Stress-regulated packaging structure for AM glass-based small-pitch display screen and preparation method thereof

Abstract

The application discloses a stress regulation type packaging structure of an AM glass-based small-pitch display screen and a preparation method thereof, and belongs to the technical field of chip packaging. The packaging structure comprises a composite glass substrate, LED chips fixed on the front surface of the substrate, and a high-thermal-conductivity packaging adhesive layer covering the LED chips and internally having a three-dimensional heat conduction network. The difference between the thermal expansion coefficients of the composite glass substrate and the high-thermal-conductivity packaging adhesive layer is less than 15 ppm / DEG C, and the change rate of the storage modulus of the high-thermal-conductivity packaging adhesive layer in the range of 25 DEG C-150 DEG C is less than 30%. The application fundamentally solves the problem of glass brittleness through the composite glass substrate structure, constructs an efficient three-dimensional heat conduction network through a synergistic orientation process of shearing force and roller pressing, releases thermal stress in cooperation with a graded curing process, and significantly improves the reliability and heat dissipation performance of the display screen.

Description

Technical Field

[0001] This application relates to the field of packaging, and more specifically, it relates to a stress-controlled packaging structure for AM glass-based small-pitch displays and a method for fabricating the same. Background Technology

[0002] With the rapid development of Mini / Micro-LED display technology, the demand for small-pitch displays (pixel pitch ≤ 0.5mm) continues to grow in high-end commercial displays, virtual reality, automotive displays, and other fields. Compared to traditional PCB substrates, active matrix (AM) glass substrates have become an ideal carrier for high-resolution Micro-LED displays due to their high flatness, low coefficient of thermal expansion, and excellent signal transmission capabilities. However, the brittleness and low thermal conductivity of glass substrates place higher demands on the packaging process.

[0003] To address the aforementioned issues, existing technology (CN120475833A) proposes a flexible packaging process for AM glass-based small-pitch displays. This process includes steps such as substrate pretreatment, LED chip mass transfer, high thermal conductivity encapsulant coating, stepped curing, and optical film lamination. It uses a polyurethane-modified epoxy resin compounded with aluminum nitride, boron nitride nanosheets, and carbon fiber fragments as a high thermal conductivity adhesive. During the coating process, an electric or magnetic field is applied to induce the directional arrangement of boron nitride sheet-like fillers to form vertical thermal conduction pathways. Simultaneously, UV pre-curing combined with multi-stage stepped thermosetting prevents filler sedimentation and reduces thermal stress.

[0004] While the existing processes have achieved some success in improving thermal conductivity and controlling thermal stress, they still face challenges in practical industrial applications, including high process complexity, high material costs, and long curing times. In particular, the brittleness of the glass substrate remains unresolved: although existing processes use flexible encapsulating adhesive layers, the substrate itself is still made of glass, and its inherent brittleness remains unchanged. During mass transfer, bonding, and curing processes, the glass substrate is prone to microcracks or even breakage due to thermal stress (such as temperature rises and falls during curing) or mechanical stress (such as roll bonding), directly impacting product yield and long-term reliability. Existing technologies only passively adapt through the flexibility of the encapsulating adhesive, failing to proactively address the reliability risks posed by glass brittleness from the perspective of the substrate structure itself or process stress control.

[0005] Therefore, how to fundamentally solve the brittleness problem of glass substrates while maintaining or even improving packaging performance, so as to improve product yield and reliability, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a stress-controlled packaging structure for AM glass-based small-pitch displays.

[0007] The technical solution provided in this application is as follows:

[0008] In a first aspect, this application provides a stress-regulating packaging structure for AM glass-based small-pitch displays, comprising:

[0009] A composite glass substrate, the composite glass substrate comprising an ultrathin glass layer and a polymer support layer adhered to the back side of the ultrathin glass layer;

[0010] LED chip, the LED chip being fixed to the front side of the composite glass substrate;

[0011] A high thermal conductivity encapsulating adhesive layer is stacked on the front side of the composite glass substrate and covers the LED chip. The high thermal conductivity encapsulating adhesive layer has a three-dimensional thermal conductive network. The three-dimensional thermal conductive network is constructed by oriented boron nitride sheets along the thickness direction of the adhesive layer to form a vertical thermal conductive framework, and spherical alumina and needle-shaped nano-carbon materials dispersed between the vertical thermal conductive framework to fill the thermal conductive nodes.

[0012] The difference in thermal expansion coefficients between the composite glass substrate and the high thermal conductivity encapsulating adhesive layer is less than 15 ppm / ℃, and the rate of change of the storage modulus of the high thermal conductivity encapsulating adhesive layer within the range of 25℃-150℃ is less than 30%.

[0013] Furthermore, the thickness of the ultrathin glass layer is 50-100 μm, and the polymer support layer is a polyimide film or a PET film with a thickness of 25-50 μm; at least one stress relief structure is provided in the edge region of the composite glass substrate, and the stress relief structure is a micro-groove or a filling hole.

[0014] Furthermore, the aforementioned high thermal conductivity encapsulating adhesive layer is formed by curing a high thermal conductivity encapsulating adhesive composition, wherein the high thermal conductivity encapsulating adhesive composition comprises, by weight parts:

[0015] The composition includes 100 parts of matrix resin, 50-120 parts of composite thermally conductive filler, 5-15 parts of stress-absorbing rubber, 0.5-2 parts of photoinitiator, and 1-5 parts of thermosetting agent.

[0016] Furthermore, the matrix resins mentioned above include polyurethane-modified epoxy resin and long-chain flexible epoxy resin, with a mass ratio of 3:1-5.

[0017] Furthermore, the aforementioned composite thermally conductive filler includes sheet-like boron nitride, spherical alumina, and needle-like nano-carbon materials, wherein the mass ratio of the sheet-like boron nitride, spherical alumina, and needle-like nano-carbon materials is 1:3-5:0.2-0.5.

[0018] Furthermore, the aforementioned sheet-like boron nitride is a surface-esterified boron nitride nanosheet with a thickness of less than 100 nm and a sheet diameter of 1-5 μm; the spherical alumina has a bimodal particle size distribution, including small-particle alumina with a particle size of 0.3-0.5 μm and large-particle alumina with a particle size of 2-5 μm, with a mass ratio of 1:2-4; the needle-like nanocarbon material is carbon nanotube or carbon nanofiber with an aspect ratio greater than 50.

[0019] Secondly, this application provides a method for fabricating the above-mentioned stress-modulated packaging structure for AM glass-based small-pitch displays, comprising the following steps:

[0020] S1: A polymer support layer is attached to the back of the ultra-thin glass layer, and the edges of the composite glass substrate are treated to form a stress-relieving structure;

[0021] S2: After surface activation treatment of the composite glass substrate, the LED chip is transferred and fixed to the predetermined position on the substrate;

[0022] S3: Prepare a high thermal conductivity encapsulating adhesive composition and coat it onto the surface of a composite glass substrate with a chip fixed on it. During the coating process, the shear force generated by the relative movement of the coating head and the substrate causes the sheet-like boron nitride to initially align along the coating direction, while the spherical alumina and needle-like carbon nanomaterials are uniformly dispersed with the resin flow. Immediately after coating, a roller press is used to apply vertical pressure to the adhesive layer, causing the sheet-like boron nitride to flip and align along the thickness direction of the adhesive layer to form a vertical thermally conductive skeleton. Under pressure, the spherical alumina and needle-like carbon nanomaterials fill the gaps between the sheet-like boron nitride to form thermally conductive nodes. Then, the above structure is fixed by a graded curing process to form a high thermal conductivity encapsulating adhesive layer.

[0023] S4: Lay an optical functional film onto the surface of the cured high thermal conductivity encapsulating adhesive layer.

[0024] Furthermore, the above-mentioned graded curing process includes: first performing UV pre-curing to shape the adhesive layer surface, and then performing step-by-step thermal curing, wherein the step-by-step thermal curing is carried out in sequence in the low temperature zone, the medium temperature zone and the high temperature zone, and after curing, the temperature is gradually reduced to room temperature.

[0025] Furthermore, the preparation method of the above-mentioned high thermal conductivity encapsulating adhesive composition includes:

[0026] The flake boron nitride is mixed with a portion of the matrix resin and processed 2-4 times using a three-roll mill to form a pre-dispersed masterbatch.

[0027] Spherical alumina, needle-shaped carbon nanomaterials and the remaining matrix resin were mixed and then subjected to planetary stirring and ultrasonic dispersion.

[0028] The pre-dispersed masterbatch was combined with the ultrasonically dispersed mixture, and stress-absorbing rubber, photoinitiator and thermosetting agent were added. After vacuum degassing, the final composition was obtained.

[0029] In summary, this application has the following beneficial effects:

[0030] 1. Addressing the problem in existing technologies where glass substrates are prone to cracking or even breakage due to thermal or mechanical stress during mass transfer, bonding, and curing, this invention employs an ultra-thin glass layer combined with a polymer support layer to form the substrate. Microgrooves and filling holes are incorporated into the edge regions to actively release thermal stress structurally. Simultaneously, by controlling the difference in thermal expansion coefficients between the encapsulating adhesive layer and the substrate to less than 15 ppm / ℃ and keeping the storage modulus change rate below 30%, stress matching between the encapsulating adhesive layer and the substrate is achieved. Testing shows that after 500 thermal cycles from -40℃ to 85℃, the pixel failure rate of the display screen of this invention is less than 0.01%, demonstrating a reliability far superior to existing technologies.

[0031] 2. This invention utilizes a synergistic process of initial orientation by shear force and vertical orientation by roll forming. This allows sheet-like boron nitride to align along the thickness of the adhesive layer, forming a vertical thermally conductive framework. Simultaneously, spherical alumina and needle-like carbon nanomaterials fill the gaps in the framework under pressure, forming thermally conductive nodes and constructing a three-dimensional thermally conductive network that extends throughout the thickness direction. This process eliminates the need for external electric / magnetic fields, significantly reducing equipment investment and process complexity. Furthermore, the multi-scale filler composite (sheet-like + spherical + needle-like) and bimodal particle size distribution design result in a denser and more efficient thermal pathway, effectively solving the problem of localized heat accumulation in small-pitch LEDs.

[0032] 3. This invention uses low-cost spherical alumina as the primary thermal filler, compounded with a small amount of lamellar boron nitride and needle-like nano-carbon materials. While ensuring a thermal conductivity ≥1.5W / (m·K), the material cost is reduced by more than 30%. Simultaneously, a graded curing process combining UV pre-curing and stepped thermal curing is employed. Through three-stage temperature control—low-temperature flow, medium-temperature orientation locking, and high-temperature complete curing—the total curing time is shortened to 20-30 minutes, balancing the fixation of the filler's orientation structure with improved production efficiency, making it more suitable for large-scale industrial applications. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of the fabrication process of the stress-controlled packaging structure provided in this application. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Specific conditions not specified in the examples shall be carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0036] Example 1

[0037] This embodiment provides a stress-controlled packaging structure for AM glass-based small-pitch displays and its fabrication method, the process flow of which is as follows: Figure 1 As shown, the specific steps are as follows:

[0038] 1. Preparation of composite glass substrate

[0039] An 80μm thick ultrathin glass was selected as the glass layer, and a 38μm thick polyimide (PI) support film was laminated on its back to form a composite glass substrate. Multiple micro-grooves with a depth of 15μm, a width of 30μm, and a spacing of 200μm between adjacent grooves were processed in the edge region of the composite glass substrate using laser etching technology, serving as stress relief structures.

[0040] The composite glass substrate was placed in a 3:1 volume ratio solution of deionized water and isopropanol and ultrasonically cleaned at 50°C for 5 minutes, then rinsed with deionized water for 2 minutes and dried with nitrogen. Subsequently, the substrate surface was activated using an oxygen plasma treatment device with a power of 100W and a treatment time of 30 seconds, using pure oxygen.

[0041] 2. Mass transfer of LED chips

[0042] A blue Micro-LED chip (30μm × 30μm in size and 10μm in thickness) was transferred to a predetermined position on the front side of an activated composite glass substrate using a flexible stamp transfer method. After transfer, the chip was temporarily fixed to the substrate by hot pressing at 150°C for 10 seconds. Subsequently, optical inspection was performed, and missing or misaligned chips were repaired with laser assistance to ensure that the chip position accuracy was better than ±1μm.

[0043] 3. Preparation of high thermal conductivity encapsulating adhesive composition

[0044] Materials are prepared in the following proportions by weight: 75 parts polyurethane-modified epoxy resin, 25 parts long-chain flexible epoxy resin, 10 parts lamellar boron nitride, 40 parts spherical alumina, 3 parts needle-shaped carbon nanofibers, 8 parts core-shell structured rubber particles (300 nm in diameter), 1 part photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 3 parts thermosetting agent modified imidazole derivative. Among these, the lamellar boron nitride consists of surface-esterified boron nitride nanosheets with a thickness of 50-80 nm and a diameter of 2-4 μm; the spherical alumina exhibits a bimodal particle size distribution, comprising small-diameter alumina (0.3-0.5 μm, accounting for 20%) and large-diameter alumina (2-5 μm, accounting for 80%), with a mass ratio of 1:4; the needle-shaped carbon nanofibers are vapor-grown carbon fibers with an aspect ratio of 60-80 and a surface coated with a SiO2 insulating layer.

[0045] The preparation process is as follows:

[0046] (1) Mix boron nitride flakes with 20 parts of polyurethane modified epoxy resin, and process it three times with a three-roll mill at a speed of 200 rpm and the roller gap gradually decreases to 10 μm to form a pre-dispersed masterbatch.

[0047] (2) Mix spherical alumina, needle-shaped carbon nanofibers with the remaining polyurethane modified epoxy resin (55 parts) and all long-chain flexible epoxy resin (25 parts), stir at 800 rpm for 20 min in a planetary mixer, and then treat in an ultrasonic disperser at 40 kHz for 15 min to make the filler uniformly dispersed.

[0048] (3) Combine the pre-dispersed masterbatch with the ultrasonic dispersion mixture, add stress-absorbing rubber, photoinitiator and thermosetting agent, stir at 500 rpm for 10 min in a planetary mixer, then transfer to a vacuum degassing chamber and degas for 30 min under -0.1 MPa conditions to obtain a high thermal conductivity encapsulating adhesive composition.

[0049] 4. High thermal conductivity encapsulation coating and orientation

[0050] The composite glass substrate with the chip fixed on it was subjected to plasma cleaning (Ar / O2 mixed gas, Ar:O2=70:30, power 80W, time 20s), and then baked in an oven at 120℃ for 10min to dehumidify.

[0051] The aforementioned high thermal conductivity encapsulating adhesive composition was coated onto the front side of a composite glass substrate using a slit coating head. The coating head gap was set to 120 μm, the coating speed was 0.3 m / min, and the coating thickness was controlled at 90 ± 5 μm. During the coating process, the shear force generated by the relative movement between the coating head and the substrate caused the flake boron nitride to initially align along the coating direction, while the spherical alumina and needle-like carbon nanofibers were uniformly dispersed with the resin flow.

[0052] Immediately after coating, the adhesive layer is processed using a precision roller pressing device at a temperature of 55℃, a pressure of 0.2MPa, and a speed of 0.3m / min. The vertical pressure causes the sheet-like boron nitride to flip and align along the thickness of the adhesive layer, forming a vertical thermally conductive framework. Spherical alumina and needle-like carbon nanofibers fill the gaps between the sheet-like boron nitride under pressure, forming thermally conductive nodes.

[0053] 5. Graded curing

[0054] The rolled substrate is then graded and cured:

[0055] UV pre-curing: Using a 365nm UV-LED light source with a light intensity of 50mW / cm², irradiation for 5s, a preliminary cross-linking layer with a thickness of about 15μm is formed on the surface of the adhesive layer.

[0056] Low-temperature flow stage: Keep warm in an 80℃ oven for 8 minutes to reduce the viscosity of the adhesive layer to about 350 cP;

[0057] Mid-temperature orientation locking stage: The temperature is increased to 120℃ at 3℃ / min and held for 6min to fix the oriented arrangement structure of the plate-like boron nitride;

[0058] High-temperature complete curing stage: Increase the temperature to 150℃ at 2℃ / min and hold for 8min to allow the adhesive layer to fully cure (curing degree ≥98%).

[0059] Gradient cooling phase: The temperature is reduced to 60℃ at a rate of 1.5℃ / min, and then allowed to cool naturally to room temperature.

[0060] The cured high thermal conductivity encapsulating adhesive layer has a thickness of 85 μm. Its vertical thermal conductivity is 1.8 W / (m·K) (ASTM D5470), breakdown voltage is 18 kV / mm (IEC60243), coefficient of thermal expansion is 22 ppm / ℃ (TMA method, -40-150℃), adhesion is 12 MPa (GB / T9286), and the storage modulus changes by 24% in the range of 25-150℃.

[0061] 6. Optical functional film bonding

[0062] The cured substrate surface was subjected to plasma cleaning (Ar / O2 mixed gas, power 50W, time 30s). A 25μm thick UV-curable OCA optical adhesive (93% light transmittance, 0.4% haze) was bonded to the surface of the encapsulation adhesive layer using a roll bonding machine at a bonding pressure of 0.4MPa and a speed of 0.5m / min.

[0063] The quantum dot film was bonded using a selective laser heating method: an infrared laser (wavelength 808nm, spot diameter 1mm, power 10W, scanning speed 20mm / s) scanned the bonding area, locally softening the OCA, while simultaneously applying 0.2MPa roller pressure to bond the quantum dot film to the OCA surface. After bonding, a 365nm UV-LED was used for irradiation with a curing dose of 1000mJ / cm² to completely cure the OCA.

[0064] Finally, an anti-reflective layer was applied using electrostatic spraying technology: SiO2 nano-sol (particle size 15±3nm, solid content 5wt%, solvent: ethanol:water = 7:3) was prepared and sprayed in two layers using an electrostatic spraying system (voltage 20kV, spraying distance 15cm, travel speed 50mm / s), with a 30s interval between each layer. After spraying, the layers were cured in hot air at 80℃ for 5 minutes, followed by annealing at 150℃ for 10 minutes to form the anti-reflective layer.

[0065] Example 2

[0066] This embodiment provides a stress-controlled encapsulation structure for AM glass-based small-pitch displays. The difference between this structure and Embodiment 1 lies only in the formulation of the high thermal conductivity encapsulating adhesive composition. Specifically:

[0067] By weight: 75 parts polyurethane modified epoxy resin, 25 parts long-chain flexible epoxy resin, 9.6 parts flake boron nitride, 28.8 parts spherical alumina, 1.9 parts needle-shaped carbon nanofibers, 5 parts core-shell structured rubber particles (particle size 300nm), 0.5 parts photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 1 part thermosetting agent modified imidazole derivative.

[0068] The high thermal conductivity encapsulating adhesive composition was prepared according to the same process steps as in Example 1. Specifically, flake boron nitride and a portion of the matrix resin were processed by a three-roll mill to form a pre-dispersed masterbatch. Then, spherical alumina, needle-shaped carbon nanofibers and the remaining matrix resin were mixed and dispersed by planetary stirring and ultrasonication. Finally, stress-absorbing rubber, photoinitiator and thermosetting agent were added and the composition was obtained after vacuum degassing.

[0069] Example 3

[0070] This embodiment provides a stress-controlled encapsulation structure for AM glass-based small-pitch displays. The difference between this structure and Embodiment 1 lies only in the formulation of the high thermal conductivity encapsulating adhesive composition. Specifically:

[0071] By weight: 83.3 parts polyurethane modified epoxy resin, 16.7 parts long-chain flexible epoxy resin, 14.6 parts flake boron nitride, 73.2 parts spherical alumina, 7.3 parts needle-shaped carbon nanofibers, 15 parts core-shell structured rubber particles (300 nm in diameter), 2 parts photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 5 parts thermosetting agent modified imidazole derivative.

[0072] Example 4

[0073] This embodiment provides a stress-controlled encapsulation structure for AM glass-based small-pitch displays. The difference between this structure and Embodiment 1 lies only in the process parameters of step 4, "High thermal conductivity encapsulant coating and orientation." Specifically:

[0074] The composite glass substrate with the chip fixed on it was subjected to plasma cleaning (Ar / O2 mixed gas, Ar:O2=70:30, power 80W, time 20s), and then baked in an oven at 120℃ for 10min to dehumidify.

[0075] A high thermal conductivity encapsulating adhesive composition was coated onto the front side of a composite glass substrate using a slit coating head. The coating head gap was set to 120 μm, the coating speed was 0.2 m / min, and the coating thickness was controlled at 90 ± 5 μm. During the coating process, the shear force generated by the relative movement between the coating head and the substrate initially oriented the flake boron nitride along the coating direction, while the spherical alumina and needle-like carbon nanofibers were uniformly dispersed with the resin flow.

[0076] Immediately after coating, the adhesive layer is processed using a precision roller pressing device at a temperature of 40℃, a pressure of 0.1MPa, and a speed of 0.2m / min. The vertical pressure causes the sheet-like boron nitride to flip and align along the thickness of the adhesive layer, forming a vertical thermally conductive framework. Spherical alumina and needle-like carbon nanofibers fill the gaps between the sheet-like boron nitride under pressure, forming thermally conductive nodes.

[0077] Example 5

[0078] This embodiment provides a stress-controlled encapsulation structure for AM glass-based small-pitch displays. The difference between this structure and Embodiment 1 lies only in the process parameters of step 4, "High thermal conductivity encapsulant coating and orientation." Specifically:

[0079] The composite glass substrate with the chip fixed on it is subjected to plasma cleaning and baking dehumidification.

[0080] A high thermal conductivity encapsulating adhesive composition was coated onto the front side of a composite glass substrate using a slotted coating head. The coating head gap was set to 120 μm, the coating speed was 0.5 m / min, and the coating thickness was controlled at 90 ± 5 μm. During the coating process, the higher coating speed generated stronger shear force, resulting in more complete orientation of the flake boron nitride along the coating direction.

[0081] Immediately after coating, the adhesive layer is processed using a precision roller pressing device at a temperature of 60℃, a pressure of 0.3MPa, and a speed of 0.5m / min. The higher roller pressing temperature and pressure facilitate filler rearrangement and densification, allowing the lamellar boron nitride to align more tightly along the thickness direction, while simultaneously promoting the full filling of gaps by spherical alumina and needle-like carbon nanofibers.

[0082] Example 6

[0083] This embodiment provides a stress-controlled packaging structure for AM glass-based small-pitch displays. The difference between this structure and Embodiment 1 lies only in the process parameters of step 5, "gradual curing." Specifically:

[0084] The rolled substrate is then subjected to graded curing with the following parameters:

[0085] UV pre-curing: Using a 365nm UV-LED light source with a light intensity of 45mW / cm², irradiation for 3 seconds, a preliminary cross-linking layer is formed on the surface of the adhesive layer;

[0086] Low-temperature flow stage: Keep warm in a 70℃ oven for 10 minutes to reduce the viscosity of the adhesive layer;

[0087] Mid-temperature orientation locking stage: The temperature is increased to 110℃ at 3℃ / min and held for 5 minutes to fix the oriented arrangement structure of the plate-like boron nitride;

[0088] High-temperature complete curing stage: Increase the temperature to 140℃ at 2℃ / min and hold for 5 minutes to allow the adhesive layer to fully cure;

[0089] Gradient cooling phase: The temperature is reduced to 60℃ at a rate of 1℃ / min, and then allowed to cool naturally to room temperature.

[0090] Example 7

[0091] This embodiment provides a stress-controlled packaging structure for AM glass-based small-pitch displays. The difference between this structure and Embodiment 1 lies only in the process parameters of step 5, "gradual curing." Specifically:

[0092] The rolled substrate is then subjected to graded curing with the following parameters:

[0093] UV pre-curing: Using a 365nm UV-LED light source with a light intensity of 55mW / cm², irradiation for 8 seconds, a preliminary cross-linking layer with a thickness of about 20μm is formed on the surface of the adhesive layer;

[0094] Low-temperature flow stage: Keep warm in a 90℃ oven for 5 minutes to reduce the viscosity of the adhesive layer;

[0095] Mid-temperature orientation locking stage: The temperature is increased to 130℃ at 5℃ / min and held for 8 minutes to fix the oriented arrangement structure of the plate-like boron nitride;

[0096] High-temperature complete curing stage: Increase the temperature to 160℃ at 3℃ / min and hold for 10 minutes to allow the adhesive layer to fully cure;

[0097] Gradient cooling phase: The temperature is reduced to 60°C at a rate of 2°C / min, and then allowed to cool naturally to room temperature.

[0098] Comparative Example 1

[0099] This comparative example uses the flexible packaging process for AM glass-based small-pitch displays disclosed in prior art document CN120475833A. The specific steps are as follows:

[0100] S1: Substrate pretreatment: The substrate surface is ultrasonically cleaned for 5 minutes at 50°C using a mixed solution of deionized water and isopropanol with a volume ratio of 3:1, rinsed with deionized water for 2 minutes and dried. Then, the substrate surface is activated by plasma of a mixed gas of oxygen and nitrogen (volume ratio of 70%:30%).

[0101] S2: Mass transfer of LED chips: Align and transfer the LED chips to predetermined positions on the activated substrate, and fix them onto the substrate.

[0102] S3: High thermal conductivity encapsulant coating: The substrate with the chip fixed is subjected to plasma cleaning and dehumidification by baking at 120°C, followed by coating with a high thermal conductivity adhesive. The high thermal conductivity adhesive is composed of the following components: 30wt% polyurethane-modified epoxy resin, 25wt% aluminum nitride, 12wt% boron nitride nanosheets, 4wt% carbon fiber fragments, 0.2wt% defoamer, and 0.5wt% photoinitiator. During the coating process, a DC electric field of 1kV / mm is applied for 15 minutes to orient the boron nitride sheet filler.

[0103] S4: High thermal conductivity adhesive curing: UV pre-curing (365nm UV light, 50mW / cm² irradiation for 5 seconds) followed by stepped thermal curing: 80℃ for 10 min, increase the temperature to 120℃ at 2℃ / min and hold for 15 min, increase the temperature to 150℃ at 1℃ / min and hold for 20 min, then decrease the temperature to 80℃ at 0.5℃ / min and allow it to cool naturally to room temperature.

[0104] S5: Optical film lamination: Quantum dot film lamination and anti-reflective layer spraying are performed on the surface of the cured substrate.

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 1 is that the high thermal conductivity encapsulating adhesive formulation in Comparative Example 1 is used, while the remaining steps are the same as in Example 1.

[0107] Comparative Example 3

[0108] The difference between this comparative example and Example 1 is that spherical alumina and needle-like nano-carbon materials are not added to the high thermal conductivity encapsulant composition. Only lamellar boron nitride is retained as a thermally conductive filler. The remaining components and their proportions are adjusted as follows (by weight): 75 parts polyurethane modified epoxy resin, 25 parts long-chain flexible epoxy resin, 12 parts lamellar boron nitride (surface esterified, thickness 50-80nm, sheet diameter 2-4μm), 8 parts core-shell structured rubber particles, 1 part photoinitiator, and 3 parts thermosetting agent.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 1 is that in step 4, "coating and orienting of high thermal conductivity encapsulant," the step of applying vertical pressure with the roller press is omitted, and the sheet-like boron nitride is oriented solely by the shear force during the coating process, as detailed below:

[0111] A high thermal conductivity encapsulating adhesive composition was applied to the front side of a composite glass substrate using a slotted coating head at a speed of 0.3 m / min, with the coating thickness controlled at 90 ± 5 μm. During the coating process, the shear force generated by the relative movement of the coating head and the substrate initially oriented the flake boron nitride along the coating direction. However, after coating, no rolling treatment was performed; the substrate directly entered the graded curing step.

[0112] Comparative Example 5

[0113] The difference between this comparative example and Example 1 is that in step 5, "gradual curing," the stepped temperature increase procedure is omitted, and constant temperature curing is used instead, as detailed below:

[0114] The rolled substrate was placed directly in a 150°C oven and cured at that temperature for 30 minutes, then allowed to cool naturally to room temperature. UV pre-curing, low-temperature flow, medium-temperature orientation locking, and gradient cooling steps were not performed.

[0115] Performance testing

[0116] Test methods

[0117] 1. Vertical thermal conductivity test: The thermal conductivity of the encapsulating adhesive layer in the thickness direction was measured using a thermal resistance tester in accordance with ASTM D5470 standard.

[0118] 2. Breakdown voltage test: The dielectric strength of the encapsulation layer is measured using a withstand voltage tester in accordance with IEC60243 standard.

[0119] 3. Thermal expansion coefficient test: Referring to the TMA method (thermomechanical analysis), the linear expansion coefficient of the encapsulating adhesive layer in the temperature range of -40℃ to 150℃ is measured using a thermomechanical analyzer.

[0120] 4. Adhesion test: Referring to the cross-cut test in GB / T9286, a 1mm×1mm grid is cut on the surface of the encapsulating adhesive layer using a cross-cut tester, with a grid number of 10×10. After sticking with special tape, peel it off and observe the coating peeling.

[0121] 5. Energy storage modulus change rate test: The change in energy storage modulus of the encapsulating adhesive layer during the process of heating from 25℃ to 150℃ was tested using a dynamic thermomechanical analyzer in tensile mode.

[0122] 6. Thermal cycling test: In accordance with the JESD22-A104 standard, the display sample was placed in a temperature control chamber and thermally cycled between -40℃ and 85℃. Each cycle lasted 30 minutes. After 500 cycles, the pixel failure was detected using a high-resolution optical microscope.

[0123] 7. Observation of cracks in glass substrate: The edge area of ​​the composite glass substrate and the area around the chip after thermal cycling test were observed using a high-magnification optical microscope (magnification 100-500x).

[0124] Test Results

[0125] As shown in Table 1.

[0126] Table 1. Performance test results of the examples and comparative examples

[0127]

[0128] As can be seen from Table 1:

[0129] A comparison of Examples 1-7 with Comparative Example 1 shows that: Examples 1-7 all used an ultra-thin glass layer (50-100μm) and a polymer support layer (PI / PET film) to form the substrate, and a stress-relieving structure was set at the edge. After 500 thermal cycles, no glass substrate cracks appeared in any of the sample examples; while Comparative Example 1 used a common glass substrate from the comparative patent, and under the same test conditions, 5% of the samples showed microcracks, with a pixel failure rate as high as 0.015%. This indicates that the present invention, by attaching a polymer support layer to the back of the glass substrate and setting a stress-relieving structure, effectively disperses and absorbs the thermal stress generated during thermal cycling, fundamentally solving the brittleness problem of the glass substrate and significantly improving the reliability of the packaging structure.

[0130] A comparison between Example 1 and Comparative Example 2 shows that, under the same process conditions, the formulation of the high thermal conductivity encapsulant has a significant impact on performance. Although the AlN / BN / carbon fiber system in Comparative Example 2 has a higher total amount of thermally conductive filler, the filler morphology is singular and the synergistic effect is insufficient, resulting in lower thermal conductivity and poor thermal stress matching, ultimately affecting the long-term reliability of the encapsulation structure.

[0131] A comparison of Example 1 and Comparative Example 3 shows that Example 1, using a composite of sheet-like boron nitride, spherical alumina, and needle-like nano-carbon materials, achieved a vertical thermal conductivity of 1.8 W / (m·K) and a coefficient of thermal expansion of 22 ppm / ℃. In contrast, Comparative Example 3, which only added sheet-like boron nitride without spherical alumina or needle-like nano-carbon materials, had a thermal conductivity of only 0.9 W / (m·K), a coefficient of thermal expansion as high as 35 ppm / ℃, reduced adhesion to 6 MPa, and a thermal cycle failure rate of 0.025%. This indicates that sheet-like boron nitride forms a vertical thermally conductive framework, spherical alumina provides isotropic thermally conductive nodes, and needle-like nano-carbon materials bridge the gaps in the framework. These three elements synergistically construct a highly efficient three-dimensional thermally conductive network spanning the thickness direction. Simultaneously, the bimodal distribution of spherical alumina effectively reduces the coefficient of thermal expansion of the encapsulating adhesive layer, achieving a balance between thermal conductivity and thermal stress.

[0132] A comparison of Example 1 and Comparative Example 4 reveals that: In Example 1, shear force was used during the coating process to initially orient the sheet-like boron nitride, and vertical pressure was applied immediately after coating using a roller pressing device, resulting in a thermal conductivity of 1.8 W / (m·K); while in Comparative Example 4, orientation was achieved solely through coating shear force, eliminating the roller pressing step, resulting in a thermal conductivity of 1.3 W / (m·K), lower than the 1.5 W / (m·K) lower limit required by the claims. This demonstrates that shear force alone can only orient the sheet-like boron nitride along the coating direction, failing to form a vertical thermal conduction path penetrating the thickness direction; whereas the vertical pressure applied by roller pressing causes the sheet-like boron nitride to flip and align along the thickness direction, while simultaneously squeezing spherical alumina and needle-like nano-carbon materials into the interstices of the framework, forming a complete three-dimensional thermal conduction network.

[0133] A comparison of Example 1 and Comparative Example 5 shows that: Example 1, employing a graded curing process of UV pre-curing + stepped thermal curing, achieved a storage modulus change rate of 24%, a coefficient of thermal expansion of 22 ppm / ℃, and a thermal cycle failure rate of 0.006%; while Comparative Example 5, using a constant temperature curing of 150℃ for 30 minutes without graded curing and gradient cooling, achieved a storage modulus change rate as high as 35%, a coefficient of thermal expansion of 30 ppm / ℃, and after thermal cycling, 2% of the samples showed microcracks, with a failure rate of 0.018%. This indicates that in the graded curing process, the low-temperature flow stage allows the adhesive layer to fully level and expel air bubbles, the medium-temperature orientation locking stage fixes the filler arrangement structure, the high-temperature complete curing stage achieves deep cross-linking, and the gradient cooling stage slowly releases thermal stress, avoiding interface debonding and microcracks caused by sudden cooling, thus ensuring the long-term stability of the encapsulation structure.

[0134] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A stress-regulating packaging structure for AM glass-based small-pitch displays, characterized in that, include: A composite glass substrate, the composite glass substrate comprising an ultrathin glass layer and a polymer support layer adhered to the back side of the ultrathin glass layer; LED chip, the LED chip being fixed to the front side of the composite glass substrate; A high thermal conductivity encapsulating adhesive layer is stacked on the front side of the composite glass substrate and covers the LED chip. The high thermal conductivity encapsulating adhesive layer has a three-dimensional thermal conductive network. The three-dimensional thermal conductive network is constructed by a vertical thermal conductive skeleton formed by sheet-like boron nitride oriented along the thickness direction of the adhesive layer, and thermal conductive nodes filled with spherical alumina and needle-shaped nano-carbon materials dispersed between the vertical thermal conductive skeleton. The difference in thermal expansion coefficients between the composite glass substrate and the high thermal conductivity encapsulating adhesive layer is less than 15 ppm / ℃, and the rate of change of the storage modulus of the high thermal conductivity encapsulating adhesive layer within the range of 25℃-150℃ is less than 30%.

2. The stress-regulating packaging structure for AM glass-based small-pitch displays according to claim 1, characterized in that, The thickness of the ultrathin glass layer is 50-100μm, and the polymer support layer is a polyimide film or a PET film with a thickness of 25-50μm; at least one stress relief structure is provided in the edge region of the composite glass substrate, and the stress relief structure is a micro-groove or a filling hole.

3. The stress-regulating packaging structure for AM glass-based small-pitch displays according to claim 1, characterized in that, The high thermal conductivity encapsulating adhesive layer is formed by curing a high thermal conductivity encapsulating adhesive composition, which comprises, by weight parts: The composition includes 100 parts of matrix resin, 50-120 parts of composite thermally conductive filler, 5-15 parts of stress-absorbing rubber, 0.5-2 parts of photoinitiator, and 1-5 parts of thermosetting agent.

4. The stress-regulating packaging structure for AM glass-based small-pitch displays according to claim 3, characterized in that, The matrix resin includes polyurethane-modified epoxy resin and long-chain flexible epoxy resin, with a mass ratio of 3:1-5.

5. The stress-regulating packaging structure for AM glass-based small-pitch displays according to claim 3, characterized in that, The composite thermally conductive filler includes sheet-like boron nitride, spherical alumina, and needle-like nano-carbon materials, wherein the mass ratio of the sheet-like boron nitride, spherical alumina, and needle-like nano-carbon materials is 1:3-5:0.2-0.

5.

6. The stress-regulating packaging structure for AM glass-based small-pitch displays according to claim 5, characterized in that, The sheet-like boron nitride is a surface-esterified boron nitride nanosheet with a thickness of less than 100 nm and a sheet diameter of 1-5 μm; the spherical alumina has a bimodal particle size distribution, including small-particle alumina with a particle size of 0.3-0.5 μm and large-particle alumina with a particle size of 2-5 μm, with a mass ratio of 1:2-4; the needle-like nanocarbon material is carbon nanotube or carbon nanofiber with an aspect ratio greater than 50.

7. A method for fabricating a stress-controlled encapsulation structure for an AM glass-based small-pitch display screen as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: A polymer support layer is attached to the back of the ultra-thin glass layer, and the edges of the composite glass substrate are treated to form a stress-relieving structure; S2: After surface activation treatment of the composite glass substrate, the LED chip is transferred and fixed to the predetermined position on the substrate; S3: Prepare a high thermal conductivity encapsulating adhesive composition and coat it onto the surface of a composite glass substrate with a chip fixed on it. During the coating process, the shear force generated by the relative movement of the coating head and the substrate causes the sheet-like boron nitride to initially align along the coating direction, while the spherical alumina and needle-like carbon nanomaterials are uniformly dispersed with the resin flow. Immediately after coating, a roller press is used to apply vertical pressure to the adhesive layer, causing the sheet-like boron nitride to flip and align along the thickness direction of the adhesive layer to form a vertical thermally conductive skeleton. Under pressure, the spherical alumina and needle-like carbon nanomaterials fill the gaps between the sheet-like boron nitride to form thermally conductive nodes. Then, the above structure is fixed by a graded curing process to form a high thermal conductivity encapsulating adhesive layer. S4: An optical functional film is laminated onto the surface of the cured high thermal conductivity encapsulating adhesive layer.

8. The method for fabricating a stress-controlled encapsulation structure for AM glass-based small-pitch displays according to claim 7, characterized in that, The graded curing process includes: first, UV pre-curing to shape the adhesive surface, then step-by-step thermal curing, wherein the step-by-step thermal curing is carried out in a low temperature zone, a medium temperature zone and a high temperature zone in sequence, and after curing, the temperature is gradually reduced to room temperature.

9. The method for fabricating a stress-controlled encapsulation structure for AM glass-based small-pitch displays according to claim 7, characterized in that, The preparation method of the high thermal conductivity encapsulating adhesive composition includes: The flake boron nitride is mixed with a portion of the matrix resin and processed 2-4 times using a three-roll mill to form a pre-dispersed masterbatch. Spherical alumina, needle-shaped carbon nanomaterials and the remaining matrix resin were mixed and then subjected to planetary stirring and ultrasonic dispersion. The pre-dispersed masterbatch was combined with the ultrasonically dispersed mixture, and stress-absorbing rubber, photoinitiator and thermosetting agent were added. After vacuum degassing, the final composition was obtained.

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