Patent Publication Number: US-2021167044-A1

Title: Display unit, display apparatus, and display unit manufacturing method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a display unit, a display apparatus, and a method for manufacturing the display unit. 
     BACKGROUND ART 
     A display apparatus with light emitting diode (LED) elements mounted on a board is known. For example, Patent Literature 1 describes a surface emitter including a board that is flexible. LED elements disposed on the board, and a top film affixed on the board. In Patent Literature 1 the top film is in intimate contact with the LED elements. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: International Publication No. WO 2009/054153 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the surface emitter of Patent Literature 1, the board and the top film expand or contract due to generation of heat from a power source or changes in ambient temperature. The board and the top film have different coefficients of linear expansion, thereby causing tensile stress to be repeatedly applied to the board or the top film. The top film, due to being thinner than the board, may be damaged by such repeatedly applied tensile stress. With the top film damaged, the surface emitter allows entry of rainwater or the like onto the board, which results in breakdown of the surface emitter. 
     In view of the above circumstances, an objective of the present disclosure is to provide a display unit, a display apparatus, and a method for manufacturing the display unit which can reduce possible damage to a waterproof film. 
     Solution to Problem 
     According to the present disclosure, a display unit includes light emitting elements, a circuit board having a mount surface on which the light emitting elements are mounted, and a waterproof film covering the light emitting elements and the mount surface. The mount surface has a first region and a first recess. In the first region, the light emitting elements are mounted and the waterproof film is adhered. The waterproof film includes a first cover portion covering the first recess and having a surface area that is greater than an area of a first projection coverage obtained by perpendicular projection of the first recess onto an imaginary plane parallel to the first region. 
     Advantageous Effects of Invention 
     According to the present disclosure, the surface area of the first cover portion of the waterproof film that covers the first recess is greater than the area of the first projection coverage obtained by perpendicular projection of the first recess onto the imaginary plane parallel to the first region, which enables tensile stress applied to the waterproof film to be relieved in the first cover portion, thereby reducing possible damage to the waterproof film. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a front side of a display unit according to Embodiment 1 of the present disclosure; 
         FIG. 2  is a schematic cross-sectional diagram of the display unit, taken along line A-A of  FIG. 1 ; 
         FIG. 3  is a schematic diagram illustrating a first cover portion and a first projection coverage in Embodiment 1 of the present disclosure; 
         FIG. 4  is a schematic diagram illustrating contraction of a circuit board and a waterproof film according to Embodiment 1 of the present disclosure; 
         FIG. 5  is a schematic diagram illustrating expansion of the circuit board and the waterproof film according to Embodiment 1 of the present disclosure; 
         FIG. 6  is a flow chart illustrating a method for manufacturing the display unit according to Embodiment 1 of the present disclosure; 
         FIG. 7  is a schematic diagram illustrating a front side of a display twit according to Embodiment 2 of the present disclosure; 
         FIG. 8  is a schematic cross-sectional diagram of the display unit, taken along line B-B of  FIG. 7 ; 
         FIG. 9  is a perspective view of a case according to Embodiment 2 of the present disclosure; 
         FIG. 10  is a schematic diagram illustrating a second cover portion and a second projection coverage according to Embodiment 2 of the present disclosure; 
         FIG. 11  is a schematic diagram illustrating contraction of a waterproof film and the case according to Embodiment 2 of the present disclosure; 
         FIG. 12  is a schematic diagram illustrating expansion of the waterproof film and the case according to Embodiment 2 of the present disclosure; 
         FIG. 13  is a flow chart illustrating a method for manufacturing the display unit according to Embodiment 2 of the present disclosure; 
         FIG. 14  is a schematic diagram illustrating a front side of a display unit according to Embodiment 3 of the present disclosure; 
         FIG. 15  is a schematic cross-sectional diagram of the display unit taken along line C-C of  FIG. 14 ; 
         FIG. 16  is a schematic diagram illustrating a second cover portion and a second projection coverage according to Embodiment 3 of the present disclosure; 
         FIG. 17  is a perspective view illustrating a display apparatus according to Embodiment 4 of the present disclosure; 
         FIG. 18  is a schematic diagram illustrating a first recess according to a variation of Embodiment 1 of the present disclosure; 
         FIG. 19  is a schematic diagram illustrating a first recess according to a variation of Embodiment 1 of the present disclosure; 
         FIG. 20  is a schematic diagram illustrating a first recess according to a variation of Embodiment 1 of the present disclosure; 
         FIG. 21  is a schematic diagram illustrating a second recess according to a variation of Embodiment 2 of the present disclosure; 
         FIG. 22  is a schematic diagram illustrating a second recess according to a variation of Embodiment 2 of the present disclosure; and 
         FIG. 23  is a schematic diagram illustrating a first recess and a first cover portion according to a variation of Embodiment 1 of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A display unit and a display apparatus according to embodiments of the present disclosure are described with reference to the drawings. 
     Embodiment 1 
     A display unit  10  according to Embodiment 1 of the present disclosure is described with reference to  FIGS. 1 to 6 . For ease of understanding, it is assumed in the description that the display unit  10  is installed outdoors, with a front side of the display unit  10  oriented perpendicularly to the ground. Here, a direction parallel to both the ground and the front side of the display unit  10  is defined as an X-axis direction. In addition, a direction perpendicular to the ground is defined as a Y-axis direction, and a direction perpendicular to the X-axis and Y-axis directions is defined as a Z-axis direction. These definitions of the axis directions are applied similarly to other embodiments. An adhesive layer  42  described later is omitted in  FIG. 1  for ease of understanding. 
     As illustrated in  FIG. 1 , the display unit  10  includes light emitting elements  20 , a circuit board  30  having a mount surface  32  on which the light emitting elements  20  are mounted, and a waterproof film  40  covering the light emitting elements  20  and the mount surface  32 . The mount surface  32  of the circuit board  30  has a first region  34  and a first recess  36 . 
     The display unit  10  is applicable as a unit installed outdoors, such as in a stadium or on a wall surface of a building. 
     The light emitting elements  20  are, for example, 3-in-1 surface mount LED elements. The light emitting elements  20  are mounted in the first region  34  on the mount surface  32  of the circuit board  30 . The light emitting elements  20  are arranged in a 4 row by 5 column matrix. 
     As illustrated in.  FIG. 2 , the light emitting elements  20  each have, on a flat top surface  21 , a light exit face  22  that emits light. A face of the light emitting element  20  located on the front side of the display unit  10  is herein taken as the top surface  21  of the light emitting element  20 . Faces of the light emitting element  20  perpendicular to the first region  34  are herein taken as side surfaces  23  of the light, emitting element  20 . 
     The light emitting element  20  includes not-illustrated three light emitting chips, a package  25 , a seal  26 , and six electrodes  27 . 
     The three light emitting chips emit light in corresponding colors of red, green, and blue. Emission intensities of the three light emitting chips are independently adjusted by power supplied via wiring of the circuit board  30  to the corresponding light emitting chips. Such adjustment of emission intensities achieves emission of different colors of light from the light emitting elements  20  at different intensities, which results in display of a color image on the display unit  10 . 
     The package  25  is made of, for example, a white or black resin. Light emitting chips are mounted on a recessed portion of the package  25 . The seal  26  seals the light emitting chips mounted on the recessed portion of the package  25 . The seal  26  is a sealing resin filled in the recessed portion of the package  25 . The sealing resin is, for example, a resin having light transmissivity, such as a silicone resin, an epoxy resin, an acrylic resin, or a polyester resin. The electrodes  27  supply power to the light emitting chips. Two electrodes  27  are connected to each of the light emitting chips. The two electrodes  27  connected to each light emitting chip are a positive electrode and a negative electrode. The electrodes  27  are electrically connected to the wiring of the circuit board  30  by soldering. 
     The circuit board  30  is made of an insulating resin. The insulating resin is, for example, a glass fiber filled epoxy resin. The circuit board  30  includes wiring and a drive integrated circuit (IC), both of which are not illustrated. The drive IC of the circuit board  30  supplies power to the light emitting elements  20  via the wiring of the circuit board  30  to drive the light emitting elements  20 . The drive IC of the circuit board  30  is powered from an external power source of the display unit  10 . 
     The circuit board  30  has the mount surface  32  on which the light emitting, elements  20  are mounted. 
     The mount surface  32  of the circuit board  30  includes the first region  34  and the first recess  36 , as illustrated in  FIGS. 1 and 2 . The first region  34  of the mount surface  32  is a region in which the light emitting elements  20  are mounted and the waterproof film  40  is adhered. The first recess  36  is, for example, a V-shaped groove formed on the mount surface  32 . As illustrated in  FIG. 1 , the first recesses  36  located, as viewed from the front side of the circuit board  30  on which the light emitting elements  20  are mounted, between the light emitting elements  20  mounted on the mount surface  32  each extend along edges of the top suffices  21  of the adjoining light emitting elements  20 . In addition, the first recesses  36  located at the periphery of the mount surface  32  extend along an array of the light emitting elements  20 . The depth of the first recess  36  from a level of the first region  34  is preferably deeper than the thickness of the waterproof film  40  described below. 
     The waterproof film  40  is made of a resin having light transmissivity. Examples of the resin having light transmissivity include a polyester resin, a polycarbonate resin, an acrylic resin, and an olefinic resin. The waterproof film  40  is pliable and flexible. The thickness of the waterproof film  40  is, for example, 50 μm to 500 μm, and from the flexibility and durability perspectives, preferably 150 μm to 300 μm. 
     The waterproof film  40  covers the light emitting elements  20  and the mount surface  32  of the circuit board  30 . Such covering of the light emitting elements  20  and the mount surface  32  of the circuit board  30  with the waterproof film  40  renders the display unit  10  waterproof. 
     The waterproof film  40  is adhered in the first region  34  by the adhesive layer  42  that extends along the first recess  36  on both sides of the first recess  36 , as illustrated in  FIG. 2 . Examples of the adhesive layer  42  include a silicone adhesive, an acrylic adhesive, and an urethane adhesive. The waterproof film  40  is in intimate contact with the top surface  21  and the side surfaces  23  of the light emitting element  20  and the first region  34 . The waterproof film  40  is also in intimate contact with the first recesses  36 , with the waterproof film  40  inserted into the first recesses  36 . Such intimate contact of waterproof film  40  with the first region  34  and the first recesses  36  enables easy adaptation of the waterproof film  40  to contraction or expansion of the circuit board  30 . 
     In the present embodiment, a portion of the waterproof film  40  covering the first recess  36  is referred to as a first cover portion  44 , as illustrated in  FIG. 3 . The first cover portion  44  of the waterproof film  40  has a surface area that is greater than an area of a first projection coverage  38  obtained by perpendicular projection of the first recess  36  onto an imaginary plane S. The imaginary plane S is a plane parallel to the first region  34  of the mount surface  32 . 
     Here, expansion and contraction of the circuit board  30  and the waterproof film  40  as well as tensile stress TS applied to the waterproof film  40  are described. For example, the circuit board  30  and the waterproof film  40  expand due to a rise in temperature outdoors where the display unit  10  is installed, and contract due to a drop in the temperature outdoors. 
     The description starts from a case in which the coefficient of linear expansion of the waterproof film  40  is higher than the coefficient of linear expansion of the circuit board  30 . 
     As the outdoor temperature drops, the waterproof film  40  attempts to contract more greatly than the circuit board  30 . In the present embodiment, the surface area of the first cover portion  44  is greater than the area of the first projection coverage  38 . Thus, as illustrated in  FIG. 4 , tensile stress TS is not applied to the waterproof film  40  until contraction of the circuit board  30  and the waterproof film  40  results in the surface area of the first cover portion  44  being the same as the area of the first projection coverage  38 . In addition, since the waterproof film  40  contracts more greatly than the circuit board  30  until the surface area of the first cover portion  44  is the same as the area of the first protection coverage  38 , the tensile stress TS applied to the waterproof film  40  becomes smaller. Thus the display unit  10  can relieve, in the first cover portion  44 , the tensile stress TS applied to the waterproof film  40 . This difference in contraction between the circuit board  30  and the waterproof film  40  creates a space  46  between the first recess  36  and the first cover portion  44 . 
     In contrast, as the outdoor temperature rises, the waterproof film  40  expands more greatly than the circuit board  30 , In this case, the tensile stress TS is not applied to the waterproof film  40 . 
     The description is next directed to a case in which the coefficient of linear expansion of the circuit board  30  is higher than the coefficient of linear expansion of the waterproof film  40 . 
     As the outdoor temperature rises, the circuit board  30  expands more greatly than the waterproof film  40 . In the present embodiment, the surface area of the first cover portion  44  is greater than the area of the first projection coverage  38 . Thus, as illustrated in  FIG. 5 , tensile stress TS is not applied to the waterproof film  40  until the surface area of the first cover portion  44  is the same as the area of the first projection coverage  38  by pulling of the waterproof film  40  by the circuit board  30 . In addition, until the surface area of the first cover portion  44  is the same as the area of the first projection coverage  38 , the circuit board  30  expands greatly compared to a difference between the surface area of the first cover portion  44  and the area of the first projection coverage  38  before rise in the outdoor temperature. The tensile stress TS applied to the waterproof film  40  thereby becomes smaller. Thus the display unit  10  can relieve, in the first cover portion  44 , the tensile straws TS applied to the waterproof film  40 . This difference in expansion between the circuit board  30  and the waterproof film  40  creates a space  46  between the first recess  36  and the first covet portion  44 . 
     As the outdoor temperature drops, the circuit board  30  contracts more greatly than the waterproof film  40 . In this case, the tensile stress TS is not applied to the waterproof film  40 . 
     As described above, the surface area of the first cover portion  44  being greater than the area of the first projection coverage  38  relieves the tensile stress TS applied to the waterproof film  40 . Through the relief of the tensile stress TS, the display unit  10  can reduce possible damage to the waterproof film  40 . 
     Next, a method for manufacturing the display unit  10  is described with reference to  FIG. 6 .  FIG. 6  is a flow chart illustrating the method for manufacturing the display unit  10 . 
     First of all, the light emitting elements  20 , the circuit board  30  having the first recesses  36  on the mount surface  32 , and the waterproof film  40  are prepared. Then the electrodes  27  of the light emitting elements  20  are reflow soldered to wiring of the circuit board  30 , and each light emitting element  20  is mounted on the circuit board  30  in the first region  34  of the mount surface  32  (Step S 11 ). Then an adhesive is applied to the first region  34  (Step S 12 ). The applied adhesive extends along the first recess  36  on both the sides of the first recess  36 . 
     The circuit board  30  with the adhesive applied and the waterproof film  40  are placed in a vacuum chamber, and then the vacuum chamber is depressurized (Step S 13 ). Within the depressurized vacuum chamber, the light emitting elements  20  and the mourn surface  32  of the circuit board  30  are covered with the waterproof film  40  (Step S 14 ). 
     Then the vacuum chamber is pressurized and the waterproof film  40  is thereby press fitted to the twin emitting elements  20  and the mount surface  32  (Step S 15 ). Through this step, the waterproof film  40  is inserted into the first recess  36  and comes into intimate contact with the top surface  21  and the side surfaces  23  of each light emitting element  20  and the first region  34  and the first recesses  36  of the mount surface  32 . The waterproof film  40  is adhered in the first region  34  to the mount surface  32  by the applied adhesive. 
     The vacuum chamber is allowed to return to atmospheric pressure, and the circuit board  30  with the waterproof film  40  attached is removed (Step S 16 ). Finally, the applied adhesive is cured (Step S 17 ). 
     The display unit  10  can be manufactured through the above steps. 
     As described above, the display unit  10  is rendered waterproof by the waterproof film  40 . The surface area of the first cover portion  44  of the waterproof film  40  being greater than the area of the first projection coverage  38  relieves the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the circuit board  30  and the waterproof film  40 . Since the tensile stress TS applied to the waterproof film  40  is relieved in the first cover portion  44 , the display unit  10  can reduce possible damage to the waterproof film  40 . 
     Embodiment 2 
     A display unit  11  according to Embodiment 2 of the present disclosure is described with reference to  FIGS. 7 to 13 . 
     As illustrated in  FIGS. 7 and 8 , the display unit  11  further includes a case  50  that holds the circuit board  30 , in addition to the light emitting elements  20 , the circuit board  30 , and the waterproof film  40 . The light emitting elements  20  and the circuit board  30  have structures similar to those in Embodiment 1. 
     As illustrated in  FIG. 9 , the case  50  is a box-shaped enclosure that has an opening on a Z-axis direction side. The case  50  has a bottom plate  51  and side plates  53 . As illustrated in  FIGS. 7 and 8 . the circuit board  30  on which the light emitting elements  20  are mounted is seated and held on the bottom plate  51 . The side plates  53  surround the circuit board  50  seated on the bottom plate  51 . As illustrated in  FIG. 8 , a second recess  50  is located between the side plates  53  and the circuit board  30 . The second recess  56  has a side surface  39  of the circuit board  30 , inner side surfaces  53   a  of the side plates  53 , and an inner bottom surface  51   a  of the bottom plate  51 . The second recess  56  is a rectangular-shaped groove. 
     The case  50  is made of a resin, such as a polycarbonate resin or an acrylic resin. 
     The waterproof film  40  is pliable and flexible, similarly to Embodiment 1. The waterproof film  40  is made of a resin having light transmissivity, such as a polyester resin, a polycarbonate resin, an acrylic resin, or an olefinic resin. 
     As illustrated in  FIGS. 7 and 8 , the waterproof film  40  covers the light emitting elements  20 , the mount surface  32  of the circuit board  30 , and the case  50 . Such covering of the light emitting elements  20 , the mount surface  32  of the circuit board  30 , and the case  50  with the waterproof film  40  renders the display unit  11  waterproof. 
     The waterproof film  40  is adhered in the first region  34  to the circuit board  30  by the adhesive layer  42 , similarly to Embodiment 1. The waterproof film  40  is adhered to top surfaces  53   b  of the side plates  53  of the case  50  and outer side surfaces  54  of the case  50  by a non-illustrated adhesive layer. The waterproof film  40  is in intimate contact with the top surface  21  and the side surfaces  23  of each light emitting element  20  and the first region  34  and the first recesses  36  of the mount surface  32 , similarly to Embodiment 1. The waterproof film  40  is also in intimate contact with the second recess  56 , with the waterproof film  40  inserted into the second recess  56 . Such intimate contact of the waterproof film  40  with the first region  34 , the first recesses  36 , and the second recess  56  enables easy adaptation of the waterproof film  40  to contraction or expansion of the circuit board  30  and the case  50 . 
     Similarly to Embodiment 1, a portion of the waterproof film  40  covering the first recess  36  is also referred to as the first cover portion  44  in the present embodiment. In addition, as illustrated in  FIG. 10 , a portion of the waterproof film  40  covering the second recess  56  is referred to as a second cover portion  48 . Similarly to Embodiment 1, the surface area of the first cover portion  44  is greater than the area of the first projection coverage  38  obtained by perpendicular projection of the first recess  36  onto the imaginary plane S. A surface area of the second cover portion  48  is greater than an area of a second projection coverage  58  obtained by perpendicular projection of the second recess  56  onto the imaginary plane S. Similarly to Embodiment 1, the imaginary plane S is a plane parallel to the first region  34  of the mount surface  32 . 
     Here, expansion and contraction of the waterproof film  40  and the case  50 , as well as tensile stress TS applied to the waterproof film  40 , are described. The relationship between the expansion and contraction of the circuit board  30  and the waterproof film  40  and the tensile stress TS applied to the waterproof film  40  is similar to that of Embodiment 1. 
     The description starts from a case in which the coefficient of linear expansion of the waterproof film  40  is higher than the coefficient of linear expansion of the case  50 . For example, the waterproof film  40  and the case  50  expand due to a rise in temperature outdoors where the display unit  10  is installed and contract due to a drop in temperature outdoors. 
     As the outdoor temperature drops, the waterproof film  40  attempts to contract more greatly than the case  50 . The surface area of the second cover portion  48  is greater than the area of the second projection coverage  58 . Thus, as illustrated in  FIG. 11 , tensile stress TS is not applied to the waterproof film  40  until the surface area of the second cover portion  48  is the same as the area of the second projection coverage  58 , similarly to the relationship between the circuit board  30  and the waterproof film  40  in Embodiment 1. In addition, since the waterproof film  40  contracts more greatly than the case  50  until the surface area of the second cover portion  48  is the same as the area of the second projection coverage  58 , the tensile stress TS applied to the waterproof film  40  becomes smaller. Thus the display unit  11  can achieve relief of the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the waterproof film  40  and the case  50 . This difference in contraction between the waterproof film  40  and the case  50  creates a space  46  between the second recess  56  and the second. cover portion  48 . 
     As the outdoor temperature rises, the waterproof film  40  expands more greatly than the case  50 . In this case, the tensile stress TS is not applied to the waterproof film  40 . 
     The description is next directed to a case in which the coefficient of linear expansion of the case  50  is higher than the coefficient of linear expansion of the waterproof film  40 . 
     As the outdoor temperature rises, the case  50  expands more greatly than the waterproof film  40 . The surface area of the second cover portion  48  is greater than the area of the second projection coverage  58 . Thus, as illustrated in  FIG. 12 , tensile stress TS is not applied to the waterproof film  40  until the surface area of the second cover portion  48  is the same as the area of the second projection coverage  58  by pulling of the waterproof film  40  by the case  50  similarly to the relationship between the circuit board  30  and the waterproof film  40  in Embodiment 1. In addition, until the surface area of the second cover portion  48  is the same as the area of the second projection coverage  58 , the case  50  expands greatly compared to a difference between the surface area of the second cover portion  48  and the area of the second projection coverage  58  before rise in the outdoor temperature. The tensile stress TS applied to the waterproof film  40  thereby becomes smaller. Thus the display unit  11  can achieve relief of the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the waterproof film  40  and the case  50 . Here again, a space  46  is created between the second recess  56  and the second cover portion  48 . 
     As described above, the surface area of the second cover portion  48  being greater than the area of the second projection coverage  58  relieves the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the waterproof film  40  and the case  50 . In addition, similarly to Embodiment 1, the surface area of the first cover portion  44  of the waterproof film  40  being greater than the area of the first projection coverage  38  relieves the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the circuit board  30  and the waterproof film  40 . Through the relief of the tensile stress TS, the display unit  11  can reduce possible damage to the waterproof film  40 . 
     Next, a method for manufacturing the display unit is described with reference to  FIG. 13 .  FIG. 13  is a flow chart illustrating the method for manufacturing the display unit  11 . 
     First of all, the light emitting elements  20 , the circuit board  30  having the first recesses  36  on the mount surface  32 , and the waterproof film  40 , and the case  50  are prepared. Then the electrodes  27  of the light emitting elements  20  are reflow soldered to wiring of the circuit board  30 , and each emitting element  20  is mounted on the circuit board  30  in the first region  34  of the mount surface  32  (Step S 21 ). Then the circuit board  30  on which the light emitting elements  20  an mounted is seated on the bottom plate  51  of the case  50 , for example, with a gap between the side surfaces  39  of the circuit board  30  and the side plates  53  of the case  50 . The circuit board  30  is then fastened by screws to the bottom plate  51  (Step S 22 ). Through the steps, the circuit board  30  is mounted on the bottom plate  51  of the case  50 , with the second recess  56  disposed between the side plates  53  and the circuit board  30 . 
     Then an adhesive is applied to the first region  34  of the circuit board  30 , the top surfaces  53   b  of the side plates  53  of the case  50 , and the side surfaces  54  of the case  50  (Step S 23 ). The adhesive applied to the first region  34  extends along the first recess  36  on both the sides of the first recess  36 . 
     The case  50  with the adhesive applied and the waterproof film  40  are placed in a vacuum chamber and the vacuum chamber is depressurized (Step S 24 ). Within the depressurized vacuum chamber, the light emitting elements  20 , the mount surface  32  of the circuit board  30 , and the case  50  are covered with the waterproof film  40  (Step S 25 ). 
     Then the vacuum chamber is pressurized, and the waterproof film  40  is thereby press fitted to the light emitting elements  20 , the mount surface  32 , and the case  50  (Step S 26 ). Through this step, the waterproof film  40  is inserted into the first recess  36  and the second recess  56 , and comes into intimate contact with the top surface  21  and the side surfaces  23  of each light emitting element  20 , the first region  34 , the first recesses  36 , and the second recess  56 . The waterproof film  40  is adhered to the lust region  34  and the case  50  by the applied adhesive. 
     The vacuum chamber is allowed to return to atmospheric pressure, and the case  50  with the waterproof film  40  attached is removed (Step S 27 ). Finally, the applied adhesive is cured (Step S 28 ). 
     The display unit  11  can be manufactured through the above steps. 
     As described above, the display unit  11  is rendered waterproof by the waterproof film  40 . The surface area of the second cover portion  48  of the waterproof film  40  being greater than the area of the second projection coverage  58  enables the display unit  11  to achieve relief of the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the waterproof film  40  and the case  50 . In addition, similarly to Embodiment 1, the surface area of the first cover portion  44  of the waterproof film  40  being greater than the area of the first projection coverage  38  enables the display unit  11  to achieve relief of the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the circuit board  30  and the waterproof film  40 . Since the tensile stress TS applied to the waterproof film  40  is relieved in the first cover portion  44  and the second cover portion  48 , the display unit  11  can reduce possible damage to the waterproof film  40 . 
     Since the circuit board  30  of the display unit  11  is held by the case  50 , the display unit  11  can reduce warp of the circuit board  30 . Since the display unit  11  includes the case  50  that holds the circuit board  30 , easy handling is achieved in assembling of a display apparatus  15  described later. 
     Embodiment 3 
     A display unit  12  according to the present embodiment is described with reference to  FIGS. 14 to 16 . 
     In Embodiment 2, the circuit board  30  of the display unit  11  has the first recess  36 . A circuit board  70  in Embodiment 3 does not have the first recess  36 . 
     The display unit  12  includes the light emitting elements  20 , the circuit board  70 , the waterproof film  40 , and the case  50 . The light emitting elements  20  and the case  50  have structures similar to those in Embodiment 2. 
     As illustrated in  FIGS. 14 and 15 , the circuit board  70  has a mount surface  72 . The light emitting elements  20  are mounted on the mount surface  72  of the circuit board  70 . The waterproof film  40  is adhered to the mount surface  72  of the circuit board  70 . The structure of the circuit board  70  is the same as the circuit board  30  in Embodiments 1 and 2 in other respects. 
     The circuit board  70  is seated and held on the bottom plate  51  of the case  50 , similarly to the circuit board  30  in Embodiment 2. As illustrated in  FIG. 15 , the circuit board  70  is seated, with the second recess  56  disposed between the side plates  53  of the case  50  and the circuit board  70 . The second recess  56  has side surfaces  74  of the circuit board  70 , inner side surfaces  53   a  of the side plates  53 , and the inner bottom surface  51   a  of the bottom plate  51 . 
     As illustrated in  FIGS. 14 and 15 , the waterproof film  40  covers the light emitting elements  20 , the mount surface  72  of the circuit board  70 , and the case  50 . Such covering of the light emitting elements  20 , the mount surface  72  of the circuit board  70 , and the case  50  with the waterproof film  40  renders the display unit  12  waterproof. 
     The waterproof film  40  is adhered to the mount surface  72  of the circuit board  70 , the top surfaces  53   b  of the side plates  53  of the case  50 , and the outer side surfaces  54  of the case  50  by the adhesive layer  42  applied on the mount surface  72  and the adhesive layer applied on the top surfaces  53   b  and the side surfaces  54  of the case  50 . The waterproof film  40  is in intimate contact with the top surface  21  and the side surfaces  23  of the light emitting element  20  and the mount surface  72  of the circuit board  70 . The waterproof film  40  is also in intimate contact with the second recess  56 , with the waterproof film  40  inserted into the second recess  56 . Such intimate contact of the waterproof film  40  with the mount surface  72  of the circuit board  70  and the second recess  56  enables easy adaptation of the waterproof film  40  to contraction or expansion of the circuit board  30  and the case  50 . 
     As illustrated in  FIG. 16 , the surface area of the second cover portion  48  of the waterproof film  40  is greater than the area of the second projection coverage  58  obtained by perpendicular projection of the second recess  56  onto the imaginary plane S. Thus, similarly to the display unit  11  in Embodiment 2, the display unit  12  can relieve the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the waterproof film  40  and the case  50 . The second cover portion  48  of the waterproof film  40  is a portion of the waterproof film  40  covering the second recess  56 , similarly to Embodiment 2. The imaginary plane S is a plane parallel to the mount surface  72 . 
     The display unit  12  is manufactured by a manufacturing method similar to the method for manufacturing the display unit  11 . Pressurizing the vacuum chamber (Step S 26 ) renders the waterproof film  40  inserted into the second recess  56  to be in intimate contact with the top surface  21  and side surfaces  23  of each light emitting element  20 , the mount surface  72  of the circuit board  70 , and the second recess  56 . 
     As described above, the display unit  12  is tendered waterproof by the waterproof film  40 . The surface area of the second cover portion  48  of the waterproof film  40  being greater than the area of the second projection coverage  58  enables the display unit  12  to achieve relief of the tensile stress TS applied to the waterproof film  40  due to the difference in the coefficients of linear expansion between the waterproof film  40  and the case  50 . Since the tensile stress TS applied to the waterproof film  40  is relieved in the second cover portion  48 , the display unit  12  can reduce possible damage to the waterproof film  40 . Since the circuit board  70  is held by the case  50 , the display unit  12  can reduce warp of the circuit board  70 . Since the display unit  12  includes the case  50  that holds the circuit board  70 , easy handling is achieved in assembling of the display apparatus  15 . 
     Embodiment 4 
     A display apparatus  15  according to Embodiment 4 of the present disclosure is described with reference to  FIG. 17 . 
     A large-scale display apparatus  15  can be achieved by combination of multiple display units  10  to  12 . The display apparatus  15  is applicable as a unit installed outdoors, such as in a stadium or on a wall surface of a building. 
     As illustrated in  FIG. 17 , the display apparatus  15  includes, for example, twelve display units  11  and an enclosure  80  that houses the twelve display unit  11 . 
     The twelve display units  11  are arranged in a 4 row by 3 column matrix. The arranged display units  11  are housed in the enclosure  80 . The display units  11  are, for example, fastened by screws to the enclosure  80 . The enclosure  80  is, for example, a box-shaped metal housing. 
     Since the display units  11  can reduce possible damage to the waterproof film  40 , the display apparatus  15  can also reduce possible damage to the waterproof film  40 . 
     Although some embodiments attic present disclosure are described above, the present disclosure is not limited thereto, and various modifications can be made without departing from the scope of the invention. 
     For example, the light emitting elements  20  are not limited to LED elements, but may be laser diode (LD) elements. The LED elements are not limited to surface-mount LED elements, but rather may a lamp type LED element. The light emitting elements  20  are not limited to 3-in-1 type elements. The light emitting elements  20  may emit monochromatic light. The light emitting element  20  may include four or more light emitting chips. 
     The light emitting elements  20  can be disposed in any arrangement. For example, the light emitting elements  20  may be arranged in a 128 row by 128 column matrix or a 256 row by 256 column matrix. The light emitting elements  20  may be arranged in an orthorhombic lattice, hexagonal lattice, rectangular lattice, houndstooth, or in any other pattern. The spacing between the light emitting elements  20  can be freely selected. 
     The Shape of the first recess  36  an the mount surface  32  in Embodiments 1 and 2 is not limited to a V shape. The first recess  36  may have any shape. The first recess  36  may have a rectangular shape, a U shape, or the like. The first recesses  36  may be arranged in X-axis and Y-axis directions, extending along an array ante light emitting elements  20 , as illustrated in  FIGS. 18 and 19 . In addition, as illustrated in  FIG. 20 , the first recesses  36  may be arranged to surround the light emitting elements  20 . 
     V-grooves cut in manufacturing the circuit board  30  may be used as the first recess  36 . The V-groove is a V-shaped groove made for cutting off of a single circuit board  30  from a board containing multiple circuit boards  30 . In manufacture of the circuit board  30 , for example, the V-grooves may be cut, in addition to at the positions for cutting off the circuit board  30 , in places where the first recesses  36  of the circuit board  30  are to be made, and the V-grooves may be used as the first recesses  36 . 
     The shape of the second recess  56  in Embodiments 2 and 3 can be freely selected. For example, the second recess  56  may be a V-shaped groove having the side surface  39  of the circuit board  30  and the inner side surface  53   a  of the side plate  53 , as illustrated in  FIG. 21 . This enables further easy adaptation of the waterproof film  40  to contraction or expansion of the case  50 . 
     In addition, as illustrated in  FIG. 22 , the second recess  56  may have an asymmetric shape by setting of a height H of the side plate  53  of the case  50  from the bottom surface  51   a  of the case  50  to be lower than a thickness D of the circuit board  30 . This enables further easy adaptation of the waterproof film  40  to contraction or expansion of the case  50 . In addition, easy manufacturing of the case  50  can be achieved. 
     The waterproof film  40  has preferably thermoplastic properties. Heating the waterproof film  40  with the thermoplastic properties in manufacture of the display unit  10  to  12  enables easy press fitting of the waterproof film  40 . In addition, the waterproof film  40  preferably has weathering resistance. The coefficient of linear expansion of the waterproof film  40  is preferably higher than the coefficient of linear expansion of the circuit board  30  and the coefficient of linear expansion of the case  50  since this can provide a wide range o selection of materials for these components. 
     The waterproof film  40  may be adhered to the light emitting elements  20 . The waterproof film  40  may be, for example, adhered to the light emitting elements  20  by an adhesive layer applied on the light emitting elements  20 . As illustrated in  FIG. 23 , the first cover portion  44  of the waterproof film  40  may be disposed not to be in intimate contact with the first recess  36  to create a space  46  between the first cover portion  44  and the first recess  36 . In addition, the second cover portion  48  of the waterproof film  40  may be disposed not to be intimate contact with the second recess  56  to create a space  46  between the second cover portion  48  and the second recess  56 . 
     A louver or a mask plate for shielding from external light may be disposed on the waterproof film  40 . The external light means light, including sunlight and illumination light, to enter the display unit  10  to  12  from the surroundings. Shielding the external light means reducing the external light entering into the light emitting elements  20  and the circuit board  30 . The louver and the mask plate are, for example, fabricated by injection molding from a black resin. 
     The number and arrangement of the display units  10  included in the display apparatus  15  can be freely selected. The display apparatus  15  may include the display unit  11  or  12 , instead of the display unit  10 . The installation site of the display units  10  to  12  and the display apparatus  15  is not limited to the outdoors, but rather the display units  10  to  12  and the display apparatus  15  may be installed indoors, such as in a gymnasium or an indoor swimming pool. 
     REFERENCE SIGNS LIST 
     
         
           10 ,  11 ,  12  Display unit 
           15  Display apparatus 
           20  Light emitting element 
           21  Top surface 
           22  Light exit face 
           23  Side surface 
           25  Package 
           26  Seal 
           27  Electrode 
           30 ,  70  Circuit board 
           32 ,  72  Mount surface 
           34  First region 
           36  First recess 
           38  First projection coverage 
           39 ,  74  Side surface 
           40  Waterproof film 
           42  Adhesive layer 
           44  First cover portion 
           46  Space 
           48  Second cover portion 
           50  Case 
           51  Bottom plate 
           51   a  Bottom surface 
           53  Side plate 
           53   a  Side surface 
           53   b  Top surface 
           54  Side surface 
           56  Second recess 
           58  Second projection coverage 
           80  Enclosure 
         TS Tensile stress 
         D Thickness 
         H Height 
         S Imaginary plane