MICRO LED DISPLAY AND METHOD FOR MANUFACTURING THE SAME

A method for manufacturing a micro light emitting diode (LED) display is provided. The method includes a first operation of applying a light-to-heat conversion layer to a first surface of a carrier substrate, a second operation of forming a first adhesive layer on the light-to-heat conversion layer a third operation of aligning a plurality of micro LED chips on the first adhesive layer, a fourth operation of positioning the plurality of micro LED chips above a circuit board at a first distance, a fifth operation of radiating a laser to the plurality of micro LED chips, and a sixth operation of causing the first adhesive layer to be deformed by the light-to-heat conversion layer, so that the plurality of micro LED chips are detached from the first adhesive layer to be attached to the circuit board. Various other embodiments are possible.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. 119(a) of a Korean patent application number 10-2019-0108845, filed on Sep. 3, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND

The disclosure relates to a micro light emitting diode (LED) display and a method for manufacturing the same.

2. Description of Related Art

In addition to the continuous development direction for high-luminance, high-resolution, and increase in size of displays mounted on various electronic devices, the demand for high-efficiency and low-power is recently increasing according to the trend of eco-electronic devices. Accordingly, organic light-emitting diode (OLED) panels have been spotlighted as a new display to replace liquid crystal display (LCD) panels, but there is a problem still remaining, relating to high price, increase in size, and reliability due to low mass production yield thereof.

As a new product to replace or supplement the OLED panels, studies on a technology to make display panels by directly mounting a light emitting diode (LED) emitting colors of red (R), green (G), and blue (B) on a substrate are being carried out.

SUMMARY

Aspects of the disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the disclosure is to provide a micro light emitting diode (LED) display which is suitable for connection of micro-sized micro LED chips and is applicable to a process for a large area with high throughput, and a method for manufacturing the same.

However, in order to realize such displays, subminiature micro LEDs that can respond to current pixels should be developed first, and problems relating to a method in which micro LED chips having a size of several tens of μm are picked, a degree of precision with which the chips are transferred onto a substrate, and a method in which electrodes having a size of several μm and located on the micro LED chips having a size of several tens of μm are electrically connected to the substrate should be firstly solved.

Another aspect of the disclosure is to provide a micro LED display in which micro LED chips can be transferred onto a circuit board at a high speed by using a light-to-heat conversion layer, and a method for manufacturing the same.

Another aspect of the disclosure is to provide a micro LED display in which ablation of an adhesive layer can be controlled by controlling a material and thickness of a light-to-heat conversion layer, and a method for manufacturing the same.

In accordance with an aspect of the disclosure, a metal wire bonding method is provided. The method may be limitedly used due to a complicate process and low throughput thereof, and instability of a metal wire connecting a substrate and an element.

A flip-chip bonding method using solder bump, which is used to replace the metal wire bonding method, has several limitations. The flip-chip bonding method should be performed by patterning bumps on electrode one by one. Moreover, patterning bumps having a size of several μm is difficult.

In accordance with an aspect of the disclosure, a method for manufacturing a micro LED display is provided. The method includes a first operation of applying a light-to-heat conversion layer on a first surface of a carrier substrate, a second operation of forming a first adhesive layer on the light-to-heat conversion layer, a third operation of aligning a plurality of micro LED chips on the first adhesive layer, a fourth operation of positioning the plurality of micro LED chips at a first distance above a circuit board, a fifth operation of radiating a laser to the plurality of micro LED chips, and a sixth operation of causing the first adhesive layer to be deformed by the light-to-heat conversion layer, so that the plurality of micro LED chips are detached from the first adhesive layer to be attached to the circuit board.

According to the disclosure, electrode elements, for example, a micro LED chip, can be easily and electrically connected to a substrate through a simple process including bonding a conductive film containing conductive particles having a size of several μm or less, laser transfer, and curing.

According to the disclosure, a manufacturing process is very simple and thus can contribute to improving the yield of a process for a large area of a display element, for example, a micro LED display.

DETAILED DESCRIPTION

FIG. 1is a cross-sectional view illustrating a structure of a micro LED display according to an embodiment of the disclosure.

Referring toFIG. 1, a display device10according to one embodiment, which functions as a display element using a structure in which a plurality of light emitting elements are arranged on a circuit board11and emit light, may be a display device having a plurality of chips, for example, micro LED chips20attached thereto. The display device10according to one embodiment may include the circuit board11, a conductive film12, an adhesive coating layer13, and the plurality of micro LED chips20.

According to one embodiment, the plurality of light emitting elements, for example, the micro LED chips20, function as a light source of the display and may become conductive after being attached to the circuit board11. For example, the micro LED chips20may have a size of approximately 100 μm or less, and may generally have a size ranging from several μm to several tens of μm.

According to one embodiment, the micro LED chips20may include a light emitting body21and a connection pad22. According to one embodiment, one surface21aof the light emitting body21may be a surface from which light is emitted, and the other surface21bthereof may be a surface on which the connection pad22is disposed. According to one embodiment, the plurality of micro LED chips20may be attached in a connection pad-down state onto the conductive film12. According to one embodiment, the connection pad22may be located within the conductive film12(anisotropic conductive film (ACF)) so that micro LED chips20may be disposed to be connected to a conductive particle122. According to one embodiment, the conductive film12may be a double-sided adhesive film obtained by mixing a heat-curable adhesive and conductive particles disposed therein and having a fine particle size.

According to one embodiment, the circuit board11may be a support base for attaching a plurality of electrical elements, for example, the micro LED chips20, used as a light emitting element of a display, to be aligned thereon. For example, the circuit board11may be formed of one of a glass material, a sapphire material, a synthetic resin, or a ceramic material. According to one embodiment, the circuit board11may be formed of a rigid material or a flexible material. According to one embodiment, a circuit part110formed of a conductive material, for example, an electrode, may be disposed on one surface11aof the circuit board11, to which the micro LED chips20are connected. For example, the circuit part110may be a thin film transistor (TFT) circuit or an indium tin oxide (ITO), or may be an upper layer disposed on the circuit board11. According to one embodiment, the circuit part110may have a layer shape and be disposed one surface of the circuit board11. According to one embodiment, the circuit part110may be disposed to protrude from one surface of the circuit board11or may be disposed to be recessed therefrom.

According to one embodiment, the conductive film12may be disposed on one surface of the circuit board11. According to one embodiment, the conductive film12, which functions as an adhesive layer for fixing the micro LED chips and connecting the micro LED chip and the circuit part to each other, may include a plurality of conductive particles122which are mutually dispersed. For example, each of the conductive particles122may have a size between 0.1 μm and 10 μm and preferably have a size of 5.5 μm or less. According to one embodiment, the conductive particles122may be disposed at equal intervals in the conductive film12. According to one embodiment, among the plurality of conductive particles122included in the conductive film12(e.g., anisotropic conductive film), the conductive particles122located between the connection pad22and the circuit part110may be plastically deformed during the manufacturing process, and thus may not have a ball shape.

According to one embodiment, the at least one conductive particle122may be a conductive structure that electrically connects the connection pad22of the micro LED chip and the circuit part110of the circuit board11to each other.

According to one embodiment, the conductive film12may be a support structure for supporting the arranged micro LED chips20, and the conductive film12may include the plurality of conductive particles122, and thus may be a part of a conductive structure that electrically connects the micro LED chips20to the circuit part110of the circuit board11.

According to one embodiment, a conductive structure of the micro LED chips20may be formed in the micro LED display (e.g., display device10) by a structure in which the connection pad22of the micro LED chips20, the plurality of conductive particles122, and the circuit part110of the circuit board11are connected to one another. According to one embodiment, a part of the conductive particles122may be incorporated into the adhesive coating layer13coated on the conductive film12.

According to one embodiment, the surface of the connection pad22or the circuit part110may be a transparent electrode, such as indium-tin-oxide (ITO), CNT, metal nanowire, graphene, and an adhesive metal deposition layer, such as Mo, Ti, and W, or may be formed of one of Au, Cu, Ni, Co, or a conductive polymer.

According to one embodiment, the adhesive coating layer13coated around each micro LED chip20may be cured and utilized as a bonding strength reinforcing structure. Hereinafter, the adhesive coating layer13will be referred to as a bonding strength reinforcing structure.

According to one embodiment, each micro LED chip20may include the bonding strength reinforcing structure (e.g., adhesive coating layer13) that surrounds the side surface thereof. According to one embodiment, a bonding strength reinforcing structure (e.g., adhesive coating layer13) may be attached to the side surface of each micro LED chip20while being attached to the anisotropic conductive film, so that the attachment state of each micro LED chip20can be fixed. For example, the bonding strength reinforcing structures (e.g., adhesive coating layer13) may be spaced apart from each other or connected to each other.

FIG. 2Ais a cross-sectional view for sequentially showing an operation of manufacturing a micro LED display according to various embodiments,FIG. 2Bis a cross-sectional view for sequentially showing an operation of manufacturing a micro LED display according to various embodiments,FIG. 2Cis a cross-sectional view for sequentially showing an operation of manufacturing a micro LED display according to various embodiments,FIG. 3Ais a cross-sectional view for sequentially showing an operation of manufacturing a micro LED display according to various embodiments,FIG. 3Bis a cross-sectional view illustrating for sequentially showing an operation of manufacturing a micro LED display according to various embodiments, andFIG. 4is a cross-sectional view for sequentially showing an operation of manufacturing a micro LED display according to various embodiments.

Referring toFIG. 2A, according to one embodiment, the prepared circuit board11may have the circuit part110disposed on one surface thereof. For example, the circuit part110, which functions as an electrode formed on a circuit board, may be a TFT circuit. According to one embodiment, the circuit part110may be formed on one surface of the circuit board11by plating, depositing, or patterning a conductive material.

Referring toFIG. 2B, according to one embodiment, the conductive film12may be pre-bonded at a first thickness onto the prepared circuit board11. According to one embodiment, the conductive film12may be attached to one surface of the circuit board11by heat and pressure. Accordingly, the conductive film12may be a bonding layer attached onto the circuit board11.

According to one embodiment, the conductive film12may include an adhesive film120and the plurality of conductive particles122contained therein. For example, the plurality of conductive particles122may be arranged on the adhesive film120at equal intervals. For example, the plurality of conductive particles122, which are metal particles, may include one of tin, bismuth, indium, copper, nickel, gold, or silver.

Referring toFIG. 2C, according to one embodiment, a second adhesive layer14may be formed by applying an adhesive onto the conductive film12. According to one embodiment, the second adhesive layer14may be applied to a part or the entire of one surface of the circuit board11. For example, when the second adhesive layer14is applied to a part of the circuit board11, the second adhesive layer14may be disposed around the circuit part110.

According to one embodiment, the second adhesive layer14may be a tacky layer which absorbs the kinetic energy of the plurality of micro LED chips20separated from the carrier substrate during the laser transfer process, prevents the positional displacement of the micro LED chips20attached thereon, and temporarily fixes the micro LED chips20thereto.

For example, the application of the second adhesive layer14onto the conductive film12may be performed by one of dispensing, jetting, stencil printing, screen printing, bar coating, rolling coating, gravure printing, and reverse-offset printing. The second adhesive layer14having a constant thickness may be disposed on the conductive film12by the various methods.

Referring toFIGS. 3A and 3B, according to one embodiment, the carrier substrate31on which the plurality of micro LED chips20are aligned and attached may include a first surface31aand a second surface31bfacing in the opposite direction to the first surface31a. According to one embodiment, the light-to-heat conversion layer (LTHC)32may be applied to the second surface31bof the carrier substrate31. The light-to-heat conversion layer32may be a layer in which light energy is converted into heat energy. According to one embodiment, the light-to-heat conversion layer32may cause ablation of a first adhesive layer33by applying heat generated by laser irradiation to the first adhesive layer33. For example, the light-to-heat conversion layer32may be applied to the second surface31bat a thickness of several tens of μm.

According to one embodiment, the light-to-heat conversion layer32may have a wavelength at which laser light can pass.

According to one embodiment, the first adhesive layer33may be applied to the light-to-heat conversion layer32. According to an embodiment, the plurality of micro LED chips20may be attached by the first adhesive layer33onto the light-to-heat conversion layer32to be aligned thereon. For example, the plurality of aligned and attached micro LED chips20may have one of R-based color, G-based color, or B-based color.

According to one embodiment, the light-to-heat conversion layer32may control the temperature generated therefrom by changing a material or thickness thereof. The first adhesive layer33which is fused by the controllable light-to-heat conversion layer32may be controlled. Through this operation, the carrier substrate31to which the plurality of micro LED chips20are attached may be prepared.

Referring toFIG. 4, the carrier substrate31prepared as shown inFIG. 3Bmay be located above the circuit board to be spaced a first distance (d) therefrom. For example, the plurality of micro LED chips20may be located in a connection pad down state on the circuit board11.

According to one embodiment, laser light may be radiated to one micro LED chip20from a laser (L1) disposed above the carrier substrate31. According to one embodiment, the laser light may be converted from the light having light energy into the light having heat energy by the light-to-heat conversion layer (LTHC)32, and the converted heat energy may be delivered to a part of the first adhesive layer33, to which the one micro LED chip20is attached. The part of the first adhesive layer33may be fused by the delivered heat and thus a deformed part330may be produced therefrom. For example, the deformed part330may have a downward convex shape. According to one embodiment, the one micro LED chip20that has been attached to the first adhesive layer33may be separated therefrom by the deformation of the first adhesive layer33to be attached to the second adhesive layer14. For example, the separated micro LED chip20may be moved by falling due to its own weight or jetting by ablation of the first adhesive layer33.

According to one embodiment, the arranged micro LED chip20or the plurality of arranged micro LED chips20may be sequentially transferred onto the circuit board11by moving the carrier substrate31or the circuit board11back and forth or left and right.

According to one embodiment, the first distance (d) may be 150 μm or less and preferably 100 μm or less.

According to one embodiment, the carrier substrate31may be formed of a material through which a specific wavelength passes or a material through which the laser (L1) passes. For example, the material of the carrier substrate31may be a glass material, and the laser (L1) may be an infrared laser or an ultraviolet laser. Each micro LED chip20may be stably placed on the above-described second adhesive layer14in the order of R, G, and B. For example, primarily, the red (R)-based micro LED chips20may be disposed on the circuit board11, secondly, the green (G)-based micro LED chips20may be placed on the circuit board11, and subsequently, the blue (B)-based micro LED chips20may be disposed on the circuit board11. When the operation of connecting and fixing the micro LED chips20is completed, a plurality of pixels configured by the plurality of RGBs may be arranged on the circuit board11at equal intervals.

According to one embodiment, the laser (L1) may be disposed fixedly or movably, and the circuit board11may also be disposed fixedly or movably. For example, if the laser (L1) is fixed, the circuit board11may be disposed movably, and if the laser (L1) is movable, the circuit board11may be disposed fixedly. According to one embodiment, when the laser (L1) is fixed, the circuit board11may be installed to be movable back and forth or to be movable left and right.

According to one embodiment, the micro LED chips20descending at a certain acceleration may be sequentially attached onto the second adhesive layer14, and the micro LED chips20falling at a constant acceleration may be stably placed on the second adhesive layer14. This is because the second adhesive layer14may serve as a cushion pad and a bonding of the micro LED chips20.

According to one embodiment, heat and pressure may be applied by a chuck to the micro LED chips20stably placed on the second adhesive layer14. According to one embodiment, the chuck which is not shown may descend to apply heat and pressure to the stably placed micro LED chips20. At least one conductive particle122disposed between the connection pad22and the circuit part110may be plastically deformed according to the operation of the chuck. The at least one conductive particle122disposed between the connection pad22and the circuit part110may be pressed by the chuck, and thus may be deformed from the original spherical shape thereof into a flat shape.

According to one embodiment, the connection pad22, the plastically deformed conductive particles122, and the circuit part110may be electrically connected to one another, to form a conductive structure, that is, a connection structure of the micro LED chips20. According to one embodiment, the plurality of micro LED chips20disposed on the second adhesive layer14may be electrically connected to the circuit board11by heating and pressing operations. The electrical connection medium between the connection pads of the micro LED chips20and the circuit board11may be a plurality of conductive particles (e.g., the conductive particles122shown inFIG. 1) included in a conductive film (e.g., the conductive film12shown inFIG. 1).

According to one embodiment, at least a part of the first adhesive layer33may be deformed by ablation phenomenon which may be occurred on parts in direct contact with the light-to-heat conversion layer32. Heat may be delivered from the light-to-heat conversion layer32directly to the deformed part330and thus may cause ablation on the deformed part330.

FIG. 5is an enlarged cross-sectional view illustrating an operation in which a micro LED chip is transferred during an operation of manufacturing a micro LED display according to an embodiment of the disclosure.

Referring toFIG. 5, according to one embodiment, a light-to-heat conversion layer321and a first adhesive layer331for attaching a plurality of micro LED chips20to the light-to-heat conversion layer321may be included on one surface of the carrier substrate31. According to one embodiment, at least one pattern may be formed on the light-to-heat conversion layer321. According to one embodiment, the light-to-heat conversion layer321may enable selective irradiation of at least one attached micro LED chip20by using at least one pattern thereof.

According to one embodiment, the light-to-heat conversion layer321may have a pattern formed only on a part where the at least one micro LED chip20is attached, so that at least one micro LED chip20may be transferred onto the circuit board11. For example, a laser (L2) light may be radiated only to a part where a pattern is formed so that light-to-heat change may be occurred on the part of the light-to-heat conversion layer321. Accordingly, a deformed convex part331aof the first adhesive layer331may be changed to be downward convex, and the at least one attached micro LED chip20may move toward the circuit board11. The deformed convex part331amay be distinguished from a part331bof the first adhesive layer331, which has no light-to-heat conversion layer and thus passes the laser (L2) light therethrough without reacting therewith.

A part of the first adhesive layer331, that is, a part in contact with a part of the light-to-heat conversion layer321may be deformed by the light-to-heat change. For example, each of the deformed convex parts331amay have a downward convex shape. The deformed convex part331amay be a part having been fused by laser light.

According to one embodiment, the micro-LED chips20may be approximatively simultaneously separated from the first adhesive layer331to be attached onto the second adhesive layer14by irradiation from the laser (L2) to the plurality of micro-LED chips20.

According to one embodiment, the plurality of micro LED chips20attached to and aligned on the first adhesive layer331may be simultaneously attached onto the second adhesive layer14by laser light irradiation.

According to one embodiment, at least one pattern formed on the light-to-heat conversion layer321may be formed through a photolithography process. For example, the pattern may be formed only on a desired part of the light-to-heat conversion layer321, so that the micro LED chips20can be selectively transferred.

FIG. 6is an enlarged cross-sectional view illustrating an operation in which a micro LED chip is transferred during an operation of manufacturing a micro LED display according to an embodiment of the disclosure.

Referring toFIG. 6, according to one embodiment, laser light may be radiated to the plurality of micro LED chips20from a laser (L3) disposed above the carrier substrate31. According to one embodiment, the laser light may be converted from the light having light energy into the light having heat energy by the light-to-heat conversion layer32, and the converted heat energy may be delivered to the first adhesive layer332to which the plurality of micro LED chips20are attached. The first adhesive layer332may be fused by the delivered heat and thus a deformed part332amay be produced therefrom. For example, the deformed part332amay have a downward convex shape. For example, the downward direction may be a direction toward the circuit board11.

According to one embodiment, the plurality of micro LED chips20that have been attached to the first adhesive layer332may be separated therefrom by the deformation of the first adhesive layer332and be attached to the second adhesive layer14. For example, the separated micro LED chip20may be moved by falling due to its own weight or jetting by ablation of the first adhesive layer332.

According to one embodiment, the plurality of arranged micro LED chips20may be transferred to the circuit board11by moving the carrier substrate31or the circuit board11back and forth or left and right.

According to one embodiment, since an area from which the laser L3can be radiated is infinite, the micro LED chips20that can be transferred at once may be infinite as the irradiation area of the light-to-heat conversion layer32is increased.

FIG. 7is an enlarged cross-sectional view illustrating an operation in which a micro LED chip is transferred during an operation of manufacturing a micro LED display according to an embodiment of the disclosure.

Referring toFIG. 7, according to one embodiment, a mask35may be disposed between the carrier substrate31and a laser (L4). According to one embodiment, the laser (L4) may be selectively radiated to the micro LED chip20by the mask35so that some light therefrom passes through the mask35and some light therefrom does not pass through the mask. For example, some of light radiated from the laser (L4) may pass through the mask35and be irradiated to the first adhesive layer33.

According to one embodiment, laser light may be converted from the light having light energy into the light having heat energy by the light-to-heat conversion layer32, and the converted heat energy may be delivered to the first adhesive layer33to which the plurality of micro LED chips20are attached. The first adhesive layer33may be fused by the delivered heat and thus a plurality of deformed parts33amay be produced therefrom. For example, each of the deformed parts33amay have a downward convex shape. According to one embodiment, the plurality of micro LED chips20that have been attached to the first adhesive layer33may be separated therefrom by the deformation of the first adhesive layer33and be attached to the second adhesive layer14. For example, the separated micro LED chip20may be moved by falling due to its own weight or jetting by ablation of the first adhesive layer33.

According to one embodiment, the irradiation from the laser (L4) using the mask35may enable simultaneous and selective transferring of the plurality of micro LED chips20.

According to one embodiment, the plurality of arranged micro LED chips20may be sequentially transferred to the circuit board11by moving the carrier substrate31or the circuit board11back and forth or left and right.

FIG. 8is a plan view illustrating a micro LED display manufactured using a display manufacturing method according to an embodiment of the disclosure.

Referring toFIG. 8, a componentized micro LED display600may be mounted on a main board and manufactured as a large screen display, and may be manufactured as displays having various sizes.

FIG. 9is a plan view illustrating a display having a large size screen, obtained by combining micro LED displays manufactured using a display manufacturing method according to an embodiment of the disclosure.

Referring toFIG. 9, a micro LED display700having various wide-widths (e.g., a large TV or a billboard, etc.) may be manufactured by assembling a plurality of micro LED displays710manufactured through the manufacturing operations illustrated inFIGS. 2A to 4.