Package Structure and Packaging Method of Mini / Micro LED Chips

Abstract

The present application discloses a packaging structure and a packaging method for Mini / Micro LED chips. The packaging method includes: respectively performing static electrode 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; 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; thermally pressing the LED chip, melting the conductive glue through heat conduction, and fixing the LED chip on the substrate through the conductive glue after cooling; coating a plastic encapsulation material on the substrate to wrap the LED chip, and completing the encapsulation of the LED chip after curing. The technical solution of the present application can make the LED chip packaging process simpler and faster, can achieve stable mechanical connection and excellent electrical connection between the LED chip and the substrate, and effectively avoids the problem of chip damage caused by excessive temperature.

Description

Technical Field

[0001] This application relates to the technical field of semiconductor light-emitting devices, and particularly to a packaging structure and method for Mini / Micro LED chips. Background Art

[0002] A display screen with higher resolution has more pixel points on the screen. For example, a 4K display screen has 8,294,400 pixel points, and an 8K display screen has 33,177,600 pixel points. And each pixel point requires 3 LED chips (red, green, and blue). In the traditional process, the positive and negative electrodes of each chip need to be welded. Therefore, the number of welded LED chips reaches tens of millions or even is measured in hundreds of millions.

[0003] In the prior art, the reflow soldering process is usually used to realize the soldering of Mini / Micro LEDs. However, due to the extremely small pad size of Mini / Micro LED chips, only 10 - 50 microns or even smaller, the solder paste is limited by the opening size of the stencil during the reflow soldering process and cannot meet the requirements of precise printing. Moreover, the solder paste has strong viscosity. In the case of a small opening size of the stencil, even if the solder paste adheres to the PCB board or the glass substrate, the solder paste may not fall off the stencil smoothly. In addition, too high reflow soldering temperature will also increase the risk of damage to the chips.

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

[0005] This application provides a packaging structure and method for Mini / Micro LED chips, aiming to solve the problems of difficult packaging and easy damage to the chips in the prior art for Mini / Micro LED chips.

[0006] To achieve the above object, this application proposes a packaging method for Mini / Micro LED chips. The method includes:

[0007] Performing static electrode polarization treatment with opposite charge polarities on the conductive particles and the pads of the substrate respectively, 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;

[0008] Aligning and attaching the LED chips to the substrate so that the pads on the LED chips contact the corresponding conductive particles;

[0009] Thermally pressing the LED chips to melt the conductive glue through heat conduction, so as to fix the LED chips on the substrate through the conductive glue after cooling;

[0010] Apply a plastic encapsulation material on the substrate to wrap the LED chip, and complete the encapsulation of the LED chip after curing.

[0011] In some embodiments, before the static electrode polarization treatment of the conductive particles and the pads of the substrate with opposite charge polarities, it further includes:

[0012] Prepare metal conductive balls; the metal conductive balls include tin balls, silver balls, and nickel balls;

[0013] Uniformly coat a conductive adhesive on the surface of the metal conductive balls to prepare and form the conductive particles.

[0014] In some embodiments, the static electrode polarization treatment of the conductive particles and the pads of the substrate with opposite charge polarities includes:

[0015] Place the conductive particles in an electrostatic pipeline, apply a voltage to make the surface of the conductive particles carry uniform positive or negative charges;

[0016] Connect the pads of the substrate through a test port, and apply a charge opposite to the surface of the conductive particles to the pads of the substrate.

[0017] In some embodiments, the step of adsorbing the conductive particles on the pads of the substrate includes:

[0018] Scan and capture the positions of the pads of the substrate to establish pad coordinate data;

[0019] According to the pad coordinate data, place the conductive particles with charge polarities on the substrate, and under the action of the attraction between opposite charges, make the conductive particles roll and adsorb on the pads of the substrate.

[0020] In some embodiments, after the conductive particles are made to roll and adsorb on the pads of the substrate, it further includes:

[0021] Detect the adsorption state of the conductive particles on the pads of the substrate; the adsorption state includes the situations of omission, overlap, or deviation of the conductive particles;

[0022] Based on the adsorption state, adjust the arrangement of the conductive particles so that the conductive particles meet the adsorption setting requirements.

[0023] In some embodiments, the step of 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 includes:

[0024] Set the hot pressing parameters, and heat and press the LED chip towards the substrate under the hot pressing parameters; the heating temperature in the hot pressing parameters is the hot melting temperature corresponding to the conductive adhesive.

[0025] Perform a cooling and temperature reduction treatment at a cooling rate of not less than 10 °C / S, so as to mechanically connect the LED chips on both sides and the substrate through the curing of the conductive adhesive, and fix the LED chips on the substrate.

[0026] In some embodiments, after fixing the LED chips on the substrate through the conductive adhesive after cooling, it further includes:

[0027] Remove the excess conductive particles and contaminants around the pads of the substrate.

[0028] Attach an LED chip protective film to form a protection for the light-emitting performance of the LED chip; the LED chip protective film includes a transparent film and a black semi-solid adhesive formed by compounding.

[0029] Perform quality inspection after the LED chips are mounted and fixed on the substrate.

[0030] In some embodiments, attaching the LED chip protective film to form a protection for the light-emitting performance of the LED chip includes:

[0031] Position and attach the LED chip protective film so that the transparent film in the LED chip protective film corresponds to the light-emitting area of the LED chip, and the black semi-solid adhesive corresponds to the peripheral side of the LED chip.

[0032] Press down the black semi-solid adhesive so that the black semi-solid adhesive detaches from the transparent film and flows to the periphery and bottom of the LED chip.

[0033] In some embodiments, performing quality inspection after the LED chips are mounted and fixed on the substrate includes:

[0034] Detect whether the appearance form is set correctly; the appearance form includes whether the LED chip protective film is attached correctly and whether the LED chips are skewed.

[0035] Test the light-emitting performance of the LED chip, and the light-emitting performance of the LED chip includes whether the chip can be lit and whether the chip brightness is consistent.

[0036] The present application also provides a packaging structure of a Mini / Micro LED chip, which is prepared by using the above-mentioned packaging method of the Mini / Micro LED chip.

[0037] The technical solution of this application proposes a packaging method for Mini / Micro LED chips. The method includes: respectively performing static electrode polarization treatment with opposite charge polarities on 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 attaching the LED chip to the substrate, and making the pads on the LED chip contact the corresponding conductive particles; thermally pressing the LED chip, melting the conductive glue through heat conduction, and fixing the LED chip on the substrate through the conductive glue after cooling; coating a plastic encapsulation material on the substrate to wrap the LED chip, and completing the encapsulation of the LED chip after curing. The technical solution of this application does not require complex physical operations. Through the method of electrostatic adsorption, the conductive particles can be quickly and evenly distributed on the pads of the substrate. Further, based on the structural design of the conductive particles, after the LED chip is aligned and attached to the substrate and thermally 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 melting temperature of the conductive glue in this implementation method is much lower than the working temperature of traditional reflow soldering, so the problem of chip damage caused by excessive temperature can be effectively prevented. 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

[0038] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings, where:

[0039] Figure 1 is a schematic flow chart of a packaging method for a Mini / Micro LED chip according to an embodiment of this application Figure 1 ;

[0040] Figure 2 is a schematic flow chart of a packaging method for a Mini / Micro LED chip according to an embodiment of this application Figure 1 ;

[0041] Figure 3 is a schematic flow chart of a packaging method for a Mini / Micro LED chip according to an embodiment of this application Figure 3 ;

[0042] Figure 4 is a schematic diagram of a packaging structure of a Mini / Micro LED chip according to an embodiment of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts belong to the scope of protection of the present application.

[0044] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present application are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0045] It should also be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can 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 can be directly connected to the other element or there may be an intermediate element at the same time.

[0046] In addition, the descriptions involving "first", "second", etc. in the present application are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present application.

[0047] Refer to Figure 1 As shown, the present application proposes a packaging method for Mini / Micro LED chips. The aim is to fix the LED chips on the substrate and achieve electrical connection with the substrate. The substrate includes a PCB board and a glass substrate. Among them, pads are correspondingly provided on the substrate and the LED chips. The LED is mounted on the substrate, and mechanical connection and electrical connection are achieved through the setting of the conductive layer between the pads of the two.

[0048] This packaging method includes:

[0049] Step S10, perform static electrode polarization treatment with opposite charge polarities on the conductive particles and the pads of the substrate respectively, and adsorb the conductive particles on the pads of the substrate.

[0050] In this step, the conductive particles are the conductive layer. Therefore, this step is actually the step of setting the conductive layer on the substrate.

[0051] Among them, static polarization refers to the change in the charge distribution inside a substance under the action of an external electric field. In this step, opposite-direction electric fields are applied to the conductive particles and the pads of the substrate respectively, so that they carry opposite charge polarities, thereby generating an electrostatic attraction between the conductive particles and the substrate, further enabling the conductive particles to be distributed quickly and evenly on the pads of the substrate, providing a good foundation for the alignment, fitting and connection of subsequent LED chips.

[0052] Refer to Figure 2 As shown, before the static polarization treatment of opposite charge polarities is carried out on the conductive particles and the pads of the substrate respectively, it also includes:

[0053] Step S1, prepare conductive particles. The preparation method of the conductive particles includes preparing metal conductive balls and then uniformly coating a conductive adhesive on the surface of the metal conductive balls.

[0054] Specifically, it includes using a gas-phase spraying method or a mechanical separation method to produce conductive metal balls. The metal conductive balls include metal balls such as tin balls, silver balls and nickel balls. The diameter of the metal conductive balls is controlled within 3 - 20μm, and the particle size error is strictly controlled within ±0.5μm, so as to ensure that the prepared conductive particles can be arranged between the pads of the LED chip and the pads of the substrate later 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 particle size consistency of the metal conductive balls.

[0055] Furthermore, a uniform and dense conductive adhesive is formed on the surface of the metal conductive balls by CVD chemical vapor deposition or spin coating process. The thickness of the conductive adhesive is controlled within the range of 3% - 10% of the diameter of the metal conductive balls (preferred thickness), and the maximum thickness does not exceed 25% of the diameter of the metal conductive balls (peak thickness); thus, while ensuring that the conductive adhesive can provide sufficient connection strength, it will not overly increase the thickness of the packaging structure. Among them, after the conductive adhesive coating is completed, the energy distribution of photoelectrons can be analyzed by XPS (X-ray photoelectron spectroscopy) to detect the chemical composition, oxidation state and thickness of the conductive adhesive layer. The XPS detection method has high resolution and can detect thickness changes at the nanometer level. Also, after the conductive adhesive coating is completed, the microstructure of the conductive adhesive can be detected by SEM (scanning electron microscope). The surface of the metal conductive balls 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 adhesive. Its resolution can reach 1nm, and the microstructure and defects of the conductive adhesive layer can be clearly observed.

[0056] In this way, through strict particle size control, precise conductive adhesive coating and advanced detection means in the preparation of the conductive particles, the production quality of the conductive particles is ensured, providing a high-quality material basis for the packaging of Mini / Micro LED chips.

[0057] Among them, the 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, providing a variety of types for selection. Specifically, silver-based conductive adhesives use silver powder as the main conductive filler, with high conductivity and excellent thermal conductivity; they are suitable for high-precision applications, can provide stable electrical connections, and are suitable for hot melt processes at lower temperatures. Copper-based conductive adhesives use copper powder as the conductive filler, with lower costs and good conductivity, suitable for scenarios that are cost-sensitive but require high conductivity, and the antioxidant performance can be improved through surface passivation treatment. Carbon-based conductive adhesives use graphite or carbon nanotubes as fillers, with conductivity slightly inferior to that of metals, but with flexibility and light weight characteristics, suitable for scenarios with strict weight requirements or high-temperature resistance requirements. Metal oxide conductive adhesives use metal oxides (such as ITO) as fillers, suitable for transparent electronic devices and encapsulation 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 flexible packaging requirements. Mixed filler conductive adhesives use silver powder, copper powder, and carbon materials, etc. in combination to balance conductivity and cost; they are suitable for scenarios that seek a balance between performance and price.

[0058] After the preparation of the conductive particles is completed, the conductive particles and the pads on the substrate can be statically polarized respectively, so that the two have opposite charge polarities, preparing for the adsorption of the metal conductive balls on the substrate. Among them:

[0059] The static polarization method of the conductive particles can be: placing the prepared conductive particles in an electrostatic pipeline, which is an enclosed space for generating and maintaining an electrostatic field. Apply a high voltage of 5 - 20 KV in the electrostatic pipeline to make the surface of the conductive particles carry uniform positive or negative charges. To ensure the uniformity and stability of the surface charges of the conductive particles, when applying the voltage, 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 charges of the conductive particles.

[0060] The static polarization method of the pads on the substrate can be: connecting all the pads on the substrate through a test port, which is an interface for applying voltage and monitoring the charge state. Then apply a charge opposite to the surface of the conductive particles to the pads on the substrate. This means that if the conductive particles carry positive charges, then the pads on the substrate need to carry negative charges; vice versa.

[0061] It should be noted that the absolute value of the voltage used for static polarization of the pads on the substrate is 1.2 to 2.0 times (preferred voltage value) the voltage value for static polarization of the conductive particles, and does not exceed 10 times (peak voltage) at most. Exemplarily, when the voltage applied in the electrostatic pipeline is ±5 kv, the static polarization voltage of the pads on the substrate is not less than ±6 kv. The selection of this voltage range can ensure that sufficient electrostatic attraction can be generated between the pads on the substrate and the conductive particles, so as to achieve rapid and uniform adsorption.

[0062] In addition, adsorbing the conductive particles onto the pads of the substrate includes: scanning and capturing the positions of the pads on 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 is used to comprehensively scan the substrate, such as a CCD camera. Then, according to the pad coordinate data, the number and positions of the pads on 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 action of the attraction between opposite charges, the conductive particles start to roll and adsorb onto the pads of the substrate.

[0063] It can be understood that since the size of the pads on the substrate is three to four times the size of the conductive particles, therefore, multiple conductive particles can be simultaneously adsorbed on the pads of the same substrate. When at least one conductive particle contacts the LED chip and the pad of the substrate on both sides at the same time, the connection between the LED chip and the substrate (including mechanical connection and electrical connection) can be realized.

[0064] Among them, before static polarization of the substrate, the surface of the pads can be pre-treated in advance, such as using a plasma cleaning device to remove the oxide layer and contaminants on the surface of the pads of the substrate with oxygen or argon to improve the adsorption effect of the conductive particles.

[0065] At the end of the arrangement of the conductive particles, the adsorption state of the conductive particles on the pads of the substrate can also be detected by an automatic optical inspection device (AOI); and based on the adsorption state, the arrangement of the conductive particles is adjusted to make the conductive particles meet the adsorption setting requirements.

[0066] Exemplarily, the AOI device uses a high-resolution camera to capture images of the pads on the substrate and the conductive particles thereon. The captured images are processed by an image processing algorithm to identify the positions, shapes and sizes of the conductive particles. Then, by comparing with the preset adsorption setting requirements, the AOI device 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 device, 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, so as to realize the automatic adjustment of the arrangement of the conductive particles.

[0067] Thus, the setting of the conductive particles (conductive layer) on the pads of the substrate is completed. Compared with the traditional reflow solder paste setting process, it can achieve precise and rapid coverage of the conductive layer on the pads of the substrate, solve the problem of solder ball pollution, and improve the conductivity and overall reliability of the substrate to the LED chip.

[0068] Step S20: Align and attach the LED chip to the substrate, and make the pads on the LED chip contact the corresponding conductive particles.

[0069] In this step, the aim is to achieve the corresponding relationship between the LED chip and the substrate, make the pads on the LED chip correspond to the pads on the substrate, so as to facilitate the connection through the conductive particles between the two pads in the subsequent steps.

[0070] It can be understood that this application is for the integrated packaging of several LED chips. There are multiple pads arranged on the substrate, and several LED chips are packaged on the substrate to form a light-emitting component such as a display screen. Among them, before the LED chips are attached to the substrate, several LED chips can be automatically arranged in a crystal. The steps include:

[0071] Several LED chips are transported to the crystal arranging device. Using a high-precision manipulator or a vacuum adsorption system, pick up the LED chips and arrange the LED chips on the PET film with the pads facing up in a preset array manner. This can significantly improve the production efficiency, reduce manual intervention and errors, and achieve efficient and accurate arrangement of LED chips, thereby laying a foundation for the subsequent packaging operation.

[0072] Then, based on the PET film, the LED chips are aligned and attached to the substrate. The steps include: Invert the PET film with the arranged crystals so that the pads of the LED chips face down, so as to align and attach with the pads on the substrate. Then use a high-precision alignment system, such as a high-precision camera, to capture the position information of the LED chips on the PET film, compare it with the position information of the pads on the substrate, and control the precise mechanical adjustment structure for fine adjustment to ensure the precise alignment between the pads of the LED chips and the substrate. After the alignment is completed, gently attach the PET film to the substrate to ensure that the pads on the LED chips are in full contact with the conductive particles and avoid damaging the LED chips and the substrate.

[0073] Among them, the whole process needs to be operated in a dust-free clean room, and strictly control environmental parameters such as temperature, humidity and cleanliness, which can reduce the pollution risk of LED chips.

[0074] Step S30: Thermally press the LED chip, melt the conductive adhesive through heat conduction, and fix the LED chip on the substrate through the conductive adhesive after cooling.

[0075] In this step, after the hot pressing operation is completed, heating is stopped and the LED chip and the substrate are cooled. 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 a reliable electrical connection to ensure the normal operation of the LED chip.

[0076] It can be understood that based on the structural setting of the conductive particles, under the action of hot pressing, the conductive adhesive at both 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, on the premise that the conductive adhesive forms a stable mechanical connection, an electrical connection mainly composed of metal conductive balls is further formed.

[0077] Specifically, this hot pressing and cooling process includes: setting hot pressing parameters, hot pressing the adhered PCB board and PET film, that is, heating and pressing the LED chip towards the substrate under the hot pressing parameters; then using compressed air or other cooling methods to rapidly reduce the temperature.

[0078] Among them, the heating temperature in the hot pressing parameters is the hot melting temperature corresponding to the conductive adhesive, generally between 100 and 150 °C (the peak does not exceed 250 °C), and the hot pressing pressure used is between 20 and 100 N (the peak does not exceed 200 N), and the hot pressing time is 5 to 30 min (the peak does not exceed 120 min). The cooling and temperature reduction speed is not less than 10 °C / S, which can reduce the influence of thermal stress on the LED chip and the welding point. In this way, by precisely controlling the hot pressing parameters and implementing measures such as close contact and rapid cooling, a stable and reliable electrical connection can be ensured between the LED chip and the substrate, improving the quality and reliability of the product.

[0079] 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 adhesive has solidified, and there is no adhesion and damage at the edge of the PET film to ensure the smooth progress of the tearing process. Then, an automated device is used to control the peeling angle, 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 between 30° and 45° to reduce the pulling force on the LED chip. The peeling speed is controlled between 0.5 and 1.5 mm / s to tear off the PET film evenly and smoothly. The peeling force is controlled between 0.1 and 0.5 N to avoid excessive force causing the displacement or damage of the LED chip.

[0080] In some embodiments, inspection and cleaning can be further performed after the connection of the LED chips is completed. This includes: using an automatic optical inspection device to inspect the chips to promptly detect and eliminate potential quality problems, ensuring the qualification rate and reliability of the products. The AOI device can utilize a high-resolution camera and image processing technology to perform precise visual inspection on the chips. The inspection content includes but is not limited to: whether the LED chips are displaced, damaged (such as cracks, fractures, or charring, etc.), and whether there are residues (such as conductive adhesive overflow, dust, or foreign objects, etc.). If the AOI inspection finds contaminants such as residues or dust on the substrate surface, it can be cleaned with a lint-free cloth or an ion air gun.

[0081] and referring to Figure 3 As shown, in some embodiments, after fixing the LED chips on the substrate with conductive adhesive after cooling, it further includes:

[0082] Step S31, removing the excess conductive particles and contaminants around the pads of the substrate.

[0083] In this step, plasma cleaning can be used for the cleaning operation, 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. Among them, if the contaminants are mainly organic substances, oxygen can be selected; if the contaminants are mainly inorganic substances or particulate matter, argon or a mixed gas can be selected. The cleaning time and power are further set to ensure safety and effectiveness during cleaning. Exemplarily, the cleaning time is set at 10 - 20 s, and the power is set at 50 - 200 watts.

[0084] Step S32, attaching the LED chip protective film to form protection for the light-emitting performance of the LED chips; the LED chip protective film includes a composite transparent film and a black semi-solid adhesive.

[0085] In this step, the transparent film and the black semi-solid adhesive in the LED chip protective film are composite formed. The transparent film is used to cover the light-emitting area of the LED chips, and the black semi-solid adhesive is used to fill around and at the bottom of the LED chips. Among them, the transparent film is usually made of silicone materials (such as epoxy resin or silica gel), so as to effectively avoid damage to the LED chips caused by external factors such as dust, moisture, and mechanical impact. The black semi-solid colloid has excellent light-shielding performance and heat-conducting performance. Therefore, it can improve the light-emitting efficiency and contrast of the LED chips while reducing the working temperature of the chips, enabling the applied LED chips to achieve a clearer image display effect and a longer service life.

[0086] The steps for laminating the protective film include: laminating a transparent film and a black semi-solid adhesive, cutting them into a size suitable for the LED chip, and precisely positioning the protective film using a CCD system. Under a slight pressure, such as a pressure of 0.5 - 1 N, the black semi-solid adhesive is made to flow around and under the chip. Then, the transparent film and the black semi-solid adhesive are fixed by UV curing (wavelength 365 nm, 10 - 30 s) or thermal curing (temperature 80 - 120 °C, time 5 - 10 min). Finally, the mounting effect of the chip protective film is inspected.

[0087] Step S33, perform quality inspection after the LED chip is mounted and fixed on the substrate.

[0088] In this step, it specifically includes: inspecting whether the appearance form is correctly set and the luminous performance of the LED chip.

[0089] Among them, the appearance form includes evaluating whether the LED chip protective film is correctly laminated on the chip by visual inspection or an automatic optical inspection device, such as no bubbles, wrinkles or peeling, etc., so as to ensure that the protective film can effectively protect the LED chip from the external environment and does not affect its luminous property; and inspecting 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 luminous effect.

[0090] The detection of the luminous performance of the chip includes applying a specified voltage and current to the LED chip and observing whether it can be normally lit to verify whether the electrical connection of the LED chip is good and whether the chip itself has the luminous ability; and being able to 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 chips and meet the requirements for light uniformity in practical applications.

[0091] It should be noted that the non-conforming LED chips detected can be further removed and replaced. Because the technical solution of this application uses a conductive adhesive to complete the mounting of the LED chip, when it is necessary to remove and replace, only the defective LED chip needs to be heated to melt the conductive adhesive between the chip and the substrate, and then the defective product can be detached, which is simple and convenient and will not cause thermal damage to other normal chips.

[0092] Finally, perform ultrasonic cleaning to remove impurities during the welding process and improve the surface cleanliness of the product. Then step S40 can be carried out.

[0093] Step S40, coat a plastic encapsulation material on the substrate to wrap the LED chip, and complete the encapsulation of the LED chip after curing.

[0094] It is understandable that the encapsulation material is an important part in the encapsulation of LED chips, which affects the performance and reliability of LED devices. Common encapsulation materials include high molecular polymers such as epoxy resin and polyimide, which have good insulation, heat resistance and mechanical strength, and can effectively protect the LED chips from damage by the external environment.

[0095] Among them, the encapsulation material can be injected into a specific area on the substrate by the mold coating method to ensure that there are no bubbles and impurities in the encapsulation material and the coating thickness is appropriate. After the coating is completed, the encapsulation material is cured at a certain temperature and for a certain time to ensure that the encapsulation material can be fully crosslinked and form good mechanical properties, so as to form a stable encapsulation structure.

[0096] And after the curing is completed, random inspections can be immediately carried out to ensure that each batch of products meets the quality standards. Then the products are shipped.

[0097] This application also provides an encapsulation structure for Mini / Micro LED chips, which is prepared by using the above-mentioned encapsulation method for Mini / Micro LED chips. As Figure 4 shown in the schematic diagram of the encapsulation structure. 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 one by one to the pads on the substrate 10 (the pads on the substrate are the first pads 11, and the pads on the LED chip are the second pads 21). And a conductive layer 30 is provided between the pads. The conductive layer includes metal conductive balls 31 and conductive glue 32 coated on the surface of the metal conductive balls 31. The conductive glue 32 is used for mechanically connecting the LED chips 20 on both sides and the substrate 10, while both ends of the metal conductive balls 31 contact the LED chip 20 and the substrate 10 to form the main electrical connection channels. And a transparent film 40 is attached to the light-emitting area of the LED chip 20, the peripheral side and the bottom are filled with black semi-solid glue 50, and finally an encapsulation material 60 is provided to wrap the LED chip 20 to form an encapsulation of the LED chip 20.

[0098] The above are only partial or preferred embodiments of this application. Whether in terms of text or drawings, the scope of protection of this application cannot be limited thereby. Any equivalent structural transformation made by using the content of the specification and drawings of this application under the overall concept of this application, or any direct / indirect application in other related technical fields is included in the scope of protection of this application.

Claims

1. A packaging method for a Mini / Micro LED chip, characterized in that: include: Conductive particles and pads of a 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 surface of the metal conductive balls; the conductive glue includes silver-based conductive glue, copper-based conductive glue, carbon-based conductive glue, metal oxide conductive glue, conductive polymer glue and mixed filler conductive glue; 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 the conductive particles and the pads of the substrate with opposite charge polarities is performed, 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 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.

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: inspecting whether the appearance is correctly set; the appearance includes whether the LED chip protection 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.

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