LU500365B1

LU500365B1 - Improvements in light emitting modules

Info

Publication number: LU500365B1
Application number: LU500365A
Authority: LU
Inventors: Eessen Wim Van; Patrick Willem; Peter Gerets; Den Bossche Bart Van
Original assignee: Barco Nv
Priority date: 2021-06-30
Filing date: 2021-06-30
Publication date: 2023-01-02
Also published as: WO2023275226A1; TW202305764A

Abstract

A light emitting modules comprising a first and a second backplane arranged in a stackup, wherein the first backplane comprises a TFT layer deposited on a first Substrate, the thin film TFT comprising a plurality of light emitting elements and first contact pads, the second backplane comprises second contact pads configured to provide driving currents and power supply to the first contact pads of the light emitting elements, the first backplane comprises through holes provided in the first Substrate at the locations of each first contact pad, and first electrical binding means are provided in the through holes of the first backplane and second electrical binding means are provided on the second contact pads, the first and second electrical binding means being connected such that the driving currents and/or power supply from the second backplane are transmitted to the first backplane.

Description

Title: IMPROVEMENTS IN LIGHT EMITTING MODULES LU500365

TECHNICAL FIELD The present disclosure relates to the field light emitting modules, methods of manufacturing such light emitting modules, display modules and tiled displays.

BACKGROUND A light emitting display is usually made of a plurality of light emitting modules. Various light emitting modules can be driven by the same carrier (for example a PCB interposer), or each module can have its own dedicated carrier. It is however important that on the assembled light emitting display, the seams between adjacent modules remain invisible. Additional challenges associated with having an assembly of light emitting modules, is that it is difficult to provide a display whose modules are perfectly aligned to provide a flat display. For example, patent application WO2020126059A1 from the same applicant provides a solution to perfectly align the various modules of the light emitting display. It teaches how to make a display with improved flatness, wherein the display tile comprises a display board and a carrier board, the carrier board being for attachment to a frame or a bracket, the display board and the carrier board being fastened together by the intermediary of a spacer positioned between the display board and the carrier board. The spacer is glue or adhesive. The adhesive forms the spacer itself. The spacer can engage in an opening in the carrier board. The display board has image forming elements and the spacer is for setting a relative position of the top of the image forming elements with respect to the carrier board. It is a current trend to use light emitting elements having a smaller size to improve the display resolution. Today’s trend is to build displays with for example micro LEDs (pLEDs). The use of micro LEDs (uLEDs) in LED display technology brings about new challenges to be solved. uLEDs have, as indicated in the name, a micrometer-size scale. Accordingly, they also require micrometer size scale contacting methods. Currently, a lot of novel methods are under investigation as traditional contacting methods, such as soldering, gluing, are not possible with uLEDs, especially since these materials need to be precisely applied on the target by either reflow stencil (limited in aperture and positioning tolerances) or XY dispensing equipment (limited in volume and XY LU500365 positioning accuracy during dispensing).

Furthermore, due to the small contact pads, the uLED architecture cannot be based on PCB anymore. In fact, the use of PCB restricts the dimensions of the wires to a size which is even larger than the LEDs themselves. The industrial manufacturing process has limitations. The substrates need to be lithographically defined (cfr LCD, OLED, silicon chips, etc.) and comprises single-sided contacts and processing due to the process technology (eg TFT LTPS technology ). Currently, most LED displays are driven by passive matrix drivers, located on the backside of the LED panels, to keep the distance between the chip and the LED as low as possible and thereby avoid performance reduction due to parasitic effects. Since the technology of uLEDs will be TFT single side based, this is not possible anymore.

In active matrix displays, the need for zero bezel displays is increasing. However, the pixel pitches are getting smaller and smaller, to achieve higher resolution displays (4K, 8K), the number of contacts on the side is exponentially increasing.

In a tillable system where we need no bezel (like LED displays), the pixel pitch determines the distance required to wire out these contacts to back electronics. In the past this could be solved with side contacting, as for example described in patent application W0O2015079058A1, however due to the space between modules and the contacts which are getting too small, this is not possible anymore.

There is therefore a need to provide a method to assemble two light emitting modules with a very small seam between the modules such that the seam is invisible to the viewer. Many contacts need to be made with a very fine pitch. It is also not possible to achieve such a fine pitch with a flex mount contact. Another possibility would be to provide a flex PCB on the top side, and then to bend it. However, the bending radius is still too big to fit in the space available due to the pixel pitch on the panel.

A (u)LED display is thus usually composed of a plurality of LED modules. There is thus the need to solve the following problems to provide a display having no visual artefacts: - provide means to connect all the drivers to the uLED module backside, without disturbing the pixel pitch, - provide means to connect all the uLED modules to a controlling unit, - provide means to create a seamless assembled module (mechanically) by reducing the seam between adjacent uLED modules. 2

- provide means to ensure that the seamless assembled module is also flat. LU500365 There is thus a need for improvement in the art.

SUMMARY Aspects of the present disclosure relate to provide a light emitting module for a light emitting display, comprising a first and a second backplane arranged in a stackup, wherein the first backplane comprises a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements and first contact pads for contacting the light emitting elements, and associated conducting tracks, the second backplane comprises second contact pads configured to provide driving currents and power supply to the first contact pads of the light emitting elements, characterized in that the first backplane further comprises through holes provided in the first substrate at the locations of each first contact pad, and wherein first electrical binding means are provided in the through holes of the first backplane and second electrical binding means are provided on the second contact pads of the second backplane, the first and second electrical binding means being connected such that the driving currents and/or power supply from the second backplane are transmitted to the first backplane.

The conducting tracks connect the light emitting elements to various electronic components, such as current drivers, power supply contacts, etc. The fist substrate can be made of an insulating material and includes an embedded TFT active matrix.

The first and the second backplanes are arranged in a stackup, or on top of each other. The first backplane, which comprises the TFT layer and the light emitting elements, is responsible to provide the multitude of driving signals and power to the light emitting elements. These driving signals may be complex, and thus require many connections. The second backplane, which can be provided by different types of backplanes, can be responsible for providing lower functionality driving means.

Providing through holes and first electrical binding means inside the through holes on the first backplane, and simultaneously, providing second electrical binding means on the second backplane, to connect the first contact pads to the second contact pads, has the advantage that side contacts are no longer needed. Therefore, the seam between adjacent light emitting modules can be drastically reduced.

The second backplane can be used as an interface to connect to an external driver, and thereby transmit the necessary driving signals and/or power signals to the light emitting elements. As the second backplane is under the first backplane, it can easily connect 3 to any type of driving means which are located behind the display. This part will remain LU500365 invisible to the viewer.

This also enables to install the driving electronics as close as possible to the light emitting elements on the TFT layer. In addition, the individual light emitting modules are easily connected to any type of controller, by means of the second backplane.

Advantageously, the second backplane is larger than the first backplane such that at least two first backplanes are configured to be provided next to each other on the second backplane.

This has the advantage that a larger display or a display module, which comprises at least two backplanes as defined above, can easily be made. In addition, as the connections are made at the back, the seam between the two first backplanes is invisible. The pixel pitch is therefore not disturbed at the seam between two adjacent displays and can be kept small, even if the light emitting elements are for example micro LEDs. There is thus no visual artefact at the seam between two adjacent displays.

Preferably, the surface of the second backplane is smaller than the surface occupied by the at least one first backplane arranged on the second backplane.

This offers the possibility to leave space for a flexible connector for example, and to connect the second backplane to additional driver electronics.

The first substrate is made of an electrically insulating material configured to receive a TFT layer, such as polyimide (PI), polymer, plastic, glass, ceramics, silicon, alumina, silicon carbide.

The insulating material or substrate does not need to be transparent, as in the LCD industry. The material may be either flat and stiff, such as glass or silicon carbide or flexible, like PI for example. The material is advantageously not brittle, such that the manufacturing of holes is simpler. In additional, the material is preferably thin.

The light emitting elements can be any one of LEDs, OLED, and variations thereof, QD-LED, EL-QLED, AMOLED, mini-LED, micro-LED. The solution provided by the present invention is independent of the type of light emitting elements. However, it is also not limited by the size of the light emitting elements. In fact, it is particularly advantageous for mini-LED or even micro-LED, for which no such solution exists.

The second backplane is any one of a PCB, or TFT layer on a substrate.

The combination of providing a TFT layer on a substrate, arranged in a stackup with a PCB is very unusual and offers many advantages, as the PCB can provide coarser driving 4 capabilities, and the TFT layer provides finer electronics for driving the light emitting elements. LU500365 However, any substrate can be used for the second backplane, such as TFT. The type of second backplane mostly depends on the type of application. Advantageously, the first electrical binding means comprise metal provided inside the through holes such that the holes are metalized holes.

Metalizing the holes is simple to provide a connection inside the through holes.

It is an advantage that the first electrical binding means comprise nano entanglements.

In fact, nano entanglements can easily be grown on the metalized holes.

It is even more preferred that the second electrical binding means comprise nano entanglements.

Thereby, the nano entanglements provided on the first and the second backplane interlace and directly provide a strong mechanical and electrical connection.

The first and second electrical binding means may also comprise conductive glue.

The first and second electrical binding means may further also comprise ACF.

The second backplane further may advantageously also comprise driving functionalities.

Preferably, the second backplane is connected to an external driver, preferably via a flexible connector. The flexible connector can for example be provided by a flex PCB.

The first and/or second electrical binding means can also be provided on a portion of the first and/or second contact pads. The remaining free portion can therefore be used for testing purposes. With the use of nano entanglements, it is easy to control the surface over which the nano entanglements are grown.

The portion can be dimensioned to state-of-the art miniature test probes or wafer probes.

Preferably said portion is arranged around a free central portion on the surface of the first/second contact pads. Thereby, it is easy to apply a needle within the central free portion for testing purposes. A needle bed can also easily be used.

In addition, it is an advantage to provide an underfill on the lower surface of the first backplane and/or on the upper surface of the second backplane, respectively. These underfills can help when aligning the first backplane on the second backplane. In addition, an underfill can also be provided on the upper surface of the second backplane at the junction between two first backplanes, for alignment purposes.

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In another aspect there is also provided a method for manufacturing a light LU500365 emitting module, the method comprising the steps of providing a first backplane comprising a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements, first contact pads for contacting the light emitting elements, and associated conducting tracks, wherein the first backplane further comprises through holes provided in the first substrate at the locations of each first contact pad, providing first electrical binding means to the first backplane, in the through holes of the first substrate under the first contact pads, providing a second backplane comprising second contact pads for contacting the first contact pads, providing second electrical binding means on the second contact pads, laminating the first backplane to the second backplane such that the first and second electrical binding means connect to transmit driving signals and/or power signals from the second backplane to the light emitting elements of the first backplane.

This method of manufacturing a light emitting module is very simple and very robust. It does not require high temperatures, and thereby does not damage the TFT layer. In addition, it provides a light emitting module wherein all the connections are inside the module, and thereby are invisible to the viewer. Using TFT has the advantage that active matrix can be embedded, and driving the light emitting elements with more complex functionalities, for example pulse width modulation is made possible.

The step of providing a first backplane may further comprise the step of providing a first backplane comprising a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements, first contact pads for contacting the light emitting elements, and associated conducting tracks, and processing through holes in the first substrate, at the locations of the first contact pads such that the through holes extend to the lower surface of the first contact pads.

There is the possibility to first process the TFT layer on the substrate, and then to manufacture the through holes. The advantage is that it is easier to process the TFT layer on a flat substrate, however, when manufacturing the holes, the contact pads shall not be damaged. 6

Alternatively, the step of providing a first backplane may further comprise the LU500365 steps of providing a first substrate, processing through-holes in the first substrate, at designed locations for providing first contact pads, and depositing a thin film transistor layer on the first substrate, the thin film transistor layer further comprising a plurality of light emitting elements, first contact pads at the locations of the through holes and associated conducting tracks.

This second possibility is to first manufacture the holes, which may be simpler. However, manufacturing the TFT on a surface with holes is possible but slightly more complex.

It is also an advantage that the step of providing a first backplane is performed with a pick and place robot. This method is very simple to implement, and very accurate. The dimensions of the light emitting module, or of the first backplane can be reduced to a minimum, even a pixel. The limit on the lowest dimensions is linked to the robot, pickup- solution and vendor or the equipment.

Advantageously, it is also possible that the step of providing a first backplane comprises the step of providing several first backplanes, the second backplane being configured to receive the several first backplanes, and wherein the step of laminating the first backplane to the second backplane comprises the step of laminating the several first backplanes on the second backplane.

Providing several first backplanes in the same step provides the advantage that display module can be manufactured in the same way as a light emitting module.

Thereby, a display module comprising several light emitting modules, or first backplanes can be easily manufactured.

In addition, the method may further comprise the step of providing a flat substrate on which all several first backplanes are assembled with the light emitting elements facing towards the flat substrate, before laminating the several first backplanes to the second backplane.

The flat substrate can be for example glass. This provides the advantage that the display module has a flatness which corresponds to the flatness of the flat substrate. Thus, the second backplane does not only provide the required electronics functionalities, but it may also provide mechanical stiffness and flatness to the display module.

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Advantageously, the step of providing first electrical binding means comprises the LU500365 step of metalizing the through holes.

Metalizing the through holes is a simple manufacturing step.

Preferably, the step of metallizing the through holes comprises the step of growing a conductive material in the through holes, and/or the step of applying a conductive material paste, wherein the conductive material is at least one of copper, silver, aluminum.

It is a further advantage that the step of providing first electrical binding means comprises the step of growing nano entanglements on the metalized holes, the nano entanglements protruding from the surface of the first substrate. Nano entanglements offer many advantages, as further described below.

The step of providing first electrical binding means may also advantageously comprise the step of growing nano entanglements on the lower surface of first contact pads until they protrude from the surface of the first substrate.

Even more preferably, the step of providing second electrical binding means comprises the step of growing nano entanglements on the second contact pads.

Nano entanglements offer many advantages. For example, growing nano entanglements can be realized at room temperature. This step is also fast and reliable.

Once the nano entanglements are provided on the first and second backplane, using mechanical force by pressing the first backplane to the second backplane, a mechanical and electrical connection is made. There is thus no need for reflow soldering (which requires higher temperatures), and the placing of the light emitting modules can be accomplished very fast and accurately by a pick and place robot for example. Soldering BGA LED modules for example, due to the melded solder, the modules tend to drift on the carrier plate, creating seams (black and white). This can be avoided in the present invention.

This method also provides means to perfectly align in height the various modules one with respect to each other, since the electrical binding means also act as vertical spacers. Thus, there is no tip-tilt nor misalignment in height between individual modules.

Another advantage of this stack up is the size of the individual light emitting modules (first backplanes). These modules can be made very small in comparison to the second backplane. When a light emitting module shows a defect, it can be replaced easily with another light emitting module, and the stuffing of the LED modules can continue. Most of the displays being made are made of a single piece, with the light emitting elements directly 8 stuffed on a big carrier, resulting in low yield displays which is an issue in producing active LU500365 matrix led displays.

Alternatively, the step of providing first and second electrical binding means may comprise the step of applying a conductive glue, or the step of providing first and second electrical binding means may further comprise the step of applying ACF.

Other means can also be used, as long as these means are not applied at high temperatures, and as long as the required precision can be maintained.

Preferably, the first substrate is made of an insulating material configured to receive a TFT layer, such as polyimide (PI), polymer, plastic, glass, ceramics, silicon, alumina, silicon carbide. The TFT layer comprises an embedded active matrix.

Even more preferably, the first substrate is polyimide. The method may further comprise the step of spin coating the polyimide layer on a glass substrate, and the method further comprises the step of delaminating the glass substrate after depositing the TFT layer.

The advantage of using a glass substrate with PI is that glass and Pl have a coefficient of thermal expansion which are sufficiently close to avid the generation of shear stresses with the substrates.

It is an advantage that the light emitting elements are any one of LEDs, OLED, and variations thereof, QD-LED, EL-QLED, AMOLED, mini-LED, micro-LED.

In fact, the present invention can be applied to any type of light emitting elements, including smaller scales light emitting elements, such as mini and micro-LEDs.

Even more preferably, the second backplane can be any one of a PCB, or TFT layer on a substrate.

The first and/or second electrical binding means can advantageously be applied on a portion of the first and/or second contact pads to use the free portion for testing purposes.

Preferably, the portion is arranged around a free central portion on the surface of the first/second contact pads.

Even more preferably, an underfill is provided on the lower surface of the first backplane and/or on the upper surface of the second backplane, respectively.

These underfills can be used for facilitating the alignment of the first backplane on the second backplane. 9

Even more preferably, an underfill is provided on the upper surface of the second LU500365 backplane, at the junction between two first backplanes, for improving the alignment of the two first backplanes.

It is an advantage that the second backplane may further comprise driving functionalities.

It is also an advantage that the second backplane may be connected to an external driver, preferably via a flexible connection, such as a flexible PCB.

The second backplane can be used as an interface to external driving means or can comprise those driving means.

In another aspect, there is also provided a light emitting module manufactured by the method described in the present invention.

In yet another aspect, there is also provided a display module manufactured by the method described in the present invention.

The method according to the present invention is perfectly scalable to the manufacturing of a display module, with any number of light emitting modules arranged on the second backplane. The dimensions of the individual light emitting modules (or first backplanes) can be as small as a pixel or may be a matrix of X pixels by Y pixels, for example wherein X=4 and Y=4. This package can then serve as a ‘component’ to the display module. An advantage of using smaller light emitting modules is that in case of failure less components need to be replaced.

There is also provided a tiled display comprising a plurality of display module according to the present invention.

The display modules may further be assembled to provide a tiled display, each tile being provided by a display module.

Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to 10 the following detailed description of the invention, which describes an exemplary embodiment LU500365 of the invention, taken in conjunction with the accompanying drawings, in which: Figure 1A is a side view of a light emitting module for a display module. Figure 1B is a close view of Figure 1A. Figure 1C is front view of a display module comprising a plurality of light emitting modules. Figure 2A is a light emitting module according to an embodiment of the present invention. Figure 2B is a process for making a light emitting module according to Figure 2A. Figure 3A is a light emitting module according to another embodiment of the present invention. Figure 3B is a process for making a light emitting module according to Figure 3A. Figure 4A is a light emitting module according to another embodiment of the present invention. Figure 4B is a process for making a light emitting module according to Figure 4A. Figure 5A is a cross section of a display module according to an embodiment of the present invention. Figure 5B is front view of the display module shown in Figure 5A according to an embodiment of the present invention. Figure 6A is a cross section of a tiled display module according to the present invention. Figure 6B is front view of the tiled display module shown in Figure 6A according to an embodiment of the present invention. Figure 7A illustrates a first or second contact pad comprising a testing surface. Figure 7B is a cross section of a display module comprising underfills for alignment purposes. Figure 7C is a cross section of a display module without underfills.

DESCRIPTION OF EMBODIMENTS Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and/or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be 11 carried out before carrying out the particular step, unless specified otherwise. Likewise it will LU500365 be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise.

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 claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps.

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. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The terms "about" or "approximate" and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated with it, where the range can be +20%, +15%, +10%, +5%, or +1%. The term "substantially" is used to indicate that a result (e.g., measurement value) is close to a targeted value, where close can mean, for example, the result is within 80% of the value, within 90% of the value, within 95% of the value, or within 99% of the value.

Definitions and Acronyms Active Matrix.

Active matrix is a type of addressing scheme used in flat panel displays. In this method of switching individual elements (pixels), each pixel is attached to a transistor and capacitor actively maintaining the pixel state while other pixels are being addressed.

Active-matrix circuits are commonly constructed with thin-film transistors (TFTs) in a semiconductor layer formed over a display substrate and employing a separate TFT circuit to control each light-emitting pixel in the display. The semiconductor layer is typically amorphous silicon, poly-crystalline silicon and is distributed over the entire flat-panel display substrate. An 12 active matrix display can also be for example an LCD or an electrophoretic reflective LU500365 transmissive emitting display or similar. A display sub-pixel can be controlled by one control element, and each control element includes at least one transistor. For example, in a simple active-matrix light-emitting diode display, each control element includes two transistors (a select transistor and a power transistor) and one capacitor for storing a charge specifying the luminance of the sub-pixel. Each LED element employs an independent control electrode connected to the power transistor and a common electrode. Control of the light-emitting elements in an active matrix known to the art is usually provided through a data signal line, a select signal line, a power or supply connection (referred to as e.g., VDD) and a ground connection. BGA Ball Grid Array Backplane is a board comprising electronic components configured to drive the light emitting display. A backplane can be for example a PCB backplane (e.g., FR4 PCB), or a TFT backplane. Carrier board refers to a board which is configured to receive at least one light emitting module or display module. It serves as a support structure of a tiled display. The carrier board can be a backplane or a mechanical support structure. It can also serve as a distribution panel for power, ground and to distribute driving signals for the light emitting elements.

Driving signals or data signals are the signals which comprise the information for driving the light emitting elements to generate an image on the display. Depending in which stage they are in the transmission flow, they may be digital signals, or analog signals, or optical pulse signals, etc.

Display A display screen can be composed of light emitting pixel structures referred to as “display pixels” or “pixels” where the amount of display pixels determines the “display resolution”, sometimes referred to as the “native display resolution” or the “native pixel resolution”. A measure of the display resolution can be the total number of display pixels in a display, for example 1920x1080 pixels. Each display pixel can emit light in all colors of the display color gamut (i.e. the set of colors the display is able to provide).

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Each display pixel can be composed of light emitting elements referred to as “sub-pixels”, LU500365 often being able to emit the colors red (R), green (G) or blue (B) (but also white, yellow or other colors are possible). À display pixel can be composed of at least three sub-pixels: One red, one green and one blue sub-pixel. Additionally, the display pixel can comprise other sub- pixels in any of the aforementioned colors (to further increase the color gamut). Depending on the types of sub-pixels, the display pixel can then be referred to as a RGB-, RGGB-, RRGB-pixel, etc. While a single display pixel can generate all colors of the display color gamut, a single sub- pixel cannot. The light emission of a single sub-pixel can be controlled individually so that each display pixel can emit the brightness and color required to form the requested image.

Display module is a module which comprises at least one light emitting module arranged on a carrier. The carrier of the display module is configured to transfer driving signals and power signals to the at least one light emitting module.

A plurality of display modules can be placed on a bigger carrier board (mechanical interface) to create a tiled display and be connected to an external driver or the display module. The functionalities of the driver can also be embedded in the display module.

Duty Cycle The term duty cycle describes the proportion of 'on' time to the regular interval or ‘period’ of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on.

FR-4 (or FR4) is a NEMA grade designation for glass-reinforced epoxy laminate material. FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing). "FR" stands for flame retardant.

Reference to Insulating implicitly assumes it is electrically insulating, such insulating ring or insulating material, or insulating substrate refers to electrically insulating ring, or electrically insulating material or electrically insulating substrate.

LED. Light Emitting Diode Light Emitting Element. A light emitting element can be e.g., a solid-state light emitting element, such as a light emitting diode such as an LED or an OLED (Organic LED).

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Light emitting module A light emitting module is an opto-mechanical-electronic carrier of a certain size which carries light emitting elements directed towards a viewer and possible light emitting elements driving and control electronics. These light emitting elements are driven to create an image, either static or dynamic (video). In the following the light emitting module will be called an “LED module”, although the invention is not restricted to LEDs. Several LED modules or OLED modules can be positioned next to each other to form a display module. Several display modules can be tiled together to form a larger tiled display.

A small LED module which is an atomic element, i.e., indivisible, can be called a “stamp”. The light emitting module can have any size and shape. It can be rectangular or square, hexagonal, triangular, any shape, if it fits in a pick and place robot used to place it on a display module. It can also comprise one pixel, which comprises a red, green, and blue light emitting element.

The light emitting module comprises at least one backplane. The top surface of the backplane comprises the light emitting elements and associated conducting tracks which connect the various light emitting elements to various electronic components (like e.g., current drivers, power supply contacts etc.). The backplane can be a PCB, TFT on glass, TFT on PI, etc.

The following patent applications, from the same applicant, provide definitions of LED displays and related terms. These are hereby incorporated by reference for the definitions of those terms. - US7972032B2 “LED Assembly” - US7176861B2 Pixel structure with optimized subpixel sizes for emissive displays - US7450085 Intelligent lighting module and method of operation of such an intelligent lighting module - US7071894 Method of and device for displaying images on a display device. MUX Multiplexer PAM Pulse Amplitude Modulation Passive Matrix (PM) Passive matrix addressing is an addressing scheme used in early LCDs. This is a matrix addressing scheme meaning that only m + n control signals are required to 15 address an m x n display. A pixel in a passive matrix must maintain its state without active LU500365 driving circuitry until it can be refreshed again. PWM Pulse Width Modulation Pulse-width modulation uses a rectangular pulse wave whose pulse width is modulated resulting in the variation of the average value of the waveform. The square wave has a period T, a lower limit 10 (typically O in our case), a higher limit 11 and a duty cycle D. The duration of one pulse P (the time during which the signal is at its higher limit) is D/100 * T (if D is expressed in %). For instance, if D = 50%, the duration of the pulse is % T. À more complete definition can be found in WO2019185935A1 from the same applicant. TGV Through Glass Via Thin-film technology (TFT) refers to the use of thin films: A film a few molecules thick deposited on a glass, ceramic, or semiconductor substrate to form for example a capacitor, resistor, coil, cryotron, or other circuit component. A film of a material from one to several hundred molecules thick deposited on a solid substrate such as glass or ceramic or as a layer on a supporting liquid. TFT can be deposited on a substrate such as glass or PI. It comprises multiple layers of wiring, semiconductors, and isolation layers.

Description While the invention is illustrated and described mostly in reference to LEDs or micro LEDs, the invention is not limited thereto, and may also be advantageous for other the types of light emitting elements, as defined in the present application.

Figures 1A, 1B and 1C illustrate a light emitting module 110 for a display module or display 100. In Figure 1C, the display module 100 comprises a plurality of light emitting elements 110 arranged on carrier 120. The light emitting elements can be any of the light emitting elements provided in the definition section. However, for the sake of clarity, LEDs will be used in the illustrated examples. Thus, an LED display (or display module) 100 comprising a plurality of LED modules 110 is hereby shown. Figure 1A provides a side view of the display, while Figure 1C provides a front view and 1B a close up of Figure 1A. Each module 110 is fixed to a carrier 120 through contacting wires 130, which provides a mechanical and electrical connection. The carrier is further connected to an external driver 140 via a flexible conductor 16

155 connected to an external driver connector 150 configured to provide driving and control ~~ LU500365 electronics.

The carrier 120 can be a PCB or TFT backplane with or without driver electronics. In the figure above the carrier 120 is a TFT backplane which is connected via a flexible conductor 155 to a driver PCB with driver electronics 140. The flexible conductor can be provided by for example a flexible PCB (flex PCB).

In Figure 1B, a closer view of the LED module 110 is shown. In this example, the LED module comprises two backplanes arranged in a stack up, a front 170 and a back 180 TFT backplanes. The front and/or the back backplanes could also be PCBs. Thus, any combination of front/back TFT backplane/PCB backplane are possible. The present example is illustrated with TFT backplanes.

The connection from the front 170 to the back 180 backplanes is usually done with a contact strip 212 on the edges. The balls 230 between the two TFT backplanes are spacers to control the distance between the two TFT backplanes. This LED module 110 is also connected to a carrier 120 through connections 240. Here in this example, the carrier 120 is a PCB. After assembly, both front 170 and back 180 TFT backplanes are glued together with spacers in between to maintain planarity and parallelism between them.

The use of micro LEDs in displays brings about new challenges. In fact, as mentioned, micro-LED displays are preferably driven in a similar way as LCD displays, i.e., by active matrix. Therefore, TFT technology should be used.

The distance between the anode and the cathode of a micro-LED is about 20-40 microns. Therefore, the space between two adjacent LEDs is also drastically reduced. In this space, the contacting pad of an LED needs to fit. The space between two adjacent contacting pads can be of about 35 microns.

To feed each micro-LED with driving signals, each pad on the TFT layer needs to be accessed by an electrical connection. However, there is no space on the sides of an LED module to provide such connections, as shown in the example of Figure 2B for example with the side contact strips 212.

There is thus a need to provide backside access to the uLEDs to avoid side contact strips and such that the driving functionalities of each LED may be arranged as close as possible to the uLED itself on the TFT.

In addition, the following constraints may need to be considered: TFT processing is limited to one side of the substate. In the case of uLEDs, there is a high need for power efficient routing because the uLEDs are individually current driven. The 17 driving of PWM based uLED displays is much more complex than current LCD and OLED LU500365 driving, thus the functionality per pixel is higher in this case.

Due to the complexity of such uLED displays, a single stack up LED module may still not provide sufficient space to provide all the functionalities required by a pixel. The LED modules may therefore comprise more than one backplane, and be a stackup of at least two backplanes, a first backplane and a second backplane. For example, a stackup of two TFT backplanes or a TFT and PCB backplane, wherein each layer of the stackup (backplane) is dedicated in the provision of certain control functionalities for driving the light emitting elements of the display.

To increase the available area on the substrate to functional designs, a new way is needed to distribute the power and/or driving signals between the uLED pixels.

The inventors of the present invention have thus imagined accessing each contacting pad of the light emitting elements provided on the TFT layer not from the side, but from under the TFT layer.

A TFT layer is usually deposited on an insulating substrate. Reference to an insulating substrate throughout the description shall be interpreted in the sense of electrically insulating substrate. To be able to electronically access the contacting pads of the light emitting elements on the TFT layer from under, through holes shall be made in the insulating substrate until the lower surface of the contacting pads has been reached.

The substrate can be made of insulating material and includes an embedded TFT active matrix.

It is therefore desirable to use a material in which through holes can easily be manufactured.

In LCD displays for example, the TFT layer is typically processed on a glass layer. To get access to the contacts at the top, a solution is to provide TGV (through glass vias) in the glass. TGV on glass is typically provided in distribution layers for silicon. However, it is less common in the field of displays due to the manufacturing costs and the higher workload required, i.e., drilling and metallization. TFT processing is also available on other materials, such as PI (Polyimide flexible substrate).

It is common to use Pl in electronics for providing flexible substrates. However, it is less common to use Plin a TFT process. Plis normally spin coated on a glass layer. The TFT layer is then deposited. This is possible since the thermal expansion of both PI and glass is very similar during the process. The glass layer can then be removed by laser ablation.

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The advantage of polyimide is that it is a flexible substrate, sufficiently thin, such | LU500365 that through holes can be manufactured within the substrate.

In fact, the first substrate provided by an insulating material may further fulfill the following requirements.

It is preferred that the material of the substrate is sufficiently flat and stiff such that TFT can be processed on it, for example, glass or silicon carbide. If the material is not stiff, but flexible, it is important that the material has a coefficient of thermal expansion similar to the substrate on which the TFT layer is processed such that no shear constraints appear during the TFT process. This is the case for example for Pl and glass.

In addition, brittle materials are less preferred as it is more difficult to manufacture holes inside. In addition, it is preferred to have a thin material.

Polyimide is a preferred material as TFT can be processed on it, as described above, and through holes can easily be made. PI has the advantage that it can be made very thin, for example with a thickness in the range of 20 to 25 microns.

The light emitting module may thus comprise a first backplane which comprises a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements and first contact pads and associated conducting tracks.

The first substrate can be any insulating material suitable to receive a TFT layer, such as polyimide (PI), polymer, plastic, glass, ceramics, silicon, alumina, silicon carbide.

The substrate can be made of an insulating material and includes an embedded TFT active matrix.

Through holes are thus provided in the first substrate at the locations of each first contact pad, to be able to contact and drive the light emitting elements of the display.

Figure 2A illustrates a light emitting module according to an embodiment of the present invention. The light emitting module 200 comprises a first backplane 210 and a second backplane 220. The first backplane comprises a thin film transistor layer 215 deposited on a first substrate 212, the thin film transistor layer further comprising a plurality of light emitting elements 255, first contact pads 251, and associated conducting tracks 256.

As illustrated in Figure 2A, a plurality of through holes 225 are provided in the first substrate 212, at the locations of the first contact pads 251. The through holes are such that they extend to the lower surface of the first contact pads.

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The light emitting module 200 also comprises a second backplane 220 which LU500365 comprises second contact pads 261 configured to provide driving currents and power supply to the first contact pads 251 of the light emitting elements 255.

To connect the second contact pads 261 to the first contact pads 251, first electrical binding means are provided in the through holes of the first backplane which connect to the lower surface of the first contact pads. Second electrical binding means are provided on the second contact pads of the second backplane, the first and second electrical binding means being connected such that the driving currents and/or power supply from the second backplane are transmitted to the first backplane.

Different methods are possible to produce such a light emitting module.

In general, the method shall comprise the following steps.

A first step may be to provide a first backplane comprising a thin film transistor layer deposited on a first substrate. The thin film transistor layer may comprise a plurality of light emitting elements, first contact pads for the plurality of light emitting elements and associated conducting tracks. The first backplane provided may already comprise the through holes or these may be provided with a processing step, the through holes being provided at the locations of each first contact pad.

As a second step, first electrical binding means may be provided to the first backplane, in the through holes of the first substrate under the first contact pads, such that they extend to the lower surface of the first contact pads.

As a third step, a second backplane comprising second contact pads for contacting the first contact pads may also be provided.

As a fourth step, second electrical binding means on the second contact pads are advantageously provided.

Finally, the first backplane may be laminated or pressed to the second backplane such that the first and second electrical binding means connect to transmit driving signals and/or power signals from the second backplane to the light emitting elements of the first backplane.

Figures 2B to 4 illustrate different embodiments to manufacture such a light emitting module. In the examples shown, the light emitting elements are assumed to be micro-LEDs.

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There are different methods to provide a first backplane. Some of these methods LUS00365 are illustrated in the Figures. However, these methods depend mostly on the type of insulating substrate which is used.

For example, referring to Figure 2B, if the first substrate is polyimide (PI), a first step may be to process the Pl layer on the glass. This is usually performed by spin coating a PI layer on a glass substrate.

After spin coating the PI layer on the glass, a TFT layer is deposited on the PI layer, as shown in step 201. The TFT layer 215 comprises LEDs 255, conducting tracks 256 and first contact pads 251 for contacting the LEDs. The first contact pads 251 are arranged between two adjacent LEDs 255.

The glass can then be removed by laser ablation (not shown) for example.

In step 202, through holes 225 are provided within the PI layer at the locations of the first contact pads 251, such that the through holes extend to the lower surface of the first contact pads 251. In this process, it is important to remove the PI layer, without damaging the contact pads. Therefore, this step can for example be made by laser ablation in order not to damage the contact pads. Given the thickness of the PI layer which is usually between 20 and 25 microns, this process can be performed by a laser.

In steps 203 and 204, the first electrical binding means 230 are provided in the through holes.

For example, the through holes 225 are first metalized in step 203. The metallization 230a of the holes can be achieved by growing a conductive material in the through holes, such as copper, or filling the holes with a conductive material paste, such as silver paste, etc. It is important that the material extends up to the lower surface of the first contact pads.

In step 204, nano entanglements 230a are further grown on the metalized holes 230a such that they protrude from the PI surface.

In step 204, a second backplane 220 is provided, wherein the second backplane comprises second contact pads 261 at locations corresponding to the locations of the first contact pads. The second backplane 220 may comprise driving electronics, chips 245 and a connector 246.

Second electrical binding means 235 are provided on the second contact pads

261. The second electrical binding means 235 may comprise nano entanglements which protrude from the surface of the second backplane.

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In a last step, the first backplane 210 is laminated onto the second backplane 220, LU500365 such that the first and second binding means connect, and driving and/or power signals provided by the driving electronics, chips and connector of the second backplane are transmitted to the LEDs on the TFT layer.

With the nano entanglements protruding at the surfaces of the PI substrate and second backplane, the nano entanglements of both surfaces easily connect and provide simultaneously a mechanical and electrical solid connection. The connection provides a connection on a larger surface area, and simultaneously a mechanical connection. Nano entanglements are described further down in the description.

Figure 3A illustrates a light emitting module obtained with the process illustrated in Figure 3B, which provides a second example to manufacture an LED module 300. It is also assumed that the first substrate is a Pl layer. It is assumed that the PI layer has already been processed by spin coating on the glass (not shown).

In a first step 301, through holes 325 are provided in the PI layer 312 on the glass carrier 311.

In a second step, the TFT layer 315 is deposited on the Pl layer 312, such that first contact pads are provided at the locations of the through holes. The glass carrier 311 may still be present. The glass carrier can then be delaminated by laser ablation for example.

The first electrical binding means 330 are then provided in the through holes 325 under the first contact pads 351.

For example, the through holes 325 are first metalized in step 303. The metallization 330a of the holes can be achieved by growing copper in the through holes, or filling the holes with a silver paste, etc. It is important that the material extends up to the lower surface of the first contact pads.

In step 304, nano entanglements 3300a are further grown on the metalized holes 330a such that they protrude from the PI surface.

In step 304, a second backplane 320 is provided, wherein the second backplane comprises second contact pads 361 at locations corresponding to the locations of the first contact pads 351. The second backplane 320 may comprise driving electronics, chips 245 and a connector 246.

Second electrical binding means 335 are provided on the second contact pads

361. The second electrical binding means 335 may comprise nano entanglements which protrude from the surface of the second backplane.

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In a last step, the first backplane 310 is laminated onto the second backplane 320, LU500365 such that the first and second binding means connect, and driving and/or power signals provided by the driving electronics, chips and connector of the second backplane are transmitted to the LEDs on the TFT layer.

An advantage of this method is that the contact pads are provided during the TFT processing, directly at the locations of the through holes. However, the process of depositing TFT on a surface which is not flat is more difficult.

In the example explained with reference to Figure 2, the through holes are manufactured after the TFT layer has been deposited on the electrically insulating substrate.

On the contrary, in the example explained in reference to Figure 3, the through holes are manufactured before depositing the TFT layer on the electrically insulating substrate.

A third example is shown in Figures 4A and 4B. Figure 4A illustrates the LED module obtained with the process shown in Figure 4B. In this example, the first electrical binding means 430 is provided differently than in the other two examples. The description of steps 401 and 402, prior to providing the first and second electrical binding means is not repeated as these steps may performed as steps 201 and 202 or 301 and 302.

Thus, in step 403; a first electrical binding means 430 is provided in each through hole 425, under the lower surface of the first contact pads 461. In this example, the first electrical binding means is provided by growing nano entanglements directly on the lower surface of the first contact pads 461. Thus, in this example, the through holes are not metalized as in the other examples. Nano entanglements can be grown up to the desired length. It is preferred that they protrude as well from the surface of the PI layer, as shown in Figure 4B.

In step 404, a second backplane 420 is provided, wherein the second backplane comprises second contact pads 461 at locations corresponding to the locations of the first contact pads 451. The second backplane 420 may comprise driving electronics, chips 445 and a connector 446.

Second electrical binding means 435 are provided on the second contact pads

261. The second electrical binding means 435 are also provided by nano entanglements which preferably protrude from the surface of the second backplane 420.

In a last step, the first backplane 410 is laminated onto the second backplane 420, such that the first and second binding means connect, and driving and/or power signals 23 provided by the driving electronics, chips and connector of the second backplane are LU500365 transmitted to the LEDs on the TFT layer.

All three cases enable to connect a second backplane such as a PCB (rigid or flexible) or other TFT on glass or on any other substrate, with or without driving electronics to the backside of the first substrate, thereby reducing the need for or the number of side contacts to the various control elements on the TFT layer.

The second backplane can thus be a PCB, but may also be a TFT on any substrate, such as glass or PI, or any of the substrates listed above. It may comprise the driver electronics ornot.

Thus, it is also possible to connect two TFT backplanes together, back to back (the back corresponds to the substrate side of the TFT backplane), such that both TFT layers are on the outside of the stackup. The frontside and backside of the light emitting module can be processed on two separate TFT backplanes. The first backplane comprising the processed electronic circuits for the light emitting module and the second substrate comprising the power- and driving electronic circuits, and the light emitting module backside. The first back plane and the second can then be attached back-to-back and fixed to each other e.g. using electrically conductive adhesive glue or fuse bonding.

Alternatively, if dual side TFT processing is available, the power - and driving circuits can be processed directly onto the backside of the first TFT backplane. 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.

If the top layer of the light emitting module would contain a full ground level-layer (layer connected to the system ground level), this would enable Electro Magnetic Interference (EMI) shielding of the total module.

In the examples outlined, there are different ways to provide the first and second electrical binding means. The electrical binding means should preferably fulfill the following requirements: depending on the application, they need to be sufficiently precise (for example, at the level of a few microns for micro-LED displays), they should preferably be applied at low temperature, preferably room temperature, such that the TFT layer is not damaged during the process. In fact, TFT is very sensitive to temperature, as its properties can be altered 24 irreversibly if higher temperatures are used. In addition, these means should preferably also | LU500365 provide a mechanical connection.

À preferred means is the use of nano entanglements. Such nano entanglements are for example described in the following patent applications: EP3711462A1 and DE102018122007A.

This technology allows to achieve both an electrical and mechanical connection simultaneously. This new method describes the possibility to grow conductive nanometer sized wires to a desired length in a controlled way on conductive surfaces (e.g., Cu, Au) in a batch process. This method further can be used on a larger scale to increase the contacting area for high current devices (power LEDs, power distribution connectors). No solder or glue is required to make the connection. This technology is very interesting for critical applications. In addition, since it is a mechanical connection, control on X, Y, Z and rotation is under control. This technology is also a Galvano process, which allows to grow nano entanglements inside cavities. In addition, itis applied at room temperature which is advantageous for not damaging the TFT layer.

In the present application, such Cu nano entanglements can be grown on both contacting areas (e.g., u LED first contact pad and a second contact pad on the second backplane).

In addition to a very good electrical connection, they also provide a high mechanical connection. Nano entanglements are irregular in shape, which results in a better contacting surface. In fact, the wires behave in a similar way to brushes. The friction and contacting surface are thus maximized when such brushes are assembled, which results in a very stable connection. In addition, they have the advantage of accommodating any surface flatness variation or roughness, as will be described later.

In all the examples shown in Figures 2A to 4B, the use of nano entanglements as electrical binding means is therefore particularly advantageous.

In the third example shown in Figures 4A and 4B, nano entanglements can be grown up to the desired length inside the through holes. In fact, the length of nano entanglements depends on the duration of the galvanization phase. Thus, the nano entanglements are grown such that they are long enough to overcome the thickness of the PI, as illustrated in Figure 4B, and these can then be easily connected to the second backplane, i.e., PCB interposer.

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Thus, after laser ablation of the holes in the PI layer, when the copper layer of the LU500365 contact pads has been reached, nano entanglements are grown on top of the copper layer throughout the holes in the Pl layer. Thus, in this process, it is not necessary to metalize the holes.

The use of nano entanglements is also advantageous in the first and second examples shown in Figures 2B and 3B. In fact, the nano entanglements can be grown both on the metalized holes and on the second backplane, i.e., PCB interposer. Contacting both surfaces results in both a very strong electrical and mechanical connection thanks to the brushes and the increased surface area of the connection.

Other electrical binding means, which offer similar advantages as those described above, are for example conductive glue, known as “UP 400" described for example in the following patent application: EP2722415A1.

Other electrical binding means include the use of ACF or anisotropic conductive foil.

Other methods like fuse bonding, thermal compression bonding (creating intermetallic with heat and pressure), laser soldering, etc. are valid solutions as long as the material can withstand the process parameters, in particular heat. There are methods of ‘mass bonding’ by thermal compression where a matrix of uLEDs is arranged on a thermal resistant tape and then mounted on a substrate by a thermal process.

If the application does not require the same resolution as micro LEDs, other technologies, which are less precise, may also be used to provide electrical binding means in the through holes. For TFT, it is important to use a process which is applied at low temperatures (room temperatures).

A solution to electrically and mechanically assemble two backplanes arranged in a stackup by avoiding side contacting to reduce the seam and provide an invisible connection between the backplanes is hereby provided. It can be generalized to any number of stackups. The teachings can also be generalized to other applications then displays. For example, instead of the light emitting elements, other types of sensors, such as for example photometers can be used.

In fact, new means to connect contact pads of a semiconductor device provided on a first backplane to a second backplane are hereby provided, the first and second backplane being arranged in a stackup.

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This is achieved by providing through holes in the first backplane, under the LU500365 contact pads, and provide electrical binding means in the through holes to connect to the second backplane. Preferably, the electrical binding means is provided by nano entanglements.

À similar approach as the one described above can further be applied to connect a light emitting module or a plurality of light emitting modules to a display module, such as a PCB interposer.

Figures 1A to 1C illustrate a display module 100 (or display), wherein a plurality of light emitting modules 110 are arranged on a carrier 120.

In general, the backside of an LED module 110 can use BGA technology, such that each LED module fans out the vias to a grid of contacts. As illustrated in Figures 1A, 1B and 1C, each LED module 110 can then be assembled on a carrier 120, which could be a PCT backplane or a TFT. A possibility to connect each LED module 110 to the carrier 120 is to solder each LED module in a similar way as a BGA.

However, the full stackup, which comprises the carrier 120 and the LED modules 110 needs to go through a reflow oven. As previously described, not every TFT backplane technology or contrast enhanced material on top of the LEDs (like quantum dots) can withstand every temperature solder profile. Another solution could be to use conductive glue, but this glue may also need curing (UV, temperature, or time).

A similar approach as the one presented above can be applied to assemble light emitting modules to a display module. The approach presented above may also be used to provide a new arrangement for a display module or display, by redefining the functionality of each layer of the stackup which constructs the display.

Figures 5A and 5B are schematic representations of a display module 500 according to the present invention. Figure 5B shows a top view of a display module 500 comprising four first backplanes 510 arranged on a second backplane 520. Figure 5A is a cross section of Figure 5B. Two first backplanes 510, comprising through holes 525 and first electrical binding means 530 as described above are configured to be arranged on a second backplane 520, which also comprises second electrical binding means 535, as described above.

In this embodiment, the second backplane 520 is thus configured to receive at least one first backplane 510 and thereby provide a display module 500. In this example, the carrier 520 takes over the function of the second backplane 220, 320, 420, as explained in the examples of Figures 2A to 4B.

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The method described above can thus be used to provide a display module 500, LUS00365 when the dimensions of the carrier (second backplane) are such that at least one first backplane 210, 310, 410 can be assembled on it.

The second backplane, or carrier 520 can be anyone of a PCB, FR4 PCB or a TFT backplane, with or without driver electronics. In the example shown on Figure 5A, the carrier 520 is a TFT backplane which is connected via a flex PCB 580 to a driver PCB 560 with driver electronics.

First and second electrical binding means 530 and 535 are provided to connect the first backplanes 510 to the second backplane 520, as described above.

Advantages of this embodiment are that instead of providing a separate second backplane to each first backplane to create an individual LED module, it is possible to use a common second backplane for a plurality of first backplanes. The combination of the plurality of first backplanes arranged on this second backplane results in a display module. A difference between a light emitting module and a display module resides thus in the number of first backplanes provided on the second backplane.

The method described above for manufacturing an LED module, may thus be used for manufacturing a display module, with the only difference that the second backplane shall be large enough to accommodate several first backplanes.

Due to the nature of the first and second electrical binding means, it is possible to provide a display module with improved flatness during the manufacturing of the display module. In fact, the method shall further comprise the step of first providing a flat substrate. The next step is to arrange the several first backplanes with the light emitting elements facing towards the flat substrate on the flat substrate. The flat substrate shall then have the dimension of the assembled display (or display module). The several first backplanes shall be placed in their final position, one with respect to the other, such that the pixel pitch remains constant over the display module. The flat substrate can be for example glass, as glass can be manufactured with improved flatness. In addition, the flat substrate may comprise alignment means to align each first backplane of the several backplanes with respect to each other. The alignment means can be provided by physical marks and/or visual marks.

The next step is to laminate or press the second backplane on the plurality of first backplanes. As the first and second electrical binding means will accommodate the roughness (non flatness) of the first and second backplane, the manufacturing method will provide a display module having improved flatness.

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Therefore, the first and second electrical binding material also have the function LU500365 of vertical spacers in addition to being electrical and mechanical binders.

When nano entanglements are used as first and second electrical binding means, since they act like brushes, they have the advantage of being capable to accommodate for the non flatness of the first and second backplanes.

Therefore, the second backplane, or carrier 520, is not only an electrical interface to the LED modules, but also a mechanical support for maintaining the LED modules in place.

The use of first and second electrical binding means has the advantage that spacers as described in patent application W02020126059A1 of the same applicant are not required anymore. Thus, the first and second electrical binding means simplify drastically the display module.

In addition, the first backplane 510 comprises a plurality of LEDs, wherein each group of 3 LEDs defines a pixel 550. The distance AP between two adjacent pixels is the pixel pitch. It is important to keep the pixel pitch constant over the display module, and particularly at the seam between two adjacent LED modules. This is made possible owing to the new way of contacting the first backplane to the second backplane, as there is sufficient space for accommodating the required electronics and side contacting can be reduced or removed.

As shown in Figures 6A and 6B, a tiled display module or a display wall can comprise a multiple of display modules 600 that are tiled next to each other. Flexible conductors 580 are then used to connect the second backplane 520 of the display modules to the driving electronics 560 and/or to each other. The bending ratio of the flexible conductor 580 is limited and therefore limits the minimum distance provided between the display modules 600, and hence may affect the pixel pitch AP.

To overcome this problem and provide sufficient space to the bending of the flexible conductors 580 (also called fanout of the flexible conductor), as illustrated in Figures 5A to 6B, the surface of the second backplane 520 can be made smaller than the surface of the combined first backplanes 510 arranged in an array on the second backplane 520.

In addition, Figures 6A and 6B illustrate how two display modules 500 can be assembled to provide a tiled display 600. AM shows the space between two adjacent LED modules, and AD shows the spacing between two adjacent carriers 520. The pixel pitch AP of the display can be kept constant within a LED module, between two adjacent LED modules and 29 between two adjacent display modules by providing the appropriate AM and AD. This is made LU500365 possible as there is sufficient space to adjust AM and AD. As illustrated in Figures 6A and 6B, the pixel pitch AP remains constant throughout the assembled display. It is important to mention that the driving functionalities of driver 560 may also be embedded in the carrier 520.

This modular approach to make a display has the advantage that the functionalities which are needed for the operation of the light emitting display can be spread or shared by different layers of the stackup. The different layers or backplanes of the stackup may also further provide a mechanical function to the assembled display, i.e., a mechanical plate for the assembly of the LED modules and display modules.

In fact, the carrier of the display module (or second backplane of LED module) can be a PCB board and simultaneously provide the required mechanical stiffness to the display.

In addition, the driving functionalities can be split according to the following: - ATFT layer (first backplane) may provide finer functionalities required for the driving of the light emitting elements, - A PCB board (second backplane) may provide coarser functionalities and simultaneously provide the required mechanical stiffness for the display.

For example, a display of 55” in diagonal may be composed of any number of LED modules arranged on a PCB carrier of 55” (or less, as shown in Figure 6B). This PCB carrier may or may not then be connected to an external driver.

When manufacturing a display module with the method described, wherein the display modules comprise several first backplanes, the several first backplanes can be assembled using a pick and place robot. For example, the several first backplanes can be assembled using a pick and place robot on the flat substrate, with the light emitting elements facing towards the flat surface. Such a pick and place robot can be very precise in the positioning of the first backplanes. Such a robot can provide a precision of up to 2-3 um in all directions. In order not to (visually) disrupt the pixel pitch between two modules, the precision can be set at approximately at most 1% of the pixel pitch. Using such a robot to assemble the first backplanes, a further advantage is that the first backplanes can be made very small, for example as small as a pixel for example. The limitations on the size may depend on the robot only. This has the advantage that if a module has a failure, it can easily be replaced by another module, without jeopardizing the entire display. Once the several first backplanes are 30 assembled on the flat substrate, the second backplane can be laminated to the several first LU500365 backplanes.

It is also possible to apply the first and/or second electrical binding means on only a portion of each of the first and/or second contact pads. This offers the possibility to use the free portion of the first and/or second contact pads for testing purposes. The free portion for testing purposes can be at least 10% of the contact pad area for example.

Figures 7A and 7B illustrate a contact pad 730A, 730B wherein the electrical binding means 732A, 732B have been applied on only a portion of the useful surface, leaving the remaining surface 731A, 732B available for testing purposes. A test needle to test the LED module 530 can be used before placing the LED module on carrier 520 for example. This module could also be tested with a needle bed.

Nano entanglements have the advantage that they can be applied very precisely and can thus be applied only on a small portion of a contact pad.

In Figure 7A, the electrical binding means have been applied on half of the surface. In Figure 7B, the electrical binding means can also be provided around a central free portion on the first and/or second contact pads, such that the central free portion is used for the test needle and/or the test needle bed.

An additional advantage of using first and/or second electrical binding means for the connection between a LED module and a carrier is that an underfill 710 can additionally be used between them for even spacing and/or alignment between adjacent LED modules and/or for alignment purposes between the second substrate and the first substrate. Figure 7B illustrates how underfills 710 can be used in the assembled display module 500.

The underfills 710 can be for example provided on the lower surface of the first backplane or the upper surface of the second backplane, or on both. The underfill 711 can also be provided on the second backplane at the junction between the two first backplanes.

Figure 7C illustrates an assembled display module 500 without the use of an underfill.

As mentioned above, the LED module may comprise more than one backplane, and be a stackup of a plurality of backplanes, each backplane being provided by any one of a PCB or a TFT backplane. The upper (first) backplane comprising the light emitting elements shall be provided by a TFT layer on a first substrate. However, all the secondary backplanes below may be provided by TFT or PCB backplanes. For example, the LED module could be a 31 stack up of two TFT backplanes. The connection between any two backplanes can be made LU500365 according to the teachings of the present invention, and/or in combination with side contacts.

While the invention has been described hereinabove with reference to specific embodiments, this was done to clarify and not to limit the invention. The skilled person will appreciate that various modifications and different combinations of disclosed features are possible without departing from the scope of the invention.

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Claims

CLAIMS LU500365

1. Alight emitting module for a light emitting display, comprising a first and a second backplane arranged in a stackup, wherein - the first backplane comprises a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements and first contact pads for contacting the light emitting elements, and associated conducting tracks, - the second backplane comprises second contact pads configured to provide driving currents and power supply to the first contact pads of the light emitting elements, wherein the first backplane further comprises through holes provided in the first substrate at the locations of each first contact pad, and wherein, first electrical binding means are provided in the through holes of the first backplane and second electrical binding means are provided on the second contact pads of the second backplane the first and second electrical binding means being connected such that driving currents and/or power supply from the second backplane are transmitted to the first backplane.

2. Light emitting module according to claim 1, wherein the second backplane is larger than the first backplane such that at least two first backplanes are configured to be provided next to each other on the second backplane.

3. Light emitting module according to claim 1 or 2, wherein the surface of the second backplane is smaller than the surface occupied by the at least one first backplane arranged on the second backplane.

4. Light emitting module according to any of the preceding claims, wherein the first substrate is made of an electrically insulating material configured to receive a TFT layer, such as polyimide (PI), polymer, plastic, glass, ceramics, silicon, alumina, silicon carbide.

5. Light emitting module according to any of the preceding claims, wherein the light emitting elements are any one of LEDs, OLED, and variations thereof, QD-LED, EL-QLED, AMOLED, mini-LED, micro-LED.

6. Light emitting module according to any of the preceding claims, wherein the second backplane is any one of a PCB, or TFT layer on a electrically insulating substrate.

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7. Light emitting module according to any of the preceding claims, wherein the first electrical LU500365 binding means comprise metal provided inside the through holes such that the holes are metalized holes.

8. Light emitting module according to any of the preceding claims, wherein the first electrical binding means comprise nano entanglements.

9. Light emitting module according to any of the preceding claims, wherein the second electrical binding means comprise nano entanglements.

10. Light emitting module according to any of claims 1 to 7, wherein the first and second electrical binding means comprise conductive glue.

11. Light emitting module according to any of claims 1 to 7, wherein the first and second electrical binding means comprise ACF.

12. Light emitting module according to any of the preceding claims, wherein the second backplane further comprises driving functionalities.

13. Light emitting module according to any of claims 1 to 11, wherein the second backplane is connected to an external driver, preferably via a flexible connector.

14. Light emitting module according to any of the preceding claims, wherein the first and/or second electrical binding means are provided on a portion of the first and/or second contact pads.

15. Light emitting module according to claim 14, wherein the portion is arranged around a free central portion on the surface of the first/second contact pads.

16. Light emitting module according to any of the preceding claims, wherein an underfill is provided on the lower surface of the first backplane and/or on the upper surface of the second backplane.

17. Display module comprising at least one light emitting module according to any of claims 1 to 16.

18. Tiled display comprising a plurality of display modules according to claim 17.

19. A method for manufacturing a light emitting module, the method comprising the steps of - providing a first backplane comprising a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements, first contact pads for contacting the light emitting elements, and associated 34 conducting tracks, wherein the first backplane further comprises through holes LU500365 provided in the first substrate at the locations of each first contact pad, - providing first electrical binding means to the first backplane, in the through holes of the first substrate under the first contact pads, - providing a second backplane comprising second contact pads for contacting the first contact pads, - providing second electrical binding means on the second contact pads, - laminating the first backplane to the second backplane such that the first and second electrical binding means connect to transmit driving signals and/or power signals from the second backplane to the light emitting elements of the first backplane.

20. Method according to claim 19, wherein the step of providing a first backplane further comprises the step of - providing a first backplane comprising a thin film transistor layer deposited on a first substrate, the thin film transistor layer further comprising a plurality of light emitting elements, first contact pads for contacting the light emitting elements, and associated conducting tracks, - processing through holes in the first substrate, at the locations of the first contact pads such that the through holes extend to the lower surface of the first contact pads.

21. Method according to claim 19, wherein the step of providing a first backplane comprises the steps of - providing a first substrate, - processing through-holes in the first substrate, at designed locations for providing first contact pads, - depositing a thin film transistor layer on the first substrate, the thin film transistor layer further comprising a plurality of light emitting elements, first contact pads at the locations of the through holes and associated conducting tracks.

22. Method according to any of claims 19 to 21, wherein the step of providing a first backplane is performed with a pick and place robot.

23. Method according to any of claims 19 to 22 wherein the step of providing a first backplane LU500365 comprises the step of providing several first backplanes, the second backplane being configured to receive the several first backplanes, and wherein the step of laminating the first backplane to the second backplane comprises the step of laminating the several first backplanes on the second backplane.

24. Method according to claim 23, further comprising the step of providing a flat substrate on which all several first backplanes are assembled with the light emitting elements facing towards the flat substrate, before laminating the several first backplanes to the second backplane.

25. Method according to any of any of claims 19 to 24, wherein the step of providing first electrical binding means comprises the step of metalizing the through holes.

26. Method according to claim 25, wherein the step of metallizing the through holes comprises the step of growing a conductive material in the through holes, and/or the step of applying a conductive material paste, wherein the conductive material is at least one of copper, silver, aluminum.

27. Method according to any of claims 19 to 26, wherein the step of providing first electrical binding means comprises the step of growing nano entanglements on the metalized holes, the nano entanglements protruding from the surface of the first substrate.

28. Method according to any of claims 19 to 27, wherein the step of providing first electrical binding means comprises the step of growing nano entanglements on the lower surface of first contact pads until they protrude from the surface of the first substrate.

29. Method according to any of claims 19 to 28, wherein the step of providing second electrical binding means comprises the step of growing nano entanglements on the second contact pads.

30. Method according to any of claims 19 to 16, wherein the step of providing first and second electrical binding means further comprises the step of applying a conductive glue.

31. Method according to any of claims 19 to 26, wherein the step of providing first and second electrical binding means further comprises the step of applying ACF.

32. Method according to any of claims 19 to 31, wherein the first substrate is made of an insulating material configured to receive a TFT layer, such as polyimide (PI), polymer, plastic, glass, ceramics, silicon, alumina, silicon carbide.

33. Method according to claim 32, wherein the first substrate is polyimide and the method may further comprises the step of spin coating the polyimide layer on a glass substrate, 36 and the method further comprises the step of delaminating the glass substrate after LU500365 depositing the TFT layer.

34. Method according to any of claims 19 to 33, wherein light emitting elements are any one of LEDs, OLED, and variations thereof, QD-LED, EL-QLED, AMOLED, mini-LED, micro-LED.

35. Method according to any of claims 19 to 34 wherein second backplane is any one of a PCB, or TFT layer on a substrate.

36. Method according to any of claims 19 to 35 wherein the first and/or second electrical binding means are applied on a portion of the first and/or second contact pads/ in order to use the free portion for testing purposes.

37. Method according to claim 36, wherein portion is arranged around a free central portion on the surface of the first/second contact pads.

38. Method according to any of claims 19 to 37, wherein an underfill is provided on the lower surface of the first backplane and/or on the upper surface of the second backplane, respectively.

39. Method according to any of claims 19 to 38 wherein the second backplane further comprises driving functionalities.

40. Method according to any of claims 19 to 39, wherein the second backplane is connected to an external driver, preferably via a flexible connection, such as a flexible PCB.

41. Light emitting module manufactured by the method of any of claims 19 to 40.

42. Display module manufactured by the method of any of claims 19 to 40.

43. Tiled display comprising a plurality of display modules according to claim 42.

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