Air atmosphere near-infrared laser sinterable copper paste and preparation method thereof

Abstract

The application provides an air atmosphere near-infrared laser sinterable oxidation-resistant copper paste and a preparation method thereof, and the main body of the paste is Cu@glass, which comprises a copper core, and a Bi2O3-B2O3-ZnO glass shell layer with a mass fraction of 5%-20% coated outside the copper core, and the particle size of the copper core is 200 nm-500 nm. The copper paste prepared by using the Cu@glass material greatly improves the near-infrared laser absorption efficiency and oxidation resistance of the Cu@glass particles under the coating structure of the glass shell, and the initial oxidation temperature and the near-infrared light absorption rate of the 10% glass-coated Cu@glass particles are 294 DEG C and 61.8% respectively, so that the stable necking and densification of the copper paste under the irradiation of the near-infrared laser are realized under the condition of the air atmosphere, and a copper conductor film layer with conductivity is obtained.

Description

Technical Field

[0001] This invention relates to the field of electronic functional materials technology, and in particular to an air-atmosphere near-infrared laser sinterable copper paste and its preparation method. Background Technology

[0002] Conductive copper paste, as an important electronic functional material, is widely used in integrated circuits, power devices, flexible electronics, and ceramic substrate metallization. Compared with precious metals such as silver and gold, copper has advantages such as high conductivity, low cost, and good resistance to electromigration, thus being considered one of the important candidate materials for achieving low-cost electronic manufacturing. However, when selectively sintering copper paste using lasers, its optical response characteristics in the near-infrared band become one of the key factors restricting the feasibility of the process.

[0003] In existing laser processing systems, near-infrared lasers with a wavelength of 1064 nm are widely used due to their high maturity, good stability, and low equipment cost. However, metallic copper has an extremely low absorption rate of laser energy in this wavelength band, typically less than 5%, with the incident laser energy mainly lost through reflection, making it difficult to effectively heat copper particles in a short time. This insufficient absorption is particularly pronounced under air atmosphere conditions, making it difficult for laser energy to accumulate in the powder layer, resulting in insufficient local temperature rise and incomplete sintering, thus limiting the application of near-infrared lasers in copper paste sintering.

[0004] To address the issue of insufficient near-infrared light absorption, existing technologies have attempted to improve the absorption capacity for 1064 nm lasers by introducing near-infrared absorbers such as carbon black into copper paste (CN112992468A). However, such methods typically rely on additional doping with high-absorbing components, which can easily disrupt the conductivity continuity and compositional uniformity of the copper paste system. Furthermore, under the instantaneous high temperature conditions of laser light, the oxidation resistance of the copper particles themselves is not improved, and there is still a significant risk of oxidation in air.

[0005] On the other hand, copper particles readily react with oxygen in the air during storage, processing, and sintering, forming a copper oxide layer on their surface. This oxide layer hinders contact and diffusion between particles, reduces the degree of densification during sintering, and further exacerbates the degradation of electrical conductivity. To address this, existing technologies have proposed methods to improve the oxidation resistance of copper particles through metal coating (such as silver (CN107252918A) or nickel (CN108411267B) coating) or the introduction of reducing additives (CN102737782B, CN104576103A). However, these methods are typically complex and rely heavily on inert or reducing atmospheres, failing to address the low absorption rate of copper materials in the near-infrared laser band and making them unsuitable for laser sintering applications in air atmospheres.

[0006] In summary, existing copper paste technologies typically address near-infrared light absorption or oxidation resistance separately at the material design level. However, they struggle to simultaneously achieve both efficient absorption of 1064 nm near-infrared laser light and stable oxidation resistance in an air atmosphere within the same material system. Therefore, there is an urgent need for a copper paste material that can synergistically enhance near-infrared light absorption and suppress high-temperature oxidation behavior within a single material structure to meet the application requirements of near-infrared laser sintering in an air atmosphere. Summary of the Invention

[0007] To address technical issues such as poor near-infrared light absorption and easy oxidation of copper particles, this invention discloses an air-atmosphere near-infrared laser sinterable copper paste and its preparation method. This copper paste can be directly written / selectively sintered with near-infrared laser in an air atmosphere to obtain copper conductor patterns with low sheet resistance and reliable adhesion. This provides a low-complexity, scalable metallization process route for ceramic (including Si3N4, AlN, Al2O3), flexible and other substrates.

[0008] The technical solution adopted by this invention is as follows:

[0009] Cu@glass material refers to glass-coated Cu particles, comprising a copper core surrounded by a Bi₂O₃–B₂O₃–ZnO glass shell. The Bi₂O₃–B₂O₃–ZnO content in the Cu@glass particles is 5%-20% by mass. The copper core has a particle size of 200 nm to 500 nm, a light absorption rate of ≥50% at a wavelength of 1064 nm, and an initial oxidation temperature of ≥250℃. The softening temperature of the Bi₂O₃–B₂O₃–ZnO glass shell is 350-400℃.

[0010] This technical solution employs a copper core coated with a Bi₂O₃–B₂O₃–ZnO glass shell, significantly improving the particles' oxidation resistance and near-infrared laser absorption efficiency. The interfacial optical modification caused by the glass coating creates a refractive index gradient layer between air, glass, and copper. Combined with the submicron shell thickness and surface micro-roughness, this generates multiple scattering / optical path enhancement and an effective medium effect at the particle layer scale, thereby significantly reducing specular reflection and enhancing effective absorption at 1064 nm. The absorbed energy is efficiently transferred to the copper-copper interface during glass softening and flow, promoting diffusion and binding. The Cu@glass particles with 10% glass coating exhibit an initial oxidation temperature of 294℃ and a near-infrared light absorptivity of 61.8%. This light absorptivity allows for stable binding and densification of the copper paste under near-infrared laser irradiation in an air atmosphere, resulting in a high-performance conductive film.

[0011] As a further improvement of the present invention, the Bi2O3–B2O3–ZnO glass shell layer accounts for 5%-10% of the mass fraction of Cu@glass particles.

[0012] As a further improvement of the present invention, in the Bi2O3–B2O3–ZnO glass shell, the mass percentages of Bi2O3, B2O3 and ZnO are 15-35%, 50-70% and 5-25%, respectively.

[0013] As a further improvement of the present invention, the average thickness of the Bi2O3–B2O3–ZnO glass shell is 14nm~35nm.

[0014] As a further improvement of the present invention, the volume average particle size D of the copper core is... 50 The average particle size D of the Cu@glass particles is 400-410 nm. 50 The wavelength is 410-440 nm.

[0015] This invention discloses a method for preparing the Cu@glass material as described above, characterized by comprising the following steps:

[0016] Step S1-1: Prepare Bi2O3–B2O3–ZnO glass precursor sol; the components of the glass precursor sol include bismuth nitrate, zinc nitrate, and boric acid;

[0017] Step S1-2: Disperse copper particles in ethanol to obtain a copper particle suspension;

[0018] Steps S1-3 involve mixing the glass precursor sol prepared in step S1-1 with a copper particle suspension, inducing gelation, and drying; then heat-treating at 380-420℃ for 0.5-2 hours in air to transform the glass precursor and densely coat the surface of the copper particles, obtaining Cu@glass particles. Further, heat-treating at 400℃ for 1 hour in air is performed.

[0019] As a further improvement of the present invention, in step S1-1, boric acid, zinc nitrate precursor solution and bismuth nitrate solution are added under stirring conditions to control the hydrolysis-condensation rate to obtain a transparent sol.

[0020] As a further improvement of the present invention, step S1-1 includes:

[0021] 1) Mix anhydrous ethanol and deionized water to obtain an ethanol precursor solution for later use;

[0022] 2) Dissolve boric acid in ethanol precursor solution, add zinc nitrate hexahydrate, and stir vigorously to obtain precursor solution A;

[0023] 3) Add an appropriate amount of bismuth nitrate pentahydrate to glycerol to obtain a transparent bismuth nitrate precursor B solution;

[0024] 4) Slowly add precursor A solution to bismuth nitrate precursor B solution and stir at room temperature for 1 hour to obtain a clear and transparent glass sol.

[0025] Furthermore, in step S1-1, the volume ratio of glycerol, deionized water, and anhydrous ethanol is 1:1:2, so that bismuth nitrate, zinc nitrate, and boric acid are fully dissolved in the system.

[0026] As a further improvement of the present invention, in steps S1-2, copper particles are dispersed in ethanol to prepare a copper particle suspension. Specifically, 5g of copper particles are mixed with 6-20ml of ethanol. Further, 5g of copper particles are mixed with 10ml of ethanol.

[0027] As a further improvement of the present invention, induced gelation includes heating in a water bath at a temperature of 55-65°C for 2-4 hours, followed by aging by standing for 12 hours. Further, the water bath temperature is 60°C, and the time is 3 hours.

[0028] This invention discloses an air-atmosphere near-infrared laser-sinterable antioxidant copper paste, comprising the following components and mass percentages: 70%–85% Cu@glass particles and 15%–30% organic carrier; wherein the Cu@glass particles are the Cu@glass material as described above. The organic carrier is a prior art organic carrier. Further, the organic carrier includes terpineol, ethyl acetate, ethyl cellulose, an antifoaming agent, and a silane coupling agent.

[0029] This invention discloses a method for preparing the air-atmosphere near-infrared laser-sinterable antioxidant copper paste as described above, comprising the following steps:

[0030] Step S1: Prepare Cu@glass particles;

[0031] Step S2: Mix Cu@glass particles with an organic carrier, disperse them to the target particle size and rheology by planetary stirring and ultrasonic stirring, heat treat at 75-85℃ for 4-8 hours, and then perform debinding treatment to obtain the air atmosphere near-infrared laser sinterable antioxidant copper paste.

[0032] The mass ratio of Cu@glass particles to organic carrier is 3-5:1. More specifically, the mass ratio of Cu@glass particles to organic carrier is 4:1.

[0033] This invention discloses the application of the air-atmosphere near-infrared laser sinterable antioxidant copper paste as described above, for obtaining a conductivity pattern on a substrate by near-infrared laser sintering in an air atmosphere.

[0034] As a further improvement of the present invention, the application of the air-atmosphere near-infrared laser sinterable antioxidant copper paste includes the following steps:

[0035] A copper paste pattern layer is formed on an insulating substrate using an air-atmosphere near-infrared laser sinterable antioxidant copper paste. The process involves scanning with a near-infrared laser of 800–1100 nm wavelength at a power of 5–30 W, a scanning speed of 10–1000 mm·s⁻¹, and a line spacing of 5–20 μm. This softens and flows the glass shell layer, providing instantaneous antioxidant shielding to the copper core, thereby achieving surface diffusion and binding of copper particles to obtain a conductive pattern. Further, a near-infrared laser of 1064 nm wavelength is used. Multiple repeated scans can be performed in the above steps, or a pre-curing process at 120°C can be combined.

[0036] Under near-infrared laser irradiation, the glass shell of the antioxidant copper paste softens first, then flows to form a transient oxygen shield, promoting copper-copper metallurgical bonding. When using a 1064 nm near-infrared laser, the powder layer's 1064 nm integrated absorptivity is ≥50%; with a film thickness of 10–20 μm, the sheet resistance of laser sintering in air is ≤100 mΩ / □.

[0037] As a further improvement of the present invention, the type of near-infrared laser is Nd:YAG near-infrared laser, and the material of the substrate is Si3N4, AlN, Al2O3, or glass.

[0038] This invention discloses an application of an article containing a copper conductor layer to obtain arbitrary conductive patterns on the surface by infrared laser direct writing. The copper conductor layer is obtained by near-infrared laser direct writing of an anti-oxidation copper paste that can be sintered in air as described above. The application of the article containing the copper conductor layer to obtain arbitrary conductive patterns on the surface by infrared laser direct writing includes metallization layers of ceramic substrates for power devices, module-level interconnects, sensing electrodes, antennas, resistor / heating films, or repair conductive paths.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects:

[0040] (1) By forming a glass coating layer on the surface of copper particles, the high reflectivity of copper to near-infrared light is reduced, the absorption ratio and photothermal conversion efficiency of light energy in the 800–1100 nm band (preferably 1064 nm) are improved, thereby reducing energy loss and enhancing energy coupling effect.

[0041] (2) The glass coating layer isolates and blocks oxygen from copper particles during storage and heating, inhibits the formation and thickening of oxide film, and reduces the risk of deterioration of conductivity and sintering obstruction caused by oxidation.

[0042] (3) Under conditions where no inert gas or reducing protective atmosphere is required, copper paste can be grown and the film can be densified under appropriate near-infrared laser process window, reducing the problem of insufficient local sintering or conductive failure caused by re-oxidation.

[0043] (4) The formed conductive pattern has a low sheet resistance and is conducive to improving the performance retention of the conductive pattern under conditions of adhesion, moisture and heat resistance and thermal cycling, thereby reducing the risk of failure of the conductive structure during service.

[0044] (5) This antioxidant copper paste is suitable for various substrates such as Si3N4, AlN, Al2O3 and glass. It has good adhesion stability and process compatibility, especially on insulating ceramic substrates, reducing the risk of peeling, cracking or resistance change caused by thermal mismatch or uneven distribution of glass phase. Attached Figure Description

[0045] Figure 1 This is a flowchart illustrating the preparation process of Cu@glass particles according to an embodiment of the present invention.

[0046] Figure 2 These are morphology images of Cu@glass particles at different stages according to an embodiment of the present invention; wherein, a) to d) are respectively after coating, after drying, after calcination, and after grinding.

[0047] Figure 3 These are surface morphologies of Cu@glass with different coating amounts and corresponding particle size distributions in embodiments of the present invention; wherein (a) to (c) are surface morphologies of Cu@glass with 5% coating amount at different magnifications, (d) is a particle size distribution of Cu@glass with 5% coating amount, (e) to (g) are surface morphologies of Cu@glass with 10% coating amount at different magnifications, (h) is a particle size distribution of Cu@glass with 10% coating amount, (i) to (k) are surface morphologies of Cu@glass with 20% coating amount at different magnifications, and (l) is a particle size distribution of Cu@glass with 20% coating amount.

[0048] Figure 4 These are the thermogravimetric analysis results of Cu@glass with different coating amounts in embodiments of the present invention.

[0049] Figure 5 These are particle light absorption rate curves of Cu@glass with different coating amounts according to embodiments of the present invention.

[0050] Figure 6 These are morphological images of the anti-oxidation copper paste after sintering with different laser powers according to embodiments of the present invention.

[0051] Figure 7This is a comparison of the electrical properties of the anti-oxidation copper paste after sintering with different laser powers according to embodiments of the present invention. Detailed Implementation

[0052] The preferred embodiments of the present invention will be described in further detail below.

[0053] Example 1

[0054] A Cu@glass material includes a copper core coated with a Bi2O3–B2O3–ZnO glass shell. In this embodiment, the Bi2O3–B2O3–ZnO glass shell accounts for 5% of the mass fraction of the Cu@glass powder. The mass percentages of Bi2O3, B2O3, and ZnO in the Bi2O3–B2O3–ZnO glass shell are 25%, 60%, and 15%, respectively. It is prepared using the following steps:

[0055] 1) Mix anhydrous ethanol and deionized water in a 2:1 ratio to form an ethanol precursor solution for later use.

[0056] 2) Dissolve boric acid in ethanol precursor solution, add zinc nitrate hexahydrate, and stir vigorously to obtain precursor solution A;

[0057] 3) Add an appropriate amount of bismuth nitrate pentahydrate to glycerol to obtain a transparent bismuth nitrate precursor solution B; wherein the amount of glycerol added is the same as the volume of deionized water.

[0058] 4) Slowly add A to B and stir at room temperature for 1 hour to obtain a clear and transparent glass sol;

[0059] 5) Add glass sol to a copper particle suspension prepared by dispersing 1g of submicron copper particles in 10mL of ethanol;

[0060] 6) Heat the copper particle suspension of glass sol in a 60°C water bath for 3 hours and let it stand for 12 hours to age;

[0061] 7) Calcination at 400℃ for 1 hour in air atmosphere.

[0062] Example 2

[0063] Based on Example 1, in this example, the Bi2O3–B2O3–ZnO glass shell layer accounts for 10% of the mass fraction of Cu@glass particles; in the Bi2O3–B2O3–ZnO glass shell layer, the mass percentages of Bi2O3, B2O3, and ZnO are 25%, 60%, and 15%, respectively.

[0064] The preparation method of this Cu@glass material is the same as in Example 1.

[0065] Example 3

[0066] Based on Example 1, in this example, the Bi2O3–B2O3–ZnO glass shell layer accounts for 20% of the mass fraction of Cu@glass particles; in the Bi2O3–B2O3–ZnO glass shell layer, the mass percentages of Bi2O3, B2O3, and ZnO are 25%, 60%, and 15%, respectively.

[0067] The preparation method of this Cu@glass material is the same as in Example 1.

[0068] Morphology images of Cu@glass particles at different stages in Example 1 are shown below. Figure 2 As shown, each stage consists of a spherical structure with a coating, and the coating process continues.

[0069] The Cu@glass samples with different coating thicknesses obtained in Examples 1-3 are shown in the following particle size distribution diagrams corresponding to their surface morphology. Figure 3 As shown, the copper particles are uniformly coated with glass particles. With the increase of glass content, the particle size generally shows an increasing trend. The average particle sizes of pure copper particles (submicron copper particles), Cu@glass particles with 5%, 10%, and 20% glass content are 405 nm, 419 nm, 424 nm, and 440 nm, respectively.

[0070] To verify the oxidation resistance of Cu@glass particles, DSC tests were performed on Cu@glass particles with different coating thicknesses from Examples 1 to 3, as well as pure copper particles. Figure 4 As shown, the thermogravimetric curves (TG) reveal that pure copper begins to oxidize at 121℃, while the oxidation temperatures of 10% and 20% glass-coated Cu@glass particles are 294℃ and 361℃, respectively, with the degree of oxidation gradually decreasing. This indicates that the Bi2O3-B2O3-ZnO glass-coated Cu@glass particles have excellent oxidation resistance.

[0071] The Cu@glass particles and pure copper particles from Examples 1 to 3 were tested using a UV-Vis-NIR spectrometer (taking 1064 nm as an example). Figure 5 As shown, the absorption rate of pure Cu particles for 1064nm wavelength light is only 0.96%, close to zero. The absorption rates of Cu@glass particles with 5%, 10%, and 15% coating for 1064nm wavelength light are 54.9%, 61.8%, and 67.1%, respectively. This demonstrates that altering the physical properties of the particles through the core-shell structure significantly improves their light absorption rate in the near-infrared region, providing a possibility for laser sintering of Cu@glass.

[0072] Example 4

[0073] The Cu@glass particles obtained in Examples 1 to 3 were used to prepare copper paste, and the steps included:

[0074] Cu@glass and an organic carrier were mixed in a 4:1 ratio and ultrasonically stirred for 2 minutes. This mixture was then repeated three times using a planetary mixer for 5 minutes followed by ultrasonic stirring for 2 minutes each time, to obtain a uniformly mixed antioxidant Cu@glass conductive copper paste. In this example, 0.4 g of Cu@glass particles and 0.1 g of organic solvent were used. The organic carrier used was one or more of terpineol, ethyl cellulose, ethyl acetate, and defoamer.

[0075] The obtained copper paste was subjected to laser sintering experiments, specifically including:

[0076] By adjusting parameters such as printing speed, squeegee pressure, and plate spacing in screen printing, a pattern with a film thickness of 15-20μm is printed on a silicon nitride substrate. To ensure that the Cu@glass particles in the conductive paste can pass through the screen mesh smoothly, and to ensure that the paste has an appropriate amount of unprinted material during the printing process, a 200-mesh screen is selected for printing.

[0077] During the sintering process, the presence of organic carriers will hinder the solid-phase diffusion between Cu@glass particles, which is not conducive to the formation of a dense, high-performance copper film. Therefore, a debinding process is required before sintering, i.e., holding at 80℃ for 360 minutes.

[0078] Finally, the laser sintering performance of the antioxidant Cu@glass conductive copper paste on Si3N4 ceramic substrates was verified. This included:

[0079] Under air atmosphere and 1064nm laser conditions, parameters were selected as follows: laser power 5-15W, laser frequency 1MHz, adjacent line spacing 5-15μm, scanning speed 10mm / s, and 1 scan. Cu@glass copper paste printed on a Si3N4 ceramic substrate was then processed. In this embodiment, near-infrared laser sintering was performed using powers of 5W, 10W, and 15W, with adjacent line spacings of 5μm, 10μm, and 15μm, respectively. The resulting sintering morphology images are shown below. Figure 6 As shown, the results indicate that a copper layer with a smooth surface and good electrical properties can be obtained under conditions of 15W laser power and 15μm spacing between adjacent lines, thus achieving metallization of silicon nitride ceramic surfaces.

[0080] The electrical properties of the sintered samples were tested, and the results are as follows: Figure 7As shown, the larger the spacing between adjacent lines, the smaller the sheet resistance; the higher the laser power, the smaller the sheet resistance. Within a certain range, the higher the laser power, the better the melting of the copper metal, which is beneficial to improving the conductivity of the sintered body. If the spacing between adjacent lines in the laser scan is too small, the tension caused by the Marangoni effect will lead to a decrease in the uniformity of the metallization layer in the horizontal direction, that is, the thickness fluctuation of the conductive layer will lead to an increase in the overall resistance.

[0081] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A Cu@glass material, characterized by: It includes a copper core, which is coated with a Bi2O3–B2O3–ZnO glass shell. The Bi2O3–B2O3–ZnO glass shell accounts for 5%-20% of the mass fraction of Cu@glass particles. The copper core has a particle size of 200 nm to 500 nm, a light absorption rate of ≥50% at a wavelength of 1064 nm, and an initial oxidation temperature of ≥250℃.

2. The Cu@glass material according to claim 1, characterized by: The Bi2O3–B2O3–ZnO glass shell layer accounts for 5%-10% of the mass fraction of Cu@glass particles; in the Bi2O3–B2O3–ZnO glass shell layer, the mass percentages of Bi2O3, B2O3, and ZnO are 15-35%, 50-70%, and 5-25%, respectively.

3. The Cu@glass material according to claim 2, characterized by: The average thickness of the Bi2O3–B2O3–ZnO glass shell is 14 nm to 35 nm; the average volume diameter of the copper core is 400-410 nm; and the average particle size of the Cu@glass particles is 410-440 nm.

4. The method for preparing Cu@glass material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1-1: Prepare Bi2O3–B2O3–ZnO glass precursor sol; the components of the glass precursor sol include bismuth nitrate, zinc nitrate, and boric acid; Step S1-2: Disperse copper particles in ethanol to obtain a copper particle suspension; Steps S1-3: The glass precursor sol prepared in step S1-1 is mixed with the copper particle suspension, induced to gel, and dried; then heat-treated at 380-420℃ for 0.5-2h in air atmosphere to transform the glass precursor and densely coat the surface of the copper particles to obtain Cu@glass particles.

5. An air atmosphere near-infrared laser sinterable, oxidation resistant copper paste, characterized in that: The components and their mass percentages are as follows: 70%–85% Cu@glass particles and 15%–30% organic carrier, wherein the Cu@glass particles are made of Cu@glass material as described in any one of claims 1 to 3.

6. A process for preparing the air atmosphere near-infrared laser sinterable oxidation resistant copper paste as claimed in claim 5, characterized by: Includes the following steps: Step S1: Prepare Cu@glass particles; Step S2: Mix Cu@glass particles with an organic carrier, disperse them to the target particle size and rheology by planetary stirring and ultrasonic stirring, and heat treat at 75-85℃ for 4-8 hours to obtain the air-atmosphere near-infrared laser sinterable antioxidant copper paste.

7. The use of infrared laser direct writing to obtain a surface arbitrary conductive pattern, characterized in that: The copper conductor layer is obtained by direct-writing conductive patterns in air using an air-atmosphere near-infrared laser sinterable antioxidant copper paste as described in claim 5 or 6; the applications include metallization layers on ceramic substrates for power devices, module-level interconnects, sensing electrodes, antennas, resistive / heating films, or repair conductive paths.

Images