A method for massive transfer, an integrated board packaging method, and an integrated board

Abstract

The present invention relates to the field of LED processing technology, and discloses a mass transfer method, an integrated board packaging method and an integrated board, including: docking a first metal layer on the top of a Micro LED chip and a second metal layer on the surface of a CMOS backplane wafer, and combining them by hot pressing to form a Micro LED array. The present invention has the following advantages and effects: Since the Micro LED chip is transferred to the CMOS backplane wafer by utilizing the hot pressing diffusion phenomenon between metals, and the metal hot pressing only needs to be aligned and heated according to the hot pressing method, the limitation of the use time of the solder paste in the solder paste method is avoided, and it can be used to build a larger integrated board, which correspondingly reduces the number of integrated boards required for the assembly of large-size screens, and correspondingly reduces the joint area of ​​the screen group, thereby improving the user experience of the LED screen. At the same time, compared with the traditional solder paste furnace hardening combination, the metal hot pressing method has higher bonding strength, no undesirable phenomena such as solder ball cracking and solder bridging, and better reliability.

Description

Technical Field

[0001] The present application relates to the technical field of LED processing, and in particular to a mass transfer method, an integrated board packaging method and an integrated board. Background Art

[0002] Currently, compared with liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs), micro light-emitting diodes (Micro LEDs) have advantages such as high contrast, low power consumption, long lifespan, and fast response time, and have received extensive attention in microdisplay applications such as augmented reality (AR), virtual reality (VR), and LIFI light sources. However, in the Micro LED flip-chip packaging technology, due to the limited use time (≤8 hours) of the solder paste in the soldering process, there are mass transfer technical problems, which severely limit the size of the integrated board for industrial production of Micro LEDs. As a result, when attaching the screen at the terminal, only multiple small-sized integrated boards can be selected and spliced into a large-sized screen group. There are many seams when assembling the large-sized screen group. At the same time, at present, there are also a large number of technical problems such as full-colorization, which seriously affect the visual experience and limit the market promotion and popularity rate. Summary of the Invention

[0003] Aiming at the defects existing in the prior art, the purpose of the present application is to provide a mass transfer method, an integrated board packaging method and an integrated board, which can be not restricted by the use time of the solder paste, can manufacture larger-sized integrated boards, can form integrated boards with higher color purity, and the light decay of the integrated boards is consistent, improving the effect after long-term use.

[0004] To achieve the above object, on the one hand, the technical solution adopted is:

[0005] The present application provides a mass transfer method, including:

[0006] Growing an epitaxial layer on a sapphire substrate, depositing a first metal layer on the top surface of the epitaxial layer, and then processing to form a plurality of Micro LED chips arranged in an array;

[0007] Depositing a second metal layer on the surface of a CMOS backplane wafer, and then dividing the second metal layer into arrays of the same size according to the size of a single Micro LED chip;

[0008] Docking the first metal layer on the top of the Micro LED chip and the second metal layer on the surface of the CMOS backplane wafer, and combining them by a hot pressing method to form a Micro LED array.

[0009] Preferably, after growing the epitaxial layer on the sapphire substrate, plating a layer of silver on the epitaxial layer to form a silver plating layer, and then depositing the first metal layer on the top surface of the silver plating layer

[0010] Preferably, the hot pressing method includes the following steps:

[0011] Align the first metal layer on the top surface of the Micro LED chip and the second metal layer on the surface of the CMOS backplane wafer and press them tightly against each other to form microplastic deformation.

[0012] Perform annealing treatment in a vacuum or protective atmosphere so that the first metal layer and the second metal layer diffuse into each other to form a solid solution.

[0013] Preferably, it further includes the following steps:

[0014] After the Micro LED chip is processed and formed, deposit a dielectric passivation layer on the side of each chip in the Micro LED chip by PECVD deposition method.

[0015] Open the n-type common cathode by inductively coupled plasma etching, and then form an n-contact layer.

[0016] This application also provides an integrated board packaging method, including the following steps:

[0017] Complete the Micro LED array according to the method described in claim 1.

[0018] Remove the sapphire substrate of the Micro LED array, and cover the glass substrate provided with a control circuit on the side where the sapphire substrate of the Micro LED array is removed.

[0019] Uniformly cover a light-shielding layer on the glass substrate.

[0020] Perform quantum dot filling at intervals of red, green, and blue colors within the light-shielding layer, and then cover the surface layer to form an integrated board, where the position of each quantum dot filling corresponds to each Micro LED chip in the Micro LED array.

[0021] Preferably, the quantum dot filling includes the following steps:

[0022] Inject quantum dot colloids of corresponding colors at intervals of red, green, and blue colors within the light-shielding layer to form filling areas of corresponding colors, where the filling area corresponding to blue injects transparent colloid or is left empty.

[0023] Cover a filter of corresponding color on the top surface of the filling area.

[0024] Preferably, the filling area is frustum-shaped, having a top surface and a bottom surface, where the bottom surface is larger than the top surface, and the bottom surface faces the glass substrate.

[0025] Preferably, it further includes the following steps:

[0026] When forming the filling area, silver is plated on the edge of the filling area and the light-shielding layer.

[0027] Preferably, the control circuit of the glass substrate is an AM addressing driving circuit implemented by a CMOS driver integrated circuit.

[0028] This application also provides an integrated board, characterized in that the manufacturing method of the integrated board includes the above method.

[0029] The beneficial effects brought by the technical solution provided by this application include:

[0030] This application can realize a mass transfer method. Since the MicroLED chips are transferred to the CMOS backplane wafer by utilizing the thermal compression diffusion phenomenon between metals, and the thermal compression of metals only requires heating according to the thermal compression method after alignment, it circumvents the limitation of the use time of solder paste in the solder paste method, can be used to construct a larger integrated board, correspondingly reduces the number of integrated boards required for assembling large-size screens, correspondingly reduces the seam area of the screen group, and improves the usage experience of the LED screen. At the same time, compared with the combination of traditional solder paste through-furnace hardening, the bonding strength of the metal thermal compression method is higher, there are no adverse phenomena such as solder ball cracking and bridging, and the reliability is better.

[0031] At the same time, for the integrated board packaging method and integrated board provided by this application, for the blue LED combined with CMOS, we adopt the method of quantum dot filling to achieve full color, and use a light-shielding layer to isolate the part filled with quantum dots, reducing the LED light leakage problem, with better color purity. At the same time, since the same batch of directly manufactured blue LEDs are used as the light-emitting basis, the properties of the light-emitting sources are consistent, making the light decay effects of all LEDs more consistent and the display effect of the formed LED integrated board better. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for the description of the embodiments. 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 be obtained based on these drawings.

[0033] Figure 1 It is a schematic structural diagram of a Micro LED in this application.

[0034] Figure 2 It is a schematic diagram of the chip array processing flow in an embodiment of this application.

[0035] Figure 3 For Figure 2 the schematic diagram of the CMOS backplane wafer processing flow in the shown embodiment.

[0036] Figure 4 ForFigure 3 Schematic diagram of the process of Micro LED mass transfer in the illustrated embodiment.

[0037] Reference numerals:

[0038] 1. Sapphire substrate; 11. Epitaxial layer; 12. First metal layer; 121. Silver plating layer; 2. Micro LED chip; 21. Dielectric passivation layer; 3. CMOS backplane wafer; 31. Second metal layer; 4. Glass substrate; 5. Light shielding layer; 6. Filling area; 61. Filter; 7. Surface layer; 8. Common cathode. Specific embodiments

[0039] In order to make the objectives, technical solutions and advantages of the present application clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] In the present application, an embodiment of a mass transfer method is provided, including the following steps

[0041] S1. Grow an epitaxial layer 11 on the sapphire substrate 1, deposit the first metal layer 12 on the top surface of the epitaxial layer 11, and then process to form a plurality of Micro LED chips 2 arranged in an array.

[0042] Specifically, reference can be made to Figure 2 the first step of, from bottom to top, a P-type GaN layer, a quantum well layer, and an N-type GaN layer, and the first metal layer 12 is deposited on the top surface of the N-type GaN. Then, a whole epitaxial layer 11 is cut in an array form through a photolithography process and plasma etching. A single epitaxial layer 11 is the Micro LED chip 2. The present application does not use solder paste, so the ITO layer is not provided accordingly.

[0043] In some embodiments, after growing the epitaxial layer 11, the metal layer is not directly grown, but a silver plating layer 121 is plated on the epitaxial layer 11, and then the first metal layer 12 is deposited on the silver plating layer 121. In general technology, the function of the ITO layer on the surface of the chip 2 is to enhance conductivity, but at the same time its light transmittance is relatively high. Therefore, in the flip-chip packaging technology, light will be emitted from the bottom of the chip 2, reducing the light extraction efficiency. In the present application, the metal layer is first used to reflect the bottom light to improve the light output of the Micro LED chip 2. And the further silver plating layer 121 can, on the one hand, adjust the conductivity, and at the same time can reflect the light escaping to the bottom to the surface of the chip 2 to a greater extent, further enhancing the light output.

[0044] In some other embodiments, after forming a plurality of Micro LED chips 2 by cutting, a dielectric passivation layer 21 is deposited on the side surfaces of the Micro LED chips 2 by using PECVD deposition method to isolate each Micro LED chip 2 and prevent current leakage, which may affect the light-emitting effect of the Micro LED chips 2. At the same time, the n-type common cathode 8 is opened by inductively coupled plasma etching, and then an n-contact layer is formed.

[0045] S2. Deposit a second metal layer 31 on the surface of the CMOS backplane wafer 3, and then divide the second metal layer 31 into an array of the same size according to the size of a single Micro LED chip 2.

[0046] Specifically, referring to Figure 3 , for the selection of the specific materials of the first metal layer 12 and the second metal layer 31, the following requirements are as follows: the diffusing atoms must have a certain solid solubility in the matrix metal so that they can dissolve into the matrix lattice to form a solid solution before solid-state diffusion can occur. Generally, the first metal layer 12 and the second metal layer 31 can adopt a combination of tin and zinc or other metal materials with similar structures or properties.

[0047] S3. Align the first metal layer 12 on the top of the Micro LED chip 2 and the second metal layer 31 on the surface of the CMOS backplane wafer 3, and bond them together by hot pressing to form a Micro LED array.

[0048] One of the embodiments performs hot pressing by the following method:

[0049] Align and tightly press the first metal layer 12 on the top surface of the Micro LED chip 2 and the second metal layer 31 on the surface of the CMOS backplane wafer 3 to form a microscopic plastic deformation;

[0050] Perform annealing treatment in a vacuum or protective atmosphere so that the first metal layer 12 and the second metal layer 31 diffuse into each other to form a solid solution.

[0051] Specifically, during the processing, first align and press tightly the first metal layer 12 that has been cut into an array arrangement along with the Micro LED chips 2 and the second metal layer 31 that has also been cut into an array arrangement on the CMOS backplane wafer 3 to prevent cross-current between adjacent Micro LED chips 2.

[0052] The first metal layer 12 and the second metal layer 31 are squeezed so that the contact surfaces form a diffusion couple, and then they are placed in a vacuum or a protective atmosphere furnace for annealing treatment. A diffusion interface layer is formed between the two phases. By controlling the annealing temperature and the annealing process, the thickness of the diffusion interface layer can be adjusted, and thus the desired phase interface can be obtained. Generally, the annealing temperature can be 150 - 500 °C. Beyond this range, the Micro LED chip 2 is likely to be damaged.

[0053] This application also provides an embodiment of an integrated board packaging method, which is mainly used for further processing the Micro LED array made in the above embodiment. Those skilled in the art can also apply this integrated board packaging method to other Micro LED arrays with similar structures according to common knowledge.

[0054] As Figure 4 shown, the embodiment of this integrated board packaging method includes the following steps. At the same time, the steps of this implementation are the subsequent processes of the method embodiment of the above massive transfer, so the step numbers continue those of the previous embodiment:

[0055] S4. Remove the sapphire substrate 1 of the Micro LED array, and cover the glass substrate 4 provided with a control circuit on the side of the Micro LED array where the sapphire substrate 1 has been removed.

[0056] Specifically, after the sapphire substrate 1 of the Micro LED array is removed, one side of the Micro LED chip 2 on the Micro LED array is exposed. Generally, a specific circuit is formed on the surface of the above glass substrate 4 by printing. The circuit is in close contact with the exposed surface of each Micro LED chip 2 in the Micro LED array to form a closed loop.

[0057] In some preferred embodiments, the control circuit of the glass substrate 4 is an AM addressing drive circuit implemented by a CMOS driver integrated circuit.

[0058] S5. Uniformly cover a light-shielding layer 5 on the glass substrate 4.

[0059] Specifically, the light-shielding layer 5 generally uses insulating glue such as black glue or photoresist. On the one hand, it prevents current leakage, and on the other hand, it has a good effect of shielding light.

[0060] S6. Perform quantum dot filling in the light-shielding layer 5 at intervals of red, green, and blue colors, and then cover the surface layer 7 to form an integrated board, where each position for quantum dot filling corresponds to each Micro LED chip 2 in the Micro LED array.

[0061] Specifically, the Micro LED chip 2 itself emits light, usually blue light, which needs to be converted to other colors. Therefore, quantum dots are used to absorb blue light and emit other primary colors, thereby forming the RGB three primary colors, and finally mixing to form a full-color display. Due to the shielding of the light-shielding layer 5, the phenomenon of light leakage between the light-emitting points of the integrated board formed by this method is suppressed, and the light-emitting effect is more pure and the color purity is higher. At the same time, quantum dot light emission will amplify the differences between different Micro LED chips 2. However, since the Micro LED array used in this embodiment is grown, cut, and processed in the same batch, the differences between each other are much smaller than those of the generally transferred Micro LED chips 2, and the light-emitting properties are more unified. Therefore, the final light-emitting effect has stronger consistency. At the same time, the light decay effects of the Micro LED chips 2 are closer, so that the display effect of the integrated board after long-term use is much better than the prior art.

[0062] The surface layer 7 mainly serves to protect the light-shielding layer 5 and the filling area 6, and is generally glass or sapphire, or other suitable transparent materials.

[0063] In some further embodiments, the quantum dot filling includes the following steps:

[0064] S61. Quantum dot colloids of corresponding colors are injected into the light-shielding layer 5 at intervals of red, green, and blue to form filling areas 6 of corresponding colors, and the filling area 6 marked blue is injected with transparent colloid or left empty;

[0065] Specifically, the arrangement of the filling positions of red, green, and blue can be selected according to design requirements. Since the Micro LED chip 2 itself emits blue light in the blue part, it does not need to be converted by quantum dot colloid. Generally, transparent colloid is filled to support the light-emitting channel of the light emitted by the Micro LED chip 2. In some embodiments, the light-emitting channel of the light emitted by the Micro LED chip 2 can also be opened by filling gas or digging the light-shielding layer 5.

[0066] In some further embodiments, the above-mentioned filling area 6 is frustum-shaped, having a top surface and a bottom surface, where the bottom surface is larger than the top surface, and the bottom surface faces the glass substrate 4. Specifically, as Figure 1 shown, the filling area 6 is frustum-shaped, which is a quadrangular frustum in this embodiment, and can also be changed to a frustum of other structures according to process requirements in other embodiments. The bottom surface of the frustum of the filling area 6 is smaller than the top surface of the frustum, and the size of the top surface of the frustum is as large as possible to reduce the occupied area of the light-shielding layer 5, thereby reducing the shadow of the light-emitting surface. And the bottom surface of the frustum should be close to the Micro LED chip 2 to receive the light emitted by the Micro LED chip 2 as much as possible and reduce waste.

[0067] Correspondingly, after the filling area 6 is disposed in the light-shielding layer 5, the light-shielding layer 5 is naturally divided into a plurality of frustum-shaped structures by the filling area 6. For details, refer to Figure 1 , wherein the area of the side facing the glass substrate 4 is smaller than the area of the side facing the surface layer 7.

[0068] In some further embodiments, silver is plated between the filling area 6 and the light-shielding layer 5. The silver plating is used to reflect the light incident on the light-shielding layer 5, prevent the light-shielding layer 5 from absorbing light, and at the same time enhance the intensity of the emitted light.

[0069] S62. A color filter 61 corresponding to the color is covered on the top surface of the filling area 6. To prevent a small amount of blue light that has not been converted by the quantum dots from being emitted, which affects the purity of the emitted light.

[0070] The present application also provides an embodiment of an integrated board, as shown in Figure 1 , including a COMS backplane wafer 3, a Micro LED chip 2, a glass substrate 4, a filling area 6, a light-shielding layer 5, and a protective layer. The directions of up, down, left, and right in this embodiment are described according to Figure 1 the up, down, left, and right directions.

[0071] Among them, the Micro LED chips 2 are arranged in an array and there are several. Among them, Figure 1 as shown, some of the MicroLED chips 2 are taken as representatives. Structures such as a common cathode 8 can be referred to Figure 4 . A first metal layer 12 is provided at the bottom end of each Micro LED chip 2, and a dielectric passivation layer 21 is provided on each side to prevent leakage. A control circuit is printed on the glass substrate 4, and the glass substrate 4 covers the Micro LED chips 2. A circuit is formed between the control circuit, the Micro LED chips 2, and the CMOS backplane wafer 3 to control whether the Micro LED chips 2 emit light.

[0072] A second metal layer 31 is provided on the surface of the CMOS backplane wafer 3. The second metal layer 31 is divided into a plurality of arrays arranged according to the size of the Micro LED chips 2. The second metal layer 31 on the top surface of the CMOS backplane wafer 3 and the first metal layer 12 on the bottom surface of the Micro LED chips 2 are formed into a whole by hot pressing.

[0073] A light-shielding layer 5 is provided above the glass substrate 4. The light-shielding layer 5 is black glue or insulating glue, and in some other embodiments, it can also be other types of black colloids. The light-shielding layer 5 is divided into a plurality of parts arranged in an array by the filling area 6. The filling area 6 is arranged according to the three primary colors of red, blue, and green. Figure 1 and Figure 4 as shown is an embodiment arranged in a column of red, green, and blue. In other embodiments, it can also be arranged according to requirements, such as red, green, and blue being located at the three corners of a triangle, etc.

[0074] Below each filling area 6, there is a corresponding Micro LED chip 2. The filling areas 6 corresponding to red and green are filled with quantum dot colloids, and the filling area 6 corresponding to blue is filled with a transparent colloid, or is left empty by means such as filling gas and excavation. A color corresponding filter 61 is provided on the top surface of each filling area 6. The filling area 6 corresponding to blue may not be provided with a filter 61. A surface layer 7 is covered above the filter 61. In this embodiment, the surface layer 7 is sapphire, and in other embodiments, it may be glass or other transparent materials.

[0075] This application is not limited to the above embodiments. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches are also regarded as within the protection scope of the present invention.

Claims

1. An integrated board packaging method, characterized in that, Including the following steps: Complete the Micro LED array according to the mass transfer method; Remove the sapphire substrate (1) of the Micro LED array, and cover the glass substrate (4) provided with a control circuit on the side of the Micro LED array where the sapphire substrate (1) is removed; Uniformly cover a light-shielding layer (5) on the glass substrate (4); the light-shielding layer (5) is made of black glue or photoresist; quantum dots are filled in the light-shielding layer (5) at intervals of red, green, and blue colors, and then a surface layer (7) is covered to form an integrated board, where the position of each quantum dot filling corresponds to each Micro LED chip (2) in the Micro LED array; The quantum dot filling includes the following steps: Inject quantum dot colloids of corresponding colors into the light-shielding layer (5) at intervals of red, green, and blue colors to form filling areas (6) of corresponding colors, and the position of each filling area (6) corresponds to a Micro LED chip (2), where the filling area (6) corresponding to blue is injected with transparent colloid or left empty; Cover a filter (61) of corresponding color on the top surface of the filling area (6); The filling area (6) is frustum-shaped, having a top surface and a bottom surface, where the top surface is larger than the bottom surface, and the bottom surface faces the glass substrate (4); The light-shielding layer (5) is divided into multiple frustum-shaped structures by the filling areas (6), where the area of the side facing the glass substrate (4) is smaller than the area of the side facing the surface layer (7); When forming the filling area (6), silver is plated between the filling area (6) and the light-shielding layer (5); Among them, the mass transfer method includes: Grow an epitaxial layer (11) on the sapphire substrate (1), deposit a first metal layer (12) on the top surface of the epitaxial layer (11), and then process to form a plurality of Micro LED chips (2) arranged in an array; Deposit a second metal layer (31) on the surface of the CMOS backplane wafer (3), and then divide the second metal layer (31) into an array of the same size according to the size of a single Micro LED chip (2); Dock the first metal layer (12) on the top of the Micro LED chip (2) and the second metal layer (31) on the surface of the CMOS backplane wafer (3), and bond them by hot pressing to form a Micro LED array; After growing the epitaxial layer (11) on the sapphire substrate (1), plate a layer of silver on the epitaxial layer (11) to form a silver-plated layer (121), and then deposit the first metal layer (12) on the top surface of the silver-plated layer (121); The hot pressing method includes the following steps: Align and tightly press the first metal layer (12) on the top of the Micro LED chip (2) and the second metal layer (31) on the surface of the CMOS backplane wafer (3) to form microscopic plastic deformation; Perform annealing treatment in a vacuum or protective atmosphere so that the first metal layer (12) and the second metal layer (31) diffuse into each other to form a solid solution.

2. The integrated board encapsulation method according to claim 1, wherein, It also includes the following steps: After processing to form the Micro LED chip (2), deposit a dielectric passivation layer (21) on the side of each Micro LED chip (2) by PECVD deposition method; Open the n-type common cathode (8) by inductively coupled plasma etching, and then form an n-contact layer.

3. The integrated board packaging method according to claim 1, wherein: The control circuit of the glass substrate (4) is an AM addressing drive circuit implemented by a CMOS driver integrated circuit.

4. An integrated board, characterized in that, The integrated board is manufactured according to the integrated board packaging method described in any one of claims 1-3.

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