Liquid plastic encapsulating material for mini-led with high light transmittance and low stress and preparation method thereof

Abstract

The present application relates to the technical field of semiconductor packaging materials, in particular to a liquid plastic packaging material for MiniLED with high light transmission and low stress and a preparation method thereof.The liquid plastic packaging material comprises the following components: vinyl MQ silicone resin, phenyl hydrogen-containing silicone resin, hydrogen-containing silicone oil, silicone epoxy resin, platinum gold catalyst, ethynyl cyclohexanol, epoxy group-containing silane coupling agent, silicone defoaming agent, fumed silica and phenyl vinyl silicone resin;the fumed silica is dried, then ground with part of the base resin to form a master batch, and then mixed with the remaining components to remove bubbles to obtain a liquid component;the catalyst and the inhibitor are respectively diluted into a premix, and then mixed in sequence and deaerated again before use.The present application realizes the extreme uniform dispersion of fumed silica and the precise release of stress by constructing a multiple crosslinking network and a double crosslinking system, combining the interface compatibilization effect and the gradient curing process, and solves the technical problem that high light transmission and low stress are difficult to be considered simultaneously.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging materials technology, and more specifically, to a liquid molding compound for MiniLEDs with high light transmittance and low stress, and its preparation method. Background Technology

[0002] MiniLED (small light-emitting diode) is a display backlight technology that uses tiny LED chips with a size between 50 and 300 micrometers as the backlight source for LCD panels. By dividing the backlight panel into numerous independently controllable dimming zones, MiniLED technology can achieve more precise brightness adjustment than traditional edge-lit backlighting, significantly improving the contrast and dynamic range of the displayed image, and is widely used in high-end display fields.

[0003] However, existing MiniLED packaging materials still have significant shortcomings in achieving synergistic control of high light transmittance and low stress.

[0004] Firstly, while traditional epoxy molding compounds or silicone materials possess basic encapsulation functions, their intrinsic light transmittance is insufficient to meet the high-density integration requirements of MiniLED chips. Due to impurity ions in the material matrix, unreacted catalyst residues, or high-temperature yellowing side reactions, light absorption and scattering are severe in the visible light band (especially the blue and red light bands), leading to a decrease in light extraction efficiency. This prevents the full utilization of the high brightness advantage of MiniLEDs, and long-term operation can easily result in transmittance decay, affecting the stability and uniformity of display quality.

[0005] Secondly, the coefficient of thermal expansion (CTE) matching between the packaging material and the substrate / chip is poor. During reflow soldering or power-on, the thermal stress generated by temperature changes cannot be effectively released, easily leading to chip misalignment, electrode breakage, or peeling of the packaging layer interface. In particular, when the curing shrinkage rate is high, residual stress will form inside the packaging material, causing birefringence, further deteriorating the uniformity of light path transmission, resulting in localized yellowing or uneven brightness of the display module.

[0006] In summary, existing MiniLED packaging materials have shortcomings in terms of light transmittance, stress control, and microstructure stability, which restrict the development of MiniLED display modules towards ultra-high brightness, ultra-long lifespan, and high image quality uniformity. Summary of the Invention

[0007] The purpose of this invention is to improve the formulation system and curing process of existing liquid encapsulation materials for MiniLEDs, so as to achieve synergistic control of high light transmittance and low stress.

[0008] The purpose of this invention is to provide a liquid encapsulant for MiniLEDs with high light transmittance and low stress, and its preparation method. Through the synergistic effect of the multiple cross-linked network and interface compatibilization system constructed by phenyl vinyl resin and MQ silicone resin, the entire process from raw material micro-dispersion to curing stress release is precisely controlled, which significantly improves the light transmittance and internal stress control capability of the encapsulation material.

[0009] To achieve the above objectives, one objective of this invention is to provide a high-transmittance, low-stress liquid molding compound for MiniLEDs, comprising the following raw materials in the following mass percentages: The composition is as follows: 5-15% vinyl MQ silicone resin, 20-35% phenyl hydrogen-containing silicone resin, 1-5% hydrogen-containing silicone oil, 3-10% silicone epoxy resin, 0.05-0.2% platinum catalyst, 0.05-0.2% ethynylcyclohexanol, 0.5-2% epoxy-containing silane coupling agent, 0.1-0.5% silicone defoamer, 1-5% fumed silica, with the balance being phenyl vinyl silicone resin.

[0010] As a further improvement to this technical solution, the phenyl vinyl silicone resin is a vinyl-terminated methylphenyl polysiloxane with a phenyl content of 10-30 mol% and a viscosity of 1000-10000 mPa·s at 25°C.

[0011] As a further improvement to this technical solution, the vinyl MQ silicone resin contains 1.5-3.5% vinyl by mass.

[0012] As a further improvement to this technical solution, the hydrogen mass percentage of the phenyl hydrogen-containing organosilicon resin is 0.5-1.2%, and the phenyl content is 5-20 mol.

[0013] As a further improvement to this technical solution, the hydrogen-containing silicone oil is methyl hydrogen-containing silicone oil with a hydrogen mass percentage of 0.3-0.8%.

[0014] A second objective of this invention is to provide a method for preparing the aforementioned high-transmittance, low-stress liquid encapsulating compound for MiniLEDs, comprising the following steps: Step S1: Weigh the raw materials according to their mass percentage; Fumed silica is vacuum dried at 120-150℃ for 2-4 hours to remove surface adsorbed moisture, and then mixed with a portion of phenyl vinyl organosilicon resin, ground and dispersed evenly to prepare resin masterbatch. Step S2: The resin masterbatch prepared above is added together with the remaining phenyl vinyl silicone resin, vinyl MQ silicone resin, phenyl hydrogen silicone resin, hydrogen silicone oil, silicone epoxy resin, epoxy-containing silane coupling agent and silicone defoamer into a disperser and stirred to obtain a uniform mixture. Subsequently, the mixture was transferred to a planetary mixer degasser and subjected to vacuum degassing under a vacuum degree of ≤-0.095 MPa. After degassing, the undispersed particles were removed by filtration to obtain the liquid component. Step S3: Dilute the platinum catalyst and ethynylcyclohexanol with phenyl vinyl silicone resin respectively to obtain catalyst premix and inhibitor premix; Step S4: Mix the liquid components with the catalyst premix and inhibitor premix in a certain proportion; Then, vacuum degassing is performed again for 5-10 minutes to obtain the final liquid molding compound.

[0015] As a further improvement to this technical solution, in step S1, the phenyl vinyl silicone resin is ground in a three-roll mill or a planetary mixer, and the portion of the phenyl vinyl silicone resin used in the grinding and dispersion process accounts for 20-30% of the total amount of phenyl vinyl silicone resin.

[0016] As a further improvement to this technical solution, in step S2, the mixture is stirred for 30-60 minutes at a speed of 800-1200 rpm in a disperser until a homogeneous mixture is obtained.

[0017] As a further improvement to this technical solution, in step S2, vacuum degassing is performed for 20-40 minutes.

[0018] As a further improvement to this technical solution, in step S4, during mixing, the inhibitor premix is ​​first added to the liquid component and stirred evenly, and finally the catalyst premix is ​​added, and stirred at 300-500 rpm for 5-10 minutes.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: In this high-transmittance, low-stress liquid molding compound for MiniLEDs and its preparation method, fumed silica is first vacuum dried and pre-ground and dispersed with a portion of phenyl vinyl silicone resin to achieve extremely uniform wetting and distribution of nanofillers in the organic matrix, laying a microscopic uniformity foundation for the optical transparency and mechanical reinforcement of the subsequent system. Subsequently, under the precise control of vacuum degassing and stepwise mixing processes, platinum catalyst and ethynylcyclohexanol were premixed separately and added sequentially. The kinetics of the hydrosilylation reaction were precisely controlled by the preferential dispersion of inhibitors, avoiding local overheating and explosive polymerization, and ensuring a uniform and dense cross-linked network structure. Finally, through a gradient temperature curing process, pregeling, network construction, and stress release were completed sequentially, transforming the highly homogeneous liquid system into a package with fully released internal stress, strong interfacial chemical bonding, and highly uniform light transmittance. This fundamentally overcomes the technical contradiction of traditional encapsulation materials, which suffer from high internal stress and low light transmittance, making it difficult to balance the high-density integration and long-term reliability of MiniLEDs. A high-transmittance, low-stress liquid encapsulation material for MiniLEDs that meets the stringent requirements of high-end display modules was successfully prepared. Attached Figure Description

[0020] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram of the birefringence differences of each group in the experimental examples of this invention; Figure 3 This is a schematic diagram of the tensile shear strength of each group in the test examples of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] One objective of this invention is to provide a liquid molding compound for MiniLEDs with high light transmittance and low stress, comprising the following raw materials in the indicated mass percentages: The composition is as follows: 5-15% vinyl MQ silicone resin, 20-35% phenyl hydrogen-containing silicone resin, 1-5% hydrogen-containing silicone oil, 3-10% silicone epoxy resin, 0.05-0.2% platinum catalyst, 0.05-0.2% ethynylcyclohexanol, 0.5-2% epoxy-containing silane coupling agent, 0.1-0.5% silicone defoamer, 1-5% fumed silica, with the balance being phenyl vinyl silicone resin.

[0023] Among them, the phenyl vinyl silicone resin is a vinyl-terminated methylphenyl polysiloxane with a phenyl content of 10-30 mol% and a viscosity of 1000-10000 mPa·s at 25℃; the vinyl MQ silicone resin has a vinyl mass percentage of 1.5-3.5%; the phenyl hydrogen silicone resin has a hydrogen mass percentage of 0.5-1.2% and a phenyl content of 5-20 mol%; and the hydrogen-containing silicone oil is a methyl hydrogen silicone oil with a hydrogen mass percentage of 0.3-0.8%.

[0024] Phenyl vinyl silicone resin serves as the base resin, constructing a crosslinkable silicone network framework. The introduction of its phenyl groups significantly increases the resin's refractive index, making it closer to that of the MiniLED chip, thereby reducing interfacial light loss and improving light extraction efficiency. Vinyl MQ silicone resin, as a reinforcing resin, has a unique cage-like or dense structure that can be uniformly dispersed in the system, providing physical crosslinking points after curing, enhancing the mechanical strength and cohesive energy of the encapsulant, while maintaining optical transparency. Phenyl hydrogen-containing silicone resin and hydrogen-containing silicone oil, together acting as crosslinking agents, undergo hydrosilylation reactions with the vinyl groups in phenyl vinyl silicone resin and vinyl MQ silicone resin to form a dense and flexible crosslinked network. The introduction of hydrogen-containing silicone oil helps to adjust the crosslinking density and the viscosity of the system, optimizing processing flowability. Silicone epoxy resin, as a toughening and tackifying agent, possesses both the flexibility of silicone segments and the reactivity of epoxy groups in its molecular structure. It can form chemical bonds with active groups on the substrate or chip surface during curing, significantly improving interfacial adhesion strength. At the same time, its low modulus characteristics help absorb and buffer thermal stress, synergistically achieving low-stress encapsulation.

[0025] Platinum catalyst (Karstedt catalyst) catalyzes the hydrosilylation reaction, ensuring efficient curing. Ethynylcyclohexanol is used to regulate the curing reaction rate, extend the operating time, and prevent explosive polymerization or stress concentration due to excessively rapid reaction. Epoxy-containing silane coupling agents further strengthen the chemical connection at the organic-inorganic interface, improving the long-term reliability of the encapsulation. Organosilicon defoamers are used to eliminate microbubbles generated during mixing and degassing, preventing bubbles from acting as light scattering centers and reducing light transmittance. Fumed silica, as a reinforcing filler, can, when added in appropriate amounts, adjust the thixotropy of the system and the mechanical strength of the cured product, and reduce the coefficient of thermal expansion without significantly affecting light transmittance.

[0026] Please see Figure 1 As shown, a second objective of this invention is to provide a method for preparing the aforementioned high-transmittance, low-stress liquid encapsulating compound for MiniLEDs, comprising the following steps: Step S1: Weigh each component according to the mass ratio.

[0027] Platinum catalysts and inhibitors should be stored separately, and pre-mixing is strictly prohibited to avoid catalyst poisoning and inactivation. Fumed silica should be vacuum dried at 120-150℃ for 2-4 hours to remove surface-adsorbed moisture, then mixed with a portion of phenyl vinyl silicone resin and milled and dispersed evenly in a three-roll mill or planetary mixer to prepare a resin masterbatch. It is worth noting that the portion of phenyl vinyl silicone resin used in the milling and dispersion process should account for 20-30% of the total phenyl vinyl silicone resin. This operation ensures thorough wetting and dispersion of the nano-sized silica, prevents agglomeration, and ensures uniform distribution in the final system without light scattering.

[0028] Step S2: The prepared resin masterbatch, along with the remaining phenyl vinyl silicone resin, vinyl MQ silicone resin, phenyl hydrogen silicone resin, hydrogen silicone oil, silicone epoxy resin, epoxy-containing silane coupling agent, and silicone defoamer, are added to a high-speed disperser and stirred at 800-1200 rpm for 30-60 minutes until a homogeneous mixture is obtained. The mixture is then transferred to a planetary stirrer for degassing and vacuum degassing at a vacuum degree ≤ -0.095 MPa for 20-40 minutes to completely eliminate microbubbles introduced by mechanical stirring. After degassing, any undispersed particles are removed by filtration to obtain the liquid component.

[0029] Step S3: Dilute the platinum catalyst and ethynylcyclohexanol separately with a small amount of phenyl vinyl silicone resin to obtain a catalyst premix and an inhibitor premix, respectively, for later use. The inhibitor must not come into direct contact with the platinum catalyst and must be stored separately.

[0030] Step S4: Before use, mix the liquid component obtained in step S2 with the catalyst premix and inhibitor premix in a specific ratio. During mixing, first add the inhibitor premix to the liquid component and stir until homogeneous, then add the catalyst premix last. Stir slowly at 300-500 rpm for 5-10 minutes to avoid introducing new air bubbles through high-speed stirring. Then, perform a short-term vacuum degassing process (5-10 minutes) to obtain the final liquid molding compound.

[0031] The mixed, degassed liquid molding compound is applied to designated areas on the MiniLED substrate via dispensing or potting processes, followed by gradient curing. First, pre-curing is performed at 80-100℃ for 30-60 minutes to gradually consume inhibitors and allow the system to initially gel. Then, medium-temperature curing is carried out at 120-150℃ for 1-2 hours to ensure sufficient cross-linking reaction and the formation of a uniform network structure. At this stage, the epoxy groups in the silicone epoxy resin bond with the substrate surface, establishing a strong interfacial adhesion. Finally, post-curing is performed at 160-180℃ for 30-60 minutes to fully release residual stress and achieve complete curing. This gradient curing process helps avoid stress concentration caused by excessively rapid curing shrinkage, achieving low-stress encapsulation.

[0032] The cured encapsulation layer has excellent light transmittance (visible light transmittance >95%), high refractive index (>1.53), low internal stress (birefringence difference <10 nm / cm) and good interfacial bonding strength, which can meet the requirements of high-end MiniLED display modules for the coordinated control of high light transmittance and low stress.

[0033] In this invention, through the synergistic compounding of phenyl vinyl silicone resin and vinyl MQ silicone resin, combined with the dual crosslinking system of phenyl hydrogen silicone resin and hydrogen silicone oil, an interpenetrating network structure with compliant silicone segments as the main body is formed under the action of platinum catalyst, realizing a functional leap from the traditional single crosslinking mode to the synergistic enhancement of multiple crosslinking networks; at the same time, through the interfacial compatibilization and chemical bonding of silicone epoxy resin and epoxy silane coupling agent, as well as the microstructure regulation of fumed silica and silicone defoamer, the internal stress concentration and light scattering loss caused by crosslinking shrinkage, thermal expansion mismatch and interfacial defects are fundamentally suppressed. In the preparation process, fumed silica and a portion of phenyl vinyl silicone resin are first pre-ground and dispersed to achieve extremely uniform wetting and distribution of nanofillers in the organic matrix, laying a microscopic uniformity foundation for the subsequent optical transparency and mechanical reinforcement of the system. Subsequently, under the control of vacuum degassing and stepwise mixing processes, platinum catalyst and ethynylcyclohexanol are premixed and added sequentially to precisely control the kinetic process of the hydrosilylation reaction, avoiding local overheating and explosive polymerization, and ensuring that the cured network structure is uniform and dense. Finally, through low-temperature slow curing and post-heat treatment, the cross-linked network is transformed into an encapsulation with fully released internal stress, strong interfacial bonding, and highly uniform light transmittance. This fundamentally overcomes the technical contradiction of traditional encapsulation materials, which suffer from high internal stress and low light transmittance, making it difficult to balance the high-density integration and long-term reliability of MiniLEDs. A high-transmittance, low-stress liquid encapsulation material for MiniLEDs that meets the stringent requirements of high-end display modules has been successfully prepared.

[0034] The following specific embodiments will further illustrate the liquid encapsulant for MiniLEDs with high light transmittance and low stress, and its preparation method. Example 1

[0035] Step S1: Weigh out the following components according to the mass ratio: 5% vinyl MQ silicone resin, 35% phenyl hydrogen-containing silicone resin, 1% hydrogen-containing silicone oil, 10% silicone epoxy resin, 0.05% platinum catalyst, 0.2% ethynylcyclohexanol, 0.5% epoxy-containing silane coupling agent, 0.5% silicone defoamer, and 1% fumed silica. The remainder is phenyl vinyl silicone resin. Specifically, the phenyl vinyl silicone resin is a vinyl-terminated methylphenyl polysiloxane with a phenyl content of 30 mol% and a viscosity of 1000 mPa·s at 25°C; the vinyl MQ silicone resin has a vinyl mass percentage of 3.5%; the phenyl hydrogen-containing silicone resin has a hydrogen mass percentage of 0.5% and a phenyl content of 20 mol%; and the hydrogen-containing silicone oil is a methyl hydrogen-containing silicone oil with a hydrogen mass percentage of 0.3%.

[0036] Platinum catalysts and inhibitors should be stored separately, and pre-mixing is strictly prohibited to avoid catalyst poisoning and inactivation. Fumed silica is vacuum-dried at 150°C for 2 hours to remove surface-adsorbed moisture, then mixed with a portion of phenyl vinyl silicone resin and milled and dispersed evenly in a three-roll mill or planetary mixer to prepare a resin masterbatch. It is noteworthy that the portion of phenyl vinyl silicone resin used in the milling and dispersion process should account for 30% of the total phenyl vinyl silicone resin. This operation ensures thorough wetting and dispersion of the nano-sized silica, preventing agglomeration and ensuring uniform distribution in the final system without light scattering.

[0037] Step S2: The prepared resin masterbatch, along with the remaining phenyl vinyl silicone resin, vinyl MQ silicone resin, phenyl hydrogen silicone resin, hydrogen silicone oil, silicone epoxy resin, epoxy-containing silane coupling agent, and silicone defoamer, are added to a high-speed disperser and stirred at 800 rpm for 60 minutes until a homogeneous mixture is obtained. The mixture is then transferred to a planetary stirrer for degassing and vacuum degassing at a vacuum degree ≤ -0.095 MPa for 20 minutes to completely eliminate microbubbles introduced by mechanical stirring. After degassing, any undispersed particles are removed by filtration to obtain the liquid component.

[0038] Step S3: Dilute the platinum catalyst and ethynylcyclohexanol separately with a small amount of phenyl vinyl silicone resin to obtain a catalyst premix and an inhibitor premix, respectively, for later use. The inhibitor must not come into direct contact with the platinum catalyst and must be stored separately.

[0039] Step S4: Before use, mix the liquid component obtained in step S2 with the catalyst premix and inhibitor premix in a specific ratio. During mixing, first add the inhibitor premix to the liquid component and stir until homogeneous, then add the catalyst premix last. Stir slowly at 500 rpm for 5 minutes to avoid introducing new air bubbles through high-speed stirring. Then, perform a short-term vacuum degassing process (10 minutes) to obtain the final liquid molding compound. Example 2

[0040] Step S1: Weigh out the following components according to the mass ratio: 10% vinyl MQ silicone resin, 28% phenyl hydrogen-containing silicone resin, 3% hydrogen-containing silicone oil, 6% silicone epoxy resin, 0.1% platinum catalyst, 0.1% ethynylcyclohexanol, 1.5% epoxy-containing silane coupling agent, 0.2% silicone defoamer, and 3% fumed silica. The remainder is phenyl vinyl silicone resin. Specifically, the phenyl vinyl silicone resin is a vinyl-terminated methylphenyl polysiloxane with a phenyl content of 20 mol% and a viscosity of 5000 mPa·s at 25°C; the vinyl MQ silicone resin has a vinyl mass percentage of 2.5%; the phenyl hydrogen-containing silicone resin has a hydrogen mass percentage of 1.0% and a phenyl content of 12 mol%; and the hydrogen-containing silicone oil is a methyl hydrogen-containing silicone oil with a hydrogen mass percentage of 0.5%.

[0041] Platinum catalysts and inhibitors should be stored separately, and pre-mixing is strictly prohibited to avoid catalyst poisoning and inactivation. Fumed silica is vacuum-dried at 130°C for 3 hours to remove surface-adsorbed moisture, then mixed with a portion of phenyl vinyl silicone resin and milled and dispersed evenly in a three-roll mill or planetary mixer to prepare a resin masterbatch. It is noteworthy that the portion of phenyl vinyl silicone resin used in the milling and dispersion process should account for 25% of the total phenyl vinyl silicone resin. This operation ensures thorough wetting and dispersion of the nano-sized silica, preventing agglomeration and ensuring uniform distribution in the final system without light scattering.

[0042] Step S2: The prepared resin masterbatch, along with the remaining phenyl vinyl silicone resin, vinyl MQ silicone resin, phenyl hydrogen silicone resin, hydrogen silicone oil, silicone epoxy resin, epoxy-containing silane coupling agent, and silicone defoamer, are added to a high-speed disperser and stirred at 1000 rpm for 45 minutes until a homogeneous mixture is obtained. The mixture is then transferred to a planetary stirrer for degassing and vacuum degassing at a vacuum degree ≤ -0.095 MPa for 30 minutes to completely eliminate microbubbles introduced by mechanical stirring. After degassing, any undispersed particles are removed by filtration to obtain the liquid component.

[0043] Step S3: Dilute the platinum catalyst and ethynylcyclohexanol separately with a small amount of phenyl vinyl silicone resin to obtain a catalyst premix and an inhibitor premix, respectively, for later use. The inhibitor must not come into direct contact with the platinum catalyst and must be stored separately.

[0044] Step S4: Before use, mix the liquid component obtained in step S2 with the catalyst premix and inhibitor premix in a specific ratio. During mixing, first add the inhibitor premix to the liquid component and stir until homogeneous, then add the catalyst premix and stir slowly at 400 rpm for 8 minutes to avoid introducing new air bubbles through high-speed stirring. Then, perform a short-term vacuum degassing process (8 minutes) to obtain the final liquid molding compound. Example 3

[0045] Step S1: Weigh out the following components according to the mass ratio: 15% vinyl MQ silicone resin, 20% phenyl hydrogen-containing silicone resin, 5% hydrogen-containing silicone oil, 3% silicone epoxy resin, 0.2% platinum catalyst, 0.05% ethynylcyclohexanol, 2% epoxy-containing silane coupling agent, 0.1% silicone defoamer, and 5% fumed silica. The remainder is phenyl vinyl silicone resin. Specifically, the phenyl vinyl silicone resin is a vinyl-terminated methylphenyl polysiloxane with a phenyl content of 10 mol% and a viscosity of 10000 mPa·s at 25°C; the vinyl MQ silicone resin has a vinyl mass percentage of 1.5%; the phenyl hydrogen-containing silicone resin has a hydrogen mass percentage of 1.2% and a phenyl content of 5 mol%; and the hydrogen-containing silicone oil is a methyl hydrogen-containing silicone oil with a hydrogen mass percentage of 0.8%.

[0046] Platinum catalysts and inhibitors should be stored separately, and pre-mixing is strictly prohibited to avoid catalyst poisoning and inactivation. Fumed silica is vacuum-dried at 120°C for 4 hours to remove surface-adsorbed moisture, then mixed with a portion of phenyl vinyl silicone resin and milled and dispersed evenly in a three-roll mill or planetary mixer to prepare a resin masterbatch. It is noteworthy that the portion of phenyl vinyl silicone resin used in the milling and dispersion process should account for 20% of the total phenyl vinyl silicone resin. This operation ensures thorough wetting and dispersion of the nano-sized silica, preventing agglomeration and ensuring uniform distribution in the final system without light scattering.

[0047] Step S2: The prepared resin masterbatch, along with the remaining phenyl vinyl silicone resin, vinyl MQ silicone resin, phenyl hydrogen silicone resin, hydrogen silicone oil, silicone epoxy resin, epoxy-containing silane coupling agent, and silicone defoamer, are added to a high-speed disperser and stirred at 1200 rpm for 30 minutes until a homogeneous mixture is obtained. The mixture is then transferred to a planetary stirrer for degassing and vacuum degassing at a vacuum degree ≤ -0.095 MPa for 40 minutes to completely eliminate microbubbles introduced by mechanical stirring. After degassing, any undispersed particles are removed by filtration to obtain the liquid component.

[0048] Step S3: Dilute the platinum catalyst and ethynylcyclohexanol separately with a small amount of phenyl vinyl silicone resin to obtain a catalyst premix and an inhibitor premix, respectively, for later use. The inhibitor must not come into direct contact with the platinum catalyst and must be stored separately.

[0049] Step S4: Before use, mix the liquid component obtained in step S2 with the catalyst premix and inhibitor premix in a specific ratio. During mixing, first add the inhibitor premix to the liquid component and stir until homogeneous, then add the catalyst premix last. Stir slowly at 300 rpm for 10 minutes to avoid introducing new air bubbles through high-speed stirring. Then, perform a short-term vacuum degassing process (5 minutes) to obtain the final liquid molding compound.

[0050] Liquid molding compound was prepared according to Examples 1-3, and then the transmittance, internal stress and interfacial bonding strength of the cured encapsulation layer were tested.

[0051] Transmittance testing: Transmittance testing is conducted in accordance with the national standard GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics" and the general specifications of the semiconductor packaging materials industry. A UV-Vis spectrophotometer with an integrating sphere accessory is used to quantitatively evaluate the transmittance of the cured encapsulation layer in the entire visible light spectrum to verify whether it meets the requirements of high luminous efficiency output of MiniLED.

[0052] Sample preparation The liquid molding compounds prepared in Examples 1-3 were used to prepare smooth, thin sheet samples with a thickness of 1.0 ± 0.1 mm using a gradient curing process (pre-curing at 80-100℃ for 30-60 min, medium-temperature curing at 120-150℃ for 1-2 h, and post-curing at 160-180℃ for 30-60 min). At least 5 parallel samples were prepared for each example. The sample surface should be smooth, clean, free of bubbles and scratches, and cleaned and dried with anhydrous ethanol before testing.

[0053] Test environment and equipment The test should be conducted in a constant temperature and humidity laboratory at (23±2)℃ and (50±5)% relative humidity. The main equipment includes: UV-Vis spectrophotometer: equipped with integrating sphere accessory, wavelength range covering 300-800nm, wavelength accuracy ±0.5nm.

[0054] Thickness gauge: with an accuracy of not less than 0.001 mm, used for accurate measurement of sample thickness.

[0055] Test Procedures and Data Processing a) Baseline calibration: Perform baseline scanning calibration with no sample placed in either the empty optical path or the reference optical path to ensure that the 100% transmittance baseline is straight.

[0056] b) Full-band scanning: The sample is closely attached to the incident window of the integrating sphere, and continuous wavelength scanning is performed in the visible light band of 400-700nm with a scanning interval of 1nm. The transmittance value of each wavelength point is recorded.

[0057] c) Characteristic wavelength test: Select typical emission wavelengths of MiniLED chip - blue light (450nm), green light (520nm) and red light (630nm) - for fixed-point testing. Repeat the test 3 times for each wavelength point and take the average value.

[0058] d) Result determination: The average value of the transmittance test values ​​of all samples at the three characteristic wavelengths of 450nm, 520nm and 630nm is taken as the final transmittance characterization value of the batch of packaging materials, and the result is recorded in Table 1.

[0059] Internal stress testing: Internal stress testing is based on the stress evaluation method of semiconductor packaging materials. It adopts a birefringence optical testing system to quantitatively assess the internal residual stress level by measuring the difference in birefringence of the packaging material after curing.

[0060] Sample preparation For the same transmittance test sample (a flat thin sheet with a thickness of 1.0 ± 0.1 mm), at least 5 parallel samples were prepared for each example.

[0061] Test environment and equipment The test was conducted in a clean environment with a temperature of (23±2)℃ and a relative humidity of (50±5)%. The main equipment included: Birefringence testing system: Equipped with a polarizing microscope, compensator and stress analysis software, the birefringence measurement accuracy is better than 0.1 nm / cm.

[0062] Thickness gauge: accuracy not less than 0.001mm.

[0063] Test Procedures and Data Processing a) System calibration: Calibrate the optical path without a sample to ensure that the initial phase difference is zero.

[0064] b) Area scanning: Place the sample on a rotating stage, and select 1mm × 1mm areas at the center of the sample and four symmetrical points 5mm from the edge for birefringence testing. Measure and record the optical path difference (Δδ) of each area.

[0065] c) Calculation of birefringence difference: Based on the measured optical path difference Δδ (unit: nm) and sample thickness d (unit: cm), calculate the birefringence difference (unit: nm / cm) according to the formula Δn = Δδ / d.

[0066] d) Result determination: The average value of Δn values ​​for all samples and all measuring points is taken as the internal residual stress characterization value of the batch of packaging materials, and the result is recorded in Table 1. (According to the background art, the birefringence difference of traditional packaging materials is usually higher than 15 nm / cm, and the goal of this invention is to be lower than 10 nm / cm.) Interface bond strength test: The interface bond strength test is conducted in accordance with the national standard GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)". The interface reliability is evaluated by measuring the tensile shear strength between the encapsulation material and the MiniLED substrate (glass or FR4).

[0067] Sample preparation Standard test pieces (glass or FR4 plate, 100mm × 25mm × 2mm) of the same material as the actual substrate were selected. The liquid molding compound prepared in Examples 1-3 was uniformly coated onto the overlapping area of ​​the two test pieces, with an overlap area of ​​12.5mm × 25mm, and the adhesive layer thickness was controlled at 0.1 ± 0.02mm. Curing was performed according to a gradient curing process. At least 10 valid samples were prepared for each example.

[0068] Test environment and equipment The test was conducted at a temperature of (23±2)℃ and a relative humidity of (50±5)%. A universal testing machine equipped with a dedicated tensile shear fixture was used, and the load cell range was suitable for the test sample.

[0069] Test steps and calculations a) Installation and Loading: Clamp the specimen symmetrically on the tensile shear fixture, ensuring that the long axis of the specimen is aligned with the direction of the applied force. Apply a tensile load to the specimen at a constant rate of 5 mm / min until the specimen fails. Record the maximum load F at failure.

[0070] b) Overlap area measurement: After the sample is damaged, use a vernier caliper to accurately measure the length and width of the actual overlap area and calculate the overlap area A.

[0071] c) Calculation of tensile shear strength: Calculate the tensile shear strength (unit: MPa) according to the formula τ=F / A, where τ is the tensile shear strength, F is the maximum failure load, and A is the overlap area.

[0072] d) Result determination: Calculate the arithmetic mean of the τ values ​​of all valid samples, and use it as the interfacial bonding strength value between the packaging material and the substrate of this batch. The result is recorded in Table 1.

[0073] Table 1 Performance parameters of the molding compound after curing in Examples 1-3

[0074] Table 1 shows that the liquid encapsulants prepared in Examples 1-3, after gradient curing, exhibit an average transmittance of over 96% across the entire visible light spectrum, with a transmittance of no less than 96.5% at the characteristic wavelength of 450-630 nm; a birefringence difference of less than 9.0 nm / cm, meeting the design target of internal stress <10 nm / cm; and an interfacial tensile shear strength of no less than 3.5 MPa, significantly superior to traditional silicone encapsulation materials. This demonstrates that the method provided by this invention can yield liquid encapsulants for MiniLEDs with high transmittance, low internal stress, and satisfactory interfacial bonding strength.

[0075] Test case To verify that the composite network constructed from phenyl vinyl silicone resin and vinyl MQ silicone resin, the dual crosslinking system composed of phenyl hydrogen-containing silicone resin and hydrogen-containing silicone oil, and the interface compatibilization synergistically achieved by silicone epoxy resin and epoxy-containing silane coupling agent in the liquid encapsulant for high light transmittance, low internal stress, and strong interfacial adhesion in this invention are key factors in achieving the synergistic improvement of high light transmittance, low internal stress, and strong interfacial adhesion, this experimental example, based on the formulation and process of Example 2, systematically changes the core technical features and designs the following four sets of comparative experiments: Control group D1: Basic without reinforcement Solution: Completely omit vinyl MQ silicone resin and silicone epoxy resin. Use phenyl vinyl silicone resin (phenyl content 20 mol%, viscosity 5000 mPa·s) as the sole resin matrix, and directly mix it with phenyl hydrogen-containing silicone resin (hydrogen content 1.0%, phenyl content 12 mol%), hydrogen-containing silicone oil (hydrogen content 0.5%), platinum catalyst 0.1%, ethynylcyclohexanol 0.1%, epoxy-containing silane coupling agent 1.5%, silicone defoamer 0.2%, and fumed silica 3%, and prepare it according to the same process as in Example 2.

[0076] Objective: To establish a performance benchmark and verify the performance of encapsulation materials relying solely on the basic crosslinking system in terms of light transmittance, internal stress, and bond strength without the introduction of reinforcing resins and toughening / tackifying agents.

[0077] Control group D2: Single cross-linking agent group Solution: Only phenyl hydrogen-containing silicone resin is used as a crosslinking agent, completely omitting hydrogen-containing silicone oil. The amount of phenyl hydrogen-containing silicone resin is adjusted to 31% (equivalent to the total amount of both in D1 and Example 2), and the remaining components and processes are the same as in Example 2.

[0078] Objective: To isolate and verify the changes in crosslinking density, network flexibility, and internal stress level of the system when using only a single hydrogen-containing resin crosslinking agent.

[0079] Control group D3: Interface-free volume expansion group Solution: Completely omit the organosilicon epoxy resin and epoxy-containing silane coupling agent. The remaining components and processes are the same as in Example 2.

[0080] Objective: To isolate and verify the differences in bonding strength and stress buffering capacity between the encapsulation material and the substrate interface when the chemical bonding of epoxy groups is lacking.

[0081] Control group D4 (Example 2 of the present invention): Complete synergistic structure group Solution: The complete solution of this invention is adopted, namely 10% vinyl MQ silicone resin, 28% phenyl hydrogen-containing organosilicon resin, 3% hydrogen-containing silicone oil, 6% organosilicon epoxy resin, and 1.5% epoxy-containing silane coupling agent. The remaining components and processes are the same as in Example 2.

[0082] Following the identical transmittance, internal stress, and interfacial bond strength testing methods described above, the cured samples of the control groups D1, D2, D3, and D4 (Example 2) were tested. Key performance data are compared in Table 2. Figure 2-3 As shown.

[0083] Table 2 Comparative Experimental Performance Data

[0084] According to Table 2 and Figure 2-3 It can be concluded that: 1. Synergy between vinyl MQ silicone reinforcement and optical integrity (comparison of D4 and D1) Results: The transmittance of the unreinforced group (D1) in the 450nm blue light band was 94.2%, which was significantly lower than that of the intact structure group (D4) at 97.2%. At the same time, the birefringence difference of D1 was 12.5nm / cm, which was higher than the target value of 10nm / cm, and the interfacial bonding strength was only 1.8MPa.

[0085] Mechanism: Group D1 relies solely on the crosslinking of the phenyl vinyl base resin. While it possesses a certain degree of light transmittance, it lacks the dense physical crosslinking points provided by MQ silicone resin, resulting in a loose and uneven network structure. This leads to fluctuations in the refractive index of micro-regions, causing light scattering (a decrease in light transmittance). Simultaneously, the loose structure results in uneven stress distribution and increased internal stress during curing shrinkage. This invention (D4) utilizes the cage-like structure of vinyl MQ silicone resin for uniform dispersion and crosslinking, enhancing the network without introducing scattering centers, thus achieving a balance between high light transmittance and mechanical reinforcement.

[0086] 2. The necessity of using hydrogen-containing silicone oil to regulate crosslinking density and stress release (comparison between D4 and D2) Results: The birefringence difference of the single crosslinking agent group (D2) was as high as 15.3 nm / cm, far exceeding the 7.5 nm / cm of the D4 group, and the transmittance was also slightly lower than that of D4.

[0087] Mechanism: Group D2 uses only phenyl hydrogen-containing organosilicon resin as a crosslinking agent. The active hydrogen distribution on its molecular chain is relatively concentrated, leading to uneven distribution of crosslinking points and excessively high local crosslinking density, forming rigid micro-regions. This results in severe internal stress concentration (increased birefringence difference) during curing shrinkage. This invention (D4) introduces methyl hydrogen-containing silicone oil (hydrogen-containing silicone oil) as an auxiliary crosslinking agent. Its linear molecular chains can be uniformly distributed in the system, adjusting the overall crosslinking density, making the network more flexible and uniform, and effectively releasing thermal stress.

[0088] 3. The criticality of interfacial chemical bonding between organosilicon epoxy and silane coupling agents (comparison of D4 and D3) Results: The interfacial bond strength of the interface-free compatibilizer group (D3) dropped sharply to 1.2 MPa, which is only about one-quarter of that of the D4 group (4.2 MPa), while its internal stress (9.2 nm / cm) was also higher than that of the D4 group.

[0089] Mechanism: Group D3 relies entirely on the physical adsorption and van der Waals forces between the silicone network and the substrate, lacking chemical bonding. This results in a fragile interfacial bond, making it highly susceptible to delamination under thermal stress. In contrast, this invention (D4) achieves a robust chemical anchoring by enabling the epoxy groups in the silicone epoxy resin to undergo a ring-opening reaction with the hydroxyl groups on the substrate surface. Simultaneously, an epoxy-containing silane coupling agent forms a molecular bridge at the organic-inorganic interface. Furthermore, the low-modulus segments of the silicone epoxy resin effectively buffer interfacial thermal stress, synergistically achieving a balance between low stress and high bond strength.

[0090] Conclusion: The comparative experiments of the above systems fully demonstrate that the synergistic compounding of phenyl vinyl silicone resin and vinyl MQ silicone resin, the dual crosslinking of phenyl hydrogen-containing silicone resin and hydrogen-containing silicone oil, and the interfacial compatibilization of silicone epoxy resin and epoxy-containing silane coupling agent proposed in this invention constitute an organically synergistic and indispensable technical system. This design successfully solves the cascading problems of traditional encapsulation materials, such as the difficulty in simultaneously achieving good light transmittance and internal stress, and insufficient interfacial reliability. The absence of any single feature will lead to a significant and observable degradation in the key optical performance, stress control, or interfacial strength indicators of the encapsulation material.

[0091] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-transmittance, low-stress liquid encapsulant for MiniLEDs, characterized in that, Includes the following steps: Step S1: Weigh out the following components by mass percentage: 5-15% vinyl MQ silicone resin, 20-35% phenyl hydrogen-containing silicone resin, 1-5% hydrogen-containing silicone oil, 3-10% silicone epoxy resin, 0.05-0.2% platinum catalyst, 0.05-0.2% ethynylcyclohexanol, 0.5-2% epoxy-containing silane coupling agent, 0.1-0.5% silicone defoamer, 1-5% fumed silica, with the remainder being phenyl vinyl silicone resin. Fumed silica is vacuum dried at 120-150℃ for 2-4 hours to remove surface adsorbed moisture, and then mixed with a portion of phenyl vinyl organosilicon resin, ground and dispersed evenly to prepare resin masterbatch. Step S2: The resin masterbatch prepared above is added together with the remaining phenyl vinyl silicone resin, vinyl MQ silicone resin, phenyl hydrogen silicone resin, hydrogen silicone oil, silicone epoxy resin, epoxy-containing silane coupling agent and silicone defoamer into a disperser and stirred to obtain a uniform mixture. Subsequently, the mixture was transferred to a planetary mixer degasser and subjected to vacuum degassing under a vacuum degree of ≤-0.095 MPa. After degassing, the undispersed particles were removed by filtration to obtain the liquid component. Step S3: Dilute the platinum catalyst and ethynylcyclohexanol with phenyl vinyl silicone resin respectively to obtain catalyst premix and inhibitor premix; Step S4: Mix the liquid components with the catalyst premix and inhibitor premix in a certain proportion; Then, vacuum degassing is performed again for 5-10 minutes to obtain the final liquid molding compound.

2. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S1, the phenyl vinyl silicone resin is a vinyl-terminated methylphenyl polysiloxane with a phenyl content of 10-30 mol% and a viscosity of 1000-10000 mPa·s at 25°C.

3. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S1, the vinyl mass percentage in the vinyl MQ silicone resin is 1.5-3.5%.

4. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S1, the hydrogen mass percentage of the phenyl hydrogen-containing organosilicon resin is 0.5-1.2%, and the phenyl content is 5-20 mol.

5. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S1, the hydrogen-containing silicone oil is methyl hydrogen-containing silicone oil with a hydrogen mass percentage of 0.3-0.8%.

6. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S1, the phenyl vinyl silicone resin is ground in a three-roll mill or a planetary mixer, and the portion of the phenyl vinyl silicone resin used in the grinding and dispersion process accounts for 20-30% of the total amount of phenyl vinyl silicone resin.

7. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S2, the mixture is stirred for 30-60 minutes at a speed of 800-1200 rpm in a disperser until a homogeneous mixture is obtained.

8. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S2, vacuum degassing is performed for 20-40 minutes.

9. The method for preparing the high-transmittance, low-stress liquid encapsulant for MiniLEDs according to claim 1, characterized in that: In step S4, during mixing, the inhibitor premix is ​​first added to the liquid component and stirred evenly, and finally the catalyst premix is ​​added and stirred at 300-500 rpm for 5-10 minutes.

10. A high-transmittance, low-stress liquid encapsulant for MiniLEDs prepared by the preparation method according to any one of claims 1-9, characterized in that, Including the following raw materials: Vinyl MQ silicone resin, phenyl hydrogen-containing silicone resin, hydrogen-containing silicone oil, silicone epoxy resin, platinum catalyst, ethynylcyclohexanol, epoxy-containing silane coupling agent, silicone defoamer, fumed silica, and phenyl vinyl silicone resin, wherein: The phenyl vinyl silicone resin serves as the base resin, constructing a crosslinkable silicone network framework. The phenyl groups introduced into its molecular chain increase the resin's refractive index. The vinyl MQ silicone resin serves as a reinforcing resin, providing physical crosslinking points after curing. The phenyl hydrogen-containing organosilicon resin and the hydrogen-containing silicone oil together act as crosslinking agents, and undergo hydrosilylation reaction with the vinyl groups in the phenyl vinyl organosilicon resin and vinyl MQ silicone resin to form a dense and flexible crosslinking network. The platinum catalyst is used to catalyze the hydrosilylation reaction; the ethynylcyclohexanol is used as a reaction inhibitor to regulate the curing reaction rate; the epoxy-containing silane coupling agent is used to strengthen the chemical connection of the organic-inorganic interface; and the organosilicon defoamer is used to eliminate microbubbles generated during mixing and defoaming. The fumed silica is used as a reinforcing filler to adjust the thixotropy of the system and the mechanical strength of the cured product, and to reduce the coefficient of thermal expansion.

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