High-temperature-resistant conductive paste for packaging, preparation method and application thereof

Abstract

The application relates to a high-temperature-resistant conductive paste for packaging and a preparation method and application thereof, and the method comprises the following steps: ball milling Ag-30Pd spherical powder with a D50 of 8-12 mu m and acetone; then adding Ag-30Pd spherical powder with a D50 of 1-12 mu m, Zn and / or Pb spherical powder with a D50 of 1-3 mu m and ball milling with acetone; uniformly mixing the obtained ball milling material, Ag-30Pd nano powder with a D50 of 20-80 nm, polyethylene glycol and acetone to obtain a mixed suspension, then performing ultrasonic stirring, again performing ultrasonic stirring at 70-90 DEG C, adding glycerol and uniformly mixing, and finally drying; adding SiO x powder with a D50 of 4-8 mu m into the obtained mixed material and uniformly mixing to prepare the high-temperature-resistant conductive paste for packaging. The application obtains the conductive paste with low-temperature sintering, high melting point and low thermal expansion coefficient, and can meet the electrical connection and fatigue performance requirements of high-temperature sensors.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging materials technology, specifically to a high-temperature resistant conductive paste for packaging, its preparation method, and its application. Background Technology

[0002] High-temperature sensors are widely used in modern technology industries, including aerospace, machinery, metallurgy, and defense, for both military and civilian applications. They monitor the normal operation of electromechanical systems under various extreme conditions. Given the rapid development and application of high-temperature sensors, researching and developing sensors capable of operating normally under even higher temperatures and other extreme environments is a common challenge faced by scholars both domestically and internationally. Taking pressure sensors commonly used in various systems as an example, the operation and monitoring of an aircraft engine requires approximately 40 high-temperature sensors. High-temperature pressure sensors can be used for long-term monitoring of critical components such as the combustion chamber, compressor, and blades, which helps improve operational and propulsion efficiency and reduce failure rates and maintenance costs. Various high-temperature sensors operating in integrated systems of various mechanical equipment can effectively ensure the correct operation of the overall system and detect damage to individual components.

[0003] In the aerospace field, the extreme and harsh environments of devices place higher demands on the service temperature of pressure sensors. A series of sensors based on the sensitive resistor principle, such as pressure sensors, employ a pn junction isolation structure between the sensitive resistor and the silicon substrate. When the operating temperature exceeds 120°C, leakage current in the pn junction leads to a sharp deterioration in sensor performance, eventually causing failure. Currently, the application of various high-temperature sensors is gradually shifting towards miniaturization and integration, improving performance by changing the materials at the connection points. For example, Kulite's high-temperature pressure sensor, based on silicon-on-insulator (SOI) technology, can reach a maximum service temperature of 500°C, while also featuring high sensitivity, high reliability, low power consumption, and ease of miniaturization and integration. In the sensor manufacturing process, packaging technology directly determines the sensor's accuracy and lifespan. During high-temperature service, sensors undergo long-term thermal fatigue. This can easily lead to problems such as breakage at the packaging interface and poor ohmic contact, hindering operational stability. The lag in packaging technology has become a core technological bottleneck restricting the development of high-temperature sensors.

[0004] Taking high-temperature pressure sensors as an example, the most common packaging solution is oil-filled packaging. Oil-filled packaging uses high-temperature silicone oil to isolate the measured medium, protecting the sensitive resistor and electrodes of the sensitive chip, while providing physical protection for the gold wire leads, thus improving the sensor's corrosion resistance and reliability. However, the gold wire leads and their solder joints are prone to fatigue fracture under high-frequency vibration or rapid pressure cycling conditions, and the silicone oil isolation structure reduces the sensor's dynamic characteristics and limits its operating temperature to no more than 200°C, failing to meet current requirements for high-temperature sensors. In contrast, leadless packaging effectively addresses the shortcomings of oil-filled packaging, fully meeting the 400°C service requirements of model development. Gold-plated terminals extend into the bonding glass holes of the pressure chip, and the holes are filled with conductive filler. Finally, physical and electrical connections between the chip and the terminals are achieved through sintering. Since the device surface where the sensitive resistor is located is protected by the bonding glass, oil-filled packaging is unnecessary, effectively reducing the package size and ultimately improving the sensor's high-temperature service reliability. Therefore, it is urgent to conduct research on leadless packaging materials and processes for high-temperature sensors, solve the reliability issues in the packaging process of high-temperature sensors, and meet the usage requirements of sensors in complex environments. Summary of the Invention

[0005] To address one or more technical problems existing in the prior art, this invention provides a high-temperature resistant conductive paste for encapsulation, its preparation method, and its application.

[0006] The present invention provides a method for preparing a high-temperature resistant conductive paste for encapsulation in a first aspect, the method comprising the following steps:

[0007] (1) Ag-30Pd spherical powder with a particle size D50 of 8-12 μm was ball-milled with acetone to obtain the first ball milling material;

[0008] (2) Add Ag-30Pd spherical powder with a particle size D50 of 1-12 μm, low-melting-point spherical powder with a particle size D50 of 1-3 μm and acetone to the first ball milling material and ball mill to obtain the second ball milling material; the low-melting-point spherical powder is Zn spherical powder and / or Pb spherical powder.

[0009] (3) Mix the second ball milling material, Ag-30Pd nanopowder with a particle size D50 of 20-80 nm, polyethylene glycol and acetone evenly to obtain a mixed suspension. Then, ultrasonically stir the mixed suspension at 70-90°C, add glycerol and mix evenly, and finally dry to obtain a mixture.

[0010] (4) Add SiO₂ with a particle size D50 of 4-8 μm to the mixture. x The powder is mixed evenly to obtain a high-temperature resistant conductive paste for encapsulation.

[0011] Preferably, the mass of the Ag-30Pd spherical powder with a particle size D50 of 8–12 μm accounts for 30–50% of the sum of the mass of the Ag-30Pd spherical powder with a particle size D50 of 8–12 μm and the mass of the Ag-30Pd spherical powder with a particle size D50 of 1–12 μm; and / or the proportion of the Ag-30Pd nanoparticles in the total mass of Ag-30Pd does not exceed 30 wt%.

[0012] Preferably, in step (1): the ratio of Ag-30Pd spherical powder with a particle size D50 of 8-12 μm to acetone is (60-100) g: (4-6) mL, preferably (60-100) g: 5 mL; during ball milling, the ball-to-material ratio is (8-12): 1, preferably 10: 1; and / or the ball milling speed is 80-200 r / min, preferably 100 r / min, and the ball milling time is 2-4 h, preferably 3 h.

[0013] Preferably, in step (2): the mass ratio of the Ag-30Pd spherical powder with a particle size D50 of 1-12 μm to the Ag-30Pd spherical powder with a particle size D50 of 8-12 μm is (100-140):(60-100); the low-melting-point spherical powder is composed of Zn spherical powder and Pb spherical powder, wherein the Ag-30Pd spherical powder with a particle size D50 of 1-12 μm and the Ag-30Pd spherical powder with a particle size D50 of 1-3 μm are... The ratio of Zn spherical powder with a particle size of m and Pb spherical powder with a particle size D50 of 1-3 μm to acetone is (100-140) g:(4-6) g:(2-3) g:(4-6) mL, preferably (100-140) g:(4-6) g:(2-3) g:5 mL; and / or the ball milling speed is 80-200 r / min, preferably 100 r / min, and the ball milling time is 2-4 h, preferably 3 h.

[0014] Preferably, in step (3): the ratio of Ag-30Pd nanopowder with a particle size D50 of 20-80 nm, polyethylene glycol, acetone, and glycerol is (20-80) g : (8-12) mL.

[0015] (80~120)mL:(4~6)mL, preferably (20~80)g:10mL:100mL:5mL; the ultrasonic stirring time of the mixed suspension is 0.5~1h, preferably 0.5h; and / or the ultrasonic stirring time at 70~90℃ is 2~4h, preferably 2h.

[0016] Preferably, in step (4): the SiO₂ with a particle size D50 of 4–8 μm xThe mass ratio of the powder to the Ag-30Pd nanopowder with a particle size D50 of 20-80 nm is (12-15):(20-80).

[0017] Preferably, in step (2), Ag-30Pd spherical powder with a particle size D50 of 1 to 3 μm is added; and / or in step (3), Ag-30Pd nanoparticles with a particle size D50 of 55 to 65 nm and Ag-30Pd nanoparticles with a particle size D50 of 25 to 35 nm are added in a mass ratio of (2.5 to 3.5):1. More preferably, Ag-30Pd nanoparticles with a particle size D50 of 60 nm and Ag-30Pd nanoparticles with a particle size D50 of 30 nm are added in a mass ratio of 3:1.

[0018] In a second aspect, the present invention provides a high-temperature resistant conductive paste for encapsulation prepared by the preparation method described in the first aspect of the present invention.

[0019] In a third aspect, this invention provides the application of the high-temperature resistant conductive paste for encapsulation prepared by the method described in the first aspect in the fabrication of a leadless packaged sensor. In fabricating the leadless packaged sensor, the high-temperature resistant conductive paste is filled into the holes of the leadless packaged sensor, then connected and encapsulated with target leads, and then sintered under inert gas protection. The sintering process involves first heating to 160–180°C at a heating rate of 1–3°C / min and then sintering at 160–180°C. Sinter at 0℃ for 0.3–0.6 h, then raise the temperature to 230–250℃ at a rate of 1–3℃ / min and sinter at 230–250℃ for 0.3–0.6 h, then raise the temperature to 335–340℃ at a rate of 4–6℃ / min and sinter at 335–340℃ for 0.3–0.6 h, and finally raise the temperature to 350–370℃ at a rate of 4–6℃ / min and sinter at 350–370℃ for 0.3–0.6 h.

[0020] In a fourth aspect, the present invention provides a leadless packaged sensor comprising a high-temperature resistant conductive paste for packaging prepared by the preparation method described in the first aspect of the present invention.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] (1) This invention addresses the leadless packaging technology requirements of high-temperature sensors by providing a high-temperature resistant conductive paste for packaging with low-temperature sintering, high melting point, and low coefficient of thermal expansion. This paste meets the electrical connection and fatigue performance requirements of high-temperature sensors and is a composite conductive paste for high-temperature sensors. Based on Ag-30Pd-based paste, this invention introduces an appropriate amount of inorganic doped heterogeneous component SiO2. xThe appropriate content of low-melting-point alloying elements, Zn / Pb, effectively reduces the thermal expansion coefficient and sintering temperature of the conductive paste through segmented sintering heat treatment. The conductive paste formulated by this invention can be sintered under normal pressure and low temperature conditions, possessing both low-temperature and normal-pressure sintering capabilities, thus meeting the low-temperature sintering requirements for leadless connectors. This invention utilizes the anti-electromigration ability of the Ag-30Pd matrix and SiO2... x The low coefficient of thermal expansion of the components enables leadless connectors to achieve high reliability, making them particularly suitable for high-temperature packaging of semiconductor packaging materials.

[0023] (2) The main materials of this invention are Ag-30Pd powder and SiO2. x Powder, utilizing the anti-electromigration ability of Ag-30Pd and SiO xThe low coefficient of thermal expansion enables long-term operation of high-temperature pressure sensors under drastic temperature changes and high-temperature conditions, avoiding pressure sensor failure due to electromigration and thermal fatigue. The nano-Ag-30Pd powder and micron-sized Ag-30Pd powder added in this invention are processed using a segmented ball milling process. By controlling the ball milling time, the micron-sized Ag-30Pd powder is processed into flake-shaped powder, and the Ag-30Pd powder is adjusted into a mixture of nanoparticles, micron-sized particles, and flake-shaped micron-sized particles. This comprehensively coordinates the flowability, viscosity, and specific surface area of ​​the high-temperature resistant conductive paste for encapsulation. This invention provides a high-temperature resistant conductive paste for encapsulation. Regarding the selection and addition of organic solvents for the high-temperature conductive paste, polyethylene glycol (PEG) is added as a dispersant, acetone as a solvent, and glycerol as a humectant during ball milling and subsequent dispersion processes. In the early mixing processes such as ball milling and ultrasonic stirring of the high-temperature conductive paste for encapsulation, acetone is used to assist in mixing Ag-30Pd powder, Pb powder, Zn powder, and the dispersant PEG. Acetone is removed during the drying stage to avoid defects caused by acetone volatilization during sintering. The alloy powder is dispersed with PEG, and glycerol is added for humectant retention, thus enabling long-term preservation of the high-temperature conductive paste for encapsulation. In the encapsulation process of the high-temperature conductive paste for encapsulation with sensors (e.g., pressure-sensitive chips), this invention employs a segmented sintering heat treatment process, achieving a dense and high-quality sintering effect. During the sintering heat treatment, the sintering holding temperatures at each stage correspond to organic phase removal and solid-phase sintering, respectively. This allows the removal of the humectant and dispersant to be carried out in segments, thereby avoiding an increase in the porosity of the conductive paste due to the removal of the organic solution. Meanwhile, since the gas pressure is maintained at atmospheric pressure during sintering, the volatilization of the organic liquid phase at room temperature can be avoided, which would affect the subsequent sintering process. In the solid-state sintering stage, the lead powder with a lower melting point pre-melts at a lower holding temperature, providing a liquid phase for the subsequent solid-state sintering process, thus effectively assisting the subsequent solid-state powder sintering process while reducing the porosity of the material. At the liquefaction temperature of lead powder, nano- and flake-like micron Ag-30Pd powders with a higher specific surface area have a higher driving force during powder sintering, thus pre-sintering at a lower temperature. At the same time, the liquid phase generated by lead melting serves as a high-speed mass transfer channel, assisting the sintering process. In the higher-temperature sintering process, micron Ag-30Pd powders with a lower specific surface area participate in the sintering process, promoting further densification of the conductive paste. Meanwhile, as the sintering temperature increases, the diffusion behavior of Ag-30Pd powder and Pb melt accelerates, causing Pb melt to dissolve in Ag-30Pd powder, thereby avoiding the adverse effects of lead on the conductive paste connector.Furthermore, this invention adds Zn spherical powder along with Pb spherical powder. The sintering temperature of the material is much lower than the melting point of Zn spherical powder. Adding zinc powder can effectively reduce the solid-state sintering temperature. Ultimately, by adjusting the powder composition and morphology, as well as the content of organic components, this invention achieves a high-density and high-strength sintering process for the high-temperature resistant conductive paste under normal pressure atmosphere protection conditions through a segmented heat treatment process. This results in a conductive paste connection structure with excellent performance, and thus also provides a leadless packaged sensor with excellent performance. Attached Figure Description

[0024] Figure 1 This is a physical image of the high-temperature resistant conductive paste for encapsulation prepared in Embodiment 1 of the present invention;

[0025] Figure 2 The images show the cross-sectional microstructure (SEM) of the high-temperature conductive slurry for packaging prepared in Example 1 of this invention after sintering, and the corresponding elemental analysis energy spectrum. In the images, (a) is the cross-sectional SEM image, and (b) is the elemental analysis energy spectrum.

[0026] Figure 3 This is a microstructure (SEM image) and energy dispersive spectroscopy (EDS) diagram of the transition layer between the high-temperature conductive paste for packaging prepared in Example 2 of this invention and the gold-plated leads after sintering. In the figures, (a) is the SEM image, (b) is the elemental analysis EDS diagram of the gold-containing region on the surface of the transition layer leads, and (c) is the elemental analysis EDS diagram of the matrix. Figure 3 In (a), the b+ shown corresponds to Figure 3 (b) shows the detection position, with c+ corresponding to... Figure 3 (c) Detection location. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] The present invention provides a method for preparing a high-temperature resistant conductive paste for encapsulation in a first aspect, the method comprising the following steps:

[0029] (1) Ball milling of Ag-30Pd spherical powder with a particle size D50 of 8 to 12 μm (e.g., 8, 9, 10, 11 or 12 μm) with acetone to obtain the first ball milling material; In this invention, the Ag-30Pd spherical powder in step (1) is also referred to as the first Ag-30Pd spherical powder.

[0030] (2) Add Ag-30Pd spherical powder with a particle size D50 of 1-12 μm (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 μm), low-melting-point spherical powder with a particle size D50 of 1-3 μm (e.g., 1, 2 or 3 μm) and acetone to the first ball milling material and ball mill to obtain the second ball milling material; the low-melting-point spherical powder is Zn (zinc) spherical powder and / or Pb (lead) spherical powder; in this invention, the Ag-30Pd spherical powder in step (2) is also referred to as the second Ag-30Pd spherical powder; in this invention, the particle size D50 of the Ag-30Pd spherical powder in steps (1) and (2) can be the same or different;

[0031] (3) The second ball milling material, Ag-30Pd nanoparticles with a particle size D50 of 20-80 nm (e.g., 20, 30, 40, 50, 60, 70, or 80 nm), polyethylene glycol, and acetone are mixed evenly to obtain a mixed suspension. The mixed suspension is then ultrasonically stirred (at room temperature), followed by ultrasonic stirring at 70-90°C (e.g., 70°C, 75°C, 80°C, 85°C, or 90°C). Glycerol is then added and mixed evenly. Finally, the mixture is dried to obtain a final product. In this invention, the polyethylene glycol... The glycol is liquid polyethylene glycol; in this invention, ultrasonic stirring refers to stirring in an ultrasonic device. This invention does not specifically limit the ultrasonic conditions, which can be conventionally selected by those skilled in the art. The ultrasonic stirring speed can be, for example, 80–200 r / min; in this invention, room temperature refers to, for example, room temperature of 20–30°C; in this invention, performing steps (1) to (3) sequentially has a significant impact on the performance of the obtained conductive paste, with the ball milling process in the first two steps having a significant effect on the particle shape of the powder. The present invention found that the powder added first undergoes two steps of ball milling (i.e., long-term ball milling), and the powder shape will change into flakes. Flake powder will increase the specific surface area of ​​the powder and thus reduce the sintering temperature, but at the same time it will also reduce the fluidity of the powder. Therefore, adding various powders at different stages can achieve uniform mixing of powders while adjusting the relative content of the three main powders in the powder: micron-sized spherical, micron-sized flake, and nano-sized spherical, so as to obtain a mixture that meets the requirements of high specific surface area and powder fluidity that meets the sintering requirements, which is beneficial to improving the sintering performance of conductive paste. The present invention found that if Ag-30Pd nanopowder is added directly in step (1), the mechanical action of ball milling will cause the nanopowder to deform and adhere to the micron powder, which will significantly reduce the sintering performance and connection quality of the obtained conductive paste. The present invention adds Ag-30Pd nanopowder, Zn (zinc) spherical powder and / or Pb (lead) spherical powder in step (3) and uses ultrasonic stirring to achieve good dispersion and avoid the problem of powder deformation caused by the mechanical action of ball milling.

[0032] (4) Add SiO₂ particles with a particle size D50 of 4–8 μm (e.g., 4, 5, 6, 7 or 8 μm) to the mixture. x The powders are mixed evenly to obtain a high-temperature resistant conductive paste for encapsulation; this invention is applicable to Ag-30Pd spherical powder, Ag-30Pd nano powder, Pb spherical powder, Zn spherical powder, and SiO2. x The source of powders, polyethylene glycol, etc., is not specifically limited; they can be directly purchased products or products synthesized by existing methods. In this invention, the high-temperature resistant conductive paste for encapsulation can withstand temperatures up to 400°C. In this invention, in SiO... x In the powder, 1 < x ≤ 2; it should be noted that for the SiO used in this invention... xFor powder materials, it is not necessary for x to take a specific value; x can be distributed within the range of 1 < x ≤ 2.

[0033] When the high-temperature conductive paste for encapsulation in this invention is used for encapsulating leadless sensors (e.g., pressure-sensitive chips), the sintering procedure is as follows: first, the temperature is raised to 160-180°C at a heating rate of 1-3°C / min, preferably 2°C / min, and sintered at 160-180°C for 0.3-0.6 hours, preferably 0.5 hours; then, the temperature is raised to 230-250°C at a heating rate of 1-3°C / min, preferably 2°C / min, and sintered at 230-250°C for 0.3-0.6 hours, preferably 0.5 hours; next, the temperature is raised to 335-340°C at a heating rate of 4-6°C / min, preferably 5°C / min, and sintered at 335-340°C for 0.3-0.6 hours, preferably 0.5 hours; finally, the temperature is raised to 350-370°C at a heating rate of 4-6°C / min, preferably 5°C / min, and sintered at 350-370°C for 0.3-0.6 hours, preferably 0.5 hours.

[0034] This invention addresses the leadless packaging requirements of high-temperature sensors by providing a high-temperature resistant conductive paste for packaging that features low-temperature sintering, a high melting point, and a low coefficient of thermal expansion. This paste meets the electrical connection and fatigue performance requirements of high-temperature sensors and is a composite conductive paste for such sensors. It is important to note that "low-temperature sintering" and "high-temperature resistance" are relative terms. "Low-temperature sintering" refers to temperatures below the sensor's operating temperature. Specifically, since the conductive paste for packaging is sintered together with the sensor (e.g., a pressure-sensitive chip), the upper limit of the sintering temperature depends on the temperature tolerance of the pressure-sensitive chip. Therefore, the lower the sintering temperature, the better. Here, "low temperature" refers to the temperature relative to the pressure-sensitive chip's tolerance. However, both the pressure-sensitive chip and the conductive paste itself operate in high-temperature environments, requiring high-temperature resistance. The high-temperature resistant conductive paste for packaging in this invention has a powder sintering temperature far below the melting point of the alloy powder, meeting the low-temperature sintering requirement, while simultaneously possessing a high melting point, thus meeting the requirements for operation at higher temperatures.

[0035] The main materials of this invention are Ag-30Pd powder and SiO2. x Powder, utilizing the anti-electromigration ability of Ag-30Pd and SiO xThe low coefficient of thermal expansion enables long-term operation of high-temperature pressure sensors under drastic temperature changes and high-temperature conditions, avoiding pressure sensor failure due to electromigration and thermal fatigue. The nano-Ag-30Pd powder and micron-sized Ag-30Pd powder added in this invention are processed using a segmented ball milling process. By controlling the ball milling time, the micron-sized Ag-30Pd powder is processed into flake-shaped powder, and the Ag-30Pd powder is adjusted into a mixture of nanoparticles, micron-sized particles, and flake-shaped micron-sized particles. This comprehensively coordinates the flowability, viscosity, and specific surface area of ​​the high-temperature resistant conductive paste for encapsulation. This invention provides a high-temperature resistant conductive paste for encapsulation. Regarding the selection and addition of organic solvents for the high-temperature conductive paste, polyethylene glycol (PEG) is added as a dispersant, acetone as a solvent, and glycerol as a humectant during ball milling and subsequent dispersion processes. In the early mixing processes such as ball milling and ultrasonic stirring of the high-temperature conductive paste for encapsulation, acetone is used to assist in mixing Ag-30Pd powder, Pb powder, Zn powder, and the dispersant PEG. Acetone is removed during the drying stage to avoid defects caused by acetone volatilization during sintering. The alloy powder is dispersed with PEG, and glycerol is added for humectant retention, thus enabling long-term preservation of the high-temperature conductive paste for encapsulation. In the encapsulation process of the high-temperature conductive paste for encapsulation with sensors (e.g., pressure-sensitive chips), this invention employs a segmented sintering heat treatment process, achieving a dense and high-quality sintering effect. During the sintering heat treatment, the sintering holding temperatures at each stage correspond to organic phase removal and solid-phase sintering, respectively. This allows the removal of the humectant and dispersant to be carried out in segments, thereby avoiding an increase in the porosity of the conductive paste due to the removal of the organic solution. Simultaneously, because the gas pressure is maintained at atmospheric pressure during sintering, the volatilization of the organic liquid phase at room temperature can be avoided, which would affect the subsequent sintering process. In the solid-state sintering stage, the lead powder with a lower melting point pre-melts at a lower holding temperature, providing a liquid phase for the subsequent solid-state sintering process, thus effectively assisting the subsequent solid-state powder sintering process while reducing the porosity of the material. At the liquefaction temperature of lead powder, nano- and sheet-like micron Ag-30Pd powders, with their high specific surface area, have a higher driving force during powder sintering, thus pre-sintering at a lower temperature. They utilize the liquid phase generated by lead melting as a high-speed mass transfer channel to assist the sintering process. During sintering at higher temperatures, the micron Ag-30Pd powder participates in the sintering process, promoting further densification of the conductive paste. Furthermore, as the sintering temperature increases, the diffusion behavior of Ag-30Pd powder and Pb melt accelerates, causing the Pb melt to dissolve in the Ag-30Pd powder, thereby avoiding the adverse effects of lead on the conductive paste linker.This invention ultimately achieves a high-density and high-strength sintering process for high-temperature resistant conductive paste under normal pressure atmosphere protection by adjusting the powder composition and morphology, as well as the content of organic components, under segmented heat treatment conditions. This results in a conductive paste connection structure with excellent performance, and thus a leadless packaged sensor with excellent performance.

[0036] According to some preferred embodiments, the mass of the Ag-30Pd spherical powder with a particle size D50 of 8–12 μm accounts for 30–50% (e.g., 30%, 35%, 40%, 45%, or 50%) of the sum of the mass of the Ag-30Pd spherical powder with a particle size D50 of 8–12 μm and the mass of the Ag-30Pd spherical powder with a particle size D50 of 1–12 μm; and / or the proportion of the Ag-30Pd nanoparticles in the total mass of Ag-30Pd does not exceed 30 wt%.

[0037] According to some preferred embodiments, in step (1): the ratio of Ag-30Pd spherical powder with a particle size D50 of 8-12 μm to acetone is (60-100) g: (4-6) mL, preferably (60-100) g: 5 mL; when ball milling, the ball-to-material ratio is (8-12): 1 (e.g., 8:1, 9:1, 10:1, 11:1 or 12:1), preferably 10:1; and / or the ball milling speed is 80-200 r / min (e.g., 80, 100, 120, 150, 180 or 200 r / min), preferably 100 r / min, and the ball milling time is 2-4 h (e.g., 2, 3 or 4 h), preferably 3 h.

[0038] According to some specific implementation methods, step (1) is as follows: select 200g of Ag-30Pd spherical powder with a particle size D50 of 10μm, add 30-50% of it to the ball mill jar, and add an additional 5mL of acetone to prevent the powder from sticking together. Use a planetary ball mill to ball mill the powder with a ball-to-material ratio of 10:1, a rotation speed of 100r / min, and ball mill for 3 hours.

[0039] According to some preferred embodiments, in step (2): the mass ratio of the Ag-30Pd spherical powder with a particle size D50 of 1-12 μm to the Ag-30Pd spherical powder with a particle size D50 of 8-12 μm is (100-140):(60-100); the low-melting-point spherical powder is composed of Zn spherical powder and Pb spherical powder, and the ratio of the Ag-30Pd spherical powder with a particle size D50 of 1-12 μm, the Zn spherical powder with a particle size D50 of 1-3 μm, the Pb spherical powder with a particle size D50 of 1-3 μm, to acetone is (100-140)g:(4-6)g:(2-3)g:( The preferred concentrations are (100-140) g: (4-6) g: (2-3) g: 5 mL. This invention has found that it is particularly important to control the amount of Pb spherical powder. If the amount of Pb spherical powder is too low, it will not significantly improve the sintering performance and bonding quality of the conductive paste. If the amount of Pb spherical powder is too high, the lead powder will no longer exist in solid solution form during high-temperature sintering, and a second phase will be generated at the powder interface, which will seriously affect the mechanical properties of the conductive paste after sintering. And / or the ball milling speed is 80-200 r / min, preferably 100 r / min, and the ball milling time is 2-4 h (e.g., 2, 3, or 4 h), preferably 3 h.

[0040] According to some specific implementation methods, step (2) is as follows: After ball milling in step (1), add 100g of Ag-30Pd spherical powder with a particle size D50 of 10μm, add 2-3g of Pb spherical powder with a particle size D50 of 2μm, add 4-6g of Zn spherical powder with a D50 of 2μm, add 5mL of acetone to prevent powder sticking, and continue ball milling for 3 hours at a speed of 80-200r / min.

[0041] According to some preferred embodiments, in step (3): the ratio of Ag-30Pd nanopowder with a particle size D50 of 20-80 nm, polyethylene glycol, acetone and glycerol is (20-80) g: (8-12) mL: (80-120) mL: (4-6) mL, preferably (20-80) g: 10 mL: 100 mL: 5 mL; the ultrasonic stirring time of the mixed suspension is 0.5-1 h, preferably 0.5 h; and / or the ultrasonic stirring time at 70-90 °C is 2-4 h (e.g. 2, 2.5, 3, 3.5 or 4 h), preferably 2 h.

[0042] According to some specific implementation methods, step (3) is as follows: The second ball milling material after step (2) is ball-milled and mixed thoroughly with 20-80g of Ag-30Pd nanoparticles with a particle size D50 of 60nm (the content should be less than 30% of the total Ag-30Pd particles), 10mL of polyethylene glycol, and 100mL of acetone, resulting in a mixed suspension with a volume of approximately 140mL. The mixed suspension is ultrasonically stirred for 30-60 minutes, and then stirred in an ultrasonic bath at 80°C for 2-4 hours, reducing the volume of the mixture to approximately 55mL. Subsequently, 5mL of glycerol is added for humidification, and the mixture is subjected to preliminary vacuum drying for 2 hours, for example, at a temperature of 50-70°C, preferably 60°C.

[0043] According to some preferred embodiments, in step (4): the SiO₂ with a particle size D50 of 4-8 μm x The mass ratio of the powder to the Ag-30Pd nanopowder with a particle size D50 of 20-80 nm is (12-15):(20-80); in this invention, preferably, the SiO2 with a particle size D50 of 4-8 μm is used. x The mass ratio of the powder to the Ag-30Pd nanopowder with a particle size D50 of 20-80 nm is (12-15):(20-80). This invention discovers that by rationally controlling the SiO2 content... x The amount of powder used can effectively reduce the overall thermal expansion coefficient of the conductive paste. For example, SiO2... x If the powder content is too low, the difference in thermal expansion coefficients between the slurry and the glass plate / holes during assembly will be too large, making it prone to cracking and affecting the mechanical properties of the conductive slurry. However, if the SiO content is too low... x Excessive content can also affect the overall mechanical properties of the conductive paste.

[0044] According to some specific implementation methods, step (4) is: adding SiO2 to the preliminarily dried mixture. x 12-15g of powder with a particle size D50 of 5μm is mixed evenly using a vacuum degassing mixer to obtain a high-temperature resistant conductive slurry. This invention does not specify the conditions for vacuum degassing and mixing, and those skilled in the art can choose conventionally. In this invention, for example, vacuum degassing and mixing is carried out under vacuum conditions below 0.1 atmospheres, with the vacuum degassing and mixing temperature being, for example, 60°C, the time being, for example, 3 hours, and the mixing speed being, for example, 100-400 r / min.

[0045] According to some preferred embodiments, in step (2), Ag-30Pd spherical powder with a particle size D50 of 1 to 3 μm (e.g., 1, 2, or 3 μm) is added; and / or in step (3), Ag-30Pd nanopowder with a particle size D50 of 55 to 65 nm and Ag-30Pd nanopowder with a particle size D50 of 25 to 35 nm are added in a mass ratio of (2.5 to 3.5):1 (e.g., 2.5:1, 3:1, or 3.5:1), preferably Ag-30Pd nanopowder with a particle size D50 of 65 to 35 nm is added in a mass ratio of 3:1. The present invention uses Ag-30Pd nanopowder with a particle size of 0 nm and Ag-30Pd nanopowder with a particle size D50 of 30 nm. In the present invention, it is preferred that in step (2), Ag-30Pd spherical powder with a particle size D50 of 1 to 3 μm is added, and in step (3), Ag-30Pd nanopowder with a particle size D50 of 55 to 65 nm and Ag-30Pd nanopowder with a particle size D50 of 25 to 35 nm are added in a mass ratio of (2.5 to 3.5): 1. This can significantly improve the connection quality of the conductive paste.

[0046] According to some preferred embodiments, the preparation of the high-temperature resistant conductive paste for encapsulation in this invention does not include step (1). Instead, in step (2), 200g of Ag-30Pd spherical powder with a particle size D50 of 1-3μm (preferably 2μm), 3g of Pb spherical powder with a particle size D50 of 1-3μm (preferably 2μm), 5g of Zn spherical powder, and 5mL of acetone are directly added and ball-milled to obtain a ball-milled material. Then, the ball-milled material, 60g of Ag-30Pd nanoparticles with a particle size D50 of 60nm, 20g of Ag-30Pd nanoparticles with a D50 of 30nm, 10mL of polyethylene glycol, and 140mL of acetone are mixed evenly to obtain a mixed suspension. The mixed suspension is then ultrasonically stirred at 70-90℃, and 5mL of glycerol is added and mixed evenly. Finally, the mixture is dried to obtain a mixture. Finally, SiO2 with a particle size D50 of 4-8μm is added to the mixture. x The powder is mixed evenly to obtain a high-temperature resistant conductive paste for encapsulation, which can significantly improve the connection quality of the conductive paste.

[0047] In a second aspect, the present invention provides a high-temperature resistant conductive paste for encapsulation prepared by the preparation method described in the first aspect of the present invention.

[0048] The present invention provides, in a third aspect, the application of the high-temperature resistant conductive paste for encapsulation prepared by the method described in the first aspect of the present invention in the preparation of a leadless encapsulated sensor. In the present invention, the leadless encapsulated sensor is a leadless encapsulated high-temperature sensor. In preparing the leadless encapsulated sensor, the high-temperature resistant conductive paste is filled into the holes of the leadless encapsulated sensor, then connected and encapsulated with a target lead (e.g., a gold-plated lead), and then sintered under inert gas protection. The temperature is first raised to 160–180°C (e.g., 160°C, 170°C, or 180°C) at a heating rate of 1–3°C / min, preferably 2°C / min, and sintered at 160–180°C (e.g., 160°C, 170°C, or 180°C) for 0.3–0.6 h, preferably 0.5 h, and then sintered at a rate of 1–3°C / min, preferably 2°C / min. The temperature is increased to 230–250°C (e.g., 230°C, 240°C, or 250°C) at a heating rate of 4–6°C / min, preferably 5°C / min, and sintered at 230–250°C (e.g., 230°C, 240°C, or 250°C) for 0.3–0.6 h, preferably 0.5 h. Then, the temperature is increased to 335–340°C (e.g., 335°C, or 340°C) at a heating rate of 4–6°C / min, preferably 5°C / min, and sintered at 335–340°C (e.g., 335°C, or 340°C) for 0.3–0.6 h, preferably 0.5 h. Finally, the temperature is increased to 350–370°C (e.g., 350°C, 360°C, or 370°C) at a heating rate of 4–6°C / min, preferably 5°C / min, and sintered at 350–370°C (e.g., 350°C, 360°C, or 370°C) for 0.3–0.6 h, preferably 0.5 h.

[0049] This invention employs a segmented sintering heat treatment process in the encapsulation of high-temperature resistant conductive paste and sensors, achieving a dense and high-quality sintering effect. During the sintering heat treatment, the sintering holding temperatures at each stage correspond to organic phase removal and solid-phase sintering, respectively. This allows for the segmented removal of humectants and dispersants, thus avoiding an increase in the porosity of the conductive paste due to the removal of organic solutions. Simultaneously, maintaining atmospheric pressure during sintering prevents the volatilization of the organic liquid phase at room temperature, which could affect subsequent sintering processes. In the solid-phase sintering stage, the low-melting-point lead powder is pre-melted at a lower holding temperature, providing a liquid phase for the subsequent solid-phase sintering process. This effectively assists in the subsequent solid-phase powder sintering process while simultaneously reducing the material's porosity. At the liquefaction temperature of lead powder, nano- and sheet-like micron-sized Ag-30Pd powders, with their high specific surface area, exhibit greater driving force during powder sintering, allowing for pre-sintering at lower temperatures. Simultaneously, the liquid phase generated by lead melting serves as a high-speed mass transfer channel, aiding the sintering process. During higher-temperature sintering, the micron-sized Ag-30Pd powder participates in the process, promoting further densification of the conductive paste. Furthermore, as the sintering temperature increases, the diffusion behavior between Ag-30Pd powder and Pb melt accelerates, causing the Pb melt to dissolve within the Ag-30Pd powder, thus avoiding the adverse effects of lead on the conductive paste connector. This invention ultimately achieves a high-density and high-strength sintering process for high-temperature resistant conductive paste under normal pressure atmosphere protection by adjusting the powder composition and morphology, as well as the organic component content, under segmented heat treatment conditions. This results in a conductive paste connector structure with excellent performance, and consequently, a leadless packaged sensor with superior performance.

[0050] According to some specific embodiments, after the high-temperature resistant conductive paste for encapsulation prepared by the preparation method described in the first aspect of the present invention is initially encapsulated with the target lead, the encapsulated component is placed in a tube furnace, and argon gas is continuously introduced for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, an argon protective atmosphere and normal pressure conditions must be maintained inside the tube; after ensuring that the air is completely purged, the sample is slowly heated to 160-180°C at a heating rate of 2°C / min and held for 0.5 hours to ensure that the acetone in the high-temperature resistant conductive paste for encapsulation is completely volatilized; then the sample is slowly heated to 230-250°C at a heating rate of 2°C / min and held for 0.5 hours to ensure that the acetone in the high-temperature resistant conductive paste for encapsulation is completely volatilized. In this invention, the polyethylene glycol is completely volatilized. Preferably, the second-stage sintering is carried out at 230-250°C. This allows for the complete volatilization of polyethylene glycol while avoiding an overly vigorous evaporation process, which is beneficial for achieving densification of the conductive paste during sintering. Subsequently, the sample is heated to 335-340°C at a heating rate of 5°C / min and held for 0.5 hours to ensure that the lead powder in the high-temperature resistant conductive paste for encapsulation melts and that the nano- and flake-like micron Ag-30Pd powders begin to sinter. Finally, the sample is heated to 350-370°C at a heating rate of 5°C / min and held for 0.5 hours to promote the overall sintering of the sample. Heating is then stopped, and the sample is cooled to room temperature under an argon atmosphere.

[0051] In a fourth aspect, the present invention provides a leadless packaged sensor comprising a high-temperature resistant conductive paste for packaging prepared by the preparation method described in the first aspect of the present invention.

[0052] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments.

[0053] Example 1

[0054] This embodiment provides a method for preparing a novel high-temperature resistant conductive paste for encapsulation, which is prepared according to the following steps:

[0055] ① Select 60g of Ag-30Pd spherical powder with a particle size D50 of 10μm and add it to the ball mill jar. Add 5mL of acetone to prevent the powder from sticking together. Use a planetary ball mill to ball mill the powder at a ball-to-powder ratio of 10:1, a rotation speed of 100r / min, and ball mill for 3 hours to obtain the first ball milling material.

[0056] ② After ball milling in step ①, add 140g of Ag-30Pd spherical powder with a particle size D50 of 10μm, 3g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent powder adhesion. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0057] ③ After ball milling in step ②, the second ball milling material is thoroughly mixed with 40g of Ag-30Pd nanoparticles with a particle size D50 of 60nm, 10mL of polyethylene glycol, and 100mL of acetone to obtain a mixed suspension. The mixed suspension is ultrasonically stirred for 30 minutes, and then stirred in an ultrasonic water bath at 80℃ for 2 hours until the volume of the mixture is reduced to about 55mL. Subsequently, 5mL of glycerol is added to keep it moist, and the mixture is initially vacuum dried at 60℃ for 2 hours to obtain the mixture.

[0058] ④ Add SiO2 to the mixture obtained after preliminary drying in step ③. x 12g of powder with a particle size D50 of 5μm was mixed evenly using a vacuum degassing mixer to obtain a high-temperature resistant conductive paste for encapsulation.

[0059] ⑤ Place the high-temperature resistant conductive paste for encapsulation obtained in step ④ into a tube furnace, and purge it with argon gas for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure conditions; after ensuring that the air is completely purged, slowly heat the sample to 170°C at a heating rate of 2°C / min and sinter at 170°C for 0.5 hours, then slowly heat it to 250°C at a heating rate of 2°C / min and sinter at 250°C for 0.5 hours; then heat the sample to 335°C at a heating rate of 5°C / min and sinter at 335°C for 0.5 hours, and finally heat it to 360°C at a heating rate of 5°C / min and sinter at 360°C for 0.5 hours; then stop heating and cool to room temperature under an argon atmosphere to obtain the sintered body.

[0060] A physical image of the high-temperature resistant conductive paste for encapsulation prepared in Example 1 is shown below. Figure 1 As shown, from Figure 1 It can be observed that the viscosity of the high-temperature resistant conductive paste for packaging prepared in Example 1 is appropriate and can meet the requirements for use during packaging.

[0061] The cross-sectional microstructure (SEM) image and corresponding elemental energy spectrum of the sintered body obtained by atmospheric pressure sintering of the high-temperature resistant conductive paste for packaging prepared in Example 1 of this invention are shown below. Figure 2 As shown, Figure 2 The microstructure of the high-temperature resistant conductive paste for packaging after sintering at atmospheric pressure is shown. It can be observed that the conductive paste is dense and has no obvious pores or defects, which can meet the long-term use requirements of the sensor.

[0062] Example 2

[0063] This embodiment provides a method for preparing a high-temperature resistant conductive paste for encapsulation and an encapsulation process:

[0064] ① Select 60g of Ag-30Pd spherical powder with a particle size D50 of 10μm and add it to the ball mill jar. Add 5mL of acetone to prevent the powder from sticking together. Use a planetary ball mill to ball mill the powder at a ball-to-powder ratio of 10:1, a rotation speed of 100r / min, and ball mill for 3 hours to obtain the first ball milling material.

[0065] ② After ball milling in step ①, add 140g of Ag-30Pd spherical powder with a particle size D50 of 10μm, 3g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent powder adhesion. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0066] ③ After ball milling in step ②, the second ball milling material is thoroughly mixed with 40g of Ag-30Pd nanoparticles with a particle size D50 of 60nm, 10mL of polyethylene glycol, and 100mL of acetone to obtain a mixed suspension. The mixed suspension is ultrasonically stirred for 30 minutes, and then stirred in an ultrasonic water bath at 80℃ for 2 hours until the volume of the mixture is reduced to about 55mL. Subsequently, 5mL of glycerol is added to keep it moist, and the mixture is initially vacuum dried at 60℃ for 2 hours to obtain the mixture.

[0067] ④ Add SiO2 to the mixture obtained after preliminary drying in step ③. x 12g of powder with a particle size D50 of 5μm was mixed evenly using a vacuum degassing mixer to obtain a high-temperature resistant conductive paste for encapsulation.

[0068] ⑤ Connect the high-temperature resistant conductive paste obtained in step ④ to the gold-plated leads for encapsulation, place it in a tube furnace, and purge with argon gas for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure conditions; after ensuring that the air is completely purged, slowly heat the sample to 170°C at a heating rate of 2°C / min and sinter at 170°C for 0.5 hours, then slowly heat to 250°C at a heating rate of 2°C / min and sinter at 250°C for 0.5 hours; then heat the sample to 335°C at a heating rate of 5°C / min and sinter at 335°C for 0.5 hours, and finally heat to 360°C at a heating rate of 5°C / min and sinter at 360°C for 0.5 hours; then stop heating and cool to room temperature under an argon atmosphere.

[0069] In this embodiment, after atmospheric pressure sintering, a dense transition layer containing gold is formed in the transition region between the lead wire and the high-temperature conductive paste. Figure 3The images show the microstructure (SEM) and energy dispersive spectroscopy (EDS) diagrams of the transition layer between the lead wire and the high-temperature conductive paste after the high-temperature conductive paste prepared in Embodiment 2 of this invention is connected to the gold-plated lead wire and sintered. The results show that the lead wire and the conductive paste are tightly bonded and have a good bond, indicating that the conductive paste and the lead wire have formed a dense connection structure after sintering.

[0070] Example 3

[0071] Example 3 is basically the same as Example 1, except that:

[0072] ① 100g of Ag-30Pd spherical powder with a particle size D50 of 10μm was added to a ball mill jar, and 5mL of acetone was added to prevent the powder from sticking together. The ball mill was used for ball milling with a ball-to-powder ratio of 10:1, a rotation speed of 100r / min, and ball milling for 3 hours to obtain the first ball milling material.

[0073] ② After ball milling in step ①, add 100g of Ag-30Pd spherical powder with a particle size D50 of 10μm, 3g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent powder adhesion. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0074] ③ After ball milling in step ②, the second ball milling material is thoroughly mixed with 20g of Ag-30Pd nanoparticles with a particle size D50 of 60nm, 10mL of polyethylene glycol, and 100mL of acetone to obtain a mixed suspension. The mixed suspension is ultrasonically stirred for 30 minutes, and then stirred in an ultrasonic water bath at 80℃ for 2 hours until the volume of the mixture is reduced to about 55mL. Subsequently, 5mL of glycerol is added to keep it moist, and the mixture is initially vacuum dried at 60℃ for 2 hours to obtain the mixture.

[0075] This embodiment reduces the raw material cost of the high-temperature conductive paste for encapsulation by reducing the particle size of Ag-30Pd nanopowder (D50: 60nm) while ensuring a certain level of bonding quality.

[0076] Example 4

[0077] Example 4 is basically the same as Example 1, except that:

[0078] ① Select 60g of Ag-30Pd spherical powder with a particle size D50 of 10μm and add it to the ball mill jar. Add 5mL of acetone to prevent the powder from sticking together. Use a planetary ball mill to ball mill the powder at a ball-to-powder ratio of 10:1, a rotation speed of 100r / min, and ball mill for 3 hours to obtain the first ball milling material.

[0079] ② After ball milling in step ①, add 140g of Ag-30Pd spherical powder with a particle size D50 of 2μm, 3g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent powder adhesion. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0080] ③ After ball milling in step ②, the second ball milling material, 60g of Ag-30Pd nanoparticles with a particle size D50 of 60nm, 20g of Ag-30Pd nanoparticles with a particle size D50 of 30nm, 10mL of polyethylene glycol, and 100mL of acetone are thoroughly mixed to obtain a mixed suspension. The mixed suspension is ultrasonically stirred for 30 minutes, and then stirred in an ultrasonic bath at 80℃ for 2 hours until the volume of the mixture is reduced to about 55mL. Then, 5mL of glycerol is added to keep it moist, and the mixture is initially vacuum dried at 60℃ for 2 hours to obtain a mixture.

[0081] This embodiment can significantly improve the connection quality of high-temperature resistant conductive paste for packaging.

[0082] Example 5

[0083] ① Add 200g of Ag-30Pd spherical powder with a particle size D50 of 2μm to a ball mill jar, then add 3g of Pb spherical powder with a particle size D50 of 2μm and 5g of Zn spherical powder with a particle size D50 of 2μm. Add 5mL of acetone to prevent powder adhesion. Use a planetary ball mill to ball mill at a ball-to-powder ratio of 10:1 for 3 hours at a speed of 100r / min to obtain the ball milled material.

[0084] ② After ball milling in step ①, the ball milling material, 60g of Ag-30Pd nanoparticles with a particle size D50 of 60nm, 20g of Ag-30Pd nanoparticles with a particle size D50 of 30nm, 10mL of polyethylene glycol, and 100mL of acetone are thoroughly mixed to obtain a mixed suspension. The mixed suspension is ultrasonically stirred for 30 minutes, and then stirred in an ultrasonic bath at 80℃ for 2 hours until the volume of the mixture is reduced to about 55mL. Then, 5mL of glycerol is added to keep it moist, and the mixture is initially vacuum dried at 60℃ for 2 hours to obtain the mixture.

[0085] ③ Add SiO2 to the mixture obtained after preliminary drying in step ② x 12g of powder with a particle size D50 of 5μm was mixed evenly using a vacuum degassing mixer to obtain a high-temperature resistant conductive paste for encapsulation.

[0086] ④ Place the high-temperature resistant conductive paste for encapsulation obtained in step ③ into a tube furnace, and purge it with argon gas for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure conditions; after ensuring that the air is completely purged, slowly heat the sample to 170°C at a heating rate of 2°C / min and sinter at 170°C for 0.5 hours, then slowly heat it to 250°C at a heating rate of 2°C / min and sinter at 250°C for 0.5 hours; then heat the sample to 335°C at a heating rate of 5°C / min and sinter at 335°C for 0.5 hours, and finally heat it to 360°C at a heating rate of 5°C / min and sinter at 360°C for 0.5 hours; then stop heating and cool to room temperature under an argon atmosphere to obtain the sintered body.

[0087] This embodiment can significantly improve the connection quality of high-temperature resistant conductive paste for packaging.

[0088] Example 6

[0089] ①The steps are the same as in Example 1.

[0090] ② After ball milling in step ①, add 140g of Ag-30Pd spherical powder with a particle size D50 of 10μm, 1g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent powder adhesion. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0091] ③ is the same as step ③ in Example 1.

[0092] ④ Add SiO2 to the mixture obtained after preliminary drying in step ③. x 5g of powder with a particle size D50 of 5μm was mixed evenly using a vacuum degassing mixer to obtain a high-temperature resistant conductive paste for encapsulation.

[0093] ⑤ is the same as step ⑤ in Example 1.

[0094] Example 7

[0095] ①The steps are the same as in Example 1.

[0096] ② After ball milling in step ①, add 140g of Ag-30Pd spherical powder with a particle size D50 of 10μm, 6g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent powder adhesion. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0097] ③ is the same as step ③ in Example 1.

[0098] ④ Add SiO2 to the mixture obtained after preliminary drying in step ③. x 35g of powder with a particle size D50 of 5μm was mixed evenly using a vacuum degassing mixer to obtain a high-temperature resistant conductive paste for encapsulation.

[0099] ⑤ is the same as step ⑤ in Example 1.

[0100] Comparative Example 1

[0101] Comparative Example 1 is basically the same as Example 1, except that:

[0102] ⑤ Place the high-temperature resistant conductive paste for encapsulation obtained in step ④ into a tube furnace, and purge it with argon gas for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure conditions; after ensuring that the air is completely purged, slowly heat the sample to 360°C at a heating rate of 5°C / minute and sinter at 360°C for 2 hours; then stop heating and cool to room temperature under argon atmosphere protection to obtain the sintered body.

[0103] Comparative Example 2

[0104] Comparative Example 2 is basically the same as Example 1, except that:

[0105] ⑤ Place the high-temperature resistant conductive paste for encapsulation obtained in step ④ into a tube furnace, and purge it with argon gas for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure conditions; after ensuring that the air is completely purged, slowly heat the sample to 250°C at a heating rate of 2°C / min and sinter at 250°C for 1 hour; then heat the sample to 360°C at a heating rate of 5°C / min and sinter at 360°C for 1 hour; then stop heating and cool to room temperature under argon atmosphere protection to obtain the sintered body.

[0106] Comparative Example 3

[0107] Comparative Example 3 is basically the same as Example 1, except that:

[0108] ⑤ Place the high-temperature resistant conductive paste for encapsulation obtained in step ④ into a tube furnace, and purge it with argon gas for 5 minutes to purge the air inside the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure conditions; after ensuring that the air is completely purged, slowly heat the sample to 170°C at a heating rate of 2°C / min and sinter at 170°C for 1 hour; then heat the sample to 335°C at a heating rate of 5°C / min and sinter at 335°C for 1 hour; then stop heating and cool to room temperature under argon atmosphere protection to obtain the sintered body.

[0109] Comparative Example 4

[0110] ① Select 200g of Ag-30Pd spherical powder with a particle size D50 of 10μm, 40g of Ag-30Pd nanopowder with a particle size D50 of 60nm, 3g of Pb spherical powder with a particle size D50 of 2μm, and 5g of Zn spherical powder with a particle size D50 of 2μm. Add them to a ball mill jar and add 5mL of acetone to prevent the powder from sticking together. Use a planetary ball mill to ball mill the powder at a ball-to-powder ratio of 10:1, a rotation speed of 100r / min, and ball mill for 3 hours to obtain the ball milling material.

[0111] ② After ball milling in step ①, the ball milling material, 10 mL of polyethylene glycol and 100 mL of acetone are thoroughly mixed to obtain a mixed suspension. The mixed suspension is ultrasonically stirred for 30 minutes, and then stirred in an ultrasonic water bath at 80°C for 2 hours until the volume of the mixture is reduced to about 55 mL. Then, 5 mL of glycerol is added to keep it moist, and the mixture is initially vacuum dried at 60°C for 2 hours to obtain the mixture.

[0112] ③ Add SiO2 to the mixture obtained after preliminary drying in step ② x 12g of powder with a particle size D50 of 5μm was mixed evenly using a vacuum degassing mixer to obtain a conductive slurry.

[0113] ④ Place the conductive paste obtained in step ③ into a tube furnace, purge with argon gas for 5 minutes to purge the air from the tube; then sintering can begin. During sintering, the tube must maintain an argon protective atmosphere and normal pressure. After ensuring that the air is completely purged, slowly heat the sample to 170°C at a heating rate of 2°C / min and sinter at 170°C for 0.5 hours. Then slowly heat to 250°C at a heating rate of 2°C / min and sinter at 250°C for 0.5 hours. Next, heat the sample to 335°C at a heating rate of 5°C / min and sinter at 335°C for 0.5 hours. Finally, heat to 360°C at a heating rate of 5°C / min and sinter at 360°C for 0.5 hours. Then stop heating and cool to room temperature under an argon atmosphere to obtain the sintered body.

[0114] Comparative Example 5

[0115] ①The steps are the same as in Example 1.

[0116] ② After ball milling in step ①, add 140g of Ag-30Pd spherical powder with a particle size D50 of 10μm and 5g of Zn spherical powder with a particle size D50 of 2μm to the first ball milling material. Add 5mL of acetone to prevent the powder from sticking together. Continue ball milling for 3 hours at a speed of 100r / min to obtain the second ball milling material.

[0117] ③ is the same as step ③ in Example 1.

[0118] ④ is the same as step ④ in Example 1.

[0119] ⑤ is the same as step ⑤ in Example 1.

[0120] The present invention conducted performance tests on the sintered bodies obtained by sintering the conductive pastes in Examples 1, 3-7 and Comparative Examples 1-5, including the density, sheet resistance and compressive strength of the sintered bodies, and the results are shown in Table 1.

[0121] Table 1

[0122]

[0123] As shown in Table 1, the high-temperature resistant conductive paste for packaging obtained by the present invention has excellent sintering and bonding properties. The sintered body obtained after sintering has high density (not less than 82%), sheet resistance (not greater than 21 mΩ / □), and compressive strength (not less than 22 MPa). The high-temperature resistant conductive paste for packaging obtained by some preferred embodiments of the present invention has even better sintering and bonding properties. The sintered body obtained after sintering has a density (not less than 86%), sheet resistance (not greater than 18 mΩ / □), and compressive strength (not less than 26 MPa).

[0124] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. The application of a high-temperature resistant conductive paste for encapsulation in the fabrication of leadless packaged sensors, characterized in that, The preparation method of the high-temperature resistant conductive paste for encapsulation includes the following steps: (1) Ag-30Pd spherical powder with a particle size D50 of 8~12μm was ball-milled with acetone to obtain the first ball milling material; (2) Add Ag-30Pd spherical powder with a particle size D50 of 1~12μm, low melting point spherical powder with a particle size D50 of 1~3μm and acetone to the first ball milling material and ball mill to obtain the second ball milling material; the low melting point spherical powder is Zn spherical powder and Pb spherical powder. (3) Mix the second ball milling material, Ag-30Pd nanopowder with a particle size D50 of 20~80nm, polyethylene glycol and acetone evenly to obtain a mixed suspension. Then, ultrasonically stir the mixed suspension at 70~90℃, add glycerol and mix evenly, and finally dry to obtain a mixture. (4) adding SiO2 powder with a particle size D50 of 4-8 μm into the mixture and mixing uniformly to obtain a high-temperature-resistant conductive paste for packaging; x powder and mixing uniformly to obtain a high-temperature-resistant conductive paste for packaging; In the fabrication of a leadless packaged sensor, the packaged sensor is filled with a high-temperature resistant conductive paste, then connected to the target lead, and finally sintered under inert gas protection. The sintering process involves first heating the temperature to 160-180℃ at a rate of 1-3℃ / min and sintering at 160-180℃ for 0.3-0.6 hours; then heating the temperature to 230-250℃ at a rate of 1-3℃ / min and sintering at 230-250℃ for 0.3-0.6 hours; then heating the temperature to 335-340℃ at a rate of 4-6℃ / min and sintering at 335-340℃ for 0.3-0.6 hours; and finally heating the temperature to 350-370℃ at a rate of 4-6℃ / min and sintering at 350-370℃ for 0.3-0.6 hours.

2. The application according to claim 1, characterized in that: The mass of the Ag-30Pd spherical powder with a particle size D50 of 8~12μm accounts for 30~50% of the sum of the mass of the Ag-30Pd spherical powder with a particle size D50 of 8~12μm and the mass of the Ag-30Pd spherical powder with a particle size D50 of 1~12μm; In the total mass of Ag-30Pd, the proportion of Ag-30Pd nanopowder does not exceed 30wt%.

3. The application according to claim 1, characterized in that, In step (1): The ratio of Ag-30Pd spherical powder with a particle size D50 of 8~12μm to acetone is (60~100)g:(4~6)mL; During the ball milling process, the ball-to-material ratio is (8~12):1; The ball mill rotates at a speed of 80-200 r / min, and the milling time is 2-4 h.

4. The application according to claim 3, characterized in that, In step (1): The ratio of Ag-30Pd spherical powder with a particle size D50 of 8~12μm to acetone is (60~100)g:5mL.

5. The application according to claim 3, characterized in that, In step (1): During the ball milling process, the ball-to-material ratio is 10:

1.

6. The application according to claim 3, characterized in that, In step (1): The ball mill rotates at 100 r / min and the milling time is 3 h.

7. The application according to claim 1, characterized in that, In step (2): The mass ratio of the Ag-30Pd spherical powder with a particle size D50 of 1~12μm to the Ag-30Pd spherical powder with a particle size D50 of 8~12μm in step (1) is (100~140):(60~100). The ratio of Ag-30Pd spherical powder with a particle size D50 of 1~12μm, Zn spherical powder with a particle size D50 of 1~3μm, and Pb spherical powder with a particle size D50 of 1~3μm to acetone is (100~140)g:(4~6)g:(2~3)g:(4~6)mL; The ball mill rotates at a speed of 80-200 r / min, and the milling time is 2-4 h.

8. The application according to claim 7, characterized in that, In step (2): The ratio of Ag-30Pd spherical powder with a particle size D50 of 1~12μm, Zn spherical powder with a particle size D50 of 1~3μm, Pb spherical powder with a particle size D50 of 1~3μm to acetone is (100~140)g:(4~6)g:(2~3)g:5mL.

9. The application according to claim 7, characterized in that, In step (2): The ball mill rotates at 100 r / min and the milling time is 3 h.

10. The application according to claim 1, characterized in that, In step (3): The ratio of Ag-30Pd nanopowder with a particle size D50 of 20~80nm, polyethylene glycol, acetone and glycerol is (20~80)g: (8~12)mL: (80~120)mL: (4~6)mL; The ultrasonic stirring time for the mixed suspension is 0.5~1h; The ultrasonic stirring time is 2-4 hours at 70-90℃.

11. The application according to claim 10, characterized in that, In step (3): The ratio of Ag-30Pd nanopowder with a particle size D50 of 20~80nm, polyethylene glycol, acetone and glycerol is (20~80)g:10mL:100mL:5mL.

12. The application according to claim 10, characterized in that, In step (3): The mixed suspension was ultrasonically stirred for 0.5 hours.

13. The application according to claim 10, characterized in that, In step (3): The ultrasonic stirring time is 2 hours at 70~90℃.

14. The application according to claim 1, characterized in that, In step (4): The SiO₂ with a particle size D50 of 4~8μm x The mass ratio of the powder to the Ag-30Pd nanopowder with a particle size D50 of 20~80nm described in step (3) is (12~15):(20~80).

15. The application according to any one of claims 1 to 14, characterized in that: In step (2), Ag-30Pd spherical powder with a particle size D50 of 1~3μm is added; In step (3), Ag-30Pd nanopowder with a particle size D50 of 55-65 nm and Ag-30Pd nanopowder with a particle size D50 of 25-35 nm are added in a mass ratio of (2.5~3.5):

1.

16. The application according to claim 15, characterized in that: In step (3), Ag-30Pd nanopowder with a particle size D50 of 60nm and Ag-30Pd nanopowder with a particle size D50 of 30nm are added in a mass ratio of 3:1.

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