portion of the sheet  141  that corresponds to the through hole  149 ) serves as the deformable portion  142 , which receives the engaging portion  112  and provides the buffering effect. In the embodiment of  FIG. 5B , the sheet  141  extends over the through hole  149  (i.e. covers the first layer  144  from the top side) and serves as the deformable portion  142 , so that the sheet  141  can be further disposed with a plurality of rubber domes for the keyswitches of the keyboard, and the plurality of rubber domes can be assembled onto the baseplate  130  by a single step. That is, the sheet  141  can be the sheet that connects the plurality of rubber domes, i.e. rubber dome sheet. In the embodiment of  FIG. 5B , when the keycap  110  moves toward the baseplate  130 , the engaging portion  112  presses the sheet  141  to pass through the through hole  149  to make the sheet  141  extend into the recessed space  132 . In an embodiment, the sheet  141  can be a polyester sheet or a rubber sheet, and the thickness of the sheet  141  is preferably smaller than the thickness of the membrane switch layer  140   f . For example, the sheet  141  can be a Mylar sheet, and the thickness thereof is preferably equal to or less than 0.075 mm, but not limited thereto. It is noted that when the deformable portion  142  is made of a material having greater deformability, the thickness of the deformable portion  142  can be larger than 0.075 mm, so that the deformable portion  142  still provides a sufficient deformation amount to absorb the impact noise generated by the engaging portion  112 . 
     In addition,  FIG. 1  illustrates the linking bar  122  only connected to the keycap  110 , but according to the key size or design requirements, the linking bar may have different configuration or amount. In another embodiment, as shown in  FIG. 6A to 6C , the keyswitch structure  200  of the invention includes a keycap  110 , a linking bar  124 , a baseplate  130 , and a buffer film  140 , wherein the keycap  110 , the baseplate  130 , and the buffer film  140  respectively have the engaging portion, the recessed space  132 , the deformable portion  142  as described above, and the buffer film  140  can be embodied as the membrane switch layer  140   a  to  140   e  shown in  FIG. 4A to 4E  or the combination of the sheet  141  and the membrane switch layer  140   f  shown in  FIGS. 5A and 5B . Hereafter, the differences between this embodiment and  FIG. 1A  will be described in detail. Particularly, the linking bar  124  is connected between the keycap  110  and the baseplate  130 . That is, one end of the linking bar  124  is connected to the keycap  110 , and the other end of the linking bar  124  is connected to the baseplate  130  to improve the linking effect of the keycap  110 . As such, when the user presses the keycap  110  on the right side, the whole keycap  110  including the left side can descend simultaneously to prevent the keycap  110  from exhibiting a slant state with the left side higher and the right side lower. In this embodiment, the linking bar  124  is a U-shaped bar, and two ends of the U-shaped bar each has an extension part  124   a  bending toward the opening of the U-shaped bar. The extension part  124   a  serves as an engaging hook to slidably engage with the baseplate  130 . Particularly, in addition to the recessed space  132 , the baseplate  130  further includes a connection part  134  for engaging with the extension  124   a  of the linking bar  124 . In this embodiment, the connection part  134  is a connection mechanism which is bent upward from the surface of the baseplate  130 , wherein the connection part  134  has a slot  134   a . It is noted that the buffer film  140  correspondingly has an opening  143 , which allows the connection part  134  to extend out, so that the extension part  124   a  can be slidably inserted into the slot  134   a . When the keycap  110  moves relative to the baseplate  130 , the extension part  124   a  moves within the slot  134   a  to increase the moving stability of the keycap  110 . Corresponding to the configuration of linking bar  124 , the keycap  110  has an engaging portion  114  for coupling with the linking bar  124 . In this embodiment, a plurality of engaging portions  114  are disposed on the lower surface  110   a  of the keycap  110  to connect corresponding portions of the bar body of the linking bar  124 , respectively. Similar to the engaging portion  112 , the engaging portion  114  protrudes from the lower surface  110   a  of the keycap  110 , and the distal end of the engaging portion  114  extends beyond the bottom surface of the key skirt. It is noted that the engaging portion  114  can be a hook-like structure similar to those in  FIG. 2A  or  FIG. 2B  to make the distal end of the engaging portion  114  be lower than the bottom of the linking bar  124  and will not elaborate again. As shown in  FIG. 6D , when the keycap  110  moves toward the baseplate  130  to the lower position, the distal end of the engaging portion  114  is lower than the linking bar  124 , and the distal end of the engaging portion  114  pushes the deformable portion  142  to make the deformable portion  142  extend into the recessed space  132 . By such a design, the keyswitch structure  200  provides the engaging portion  114  of the keycap  110  with enough space for moving downward, and the deformable portion  142  of the buffer film  140  serves like a bouncing pad to absorb the impact noise generated by the engaging portion  114 . 
     In another embodiment, as shown in  FIG. 7A to 7C , the keyswitch structure  300  of the invention includes a keycap  110 , linking bars  122  and  124 , a baseplate  130 , and a buffer film  140 . In other words, the keyswitch structure  300  has both the kinking bar  122  of  FIG. 1A  and the linking bar  124  of  FIG. 6A , and the keycap  110  has a plurality of engaging portions  112  and  114 . In this embodiment, the linking bar  124  is preferably disposed on an outer side of the linking bar  122  to serve as the connection bar between the keycap  110  and the baseplate  130 . That is, the linking bar  124  is neighboring to the edge of the keycap  110 , and the linking bar  122  is neighboring to the center of the keycap  110 . Moreover, the recessed space  132  of the baseplate  130  and the deformable portion  142  can be designed to have appropriate size and location, so that adjacent engaging portions  112  and  114  can push different parts of a same deformable portion  142  to make different parts of the deformable portion  142  extend into a same recessed space  132  (as shown in  FIG. 7D ), but not limited thereto. In another embodiment, the recessed space  132  of the baseplate  130  and the deformable portion  142  of the buffer film  140  correspond to the engaging portion  112  or  114  separately, so that the engaging portions  112  and  114  can push different deformable portions  142  and make the deformable portions  142  extend into corresponding recessed spaces  132 , respectively. 
     In an embodiment, as shown in  FIG. 8A , the linking bar  122  preferably has a curved cross-section, so that the middle section  122   b  of the linking bar  122  is lower than the two end sections  122   c . Specifically, the keycap  110  has a longitudinal axis, and the linking bar  122  has a middle section  122   b  and two end sections  122   c  respectively extending from two ends of the middle section  122   b . The two end sections  122   c  are neighboring to the opposite ends of the longitudinal axis and the middle section  122   b  is neighboring to the center of the longitudinal axis. The two end sections  122   c  are positioned higher than the middle section  122   b , so the cross-section of the linking bar  122  is curved as U-shaped. Correspondingly, the length of the engaging portion  1121  connected to the middle section  122   b  is larger than the length of the engaging section  1122  connected to the end section  122   c , and the engaging portion  1121  is disposed closer to the center of the keycap  110  than the engaging portion  1122  is. That is, the distance of the engaging portion  1121  extending from the lower surface  110   a  of the keycap  110  to the bottom of the engaging groove  1121   a  is larger than the distance of the engaging portion  1122  extending from the lower surface of the keycap  110  to the bottom of the engaging groove  1122   a , so that the linking bar  122  can maintain the U-shaped cross section. 
     Moreover, the length of the engaging portion  112  that is connected to the linking bar  122  is preferably larger than (as shown in  FIG. 8B ) or equal to (as shown in  FIG. 7C ) the length of the engaging portion  114  that is connected to the linking bar  124  disposed on the outer side. Specifically, the engaging portion (e.g.  112 ) disposed on the inner side of the lower surface  110   a  of the keycap  110  has a larger length than the engaging portion (e.g.  114 ) disposed on the outer side. That is, from the cross-sectional view shown in  FIG. 8B , the engaging portion (e.g.  112 ) closer to the center of the keycap  110  preferably has a larger length than the engaging portion (e.g.  114 ) closer to the edge of the keycap  110 . 
     In another embodiment, as shown in  FIG. 9 , the invention provides a keyboard device  10  including the keyswitch structure  100 ,  200 , and/or  300 . The keyboard device  10  can reduce the impact noise by the keyswitch structure  100 ,  200 , or  300 , which can provide the buffering effect to prevent the keycap from directly hitting the baseplate during operation. Moreover, the keyboard device  10  can utilize the multiple-layered configuration of the membrane switch layer to achieve the buffering design and effectively reduce the operation noise without increasing the material cost. 
     Although the preferred embodiments of the invention have been described herein, the above description is merely illustrative. The preferred embodiments disclosed will not limit the scope of the invention. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.