Packaging structure and packaging method of Mini / Micro LED chip

Abstract

The invention discloses a packaging structure and a packaging method of a Mini / Micro LED (Light Emitting Diode) chip. The packaging method comprises the following steps: respectively carrying out electrostatic polarization treatment with opposite charge polarities on conductive particles and a bonding pad of a substrate, and adsorbing the conductive particles on the bonding pad of the substrate; each conductive particle comprises a metal conductive ball and a conductive adhesive coating the surface of the metal conductive ball; an LED chip is attached to the substrate in a counterpoint mode, and a bonding pad on the LED chip makes contact with the corresponding conductive particles; hot-pressing the LED chip, melting the conductive adhesive through heat conduction, and fixing the LED chip on the substrate through the conductive adhesive after cooling; and coating a plastic packaging material on the substrate to wrap the LED chip, and curing to complete packaging of the LED chip. According to the technical scheme, the LED chip packaging process can be simpler, more convenient and faster, stable mechanical connection and excellent electrical connection between the LED chip and the substrate can be achieved, and the problem of chip damage caused by too high temperature is effectively avoided.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor light-emitting devices, and in particular to a packaging structure and packaging method of a Mini / Micro LED chip. Background Art

[0002] The higher the resolution of the display screen, the more pixels it has on the screen. For example, a 4K display screen has 8,294,400 pixels, and an 8K display screen has 33,177,600 pixels. Each pixel requires three LED chips (red, green, and blue). In traditional processes, each chip needs to be welded with positive and negative electrodes. Therefore, the number of LED chips welded reaches tens of millions or even hundreds of millions.

[0003] In the prior art, the reflow soldering process is usually used to achieve the welding of Mini / Micro LED. However, since the pad size of the Mini / Micro LED chip is extremely small, only 10-50 microns, or even smaller, the solder paste is limited by the size of the steel mesh opening during the reflow soldering process, and the requirement of precise printing cannot be met. In addition, the solder paste has strong viscosity. When the size of the steel mesh opening is small, even if the solder paste is attached to the PCB board or glass substrate, it may not fall off the steel mesh smoothly. In addition, excessively high reflow soldering temperature will also increase the risk of chip damage.

[0004] Therefore, it is necessary to improve the existing packaging structure and packaging method of Mini / Micro LED chips. Summary of the invention

[0005] The present application provides a packaging structure and packaging method of a Mini / Micro LED chip, aiming to solve the problem in the prior art that Mini / Micro LED chips are difficult to package and are prone to damage to the chips.

[0006] To achieve the above objectives, the present application proposes a packaging method for Mini / Micro LED chips. The method comprises: Conductive particles and pads of the substrate are subjected to electrostatic polarization treatment with opposite charge polarities, and the conductive particles are adsorbed on the pads of the substrate; the conductive particles include metal conductive balls and conductive glue coated on the surfaces of the metal conductive balls; Aligning and laminating the LED chip on the substrate so that the pads on the LED chip contact the corresponding conductive particles; Hot pressing the LED chip to melt the conductive adhesive by heat conduction, so that the LED chip is fixed on the substrate by the conductive adhesive after cooling; A plastic packaging material is coated on the substrate to wrap the LED chip, and the packaging of the LED chip is completed after curing.

[0007] In some embodiments, before the electrostatic polarization treatment of the conductive particles and the pads of the substrate with opposite charge polarities is performed, the method further comprises: Preparing metal conductive balls; the metal conductive balls include tin balls, silver balls and nickel balls; Conductive glue is evenly coated on the surface of the metal conductive ball to prepare the conductive particles.

[0008] In some embodiments, the electrostatic polarization treatment of the conductive particles and the pads of the substrate with opposite charge polarities comprises: Placing conductive particles in an electrostatic pipe and applying voltage so that the surface of the conductive particles has a uniform positive or negative charge; The pads of the substrate are connected via a test port, and charges opposite to those on the surfaces of the conductive particles are applied to the pads of the substrate.

[0009] In some embodiments, the step of adsorbing the conductive particles onto the pads of the substrate includes: Scan and capture the pad positions of the substrate to establish pad coordinate data; According to the pad coordinate data, the conductive particles with charge polarity are placed on the substrate, and under the effect of mutual attraction between charges of different types, the conductive particles are rolled and adsorbed on the pad of the substrate.

[0010] In some embodiments, after causing the conductive particles to roll and adsorb on the pads of the substrate, the step further includes: Detecting the adsorption state of the conductive particles on the pads of the substrate; the adsorption state includes whether the conductive particles are missing, overlapped or offset; Based on the adsorption state, the arrangement of the conductive particles is adjusted so that the conductive particles meet adsorption setting requirements.

[0011] In some embodiments, the hot pressing of the LED chip to melt the conductive adhesive by heat conduction, and fixing the LED chip on the substrate by the conductive adhesive after cooling, comprises: Setting hot pressing parameters, and heating and pressing the LED chip toward the substrate under the hot pressing parameters; the heating temperature in the hot pressing parameters corresponds to the hot melting temperature of the conductive adhesive; The cooling process is performed at a cooling rate of not less than 10°C / S, so that the LED chip and the substrate on both sides are mechanically connected through the curing of the conductive adhesive, and the LED chip is fixed on the substrate. In some embodiments, after the LED chip is fixed on the substrate by the conductive adhesive after cooling, the method further includes: Removing excess conductive particles and contaminants from around the pads of the substrate; Laminating an LED chip protection film to protect the light-emitting performance of the LED chip; the LED chip protection film comprises a composite transparent film and a black semi-solid glue; Perform quality inspection after the LED chip is mounted and fixed on the substrate.

[0012] In some embodiments, the step of attaching the LED chip protective film to protect the light emitting performance of the LED chip includes: Positioning and laminating the LED chip protection film so that the transparent film in the LED chip protection film corresponds to the light-emitting area of ​​the LED chip, and the black semi-solid glue corresponds to the peripheral side of the LED chip; The black semi-solid glue is pressed downward to separate the black semi-solid glue from the transparent film and flow to the periphery and bottom of the LED chip.

[0013] In some embodiments, the quality inspection after the LED chip is mounted and fixed on the substrate includes: Detect whether the appearance is correctly set; the appearance includes whether the LED chip protective film is correctly attached and whether the LED chip is skewed; The light emitting performance of the LED chip is tested, and the light emitting performance of the LED chip includes whether the chip can be lit and whether the brightness of the chip is consistent.

[0014] The present application also provides a packaging structure of a Mini / Micro LED chip, which is prepared using the packaging method of the Mini / Micro LED chip as described above.

[0015] The technical solution of the present application proposes a packaging method for Mini / Micro LED chips. The method includes: performing electrostatic polarization treatment of opposite charge polarities on the conductive particles and the pads of the substrate, and adsorbing the conductive particles on the pads of the substrate; the conductive particles include metal conductive balls and conductive glue coated on the surface of the metal conductive balls; aligning and bonding the LED chip on the substrate, and making the pads on the LED chip contact the corresponding conductive particles; hot pressing the LED chip, melting the conductive glue by heat conduction, and fixing the LED chip on the substrate by the conductive glue after cooling; coating the plastic packaging material on the substrate to wrap the LED chip, and completing the packaging of the LED chip after curing. The technical solution of the present application does not require complex physical operations. The conductive particles can be quickly and evenly distributed on the pads of the substrate by electrostatic adsorption. Further, based on the structural design of the conductive particles, after the LED chip is aligned and bonded to the substrate and hot-pressed and cooled, a stable mechanical connection between the LED chip and the substrate can be achieved through the conductive glue, and excellent electrical connection can be achieved through the contact of the metal balls with the LED chips and the substrate on both sides. In addition, the hot melt temperature of the conductive adhesive in this implementation is much lower than the working temperature of traditional reflow soldering, which can also effectively prevent the problem of chip damage caused by excessive temperature. The technical solution of this application also provides a packaging structure of a Mini / Micro LED chip prepared by the above packaging method. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work, among which: Figure 1 The process diagram of the packaging method of Mini / Micro LED chip according to an embodiment of the present application is shown in FIG. Figure 1 ; Figure 2 The process diagram of the packaging method of Mini / Micro LED chip according to an embodiment of the present application is shown in FIG. Figure 1 ; Figure 3 The process diagram of the packaging method of Mini / Micro LED chip according to an embodiment of the present application is shown in FIG. Figure 3 ; Figure 4 Schematic diagram of the packaging structure of a Mini / Micro LED chip according to an embodiment of the present application. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0019] It should also be noted that when an element is referred to as being "fixed on" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element at the same time. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0020] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0021] See also Figure 1 As shown, the present application proposes a packaging method for Mini / Micro LED chips. The purpose is to fix the LED chip on a substrate and achieve electrical connection with the substrate. The substrate includes a PCB board and a glass substrate. Among them, solder pads are correspondingly arranged on the substrate and the LED chip, and the LED is mounted on the substrate, and mechanical and electrical connections are achieved through the conductive layer between the solder pads of the two.

[0022] The packaging method includes: Step S10 , performing electrostatic polarization treatment with opposite charge polarities on the conductive particles and the pads of the substrate, and adsorbing the conductive particles on the pads of the substrate.

[0023] In this step, the conductive particles are the conductive layer, so this step is actually a step of disposing the conductive layer on the substrate.

[0024] Among them, electrostatic polarization refers to the change of charge distribution inside a substance through the action of an external electric field. In this step, electric fields in opposite directions are applied to the conductive particles and the pads of the substrate, respectively, so that they have opposite charge polarities, thereby generating electrostatic attraction between the conductive particles and the substrate, further allowing the conductive particles to be quickly and evenly distributed on the pads of the substrate, providing a good foundation for the subsequent alignment, bonding and connection of the LED chip.

[0025] See also Figure 2 As shown, before the electrostatic polarization treatment of opposite charge polarities is performed on the conductive particles and the pads of the substrate, the following steps are also included: Step S1, preparing conductive particles. The method for preparing the conductive particles comprises preparing metal conductive balls, and then uniformly coating the surfaces of the metal conductive balls with conductive glue.

[0026] Specifically, the conductive metal balls are produced by using a gas phase jet method or a mechanical separation method. The conductive metal balls include tin balls, silver balls, nickel balls and other metal balls. The diameter of the conductive metal balls is controlled at 3 to 20 μm, and the particle size error is strictly controlled within ±0.5 μm, so as to ensure that the prepared conductive particles can be set between the pads of the LED chip and the pads of the substrate to form good contact and electrical connection. Among them, the particle size distribution can be detected by a laser particle size analyzer to ensure the consistency of the particle size of the conductive metal balls.

[0027] Further, a CVD chemical vapor deposition or spin coating process is used to form a uniform and dense conductive glue on the surface of the metal conductive ball. The thickness of the conductive glue is controlled in the range of 3% to 10% of the diameter of the metal conductive ball (preferred thickness), and the maximum thickness does not exceed 25% of the diameter of the metal conductive ball (peak thickness); thereby ensuring that the conductive glue can provide sufficient connection strength without excessively increasing the thickness of the packaging structure. Among them, after the conductive glue is applied, XPS (X-ray photoelectron spectroscopy) can be used to analyze the energy distribution of photoelectrons and detect the chemical composition, oxidation state and thickness of the conductive glue layer. The XPS detection method has a high resolution and can detect nanometer-level thickness changes. In addition, after the conductive glue is applied, the microstructure of the conductive glue can also be detected by SEM (scanning electron microscope). The surface of the metal conductive ball is scanned by a high-energy electron beam, and a high-resolution image is generated by detecting the reflected electrons to observe the morphology and uniformity of the conductive glue. The resolution can reach 1nm, and the microstructure and defects of the conductive glue layer can be clearly observed.

[0028] In this way, the preparation of conductive particles ensures the production quality of conductive particles through strict particle size control, precise conductive glue coating and advanced detection methods, providing a high-quality material foundation for the packaging of Mini / Micro LED chips.

[0029] Among them, conductive adhesives include silver-based conductive adhesives, copper-based conductive adhesives, carbon-based conductive adhesives, metal oxide conductive adhesives, conductive polymer adhesives and mixed filler conductive adhesives. To provide a variety of types to choose from, specifically, silver-based conductive adhesives use silver powder as the main conductive filler, have high conductivity and excellent thermal conductivity; suitable for high-precision applications, can provide stable electrical connections, and are suitable for hot melt processes with lower temperatures. Copper-based conductive adhesives use copper powder as a conductive filler, have low cost, and have good conductivity. They are suitable for cost-sensitive but high-conductivity scenarios, and can be improved through surface passivation treatment. Carbon-based conductive adhesives use graphite or carbon nanotubes as fillers, and their conductivity is slightly inferior to that of metals, but they have flexibility and lightness, and are suitable for scenarios with strict weight requirements or high temperature resistance. Metal oxide conductive adhesives use metal oxides (such as ITO) as fillers, which are suitable for transparent electronic devices and packaging scenarios with requirements for light transmittance. Conductive polymer adhesives are based on conductive polymers (such as polypyrrole or polyaniline), suitable for flexible electronic devices, and suitable for flexible packaging needs. Mixed filler conductive adhesive uses a mixture of silver powder, copper powder and carbon materials to balance conductivity and cost; it is suitable for scenarios where a balance is sought between performance and price.

[0030] After the conductive particles are prepared, the conductive particles and the pads of the substrate can be electrostatically polarized so that they have opposite charge polarities, preparing for the adsorption of the metal conductive balls on the substrate. The electrostatic polarization method of the conductive particles can be: the prepared conductive particles are placed in an electrostatic pipe, which is a closed space used to generate and maintain an electrostatic field. A high voltage of 5 to 20 kV is applied in the electrostatic pipe to make the surface of the conductive particles carry a uniform positive or negative charge. To ensure the uniformity and stability of the surface charge of the conductive particles, when the voltage is applied, the voltage stability error is controlled within ±5%, and an electrostatic voltmeter can be used for real-time monitoring to ensure the uniformity of the surface charge of the conductive particles.

[0031] The electrostatic polarization of the pads of the substrate can be done by connecting all the pads on the substrate through a test port, which is an interface for applying voltage and monitoring the charge state. Then, a charge opposite to that on the surface of the conductive particles is applied to the pads of the substrate. This means that if the conductive particles have a positive charge, the pads of the substrate need to have a negative charge, and vice versa.

[0032] It is worth noting that the absolute value of the voltage used for electrostatic polarization of the pad of the substrate is 1.2 to 2.0 times (preferred voltage value) of the voltage value for electrostatic polarization of the conductive particles, and the maximum value is not more than 10 times (peak voltage). Exemplarily, when the voltage applied in the electrostatic pipe is ±5kv, the electrostatic polarization voltage of the pad of the substrate is not less than ±6kv. The selection of this voltage range can ensure that sufficient electrostatic attraction can be generated between the pad of the substrate and the conductive particles, thereby achieving rapid and uniform adsorption.

[0033] And, adsorbing the conductive particles on the pads of the substrate includes: scanning and capturing the pad positions of the substrate to establish pad coordinate data, and these pad coordinate data are used to determine the subsequent placement and positioning of the conductive particles. Among them, a high-precision scanning device, such as a CCD camera, is used to fully scan the substrate. Then, based on the pad coordinate data, the number and position of the pads of the substrate can be determined, and then a certain number of conductive particles with charge polarity are placed on the substrate in a specific area. Under the effect of mutual attraction between different charges, the conductive particles begin to roll and adsorb on the pads of the substrate.

[0034] It is understandable that because the size of the soldering pad of the substrate is three to four times the size of the conductive particles, multiple conductive particles can be adsorbed on the soldering pad of the same substrate at the same time. When there is a soldering pad with at least one conductive particle contacting both sides of the LED chip and the substrate, the connection between the LED chip and the substrate (including mechanical connection and electrical connection) can be achieved.

[0035] Before the substrate is electrostatically polarized, the pad surface may be pre-treated, such as by using plasma cleaning equipment to remove oxide layers and contaminants on the pad surface of the substrate using oxygen or argon gas to improve the adsorption effect of the conductive particles.

[0036] At the end of the arrangement of the conductive particles, the adsorption state of the conductive particles on the pads of the substrate can be detected by an automatic optical inspection device (AOI); and based on the adsorption state, the arrangement of the conductive particles can be adjusted so that the conductive particles meet the adsorption setting requirements.

[0037] Exemplarily, the AOI equipment uses a high-resolution camera to capture images of the pads of the substrate and the conductive particles thereon. The captured images are processed by an image processing algorithm to identify the position, shape and size of the conductive particles. Then, by comparing them with the preset adsorption setting requirements, the AOI equipment can evaluate the adsorption state of the conductive particles, including whether there are omissions, overlaps or offsets. Based on the detection results of the AOI equipment, the arrangement of the conductive particles can be adjusted automatically or manually, such as accurately adsorbing, moving and releasing the conductive particles through a micro-suction device, thereby achieving automatic adjustment of the conductive particle arrangement.

[0038] At this point, the conductive particles (conductive layer) are set on the pads of the substrate. Compared with the traditional reflow solder paste setting process, it can achieve accurate and rapid coverage of the conductive layer on the pads of the substrate, while solving the problem of solder ball contamination and improving the conductivity and overall reliability of the substrate to the LED chip.

[0039] Step S20, aligning and laminating the LED chip on the substrate, and making the pads on the LED chip contact the corresponding conductive particles.

[0040] This step aims to achieve a corresponding relationship between the LED chip and the substrate, so that the pads on the LED chip correspond to the pads on the substrate, so as to facilitate connection through the conductive particles between the pads of the two in subsequent steps.

[0041] It can be understood that the present application is an integrated package of several LED chips, a plurality of pads are arranged on a substrate, and several LED chips are packaged on the substrate to form a light-emitting device such as a display screen. Before the LED chips are attached to the substrate, several LED chips can be automatically arranged in advance. Including: Several LED chips are transported to the wafer arrangement equipment, and a high-precision robot or vacuum adsorption system is used to pick up the LED chips and arrange them on the PET film with the pad facing up according to the preset array method. This can significantly improve production efficiency, reduce manual intervention and errors, and achieve efficient and accurate LED chip arrangement, thus laying the foundation for subsequent packaging operations.

[0042] Then, the LED chip is aligned and bonded to the substrate based on the PET film. This includes: reversing the arranged PET film so that the pads of the LED chip face downwards, so as to align and bond with the pads on the substrate. Then, a high-precision alignment system, such as a high-precision camera, is used to capture the position information of the LED chip on the PET film, and compare it with the position information of the pads on the substrate, and control the precise mechanical adjustment structure for fine-tuning to ensure accurate alignment between the LED chip and the pads on the substrate. After the alignment is completed, the PET film is gently bonded to the substrate to ensure that the pads on the LED chip are in full contact with the conductive particles, and to avoid damage to the LED chip and the substrate.

[0043] The entire process needs to be carried out in a dust-free clean room, and environmental parameters such as temperature, humidity and cleanliness must be strictly controlled to reduce the risk of contamination of LED chips.

[0044] Step S30, hot pressing the LED chip to melt the conductive adhesive by heat conduction, and fixing the LED chip on the substrate by the conductive adhesive after cooling.

[0045] In this step, after the hot pressing operation is completed, the heating is stopped and the LED chip and the substrate are allowed to cool. During the cooling process, the conductive adhesive will gradually solidify. The solidified conductive adhesive not only has sufficient mechanical strength to fix the LED chip, but also can provide reliable electrical connection to ensure that the LED chip can work normally.

[0046] It can be understood that based on the structural setting of the conductive particles, under the action of heat pressing, the conductive glue at the two ends of the conductive particles is squeezed to both sides, so that the metal conductive balls in the conductive particles are exposed and contact the pads of the LED chips and the substrate on both sides. In this way, when the conductive glue forms a stable mechanical connection, an electrical connection mainly based on the metal conductive balls is further formed.

[0047] Specifically, the hot pressing cooling process includes: setting hot pressing parameters, hot pressing the bonded PCB board and PET film, that is, heating and pressing the LED chip toward the substrate under the hot pressing parameters; and then using compressed air or other cooling methods to quickly reduce the temperature.

[0048] Among them, the heating temperature in the hot pressing parameters corresponds to the hot melting temperature of the conductive adhesive, which is generally between 100 and 150°C (peak value does not exceed 250°C), and the hot pressing pressure used is between 20 and 100N (peak value does not exceed 200N), and the hot pressing time is 5 to 30 minutes (peak value does not exceed 120 minutes). The cooling rate is not less than 10°C / S, which can reduce the impact of thermal stress on the LED chip and the welding point. In this way, by accurately controlling the hot pressing parameters, achieving close contact and rapid cooling, etc., it is possible to ensure a stable and reliable electrical connection between the LED chip and the substrate, and improve the quality and reliability of the product.

[0049] After the contact between the LED chip and the substrate is completed, the PET film can be torn off. This includes pre-checking to ensure that the hot pressing and cooling processes have been completed, the conductive glue has been solidified, and there is no adhesion or damage to the edges of the PET film to ensure the smooth progress of the tearing process. Then use automated equipment to control the peeling focal length, peeling speed and peeling force of the PET film to achieve a stable film tearing process and improve production efficiency. Exemplarily, the peeling angle is controlled at 30° to 45° to reduce the pulling force on the LED chip. The peeling speed is controlled at 0.5 to 1.5 mm / s to tear off the PET film evenly and smoothly. The peeling force is controlled at 0.1 to 0.5N to avoid excessive force causing displacement or damage to the LED chip.

[0050] In some embodiments, the LED chip can be further inspected and cleaned after the connection is completed. This includes: using automatic optical inspection equipment to inspect the chip to promptly discover and eliminate potential quality problems to ensure the product's pass rate and reliability. AOI equipment can use high-resolution cameras and image processing technology to perform precise visual inspection of the chip. The inspection content includes but is not limited to: whether the LED chip is displaced, damaged (such as cracks, breaks or burns, etc.) and whether there are residues (such as conductive glue overflow, dust or foreign matter, etc.). If the AOI inspection finds that there are residues or dust and other contaminants on the surface of the substrate, it can be cleaned with a dust-free cloth or an ion air gun.

[0051] Also see Figure 3 As shown, in some embodiments, after the LED chip is fixed on the substrate by the conductive adhesive after cooling, the method further includes: Step S31, removing excess conductive particles and contaminants around the pads of the substrate.

[0052] In this step, plasma cleaning can be used for cleaning, which has the advantages of good cleaning effect, no chemical residue, and minimal damage to the substrate. The preferred working gas is oxygen or argon. If the pollutants are mainly organic matter, oxygen can be selected; if the pollutants are mainly inorganic or particulate matter, argon or a mixed gas can be selected. The cleaning time and cleaning power are further set to ensure safety and effectiveness during cleaning. For example, the cleaning time is set at 10 to 20 seconds and the power is set at 50 to 200 watts.

[0053] Step S32, attaching an LED chip protection film to protect the light-emitting performance of the LED chip; the LED chip protection film includes a composite transparent film and a black semi-solid glue.

[0054] In this step, the transparent film and the black semi-solid glue in the LED chip protective film are compounded. The transparent film is used to cover the light-emitting area of ​​the LED chip, and the black semi-solid glue is used to fill the surroundings and bottom of the LED chip. Among them, the transparent film is usually made of silicone material (such as epoxy resin or silicone), so that the LED chip can be effectively protected from damage by external dust, moisture, mechanical impact and other factors, and the black semi-solid colloid has excellent light-shielding performance and thermal conductivity, so that it can improve the luminous efficiency and contrast of the LED chip while reducing the operating temperature of the chip, so that the LED chip used can achieve clearer image display effects and longer service life.

[0055] The steps of laminating the protective film include: compounding the transparent film and the black semi-solid glue, cutting them into the size suitable for the LED chip, and using the CCD system to accurately position the protective film. Under slight pressure, such as 0.5 to 1N, the black semi-solid glue flows around and to the bottom of the chip. Then, the transparent film and the black semi-solid glue are fixed by UV curing (wavelength 365nm, 10 to 30s) or thermal curing (temperature 80 to 120°C, time 5 to 10min). Finally, the mounting effect of the chip protective film is tested.

[0056] Step S33, performing quality inspection after the LED chip is mounted and fixed on the substrate.

[0057] This step specifically includes: detecting whether the appearance is correctly set and the luminous performance of the LED chip.

[0058] Among them, the appearance includes evaluating whether the LED chip protective film is correctly attached to the chip through visual inspection or automatic optical inspection equipment, such as the absence of bubbles, wrinkles or peeling, so as to ensure that the protective film can effectively protect the LED chip from damage by the external environment without affecting its luminescence; and detecting whether the LED chip is skewed, that is, whether the angle between the LED chip and the substrate is within the specified range to ensure good electrical connection and luminescence effect.

[0059] The chip's luminous performance test includes applying specified voltage and current to the LED chip to observe whether it can light up normally, so as to verify whether the electrical connection of the LED chip is good and whether the chip itself has the ability to emit light; and it can measure the brightness of multiple LED chips under the same test conditions and compare the differences between them to ensure the brightness consistency of the LED chip and meet the requirements for light uniformity in practical applications.

[0060] It is worth noting that LED chips that do not meet the requirements can be further removed and replaced, because the technical solution of the present application uses conductive glue to complete the mounting of LED chips. When they need to be removed and replaced, it is only necessary to heat the defective LED chips to melt the conductive glue between the chip and the substrate to remove the defective products. This is simple and convenient, and will not cause thermal damage to other normal chips.

[0061] Finally, ultrasonic cleaning is performed to remove impurities in the welding process and improve the surface cleanliness of the product. Then, step S40 can be performed.

[0062] Step S40, coating a plastic packaging material on the substrate to wrap the LED chip, and completing the packaging of the LED chip after curing.

[0063] It is understandable that plastic encapsulation materials are an important part of LED chip packaging, affecting the performance and reliability of LED devices. Common plastic encapsulation materials include epoxy resin, polyimide and other polymers, which have good insulation, heat resistance and mechanical strength, and can effectively protect LED chips from damage by the external environment.

[0064] Among them, the plastic encapsulation material can be injected into a specific area on the substrate by a mold coating method to ensure that there are no bubbles and impurities in the plastic encapsulation material and the coating thickness is moderate. After the coating is completed, the plastic encapsulation material is subjected to a certain temperature and time curing treatment to ensure that the plastic encapsulation material can be fully cross-linked and form good mechanical properties, so that it forms a stable packaging structure.

[0065] After curing is completed, random inspections can be performed to ensure that each batch of products meets quality standards before shipment.

[0066] The present application also provides a packaging structure of a Mini / Micro LED chip, which is prepared by the packaging method of the Mini / Micro LED chip as described above. Figure 4 The schematic diagram of the packaging structure is shown. It includes a substrate 10 and an LED chip 20. The LED chip 20 is mounted on the substrate 10. The pads on the LED chip 20 correspond to the pads on the substrate 10 one by one (the pads on the substrate are the first pads 11, and the pads on the LED chip are the second pads 21). A conductive layer 30 is provided between the pads. The conductive layer includes a metal conductive ball 31 and a conductive glue 32 coated on the surface of the metal conductive ball 31. The conductive glue 32 is used to mechanically connect the LED chip 20 and the substrate 10 on both sides. The two ends of the metal conductive ball 31 contact the LED chip 20 and the substrate 10 to form a main electrical connection channel. A transparent film 40 is attached to the light-emitting area of ​​the LED chip 20. The surrounding side and the bottom are filled with black semi-solid glue 50. Finally, a plastic packaging material 60 is provided to wrap the LED chip 20 to form a package for the LED chip 20.

[0067] The above description is only a partial or preferred embodiment of the present application. Neither the text nor the drawings can limit the scope of protection of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the overall concept of the present application, or direct / indirect application in other related technical fields are included in the scope of protection of the present application.

Claims

1. A packaging method for a Mini / Micro LED chip, characterized in that: include: Conductive particles and pads of the substrate are subjected to electrostatic polarization treatment with opposite charge polarities, and the conductive particles are adsorbed on the pads of the substrate; the conductive particles include metal conductive balls and conductive glue coated on the surfaces of the metal conductive balls; Aligning and laminating the LED chip on the substrate so that the pads on the LED chip contact the corresponding conductive particles; Hot pressing the LED chip to melt the conductive adhesive by heat conduction, so that the LED chip is fixed on the substrate by the conductive adhesive after cooling; A plastic packaging material is coated on the substrate to wrap the LED chip, and the packaging of the LED chip is completed after curing.

2. The packaging method of Mini / Micro LED chip according to claim 1, characterized in that: Before the electrostatic polarization treatment of opposite charge polarities is performed on the conductive particles and the pads of the substrate, the conductive particles are prepared. The preparation steps of the conductive particles include: Preparing metal conductive balls; the metal conductive balls include tin balls, silver balls and nickel balls; Conductive glue is evenly coated on the surface of the metal conductive ball to prepare the conductive particles.

3. The packaging method of Mini / Micro LED chip according to claim 2, characterized in that: The electrostatic polarization treatment of the conductive particles and the pads of the substrate with opposite charge polarities comprises: Placing conductive particles in an electrostatic pipe and applying voltage so that the surface of the conductive particles has a uniform positive or negative charge; The pads of the substrate are connected via a test port, and charges opposite to those on the surfaces of the conductive particles are applied to the pads of the substrate.

4. The packaging method of Mini / Micro LED chip according to claim 3, characterized in that: The step of adsorbing the conductive particles onto the pads of the substrate comprises: Scan and capture the pad positions of the substrate to establish pad coordinate data; According to the pad coordinate data, the conductive particles with charge polarity are placed on the substrate, and under the effect of mutual attraction between charges of different types, the conductive particles are rolled and adsorbed on the pad of the substrate.

5. The packaging method of Mini / Micro LED chip according to claim 4, characterized in that: After the conductive particles are rolled and adsorbed on the pads of the substrate, the method further comprises: Detecting the adsorption state of the conductive particles on the pads of the substrate; the adsorption state includes whether the conductive particles are missing, overlapped or offset; Based on the adsorption state, the arrangement of the conductive particles is adjusted so that the conductive particles meet adsorption setting requirements.

6. The packaging method of Mini / Micro LED chip according to claim 1, characterized in that: The step of hot pressing the LED chip to melt the conductive adhesive by heat conduction, and fixing the LED chip on the substrate by the conductive adhesive after cooling, comprises: Setting hot pressing parameters, and heating and pressing the LED chip toward the substrate under the hot pressing parameters; the heating temperature in the hot pressing parameters corresponds to the hot melting temperature of the conductive adhesive; The cooling process is performed at a cooling rate of not less than 10°C / S, so that the LED chip and the substrate on both sides are mechanically connected through the curing of the conductive adhesive, and the LED chip is fixed on the substrate.

7. The packaging method of Mini / Micro LED chip according to claim 1, characterized in that: The method further comprises fixing the LED chip on the substrate by the conductive adhesive after cooling: Removing excess conductive particles and contaminants from around the pads of the substrate; Laminating an LED chip protection film to protect the light-emitting performance of the LED chip; the LED chip protection film comprises a composite transparent film and a black semi-solid glue; Perform quality inspection after the LED chip is mounted and fixed on the substrate.

8. The packaging method of Mini / Micro LED chip according to claim 7, characterized in that: The step of laminating the LED chip protective film to protect the light emitting performance of the LED chip includes: Positioning and laminating the LED chip protection film so that the transparent film in the LED chip protection film corresponds to the light-emitting area of ​​the LED chip, and the black semi-solid glue corresponds to the peripheral side of the LED chip; The black semi-solid glue is pressed downward to separate the black semi-solid glue from the transparent film and flow to the periphery and bottom of the LED chip.

9. The packaging method of Mini / Micro LED chip according to claim 7, characterized in that: The quality inspection after the LED chip is mounted and fixed on the substrate includes: Detect whether the appearance is correctly set; the appearance includes whether the LED chip protective film is correctly attached and whether the LED chip is skewed; The light-emitting performance of the LED chip is tested; the light-emitting performance of the LED chip includes whether the chip can be lit and whether the brightness of the chip is consistent.

10. A packaging structure of a Mini / Micro LED chip, characterized in that: It is prepared by the packaging method of the Mini / Micro LED chip as described in any one of claims 1 to 9.

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