Transfer method for LED element, and transfer member

Abstract

To evenly and collectively transfer LED elements formed on each of a plurality of different LED wafers.SOLUTION: A transfer method for LED elements includes the steps of: forming a resin layer in a first state on a support plate, the resin layer containing a resin material; embedding at least one or more LED wafers, each of which has one side where a plurality of LED elements are provided, into the resin layer by pressing the resin layer against a second side, of each LED wafer, opposite the first side; transferring the resin layer in the first state into a second state where viscosity is higher than the first state and Young's modulus is higher than internal stress of each LED wafer; and connecting a plurality of electrodes and the LED elements provided on the respective LED wafers by pressing the LED wafer embedded into the resin layer against a circuit board provided with the electrodes, each electrode having a convex shape corresponding to each LED element.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for transferring an LED element and a transfer member. [Background technology]

[0002] In recent years, micro LED (Light Emitting Diode) displays have been attracting attention as a new display technology. A micro LED display is a display device in which miniaturized LED elements are arranged in an array on the display surface as pixels. By individually controlling the light emission of the LED elements of each pixel, a micro LED display can display images with high contrast and high response speed.

[0003] In the manufacturing process of such micro LED displays, a method is being considered in which multiple LED elements are formed on a wafer suitable for crystal growth of compound semiconductors, and then the wafer is bonded to a circuit board to transfer the multiple LED elements to the circuit board at once.

[0004] Also, a method has been considered in which multiple wafers on which LED elements are formed are attached to a wafer support substrate, so that the multiple LED elements formed on each of the multiple wafers can be transferred to a circuit board at the same time. However, since the thickness of the wafer on which the LED elements are formed varies relatively widely, the height of the multiple LED elements formed on the wafer also varies.

[0005] For example, Patent Document 1 listed below discloses that when multiple chip components of different heights cut from different wafers are mounted on a circuit board, pressure is applied to the back surfaces of the multiple chip components via a buffer layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-256311 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology disclosed in the above Patent Document 1 is a technology used when mounting individual chip components cut out from a wafer on a circuit board, and therefore it is not appropriate to apply the technology disclosed in the above Patent Document 1 to a case where multiple LED elements formed on multiple wafers attached to a wafer support substrate are transferred to a circuit board at the same time.

[0008] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a new and improved LED element transfer method and transfer member that are capable of uniformly transferring LED elements formed on multiple LED wafers of different thicknesses in one go. [Means for solving the problem]

[0009] In order to solve the above problem, according to one aspect of the present invention, there is provided a method for transferring LED elements, comprising the steps of: forming a resin layer in a first state containing a resin material on a support plate; pressing the resin layer against a second surface of an LED wafer having a first surface on the opposite side to the first surface, thereby embedding at least one of the LED wafers in the resin layer; transitioning the resin layer from the first state to a second state having a higher viscosity than the first state and a higher Young's modulus than the internal stress of the LED wafer; and pressing the LED wafer embedded in the resin layer against a circuit board on which a plurality of electrodes having convex shapes corresponding to the plurality of LED elements are provided, thereby connecting the plurality of LED elements provided on the LED wafer to the plurality of electrodes.

[0010] In addition, in order to solve the above-mentioned problems, according to another aspect of the present invention, there is provided a transfer member comprising: a support plate; a resin layer containing a resin material and provided on the support plate; and at least one LED wafer having a first surface on which a plurality of LED elements are provided and a second surface opposite to the first surface embedded in the resin layer, wherein the resin layer is capable of transitioning from a first state to a second state having a higher viscosity than the first state and a higher Young's modulus than the internal stress of the LED wafer. Effect of the Invention

[0011] As described above, according to the present invention, it is possible to uniformly transfer LED elements formed on a plurality of different LED wafers all at once. [Brief description of the drawings]

[0012] [Figure 1] 1A to 1C are schematic cross-sectional views illustrating a method for transferring an LED element according to one embodiment of the present invention. [Diagram 2] 5A to 5C are schematic cross-sectional views illustrating a method for transferring an LED element according to the embodiment. [Diagram 3] 5A to 5C are schematic cross-sectional views illustrating a method for transferring an LED element according to the embodiment. [Figure 4] 5A to 5C are schematic cross-sectional views illustrating a method for transferring an LED element according to the embodiment. [Diagram 5] 4 is a flowchart showing the flow of a transfer method of an LED element according to the embodiment. FIG. [Figure 6] 10A to 10C are schematic cross-sectional views illustrating a method for transferring an LED element according to a first modified example. [Figure 7] 13A to 13C are schematic cross-sectional views illustrating a method for transferring an LED element according to a second modified example. [Figure 8] FIG. 1 is a schematic cross-sectional view illustrating the background of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and duplicated explanations will be omitted.

[0014] 1. Background of the Invention First, the background of the present invention will be described with reference to Fig. 8. Fig. 8 is a schematic cross-sectional view for explaining the background of the present invention.

[0015] 8, for example, in the manufacturing process of a micro LED display device, it is considered to transfer a plurality of LED elements 110 formed on a plurality of LED wafers 100 all at once to a circuit board 300. Specifically, it is considered to transfer a plurality of LED elements 110 all at once to the circuit board 300 by adhering a plurality of LED wafers 100 on which a plurality of LED elements 110 are formed to one main surface of a support plate 200 via an adhesive layer 290, and then pressing the support plate 200 against the circuit board 300.

[0016] The circuit board 300 is a board provided with a drive circuit for individually driving each of the transferred LED elements 110 and a control circuit for controlling the drive of each of the LED elements 110. The circuit board 300 may be, for example, a glass board, a glass epoxy board, an epoxy board, a polyimide board, or a (meth)acrylic board, or may be a flexible board made of polyester or polyethersulfone. The circuit board 300 may be, for example, a pixel array board of a micro LED display device.

[0017] An electrode 310 having a convex shape such as a cone shape, a cylinder shape, or a tapered shape is provided on the surface of the circuit board 300 to which the LED element 110 is transferred. The electrode 310 is a connection terminal whose surface is made of metal and electrically connects the driving circuit and the control circuit provided on the circuit board 300 to the electrode of the LED element 110. The electrode 310 may be made of, for example, a single metal or a plurality of metals, or may be made by coating the surface of a resin with a metal. The electrode 310 may also be made of a bump, a conductive adhesive, or a solder. For example, a plurality of electrodes 310 may be provided per pixel in an arrangement corresponding to the pixel pitch of the micro LED display device.

[0018] The LED wafer 100 is a substrate on one of its main surfaces on which a plurality of LED elements 110 are formed in a matrix. Specifically, a pn junction is formed in the stacking direction by crystal growth of a compound semiconductor on one of its main surfaces. The crystal-grown compound semiconductor layer is then patterned into a lattice shape, thereby forming the LED elements 110 in a matrix on one of its main surfaces. Each of the patterned LED elements 110 has two electrodes formed thereon, each of which functions as a positive electrode or a negative electrode, for example.

[0019] For example, the LED wafer 100 may be a transparent sapphire substrate having a disk or rectangle shape suitable for crystal growth of a compound semiconductor that constitutes the LED element 110. The compound semiconductor that constitutes the LED element 110 may be, for example, InGaN, GaN, AlGaN, or the like.

[0020] The support plate 200 is a rigid substrate having a main surface with an area larger than that of the LED wafer 100. Specifically, the support plate 200 is a substrate having a main surface with an area corresponding to the plurality of LED wafers 100, and the plurality of LED wafers 100 are bonded to the main surface of the support plate 200 via an adhesive layer 290. The support plate 200 can simultaneously transfer the plurality of LED elements 110 formed on each of the LED wafers 100 to the circuit board 300 by pressing the main surface to which the plurality of LED wafers 100 are bonded against the circuit board 300.

[0021] The support plate 200 may be, for example, a transparent glass substrate having a flat main surface. By attaching the LED wafer 100 to the flat main surface of the support plate 200, warping caused by the formation of the LED elements 110 can be corrected.

[0022] The adhesive layer 290 is a layer that bonds the support plate 200 and the LED wafer 100. The adhesive layer 290 may be made of a polyimide-based adhesive, an epoxy-based adhesive, or an acrylic-based adhesive.

[0023] The LED wafers 100 are attached to the support plate 200 such that the pitch of the LED elements 110 is the same among the LED wafers 100. That is, the LED wafers 100 are attached to the main surface of the support plate 200 such that the LED elements 110 are arranged at a pitch corresponding to the arrangement pitch of the electrodes 310 provided on the circuit board 300.

[0024] Here, if the tolerance of the thickness of the LED wafer 100 is larger than the height of the electrodes 310 provided on the circuit board 300, the LED elements 110 formed on the LED wafers 100 having different thicknesses are pressed unevenly against the electrodes 310 of the circuit board 300. For example, the LED elements 110 formed on the LED wafer 100 having a large thickness are pressed with excessive pressure against the electrodes 310 provided on the circuit board 300. On the other hand, the LED elements 110 formed on the LED wafer 100 having a small thickness may not be pressed against the electrodes 310 provided on the circuit board 300.

[0025] The present invention has been conceived in view of the above circumstances. The present invention makes it possible to align the heights of the LED elements 110 formed on the LED wafers 100 regardless of the thickness of the LED wafers 100 by embedding the LED wafers 100 in a resin layer provided on a support plate 200. According to the present invention, since the heights from the support plate 200 to the LED elements 110 can be uniformly aligned, it is possible to uniformly transfer the LED elements 110 formed on the LED wafers 100 to the electrodes 310 of the circuit board 300 all at once.

[0026] <2. Embodiment> Next, a method for transferring an LED element 110 according to one embodiment of the present invention will be described with reference to Figures 1 to 4. Figures 1 to 4 are schematic cross-sectional views illustrating the method for transferring an LED element 110 according to this embodiment.

[0027] As shown in Fig. 1, in this embodiment, a resin layer 210 is provided on a main surface of a support plate 200. The resin layer 210 is a layer that contains a resin material and can transition from a first state to a second state. In Fig. 1, the resin layer 210 is provided in the first state.

[0028] The first state is a state in which the viscosity is low enough to allow the LED wafer 100 to be embedded inside the resin layer 210, and the fluidity of the resin layer 210 is high. On the other hand, the second state is a state in which the viscosity is higher than the first state, and the Young's modulus is higher than the internal stress of the LED wafer 100. The resin material contained in the resin layer 210 can transition from the first state to the second state by a stimulus such as heat, light, or a chemical reaction.

[0029] Specifically, the resin material contained in the resin layer 210 may be a curable resin. For example, the resin material contained in the resin layer 210 may be a thermosetting resin that transitions from a first state to a second state by heat, or a photocurable resin that transitions from a first state to a second state by light such as ultraviolet light. These resin materials can transition the resin layer 210 from the first state to the second state by receiving a stimulus of heat or light.

[0030] Alternatively, the resin material contained in the resin layer 210 may be an adhesive. For example, the resin material contained in the resin layer 210 may be a moisture-curing adhesive that transitions from a first state to a second state by a chemical reaction with moisture in the air, a solvent-volatilizing adhesive that transitions from a first state to a second state by the evaporation of a solvent, or a hardener-mixed adhesive that transitions from a first state to a second state by a chemical reaction with a hardener. These adhesives can transition the resin layer 210 from the first state to the second state over time after the formation of the resin layer 210.

[0031] Furthermore, the resin material contained in the resin layer 210 may be a thermoplastic resin or a hot-melt adhesive that transitions from a second state to a first state by heat. The thermoplastic resin or the hot-melt adhesive transitions to a first state that is liquid and has high fluidity when heated, and transitions to a second state that is solid and has low fluidity when cooled. In other words, the thermoplastic resin or the hot-melt adhesive can be considered to be a resin material that transitions from a first state to a second state by cooling.

[0032] On the other hand, the multiple LED wafers 100 are placed on the temporary fixing table 500 with the main surface on which the multiple LED elements 110 are provided facing down. At this time, the multiple LED elements 110 may be vacuum-adsorbed to the temporary fixing table 500. The multiple LED wafers 100 may be warped in the thickness direction due to the formation of the multiple LED elements 110. Therefore, the temporary fixing table 500 vacuum-adsorbs the multiple LED elements 110 formed on the multiple LED wafers 100 placed thereon, thereby correcting the warping of the multiple LED wafers 100 so that the mounting surface for the multiple LED elements 110 is flat.

[0033] Next, as shown in FIG. 2, the support plate 200 presses the resin layer 210 in the first state against the LED wafers 100 placed on the temporary fixing base 500, thereby embedding the LED wafers 100 in the resin layer 210. Specifically, the support plate 200 is pressed by the press member 400, so that the LED wafers 100 can be embedded in the resin layer 210 in the first state from the back surface side opposite to the main surface on which the LED elements 110 are provided. At this time, the resin layer 210 in the first state has low viscosity and high fluidity. Therefore, the LED wafers 100 are embedded in the resin layer 210 to a depth corresponding to their respective thicknesses by the pressure from the press member 400.

[0034] 3, a stimulus S is applied to the resin layer 210 in which the LED wafers 100 are embedded to transition from the first state to the second state. The stimulus S is, for example, heat, light, a chemical reaction, or the passage of time, and is selected according to the resin material contained in the resin layer 210.

[0035] By transitioning to the second state, the resin layer 210 has a higher viscosity than the first state and a higher Young's modulus than the internal stress of the LED wafer 100. That is, the resin layer 210 transitions from the first state, which is a highly fluid state, to the second state, which is a hardened state, by the stimulus S. As a result, the LED wafers 100 are embedded and fixed in the resin layer 210 with the heights from the support plate 200 to the LED elements 110 being uniform. In addition, since the resin layer 210 in the second state has a higher Young's modulus than the internal stress of the LED wafer 100, the LED wafer 100 is embedded and fixed in the resin layer 210 with the warp of the LED wafer 100 placed on the temporary fixing base 500 corrected.

[0036] According to this, as shown in Fig. 4, the LED wafers 100 are in a state where the height from the support plate 200 to the LED elements 110 is uniform. Therefore, by pressing the LED elements 110 against the circuit board 300 in this state, the support plate 200 can uniformly transfer the LED elements 110 formed on the LED wafers 100 of different thicknesses to the circuit board 300 at once. The laminate of the LED wafers 100, the resin layer 210, and the support plate 200 shown in Fig. 4 is an embodiment of the transfer member of the present invention.

[0037] Furthermore, the flow of the method for transferring the LED element 110 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flow chart showing the flow of the method for transferring the LED element 110 according to this embodiment.

[0038] 5, first, a resin layer 210 in a first state is formed on one main surface of the support plate 200 (S101). Specifically, a resin material in a first state is applied to one main surface of the support plate 200 to form the resin layer 210 in the first state. As described above, the resin material may be any one of a thermosetting resin, a photocurable resin, a moisture-curing adhesive, a solvent-volatile adhesive, a curing agent-mixed adhesive, a thermoplastic resin, and a hot-melt adhesive.

[0039] Next, the plurality of LED wafers 100 on which the LED elements 110 are formed are placed on the temporary fixing base 500 (S103). Specifically, the plurality of LED wafers 100 are placed on the temporary fixing base 500 with the main surface on which the LED elements 110 are formed facing the temporary fixing base 500. At this time, the temporary fixing base 500 may vacuum-suck the plurality of LED elements 110 to correct warpage of the placed LED wafer 100.

[0040] Next, the resin layer 210 is pressed against the LED wafers 100 placed on the temporary fixing base 500, thereby embedding the LED wafers 100 in the resin layer 210 (S105). Specifically, the support plate 200 may embed the LED wafers 100 in the resin layer 210 in the first state by pressing the resin layer 210 against the back surface opposite to the main surface on which the LED elements 110 are formed. At this time, since the resin layer 210 in the first state has low viscosity and high fluidity, the LED wafers 100 are embedded in the resin layer 210 to a depth corresponding to the thickness of each of the LED wafers 100.

[0041] Next, the resin layer 210 is transitioned from the first state to the second state by a stimulus S corresponding to the resin material contained in the resin layer 210 (S107). For example, the resin layer 210 may be transitioned from the first state to the second state by a stimulus S such as heat, light, a chemical reaction, or the passage of time. By transitioning the resin layer 210 to the second state, the multiple LED wafers 100 embedded in the resin layer 210 are fixed in a state in which the heights from the support plate 200 to the LED elements 110 are uniform and warping is corrected.

[0042] Next, the LED wafer 100 and the circuit board 300 are placed opposite each other, and the support plate 200 is pressed against the circuit board 300, thereby bonding the LED elements 110 to the circuit board 300 (S109). Specifically, the support plate 200 is pressed against the circuit board 300 in a state in which the LED elements 110 formed on the LED wafers 100 embedded in the resin layer 210 face the electrodes 310 of the circuit board 300. As a result, the LED elements 110 (more specifically, the electrodes provided on the LED elements 110) are bonded to the electrodes 310, respectively, and the LED elements 110 are bonded to the circuit board 300 by the adhesive. At this time, the LED elements 110 are uniformly pressed against the electrodes 310 of the circuit board 300, since the heights of the LED elements 110 from the support plate 200 are uniform.

[0043] Next, the LED wafers 100 are peeled off from the LED elements 110 by laser lift-off (S111). Specifically, by irradiating the interfaces between the LED wafers 100 and the LED elements 110 with laser light, a part of the LED elements 110 is vaporized, and the LED wafers 100 are peeled off from the LED elements 110. As a result, the LED wafers 100, the resin layer 210, and the support plate 200 are peeled off from the LED elements 110 transferred to the circuit board 300.

[0044] According to the above process, the method for transferring the LED elements 110 according to this embodiment can align the heights of the multiple LED elements 110 from the support plate 200, making it possible to uniformly transfer the multiple LED elements 110 to the circuit board 300 at once.

[0045] <3. Modifications> (3.1. First Modification) Next, a first modified example of the method for transferring the LED element 110 will be described with reference to Fig. 6. Fig. 6 is a schematic cross-sectional view illustrating the method for transferring the LED element 110 according to the first modified example.

[0046] As shown in FIG. 6, the support plate 200 may further be provided with a plurality of protrusions 220 for pressing the plurality of LED wafers 100 embedded in the resin layer 210 with a predetermined pressure distribution.

[0047] The multiple protrusions 220 are made of a material having a higher Young's modulus than the internal stress of the LED wafer 100, and are provided so as to protrude from the resin layer 210 or to be embedded in the resin layer 210. When the LED wafer 100 is embedded in the resin layer 210, the multiple protrusions 220 press the back surface of the LED wafer 100 opposite to the main surface on which the LED elements 110 are formed with a predetermined pressure distribution. As a result, the multiple protrusions 220 assist in correcting the warpage of the LED wafer 100, thereby making it possible to more reliably correct the warpage of the LED wafer 100.

[0048] Specifically, the multiple protrusions 220 may be made of a resin material having a convex shape such as a cone shape, a cylinder shape, a pillar shape, or a tapered shape. The multiple protrusions 220 are patterned by photolithography to be formed with a height, shape, and density that generate a pressure distribution that corrects the warped state of the LED wafer 100. That is, the multiple protrusions 220 may be formed with a height, shape, and density that generate a pressure distribution set based on the warped state of the LED wafer 100. For example, the multiple protrusions 220 may be provided with a pressure distribution that presses the outer periphery of the LED wafer 100 more strongly than the center, so as to correct the warp caused by the expansion of the main surface side on which the LED elements 110 of the LED wafer 100 are formed and the contraction of the back surface side opposite to the main surface.

[0049] However, it is desirable that the multiple protrusions 220 have elasticity that allows them to be deformed by pressure when embedding the multiple LED wafers 100 in the resin layer 210. This is because if the multiple protrusions 220 do not easily deform, the multiple LED elements 110 formed on the multiple LED wafers 100 may not be uniform in height due to pressure applied to the multiple LED wafers 100 by the multiple protrusions 220.

[0050] According to the method for transferring the LED elements 110 of the first modified example, the warpage occurring in the LED wafer 100 can be corrected more reliably, so that the multiple LED elements 110 formed on the LED wafer 100 can be transferred more uniformly to the circuit board 300.

[0051] (3.2. Second Modification) Next, a second modified example of the method for transferring the LED element 110 will be described with reference to Fig. 7. Fig. 7 is a schematic cross-sectional view illustrating the method for transferring the LED element 110 according to the second modified example.

[0052] 7, the support plate 200 may be divided for each LED wafer 100. Specifically, the support plate 200 may be divided into a plurality of pieces, and each LED wafer 100 may be embedded in one support plate 200 in a one-to-one correspondence.

[0053] In such a case, the multiple LED wafers 100 are embedded in the resin layers 210 of the multiple support plates 200 so that the height from the support plate 200 to the LED elements 110 is uniform among the multiple support plates 200. In this manner, the multiple support plates 200 simultaneously transfer the LED elements 110 to the circuit board 300, so that the height from the support plate 200 to the LED elements 110 is uniform, and the multiple LED elements 110 can be uniformly transferred to the electrodes 310 of the circuit board 300.

[0054] According to the transfer method of the LED elements 110 of the second modified example, even if multiple LED wafers 100 are not adhered to one support plate 200, it is possible to transfer multiple LED elements 110 formed on multiple LED wafers 100 to the circuit board 300 all at once.

[0055] Although the preferred embodiment of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to such an example. It is clear that a person having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present invention. [Explanation of symbols]

[0056] 100...LED wafer, 110...LED element, 200...support plate, 210...resin layer, 220...projection portion, 290...adhesive layer, 300...circuit board, 310...electrode, 400...press member, 500...temporary fixing base, S...stimulus

Claims

1. forming a resin layer in a first state containing a resin material on a support plate; a step of pressing the resin layer against a second surface of an LED wafer, the second surface being opposite to the first surface of the LED wafer, to embed at least one of the LED wafers in the resin layer; transitioning the resin layer from the first state to a second state having a higher viscosity than the first state and a higher Young's modulus than an internal stress of the LED wafer; a step of pressing the LED wafer embedded in the resin layer against a circuit board on which a plurality of electrodes having convex shapes corresponding to the plurality of LED elements are provided, thereby connecting the plurality of LED elements provided on the LED wafer to the plurality of electrodes; A method for transferring an LED element, comprising:

2. 2. The method for transferring an LED element according to claim 1, wherein a plurality of the LED wafers having different thicknesses are embedded in the resin layer so that the heights of the plurality of LED elements from the support plate are uniform.

3. 3. The method for transferring an LED element according to claim 2, wherein the resin layer is pressed against the second surface of the LED wafer in a state in which the LED elements are placed on a temporary fixing table with the LED wafer facing down.

4. The method for transferring an LED element according to claim 3 , wherein the LED elements are vacuum-adsorbed onto the temporary fixing table.

5. The method for transferring an LED element according to claim 1 , wherein the transition from the first state to the second state is performed by heat, light, or a chemical reaction.

6. 6. The method for transferring an LED element according to claim 1, wherein the support plate is further provided with a plurality of protrusions for pressing the second surface of the LED wafer with a predetermined pressure distribution.

7. 7. The method for transferring an LED element according to claim 6, wherein the predetermined pressure distribution is set based on a warped state of the LED wafer.

8. The method for transferring an LED element according to claim 6 , wherein the plurality of protrusions are made of a material having a Young's modulus higher than an internal stress of the LED wafer.

9. A support plate; A resin layer including a resin material and provided on the support plate; At least one LED wafer having a first surface on which a plurality of LED elements are provided and a second surface on the opposite side to the first surface is embedded in the resin layer; Equipped with The resin layer is capable of transitioning from a first state to a second state in which the viscosity of the resin layer is higher than that of the first state and the Young's modulus is higher than the internal stress of the LED wafer.

Images