WO2021255203A2

WO2021255203A2 - System and method for connecting display panels

Info

Publication number: WO2021255203A2
Application number: PCT/EP2021/066505
Authority: WO
Inventors: Wim VAN EESSEN; Patrick Willem; Bart Van Den Bossche; Peter Gerets
Original assignee: Barco N.V.
Priority date: 2020-06-18
Filing date: 2021-06-17
Publication date: 2021-12-23
Also published as: WO2021255203A3

Abstract

A display panel having a frontside and a backside with electrically conductive tracks that are able to be connected with an electrically conductive member along the display panel (or substrate) short edge for connecting electrical components on the front side and the backside of the display panel. The electrically conductive tracks and the electrically conductive member can be interfaced with conductive bumps, which are located on an outside surface of the display panel and arranged to electrically connect the electrically conductive track on the substrate to the electrically conductive member. Additionally, an alignment tool for assembling multiple display panels that can have different inclination of their front surfaces, e.g., the average plane of the light sources, where the alignment tool can align the front surfaces of all display panels to lie within the same plane.

Description

SYSTEM AND METHOD FOR CONNECTING DISPLAY PANELS

[0001] FIELD OF THE INVENTION

[0002] The present invention relates to the field of LED displays and tiled display walls where the individual display panels can be implemented with an active matrix technology, for example using TFT (Thin Film Technology) and connections thereof.

[0003] BACKGROUND OF THE INVENTION

[0004] The use of TFT-on-glass design can reduce monetary cost as well as enable a decreased pixel size, and in turn a reduced pixel pitch (i.e., distance between neighbouring pixels). However, with this technology there are some challenges. For example, when tiling LED displays or panels next to each other in a wall configuration, it is desired to decrease the seams between the modules and hence the pixel pitch of the neighbouring pixels from two different panels, which is not always practical, since this leaves less space on the individual panels to place electronics, e.g. power- and driving electronics. Via-holes can connect the two opposite sides of one or more substrates, but when working with TFT films and very small dimensions of conductor tracks, these can be difficult to implement.

[0005] Additionally, when the seams between each display panel are narrowed down, it becomes increasingly important that each display panel is aligned with its neighbouring display panels. Such alignment can be performed with mechanical solutions, e.g. positioning screws, but such solutions add bulky additional structures to the tiled display wall. It is undesired and impracticable to add such structure to a slim TFT-on-glass design. [0006] Therefore, embodiments of the present invention are directed to overcoming at least some of the above-mentioned deficiencies.

[0007] SUMMARY OF THE INVENTION

[0008] One embodiment of the present invention includes a display panel having a frontside and a backside with electrically conductive tracks that are able to be connected with an electrically conductive member along the display panel (or substrate) short edge for connecting electrical components on the front side and the backside of the display panel, e.g. to power- and driving- circuits on the backside of the display panel. The electrically conductive tracks and the electrically conductive member can be interfaced with conductive bumps, which are located on an outside surface of the display panel and arranged to electrically connect the electrically conductive track on the substrate to the electrically conductive member. [0009] In another embodiment of the present invention, the display panel includes at least two display panels or substrate that can be connected to each other using an electrically conductive member and conductive bumps. The power- and control electronics for one display panel can then be used to drive and control other display panels that are electrically connected thereto.

[0010] In yet another embodiment of the present invention, the electrically conductive tracks on the substrate can be narrower or wider than conductive tracks on the electrically conductive member.

[0011] In still another embodiment of the present invention, the display panel can comprise power- and control electronics on its backside, where the power- and control electronics can be embedded with TFT circuits that are manufactured on a separate substrate or in the same substrate as electronic components such as light sources.

[0012] The present invention is also directed to an alignment tool for assembling multiple display panels that can have different inclination of their front surfaces, e.g., the average plane of the light sources, where the alignment tool can align the front surfaces of all display panels to lie within the same plane.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other technical effects and advantages of embodiments of the present invention will now be described in more detail with reference to the accompanying figures, in which:

[0015] FIG. 1 shows a prior art tiled display wall;

[0016] FIG. 2 shows a prior art substrate connected to a PCB with a flexible conductor; [0017] FIG. 3 shows a prior art substrate connected to a PCB with a rotated flexible conductor;

[0018] FIGS. 4A, 4B, 4C, 4D show an embodiment of the present invention comprising an electrical connection from the front side to the back side of a display panel;

[0019] FIG. 5 shows an embodiment of the present invention where two display panels share electronics on the backside of the display panels; [0020] FIGS. 6A, 6B, 6C, 6D show an embodiment of the present invention comprising conductive tracks of different widths;

[0021] FIGS. 7A, 7B show an embodiment of the present invention comprising a conductive bump; [0022] FIG. 8A and FIG. 8B show an embodiment of the present invention for manufacturing multiple TFT processed electronic circuits on one substrate;

[0023] FIG. 9 A and FIG. 9B show an embodiment of the present invention for manufacturing multiple TFT processed electronic circuits on one or two substrates;

[0024] FIG. 10 shows an embodiment of the present invention comprising a tool for aligning a display panel front surface.

[0025] DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the various descriptions of the invention. The drawings described are only schematic and are non-limiting, where various descriptions of the features are combinable with any of the described embodiments and certain prior art designs.

[0027] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein. Similarly, the terms “front,” “back,” “top,” “bottom”, “middle” are used for distinguishing between similar elements and are not necessarily for describing specific positions thereof.

[0028] The term "comprising", used in the claims, should not be interpreted as being restricted to the features listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Similarly, it is to be noticed that the terms “coupled,” “attached”, “connected” etc. also used in the description or claims, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression "a device A coupled to a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means.

[0029] Definitions

[0030] Abbreviations

[0031] ACF = Anisotropic conductive film

[0032] COB = Chip On Board

[0033] DDIC = Display Driver Integrated Circuit [0034] EMC = Electromagnetic Compatibility

[0035] EMI = Electromagnetic Interference

[0036] ENIG = Electroless Nickel Immersion Gold [0037] LED = Light Emitting Diode

[0038] OLED = Organic Light Emitting Diode [0039] PCB = Printed Circuit Board

[0040] TFT = Thin Film Technology

[0041] An “active matrix” is a type of electronic circuit used in display technology to drive the display pixels. The circuit is configured so that the state of each pixel can be individually accessed and controlled. For example, LED light sources can be implemented as COB using an insulating substrate (e.g. glass) that has embedded electronics implemented with TFT technology. The electronics is then often configured as an active matrix.

[0042] A tiled “display wall” can comprise a multiple of smaller display units or “display panels or modules” that are tiled next to each other so that they together can create a large display. The “display panel” can include a substrate to carry the display light sources and the necessary electronic circuits (e.g. electronic control- or driving circuits) and other electrical components. The display module can include a display panel and additional features, e.g. supporting mechanical structures, but a display panel may also be used as a display module.

[0043] An “edge contact” is an electrical contact that is located along the short side or edge of a substrate. The short side or edge extends in a direction that is not parallel with the front- or backside. If the substrate has electronic circuits on its front- and backside, edge contacts can be used to connect the front- and backside electronic circuits. [0044] A “peripheral contact” is an electrical contact that is located at the rim of the front- or backside of a substrate and extends parallel with the substrate front- or backside. [0045] “Conductive bumps” or just bumps refers to electrically conductive bumps that can be realized with a variety of techniques, such as conductive bumps manufactured using, for example, ACF Hotstamping, induction welding of conductive bumps, stencil printing (screenprinting with a fine metal stencil), inkjet-like printing on sides of glass, “nano hair” Klett- welding, tampoprint, solder ball jet printing, etc.

[0046] The illustrations of display panels are oriented so that the viewing direction is in the z direction, if not otherwise indicated.

[0047] Tiled display wall

[0048] FIG. 1 shows a prior art tiled display wall 1 comprising multiple display panels or modules, where only display panels or modules 2, 3 and 4 are referenced. As can be seen in the figure, due to the side-by-side arrangement of the display panels or modules, it is desired to keep the area between each display panel (or module), often referred to as the seam, as narrow as possible to not disturb the content displayed over the full area of the display wall 1, for example, the seam 5 between panels 2 and 3, e.g., dark spaces created by the seams that are not illuminated by the light sources of the display panel or module. Additionally, since the light sources on the front side of each display panel need to be electrically connected with electronic circuits for driving and controlling, it is necessary to include electronic circuits for control thereof on the display panel or module. These electronic circuits are often located on the back side of the display panel in order to not increase the seam width or in other ways reduce the display area. The light sources, electronic circuits, and/or control circuitry can be connected using flexible conductors to connect the front- and back side of a display panel.

[0049] Electronics on the display backside using a flexible conductor

[0050] FIG. 2 shows a prior art example using a flexible connector, where a rigid substrate 10 comprises a DDIC (Digital Driver Integrated Circuit) 11 which is connected to a PCB 13 via a flexible conductor 12. A flexible substrate, e.g. a polyimide substrate (not shown) can be used which can be connected directly to the PCB 13. Alternatively, the DDIC can be connected to the flexible conductor or to the flexible substrate. [0051] Rotated flexible conductor

[0052] FIG. 3 shows an example of a prior art design of a flexible conductor which is a side view of a display panel (e.g., the viewing direction is along the z axis) where a substrate 20 and a conductive track 21 are connected to a flexible conductor 22, for example, a fl exfoil. This set-up allows the flexible conductor 22 to only bend behind the substrate 20 and hence take up less space at the short edge of the substrate along the x direction. Conduction between the substrate 20 and the flexible conductor 22 takes place through the interface area 23. In conventional PCB substrates, the interface area 23 may not be an issue since the cross-section of the conductor is “large”. However, when using TFT conductive tracks on insulating substrates, a problem may arise since the interface area 23 may be much smaller. For example, TFT conductive tracks associated with glass substrates can have dimensions in the order of 80 x 1 micrometers = 80 square micrometers. Hence, the available contact area will be limited such dimensions. When using light sources that demand relatively high driving currents, for example Light Emitting Diodes (LED’s), such interface area may be a bottle neck. Since power is the product of resistance and squared current, a quenched current flow can result in that the conductive tracks getting overheated and even burning out, which would result in failure of the LED and/or display panel or module.

[0053] Display panel with electronics on the front- and backside

[0054] FIG. 4A shows an embodiment of the present invention that overcomes the deficiencies of the prior art designs, where a display panel 400 comprises at least two substrates 40 and 41 attached or bonded to each other with an adhesive 42, e.g. a glue, or acrylic glue with spheres such as Sadechaf Uvacryl 2151 from SADECHAF UV BVBA (Turnhout, Belgium), or fuse bonding. The substrate(s) can be made of insulating material, such as, glass, or clear polymer/plastic/polyimide and can be rigid or flexible. The adhesive 42 may be electrically conductive and it may comprise spacer materials such as small spheres which aid in alignment of the two substrates 40, 41 and/or provide electrical conductivity, e.g., plastic spheres plated with metal. The outer surface of substrates 40, 41, e.g., that form the frontside and/or the backside of the display panel, comprises electrically conductive tracks 43 and 44, respectively. The electrically conductive tracks can be connected to display drivers that are implemented using TFT technology and/or chip-on- board technology (for example, chip-on-glass, chip-on-plastic or chip-on-film where integrated circuits are wired and bonded to the board). It is understood that the electrically conductive tracks can be used as or connected to edge contacts along a short edge of the substrate or peripheral contacts along the frontside of the substrate to electrically connect electrical components, e.g., light sources such as LEDs, OLED, and variations thereof, QD- LED, EL-QLED, AMOLED, etc., to power- and driving- circuits.

[0055] An electrically conductive member 47, e.g. a flexible conductor cable, film, or wire, is electrically connected to the electrically conductive tracks 43, 44 along the short edge of the substrate(s) and connects the electrically conductive tracks 43, 44 on the outer surfaces of the substrates to each other. The electrically conductive member 47 has conductive means 48 for electrically connecting its frontside, e.g., the side facing the substrates, to its backside, e.g., the side opposite the substrates that faces along the positive x axis (in FIG. 4A). This may be implemented with for example using via connectors through the electrically conductive member (along the x axis), or a conductive coating along its surface that connects the frontside and backside of the electrically conductive member 47.

[0056] Conductive bumps 45 and 46 can be added to interface with the electrically conductive member 47 and the electrically conductive tracks 43 and 44, respectively, e.g., the conductive bumps 45, 46 contact both the electrically conductive member 47 and the respective electrically conductive tracks 43, 44. The conductive bumps can comprise a conductive metal, e.g., gold, silver, copper, indium, tin, lead, etc., or conductive polymer, and have an increased interface area between the electrically conductive tracks on the substrate and the electrically conductive member. Further advantages can be gained by having the electrically conductive tracks as edge contacts which further increases the interface area between the electrically conductive tracks of the substrate and the electrically conductive member. In view of such structure, an electrical connection between the two substrates 40 and 41 is established. In some embodiments, the substrate 40 comprises light sources and related electronic circuits, while substrate 41 comprises power- and driving electronic circuits and/or the DDIC. Of course, other electronic circuits for driving and controlling the display panel are included as well. Accordingly, the two substrates 40, 41 can be electrically connected without using via holes through the substrates, but instead are connected along their outer surfaces by the electrically conductive tracks 43, 44.

[0057] FIG. 4B illustrates another embodiment of the present invention wherein the display panel 500 comprises a single substrate 50. The substrate 50 has electrically conductive tracks 53 and 54, which interface the electrically conductive member 57 with conductive bumps 55 and 56, respectively. The electrically conductive member 57 has conductive means 58 for electrically connecting its frontside to its backside, e.g., similarly as described with respect to electrically conductive member 47, as discussed above. As with display panel 400, it is possible in this embodiment to have the light sources and related electronic circuits on one substrate side and the power- and driving electronic circuits on the opposite side. Such single substrate display panel can be implemented by using dual side TFT (Thin Film Technology) processing which provides a compact single-substrate design.

[0058] FIG. 4C shows another embodiment of the present invention where the display panel 600 comprises a substrate 61 and an electrically conductive member 67, where a part of the power- and driving electronic circuits can be implemented as separate units 69 or 70, e.g., TFT circuits embedded in a substrate. The separate units 69, 70 can be placed on the display panel backside and/or elsewhere, for example, on a separate PCB board 71 and/or on the electrically conductive member itself. It is understood that the display panel 600 is not limited to a single substrate, but provided for ease of understanding, and the display panel 600 may comprise two or more substrates, e.g., similar to display panel 400.

[0059] The electrically conductive members 47, 57 and 67 can be attached to the substrate(s) by using an ACF (Anisotropic Conductive Film) and a hotbar pressing technique or other method as known in the art, e.g., soldering, deposition techniques, electrically conductive pastes, etc. For example, as seen in FIG. 4D, the display panel 700 comprises a substrate 50, electrically conductive member 57 that is connected to electrically conductive tracks 53, 54, conductive bumps 55, 56 that interface with the electrically conductive member 57 and the electrically conductive tracks 53, 54, and an ACF 75 between the electrically conductive member 57 and substrate 50, where arrow 76 indicates the direction of the applied pressure for connecting the electrically conductive member 57 to the substrate 50 and the ACF 75 therebetween.

[0060] Control electronics module for more than one display panel

[0061] FIG. 5 shows another embodiment of the present invention where two display panels 80 and 81 are electrically connected edge-to-edge with an electrically conductive member 87 sandwiched between the display panels 80, 81. Display panels 80, 81 comprise electrically conductive tracks 83, 84, and conductive bumps 85, 86, respectively. The display panel 80 can be further connected to an electrically conductive member 89, which provides electrical connection to a separate PCB 77 comprising electrically conductive tracks 88 and electronics, e.g. power- and driving electronics 78. Solder bumps 82 and 79 may be added to interface between the electrically conductive member 89 and the electrically conductive tracks 83 and 88. Alternatively or additionally, the power- and driving electronics 78 can also be located in any configuration described above with respect to any of the disclosed embodiments. The electrically conductive members 87 and 89 are of the same type as electrically conductive members 47, 57 and 67, described above, e.g., a flexible conductor film. Since display panel 80 is electrically connected to display panel 81, the power- and driving electronics 78 can serve to power and control both display panel 80 and display panel 81. It is understood, however, that there is a trade-off between the display area of a display wall, the number of connected display panels, and the current yield required for the number (e.g., amount) of displays that can be served by a single module for power- and driving electronics 78.

[0062] Different sized conductive tracks

[0063] FIG. 6A shows another embodiment of the present invention, where a substrate 90 comprises multiple electrically conductive tracks, where only 91 and 92 are referenced, that are connected to electrical components (not shown), e.g., light sources such as LEDs, and are interfaced/connected to an electrically conductive member 93 having a multiple of electrically conductive tracks, where only 94 and 95 are referenced. At least in view of the multiple electrically conductive tracks, it may be difficult to obtain good alignment between the electrically conductive tracks 91, 92 on the substrate 90 and the electrically conductive tracks 94, 95 on the electrically conductive member 93. For example, if the flexible conductor 93 is shifted along the arrow 96, the interface area between the electrically conductive tracks can be heavily reduced, and in a worst case, the electrical contact is lost, e.g., current cannot be supplied and/or received from/to the electrical components. This difficulty could be further increased if the electrically conductive tracks are very narrow, e.g., if the conductive tracks are in the order of micrometers in thickness.

[0064] FIG. 6B shows another embodiment of the present invention where a substrate 100 comprises a wide conductive track 102 to aid in the alignment with the electrically conductive tracks on the electrically conductive member, e.g., the flexible conductor 103. The electrically conductive member 103 has a multiple of electrically conductive tracks 104, 105, 106, 107, 108 and 109. When the flexible conductor 103 and the substrate 100 are in contact, the electrically conductive tracks 105, 106, 107 and 108 can overlap with the conductor line 102, while the electrically conductive tracks 104 and 109 have no overlap. If the flexible conductor 103 is slightly shifted in the directions of the arrow 101, there will still be several electrically conductive tracks connected to the conductor line 102. For example, as seen in FIG. 6C, which is a top view of the embodiment in FIG. 6B where additional electrically conductive tracks are shown on the substrate 100 and the electrically conductive member 103 and the electrically conductive member 103 and the substrate 100 have been separated for clarity, even if the substrate 100 and the electrically conductive member 103 are shifted relative to each other along the x axis, there will always be some overlap between narrow and wide electrically conductive tracks, e.g., at least due to the width of the electrically conductive track 102 electrical connection between the electrical components and any driving and/or power circuits will still be provided. FIG. 6D shows how the electrical connection can be further increased by using conductive bumps, e.g., 116, 117, at the interface area between the flexible conductor 103 and the substrate 100 to electrically connect the electrically conductive tracks.

[0065] Alternatively, the wide and narrow electrically conductive tracks can be placed on either the electrically conductive member 103 and the substrate 100, respectively, or there can be a mix of wide and narrow electrically conductive tracks on both the substrate 100 and on the electrically conductive member 103. The electrically conductive member can be a flexible conductor or a “flat-wire” or any generic conducting element suitable to interface and electrically connect with one or more substrates.

[0066] Manufacturing Method

[0067] The present invention is also directed to a method for manufacturing a display panel as discussed above. In such an exemplary method, the method comprises the steps of forming at least one substrate layer having a frontside and a backside, where the at least one substrate layer comprises insulating material, such as glass, or plastic (e.g. Polyimide (PI), polyethylene terephthalate (PET), Polymethylmethacrylate (PMMA), etc.), where the substrate layer can be a rigid or flexible substrate. Next, electrically conductive tracks are formed on at least the frontside of the at least one substrate, which will form a frontside of the display panel. The electrically conductive tracks can be formed as TFT circuits or layers by etching, stripping, deposition methods, masking, adhesion of metal foils, pastes, etc. and con further include buffer layers, insulation layers, or other layers that protect the substrate/TFT circuits. An electrically conductive member is then connected to the electrically conductive tracks, where the electrically conductive member is connected using pastes, adhesives, ACF and hotbar pressing techniques, etc. to the substrate.

[0068] It is understood at the at least one substrate can include integrated circuits, such as TFT circuits that form an active matrix, which are embedded in the substrate, where the TFT circuits can be formed from metal oxide semiconductor materials, metals and oxides thereof, organometallic powders, electrically conductive polymers, and/or polycrystalline semiconductor materials, but is not limited thereto. The TFT circuits/active matrix is configured so that the state of each pixel can be individually accessed and controlled. For example, LED light sources can be implemented as COB using an insulating substrate (e.g. glass) that has embedded electronics implemented with TFT technology.

[0069] A plurality of electrical components can be attached to the at least one substrate and electrically connected to the electrically conductive tracks and/or integrated circuits/active matrix. For example, the plurality of electrical components can be attached to the substrate via soldering or using adhesives and by providing a conductive layer and/or protective layer (e.g., ENIG). The substrate is then connected to power- and driving- circuits (on the same substrate or different substrate that forms a backside of the display panel) to control the electrical components, such as the light sources.

[0070] Multiple display panels or modules can then be assembled to form a display wall, as discussed further below.

[0071] Conductive bumps for increased interface area

[0072] In order to increase the interface area between the electrically conductive tracks and the electrically conductive members, “conductive bumps”, or just bumps, can be placed at the end of the electronic circuit layout on the at least one substrate where a part of the at least one substrate is later cut off. Since the bumps are placed over the cutting line, they can be cut while cutting the substrate. In this way, one can obtain an enlarged flat contact surface for, e.g., attaching a side contact to the bump.

[0073] FIG. 7A shows an embodiment of the present invention comprising a sphere-shaped conductive bump 30 deposited onto an electrically conductive track 31 on a substrate 32. The cross-section line 33 indicates where the substrate can be cut along the y-axis. FIG. 7B shows the resulting cross-section surface. Hence, by adding the conductive bump 30 during the fabrication of the substrate, the total conductive interface area can be increased from area 34 to area 34 and area 35. If the conductive bump has a spherical or ellipsoidal shape, the cutting plane can be placed close to the bump center in order to maximize the cross- section area of the bump. If the bump has another shape, the cutting trajectory (e.g. along a plane) can be selected so that the total cut area is as large as possible. The substrate with bumps can be cut or diced by using sawing, e.g. wire sawing, laser cutting, etc. The conductive bump can comprise a low temperature solder material (for example, having a melting point between 110 and 260 deg C, such as tin, indium, bismuth, silver, etc. or paste) or Cu, or a conductive glue and can be realized with a variety of techniques, such as conductive bumps manufactured using, for example, ACF Hotstamping, induction welding of conductive bumps, stencil printing (screen-printing with a fine metal stencil), inkjet-like printing on sides of glass, “nano hair” Klett- welding, tampoprint, solder ball jet printing, etc. In so doing, the conductive bump made by such a method increases the interface area between the electrically conductive tracks on the substrate(s) and the electrically conductive member, and can assist in electrically connecting the members due to any mis alignment.

[0074] In another embodiment of the present invention the manufacturing method further comprises forming the driving- and power electronic circuits by implementing the electrically conductive tracks and/or electrical circuits on the same substrate as the display panel. This is advantageous since multiplexers and current mirrors can be added inside the driving electronic circuit so that the number of contacts to the driving electronics on the PCB can be greatly reduced. Further, the driver and power electronic circuits can contain functional designs by TFT to reduce the driving overhead needed to light up the display panel. In so doing, the DDIC described above may no longer be necessary, in some embodiments of the invention.

[0075] For example, FIG. 8A illustrates a snapshot during the substrate manufacturing process of the display panel. The substrate 140 having the embedded integrated circuits, e.g., TFT electronic circuits, can be divided into a multiple of segments 141, 142 and 143, where each segment comprises TFT electronic circuits for use with different purposes. This design is advantageous since it can enable the processing of electronic circuits for a multiple of purposes at the same time on the same substrate. For example, the display segment 141 can have TFT electronic circuits for driving the light sources. Flanking segments 142 and 143 can be used for distributing power to the display as well as having line select capabilities (e.g. accessing each line separately by scanning of the display). Segment 144 can be used to handle level shifting, e.g. translate driving levels into TFT voltage levels. It can also comprise current mirroring, e.g. multiplying one current source into many current sources. The comer segments 145 and 146 can be disposed or used for e.g. test circuits. In practice, available space on existing etching masks can be used for any of the segments. The present invention is not limited to this specific placement of the functionalities on the flanking segments, but such placement and functionalities are provided as examples thereof.

[0076] The substrate segments 143, 144 and 145 can then be separated from the display segments 142 and placed back-to-back on the display panel, e.g. by using electrically conductive adhesives or fuse bonding. FIG. 8B shows the backside 147 of the substrate with the cut off segments 142, 143 and 144 attached to the substrate. It is appreciated that the size of the cut-off segments and the corresponding electronic circuits can be adapted to fit on the backside 147.

[0077] A further advantage of this embodiment of the present invention is that it can provide perfect alignment between the electrical conductors on the display panel and electrical conductors on the control or driver panel since they can be continuously drawn as one over the different segments before they are cut, see exemplary line 148. Another advantage with such display panel is that it can be made without having to allocate area for power- and driving circuits on the display front side. If such display panel is used in a tiled display wall, e.g., as seen in FIG. 1, the display panel is provided so that the distance between pixels on two neighbouring display panels can be significantly decreased.

[0078] FIGS. 9A and 9B shows another embodiment of the present invention where the frontside and backside of the display panel are processed on two separate substrates. FIG. 9A shows the first substrate 150 comprising the processed electronic circuits 151 for the display segment. FIG. 9B shows the second substrate 160 comprising the power- and driving electronic circuits 162, 163 and 164, and the display segment backside 161. The substrates 150 and 160 can then be attached back-to-back and fixed to each other e.g. using electrically conductive adhesive glue or fuse bonding.

[0079] Alternatively, it is understood that if dual side TFT processing is available, the power- and driving circuits 162, 163 and 164 can be processed directly onto the backside of the first substrate 150. This results in a compact design having a thickness of only one substrate or display panel. An additional advantage is that a monolithic stack reduces assembly time.

[0080] The embodiments of FIGS. 8A-8B and 9A-9B comprise means for electronic connection between the front- and back sides, for example using via connectors or peripheral contacts or edge contacts as described above, but preferably includes the electrically conductive member and conductive bump connection for the electrically conductive tracks on the substrate and the electrically conductive member.

[0081] Aligning the display panel front surface

[0082] When tiling several display panels together to form a display wall as in FIG. 1, it is desirable to have the front surface, e.g., frontside, of all individual display panels aligned with its neighbour display panel in the intended plane (flat or curved) to not disturb the visual experience, e.g., avoid seams and/or breaks in illumination of the display panel. The display panel “front surface” can be defined as the average distance from the light source elements to the display back plane, e.g., backside.

[0083] Each display panel or tile can comprise sub-tiles, where the sub-tiles should also be aligned with the same intended plane. The alignment will be even more important to reduce the pixel pitch. While it is possible to add mechanical adjustment systems, such systems add additional costs, complexity and weight to the display wall. Another embodiment of the present invention solves these deficiencies by providing an alignment tool that can be used during assembly of the display wall and panels.

[0084] FIG. 10 shows an embodiment of the present invention comprising an alignment tool 200. Three light sources 201, 202 and 203, e.g., LEDs, are mounted onto a display substrate 204 so that their centers are distributed in an average plane 205. The average plane 205 may be misaligned with an angle 206 to the display substrate 204. The misalignment can be due to tolerances of the components and in a pre-alignment process. So, if the display substrate 204 would be mounted directly onto a surface (e.g. a building wall) parallel to a backplane 207, the average plane 205 would have an angle 206 towards the viewer 208. Eventually the tiled display, and one or more display substrates, could be oriented in arbitrary angles towards the viewer. In order to solve the at least said problem the present invention comprises an alignment tool having hollow structures 209 and 210, e.g., cavities, coupled to or on the backside of the display substrate 204. A back substrate 211 which comprises studs 212 and 213 can be inserted into the hollow structures 209 and 210. A desired alignment of the average plane 205 can be obtained by placing the substrate onto a support surface 215 so that the light sources 201, 202 and 203 are aligned with the support surface 215, for example by letting the light sources touch the support surface 215. The back substrate 211 can now be lowered towards the display substrate 204 until a desired distance is obtained between the two substrates, for example, by using one or more spacer support, where two spacer supports 216 and 217 are shown. If only one spacer support is used it will typically be rigidly attached to the back substrate 211. Meanwhile, the studs 212 and 213 can be inserted inside the hollow structures 209 and 210, e.g., having a cup like structure. The hollow structures 209 and 210 can comprise or be filled with a fixation medium 214, e.g. a glue or resin, which can be cured when the display substrate 204 has adopted the desired position or can use mechanical fasteners, such as screws, bolts, etc. The back substrate 211 can then be removed, or it can be left as a part of the display system. [0085] The above content is illustrative rather than restrictive. Any equivalent modification or change made to the present invention without departing from the scope thereof should be included in the various embodiments of the invention. Accordingly, it is intended that the invention covers modifications and variations of the invention which includes various combinations of different aspects of the invention and can be included in the prior art designs, e.g., tiled display wall, having the inventive subject matter herein.

Claims

Claims:

1. A display panel having a front side and a backside comprising: at least one substrate having a frontside and a backside, electrically conductive tracks formed on the frontside and the backside of the display panel, wherein said electrically conductive tracks are provided on the frontside of the at least one substrate to form the frontside of the display panel, an electrically conductive member connecting the electrically conductive tracks on the frontside of the at least one substrate to the electrically conductive tracks on the backside of the display panel, and at least one conductive bump that is arranged to contact at least one electrically conductive track on the substrate so that the electrically conductive track on the substrate is interfaced with the electrically conductive member, wherein the at least one conductive bump is located on at least one of an outer surface of the frontside and the backside of the display panel.

2. The display panel according to claim 1, further comprising at least one second substrate, wherein the electrically conductive tracks are provided on the at least one second substrate to form the backside of the display panel.

3. The display panel according to claim 1 or claim 2, wherein the display panel only comprises the at least one substrate, wherein the electrically conductive tracks are provided on the backside of the at least one substrate to form the backside of the display panel.

4. The display panel according to any of the preceding claims, wherein the conductive bump has a spherical or elliptical form.

5. The display panel according to any of the preceding claims, wherein the conductive bump is formed from a dicing or cutting at a center of the conductive bump when cutting the at least one substrate.

6. The display panel according to any of the preceding claims, wherein the at least one substrate is further connected to a separate printed circuit board (PCB), said separate printed circuit board having power and driving electronic circuits for driving electrical components on the at least one substrate.

7. The display panel according to any of the preceding claims, wherein the electrically conductive member comprises a second multiple of electrically conductive tracks, wherein at least one of the electrically conductive tracks on the frontside of the at least one substrate or the backside of the display panel has a width that is wider or narrower than a width of the second multiple of electrically conductive tracks.

8. A display wall comprising at least two display panels according to claim 1, wherein the display wall comprises: a first electrically conductive member connecting electrically conductive tracks on a first substrate of a first display panel to electrically conductive tracks on a second substrate of a second display panel, a second electrically conductive member connecting the electrically conductive tracks on the first substrate of the first display panel to electrically conductive tracks on a backside of at least one of the first display panel or the second display panel, and at least one conductive bump that is arranged to contact each electrically conductive track so that the electrically conductive track is interfaced with the first electrically conductive member and/or the second electrically conductive member, wherein the at least one conductive bump is located on at least one of an outer surface of the frontside and the backside of the display panel.

9. A method for manufacturing a display panel comprising the steps of: forming at least one substrate, wherein integrated circuits are embedded in the at least one substrate; forming electrically conductive tracks on a front side of the at least one substrate; attaching an electrically conductive member to the at least one substrate so that the electrically conductive member is electrically connected to at least one of the electrically conductive tracks formed on the at least one substrate; forming at least one conductive bump that contacts and connects at least one electrically conductive track on the at least one substrate to the electrically conductive member.

10. The method for forming a display panel according to claim 9, the method further comprising the steps of: segmenting the at least one substrate into at least two segments; and forming the display panel, wherein one of the at least two segments is provided on a front side of the display panel, and the other of the at least two segments is provided on a back side of the display panel.

11. The method according to claim 10, wherein the at least two segments comprise at least two of the following: driving electronic circuits, power electronic circuits, circuits for driving the plurality of electronical components, circuits for current mirroring, circuits for level shifting, and circuits for distributing power to the display panel as well as line selecting capabilities.

12. The method for forming a display panel according to any of claims 9 to 11, said method further comprising the steps of: forming at least one second substrate comprising integrated circuits, wherein the at least one substrate comprises a plurality of electronic circuits for display and the at least one second substrate comprises power and driving electronic circuits; combining the at least one substrate with the at least one second substrate, wherein the at least one substrate forms a front side of the display panel and the at least one second substrate forms a back side of the display panel.

13. The method for forming a display panel according to any of claims 9 to 12, wherein forming the at least one substrate comprises forming the at least one substrate as an at least one dual side substrate comprising thin-film-transistor circuits as the integrated circuits, wherein a first side of the dual side substrate comprises a plurality of electronic circuits for display and a second side of the dual side substrate comprises power and driving electronic circuits, wherein the first side forms a front side of the display panel and the second side forms a back side of the display panel.

14. A system for aligning display panels for a display wall, the system comprising: at least one first display panel comprising a first substrate having at least two light sources on a front side of the first substrate and at least one hollow structure on a backside of the first substrate, a second substrate located behind the first substrate on an opposite side of the at least two light sources, said second substrate comprising at least one stud mounted on the second substrate and configured to be inserted into the at least one hollow structure of the first substrate, a support surface located in front of the at least two light sources on the first substrate and configured to be in parallel to the second substrate by at least one spacer support, wherein the at least two light sources are configured to contact the support surface, and wherein a fixation medium is provided in the at least one hollow structure for fixing the stud of the second substrate fixed inside the at least one hollow structure of the first substrate.

15. The system according to claim 14, wherein the second substrate and the support surface are curved.

16. The system according to claim 14 or 15, wherein the first substrate comprises at least two hollow structures and the second substrate comprises at least two studs.