Abstract:
A backlight keyboard ( 100 ) includes a plurality of keys ( 120 ), a light guide plate ( 140 ), and an elastic element ( 160 ). Each key includes a key cover ( 124 ) and a keypad ( 122 ) integrally connected to each other. Further, keypad portions of adjacent keys are integrally connected, as well. The light guide plate is arranged below the keys. The light guide plate defines a plurality of through holes ( 142 ), each through hole corresponding to one key. An opaque film ( 144 ) is coated on a top surface of the light guide plate. The elastic element is positioned under the light guide plate and is configured for exerting a biasing force on at least one key so as to enable the key to return to its previous position when pressed and released.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to backlight keyboards and, particularly, to a backlight board used in a portable electronic device. 
   2. Description of Related Art 
   In a portable electronic device, a typical keyboard includes a plurality of keys, which display symbols, such as those found on typical alphanumeric keys, on their top surfaces. Moreover, this kind of keyboard is activated by depression of a key for identifying a particular symbol embedded on the top of the key. A problem with this kind of keyboard is that it is often difficult to discern the symbol appearing on the top of the key, under poor lighting conditions. 
   In order to solve the above problem, discrete light-emitting diodes (LEDs) are surface-mounted on a circuit board to provide illumination to a keypad. A light guide plate is arranged between the keypad and the circuit board for guiding light from one or more light sources on the circuit board to the proximity of the keypads. 
   However, the light guide plate not only guides light to each key, but also guides light to the area around keys. Accordingly, light from the LEDs not only illuminates each key but also illuminates other areas around keys. This wastes light and makes the symbols on the keys harder to discern/view. 
   Therefore, a backlight keyboard, which will efficiently use light from LEDs, is desired in order to overcome the above-described shortcomings. 
   SUMMARY OF THE INVENTION 
   One present embodiment of a backlight keyboard includes a plurality of keys, a light guide plate, and an elastic element. Each key includes a key cover and a keypad connected to each other. The light guide plate is arranged below the keys. The light guide plate defines a plurality of through holes, with each through hole corresponding to a key. An opaque film covers (either partially or wholly) a top surface thereof. The elastic element is positioned under the light guide plate and is configured for exerting a force on at least one key, so as to enable the key to return to its previous position upon being pressed and released. 
   Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Many aspects of the backlight keyboard can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present backlight keyboard. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a cross-sectional view of a backlight keyboard, according to one present embodiment. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring now to the drawing in detail,  FIG. 1  shows a backlight keyboard  100 , in accordance with one embodiment. The backlight keyboard  100  includes a plurality of keys  120 , a light guide plate  140 , and an elastic member  160 . The keys  120  are arranged above the light guide plate  140 , and the elastic member  160  is positioned below the light guide plate  140 . 
   Each key  120  includes a key body  121  and a key cap  128 . Each pair of adjacent key covers  124  has a space therebetween and is integrally linked via a portion of a keypad  122 . The key body  121  is beneficially made of light diffusing transparent material, such as rubber, so that light may diffusively pass therethrough. The key body  121  includes the keypad  122 , a key cover  124 , and a connecting portion  126 . The keypad  122  has an upper surface  123  and a lower surface  125  on a side of the keypad  122  opposite to the upper surface  123 . The key cover  124  is, usefully, substantially cylindrical but could instead be, e.g., substantially rectangular, depending on the desired key shape. The key cover  124  is positioned directly on the keypad  122 , and the connecting portion  126  integrally connects the key cover  124  to the keypad  122 . The connecting portion  126  is thinner than the keypad  122  and is thus configured for performing a clicking/spring-bias movement and for supporting the key cover  120 . The key cover  124  has a projection  127  integrally formed on/from a bottom thereof. The key cap  128  is, beneficially, made of plastic material, allowing for a greater level of hardness and durability. The key cap  128  is placed over the key cover  124  and can be fixed on the key cover  124  using an adhesive. Each key cap  128  has a light-permeable letter, character, a symbol, a figure, and/or the like for identifying each key  120 . It is understood that the key cap  128  may be manufactured in such a way that the key-identifying character/symbol is more light permeable than the remainder of the given key cap  128 , in order to allow the given key-identifying character/symbol to be more readily distinguished, even under low-light conditions. 
   The light guide plate  140  is made of light-transmitting material, such as methacrylate resin, polycarbonate (PC), polymethyl methacrylate (PMMA), and/or acrylonitrile butadiene styrene (ABS) resin. The light guide plate  140  has a top surface  143 , a bottom surface  145 , and four sidewalls  147 . The light guide plate  140  defines a plurality of through holes  142  therein. Each through hole  142  is positioned corresponding to its respective key cover  124 . Each through hole  142  communicates with the top surface  143  and the bottom surface  145 . A diameter of each through hole  142  is approximately the same as that of the key cover  124 . An opaque film  144  covers (either partially or wholly) the top surface  143  of the light guide plate  140 , except in the places corresponding to the through holes  142  thereof. It is to be understood that the opaque film  144  could take the form of a reflective film, with the reflective side thereof facing the bottom surface  145 , in order to help maximize light use within the light guide plate  140 . A plurality of light sources  146  such as LEDs are positioned parallel along one of sidewalls  147  of the light guide plate  140  for illuminating the whole light guide plate  140 . 
   An exemplary method of forming the opaque film  144  is that used in forming a baked-on varnish/enamel. In this method, the initial/unfinished light guide plate  140  is firstly hung in place on a rack. Then, the light guide plate  140  is treated using electrostatic dust for removing dust and static electricity. After that, the light guide plate  140  is coated. The coating process is, advantageously, carried out three times so as to achieve a suitable thickness for the opaque film  144 , although it is to be understood that such number of process times could be varied, depending, e.g., on the thickness desired and the coating materials being employed. After each coating process is finished, the light guide plate  140  is left to stand for some time to allow for drying/curing (depending on the coating material employed). This multi-step coating process helps achieve a uniform top surface  143 . Next, the light guide plate  140  is baked, thereby finishing the process of creating the baked-on varnish. Finally, the light guide plate  140  needs to be cut so as to form the plurality of through holes  142 . 
   The opaque film  144  may instead be formed by electroplating. In such a case, the light guide plate  140  should be made of a material that can undergo plating, such as a compound of PC and ABS. The plating material may be nickel, chromium, or the like. Alternatively, the opaque film  144  may be formed by physical vapor deposition (PVD) method. The coating material may be aluminium, stainless steel, or a titanium compound, such as TiC, TiCN, or TiAlN (wherein C is carbon, Al is aluminum, and N is nitrogen). Alternatively, the opaque film  144  may be formed by printing, and the printing material can be made of a light silver ink. 
   This opaque film  144  is made of an opaque material. The opaque material may have absorbing properties or may have highly reflective properties, thereby blocking light which would otherwise be emitted from the area around the key cover  124  of the key  120 . Therefore, only the key covers  122  and key caps  128  are irradiated/illuminated and so there is effective irradiation/illumination and as little light loss as possible. If the material of the opaque film  144  has an absorbing property, the light energy from the light sources  146  cannot escape from around the key covers  124 , thus ensuring effectively irradiation/illumination of the corresponding keys  120 . If the opaque film  144  is highly reflective, the opaque film  144  may repeatedly reflect light from LEDs  146  in the light guide plate  140  so as to effectively reflect light to the corresponding keys  120 . Therefore, light is not leaked to the outside making it possible to light the keys  120  even more brightly. 
   The elastic member  160  includes a plurality of dome sections  162  constructed so as to allow their elastic deformation. The elastic member  160  is mounted to the bottom surface  145  of the light guide plate  140 , and the dome sections  162  thereof respectively extend into the corresponding through holes  142  and away from the bottom surface  145 . The dome sections  162  are each so formed that a front surface of each dome section  162  expands outwardly toward a respective one of projections  127 . The dome sections  162  each have a contact  164  formed on a rear surface thereof. The dome sections  162  each abut against a corresponding one of the projections  127  so that the key cover  124  may be forcedly pressed against the corresponding dome section  162  and thereby deform such dome section  162  so as to bring the contacts  164  into contact, electrically, with a printed circuit board. 
   In assembly, the keys  120  are positioned above the light guide plate  140 , and the lower surfaces  125  of the keypads  122  are on an opposite side to the top surface  143  of the light guide plate  140 . The projection  127  of each key cover  124  extends into the corresponding through hole  142 , via the top surface  144  of the light guide plate  140 . The elastic member  160  is positioned under the light guide plate  140 . Each dome section  162  is positioned opposite to a corresponding through hole  142  and is received therein. Each projection  127 , in turn, is located opposite to a corresponding dome section  162 . 
   In use, when a force is applied to the key cap  128  of the key  120 , the key cover  124  moves downward. The projection  127  further pushes the dome section  162  of the elastic member  160 , causing the dome section  162  to deform. Accordingly, with sufficient deformation of the dome section  162 , the contact  164  contacts with the printed circuit board so as to create an electrical connection. When the force is removed, the key cover  124  returns to an original state under the biasing role of the connecting portion  126  and the dome section  162 , so as to finish the operation process of the key  120 . Because there is a non-light-transmitting coating formed on the top surface of the light guide plate  140 , except where the keys  120  are located, light is not leaked to the outside, making it possible to light the keys  120  even more brightly. 
   A main advantage of the backlight keyboard  100  is that the specified places in the key cover  124  that need to be irradiated/illuminated become bright, while the rest stays dark. Thus, the key cover  124  is uniformly irradiated/illuminated, and the display characters and symbols are easy to see. In addition, it is possible to make the illuminated keyboard thinner and thus more portable. Moreover, each dome section  164  and each projection  127  are received in the through hole  142  of the light guide plate  140 . Therefore, the dome section  164  and the projection  127  do not need to include an extra space to be provided by the keyboard  100 , thereby further contributing to a reduced thickness needed for the keyboard  100 . 
   Understandably, the opaque film  144  may, alternatively or additionally, be formed on the bottom surface  145  and/or the sidewalls  146  of the light guide plate  140  except for at the portions of the sidewall  146  adjacent to the light sources  146 . In an alternative embodiment, the opaque film  144  may be formed on the upper surface  123  of the keypad  122 , so as to block light which would otherwise be emitted from the areas around the key cover  124  of the key  120 . 
   It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.