Patent Publication Number: US-11664177-B2

Title: Backlight module

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This non-provisional application is a Division of application Ser. No. 16/792,008, filed on Feb. 14, 2020, with claiming priority under 35 U.S.C. § 119(a) to Patent Application No. 108133123 filed in Taiwan, R.O.C. on Sep. 12, 2019, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to a backlight module, and in particular, to a backlight module having a reflective sheet to guide the backlight emitted from the backlight module. 
     Related Art 
     A keyboard is a common input apparatus for an electronic device such as a desktop computer, a notebook computer, a tablet computer and a mobile phone. A desktop computer and a notebook computer are usually equipped with a physical keyboard, and a tablet computer and a mobile phone may be equipped with a virtual keyboard. 
     When using a physical keyboard, a user sometimes needs to see symbols on keys to press correct keys. However, when using the physical keyboard in a dim or dark environment, the user may fail to locate the correct keys. Therefore, an illuminated keyboard is provided. During use, the illuminated keyboard emits light to illuminate symbols on keys, so that a user can see the symbols and correctly press the desired keys in a dark environment. 
     SUMMARY 
     In view of the foregoing, the present invention provides a backlight module, adapted to a keyboard to illuminate at least one keycap of the keyboard. 
     According to some embodiments, a backlight module includes a light source assembly, a light guide film, and a reflective sheet. The light source assembly includes a light-emitting component. The light-emitting component includes an LED and a lens. The light guide film has a top surface, a bottom surface, a through hole and a light-exit pattern. The light-emitting component is correspondingly located below the through hole. A size of an opening area of the through hole is smaller than a size of an extension area except the height of the light-emitting component. The light of the light-emitting component is emitted upward toward the through hole. The light-exit pattern is on the bottom surface. The light-exit pattern encloses the through hole. The reflective sheet is located above the through hole. A size of the reflective sheet is larger than or equal to the size of the through hole. A distance from the through hole to an outer edge of the light-exit pattern is greater than a distance from to the through hole to an outer edge of the reflective sheet. 
     According to some embodiments, the backlight module further includes a shading ring. The shading ring is above the top surface of the light guide film. The shading ring has an opening. The opening corresponds to the light-exit pattern. 
     According to some embodiments, the light guide film further has a light-blocking band. The light-blocking band corresponds to the shading ring or the light-exit pattern. The light source assembly further includes a circuit board. The light-emitting component is on the circuit board. The backlight module further includes a light-blocking ring. The light-blocking ring is between the circuit board and the light guide film and corresponds to the light-blocking band. 
     According to some embodiments, the light-blocking band includes a plurality of light-blocking gap segments. The light-blocking gap segments cooperate with each other to form a non-closed rectangular ring. 
     According to some embodiments, the light-blocking gap segments are respectively filled with light-blocking strips. The light-blocking strips corresponds to the light-blocking gap segments; and the light-blocking strips are disposed on one side of the light-blocking ring which faces the light guide film. 
     According to some embodiments, the light guide film has two light-exit patterns. The two light-exit patterns are adjacent to the same through hole. The backlight module further includes a shading ring. The shading ring is above the top surface of the light guide film. The shading ring has two openings, and the two openings correspond to the two light-exit patterns respectively. 
     According to some embodiments, the through hole has two light-collecting corners, and the light-collecting corners correspond to the two light-exit patterns respectively. 
     According to some embodiments, the light guide film has three light-exit patterns. The three light-exit patterns are adjacent to the same through hole. The backlight module further includes a shading ring. The shading ring is above the top surface of the light guide film. The shading ring has three openings, and the three openings correspond to the three light-exit patterns respectively. 
     According to some embodiments, the through hole has three light-collecting corners, and the light-collecting corners correspond to the three light-exit patterns respectively. 
     According to some embodiments, the backlight module further includes a protection plate. The protection plate located on the light guide film. 
     According to some embodiments, the light source assembly further includes a reflective layer. The reflective layer is configured to reflect the light emitted from the light-emitting component and the light leaked from the bottom surface of the light guide film. 
     According to some embodiments, the light source assembly includes a plurality of light-emitting components, and at least two of the light-emitting components emit light of different colors. 
     In conclusion, according to some embodiments, in the backlight module, the through hole with a relative small size on the light guide film cooperates with the reflective sheet, so that the light emitted by the light-emitting component can be directed to the keycaps more efficiently, to illuminate the keycaps with higher luminance for a user to see the keycaps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a schematic three-dimensional exploded view of an illuminated keyboard according to some embodiments; 
         FIG.  2 A  illustrates a schematic partial top view of a backlight module (omitting a keyboard assembly) corresponding to a single keycap according to some embodiments; 
         FIG.  2 B  illustrates a schematic partial sectional view of an illuminated keyboard according to some embodiments; 
         FIG.  2 C  illustrates a schematic diagram showing the distribution of intensity of light emitted by a light-emitting component of a light source assembly changing with a spatial angle according to some embodiments; 
         FIG.  3 A  to  FIG.  3 D  illustrate schematic structural top views of a through hole and a light-incident pattern of a light guide film according to some embodiments; 
         FIG.  4 A  illustrates a schematic partial top view of a backlight module (omitting a keyboard assembly) corresponding to a single keycap according to some embodiments; 
         FIG.  4 B  illustrates a schematic partial sectional view of an illuminated keyboard according to some embodiments; 
         FIG.  5    illustrates a schematic top view of a backlight module according to some embodiments; 
         FIG.  6 A  illustrates a schematic top view of a portion of the backlight module showing a key group area corresponding to two keycaps according to some embodiments; 
         FIG.  6 B  illustrates a schematic top view of a portion of the backlight module showing a key group area corresponding to three keycaps according to some embodiments; 
         FIG.  7 A  illustrates a schematic partial sectional view of an illuminated keyboard according to some embodiments; and 
         FIG.  7 B  and  FIG.  7 C  illustrate schematic partial top views of a keycap and a light guide film according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Refer to  FIG.  1   ,  FIG.  2 A , and  FIG.  2 B  together.  FIG.  1    is a schematic three-dimensional exploded view of an illuminated keyboard according to some embodiments.  FIG.  2 A  is a schematic partial top view of a backlight module (omitting a keyboard assembly) corresponding to a single keycap according to some embodiments.  FIG.  2 B  is a schematic partial (i.e., a part corresponding to a single keycap) sectional view of an illuminated keyboard according to some embodiments. According to some embodiments, an illuminated keyboard includes a keyboard assembly  10  and a backlight module  50 . The backlight module  50  is located below the keyboard assembly  10 . The backlight module  50  includes a light source assembly  60  and a light guide film  70 . The light source assembly  60  includes a light-emitting component  62 . The light-emitting component  62  is configured to emit light. The light guide film  70  has a top surface  72   a , a bottom surface  72   b , a through hole  74 , a light-incident pattern  76  and a light-exit pattern  78 . A size of the through hole  74  is smaller than a size of the light-emitting component  62 . The light of the light-emitting component  62  is toward the through hole  74 . The light-incident pattern  76  is located on at least one of the top surface  72   a  and the bottom surface  72   b  and is adjacent to the through hole  74  (for example, according to the embodiments shown in  FIG.  2 A  and  FIG.  2 B , the light-incident pattern  76  is located adjacent to the through hole  74  on the bottom surface  72   b . The light-exit pattern  78  is located on the bottom surface  72   b . A distance from the through hole  74  to the light-exit pattern  78  is greater than a distance from the through hole  74  to the light-incident pattern  76 . In one embodiment, as shown in  FIG.  2 A  and  FIG.  2 B , the light-incident pattern  76  encloses the through hole  74 , and the light-exit pattern  78  encloses the through hole  74 . 
     When the light-emitting component  62  is driven, the light-emitting component  62  emits the light toward the through hole  74 . As the size (e.g., the opening area) of the through hole  74  is smaller than the size (e.g., the area from the top view) of the light-emitting component  62 , the light irradiates the inner wall of the through hole  74  and the light-incident pattern  76  near the through hole  74  on the top surface  72   a  and/or the bottom surface  72   b  of the light guide film  70 , so that a relatively large amount of light can directly enter the light guide film  70 , and some of the light that enters the light guide film  70  propagates through the way of total inner reflection (in which the light travels inside the light guide film  70  toward the left side and the right side shown in  FIG.  2 B ). When the light that enters the light guide film  70  reaches the light-exit pattern  78 , the propagation direction of some of the light is changed by the light-exit pattern  78  to travel toward the top shown in  FIG.  2 B  then passing through the top surface  72   a , so as to illuminate a keycap  12 . Therefore, in the illuminated keyboard, the keycap  12  with the light-emitting component  62  would have the light emitted from below. In some embodiments, the keycap  12  has at least one symbol. The keycap  12  may be made of a translucent material or the symbol of the keycap  12  has a translucent design. Therefore, the light that passes through the top surface  72   a  can illuminate the symbol for a user to see it. The symbol may be any symbol required for a keyboard function, and, for example, but not limited to, is an English character, a number or a special symbol. 
     The keyboard assembly  10  includes a plurality of keycaps  12 , a plurality of elastic elements  14 , a plurality of switches  16 , and a switching circuit  18 . The keycaps  12 , the elastic elements  14 , and the switches  16  are in a one-to-one relationship. The switch  16  is electrically connected to the switching circuit  18 . The elastic element  14  normally maintains a thrust to keep the keycap  12  at a position shown in  FIG.  2 B . When the user presses the keycap  12 , the switch  16  is pressed by the bottom of the keycap  12 . The switching circuit  18  outputs a signal corresponding to the keycap  12  when detecting that the switch  16  is pressed. When the user releases the keycap  12 , the elastic element  14  pushes the keycap  12  back to the position shown in  FIG.  2 B . In some embodiments, the elastic element  14  has a scissor mechanism. However, the present invention is not limited thereto. In some other embodiments, the elastic element  14  may have a dome mechanism, a pillar mechanism, a butterfly mechanism or the like. 
     The light source assembly  60  of the backlight module  50  has a flat cable  58  (as shown in  FIG.  1   ) for electrical connection to an external device. The external device is, for example, but not limited to, a computer control system (not shown in the drawings). The computer control system may control whether the light-emitting component  62  of the light source assembly  60  emits light or not. The light guide film  70  is configured to direct the light emitted by the light source assembly  60  to irradiate the keycap  12 , so that the user can clearly see the symbol on the keycap  12  in a dim environment. In some embodiments, the light guide film  70  may be divided into a plurality of key group areas  52 ,  54 ,  56 , and each key group area  52 ,  54 ,  56  corresponds to one or more keycaps  12 . The key group area  52  of the backlight module  50  in  FIG.  1    corresponds to two keycaps  12 . The key group area  54  corresponds to three keycaps  12 . The key group area  56  corresponds to four keycaps  12 . 
     The light-emitting component  62  is configured to emit light. Refer to  FIG.  2 C .  FIG.  2 C  is a schematic diagram showing the distribution of intensity of light (light-field intensity distribution) emitted by a light-emitting component of a light source assembly changing with a spatial angle according to some embodiments. As shown in  FIG.  2 C , the light emitted by the light-emitting component is mainly concentrated in an area between spatial angles of plus 60° and minus 60° with respect to a main optical axis  610 . The intensity of light is relatively high in the directions of plus 30°, minus 30°, and 0°. In some embodiments, the light-emitting component  62  includes a light emitting chip  61   b  and a lens  61   a  shown in  FIG.  2 B . The light emitting chip  61   b  may be, but not limited to, a light emitting diode (LED). The lens  61   a  is configured to adjust the pattern of light emitted by the light emitting chip  61   b , so that the pattern is more suitable for a light guide design of the light guide film  70 . For example, the pattern is a distribution diagram of the intensity of light changing with a spatial angle when the light emitting chip  61   b  emits light. In some embodiments, a plurality of light-emitting components  62  of the light source assembly  60  emits light of the same color. In some embodiments, at least two of the plurality of light-emitting components  62  of the light source assembly  60  emit light of different colors. 
     Referring to  FIG.  2 A  and  FIG.  2 B , when the size of the through hole  74  is smaller than the size of the light-emitting component  62 , it means that the size (i.e., the opening area) of the through hole  74  shown in the top view  2 A is smaller than the size (i.e., the extension area except the height) of the light-emitting component  62  shown in the top view  2 A, so that the light-emitting component  62  is not completely accommodated in the through hole  74 . That is, the light-emitting component  62  is located below the through hole  74 . In the embodiment shown in  FIG.  2 A , both the through hole  74  and the light-emitting component  62  are circular as seen in the top view. In addition, as can be seen from the top view, the diameter of the through hole  74  is less than the diameter of the light-emitting component  62 . In some embodiments, a shape of the through hole  74  as seen in the top view is a circle, and a shape of the light-emitting component  62  as seen in the top view is a rectangle. In this case, a diameter of the through hole  74  is less than a length of the diagonal of the rectangle of the light-emitting component  62 . 
     The light of the light-emitting component  62  propagates toward the through hole  74 . For example, the main optical axis  610  (as shown in  FIG.  2 C ) of the light-emitting component  62  is toward the through hole  74 . In some embodiments, the main optical axis  610  of the light-emitting component  62  is parallel to a central axis  74   a  of the through hole  74  or is at an acute angle with respect to the central axis  74   a  of the through hole  74 . In some embodiments, the main optical axis  610  of the light-emitting component  62  passes through the through hole  74 . That is, the main optical axis  610  of the light-emitting component  62  does not intersect with the hole wall of the through hole  74 . In this case, in the foregoing embodiments, the light emitted by the light-emitting component  62  can propagates toward the through hole  74 , so that the light enters the light guide film  70  adequately. 
     The foregoing light-incident pattern  76  is located on the top surface  72   a  or the bottom surface  72   b  of the light guide film  70 . In the embodiment shown in  FIG.  2 B , the light-incident pattern  76  is located adjacent to the through hole  74  on the bottom surface  72   b .  FIG.  2 B  shows that the inner edge of the light-incident pattern  76  approximately contacts the through hole  74 . As shown in  FIG.  2 A , the light-incident pattern  76  surrounds the through hole  74 , so that the light from the light-emitting component  62  enters the light guide film  70  from the inner circumferential surface of the through hole  74 . That is, the light may be refracted by the light-incident pattern  76 , and then enters the light guide film  70  to be transmitted through the way of total inner reflection. 
     Other embodiments of the through hole  74  and the light-incident pattern  76  are, for example, but not limited to, those shown in  FIG.  3 A  to  FIG.  3 D .  FIG.  3 A  to  FIG.  3 D  are schematic structural top views of a through hole and a light-incident pattern of a light guide film according to some embodiments. The inner edge of a light-incident pattern  760  shown in  FIG.  3 A  is near but not contacting a through hole  740 . A through hole  742  shown in  FIG.  3 B  is triangular when viewed from the top, and a light-incident pattern  762  shown in  FIG.  3 B  is also triangular when viewed from the top. A through hole  744  and a light-incident pattern  764  shown in  FIG.  3 C  are both octagonal when viewed from the top. A through hole  746  and a light-incident pattern  766  shown in  FIG.  3 D  are both X-shaped when viewed from the top. 
     Referring to  FIG.  2 A  and  FIG.  2 B , the light-exit pattern  78  is located on the bottom surface  72   b . A distance from the through hole  74  to the light-exit pattern  78  is greater than a distance from the through hole  74  to the light-incident pattern  76 . For example, in the top view of  FIG.  2 A , the light-exit pattern  78  is located at the periphery of the light-incident pattern  76 . A distance between the central axis  74   a  of the through hole  74  in the top view of  FIG.  2 A  and an intersection point formed by a (imaginary) straight line that starts from the central axis  74   a  and extends in the radial direction crossing the outer edge of the light-incident pattern  76  is defined as a first distance D 1 . In some embodiments, the first distance D 1  is the longest distance between the central axis  74   a  and the intersection point of the straight line and the outer edge of the light-incident pattern  76 . A distance between the central axis  74   a  and an intersection point formed by the straight line crossing the inner edge of the light-exit pattern  78  is defined as a second distance D 2 . In some embodiments, the second distance D 2  is the shortest distance between the central axis  74   a  and the intersection point of the straight line and the inner edge of the light-exit pattern  78 . The second distance D 2  is greater than the first distance D 1 . In some embodiments, an area encircled by the outer edge of the light-exit pattern  78  as seen in the top view (for example,  FIG.  2 A ) is not greater than a vertically-projected area from the keycap  12  onto the light guide film  70  (which means that the keycap  12  fully covers the light-exit pattern  78 , as shown in  FIG.  2 B ). In some embodiments, the light-exit pattern  78  is located near the edge of the keycap  12 . In the embodiment shown in  FIG.  2 B , the central axis  74   a  of the through hole  74  is approximately aligned with a geometric center line of the keycap  12 , so that the light that passes through the through hole  74  may directly irradiate the keycap  12 . 
     In the embodiment shown in  FIG.  2 B , a cross section of each single unit (e.g., optical dot) within the light-incident pattern  76  and the light-exit pattern  78  (also known as microstructures, mesh-dot portions, or light-dot portions) is semicircular. However, the present invention is not limited thereto. The cross section may be any shape, such as an irregular shape, a cone, a square, a triangle, and a trapezoid. In the embodiment shown in  FIG.  2 B , the light-incident pattern  76  and the light-exit pattern  78  do not protrude from the bottom surface  72   b , but are recessed toward the inside of the light guide film  70  (concave dots). In some other embodiments, the light-incident pattern  76  and the light-exit pattern  78  may protrude out from the bottom surface  72   b  (convex dots). The shapes and the sizes of the light-incident pattern  76  and the light-exit pattern  78 , and the distances between adjacent concave or/and convex dots of the light-incident pattern  76  and the light-exit pattern  78  may be adjusted according to the pattern of the light emitted by the light-emitting component  62 , the shape of the through hole  74  from its top view, the material of the light guide film  70 , the surface roughness of the light guide film  70 , and the like. Preferred design solutions may be obtained through the foregoing adjustment by finite experiments. In addition, in some embodiments, the light-incident pattern  76  and the light-exit pattern  78  may also be formed by printed ink on the top surface  72   a  or the bottom surface  72   b  of the light guide film  70 . 
     In some embodiments, the backlight module  50  further includes a protection plate  79  (as shown in  FIG.  2 B ) located between the light guide film  70  and the keyboard assembly  10  to protect the light guide film  70 . The protection plate  79  is a transparent film for the light of the light-emitting component  62  to pass through. In the embodiment shown in  FIG.  2 B , after passing through the through hole  74 , the light emitted from the light-emitting component  62  can directly travel through the protection plate  79  to illuminate the keycap  12 . 
     The light source assembly  60  further includes a substrate  64 , a circuit layer  66  and a reflective layer  68 . The light-emitting component  62  is electrically connected to the circuit layer  66 . The circuit layer  66  is electrically connected to the flat cable  58  (see  FIG.  1   ). Therefore, the external device may control the light-emitting component  62 , through the flat cable  58  and the circuit layer  66 , to emit light. The reflective layer  68  is configured to reflect the light from the light-emitting component  62  and the light leaked from the bottom surface  72   b  of the light guide film  70 , so as to increase an amount of light that enters and reenters the light guide film  70  for total inner reflection. In some embodiments, the circuit layer  66  and the reflective layer  68  are separately printed on the substrate  64 . In some embodiments, the circuit layer  66  and the reflective layer  68  are separately attached on the substrate  64 . In some embodiments, the circuit layer  66  and the reflective layer  68  are respectively printed and attached on the substrate  64 . The substrate  64  and the circuit layer  66  may be referred to as a circuit board. The circuit board may be, but not limited to, a flexible printed circuit board (FPCB). 
     Refer to  FIG.  4 A  and  FIG.  4 B .  FIG.  4 A  is a schematic partial top view of a backlight module (omitting a keyboard assembly) corresponding to a single keycap according to some embodiments.  FIG.  4 B  is a schematic partial sectional view of an illuminated keyboard according to some embodiments. In embodiments shown in  FIG.  4 A  and  FIG.  4 B , the light-incident pattern  76  of the light guide film  70  includes an upper light-incident pattern  76   a  located on the top surface  72   a  and a lower light-incident pattern  76   b  located on the bottom surface  72   b . By appropriately adjusting the designs of the upper light-incident pattern  76   a  and the lower light-incident pattern  76   b  (for example, by adjusting the arrangement positions, the arrangement patterns or the layout densities of the upper light-incident pattern  76   a  and the lower light-incident pattern), the amount of the light that enters the light guide film  70  and is transmitted through total inner reflection may be increased. In one embodiment, as shown in  FIG.  4 A  and  FIG.  4 B , the light-incident pattern  76  encloses the through hole  74 , and the light-exit pattern  78  encloses the through hole  74 . 
     In some embodiments, the backlight module  50  further includes a reflective sheet  75 . The reflective sheet  75  is located between the light guide film  70  and the keyboard assembly  10 , and corresponds to the through hole  74 . In the embodiment shown in  FIG.  4 B , the reflective sheet  75  is rectangular as seen in a top view (for example, the top view  4 A). A size of the reflective sheet  75  is larger than the size of the through hole  74 . The reflective sheet  75  completely covers the through hole  74 . Therefore, the light-emitting component  62  emits the light upward to the reflective sheet  75 , and the light is reflected by the reflective sheet  75 , so as to effectively enhance a possibility that the light is reflected only once to enter the light guide film  70 . In this case, more light may enter the light guide film  70  with almost no loss of energy, and is transmitted through total inner reflection inside the light guide film  70 . The light then changes its propagation direction by reaching the light-exit pattern  78 , and is emitted from the light guide film  70  toward the location of the keycap  12 . In some embodiments, the size of the reflective sheet  75  seen in the top view can be smaller than or equal to the size of the through hole  74 . That is, the reflective sheet  75  may cover the through hole  74  incompletely. In some embodiments, the reflective sheet  75  is a reflective film, and is printed or bonded on the light guide film  70 . In some embodiments, the reflective sheet  75  is a reflective film, and is printed or bonded on the protection plate  79 . 
     In some embodiments, the backlight module  50  further includes a shading ring  77 . The shading ring  77  is located between the light guide film  70  and the keyboard assembly  10 . The shading ring  77  has an opening  770 . The opening  770  corresponds to the light-exit pattern  78 . Therefore, the light directed upward due to the light-exit pattern  78  may pass through the opening  770  to irradiate the keycap  12 . In some embodiments, the light-exit pattern  78  and the shading ring  77  overlap partially (while seen from a top view similar to the viewpoint of  FIG.  4 A ). In some embodiments, as shown in  FIG.  4 B , if seen from a top view (similar to the viewpoint of  FIG.  4 A ), an inner edge of the shading ring  77  is located inside the outer edge of the keycap  12 . Therefore, the light that passes through the opening  770  and is emitted toward the keycap  12  is prevented from being leaked through a gap between the keycap  12  and another adjacent keycap  12  to dazzle a user. In some embodiments, the shading ring  77  is a shading film, and is printed or bonded on the light guide film  70 . In some embodiments, the shading ring  77  is a shading film, and is printed or bonded on the protection plate  79 . 
     Further refer to  FIG.  5    and  FIG.  6 A .  FIG.  5    is a schematic top view of a backlight module according to some embodiments.  FIG.  6 A  is a schematic top view of a key group area on the light guide film corresponding to two keycaps according to some embodiments. In this embodiment, the key group area  52  corresponds to two keycaps  12  (see  FIG.  1   ). The through hole  741  is located between the two keycaps  12  (while seen in a top view). Specifically, the central axis of the through hole  741  is toward a position between the two adjacent keycaps  12 . In some embodiments, the central axis of the through hole  741  is toward the central position between the two adjacent keycaps  12 . The light guide film  70  has two light-exit patterns  780 ,  781 . The two light-exit patterns  780 ,  781  correspond to the two keycaps  12 , respectively. The backlight module  50  further includes a shading ring  771 . The shading ring  771  is located between the light guide film  70  and the keyboard assembly  10 . The shading ring  771  has two openings  772 ,  773 . The two openings  772 ,  773  correspond to the two light-exit patterns  780 ,  781 , respectively. In this embodiment, a light-incident pattern  761  of the light guide film  70  surrounds the through hole  741 . The shape of the through hole  741  as seen in the top view (i.e.,  FIG.  6 A ) is approximately a circle. The through hole  741  has two light-collecting corners  743 ,  745  at positions toward the two light-exit patterns  780 ,  781 , respectively. In some embodiments, opening angles of the light-collecting corners  743 ,  745  are acute angles. The light-collecting corners  743 ,  745  enable a relatively large amount of light to be refracted to converge and travel toward the two light-exit patterns  780 ,  781  (compared with the through hole  74  shown in FIG.  2 A whose shape is a complete circle). In some embodiments, a layout density of microstructural units (or convex dots, concave dots, mesh dots, light dots, etc.) of a part of the light-exit patterns  780 ,  781  which is farther from the through hole  741  is higher than that of another part of the light-exit patterns  780 ,  781  which is nearer to the through hole  741 . In more detail, refer to  FIG.  6 A .  FIG.  6 A  illustrates a first partial enlarged view MV 1  and a second partial enlarged view MV 2  of the light-exit pattern  781 . A distance from the position on the light-exit pattern  781  which is enlarged in the first partial enlarged view MV 1  to the center of the through hole  741  is a first distance L 1 . A distance from the position on the light-exit pattern  781  which is enlarged in the second partial enlarged view MV 2  to the center of the through hole  741  is a second distance L 2 . The second distance L 2  is greater than the first distance L 1 . A layout density of the microstructural units of the light-exit pattern  781  shown in the first partial enlarged view MV 1  is lower than that shown in the second partial enlarged view MV 2 , thereby achieving overall uniform luminance when the light is directed by the light-exit pattern  781  upward to the keycap  12 . 
     Further refer to  FIG.  5    and  FIG.  6 B .  FIG.  6 B  is a schematic top view of a key group area on the light guide film corresponding to three keycaps according to some embodiments. In this embodiment, a key group area  54  corresponds to three keycaps  12  (see  FIG.  1   ). The through hole  747  is located among the three keycaps  12  (while seen in a top view). Specifically, a central axis of the through hole  747  is toward a position among the three adjacent keycaps  12 . In some embodiments, the central axis of the through hole  747  is toward the central position between the three adjacent keycaps  12 . The light guide film  70  has three light-exit patterns  783 ,  784 ,  785 . The three light-exit patterns  783 ,  784 ,  785  correspond to the three keycaps  12 , respectively. The backlight module  50  further includes a shading ring  774 . The shading ring  774  is located between the light guide film  70  and the keyboard assembly  10 . The shading ring  774  has three openings  775 ,  776 ,  777 . The three openings  775 ,  776 ,  777  correspond to the three light-exit patterns  783 ,  784 ,  785 , respectively. In this embodiment, a light-incident pattern  763  of the light guide film  70  surrounds the through hole  747 . The shape of the through hole  747  as seem in the top view (i.e.,  FIG.  6 B ) is a polygon with three light-collecting corners  749 . Openings of the three light-collecting corners  749  are toward the three light-exit patterns  783 ,  784 ,  785 , respectively. In some embodiments, an opening angle of the light-collecting corner  749  is an acute angle. The three light-collecting corners  749  enable a relatively large amount of light to be refracted to converge and respectively travel toward the three light-exit patterns  783 ,  784 ,  785  (compared with a hexagonal through hole without a light-collecting corner  749 ). 
     As can be seen from the foregoing embodiments, each of the key group areas  52  and  54  is provided with one through hole  741 ,  747  and one light-emitting component  62 . However, a key group area  56  (see  FIG.  1    and  FIG.  5   ) is provided with four through holes  74  and four light-emitting components  62 . Therefore, the configuration of a quantity of through holes and a quantity of light-emitting components related to one specific key group area may be adjusted according to a specific design requirement of keyboard functions. 
       FIG.  6 B  shows a third partial enlarged view MV 3  and a fourth partial enlarged view MV 4  of the light-exit pattern  784 . A distance from the position on the light-exit pattern  784  which is enlarged in the third partial enlarged view MV 3  to the center of the through hole  747  is a third distance L 3 . A distance from the position on the light-exit pattern  784  which is enlarged in the fourth partial enlarged view MV 4  to the center of the through hole  747  is a fourth distance L 4 . The fourth distance L 4  is greater than the third distance L 3 . A layout density of the microstructural units of the light-exit pattern  784  shown in the third partial enlarged view MV 3  is lower than that shown in the fourth partial enlarged view MV 4 , thereby achieving overall uniform luminance when the light is directed by the light-exit pattern  784  upward to the keycap  12 . 
     Refer to both  FIG.  7 A  and  FIG.  7 B .  FIG.  7 A  is a schematic partial sectional view of an illuminated keyboard according to some embodiments.  FIG.  7 B  is a schematic partial top view of a keycap and a light guide film according to some embodiments. In some embodiments, the light guide film  70  further has a light-blocking band  778 . As can be seen from  FIG.  7 B , the light-blocking band  778  is a closed ring and is located on the outside of the keycap  12  (while seen in the top view), to prevent light corresponding to the through hole  74  from reaching the outside of the light-blocking band  778 , and to restrict an effective transmission range of the light that enters the light guide film  70  from the through hole  74 . In some embodiments, the light-blocking band  778  is a blackening band that may be formed by irradiating a specific area on the light guide film  70  through a laser. In some embodiments, the backlight module  50  further includes a light-blocking ring  779 . The light-blocking ring  779  is located between the light guide film  70  and the reflective layer  68  above a circuit board (e.g., a circuit-functioning board consisting of the substrate  64  and the circuit layer  66  shown in  FIG.  7 A ) and corresponds to the light-blocking band  778 . The shape of the light-blocking ring  779  seen in the top view is the same as that of the light-blocking band  778  shown in  FIG.  7 B . The light-blocking ring  779  is configured to prevent the light emitted by the light-emitting component  62  from leaking out the light-blocking ring  779 , and to restrict an effective illumination area of the light-emitting component  62 . In some embodiments, for example referring to  FIGS.  7 A and  7 B , the light-blocking band  778  corresponds to the light-exit pattern  78 , and the light-blocking ring  779  corresponds to the light-blocking band  778 . In some embodiments, the light-blocking ring  779  and the light-blocking band  778  surround the light-exit pattern  78  while seen in a top view. In the embodiment shown in  FIG.  7 A , a light-incident pattern  76  of the light guide film  70  is located on the top surface  72   a  only. However, the present invention is not limited thereto. 
     Refer to both  FIG.  6 A  and  FIG.  6 B . In some embodiments, an area surrounded by a light-blocking band  778  may correspond to a range of the key group area  52 ,  54 , or  56  distinctively. For example, in the embodiment shown in  FIG.  6 A , a light-blocking band  778   c  is located on the light guide film  70  and surrounds the outer edge of the shading ring  771 . In this embodiment, the external contour of the light-blocking band  778   c  is rectangular. Further, in the embodiment shown in  FIG.  6 B , a light-blocking band  778   d  is located on the light guide film  70  and surrounds the outer edge of the shading ring  774 . In this embodiment, the external contour of the light-blocking band  778   d  is T-shaped. In some embodiments, a light-emitting component  62  in an area surrounded by the light-blocking band  778 ,  778   a ,  778   c , or  778   d  (see  FIG.  7 B ,  FIG.  7 C ,  FIG.  6 A , and  FIG.  6 B , respectively) and a light-emitting component  62  outside the area surrounded by the light-blocking band  778 ,  778   a ,  778   c , or  778   d  emit light of different colors. Through the configuration of the light-blocking band  778 ,  778   a ,  778   c , or  778   d , a specific color of the light used in the key group area  52 ,  54 , or  56  may be prevented from leaking to other keycaps which are outside the key group area  52 ,  54 , or  56 , so as to prevent the undesired color mixing of the light. 
       FIG.  7 C  is a schematic partial top view of a keycap and a light guide film according to some embodiments. In the embodiment shown in  FIG.  7 C , the light-blocking band  778   a  includes a plurality of light-blocking gap segments. The light-blocking gap segments cooperate with each other to form a non-closed rectangular ring. Each light-blocking gap segment is a slit pierced through the light guide film  70 . Therefore, the light is forced to be refracted and reflected when passing through the light-blocking gap segments, so as to reduce the light that leaks out an area surrounded by the light-blocking band  778   a . In some embodiments, the light-blocking gap segments are respectively filled with light-blocking strips  778   b  which are used to more effectively prevent the light from leaking out the area surrounded by the light-blocking band  778   a . In some embodiments, a plurality of light-blocking strips  778   b  corresponding to the light-blocking gap segments are disposed on one side of the light-blocking ring  779  which faces the light guide film  70 , and seamlessly fill the aforementioned light-blocking gap segments. 
     Refer to  FIG.  4 A  and  FIG.  4 B . According to some embodiments, a backlight module  50  includes a light source assembly  60  and a light guide film  70 . The light source assembly  60  includes a light-emitting component  62 . The light-emitting component  62  is configured to emit light. The light guide film  70  has a top surface  72   a , a bottom surface  72   b , a through hole  74 , a light-incident pattern  76  and a light-exit pattern  78 . A size of the through hole  74  is smaller than a size of the light-emitting component  62 . The light of the light-emitting component  62  is propagated toward the through hole  74 . The light-incident pattern  76  is located on at least one of the top surface  72   a  and the bottom surface  72   b , and is adjacent to the through hole  74  (according to the embodiment shown in  FIG.  4 B , the light-incident pattern  76  is on both the top surface  72   a  and the bottom surface  72   b ). The light-exit pattern  78  is located on the bottom surface  72   b . A distance from the through hole  74  to the light-exit pattern  78  is greater than a distance from the through hole  74  to the light-incident pattern  76 . 
     In some embodiments, the backlight module  50  further includes a reflective sheet  75 . The reflective sheet  75  is located above the top surface  72   a  of the light guide film  70  and corresponds to the through hole  74 . In some embodiments, the backlight module  50  further includes a shading ring  77 . The shading ring  77  is located above the top surface  72   a  of the light guide film  70 . The shading ring  77  has an opening  770 . The opening  770  corresponds to the light-exit pattern  78 . 
     The backlight module  50  may have, as shown in  FIG.  5   , a plurality of key group areas  52 ,  54 ,  56 . In some embodiments, referring to the key group area  52  in  FIG.  6 A , corresponding to the backlight module  50 , the light guide film  70  has a light-blocking band  778   c  around the key group area  52 . The light-blocking band  778   c  corresponds to the shading ring  771 . The light source assembly  60  includes a circuit board (which may consist of a substrate  64 , a circuit layer  66 , and a reflective  68  shown in  FIG.  4 B ). The light-emitting component  62  is located on the circuit board. The backlight module  50  further includes a light-blocking ring (similar to the light-blocking ring  779  shown in  FIG.  7 A ). The light-blocking ring  779  is located between the circuit board and the light guide film  70  and corresponds to the light-blocking band  778   c.    
     On the other hand, refer to  FIG.  4 A  and  FIG.  4 B . According to some embodiments, a backlight module  50  includes a light source assembly  60 , a light guide film  70  and a reflective sheet  75 . The light source assembly  60  includes a light-emitting component  62 . The light-emitting component  62  is configured to emit light. The light guide film  70  has a bottom surface  72   b , a through hole  74  and a light-exit pattern  78 . A size of the through hole  74  is smaller than a size of the light-emitting component  62 . The light of the light-emitting component  62  is propagated toward the through hole  74 . The light-exit pattern  78  is located on the bottom surface  72   b . The reflective sheet  75  is located above the through hole  74 . A size of the reflective sheet  75  is larger than or equal to the size of the through hole  74 . In some embodiments, a distance from the through hole  74  to the outer edge of the light-exit pattern  78  is greater than a distance from the through hole  74  to the outer edge of the reflective sheet  75  (for example, viewed from a top view as shown in  FIG.  4 A ). However, a distance from the through hole  74  to the inner edge of the light-exit pattern  78  is less than a distance from the through hole  74  to the outer edge of the reflective sheet  75  (differing from the embodiment shown in  FIG.  4 A ). In this way, some of the light directed upward by the light-exit pattern  78  is reflected by the reflective sheet  75  and continues to be transmitted inside the light guide film  70 . In some embodiments, a distance from the through hole  74  to the inner edge of the light-exit pattern  78  is greater than a distance from the through hole  74  to the outer edge of the reflective sheet  75  (similar to the embodiment shown in  FIG.  4 A ). In this way, almost all of the light directed upward by the light-exit pattern  78  is not reflected by the reflective sheet  75 , and can be emitted to the keycap  12  above. In other words, the luminance of a particular keycap  12  on the keyboard assembly  10  can be finely adjusted according to the size of the corresponding reflective sheet  75  below the keycap  12 . 
     In conclusion, according to some embodiments, in the backlight module  50 , the through hole  74  with a relative small size on the light guide film  70  cooperates with the light-incident pattern  76  or the reflective sheet  75 , so that the light emitted by the light-emitting component  62  can be directed to the keycaps  12  more efficiently, to illuminate the keycaps  12  with higher luminance for a user to see the keycaps  12 .