Nano copper paste as well as preparation method and application thereof
By preparing a nano-copper paste with multi-scale nano-copper particles and an organic carrier composite solvent, the reliability problem of tin-based alloy solder in high-temperature environments was solved, and a low-temperature sintering packaging interconnect structure was realized, thereby improving the packaging interconnect performance of high-power chips.
Patent Information
- Application Number
- CN202511053367.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-30
- Publication Date
- 2025-10-21
AI Technical Summary
Existing tin-based alloy solders are prone to reliability issues such as excessive IMC growth, mismatch in thermal expansion coefficients, and porosity under high-temperature environments, making it difficult to meet the extreme environmental requirements of aerospace, new energy vehicles, and other fields.
Nano-copper paste was prepared by grinding a mixture of multi-scale nano-copper particles and an organic carrier composite solvent. During the sintering process, the organic carrier was volatilized or decomposed in stages, which inhibited the formation of copper oxides and promoted the sintering diffusion of particles, resulting in a tightly packed structure.
A packaging interconnect structure sintered at low temperatures below 240℃ was achieved, exhibiting high strength and reliability. As a substitute for silver solder paste and tin-based alloy solder, it improves the packaging interconnect performance of high-power chips.
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Figure CN120815971A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor packaging interconnection technology, and in particular to a nano copper paste and a preparation method and application thereof. Background Art
[0002] With the rapid development of aerospace, new energy vehicles, rail transit, and other application fields, electronic equipment is often exposed to extreme environments such as high temperature, high pressure, and thermal shock. However, the currently widely used tin-based alloy solders have low melting points and poor thermal stability. When operating in high-temperature environments, they are prone to reliability issues such as excessive IMC growth, thermal expansion coefficient mismatch, and voiding. Therefore, to cope with these more demanding service environments, it is crucial to develop advanced alternative materials with high temperature resistance and high thermal conductivity for power chip interconnects.
[0003] In view of this, the present invention is proposed. Summary of the Invention
[0004] The purpose of the present invention is to provide a nano copper paste and a preparation method and application thereof, so as to solve or improve the above technical problems.
[0005] The present invention can be achieved like this: In a first aspect, the present invention provides a method for preparing a nano copper paste, comprising the following steps: grinding a mixture of multi-scale nano copper particles and an organic carrier composite solvent; The particle size of the multi-scale nano-copper particles is 10 nm to 200 nm, wherein the number ratio of the nano-copper particles with a particle size of 10 nm to 40 nm, the nano-copper particles with a particle size of 40 nm to 80 nm, and the nano-copper particles with a particle size of 80 nm to 200 nm is (4 to 10): (2 to 6): 1; The organic carrier composite solvent comprises a reducing organic solvent, a carrier solvent and an organic active agent.
[0006] In an optional embodiment, the mass ratio of the multi-scale nano-copper particles to the organic carrier composite solvent is 7:3 to 9:1.
[0007] In an optional embodiment, the multi-scale nano-copper particles are prepared from a copper compound by a one-step chemical reduction method.
[0008] In an optional embodiment, the preparation of multi-scale nano-copper particles includes: mixing a copper salt solution with a reducing solution to obtain a reaction solution; stirring the reaction solution until the color of the reaction solution no longer changes; Among them, copper salt solution is obtained by mixing copper compound with water; The reducing solution includes an organic solvent, a reducing agent, an antioxidant and a regulator.
[0009] In an optional embodiment, the preparation of multi-scale nano-copper particles further includes at least one of the following features: Feature 1: The temperature of the reaction solution is maintained at 70°C to 100°C; Feature 2: The reaction solution is in a water bath environment; Feature 3: The reaction solution is subjected to solid-liquid separation, and the solid after solid-liquid separation is washed.
[0010] In an optional embodiment, solid-liquid separation is performed by centrifugation, wherein the centrifugal speed is 4000 r / min to 8000 r / min and the centrifugal time is 3 min to 5 min; In an optional embodiment, anhydrous ethanol is used for washing, and the number of washing times is 2 to 4 times.
[0011] In an optional embodiment, the copper salt solution includes at least one of the following characteristics: Feature 4: The copper compound includes at least one of copper formate, copper acetate, copper oxalate, copper citrate, copper sulfate and copper chloride; Feature 5: The concentration of the copper salt solution is 0.5 mol / L~1 mol / L.
[0012] In an optional embodiment, the reducing liquid includes at least one of the following characteristics: Feature 6: In the reducing solution, the mass concentration ratio of the reducing agent, antioxidant, and regulator is (15-40):(4-10):(1-5); Feature 7: The organic solvent is a polyol; preferably, the polyol includes at least one of ethylene glycol, propylene glycol, glycerol, diethylene glycol, butylene glycol and polyethylene glycol; Feature 8: The reducing agent includes at least one of sodium phosphite, potassium tartrate, sodium sulfite and sodium borohydride; Feature 9: The antioxidant includes at least one of ascorbic acid and glucose; Feature 10: The regulator is a long carbon chain organic acid having ≥4 carbon atoms. Preferably, the regulator comprises at least one of succinic acid, glutaric acid, suberic acid, adipic acid, pimelic acid, tartaric acid, oleic acid, and lauric acid. Feature 11: The reducing solution is obtained by adding a reducing agent, an antioxidant, and a regulator into an organic solvent in sequence and stirring and dissolving them.
[0013] In an optional embodiment, the organic carrier composite solvent includes at least one of the following characteristics: Feature 12: The mass ratio of the reducing organic solvent, the carrier solvent and the organic active agent is (5-25):(4-24):1; Feature 13: The reducing organic solvent includes at least one of ethylene glycol, propylene glycol, glycerol, diethylene glycol, neopentyl glycol, polyethylene glycol, terpineol, and octanol; Feature 14: The carrier solvent includes a glycol ether, preferably, the carrier solvent includes at least one of ethylene glycol methyl ether, diethylene glycol monohexyl ether, ethylene glycol dimethyl ether, ethylene glycol butyl ether, ethylene glycol diglycidyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether and dipropylene glycol butyl ether; Feature 15: The organic surfactant is a short-chain carboxylic acid having 2 to 6 carbon atoms. Preferably, the organic surfactant includes at least one of lactic acid, glycolic acid, oxalic acid, malonic acid, citric acid and tartaric acid.
[0014] In a second aspect, the present invention provides a nano copper paste, which is prepared by the preparation method of any one of the aforementioned embodiments.
[0015] In a third aspect, the present invention provides a use of the nano copper paste according to the aforementioned embodiment in a package interconnection structure.
[0016] In a fourth aspect, the present invention provides a package interconnect structure, which is obtained by hot-pressing and sintering a pure copper substrate, the nano-copper paste of the aforementioned embodiment, and a pure copper sheet or a copper-plated silicon-based chip.
[0017] In an optional embodiment, the temperature of the hot pressing sintering is 200° C. to 300° C., the time of the hot pressing sintering is no more than 30 minutes, and the pressure of the hot pressing sintering is 5 MPa to 20 MPa.
[0018] In an optional embodiment, before hot pressing and sintering, preheating is performed at 80° C. to 150° C. for 2 min to 10 min.
[0019] The beneficial effects of the present invention include: The nano copper paste provided by the present invention is obtained by grinding a mixture of multi-scale nano copper particles and an organic carrier composite solvent. The multi-scale nano copper particles have long-term storage stability, and the addition of a reducing solution can effectively control the oxygen content of the preparation environment and form an organic protective layer, so that the prepared multi-scale nano copper particles have excellent antioxidant properties. The compounded organic carrier composite solvent exhibits step-by-step volatilization or decomposition during the sintering process, which can effectively inhibit the formation of copper oxides and promote the reduction of the original copper oxides on the particle surface. The fresh copper atoms produced by the decomposition further promote the sintering and diffusion of the multi-scale nano copper particles, thereby effectively promoting the overall sintering process and reducing the process requirements and preparation costs of the nano copper paste sintering.
[0020] This nano-copper paste can be sintered at temperatures below 240°C to create packaging interconnect structures. The resulting interconnects exhibit high strength and reliability, making it a viable alternative to silver solder paste and traditional tin-based alloy solders. The copper particles in this nano-copper paste exhibit a gradient, multi-scale distribution. Small copper particles effectively fill and accumulate in the pores between larger copper particles, forming a compact stacking structure. This offers significant advantages for low-temperature sintering, significantly improving the density of the low-temperature sintered interconnect layer and holding great promise for high-power chip packaging interconnects. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.
[0022] Figure 1 This is a SEM image of the multi-scale nano-copper particles prepared in Example 1 of the present invention; Figure 2 This is a statistical diagram of the particle size distribution of multi-scale nano-copper particles prepared in Example 1 of the present invention; Figure 3 1 is a graph showing the shear strength test results of the interconnecting joint in Example 1 of the present invention; Figure 4 This is a SEM image of the cross-section of the package interconnect structure prepared in Example 1 of the present invention. DETAILED DESCRIPTION
[0023] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.
[0024] The nano copper paste provided by the present invention and its preparation method and application are described in detail below.
[0025] The inventors proposed that the small size effect of metal nanoparticles is expected to achieve low-temperature interconnection, but the size effect also gives nano-copper particles a stronger tendency to oxidize. Oxides are very likely to appear during the preparation and sintering process under ambient conditions, thereby hindering the effective sintering of nano-copper particles at low temperatures. In addition, the porosity of the sintered body of single-sized copper particles is large, and the interconnection reliability is relatively poor.
[0026] In view of this, the present invention provides a nano copper paste, and the preparation method thereof may include the following steps: grinding and stirring a mixture of multi-scale nano copper particles and an organic carrier composite solvent.
[0027] The multi-scale nano-copper particles exhibit long-term storage stability. The addition of a reducing solution effectively controls the oxygen content in the preparation environment and forms an organic protective layer, resulting in excellent antioxidant properties. The compounded organic carrier and solvent exhibit a step-wise volatilization or decomposition during the sintering process, effectively inhibiting the formation of copper oxides and promoting the reduction of existing copper oxides on the particle surface. The fresh copper atoms produced by the decomposition further promote the sintering and diffusion of the multi-scale nano-copper particles, thereby effectively accelerating the overall sintering process and reducing the process requirements and preparation costs of the nano-copper paste.
[0028] In some optional embodiments, the mass ratio of the multi-scale nano-copper particles to the organic carrier composite solvent can be 7:3 to 9:1, such as 7:3, 7.5:2.5, 8:2, 8.5:1.5 or 9:1, or other values within the range of 7:3 to 9:1.
[0029] If the mass ratio of multi-scale nano-copper particles to organic carrier composite solvent is lower than 7:3 (such as 6:4 or 5:5, etc.), it is not conducive to the sintering and densification of nano-copper paste; if the mass ratio of multi-scale nano-copper particles to organic carrier composite solvent is higher than 9:1 (such as 9.5:0.5, etc.), it is not conducive to the printing and sintering of nano-copper paste.
[0030] The particle size of the multi-scale nano-copper particles is 10nm~200nm, wherein the number ratio of nano-copper particles with a particle size of 10nm~40nm, nano-copper particles with a particle size of 40nm~80nm, and nano-copper particles with a particle size of 80nm~200nm is (4~10):(2~6):1.
[0031] In some optional embodiments, the ratio of the number of nano-copper particles with a particle size of 10 nm to 40 nm to the number of nano-copper particles with a particle size of 80 nm to 200 nm can be 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, or other values within the range of (4 to 10): 1. The ratio of the number of nano-copper particles with a particle size of 40 nm to 80 nm to the number of nano-copper particles with a particle size of 80 nm to 200 nm can be 2:1, 3:1, 4:1, 5:1, or 6:1, or other values within the range of (2 to 6): 1.
[0032] Too few nano-copper particles with a particle size of 10nm-40nm are not conducive to low-temperature sintering and diffusion of the nano-copper particles; too many nano-copper particles with a particle size of 10nm-40nm are not conducive to the long-term stable storage of the nano-copper paste. Too few nano-copper particles with a particle size of 40nm-80nm are not conducive to the formation of a dense stacking structure; too many nano-copper particles with a particle size of 40nm-80nm are not conducive to the densification of sintering pores.
[0033] In some optional embodiments, multi-scale nano-copper particles are prepared from copper compounds by a one-step chemical reduction method, which is simple, rapid, and low-cost.
[0034] For example, the preparation of the multi-scale nano-copper particles may include: mixing a copper salt solution with a reducing solution to obtain a reaction solution; and stirring the reaction solution (the stirring speed may be, for example, 500 rpm to 700 rpm) until the color of the reaction solution no longer changes.
[0035] Wherein, the copper salt solution is obtained by mixing a copper compound with water. For example, the copper compound can be added to deionized water and stirred at 60°C to 80°C to accelerate its dissolution to form a copper salt solution. The copper compound can illustratively but not limitatively include at least one of copper formate, copper acetate, copper oxalate, copper citrate, copper sulfate and copper chloride. The concentration of the copper salt solution can be 0.5mol / L~1mol / L, such as 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L or 1mol / L, etc., or other values within the range of 0.5mol / L~1mol / L.
[0036] The reducing solution may include an organic solvent, a reducing agent, an antioxidant, and a regulator.
[0037] In some optional embodiments, the organic solvent may be a polyol. Optionally, the polyol may illustratively but not limitatively include at least one of ethylene glycol, propylene glycol, glycerol, diethylene glycol, butylene glycol, and polyethylene glycol.
[0038] In some optional embodiments, the reducing agent may illustratively but not limitatively include at least one of sodium phosphite, potassium tartrate, sodium sulfite and sodium borohydride.
[0039] In some optional embodiments, the antioxidant may illustratively but not limitedly include at least one of ascorbic acid and glucose.
[0040] In some optional embodiments, the regulator can be a long-chain organic acid having ≥4 carbon atoms. Alternatively, the regulator can include, by way of example but not limitation, at least one of succinic acid, glutaric acid, suberic acid, adipic acid, pimelic acid, tartaric acid, oleic acid, and lauric acid. The regulator can be used to adjust the morphology of the multi-scale nano-copper particles and the pH of the reaction solution.
[0041] In some optional embodiments, in the reducing solution, the mass concentration ratio of the reducing agent, the antioxidant, and the regulating agent can be (15-40): (4-10): (1-5). By controlling the mass concentration ratio of the reducing agent, the antioxidant, and the regulating agent within the above range, the particle size of the nano-copper particles can be made to present a multi-scale distribution. It should be noted that in the above-mentioned reducing solution, the reducing agent and the antioxidant must be used simultaneously. If only the reducing agent or the antioxidant is used, it is not conducive to the controllable preparation of multi-scale nano-copper particles.
[0042] In some optional embodiments, the reducing solution is prepared by sequentially adding a reducing agent, an antioxidant, and a regulating agent to an organic solvent and stirring until completely dissolved. The stirring speed may be, for example, 500 r / min to 700 r / min, such as 500 r / min, 550 r / min, 600 r / min, 650 r / min, or 700 r / min, or other values within the range of 500 r / min to 700 r / min.
[0043] The nano-copper particles prepared by the above method are distributed in multiple scales and are irregularly spherical. They are stable in storage and not easily oxidized. They can be sintered at a low temperature below 240°C to prepare package interconnection structures.
[0044] In some optional embodiments, the organic carrier composite solvent includes a reducing organic solvent, a carrier solvent, and an organic active agent.
[0045] Among them, the role of the reducing organic solvent is mainly to enhance the self-reduction ability of the sintering environment, the role of the carrier solvent is mainly to provide good rheological properties for printing and sintering, and the role of the organic active agent is mainly to remove the surface oxide of the nano-copper particles and activate the surface atoms of the nano-copper particles.
[0046] In some optional embodiments, the mass ratio of the reducing organic solvent, the carrier solvent and the organic active agent can be (5-25):(4-24):1.
[0047] The mass ratio of the reducing organic solvent to the organic active agent can be 5:1, 8:1, 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, or 25:1, or other values within the range of (5 to 25):1. The mass ratio of the carrier solvent to the organic active agent can be 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, or 24:1, or other values within the range of (4 to 24):1.
[0048] In some optional embodiments, the reducing organic solvent may illustratively but not limitatively include at least one of ethylene glycol, propylene glycol, glycerol, diethylene glycol, neopentyl glycol, polyethylene glycol, terpineol, and octanol.
[0049] In some optional embodiments, the carrier solvent includes a glycol ether. Alternatively, the carrier solvent may illustratively but not limitatively include at least one of ethylene glycol methyl ether, diethylene glycol monohexyl ether, ethylene glycol dimethyl ether, ethylene glycol butyl ether, ethylene glycol diglycidyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, and dipropylene glycol butyl ether. The carrier solvent is used to adjust the viscosity of the nano copper paste and to cause the decomposition temperature of the organic carrier composite solvent to present a gradient change.
[0050] In some optional embodiments, the organic active agent is a short-chain carboxylic acid having 2 to 6 carbon atoms. Alternatively, the organic active agent may illustratively but not limitatively include at least one of lactic acid, glycolic acid, oxalic acid, malonic acid, citric acid, and tartaric acid.
[0051] The present invention uses short-chain carboxylic acid as the organic active agent, which has the advantages of being easy to decompose and having a single and volatile decomposition product compared to long-chain carboxylic acid.
[0052] In some optional embodiments, the temperature of the reaction solution is maintained at 70°C~100°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, or other values within the range of 70°C~100°C.
[0053] If the temperature of the reaction solution is lower than 70°C, the reaction rate is too slow, which is not conducive to the formation of multi-scale nano-copper particles; if the temperature of the reaction solution is higher than 100°C, the reaction rate is too fast, which is not conducive to the stable dispersion of nano-copper particles.
[0054] In some optional embodiments, the reaction solution is in a water bath environment.
[0055] Furthermore, the reaction solution is subjected to solid-liquid separation, and the solid after solid-liquid separation is washed.
[0056] In some optional embodiments, solid-liquid separation can be performed by centrifugation. The centrifugal speed can be 4000 r / min to 8000 r / min, such as 4000 r / min, 4500 r / min, 5000 r / min, 5500 r / min, 6000 r / min, 6500 r / min, 7000 r / min, 7500 r / min, or 8000 r / min, or other values within the range of 4000 r / min to 8000 r / min. The centrifugal time can be 3 min to 5 min, such as 3 min, 3.5 min, 4 min, 4.5 min, or 5 min, or other values within the range of 3 min to 5 min.
[0057] In some optional embodiments, anhydrous ethanol can be used for washing. The number of washing times can be, for example, 2 to 4 times, such as 2 times, 3 times or 4 times.
[0058] As mentioned above, the preparation cost of the nano copper paste provided by the present invention is relatively low while ensuring the excellent electrical conductivity and thermal conductivity of the material. In addition, the preparation method is simple to operate and the materials used are green and environmentally friendly.
[0059] Correspondingly, the present invention also provides a nano copper paste, which is prepared by the above preparation method.
[0060] This nano-copper paste can be sintered at temperatures below 240°C to create packaging interconnect structures. The resulting interconnects exhibit high strength and reliability, making it a viable alternative to silver solder paste and traditional tin-based alloy solders. The copper particles in this nano-copper paste exhibit a gradient, multi-scale distribution. Small copper particles effectively fill and accumulate in the pores between larger copper particles, forming a compact stacking structure. This offers significant advantages for low-temperature sintering, significantly improving the density of the low-temperature sintered interconnect layer and holding great promise for high-power chip packaging interconnects.
[0061] In addition, the present invention also provides an application of the nano copper paste in a packaging interconnection structure.
[0062] Correspondingly, the present invention also provides a package interconnection structure, which is obtained by hot pressing and sintering a pure copper substrate, a nano copper paste, and a pure copper sheet or a copper-plated silicon-based chip.
[0063] For example, nano-copper paste can be printed on a pure copper substrate, a copper-plated silicon-based chip or a pure copper sheet can be lightly attached to the printed nano-copper paste, and a package interconnection structure can be formed through a hot pressing and sintering process.
[0064] In some optional embodiments, the hot-pressing sintering temperature may be 200° C. to 300° C., such as 200° C., 250° C., or 300° C., or other values within the range. The hot-pressing sintering time may not exceed 30 minutes, such as 30 minutes, 25 minutes, 20 minutes, 15 minutes, 10 minutes, or 5 minutes. The hot-pressing sintering pressure may be 5 MPa to 20 MPa, such as 5 MPa, 10 MPa, 15 MPa, or 20 MPa, or other values within the range.
[0065] In some optional embodiments, before hot pressing and sintering, preheating may be performed at 80°C to 150°C (such as 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, etc.) for 2 min to 10 min (such as 2 min, 5 min, 8 min or 10 min, etc.).
[0066] The features and performance of the present invention are further described in detail below with reference to the embodiments.
[0067] Example 1 This embodiment provides a multi-scale low-temperature sintered nano-copper paste for packaging interconnection, the preparation of which includes the following steps: S1: Preparation of multi-scale nano-copper particles.
[0068] Using ethylene glycol as the organic solvent, sodium hypophosphite as the reducing agent, ascorbic acid as the antioxidant, and suberic acid as the regulating agent, sodium hypophosphite, ascorbic acid, and suberic acid were sequentially added to the ethylene glycol and stirred (at 600 rpm) until completely dissolved to form a reducing solution. The mass concentration ratio of sodium hypophosphite, ascorbic acid, and suberic acid was 22:6:4. Copper acetate was used as the copper compound, and copper acetate was added to deionized water, and stirred at 60° C. to accelerate its dissolution, thereby forming a copper salt solution with a concentration of 0.5 mol / L.
[0069] A copper salt solution was added to a reducing solution to form a reaction solution. The reaction solution was maintained at 90° C. in a water bath and mechanically stirred at 600 rpm until the color of the reaction solution no longer changed. The solution was centrifuged at 5000 rpm for 4 minutes and washed twice with anhydrous ethanol to obtain multi-scale nano-copper particles.
[0070] S2: preparing an organic carrier composite solvent.
[0071] Ethylene glycol is used as a reducing organic solvent, diethylene glycol monohexyl ether is used as a carrier solvent, and lactic acid is used as an organic active agent; ethylene glycol, diethylene glycol monohexyl ether and lactic acid are uniformly mixed to form an organic carrier composite solvent; wherein the mass ratio of ethylene glycol, diethylene glycol monohexyl ether and lactic acid is 10:9:1.
[0072] S3: preparing nano copper paste.
[0073] The multi-scale nano-copper particles and the organic carrier composite solvent were fully ground and stirred in a mass ratio of 8:2 to form a nano-copper paste.
[0074] Example 2 The difference between this embodiment and embodiment 1 is that: In S1, the reducing agent is sodium sulfite and the regulating agent is oleic acid.
[0075] The reaction solution was maintained at 80° C. in a water bath environment; the centrifugal speed was 6000 r / min.
[0076] In S2, the carrier solvent is ethylene glycol methyl ether, and the organic active agent is malonic acid. In S3, the multi-scale nano-copper particles and the organic carrier composite solvent are fully ground and stirred in a mass ratio of 7:3 to form a nano-copper paste.
[0077] Example 3 The difference between this embodiment and embodiment 1 is that: In S1, glucose is used as an antioxidant, succinic acid is used as a regulator, and copper formate is used as a copper compound.
[0078] In S2, the carrier solvent is ethylene glycol methyl ether.
[0079] Example 4 The difference between this embodiment and embodiment 1 is that: In S1, the mass concentration ratio of sodium hypophosphite, ascorbic acid and suberic acid is 22:6:1.
[0080] Example 5 This embodiment provides a multi-scale low-temperature sintered nano-copper paste for packaging interconnection, the preparation of which includes the following steps: S1: Preparation of multi-scale nano-copper particles.
[0081] Using propylene glycol as the organic solvent, potassium tartrate as the reducing agent, ascorbic acid as the antioxidant, and tartaric acid as the regulating agent, potassium tartrate, ascorbic acid, and tartaric acid are sequentially added to the propylene glycol and stirred until completely dissolved to form a reducing solution. The mass concentration ratio of potassium tartrate, ascorbic acid, and tartaric acid is 15:4:1.
[0082] Copper oxalate was used as the copper compound, and the copper oxalate was added to deionized water, and stirred at 70° C. to accelerate dissolution, thereby forming a copper salt solution with a concentration of 1 mol / L.
[0083] A copper salt solution was added to a reducing solution to form a reaction solution. The reaction solution was maintained at 70° C. in a water bath and mechanically stirred at 600 rpm until the color of the reaction solution no longer changed. The solution was centrifuged at 4000 rpm for 5 minutes and washed three times with anhydrous ethanol to obtain multi-scale nano-copper particles.
[0084] S2: preparing an organic carrier composite solvent.
[0085] Propylene glycol is used as a reducing organic solvent, ethylene glycol diglycidyl ether is used as a carrier solvent, and oxalic acid is used as an organic active agent; propylene glycol, ethylene glycol diglycidyl ether and oxalic acid are uniformly mixed to form an organic carrier composite solvent; wherein the mass ratio of propylene glycol, ethylene glycol diglycidyl ether and oxalic acid is 5:4:1.
[0086] S3: preparing nano copper paste.
[0087] The multi-scale nano-copper particles and the organic carrier composite solvent are fully ground and stirred in a mass ratio of 7:3 to form a nano-copper paste.
[0088] Example 6 This embodiment provides a multi-scale low-temperature sintered nano-copper paste for packaging interconnection, the preparation of which includes the following steps: S1: Preparation of multi-scale nano-copper particles.
[0089] Using butanediol as the organic solvent, sodium borohydride as the reducing agent, ascorbic acid as the antioxidant, and lauric acid as the regulating agent, sodium borohydride, ascorbic acid, and lauric acid are sequentially added to butanediol and stirred until completely dissolved to form a reducing solution. The mass concentration ratio of sodium borohydride, ascorbic acid, and lauric acid is 40:10:5.
[0090] Copper chloride was used as the copper compound, and the copper chloride was added to deionized water, and stirred at 80° C. to accelerate its dissolution, thereby forming a copper salt solution with a concentration of 0.5 mol / L.
[0091] A copper salt solution was added to a reducing solution to form a reaction solution. The reaction solution was maintained at 100° C. in a water bath environment and mechanically stirred at a speed of 600 r / min until the color of the reaction solution no longer changed. The solution was centrifuged at 8000 r / min for 3 minutes and washed four times with anhydrous ethanol to obtain multi-scale nano-copper particles.
[0092] S2: preparing an organic carrier composite solvent.
[0093] Polyethylene glycol is used as a reducing organic solvent, propylene glycol butyl ether is used as a carrier solvent, and tartaric acid is used as an organic active agent; polyethylene glycol, propylene glycol butyl ether and tartaric acid are uniformly mixed to form an organic carrier composite solvent; wherein the mass ratio of polyethylene glycol, propylene glycol butyl ether and tartaric acid is 25:24:1.
[0094] S3: preparing nano copper paste.
[0095] The multi-scale nano-copper particles and the organic carrier composite solvent were fully ground and stirred in a mass ratio of 9:1 to form a nano-copper paste.
[0096] Comparative Example 1 The difference between this comparative example and Example 1 is that the multi-scale nano-copper particles are replaced by nano-copper particles of a single scale range, specifically a scale of 10 nm to 40 nm.
[0097] Comparative Example 2 The difference between this comparative example and Example 1 is that the reducing solution does not contain an antioxidant.
[0098] Test Example 1 The morphology and particle size of the multi-scale nanoparticles prepared in each embodiment and comparative example were compared, and some of the results are as follows: A. The SEM image of the multi-scale nano-copper particles prepared in Example 1 is shown in FIG1 . Figure 1 It can be seen that the multi-scale nano-copper particles prepared in this embodiment present an irregular spherical shape with multi-scale continuous distribution, and the particle size thereof is 20 nm to 140 nm.
[0099] The particle size distribution of the multi-scale nano copper particles prepared in Example 1 is as follows: Figure 2 As shown, the number ratio of 20nm~40nm, 40nm~80nm, and 80nm~140nm is 6:2:1.
[0100] The multi-scale nano-copper particles prepared in Example 1 have an effective storage period of more than 20 days under ambient conditions.
[0101] It should be noted that the effective storage period is determined as follows: multi-scale nano-copper particles stored for x days are prepared into a nano-copper paste and sintered at 200°C. If the XRD diffraction pattern corresponding to the sintered product shows a diffraction peak of copper oxide, it is judged to be unqualified, that is, the multi-scale nano-copper particles cannot be stored for x days.
[0102] B. The particle size distribution of the multi-scale nano-copper particles prepared in Example 2 is 10 nm to 140 nm, wherein the number ratio of 10 nm to 40 nm, 40 nm to 80 nm, and 80 nm to 140 nm is 6:2:1.
[0103] The multi-scale nano-copper particles prepared in Example 2 have an effective storage period of up to 20 days under ambient conditions.
[0104] C. The multi-scale nano-copper particles prepared in Example 3 have a particle size distribution of 20 nm to 160 nm, wherein the number ratio of 20 nm to 40 nm, 40 nm to 80 nm, and 80 nm to 140 nm is 6:3:1.
[0105] The multi-scale nano-copper particles prepared in Example 3 have an effective storage period of more than 20 days under ambient conditions.
[0106] D. The particle size of the multi-scale nano-copper particles prepared in Example 4 is 30 nm to 200 nm, wherein the number ratio of 30 nm to 40 nm, 40 nm to 80 nm, and 80 nm to 200 nm is 4:6:1.
[0107] The multi-scale nano-copper particles prepared in Example 4 have an effective storage period of up to 25 days under ambient conditions.
[0108] E. The nano-copper particles of a single size range prepared in Comparative Example 1 have a specific size range of 10 nm to 40 nm.
[0109] The nano-copper particles of a single size range prepared in Comparative Example 1 have an effective storage period of up to 14 days under ambient conditions.
[0110] F. The particle size of the multi-scale nano-copper particles prepared in Comparative Example 2 is 30 nm to 200 nm, wherein the number ratio of 30 nm to 40 nm, 40 nm to 80 nm, and 80 nm to 200 nm is 5:4:1.
[0111] The multi-scale nano-copper particles prepared in Comparative Example 2 have an effective storage period of up to 5 days under ambient conditions.
[0112] Test Example 2 The nano copper pastes prepared in the examples and comparative examples were used to realize package interconnection. The shear strength test of the obtained package interconnection joints was performed. The test results are as follows: A. The nano-copper paste prepared in Example 1 was used to achieve package interconnection. Specifically, a pure copper sheet was ground with 2000# sandpaper, soaked in a 3 vol% dilute hydrochloric acid solution, and cleaned with anhydrous ethanol. The nano-copper paste was then printed on a pure copper substrate. The pure copper sheet was gently attached to the printed nano-copper paste. The nano-copper paste was preheated at 80°C for 5 min, and heated to a specified temperature at a heating rate of 10°C / min under a nitrogen atmosphere. An auxiliary pressure of 10 MPa was applied to sinter the resulting package interconnection structure.
[0113] The specified sintering temperature is 200℃~280℃, the sintering time at the specified temperature is 20min, and the shear strength results of the interconnected joints after sintering are as follows Figure 3 As shown. Figure 3 It can be seen that the shear strength of the interconnected joint after sintering at a low temperature of 240°C for 20 minutes is 33.3 MPa, and the corresponding maximum shear strength of the interconnected joint after sintering at a low temperature of 280°C for 20 minutes can reach more than 60 MPa.
[0114] In addition, the cross section of the interconnected joints sintered at 240℃ for 20min was observed using a scanning electron microscope. Figure 4 As shown by Figure 4 It can be seen that obvious necking fracture morphology is observed in the fracture morphology, indicating that high-strength interconnection can be achieved at low temperature.
[0115] B. The nano-copper paste prepared in Example 2 was used to achieve copper-copper bonding. Specifically, a pure copper sheet was ground with 2000# sandpaper, soaked in a 3 vol% dilute hydrochloric acid solution, and cleaned with anhydrous ethanol. The nano-copper paste was then printed on a pure copper substrate. The pure copper sheet was gently placed on the printed nano-copper paste. The copper-copper interconnect was preheated at 120°C for 5 minutes, heated to the specified temperature at a heating rate of 10°C / min under a nitrogen atmosphere, and sintered with an auxiliary pressure of 10 MPa to form a copper-copper interconnect. After sintering at 240°C for 20 minutes, the corresponding interconnect had a shear strength of 25.8 MPa. When the temperature was increased to 280°C, the maximum shear strength of the interconnect reached over 50 MPa.
[0116] C. The nano-copper paste prepared in Example 3 was used to achieve copper-copper bonding. Specifically, a pure copper sheet was ground with 2000# sandpaper, soaked in a 3 vol% dilute hydrochloric acid solution, and cleaned with anhydrous ethanol. The nano-copper paste was then printed on a pure copper substrate. The pure copper sheet was gently placed on the printed nano-copper paste. The copper-copper interconnect was preheated at 100°C for 5 minutes, heated to the specified temperature under a nitrogen atmosphere at a heating rate of 10°C / min, and sintered with an auxiliary pressure of 10 MPa to form a copper-copper interconnect. After sintering at 240°C for 20 minutes, the corresponding interconnect achieved a shear strength of 23.1 MPa. When the temperature was increased to 280°C, the maximum shear strength of the interconnect reached over 42 MPa.
[0117] D. The nano copper paste prepared in Example 4 is used to realize package interconnection. The specific method and conditions are the same as those in Example 1 above.
[0118] After sintering at 240°C for 20 minutes, the corresponding interconnecting joint of Example 4 has a shear strength of 24.4 MPa.
[0119] E. The nano copper paste prepared in Comparative Example 1 is used to realize package interconnection. The specific method and conditions are the same as those in Example 1 above.
[0120] After sintering at a low temperature of 240°C for 20 minutes, the shear strength of the interconnecting joint corresponding to Comparative Example 1 is 19.34 MPa; when the temperature is loaded to 280°C, the maximum shear strength of the interconnecting joint reaches 39 MPa.
[0121] F. The nano copper paste prepared in Comparative Example 2 is used to realize package interconnection. The specific method and conditions are the same as those in Example 1 above.
[0122] After sintering at a low temperature of 240°C for 20 minutes, the shear strength of the interconnecting joint corresponding to Comparative Example 2 is 10.41 MPa; when the temperature is loaded to 280°C, the maximum shear strength of the interconnecting joint reaches 26 MPa.
[0123] In summary, the solution provided by the present invention has at least the following advantages: (1) The multi-scale nano-copper particles in the present invention are prepared by a one-step chemical reduction method, which is simple, fast and low-cost.
[0124] (2) The multi-scale nano-copper particles of the present invention have long-term storage stability. The addition of reducing components effectively controls the oxygen content of the preparation environment and forms an organic protective layer, so that the prepared multi-scale nano-copper particles have excellent antioxidant properties. In addition, the compounded organic carrier composite solvent exhibits step-by-step volatilization or decomposition during the sintering process, effectively inhibiting the formation of copper oxides and promoting the reduction of the original copper oxides on the particle surface. The fresh copper atoms produced by the decomposition further promote the sintering and diffusion of the multi-scale nano-copper particles, effectively promoting the overall sintering process and reducing the process requirements and preparation costs of the nano-copper paste sintering.
[0125] (3) The sintering temperature of the nano-copper paste in the present invention is as low as 240°C, in which the copper particles show a multi-scale distribution characteristic with gradient changes. The small-scale copper particles effectively fill and accumulate in the pores between the large-scale copper particles, forming a compact stacking structure, which gives it an obvious low-temperature sintering advantage and greatly improves the density of the sintered connection layer at low temperature. It has great application prospects for the packaging and interconnection of high-power chips.
[0126] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.
Claims
1. A method for preparing a nano copper paste, characterized in that: The following steps are involved: grinding a mixture of multi-scale nano-copper particles and an organic carrier composite solvent; The multi-scale nano-copper particles have a particle size of 10 nm to 200 nm, wherein the number ratio of the nano-copper particles with a particle size of 10 nm to 40 nm, the nano-copper particles with a particle size of 40 nm to 80 nm, and the nano-copper particles with a particle size of 80 nm to 200 nm is (4-10):(2-6):1; The organic carrier composite solvent comprises a reducing organic solvent, a carrier solvent and an organic active agent.
2. The preparation method according to claim 1, characterized in that The mass ratio of the multi-scale nano-copper particles to the organic carrier composite solvent is 7:3 to 9:
1.
3. The preparation method according to claim 1, characterized in that The multi-scale nano copper particles are prepared from copper compounds through a one-step chemical reduction process; Preferably, the preparation of the multi-scale nano-copper particles comprises: mixing a copper salt solution with a reducing solution to react to obtain a reaction solution; stirring the reaction solution until the color of the reaction solution no longer changes; Wherein, the copper salt solution is obtained by mixing a copper compound with water; The reducing solution comprises an organic solvent, a reducing agent, an antioxidant and a regulator.
4. The preparation method according to claim 3, characterized in that The preparation of the multi-scale nano-copper particles also includes at least one of the following features: Feature 1: The temperature of the reaction solution is maintained at 70°C to 100°C; Feature 2: The reaction solution is in a water bath environment; Feature 3: performing solid-liquid separation on the reaction solution, and washing the solid after solid-liquid separation; Preferably, solid-liquid separation is performed by centrifugation, wherein the centrifugal speed is 4000 r / min to 8000 r / min and the centrifugal time is 3 min to 5 min; Preferably, anhydrous ethanol is used for washing, and the number of washing times is 2 to 4 times.
5. The preparation method according to claim 4, characterized in that The copper salt solution includes at least one of the following characteristics: Feature 4: The copper compound includes at least one of copper formate, copper acetate, copper oxalate, copper citrate, copper sulfate and copper chloride; Feature 5: The concentration of the copper salt solution is 0.5 mol / L~1 mol / L.
6. The preparation method according to claim 4, characterized in that The reducing liquid includes at least one of the following characteristics: Feature 6: In the reducing solution, the mass concentration ratio of the reducing agent, the antioxidant, and the regulator is (15-40):(4-10):(1-5); Feature 7: The organic solvent is a polyol; preferably, the polyol includes at least one of ethylene glycol, propylene glycol, glycerol, diethylene glycol, butylene glycol and polyethylene glycol; Feature 8: The reducing agent includes at least one of sodium phosphite, potassium tartrate, sodium sulfite and sodium borohydride; Feature 9: The antioxidant comprises at least one of ascorbic acid and glucose; Feature 10: The regulator is a long-chain organic acid having ≥4 carbon atoms. Preferably, the regulator comprises at least one of succinic acid, glutaric acid, suberic acid, adipic acid, pimelic acid, tartaric acid, oleic acid, and lauric acid. Feature 11: The reducing solution is obtained by sequentially adding the reducing agent, the antioxidant, and the regulator to the organic solvent and stirring and dissolving them.
7. The preparation method according to claim 1, characterized in that The organic carrier composite solvent includes at least one of the following characteristics: Feature 12: The mass ratio of the reducing organic solvent, the carrier solvent, and the organic active agent is (5-25):(4-24):1; Feature 13: The reducing organic solvent includes at least one of ethylene glycol, propylene glycol, glycerol, diethylene glycol, neopentyl glycol, polyethylene glycol, terpineol and octanol; Feature 14: The carrier solvent includes a glycol ether, preferably, the carrier solvent includes at least one of ethylene glycol methyl ether, diethylene glycol monohexyl ether, ethylene glycol dimethyl ether, ethylene glycol butyl ether, ethylene glycol diglycidyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether and dipropylene glycol butyl ether; Feature 15: The organic surfactant is a short-chain carboxylic acid having 2 to 6 carbon atoms. Preferably, the organic surfactant includes at least one of lactic acid, glycolic acid, oxalic acid, malonic acid, citric acid and tartaric acid.
8. A nano copper paste, characterized in that: The nano copper paste is prepared by the preparation method according to any one of claims 1 to 7.
9. Use of the nano copper paste according to claim 8 in a packaging interconnection structure.
10. A package interconnect structure, characterized in that: The package interconnect structure is obtained by hot pressing and sintering a pure copper substrate, the nano copper paste according to claim 6, and a pure copper sheet or a copper-plated silicon-based chip; Preferably, the temperature of hot pressing sintering is 200° C. to 300° C., the time of hot pressing sintering is no more than 30 minutes, and the pressure of hot pressing sintering is 5 MPa to 20 MPa; Preferably, before hot pressing and sintering, the material is preheated at 80° C. to 150° C. for 2 min to 10 min.