Preparation method of LED display module and LED display module

Abstract

The present application provides a method for preparing an LED display module and an LED display module, the method comprising: welding a flip-chip LED chip to a circuit substrate, the flip-chip LED chip comprising an epitaxial layer, a sacrificial layer and a substrate; using a laser lift-off process to decompose the sacrificial layer into metal Ga and nitrogen to obtain a first LED display module; immersing the first LED display module in a first organic solvent and performing ultrasonic cleaning to at least cause the substrate to fall off into the first organic solvent to obtain a second LED display module; immersing the second LED display module in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate to obtain a third LED display module; encapsulating at least the third LED display module to obtain an encapsulation layer, the encapsulation layer covering the epitaxial layer and the circuit substrate. The present application solves the problem of complex and high-cost substrate-free Micro LED process in the prior art.

Description

Technical Field

[0001] The present application relates to the technical field of LED (Light Emitting Diode) display modules, and in particular to a method for preparing an LED display module and an LED display module. Background Art

[0002] Existing LED display screens, if using flip-chip RGB LED (Red Green Blue Light Emitting Diode) chips, will have the problem of side viewing angle color cast, that is, the screen's front viewing angle and side viewing angle color are inconsistent; the main reason for the color cast is that the half-power angles of RGB LED chips are different, and the half-power angle of R is smaller than that of G and B. There are two main factors that cause this problem. First, the sapphire substrate used by GB LED chips is mostly a graphic substrate, which expands the half-power angle of G and B; second, although the light-emitting surface of the flip-chip RGB is sapphire, the red light epitaxial layer luminescent material is AlGaInP, the material refractive index is much greater than that of sapphire, and the total reflection angle is small; while the luminescent material of G and B is GaN, the refractive index difference with sapphire is smaller, so the total reflection angle is greater than that of red light LED. The above two factors cause the half-power angle of GB to be greater than that of red light. If such RGB chips are used in LED display screens, it will cause color cast of the display screen.

[0003] There is no unique improvement technology for the above-mentioned problems in the existing technology. However, in the LED display industry, the size of LED chips is getting smaller and smaller, and the miniaturization of LED chips is the development trend of the industry. As the size of LED chips decreases, the cutting yield of LED chips with sapphire substrates is too low to be applied. Therefore, sapphire substrate peeling is also the development trend of the industry. The half-power angles of RGB LEDs after sapphire peeling tend to be consistent, so the color cast problem of LED display screens can be solved; however, after sapphire peeling, the LED is only a thin film of about 5μm, and traditional crystal bonding technology cannot be used for welding. Only laser mass transfer technology can be used to transfer the substrate-free Micro LED to the circuit substrate, and the LED after substrate peeling cannot be point-tested, and the yield cannot be guaranteed. Therefore, the above-mentioned technology is still under development and has not yet fully matured. Summary of the invention

[0004] The main purpose of the present application is to provide a method for preparing an LED display module and an LED display module to solve the problem of complex and high cost of substrate-free Micro LED process in the prior art.

[0005] To achieve the above-mentioned purpose, according to one aspect of the present application, a method for preparing an LED display module is provided, comprising: soldering a flip-chip LED chip to a circuit substrate, wherein the flip-chip LED chip comprises an epitaxial layer, a sacrificial layer and a substrate stacked in sequence, the material of the sacrificial layer comprises GaN, the material of the substrate comprises sapphire, and the epitaxial layer is in contact with the circuit substrate; using a laser lift-off process, focusing a laser light source on the position where the sacrificial layer is located, and performing laser scanning to decompose the sacrificial layer into metal Ga and nitrogen to obtain a first LED display module; immersing the first LED display module in a first organic solvent, and performing ultrasonic cleaning to at least make the substrate fall off into the first organic solvent to obtain a second LED display module; immersing the second LED display module in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate to obtain a third LED display module; and encapsulating at least the third LED display module to obtain an encapsulation layer, wherein the encapsulation layer covers the epitaxial layer and the circuit substrate.

[0006] Optionally, immersing the first LED display module in a first organic solvent and performing ultrasonic cleaning to at least cause the substrate to fall off into the first organic solvent, including: immersing the first LED display module in acetone and performing ultrasonic cleaning to at least cause the substrate to fall off into the acetone.

[0007] Optionally, immersing the second LED display module in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate includes: immersing the second LED display module in dilute hydrochloric acid to dissolve the metal Ga.

[0008] Optionally, soldering the flip-chip LED chip to the circuit substrate includes: soldering the flip-chip LED chip to a predetermined surface of the circuit substrate, after soldering the flip-chip LED chip to the predetermined surface of the circuit substrate, and before using a laser lift-off process to focus the laser light source on the position where the sacrificial layer is located, the method also includes: covering the predetermined surface and the flip-chip LED chip with a preliminary protective layer, the material of the preliminary protective layer including a photosensitive resin, and the properties of the photosensitive resin do not change at a temperature of 120°C-180°C; removing part of the preliminary protective layer, and the remaining preliminary protective layer forms a protective layer, the protective layer is located on the predetermined surface not covered by the flip-chip LED chip, and a first distance is not greater than a second distance, the first distance being the distance between the surface of the protective layer away from the circuit substrate and the predetermined surface, and the second distance being the distance between the surface of the sacrificial layer away from the circuit substrate and the predetermined surface.

[0009] Optionally, the thickness of the protective layer is greater than the thickness of the epitaxial layer. After obtaining the third LED display module and before at least packaging the third LED display module, the method further includes: using a dispensing device to dispense glue on the surface of the epitaxial layer away from the circuit substrate and baking to form a lens.

[0010] Optionally, the flip-chip LED chip also includes a buffer layer, wherein the buffer layer is located between the sacrificial layers of the substrate, and the first LED display module is immersed in a first organic solvent and ultrasonically cleaned so that at least the substrate falls off into the first organic solvent, comprising: immersing the first LED display module in the first organic solvent and ultrasonically cleaning so that the substrate and the buffer layer fall off into the first organic solvent.

[0011] Optionally, the flip-chip LED chip comprises a flip-chip red LED chip, a flip-chip green LED chip and a flip-chip blue LED chip spaced apart in a first direction, the flip-chip green LED chip is located between the flip-chip red LED chip and the flip-chip blue LED chip, the flip-chip red LED chip comprises a first sub-epitaxial layer, a first sub-sacrificial layer and a first sub-substrate stacked in sequence, the flip-chip green LED chip comprises a second sub-epitaxial layer, a second sub-sacrificial layer and a second sub-substrate stacked in sequence, the flip-chip blue LED chip comprises a third sub-epitaxial layer, a third sub-sacrificial layer and a third sub-substrate stacked in sequence, The first sub-epitaxial layer, the second sub-epitaxial layer and the third sub-epitaxial layer constitute the epitaxial layer, the first sub-sacrificial layer, the second sub-sacrificial layer and the third sub-sacrificial layer constitute the sacrificial layer, the first sub-substrate, the second sub-substrate and the third sub-substrate constitute the substrate, the first direction is a direction perpendicular to the thickness of the substrate, and at least the third LED display module is packaged, including: using deionized water to clean the third LED display module and drying the cleaned third LED display module; using glue to package the dried third LED display module.

[0012] Optionally, the flip-chip LED chip includes a first sub-flip-chip LED chip, a second sub-flip-chip LED chip and a third sub-flip-chip arranged at intervals in a first direction, the second sub-flip-chip LED chip is located between the first sub-flip-chip LED chip and the third sub-flip-chip LED chip, the first sub-flip-chip LED chip includes a first sub-epitaxial layer, a first sub-sacrificial layer and a first sub-substrate stacked in sequence, the second sub-flip-chip LED chip includes a second sub-epitaxial layer, a second sub-sacrificial layer and a second sub-substrate stacked in sequence, the third sub-flip-chip LED chip includes a third sub-epitaxial layer, a third sub-sacrificial layer and a third sub-substrate stacked in sequence, the first sub-epitaxial layer, the second sub-epitaxial layer and the third sub-epitaxial layer constitute the epitaxial layer, the first sub-sacrificial layer, the second sub-sacrificial layer and the third sub-sacrificial layer constitute the sacrificial layer, the first sub-substrate, the second sub-substrate and the third sub-substrate constitute the substrate, the first sub-flip-chip LED chip, the second sub-flip-chip LED chip and the third sub-flip-chip LED chip have the same luminous color, which is red, green and blue One of the above, wherein the first direction is a direction perpendicular to the thickness of the substrate, after dispensing and baking on the surface of the epitaxial layer away from the circuit substrate to form a lens, and before at least packaging the third LED display module, the method further comprises: when the luminous color of the flip-chip LED chip is the red color, green quantum dots are mixed into the lens on the surface of the second sub-flip-chip LED chip, and blue quantum dots are mixed into the lens on the surface of the third sub-flip-chip LED chip; when the luminous color of the flip-chip LED chip is the green color, red quantum dots are mixed into the lens on the surface of the first sub-flip-chip LED chip, and blue quantum dots are mixed into the lens on the surface of the third sub-flip-chip LED chip; when the luminous color of the flip-chip LED chip is the blue color, red quantum dots are mixed into the lens on the surface of the first sub-flip-chip LED chip, and green quantum dots are mixed into the lens on the surface of the second sub-flip-chip LED chip.

[0013] Optionally, soldering the flip-chip LED chip to the circuit substrate includes: soldering a plurality of the flip-chip LED chips spaced apart in a first direction to the circuit substrate, wherein the first direction is a direction perpendicular to the thickness of the substrate.

[0014] According to another aspect of the present application, there is provided an LED display module, which is prepared by any one of the methods for preparing an LED display module, and comprises: a circuit substrate; an epitaxial layer located on the surface of the circuit substrate; and a packaging layer covering the epitaxial layer and the circuit substrate.

[0015] By applying the technical solution of the present application, a flip-chip LED chip including an epitaxial layer, a sacrificial layer and a substrate is first welded to a circuit substrate, the material of the sacrificial layer including GaN, and then a laser lift-off process is adopted to focus the laser light source on the position where the sacrificial layer is located, and laser scanning is performed to decompose the sacrificial layer into metal Ga and nitrogen to obtain a first LED display module, and then the first LED display module is immersed in a first organic solvent and ultrasonically cleaned to at least make the substrate fall off into the first organic solvent to obtain a second LED display module, and the second LED display module is immersed in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate to obtain a third LED display module, and finally at least the third LED display module is packaged to obtain a packaging layer. Compared with the problem of complex and high cost of substrate-free Micro LED process in the prior art, the present application welds the flip-chip LED chip to the circuit substrate, and uses a laser stripping process after welding to decompose the sacrificial layer into metal Ga and nitrogen, and uses an organic solvent to remove the substrate and dissolve the metal Ga, successfully stripping the sapphire substrate. There is no need to strip the sapphire substrate at the LED chip stage, and no mass transfer process is required. The process is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0017] Figure 1 A schematic diagram showing a process of a method for preparing an LED display module provided in an embodiment of the present application is shown;

[0018] Figures 2 to 6 The schematic diagrams respectively show the structure of an LED display module formed after each process step according to a method for preparing an LED display module provided in an embodiment of the present application.

[0019] The above drawings include the following reference numerals:

[0020] 10. Flip-chip LED chip; 11. Circuit board; 101. Epitaxial layer; 102. Sacrificial layer; 103. Substrate; 1021. Metal Ga; 12. First LED display module; 13. Encapsulation layer; 110. Predetermined surface; 15. Protective layer; 16. Lens; 17. Flip-chip red LED chip; 18. Flip-chip green LED chip; 19. Flip-chip blue LED chip; 171. First sub-epitaxial layer; 172. First sub-sacrificial layer; 173. First sub-substrate; 181. Second sub-epitaxial layer; 182. Second sub-sacrificial layer; 183. Second sub-substrate; 191. Third sub-epitaxial layer; 192. Third sub-sacrificial layer; 193. Third sub-substrate. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be intermediate elements. Moreover, in the specification and claims, when it is described that an element is "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element through a third element.

[0024] As introduced in the background technology, the substrate-free Micro LED process in the prior art is complex and costly. To solve the above problems, the embodiments of the present application provide a method for preparing an LED display module and an LED display module.

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0026] Figure 1 1 is a flow chart of a method for preparing an LED display module according to an embodiment of the present application. Figure 1 As shown, the method comprises the following steps:

[0027] Step S101, as Figure 2As shown, a flip-chip LED chip 10 is soldered to a circuit substrate 11, wherein the flip-chip LED chip 10 comprises an epitaxial layer 101, a sacrificial layer 102 and a substrate 103 stacked in sequence, the material of the sacrificial layer 102 comprises GaN, the material of the substrate 103 comprises sapphire, and the epitaxial layer 101 is in contact with the circuit substrate 11;

[0028] Step S102, as Figure 3 and Figure 4 As shown, a laser lift-off process is adopted to focus the laser light source on the location of the sacrificial layer 102, and laser scanning is performed to decompose the sacrificial layer 102 into metal Ga1021 and nitrogen (not shown), thereby obtaining a first LED display module 12;

[0029] Step S103, as Figure 4 and Figure 5 As shown, the first LED display module 12 is immersed in a first organic solvent and ultrasonically cleaned, so that at least the substrate 103 falls off into the first organic solvent, thereby obtaining a second LED display module (not shown);

[0030] Step S104, as Figure 4 and Figure 5 As shown, the second LED display module is immersed in a second organic solvent to dissolve the metal Ga1021 located on the surface of the epitaxial layer 101 away from the circuit substrate 11 to obtain a third LED display module (not shown);

[0031] Step S105, as Figure 4 and Figure 5 As shown, at least the third LED display module is packaged to obtain a packaging layer 13 , and the packaging layer 13 covers the epitaxial layer 101 and the circuit substrate 11 .

[0032] According to this embodiment, a flip-chip LED chip including an epitaxial layer, a sacrificial layer and a substrate is first welded to a circuit substrate, the material of the sacrificial layer including GaN, and then a laser lift-off process is adopted to focus the laser light source on the position where the sacrificial layer is located, and laser scanning is performed to decompose the sacrificial layer into metal Ga and nitrogen to obtain a first LED display module, and then the first LED display module is immersed in a first organic solvent and ultrasonically cleaned to at least make the substrate fall off into the first organic solvent to obtain a second LED display module, and the second LED display module is immersed in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate to obtain a third LED display module, and finally at least the third LED display module is packaged to obtain a packaging layer. Compared with the problem of complex and high cost of substrate-free Micro LED process in the prior art, the present application welds the flip-chip LED chip to the circuit substrate, and uses a laser stripping process after welding to decompose the sacrificial layer into metal Ga and nitrogen, and uses an organic solvent to remove the substrate and dissolve the metal Ga, successfully stripping the sapphire substrate. There is no need to strip the sapphire substrate at the LED chip stage, and no mass transfer process is required. The process is simple and the cost is low.

[0033] In addition, since the sapphire substrate is peeled off, it can be ensured that the final LED display screen (i.e. LED display module) will not have color cast.

[0034] Specifically, since the flip-chip LED chip has a sapphire substrate, the welding of the flip-chip LED chip and the circuit substrate can be completed by using ordinary die bonding, die pricking, etc. combined with reflow soldering processes.

[0035] Specifically, the thickness of the flip-chip LED chip is 50 μm to 100 μm.

[0036] Specifically, laser lift-off can use an excimer laser with a wavelength of 248nm or a YAG laser with a wavelength of 355nm. The lift-off energy density is between 0.3 J / cm² and 0.8 J / cm² to ensure that the laser energy does not damage the epitaxial layer.

[0037] In an optional solution, the first LED display module is immersed in a first organic solvent and ultrasonically cleaned, so that at least the substrate is removed into the first organic solvent, including: immersing the first LED display module in acetone and ultrasonically cleaning, so that at least the substrate is removed into the acetone. In this embodiment, the substrate is removed by acetone, which ensures that the substrate can be removed well and the epitaxial layer is less affected, thereby further ensuring that the final LED display module will not have color cast.

[0038] According to some exemplary embodiments of the present application, the second LED display module is immersed in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate, including: immersing the second LED display module in dilute hydrochloric acid to dissolve the metal Ga. In this embodiment, the use of dilute hydrochloric acid to dissolve the metal Ga ensures that the metal Ga can be dissolved well, and further ensures that the epitaxial layer is less affected, thereby further ensuring that the final LED display module will not be color cast.

[0039] Specifically, the concentration of the dilute hydrochloric acid solution is 5% to 15%, and the immersion time is 2 minutes to 6 minutes.

[0040] In other embodiments, Figures 3 to 6 As shown, the flip-chip LED chip 10 is welded to the circuit substrate 11, comprising: welding the flip-chip LED chip 10 to the predetermined surface 110 of the circuit substrate 11, after welding the flip-chip LED chip 10 to the predetermined surface 110 of the circuit substrate 11, before using the laser lift-off process to focus the laser light source on the position where the sacrificial layer 102 is located, the method further comprises: covering the predetermined surface 110 and the flip-chip LED chip 10 with a preliminary protective layer (not shown), the material of the preliminary protective layer comprising a photosensitive resin, and the properties of the photosensitive resin do not change at a temperature of 120°C-180°C; removing part of the preliminary protective layer, and the remaining preliminary protective layer forms a protective layer 15, and the protective layer 15 is located on the predetermined surface 110 not covered by the flip-chip LED chip 10. The first distance is not greater than the second distance, the first distance is the distance between the surface of the protective layer away from the circuit substrate and the predetermined surface, and the second distance is the distance between the surface of the sacrificial layer away from the circuit substrate and the predetermined surface. In this embodiment, before laser stripping, a preparatory protective layer of covering material including photosensitive resin is formed on the predetermined surface and on the flip-chip LED chip, which can protect the circuits on the circuit substrate from being affected during laser stripping and protect the welding points between the LED and the circuit substrate from being corroded during the subsequent dilute hydrochloric acid cleaning process.

[0041] In addition, if the flip-chip LED chip is an RGB LED chip, the preliminary protective layer can also serve as an isolation layer between the RGB LEDs to avoid light crosstalk.

[0042] Specifically, a layer of black high-temperature resistant photosensitive resin (i.e., a preliminary protective layer) is provided on the side of the circuit substrate where the LED is installed, the LED chip is exposed by etching or photolithography, and the black high-temperature resistant photosensitive resin is cured. The black high-temperature resistant photosensitive resin is combined with the circuit substrate by spin coating, lamination, etc., and its thickness is between 20μm and 50μm.

[0043] Specifically, the packaging of the LED surface can be carried out by film pressing, film pasting and other processes. Since the black high-temperature resistant resin can improve the surface blackness of the LED display module to a certain extent, the transmittance of the packaging material can be selected between 30% and 90%.

[0044] According to other exemplary embodiments of the present application, Figure 6 As shown, the thickness of the protective layer 15 is greater than the thickness of the epitaxial layer 101. After obtaining the third LED display module (not shown), before at least packaging the third LED display module, the method further includes: using a dispensing device to dispense glue on the surface of the epitaxial layer 101 away from the circuit substrate 11 and baking to form a lens 16. In this embodiment, the lens can increase the brightness of the LED display module or reduce power consumption.

[0045] Specifically, because the thickness of the protective layer is greater than that of the epitaxial layer, pits are naturally formed on the surface of the LED after cleaning. Precision dispensing equipment can be used to dispense glue at the pits (i.e., on the surface of the epitaxial layer away from the circuit substrate) and bake to form a lens, thereby increasing the brightness of the LED display module or reducing power consumption.

[0046] According to some further exemplary embodiments of the present application, the flip-chip LED chip further includes a buffer layer, the buffer layer is located between the sacrificial layers of the substrate, and the first LED display module is immersed in a first organic solvent and ultrasonically cleaned, so that at least the substrate falls off into the first organic solvent, including: immersing the first LED display module in the first organic solvent and ultrasonically cleaning, so that the substrate and the buffer layer fall off into the first organic solvent. In this embodiment, the buffer layer can play a buffering role between the substrate and the sacrificial layer.

[0047] In some other optional schemes of this application, such as Figures 2 to 6As shown, the flip-chip LED chip 10 includes a flip-chip red LED chip 17, a flip-chip green LED chip 18 and a flip-chip blue LED chip 19 which are spaced apart in a first direction, the flip-chip green LED chip 18 is located between the flip-chip red LED chip 17 and the flip-chip blue LED chip 19, the flip-chip red LED chip 17 includes a first sub-epitaxial layer 171, a first sub-sacrificial layer 172 and a first sub-substrate 173 which are stacked in sequence, the flip-chip green LED chip 18 includes a second sub-epitaxial layer 181, a second sub-sacrificial layer 182 and a second sub-substrate 183 which are stacked in sequence, The above-mentioned flip-chip blue LED chip 19 comprises a third sub-epitaxial layer 191, a third sub-sacrificial layer 192 and a third sub-substrate 193 stacked in sequence, the above-mentioned first sub-epitaxial layer 171, the above-mentioned second sub-epitaxial layer 181 and the above-mentioned third sub-epitaxial layer 191 constitute the above-mentioned epitaxial layer 101, the above-mentioned first sub-sacrificial layer 172, the above-mentioned second sub-sacrificial layer 182 and the above-mentioned third sub-sacrificial layer 192 constitute the above-mentioned sacrificial layer 102, the above-mentioned first sub-substrate 173, the above-mentioned second sub-substrate 183 and the above-mentioned third sub-substrate 193 constitute the above-mentioned substrate 103, and the above-mentioned first direction is a direction perpendicular to the thickness of the above-mentioned substrate 103. At least the above-mentioned third LED display module is packaged, including: using deionized water to clean the above-mentioned third LED display module, and drying the above-mentioned third LED display module after cleaning; using glue to package the above-mentioned third LED display module after drying. In this embodiment, the flip-chip LED chips (i.e., RGB LED chips) include a flip-chip red LED chip, a flip-chip green LED chip, and a flip-chip blue LED chip. The third LED display module is cleaned and dried with deionized water and finally packaged, which further ensures that the quality of the final LED display module is good.

[0048] Specifically, the circuit substrate is cleaned with deionized water and dried, and the side of the circuit substrate equipped with LED is encapsulated with glue to obtain an LED display module. After cleaning, it is rinsed with deionized water, and the cleaned third LED display module is placed in an oven with a temperature less than 100° C. to dry.

[0049] Specifically, after cleaning, only the epitaxial layer of the LED is left, with a thickness of about 5μm. Because there is no influence of sapphire, the half-power viewing angle of the RGB LED chip can remain consistent, and the LED display module will not have color cast.

[0050] Specifically, the length and width of the flip-chip red LED chip, the flip-chip green LED chip and the flip-chip blue LED chip are between 60μm and 300μm, wherein the length is the length in the first direction and the width is the width in the second direction, the second direction is perpendicular to the first direction, and the second direction is perpendicular to the direction of the substrate thickness.

[0051] Specifically, the flip-chip green LED chip or flip-chip blue LED chip in the present application includes, from top to bottom, a sapphire substrate (i.e., a second sub-substrate or a third sub-substrate), a GaN buffer layer, a GaN sacrificial layer (i.e., a second sub-sacrificial layer or a third sub-sacrificial layer), a GaN epitaxial layer (i.e., a second sub-epitaxial layer or a third sub-epitaxial layer), a positive electrode and a negative electrode, wherein the GaN epitaxial layer includes an N-type GaN layer, a multi-quantum well structure layer, a P-type GaN layer, an electron blocking layer and an ITO current spreading layer, etc.

[0052] Specifically, the flip-chip red LED chip of the present application includes, from top to bottom, a sapphire substrate (i.e., the first sub-substrate), a GaN buffer layer, a GaN sacrificial layer (i.e., the first sub-sacrificial layer), a bonding layer, an AlGaInP epitaxial layer (i.e., the first sub-epitaxial layer), a positive electrode and a negative electrode, wherein the AlGaInP epitaxial layer includes an N-type AlGaInP expansion layer, an N-type AlInP restriction layer, a multi-quantum well structure layer, a P-type AlInP restriction layer and a P-type current expansion layer, etc. In the prior art, ordinary flip-chip red LED chips do not include a GaN buffer layer and a GaN sacrificial layer, while the flip-chip red LED chip of the present application includes a GaN buffer layer and a GaN sacrificial layer, the purpose of which is to facilitate the removal of the sapphire substrate after the LED chip is welded to the substrate.

[0053] In some further optional schemes of the present application, the above-mentioned flip-chip LED chip includes a first sub-flip-chip LED chip, a second sub-flip-chip LED chip and a third sub-flip-chip arranged at intervals in a first direction, the above-mentioned second sub-flip-chip LED chip is located between the above-mentioned first sub-flip-chip LED chip and the above-mentioned third sub-flip-chip LED chip, the above-mentioned first sub-flip-chip LED chip includes a first sub-epitaxial layer, a first sub-sacrificial layer and a first sub-substrate stacked in sequence, the above-mentioned second sub-flip-chip LED chip includes a second sub-epitaxial layer, a second sub-sacrificial layer and a second sub-substrate stacked in sequence, the above-mentioned third sub-flip-chip LED chip includes a third sub-epitaxial layer, a third sub-sacrificial layer and a third sub-substrate stacked in sequence, the above-mentioned first sub-epitaxial layer, the above-mentioned second sub-epitaxial layer and the above-mentioned third sub-epitaxial layer constitute the above-mentioned epitaxial layer, the above-mentioned first sub-sacrificial layer, the above-mentioned second sub-sacrificial layer and the above-mentioned third sub-sacrificial layer constitute the above-mentioned sacrificial layer, the above-mentioned first sub-substrate, the above-mentioned second sub-substrate and the above-mentioned third sub-substrate constitute the above-mentioned substrate, the above-mentioned first sub-flip-chip LED chip, the second sub-flip-chip LED chip and the third sub-flip-chip LED chip have the same luminous color, and the above-mentioned luminous color is red, One of green and blue, the first direction is a direction perpendicular to the thickness of the substrate, after the lens is formed by dispensing glue and baking on the surface of the epitaxial layer away from the circuit substrate, and before at least the third LED display module is packaged, the method further includes: when the luminous color of the flip-chip LED chip is the red, green quantum dots are mixed into the lens on the surface of the second sub-flip-chip LED chip, and blue quantum dots are mixed into the lens on the surface of the third sub-flip-chip LED chip; when the luminous color of the flip-chip LED chip is the green, red quantum dots are mixed into the lens on the surface of the first sub-flip-chip LED chip, and blue quantum dots are mixed into the lens on the surface of the third sub-flip-chip LED chip; when the luminous color of the flip-chip LED chip is the blue, red quantum dots are mixed into the lens on the surface of the first sub-flip-chip LED chip, and green quantum dots are mixed into the lens on the surface of the second sub-flip-chip LED chip. In this embodiment, the flip-chip LED chip includes a first sub-flip-chip LED chip, a second sub-flip-chip LED chip and a third sub-flip-chip LED chip. By adding quantum dots of different colors in the dispensing glue, only one color of flip-chip LED chip is needed to achieve RGB full-color display, which further ensures the simplicity of the process and further ensures that the LED display screen is not color cast.

[0054] Specifically, because the protective layer naturally forms an isolation layer between chips and avoids light crosstalk, quantum dots can be mixed into the lens and a color conversion layer can be formed using an inkjet process. Therefore, only one flip-chip LED chip with a luminous color (such as blue) is needed, and red and green quantum dots are added to its epitaxial layer respectively to complete RGB full-color display. The process is simple.

[0055] In other embodiments, soldering the flip-chip LED chip to the circuit substrate includes: soldering a plurality of the flip-chip LED chips spaced apart in a first direction to the circuit substrate, wherein the first direction is a direction perpendicular to the thickness of the substrate. In this embodiment, soldering a plurality of flip-chip LED chips to the circuit substrate further ensures that the quality of the final LED display module is good and the process is simple.

[0056] In summary, the preparation method of the LED display module of the present application can, on the one hand, adopt existing larger-sized LED chips and ensure that the LED display screen will not have color cast; on the other hand, it can avoid the bottleneck of the existing substrate-free Micro LED process and the immaturity of mass transfer technology.

[0057] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the implementation process of the method for preparing the LED display module of the present application will be described in detail below in conjunction with specific embodiments.

[0058] This embodiment relates to a specific method for preparing an LED display module, comprising the following steps:

[0059] Step S1: soldering a flip-chip LED chip to a circuit substrate, wherein the flip-chip LED chip comprises an epitaxial layer, a sacrificial layer and a substrate stacked in sequence, the sacrificial layer is made of GaN, the substrate is made of sapphire, and the epitaxial layer is in contact with the circuit substrate;

[0060] Step S2: a layer of black high temperature resistant photosensitive resin is provided on the side of the circuit substrate on which the flip-chip LED chip is mounted, the flip-chip LED chip is exposed by etching or photolithography, and the black high temperature resistant photosensitive resin is cured;

[0061] Step S3: using a laser lift-off process, focusing the laser light source on the GaN sacrificial layer position of the flip-chip LED chip, and performing laser scanning. After the laser scanning, the GaN sacrificial layer on the flip-chip LED chip is decomposed into metal Ga and nitrogen;

[0062] Step S4: soaking the decomposed circuit substrate with LED in acetone and performing ultrasonic cleaning, so that the sapphire substrate falls off from the LED epitaxial layer into the acetone;

[0063] Step S5: soaking the circuit substrate after the substrate is peeled off in dilute hydrochloric acid, which can dissolve the metal Ga left on the epitaxial layer after laser stripping;

[0064] Step S6: the circuit substrate after the metal Ga is dissolved is cleaned with deionized water and dried, and the side of the circuit substrate equipped with the LED is packaged with glue to obtain an LED display module.

[0065] The present application also provides an LED display module, which is prepared by any of the above-mentioned methods for preparing LED display modules. Figure 5 As shown, the LED display module includes: a circuit substrate 11; an epitaxial layer 101 located on the surface of the circuit substrate 11; and a packaging layer 13 covering the epitaxial layer 101 and the circuit substrate 11.

[0066] In the above embodiment, the LED display module is prepared by the preparation method of the LED display module, and the LED display module includes a circuit substrate, an epitaxial layer and a packaging layer. Compared with the problem of complicated and high cost of substrate-free Micro LED process in the prior art, in the preparation method of the LED display module of the present application, the flip-chip LED chip is welded to the circuit substrate, and after welding, the sacrificial layer is decomposed into metal Ga and nitrogen by laser stripping process, and the substrate is removed by organic solvent, and the metal Ga is dissolved, and the sapphire substrate is successfully stripped. The sapphire substrate does not need to be stripped at the LED chip stage, and a mass transfer process is not required. The process is simple and the cost is low. In addition, since the sapphire substrate is stripped, it is guaranteed that the obtained LED display module will not be color cast.

[0067] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0068] 1) In the preparation method of the LED display module of the present application, a flip-chip LED chip including an epitaxial layer, a sacrificial layer and a substrate is first welded to a circuit substrate, and the material of the sacrificial layer includes GaN. Then, a laser lift-off process is adopted to focus the laser light source on the position where the sacrificial layer is located, and laser scanning is performed to decompose the sacrificial layer into metal Ga and nitrogen to obtain a first LED display module. The first LED display module is then immersed in a first organic solvent and ultrasonically cleaned to at least make the substrate fall off into the first organic solvent to obtain a second LED display module. The second LED display module is immersed in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate to obtain a third LED display module. Finally, at least the third LED display module is encapsulated to obtain an encapsulation layer. Compared with the problem of complex and high cost of substrate-free Micro LED process in the prior art, the present application welds the flip-chip LED chip to the circuit substrate, and uses a laser stripping process after welding to decompose the sacrificial layer into metal Ga and nitrogen, and uses an organic solvent to remove the substrate and dissolve the metal Ga, successfully stripping the sapphire substrate. There is no need to strip the sapphire substrate at the LED chip stage, and no mass transfer process is required. The process is simple and the cost is low.

[0069] 2) In the LED display module of the present application, the LED display module is prepared by the preparation method of the LED display module, and the LED display module includes a circuit substrate, an epitaxial layer and a packaging layer. Compared with the problem of complicated and high cost of substrate-free Micro LED process in the prior art, in the preparation method of the LED display module of the present application, the flip-chip LED chip is welded to the circuit substrate, and after welding, the sacrificial layer is decomposed into metal Ga and nitrogen by laser stripping process, and the substrate is removed and the metal Ga is dissolved by organic solvent, and the sapphire substrate is successfully stripped. There is no need to strip the sapphire substrate at the LED chip stage, and no mass transfer process is required. The process is simple and the cost is low. In addition, since the sapphire substrate is stripped, it is guaranteed that the obtained LED display module will not have color cast.

[0070] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an LED display module, characterized in that: include: Soldering a flip-chip LED chip to a circuit substrate, wherein the flip-chip LED chip comprises an epitaxial layer, a sacrificial layer and a substrate stacked in sequence, the sacrificial layer is made of GaN, the substrate is made of sapphire, and the epitaxial layer is in contact with the circuit substrate; Using a laser lift-off process, focusing a laser light source on the location of the sacrificial layer, and performing laser scanning to decompose the sacrificial layer into metal Ga and nitrogen, thereby obtaining a first LED display module; Immersing the first LED display module in a first organic solvent and performing ultrasonic cleaning, so that at least the substrate falls off into the first organic solvent, to obtain a second LED display module; Immersing the second LED display module in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate, thereby obtaining a third LED display module; At least the third LED display module is packaged to obtain a packaging layer, and the packaging layer covers the epitaxial layer and the circuit substrate.

2. The method for preparing an LED display module according to claim 1, characterized in that: The first LED display module is immersed in a first organic solvent and ultrasonically cleaned to at least cause the substrate to fall off into the first organic solvent, comprising: The first LED display module is immersed in acetone and ultrasonically cleaned, so that at least the substrate falls off into the acetone.

3. The method for preparing an LED display module according to claim 1, characterized in that: The second LED display module is immersed in a second organic solvent to dissolve the metal Ga located on the surface of the epitaxial layer away from the circuit substrate, comprising: The second LED display module is immersed in dilute hydrochloric acid to dissolve the metal Ga.

4. The method for preparing an LED display module according to claim 1, characterized in that: Soldering a flip-chip LED chip onto a circuit substrate comprises: soldering the flip-chip LED chip onto a predetermined surface of the circuit substrate, After the flip-chip LED chip is soldered to the predetermined surface of the circuit substrate, and before the laser light source is focused on the position of the sacrificial layer by using a laser lift-off process, the method further includes: covering the predetermined surface and the flip-chip LED chip with a preliminary protective layer, the material of the preliminary protective layer comprising a photosensitive resin, and the properties of the photosensitive resin do not change at a temperature of 120°C-180°C; removing part of the preliminary protective layer, and the remaining preliminary protective layer forms a protective layer, the protective layer is located on the predetermined surface not covered by the flip-chip LED chip, and a first distance is not greater than a second distance, the first distance being the distance between the surface of the protective layer away from the circuit substrate and the predetermined surface, and the second distance being the distance between the surface of the sacrificial layer away from the circuit substrate and the predetermined surface.

5. The method for preparing an LED display module according to claim 4, characterized in that: The thickness of the protective layer is greater than the thickness of the epitaxial layer. After obtaining the third LED display module and before at least packaging the third LED display module, the method further includes: Adhesive dispensing equipment is used to dispense glue on the surface of the epitaxial layer away from the circuit substrate and then bake to form a lens.

6. The method for preparing an LED display module according to claim 1, characterized in that: The flip-chip LED chip further includes a buffer layer, the buffer layer is located between the sacrificial layers of the substrate, the first LED display module is immersed in a first organic solvent, and ultrasonic cleaning is performed to at least make the substrate fall off into the first organic solvent, comprising: The first LED display module is immersed in the first organic solvent and ultrasonically cleaned so that the substrate and the buffer layer fall off into the first organic solvent.

7. The method for preparing an LED display module according to claim 1, characterized in that: The flip-chip LED chip comprises a flip-chip red LED chip, a flip-chip green LED chip and a flip-chip blue LED chip which are spaced apart in a first direction, the flip-chip green LED chip is located between the flip-chip red LED chip and the flip-chip blue LED chip, the flip-chip red LED chip comprises a first sub-epitaxial layer, a first sub-sacrificial layer and a first sub-substrate which are stacked in sequence, the flip-chip green LED chip comprises a second sub-epitaxial layer, a second sub-sacrificial layer and a second sub-substrate which are stacked in sequence, the flip-chip blue LED chip comprises a third sub-epitaxial layer, a third sub-sacrificial layer and a third sub-substrate which are stacked in sequence, the first sub-epitaxial layer, the second sub-epitaxial layer and the third sub-epitaxial layer constitute the epitaxial layer, the first sub-sacrificial layer, the second sub-sacrificial layer and the third sub-sacrificial layer constitute the sacrificial layer, the first sub-substrate, the second sub-substrate and the third sub-substrate constitute the substrate, the first direction is a direction perpendicular to the thickness of the substrate, at least the third LED display module is packaged, including: Using deionized water to clean the third LED display module, and drying the cleaned third LED display module; The dried third LED display module is packaged using glue.

8. The method for preparing an LED display module according to claim 5, characterized in that: The flip-chip LED chip comprises a first sub-flip-chip LED chip, a second sub-flip-chip LED chip and a third sub-flip-chip LED chip which are spaced apart in a first direction, the second sub-flip-chip LED chip is located between the first sub-flip-chip LED chip and the third sub-flip-chip LED chip, the first sub-flip-chip LED chip comprises a first sub-epitaxial layer, a first sub-sacrificial layer and a first sub-substrate which are stacked in sequence, the second sub-flip-chip LED chip comprises a second sub-epitaxial layer, a second sub-sacrificial layer and a second sub-substrate which are stacked in sequence, the third sub-flip-chip LED chip comprises a third sub-epitaxial layer, a third sub-sacrificial layer and a third sub-substrate which are stacked in sequence, the first sub-epitaxial layer, the second The sub-epitaxial layer and the third sub-epitaxial layer constitute the epitaxial layer, the first sub-sacrificial layer, the second sub-sacrificial layer and the third sub-sacrificial layer constitute the sacrificial layer, the first sub-substrate, the second sub-substrate and the third sub-substrate constitute the substrate, the first sub-flip-chip LED chip, the second sub-flip-chip LED chip and the third sub-flip-chip LED chip have the same luminous color, which is one of red, green and blue, the first direction is a direction perpendicular to the thickness of the substrate, after dispensing glue on the surface of the epitaxial layer away from the circuit substrate and baking to form a lens, before at least packaging the third LED display module, the method further includes: When the light emission color of the flip-chip LED chip is red, green quantum dots are mixed into the lens located on the surface of the second sub-flip-chip LED chip, and blue quantum dots are mixed into the lens located on the surface of the third sub-flip-chip LED chip; When the light emission color of the flip-chip LED chip is green, red quantum dots are mixed into the lens located on the surface of the first sub-flip-chip LED chip, and blue quantum dots are mixed into the lens located on the surface of the third sub-flip-chip LED chip; When the luminous color of the flip-chip LED chip is blue, the red quantum dots are mixed in the lens located on the surface of the first sub-flip-chip LED chip, and the green quantum dots are mixed in the lens located on the surface of the second sub-flip-chip LED chip.

9. The method for preparing an LED display module according to claim 1, characterized in that: Solder the flip-chip LED chip to the circuit substrate, including: A plurality of flip-chip LED chips spaced apart in a first direction are soldered to the circuit substrate, wherein the first direction is a direction perpendicular to the thickness of the substrate.

10. An LED display module, characterized in that: The LED display module is prepared by the method for preparing an LED display module according to any one of claims 1 to 9, and the LED display module comprises: Circuit board; An epitaxial layer, located on the surface of the circuit substrate; A packaging layer covers the epitaxial layer and the circuit substrate.

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