A welding method for Mini / Micro LED LED chips

Abstract

The present invention relates to the technical field of LED display, and discloses a method for welding Mini / Micro LED chips. The welding method comprises: placing a provided hydrophobic nano-steel mesh having a plurality of steel holes on a provided substrate having a plurality of solder pads and aligning the mesh so that each steel hole is aligned with each solder pad; adding a provided anisotropic conductive glue to the hydrophobic nano-steel mesh and evenly scraping the hydrophobic nano-steel mesh so that the anisotropic conductive glue is printed on the solder pads; peeling the hydrophobic nano-steel mesh; attaching the provided LED chip to the anisotropic conductive glue located on the solder pads; heating and pressurizing the LED chip located on the anisotropic conductive glue so that the insulating film is longitudinally ruptured to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls are respectively in contact with the LED chip and the solder pads to form a vertical conductive path, and preliminarily solidifying the insulating glue so that the LED chip is welded to the substrate. Stable welding quality is achieved, maintenance difficulty is low, and maintenance cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of LED displays, and in particular to a welding method for Mini / Micro LED chips. Background Art

[0002] Although the reflow process is widely used in electronics manufacturing, it also has some temperature-related disadvantages. The following are the disadvantages of the reflow process when applied to Mini / Micro LED display soldering:

[0003] 1) During the reflow soldering process, the soldering temperature is usually high. High-temperature soldering can easily damage the chip, resulting in unstable soldering quality.

[0004] 2) Furthermore, when a chip fails, the PCB or glass substrate must be heated to a high temperature to melt the solder paste and remove the chip. However, due to the physical phenomena of heat diffusion and heat conduction, the high temperature is quickly transferred to surrounding chips, making it difficult to precisely target the damaged chip with the heating area. This can damage nearby healthy chips and increase the risk during the repair process.

[0005] 3) Because ACF is a single sheet of conductive film, repairing a single chip with a poor connection or malfunction is extremely difficult. Because the film already has thousands of chips connected to it, repairs often require replacing the entire sheet, rendering all chips on the ACF useless and resulting in high repair costs. Summary of the Invention

[0006] The main purpose of the present invention is to provide a welding method for Mini / Micro LED LED chips, aiming to solve the technical problems of unstable welding quality, difficult maintenance and high maintenance cost of existing LED chips.

[0007] To achieve the above objectives, the present invention provides a method for soldering Mini / Micro LED chips, the method comprising: providing a hydrophobic nano-steel mesh having a plurality of steel holes and a substrate having a plurality of solder pads, placing the hydrophobic nano-steel mesh on the substrate, and aligning the mesh so that each of the steel holes is aligned with each of the solder pads, wherein the substrate is a circuit board or a glass substrate;

[0008] Providing anisotropic conductive adhesive, adding the anisotropic conductive adhesive to the side of the hydrophobic nano-steel mesh away from the pad, and evenly applying the anisotropic conductive adhesive to the hydrophobic nano-steel mesh by a doctor blade method, so that the anisotropic conductive adhesive is printed onto the pad through the steel hole;

[0009] peeling off the hydrophobic nano-steel mesh;

[0010] Providing an LED chip, and mounting the LED chip on the anisotropic conductive adhesive located on the pad;

[0011] The LED chip located on the anisotropic conductive adhesive is heated and pressurized through a hot pressing process, so that the insulating film of the anisotropic conductive adhesive is longitudinally ruptured to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls are respectively in contact with the LED chip and the soldering pad to form a vertical conductive path, and the insulating glue of the anisotropic conductive adhesive is initially solidified, so that the LED chip is soldered to the substrate.

[0012] Furthermore, in one embodiment, the step of providing anisotropic conductive adhesive is formed in three steps, including:

[0013] Prepare metal conductive particle balls by mechanical separation process or spraying process;

[0014] Coating a layer of insulating coating on the surface of the metal conductive particle ball through a coating process and air-drying the coating to form an insulating film;

[0015] An insulating glue is provided, and the metal conductive particle balls coated with the insulating film are placed in the insulating glue and stirred to form an anisotropic conductive glue.

[0016] Furthermore, in one embodiment, the material of the insulating film is one or more of a resin, a polymer or a thermoplastic polymer; and / or,

[0017] The material of the insulating glue is modified epoxy resin.

[0018] Furthermore, in one embodiment, the material of the metal conductive particle balls is one or more of tin powder, silver powder, nickel powder, gold powder, tin alloy powder, copper powder, and aluminum powder.

[0019] Furthermore, in one embodiment, the diameter of the metal conductive particle ball is 10 μm-20 μm; and / or,

[0020] The thickness of the insulating film is 3%-25% of the diameter of the metal conductive particle balls.

[0021] Furthermore, in one embodiment, the step of providing an insulating glue includes:

[0022] Providing an insulating glue, placing the metal conductive particle balls coated with the insulating film into the insulating glue, and stirring at a low speed so that the plurality of metal conductive particle balls are evenly distributed in the insulating glue to form an anisotropic conductive glue; or,

[0023] An insulating glue is provided, and metal conductive particle balls coated with the insulating film are placed in the insulating glue. The metal conductive particle balls are stirred by a planetary mixer through a combined motion of rotation and revolution, so that multiple metal conductive particle balls are evenly distributed in the insulating glue to form anisotropic conductive glue.

[0024] Furthermore, in one embodiment, the step of coating a layer of insulating coating on the surface of the metal conductive particle ball by a coating process and air-drying the coating to form an insulating film includes:

[0025] Soaking the metal conductive particle balls in a chemical solution by chemical deposition, forming an insulating coating on the surface of the metal conductive particle balls by chemical reaction, and air-drying the insulating coating to form an insulating film; or

[0026] The insulating coating material is deposited onto the surface of the metal conductive particle ball by physical vapor deposition to form an insulating coating, and the insulating coating is air-dried to form an insulating film.

[0027] Furthermore, in one embodiment, the step of providing a hydrophobic nano-steel mesh having a plurality of steel pores is formed in two steps, including:

[0028] Providing a steel plate, and drilling steel holes on the steel plate corresponding to the welding pads of the substrate to form a steel mesh;

[0029] A layer of nano-hydrophobic coating is coated on the steel mesh to obtain a hydrophobic nano-steel mesh.

[0030] Furthermore, in one embodiment, after the LED chip on the anisotropic conductive adhesive is heated and pressurized by the hot pressing process to longitudinally rupture the insulating film of the anisotropic conductive adhesive to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls respectively contact the LED chip and the soldering pad to form a vertical conductive path, and the insulating adhesive of the anisotropic conductive adhesive is initially cured, so that the LED chip is soldered to the substrate, the method further includes:

[0031] Testing the LED chip;

[0032] When the LED chip is defective, the LED chip is heated to melt the anisotropic conductive adhesive, and the defective LED chip is removed and replaced with a good LED chip.

[0033] Furthermore, in one embodiment, the step of providing an LED chip and mounting the LED chip on the anisotropic conductive adhesive located on the pad includes:

[0034] The LED chip is mounted on the anisotropic conductive adhesive on the pad through a mass transfer process or a SMT process.

[0035] In the technical solution provided by the present invention, the hydrophobic nano-steel mesh and the substrate are first aligned, and the steel holes of each hydrophobic nano-steel mesh are aligned with each soldering pad respectively. Then, anisotropic conductive glue is added to the hydrophobic nano-steel mesh, and the anisotropic conductive glue is evenly scraped on the surface of the hydrophobic nano-steel mesh by scraping, so that the anisotropic conductive glue is printed on the soldering pad; the LED chip is mounted on the anisotropic conductive glue located on the soldering pad, and the insulating film of the anisotropic conductive glue is longitudinally (Z-axis direction) ruptured by heating and pressurizing. The insulating film is exposed to the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls can contact the LED chip and the soldering pad respectively to form a vertical contact. The conductive path is formed, and the insulating glue of the anisotropic conductive glue is initially solidified, so that the LED chip is welded on the substrate. Since the anisotropic conductive glue contains multiple metal conductive particle balls, as long as there is a metal conductive particle ball among the many metal conductive particle balls that is conductive, the LED chip can be normally lit, and it is not necessary for all metal conductive particles to be conductive at the same time, which reduces the difficulty of welding and improves the welding quality. In addition, the insulating glue has an open time of 4 hours to 8 hours. The insulating glue can be melted by reheating, so that the defective LED chip can be easily removed and replaced with a good LED chip without damaging the LED chip, making the maintenance difficulty small and the maintenance cost low. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0037] Figure 1 This is a flow chart of a first embodiment of a method for soldering a Mini / Micro LED chip in an embodiment of the present invention;

[0038] Figure 2 Flowchart of a second embodiment of a method for soldering a Mini / Micro LED chip in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] To facilitate understanding of the present invention, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly attached to the other element, or one or more elements can be interposed therebetween. When an element is described as being "connected to" another element, it can be directly connected to the other element, or one or more elements can be interposed therebetween. The terms "vertical," "horizontal," "left," "right," "inner," "outer," and similar expressions used in this specification are for illustrative purposes only. In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating relative importance or implicitly specifying the number of technical features indicated. Therefore, unless otherwise specified, features specified as "first" or "second" may explicitly or implicitly include one or more of such features; "plurality" means two or more. The term "comprising" and any variations thereof are intended to be non-exclusive, and one or more other features, integers, steps, operations, units, components, and / or combinations thereof may be present or added.

[0040] In addition, unless otherwise expressly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or internal communication between two components. All technical and scientific terms used in this specification have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more related listed items.

[0041] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 1 The first embodiment of the Mini / Micro LED chip welding method in the present invention includes:

[0043] S1. Providing a hydrophobic nano-steel mesh having a plurality of steel holes and a substrate having a plurality of solder pads, placing the hydrophobic nano-steel mesh on the substrate, and aligning the mesh so that each of the steel holes is aligned with each of the solder pads, wherein the substrate is a circuit board or a glass substrate;

[0044] In this step, a substrate having a plurality of pads is provided, and steel holes are opened on the steel plate according to the distribution of the pads of the substrate to form a steel mesh. A hydrophobic nano-coating is coated on the steel mesh to prevent the anisotropic conductive adhesive from adhering to the steel holes to form a hydrophobic nano-steel mesh. After the hydrophobic nano-steel mesh and the substrate are prepared, the substrate is first mounted on a fixture of a steel mesh printer. The fixture has adjustable supports and positioning pins to ensure the accurate position of the substrate. The hydrophobic nano-steel mesh is then fixed to the frame of the printer. The positioning mark (Fiducial Mark) of the substrate is automatically detected by the visual positioning system of the printer for correction, so that the position of the substrate and the hydrophobic nano-steel mesh are aligned, and each steel hole is aligned with each pad, that is, each steel hole is located directly below each pad. The substrate is then fixed to the printing platform by vacuum adsorption or mechanical clamping to prevent movement during the printing process.

[0045] S2. Providing anisotropic conductive adhesive, adding the anisotropic conductive adhesive to the side of the hydrophobic nano-steel mesh away from the pad, and evenly coating the anisotropic conductive adhesive on the hydrophobic nano-steel mesh by a doctor blade method, so that the anisotropic conductive adhesive is printed onto the pad through the steel holes;

[0046] In this step, anisotropic conductive adhesive is applied to the surface of a hydrophobic nano-steel mesh using a squeegee (typically made of metal or polyurethane) in a stencil printer. The adhesive is then applied along the hydrophobic nano-steel mesh at a set speed and pressure. The squeegee moves back and forth across the hydrophobic nano-steel mesh, forcing the adhesive through the mesh's pores and onto the substrate's pads. The adhesive is applied to the pads at a consistent height, with any excess adhesive collected by the squeegee and returned to the surface above the hydrophobic nano-steel mesh. The squeegee speed is 20-100 mm / s, the pressure is 0.5-1.5 kg, and the printing environment is kept clean and dry, with humidity below 60%.

[0047] S3, peeling off the hydrophobic nano-steel mesh;

[0048] In this step, after the anisotropic conductive adhesive is printed, the control system of the steel screen printer slowly lifts the hydrophobic nano-steel mesh to gradually separate the hydrophobic nano-steel mesh from the substrate. Generally, the hydrophobic nano-steel mesh is gradually separated from the top to the bottom or from the bottom to the top to ensure that the anisotropic conductive adhesive filled on the pad remains intact and clear, which facilitates the subsequent mounting of the LED chip on the anisotropic conductive adhesive.

[0049] S4. Provide an LED chip, and mount the LED chip on the anisotropic conductive adhesive on the pad;

[0050] In this step, the LED chip can be either an unpackaged LED chip or a packaged LED chip. The unpackaged or packaged LED chip is mounted on the anisotropic conductive adhesive on the pads via a mass transfer process or a surface-mount mounting (SMT) process. Because the anisotropic conductive adhesive is directly applied to the pads via a hydrophobic nano-steel mesh, a separate adhesive dispensing process is unnecessary, saving process steps and reducing costs.

[0051] S5. The LED chip on the anisotropic conductive adhesive is heated and pressurized through a hot pressing process, so that the insulating film of the anisotropic conductive adhesive is longitudinally ruptured to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls are respectively in contact with the LED chip and the soldering pad to form a vertical conductive path, and the insulating glue of the anisotropic conductive adhesive is initially solidified, so that the LED chip is soldered to the substrate.

[0052] In this step, the hot pressing process is to apply pressure while heating. Specifically, the LED chip mounted on the anisotropic conductive adhesive on the pad is heated, and pressure is applied in the longitudinal direction of the LED chip, causing excess insulating glue to overflow and the insulating film to rupture. Specifically, when heated to 120°C-250°C, the insulating film of the anisotropic conductive adhesive softens. Then, a vertical uniform pressure of 30N·m-100N·m is applied to the LED chip through a flat pressure plate, causing the softened insulating film to rupture in the Z-axis direction. Since the insulating film wraps the metal conductive particle balls, the metal conductive particle balls are exposed when the insulating film ruptures. The exposed metal conductive particle balls are in contact with the LED chip and the soldering pad respectively to form a vertical conductive path. Since the insulating film is not broken in the X-axis and Y-axis directions, and after the insulating film is cured, it is prevented from being damaged by external force or environmental influences during use, and the short circuit caused by contact between two adjacent metal conductive particle balls in the X-axis and Y-axis directions is avoided, thereby forming permanent insulation in the X-axis and Y-axis directions. Under pressure, the LED chip, the metal conductive particle balls and the soldering pad are in closer contact, thereby improving the stability of the electrical connection. In addition, the insulating glue of the anisotropic conductive adhesive is initially cured, so that the LED chip is soldered to the substrate.

[0053] One LED chip is soldered on one pad, and the current driving a single LED chip is very small. The maximum driving current of each LED chip is usually less than 3-5mA. In normal operation, the driving current is often only a few tenths of a milliampere.

[0054] The current required to drive a single LED chip is very small, and the anisotropic conductive adhesive on one pad contains multiple metal conductive particle balls, and one LED chip is soldered on one pad. Therefore, as long as one or two of the multiple metal conductive particle balls are conductive, the LED chip can be lit normally. It is not necessary for all the metal conductive particles to be conductive at the same time, which reduces the difficulty of welding and improves the welding quality.

[0055] In this embodiment, the hydrophobic nano-steel mesh and the substrate are first aligned, and the steel holes of each hydrophobic nano-steel mesh are aligned with each solder pad. Then, anisotropic conductive glue is added to the hydrophobic nano-steel mesh and evenly applied to the surface of the hydrophobic nano-steel mesh by scraping, so that the anisotropic conductive glue is printed on the solder pad. The LED chip is mounted on the anisotropic conductive glue located on the solder pad, and the insulating film of the anisotropic conductive glue is longitudinally (in the Z-axis direction) ruptured by heating and pressurizing, thereby exposing the metal conductive particle balls wrapped in the insulating film. The metal conductive particle balls can respectively contact the LED chip and the solder pad to form a vertical conductive path. The anisotropic conductive adhesive is preliminarily solidified to allow the LED chip to be welded to the substrate. Since the anisotropic conductive adhesive contains multiple metal conductive particle balls, as long as there is a metal conductive particle ball among the numerous metal conductive particle balls that is conductive, the LED chip can be normally lit. It is not necessary for all metal conductive particles to be conductive at the same time, which reduces the difficulty of welding and improves the welding quality. In addition, the insulating glue has an open time of 4 hours to 8 hours. The insulating glue can be melted by reheating, so that the defective LED chip can be easily removed and replaced with a good LED chip without damaging the LED chip, making the maintenance difficulty small and the maintenance cost low.

[0056] See also Figure 2 As shown, the present invention also discloses a second embodiment of a method for welding a Mini / Micro LED chip, comprising:

[0057] S10, preparing metal conductive particle balls by a mechanical separation process or a spraying process;

[0058] In this step, the material of the metal conductive particle balls is one or more of tin powder, silver powder, nickel powder, gold powder, tin alloy powder, copper powder, and aluminum powder, so that the metal conductive particle balls can conduct electricity.

[0059] For example, when the metal conductive particle balls are made of tin powder, the specific steps for preparing them using a mechanical separation process are as follows: heating the tin powder above its melting point to liquidize it; using a high-speed rotating disk or vibrating nozzle to divide the molten tin into tiny droplets, and controlling the rotation speed and vibration frequency of the rotating disk to control the droplet diameter to 10μm-20μm; the liquid tin droplets are sphericalized by centrifugal or mechanical forces, as molten tin naturally tends to form spheres due to surface tension; ensuring that the liquid tin droplets are rapidly cooled in air or an inert gas (such as nitrogen) to solidify into tin balls with a diameter of 10μm-20μm; using a screen or particle size classification equipment to select tin balls that meet the required size and remove unqualified tin balls, ultimately obtaining tin balls with a diameter of 10μm-20μm. The principle of the mechanical separation process for preparing tin balls is to separate molten tin metal into fine particles to form tin balls. This method typically involves mechanical force or vibration to control the size and distribution of the liquid tin droplets.

[0060] When the metal conductive particle balls are made of tin powder, the specific steps for producing them using a spraying process are as follows: The tin powder is heated above its melting point to completely melt it; the molten tin is sprayed through a nozzle while a high-pressure inert gas (such as nitrogen or argon) is used to disperse the tin stream into tiny droplets; the molten tin is introduced into a high-speed rotating disk or spray cup, where centrifugal force ejects the molten tin into tiny droplets; during the spraying process, the tin droplets rapidly cool in air or inert gas, where surface tension causes them to naturally form spheres and solidify; the cooled tin balls are recovered through a collection device and then separated through screening or grading equipment to produce balls with a diameter of 10μm-20μm. The principle of the spraying process for producing tin balls is to use a high-speed airflow or centrifugal force to break the molten tin into tiny droplets, which then form tin balls during the cooling process.

[0061] S11, coating a layer of insulating coating on the surface of the metal conductive particle ball through a coating process, and air-drying it to form an insulating film; further, this step specifically includes the following two methods:

[0062] 1) immersing the metal conductive particle balls in a chemical solution by a chemical deposition method, forming an insulating coating on the surface of the metal conductive particle balls through a chemical reaction, and air-drying the insulating coating to form an insulating film;

[0063] 2) depositing an insulating coating material onto the surface of the metal conductive particle ball by physical vapor deposition to form an insulating coating, and air-drying the insulating coating to form an insulating film;

[0064] In this step, a layer of insulating coating with a thickness of 3%-25% of the diameter of the metal conductive particle ball is coated on the surface of the metal conductive particle ball through a chemical coating process or a physical coating process, and the insulating coating is air-dried at 50°C - 80°C, and the air-drying time is 10 minutes - 30 minutes, and the air flow speed is controlled at 1m / s - 2 m / s, so that the insulating coating is cured and forms an insulating film with uniform thickness, good adhesion and stable mechanical properties. At this time, the insulating film wraps the metal conductive particle ball.

[0065] The chemical deposition method is a chemical reduction process that uses a suitable reducing agent to reduce the metal ions in the plating solution and deposit them on the surface of the substrate. Specifically, the metal conductive particle balls are immersed in a chemical solution, causing the metal ions in the insulating coating material to be reduced and deposited on the surface of the metal conductive particle balls, forming an insulating coating with a thickness of 3%-25% of the diameter of the metal conductive particle balls. The insulating coating is then air-dried at 50°C-80°C for 10-30 minutes at an airflow rate of 1m / s-2m / s, allowing the insulating coating to solidify and form an insulating film with uniform thickness, good adhesion, and stable mechanical properties. The insulating film then wraps around the metal conductive particle balls.

[0066] Physical vapor deposition is a method that uses physical methods (such as evaporation or sputtering) to vaporize the coating material and deposit it on the surface of the substrate to form a film. Specifically, in a vacuum environment, the insulating coating material is deposited on the surface of the metal conductive particle balls by evaporation or sputtering, forming an insulating coating with a thickness of 3%-25% of the diameter of the metal conductive particle balls. The insulating coating is then air-dried at 50°C to 80°C for 10 to 30 minutes, with the air flow rate controlled at 1m / s to 2m / s, so that the insulating coating solidifies and forms an insulating film with uniform thickness, good adhesion, and stable mechanical properties. At this time, the insulating film wraps around the metal conductive particle balls.

[0067] The insulating film is made of one or more of a resin, a polymer, or a thermoplastic polymer. For example, the resin may be epoxy resin, which has excellent mechanical strength, electrical insulation, and heat resistance. The polymer may be polyimide, which has excellent heat resistance, electrical insulation, and flexibility, making it suitable for high-temperature processes. The thermoplastic polymer may be polyethylene terephthalate, polyethylene, polypropylene, or ethylene-vinyl acetate copolymer. Polyethylene terephthalate is relatively low-cost and has good electrical properties and mechanical strength. The insulating film made of the above materials can prevent short circuits between the metal conductive particle balls, allow the metal conductive particle balls to conduct electricity along the Z-axis under a specific pressure, and protect the conductors from external environmental influences (such as oxidation). Furthermore, it ensures the positioning and pressure-bonding of the conductors during bonding, i.e., stability during hot pressing.

[0068] If the thickness of the insulating film exceeds 25%, the vertical surface may not break during extrusion. If the insulating film does not break, it will still be in an insulating state, and current cannot pass through, and the metal conductive particle balls cannot be conductive. If the insulating film is less than 3%, the insulating film is too thin, which may lead to insufficient mechanical strength of the insulating film. Therefore, the thickness of the insulating film is controlled to 3%-25% of the diameter of the metal conductive particle balls, so that under appropriate pressure and temperature conditions, the insulating film can easily break in the Z-axis direction and expose the metal conductive particle balls, allowing current to pass through the metal conductive particle balls.

[0069] For example, when the insulating film material is made of a material with a melting or softening temperature of approximately 150°C, such as polyethylene (PE), polypropylene (PP), or ethylene-vinyl acetate (EVA), during the packaging process, when the temperature rises to approximately 150°C, the insulating film softens. Due to its thinness, the insulating film may crack in the Z-axis direction under vertical pressure.

[0070] It is worth noting that the Z-axis direction is perpendicular to the surface of the substrate and consistent with the direction of the conductive path, that is, the direction in which the insulating film is broken and the metal conductive particle balls are exposed; the X-axis direction and the Y-axis direction are both parallel to the surface of the substrate, which are the directions in which insulation needs to be maintained between the metal conductive particle balls, that is, the part of the insulating film that is not broken.

[0071] The insulating film can not only make the metal conductive particle balls contact with the soldering pads of the LED chip and the substrate respectively to form a vertical conductive path, but also prevent two adjacent metal conductive particle balls from short-circuiting in the X-axis and Y-axis directions, that is, the insulation effect. Since the two adjacent metal conductive particle balls are insulated in the X-axis and Y-axis directions, multiple LED chips are used as a collection, and no short circuit will occur between the two adjacent LED chips. Therefore, when designing the steel holes of the hydrophobic nano-steel mesh, the diameter of the steel holes can be designed to be larger than the size of a soldering pad on the substrate (one soldering pad corresponds to one LED chip). Specifically, the diameter of the steel holes can be designed to accommodate the size of three soldering pads. Since the diameter of the steel holes at this time is 2 times larger than the diameter of the steel holes that accommodate one soldering pad, when printing anisotropic conductive adhesive, the anisotropic conductive adhesive is easier to fill into the soldering pad through the steel holes, making it more suitable for welding LED chips with small pixels and used in ultra-high-resolution Mini / Micro The LED display screen can of course also design the diameter of the steel hole to accommodate the size of two, four, five, six pads, etc. This embodiment does not impose a specific limit on the number of pads that the diameter of the steel hole can be designed to accommodate.

[0072] S12, providing an insulating glue, placing the metal conductive particle balls coated with the insulating film into the insulating glue, and stirring to form an anisotropic conductive glue; further, this step specifically includes the following two methods:

[0073] 1) providing an insulating glue, placing the metal conductive particle balls coated with the insulating film into the insulating glue, and stirring at a low speed so that the plurality of metal conductive particle balls are evenly distributed in the insulating glue to form an anisotropic conductive glue;

[0074] 2) providing an insulating glue, placing the metal conductive particle balls coated with the insulating film into the insulating glue, and stirring the metal conductive particle balls by a planetary mixer with a combined motion of rotation and revolution so that the plurality of metal conductive particle balls are evenly distributed in the insulating glue to form an anisotropic conductive glue.

[0075] In this step, an insulating glue with a certain viscosity and consistency is provided, and the consistency of the insulating glue must ensure the bonding performance while making the metal conductive particle balls wrapped with the insulating film easier to disperse; the metal conductive particle balls wrapped with the insulating film are placed in the insulating glue and stirred by a low-speed stirring method. The low-speed stirring method can reduce the aggregation of the metal conductive particle balls wrapped with the insulating film and the generation of bubbles, which helps to evenly distribute the metal conductive particle balls wrapped with the insulating film in the insulating glue. A dispersant can also be added to the insulating glue. The dispersant can reduce the interaction between the metal conductive particle balls wrapped with the insulating film and reduce agglomeration. The dispersant can be a surfactant or an organic solvent.

[0076] In addition to the low-speed stirring method, a planetary stirring method can also be used. The metal conductive particle balls wrapped with the insulating film are stirred by the combined motion of rotation and revolution of the planetary mixer, so that the metal conductive particle balls wrapped with the insulating film are more evenly distributed.

[0077] Because the current driving a single LED chip is very small, the maximum driving current for each LED chip is typically less than 3-5mA. In many cases, the driving current is even as low as a few tenths of a milliampere during normal operation. Therefore, as long as the metal conductive particles can simultaneously touch the solder pads of the LED chip and the substrate, current can be conducted and the LED chip can be properly lit.

[0078] Therefore, under such low current requirements, even if some solder balls do not fully contact the pads during soldering, it will not affect the normal power supply and lighting of the chip. However, to ensure long-term stability and reliability, it is necessary to ensure that all solder balls can make good contact with the pads. Therefore, due to the viscosity and consistency of the glue, the metal conductive particle balls wrapped in the insulating film may have a small amount of adhesion. However, this small amount of adhesion does not affect the basic working principle of the metal conductive particle balls.

[0079] S13, providing a hydrophobic nano-steel mesh having a plurality of steel holes and a substrate having a plurality of solder pads, placing the hydrophobic nano-steel mesh on the substrate, and aligning the mesh so that each of the steel holes is aligned with each of the solder pads, wherein the substrate is a circuit board or a glass substrate;

[0080] The specific steps of providing a hydrophobic nano-steel mesh having a plurality of steel pores in this step are:

[0081] 1) Providing a steel plate, and drilling steel holes on the steel plate corresponding to the welding pads of the substrate to form a steel mesh;

[0082] 2) coating the steel mesh with a layer of nano-hydrophobic coating to obtain a hydrophobic nano-steel mesh;

[0083] In this step, the substrate can be one of a circuit board or a glass substrate, and the printing of the anisotropic conductive adhesive is completed by a steel screen printer. First, a hydrophobic nano steel mesh is prepared. Specifically, a steel plate is provided, and steel holes of the same size as the pads are opened on the steel plate corresponding to the pad positions of the substrate, and the distribution of the steel holes is the same as the distribution of the pads to obtain a steel mesh; a layer of nano hydrophobic coating is applied to the steel mesh to obtain a hydrophobic nano steel mesh. Among them, the nano hydrophobic coating can be a fluoride-based nano coating, a silane-based nano coating or a nano silica coating. Exemplarily, the fluoride-based nano coating material is polytetrafluoroethylene or a perfluoroalkyl silane compound. The fluoride-based nano coating has extremely high hydrophobicity, and the water contact angle can reach 120°-150°, which keeps the surface of the hydrophobic nano steel mesh clean and improves printing accuracy; it has extremely low surface energy, prevents anisotropic conductive adhesive from adhering to the steel holes of the hydrophobic nano steel mesh, reduces clogging, and extends the service life of the hydrophobic nano steel mesh; it has excellent corrosion resistance and chemical stability. Silane-based nanocoatings, made from octyltriethoxysilane or methyltrichlorosilane, exhibit excellent hydrophobicity, with water contact angles reaching 110°-130°. This prevents anisotropic conductive adhesives from adhering to the pores of hydrophobic nanosteel meshes. They also possess strong chemical bonding, resulting in a stable and wear-resistant coating. They are easy to process and prepare, exhibit excellent adhesion, and are suitable for forming a long-lasting, effective anti-sticking layer on steel mesh surfaces. Nanosilica coatings also exhibit excellent hydrophobicity, with properties that can be enhanced through chemical modification. They also offer excellent wear resistance and thermal stability, and are relatively low-cost, making them suitable for mass-produced steel mesh surface treatments.

[0084] After the hydrophobic nano-steel mesh and the substrate are prepared, the substrate is first mounted on the fixture of the stencil printer. The fixture has adjustable supports and positioning pins to ensure the accurate position of the substrate. The hydrophobic nano-steel mesh is then fixed to the frame of the printer. The printer's visual positioning system automatically detects the positioning mark (FiducialMark) of the substrate for correction, so that the position of the substrate and the hydrophobic nano-steel mesh are aligned, and each steel hole is aligned with each pad, that is, each steel hole is located directly below each pad. The substrate is then fixed to the printing platform by vacuum adsorption or mechanical clamping to prevent movement during the printing process. The stencil printer's squeegee (usually made of metal or polyurethane) pushes the anisotropic conductive adhesive onto the surface of the hydrophobic nano-steel mesh and applies it along the mesh at a set speed and pressure. The squeegee moves back and forth across the mesh, squeezing the adhesive through the mesh's pores and onto the substrate's pads. This ensures a consistent level of adhesive on the pads, with any excess adhesive collected by the squeegee and returned to the surface above the mesh. After the adhesive is applied, the stencil printer's control system slowly lifts the mesh, gradually separating it from the substrate. The squeegee speed is 20-100 mm / s, the pressure is 0.5-1.5 kg, and the printing environment is kept clean and dry, with humidity below 60%.

[0085] S14, adding the anisotropic conductive adhesive to the side of the hydrophobic nano-steel mesh away from the pad, and evenly coating the anisotropic conductive adhesive on the hydrophobic nano-steel mesh by a doctor blade method, so that the anisotropic conductive adhesive is printed onto the pad through the steel holes;

[0086] In this step, the description of the above step S14 refers to S2 of the first embodiment, and this step will not be repeated.

[0087] S15, peeling off the hydrophobic nano-steel mesh;

[0088] In this step, the description of the above step S15 refers to S3 of the first embodiment, and this step will not be repeated.

[0089] S16, mounting the LED chip onto the anisotropic conductive adhesive on the pad through a mass transfer process or an SMT process;

[0090] In this step, mass transfer process or standard SMT process is adopted according to different mounting objects.

[0091] When the mounting targets are unpackaged LED chips, a mass transfer process can be employed. Specifically, a transfer head equipped with an elastic mold or electromagnetic suction head is used to pick up LED chips in batches from a temporary carrier. A visual recognition system precisely aligns the picked LED chips with the anisotropic conductive adhesive on the pads, and the LED chips are then released onto the anisotropic conductive adhesive. The alignment accuracy is ±1μm to 2μm, the release pressure is 0.2MPa to 1.0MPa, and the temperature is 80°C to 150°C. The mass transfer process enables the transfer of large quantities of LED chips from their carriers and their precise placement onto the anisotropic conductive adhesive on the pads, improving mounting efficiency, saving time, reducing costs, and ensuring high-quality electrical connections and mechanical strength.

[0092] When mounting a packaged LED chip, standard SMT processes are used to mount the packaged LED chip onto the anisotropic conductive adhesive on the pad. Specifically, a transfer head with an elastic mold or electromagnetic suction head is used to pick up the packaged LED chip using a placement machine. The placement machine's vision system precisely aligns the packaged LED chip with the anisotropic conductive adhesive on the pad. The packaged LED chip is precisely placed on the anisotropic conductive adhesive, ensuring high-quality electrical connections and mechanical strength.

[0093] S17, heating and pressurizing the LED chip on the anisotropic conductive adhesive by a hot pressing process, so that the insulating film of the anisotropic conductive adhesive is longitudinally ruptured to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls are respectively in contact with the LED chip and the soldering pad to form a vertical conductive path, and the insulating adhesive of the anisotropic conductive adhesive is initially cured, so that the LED chip is soldered to the substrate;

[0094] In this step, the description of the above step S17 refers to S5 of the first embodiment, and this step will not be repeated.

[0095] S18, testing the LED chip;

[0096] In this step, since it takes 4 hours to 8 hours for the insulating glue to be completely cured, that is, the insulating glue is in a preliminary curing state during 4 hours to 8 hours, the insulating glue has an open time of 4 hours to 8 hours, and the LED chip can be tested during this time.

[0097] S19. When the LED chip is defective, heat the LED chip to melt the anisotropic conductive adhesive, remove the defective LED chip and replace it with a good LED chip.

[0098] In this step, when it is detected that the LED chip is defective, the anisotropic conductive glue can be reactivated by heating it to 120°C-250°C to melt the insulating glue. The junction temperature of the LED chip is 125°C-150°C. Therefore, a heating temperature of 120°C-250°C can not only remelt the insulating glue, but also will not damage the LED chip. After the insulating glue is melted, the defective LED chip can be easily removed and replaced with a good LED chip. The insulating glue has an open time of 4 hours to 8 hours, so that during maintenance, defective products can be repaired and replaced, making maintenance less difficult, ensuring that the product yield is close to 100%, avoiding scrapping of the entire substrate or display module, and low maintenance costs. The insulating glue has an open time of 4 to 8 hours, allowing defective LED chips to be repaired by heating during the open time, ensuring a product yield close to 100% and avoiding scrapping of the entire substrate or display module. If problems are discovered after curing, the entire substrate or display module may be scrapped. Repairing within the open time greatly reduces production waste and material loss, allowing the production line to flexibly handle quality inspection and repair, reducing the risk of batch scrapping.

[0099] The open time of the insulating glue can also be adjusted by adding specific chemical materials to the insulating glue; for example, the material that extends the open time can be a retardant or a plasticizer; the material that accelerates curing can be a catalyst or an initiator; it is also possible to use a moisture-curing glue so that the insulating glue gradually cures by absorbing moisture (humidity) in the air.

[0100] Among them, the LED chips can be blue LED chips, green LED chips and red LED chips. The maximum junction temperature of the blue LED chips and the green LED chips is 150°C. At this temperature, even if heating is continued for 30 minutes, it will not have a significant impact on the lifespan of the blue LED chips and the green LED chips; the maximum junction temperature of the red LED chip is 125°C. Laboratory tests show that hot pressing at 150°C for 30 minutes will not significantly affect the lifespan of the red LED chips; of course, the heating temperature and heating time are coordinated with each other. When heated to 250°C, the heating time is 1 second to 8 seconds; when heated to 150°C, the heating time is 30 minutes to ensure that the anisotropic conductive adhesive can be heated to reactivate the insulating glue, so that the insulating glue melts and the LED chips are not damaged; but when the heating temperature exceeds 250°C and the heating time exceeds 10 seconds, the LED chips may be damaged.

[0101] In this embodiment, metal conductive particle balls with a diameter of 10 μm-20 μm are prepared by a mechanical separation process or a spraying process, and an insulating coating is applied to the surface of the metal conductive particle balls by a coating process to form an insulating film with a thickness of 3%-25% of the diameter of the metal conductive particle balls, so that the insulating film softens when heated to 120°C-250°C and ruptures under vertical pressure, exposing the metal conductive particles at the rupture. The metal conductive particle balls coated with the insulating film are placed in an insulating glue and stirred to form an anisotropic conductive glue. The insulating glue fixes and connects the LED chip, the metal conductive particle balls and the solder pad, thereby improving the stability of the electrical connection. The hydrophobic nano-steel mesh is aligned with the substrate, and the steel holes of each hydrophobic nano-steel mesh are aligned with each solder pad respectively. Then, the anisotropic conductive glue is added to the hydrophobic nano-steel mesh, and the anisotropic conductive glue is evenly scraped on the surface of the hydrophobic nano-steel mesh by scraping, so that the anisotropic conductive glue is printed on the solder pad. On top, the LED chip is mounted on the anisotropic conductive adhesive on the pad, and heat and pressure are applied to cause the insulating film of the anisotropic conductive adhesive to rupture longitudinally (Z-axis direction) to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls can contact the LED chip and the pad respectively to form a vertical conductive path, and the insulating glue of the anisotropic conductive adhesive is initially solidified, so that the LED chip is soldered to the substrate. Since the anisotropic conductive adhesive contains multiple metal conductive particle balls, as long as there is a metal conductive particle ball among the many metal conductive particle balls that is conductive, the LED chip can be normally lit, and it is not necessary for all metal conductive particles to be conductive at the same time, which reduces the difficulty of welding and improves the welding quality. In addition, the insulating glue has an open time of 4 hours to 8 hours. The insulating glue can be melted by reheating, so that the defective LED chip can be easily removed and replaced with a good LED chip without damaging the LED chip, making the maintenance difficulty small and the maintenance cost low.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the present invention as described above. For the sake of simplicity, they are not provided in detail. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions described in the above embodiments, or to make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for soldering a Mini / Micro LED chip, characterized in that: The welding method comprises: Providing a hydrophobic nano-steel mesh having a plurality of steel holes and a substrate having a plurality of solder pads, placing the hydrophobic nano-steel mesh on the substrate and aligning the mesh so that each of the steel holes is aligned with each of the solder pads, wherein the substrate is a circuit board or a glass substrate; An anisotropic conductive adhesive is provided, wherein the anisotropic conductive adhesive comprises metal conductive particle balls uniformly distributed in an insulating adhesive and coated with an insulating film. The metal conductive particle balls are immersed in a chemical solution by a chemical deposition method, an insulating coating is formed on the surface of the metal conductive particle balls by a chemical reaction, and the insulating coating is air-dried to form an insulating film. The anisotropic conductive adhesive is added to a side of a hydrophobic nano-steel mesh away from the pad and uniformly scraped onto the hydrophobic nano-steel mesh by a doctor blade method, so that the anisotropic conductive adhesive is printed onto the pad through the steel holes, so that a plurality of metal conductive particle balls are contained in the anisotropic conductive adhesive on a pad. peeling off the hydrophobic nano-steel mesh; Providing an LED chip, and mounting the LED chip on the anisotropic conductive adhesive located on the pad; The LED chip on the anisotropic conductive adhesive is heated and pressurized by a hot pressing process, so that the insulating film of the anisotropic conductive adhesive is longitudinally ruptured to expose the metal conductive particle balls wrapped in the insulating film, so that the metal conductive particle balls contact the LED chip and the solder pad respectively to form a vertical conductive path, and the insulating adhesive of the anisotropic conductive adhesive is initially cured, so that the LED chip is soldered to the substrate; the material of the insulating adhesive is a modified epoxy resin with an open time of 4-8 hours; The LED chip is inspected; when the LED chip is defective, the LED chip is heated to melt the anisotropic conductive adhesive, the defective LED chip is removed and replaced with a good LED chip.

2. The welding method according to claim 1, characterized in that The step of providing anisotropic conductive adhesive is formed in three steps, including: Prepare metal conductive particle balls by mechanical separation process or spraying process; Coating a layer of insulating coating on the surface of the metal conductive particle ball through a coating process and air-drying the coating to form an insulating film; An insulating glue is provided, and the metal conductive particle balls coated with the insulating film are placed in the insulating glue and stirred to form an anisotropic conductive glue.

3. The welding method according to claim 2, characterized in that The insulating film is made of resin.

4. The welding method according to claim 2, characterized in that The material of the metal conductive particle balls is one or more of tin powder, silver powder, nickel powder, gold powder, tin alloy powder, copper powder, and aluminum powder.

5. The welding method according to claim 2, characterized in that The diameter of the metal conductive particle ball is 10 μm-20 μm; and / or the thickness of the insulating film is 3%-25% of the diameter of the metal conductive particle ball.

6. The welding method according to claim 2, characterized in that The step of providing an insulating glue comprises: An insulating glue is provided, metal conductive particle balls coated with the insulating film are placed in the insulating glue, and the metal conductive particle balls are evenly distributed in the insulating glue by low-speed stirring, thereby forming an anisotropic conductive glue; or, an insulating glue is provided, metal conductive particle balls coated with the insulating film are placed in the insulating glue, and the metal conductive particle balls are evenly distributed in the insulating glue by a planetary mixer through a combined motion of rotation and revolution, thereby forming an anisotropic conductive glue.

7. The welding method according to claim 1, wherein: The step of providing a hydrophobic nano-steel mesh having a plurality of steel pores is formed in two steps, including: Providing a steel plate, and drilling steel holes on the steel plate corresponding to the welding pads of the substrate to form a steel mesh; A layer of nano-hydrophobic coating is coated on the steel mesh to obtain a hydrophobic nano-steel mesh.

8. The welding method according to claim 1, wherein: The steps of providing an LED chip and mounting the LED chip on the anisotropic conductive adhesive on the pad include: The LED chip is mounted on the anisotropic conductive adhesive on the pad through a mass transfer process or a SMT process.

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