Patent Publication Number: US-2022238768-A1

Title: Display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 110103100, filed on Jan. 27, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technology Field 
     The disclosure relates to a display technology, and particularly to a display apparatus. 
     Description of Related Art 
     Light-emitting diode (LED) panels include an active element device substrate and a plurality of light-emitting diode elements transferred on the active element device substrate. Inheriting the characteristics of light-emitting diodes, a light-emitting diode panel is expected to become the mainstream of the next generation of display panels due to the advantages of power saving, high efficiency, high brightness, and fast response time. Currently, there are two main packaging methods for LED display panels. One is a packaging method that uses a traditional package and is fixed through a surface mounted device (SMD). The other is a packaging method in which light-emitting diode elements are directly bonded to the bonding pads of a chip on board (COB) and encapsulated with epoxy. 
     Although the light-emitting diode panel adopting SMD packaging method has better light extraction efficiency, color uniformity, and reworkability, its light-emitting diode elements are more susceptible to damage by external impact, and the light-emitting diode panel has poor flatness of the overall display surface. While the light-emitting diode panel adopting the other COB packaging method can achieve better surface flatness, the light-emitting diode panel has poor light extraction efficiency and poor color uniformity, and repairing the light-emitting diode elements causes great difficulties. 
     SUMMARY 
     The disclosure provides a display apparatus having better reworkability and performance in the dark state. 
     The display apparatus of the disclosure includes a circuit substrate, a plurality of light-emitting elements, an optical film, and an adhesive layer. The light-emitting elements are electrically bonded to the circuit substrate. The optical film overlaps the light-emitting elements. The light-emitting elements are disposed between the optical film and the circuit substrate. The adhesive layer is disposed between the optical film and the circuit substrate and connects the light-emitting elements and the optical film. There is a cavity between the light-emitting elements, the circuit substrate and the adhesive layer. 
     In an embodiment of the disclosure, in the display apparatus, the film thickness of part of the adhesive layer that does not overlap the light-emitting elements is greater than the film thickness of another part of the adhesive layer that overlaps the light-emitting elements. 
     In an embodiment of the disclosure, in the display apparatus, the film thickness of the part of the adhesive layer ranges from 0.02 mm to 1.0 mm. 
     In an embodiment of the disclosure, in the display apparatus, the light-emitting elements have an element surface. The element surface has a height relative to a substrate surface of the circuit substrate in a direction. The adhesive layer has a surface facing the substrate surface. There is a distance between the surface of the adhesive layer and the element surface of the light-emitting elements in the direction, and a percentage value of the distance to the height ranges from 1% to 70%. 
     In an embodiment of the disclosure, in the display apparatus, the light-emitting elements are disposed on the circuit substrate at a first pitch and a second pitch in a first direction and a second direction, respectively. Each of the light-emitting elements has a first width and a second width in the first direction and the second direction, the first direction is perpendicular to the second direction, and a percentage value of a product of the first width and the second width to a product of the first pitch and the second pitch ranges from 1% to 70%. 
     In an embodiment of the disclosure, in the display apparatus, transmittance of the adhesive layer is greater than or equal to 90%. 
     In an embodiment of the disclosure, in the display apparatus, an optical density of the adhesive layer ranges from 0 to 1.0. 
     In an embodiment of the disclosure, in the display apparatus, the adhesive layer has a plurality of scattering particles. 
     In an embodiment of the disclosure, in the display apparatus, a Shore hardness value of the adhesive layer ranges from A20 to D80. 
     In an embodiment of the disclosure, in the display apparatus, the optical film includes a polarizing layer. 
     In an embodiment of the disclosure, in the display apparatus, the optical film further includes a plurality of optical microstructures disposed on a side of the polarizing layer away from the light-emitting elements. 
     In an embodiment of the disclosure, in the display apparatus, the optical film has a surface treatment layer disposed on a side of the adhesive layer away from the light-emitting elements, and the surface treatment layer is an anti-glare layer, an anti-reflection layer, an anti-glare low-reflection layer, and an anti-reflection anti-glare layer, or a low-reflection layer. 
     In an embodiment of the disclosure, in the display apparatus, a reflecting layer is disposed on part of a surface of the circuit substrate that does not overlap the light-emitting elements. 
     In an embodiment of the disclosure, in the display apparatus, a plurality of optical microstructures are disposed on an element surface of the light-emitting elements away from the circuit substrate. 
     In summary, in the display apparatus of an embodiment of the disclosure, the optical film is connected to a plurality of light-emitting elements through the adhesive layer. The light-emitting elements disposed on the circuit substrate are covered by the optical film to improve the surface flatness of the display apparatus on one side of the display surface. On the other hand, there is a cavity between the light-emitting elements between part of the adhesive layer that is not connected to the light-emitting elements and the circuit substrate. With the configuration of the cavity, it is much easier for the optical film to rework, the difficulty of repairing the light-emitting elements is effectively reduced, and thereby the repair yield of the display apparatus is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic top view of a display apparatus according to a first embodiment of the disclosure. 
         FIG. 2  is a schematic cross-sectional view of the display apparatus of  FIG. 1 . 
         FIG. 3  is a schematic cross-sectional view of a display apparatus according to a second embodiment of the disclosure. 
         FIG. 4  is a schematic cross-sectional view of a display apparatus according to a third embodiment of the disclosure. 
         FIG. 5  is a schematic cross-sectional view of a display apparatus according to a fourth embodiment of the disclosure. 
         FIG. 6  is a schematic cross-sectional view of a display apparatus according to a fifth embodiment of the disclosure. 
         FIG. 7  is a schematic cross-sectional view of a display apparatus according to a sixth embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The term “about”, “approximately”, “essentially” or “substantially” used herein includes the value and an average value within an acceptable deviation range of specific values determined by a person of ordinary skill in the art, taking into account discussed measurements and a specific number of measurement-related errors (i.e., limitations of a measuring system). For example, the term “about” may mean being within one or more standard deviations of the value, or within, for example, ±30%, ±20%, ±10%, and ±5%. Moreover, the term “about”, “approximately”, “essentially” or “substantially” used herein may mean selecting a more acceptable deviation range or standard deviations according to measurement properties, cutting properties or other properties, without applying a single standard deviation to all properties. 
     In the drawings, for clarity, a thickness of each film, layer, panel, region, and/or structure may be enlarged. It should be understood that when a device such as a layer, film, region, or substrate is referred to as being “on” or “connected to” another device, it may be directly on or connected to another device, or intervening devices may also be present. In contrast, when a device is referred to as being “directly on” or “directly connected to” another device, there are no intervening devices present. As used herein, “connected” may mean being physically and/or electrically connected. Furthermore, two elements being “electrically connected” or “coupled” may mean that there are other elements between the two elements. 
     Reference will now be made in detail to the exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals are used to represent the same or similar parts in the accompanying drawings and description. 
       FIG. 1  is a schematic top view of a display apparatus according to a first embodiment of the disclosure.  FIG. 2  is a schematic cross-sectional view of the display apparatus of  FIG. 1 . Referring to  FIG. 1  and  FIG. 2 , a display apparatus  10  includes a circuit substrate  100 , a plurality of light-emitting elements  120 , an adhesive layer  140 , and an optical film  160 . The light-emitting elements  120  are dispersedly disposed on a substrate surface  100   s  of the circuit substrate  100  and are electrically bonded to the circuit substrate  100 . For example, the light-emitting elements  120  may be disposed in multiple columns and multiple rows along the direction X and the direction Y, respectively. The direction X is perpendicular to the direction Y. That is, the light-emitting elements  120  can be disposed in an array on the circuit substrate  100 , but the disclosure is not limited thereto. 
     In the embodiment, the circuit substrate  100  is a printed circuit substrate (PCB), for example, but the disclosure is not limited thereto. In other embodiments, the circuit substrate  100  may also be a combination of a glass substrate and a pixel circuit layer. The pixel circuit layer is formed on the glass substrate using a semiconductor process, and the pixel circuit layer can include active elements (e.g., thin film transistors) and various signal lines (e.g., data lines, scan lines, or power lines), but the disclosure is not limited thereto. 
     The light-emitting element  120  is a micro light-emitting diode (micro LED), a mini light-emitting diode (mini LED), or other sizes of light-emitting diodes, for example. According to different types of structures, the light-emitting element  120  of the embodiment can be a flip-chip type of light-emitting diode, a vertical type of light-emitting diode, or a lateral type of light-emitting diode. For example, the light-emitting elements  120  can be used to emit light of different colors, respectively. The light can have different light intensities according to the image data to be displayed, and the effect of color display is achieved. 
     Note that the connection between the light-emitting element  120  and the circuit substrate  100  depends on the type of the circuit substrate  100  and the light-emitting element  120 , so the drawings in the embodiment only schematically illustrate the connection relationship of the light-emitting element  120  and the circuit substrate  100 . For example, in an embodiment not shown, the circuit substrate  100  may have a plurality of bonding pads, the light-emitting element  120  is a flip-chip light-emitting diode, and the light-emitting element  120  is mutually bonded with two corresponding bonding pads on the circuit substrate  100  through two electrodes disposed on the same side of the epitaxial structure, but the disclosure is not limited thereto. In another embodiment not shown, the light-emitting element  120  may also be a vertical light-emitting diode, and the electrode on the side of the light-emitting element  120  away from the circuit substrate  100  is electrically connected to the circuit substrate  100  through connecting wires. 
     To improve the visual quality of the display apparatus  10  in the dark state (e.g., the contrast in the dark state), an optical film  160  is disposed on the side of the light-emitting elements  120  away from the circuit substrate  100 , and the optical film  160  is attached to the light-emitting elements  120  through the adhesive layer  140 . That is, the adhesive layer  140  is disposed between the optical film  160  and the circuit substrate  100  and connects the light-emitting elements  120  and the optical film  160 . In the embodiment, the optical film  160  is an overlapped structure of a polarizing layer  161  and an anti-glare anti-reflection layer  162 , for example. The polarizing layer  161  is a circular polarizing layer, for example, but the disclosure is not limited thereto. In other embodiments, the polarizing layer  161  may also be a linear polarizing layer. For example, the anti-glare anti-reflection layer  162  includes a plurality of surface microstructures and an anti-reflection film plated on the surface microstructures, but the disclosure is not limited thereto. 
     With the configuration of overlapping the optical film  160  and the light-emitting elements  120 , the overall reflectivity of the display apparatus  10  under ambient light irradiation can be significantly reduced. In other words, the anti-glare and anti-reflection characteristics of the display apparatus  10  in the dark state can be effectively improved. Considering the process variation, after each light-emitting element  120  is bonded to the circuit substrate  100 , the configuration relationship (e.g., parallel to each other or inclined to each other) between an element surface  120   s  and the substrate surface  100   s  of the circuit substrate  100  may be slightly different, resulting in poor surface flatness of the display apparatus on the light emitting side. Therefore, with the configuration of the optical film  160 , the surface flatness of the display apparatus  10  on the display surface side can also be improved. 
     Note that the adhesive layer  140  connecting the element surfaces  120   s  of the light-emitting elements  120  further extends into the gaps between the light-emitting elements  120  and covers part of the sidewall surfaces of the light-emitting elements  120 . In other words, in the normal direction (e.g., direction Z) of the substrate surface  100   s  of the circuit substrate  100 , a film thickness t1 of part of the adhesive layer  140  that does not overlap the light-emitting elements  120  is greater than a film thickness t2 of another part of the adhesive layer  140  that overlaps the light-emitting elements  120 . For example, the film thickness t1 of the adhesive layer  140  may range from 0.02 mm to 1.0 mm. 
     From another view, the element surface  120   s  of the light-emitting element  120  has a height h relative to the substrate surface  100   s  of the circuit substrate  100  in the direction Z, the surface  140   s  of the adhesive layer  140  facing the substrate surface  100   s  and the element surface  120   s  of the light-emitting element  120  have a distance d in the direction Z, and the percentage value of the distance d and the height h can range from 1% to 70%. That is, the adhesive layer  140  does not fill the gaps between the light-emitting elements  120 , and the substrate surface  100   s , part of the sidewalls of the light-emitting elements  120 , and the surface  140   s  of the adhesive layer  140  can define a cavity CA between the light-emitting elements  120 . With the configuration of the cavity CA, it is much easier for the optical film  160  to rework, the difficulty of repairing the light-emitting elements  120  can be effectively reduced, and thereby the repair yield of the display apparatus  10  is improved. 
     On the other hand, the light-emitting elements  120  are disposed on the circuit substrate  100  at pitches Px and Py in the direction X and the direction Y, respectively, and each light-emitting element  120  has a width Wx and a width Wy in the direction X and Y, respectively. To increase the light extraction efficiency of the light-emitting elements  120  at the side viewing angle to improve the light energy utilization rate of the display apparatus  10 , the percentage value of the product of the width Wx and the width Wy to the product of the pitch Px and the pitch Py can be set from 1% to 70%. 
     The material of the adhesive layer  140  includes optical clear adhesives (OCAs), optical sensitive adhesives (PSAs), silicone adhesives, polyurethane reactive (PUR) glue, polyurethane (PU) glue, or other suitable optical-grade adhesive materials. In particular, in the embodiment, the anti-reflection and anti-glare performance of the display apparatus  10  is improved with the configuration of the optical film  160 , so the adhesive layer  140  can be selected from optical adhesives with higher transmittance (e.g., optical transparent adhesives). For example, in the embodiment, the transmittance of the adhesive layer  140  may be greater than 90%, but the disclosure is not limited thereto. 
     Note that the Shore hardness value of the adhesive layer  140  can range from A20 to D80 to serve as a buffer layer for the optical film  160  and the light-emitting elements  120 . For example, when the optical film  160  is impacted or squeezed by an external force, the elastic adhesive layer  140  absorbs most of the external force through contraction and deformation, and the light-emitting element  120  is prevented from being damaged by the external force. 
     In the embodiment, the display apparatus  10  may also optionally include a side sealant  180 . The material of the side sealant  180  may include PUR glue, epoxy, silicon glue, photosensitive glue material, or other suitable glue materials. The side sealant  180  is disposed on the periphery of the circuit substrate  100  and is disposed around the light-emitting elements  120 . Specifically, the side sealant  180  connects the circuit substrate  100 , the adhesive layer  140 , and the optical film  160  to define a sealed chamber, and the light-emitting elements  120  are disposed in the sealed chamber. With the configuration of the side sealant  180 , not only can the connection relationship between the optical film  160  and the circuit substrate  100  be further stabilized, but also foreign matters in the external environment can be prevented from entering the cavity CA between the light-emitting elements  120 . 
     Other embodiments are provided below for explanation of the disclosure in detail. The same reference numerals are used to indicate the same elements, and the description of the same technical content is omitted. For the description of the omitted parts, reference may be made to the foregoing embodiments, and the same content will not be iterated in the following embodiments. 
       FIG. 3  is a schematic cross-sectional view of a display apparatus according to a second embodiment of the disclosure. Referring to  FIG. 3 , the main difference between a display apparatus  11  of the embodiment and the display apparatus  10  of  FIG. 2  is that the composition of the optical film is different. Specifically, an optical film  160 A of the display apparatus  11  has an overlapped structure of the polarizing layer  161 , an anti-glare adhesive layer  163 , and a surface treatment layer  165 . The anti-glare adhesive layer  163  is disposed between the polarizing layer  161  and the adhesive layer  140 . The polarizing layer  161  is disposed between the anti-glare adhesive layer  163  and the surface treatment layer  165 . In the embodiment, the anti-glare adhesive layer  163  may include a glue material and a plurality of scattering particles  163 P doped in the glue material. For example, the glue material is an optical pressure sensitive adhesive, and the material of the scattering particles  163 P includes silicone resin or poly(methyl methacrylate) (PMMA), but the disclosure is not limited thereto. 
     However, the disclosure is not limited thereto. In other embodiments not shown, the optical film  160 A can also be directly attached to the light-emitting elements  120  through the anti-glare adhesive layer  163 . Therefore, the display apparatus requires no configuration of the adhesive layer  140  of the foregoing embodiment. In the embodiment, the surface treatment layer  165  is formed by roughening the upper surface of the polarizing layer  161 , for example. That is, the surface treatment layer  165  may be a surface roughness layer, but the disclosure is not limited thereto. 
       FIG. 4  is a schematic cross-sectional view of a display apparatus according to a third embodiment of the disclosure.  FIG. 5  is a schematic cross-sectional view of a display apparatus according to a fourth embodiment of the disclosure. Referring to  FIG. 4 , the difference between a display apparatus  12  of the embodiment and the display apparatus  10  of  FIG. 2  is that the compositions of the optical film and the adhesive layer are different. In the embodiment, an adhesive layer  140 A may also have a plurality of light-absorbing particles  141 , and the light-absorbing particles  141  are adapted for absorbing ambient light from the outside. The material of the light-absorbing particles  141  may include carbon black or masterbatch pigment/dye. For example, the optical density (OD) of the adhesive layer  140 A may range from 0 to 1.0. 
     By doping the light-absorbing particles  141  in the adhesive layer  140 A, the design flexibility of an optical film  160 B can be increased. In the embodiment, the optical film  160 B may be an anti-glare low-reflection layer or a low-reflection layer. However, the disclosure is not limited thereto. Referring to  FIG. 5 , in other embodiments, an optical film  160 C of a display apparatus  13  may also be a surface treatment layer with a rough surface. 
       FIG. 6  is a schematic cross-sectional view of a display apparatus according to a fifth embodiment of the disclosure. Referring to  FIG. 6 , the difference between a display apparatus  14  of the embodiment and the display apparatus  10  of  FIG. 2  is that the composition of the optical film is different. Specifically, an optical film  160 D of the display apparatus  14  is an overlapped structure of the polarizing layer  161 , a refracting layer  164 , and a surface treatment layer  166 , and the refracting layer  164  is disposed between the surface treatment layer  166  and the polarizing layer  161 . 
     For example, in the embodiment, the refracting layer  164  may have a plurality of optical microstructures  164 MS. For example, the optical microstructures  164 MS are a plurality of microprisms and adapted for deflecting light LB from the light-emitting element  120  to a specific light emitting range, and the light concentration of the display apparatus  14  is increased. In the embodiment, the surface treatment layer  166  is an anti-glare layer, an anti-reflection layer, an anti-glare low-reflection layer, an anti-reflection anti-glare layer, or a low-reflection layer, for example, but the disclosure is not limited thereto. 
       FIG. 7  is a schematic cross-sectional view of a display apparatus according to a sixth embodiment of the disclosure. Referring to  FIG. 7 , the difference between a display apparatus  15  of the embodiment and the display apparatus  10  of  FIG. 2  is that a plurality of optical microstructures  120 MS are disposed on the element surface  120   s  of the light-emitting element  120 A of the display apparatus  15 . The optical microstructures  120 MS can increase the roughness of the element surface  120   s  so that the reflectivity of the element surface  120   s  to external ambient light is reduced. 
     On the other hand, in the embodiment, a reflecting layer  110  is further disposed on part of the substrate surface  100   s  of the circuit substrate  100  that does not overlap the light-emitting elements  120 . For example, the reflecting layer  110  is a white paint or a mirror coating to further increase the light extraction efficiency of the display apparatus  15 . In particular, due to the configuration of the optical film  160 , even if the reflecting layer  110  is disposed on the substrate surface  100   s  of the circuit substrate  100  to increase the light extraction efficiency, the display apparatus  15  can still have anti-glare and anti-reflection characteristics in the dark state. 
     In summary, in the display apparatus of an embodiment of the disclosure, the optical film is connected to a plurality of light-emitting elements through the adhesive layer. The light-emitting elements disposed on the circuit substrate are covered by the optical film to improve the surface flatness of the display apparatus on one side of the display surface. On the other hand, there is a cavity between the light-emitting elements between part of the adhesive layer that is not connected to the light-emitting elements and the circuit substrate. With the configuration of the cavity, it is much easier for the optical film to rework, the difficulty of repairing the light-emitting elements is effectively reduced, and thereby the repair yield of the display apparatus is improved.