Method for connecting electrode pad of micro LED and display device manufactured thereby

Abstract

A method for connecting an electrode pad of a micro LED according to the present invention comprises: a transfer preparation step for providing at least one carrier substrate on which an LED chip is attached; a backplane providing step for providing a backplane on which an electrode pad is provided; a transfer step for transferring the LED chip on the carrier substrate onto the backplane; and a step for providing a plating layer between the electrode pad of the LED chip and the electrode pad of the backplane. According to the present invention, corrosion of a connection area of the micro LED electrode pad can be prevented.

Description

Method for connecting electrode pads of micro LED and display device manufactured thereby

[0001] The present invention relates to a method for connecting electrode pads of a micro LED and a display device manufactured thereby, and more particularly, to a method for connecting pads of a backplane and electrode pads of a micro LED and a display device manufactured using the same.

[0002] A light-emitting diode (LED) is a type of light-emitting device that emits light when current is applied. Because LEDs can emit high-efficiency light at low voltages, they offer excellent energy-saving benefits.

[0003] Recently, the brightness problem of light-emitting diodes has been greatly improved, and they are being applied to various devices such as backlight units of liquid crystal displays, electronic billboards, indicators, and home appliances.

[0004] The size of micro light-emitting diodes (μ-LEDs) is very small, at the level of 1 to 100 μm, and approximately 25 million pixels are required to implement a 40-inch display device.

[0005] Therefore, there is a problem that it takes at least a month to manufacture one 40-inch display device using a simple pick and place method.

[0006] Conventional micro light-emitting diodes (μ-LEDs) are manufactured in multiple units on a sapphire substrate, and then transferred one by one to a glass or flexible substrate using a mechanical transfer method called pick and place.

[0007] Electrical connections between existing micro LED pads and backplane pads have relied on solder or eutectic bonding. While solder has been widely used in existing SMT methods, it is not feasible due to the dimensional limitations of micro LED chips, which can lead to short circuits. Furthermore, eutectic bonding requires high temperatures and high pressures, as well as precise alignment between the micro LED pads and the backplane pads. Furthermore, backplane flatness issues hinder electrical connection. Therefore, research and development is needed to address these electrical connection challenges.

[0008] [Prior Art Literature]

[0009] [Patent Document]

[0010] (Patent Document 1) Korean Patent Publication No. 10-2020-0106701 (Published: September 15, 2020)

[0011] (Patent Document 2) Korean Patent Publication No. 10-2021-0054436 (Published: May 13, 2021)

[0012] (Patent Document 3) Korean Patent Publication No. 10-2023-0025713 (Published: February 22, 2023)

[0013] The present invention has been conceived in consideration of the aforementioned technical requirements, and introduces copper (Cu) plating technology for electrical connection of a backplane. That is, the purpose of the present invention is to provide a method for electrically connecting a micro LED pad and a backplane pad using a photoresist layer and copper electroless plating.

[0014] The micro LED electrode pad connection method according to the present invention for achieving the above object includes a transfer preparation step of providing one or more carrier substrates to which LED chips are attached, a backplane providing step of providing a backplane on which electrode pads are formed, a transfer step of transferring an LED chip on the carrier substrate onto the backplane, and a step of forming a plating layer between the electrode pads of the LED chip and the electrode pads of the backplane.

[0015] And, in the above transfer step, electrical connection may not be made between the electrode pads of the LED chip and the electrode pads of the backplane.

[0016] In addition, the method may further include an LED chip growth step of growing an R LED chip, a G LED chip, and a B LED chip on one or more wafers; and the transfer preparation step may include a step of attaching the R LED chip to a first carrier substrate; a step of attaching the G LED chip to a second carrier substrate; and a step of attaching the B LED chip to a third carrier substrate.

[0017] And, the step of providing the backplane may include a step of forming (+) pads and (-) pads spaced apart by a predetermined distance on the backplane; and a step of forming a patterned photoresist between the (+) pads and the (-) pads.

[0018] Additionally, the height of the (+) pad and (-) pad may be lower than the height of the photoresist.

[0019] And, the step of forming the photoresist may include a step of forming a photoresist coating layer on the backplane on which the (+) pad and (-) pad are formed; a step of placing a photomask on the photoresist coating layer; and a step of irradiating ultraviolet rays onto the photomask.

[0020] Additionally, the patterned photoresist can separate the electrode pads of the LED chip transferred from the carrier substrate to the backplane from the electrode pads of the backplane.

[0021] In addition, the step of forming the plating layer may include a first plating step for electrical connection between the electrode pad of the LED chip and the electrode pad of the backplane; and a second plating step for preventing corrosion of a connection area between the electrode pad of the LED chip and the electrode pad of the backplane.

[0022] In addition, the first plating step may include a step of adsorbing palladium (Pd) on a part or the entire area of ​​the electrode pad of the LED chip and the electrode pad of the backplane; and a step of performing electroless plating on the area where the palladium is adsorbed to form a copper (Cu) layer between the electrode pad of the LED chip and the electrode pad of the backplane.

[0023] And, the second plating step can be performed using ENIG (electroless nickel immersion gold) plating on the exposed copper layer.

[0024] Meanwhile, a display device according to the present invention for achieving the above purpose can be manufactured by the above method for connecting electrode pads of the micro LED.

[0025] Meanwhile, a display device according to the present invention for achieving the above object includes: a backplane having a plurality of first electrode pads formed thereon; a plurality of LED chips disposed on the backplane and including second electrode pads; and a plating layer formed between the first electrode pads and the second electrode pads to form an electrical connection between the first electrode pads and the second electrode pads.

[0026] And, the plating layer includes a copper plating layer formed between the first electrode pad and the second electrode pad; and an ENIG (electroless nickel immersion gold) plating layer formed on the copper plating layer.

[0027] In addition, it may further include a photoresist layer formed in an area between the (+) pad and the (-) pad of the first electrode pad and an area between the (+) pad and the (-) pad of the second electrode pad.

[0028] And, the photoresist layer may have a height that is the sum of the height of the first electrode pad, the height of the second electrode pad, and the height of the plating layer.

[0029] According to the present invention, the following technical effects can be achieved.

[0030] ① It is possible to prevent corrosion of the connection area of ​​the micro LED electrode pad.

[0031] ② By introducing a patterned photoresist layer, micro LEDs can be stably arranged on the backplane.

[0032] ③ The micro LED is adhered to the backplane with a photoresist layer, ensuring strong adhesion.

[0033] ④ By electrically connecting the micro LED pad and the pad of the backplane through Cu plating, low contact resistance can be achieved.

[0034] ⑤ Since electrical connection is made by pure Cu plating without pressurization, the flatness issue of the backplane is not very important.

[0035] ⑥ The presence of a patterned photoresist layer between the micro LED chip pads fundamentally blocks short-circuit issues.

[0036] Figures 1a to 1f are drawings for explaining each process of a method for connecting electrode pads of a micro LED according to the present invention.

[0037] Figures 2a to 2m illustrate a method for manufacturing a display device according to the present invention.

[0038] In the description of the embodiment, when it is described as being formed “above or below” each component, “above” or “below” includes both two components being in direct contact with each other or one or more other components being disposed between two components.

[0039] Additionally, when expressed as "upper or lower", it can include the meaning of not only the upward direction but also the downward direction based on one component.

[0040] In the drawings, the thickness and size of each layer are exaggerated, omitted, or schematically illustrated for convenience and clarity. Furthermore, the size of each component does not entirely reflect its actual size.

[0041] The chip used in the present invention is a concept that includes LED chips, RGB chips, R chips, G chips, B chips, mini LED chips, and micro LED chips. Hereinafter, for convenience of explanation, the chip is described as an R LED chip, G LED chip, or B LED chip, but it should be noted that the chip is not limited to only an R chip, G chip, or B chip.

[0042] Figures 1a to 1f are drawings for explaining each process of a method for connecting electrode pads of a micro LED according to the present invention.

[0043] The method for connecting electrode pads of a micro LED according to the present invention includes a transfer preparation step, a backplane provision step, a transfer step, and a plating layer creation step.

[0044] First, as illustrated in Fig. 1a, one or more carrier substrates (10) having LED chips (20) attached thereto are provided. The LED chips (20) include light-emitting elements (21) and electrode pads (22). At this time, one or more carrier substrates (10) may be carrier substrates for transferring R LED chips, G LED chips, and B LED chips, respectively, or simultaneously.

[0045] Before the transfer preparation step of attaching the LED chip (20) to the carrier substrate (10), an LED chip growth step of growing an R LED chip, a G LED chip, and a B LED chip on one or more wafers may be performed. Specifically, the LED chip growth may be performed by a process of growing an epitaxial layer that emits a predetermined light on one surface of each of three wafers, and forming an electrode pad on each of the grown epitaxial layers. Here, the wafer may be any one of sapphire (Al2O3), silicon, gallium arsenide (GaAs), gallium nitride (GaN), and zinc nitride (ZnN). However, the present invention is not limited thereto, and any substrate that can be used as a wafer may be used. In addition, in other embodiments, the formation of the LED chip may be performed by employing various existing methods, and the present invention is not limited to a specific LED chip formation process.

[0046] Each LED chip can be manufactured into a new concept of small package in the form of a CSP by configuring sub-pixels for R, G, and B, respectively. The R LED chip, the G LED chip, and the B LED chip can constitute a single light-emitting element or light-emitting body. Each chip is attached to a carrier substrate (10) in multiple rows and columns, and can be sequentially and selectively transferred from the carrier substrate (10) to a backplane (110) to be described later.

[0047] In order to form an RGB pixel array, transfer preparation steps for transferring the R LED chip, the G LED chip, and the B LED chip may be performed respectively. Specifically, the transfer preparation step may include a step of attaching the R LED chip to a first carrier substrate, a step of attaching the G LED chip to a second carrier substrate, and a step of attaching the B LED chip to a third carrier substrate. The process of attaching the LED chip to the carrier substrate may be performed in various ways.

[0048] The transfer of the LED chip from the wafer to the carrier substrate (10) can be performed using a glass substrate (not shown). Specifically, the glass substrate is attached to the LED chip in the opposite direction of the wafer. That is, the glass substrate is attached to the electrode pad side of the LED chip. The glass substrate may include a base substrate and a photosensitive transfer resin layer, and the base substrate may be composed of any one of glass, quartz, synthetic quartz, and metal, but is not limited thereto. In addition, the photosensitive transfer resin layer may be a photosensitive resin containing a photoactive agent of a predetermined weight percent (wt%) or more. Thereafter, when the wafer is removed by an LLO (Laser Lift Off) or CLO (Chemical Lift Off) process, the LED chip (20) is placed in a state in which it is attached to the glass substrate, and at this time, the direction of the LED chip (20) is arranged in a state in which the light-emitting body is exposed in the opposite direction. The glass substrate may include a glass substrate having an R LED chip attached, a glass substrate having a G LED chip attached, and a glass substrate having a B LED chip formed thereon. Thereafter, each LED chip is selectively transferred from the glass substrate to the carrier substrate (10). The selective transfer from the glass substrate to the carrier substrate (10) begins with first placing the carrier substrate (10) on the glass substrate having the LED chip array formed thereon. At this time, the adhesive layer of the carrier substrate (10) is brought into contact with the LED chips so that they are attached to each other. Here, the carrier substrate (10) may include an adhesive layer. With the glass substrate and the carrier substrate (10) facing each other with the LED chips interposed therebetween, a mask is placed on the back surface of the glass substrate, and then UV is irradiated. Only a specific area of ​​the photosensitive transfer resin layer can be exposed by the pattern of the mask and the UV irradiation. Here, the degree of exposure can be adjusted by controlling the UV irradiation amount (UV Exposure Energy).The exposed portion of the photosensitive transfer resin layer according to the UV irradiation amount can be called a photo-active layer (Photo-induced Activation). When heat is applied to the photo-active layer, the resin layer expands and the adhesive force of the LED chip is reduced to zero, so that only the LED chip at the corresponding position can be selectively transferred from the glass substrate to the carrier substrate (10). When heat is applied to the upper portion of the glass substrate, the temperature at which the resin layer can expand becomes high, the volume of the resin layer expands, and the position at which the volume can expand may be the area where the photo-active layer exists. At this time, the heat applied to the upper portion of the glass substrate may mean the temperature at which the resin layer can expand. The expanded resin layer increases in size, and the pressure (expansion force) when the volume expands pushes out the LED chip, thereby reducing the adhesive force of the LED chip to zero, and the LED chip adhered to the corresponding position is peeled (or transferred) so that it can be transferred to the carrier substrate (10). By this, only specific LED chips can be selectively peeled and transferred from the glass substrate to the carrier substrate (10). The transfer of the LED chip to the carrier substrate (10) described above is only one embodiment, and various existing transfer methods can be used in other embodiments.

[0049] When the transfer preparation step for transferring the LED chip from the carrier substrate (10) to the backplane (110) is completed, a backplane (110) to which the LED chip (20) is to be transferred is provided (backplane provision step), as illustrated in FIG. 1B. Here, the backplane (110) may be a TFT (Thin Film Transistor) substrate, but is not limited thereto. An electrode pad (120) including a (+) pad and a (-) pad for electrical connection with the LED chip (20) is formed on the backplane (110).

[0050] Meanwhile, as illustrated in FIG. 1c, a photoresist (130) may be formed between the (+) pad and the (-) pad constituting the electrode pad of the backplane (110). Consequently, the backplane providing step may include a step of forming (+) pads and (-) pads spaced apart by a predetermined distance on the backplane (110), and a step of forming a patterned photoresist (130) between the (+) pad and the (-) pad. Since the patterned photoresist (130) exists between the micro LED chip pads, a short circuit issue can be fundamentally prevented. In addition, by introducing the patterned photoresist (130), the micro LED chip (20) can be stably arranged on the backplane (110), and since the micro LED chip (20) is adhered to the backplane (110) with the photoresist (130), a strong adhesive force can be secured. The step of forming the photoresist (130) will be described in more detail below.

[0051] At this time, the height of the (+) pad and (-) pad of the backplane (110) may be lower than the height of the photoresist (130) formed therebetween. More specifically, the sum of the height of the electrode pad (120) of the backplane (110) and the height of the electrode pad (22) of the LED chip may be lower than the height of the photoresist (130). Therefore, the photoresist (130) separates the electrode pad (22) of the LED chip and the electrode pad (120) of the backplane (110) by a predetermined distance. By adjusting the thickness of the photoresist (130), the separation distance between the electrode pad (22) of the LED chip and the electrode pad (120) of the backplane (110) can be maintained at 1 to 5 μm. In addition, due to this, in the transfer step (LED chip movement step) described later, electrical connection is not made between the electrode pads of the LED chip and the electrode pads of the backplane, and a separate plating process for electrical connection is included. That is, the gap between the electrode pads (22) of the LED chip and the electrode pads (120) of the backplane (110) is electrically connected through copper plating.

[0052] Next, a transfer step is performed to transfer the LED chip (20) on the carrier substrate (10) onto the backplane (110), as illustrated in FIG. 1D. As illustrated in FIG. 1D, since the sum of the height of the electrode pad (120) of the backplane (110) and the height of the electrode pad (22) of the LED chip is smaller than the height of the photoresist (130), the electrode pad (22) of the LED chip and the electrode pad (120) of the backplane (110) do not contact each other.

[0053] Meanwhile, the transfer step of transferring the LED chips (20) from the carrier substrate (10) to the backplane (110) can be performed in various ways. After the LED chips are transferred (attached) to the carrier substrate (10), a method of sequentially and selectively transferring the LED chips (20) attached to the carrier substrate (10) to the backplane (110) will be briefly described. First, the backplane (110) is placed on the carrier substrate (10) on which the LED chips (20) are formed. A plurality of electrode pads (120) can be formed on the backplane (110). The backplane (110) can be defined to include a structure in which a display panel and a TFT array substrate are arranged vertically. The LED chips (20) attached to the carrier substrate (10) are placed so as to face the backplane (110), and the electrode pads (22) of the LED chips (20) are arranged on the electrode pads (120) of the backplane (110). That is, the carrier substrate (10) and the backplane (110) are placed facing each other with the LED chip (20) in between. Then, heat or a laser is applied to the upper portion of the carrier substrate (10) to transfer all the LED chips from the carrier substrate (10) to the backplane (110). By repeatedly performing these processes, it is possible to sequentially transfer R, G, and B LED chips onto the backplane (110).

[0054] Thereafter, when the transfer of the LED chip to the backplane (110) is completed, a step of forming a plating layer for electrical connection between the electrode pad (22) of the LED chip and the electrode pad (120) of the backplane (110) is performed, as illustrated in FIG. 1e. The plating layer (140) is formed in the space between the electrode pad (22) of the LED chip and the electrode pad (120) of the backplane (110). Electrical connection between the electrode pad (22) of the LED chip and the electrode pad (120) of the backplane (110) is achieved through physical contact between the two via the plating layer (140).

[0055] The formation of the plating layer (140) is carried out in the space between the positive electrode pads (22, 120), as illustrated in FIG. 1f, and an electrical connection between the electrode pads (22, 120) is established through primary plating using electroless copper plating, and a corrosion prevention effect is achieved through secondary plating using ENIG (Electroless Nickel Immersion Gold) plating. The formation process of the plating layer (140) will be described in more detail below.

[0056] Figures 2a to 2m illustrate a method for manufacturing a display device according to the present invention.

[0057] First, as shown in Fig. 2a, a first carrier (10r) for transferring an R LED chip (10r), a second carrier (10g) for transferring a G LED chip (10g), and a third carrier (10b) for transferring a B LED chip (10b) are provided.

[0058] The first to third carriers (10r, 10g, 10b) are provided with R LED chips (20r), G LED chips (20g), and B LED chips (20b) grown on one or more wafers. Specifically, the first carrier (10r) has an R LED chip (20r) grown on a wafer attached to one surface thereof, and the R LED chip (20r) includes an R light-emitting element (21r) and an electrode pad (22r). The second carrier (10g) has a G LED chip (20g) grown on a wafer attached to one surface thereof, and the G LED chip (20g) includes a G light-emitting element (21g) and an electrode pad (22g). The third carrier (10b) has a B LED chip (20b) grown on a wafer attached to one surface thereof, and the B LED chip (20b) includes a B light-emitting element (21b) and an electrode pad (22b). Here, R, G, B can mean red, green, and blue, but are not limited thereto.

[0059] Meanwhile, as illustrated in FIG. 2b, the backplane (110) to which the R LED chip (20r), G LED chip (20g), and B LED chip (20b) described above are to be transferred includes electrode pads (120) to be electrically connected to the electrode pads (22r) of the R LED chip (20r), the electrode pads (22g) of the G LED chip (20g), and the electrode pads (22b) of the B LED chip (20b), respectively. The electrode pads (120) of the backplane (110) may be formed in a pattern corresponding to the RGB pixel array. At this time, the electrode pads (120) of the backplane (110) include (+) pads and (-) pads, and the (+) pads and (-) pads are spaced apart from each other by a predetermined distance.

[0060] Thereafter, as illustrated in FIG. 2c, when an electrode pad (120) is formed on a backplane (110), the upper surface of the backplane (110) including the electrode pad (120) is coated with a photoresist (130) to form a photoresist coating layer. The thickness of the photoresist (130) is preferably thicker than the height of the electrode pad (120).

[0061] Next, as illustrated in FIG. 2d, a photomask (150) is placed on the upper surface of the photoresist (130). The photomask (150) is used to pattern the photoresist (130), and the photoresist (130) remains only in the gap between the (+) pad and the (-) pad constituting the electrode pad (120) of the backplane (110).

[0062] That is, as illustrated in FIG. 2e, when ultraviolet (UV) is irradiated on the photomask, the photoresist existing in the remaining area except for the space between the (+) pad and the (-) pad is etched. Accordingly, as illustrated in FIG. 2f, the photoresist (130) exists between the (+) pad and the (-) pad constituting the electrode pad (120) of the backplane (110). It is preferable that the height (d1) of the photoresist (130) be higher than the height (d2) of the (+) pad / (-) pad. More preferably, the height of the photoresist (130) is preferably greater than the sum of the height of the electrode pad (120) of the backplane (110) and the height of the electrode pad (22) of the LED chip. Furthermore, the height of the photoresist (130) may be equal to the sum of the height of the electrode pad (120) of the backplane (110), the height of the electrode pad (22) of the LED chip, and the height of the plating layer formed therebetween.

[0063] Afterwards, the transfer of the R / G / B LED chip is performed. First, as illustrated in FIG. 2g, the first carrier substrate (10r) to which the R LED chip (20r) is attached is aligned on the backplane (110), and the R LED chip (20r) is transferred from the first carrier substrate (10r) onto the backplane (110). At this time, the electrode pad (22r) of the R LED chip (20r) includes a (+) pad and a (-) pad spaced apart by a predetermined distance, and the R LED chip (20r) can be transferred after the first carrier substrate (10r) and the backplane (110) are aligned so that the (+) pad and the (-) pad of the electrode pad (22r) of the R LED chip (20r) face the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110). At this time, the distance between the (+) pad and the (-) pad of the electrode pad (22r) of the R LED chip (20r) may be the same as the distance between the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110), but is not limited thereto. Even if the R LED chip (20r) is transferred onto the backplane (110), as illustrated in FIG. 2h, the (+) pad and the (-) pad of the electrode pad (22r) of the R LED chip (20r) do not come into contact with the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110) due to the photoresist (130).

[0064] Next, as illustrated in FIG. 2i, a second carrier substrate (10g) having a G LED chip (20g) attached thereto is aligned on a backplane (110), and the G LED chip (20g) is transferred from the second carrier substrate (10g) onto the backplane (110). At this time, the electrode pad (22g) of the G LED chip (20g) includes a (+) pad and a (-) pad spaced apart by a predetermined distance, and the G LED chip (20g) can be transferred after the second carrier substrate (10g) and the backplane (110) are aligned so that the (+) pad and the (-) pad of the electrode pad (22g) of the G LED chip (20g) face the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110). At this time, the distance between the (+) pad and the (-) pad of the electrode pad (22g) of the G LED chip (20g) may be the same as the distance between the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110), but is not limited thereto. Even if the G LED chip (20g) is transferred onto the backplane (110), as illustrated in FIG. 2j, the (+) pad and the (-) pad of the electrode pad (22g) of the G LED chip (20g) do not come into contact with the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110) due to the photoresist (130).

[0065] Next, as illustrated in FIG. 2k, the third carrier substrate (10b) having the B LED chip (20b) attached thereto is aligned on the backplane (110), and the B LED chip (20b) is transferred from the third carrier substrate (10b) onto the backplane (110). At this time, the electrode pad (22b) of the B LED chip (20b) includes a (+) pad and a (-) pad spaced apart by a predetermined distance, and the B LED chip (20b) can be transferred after the third carrier substrate (10b) and the backplane (110) are aligned so that the (+) pad and the (-) pad of the electrode pad (22b) of the B LED chip (20b) face the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110). At this time, the distance between the (+) pad and the (-) pad of the electrode pad (22b) of the B LED chip (20b) may be the same as the distance between the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110), but is not limited thereto. Even if the B LED chip (20b) is transferred onto the backplane (110), as illustrated in FIG. 2l, the (+) pad and the (-) pad of the electrode pad (22b) of the B LED chip (20b) do not come into contact with the (+) pad and the (-) pad of the electrode pad (120) formed on the backplane (110) due to the photoresist (130).

[0066] Finally, as shown in FIG. 2m, a plating layer (140) formation process is performed for electrical connection between the electrode pads (22r, 22g, 22b) of the LED chips spaced apart from each other and the electrode pad (120).

[0067] The plating layer (140) may be formed by a two-step plating process. This may consist of a first plating step for electrical connection between the electrode pads of the LED chip and the electrode pads of the backplane, and a second plating step for preventing corrosion of the connection area between the electrode pads of the LED chip and the electrode pads of the backplane.

[0068] The first plating step can be performed using electroless copper plating. This is a method of plating through a chemical reaction rather than using electricity to electrically conduct the inside of a hole after it has been processed on a double-sided PCB. In other words, a hole that can electrically conduct the upper and lower surfaces of the outer layer is plated using electroless copper plating, and the hole formed thereby is also called a PTH (Plated Through-Hole). More specifically, electroless copper plating can use ionic or colloidal catalysts. Electroless copper plating can be classified into a pretreatment process and a chemical copper plating process. The pretreatment process can include a cleaning process to remove foreign substances on the outside of the plating before starting plating, a soft etching process to remove an oxide film, a pre-dip process to remove foreign substances so that the palladium catalyst can be well adsorbed on the inner wall of the hole, a palladium adsorption process, and an activation process to remove substances other than palladium to facilitate bonding with copper. The chemical copper plating process is a process that enables electrical conduction through chemical copper plating through an oxidation-reduction reaction on palladium adsorbed on the non-conductive portion of the inner wall of the hole.

[0069] Specifically, the first plating step is to adsorb palladium (Pd) to a portion or the entire area of ​​the electrode pads (22r, 22g, 22b) of the LED chip (20r, 20g, 20b) and the electrode pads (120) of the backplane (110), and then perform electroless plating on the area where the palladium (Pd) is adsorbed to form a copper (Cu) layer between the electrode pads (22r, 22g, 22b) of the LED chip (20r, 20g, 20b) and the electrode pads (120) of the backplane (110).

[0070] Meanwhile, the secondary plating step is performed using Electroless Nickel Immersion Gold (ENIG) plating on the exposed copper layer formed by electroless copper plating. This is achieved by electrolessly plating nickel (Ni) onto the exposed copper (Cu) and performing displacement plating to replace the nickel layer on the nickel surface with gold (Au). In other words, displacement occurs due to a difference in reduction potential, which promotes corrosion prevention.

[0071] More specifically, ENIG is a process that involves plating electroless nickel over a copper plating layer, followed by electroless gold plating. Unlike HAL (Hot Air Leveling), ENIG does not contain solder and allows for selective absorption, preventing bridging between patterns or pads.

[0072] Meanwhile, the display device according to the present invention can be manufactured by the method for connecting the electrode pads of the micro LED described above.

[0073] Meanwhile, referring again to FIG. 2m, a display device according to the present invention may include a backplane (110) on which a plurality of first electrode pads (120) are formed, a plurality of LED chips (20r, 20g, 20b) disposed on the backplane (110) and including second electrode pads (22r, 22g, 22b), and a plating layer (140) formed between the first electrode pads (120) and the second electrode pads (22r, 22g, 22b) to form an electrical connection therebetween.

[0074] At this time, the plating layer (140) may include a copper plating layer (not shown) formed between the first electrode pad (120) and the second electrode pad (22r, 22g, 22b) and an ENIG (electroless nickel immersion gold) plating layer (not shown) formed on the copper plating layer (not shown).

[0075] Meanwhile, a photoresist layer (130) formed in an area between the (+) pad and the (-) pad of the first electrode pad (120) and an area between the (+) pad and the (-) pad of the second electrode pad (22r, 22g, 22b) may be further included. At this time, the photoresist layer (130) may have a height that is the sum of the height of the first electrode pad (120), the height of the second electrode pad (22r, 22g, 22b), and the height of the plating layer (140).

[0076] The features, structures, effects, etc. described in the embodiments above are included in at least one embodiment of the present invention, and are not necessarily limited to just one embodiment. Furthermore, the features, structures, effects, etc. exemplified in each embodiment can be combined or modified in other embodiments by those skilled in the art to which the embodiments pertain. Therefore, the contents related to such combinations and modifications should be construed as falling within the scope of the present invention.

[0077] In addition, although the above description focuses on embodiments, these are merely examples and do not limit the present invention. Those skilled in the art to which the present invention pertains will appreciate that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiment. For example, each component specifically shown in the embodiments can be modified and implemented. In addition, differences related to such modifications and applications should be interpreted as being included within the scope of the present invention defined in the appended claims.

[0078] [Explanation of symbols]

[0079] 10, 10r, 10g, 10b: carrier substrate

[0080] 20, 20r, 20g, 20b: LED chips

[0081] 21, 21r, 21g, 21b: LED elements

[0082] 22, 22r, 22g, 22b: Electrode pad (second electrode pad)

[0083] 110: Backplane

[0084] 120: Electrode pad (first electrode pad)

[0085] 130: Photoresist

[0086] 140: Plating layer

[0087] 150: Photomask

Claims

1. A transfer preparation step of providing one or more carrier substrates having LED chips attached thereto; A backplane providing step of providing a backplane on which electrode pads are formed; A transfer step of transferring an LED chip on the carrier substrate onto the backplane; and A method for connecting electrode pads of a micro LED, comprising: forming a plating layer between the electrode pads of the LED chip and the electrode pads of the backplane.

2. In paragraph 1, A method for connecting electrode pads of a micro LED, wherein no electrical connection is made between the electrode pads of the LED chip and the electrode pads of the backplane in the above transfer step.

3. In paragraph 1, Further comprising an LED chip growth step of growing R LED chips, G LED chips and B LED chips on one or more wafers; The above warrior preparation steps are: A step of attaching the R LED chip to the first carrier substrate; A step of attaching the G LED chip to a second carrier substrate; and A method for connecting electrode pads of a micro LED, comprising the step of attaching the B LED chip to a third carrier substrate.

4. In paragraph 1, The above backplane provision step is: A step of forming (+) pads and (-) pads spaced apart by a predetermined distance on a backplane; and A method for connecting electrode pads of a micro LED, comprising: forming a patterned photoresist between the (+) pad and the (-) pad.

5. In paragraph 4, A method for connecting electrode pads of a micro LED, wherein the height of the (+) pad and the (-) pad is lower than the height of the photoresist.

6. In paragraph 4, The step of forming the above photoresist is: A step of forming a photoresist coating layer on the backplane on which the (+) pad and (-) pad are formed; A step of placing a photomask on the photoresist coating layer; and A method for connecting electrode pads of a micro LED, comprising: a step of irradiating ultraviolet rays onto the photomask.

7. In paragraph 6, A method for connecting electrode pads of a micro LED, wherein the patterned photoresist separates the electrode pads of an LED chip transferred from the carrier substrate to the backplane from the electrode pads of the backplane.

8. In paragraph 1, The step of forming the above plating layer is: A first plating step for electrical connection between the electrode pads of the LED chip and the electrode pads of the backplane; and A method for connecting electrode pads of a micro LED, comprising a second plating step for preventing corrosion of a connection area between the electrode pads of the LED chip and the electrode pads of the backplane.

9. In paragraph 8, The above first plating step is, A step of adsorbing palladium (Pd) to a part or the entire area of the electrode pad of the LED chip and the electrode pad of the backplane; and A method for connecting electrode pads of a micro LED, comprising: performing electroless plating on the area where palladium is adsorbed to form a copper (Cu) layer between the electrode pads of the LED chip and the electrode pads of the backplane.

10. In paragraph 9, A method for connecting electrode pads of a micro LED, wherein the second plating step is performed using ENIG (electroless nickel immersion gold) plating on the exposed copper layer.

11. A display device manufactured by the method for connecting electrode pads of a micro LED as described in any one of claims 1 to 11.

12. A backplane having a plurality of first electrode pads formed thereon; A plurality of LED chips arranged on the backplane and including a second electrode pad; and A display device, comprising a plating layer formed between the first electrode pad and the second electrode pad to form an electrical connection between the first electrode pad and the second electrode pad.

13. In paragraph 12, The above plating layer is, A copper plating layer formed between the first electrode pad and the second electrode pad; and A display device comprising an ENIG (electroless nickel immersion gold) plating layer formed on the copper plating layer.

14. In paragraph 12, A display device further comprising a photoresist layer formed in an area between the (+) pad and the (-) pad of the first electrode pad and an area between the (+) pad and the (-) pad of the second electrode pad.

15. In paragraph 14, A display device, wherein the photoresist layer has a height that is the sum of the height of the first electrode pad, the height of the second electrode pad, and the height of the plating layer.

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