Patent Publication Number: US-11653556-B2

Title: Flex-tolerant structure, and display panel using same

Description:
FIELD 
     The subject matter herein generally relates to displays, specifically a flex-tolerant structure and a display panel. 
     BACKGROUND 
     Generally, a display panel defines a display area for displaying images and a binding area for binding with a driving circuit. In order to realize a narrow border of the display panel, a bent or folded structure is used to fold the driving circuit in the binding area to a side of the display panel away from its display surface. However, the electrical traces on such structure may be broken and faulty. 
     Therefore, there is room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present disclosure will now be described, by way of embodiment, with reference to the attached figures. 
         FIG.  1    is a top view of a flex-tolerant structure according to an embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view along line II-II of  FIG.  1   . 
         FIG.  3    is a cross-sectional view of the structure of  FIG.  1    when folded. 
         FIG.  4    is a schematic diagram showing the flex-tolerant structure in a bending test according to an embodiment of the present disclosure. 
         FIG.  5    is a diagram showing relationships between a change rate of resistance and number of flexes of the flex-tolerant structure of an embodiment according to the present disclosure and a prior art. 
         FIG.  6    are photographs showing relationships between change in appearance and number of flexes in the bending test of the flex-tolerant structure according to an embodiment of the present disclosure. 
         FIG.  7    are photographs showing relationships between appearance change and number of flexes of the structure in bending test of the prior art. 
         FIG.  8    is a schematic diagram of a tensile test of the unstretched flex-tolerant structure according to an embodiment of the present disclosure. 
         FIG.  9    shows schematic diagrams of tensile rate vs. resistance of the flex-tolerant structure of the present disclosure in the tensile test illustrated in  FIG.  8   . 
         FIG.  10    is a cross-sectional view of a flex-tolerant structure according to another embodiment of the present disclosure. 
         FIG.  11    is a schematic diagram of the flex-tolerant structure of  FIG.  10    in a bent or folded state. 
         FIG.  12    is a top view of a display panel according to an embodiment of the present disclosure. 
         FIG.  13    is a cross-sectional view along line XIII-XIII of  FIG.  12   . 
         FIG.  14    is a top view of the display panel in  FIG.  13    when the substrate is not bent. 
         FIG.  15    is a cross-sectional view of part of the display panel in  FIG.  14   . 
         FIG.  16    is a cross-sectional view of part of a display panel according to another embodiment of the present disclosure. 
         FIG.  17    is a top view of a display panel according to another embodiment of the present disclosure. 
         FIG.  18    is a cross-sectional view along line XVIII-XVIII in  FIG.  17   . 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the exemplary embodiments described herein may be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the exemplary embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one”. The term “circuit” is defined as an integrated circuit (IC) with a plurality of electric elements, such as capacitors, resistors, amplifiers, and the like. 
       FIG.  1    shows a flex-tolerant structure  10  according to an embodiment. As shown in  FIG.  1   , the flex-tolerant structure  10  includes a substrate  12  and a plurality of traces  14  on a surface of the substrate  12 . Each trace  14  extends along a first direction D 1 . The traces  14  are spaced apart and electrically insulated from each other along a second direction D 2 . The second direction D 2  intersects with the first direction D 1 . The number, shape, extension direction and arrangement of the traces  14  can be adjusted according to actual needs. In one embodiment, the flex-tolerant structure  10  is a flexible circuit board. In other embodiments, the flex-tolerant structure  10  is a flexible display panel, as shown in  FIG.  12    through  FIG.  18   . 
     The substrate  12  is flexible and deformable. The material of the substrate  12  can be polyimide (PI), polyamide (PA), polycarbonate (PC), polyphenylether sulfone (PES), polymeric methyl methacrylate (PMMA), polyethylene glycol terephthalate (PET), or cycloolefin copolymer, COC). 
     As shown in  FIG.  2   , the substrate  12  defines a first non-bending area  12   a,  a second non-bending area  12   b,  and a foldable area  12   c  connecting and between the first and second non-bending areas  12   a  and  12   b.  Each trace  14  includes a stretch-resistant layer  142  and a metal layer  144  covering the stretch-resistant layer  142 . The metal layer  144  completely covers a surface of the stretch-resistant layer  142  away from the substrate  12 . The traces  14  or some at least are contained in the foldable area  12   c.    
     As shown in  FIG.  3   , the substrate  12  is bent in the foldable area  12   c  along the length direction (first direction D 1 ) of the traces  14 , and the traces  14  will be bent as the substrate  12  is bent. The foldable area  12   c  has a substantially “C” shape after bending, and the first and second non-foldable areas  12   a  and  12   b  are opposite to each other after bending. The traces  14  in the first non-bending area  12   a  and the traces  14  in the second non-bending area  12   b  are arranged back-to-back. 
     In other embodiments, the bending direction of the substrate  12  is unlimited. For example, the substrate  12  can be bent along the width direction of the trace  14   s  (the second direction D 2 ), or after the substrate  12  is bent, the traces  14  in the first non-bending area  12   a  and the traces  14  in the second non-bending area  12   b  are arranged face-to-face. 
     In one embodiment, the material of the stretch-resistant layer  142  is a composite material of metal and polymer, such as conductive silver paste. The material of the metal layer  144  can be, but is not limited to, copper or copper alloy. In other embodiments, the stretch-resistant layer  142  can be, but is not limited to, carbon nanotubes (CNTs), nano metals (such as nano silver), conductive polymers (PEDOT), composites of CNTs and PEDOT, composites of nano metals and PEDOT, or composites of nano metals and graphene. 
     In one embodiment, the stretch-resistant layer  142  is formed by screen printing or laser patterning. The metal layer  144  is formed by chemical plating, electroplating, or sputtering combined with a yellow light process. 
     As shown in  FIG.  4   , the flex-tolerant structure  10  is substantially in “C”-shaped after bending. In one embodiment, a bending test is carried out on the flex-tolerant structure  10  with a bending radius R of 1 mm. After bending a number of different times, the change rate of resistance and appearance change are examined. As a comparative example, the bending test of a bending structure according to prior art is also carried out with a bending radius R of 1 mm. 
     In  FIG.  5   , the broken line a represents a relationship between the change rate of resistance and number of flexes of the flex-tolerant structure  10  in the bending test. 
     As shown in  FIG.  5   , even after the substrate  12  is bent many times, the change rate of resistance of the substrate  12  is still small. After the substrate  12  is bent 10 times, the change rate of resistance is about 200%. As shown in  FIG.  6   , after the substrate  12  is bent 10 times, the traces  14  have cracks on the metal layer  144  side. However, since the stretch-resistant layer  142  under the metal layer  144  has good tensile resistance, the traces  14  maintain their conductivity through the stretch-resistant layer  142  at cracks of the metal layer  144 . The reliability of the traces  14  is improved, and the phenomenon that the traces  14  are broken during the bending process and cannot conduct is avoided. In addition, even after repeated bending, the resistance of the traces  14  does not change much, and electrical flow is stable. 
     In  FIG.  5   , the broken line b represents the relationship between the change rate of resistance and the number of flexes of a bending structure according to prior art (the electrical traces of the bending structure are made of a single metal layer).  FIG.  7    shows the relationship between the appearance change and number of flexes of the bending structure in the bending test according to prior art. 
     As shown in  FIG.  5    and  FIG.  7   , in prior art (broken line a), after the substrate is bent once, the change rate of resistance is as high as 800%, and after the substrate is bent five times, obvious cracks have been found in the traces (as shown in  FIG.  7   ), which cannot conduct (in  FIG.  5   , the change rate of resistance cannot be measured). 
       FIG.  8    is a schematic diagram of tensile test of the unstretched flex-tolerant structure  10  according to an embodiment. There are three traces  14  on the substrate  12 , which are traces c, d and e. In one embodiment, the material of the substrate  12  is PC. The trace c is a straight line segment with a line width of 0.5 mm, the trace d is a straight line segment with a line width of 1.0 mm, and the trace e is a roughly zigzag segment with a line width of 1.0 mm. 
     As shown in  FIG.  9   , when the stretching rates of traces c, d and e is greater than 90%, the resistance of traces c, d and e can each be detected. That is, the traces c, d, and e are not broken when the stretching rate is not less than 90%. In addition, as shown in  FIG.  8    and  FIG.  9   , the stretching rate and change rate of resistance of trace c are better than those of trace d and trace e. 
       FIG.  10    shows a bending-resistant structure  10  according to another embodiment. As shown in  FIG.  10   , in the flex-tolerant structure  10 , at least some of the stretch-resistant layer  142  is in the foldable area  12   c.  The metal layer  144  extends beyond the stretch-resistant layer  142  and covers the surface of the substrate  12 . That is, the metal layer  144  covers all surfaces of the stretch-resistant layer  142  that are not in contact with the substrate  12  and layer  144  extends beyond the stretch-resistant layer  142 . 
     As shown in  FIG.  11   , after the substrate  12  is bent in the foldable area  12   c,  the traces  14  are bent along with the bending of the substrate  12 . The first and second non-bending areas  12   a  and  12   b  are opposite to each other after being bent. The traces  14  in the first and second non-bending areas  12   a  and  12   b  may have a section including the metal layer  144  and not including the stretch-resistant layer  142 . That is, the stretch-resistant layer  142  is arranged at least in the foldable area  12   c,  so as to improve the flex-toleration of the traces  14  in the foldable area  12   c.    
       FIG.  12    shows a display panel  100  according to an embodiment. The display panel  100  defines a display area AA for displaying images and a border area NA surrounding the display area AA. The border area NA is used to set the traces  14 . The display panel  100  may be, for example, a mobile phone, a tablet computer, a smart wearable device (such as a smart watch), and the like. 
     As shown in  FIG.  13   , the display panel  100  includes a cover plate  20 , a touch layer  30 , an organic light emitting device layer  40 , a flex-tolerant structure  10 , a driving circuit  50 , and a conductive adhesive  60 . 
     The substrate  12  is on the cover plate  20 . The substrate  12  includes a main portion  122  (the first non-bending area  12   a ), a bendable portion  124  (the foldable area  12   c ), and a binding portion  126  (the second non-bending area  12   b ). The main portion  122  is in the display area AA. The bendable portion  124  extends from the main portion  122  and is in the border area NA. The binding portion  126  connects the bendable portion  124  and is on a side of the main portion  122  away from the cover plate  20 . The organic light emitting device layer  40  is on a surface of the main portion  122  close to the cover plate  20 . The driving circuit  50  is on a surface of the binding portion  126  away from the cover plate  20 . The touch layer  30  is between the organic light emitting device layer  40  and the cover plate  20  and is in the display area AA and the border area NA. The traces  14  are at least on a surface of the bendable portion  124  away from the display area AA. The traces  14  are electrically connected to the organic light emitting device layer  40  and the driving circuit  50 . 
     In one embodiment, the organic light emitting device layer  40  includes an organic light emitting diode (OLED) array layer and a thin film transistor (TFT) array layer. The OLED array layer includes a lower electrode layer (not shown), an organic light emitting layer (not shown) and an upper electrode layer (not shown) on the substrate  12 . The organic light emitting layer may include an electron transport layer, an organic material layer, a hole transport layer, a hole injection layer, and the like. When a voltage difference is formed between the lower electrode layer and the lower electrode layer, the organic light emitting layer emits light, and the display panel  100  displays images. 
     In an embodiment, the touch layer  30  includes a self-capacitive touch sensing structure or a mutual-capacitive touch sensing structure. When a conductive object (e.g., a finger) touches the cover plate  20 , a difference occurs in the capacitance sensing signal in the area. After the capacitance sensing signal is processed and converted, a relative position of the touch point is obtained. 
     In one embodiment, the touch layer  30  is flexible and foldable. The material of the self-capacitive touch sensing structure or the mutual-capacitive touch sensing structure can be conductive materials with good flex resistance, such as metal mesh, nano silver wires, nano copper wires, carbon nanotubes, graphene, conductive polymer, and other conductive materials with high flex toleration. 
     In one embodiment, the drive circuit  50  includes a driving chip  52  or a flexible circuit board  54 . The driving circuit  50  is electrically connected to the organic light emitting device layer  40  through the traces  14  to drive the display panel  100 . In  FIG.  13   , the driving chip  52  is bound to the substrate  12  by means of a chip on film (COF). The flexible circuit board  54  is bound to the binding portion  126  through the conductive adhesive  60 , and is electrically connected with the traces  14 . 
     Since the display panel  100  uses a flexible and folded substrate  12 , and the driving chip  52  is integrated on the substrate  12  by means of COF, and the binding portion  126  is bent to the side of the display panel  100  away from its display surface, the frame area NA is narrow, and a screen-to-body ratio of the display panel  100  is increased. 
       FIG.  14    shows the display panel  100  in  FIG.  13    when the substrate  12  is not bent. As shown in  FIG.  14   , the traces  14  are on the surfaces of the bent portion  124  and the binding portion  126  of the substrate  12 . The main portion  122  of the substrate  12  has a substantially rectangular shape as large as the display area AA. The bendable portion  124  extends from an edge of the main portion  122 . 
       FIG.  15    is a sectional view of part of the display panel  100  in  FIG.  14   . For clarity of description, some elements are omitted in  FIG.  15   . As shown in  FIG.  15   , the traces  14  are bent as the substrate  12  is bent. The bendable portion  124  is substantially “C” -shaped after being bent. The binding portion  126  is on a side of the main portion  122  away from the organic light emitting device layer  40 . Each trace  14  includes a stretch-resistant layer  142  and a metal layer  144  covered with the stretch-resistant layer  142 . The metal layer  144  covers the surface of the stretch-resistant layer  142  away from the substrate  12 . 
     In one embodiment, the material of the stretch-resistant layer  142  is a composite material of metal and polymer, such as conductive silver paste. The material of the metal layer  144  can be, but is not limited to, copper or copper alloy. In other embodiments, the stretch-resistant layer  142  can be, but is not limited to, carbon nanotubes (CNTs), nano-metals (such as nano-silver), conductive polymers (PEDOT), composites of CNTs and PEDOT, composites of nano metals and PEDOT, or composites of nano metals and graphene. 
     In one embodiment, the stretch-resistant layer  142  is formed by screen printing or laser patterning. The metal layer  144  is formed by chemical plating, electroplating or sputtering combined with a yellow light process. 
     Because the stretch-resistant layer  142  under the metal layer  144  has good tensile resistance, the resistance of each trace  14  does not change much after being bent multiple times, and the electrical flow is stable. In addition, even if cracks occur on the surface of the metal layer  144  after being repeated flexes, the traces  14  can conduct through the stretch-resistant layer  142 . The reliability of the traces  14  is improved, and broken and non-conducting traces  14  are avoided. 
       FIG.  16    shows the display panel  100  according to another embodiment. In the display panel  100 , the stretch-resistant layer  142  is at least in the foldable area  12   c.  The metal layer  144  extends beyond the stretch-resistant layer  142  and covers the surface of the substrate  12 . That is, the metal layer  144  covers all surfaces of the stretch-resistant layer  142  that are not in contact with the substrate  12  and layer  144  extends beyond the stretch-resistant layer  142 . The traces  14  at the bendable portion  124  and the binding portion  126  may have a section including only the metal layer  144  and not including the stretch-resistant layer  142 . Since the stretch-resistant layer  142  is arranged at least to correspond to the bendable portion  124 , the flex toleration of the traces  14  at the bending  124  is improved. 
       FIG.  17    and  FIG.  18    show a display panel  200  according to another embodiment. The difference between the display panel  200  and the display panel  100  is that the display panel  200  only includes a border area NA on one side of the display area AA, which further increases a screen ratio of the display panel  200 . 
     It is to be understood, even though information and advantages of the present exemplary embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present exemplary embodiments, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present exemplary embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.