Patent Publication Number: US-2023154697-A1

Title: Illuminated keyswitch structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/339,978, filed on May 10, 2022. Further, this application is a continuation-in-part of U.S. application Ser. No. 17/909,991, filed on Sep. 8, 2022. The contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keyswitch structure, and more particularly to an illuminated keyswitch structure. 
     2. Description of the Prior Art 
     One-to-one illuminated keys are usually provided with a light source under each keycap. The light source is used to emit light to form a backlight. When the keycap has a permeable area corresponding to characters such as letters or symbols, the corresponding light source that is usually disposed opposite to the characters emits light toward the characters. In actual products, there are often other components between the light source and the permeable area of the keycap, such as supports, base plate, circuit board, etc., which interfere with the light transmission path and cause uneven color of the characters on the keycap. In the case where the light source can emit light of multiple colors, the problem of serious color deviation also occurs. 
     SUMMARY OF THE INVENTION 
     In view of the problems in the prior art, an objective of the invention is to provide an illuminated keyswitch structure, which uses a light-emitting die package having a plurality of light-emitting dies so that light emitted by each light-emitting dies can travel in a similar path. 
     An illuminated keyswitch structure of an embodiment according to the invention includes a base plate, a keycap, and a light-emitting die package. The keycap is movably disposed above the base plate in a vertical direction. The light-emitting die package is disposed under the keycap and includes a plurality of light-emitting dies. The plurality of light-emitting dies generate light of at least three colors. The plurality of light-emitting dies are distributed in a plane and are monochromatic light-emitting dies. Therein, among the plurality of light-emitting dies, adjacent two light-emitting dies that are arranged in a first arrangement direction perpendicular to the vertical direction emit light of different colors. Among the plurality of light-emitting dies, adjacent two light-emitting dies that are arranged in a second arrangement direction perpendicular to the vertical direction emit light of different colors. The first arrangement direction and the second arrangement direction are non-parallel. Thereby, the plurality of light-emitting dies are packaged in a single package, so that the light emitted by each light-emitting die can travel in a similar path. Furthermore, the plurality of light-emitting dies reduce the excessive concentration of the light-emitting dies of the same color light through the arrangement, which also helps the light to illuminate the keycap evenly. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating an illuminated keyswitch structure according to an embodiment. 
         FIG.  2    is an exploded view of the illuminated keyswitch structure in  FIG.  1   . 
         FIG.  3    is a sectional view of the illuminated keyswitch structure along the line X-X in  FIG.  1   . 
         FIG.  4 A  is a schematic diagram illustrating a top view configuration of a switch circuit board and light-emitting dies. 
         FIG.  4 B  is a schematic diagram illustrating a top view configuration of another embodiment extended from  FIG.  4 A . 
         FIG.  4 C  is a schematic diagram illustrating a top view configuration of another embodiment extended from  FIG.  4 A . 
         FIG.  5    is a schematic diagram illustrating a top view configuration of the switch circuit board and the light-emitting dies in  FIG.  4 A  according to another embodiment. 
         FIG.  6    is a schematic diagram illustrating a top view configuration of the switch circuit board and the light-emitting dies in  FIG.  4 A  according to another embodiment. 
         FIG.  7    is a top view of the illuminated keyswitch structure in  FIG.  1   . 
         FIG.  8    is a schematic diagram illustrating a portion of a top view configuration of the switch circuit board and the light-emitting dies according to another embodiment. 
         FIG.  9    is a sectional view along the line Y-Y corresponding to the embodiment in  FIG.  8   . 
         FIG.  10    is a schematic diagram illustrating an illuminated keyswitch structure according to another embodiment. 
         FIG.  11 A  is a top view of the illuminated keyswitch structure after the keycap is removed. 
         FIG.  11 B  is a schematic diagram illustrating a top view configuration of another embodiment extended from  FIG.  11 A . 
         FIG.  12    is a sectional view along the line Z-Z in  FIG.  11 A . 
         FIG.  13 A  is a top view of the illuminated keyswitch structure in  FIG.  10   . 
         FIG.  13 B  is a top view of a portion of another embodiment extended from  FIG.  13 A . 
         FIG.  14    is a schematic diagram illustrating a light-emitting die package according to a first embodiment. 
         FIG.  15    is a sectional view of the light-emitting die package along the line W-W in  FIG.  14   . 
         FIG.  16    is a schematic diagram illustrating a variation example of the light-emitting die package in  FIG.  14   . 
         FIG.  17    is a schematic diagram illustrating a top view configuration of the light-emitting die package in  FIG.  14   . 
         FIG.  18    is a schematic diagram illustrating a top view configuration of a light-emitting die package according to a second embodiment. 
         FIG.  19    is a schematic diagram illustrating a top view configuration of a light-emitting die package according to a third embodiment. 
         FIG.  20    is a schematic diagram illustrating a top view configuration of a light-emitting die package according to a fourth embodiment. 
         FIG.  21    is a schematic diagram illustrating a top view configuration of a light-emitting die package according to a fifth embodiment. 
         FIG.  22    is a schematic diagram illustrating a top view configuration of a light-emitting die package according to a sixth embodiment. 
         FIG.  23    is a top view configuration of  FIG.  4 A , in which the light-emitting dies are replaced by the light-emitting die package of the sixth embodiment. 
         FIG.  24    is a sectional view of an illuminated keyswitch structure corresponding to  FIG.  23   . 
         FIG.  25    is a schematic diagram illustrating a top view configuration of the switch circuit board and the light-emitting die package on the base plate in a variation example of the through hole. 
         FIG.  26    is a schematic diagram illustrating a top view configuration of the switch circuit board and the light-emitting die package on the base plate in another variation of the through hole. 
         FIG.  27    is a top view configuration of  FIG.  8   , in which the light-emitting dies are replaced by the light-emitting die package of the sixth embodiment. 
         FIG.  28    is a top view configuration of  FIG.  11 A , in which the light-emitting dies are replaced by the light-emitting die package of the sixth embodiment. 
         FIG.  29    is a top view configuration of  FIG.  13 B , in which the light-emitting dies are replaced by the light-emitting die package of the sixth embodiment. 
         FIG.  30    is a sectional view of an illuminated keyswitch structure according to an embodiment. 
         FIG.  31    is a sectional view of the illuminated keyswitch structure in  FIG.  30    further with a mask layer. 
         FIG.  32    is a sectional view of a variation example of the illuminated keyswitch structure in  FIG.  31   . 
         FIG.  33    is a top view configuration of the switch contact pad, the light-emitting die package, and the permeable area of the mask layer on the base plate in  FIG.  32   . 
         FIG.  34    is a sectional view of an illuminated keyswitch structure corresponding to  FIG.  33   . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG.  1    to  FIG.  3   .  FIG.  1    is a schematic diagram illustrating an illuminated keyswitch structure according to an embodiment.  FIG.  2    is an exploded view of the illuminated keyswitch structure in  FIG.  1   .  FIG.  3    is a sectional view of the illuminated keyswitch structure along the line X-X in  FIG.  1   . An illuminated keyswitch structure  1  according to an embodiment includes a keycap  12 , a base plate  14 , a first support  16 , a second support  18 , a transparent switch circuit board  20 , and one or more light-emitting dies (for example, but not limited to, three light-emitting dies  22   a ,  22   b  and  22   c , the light-emitting dies are used for emitting light of different color lights, such as red light, green light and blue light; besides, the light-emitting dies  22   a ,  22   b  and  22   c  can be realized by, but not limited to, light-emitting diodes). The keycap  12  is disposed above the base plate  14 . Both the first support  16  and the second support  18  are connected to and between the keycap  12  and the base plate  14  to support the keycap  12  so that the keycap  12  is movable in a vertical direction D 1  (indicated by a double-headed arrow in  FIG.  1    and  FIG.  3   ) through the first support  16  and the second support  18 . The switch circuit board  20  is placed on the base plate  14  (i.e., under the keycap  12 ). The light-emitting dies  22   a ,  22   b  and  22   c  are disposed under the switch circuit board  20 , e.g., fixed on a light source circuit board  24  (the light source circuit board  24  is, for example, but not limited to, a flexible printed circuit board) disposed under the base plate  14 . The base plate  14  forms a corresponding through hole  142  to expose the light-emitting dies  22   a ,  22   b  and  22   c ; in practice, the light-emitting dies  22   a ,  22   b  and  22   c  can partially or fully enter the through hole  142 . Please refer to  FIG.  1    and  FIG.  3   . The light-emitting dies  22   a ,  22   b  and  22   c  are not higher than the base plate  14 . The light-emitting dies  22   a ,  22   b  and  22   c  are located within a projection of the through hole  142  in the vertical direction D 1 . The circuitry of the switch circuit board  20  (which is partially shown in dashed lines in  FIG.  2   ) does not cover the light-emitting dies  22   a ,  22   b  and  22   c , so that light emitted upward by the light-emitting dies  22   a ,  22   b  and  22   c  can pass through the switch circuit board  20  to illuminate the keycap  12 . 
     In the embodiment, the switch circuit board  20  may be realized by a membrane circuit board, which is usually formed by stacking three layers of transparent sheets, in which the required circuitry is formed on the upper and lower transparent sheets, and the middle transparent sheet provides the insulation for the circuitry. The circuitry of the switch circuit board  20  includes switch contact pads  202  and several trace segments (the hidden profiles of which are shown in dotted lines in  FIG.  2   ). The illuminated keyswitch structure  1  uses a preamble resilient dome  26  as a returning part. The resilient dome  26  aligns with the switch contact pads  202 . The resilient dome  26  is disposed on the switch circuit board  20  and covers the switch contact pads  202  and the light-emitting dies  22   a ,  22   b  and  22   c  in the vertical direction D 1 . The keycap  12  can be pressed (e.g., by a finger of a user) to squeeze the resilient dome  26  downward, thereby triggering the switch contact pads  202 . After the external force applied to the keycap  12  is removed (e.g., the user removes his finger from the keycap  12 ), the squeezed resilient dome  26  can be restored to push the keycap  12  upwards back to its original position. 
     Please also refer to  FIG.  4 A .  FIG.  4 A  is a schematic diagram illustrating a top view configuration of a portion of the switch circuit board and light-emitting dies of the illuminated keyswitch structure in  FIG.  2   . Therein, the circuitry of the switch circuit board  20  and the hidden profiles of the light-emitting dies  22   a ,  22   b  and  22   c  are shown in solid lines. The switch contact pad  202  has a non-circular profile, e.g., but not limited to, a cut-flat circular profile with a flat edge  202   a . The light-emitting dies  22   a ,  22   b  and  22   c  are arranged in an arrangement direction D 2  (indicated by a double-headed arrow in  FIG.  4 A ). The arrangement direction D 2  is parallel to the flat edge  202   a . There is a light-emitting distance d 1  in a horizontal direction D 3  (indicated by a double-headed arrow in the figures) between the light-emitting dies  22   a ,  22   b  and  22   c  and the switch contact pad  202  (that is, the distance from the projection of the whole profiles of the light-emitting areas of the light-emitting dies  22   a ,  22   b  and  22   c  on the switch circuit board  20  to the flat edge  202   a ). In principle, the farther the light-emitting dies  22   a ,  22   b  and  22   c  are away from the switch contact pads  202 , the more the situation that the switch contact pads  202  shields the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  can be reduced. In practice, the light-emitting distance d 1  can be designed to be between 0.3 mm and 0.5 mm. Furthermore, in the embodiment, the cut-flat circular profile has a center  202   b  and a radius  202   c . A ratio of a distance  202   d  from the center  202   b  to the flat edge  202   a  to the radius  202   c  is greater than 0.5. In principle, the switch contact pads  202  can maintain acceptable contact conduction characteristics. 
     Please refer to  FIG.  4 B  and  FIG.  4 C . Each of  FIG.  4 B  and  FIG.  4 C  is a schematic diagram illustrating a top view configuration of another embodiment extended form  FIG.  4 A . A portion of the arc edge of the through hole  142 ′ of the base plate  14  (whose profile projection is shown in dashed lines in the figures) is parallel to the arc edge of the switch contact pad  202 , and the other side of the through hole  142 ′ consists of three mutually perpendicular edges, which form a bullet-shaped through hole  142 ′ as a whole. In  FIG.  4 B , the light-emitting dies  22   a ,  22   b  and  22   c  are all arranged in the arrangement direction D 2 . The light-emitting dies  22   a ,  22   b  and  22   c  are not only adjacent to the flat edge  202   a  of the switch contact pad  202 , but also adjacent to a straight hole edge  142   a ′ of the through hole  142 ′ of the base plate  14 . In this case, the suitable configuration is that the arrangement direction D 2  for the light-emitting dies  22   a ,  22   b  and  22   c  is parallel (or roughly parallel) to the hole edge  142   a ′ of the through hole  142 ′ of the base plate  14 , and also parallel (or roughly parallel) to the flat edge  202   a  of the switch contact pad  202 . In  FIG.  4 C , the light-emitting dies  22   a ,  22   b  and  22   c  are arranged in a triangle. The light-emitting die  22   a  is toward the straight hole edge  142   a ′ of the through hole  142 ′ of the base plate  14 . The light-emitting die  22   c  is not located within a union range of the light-emitting dies  22   a  and  22   b . The light-emitting dies  22   b  and  22   c  are arranged straight in the arrangement direction D 2  with edges parallel to each other. In this case, the arrangement direction of the at least two light-emitting dies  22   b  and  22   c  is parallel (or roughly parallel) to the straight hole edge  142   a ′ of the through hole  142 ′ of the base plate  14 , and also parallel (or roughly parallel) to the flat edge  202   a  of the switch contact pad  202 . However, it is not limited thereto in practice. For example, the at least two light-emitting dies  22   b  and  22   c  may be arranged in the horizontal direction D 3 , so that the arrangement direction of the at least two light-emitting dies  22   b  and  22   c  is perpendicular (or roughly perpendicular) to the straight hole edge  142   a ′ of the through hole  142 ′ of the base plate  14 , and also perpendicular (or roughly perpendicular) to the flat edge  202   a  of the switch contact pad  202 , but parallel to the horizontal direction D 3 . In another embodiment, in the bullet-shaped through hole  142 ′ of the base plate  14  in  FIG.  4 B  and  FIG.  4 C , the three mutually perpendicular edges can be reduced as needed, and become a key-shaped through hole  142 ′ with an arc end portion and a narrow and long end portion. In this case, all or at least two of the light-emitting dies  22   a ,  22   b  and  22  may be arranged in a straight line perpendicular to the flat edge  202   a  of the switch contact pad  202  and the hole edge  142   a ′ at the end. 
     The hole edge  142   a ′ of the through hole  142 ′ of the base plate  14  and the flat edge  202   a  of the switch contact pad  202  are both heterochromatic sensitive areas. The heterochromatic sensitive area will cause the problem of uneven light mixing and color deviation. Therefore, the above technical solutions all are to dispose the plurality of light-emitting dies  22   a ,  22   b  and  22   c  at the same side of the heterochromatic sensitive area; that is, the light-emitting dies  22   a ,  22   b  and  22   c  are simultaneously disposed at the same side of the hole edge  142   a ′ of the through hole  142 ′ of the base plate  14 , and/or the light-emitting dies  22   a ,  22   b  and  22   c  are simultaneously disposed at the same side of the flat edge  202   a  of the switch contact pad  202 . The distances from the plurality of light-emitting dies  22   a ,  22   b  and  22   c  to the same heterochromatic sensitive area are close to each other. Since the process technology for the light-emitting dies  22   a ,  22   b  and  22   c  has reached the millimeter or even micron level, even if the light-emitting dies  22   a ,  22   b  and  22   c  are not arranged in a straight line, the distances to the same heterochromatic sensitive area are very close to each other. For clear display, the plurality of light-emitting dies in each figure of the present disclosure are drawn in a larger size, and the distances between the plurality of light-emitting dies are relatively large. In actual implementation, the scale of the light-emitting dies is much smaller than that in the figures of the disclosure. 
     In addition, in practice, the switch contact pad of the switch circuit board  20  may have different shapes. For example, as shown by  FIG.  5   , the switch contact pad  203   a  according to an embodiment includes a peripheral portion  2032   a  and a central portion  2034   a  and two connecting portions  2036   a  which are located at the inner side the peripheral portion  2032   a . The two connecting portions  2036   a  are located at opposite sides of the central portion  2034   a  and connect the peripheral portion  2032   a  and the central portion  2034   a . The peripheral portion  2032   a  extends incompletely along a circular path (indicated by a dashed line in the figure) and is C-shaped. The central portion  2034   a  has a circular profile. The light-emitting dies  22   a ,  22   b  and  22   c  are located between two ends of the peripheral portion  2032   a  (i.e., at the opening). The circular path passes through the light-emitting dies  22   a ,  22   b  and  22   c  (i.e., the light-emitting dies  22   a ,  22   b  and  22   c  are arranged on the circular path). The light-emitting dies  22   a ,  22   b  and  22   c  are closer to the central portion  2034   a  and there is a light-emitting distance d 1   a  between the light-emitting dies  22   a ,  22   b  and  22   c  and the central portion  2034   a . Similarly, in practice, the light-emitting distance d 1   a  can be designed to be between 0.3 mm and 0.5 mm. If the light-emitting dies  22   a ,  22   b  and  22   c  are closer to the two ends of the peripheral portion  2032   a  and there is a light-emitting distance d 1   a ′ between the light-emitting dies  22   a ,  22   b  and  22   c  and the peripheral portion  2032   a . Similarly, in practice, the light-emitting distance d 1   a ′ can also be designed to be between 0.3 mm and 0.5 mm. 
     For another example, as shown by  FIG.  6   , the switch contact pad  203   b  according to an embodiment includes a peripheral portion  2032   b  and a central portion  2034   b  and a connecting portion  2036   b  which are located at the inner side the peripheral portion  2032   b . The connecting portion  2036   b  connects the peripheral portion  2032   b  and the central portion  2034   b . The peripheral portion  2032   b  extends incompletely along a convex polygonal path (e.g., but not limited to a pentagonal path, indicated by dashed lines in the figure) and is roughly C-shaped. The central portion  2034   b  has a convex polygonal profile (e.g., but not limited to a quadrilateral). The convex polygonal path passes through the light-emitting dies  22   a ,  22   b  and  22   c . The light-emitting dies  22   a ,  22   b  and  22   c  are closer to the central portion  2034   b  and there is a light-emitting distance d 1   b  between the light-emitting dies  22   a ,  22   b  and  22   c  and the central portion  2034   b . Similarly, in practice, the light-emitting distance d 1   b  can be designed to be between 0.3 mm and 0.5 mm. If the light-emitting dies  22   a ,  22   b  and  22   c  are closer to the peripheral portion  2032   b  and there is a light-emitting distance d 1   b ′ between the light-emitting dies  22   a ,  22   b  and  22   c  and the peripheral portion  2032   b . Similarly, in practice, the light-emitting distance d 1   b ′ can also be designed to be between 0.3 mm and 0.5 mm. Furthermore, in  FIG.  5    and  FIG.  6   , the convex polygonal path can also be a triangular path, a hexagonal path, etc. in practice. The profiles of the central portions  2034   a  and  2034   b  can also be other convex polygonal profiles, e.g. a triangular profile, a hexagonal profile, etc. 
     Please refer to  FIG.  1    to  FIG.  3   . In the embodiment, the keycap  12  has a permeable indicator area  12   a  (shown by a dashed frame in the figures). Light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  can pass through the permeable indicator area  12   a  to produce a visual indication effect. In practice, the permeable indicator area  12   a  may be numbers, symbols, letters, characters, graphics or combinations thereof, etc.; in other words, the permeable indicator area  12   a  may contain a plurality of permeable characters, and the permeable characters may be numbers, symbols, letters, characters, graphics or combinations thereof; in other words, the permeable indicator area  12   a  may include a plurality of permeable characters, and the permeable character may be number, symbol, letter, character or graphic. 
     Please also refer to  FIG.  7    (in which the hidden profiles of the light-emitting dies  22   a ,  22   b  and  22   c  are shown in thin lines).  FIG.  7    is a top view of the illuminated keyswitch structure in  FIG.  1   . In the embodiment, the permeable indicator area  12   a  has a lengthwise direction  12   b  (e.g. the arrangement direction of the letters in the figure, indicated by a double-headed arrow in  FIG.  7   ). The light-emitting dies  22   a ,  22   b  and  22   c  are arranged under the permeable indicator area  12   a  perpendicular to the lengthwise direction  12   b  (that is, the arrangement direction D 2  is perpendicular to the lengthwise direction  12   b ), thereby reducing or eliminating the influence of uneven light mixing on the permeable indicator area  12   a  caused by excessive arrangement spacing of the light-emitting dies  22   a ,  22   b , and  22   c . In other words, the two ends of the permeable indicator area  12   a  (and the permeable indicator area  12   a ′ of the following embodiment) are heterochromatic sensitive areas, which are prone to uneven light mixing which causes color deviation of the light when exiting from the keycap  12 . The permeable indicator area  12   a  may include a plurality of permeable characters. The plurality of permeable characters are arranged along a long axis. The so-called heterochromatic sensitive area is the end character on both sides of the plurality of permeable characters. 
     Furthermore, in the embodiment, the permeable indicator area  12   a  is rectangular, on which a long axis  12   c  and a short axis  12   d  are defined (both are shown in dashed lines in  FIG.  7   ). The long axis  12   c  is parallel to the lengthwise direction  12   b . The short axis  12   d  is perpendicular to the lengthwise direction  12   b . The permeable indicator area  12   a  is symmetrical with respect to the long axis  12   c  and the short axis  12   d  respectively. In terms of vertical projection, the light-emitting dies  22   a ,  22   b  and  22   c  as a whole (that is, the plurality of light-emitting dies are regarded as a whole, the same below) pass through the long axis  12   c  and the center of the light-emitting dies  22   a ,  22   b ,  22   c  as a whole (i.e. the light-emitting die  22   b  In this embodiment) is located on the long axis  12   c . In practice, the light-emitting dies  22   a ,  22   b  and  22   c  as a whole can also be designed to pass through the center of the long axis  12   c , as shown by the rectangles in dashed lines in  FIG.  7   . In this case, the light-emitting dies  22   a ,  22   b  and  22   c  as a whole also pass through the center of the short axis  12   d . The center of the light-emitting dies  22   a ,  22   b  and  22   c  as a whole (i.e. the light-emitting die  22   b  in this embodiment) is also located at the centers of the long axis  12   c  and the short axis  12   d ; however, it is not limited thereto. For example, the light-emitting dies  22   a ,  22   b  and  22   c  are offset parallel to the short axis  12   d , so that the center of the light-emitting dies  22   a ,  22   b  and  22   c  as a whole deviates from the centers of the long axis  12   c  and the short axis  12   d  (for example, the light-emitting die  22   a  or  22   c  is located at the centers of long axis  12   c  and short axis  12   d ; for another example, the light-emitting dies  22   a ,  22   b  and  22   c  are not located at the centers of long axis  12   c  and short axis  12   d , as shown by rectangles in dashed lines in  FIG.  7   ). In addition, in the illuminated keyswitch structure  1 , although the light-emitting dies  22   a ,  22   b  and  22   c  are arranged in a straight line, they can also be arranged in a non-linear arrangement in practice, e.g. in a triangular arrangement. In this case, when the light-emitting dies  22   a ,  22   b  and  22   c  can be close enough to each other (which can be obtained through the actual test of the product), the influence of uneven light mixing on the permeable indicator area  12   a  caused by excessive arrangement spacing of the light-emitting dies  22   a ,  22   b , and  22   c  can also be reduced or eliminated. The technical solutions in this embodiment are to dispose the plurality of light-emitting dies  22   a ,  22   b  and  22   c  at the same side of the heterochromatic sensitive area; that is, the light-emitting dies  22   a ,  22   b  and  22   c  are simultaneously disposed at the same side of the end character of the plurality of permeable characters. For the end character “L”, the light-emitting dies  22   a ,  22   b  and  22   c  are arranged together at the same side of the end character “L”; for the end character “d” on the other side, the plurality of light-emitting dies  22   a ,  22   b  and  22   c  are arranged together at the same side of the end character “d”. As far as the end character “L” regarded as a heterochromatic sensitive area is concerned, the arrangement direction of the light-emitting dies  22   a ,  22   b  and  22   c  is at least partially perpendicular to the permeable indicator area  12   a , so that the distances to the same heterochromatic sensitive area (the end character “L”) are close to each other, which can reduce the color deviation. Similarly, as far as the end character “d” regarded as a heterochromatic sensitive area is concerned, the arrangement direction of the light-emitting dies  22   a ,  22   b  and  22   c  is at least partially perpendicular to the permeable indicator area  12   a , so that the distances to the same heterochromatic sensitive area (the end character “d”) are close to each other, which can also reduce the color deviation. 
     In the present disclosure, a coverage space of the keycap  12  in the vertical direction D 1  has a heterochromatic sensitive area. The heterochromatic sensitive area is, for example, an end of the permeable indicator area  12   a  of the keycap  12 . The plurality of light-emitting dies  22   a ,  22   b  and  22   c  are located at the same side of the projection of the heterochromatic sensitive area (the end of the permeable indicator area  12   a ) in the vertical direction D 1 . Because the distances from the plurality of light-emitting dies  22   a ,  22   b  and  22   c  to the end of the permeable indicator area  12   a  are close to each other, the light of different colors emitted by the plurality of light-emitting dies  22   a ,  22   b  and  22   c  can travel to the end of the permeable indicator area  12   a  at similar distances, which can suppress the influence of uneven light mixing and color deviation. 
     In the illuminated keyswitch structure  1 , the switch contact pads  202  are approximately located in the central area, but it is not limited to this in practice. For example, the switch contact pads  202  are offset from the center area and are triggered by the keycap  12  (e.g. by a downwardly protruding structure) or the support (the first support  16  or the second support  18 ). In this case, the light-emitting dies  22   a ,  22   b  and  22   c  can be kept far below the resilient dome  26 , so that the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  does not need to pass through the resilient dome  26 , reducing light intensity attenuation. Furthermore, the circuitry of the switch circuit board  20  generally refers to a collection of a plurality of traces and a plurality of circuit elements (e.g., the switch contact pads  202  mentioned above), which are the objects that the light-emitting dies  22   a ,  22   b  and  22   c  need to avoid. In detail, in the illuminated keyswitch structure  1 , the light-emitting dies  22   a ,  22   b  and  22   c  are closer to the switch contact pads  202  than other parts of the circuitry. However, in practice, the light-emitting dies  22   a ,  22   b  and  22   c  may also be closer to other parts of the circuitry than the switch contact pads  202 . 
     For example, in another embodiment, as shown by  FIG.  8    (in which the hidden profile of the circuitry of the switch circuit board  20  is shown in thin lines), the light-emitting dies  22   a ,  22   b  and  22   c  are disposed close to a trace segment  204 . The trace segment  204  extends straight. The arrangement direction D 2 ′ of the light-emitting dies  22   a ,  22   b  and  22   c  is parallel to the trace segment  204 . There is a light-emitting distance d 2  (i.e. the distance from the projection of the whole profiles of the light-emitting areas of the light-emitting dies  22   a ,  22   b  and  22   c  on the switch circuit board  20  to the trace segment  204 ) in the horizontal direction D 3 ′ between the light-emitting dies  22   a ,  22   b  and  22   c  and the trace segment  204 . In practice, the light-emitting distance d 2  can also be designed to be between 0.3 mm and 0.5 mm. 
     In practice, the switch circuit board  20  may also be disposed under the base plate  14  as required. In this case, the switch circuit board  20  is closer to the lowermost light-emitting die  22   a ,  22   b  and  22   c  and covers a larger light-emitting range, and it is necessary to be farther away from the circuitry of the switch circuit board  20  to a greater extent. For circuit elements (e.g. the switch contact pads  202 ) or traces (e.g. the trace segment  204 ) that make up the circuitry, proper values for the light-emitting distances d 1  and d 2  may exceed the above-mentioned higher boundary value, 0.5 mm. In some practicable examples, the proper values for the light-emitting distances d 1  and d 2  are 0.59 mm, 0.66 mm and 0.78 mm. When the circuitry of the switch circuit board  20  is far away from the light-emitting dies  22   a ,  22   b  and  22   c , e.g., using the base plate  14  with a larger thickness, or because of other structural parts that are added due to the illuminated keyswitch structure  1  (e.g. a movable plate, a magnetic, protrusions, etc. that are used for magnetic restoration or keyboard sinking), the proper values for the light-emitting distances d 1  and d 2  may be less than the lower boundary value. For example, in some practicable examples, the proper values for the light-emitting distances d 1  and d 2  are 0.27 mm, 0.23 mm and 0.17 mm. Therefore, according to the experimental data of different product models, the light-emitting distances d 1  and d 2  are preferably within the range from 0.17 mm to 0.78 mm. 
     Besides, the switch contact pads  202  may be printed on the upper and lower transparent sheets of the switch circuit board  20 , respectively. The switch contact pads  202  on the upper and lower transparent sheets may have different patterns and outer diameters. The light-emitting dies  22   a ,  22   b  and  22   c  usually need to avoid the outermost edges of the switch contact pads  202  on the upper layer and lower layer of the switch circuit board  20 ; that is, the above light-emitting distance d 1  have to be based on the overall outline of the switch contact pads  202  as a whole on the upper layer and lower layer. 
     Furthermore, please also refer to  FIG.  8    and  FIG.  9   .  FIG.  9    is a sectional view along the line Y-Y corresponding to the embodiment in  FIG.  8   . In this embodiment, the switch circuit board  20  has a through hole  206 . The light-emitting dies  22   a ,  22   b  and  22   c  are disposed opposite right to a through hole  142 ″ of the base plate  14  and the through hole  206 , so that light emitted upward by the light-emitting dies  22   a ,  22   b  and  22   c  can pass through the through hole  142 ″ and the through hole  206  to illuminate the keycap  12 , which can eliminate the intensity attenuation that occurs when the light passes through the physical structure of the switch circuit board  20 . In the configuration shown by  FIG.  4 A , if the structural design allows, the switch circuit board  20  can also form through holes opposite right to the light-emitting dies  22   a ,  22   b  and  22   c  near the switch contact pads  202  to reduce the intensity attenuation of light. 
     In addition, in the embodiment, all the light-emitting dies  22   a ,  22   b  and  22   c  for providing the keycap  12  backlight are arranged in a straight line parallel to the flat edge  202   a , but it is not limited thereto in practice. For example, the light-emitting dies  22   a ,  22   b  and  22   c  are arranged in other arrangements (e.g. arcs, triangles, polygons, arrays, etc.); therein, the distance in the horizontal direction D 3  between the light-emitting die  22   a ,  22   b  or  22   c  closest to the switch contact pad  202  and the switch contact pad  202  is defined as the light-emitting distance. Similarly, the portion of the profile of the switch contact pad  202  close to the light-emitting dies  22   a ,  22   b  and  22   c  is not limited to a straight line. The trace segment  204  close to the light-emitting dies  22   a ,  22   b  and  22   c  is also not limited to a straight line. The closer the light-emitting dies  22   a ,  22   b  and  22   c  can be disposed to the circuitry, the more the range for the light-emitting dies  22   a ,  22   b  and  22   c  to dispose can be increased, that is, increasing the design flexibility of the permeable indicator area  12   a.    
     Please refer to  FIG.  10    and  FIG.  11 A , which show an illuminated keyswitch structure  3  according to another embodiment. The illuminated keyswitch structure  3  is structurally similar to the illuminated keyswitch structure  1 . The illuminated key switch structure  3  in principle follows the component symbols of the illuminated key switch structure  1 . For other descriptions about the illuminated keyswitch structure  3 , please refer to the relevant descriptions of the same named components and their variations in the illuminated keyswitch structure  1  in the foregoing. In the illuminated keyswitch structure  3 , the first support  16  and the second support  18  are disposed opposite to each other and are light permeable, and are connected together to the bottom side of the keycap  12  and the top side of the base plate  14 . 
     When the keycap  12  is not pressed yet, the permeable first support  16  and the permeable second support  18  are an X-shaped scissors support in an extended state (as shown in  FIG.  10    or refer to  FIG.  3   ). In other words, light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  disposed under the base plate  14  has different transmission paths and angles of incidence/reflection/refraction at different surface of different portions of sloping upper and lower halves and upper and lower ends of the first support  16  and the second support  18 . The adjacent portions of the first support  16  and the second support  18  belong to the heterochromatic sensitive area, or the vertical space covering a gap projection G is the heterochromatic sensitive area, which is prone to uneven light mixing which causes color deviation of the light when reaching the keycap  12 . If a monochromatic light source is disposed within the gap projection G (represented by dashed hatching in  FIG.  11 A , that is, the projection of the gap between the first support  16  and the second support  18  in the vertical direction D 1 ) of the first support  16  and the second support  18 , the light will be directly or indirectly transmitted through different portions of the first support  16  and the second support  18  to illuminate the keycap  12 , which will eventually cause serious uneven illumination. If light sources of different colors such as the light-emitting dies  22   a ,  22   b  and  22   c  are disposed in the gap projection G (or overlapping with the gap projection G), color deviation will occur at different positions of the keycap  12  due to uneven light mixing. 
     Please refer to  FIG.  10    and  FIG.  11 A . Therefore, in the embodiment, all the light-emitting dies  22   a ,  22   b  and  22   c  (whose hidden profile is shown in bold lines in  FIG.  11 A ) for providing backlight are disposed under the first support  16  (that is, the light-emitting dies  22   a ,  22   b  and  22   c  are located within the projection of the first support  16  in the vertical direction D 1 ) and located within the through hole  144  (or under the base plate opposite right to the through hole  144  of the base plate  14 ; that is, the light-emitting dies  22   a ,  22   b  and  22   c  are located within the projection of the through hole  144  in the vertical direction D 1 ). The light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  travels upward from the through hole  144  and passes through the first support  16  (or passes through the through hole  144  and the first support  16 ) to illuminate the keycap  12 . Since the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  passes through the same support, in principle, the light is affected very similarly (e.g. intensity attenuation, divergence or deviation of travelling path, etc.), which can suppress the degree of color deviation of the light that may occur after the light passes through the structural parts. Furthermore, in the embodiment, the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  enters the first support  16  from the lower surface  162  of the first support  16  and exits out the first support  16  from the upper surface  164  of the first support  16 . The lower surface  162  and the upper surface  164  are parallel. This structural configuration also helps to suppress the degree of color deviation of the light that may occur after the light passes through the structural parts. Similarly, in practice, the light-emitting dies  22   a ,  22   b  and  22   c  can also be changed to be disposed under the second support  18 , as shown in dashed lines in  FIG.  11 A . In this way, as long as the gap projection G (i.e. the projection area of the gap between the first support  16  and the second support  18  in the vertical direction) of the first support  16  and the second support  18  does not overlap with the light-emitting dies  22   a ,  22   b  and  22   c , which can avoid color deviation. That the gap projection G of the first support  16  and the second support  18  does not overlap with the light-emitting dies  22   a ,  22   b  and  22   c  not only means that the gap projection G does not directly overlap with any one of the light-emitting dies  22   a ,  22   b  and  22   c  itself, but also contains the situation that the gap projection G does not pass through the gaps between any adjacent two of the light-emitting dies  22   a / 22   b  and  22   b / 22   c  (that is, the gap projection G does not overlap with or pass through the whole light-emitting dies  22   a ,  22   b  and  22   c ). The light-emitting dies  22   a ,  22   b  and  22   c  as a whole can be logically represented by a single convex polygonal region that can cover all light-emitting dies  22   a ,  22   b  and  22   c . For example, the light-emitting dies  22   a ,  22   b  and  22   c  are not arranged in a straight line (shown by dashed rectangles in the enlarged view in  FIG.  11 A ), and the whole can be covered by a convex hexagonal region (shown by a dashed polygon in  FIG.  11 A , or in terms of lines connecting their centers, they are arranged in a triangle). On the premise that the gap projection G does not overlap with or pass through the whole light-emitting dies  22   a ′,  22   b ′ and  22   c ′, the arrangement of the light-emitting dies  22   a ′,  22   b ′ and  22   c ′ and the gap projection G may also have a specific relative relationship. For example, at least two of the light-emitting dies  22   a ′,  22   b ′ and  22   c ′ that are arranged in a triangle in  FIG.  11 A  are arranged in the horizontal direction D 3 ″ (that is, at least two of the light-emitting dies  22   a ′,  22   b ′ and  22   c ′ are arranged parallel to the horizontal direction D 3 ″) and perpendicular to the gap projection G (that is, the gap projection G extends roughly parallel to the arrangement direction D 2 ″). 
     Besides, as shown by the three light-emitting dies  22   a ′,  22   b ′ and  22   c ′ shown in dashed lines in  FIG.  11 B  and arranged in a triangle on the second support  18 , when the light-emitting dies  22   a ′,  22   b ′ and  22   c ′ in dashed lines are arranged in a triangle (in terms of their central connections), the light emitting dies  22   b ′ and  22   c ′ are arranged in a straight line with edges parallel to each other (i.e. parallel to each other), and the light-emitting die  22   a ′ is not located within the union range of the light-emitting dies  22   b ′ and  22   c ′ (e.g., the axes of the light-emitting die  22   b ′ and the light-emitting die  22   c ′ are a straight line, and the axis of the light-emitting die  22   a ′ is not located on the straight line). In order to avoid local slight color deviation caused by at least two of the light-emitting dies  22   a ′,  22   b ′ and  22   c ′ in dashed lines that are adjacent to the gap projection G between the adjacent portions of the first support  16  and the second support  18  at the same time, but have unequal distances to the gap projection G, the arrangement direction D 2 ″ of the at least two of the light-emitting dies  22   a ′,  22   b ′ and  22   c ′ in dashed lines that are adjacent to the gap projection G can be parallel to the gap projection G and perpendicular to the horizontal direction D 3 ″. As for the third light-emitting dies  22   a ′,  22   b ′ or  22   c ′ arranged in the triangle, it is roughly located on the line connecting the centers of the two light-emitting dies  22   a ′,  22   b ′ or  22   c ′ in dashed lines. The third light-emitting dies  22   a ′,  22   b ′ or  22   c ′ in dashed lines can be farther from the gap projection G, or can be closer to the gap projection G than the other two. 
     Furthermore, in the embodiment, the whole first support  16  shows a rectangular frame. The light-emitting dies  22   a ,  22   b  and  22   c  are located under a frame portion  166   a  of the rectangular frame. A projection of the frame portion  166   a  in the vertical direction D 1  has a lengthwise direction (in the view point of  FIG.  11 A , the lengthwise direction is equivalent to the arrangement direction D 2 ″ of the light-emitting dies  22   a ,  22   b  and  22   c ). The lengthwise direction is parallel to the arrangement direction D 2 ″ of the light-emitting dies  22   a ,  22   b  and  22   c . In practice, the light-emitting dies  22   a ,  22   b  and  22   c  can be located under a frame portion  166   b  of the rectangular frame. The light-emitting dies  22   a ,  22   b  and  22   c  are arranged parallel to the lengthwise direction (or extension direction) of the frame portion  166   b . Furthermore, the first support  16  may also be realized by frames in other geometric configurations, such as U-shaped (or n-shaped) frames. 
     To sum up, the above technical solutions in this embodiment are to dispose the light-emitting dies  22   a ,  22   b ,  22   c  and  22   a ′,  22   b ′ or  22   c ′ at the same side of the heterochromatic sensitive area, i.e. the gap projection G. At the same time, for the light-emitting dies  22   a ,  22   b  and  22   c , the distances to the same heterochromatic sensitive area (i.e. the gap projection G) are close to each other. For the light-emitting die  22   a ′,  22   b ′ or  22   c ′, the distances to the same heterochromatic sensitive area (i.e. the gap projection G) are also close to each other. For example, the size of the keycap is in the order of cm, and the distances between the plurality of light-emitting dies are less than 1 mm. In this way, that the distances to the same heterochromatic sensitive area are close to each other means that the differences between the distances from each light-emitting die to the same heterochromatic sensitive area (the gap projection G) are almost negligible (e.g., the differences between the distances from each light-emitting die to the same heterochromatic sensitive area are less than 1 mm). The color deviation caused by such a small distance difference is not discernible by the human eye. 
     In the present disclosure, the coverage space of the keycap  12  in the vertical direction D 1  has a heterochromatic sensitive area. The heterochromatic sensitive area is, for example, the gap projection G between the first support  16  and the second support  18 . The plurality of light-emitting dies  22   a ,  22   b  and  22   c  as a whole do not overlap with the gap projection G. Since the light of different colors emitted by the multiple light-emitting dies  22   a ,  22   b  and  22   c  can travel at similar distances, the influence of the gap projection G on uneven light mixing and color deviation can be suppressed. 
     Furthermore, please also refer to  FIG.  10    and  FIG.  12   . In the embodiment, the base plate  14  has an outer plate edge  146  in the horizontal direction D 3 ″ that is closest to the light-emitting dies  22   a ,  22   b  and  22   c . There is a light-emitting distance d 3  between the light-emitting dies  22   a ,  22   b  and  22   c  and the outer plate edge  146 . In principle, the farther the light-emitting dies  22   a ,  22   b  and  22   c  are away from the outer plate edge  146 , the more the base plate  14  can restrain the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c  from escaping from the outer plate edge  146 . In practice, the proper values for the light-emitting distance d 3  of multiple models are 4.8 mm, 5.3 mm, 6.2 mm, 7.1 mm and 7.7 mm. The light-emitting distance d 3  is preferably within the range from 4.8 mm to 7.7 mm. Furthermore, in the embodiment, the arrangement direction D 2 ″ of the light-emitting dies  22   a ,  22   b  and  22   c  is parallel to the outer plate edge  146 , but it is not limited thereto in practice. 
     Furthermore, please also refer to  FIG.  13 A .  FIG.  13 A  is a top view of the illuminated keyswitch structure in  FIG.  10   , in which the hidden profiles of the light-emitting dies  22   a ,  22   b  and  22   c  are shown in thin lines. In general, the arrangement direction of monochromatic light sources does not need to consider the lengthwise direction  12   b ′ of the permeable indicator area  12   a ′ of the keycap  12 . However, in the case of multi-color light sources, e.g. mixing light of three colors emitted by the light-emitting dies  22   a ,  22   b  and  22   c  into various colors that need to be presented, if the arrangement direction D 2 ″ of the light-emitting dies  22   a ,  22   b  and  22   c  is perpendicular to the lengthwise direction  12   b ′ of the permeable indicator area  12   a ′ of the keycap  12 , the two light-emitting dies  22   a  and  22   c  on the outside provide the most sufficient light to the adjacent character section, but the character section far away from the light-emitting dies  22   a  and  22   c  has the problem of insufficient light, which causes color deviation on the two distal sections of the permeable indicator area  12   a ′ in the lengthwise direction  12   b ′. Besides,  FIG.  13 B  is a top view of a portion of another embodiment extended form  FIG.  13 A , in which the light-emitting dies  22   a ,  22   b  and  22   c  are arranged in a triangle (in terms of lines connecting their centers); that is, the long edge of the light-emitting die  22   b ″ and the long edge of the light-emitting die  22   c ″ are arranged perpendicular to the arrangement direction D 2 ″, and the light-emitting die  22   a ″ is not located in the union range of the light-emitting dies  22   b ″ and  22   c ″. If necessary, the long edge of the light-emitting die  22   a ″ is parallel to the short edges of the light-emitting dies  22   b ″ and  22   c ″, but the long edge of the light-emitting die  22   a ″ is perpendicular to the long edges of the light-emitting dies  22   b ″ and  22   c ″. The arrangement direction D 2 ″ of at least two light-emitting dies  22   b ″ and  22   c ″ is perpendicular to the lengthwise direction  12   b ′/long axis direction  12   c ′ of the permeable indicator area  12   a ′, also perpendicular to the horizontal direction D 3 ″, and parallel to the short axis direction  12   d ′. The light-emitting dies  22   b ″ and  22   c ″ are located at the same side of the same heterochromatic sensitive area, i.e., the same side of the first permeable character “L” or second permeable character “d” of the end characters, and the distances to the same heterochromatic sensitive area, i.e., the end character “L” or “d” are already close to each other, so the color deviation can be eliminated. As for the third light-emitting die  22   a ′, it is disposed preferably adjacent to the center line of the short axis  12   d ′ of the permeable indicator area  12   a ′. In this case, there is no other light-emitting part under the permeable indicator area  12   a ′, except for the light-emitting dies  22   a ″,  22   b ″ and  22   c ″. If necessary, the line connecting the first permeable character “L” and the second permeable character “d” passes through the union range of the light-emitting dies  22   a ″,  22   b ″ and  22   c ″, or the line connecting the first permeable character “L” and the second permeable character “d” passes through the light-emitting die  22   a ″, or the center of the union range of the light-emitting dies  22   a ″,  22   b ″ and  22   c ″ is located at the center point of the long axis of the permeable indicator area  12   a ′. Overall, the light-emitting dies  22   a ″,  22   b ″ and  22   c ″ are preferably adjacent to the geometric center of the permeable indicator area  12   a′.    
     In the embodiment, in the keycap  12 , the lengthwise direction  12   b ′ of the permeable indicator area  12   a ′ above the light-emitting dies  22   a ,  22   b  and  22   c  is perpendicular to the arrangement direction D 2 ″, thus reducing or eliminating the influence of uneven light mixing on the permeable indicator area  12   a ′ caused by the spaced arrangement of the light-emitting dies  22   a ,  22   b  and  22   c . In addition, for other descriptions about the relative position relationship between the light-emitting dies  22   a ,  22   b  and  22   c  and the permeable indicator area  12   a ′, please refer to the relevant descriptions of the relative position relationship between the light-emitting dies  22   a ,  22   b  and  22   c  and the permeable indicator area  12   a  and variations thereof, which will not be repeated. In addition, in the embodiment, the through hole  144  is roughly rectangular. Hole edges  144   a  and  144   b  of the through hole  144  are parallel to an edge of the permeable indicator area  12   a ′. The arrangement direction D 2 ″ of the light-emitting dies  22   a ,  22   b  and  22   c  is parallel to the hole edges  144   a  and  144   b  (equivalent to inner plate edges) of the through hole  144 , as shown by  FIG.  10    and  FIG.  12   . This configuration is conducive to reduction of the influence of the through hole  144  on the light field provided by the light-emitting dies  22   a ,  22   b  and  22   c  to the permeable indicator area  12   a ′. The above description also applies to the arrangement of the light-emitting dies  22   a ,  22   b  and  22   c  relative to the through hole  142 ″ in  FIG.  8    and  FIG.  9    (in which the light-emitting dies  22   a ,  22   b  and  22   c  are also disposed parallel to the hole edge  142   a ″). Furthermore, the arrangement parallel to the hole edge can also apply to the disposition of the light-emitting dies  22   a ,  22   b  and  22   c  relative to the through hole  142  (e.g., modified to be a rectangular hole) in the illuminated keyswitch structure  1 , which will not be repeated. 
     In addition, in the illuminated keyswitch structure, in practice, the light-emitting dies  22   a ,  22   b  and  22   c  can also be modified to be arranged above the base plate  14 , which can avoid the interference of the base plate  14  to the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c . In this case, the base plate  14  does not need to form a through hole corresponding to the light-emitting dies  22   a ,  22   b  and  22   c , which is conducive to the strength of the base plate  14 . Furthermore, the light-emitting dies  22   a ,  22   b  and  22   c  can be integrated into the circuitry of the switch circuit board  20 . For example, the light-emitting dies  22   a ,  22   b  and  22   c  are disposed directly on the lower transparent sheet of the switch circuit board  20  and are powered by the circuitry on the lower transparent sheet. The middle and upper transparent sheets form openings correspondingly, so as to expose the light-emitting dies  22   a ,  22   b  and  22   c . This structural configuration can eliminate the interference of the switch circuit board  20  to the light emitted by the light-emitting dies  22   a ,  22   b  and  22   c.    
     Furthermore, in the illuminated keyswitch structures  1  and  3 , the first support  16  and the second support  18  are pivotally connected with each other around the pivot axis A 1  (indicated by a dashed line in the figures) through their middle portions to form an X-shaped scissors support; however, it is not limited thereto in practice. For example, the first support  16  and the second support  18  can be changed to be pivotally connected with each other through their end portions, or form a V-shaped butterfly support or an inverted V-shaped support by being directly connected onto the base plate  14  through their end portions. For another example, the first support  16  and the second support  18  can be changed to be opposite and spaced apart (e.g., each of them is rotatably connected to the base plate  14 ), and a linkage support is used to link the first support  16  and the second support  18 . Furthermore, the illuminated keyswitch structures  1  and  3  use the resilient dome  26  as the restoring force mechanism; however, it is not limited thereto in practice. For example, the restoring force mechanism is realized by a spring or a magnetic attraction mechanism. 
     In practice, as shown by  FIG.  10   , in the embodiment, the keycap  12  has a permeable indicator area  12   a ′. The permeable indicator area  12   a ′ has a lengthwise direction  12   b ′. The pivot axis A 1  is parallel to the lengthwise direction  12   b ′ of the permeable indicator area  12   a ′. When the light-emitting dies  22   a ,  22   b  and  22   c  are arranged as shown by  FIG.  11 A , the light of different colors emitted by the light-emitting dies  22   a ,  22   b  and  22   c  can travel to the ends of the permeable indicator area  12   a ′ at similar distances, thereby suppressing the uneven light mixing and color deviation. 
     Furthermore, the foregoing describes the relative position relationships of the light-emitting dies  22   a ,  22   b  and  22   c  relative to the circuitry of the switch circuit board  20 , and the first and second supports  16  and  18  with the illuminated keyswitch structures  1  and  3 , respectively. In other embodiments, the illuminated keyswitch structure may also have both cases. For example, the switch contact pad  202  is located under the first support  16  or the second support  18  or adjacent to the position under the first support  16  or the second support  18 , and the light-emitting dies  22   a ,  22   b  and  22   c  are located under the first support  16  or the second support  18 . For another example, the light-emitting dies  22   a ,  22   b  and  22   c  located under the first support  16  or the second support  18  is also adjacent to the circuitry of the switch circuit board  20 . Furthermore, in practice, some structural features of each embodiment may also be applied to other embodiments. For example, when the light-emitting dies  22   a ,  22   b  and  22   c  under the base plate  14  is disposed near the circuitry of the switch circuit board  20 , the light-emitting dies  22   a ,  22   b  and  22   c  may be also near edges of the base plate  14 , and hence the above illuminated keyswitch structure  3  is applicable herein. 
     Although the foregoing discloses the above preferably practical ranges of the light-emitting distances d 1 , d 2  and d 3  through actual implementation data, in practice, practical ranges of the light-emitting distances d 1 , d 2  and d 3  may be used with slightly reducing lighting effect relative to the above preferably practical ranges, which still can achieve a certain level of overall optical design benefits. Therefore, an addition or subtraction of 15% to 20% of the upper and lower boundary values of the preferably practical ranges of the light-emitting distances d 1 , d 2  and d 3  disclosed in the foregoing should still belong to the coverage range of the light-emitting distances d 1 , d 2 , and d 3  in the foregoing. 
     In addition, in the above embodiments, the light-emitting dies  22   a ,  22   b  and  22   c  (or the light-emitting dies  22   a ′,  22   b ′ and  22   c ′, or the light-emitting dies  22   a ″,  22   b ″ and  22   c ″) may be packed together in the same package in practice, or individually packed. Furthermore, in the case of packaging multiple light-emitting dies in a single package, the single package can package three or more light-emitting dies. For example, please refer to  FIG.  14    and  FIG.  15   .  FIG.  14    is a schematic diagram illustrating a light-emitting die package  42  according to a first embodiment.  FIG.  15    is a sectional view of the light-emitting die package along the line W-W in  FIG.  14   . The light-emitting die package  42  includes a carrier  420 , a plurality of light-emitting dies (including three light-emitting dies  422   a ,  422   b  and  422   c  in the embodiment) disposed on the carrier  420 , and a permeable package material  424  covering the plurality of light-emitting dies  422   a ,  422   b  and  422   c  (in which because the permeable package material  424  is light-transmitting, the profiles of the light-emitting dies  422   a ,  422   b  and  422   c  are shown in thin lines in  FIG.  14   ). In the embodiment, the carrier  420  has side walls  420   a  on its periphery to form an accommodating space  420   b . The light-emitting dies  422   a ,  422   b  and  422   c  are accommodated in the accommodating space  420   b . The accommodating space  420   b  is filled with the permeable package material  424 . The permeable package material  424  covers the light-emitting dies  422   a ,  422   b  and  422   c . In practice, the carrier  420  may include a lead frame and a container joined with the lead frame (e.g., but not limited thereto, by injection molding). For simplification of drawings, the carrier  420  is shown by a simple structure in the figures. Taking the light-emitting die  422   a  as an example, the light-emitting die  422   a  has a top light-emitting surface  4222   a  and four side light-emitting surfaces  4224   a . The light-emitting die  422   a  emits light from the top light-emitting surface  4222   a  and the side light-emitting surfaces  4224   a . The light-emitting dies  422   b  and  422   c  are also the same, which will not be repeated in addition. Furthermore, the disposition distances between the light-emitting dies  422   a ,  422   b  and  422   c  depend on the actual manufacturing process, which will not be described in detail. For example, if mini-LEDs are used, the disposition distances can be hundreds of microns. 
     Furthermore, in the embodiment, the carrier  420  may be opaque. The carrier  420  can reflect light (e.g., using white material to make the carrier  420  or coating the inner side surfaces in the accommodating space  420   b  with a reflective layer, for increasing light reflection efficiency), or the white material may be partially reflective and semi-transparent by controlling the thickness of the white material. Both help to improve the light mixing effect (that is, to increase the uniformity of the light exiting the light-emitting die package  42  from the top surface  424   a  of the permeable package material  424 ). Furthermore, in the embodiment, light exits the light-emitting die package  42  from the top surface  424   a  of the permeable package material  424  roughly in the vertical direction D 1 . In practice, the carrier  420  may not include the protruding side walls  420   a . For example, in  FIG.  16   , the carrier  420 ′ is provided without protruding side walls, so that light can also be emitted out of the light-emitting die package  42  in horizontal directions D 4   a  and D 4   b . Therein, the permeable package material  424 ′ has exposed side surfaces  424   b  and  424   c . The side surface  424   b  is parallel to the vertical direction D 1  and the horizontal direction D 4   a . The side surface  424   c  is parallel to the vertical direction D 1  and the horizontal direction D 4   b . Furthermore, the horizontal directions D 4   a  and D 4   b  are perpendicular to each other; however, it is not limited thereto in practice. 
     For simplification of drawings, in  FIG.  17    (which is a top view configuration of the light-emitting die package  42  (or  42 ′)), the overall outline of the light-emitting die package  42  (or  42 ′) is shown by a single thick box, and the light-emitting dies  422   a ,  422   b  and  422   c  thereof are shown by thin boxes, respectively. The colors of the light emitted by the light-emitting dies  422   a ,  422   b  and  422   c  are also indicated in the figure (e.g., red is indicated by the letter “R”, green by the letter “G”, blue by the letter “B”). As shown by  FIG.  14    and  FIG.  17   , in the first embodiment, the light-emitting dies  422   a ,  422   b  and  422   c  are distributed in a plane and are monochromatic light-emitting dies. Therein, the light-emitting die  422   a  emits red light, the light-emitting die  422   b  emits green light, and the light-emitting die  422   c  emits green light. As shown by  FIG.  17   , in the light-emitting dies  422   a ,  422   b  and  422   c , the two adjacent light-emitting dies  422   a  and  422   b  which are arranged in a first arrangement direction (i.e., the horizontal direction D 4   a ) perpendicular to the vertical direction D 1  (e.g., arranged along the horizontal dashed line in the drawing) emit light of different colors (red light and green light, respectively). In the light-emitting die package  42 ′ (which has the exposed side surfaces  424   b  and  424   c ; on the contrary, in the light-emitting die package  42 , the side surfaces of the permeable package material  424  are covered by the protruding side walls  420   a ), this disposition configuration makes the light emitted by the light-emitting die package  42  in a direction perpendicular to the horizontal direction D 4   a  not only have a single color (based on the orientation of the drawing of  FIG.  17   , red light and green light can be directly received at the same time at the lower side of the light-emitting die package  42 ), which helps to reduce the degree of color deviation in this direction. 
     Similarly, the two adjacent light-emitting dies  422   b  and  422   c  which are arranged in a second arrangement direction (i.e., the horizontal direction D 4   b ) perpendicular to the vertical direction D 1  (e.g., arranged along the vertical dashed line in the drawing) emit light of different colors (green light and blue light, respectively). In the light-emitting die package  42 ′, this disposition configuration makes the light emitted by the light-emitting die package  42  in a direction perpendicular to the horizontal direction D 4   a  not only have a single color (based on the orientation of the drawing of  FIG.  17   , green light and blue light can be directly received at the same time at the right side of the light-emitting die package  42 ), which helps to reduce the degree of color deviation in this direction. 
     As shown by  FIG.  16   , the light-emitting dies  422   a  and  422   b  are arranged closer to the side surface  424   b  of the light-emitting die package  42 ′ than the other light-emitting die  422   c . The light-emitting dies  422   a  and  422   b  have die edges  4226   a  and  4226   b  parallel to the side surface  424   b , respectively. One side light-emitting surface  4224   a  of the light-emitting die  422   a  faces the same direction as the side surface  424   b ; the same is true for the light-emitting die  422   b , which will not be repeated in addition. Furthermore, the above descriptions of the light-emitting die package  42 ′ are also applicable to the light-emitting die package  42 , and will not be repeated in addition. 
     Furthermore, as shown by  FIG.  17   , the light-emitting dies  422   a ,  422   b  and  422   c  emit light of three colors (red, green and blue), the area of the top light-emitting surface corresponding to each color light is equal (in the embodiment, the top light-emitting surfaces of the light-emitting dies  422   a ,  422   b  and  422   c  are equal). However, in practice, the light-emitting die package  42  is not limited to including three light-emitting dies. Please refer to  FIG.  18   , which is a top view configuration of a light-emitting die package  43  according to a second embodiment. The light-emitting die package  43  includes four light-emitting dies, emitting green light, blue light, green light, and red light, respectively. The relevant descriptions of the aforementioned light-emitting die packages  42  and  42 ′ are also applicable herein, where will not be repeated in addition. For another example, as shown by  FIG.  19   , a light-emitting die package  43   a  according to a third embodiment also includes four light-emitting dies, emitting green light, blue light, green light, and red light, respectively. Similarly, the relevant descriptions of the aforementioned light-emitting die packages  42  and  42 ′ are also applicable herein, where will not be repeated in addition. 
     For another example, as shown by  FIG.  20   , a light-emitting die package  43   b  according to a fourth embodiment includes five light-emitting dies, emitting green light, blue light, red light, green light, and blue light, respectively. Similarly, the relevant descriptions of the aforementioned light-emitting die packages  42  and  42 ′ are also applicable herein, where will not be repeated in addition. 
     For another example, as shown by  FIG.  21   , a light-emitting die package  43   c  according to a fifth embodiment includes six light-emitting dies, emitting green light, blue light, red light, green light, blue light, and red light, respectively. Similarly, the relevant descriptions of the aforementioned light-emitting die packages  42  and  42 ′ are also applicable herein, where will not be repeated in addition. 
     For another example, as shown by  FIG.  21   , a light-emitting die package  43   d  according to a sixth embodiment includes eight light-emitting dies, emitting green light, red light, blue light, green light, red light, green light, blue light, and red light, respectively. Similarly, the relevant descriptions of the aforementioned light-emitting die packages  42  and  42 ′ are also applicable herein, where will not be repeated in addition. Furthermore, in the embodiment, the light-emitting dies of the light-emitting die package  43   d  are arranged in a rectangular ring. Any two adjacent light-emitting dies along the rectangular ring emit light of different colors. 
     In the light-emitting die packages  42 ,  42 ′,  43   a ,  43   b ,  43   c  and  43   d  of the above embodiments, each light-emitting die has at least one side facing outwards. For example, in the light-emitting die package  43   d  shown by  FIG.  22    (based on the orientation of the drawing of  FIG.  22   ), the right and upper sides of the right light-emitting die of blue light face outwards, the right side of the right light-emitting die of green light faces outwards, the right and lower sides of the right light-emitting die of red light face outwards, the upper side of the middle light-emitting die of red light faces outwards, the lower side of the middle light-emitting die of green light faces outwards, and so on. This configuration helps to improve the utilization of the light emitted by the light-emitting die package through its side surfaces. However, it is not limited thereto in practice. For example, a light-emitting die is also disposed at the location indicated by a dashed box in  FIG.  22   . 
     In actual applications, the above light-emitting die packages  42 ,  42 ′,  43   a ,  43   b ,  43   c  and  43   d  may directly replace the above light-emitting dies  22   a ,  22   b  and  22   c , the above light-emitting dies  22   a ′,  22   b ′ and  22   c ′ or the above light-emitting dies  22   a ″,  22   b ″,  22   c ″ and be disposed in the illuminated keyswitch structures  1  and  3 . For example, the light-emitting die package  43   d  (as shown by  FIG.  19   ) replaces the light-emitting dies  22   a ,  22   b  and  22   c  (of the illuminated keyswitch structure  1 ) in  FIG.  4 A  and is fixed on the light source circuit board  24  (also referring to  FIG.  2   ). The top view configuration thereof is shown as  FIG.  23   ; the sectional view thereof is shown as  FIG.  24    (equivalent to the case that the light-emitting dies  22   a ,  22   b  and  22   c  in  FIG.  3    are replaced with the light-emitting die package  43   d ). The circuitry (including the switch contact pads  202 ) of the switch circuit board  20  does not overlap with the light-emitting die package  43   d . In the light-emitting die package  43   d , some of the plurality of light-emitting dies (i.e., based on the orientation of the drawing of  FIG.  17   , the light-emitting die of blue light, the light-emitting die of green light, and the light-emitting die of red light on the lower side) are closer to the flat edge  202   a  of the switch contact pad  202  than the other light-emitting dies in the horizontal direction D 3  (perpendicular to the vertical direction D 1 ) and are arranged parallel to the flat edge  202   a  (i.e., arranged in the direction D 2 ). 
     Furthermore, as shown by  FIG.  24   , the light-emitting die package  43   d  is located in the through hole  142  of the base plate  14 . The vertical projections of the switch contact pad  202  and the light-emitting die package  43   d  on the base plate  14  are located within the through hole  142 . The light-emitting die package  43   d  is not higher than an upper surface  142   c  of the base plate  14  in the vertical direction D 1  (that is, the top surface of the light-emitting die package  43   d  (e.g., the top surface  424   a  of the permeable package material  242 , referring to  FIG.  14    or  FIG.  15   ) is lower than or equal to the upper surface  142   c ). 
     In this embodiment, the through hole  142  (as shown by  FIG.  2   ) is circular; however, it is not limited thereto. For example, in a variation example of the through hole  142 , part of the arc edge of the through hole  142 ′ (the profile projection of which is shown in dashed lines in  FIG.  23   ) of the base plate  14  is parallel to the arc edge of the switch contact pad  202 , and at the other side of the through hole  142 , three edges are perpendicular to each other, thereby constituting a bullet-shaped through hole as a whole. Therein, based on the orientation of the drawing of  FIG.  23   , the adjacent light-emitting dies on the left side of the light-emitting die package  43   d  (i.e., the light-emitting die of blue light, the light-emitting die of red light, and the light-emitting die of green light) are closer to the hole edge  142   b ′ than the other light-emitting dies in a horizontal direction (equivalent to the direction D 2 ) perpendicular to the vertical direction D 1  and are arranged parallel to the straight hole edge  142   b ′ (i.e., arranged in the direction D 3 , or arranged perpendicular to the straight hole edge  142   a ′). Thereby, the hole edge  142   b ′ has similar shading conditions for each of the light-emitting dies on the left of the light-emitting die package  43   d , which helps to reduce the influence of the hole edge  142   b ′ on the uniformity of the backlight provided by the light-emitting die package  43   d . For the straight hole edges  142   a ′ and  142   c ′, the light-emitting die package  43   d  also has the light-emitting dies that are adjacent to the straight hole edges  142   a ′ and  142   c ′ and are arranged parallel to the straight hole edges  142   a ′ and  142   c ′, which will not be described in addition. 
     For another example, in a variation example of the through hole  142 , as shown by  FIG.  25   , the through hole  143  (the profile of which is shown in bold lines in the figure) of the base plate  14  includes a main hole portion  143   a  and two extension portion  143   b  extending from two sides of the main hole portion  143   a . The vertical projection (shown in thin lines in the figure) of the switch contact pad  202 ′ on the base plate  14  is located within the main hole portion  143   a . The vertical projection (shown in thin lines in the figure) of the light-emitting die package  43   d  on the base plate  14  is located within one of the extension portions  143   b . In the embodiment, another light-emitting die package  43   d  (shown in dashed lines in the figure) is disposed according to the other extension portions  143   b . Thereby, the switch contact pad  202 ′ also can avoid covering the light-emitting die package  43   d  directly. In addition, the two extension portions  143   b  are arranged at 180 degrees; however, it is not limited thereto in practice. For example, the two extension portions  143   b  can be arranged at 120 degrees (logically, this still belongs to the arrangement on both sides of the main hole part  143 ). 
     For another example, in a variation example of the through hole  142 , as shown by  FIG.  26   , the base plate  14  has a through hole  143 ′ (the profile of which is shown in bold lines in the figure). The vertical projection (shown in thin lines in the figure) of the switch contact pad  202 ″ on the base plate  14  is located outside the through hole  143 ′ and beside the through hole  143 ′. The vertical projection (shown in thin lines in the figure) of the light-emitting die package  43   d  on the base plate  14  is located within the through hole  143 ′. Thereby, the switch contact pad  202 ″ also can avoid covering the light-emitting die package  43   d  directly. Furthermore, the through hole  143 ′ is a circular sector and (in the view point of  FIG.  26   ) extends along the inner edge of the through hole  143 ′. In addition, in practice, it is practicable to dispose another through hole  143 ′ (shown in dashed lines in the figure), and another light-emitting die package  43   d  (shown in dashed lines in the figure) is also disposed according to this through hole  143 ′. Furthermore, in practice, the central angle corresponding to the circular sector is not limited to the case shown in the figure that is less than 180 degrees. The two through holes  143 ′ are not limited to configurations with the same profile and symmetrical disposition. In the embodiment, the through hole  143 ′ is disposed to avoid the circuitry layout, so the through holes  143 ′ may be formed in a single C-shaped profile in practice (for example, modify the leads of the switch contact pad  202 ″ in the figure so that they are on the same side); however, it is not limited thereto in practice. Furthermore, in practice, the profile of the through hole  143 ′ is not limited to a circular sector. 
     In the foregoing, as shown by  FIG.  8   , the light-emitting dies  22   a ,  22   b  and  22   c  and the trace segment  204  are staggered (i.e., not overlapping in the vertical direction D 1 ). Similarly, in actual applications, the light-emitting dies  22   a ,  22   b  and  22   c  may be replaced with the light-emitting die package  43   d , as shown by  FIG.  27   . The trace segment  204  extends straight. In the light-emitting die package  43   d , some of the light-emitting dies (i.e., based on the orientation of the drawing of  FIG.  27   , the left light-emitting die of green light, the left light-emitting die of red light, the left light-emitting die of blue light (e.g. referring to  FIG.  22   )) that are closer to the trace segment  204  than the other light-emitting dies in the horizontal direction D 3 ′ (perpendicular to the vertical direction D 1 ) are arranged parallel to and near to the trace segment  204  (i.e., arranged in the direction D 2 ). The relevant descriptions about  FIG.  8    and  FIG.  9    in the foregoing are also applied herein if they are applicable, where will not be repeated in addition. 
     In the foregoing, as shown by  FIG.  11 A , the light-emitting dies  22   a ,  22   b  and  22   c  are located under one of the supports (e.g., the first support  16 ). In actual applications, the light-emitting dies  22   a ,  22   b  and  22   c  may be replaced with the light-emitting die package  43   d , as shown by  FIG.  28   . In the light-emitting die package  43   d , some of the light-emitting dies (i.e., based on the orientation of the drawing of  FIG.  28   , the left light-emitting die of green light, the left light-emitting die of red light, the left light-emitting die of blue light (e.g. referring to  FIG.  22   )) that are closer to the gap projection G (which has a lengthwise direction equivalent to the direction D 2 ″; the gap projection G extends roughly in the lengthwise direction) than the other light-emitting dies in a horizontal direction D 3 ″ perpendicular to the vertical direction D 1  are arranged parallel to the lengthwise direction and have a die edge (e.g., the left edges of the above light-emitting dies) parallel to the lengthwise direction. Thereby, the gap projection G has similar shading conditions for each of the light-emitting dies on the left of the light-emitting die package  43   d , which helps to reduce the influence of the gap projection G on the uniformity of the backlight provided by the light-emitting die package  43   d . Furthermore, in the embodiment, the light-emitting die package  43   d  is completely below the first support  16 , so that the light emitted by each light-emitting die in the light-emitting die package  43   d  can travel in a similar path, thereby reducing the degree of color deviation that may occur after the light passes through the first support  16 . The relevant descriptions about  FIG.  11 A  in the foregoing are also applied herein if they are applicable, where will not be repeated in addition. For example, the light-emitting die package  43   d  can be changed to be disposed under the second support  18  (e.g., the light-emitting die package  43   d  shown in dashed lines in the figure). 
     In the foregoing, as shown by  FIG.  7   ,  FIG.  13 A  and  FIG.  13 B , the light-emitting dies  22   a ,  22   b  and  22   c  as a whole overlaps with the permeable indicator areas  12   a  and  12   a ′ in the vertical direction D 1 . In actual applications, the light-emitting dies  22   a ,  22   b  and  22   c  may be replaced with the light-emitting die package  43   d . As shown by  FIG.  29   , the permeable indicator area  12   a ′ is rectangular and thereon defines a long axis  12   c ′ and a short axis  12   d ′ (indicated by chain lines in the figure). The long axis  12   c ′ is parallel to the lengthwise direction  12   b ′. The short axis  12   d ′ is perpendicular to the lengthwise direction  12   b ′ (and also parallel to the direction D 2 ″). The geometric center of the permeable indicator area  12   a ′ (equivalent to the intersection of the long axis  12   c ′ and the short axis  12   d ′) overlaps with the light-emitting die package  43   d  in vertical direction D 1  (or the geometric center falls within the range of light-emitting die package  43   d ). Furthermore, in the embodiment, the geometric center of the permeable indicator area  12   a ′ coincides with the geometric center of the light-emitting die package  43   d ; however, it is not limited thereto in practice. For example, the geometric center of the light-emitting die package  43   d  deviates from the geometric center of the permeable indicator area  12   a ′, referring to the light-emitting die package  43   d  shown in dashed lines in the figure. Therein, in this case, the vertical projection of the whole light-emitting die package  43   d  still falls within the extent of the permeable indicator area  12   a ′; however, it is not limited thereto in practice. For example, the vertical projection of the whole light-emitting die package  43   d  exceeds the extent of the permeable indicator area  12   a ′ (e.g., in  FIG.  13 A , both vertical projections of the light-emitting dies  22   a  and  22   c  are beyond the extent of the permeable indicator area  12   a ′, so that the vertical projection of the light-emitting dies  22   a ,  22   b  and  22   c  as a whole partially exceeds the extent of the permeable indicator area  12   a ′). Furthermore, in the embodiment, the permeable indicator area  12   a ′ includes a plurality of permeable characters (e.g. “Legend” in the figure) arranged along the lengthwise direction  12   b ′. In the light-emitting die package  43   d , the die edges of the light-emitting dies are parallel to or perpendicular to the lengthwise direction  12   b ′ (for example, for the light-emitting die of green light in the upper left corner, its upper and lower side edges are parallel to the lengthwise direction  12   b ′ (i.e., parallel to the long axis  12   c ′), and its left and right side edges are perpendicular to the lengthwise direction  12   b ′). The relevant descriptions about  FIG.  7   ,  FIG.  13 A  and  FIG.  13 B  in the foregoing are also applied herein if they are applicable, where will not be repeated in addition. 
     The foregoing is described with the light-emitting die package  43   d  replacing the light-emitting dies  22   a ,  22   b  and  22   c  as an example. In principle, the light-emitting die packages  42 ,  42 ′,  43   a ,  43   b ,  43   c  and  43   d  can also be used to replace the above light-emitting dies  22   a ,  22   b  and  22   c , the above light-emitting dies  22   a ′,  22   b ′ and  22   c ′, or the above light-emitting dies  22   a ″,  22   b ″ and  22   c ″ and be applied to each of the above embodiments, which will not be further described in detail. 
     In addition, in practice, the above embodiments may be provided with a light-guiding sheet to guide and mix light emitted by the light-emitting die packages  42 ,  42 ′,  43   a ,  43   b ,  43   c  and  43   d  and the light-emitting dies  22   a ,  22   b ,  22   c ,  22   a ′,  22   b ′,  22   c ′,  22   a ″,  22   b ″ and  22   c ″. Please refer to  FIG.  30   . An illuminated keyswitch structure  4  shown by  FIG.  30    is similar to the illuminated keyswitch structure  1 , so the illuminated keyswitch structure  4  follows the component symbols of the illuminated key switch structure  1 . For other descriptions about the illuminated keyswitch structure  4 , please refer to the relevant descriptions of the illuminated keyswitch structure  1  and variations thereof in the foregoing, which will not be repeated in addition. A main difference between the illuminated keyswitch structure  4  and the illuminated keyswitch structure  1  is roughly that the illuminated keyswitch structure  4  further includes a light-guiding sheet  28  that is disposed under the base plate  14 . The light-guiding sheet  28  has an accommodating recess  282  (e.g., realized by a through hole). The light-emitting die package  43   d  (or other light-emitting die packages  42 ,  42 ′,  43   a ,  43   b  and  43   c ) is located in the accommodating recess  282 , so that the light emitted by the light-emitting die package  43   d  enters the light-guiding sheet  28  from an inner wall surface  282   a  of the accommodating recess  282 . The light entering the light-guiding sheet  28  can leave the light-guiding sheet  28  from an upper surface  284  of the light-guiding sheet  28 . As shown by  FIG.  30   , the base plate  14  does not cover the light-guiding sheet  28  at its through hole  142 , so the light can illuminate the keycap  12  upwards through the through hole  142 . In terms of structural properties, the base plate  14  has an opaque effect in principle, and therefore can be used as a mask layer at the same time. In addition, in the embodiment, the projection of the switch contact pad  202  of the switch circuit board  20  on the base plate  14  is also located within the through hole  142 ; however, it is not limited thereto in practice. For example, the switch contact pad  202  is moved to another place (away from the through hole  142 ) or there is also a physical structure of the base plate  14  under the switch contact pad  202 , so that the light exiting from the upper surface  284  of the light-guiding sheet  28  will not directly irradiate the switch contact pad  202 , which helps to reduce the possible influence of the light reflected by the circuitry of the circuit board  20  (e.g., the color of the reflected light is changed). 
     Furthermore, in practice, a mask layer  30  may be disposed on the upper surface  284  of the light-guiding sheet  28 , for a shielding design for the light-guiding sheet  28 , as shown by  FIG.  31   . In practice, the mask layer  30  can be realized by an opaque thin sheet disposed right above the light-emitting die package  43   d . The mask layer  30  covers the accommodating recess  282  (together with the light-emitting die package  43   d  accommodated therein) and forms a permeable area  302   a  at the desired area (e.g. by making holes on this thin sheet), e.g. corresponding to the through hole  142 . The quantity and profile of the permeable area  302   a  can be designed according to product requirements, without being troubled by the structural design of the base plate  14  itself (such as the light leakage caused by the hollow structure for forming the connection structure of the supports). In the embodiment, the vertical projection of the permeable area  302   a  on the base plate  14  is located within the through hole  142 . In addition, in practice, the accommodating recess  282  is not limited to a through hole. For example, the accommodating recess may be realized by a blind hole or recess. In this case, the accommodating recess opens downwards, and will not communicate with the upper surface  284 . The mask layer  30  may be realized by an opaque coating layer coated on the upper surface  284  (e.g., but not limited to, by printing). 
     Please refer to  FIG.  32    and  FIG.  33   ; therein, in  FIG.  33   , the profile of the switch contact pad  203   c  is shown in thin lines, the profile of the light-emitting die package  43   d  is shown by a bold frame, and the profile of the accommodating recess  282  of the light-guiding sheet  28 ′ and the profile of the permeable areas  302   b  of the mask layer  30 ′ are shown in dashed lines. In this example, the vertical projections of the switch contact pad  203   c , the accommodating recess  282  of the light-guiding sheet  28 ′ (together with the light-emitting die package  43   d ), and the permeable area  302   b  of the light-guiding sheet  28 ′ on the base plate  14  are located in the through hole  142 . Furthermore, the light-emitting die package  43   d  is located under the switch contact pad  203   c . On the other hand, the switch contact pad  203   c  and the light-emitting die package  43   d  overlap in the vertical direction D 1 . The permeable areas  302   b  of the mask layer  30 ′ are disposed on the periphery of the projection of the light-emitting die package  43   d  on the mask layer  30 ′. In the embodiment, the permeable area  302   b  is a circular sector (as shown by  FIG.  33   ) and extends around the projection of the light-emitting die package  43   d  on the mask layer  30 ′. In the embodiment, the permeable area  302   b  also extends around the projection of the switch contact pad  203   c  on the mask layer  30 ′; the permeable area  302   b  extends roughly beside the projection of the switch contact pad  203   c  on the mask layer  30 ′. Furthermore, in practice, the central angle corresponding to the circular sector is not limited to the case shown in the figure that is less than 180 degrees. The two permeable areas  302   b  are not limited to configurations with the same profile and symmetrical disposition. In the embodiment, the permeable area  302   b  is disposed to avoid the circuitry layout, so the permeable areas  302   b  may be formed in a single C-shaped profile in practice (for example, modify the leads of the switch contact pad  203   c  in the figure so that they are on the same side); however, it is not limited thereto in practice. Furthermore, in practice, the profile of the permeable area  302   b  is not limited to a circular sector. On the other hand, a vertical projection of an opaque portion of the mask layer  30  on the base plate  14  at least partially falls within the through hole  142 . For example, as shown by  FIG.  32   , a portion of the mask layer  30  above the light-emitting die package  43   d  (which may be defined as an impermeable area of the mask layer  30 ) falls within the through hole  142 . For another example, as shown by  FIG.  32   , a left portion of the mask layer  30  (which may be defined as another impermeable area of the mask layer  30 ) forms a portion of the profile of the permeable area  302   b ; the vertical projection of the left portion on the base plate  14  partially falls within the through hole  142 . 
     In addition, in the embodiment, in practice, there may also be a physical structure of the base plate  14  between the switch contact pad  203   c  and the mask layer  30 ′, for providing structural support for the switch contact pad  203   c , as shown by  FIG.  34   . In this embodiment, the base plate  14  forms a through hole  145  corresponding to the permeable area  302   b  to expose the corresponding permeable area  302   b . In practice, the through hole  145  may be (but is not limited to) a circular sector and similar in profile to the permeable area  302   b . The vertical projection of the switch contact pad  203   c  on the base plate  14  is located outside the through hole  145  and beside the through hole  145 . 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.