CoWoS packaging bottom filling material and preparation method thereof

Abstract

The invention discloses a CoWoS packaging bottom filling material and a preparation method thereof, and relates to the technical field of semiconductor packaging materials, and the filling material comprises the following components by mass: 50-80 wt% of a polyaryletherketone matrix; 20-50 wt% of a hybrid filler; the hybrid filler is prepared from nickel-plated graphene nanosheets, silicon carbide whiskers, boron nitride nanosheets and graphene quantum dots; wherein the nickel-plated graphene nanosheets account for 30-50 wt% of the hybrid filler, the silicon carbide whiskers account for 25-40 wt% of the hybrid filler, the boron nitride nanosheets account for 20-35 wt% of the hybrid filler, and the graphene quantum dots account for 1-5 wt% of the hybrid filler; by optimizing the composition and interface design of the hybrid filler, different fillers have a synergistic effect, the heat conduction and mechanical properties are improved, and the high-density packaging requirement is met; quantum dot modification, in-situ polymerization and melt blending processes are integrated, the structure and performance of the material are accurately regulated and controlled, a continuous functional network is formed, the purity and stability are improved through post-treatment, the material adapts to a high-temperature environment, and long-term reliable operation is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging materials technology, specifically to a CoWoS packaging underfill material and its preparation method. Background Technology

[0002] As the chip industry rapidly develops towards higher density and higher integration, advanced packaging technology has become a key link in improving chip performance and functionality. Among them, CoWoS packaging technology, with its advantages in multi-chip integration and high-bandwidth interconnection, is widely used in high-performance computing, artificial intelligence, and high-end consumer electronics. In the CoWoS packaging process, the underfill material plays a crucial role. Its main function is to fill the tiny gaps between the chip and the substrate, protect the solder joints from the influence of the external environment, conduct heat generated during chip operation, and enhance the overall mechanical stability of the packaging structure. As the packaging density continues to increase and the chip operating power gradually increases, higher requirements are placed on the comprehensive performance of the underfill material. It not only needs to have excellent thermal conductivity to achieve efficient thermal management, but also needs to have good mechanical strength, thermal stability, and interface bonding ability to meet the stringent standards of material reliability and durability of high-density packaging structures and support the long-term stable operation of high-end chips.

[0003] Traditional CoWoS packaging underfill materials have many limitations in performance and application. On the one hand, traditional materials often use a single type or a simple mixture of fillers combined with the matrix. The filler has poor dispersion in the matrix and is prone to agglomeration, resulting in uneven thermal conductivity. This makes it difficult to effectively conduct the heat generated by the chip, easily causing local overheating and affecting chip operating efficiency and lifespan. At the same time, the interfacial bonding between the filler and the matrix is ​​weak, resulting in insufficient mechanical properties of the material. When subjected to external impacts, vibrations, or temperature changes after packaging, defects such as voids and cracks are likely to occur, reducing the reliability of the packaging structure. On the other hand, traditional manufacturing processes are difficult to precisely control the material structure. Some processes have problems such as incomplete removal of residual solvents and uneven mixing of components, leading to decreased thermal stability of the material. It cannot adapt to the high-temperature processing environment in CoWoS packaging and is prone to performance degradation during long-term use. This makes it difficult to meet the continuous upgrading requirements of high-density packaging technology for the comprehensive performance of underfill materials, thus restricting the further development of high-end packaging technology. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a CoWoS packaging underfill material and its preparation method. Using polyaryletherketone (PAK) as a matrix, a hybrid filler composed of nickel-plated graphene nanosheets, silicon carbide whiskers, boron nitride nanosheets, and graphene quantum dots is incorporated. Prepared through a specific ratio and process, this material combines high thermal conductivity and low electrical resistance. The preparation process includes quantum dot-modified boron nitride, in-situ polymerization of the prepolymer, melt blending, and post-processing steps. The final product exhibits excellent thermal stability and mechanical properties, making it suitable for high-performance electronic packaging and meeting the high requirements of advanced chips for heat dissipation and electrical performance.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: On one hand, a CoWoS encapsulation bottom filling material, comprising, by mass percentage: 50-80 wt% polyaryletherketone matrix; 20-50 wt% hybrid filler; wherein the hybrid filler is composed of nickel-plated graphene nanosheets, silicon carbide whiskers, boron nitride nanosheets, and graphene quantum dots, wherein the nickel-plated graphene nanosheets account for 30-50 wt% of the hybrid filler, the silicon carbide whiskers account for 25-40 wt% of the hybrid filler, the boron nitride nanosheets account for 20-35 wt% of the hybrid filler, and the graphene quantum dots account for 1-5 wt% of the hybrid filler; the graphene quantum dots are adsorbed onto the surface of the boron nitride nanosheets through π-π interactions, and are bonded to the active groups on the surface of the nickel-plated graphene nanosheets and silicon carbide whiskers through hydroxyl coordination bonds.

[0006] Furthermore, the polyaryletherketone matrix is ​​selected from polyetheretherketone, polyetherketoneketone, or polyetheretherketoneketone, with a number average molecular weight of 50,000-100,000, a glass transition temperature ≥140℃, a melting point of 340-350℃, and a thermal decomposition temperature ≥500℃.

[0007] Furthermore, the nickel-plated graphene nanosheets are prepared using a chemical nickel plating process, with a nickel plating layer thickness of 5-20 nm, a sheet diameter of 1-5 μm, 5-15 layers, a volume resistivity of ≤10 Ω·cm, and an overall thermal conductivity of ≥450 W / (m·K) after nickel plating.

[0008] Furthermore, the silicon carbide whiskers are β-type, with a diameter of 50-200 nm, a length of 5-20 μm, an aspect ratio of 50:1-150:1, and a purity ≥99.5%; the boron nitride nanosheets are hexagonal boron nitride, with a sheet diameter of 2-10 μm, 3-10 layers, an interlayer spacing of 0.330-0.340 nm, and a purity ≥99.8%.

[0009] Furthermore, the graphene quantum dots have a particle size of 2-10 nm, a surface hydroxyl content of 5-15 wt%, a specific surface area of ​​≥1000 m² / g, a dispersion concentration of ≥10 mg / mL in anhydrous ethanol, and an aggregate particle size of ≤50 nm after standing for 72 h; the mass ratio of the graphene quantum dots to the boron nitride nanosheets is 1:8-1:12.

[0010] On the other hand, a method for preparing a CoWoS encapsulation bottom filler material includes the following steps:

[0011] S100, preparation of quantum dot modified boron nitride: boron nitride nanosheets and graphene quantum dots were added to anhydrous ethanol at a mass ratio of 1:8-1:12, ultrasonically dispersed for 30-60 min at an ultrasonic power of 150-250 W, and then vacuum dried at 60-80℃ for 12-24 h to obtain quantum dot modified boron nitride nanosheets.

[0012] S200, Preparation of in-situ polymerized prepolymer: Polyaryletherketone monomer and nickel-plated graphene nanosheets are added to a reaction vessel in a certain proportion, N-methylpyrrolidone solvent is added, and under nitrogen protection, the temperature is raised to 160-180℃ and the reaction is stirred for 4-6 hours to form nickel-plated graphene polyaryletherketone prepolymer; the nickel-plated graphene nanosheets account for 5-15 wt% of the total mass of the prepolymer;

[0013] S300, melt blending composite: The obtained prepolymer, quantum dot modified boron nitride nanosheets and silicon carbide whiskers are added to a twin-screw extruder in proportion, melt blending and extruding, the extrusion temperature is 360-400℃, the screw speed is 80-120r / min, and after water cooling and pelletizing, composite material particles are obtained.

[0014] S400, post-processing: Vacuum dry the composite material particles at 120-150℃ for 8-12 hours to remove residual solvent and moisture, and obtain the CoWoS encapsulation bottom filler material.

[0015] Furthermore, in S100, during the preparation of quantum dot-modified boron nitride, the graphene quantum dots have a particle size of 2-10 nm, a surface hydroxyl content of 5-15 wt%, a specific surface area ≥1000 m² / g, a dispersion concentration in anhydrous ethanol ≥10 mg / mL, and an aggregate particle size ≤50 nm after standing for 72 h; the mass ratio of the graphene quantum dots to the boron nitride nanosheets is 1:8-1:12.

[0016] Furthermore, in the S200 in-situ polymerization prepolymer preparation, the polyaryletherketone monomers are 4,4'-difluorobenzophenone and hydroquinone, with a molar ratio of 1:1.05-1:1.1, and both have a purity ≥99.5%; the solvent N-methylpyrrolidone is anhydrous, with a water content ≤0.02%, and the amount used is 2.5-3.5 times the total mass of the polyaryletherketone monomers; under nitrogen protection, the nitrogen purity is ≥99.999%, and the air in the reactor is replaced 3-4 times, with each replacement pressure being 0.25-0.35 MPa and the holding time being 4-6 min.

[0017] Furthermore, in the S300 melt blending composite, the length-to-diameter ratio of the twin-screw extruder is 40:1 to 50:1, and the screw configuration includes 3-5 sets of reverse screw shearing elements; the mass ratio of the prepolymer, quantum dot-modified boron nitride nanosheets, and silicon carbide whiskers is 50-80:5-20:5-15; the melt blending extrusion adopts a three-stage temperature control, with the first zone temperature at 380-400℃, the second zone temperature at 360-380℃, and the third zone temperature at 340-360℃; the water temperature of the water cooling tank is 25-30℃, the pelletizer speed is 280-320 r / min, and the resulting composite material particles have a particle size of 2-3 mm and a length of 2-4 mm.

[0018] Furthermore, in the S400 post-processing, the vacuum degree of the vacuum drying is -0.095MPa to -0.099MPa, and the vacuum is vented once per hour for 4 hours before drying, with each venting time lasting 40-80 seconds; after drying, the moisture content of the composite material is ≤0.1%, and the residual amount of N-methylpyrrolidone is ≤500ppm; the finished product is sealed in an aluminum foil bag containing silica gel desiccant, with the amount of silica gel desiccant being 4% to 6% of the mass of the composite material, and the storage environment temperature is 18-26℃, with a relative humidity ≤35%.

[0019] Compared with existing technologies, this CoWoS encapsulation bottom filling material and its preparation method have the following advantages:

[0020] I. This invention optimizes the composition and interfacial design of hybrid fillers, allowing different fillers to leverage their respective advantages and form a synergistic effect. Graphene quantum dots and boron nitride nanosheets form a stable bond, while simultaneously connecting other fillers to the matrix through specific interactions. This effectively improves the dispersion of fillers in the matrix, reduces agglomeration, and strengthens the interfacial bonding force between the fillers and the matrix. This structural design not only enhances the thermal conductivity of the material but also ensures mechanical stability, enabling rapid heat conduction during the encapsulation process and preventing localized overheating from damaging the device. Furthermore, it enhances the filling density of the material in the encapsulation gaps, reduces void formation, and improves the overall reliability of the encapsulation structure. This meets the dual requirements of high-density encapsulation for the bottom filler material in terms of both thermal conductivity and mechanical properties, adapting to the stringent requirements of advanced encapsulation technology for the comprehensive performance of materials.

[0021] II. This invention achieves precise control over the material structure and properties by integrating a multi-step preparation process of quantum dot modification, in-situ polymerization, and melt blending. The quantum dot modification step lays the foundation for subsequent interfacial bonding, the in-situ polymerization process allows specific fillers to form a uniform prepolymer structure with the matrix, and the melt blending process further promotes the full mixing of each component, ensuring that the hybrid filler forms a continuous functional network in the matrix. The post-processing step effectively removes residual solvents and moisture, improving the purity and stability of the material. The entire process is closely connected, ensuring the full utilization of the functions of each component and endowing the material with excellent thermal stability and environmental adaptability. It can adapt to the high-temperature processing environment of related packaging and maintain stable performance during long-term use, providing strong support for the long-term reliable operation of high-end packaging devices and broadening the application scenarios of bottom filler materials in the field of high-density packaging.

[0022] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0024] Figure 1 This is a flowchart of a method for preparing a bottom filler material for CoWoS packaging. Detailed Implementation

[0025] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0026] Example 1:

[0027] The CoWoS packaging design for high-end AI chips using a 5nm process requires efficient filling of the gap between the chip and the substrate, while simultaneously meeting the requirements of high thermal conductivity, low volatile residue, and long-term mechanical stability under high-density packaging. The detailed implementation process is as follows: Figure 1 As shown.

[0028] Raw material specifications and proportions:

[0029] Raw material specifications:

[0030] Polyaryletherketone matrix: Polyetheretherketone (PEEK) is selected with a number average molecular weight of 70,000, a glass transition temperature of 150℃, a melting point of 345℃, and a thermal decomposition temperature of 520℃. This specification ensures that the material does not soften or decompose under packaging, soldering, and long-term high-temperature operating conditions of chips, and is suitable for the heat resistance requirements of high-end chips.

[0031] Nickel-plated graphene nanosheets: prepared by chemical nickel plating process, with a nickel plating thickness of 10nm, a sheet diameter of 3μm, 10 layers, a volume resistivity of 8Ω・cm, and an overall thermal conductivity of 480W / (m・K) after nickel plating. The nickel plating can enhance the interfacial bonding force between graphene and the substrate, and the high thermal conductivity can quickly transfer the local high heat generated during chip operation.

[0032] Silicon carbide whiskers: β type, 100nm in diameter, 12μm in length, aspect ratio 100:1, purity 99.6%. The slender whisker structure can form a continuous mechanical support network inside the material, improving the bending resistance of the filler material and avoiding cracking caused by thermal stress after chip packaging.

[0033] Boron nitride nanosheets: Hexagonal boron nitride, 6μm in diameter, 6 layers, 0.335nm interlayer spacing, 99.9% purity. The hexagonal structure combines excellent thermal conductivity and electrical insulation, which can transfer heat while avoiding the risk of leakage between the chip and the substrate, and is suitable for the electrical performance requirements of CoWoS packaging.

[0034] Graphene quantum dots: 6nm particle size, 10wt% surface hydroxyl content, 1200m² / g specific surface area, 12mg / mL dispersion concentration in anhydrous ethanol, and 40nm aggregate particle size after 72h. The high specific surface area and surface hydroxyl content can enhance the interfacial bonding between them and other fillers. At the same time, the small particle size can fill the tiny gaps between other fillers and improve the overall density of the material.

[0035] Auxiliary raw materials: 4,4'-difluorobenzophenone (purity 99.6%), hydroquinone (purity 99.6%), high-purity monomers can avoid introducing impurities during polymerization that affect material properties; anhydrous N-methylpyrrolidone (water content 0.01%), low water content can prevent side reactions during polymerization; anhydrous ethanol, as a dispersion solvent, can ensure uniform mixing of quantum dots and boron nitride; silica gel desiccant, used to adsorb moisture during finished product storage.

[0036] Raw material ratio (total mass 100kg):

[0037] Polyaryletherketone matrix: 65kg (65wt%). This ratio balances the mechanical strength and processing fluidity of the material, ensuring that it can smoothly penetrate into the tiny gaps between the chip and the substrate during filling.

[0038] Hybrid packing: 35kg (35wt%), of which:

[0039] Nickel-plated graphene nanosheets: 14 kg (accounting for 40 wt% of hybrid fillers), improving the thermal conductivity of the main material;

[0040] Silicon carbide whiskers: 10.5 kg (accounting for 30 wt% of hybrid fillers), mainly used to enhance the mechanical support capacity of the material;

[0041] Boron nitride nanosheets: 9.8 kg (accounting for 28 wt% of hybrid filler), synergistically improving thermal conductivity and ensuring electrical insulation;

[0042] Graphene quantum dots: 0.7 kg (accounting for 2 wt% of hybrid fillers), fill the gaps between fillers and strengthen the interfacial bonding. The four components work together to achieve a balance of thermal conductivity, mechanical properties and insulation.

[0043] Solvent dosage: The amount of N-methylpyrrolidone is 3 times the total mass of the polyaryletherketone monomer. This dosage ensures that the monomer and the nickel-plated graphene nanosheets are completely dissolved and dispersed, avoiding local agglomeration during the polymerization process.

[0044] Preparation steps:

[0045] S100, preparation of quantum dot-modified boron nitride:

[0046] 9.8 kg of boron nitride nanosheets and 0.7 kg of graphene quantum dots were added to 50 L of anhydrous ethanol, ensuring that all solid materials were completely submerged in the solvent. The ultrasonic equipment was turned on and the ultrasonic power was set to 200 W. The ultrasonic dispersion was continued for 45 min. The high-frequency vibration of the ultrasonic waves caused the graphene quantum dots to be uniformly dispersed in the solvent and fully adsorbed on the surface of the boron nitride nanosheets through π-π interactions, reducing the agglomeration of boron nitride in subsequent processes. After ultrasonication, the dispersion was transferred to a vacuum drying oven, and the drying temperature was set to 70 °C and the vacuum degree to -0.09 MPa. The drying was continued for 18 h, and the anhydrous ethanol was gradually removed. Finally, a dry boron nitride nanosheet material with uniformly loaded quantum dots on the surface was obtained. It should be placed in a dry environment for later use to prevent moisture absorption from affecting the subsequent mixing effect.

[0047] S200, preparation of in-situ polymerized prepolymer:

[0048] 65 kg of polyaryletherketone monomer and 14 kg of nickel-plated graphene nanosheets were added to a 500 L high-pressure reactor. Then, 195 kg of anhydrous N-methylpyrrolidone was added as a solvent. The reactor was closed, and 99.999% pure nitrogen gas was introduced to perform three air replacements. Each replacement was performed at a pressure of 0.3 MPa for 5 minutes to completely remove oxygen from the reactor and prevent it from interfering with the monomer polymerization reaction or causing oxidation of the nickel-plated graphene. After the replacements were completed, the stirring device was turned on, and the temperature was increased to 170 °C at a rate of 5 °C / min. The reactor was then stirred at a constant temperature for 5 hours under nitrogen protection, allowing 4,4'-difluorobenzophenone and hydroquinone to gradually polymerize, forming polyaryletherketone segments. Simultaneously, the active groups on the surface of the nickel-plated graphene nanosheets bonded to the polymer segments through hydroxyl coordination bonds, ultimately yielding a uniformly dispersed polyaryletherketone prepolymer with nickel-plated graphene. The prepolymer must be kept in a liquid state to prevent clumping after cooling, which would affect subsequent extrusion.

[0049] S300, melt blend composite:

[0050] A twin-screw extruder with a length-to-diameter ratio of 45:1 and a screw configuration including four sets of reverse-thread shearing elements was selected. These four sets of reverse-thread shearing elements enhance the shearing and mixing effect of the material within the barrel, preventing filler agglomeration. Nickel-plated graphene polyaryletherketone prepolymer (total mass 79 kg) prepared by S200, quantum dot-modified boron nitride nanosheets (10.5 kg) prepared by S100, and 10.5 kg of silicon carbide whiskers were added to the extruder hopper in a specific ratio. The hopper was equipped with a drying device to prevent moisture absorption. The screw speed was set to 100 r / min, and a three-stage extrusion process was employed. Temperature control mode: Zone 1 temperature 390℃, Zone 2 temperature 370℃, Zone 3 temperature 350℃. After the material is melted, sheared and mixed in the barrel for 20-30 minutes, it is extruded from the die head to form a continuous strip. The strip immediately enters the water cooling tank at 28℃ for rapid cooling and shaping to avoid secondary polymerization or oxidation of the material at high temperature. Then it is pelletized by a pelletizer at 300r / min to obtain composite material particles with a particle size of 2.5mm and a length of 3mm. The uniform particle size can ensure the feeding stability during subsequent molding and processing.

[0051] S400, Post-processing:

[0052] The composite material particles obtained from S300 were transferred to a vacuum drying oven, with the thickness controlled to within 5 cm. The drying temperature was set to 135℃ and the vacuum degree to -0.097 MPa. For the first 4 hours of drying, the exhaust valve was opened once per hour for 60 seconds each time to quickly remove residual N-methylpyrrolidone and adsorbed moisture from the particles, preventing bubbles from forming due to solvent evaporation during subsequent encapsulation, which would affect the bonding strength between the chip and the substrate. After continuous drying for 10 hours, the moisture content of the composite material was tested to be ≤0.08%, and the residual N-methylpyrrolidone was ≤450 ppm, meeting the bubble-free encapsulation requirements. The qualified finished particles were sealed in an aluminum foil bag containing silica gel desiccant, with the amount of silica gel desiccant being 5% of the mass of the composite material. The aluminum foil bag can isolate external moisture and oxygen, while the silica gel desiccant continuously adsorbs trace amounts of moisture inside the bag. After sealing, the aluminum foil bag was stored in an environment with a temperature of 22℃ and a relative humidity of 30% to prevent the finished product from absorbing moisture and reducing its fluidity, ensuring the process stability during subsequent dispensing and encapsulation.

[0053] Product application scenario adaptability:

[0054] The CoWoS packaging bottom filler material prepared in this embodiment achieves uniform dispersion of boron nitride through quantum dot modification in S100, strengthens the bonding between nickel-plated graphene and the substrate through in-situ polymerization in S200, ensures the synergistic effect of multiple fillers through shear mixing in S300, and avoids packaging defects through low-residue treatment in S400. The final product can be smoothly penetrated into the tiny gaps in the 5nm AI chip CoWoS packaging through the dispensing process. Its high thermal conductivity can quickly dissipate the heat during high-power operation of the chip and avoid local overheating. Its excellent mechanical properties can resist the stress caused by the difference in thermal expansion coefficients between the chip and the substrate. The low-residue characteristics ensure that there is no risk of bubble detachment after long-term use after packaging, which is fully adapted to the high-density and high-reliability CoWoS packaging requirements of high-end AI chips.

[0055] In summary, this embodiment addresses the CoWoS packaging requirements of high-end AI chips using a 5nm process. Raw materials were selected and their proportions optimized strictly according to patent parameters. The polyaryletherketone matrix ensures heat resistance, while hybrid fillers synergistically achieve a balance between thermal conductivity, mechanical properties, and insulation. During fabrication, quantum dot modification reduces boron nitride agglomeration, in-situ polymerization strengthens the bonding between nickel-plated graphene and the matrix, shear mixing ensures uniform filler dispersion, and post-processing reduces residue to avoid encapsulation bubbles. The final product can smoothly penetrate the tiny gaps between the chip and the substrate, possessing high thermal conductivity, excellent mechanical properties, and low residue characteristics, perfectly meeting the high-density, high-reliability CoWoS packaging requirements.

[0056] Example 2:

[0057] Example of stability testing of bottom filler material for CoWoS packaging.

[0058] This embodiment is based on the raw material ratio and preparation process of the aforementioned Embodiment 1 (the amount of substances and the production process remain completely unchanged), and tests the stability of the finished product under standard storage conditions. The storage environment strictly follows the patent requirements: sealed in an aluminum foil bag containing 5% silica gel desiccant, with the temperature controlled at 22°C and the relative humidity at 30%. Thermal conductivity, flexural strength, moisture content, N-methylpyrrolidone (NMP) residue, and agglomerate particle size were selected as the core test indicators. Samples were taken and tested at 0 days, 30 days, 60 days, and 90 days of storage, respectively. Only the material itself was compared at different time points. The test results are shown in the table below:

[0059] Detection time Thermal conductivity [W / (m・K)] Bending strength [MPa] Moisture content [%] NMP residue [ppm] Aggregate particle size [nm] Day 0 (Initial) 35.2 122.5 0.08 430 40 30 days 34.8 121.8 0.09 425 42 60 days 34.5 120.3 0.09 420 45 90 days 34.2 119.6 0.10 415 48

[0060] Stability test summary:

[0061] This embodiment continuously monitored the CoWoS packaging bottom filler material under standard storage conditions for 90 days, and the results showed that the material has excellent storage stability. The test data showed that none of the core performance indicators fluctuated significantly at different time points: the thermal conductivity decreased from an initial 35.2 W / (m·K) to 34.2 W / (m·K) after 90 days, a decrease of only 2.8%, still meeting the chip's heat dissipation requirements; the flexural strength decreased slightly from 122.5 MPa to 119.6 MPa, a decrease of less than 2.4%, maintaining stable mechanical support; the moisture content was consistently controlled below 0.10%, and the NMP residue decreased slowly from 430 ppm to 415 ppm, both meeting the patent-defined requirements of ≤0.1% and ≤500 ppm, respectively, without any solvent residue rebound or excessive moisture absorption; the agglomerate particle size increased from 40 nm to 48 nm, an increase of 20%, and remained below the critical value of 50 nm, without significant agglomeration.

[0062] The material's excellent stability stems from its scientific formulation design and preparation process: the graphene quantum dots in the hybrid filler strengthen the interfacial bonding between components through π-π interactions and hydroxyl coordination bonds, inhibiting separation and aggregation during long-term storage; the deep vacuum drying in the post-processing stage removes residual solvents and moisture, laying the foundation for stability; and standard sealed storage conditions further isolate it from the influence of external moisture and oxygen. In summary, this CoWoS packaging bottom filler material exhibits stable performance over a 90-day storage period, with minimal fluctuations in core indicators, fully meeting the long-term storage reliability requirements of high-end chip packaging materials.

[0063] Example 3:

[0064] Example of CoWoS encapsulation bottom filler material (variable amount of polyaryletherketone matrix).

[0065] This embodiment is based on the aforementioned preparation scheme for the 5nm process AI chip CoWoS packaging scenario. Only the amount of polyaryletherketone matrix is ​​adjusted, and five groups are set up. The total preparation mass of each group is 100kg. The total amount of hybrid filler is adjusted in the opposite direction to the amount of matrix. The proportion of each component in the hybrid filler, the amount of other auxiliary raw materials, the preparation steps and process parameters remain completely unchanged.

[0066] Raw material ratios for each group (total mass 100kg):

[0067] Group Amount of polyaryletherketone matrix (wt% / kg) Total amount of hybrid packing material used (wt% / kg) Mass of each component of the hybrid filler (kg, proportions unchanged: nickel-plated graphene 40%, silicon carbide 30%, boron nitride 28%, quantum dots 2%) Group 1 50wt% / 50 50wt% / 50 Nickel-plated graphene 20, silicon carbide 15, boron nitride 14, graphene quantum dot 1 Group 2 60wt% / 60 40wt% / 40 Nickel-plated graphene 16%, silicon carbide 12%, boron nitride 11.2%, graphene quantum dots 0.8%. Group 3 65wt% / 65 35wt% / 35 Nickel-plated graphene 14, silicon carbide 10.5, boron nitride 9.8, graphene quantum dots 0.7 Group 4 70wt% / 70 30wt% / 30 Nickel-plated graphene 12%, silicon carbide 9%, boron nitride 8.4%, graphene quantum dots 0.6%. Group 5 80wt% / 80 20wt% / 20 Nickel-plated graphene (8%), silicon carbide (6%), boron nitride (5.6%), graphene quantum dots (0.4%)

[0068] Preparation and detection methods:

[0069] Preparation steps: The process parameters of S100 (quantum dot modified boron nitride), S200 (in-situ polymerization prepolymer), S300 (melt blending composite), and S400 (post-treatment) are completely followed. The only difference is that in S200, the total mass of monomers (4,4'-difluorobenzophenone and hydroquinone) is adjusted according to the amount of polyaryletherketone matrix used in each group. The amount of solvent N-methylpyrrolidone is still 3 times the total mass of monomers. Other steps remain unchanged.

[0070] Performance testing: The bending strength, thermal conductivity, melt flowability (melt index, according to the thermal decomposition temperature) of the finished products in each group were tested to ensure that the testing conditions were consistent.

[0071] Comparison table of the effects of polyaryletherketone matrix on the properties of filler materials:

[0072] Group Amount of polyaryletherketone matrix (wt%) Bending strength (MPa) Thermal conductivity (W / (m・K)) Melt flowability (g / 10min) Thermal decomposition temperature (°C) Group 1 50 98.5 42.3 8.2 518 Group 2 60 110.2 38.6 10.5 519 Group 3 65 118.7 35.4 12.1 520 Group 4 70 125.3 32.1 13.8 521 Group 5 80 132.6 28.5 15.6 522

[0073] In summary, this embodiment verified the effect of polyaryletherketone matrix (50-80wt%) on the performance of the filler material through five groups. The results show that when the dosage is within the patent range, the material properties change regularly and controllably: with the increase of matrix dosage, the flexural strength increases from 98.5MPa to 132.6MPa, because the matrix acts as a continuous phase to enhance mechanical support; melt flowability increases from 8.2g / 10min to 15.6g / 10min, adapting to different dispensing and encapsulation requirements; thermal conductivity decreases from 42.3W / (m・K) to 28.5W / (m・K), still meeting the chip heat dissipation requirements; the thermal decomposition temperature remains stable at 518-522℃, meeting the heat resistance standard. The advantage of this range is that the dosage can be adjusted as needed, taking into account mechanical properties, flowability, and thermal conductivity, adapting to different CoWoS encapsulation scenarios, proving that the matrix dosage range limited by the patent is scientifically reasonable, ensuring that the material performance meets the standards and is flexibly adjustable.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A CoWoS encapsulation bottom filler material, characterized in that, The filler material comprises, by mass percentage: 50-80 wt% polyaryletherketone matrix; 20-50 wt% hybrid filler; wherein the hybrid filler is composed of nickel-plated graphene nanosheets, silicon carbide whiskers, boron nitride nanosheets, and graphene quantum dots, wherein nickel-plated graphene nanosheets account for 30-50 wt% of the hybrid filler, silicon carbide whiskers account for 25-40 wt% of the hybrid filler, boron nitride nanosheets account for 20-35 wt% of the hybrid filler, and graphene quantum dots account for 1-5 wt% of the hybrid filler.

2. The CoWoS encapsulation bottom filler material according to claim 1, characterized in that, The polyaryletherketone matrix is ​​selected from one of polyetheretherketone, polyetherketoneketone, or polyetheretherketoneketone, with a number average molecular weight of 50,000-100,000, a glass transition temperature ≥140℃, a melting point of 340-350℃, and a thermal decomposition temperature ≥500℃.

3. The CoWoS encapsulation bottom filler material according to claim 1, characterized in that, The nickel-plated graphene nanosheets are prepared by chemical nickel plating process, with a nickel plating thickness of 5-20 nm, a sheet diameter of 1-5 μm, 5-15 layers, a volume resistivity of ≤10 Ω·cm, and an overall thermal conductivity of ≥450 W / (m·K) after nickel plating.

4. The CoWoS encapsulation bottom filler material according to claim 1, characterized in that, The silicon carbide whiskers are β-type, with a diameter of 50-200 nm, a length of 5-20 μm, an aspect ratio of 50:1-150:1, and a purity of ≥99.5%; the boron nitride nanosheets are hexagonal boron nitride, with a sheet diameter of 2-10 μm, 3-10 layers, an interlayer spacing of 0.330-0.340 nm, and a purity of ≥99.8%.

5. The CoWoS encapsulation bottom filler material according to claim 1, characterized in that, The graphene quantum dots have a particle size of 2-10 nm, a surface hydroxyl content of 5-15 wt%, a specific surface area of ​​≥1000 m² / g, a dispersion concentration of ≥10 mg / mL in anhydrous ethanol, and an aggregate particle size of ≤50 nm after standing for 72 h; the mass ratio of the graphene quantum dots to the boron nitride nanosheets is 1:8-1:

12.

6. A method for preparing a CoWoS package underfill material, the method being used to prepare the CoWoS package underfill material according to any one of claims 1-5, characterized in that, The specific steps of this method are as follows: S100, preparation of quantum dot modified boron nitride: boron nitride nanosheets and graphene quantum dots were added to anhydrous ethanol at a mass ratio of 1:8-1:12, ultrasonically dispersed for 30-60 min at an ultrasonic power of 150-250 W, and then vacuum dried at 60-80℃ for 12-24 h to obtain quantum dot modified boron nitride nanosheets. S200, Preparation of in-situ polymerized prepolymer: Polyaryletherketone monomer and nickel-plated graphene nanosheets are added to a reaction vessel in a certain proportion, N-methylpyrrolidone solvent is added, and under nitrogen protection, the temperature is raised to 160-180℃ and the reaction is stirred for 4-6 hours to form nickel-plated graphene polyaryletherketone prepolymer; the nickel-plated graphene nanosheets account for 5-15 wt% of the total mass of the prepolymer; S300, melt blending composite: The obtained prepolymer, quantum dot modified boron nitride nanosheets and silicon carbide whiskers are added to a twin-screw extruder in proportion, melt blending and extruding, the extrusion temperature is 360-400℃, the screw speed is 80-120r / min, and after water cooling and pelletizing, composite material particles are obtained. S400, post-processing: Vacuum dry the composite material particles at 120-150℃ for 8-12 hours to remove residual solvent and moisture, and obtain the CoWoS encapsulation bottom filler material.

7. The CoWoS encapsulation bottom filling material and its preparation method according to claim 6, characterized in that, In the preparation of S100, which involves quantum dot-modified boron nitride, the graphene quantum dots have a particle size of 2-10 nm, a surface hydroxyl content of 5-15 wt%, a specific surface area ≥1000 m² / g, a dispersion concentration in anhydrous ethanol ≥10 mg / mL, and an aggregate particle size ≤50 nm after standing for 72 h. The mass ratio of the graphene quantum dots to the boron nitride nanosheets is 1:8-1:

12.

8. The CoWoS encapsulation bottom filling material and its preparation method according to claim 6, characterized in that, In the preparation of the S200 in-situ polymerization prepolymer, the polyaryletherketone monomers are 4,4'-difluorobenzophenone and hydroquinone, with a molar ratio of 1:1.05-1:1.1 and a purity of ≥99.5%; the solvent N-methylpyrrolidone is anhydrous, with a water content ≤0.02%, and the amount used is 2.5-3.5 times the total mass of the polyaryletherketone monomers; under nitrogen protection, the nitrogen purity is ≥99.999%, and the air in the reactor is replaced 3-4 times, with a replacement pressure of 0.25-0.35 MPa each time and a holding time of 4-6 min.

9. The CoWoS encapsulation bottom filling material and its preparation method according to claim 6, characterized in that, In the S300 melt blending composite process, the length-to-diameter ratio of the twin-screw extruder is 40:1 to 50:1, and the screw configuration includes 3-5 sets of reverse screw shearing elements; the mass ratio of the prepolymer, quantum dot-modified boron nitride nanosheets, and silicon carbide whiskers is 50-80:5-20:5-15; the melt blending extrusion adopts a three-stage temperature control, with the first zone temperature at 380-400℃, the second zone temperature at 360-380℃, and the third zone temperature at 340-360℃; the water temperature of the water cooling tank is 25-30℃, the pelletizer speed is 280-320 r / min, and the resulting composite material particles have a particle size of 2-3 mm and a length of 2-4 mm.

10. The CoWoS encapsulation bottom filling material and its preparation method according to claim 6, characterized in that, In the S400 post-processing, the vacuum degree of the vacuum drying is -0.095MPa to -0.099MPa. For the first 4 hours of drying, the vacuum is vented once per hour, with each venting lasting 40-80 seconds. After drying, the moisture content of the composite material is ≤0.1%, and the residual N-methylpyrrolidone content is ≤500ppm. The finished product is sealed in an aluminum foil bag containing silica gel desiccant, with the amount of silica gel desiccant being 4% to 6% of the composite material's mass. The storage environment temperature is 18-26℃, and the relative humidity is ≤35%.

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