JP2021110875A - Manufacturing method for display device, display device, and intermediate for manufacturing display device - Google Patents

Abstract

To provide a manufacturing method for a display device capable of reducing replacement of a defective chip after joining to a driving substrate.SOLUTION: A manufacturing method for a display device has a plurality of micro LED chips 11 each having a chip side electrode 12. The manufacturing method for the display device includes: a relay stage for holding the plurality of chips 11 on a relay substrate 14 so that the chip side electrodes 12 are exposed; and a joining stage for transferring the plurality of chips 11 onto a driving substrate 20 having a driving substrate side electrode 21 from the relay substrate 14 and joining the chip side electrode 12 and the driving substrate side electrode 21.SELECTED DRAWING: Figure 8

Description

The present invention relates to a method for manufacturing a display device, a display device, and an intermediate for manufacturing a display device.

In recent years, display devices using micro LEDs (micro-light emitting diodes) as light emitting elements have been in the limelight. A display device using a micro LED (hereinafter, simply referred to as a “display device”) is a next-generation display device capable of displaying a high-brightness, high-definition image with low power consumption without causing a high response speed or burning.

In the conventional manufacturing technology of a display device, micro LED chips are joined on a drive substrate so as to have a predetermined arrangement pitch, and then inspected for defective chips. Then, in the prior art, if there is a defective chip as a result of inspection, it is removed from the drive board and a good chip is joined to the drive board (Patent Documents 1 to 3).

Further, in another conventional technique, a plurality of micro LED chips are arranged on the first substrate, and the chips are collectively bonded to the electrodes on the second substrate. In this prior art, there is no disclosure about inspection of chips after joining (Patent Document 4).

Korean Registered Patent No. 1890934 Korean Registered Patent No. 1918106 U.S. Patent Application Publication No. 2017-0140961 U.S. Pat. No. 10,283,684

In the prior art, after joining a plurality of chips to the drive board, each chip is inspected and if there is a defect, it is replaced.

However, since the chip bonded to the drive board is firmly bonded to the drive board by solder, it is not easy to remove the chip from the drive board. In particular, the micro LED chip is extremely small, 100 μm or less, as its name suggests, so even if you try to remove only the defective chip from the board, the good chip around the defective chip may be damaged, or you may dare to damage the peripheral chip. It was necessary to replace the entire chip.

Therefore, the present invention provides a method for manufacturing a display device, a display device, and an intermediate for manufacturing a display device, which can reduce the replacement of defective chips after joining to a drive substrate.

The above task is achieved by the following means.

(1) A method for manufacturing a display device having a plurality of micro-light emitting elements, each having an electrode on the element side.
A relay stage in which a plurality of the micro light emitting elements are held on the relay substrate so that the element side electrodes are exposed, and
A joining step in which a plurality of the micro light emitting elements are transferred from the relay board onto a drive board having a drive board side electrode to join the element side electrode and the drive board side electrode.
A method of manufacturing a display device.

(2) The relay stage is
It has an adhesion step in which the micro light emitting element is attached to the resin material formed on the relay substrate.
After the relay stage
The element-side electrode of the micro-light emitting element held on the relay substrate is energized to detect a defective element whose emission brightness is less than a predetermined value and / or a defective element which does not satisfy a predetermined emission spectrum. , An electrical inspection stage that stores the position of the defective element,
It further has a repair step of removing the defective element from the relay board based on the position of the defective element and attaching a new micro light emitting element to the relay board in place of the removed defective element.
The method for manufacturing a display device according to (1) above, wherein the electrical inspection step and the repair step are repeated until the number of defective elements becomes less than a predetermined number of defective products, and then the joining step is carried out.

(3) A semiconductor layer forming step of forming the semiconductor layer to be the micro light emitting element on the initial substrate, and
The element-side electrode forming step of forming the element-side electrode on the semiconductor layer, and
It further includes a holding substrate transfer stage in which the semiconductor layer is divided into the micro light emitting elements and transferred to the holding substrate.
In the holding substrate transfer step, the micro light emitting elements are arranged on the holding substrate at a predetermined arrangement pitch so that the electrode side on the element side faces the holding substrate side.
The relay stage is
The method for manufacturing a display device according to (1) or (2) above, wherein the micro light emitting element is transferred from the holding substrate to the relay substrate so that the electrode on the element side is exposed.

(4) The joining stage is
The melting temperature of the solder is fused between the element-side electrode and the drive board-side electrode by fluxlessly facing each other via solder and pressurizing the relay board and the drive board in a direction in which they are relatively close to each other. A temporary joining step in which the element-side electrode and the drive board-side electrode are crimped via solder by heating at a temperature lower than
After the pressurization is released, the relay board separation step of removing the relay board from the micro light emitting element, and
A reflow stage in which the drive substrate to which the micro light emitting element is crimped is heated at a temperature equal to or higher than the melting temperature of the solder.
The method for manufacturing a display device according to any one of (1) to (3) above.

(5) After the relay board separation step,
Further, a flux application step of applying flux to the surface of the drive substrate having the micro light emitting element is provided.
The method for manufacturing a display device according to (4) above, wherein the reflow step is carried out after the flux application step.

(6) The method for manufacturing a display device according to any one of (1) to (5) above, wherein the relay board transmits 50% or more of visible light.

(7) Micro light emitting element and
The element-side electrode provided on the micro-light emitting element and
A drive board on which the plurality of micro light emitting elements are mounted, and
The drive board side electrodes provided on the drive board and
A metal material that joins the element-side electrode and the drive board-side electrode,
Have,
A display device in which no flux is present at the interface between the element-side electrode and the metal material and / or at the interface between the drive substrate-side electrode and the metal material.

(8) The metal material is
The display device according to (7) above, which has a eutectic metal of the solder and the element-side electrode and / or a eutectic metal of the solder and the drive board-side electrode.

(9) The display device according to (7) or (8) above, wherein the element-side electrode and the drive substrate-side electrode have at least one metal selected from the group consisting of copper, gold, and aluminum.

(10) Micro light emitting element and
With the relay board
The resin material formed on the relay board and
Have,
An intermediate for manufacturing a display device, wherein a plurality of the micro light emitting elements are attached to the resin material at a predetermined arrangement pitch.

(11) The plurality of the micro light emitting elements are arranged on the relay substrate in just proportion to a predetermined number, and the number of defective elements having less than the predetermined emission brightness is less than the predetermined number of defective products. 10) The intermediate for manufacturing a display device according to the above.

(12) The intermediate for manufacturing a display device according to (10) or (11) above, wherein the relay board transmits 50% or more of visible light.

According to the present invention, the chip is transferred from the relay board to the drive board, and the chip side electrode and the drive board side electrode are joined. Therefore, the chip-side electrode and the drive substrate-side electrode can be joined by a metal component, and the generation of voids at the interface between the electrodes is reduced. Thereby, in the present invention, the defect of the chip on the drive board can be reduced, and the replacement of the chip after joining to the drive board can be reduced.

It is a schematic cross-sectional view for demonstrating the formation of a micro LED. It is the schematic sectional drawing which shows the holding substrate which held the chip. It is a top view which shows the holding substrate in the state which the chip is held for each color. It is a top view which shows the holding substrate in the state which the chip is held for each color. It is a top view which shows the holding substrate in the state which the chip is held for each color. It is schematic cross-sectional view which shows the state which the part of the sapphire substrate is removed from the chip held on the holding substrate. It is schematic cross-sectional view for demonstrating the process of transferring a chip from a holding substrate to a relay substrate. It is the schematic sectional drawing which shows the relay board in the state which the holding board is removed. It is a top view which shows the relay board in the state which all the color chips are held. It is schematic cross-sectional view for demonstrating transfer | transfer of a chip from a relay board to a drive board. It is a schematic cross-sectional view which shows the drive board after the relay board is removed from a chip. It is a schematic cross-sectional view which shows the drive board after reflow. It is a schematic enlarged cross-sectional view which shows the state after reflow of the chip joint part by the prior art. It is a schematic enlarged cross-sectional view which shows the state after reflow of the chip joint part by embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings below, the same reference numerals refer to the same components, and in the drawings, the size of each component is also exaggerated for clarity and convenience of description. On the other hand, the embodiments described below are merely exemplary and can be modified in various ways from such embodiments.

In the following, the places described as "upper" and "above" may include not only those that are directly above in contact but also those that are not in contact and are above. Similarly, the places described as "bottom" and "bottom" may include not only those that are directly below in contact but also those that are not in contact and are below.

A singular expression has multiple expressions unless they have distinctly different meanings in the context. Also, when a part "contains" or "has" a component, it does not exclude other components unless otherwise stated to be the opposite, and may further include other components. It means good.

Also, the use of the term "above" and similar directives applies to both the singular and the plural.

Unless there is a clear order or vice versa for the steps that make up the method, the steps are performed in the proper order. It is not necessarily limited to the description order of the above steps. The use of all examples, or exemplary terms (eg, etc.), is solely for the purpose of explaining technical ideas and is not limited by the claims, and is scoped by the examples or exemplary terms. Is not limited.

A method of manufacturing a display device according to an exemplary embodiment of the present invention will be described.

FIG. 1 is a schematic cross-sectional view for explaining the formation of a micro LED.

In the method of manufacturing a display device, first, as shown in FIG. 1, a semiconductor layer 102 to be a micro LED (micro light emitting element) is formed on a sapphire substrate 101 (initial substrate).

The semiconductor layer 102 is a light emitting layer that emits light having a predetermined light emission spectrum. In this embodiment, three-color micro LEDs are used. The three colors are red (R), green (G), and blue (B). Therefore, in the present embodiment, the sapphire substrate 101 is prepared for each color, and the semiconductor layer 102 having a composition different for each color is formed on the sapphire substrate 101. Although the semiconductor layers 102 of each color have different compositions and structures, they are known and their manufacturing methods are also known, so detailed description thereof will be omitted.

An electrode is further formed on the semiconductor layer 102 at a position corresponding to the chip of each micro LED after division. In the present embodiment, this electrode is referred to as a chip side electrode 12 (element side electrode).

The chip-side electrodes 12 are formed corresponding to the arrangement pitch of the chips arranged on the drive substrate 20 described later. The chip-side electrode 12 may be a part of the metal wiring electrically connected to the semiconductor layer 102 as it is, or may be formed as a metal pad in direct contact with the semiconductor layer 102.

The chip side electrode 12 is formed by using, for example, any one of Au, Ag, Cu, Al, Pt, Ni, Cr, Ti, and ITO metal or graphene. Of these, Au, Ag, and Cu are preferable.

Further, micro bumps made of solder 13 (metal material) are formed on the chip side electrode 12. For the solder 13, for example, SAC (SnAgCu) is used.

Subsequently, dicing to the micro LED and transfer to the holding substrate are performed (holding substrate transfer stage). At the holding substrate transfer stage, first, the semiconductor layer 102 together with the sapphire substrate 101 is divided into the form of the micro LED chip 11 by using a known dicing method. However, the sapphire substrate 101 is not completely divided, is in a half-cut state, and is attached to the chip 11.

Subsequently, the chip 11 with the sapphire substrate 101 still attached is attached to the holding substrate 112. FIG. 2 is a schematic cross-sectional view showing a holding substrate 112 in which the chip 11 is held.

As shown in FIG. 2, the divided chip 11 is attached by the resin layer 111 so that the surface on which the chip side electrode 12 is formed faces the holding substrate 112 side. Although only the chips 11 for one color are shown in FIG. 2, in the present embodiment, the holding substrate 112 is prepared for each color at this stage, and the chips 11 of each color are provided on each holding substrate 112. Is pasted. Further, the chips 11 of each color are individually attached to the holding substrate 112 at a predetermined arrangement pitch. At this stage, the arrangement pitch is set to be the final arrangement pitch on the drive substrate 20.

3A to 3C are plan views showing a holding substrate 112 in a state where the chip 11 is held for each color, FIG. 3A is a holding substrate 112R in a state where the chip 11R that emits red light is held, and FIG. 3B is green. The holding substrate 112G in which the chip 11G that emits light is held, and FIG. 3C shows the holding substrate 112B in which the chip 11B that emits blue light is held.

As shown in the figure, the red holding substrate 112R has a chip 11R that emits red light, the green holding substrate 112G has a chip 11G that emits green light, and the blue holding substrate 112B has a chip 11B that emits blue light. It is held at the array pitch of. In the description of the present embodiment, in the description that it is not necessary to distinguish each color, for example, an alkali-free glass or a quartz glass substrate is used as the holding substrate 112 referred to as the holding substrate 112. Further, the resin layer 111 was selected from the group consisting of, for example, a polyimide resin, an acrylic resin (for example, PMMA (Polymethyl methylate)), an epoxy resin, a PP (Polypolyrene) resin, a polycarbonate resin, and an ABS (Acrylontile Butadiene Style) resin. Any one resin is used. When using the illustrated resin, a thermosetting agent may be blended. Further, as the resin layer 111, another thermosetting resin may be used.

Subsequently, the sapphire substrate 101 is separated and removed from the chip 11. FIG. 4 is a schematic cross-sectional view showing a state in which the portion of the sapphire substrate 101 is removed from the chip 11 held by the holding substrate 112.

The separation of the sapphire substrate 101 uses, for example, a laser lift-off technique. Specifically, a laser beam having an ultraviolet wavelength is irradiated from the side of the sapphire substrate 101 so as to scan the entire surface thereof. As the laser light, for example, a KrF excimer laser having a wavelength of 248 nm is used. The wavelength used is not limited to this, and any wavelength that can separate the sapphire substrate 101 from the semiconductor layer 102 may be used. As shown in FIG. 4, the portion of the sapphire substrate 101 is separated from the semiconductor layer 102 and removed by laser light irradiation.

The chip 11 has a shape as a micro LED by removing the portion of the sapphire substrate 101. The chip 11 (without the portion of the sapphire substrate 101) has a three-dimensional shape such as a substantially rectangular parallelepiped or a substantially cube, and has a quadrangular planar shape. The length of one side of the quadrangle is, for example, 1 μm or more and 100 μm or less. Further, the chip 11 has, for example, a cylindrical shape and has a circular planar shape. The circular diameter is 1 μm or more and 100 μm or less. The quadrangular or circular planar portion is, for example, the light extraction surface of the micro LED. The chip 11 is not limited to the above-mentioned shape, but has a plane shape having the same size as the above-mentioned quadrangle or circle.

At this stage, the chip 11 has the holding substrate 112 side on the side where the chip side electrode 12 is located, and the bottom surface side opposite to the chip side electrode 12 is exposed. This bottom surface serves as a light extraction surface.

Subsequently, the chip 11 is transferred from the holding substrate 112 to the relay substrate 14 (relay stage). FIG. 5 is a schematic cross-sectional view for explaining a process of transferring the chip 11 from the holding substrate 112 to the relay substrate 14.

The relay board 14 is preferably made of a material having a thermal expansion coefficient equivalent to that of the drive board 20 described later and transmitting visible light by 50% or more. The visible light transmittance is preferably 50% or more with the silicone resin (described later) coated on the relay substrate 14.

For the relay substrate 14, for example, quartz glass, non-alkali glass, or the like is used. This is so that the light emission of the chip 11 can be observed during the electrical inspection of the chip 11, which will be described later.

The size of the relay board 14 is preferably the same as or larger than that of the drive board 20. With such a size, the chip 11 can be transferred to the drive board 20 described later only once. However, the size of the relay board 14 is not limited to this. For example, the size of one relay board 14 may be 1/10 to 1/2 of that of the drive board 20. When the size of the relay board 14 is smaller than that of the drive board 20, the transfer of the chip 11 from the relay board 14 to the drive board 20 may be repeated.

In the transfer from the holding substrate 112 to the relay substrate 14, the chip 11 is attached to the relay substrate 14 from the bottom surface side of the chip 11 (adhesion step). In order to attach the chip 11 and the relay substrate 14, for example, a silicone resin (also referred to as a silicone elastomer) is used.

To this end, first, as a silicone resin, PDMS resin 31 (Polydimethicyloxylone) is applied to the relay substrate 14 with a uniform film thickness by spin coating, lamination, slit coating, molding, or the like.

After that, the PDMS resin 31 is heated together with the relay substrate 14 to thermally crosslink the PDMS. The heat-crosslinked PDMS resin 31 is adjusted so that the rubber hardness (shore A) is about 20 to 100. The hardness is adjusted by adjusting the amount of the cross-linking agent and the curing temperature. The PDMS resin 31 having such hardness has rubber properties, and the chip 11 can be attached to it.

The thickness of the PDMS resin 31 after cross-linking on the drive substrate 20 may be such that the chip 11 is attached, and is, for example, about 1 μm to 1 mm. With such a thickness, the chip 11 can be reliably attached to the PDMS resin 31. Further, if the thickness of the PDMS resin 31 is about 1 μm to 1 mm, sufficient light for the inspection passes through the PDMS resin 31 when the LED is made to emit light during the electrical inspection described later.

The transfer of the chip 11 is performed for each holding substrate 112 that holds the chip 11 of each color. Stamping or laser ablation is used to transfer the chip 11. In this embodiment, an example using a stamp will be described.

To transfer the chip 11, as shown in FIG. 5, first, the chip 11 together with the holding substrate 112 is pressed against the PDMS resin 31. The chip 11 adheres to the PDMS resin 31 due to the rubber properties of the PDMS resin 31. In the transfer of the chip 11 onto the relay board 14, the chip 11 may be pressed onto the PDMS resin 31 and then the chip 11 may be further pressed in the direction of the relay board 14 so that the chips 11 are brought into close contact with each other. good.

Since the chip 11 after transfer adheres due to the rubber characteristics of the PDMS resin 31, the position of the chip 11 does not easily change, and even if the surface on which the chip 11 is located faces downward, the chip 11 does not fall off from the relay board 14.

Subsequently, the holding substrate 112 is removed from the chip 11. FIG. 6 is a schematic cross-sectional view showing a relay board 14 in a state where the holding board 112 is removed. Laser lift-off technology is used, for example, to remove the holding substrate 112. Removal of the holding substrate 112 by the laser lift-off technique is performed, for example, as follows. First, a laser beam having an ultraviolet wavelength is irradiated from the holding substrate 112 side so as to scan the entire surface of the holding substrate 112. The laser light used is, for example, a KrF excimer laser having a wavelength of 248 nm. The wavelength used is not limited to this, and may be appropriately determined depending on the resin material used as the resin layer 111. The resin layer 111 is melted by irradiation with laser light, and the holding substrate 112 is separated from the surface of the chip side electrode 12. Therefore, the holding substrate 112 can be removed from the chip 11. When laser ablation is used, the chip 11 is blown from the holding substrate 112 to the relay substrate 14 by the laser ablation, so that the step of removing the holding substrate 112 becomes unnecessary.

After removing the holding substrate 112, the resin layer 111 remaining on the surface of the chip-side electrode 12 is removed by a cleaning treatment. The cleaning process is removed by performing dry etching such as oxygen plasma ashing for a desired time. Alternatively, it may be removed by wet etching using a chemical solution capable of dissolving the resin layer 111.

FIG. 7 is a plan view showing a relay board 14 in a state where chips 11 of all colors are held. When the transfer of the chip 11 to the relay board 14 is completed, as shown in FIG. 7, all the chips 11R, 11G, and 11B of all colors are arranged on the relay board 14 by the PDMS resin 31. All chips 11 are arranged at a predetermined array pitch. The arrangement pitch is the arrangement pitch on the drive substrate 20. Further, in the chip 11, the chip side electrode 12 (microbump solder 13) is exposed.

Subsequently, a visual inspection and an electrical inspection are performed (visual inspection stage and electrical inspection stage). In the visual inspection, an automated optical inspection (AOI) detects defects in appearance such as inclination of the chip 11 on the relay board 14, height difference between the plurality of chips 11, and chip 11 coming off. The position of the defective chip detected by the AOI and the position of the chip missing are stored in the storage device in the AOI device. Further, the position of the defective chip and the position of the chip missing may be separately stored in a storage device in a computer or the like that acquires inspection information from the AOI device.

After that, the defective chip is replaced with a non-defective chip 11 based on the stored position of the defective chip. In the chip removal, a new chip 11 is replenished based on the stored chip removal position, and the chip is attached to the relay board 14. In this embodiment, the replacement and replenishment of defective chips based on the result of AOI is referred to as a first repair step.

After the first repair, an electrical inspection of the chip 11 is performed. The electrical inspection is a light emission test in which each chip 11 is energized from the chip side electrode 12 to confirm whether or not the LED emits light well. As an electrical inspection, it is inspected whether or not the emission brightness is less than a predetermined value. The case where the emission brightness is less than the predetermined value includes a case where the light is not lit and a case where the brightness is insufficient. Further, as an electrical inspection, it is inspected whether or not a predetermined emission spectrum is satisfied. A chip 11 that is less than a predetermined emission brightness or deviates from a predetermined emission spectrum is regarded as a defective chip (defective element). The position of the defective chip detected by the electrical inspection is stored in the storage device in the electrical device. Further, the position of the defective chip may be separately stored in a storage device in a computer or the like that acquires inspection information from an electrical device.

The predetermined emission brightness and the predetermined emission spectrum are standards for light emission observed through the relay substrate 14, and may differ from the standards for the final display device. Further, in the electrical inspection step, it is preferable to inspect both the emission brightness and the emission spectrum, but only one of them may be inspected.

After that, the defective chip is replaced with a good chip based on the stored position of the defective chip. In the present embodiment, the replacement of the defective chip based on the result of the electrical inspection is referred to as a second repair stage.

For electrical inspection, for example, an electrical inspection probe may be individually applied to the chip side electrodes 12 of each chip, or an inspection device capable of inspecting a plurality of chips 11 at once is prepared. You may inspect.

As described above, the relay board 14 uses a light-transmitting board, so that when the chip 11 is turned on, light can be measured from the relay board 14 side. In the electrical inspection, the brightness, wavelength, and the like of each chip 11 are inspected from the relay board 14 side.

The first and second repair steps are performed, for example, as follows. First, if a defective chip is confirmed on the relay board 14, the defective chip is removed from the relay board 14 with an adhesive stamp or the like. The adhesive stamp is, for example, a sticker having an adhesive force stronger than the force with which the PDMS resin 31 holds the chip 11 or a needle having an adhesive attached to the tip thereof. When removing the defective chip, the defective chip is adhered or adhered to the tip of the needle and pulled out from the relay board 14. As described above, the defective chips are only attached to the PDMS resin 31 on the relay board 14, so that each chip can be pulled out individually and easily.

After removing the defective chip, the good chip is rearranged at that position. When chip omission is detected in AOI, a non-defective chip is placed in the missing portion.

As described above, in the present embodiment, the repair for exchanging the defective chip with the non-defective chip is carried out on the relay board 14.

The first repair may be omitted, and after the electrical inspection, the defective chips in the AOI and the electrical inspection may be replaced or the missing chips 11 may be arranged by one repair.

Here, the action of repair in this embodiment will be described.

The repair on the drive board 20 in the prior art is performed after the drive board 20 and the chip 11 are fixed by the solder 13. Therefore, it is not easy to remove the defective chip from the drive board 20. For example, when a defective chip is pulled out from the drive board 20, the drive board 20 may be damaged if a force is applied forcibly. Further, when the solder 13 is melted and pulled out, it is difficult to locally heat only the defective chips, and the solder 13 fixing the peripheral chips 11 is also melted or loosened, so that the peripheral chips other than the defective chips are melted or loosened. Will come off or move.

On the other hand, in the present embodiment, the chip 11 is attached by the PDMS resin 31 formed on the relay substrate 14. Therefore, the force for pulling out the defective chip from the relay board 14 is weaker than the force for pulling out the chip 11 from the drive board 20 in the prior art. Further, in the present embodiment, heating at a high temperature such as solder melting is not required. Therefore, in the present embodiment, only the defective chip can be pulled out from the relay board 14. Therefore, the repair on the relay board 14 according to the present embodiment is easier than the repair on the drive board 20 in the prior art.

AOI and electrical tests, followed by repairs, are repeated. These steps are repeated until the number of defective chips on the relay board 14 becomes less than a predetermined number of defective products. The predetermined number of defective products is determined based on, for example, the number of defective pixels allowed as defective pixels such as non-lighting and insufficient brightness when the display device is finally completed.

Subsequently, the chip 11 is transferred from the relay board 14 to the drive board 20 (joining stage). The drive substrate 20 is formed with an electrode for joining with the chip side electrode 12 together with wiring and a TFT (thin-film-transistor) necessary for supplying electric power to each chip 11 of the micro LED. In the present embodiment, the electrode provided on the drive substrate 20 is referred to as a drive substrate side electrode 21. A part of the metal wiring formed on the drive board 20 may be used as it is, or a metal pad connected to the wiring may be formed on the drive board side electrode 21. For the drive board side electrode 21, the same metal as the chip side electrode 12 described above is used. The top of the drive board side electrode 21 may be left as it is, but micro bumps of the solder 13 may be formed.

FIG. 8 is a schematic cross-sectional view for explaining the transfer of the chip 11 from the relay board 14 to the drive board 20. The transfer of the chip 11 from the relay board 14 to the drive board 20 is performed by fluxless temporary joining (temporary joining stage). As shown in FIG. 8, the temporary bonding is performed with the relay board 14 so that the chip side electrode 12 of the chip 11 attached to the relay board 14 and the drive board side electrode 21 formed on the drive board 20 are in contact with each other. The drive boards 20 are overlapped. After that, while pressurizing the relay board 14 and the drive board 20 in the direction of approaching each other, the whole is heated at a temperature exceeding room temperature and lower than the solder melting temperature. As a result, the chip side electrode 12 and the drive board side electrode 21 are joined. Moreover, even if the temperature is lower than the solder melting temperature, the chip-side electrode 12 and the drive substrate-side electrode 21 are coupled with a certain force.

This means that even if the temperature is lower than the solder melting temperature, the metal atom of tin (Sn), which is the main component of the solder 13, and gold (Au), copper (Cu), or aluminum (Cu), which are the materials of the electrodes, can be pressed by pressurization. This is because a phenomenon occurs in which Al) and the like are diffused and bonded to each other. Regarding this diffusion bonding, the definition of 22702 of JIS standard Z3001-2 states that "the base metal is brought into close contact with each other, and under temperature conditions below the melting point of the base metal, pressure is applied to the extent that plastic deformation does not occur as much as possible, and the diffusion bonding occurs between the bonding surfaces. It is defined as "a method of joining using the diffusion of atoms". For other references, see Kajihara Laboratory, Department of Materials Physical Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology "Au-Sn-based solid-phase reaction diffusion" URL = http: //j2www.materia.titech.ac. There is jp / kajihara / chapters / chap01 / detail.html.

The heating temperature and pressing force differ depending on the material of the solder 13 used for the micro bumps on the chip side electrode 12. For example, in the case of SAC (Sn96.5%, Ag3.0%, Cu0.5%), the melting point is 217 to 220 ° C. Therefore, at the time of temporary joining, for example, it is preferable to heat the solder so that the temperature of the solder is 200 to 216 ° C., and the pressing force for pressurizing the relay board 14 to the drive board side electrode 21 is 0.5 to 1. It is preferably 0.0 MPa.

By setting the temperature and the pressing force within this range, the chip 11 and the drive substrate 20 can be joined without melting the solder 13. Further, within this temperature range, the PDMS resin 31 does not deteriorate.

No flux is used for joining the chip 11 and the drive substrate 20 at this stage. Therefore, the interface between the solder 13 of the chip side electrode 12 and the drive board side electrode 21 can be joined without the presence of components other than metal.

Subsequently, the relay board 14 is removed from the chip 11 (relay board separation step). FIG. 9 is a schematic cross-sectional view showing the drive board 20 after the relay board 14 is removed from the chip 11.

To remove the relay board 14 from the chip 11, the relay board 14 is peeled off from the chip 11. As described above, the chip 11 on the relay board 14 is only attached to the PDMS resin 31. Therefore, the force of the chip 11 on the relay board 14 adhering to the PDMS resin 31 is weaker than the force of being temporarily joined to the drive board 20. Therefore, the relay board 14 can be easily peeled off from the chip 11, so that the chip 11 is temporarily joined to the drive board 20 as shown in FIG.

After that, the drive substrate 20 is heated to a temperature equal to or higher than the solder melting temperature to firmly bond the chip 11 and the drive substrate side electrode 21 (reflow stage). FIG. 10 is a schematic cross-sectional view showing the drive substrate 20 after reflow.

In reflow, flux is applied to the surface of the drive substrate 20 on which the chip 11 is placed (flux application stage) before heating. At this reflow stage, the interface between the solder 13 and the drive board side electrode 21 is already joined. Therefore, the applied flux does not penetrate the interface between the solder 13 and the drive board side electrode 21. When reflowing in this state, as shown in FIG. 10, when the solder 13 is melted and then solidified (eutectic metallization), the chips 11 can be mounted in a state of being well aligned by the self-alignment effect. Further, in the present embodiment, since the flux is applied and then the reflow is performed, the solder 13 is slightly rotated around the electrodes protruding from the substrate surface, and the chip side electrodes 12 and the drive board side electrodes 21 are made stronger. Be joined.

In the present embodiment, the solder 13 which is a micro bump formed on the chip side electrode 12 and the drive board side electrode 21 become eutectic metal by reflow and are firmly bonded. Further, in the present embodiment, only the solder 13 (metal material) is interposed between the chip side electrode 12 and the drive substrate side electrode 21, and the flux component is not present and the bonding is performed.

When the size of the relay board 14 is smaller than that of the drive board 20, all the chips 11 are first transferred from the relay board 14 to the drive board 20 by temporary joining. After that, the entire drive board 20 is reflowed.

In the reflow stage, reflow may be performed without applying flux. Even if no flux is applied, the solder 13 and the drive substrate side electrode 21 can be eutectic metallized and firmly bonded by being heated to a temperature equal to or higher than the melting point of the solder 13.

Here, the operation of electrode bonding in the present embodiment will be described. 11 and 12 are schematic enlarged cross-sectional views showing a state after reflow of the chip joining portion, FIG. 11 shows a conventional joining state and shows the time when a defect occurs, and FIG. 12 shows a joining state according to the present embodiment. Shown.

In conventional bonding, flux is applied to the electrode surface on the drive board side before reflow. Therefore, in the conventional bonding, when the solder 13 of the microbumps on the chip side electrode 12 is brought into contact with the drive board side electrode 21, a flux component is present at the interface between the solder 13 and the drive board side electrode 21. .. Therefore, in the conventional bonding, when reflow heating is performed in this state, the flux component expands near the interface and void 50 is generated, as shown in FIG. The generation of voids 50 causes defects such as tilting of the chip 11. In particular, since the chip 11 of the micro LED is extremely small, if it is worse, the chip 11 will come off due to the generation of the void 50.

On the other hand, in the present embodiment, since the solder 13 and the drive board side electrode 21 are in complete contact with each other by temporary bonding before the reflow, flux does not enter the bonding interface. Therefore, in the present embodiment, the solder 13 is eutectic with the metal of the drive board side electrode 21 as it is at the time of reflow. Therefore, in the present embodiment, as shown in FIG. 12, the void 50 due to the flux component is not generated by the reflow. Therefore, in the present embodiment, the tip 11 does not tilt or come off in the reflow stage.

<Example>
As an example, according to the above-described embodiment, a display in which a micro LED is mounted on a drive board 20 is manufactured.

In this embodiment, a large number of micro LEDs are collectively mounted on a drive substrate 20 formed of a non-alkali glass substrate. In actual manufacturing, the size of the drive substrate 20 corresponds to the display size, and the number of pixels corresponds to the resolution of the display. In this embodiment, for the experiment, the size of the drive substrate 20 is 35 × 35 mm, and the number of pixels (that is, the number of chips) is 80 × 80 × RGB.

A TFT, wiring, and Cu electrode pads are formed on the drive substrate 20. The electrode pad corresponds to the drive board side electrode 21 in the description of the embodiment. The number of electrode pads is formed according to the number of pixels, that is, the number of micro LED chips 11 to be joined.

As the relay board 14, a non-alkali glass board having the same size as the drive board 20 and a thickness of 0.7 mm was used. PDMS resin 31 was formed on the relay substrate 14 with a thickness of 10 μm.

To form the PDMS resin 31, the PDMS resin 31 was coated on the surface of the substrate with a uniform film thickness by laminating, and heated in an oven at 100 ° C. for 1 hour to thermally crosslink the PDMS resin 31. The PDMS resin 31 was prepared by blending Shin-Etsu Silicone SIM360 and CAT360 manufactured by Shin-Etsu Chemical Co., Ltd. to adjust the hardness of the finished product. The hardness of the finished product (after thermal cross-linking) was rubber hardness Shore A60.

The micro LED chip 11 was diced from the sapphire substrate 101 on which the semiconductor layer 102 was formed, transferred to the holding substrate 112, and then further transferred to the relay substrate 14. A chip-side electrode 12 is formed on the chip 11, and micro-bumps made of solder 13 having a height of 5 μm are formed on the electrode. SAC (SnAgCu) was used as the solder 13.

In the transfer to the relay board 14, the micro LED chips 11 were arranged on the relay board 14 at the pixel pitch of the product by using stamps. The chip side electrode 12 of the chip 11 is exposed.

Next, after removing the resin residue remaining on the chip 11 on the relay substrate 14 and the chip side electrode 12 with an oxygen asher, an Ar plasma treatment treatment was performed.

Next, by AOI inspection, appearance defects such as inclination of the chip 11 on the relay board 14, uneven height, and absence of the chip 11 were detected, and the defective chip and the absence were replaced and rearranged. ..

Next, the probe was brought into contact with the chip-side electrode 12 on the relay substrate 14 to perform an electrical inspection, and defective chips whose lighting defects, brightness, emission spectrum, etc. were out of specification were replaced and rearranged.

This AOI inspection and the first repair, and the electrical inspection and the second repair are repeated several times to replace all the defective chips from the relay board 14 with non-defective products so that the relay board 14 becomes 100% non-defective chips. I made it. That is, on the relay board 14 after the repair, the chips 11 are arranged without excess or deficiency, and are composed only of non-defective products without non-lighting chips.

Both the first repair and the second repair were easy without requiring a large force when pulling out the defective chip from the relay board 14. Further, the non-defective chip for replacement could be easily attached to the PDMS resin 31 on the relay board 14.

Next, after the drive substrate 20 and the relay substrate 14 were aligned, they were collectively bonded at a position where the electrodes overlap at a temperature equal to or lower than the solder melting temperature. As a result, the chip-side electrode 12 and the drive board-side electrode 21 are temporarily joined via the solder 13.

Next, the relay substrate 14 was peeled off and removed. All the chips 11 were bonded to the drive substrate 20, and the absence of the chips was not confirmed.

Next, an electrical inspection was carried out via the drive board 20. A few defective chips were detected, but they could be easily replaced. In this embodiment, since it is in a temporary bonding state at this stage, the defective chips can be easily removed by heating to a temperature lower than the melting point of the solder 13. Then, the non-defective chip may be temporarily joined while locally heating the mounting position at a temperature lower than the melting point of the solder 13. Therefore, in this embodiment, the defective chips can be replaced one by one on the drive board 20, and the defective chips can be replaced more easily than the chips 11 bonded to the drive board 20 by the conventional manufacturing method. ..

Next, a flux was applied to the surface of the drive substrate 20 to which the chips 11 were temporarily joined, and heat treatment was performed in the reflow furnace at a temperature equal to or higher than the solder melting temperature. By this reflow, in this embodiment, the solder 13 which is a micro bump formed on the chip side electrode 12 and the drive board side electrode 21 are firmly bonded to each other as a eutectic metal. Further, in the reflow, the micro LED chip 11 was mounted in a state of being well aligned by the self-alignment effect when the solder 13 was melted and then eutectic metallized.

The defect rate (= defective chips / total number of chips) according to this example was 0.01% (2/19, 200).

For comparison, a display device was manufactured by a manufacturing method to which the present invention is not applied (comparative example).

In the comparative example, the relay board, the drive board, the number of chips, and the micro LED chip are the same as those in the embodiment. In the comparative example, the micro LED chip was adhered to the relay substrate with an epoxy resin. After that, in the comparative example, the chip is positioned from the relay board to the drive board after flux application without performing repair on the relay board, and as it is (without temporary joining), at a temperature suitable for joining above the solder melting point. Reflow was performed. For transfer from the relay board to the drive board, the chip was separated from the epoxy resin by laser lift-off. Therefore, in the comparative example, the relay board coated with the silicone resin is not used, and the repair on the relay board is not performed.

In the comparative example, the defective rate was 0.8% (154/19, 200). The defect rate of 0.8% corresponds to the number of defective chips of 199,065 when corresponding to the number of 4K pixels (3,840 x 2,160 x RGB), and it takes an enormous amount of time to repair all of them. Therefore, it is not realistic.

In the case of the above-described embodiment, the number of defective chips detected on the drive substrate 20 after completion is extremely smaller than that of the manufacturing method of the comparative example, and therefore, it is suitable for manufacturing a high-quality display device.

According to the embodiments and examples described above, the following effects are obtained.

In the embodiment and the embodiment, the chip side electrode 12 and the drive board side electrode 21 are bonded without flux. Therefore, the interface between the solder 13 of the chip side electrode 12 and the drive board side electrode 21 does not contain any component other than metal. Therefore, in the display device according to the present embodiment and the embodiment, the generation of voids 50 is extremely small at the bonding interface of the chip 11. Therefore, the manufacturing method of the display device according to the present embodiment and the embodiment can extremely reduce the bonding failure of the chip 11 on the drive substrate 20. Therefore, in the present embodiment, the replacement of defective chips on the drive substrate 20 can be extremely reduced, and the decrease in yield can be suppressed.

Further, in the present embodiment, since the generation of voids in the chip joint portion is extremely small, a highly reliable micro LED module (display device) can be manufactured. Such a display device according to the present embodiment and the embodiment is suitable for applications requiring high durability and high reliability, such as signage that may be installed outdoors and an in-vehicle display that causes a lot of vibration, and a wide range of displays. Products can be provided.

Further, in the embodiment and the embodiment, by arranging the chips 11 on the relay board 14 using the silicone resin, the appearance inspection and the electrical inspection on the relay board 14 are carried out, and the defective chips are repaired. It was decided to. As a result, it becomes much easier to replace the defective chip as compared with the repair that has been conventionally performed after mounting the drive board. Therefore, the yield when the chip 11 is mounted on the drive board 20 is improved.

Although the embodiments and examples of the present invention have been described above, various modifications are possible.

In the above-described embodiment, the chip 11 and the drive substrate 20 are joined by directly joining the chip side electrode 12 and the drive substrate side electrode 21 on which microbumps formed by the solder 13 are formed. However, the bonding between the chip 11 and the drive substrate 20 is not limited to this. The chip 11 and the drive substrate 20 can be joined, for example, by laminating the surface of the drive substrate 20 on which the electrodes are located with an ACF (anisotropic conductive film) or an NCF (Non Conductive Film) to join the chip 11. ..

As described above, even in the bonding using ACF or NCF, the repair on the relay board 14 is carried out, so that the defect of the chip after bonding to the drive board 20 can be extremely reduced.

Further, after performing inspection and repair on the relay board 14, flux may be applied to the drive board 20, the chip 11 may be transferred, and then the solder may be reflowed and joined by heating. In this case, there is a merit in the process that the chip can be transferred at room temperature. Also in this case, by performing inspection and repair on the relay board 14, it is possible to extremely reduce chip defects after joining the chip 11 to the drive board 20.

Further, as one embodiment, a resin material (for example, a silicone resin such as PDMS resin) is formed on a substrate to be a relay substrate, and an intermediate for manufacturing a display device in which a plurality of micro light emitting elements are attached to the resin material is provided. Can be provided. As an embodiment of this display device manufacturing intermediate, a plurality of chips 11 are arranged on a relay board 14 at a predetermined arrangement pitch, as described above. In the intermediate for manufacturing a display device, the chips 11 are arranged in just proportion to the predetermined number used as the display device on the relay board 14, and defective elements such as insufficient brightness including non-lighting are predetermined defects. It is provided in a state of less than the number of items.

The present invention can be modified in various ways based on the configurations described in the claims, and these are also within the scope of the present invention.

11 chips,
12 Chip side electrode,
13 Solder,
14 Relay board,
20 drive board,
21 Drive board side electrode,
31 PDMS resin,
50 voids,
101 sapphire substrate,
102 Semiconductor layer,
112 Retaining substrate.

Claims (12)

It is a method of manufacturing a display device each having a plurality of micro light emitting elements each having an electrode on the element side.
A relay stage in which a plurality of the micro light emitting elements are held on the relay substrate so that the element side electrodes are exposed, and
A joining step in which a plurality of the micro light emitting elements are transferred from the relay board onto a drive board having a drive board side electrode to join the element side electrode and the drive board side electrode.
A method of manufacturing a display device. The relay stage is
It has an adhesion step in which the micro light emitting element is attached to the resin material formed on the relay substrate.
After the relay stage
The element-side electrode of the micro-light emitting element held on the relay substrate is energized to detect a defective element whose emission brightness is less than a predetermined value and / or a defective element which does not satisfy a predetermined emission spectrum. , An electrical inspection stage that stores the position of the defective element,
It further has a repair step of removing the defective element from the relay board based on the position of the defective element and attaching a new micro light emitting element to the relay board in place of the removed defective element.
The method for manufacturing a display device according to claim 1, wherein the electrical inspection step and the repair step are repeated until the number of defective elements becomes less than a predetermined number of defective products, and then the joining step is carried out. The semiconductor layer forming step of forming the semiconductor layer to be the micro light emitting element on the initial substrate, and
The element-side electrode forming step of forming the element-side electrode on the semiconductor layer, and
It further includes a holding substrate transfer stage in which the semiconductor layer is divided into the micro light emitting elements and transferred to the holding substrate.
In the holding substrate transfer step, the micro light emitting elements are arranged on the holding substrate at a predetermined arrangement pitch so that the electrode side on the element side faces the holding substrate side.
The relay stage is
The method for manufacturing a display device according to claim 1 or 2, wherein the micro light emitting element is transferred from the holding substrate to the relay substrate so that the electrode on the element side is exposed. The joining step is
The melting temperature of the solder is fused between the element-side electrode and the drive board-side electrode by fluxlessly facing each other via solder and pressurizing the relay board and the drive board in a direction in which they are relatively close to each other. A temporary joining step in which the element-side electrode and the drive board-side electrode are crimped via solder by heating at a temperature lower than
After the pressurization is released, the relay board separation step of removing the relay board from the micro light emitting element, and
A reflow stage in which the drive substrate to which the micro light emitting element is crimped is heated at a temperature equal to or higher than the melting temperature of the solder.
The method for manufacturing a display device according to any one of claims 1 to 3. After the relay board separation step,
Further, a flux application step of applying flux to the surface of the drive substrate having the micro light emitting element is provided.
The method for manufacturing a display device according to claim 4, wherein the reflow step is carried out after the flux application step. The method for manufacturing a display device according to any one of claims 1 to 5, wherein the relay board transmits 50% or more of visible light. With a micro light emitting element
The element-side electrode provided on the micro-light emitting element and
A drive board on which the plurality of micro light emitting elements are mounted, and
The drive board side electrodes provided on the drive board and
A metal material that joins the element-side electrode and the drive board-side electrode,
Have,
A display device in which no flux is present at the interface between the element-side electrode and the metal material and / or at the interface between the drive substrate-side electrode and the metal material. The metal material is
The display device according to claim 7, further comprising a eutectic metal of the solder and the element-side electrode and / or a eutectic metal of the solder and the drive board-side electrode. The display device according to claim 7 or 8, wherein the element-side electrode and the drive substrate-side electrode have at least one metal selected from the group consisting of copper, gold, and aluminum. With a micro light emitting element
With the relay board
The resin material formed on the relay board and
Have,
An intermediate for manufacturing a display device, wherein a plurality of the micro light emitting elements are attached to the resin material at a predetermined arrangement pitch. The tenth aspect of the present invention, wherein the plurality of micro light emitting elements are arranged on the relay substrate in just proportion to a predetermined number, and the number of defective elements having less than the predetermined emission brightness is less than the predetermined number of defective products. Intermediate for manufacturing display equipment. The intermediate for manufacturing a display device according to claim 10 or 11, wherein the relay board transmits 50% or more of visible light.

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