Preparation method of nano-particle conductive film and chip sintering interconnection method of nano-particle conductive film

Abstract

The invention relates to the technical field of electronic packaging, in particular to a preparation method of a nano-particle conductive thin film and a chip sintering interconnection method of the nano-particle conductive thin film. The preparation method comprises the following steps: S1, mixing conductive nano-particle powder and an ink organic matter solvent carrier into conductive nano-ink; s2, conductive nano ink is injected into an atomization cavity, atomized liquid flow is generated at a nozzle through ultrasonic oscillation, and a conductive film with the uniform and controllable thickness is deposited on the substrate by adjusting parameters; s3, placing the substrate with the conductive film on a heating table for preheating; and S4, directly covering a chip above the substrate with the conductive thin film, and transferring the substrate into a vacuum hot pressing furnace for vacuum hot pressing sintering to obtain a chip-conductive thin film-substrate sintered joint. According to the method, the thickness of the deposited film / the thickness of the sintering layer is accurately controlled, preparation of the uniform and compact conductive nanoparticle film is achieved, a high-quality bonding interface can be obtained through the vacuum hot pressing sintering technology, and preparation of the ultra-high-strength sintering connector is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic packaging, and in particular to a method for preparing a nano-particle conductive film and a chip sintering and interconnecting method thereof. Background Art

[0002] Wide-bandgap semiconductor materials, represented by SiC and GaN, are key materials for advanced power electronic devices and hold broad development prospects in cutting-edge fields such as electric vehicles, solar energy production, aerospace, and artificial intelligence. However, the service environment in which wide-bandgap semiconductor devices operate is extremely harsh, placing higher demands on packaging materials. For example, sustained high temperatures exceeding 300°C render traditional Sn-based solders, with their low melting point and poor thermal conductivity, unsuitable for packaging. Nanomaterials, with their unique "low-temperature sintering and high-temperature service" properties, perfectly meet the practical needs of chip mounting in power electronic devices. Metal nanoparticles, such as silver and copper, enable high electrical and thermal conductivity and high-strength interconnection between the chip and the substrate, attracting widespread attention and in-depth research interest from researchers.

[0003] In existing nanoparticle sintering processes, nanoparticle solder paste is often coated using methods such as screen printing and steel screen printing, resulting in a sintered layer with a thickness ranging from several microns to tens of microns. In this case, the accumulation and agglomeration of a large number of nanoparticles will seriously hinder the smooth volatilization of organic matter in the solder paste, and thus inevitably leave pore defects and even unwelded areas in the central area of ​​the sintered structure. At the same time, compared with direct solid-phase bonding, the presence of a large number of pore structures within the sintered body objectively leads to a decrease in the thermal conductivity and strength of the nanoparticle sintered interconnection joints. Therefore, it is feasible and inevitable to improve the strength and thermal conductivity of nanoparticle sintered joints by reducing the thickness of the sintered layer while ensuring particle uniformity, reducing porosity, and reducing the organic solvent content. Summary of the Invention

[0004] The present invention provides a method for preparing a nanoparticle conductive film and a chip sintering interconnection method thereof, aiming to solve the problems of complex preparation process, uneven structure, high porosity and low joint strength of the nanoparticle sintered layer in the prior art.

[0005] The present invention provides a method for preparing a nanoparticle conductive film, comprising the following steps: S1. Preparation of conductive nano-ink: obtaining conductive nanoparticles, mixing conductive nanoparticle powder and an organic solvent carrier of ink to form a conductive nano-ink; S2. Ultrasonic atomization spraying: Conductive nano-ink is injected into the atomization chamber and ultrasonic oscillation is used to generate an atomized liquid flow at the nozzle. By adjusting one or more parameters including ultrasonic power, spray liquid feed speed, and auxiliary gas pressure, a conductive film with uniform and controllable thickness is deposited on the substrate. S3. Preheating treatment: Place the substrate with the conductive film on a heating table and preheat it for 3 to 5 minutes at a preheating temperature of 60°C to volatilize the residual organic solvent carrier to obtain a substrate with a conductive film after preheating.

[0006] As a further improvement of the present invention, in step S1, the viscosity of the conductive nano-ink is 1-100 cP, the mass fraction of the conductive nano-particles in the conductive nano-ink is 12-20%, and the average conductive nano-particle size is 50-400 nm.

[0007] As a further improvement of the present invention, the conductive nanoparticles are one or more of Cu, Ag, Ni, Au, and Al material components.

[0008] As a further improvement of the present invention, during the ultrasonic atomization spraying process in step S2, the applied ultrasonic power is 3-4 W, the spraying liquid feed speed is 0.2-0.4 ml / min, and the auxiliary gas pressure is 0.03 MPa.

[0009] As a further improvement of the present invention, the ink organic solvent carrier includes one or more of terpineol, ethyl cellulose, ethyl acetate, and ethanol.

[0010] As a further improvement of the present invention, the solid-liquid mixing ratio of the conductive nanoparticle powder and the ink organic solvent carrier is 15-20:80-85.

[0011] The present invention also provides a chip sintering interconnection method of a nanoparticle conductive film, comprising the steps of: S4. Sintering interconnection of chip and substrate: take the preheated substrate obtained according to the preparation method of the nanoparticle conductive film, directly cover the chip on the substrate with the conductive film, transfer it to a vacuum hot pressing furnace, adjust the vacuum degree in the furnace, wait for the vacuum degree in the cavity to stabilize, start the heating device for sintering; start the hydraulic device to apply pressure to the chip when the temperature reaches the preset temperature point, wait for the pressure sensor reading to stabilize, and then record the holding time. After the preset holding time, release the pressure to obtain a three-layer structure sintered joint of chip-conductive film-substrate.

[0012] As a further improvement of the present invention, when the conductive nanoparticles are Cu nanoparticles, the specific process parameters of step S4 are: vacuum degree of 5×10 -1Torr, the pressure applied to the chip is 3~5 MPa, the sintering temperature is 250~300℃, and the sintering holding time is 10~20 min.

[0013] As a further improvement of the present invention, when the conductive nanoparticles are Ag nanoparticles, the specific process parameters of step S4 are: no vacuum environment is required, the pressure applied to the chip is 3-5 MPa, the sintering temperature is 200-250°C, and the sintering holding time is 10-20 min.

[0014] As a further improvement of the present invention, the average thickness of the conductive film in the three-layer sintered joint is 200-400 nm.

[0015] The beneficial effects of the present invention are: (1) The technical solution of the present invention improves the traditional nano-solder paste printing method and uses high-precision ultrasonic atomization spraying technology to achieve the preparation of nano-particle sintering interconnection layers between chips and substrates. By optimizing key parameters such as ultrasonic power, spraying rate, and gas pressure, the thickness of the deposited film can be precisely controlled to achieve the preparation of uniform and dense conductive nano-particle films at the near-monolayer or submicron level. The film thickness can be as low as 300 nm and the roughness can be as low as 95 nm.

[0016] (2) Compared with the traditional solder paste screen printing process, during the ultrasonic atomization spraying process, as the trace solvent in the nano ink evaporates rapidly, the stably deposited nanoparticles will present a more active surface state. This helps to promote the "contact activation" interaction between the nanoparticles during the subsequent sintering process, significantly reducing the porosity of the film (as low as 1.6%) and obtaining a high-quality interface without crack defects. In addition, the use of large amounts of organic solvents in the nano solder paste is avoided, significantly reducing manufacturing costs, and reducing the pollution of organic solvent volatiles and residual waste liquid to the environment, which is in line with the production concept of green and low-carbon manufacturing.

[0017] (3) Compared with the conventional inkjet printing process, the ultrasonic atomization spraying technology proposed in the present invention not only has a larger working area (30 cm × 30 cm), but also has higher production efficiency (more than 40 SiC chips can be accurately sprayed at one time), which is particularly suitable for large-scale and large-area nanoparticle film preparation scenarios.

[0018] (4) Compared with the traditional vacuum hot pressing sintering process, the sintering conditions required in this technical solution are relatively mild. Due to the contact effect and low agglomeration phenomenon of ultrasonic atomization spraying, this technical solution can achieve the preparation of ultra-high strength (above 90 MPa) sintered joints under the conditions of sintering temperature as low as 200-300℃, sintering pressure as low as 5 MPa, and reaction time as low as 15 min, with an interface bonding rate as high as 94%.

[0019] (5) Due to the atomization spraying method, this technology only requires simple mask operations to prepare various complex conductive patterns. It is easy to operate and can also adapt to the needs of various complex 3D packaging structures. It provides a practical and valuable technical path and solution for the large-scale, high-integration 3D packaging of wide-bandgap semiconductor materials and ensures their application under high service reliability requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the ultrasonic atomization spraying process and vacuum hot pressing sintering in Examples 1 to 3 of the present invention; Figure 2 Scanning electron microscope / secondary electron microscope (SEM / SE) images of the conductive Cu nanoparticles prepared by the liquid phase reduction method in Examples 1 to 3 of the present invention; Figure 3 Figures of the Cu nanoparticle atomized liquid flow obtained at different ultrasonic powers in Example 1 of the present invention: (a) 1 W, (b) 2 W, (c) 3 W, and (d) 4 W. Figure 4 The morphologies of the Cu nanoparticle atomized liquid flow obtained at different spraying speeds in Example 2 of the present invention are: (a) 0.1 ml / min, (b) 0.2 ml / min, (c) 0.4 ml / min, and (d) 1 ml / min; Figure 5 The morphologies of the Cu nanoparticle atomized liquid flow obtained under different gas pressures in Example 3 of the present invention are: (a) 0.01Pa, (b) 0.02Pa, (c) 0.03Pa, and (d) 0.04Pa; Figure 6 The topography of the conductive Cu nanoparticle film obtained in Example 3 of the present invention: (a) optical microscopy, (b) surface roughness, and (c) thickness; Figure 7 The microstructure morphology of the middle sintered layer of the sintered interconnection joint obtained in Example 4 of the present invention and its partial enlarged view; Figure 8 The microstructure morphology of the middle sintered layer of the sintered interconnection joint obtained in Comparative Example 1 and its partial enlarged view; Figure 9 Graph showing the strength changes of the sintered interconnect joints obtained in Example 4 of the present invention and Comparative Example 1 at different sintering temperatures during shear tests. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0022] A method for preparing a nanoparticle conductive film of the present invention comprises the following steps: S1. Preparation of Conductive Nano-Ink: Obtain conductive nanoparticles and prepare them using a known reduction system. Alternatively, commercially available conductive nanoparticles can be purchased. Mix the conductive nanoparticle powder and an organic solvent carrier in a solid-to-liquid ratio of 15-20:80-85 to form a conductive nano-ink. S2. Ultrasonic atomization spraying: Conductive nano-ink is injected into the atomization chamber, and ultrasonic oscillation-induced atomization generates an atomized liquid stream at the nozzle. By adjusting one or more parameters such as ultrasonic power, spray feed speed, and auxiliary gas pressure, a conductive film with uniform and controllable thickness is deposited on the substrate. S3. Preheating treatment: Place the substrate with the conductive film on a heating table and preheat it for 3 to 5 minutes at a preheating temperature of 60°C to volatilize the residual organic solvent carrier to obtain a substrate with a conductive film after preheating.

[0023] The conductive nanoparticles in step S1 can be one or more materials such as Cu, Ag, Ni, Au, and Al. The organic solvent carrier for the ink includes one or more of terpineol, ethyl cellulose, ethyl acetate, and ethanol. The solid-liquid ratio of the conductive nanoparticle powder to the organic solvent carrier for the ink is 15-18:82-85.

[0024] The viscosity of the nano-ink described in step S1 is 1-100 cP. When the ink viscosity is too low, the nano-film obtained by spray deposition tends to flow outside the substrate, resulting in ink waste. Excessive viscosity (>100 cP) can lead to difficulty in atomization, uneven atomized droplet size, and even nozzle clogging. If the viscosity of the nano-ink is still high, it can be diluted with ethanol solvent. The mass fraction of the nanoparticles is 12-20%. Excessively high mass fractions can easily lead to nozzle clogging or cracking of the film. The average particle size is 50-400 nm to ensure that the particles are evenly suspended in the ink and can be stably deposited during the ultrasonic atomization process. If the particle size is too large, premature sedimentation may occur or block the transmission channel of the atomization chamber, reducing the atomization effect.

[0025] During the ultrasonic atomization spraying process described in step S2, a convergent ultrasonic nozzle was used to improve spraying accuracy. To ensure thickness uniformity and improve spraying efficiency, 6-9 substrates were sprayed simultaneously. The mechanical arm motion parameters of the spraying equipment were set to: a working speed of 50-70 mm / s, a fast forward speed of 70-90 mm / s, a motion range of 30 cm × 30 cm, a distance between the substrate and the nozzle of 15 cm, and 3-4 spraying cycles. These mechanical motion parameters further improved the process stability of the ultrasonic atomization spraying and the uniformity of the film thickness.

[0026] During the ultrasonic atomization spraying process in step S2, the preferred spraying liquid feed rate is 0.2-0.4 ml / min, the auxiliary gas pressure is 0.03 MPa, and the applied ultrasonic power is 3-4 W. These process parameters are closely related to the atomization quality and film uniformity, and further affect the quality of the subsequent sintered joint.

[0027] For ultrasonic power, when the ultrasonic power is as low as 1 W, the vertical vibration amplitude of the capillary wave below the nozzle is small, which is not enough to separate it from the liquid film surface. As the liquid flow is injected, the liquid film at the nozzle accumulates too much, causing the droplets to coalesce under the action of gravity and vibration, such as Figure 3 (a) in Figure 2. When the ultrasonic power is increased to 2 W, Figure 3 In (b), only a part of the liquid film is atomized at the nozzle, and the atomized liquid flow is uneven. When the ultrasonic power is increased to 3~4 W, the capillary wave is subjected to high amplitude, and a good atomization effect is achieved at the entire nozzle interface. Fine atomized droplets and a uniform columnar flow appear at the nozzle, as shown in Figure 2. Figure 3 Therefore, an ultrasonic power of 3 to 4 W is more suitable for the ultrasonic atomization spraying process.

[0028] Maintaining the ultrasonic power at 3 W and changing the spraying speed, it can be seen that under the premise of maintaining a good atomization effect, as the spraying speed increases, the diameter of the atomized liquid flow is significantly affected by the spraying speed. At a lower spraying speed (0.1 ml / min), Figure 4 In (a), the atomized liquid flow is not obvious, and the extremely low spray deposition rate is not conducive to improving production efficiency. When the liquid inlet speed is too high to 1 ml / min, the atomized liquid flow diameter is too large, resulting in a decrease in spraying accuracy; at the same time, due to the large influx of droplets in a short period of time, the high-frequency collision between droplets and between droplets and substrates also makes the atomized droplet splashing phenomenon more serious, such as Figure 4 Therefore, a spraying speed of 0.2–0.4 ml / min was selected to balance productivity and film uniformity.

[0029] The auxiliary gas pressure helps to disperse the droplets during the atomization process. Due to the possible air flow disturbance in the air, when the gas pressure is as low as 0.01 MPa, such as Figure 5 In (a), the atomized liquid flow is easily affected by air disturbance and deflected. This displacement of the atomized liquid flow will cause contamination of the non-bonding area and will also cause unforeseen defects in the morphology and thickness of the deposited layer. When the gas pressure is increased to above 0.03 MPa, such as Figure 5In (c) to (d) in Figure 1, the ultrasonic atomized droplets achieved a good gathering effect and were evenly deposited on the substrate with the smallest liquid flow diameter, improving the spray deposition quality. Therefore, 0.03 MPa was selected as the optimal gas pressure parameter.

[0030] By adjusting the ultrasonic atomization spraying process (ultrasonic power, spraying speed, gas pressure, etc.), a stable deposition of nearly a single layer of nanoparticles can be achieved, and a large area of ​​30 cm × 30 cm with uniform and controllable thickness of submicron-level conductive nanoparticle films can be obtained, such as Figure 6 .

[0031] The present invention also provides a chip sintering interconnection method for a nanoparticle conductive film. After step S3 of the method for preparing the nanoparticle conductive film is completed, the following steps are further performed: S4. Chip-substrate sintering: After preheating the substrate, place the chip directly on top of the conductive film-coated substrate. Then, place the chip in a vacuum hot press. Start the vacuum pump and wait for the vacuum in the chamber to stabilize before starting the heating mechanism. Once the temperature reaches the preset point, activate the hydraulic mechanism. Wait for the pressure sensor reading to stabilize before recording the hold time. After the preset hold time, remove the auxiliary pressure and turn off the vacuum pump, resulting in a three-layer sintered joint: chip, conductive film, and substrate.

[0032] When the conductive nanoparticles are Cu nanoparticles, the specific process parameters for the chip sintering interconnection in step S4 are: vacuum degree of 5×10 -1 Torr, the pressure applied on the chip is 3~5 MPa, the temperature is 250~300℃, and the sintering time is 10~20 min.

[0033] After the trace amount of solvent evaporates, a significant "contact activation effect" occurs between the particles and the substrate in the intermediate sintered layer at the near-monolayer or submicron level, and the interface bonding between the particles and the substrate is quickly achieved during the hot pressing sintering process. Under low sintering temperatures (250-300°C) and short-term low-pressure conditions, no obvious cracks are produced at the interface between the intermediate sintered layer and the chip above and the substrate below. At the same time, the interface bonding rate of the sintered joint can reach 94%, and the porosity of the sintered layer is as low as 1.6%, demonstrating ultra-high interface bonding ability. From the microstructure, it can be seen that ultra-thinness, low porosity and no cracks are the three obvious characteristics of the sintered joint, such as Figure 7 In addition, this contact activation effect reduces the oxidation rate of easily oxidized particles such as Cu, so the required vacuum degree does not need to reach the conventional 10 -2 Torr vacuum requirements.

[0034] Compared with the traditional solder paste printing and subsequent sintering process, obvious long and thin cracks will appear at the interface of the sintered joint, such as Figure 8As shown by the middle arrows, some cracks reach 2–4 μm in length. Due to the increased solder paste thickness and the difficulty in completely evaporating the organic solvent, some particles are located in a unique peninsula position and are not connected by the sintering neck. The interface bonding rate reaches only 71%, and the porosity remains at around 8.6%, indicating poor interface bonding.

[0035] Step S4 also applies to the sintering of Ag nanoparticles. When the conductive nanoparticles are Ag nanoparticles, unlike Cu nanoparticles, the specific process parameters for chip sintering in step S4 are: air environment (no vacuum treatment required), pressure applied to the chip of 3-5 MPa, temperature of 200-250°C, and sintering time of 10-20 minutes. Due to Ag's resistance to oxidation, vacuum conditions are not required at this stage. Bulk Ag has a lower melting point than bulk Cu, so Ag particles require a lower sintering temperature than Cu particles, which is why the sintering temperature is lowered at this stage.

[0036] The average thickness of the middle sintered layer of the sintered joint obtained in step S4 is 200-400 nm. Figure 7 As shown in Figure 2, the sintered joint has extremely low interfacial porosity (1.6%) and ultra-high shear strength (over 90 MPa), as shown in Figure 2. Figure 9 shown.

[0037] In order to better explain the present invention and facilitate understanding, the present invention is further elaborated in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1:

[0039] This embodiment provides a large-area preparation method of a nanoparticle conductive film by ultrasonic spraying, comprising the following steps: S1. Preparation of conductive nano-ink: First, Cu nanoparticles were prepared using a liquid phase reduction synthesis system. In the synthesis system, ascorbic acid was used as a reducing agent, polyvinyl pyrrolidone was used as a stabilizer, and ethylene glycol was used as a solvent. The average particle size of the obtained Cu nanoparticles was 200 nm. Figure 2 As shown; the above-mentioned Cu nanoparticle powder and organic solvent carriers such as terpineol, ethyl cellulose, and ethanol are mixed into a conductive Cu ink at a solid-liquid ratio of 15:85 to ensure that the Cu particles can be evenly suspended in the ink and can be stably deposited during the ultrasonic atomization process.

[0040] S2. Ultrasonic atomization spraying, such as Figure 1As shown: a convergent ultrasonic nozzle is used to improve the spraying accuracy; to ensure thickness uniformity and improve spraying efficiency, 9 substrates are sprayed at the same time, and the motion parameters of the robotic arm of the spraying equipment are set as follows: working speed 60 mm / s, fast speed 80 mm / s, movement route range 30 cm×30 cm, substrate and nozzle distance 15 cm, and spraying times 4 times.

[0041] The specific operation of spraying is as follows: inject the conductive Cu ink into the atomization chamber, use the atomization effect caused by ultrasonic oscillation to generate atomized liquid flow at the nozzle; adjust the ultrasonic power to 1~4 W, and observe the shape of the atomized liquid flow to make fine atomized droplets and uniformly descending columnar flow appear at the nozzle, such as Figure 3 As shown, this is conducive to depositing a conductive film with uniform thickness.

[0042] S3. Preheating treatment: Place the substrate with the conductive film on a heating table and preheat for 3 to 5 minutes to volatilize the residual organic solvent carrier. The preheating temperature is 60°C.

[0043] The above process forms a uniform atomized liquid flow by regulating a single parameter of ultrasonic power, and prepares a conductive Cu film with relatively uniform thickness.

[0044] Example 2:

[0045] This embodiment provides another method for preparing a large-area conductive film of nanoparticles by ultrasonic spraying, which differs from the first embodiment in that: On the basis of Example 1, the ultrasonic power was maintained at 3 W and the spraying speed was changed to 0.1-1 ml / min.

[0046] From the atomization results, it can be seen that under the premise of maintaining a good uniform columnar liquid flow, as the spraying speed increases, the diameter of the atomized liquid flow is obviously affected by the spraying speed, such as Figure 4 At a lower spraying speed (0.1 ml / min), such as Figure 4 In (a), the atomized liquid flow is not obvious, and the extremely low spray deposition rate is not conducive to improving production efficiency. When the liquid inlet speed is too high to 1 ml / min, the atomized liquid flow diameter is too large, resulting in a decrease in spraying accuracy; at the same time, due to the large influx of droplets in a short period of time, the high-frequency collision between droplets and between droplets and substrates also makes the atomized droplet splashing phenomenon more serious, such as Figure 4 Therefore, a spraying speed of 0.2–0.4 ml / min was selected to balance productivity and film uniformity.

[0047] The above process effectively controls phenomena such as liquid splashing by regulating a single parameter of spraying speed while maintaining the optimal ultrasonic power, and prepares a conductive Cu film with relatively uniform thickness and no cracks on the surface.

[0048] Example 3:

[0049] This embodiment provides another method for preparing the aforementioned anti-oxidation nano-copper powder and a low-temperature sintering interconnection method thereof, which differs from the first and second embodiments in that: On the basis of Example 1 and Example 2, the ultrasonic power was maintained at 3 W, the spraying speed was maintained at 0.2 ml / min, and the auxiliary gas pressure was changed to 0.01-0.04 MPa.

[0050] From the atomization results, it can be seen that the auxiliary gas pressure helps to disperse the droplets during the atomization process. Due to the possible air flow disturbance in the air, when the gas pressure is as low as 0.01 MPa, such as Figure 5 In (a), the atomized liquid flow is easily affected by air disturbance and deflected. This displacement of the atomized liquid flow will cause contamination of the non-bonding area and will also cause unforeseen defects in the morphology and thickness of the deposited layer. When the gas pressure is increased to above 0.03 MPa, as shown in Figure 5 In (c)-(d), the ultrasonic atomized droplets achieve a good gathering effect and are evenly deposited on the substrate with the smallest liquid flow diameter, improving the spray deposition quality. Therefore, 0.03 MPa is selected as the optimal gas pressure parameter.

[0051] The above process ensures the uniform dispersion and stable deposition of nanoparticles in the atomized liquid flow by maintaining the optimal ultrasonic power and optimal spraying speed while regulating the single parameter of gas pressure. This results in the preparation of a conductive Cu film with relatively uniform thickness and no surface cracks. The initial contact area of ​​the nanoparticles in the film is also greatly increased. Finally, after adjusting the ultrasonic atomization spraying process (ultrasonic power, spraying speed, gas pressure, etc.), the stable deposition of nearly a single layer of nanoparticles was achieved, resulting in a large area of ​​30 cm × 30 cm, submicron-level conductive nanoparticle film with uniform and controllable thickness. The film thickness can be as low as 300 nm, and the roughness can be as low as 95 nm. Figure 6 In addition, the use of large amounts of organic solvents in nano solder paste is avoided, which significantly reduces manufacturing costs and reduces the environmental pollution caused by volatile organic solvents and residual waste liquids, which is in line with the production concept of green and low-carbon manufacturing.

[0052] Example 4:

[0053] This embodiment provides another method for preparing a large-area conductive film of nanoparticles by ultrasonic spraying and a chip sintering interconnection method as described above. The difference from the first to third embodiments is that: Based on the conductive Cu films prepared in Examples 1 to 3, vacuum hot pressing sintering is performed to achieve sintering interconnection between the chip and the substrate. The specific operations are as follows: Step S4. Sintering interconnection between chip and substrate: After preheating, directly cover the chip on the substrate with conductive Cu film, transfer it into the vacuum hot pressing furnace, turn on the vacuum pump, and wait until the vacuum degree in the chamber reaches 5×10 -1 After 1000 Torr, the heating device was started. When the temperature reached 250-300°C, the hydraulic device was started. After the pressure reached 5 MPa, the holding time was recorded. After the preset holding time of 15 minutes, the auxiliary pressure was released and the vacuum pump was turned off to obtain a "sandwich" sintered joint of the chip, conductive film, and substrate.

[0054] After the trace amount of solvent evaporates, a significant "contact activation effect" occurs between the particles and the substrate in the intermediate sintered layer at the near-monolayer or submicron level, and the interface bonding between the particles and the substrate is quickly achieved during the hot pressing sintering process. Under low sintering temperatures (250-300°C) and short-term low-pressure conditions, no obvious cracks are generated at the interface between the intermediate sintered layer and the upper chip and the lower substrate, and the interface bonding rate of the sintered joint can reach 94%. Figure 7 The porosity of the sintered layer is as low as 1.6%, showing an ultra-high interface bonding ability. From the microstructure, it can be seen that ultra-thinness, low porosity and no cracks are the three obvious characteristics of the sintered joint, such as Figure 7 In addition, this contact activation effect reduces the oxidation rate of easily oxidized particles such as Cu, so the required vacuum degree does not need to reach the conventional 10 -2 Torr vacuum requirements.

[0055] The above process improves the traditional nano solder paste printing method and uses high-precision ultrasonic atomization spraying technology to realize the preparation of nanoparticle sintering interconnection layer between chip and substrate. The average thickness of the middle sintering layer of the sintered joint is 200~400 nm. Figure 7 . Due to the "contact activation" interaction between the nanoparticles, the porosity of the film is significantly reduced (as low as 1.6%), and a high-quality interface without crack defects is obtained. At the same time, compared with the traditional vacuum hot pressing sintering process, the sintering conditions required in this technical solution are relatively mild. This technical solution can achieve the preparation of ultra-high strength sintered joints under the conditions of sintering temperatures as low as 250~300℃, sintering pressures as low as 5MPa, and reaction times as low as 15 min. The shear strength can reach 90~120MPa, such as Figure 9 , the interface bonding rate is as high as 94%.

[0056] Embodiment 5:

[0057] This embodiment provides another large-area preparation method of the aforementioned ultrasonic spraying nanoparticle conductive film and chip sintering interconnection method. The difference from the first to fourth embodiments is that the conductive nanoparticles are Ag nanoparticles.

[0058] Step S1. Preparation of conductive nano-ink: Commercial Ag nanoparticles are purchased directly, and Ag nanoparticle powder is mixed with an organic solvent carrier such as terpineol, ethyl cellulose, ethyl acetate, or ethanol at a solid-liquid ratio of 18:82 to form a conductive Ag ink; Step S2. Ultrasonic atomization spraying: Conductive Ag ink is injected into the atomization chamber, and ultrasonic oscillation-induced atomization generates an atomized liquid stream at the nozzle. The spraying process parameters used are the same as those for Cu nanoparticles, depositing a conductive Ag film with uniform and controllable thickness on the substrate. Step S3. Preheating: Place the substrate with the conductive Ag film on a heating table and preheat for 3-5 minutes to volatilize the residual organic solvent carrier. The preheating temperature is 60°C. Step S4. Chip-substrate sintering: After preheating, the chip is placed directly on top of the substrate with the conductive Ag film. The chip is then placed in a hot press furnace, where the heating device is activated. When the temperature reaches 200-250°C, the hydraulic pressure is activated. After the pressure reaches 5 MPa, the holding time is recorded. After 10 minutes of the preset holding time, the auxiliary pressure is released and the vacuum pump is turned off, resulting in a sintered "chip-conductive film-substrate" sandwich joint. Due to Ag's resistance to oxidation, vacuum conditions are not required at this stage. Bulk Ag has a lower melting point than bulk Cu, so Ag particles require a lower sintering temperature than Cu particles. Therefore, the sintering temperature is lowered at this stage.

[0059] The above process also achieves the preparation of ultra-thin sintered joints with no interfacial cracks, low porosity and high strength under mild sintering conditions.

[0060] Comparative Example 1:

[0061] Based on Examples 1 to 5, the preparation method of the nanofilm in this comparative example is different, mainly as follows: Step S1. Preparation of conductive nano solder paste: Cu nanoparticle powder and organic solvent carriers such as terpineol and ethyl cellulose are mixed at a solid-liquid ratio of 20:80 to form a conductive Cu solder paste; after thorough stirring, the mixture is placed in a paste mixer for degassing and mixing, and the process is repeated three times to obtain a Cu solder paste for printing.

[0062] Step S2. Stencil printing: Solder paste is applied on a vertical screen printing machine and printed on the substrate using a stencil with a thickness of 80-200 μm to form a Cu nanofilm. Step S3 and step S4 are consistent with the above steps.

[0063] Obvious long and thin cracks will appear at the interface of the printed sintered joint obtained by the above process, such as Figure 8As shown by the middle arrow, some cracks are 2~4 μm long. Due to the increased thickness of the solder paste and the difficulty in completely evaporating the organic solvent, some particles are located in a unique peninsula position, such as Figure 8 The local enlarged image is not connected by the sintering neck, the interface bonding rate can only reach 71%, and the porosity remains at around 8.6%, showing a poor interface bonding state. The strength of the printed sintered joint changes with the sintering temperature. Figure 9 The strength of the hot-pressed sintered joint produced by ultrasonic atomization spraying is much lower than that of the present invention, with a difference of about 70 MPa. The comparison of microstructure and shear strength shows that the present invention has significant advantages such as crack-free interface, low porosity, uniform density, and high strength.

[0064] In summary, the technical solution of the present invention improves the traditional nano solder paste printing method, utilizes high-precision ultrasonic atomization spraying technology to realize the preparation of nanoparticle sintered interconnection layer between chip and substrate, and avoids the use of large amounts of organic solvents in nano solder paste. By optimizing key parameters such as ultrasonic power, spraying rate, and gas pressure to accurately control the thickness of the deposited film, the preparation of large-area, near-monolayer or submicron-level uniform and dense conductive nanoparticle films is achieved. On this basis, with the help of the "contact activation" effect and the absence of agglomeration between nanoparticles, a low porosity, no interface crack defects, uniform and dense high-quality bonding interface is obtained through mild vacuum hot pressing sintering process conditions, realizing the preparation of ultra-high strength sintered joints. This technology can realize the preparation of various complex conductive patterns and adapt to the needs of various complex 3D packaging structures, providing a practical and valuable technical path and solution for the realization of large-scale, high-integration 3D packaging of wide bandgap semiconductor materials and ensuring their application under high service reliability requirements.

[0065] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a nanoparticle conductive film, characterized in that: The following steps are involved: S1. Preparation of conductive nano-ink: obtaining conductive nanoparticles, mixing conductive nanoparticle powder and an organic solvent carrier of ink to form a conductive nano-ink; S2. Ultrasonic atomization spraying: Conductive nano-ink is injected into the atomization chamber and ultrasonic oscillation is used to generate an atomized liquid flow at the nozzle. By adjusting one or more parameters including ultrasonic power, spray liquid feed speed, and auxiliary gas pressure, a conductive film with uniform and controllable thickness is deposited on the substrate. S3. Preheating treatment: Place the substrate with the conductive film on a heating table and preheat it for 3 to 5 minutes at a preheating temperature of 60°C to volatilize the residual organic solvent carrier to obtain a substrate with a conductive film after preheating.

2. The method for preparing the nanoparticle conductive film according to claim 1, characterized in that: In step S1, the viscosity of the conductive nano-ink is 1-100 cP, the mass fraction of the conductive nano-particles in the conductive nano-ink is 12-20%, and the average size of the conductive nano-particles is 50-400 nm.

3. The method for preparing the nanoparticle conductive film according to claim 1, characterized in that: The conductive nanoparticles are one or more of Cu, Ag, Ni, Au, and Al.

4. The method for preparing the nanoparticle conductive film according to claim 1, characterized in that: During the ultrasonic atomization spraying process in step S2, the applied ultrasonic power is 3-4 W, the spraying liquid feed rate is 0.2-0.4 ml / min, and the auxiliary gas pressure is 0.03 MPa.

5. The method for preparing the nanoparticle conductive film according to claim 1, characterized in that: The ink organic solvent carrier includes one or more of terpineol, ethyl cellulose, ethyl acetate, and ethanol.

6. The method for preparing the nanoparticle conductive film according to claim 1, characterized in that: The solid-liquid mixing ratio of the conductive nanoparticle powder and the ink organic solvent carrier is 15-20:80-85.

7. A chip sintering interconnection method of nanoparticle conductive film, characterized in that: Including steps: S4. Sintering interconnection of chip and substrate: take the preheated substrate obtained by the preparation method of the nanoparticle conductive film according to any one of claims 1 to 6, directly cover the chip on the substrate with the conductive film, transfer it to a vacuum hot pressing furnace, adjust the vacuum degree in the furnace, wait for the vacuum degree in the cavity to stabilize, start the heating device for sintering; start the hydraulic device to apply pressure to the chip when the temperature reaches the preset temperature point, wait for the pressure sensor reading to stabilize, and then record the holding time. After the preset holding time, release the pressure to obtain a three-layer structure sintered joint of chip-conductive film-substrate.

8. The chip sintering interconnection method of the nanoparticle conductive film according to claim 7, characterized in that: When the conductive nanoparticles are Cu nanoparticles, the specific process parameters of step S4 are: vacuum degree of 5×10 -1 Torr, the pressure applied to the chip is 3~5 MPa, the sintering temperature is 250~300℃, and the sintering holding time is 10~20 min.

9. The chip sintering interconnection method of the nanoparticle conductive film according to claim 7, characterized in that: When the conductive nanoparticles are Ag nanoparticles, the specific process parameters of step S4 are: no vacuum environment is required, the pressure applied to the chip is 3-5 MPa, the sintering temperature is 200-250° C., and the sintering holding time is 10-20 min.

10. The chip sintering interconnection method of the nanoparticle conductive film according to claim 7, characterized in that: The average thickness of the conductive film in the three-layer sintered joint is 200-400 nm.

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