CN111975011B - Nano copper paste for chip pressureless sintering interconnection and preparation method and application thereof - Google Patents
Nano copper paste for chip pressureless sintering interconnection and preparation method and application thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/054—Nanosized particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
- B22F1/102—Metallic powder coated with organic material
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- H01L23/52—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames
Abstract
The invention discloses a nano copper paste for chip pressureless sintering interconnection and a preparation method and application thereof. The preparation of the nano-copper is that the reaction liquid is poured into the reduction liquid which is heated continuously and has the temperature of 80-120 ℃, the reaction is carried out under the stirring, the centrifugation is carried out after the reaction is finished, and the nano-copper particles are obtained after the cleaning. The reaction solution and the reducing solution prepared from the nano-copper both contain a composite coating agent formed by mixing polybasic acid and amine additives, and the prepared nano-copper particles are nano-aggregates with the size presenting a bimodal distribution characteristic. The preparation of the nano copper takes the sintering copper slurry for interconnection as an application background, the coating agent and the compound solvent used for preparation are completely volatilized or decomposed in the sintering process and have a reduction effect, and the nano copper particles with bimodal distribution in size can realize low-temperature sintering and simultaneously form a large amount of compact interconnections, so that the slurry can realize high-efficiency sintering and high-performance interconnection under the pressureless condition.
Description
Technical Field
The invention relates to nano copper paste, in particular to nano copper paste for chip pressureless sintering interconnection and a preparation method and application thereof; belongs to the field of power electronic device interconnection technology and electronic packaging.
Background
In recent years, renewable energy technologies such as wind energy, solar energy, biomass energy, and the like have been receiving attention in order to reduce carbon emissions. In order to improve the energy conversion efficiency of these renewable energy sources, a power semiconductor device, which is one of energy conversion key devices, needs to satisfy strict conditions to accommodate higher current density, higher power dissipation, and higher reverse breakdown voltage. Compared with the traditional silicon semiconductor, the third generation semiconductor such as silicon carbide and gallium nitride has wider application in power devices due to larger forbidden bandwidth, higher critical breakdown electric field, better thermal conductivity and higher working temperature.
At present, the commonly used interconnection materials of the power device packaging chip mainly comprise high lead alloy, gold alloy, nano silver paste and the like. However, in consideration of environmental protection and continuous increase of chip junction temperature, high-lead alloy is not recommended, and gold alloy and nano silver paste mainly contain noble metal, so that the cost is high, and the method is not suitable for popularization and application. This makes more and more researchers dedicated to develop chip interconnection materials with lower cost, and also provides the device with the advantages of higher use temperature and connection strength, excellent heat dissipation performance, and efficient signal transmission.
Copper has electric conduction and heat conduction performance similar to that of silver, and the price of raw materials is about one percent of that of the silver, so that the copper becomes a research hotspot of interconnection materials. The traditional micron copper powder slurry is difficult to sinter at a lower temperature due to a higher melting point, and the sintering temperature of the nano copper particles with high specific surface energy is far lower than that of micron copper powder. By utilizing the nanometer effect, the nanometer copper particles are prepared into copper slurry, and the nanometer copper slurry which is sintered at a lower temperature and forms good interconnection can be obtained. Because the used solvent is organic matter with low melting point, the solvent can be completely volatilized in the sintering process, and finally the interconnecting joint with the copper content of more than 99 percent can be obtained. The joint can well inherit the advantages of high use temperature, excellent heat conducting performance, electric conducting performance and the like of the bulk metal copper. However, the surface atoms of the nano-copper have high activity and are very easy to form copper oxide, and the oxide on the surface of the copper nano-particles can block the diffusion of the copper atoms and influence the sintering process, so that the interconnection joint is difficult to form reliable connection at a lower temperature. Therefore, solving the problem of copper oxidation in the copper paste is crucial to improving the copper paste sintering process and the copper paste interconnection performance. In order to prevent the oxidation of copper and enhance the sintering capability of copper paste, a certain pressure needs to be applied to the copper paste in the sintering process, which significantly increases the process difficulty and the production cost, and may cause certain damage to the power chip. Therefore, the development of the high-performance nano copper paste for the pressureless sintering interconnection of the chip has important significance for realizing the large-scale industrial application of the nano copper paste.
The Chinese invention patent CN106825998A discloses a non-oxidation nano-copper soldering paste used for high-power chip packaging and a preparation method thereof; the method adopts copper nanoparticles with the particle size of 30nm-60nm and non-oxidized surfaces, the copper nanoparticles are mixed with an organic solvent according to the mass ratio of 2:1-5:1, and the nano-copper soldering paste is obtained after mechanical stirring and planetary gravity stirring are fully carried out; the oxide on the surface of the nano-copper particles in the preparation process is removed by treating the prepared nano-copper with organic acid, so that the influence of the oxide on the interconnection performance of the slurry during copper slurry sintering is solved. However, this method adds a post-treatment process, increases a preparation process, increases preparation costs, and uses a pressure of 5 to 10MPa in a subsequent sintering process, introduces a hydrogen atmosphere, which may damage a power chip and increase process costs.
Chinese patent application CN109317859A discloses a nano-copper solder paste, a preparation method thereof and a copper-copper bonding method; the nano copper soldering paste comprises, by mass, 50-90% of nano copper particles, 5-25% of alcohol amine and 0-45% of viscosity regulator. The nano copper soldering paste provided by the invention is used for carrying out copper-copper bonding, so that the sintering temperature can be reduced, and the oxidation and agglomeration of nano copper particles can be avoided; sintering can be completed in the air atmosphere of 200 ℃ to obtain the copper-copper interconnection structure with higher shear strength. According to the invention, alcohol amine is used as a solvent, so that the oxidation of copper in the sintering process can be effectively reduced, but a large pressure is also required to be applied in the sintering process, and the burden is caused on the chip and the process cost.
Disclosure of Invention
In order to solve the problems in the preparation and application processes of the nano copper paste, the invention provides the high-performance nano copper paste for chip pressureless sintering interconnection and the preparation method thereof, which overcome the problem that the copper paste performance is deteriorated due to the existence of copper oxide in the existing copper paste, solve the problem of pressure sintering of the existing copper paste and simplify the sintering process.
The invention also aims to provide the application of the nano copper paste for pressureless sintering interconnection of chips in the preparation of interconnection joints, wherein the shear strength of the interconnection joints exceeds 40 MPa.
In order to achieve the above purpose, the invention provides the following technical scheme:
a method for preparing nano copper slurry for chip pressureless sintering interconnection comprises two steps of nano copper preparation and copper slurry mixing:
1) preparing nano copper: pouring the reaction solution into a reduction solution which is heated continuously and has the temperature of 80-120 ℃, reacting under stirring, centrifuging after the reaction is finished, and cleaning to obtain nano copper particles;
the reaction solution and the reduction solution both contain a composite coating agent and an organic solvent; the reaction solution is formed by mixing a copper-containing compound, a composite coating agent and an organic solvent; the reducing solution is formed by mixing a reducing agent, a composite coating agent and an organic solvent; the copper-containing compound is one or more of copper sulfate pentahydrate, copper acetate monohydrate, copper nitrate trihydrate, copper chloride and copper hydroxide; the reducing agent is one or two of L-ascorbic acid and sodium hypophosphite monohydrate;
the composite coating agent is formed by mixing polybasic acid and amine additives; the polybasic acid is one or more of oxalic acid, malonic acid, citric acid, ascorbic acid, acetic acid, butyric acid, lactic acid and tartaric acid; the amine additive is one or more of monoethanolamine, diethanolamine, triethanolamine, 3-propanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-dimethylethanolamine and N, N-diethylethanolamine; the mass ratio of the polybasic acid to the amine additive in the composite coating agent is 7: 1-1: 1;
2) mixing copper slurry: mixing the prepared nano copper with a compound organic solvent; the compound organic solvent is two or more than two of ethylene glycol, diethylene glycol, propylene glycol, glycerol and polyethylene glycol.
To further achieve the purpose of the present invention, preferably, the concentration of the composite coating agent in the reaction solution is 500-1000 g/L.
Preferably, the concentration of the composite coating agent in the reducing solution is 250-500 g/L.
Preferably, the concentration of the copper-containing compound in the reaction liquid is 150-400 g/L; the concentration of the reducing agent in the reducing liquid is 400-550 g/L.
Preferably, the organic solvent in the reaction solution and the reduction solution is ethylene glycol.
Preferably, the mass concentration ratio of the copper-containing compound in the reaction solution, the reducing agent in the reducing solution, and all the composite coating agents in the reaction solution and the reducing solution is 1:2: 2-4: 5: 5.
Preferably, the stirring is mechanical stirring; the stirring speed of mechanical stirring is 400-6000 r/min, the reaction time under stirring is 10-60min, the cleaning and centrifuging speed is 3000-6000r/min, and the centrifuging time is 1-3 min; the cleaning is ethanol cleaning.
Preferably, the copper slurry is mixed by mixing the prepared nano copper with a compound organic solvent by using a planetary gravity mixer.
A nano copper slurry for chip pressureless sintering interconnection: prepared by the preparation method; the nano copper slurry for non-pressure sintering interconnection of the chips comprises 70-90% by mass of nano copper and 30-10% by mass of a compound organic solvent; the particle size of the nano copper presents a bimodal distribution characteristic, the particle size of large-particle copper is 120-200 nm, the particle size of small-particle copper is 5-20 nm, the mass ratio of the large-particle copper to the small-particle copper is 1: 1-19: 1, and the small-particle copper is tightly stacked around the large-particle copper to form a nano copper aggregate structure.
The application of the nano copper paste for chip pressureless sintering interconnection in the preparation of interconnection joints is as follows: printing the nano copper paste on a pure copper substrate by using a steel mesh printing method, wherein the thickness of the nano copper paste is 100-200 mu m, placing a simulation chip on the printed nano copper paste, applying pressure of 0-0.1 MPa to the simulation chip, maintaining the pressure for 1-5 min, and then sintering at the temperature of 260-300 ℃ for 10-60min under the condition of no pressure assistance and in a nitrogen atmosphere to form an interconnection joint; the pure copper substrate and the simulation chip are both ground by 2000# sand paper, soaked by 3-10 vol.% dilute sulfuric acid and finally cleaned by ethanol; the simulation chip is a silver-plated copper sheet, and the thickness of a plating layer is 1-10 mu m.
Compared with the prior art, the invention has the advantages that:
1. the particle size of the nano-copper prepared by the method shows a bimodal distribution characteristic, namely, a large amount of small-particle copper with the particle size of 5-20 nm is tightly packed around large-particle copper with the particle size of 120-200 nm to form a copper nano-particle aggregate.
This is because the composite coating agent used in the present invention is a mixture of a polybasic acid and an amine, the amine can form a complex with copper hydroxide at the initial stage of the reaction to slow down the reaction rate, and at this time, the polybasic acid as the main coating agent is likely to generate large-particle copper nanoparticles because the carbon chain is short and the coating effect is weak. In the later reaction period, along with the continuous reduction of copper ions in the complex, the released amine and the polybasic acid can be used as a coating agent together, and the bonding capability of nitrogen atoms in the amine and the copper surface is stronger, so that the coating effect of the coating agent is obviously enhanced, and nano copper particles with smaller particle size can be formed and adsorbed around large-particle copper. Copper nanoparticle aggregates with such a bimodal distribution of sizes have already completed a certain degree of aggregation before sintering, which makes it easier to form a dense body during sintering, increasing the strength of the interconnect layer.
2. When the slurry is sintered, the oxide in the original copper particles can be reduced and gradually disappears, so that the process requirements of copper particle preparation and slurry sintering are reduced, and the preparation cost is reduced. This is because the coating agent in the present invention is a composite coating agent using polybasic acid as a matrix, and during the sintering and heating process, the polybasic acid can react with the copper oxide in the slurry to form copper carboxylate, which can be decomposed into copper, carbon dioxide and water at a higher temperature, thereby achieving the effect of reducing the copper oxide. The process can eliminate the negative effect of oxide on the interconnection performance, and the produced copper is copper without coating agent, has high surface activity and fast atomic diffusion, can promote the sintering of copper slurry and improve the interconnection layer performance.
3. The nano copper paste can be sintered under a pressureless condition, and good interconnection performance is obtained. When the slurry is used for interconnecting the chips, the damage to the chips is small, the product yield is improved, additional pressure auxiliary equipment is not required to be added on the equipment, the sintering process is simplified, and the production cost is saved.
4. The preparation of the nano copper takes the sintering copper slurry for interconnection as an application background, the coating agent and the compound solvent used for preparation are completely volatilized or decomposed in the sintering process and have a reduction effect, and the nano copper particles with bimodal distribution in size can realize low-temperature sintering and simultaneously form a large amount of compact interconnections, so that the slurry can realize high-efficiency sintering and high-performance interconnection under the pressureless condition.
Drawings
Fig. 1 is a Transmission Electron Microscope (TEM) image of the nano-copper particles prepared in example 1.
Fig. 2 is a distribution diagram of the particle size of the nano-copper particles prepared in example 1.
FIG. 3 is a Scanning Electron Microscope (SEM) image of the joint fracture morphology after forming the interconnect joint from the copper paste prepared in example 1.
Fig. 4 is a Transmission Electron Microscope (TEM) image of the nano-copper particles prepared in comparative example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further explained with reference to the following embodiments and accompanying drawings. It should be understood that the examples are for illustrative purposes only and are not intended to limit the scope of the present invention.
Example 1
A method for preparing nano copper slurry for chip pressureless sintering interconnection comprises two steps of nano copper preparation and copper slurry mixing:
1) preparing copper nanoparticles with a wrapping structure and a bimodal distribution of particle sizes: preparing a composite coating agent taking polybasic acid as a matrix, wherein the polybasic acid is oxalic acid, the amine additive is isopropanolamine, and the weight ratio of the oxalic acid to the isopropanolamine is 6: 1. Preparing 10mL of a glycol solution containing 200g/L copper hydroxide and 500g/L composite coating agent, and uniformly stirring to form a reaction solution; preparing 40mL of glycol solution containing 500g/L sodium hypophosphite monohydrate and 500g/L composite coating agent, heating to 90 ℃, and stirring to dissolve to form reducing solution. And when the temperature of the reducing solution is maintained at 90 ℃, pouring the reaction solution into the reducing solution, mechanically stirring the reaction system at the rotating speed of 600r/min, finishing the reaction after reacting for 10min, and cooling to room temperature by water. And centrifuging the obtained reaction product for 3min at the speed of 4000r/min by using a centrifugal machine, and repeatedly cleaning the reaction product for 3 times by using ethanol to prepare the nano copper particles.
As shown in fig. 1, the nano-copper particles exhibit a packing structure in which small particles are adsorbed around large particles, forming aggregates. Taking TEM images of several copper nanoparticles, and counting the particle size of the copper nanoparticles by image analysis software, wherein the particle size distribution is shown in FIG. 2, the size of the small particles is between 5-20 nm, and the particle size of the large particles is between 120-200 nm.
2) Mixing copper slurry: mixing ethylene glycol and glycerol in a mass ratio of 1:1, uniformly stirring, standing for 30min, and removing bubbles to obtain a compound organic solvent for copper slurry; mixing the prepared nano-copper particles with the mass percentage of 80% with a compound organic solvent with the mass percentage of 20%, uniformly stirring by using a planetary gravity mixer, and defoaming to form nano-copper slurry.
The pure copper substrate and the silver-plated copper sheet with the plating thickness of 5 mu m are ground by using No. 2000 abrasive paper, and then the pure copper substrate and the silver-plated copper sheet are soaked in 3 vol.% dilute sulfuric acid solution, finally washed by ethanol and dried for later use. Printing the nano copper paste with the thickness of 150 microns on the pure copper substrate by using a steel mesh, attaching the silver-plated copper sheet to the nano copper paste, applying pressure of 0.1MPa and maintaining the pressure for 1min to ensure that the silver-plated copper sheet is fully contacted with the nano copper paste; heating to 280 ℃ at the speed of 10 ℃/min in the nitrogen atmosphere, and carrying out heat preservation sintering for 20 min; and cooling along with the furnace after the heat preservation is finished to form the silver-plated copper sheet/nano copper slurry sintered body/pure copper substrate interconnection joint. The MFM1200 type multifunctional shear force tester is used for carrying out shear test on the interconnection joint, and the measured shear strength is up to 54.2MPa, which is obviously higher than the shear strength of the interconnection joint disclosed in the Chinese invention patent CN106825998A by 41.4-45.3 MPa. Fracture morphology observation of the interconnect joint is carried out by using a scanning electron microscope, and a photograph shown in fig. 3 is obtained, wherein contraction fracture similar to bulk copper is observed in the fracture morphology of the interconnect joint, which is a main reason for high strength of the interconnect joint.
It is possible that the copper nanoparticle aggregates having a bimodal distribution of sizes have completed a certain degree of aggregation before sintering, which makes it easier to form a dense body during sintering, increasing the strength of the interconnect layer. Meanwhile, the coating agent in the embodiment is a composite coating agent taking polybasic acid as a matrix, the polybasic acid can react with copper oxide in the slurry in the sintering and heating process to form copper carboxylate, and the copper carboxylate can be decomposed into copper, carbon dioxide and water at a higher temperature, so that the effect of reducing the copper oxide is achieved. The process can eliminate the negative effect of oxide on the interconnection performance, and the produced copper is copper without coating agent, has high surface activity and fast atomic diffusion, can promote the sintering of copper slurry and improve the interconnection layer performance. In the present embodiment, the interconnection strength of more than 50MPa can be obtained by sintering at 280 ℃ for 20min under pressureless conditions, while the prior art needs at least 10MPa pressure and the sintering temperature is 320 ℃ to obtain the interconnection strength. Therefore, compared with the prior art, the high-performance nano copper paste for the pressureless sintering interconnection of the chips used in the embodiment can save sintering energy, and the pressureless sintering characteristic of the high-performance nano copper paste makes the copper paste very suitable for interconnection of thin and fragile chips.
Comparative example 1
Preparing copper nanoparticles with continuously distributed particle sizes: preparing 10mL of 200g/L copper hydroxide glycol solution, and uniformly stirring to form a reaction solution; preparing 40mL of oxalic acid with the concentration of 250g/L and 500g/L of sodium hypophosphite monohydrate glycol solution, heating to 90 ℃, and stirring to dissolve to form reducing solution; when the temperature of the reducing solution reaches 90 ℃, pouring the reaction solution into the reducing solution, mechanically stirring the reaction system at the rotating speed of 600r/min, finishing the reaction after 10min of reaction, and cooling to room temperature by water. And centrifuging the obtained reaction product by using a centrifugal machine for 3min at the speed of 4000r/min, and repeatedly cleaning the reaction product for 3 times by using ethanol to prepare the nano copper particles. Taking TEM images of a plurality of copper nanoparticles, and counting the particle size of the copper nanoparticles by image analysis software, wherein the particle size of the prepared copper nanoparticles is continuously distributed between 10 nm and 100nm, as shown in FIG. 4.
Mixing copper slurry: mixing ethylene glycol and glycerol in a mass ratio of 1:1, uniformly stirring, standing for 30min, and removing bubbles to obtain a compound organic solvent for copper slurry; mixing the prepared nano-copper particles with the mass percentage of 80% with a compound organic solvent with the mass percentage of 20%, uniformly stirring by using a planetary gravity mixer, and defoaming to form nano-copper slurry.
The pure copper substrate and the silver-plated copper sheet with the plating thickness of 5 mu m are ground by using No. 2000 abrasive paper, and then the pure copper substrate and the silver-plated copper sheet are soaked in 3 vol.% dilute sulfuric acid solution, finally washed by ethanol and dried for later use. Printing the copper paste with the thickness of 150 mu m on a pure copper substrate by using a steel mesh, attaching a silver-plated copper sheet to the copper paste, applying pressure of 0.1MPa and maintaining the pressure for 1min to ensure that the silver-plated copper sheet is fully contacted with the copper paste; heating to 280 ℃ at the speed of 10 ℃/min in the nitrogen atmosphere, and carrying out heat preservation sintering for 20 min; and after the heat preservation is finished, cooling the furnace to form the silver-plated copper sheet/nano copper slurry sintered body/pure copper substrate interconnecting joint. The interconnect was shear tested using a MFM1200 model multifunctional shear tester and the shear strength of the interconnect was 11.3 MPa.
Compared with the example 1, the copper nanoparticles with different particle size distributions are obtained by changing the adding mode and the adding amount of the composite coating agent. In the slurry sintering process, the nano copper particles with bimodal distribution are more in small-size nano particles and wrapped around large particles, so that the interconnection layer can be rapidly sintered under the influence of high surface energy of the smaller nano particles, the large particles are connected with the large particles, and a large-area sintered compact body is generated, which is the main reason for high strength of the interconnection joint. While the copper nanoparticles continuously distributed in the comparative example have slower atomic diffusion during sintering and form a porous network structure due to the more continuous size distribution among the particles, and the strength is mainly provided by the weaker sintering necks, so the joint strength is lower.
Example 2
A method for preparing nano copper slurry for chip pressureless sintering interconnection comprises two steps of nano copper preparation and copper slurry mixing:
1) preparing copper nanoparticles with special coating structures and bimodal particle size distribution: preparing a composite coating agent with polybasic acid as a matrix, wherein the polybasic acid is ascorbic acid, the amine additive is triethanolamine, and the weight ratio of the ascorbic acid to the triethanolamine is 4: 1. Preparing 10mL of glycol solution containing copper hydroxide with the concentration of 300g/L and 700g/L of composite coating agent, and uniformly stirring to form reaction liquid; preparing 40mL of ethylene glycol solution containing 400g/L sodium hypophosphite monohydrate and 250g/L composite coating agent, heating to 90 ℃, and stirring to dissolve to form reducing solution. And when the temperature of the reducing solution is maintained at 100 ℃, pouring the reaction solution into the reducing solution, mechanically stirring the reaction system at the rotating speed of 400r/min, finishing the reaction after reacting for 30min, and cooling to room temperature by water. Centrifuging the obtained reaction product by a centrifugal machine for 3min at the speed of 6000r/min, and repeatedly cleaning the reaction product by ethanol for 3 times to prepare the nano-copper particles. Taking TEM images of a plurality of copper nanoparticles, and counting the particle size of the copper nanoparticles by image analysis software to obtain particles with the size of 5-20 nm and particles with the size of 120-200 nm.
2) Mixing copper slurry: mixing diethylene glycol and propylene glycol in a mass ratio of 1:3, uniformly stirring, standing for 30min to remove bubbles, and forming a compound organic solvent for copper slurry; and mixing the nano copper particles with a solvent, and uniformly mixing the nano copper particles and the solvent by using mechanical stirring to form nano copper slurry. The slurry comprises 85 mass percent of prepared nano-copper particles and 15 mass percent of compound organic solvent.
Grinding a pure copper substrate and a silver-plated copper sheet with a plating thickness of 5 mu m by using No. 2000 abrasive paper, then soaking the pure copper substrate and the silver-plated copper sheet in 3 vol.% of dilute sulfuric acid solution, finally cleaning the pure copper substrate and the silver-plated copper sheet by using ethanol, and drying the pure copper substrate and the silver-plated copper sheet for later use; printing the copper paste with the thickness of 150 mu m on a pure copper substrate by using a steel mesh, attaching a silver-plated copper sheet to the copper paste, applying pressure of 0.1MPa, and maintaining the pressure for 1min to ensure that the silver-plated copper sheet is fully contacted with the nano copper paste; heating to 280 ℃ at the speed of 10 ℃/min in the nitrogen atmosphere, and preserving the heat for 20 min; after the heat preservation is finished, cooling the furnace to form a silver-plated copper sheet/nano copper slurry sintered body/pure copper substrate interconnecting joint; the interconnect was shear tested using a MFM1200 model multifunctional shear tester and the interconnect shear strength was 42.6 MPa.
Example 3
A method for preparing nano copper slurry for chip pressureless sintering interconnection comprises two steps of nano copper preparation and copper slurry mixing:
1) preparing copper nanoparticles with special coating structures and bimodal particle size distribution: preparing a composite coating agent with polybasic acid as a matrix, wherein the polybasic acid is acetic acid, the amine additive is triisopropanolamine, and the weight ratio of the acetic acid to the triisopropanolamine is 2: 1. Preparing 10mL of glycol solution containing copper hydroxide with the concentration of 400g/L and 500g/L of composite coating agent, and uniformly stirring to form reaction liquid; preparing 40mL of glycol solution containing 550g/L of L-ascorbic acid and 300g/L of composite coating agent, heating to 120 ℃, and stirring to dissolve to form reducing solution. And when the temperature of the reducing solution is maintained at 120 ℃, pouring the reaction solution into the reducing solution, mechanically stirring the reaction system at the rotating speed of 600r/min, finishing the reaction after the reaction is carried out for 20min, and cooling the reaction system to room temperature by water. Centrifuging the obtained reaction product by a centrifugal machine for 1min at the speed of 6000r/min, and repeatedly cleaning the reaction product by ethanol for 3 times to prepare the nano-copper particles. Taking TEM images of a plurality of copper nanoparticles, and counting the particle size of the copper nanoparticles by image analysis software to obtain particles with the size of 5-20 nm and particles with the size of 120-200 nm.
2) Mixing copper slurry: mixing and uniformly stirring ethylene glycol, propylene glycol and glycerol in a mass ratio of 1:1:1, standing for 30min to remove bubbles, and forming a compound organic solvent for copper slurry; and mixing the nano copper particles with a solvent, and uniformly mixing the nano copper particles and the solvent by using mechanical stirring to form nano copper slurry. The slurry comprises 90 mass percent of prepared nano-copper particles and 10 mass percent of compound organic solvent.
Grinding a pure copper substrate and a silver-plated copper sheet with a plating thickness of 5 mu m by using No. 2000 abrasive paper, then soaking the pure copper substrate and the silver-plated copper sheet in 3 vol.% of dilute sulfuric acid solution, finally cleaning the pure copper substrate and the silver-plated copper sheet by using ethanol, and drying the pure copper substrate and the silver-plated copper sheet for later use; printing the copper paste with the thickness of 150 mu m on a pure copper substrate by using a steel mesh, attaching a silver-plated copper sheet to the copper paste, applying pressure of 0.1MPa, and maintaining the pressure for 1min to ensure that the silver-plated copper sheet is fully contacted with the nano copper paste; heating to 260 ℃ at the speed of 10 ℃/min in the nitrogen atmosphere, and keeping the temperature for 60 min; cooling the copper plate and the nano copper slurry together with the furnace after the heat preservation is finished to form a silver-plated copper sheet/nano copper slurry sintered body/pure copper substrate interconnecting joint; the interconnect was shear tested using a MFM1200 model multifunctional shear tester and the interconnect shear strength was measured to be 45.4 MPa.
The embodiments of the present invention are not limited to the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.
Claims (10)
1. A method for preparing nano copper slurry for chip pressureless sintering interconnection is characterized by comprising two steps of preparing nano copper and mixing the copper slurry:
1) preparing nano copper: pouring the reaction solution into a reduction solution which is heated continuously and has the temperature of 80-120 ℃, reacting under stirring, centrifuging after the reaction is finished, and cleaning to obtain nano copper particles;
the reaction solution and the reduction solution both contain a composite coating agent and an organic solvent; the reaction solution is formed by mixing a copper-containing compound, a composite coating agent and an organic solvent; the reducing solution is formed by mixing a reducing agent, a composite coating agent and an organic solvent; the copper-containing compound is one or more of copper sulfate pentahydrate, copper acetate monohydrate, copper nitrate trihydrate, copper chloride and copper hydroxide; the reducing agent is one or two of L-ascorbic acid and sodium hypophosphite monohydrate;
the composite coating agent is formed by mixing polybasic acid and amine additives; the polybasic acid is one or more of oxalic acid, malonic acid, citric acid, ascorbic acid, acetic acid, butyric acid, lactic acid and tartaric acid; the amine additive is one or more of monoethanolamine, diethanolamine, triethanolamine, 3-propanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-dimethylethanolamine and N, N-diethylethanolamine; the mass ratio of the polybasic acid to the amine additive in the composite coating agent is 7: 1-1: 1;
2) mixing copper slurry: mixing the prepared nano copper with a compound organic solvent; the compound organic solvent is two or more than two of ethylene glycol, diethylene glycol, propylene glycol, glycerol and polyethylene glycol.
2. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: the concentration of the composite coating agent in the reaction liquid is 500-1000 g/L.
3. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: the concentration of the composite coating agent in the reducing liquid is 250-500 g/L.
4. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: the concentration of the copper-containing compound in the reaction liquid is 150-400 g/L; the concentration of the reducing agent in the reducing liquid is 400-550 g/L.
5. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: the organic solvent in the reaction solution and the reduction solution is ethylene glycol.
6. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: the mass concentration ratio of the copper-containing compound in the reaction liquid, the reducing agent in the reducing liquid, and all the composite coating agents in the reaction liquid and the reducing liquid is 1:2: 2-4: 5: 5.
7. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: the stirring is mechanical stirring; the stirring speed of mechanical stirring is 400-6000 r/min, the reaction time under stirring is 10-60min, the cleaning and centrifuging speed is 3000-6000r/min, and the centrifuging time is 1-3 min; the cleaning is ethanol cleaning.
8. The method for preparing the nano-copper paste for the chip pressureless sintering interconnection according to claim 1, wherein the method comprises the following steps: and the copper slurry is mixed by mixing the prepared nano copper with a compound organic solvent by using a planetary gravity mixer.
9. A nanometer copper slurry for chip pressureless sintering interconnection is characterized in that: which is obtained by the production method according to any one of claims 1 to 8; the nano copper slurry for non-pressure sintering interconnection of the chips comprises 70-90% by mass of nano copper and 30-10% by mass of a compound organic solvent; the particle size of the nano copper presents a bimodal distribution characteristic, the particle size of large-particle copper is 120-200 nm, the particle size of small-particle copper is 5-20 nm, the mass ratio of the large-particle copper to the small-particle copper is 1: 1-19: 1, and the small-particle copper is tightly stacked around the large-particle copper to form a nano copper aggregate structure.
10. The use of the nano-copper paste for pressureless sintering interconnection of chips as claimed in claim 9 in the preparation of interconnection joints, characterized in that: printing the nano copper paste on a pure copper substrate by using a steel mesh printing method, wherein the thickness of the nano copper paste is 100-200 mu m, placing a simulation chip on the printed nano copper paste, applying pressure of 0-0.1 MPa to the simulation chip, maintaining the pressure for 1-5 min, and then sintering at the temperature of 260-300 ℃ for 10-60min under the condition of no pressure assistance and in a nitrogen atmosphere to form an interconnection joint; the pure copper substrate and the simulation chip are both ground by 2000# sand paper, soaked by 3-10 vol.% dilute sulfuric acid and finally cleaned by ethanol; the simulation chip is a silver-plated copper sheet, and the thickness of a plating layer is 1-10 mu m.
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