CN117900469A - Copper powder of two kinds of copper powder with nanometer particle size and densely coated with copper powder with micrometer size, preparation method and application of copper powder in preparation of copper paste - Google Patents

Abstract

The invention discloses copper powder of two copper powder densely coated micrometer copper sheets with nanometer particle sizes, a preparation method thereof and application of the copper powder in preparing copper paste; the copper powder of the copper powder densely coated with the copper powder with the two nanometer particle sizes consists of copper powder with the micrometer size of 1-2 mu m and nanometer copper particles with the diameter of 5-15nm and 40-100 nm; wherein the micrometer copper sheet is completely and tightly wrapped by two nanometer copper particles with the particle diameters, and the nanometer copper particles with the particle diameters of 5-15nm are tightly wrapped around the nanometer copper particles with the particle diameters of 40-100 nm; the copper powder is prepared by adopting a one-step synthesis method of a two-step process, the copper powder and an organic solvent are mixed and stirred to prepare copper paste, and the obtained copper paste can promote copper particles to realize sintering and tissue densification under low-temperature sintering and obtain a high-strength interconnection structure, and is suitable for low-temperature pressureless sintering interconnection packaging of power chips and power devices.

Description

Copper powder of two kinds of copper powder with nanometer particle size and densely coated with copper powder with micrometer size, preparation method and application of copper powder in preparation of copper paste

Technical Field

The invention relates to copper powder for copper paste, in particular to copper powder with two kinds of copper powder with nanometer particle sizes densely coated with a micrometer copper sheet, a preparation method thereof and application of the copper powder in preparing copper paste; the copper paste is suitable for the technical field of power chips and power device packaging materials.

Background

With the increasing demands of electric vehicles, 5G communication, aerospace, industrial automation, new energy and other fields for high-performance, high-reliability energy conversion and high-frequency operation, the role of power semiconductors in power conversion and high-efficiency energy utilization is increasingly important. However, the conventional silicon-based semiconductor device has been increasingly limited in its performance under severe conditions such as high temperature, high voltage, and high frequency. Third generation semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN), are gradually leading to new developments in power semiconductor technology due to their excellent characteristics of high frequency, high power, high temperature resistance, and lower energy loss.

The appearance of third-generation semiconductor materials and devices puts higher requirements on packaging materials, however, the conventional packaging materials cannot meet the severe requirements of high-temperature service of the packaged structure. At present, a low-temperature sintering technology of nano silver paste for packaging high-power devices is widely researched and applied, but the sintered silver joints have high electron mobility and ion mobility, and short circuits are easily generated on small-space silver interconnection joints of chips or devices to cause faults; meanwhile, the silver is expensive, so that the application of the nano silver paste in the package of high-power devices is greatly limited. Because the price of copper is about one percent of that of silver, and the copper has better electric conduction and heat conduction and stronger electromigration and ion migration resistance, the nano copper paste sintering interconnection technology is focused by a plurality of researchers because of great development potential and wide application prospect.

At present, copper paste is mostly prepared by adopting copper powder with single-scale particle size, and more gaps exist among particles in the copper paste prepared by the copper powder with single-scale particle size, so that more gaps exist in the sintered body after sintering, and the compactness is lower. Researchers mostly mechanically mix independent nanometer copper powder and micron copper powder to improve the stacking density of copper powder so as to realize higher density of copper paste after sintering. However, this method requires separately preparing copper powder of two or more particle sizes, increases the complexity of the preparation process, and easily causes the problem of uneven mixing of the two-scale powders. In addition, copper is susceptible to oxidation, and the resulting oxides hinder inter-particle atomic diffusion and sintering, deteriorating interconnect joint performance, making it difficult for copper pastes to form reliable interconnect joints at lower temperatures below 200 ℃. To obtain a dense sintered structure and a high strength interconnect joint, a large pressure is applied during sintering, which can significantly increase process complexity and production cost, and even damage the power chip.

Chinese patent CN109926577B discloses a copper paste that can be used for low temperature sintering and can obtain low porosity. The copper paste comprises: spherical copper particles, flaky indium particles and a high-linking resin; the ratio of the two copper particles is more than 80%, the ratio of the indium particles is between 10 and 20%, and the ratio of the high-linking resin is between 0 and 10%. Under the condition of no pressure, the sintering temperature of the copper paste can be reduced to about 180-250 ℃, and the density after sintering is more than 95%. The copper paste is added with 10-20% of indium particles, which is favorable for reducing sintering temperature, but has high price and limited practicability, and is difficult to apply on a large scale.

Chinese patent CN 114054746B discloses copper powder with particle size ranging from nanometer to micrometer, which is composed of 5-15nm nanometer particle copper powder, 120-210nm submicron particle copper powder and 1-2 μm micrometer flake copper powder; the surfaces of submicron particle copper powder and micron sheet copper powder are coated with nanometer particle copper powder. Copper powder of the technology is obtained by stirring a reducing agent and a reaction solution at 80-100 ℃ for reaction, centrifuging a reaction product and cleaning; the reaction liquid is obtained by mixing a composite dispersing agent formed by copper salt, organic acid and organic amine with ethylene glycol. However, as is apparent from the description of the patent specification and the accompanying fig. 1, the nanoparticle copper powder in the trimodal copper powder is coated on the surfaces of submicron particle copper powder and micron sheet copper powder, the submicron particle copper powder is not coated on the surfaces of micron sheet copper powder, and especially the content of small nanoparticle copper powder easy to sinter is low, the nanoparticle copper powder is not formed into compact coating on the surfaces of submicron particle copper powder or on the surfaces of micron sheet copper powder, and the formed copper powder has low overall bulk density, so that the interface bonding capability of the formed copper powder to power chip packaging is poor, therefore, the patent technology is mainly applied to direct printed circuits of flexible substrates, but is difficult to apply to power chips and power device packaging.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides the copper powder which can be prepared by a two-step process at one time, has good repeatability and low cost, is favorable for large-scale production, and is densely packed with two kinds of copper powder with nanometer particle sizes and three-peak distribution, and the copper powder is densely coated with the copper powder with the nanometer particle sizes and the preparation method thereof.

The invention further aims to provide the application of the copper powder of the two nanometer particle size copper powder densely coated with the micrometer copper sheet in preparing copper paste, the difficult problem that a compact sintering structure and a high-strength interconnection joint are difficult to obtain under the low-temperature and pressureless sintering condition in the existing copper paste is solved, meanwhile, the sintering process is simplified, and the copper paste can be applied to power chips and power device packages.

In order to achieve the above object, the present invention provides the following technical solutions:

Copper powder of two kinds of nanometer particle diameter copper powder densely coated with micron copper sheet consists of micron copper sheet of length of 1-2 microns and nanometer copper particle of diameter of 5-15nm and 40-100 nm; wherein the micrometer copper sheet is completely and tightly wrapped by two kinds of nanometer copper particles with the particle sizes, the nanometer copper particles with the particle sizes of 5-15nm are tightly wrapped around the nanometer copper particles with the particle sizes of 40-100nm, and the three kinds of copper powder show aggregation bodies with the particle sizes distributed in a trimodal manner and densely packed particles.

The preparation method of the copper powder of the two copper powder compact coated micrometer copper sheets with nanometer particle size comprises the following steps: adding a weak reducing agent into the first prefabricated liquid in the reaction kettle to obtain an initial reaction liquid, and continuously stirring the initial reaction liquid at the temperature of 80-120 ℃ to obtain a flaky copper powder suspension; adding a strong reducing agent into the flaky copper powder suspension, adding a second prefabricated solution to form a final reaction solution, and continuously stirring at the temperature of 80-120 ℃ to obtain three copper powder suspensions with different particle diameters; cooling, centrifuging and washing to obtain copper powder with two kinds of copper powder with nanometer particle size densely coated with micrometer copper sheet;

The first prefabricated liquid is obtained by mixing inorganic copper salt, organic acid, amine compound and polyalcohol solvent and continuously stirring at 80-100 ℃;

the second prefabricated liquid is obtained by mixing organic copper salt, organic acid and a polyalcohol solvent and continuously stirring at the temperature of 80-100 ℃;

preferably, the inorganic copper salt is one or more of copper carbonate, basic copper carbonate, copper sulfate, copper hydroxide, copper chloride and copper nitrate trihydrate;

The organic acid is one or more of oxalic acid, glycine, citric acid, tartaric acid, lactic acid, propionic acid and oleic acid;

The amine compound is one or more of oleylamine, ethylenediamine, methanolamine, triethanolamine, N-dimethylethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine and diethylenetriamine;

the polyalcohol solvent is one or more of ethylene glycol, diethylene glycol, propylene glycol, glycerol, isopropanol and n-propanol;

The organic copper salt is one or more of copper acetate, copper amino acid, copper rosinate, copper citrate and copper ammine.

Preferably, in the first prefabricated liquid, the concentration of the inorganic copper salt is 30-80g/L, the total concentration of the organic acid and the amine compound is 300-600g/L, and the mass concentration ratio of the organic acid to the amine compound is 1:1-5:1;

In the second prefabricated liquid, the concentration of the organic copper salt is 30-80g/L, and the concentration of the organic copper salt is 400-1200g/L.

Preferably, the weak reducing agent is one or more of sodium citrate, sodium hypophosphite, sodium phosphite, potassium tartrate, hydrogen peroxide and glucose;

the strong reducing agent is one or more of hydrazine hydrate, hydrazine sulfate, sodium borohydride, ascorbic acid and tetrabutylammonium borohydride.

Preferably, the concentration of the weak reducing agent in the initial reaction solution is 400-800g/L; the concentration of the strong reducing agent in the final reaction solution is 200-500g/L.

Preferably, in the preparation of the flaky copper powder suspension, the three copper powder suspensions with different particle sizes, the first preformed liquid and the second preformed liquid, the continuous stirring speed is 400-600r/min, the stirring time in the preparation of the first preformed liquid and the second preformed liquid is 5-20min, the stirring time in the preparation of the flaky copper powder suspension is 10-60min, and the stirring time in the preparation of the three copper powder suspensions with different particle sizes is 10-30min;

The cooling is to cool to room temperature;

Centrifuging the cooled reaction product by adopting a centrifuge at a rotating speed of 3000-6000r/min for 3-10 minutes;

The washing is carried out by repeatedly washing with one or more of ethanol, deionized water and acetone for 2-5 times.

The copper powder of the two nanometer particle size copper powder densely coated micrometer copper sheets is used for preparing copper paste.

Preferably, copper powder of the two copper powder dense coating micron copper sheets with nanometer particle size and an organic solvent are uniformly stirred and defoamed to prepare copper paste; the organic solvent is one or more of ethylene glycol, propylene glycol, glycerol, diethylene glycol, terpineol and polyethylene glycol.

Preferably, the uniform stirring is mixing by a planetary gravity stirrer;

the copper powder of the two nanometer particle size copper powders densely coated with the micrometer copper sheet accounts for 75-90% by mass percent, and the organic solvent accounts for 25-10%;

the application of the copper paste in preparing the sintered joint comprises the following steps: printing on the surface of a lower pure copper substrate by adopting a screen printing method, wherein the thickness of copper paste is 10-400 mu m, placing a power chip or a power device on the printed copper paste surface, applying patch pressure of 0-0.5MPa, and keeping the pressure for 1-5min to obtain a chip/copper paste/copper substrate sandwich structure to-be-sintered assembly; sintering at 160-240 deg.c for 10-40min in nitrogen atmosphere without pressure assistance to form sintered joint.

Compared with the prior art, the invention has the advantages that:

1) The copper powder of the two copper powder densely coated micrometer copper sheets with nanometer particle sizes consists of micrometer copper sheets with larger sizes of 1-2 mu m and nanometer copper particles with smaller sizes of 5-15nm and 40-100 nm; wherein the micrometer copper sheet is tightly wrapped by two kinds of nanometer copper particles with the particle sizes, the nanometer copper particles with the particle sizes of 5-15nm are tightly wrapped around the nanometer copper particles with the particle sizes of 40-100nm to form an aggregate, and the whole copper powder has the characteristics of three-peak distribution and compact accumulation of the particle sizes. The micron copper sheet has higher strength, more excellent oxidation resistance and stability as a reinforced 'skeleton'; the sintering driving force of the nano copper particles with high surface energy is larger, and the nano copper particles have good low-temperature sintering performance; the prepared copper powder has the advantages of both the micron copper sheet and the nanometer copper particles, more importantly, a large number of nanometer copper particles with two dimensions play a role in filling gaps of the micron copper sheet, the compactness of the copper powder structure is improved, the complete coating is truly realized, no obvious gaps are left, and the micron copper sheets serving as a framework are connected after the nanometer copper particles with two dimensions are sintered, diffused and fused at low temperature, so that a compact sintered structure is obtained. The copper powder is ensured to be suitable for the technical field of power chips and power device packaging materials, and the strength of the interconnection joint after sintering is over 20MPa under the condition of low-temperature pressureless sintering at 200 ℃.

2) The copper paste prepared from the copper powder with the particle size distributed in a trimodal manner and densely packed particles can be sintered at low temperature and under no pressure in nitrogen atmosphere to obtain the high-strength interconnection joint. In the process of chip sintering interconnection by using the copper paste, the organic acid adsorbed on the surface of the copper powder and the reducing alcohol organic solvent in the copper paste can inhibit copper powder oxidation without introducing a reducing atmosphere, so that the use of the reducing atmosphere (such as formic acid) and the damage to sintering equipment and the harm to human health and safety are avoided. Meanwhile, the grain sizes of the copper powder are greatly different from each other, the driving force caused by the size difference enables the copper nanoparticles to be fused on the copper powder rapidly, and the surface energy released by fusion can cause the local temperature at the sintering neck to rise, so that the copper powder can be sintered rapidly at low temperature, the sintering temperature can be as low as 200 ℃, and the electric power energy cost is greatly reduced.

3) The sintering process for preparing the copper paste does not need to apply pressure, so that the sintering process can be further greatly simplified, and the production cost can be reduced.

4) The invention adopts a two-step process one-step synthesis method to prepare three copper powders with different particle diameters and densely packed particles. The copper powder is prepared into suspension containing micron flake copper powder through a one-step synthesis method, nano copper particles with two sizes are formed on the micron flake copper powder in a nucleation mode, and finally the copper powder with three-peak particle size distribution and densely packed particles is obtained. Compared with the traditional mechanical mixing method and one-step process synthesis method of copper powder with different particle sizes, the two-step process one-step synthesis method can realize accurate regulation and control of copper powder proportion and ensure more uniform distribution and close packing of copper powder.

5) The invention can regulate the shape and the particle size distribution of copper powder by regulating the dosage of copper salt, organic acid and amine compound according to the requirement. When the content of the organic acid is low, the amine compound plays a main role in regulating the shape and particle size distribution of copper powder, can react with inorganic copper salt to generate complex, and prevent oxidation-reduction reaction, and has good selective adsorption effect on copper nanocrystals, thereby being beneficial to promoting the generation of micron copper sheets. When the content of the organic acid is higher, the organic acid plays a main role in regulating the shape and particle size distribution of the copper powder, the organic acid accelerates the oxidation-reduction reaction rate, more copper crystal nuclei are generated in unit time, and the generation of nano particles with smaller sizes is promoted.

Drawings

Fig. 1 is a Scanning Electron Microscope (SEM) photograph of copper powder densely coated with micro copper flakes of two kinds of nano-sized copper powder prepared in example 1.

Fig. 2 is a Transmission Electron Microscope (TEM) photograph of copper powder densely coated with micro copper flakes of two kinds of nano-particle size copper powder prepared in example 1.

Fig. 3 is a Scanning Electron Microscope (SEM) photograph of the fracture morphology of the copper paste sintered interconnect joint prepared in example 1.

Fig. 4 is a Scanning Electron Microscope (SEM) image of a copper micro-sheet coated with small-sized copper powder prepared in comparative example 2.

Detailed Description

For a better understanding of the present invention, reference will now be made to the following description of embodiments of the invention, taken in conjunction with the accompanying drawings and examples.

Compared with the copper powder with the particle size of nanometer-micrometer three-peak distribution of Chinese invention patent CN 114054746B, the copper powder of the invention looks like the copper powder with similar particle size, mainly the submicron particle copper powder with the particle size of 120-210nm is different from the nanometer particle copper powder with the particle size of 40-100 nm; but the essential difference is the amount of the nano-particle copper powder and the combination of the three copper powders; the surface of submicron particle copper powder and micron sheet copper powder of China patent CN 114054746B is coated with nanometer particle copper powder, no matter the surface of submicron particle copper powder or the surface of micron sheet copper powder is less, no compact coating is formed, and the whole stacking density of the formed copper powder is low, so that the interface bonding capability of the formed copper powder for packaging a power chip is poor, and therefore, the patent technology is mainly applied to a direct printed circuit of a flexible substrate, but is difficult to apply to packaging of a power chip and a power device. The three kinds of copper powder with different particle diameters are densely stacked, and consist of micrometer copper sheets with larger sizes of 1-2 mu m and nanometer copper particles with smaller sizes of 5-15nm and 40-100 nm; wherein the micron copper sheet is tightly wrapped by nano copper particles with two particle sizes, and the nano copper particles with the particle sizes of 5-15nm are tightly wrapped around the nano copper particles with the larger particle sizes of 40-100nm to form an aggregate, the synthesized copper powder integrally shows the three-peak distribution and compact stacking characteristics of the particle sizes, and the copper powder with the nano copper particles with the two particle sizes really realizes the complete wrapping of the micron copper sheet.

The preparation method of copper powder densely coated with copper powder with nanometer particle size and copper powder with micrometer particle size comprises the steps of one-step synthesis by two-step process, preparation of large-scale flaky copper powder suspension in the same reaction kettle, preparation of three-particle-size copper powder suspension, and centrifugal cleaning to obtain three densely-stacked copper powder with different particle size and size characteristics. Specifically, the preparation method of copper powder with two kinds of copper powder with nanometer particle sizes and densely coated with micrometer copper sheet comprises the steps of adding a weak reducing agent into a first prefabricated liquid in a reaction kettle to obtain an initial reaction liquid, and continuously stirring the initial reaction liquid at 80-120 ℃ to obtain a flaky copper powder suspension; adding a strong reducing agent into the flaky copper powder suspension, adding a second prefabricated solution to form a final reaction solution, and continuously stirring at the temperature of 80-120 ℃ to obtain three copper powder suspensions with different particle diameters; cooling, centrifuging and washing to obtain copper powder with two kinds of copper powder with nanometer particle size densely coated with micrometer copper sheet; the first prefabricated liquid is obtained by mixing inorganic copper salt, organic acid, amine compound and polyalcohol solvent and continuously stirring at 80-100 ℃; the second prefabricated liquid is obtained by mixing organic copper salt, organic acid and a polyalcohol solvent and continuously stirring at the temperature of 80-100 ℃. In this preparation method, the specific constitution of the first preformed liquid and the second preformed liquid is an important technical measure of the present invention which is different from the prior art, and as for the inorganic copper salt, the organic acid, the amine compound, the polyhydric alcohol solvent and the organic copper salt, the specific constitution thereof can be selected and adjusted by the person skilled in the art according to the purpose of the present invention, and the specific explanation is as follows:

The preparation of the first prefabricated liquid in the method can be properly referred to the preparation method of the Chinese invention patent CN 114054746B, and the shape and the particle size distribution of copper powder can be regulated and controlled mainly by regulating the dosage of copper salt, organic acid and amine compounds according to the needs. When the content of the organic acid is low, the amine compound plays a main role in regulating the shape and particle size distribution of copper powder, can react with inorganic copper salt to generate complex, and prevent oxidation-reduction reaction, and has good selective adsorption effect on copper nanocrystals, thereby being beneficial to promoting the generation of micron copper sheets. When the content of the organic acid is higher, the organic acid plays a main role in regulating the shape and particle size distribution of the copper powder, the organic acid accelerates the oxidation-reduction reaction rate, more copper crystal nuclei are generated in unit time, and the generation of nano particles with smaller sizes is promoted. Although the method is an important control means in the preparation method of the invention, the copper powder of which the two nano-particle-size copper powders are densely coated on the micro-copper sheet can be completely defined from the composition and coating modes.

Example 1

1) 2G of copper hydroxide, 8g of oleic acid and 5g of triisopropanolamine are mixed in 40ml of glycol solution, stirred at a rotation rate of 600r/min and heated to 90 ℃ to form a uniformly mixed first prefabricated solution, then 20g of sodium hypophosphite is added, and the mixture is continuously stirred at the same rotation rate for reaction for 20min to obtain a suspension containing micron-sized flake copper powder.

2) And sequentially pouring 20g of ascorbic acid and a reconstituted second prefabricated liquid formed by mixing 2g of copper acetate, 25g of oleic acid and 40ml of ethylene glycol into the prepared suspension, continuously reacting for 15min under the condition of constant temperature and continuous stirring, cooling to room temperature, centrifuging the cooled reaction product at 4000r/min for 3 min by adopting a centrifuge, and repeatedly washing with ethanol for 2 times to obtain copper powder with three-peak particle size distribution and densely packed particles. As shown in fig. 1 and 2, according to statistical analysis of image analysis software, the copper powder consists of a micrometer copper sheet with a larger size of 1-2 μm and nanometer copper particles with a smaller size of 5-15nm and a smaller size of 40-100 nm; wherein the micrometer copper sheet is tightly wrapped by nanometer copper particles with two particle sizes, and simultaneously 5-15nm nanometer copper particles are tightly wrapped around 40-100nm nanometer copper particles to form an aggregate, and the copper powder has the characteristics of three-peak distribution of particle sizes and compact accumulation of particles. The copper powder with three-peak distribution of particle size obtained in the embodiment is synthesized by a one-step oxidation-reduction method through a two-step process, and the nano copper particles with two particle sizes tightly and uniformly wrap the micrometer copper sheets.

Mixing polyethylene glycol and glycerol at a mass ratio of 1:1, fully stirring, and standing for 30min to allow bubbles to escape, thus obtaining the organic solvent for preparing the copper paste. And uniformly stirring and defoaming the copper powder with the mass percent of 80% and the densely packed particles and the organic solvent with the mass percent of 20% by adopting a planetary gravity stirrer to prepare the copper paste. The organic solvent has good reducibility and adhesiveness; the copper powder is uniformly dispersed in the copper paste, the viscosity, the adhesiveness and the printing performance of the copper paste can be adjusted, and the copper paste has good reducibility and can inhibit the oxidation of the copper powder in the sintering process. The following examples are not intended to be limiting, as to the same organic solvents used in the preparation of copper pastes.

The pure copper substrate was immersed in a 3vol.% dilute sulfuric acid solution for 2min, then the pure copper substrate was cleaned with ethanol and carefully wiped with a dust-free cloth to ensure clean dust-free substrate surface and dried for later use. And printing the copper paste prepared in the embodiment with the thickness of 150 mu m on a pure copper substrate by using a screen printing plate, then pasting the analog power chip on the printed copper paste, applying the pressure of 0.5MPa, and maintaining the pressure for 1min to ensure that the analog chip is in full close contact with the printed copper paste and the pure copper substrate, thereby preparing the assembly to be sintered. And then placing the assembly to be sintered in a sintering furnace, heating to 200 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, preserving heat for 10min, cooling along with the furnace after the heat preservation is finished, and finally preparing the interconnection joint after the sintering is finished. And the shearing strength of the sintered interconnection joint is 23.2MPa by using a mechanical property tester. Morphology observations of sintered interconnect joint fractures were performed using a Scanning Electron Microscope (SEM), as shown in fig. 3. From fig. 3, it can be clearly observed that a large number of large-scale sintered copper structures appear in the fracture, because the nano copper particles are rapidly sintered, fused and grown to connect the micrometer copper sheets, good sintering connection is realized, and a plurality of ductile pits and obvious plastic deformation marks exist in the sintered structures, so that the sintered interconnection joint is fully shown to have good strength, plasticity and other mechanical properties.

The copper powder of the two nanometer-size copper powder densely coated micrometer copper sheets obtained by the embodiment has the particle size trimodal distribution characteristic and densely stacked particles, wherein a large number of nanometer copper particles with two dimensions have the effect of filling gaps among the micrometer copper sheets, and the compactness of the copper powder structure is improved. And (3) connecting the micro copper sheets serving as a framework after the low-temperature sintering fusion of the two-scale nano copper particles to obtain a compact sintering structure. In this example, the shear strength of the sintered joint obtained after pressureless sintering at 200℃for 10min in a nitrogen atmosphere was more than 20MPa.

It should be noted that, the organic acid used in this embodiment and polyethylene glycol and glycerol used to prepare the copper paste have reducing characteristics, can inhibit oxidation of copper particles in the sintering process, and the organic acid can react with copper oxide, so that the generated organic acid copper can be decomposed into tiny nano copper particles at a higher temperature, further promoting sintering of the copper paste matrix and element diffusion of the sintered copper paste matrix and the chip and the pure copper substrate, and can improve the performance of the sintered interconnection joint to a certain extent, but the core effect is that the nano copper particles with two dimensions in copper powder completely cover the micron copper sheets.

In addition, the copper paste prepared by densely coating copper powder of the micron copper sheets with the copper powder with the two nanometer particle sizes adopted in the embodiment can obtain a high-strength sintered interconnection joint under the low-temperature pressureless sintering condition, thereby greatly reducing the production cost and avoiding the damage to the chip.

Example 2

1) 2G of basic copper carbonate, 9g of citric acid and 5g of N, N-dimethylethanolamine are mixed in 40ml of propylene glycol solution, stirred at a rotation rate of 400r/min and heated to 95 ℃ to form uniformly mixed first prefabricated liquid, 18g of sodium citrate is then added, and the mixture is continuously stirred at the same rotation speed for reaction for 30min to obtain the suspension containing the micron flaky copper powder.

2) And (3) sequentially pouring 22g of sodium borohydride and a reconstituted second prefabricated liquid formed by mixing 2g of cupric citrate, 35g of citric acid and 40ml of propylene glycol into the prepared suspension, continuously reacting for 10min under the condition of constant temperature and continuous stirring, cooling to room temperature, centrifuging the cooled reaction product at 3000r/min for 10min by adopting a centrifuge, and repeatedly washing for 3 times by using acetone to obtain copper powder with three-peak particle size distribution and densely packed particles.

Mixing ethylene glycol and propylene glycol in a mass ratio of 3:1, fully stirring, and standing for 30min to remove bubbles to obtain the organic solvent for preparing the copper paste. And uniformly stirring and defoaming the copper powder with the mass percent of 75% and the densely packed particles and the organic solvent with the mass percent of 25% by adopting a planetary gravity stirrer to prepare the copper paste.

The pure copper substrate is soaked in a dilute sulfuric acid solution with the concentration of 5vol.% for 2min, then the pure copper substrate is cleaned by ethanol and carefully wiped by dust-free cloth, so that the surface of the substrate is ensured to be clean and dust-free, and the substrate is dried for later use. And printing the copper paste with the thickness of 300 mu m on a pure copper substrate by using a screen printing plate, then pasting the simulation chip on the printed copper paste, applying a pressure of 0.1MPa, and maintaining the pressure for 5min to ensure that the simulation chip is in full close contact with the printed copper paste and the pure copper substrate, thereby preparing the assembly to be sintered. And then placing the assembly to be sintered in a sintering furnace, heating to 160 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, preserving heat for 20min, cooling along with the furnace after the heat preservation is finished, and finally preparing the interconnection joint after the sintering is finished. The shear strength of the sintered interconnection joint is measured to be 16.2MPa by adopting a mechanical property tester.

Example 3

1) 2G of copper nitrate trihydrate, 15g of lactic acid and 5g of triethanolamine are mixed in 40ml of diethylene glycol solution, stirred at a rotation speed of 500r/min and heated to 85 ℃ to form uniformly mixed first prefabricated liquid, 18g of sodium phosphite is added, and the mixture is continuously stirred at the same rotation speed for reaction for 20min to obtain suspension containing micron-sized flake copper powder.

2) And (3) sequentially pouring 22g of hydrazine sulfate and a reconstituted second prefabricated liquid formed by mixing 2g of ammoniacal copper, 30g of lactic acid and 40ml of diethylene glycol into the prepared suspension, continuously reacting for 30min under the condition of constant temperature and continuous stirring, cooling to room temperature, centrifuging the cooled reaction product at 6000r/min for 5 min by adopting a centrifuge, and repeatedly washing for 4 times by using deionized water to obtain copper powder with three-peak particle size distribution and densely packed particles.

Mixing ethylene glycol, propylene glycol and glycerol in a mass ratio of 1:1:1, fully stirring, and standing for 30min to remove bubbles to obtain the organic solvent for preparing the copper paste. And uniformly stirring and defoaming the copper powder with the mass percent of 85% and the densely packed particles and the organic solvent with the mass percent of 15% by adopting a planetary gravity stirrer to prepare the copper paste.

The pure copper substrate is soaked in a dilute sulfuric acid solution with the concentration of 5vol.% for 2min, then the pure copper substrate is cleaned by ethanol and carefully wiped by dust-free cloth, so that the surface of the substrate is ensured to be clean and dust-free, and the substrate is dried for later use. And printing the copper paste with the thickness of 200 mu m on a pure copper substrate by using a screen printing plate, then pasting the simulation chip on the printed copper paste, applying a pressure of 0.1MPa, and maintaining the pressure for 5min to ensure that the simulation chip is in full close contact with the printed copper paste and the pure copper substrate, thereby preparing the assembly to be sintered. And then placing the assembly to be sintered in a sintering furnace, heating to 240 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, preserving heat for 10min, cooling along with the furnace after the heat preservation is finished, and finally preparing the interconnection joint after the sintering is finished. The shear strength of the sintered interconnection joint was measured to be 26.7MPa using a mechanical property tester.

Example 4

1) 2G of copper chloride, 15g of glycine and 5g of oleylamine are mixed into 40ml of normal propyl alcohol solution, stirred at a rotation speed of 400r/min and heated to 90 ℃ to form uniformly mixed first prefabricated liquid, 20g of glucose is added, and the mixture is continuously stirred at the same rotation speed for reaction for 50min to obtain suspension containing micron-sized flake copper powder.

2) And sequentially pouring 20g of hydrazine hydrate and a reconstituted second prefabricated liquid formed by mixing 2g of amino acid copper, 40g of glycine and 40ml of n-propanol into the prepared suspension, continuously reacting for 20min under the condition of constant temperature and continuous stirring, cooling to room temperature, centrifuging the cooled reaction product at 5000r/min for 5 min by adopting a centrifuge, and repeatedly washing for 5 times by using acetone to obtain copper powder with three-peak particle size distribution and densely packed particles.

Mixing terpineol and diethylene glycol in a mass ratio of 2:1, fully stirring, and standing for 30min to remove bubbles to obtain the organic solvent for preparing the copper paste. And uniformly stirring and defoaming the copper powder with the mass percent of 80% and the densely packed particles and the organic solvent with the mass percent of 20% by adopting a planetary gravity stirrer to prepare the copper paste.

The pure copper substrate is soaked in a 3vol.% dilute sulfuric acid solution for 2min, then the pure copper substrate is cleaned with ethanol and carefully wiped with dust-free cloth, ensuring that the surface of the substrate is clean and dust-free and dried for later use. And printing the copper paste with the thickness of 100 mu m on a pure copper substrate by using a screen printing plate, then pasting the simulation chip on the printed copper paste, applying a pressure of 0.5MPa, and maintaining the pressure for 1min to ensure that the simulation chip is in full close contact with the printed copper paste and the pure copper substrate, thereby preparing the assembly to be sintered. And then placing the assembly to be sintered in a sintering furnace, heating to 180 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, preserving heat for 30min, cooling along with the furnace after the heat preservation is finished, and finally preparing the interconnection joint after the sintering is finished. And the shearing strength of the sintered interconnection joint is 18.3MPa measured by a mechanical property tester.

Comparative example 1

Preparing non-compactly wrapped flaky copper powder by centrifugally cleaning a suspension containing micron copper sheets: mixing 2g of copper hydroxide, 8g of oleic acid and 5g of triisopropanolamine into 40ml of glycol solution, stirring at a rotation rate of 600r/min, heating to 90 ℃ to form uniformly mixed prefabricated solution, adding 20g of sodium hypophosphite, continuously stirring at the same rotation speed for reacting for 20min, cooling to room temperature, centrifuging the cooled reaction product at a rotation speed of 4000r/min for 3 min by adopting a centrifuge, and repeatedly washing with ethanol for 2 times to prepare the non-compactly coated flaky copper powder, wherein the particle size of small nano copper particles is 5-15nm, and the particle size of a micrometer copper sheet is 1-2 mu m.

Mixing polyethylene glycol and glycerol at a mass ratio of 1:1, fully stirring, and standing for 30min to remove bubbles to obtain the organic solvent for preparing the copper paste. And uniformly stirring the prepared non-compactly wrapped sheet copper powder with the mass percentage of 80% and an organic solvent with the mass percentage of 20% by adopting a planetary gravity stirrer, and defoaming to prepare copper paste.

The pure copper substrate is soaked in a 3vol.% dilute sulfuric acid solution for 2min, then the pure copper substrate is cleaned with ethanol and carefully wiped with dust-free cloth, ensuring that the surface of the substrate is clean and dust-free and dried for later use. And printing the copper paste with the thickness of 150 mu m on a pure copper substrate by using a screen printing plate, then pasting the simulation chip on the printed copper paste, applying a pressure of 0.5MPa, and maintaining the pressure for 1min to ensure that the simulation chip is in full close contact with the printed copper paste and the pure copper substrate, so as to prepare the assembly to be sintered. And then placing the assembly to be sintered in a sintering furnace, heating to 200 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, preserving heat for 10min, cooling along with the furnace after preserving heat, checking that the prepared sintered interconnection joint basically has no interface bonding, and measuring the shearing strength of the sintered interconnection joint to be only 0.3MPa by adopting a mechanical property tester.

Comparative example 1 compared with example 1, the number of nano copper particles coated on the surface of the micrometer copper sheet is obviously reduced, the initial bulk density of copper powder is low, the sintering process is insufficient, and the sintering structure is not compact enough. The reduction in the number of nano-copper particles with higher sintering driving force results in a weakening of the diffusion driving force between the copper paste and the chip and pure copper substrate, ultimately resulting in a difficult to achieve good metallurgical connection in the sintered joint.

Comparative example 2

This comparative example is provided entirely in accordance with example 1 of chinese patent No. CN 114054746B.

Preparing copper powder with particle size of nanometer to micrometer three-peak distribution characteristic. 2g of copper acetate, 10g of lactic acid and 6g of triethanolamine are added into 40ml of glycol solution to obtain a reaction solution; after the reaction solution was heated to 85 ℃, 20g of sodium hypophosphite was added thereto, and stirred at 600rpm for dissolution; after reacting for 10min, centrifuging at 4000rpm with a centrifuge, and centrifuging and washing with ethanol twice to obtain copper powder with three-peak particle size distribution and coating structure, wherein the particle size of nanometer copper particles is 5-9nm, the particle size of submicron copper particles is 120-180nm, and the particle size of micron copper sheets is 1-2 μm.

Mixing polyethylene glycol and glycerol at a mass ratio of 1:1, fully stirring, and standing for 30min to remove bubbles to obtain the organic solvent for preparing the copper paste. And uniformly stirring and defoaming the prepared copper powder with the mass percentage of 80% and the organic solvent with the mass percentage of 20% by adopting a planetary gravity stirrer to prepare copper paste.

The pure copper substrate is soaked in a 3vol.% dilute sulfuric acid solution for 2min, then the pure copper substrate is cleaned with ethanol and carefully wiped with dust-free cloth, ensuring that the surface of the substrate is clean and dust-free and dried for later use. And printing the copper paste with the thickness of 150 mu m on a pure copper substrate by using a screen printing plate, then pasting the simulation chip on the printed copper paste, applying a pressure of 0.5MPa, and maintaining the pressure for 1min to ensure that the simulation chip is in full close contact with the printed copper paste and the pure copper substrate, so as to prepare the assembly to be sintered. And then placing the assembly to be sintered in a sintering furnace, heating to 200 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, preserving heat for 10min, cooling along with the furnace after preserving heat, checking that the prepared sintered interconnection joint has no interface bonding, and measuring the shearing strength of the sintered interconnection joint to be 0MPa by adopting a mechanical property tester.

Fig. 4 is a Scanning Electron Microscope (SEM) image of copper microplates coated with small-sized copper powder obtained in example 1 of chinese patent No. CN 114054746B. As is apparent from comparing fig. 1 and fig. 4, in comparative example 2, copper powder contains micro copper sheets, submicron copper particles and nano copper particles, while submicron copper particles are not coated on the surface of the micro copper sheets, and the number of small nano copper particles coated on the surface of the micro copper sheets, which are easy to sinter, is small, so that the overall bulk density of the formed copper powder is low, and the sintering structure is not compact enough. Meanwhile, fewer nano copper particles with higher sintering driving force make the interface bonding capability between the copper paste and the chip and the pure copper substrate worse, and cannot realize metallurgical connection. The copper powder obtained in comparative example 2 cannot be used for power chip and power device packaging.

The embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principles of the invention should be made and equivalents should be construed as falling within the scope of the present invention.

Claims (10)

1. Copper powder of two kinds of nanometer particle diameter copper powder densely coated with micron copper sheet, characterized by, it is by length of 1-2 microns micron copper sheet and diameter of 5-15nm and 40-100nm two kinds of nanometer copper particle composition of particle diameter; wherein the micrometer copper sheet is completely and tightly wrapped by two kinds of nanometer copper particles with the particle sizes, the nanometer copper particles with the particle sizes of 5-15nm are tightly wrapped around the nanometer copper particles with the particle sizes of 40-100nm, and the three kinds of copper powder show aggregation bodies with the particle sizes distributed in a trimodal manner and densely packed particles.

2. The method for preparing copper powder of two kinds of copper powder densely coated with copper powder with nanometer particle size and micrometer copper sheet as set forth in claim 1, wherein weak reducing agent is added into first preformed liquid in a reaction kettle to obtain initial reaction liquid, and the initial reaction liquid is continuously stirred at 80-120 ℃ to obtain flake copper powder suspension; adding a strong reducing agent into the flaky copper powder suspension, adding a second prefabricated solution to form a final reaction solution, and continuously stirring at the temperature of 80-120 ℃ to obtain three copper powder suspensions with different particle diameters; cooling, centrifuging and washing to obtain copper powder with two kinds of copper powder with nanometer particle size densely coated with micrometer copper sheet;

The first prefabricated liquid is obtained by mixing inorganic copper salt, organic acid, amine compound and polyalcohol solvent and continuously stirring at 80-100 ℃;

the second prefabricated liquid is obtained by mixing organic copper salt, organic acid and a polyalcohol solvent and continuously stirring at the temperature of 80-100 ℃.

3. The method for preparing copper powder densely coated with copper powder with micron particle size according to claim 2, wherein the inorganic copper salt is one or more of copper carbonate, basic copper carbonate, copper sulfate, copper hydroxide, copper chloride and copper nitrate trihydrate;

The organic acid is one or more of oxalic acid, glycine, citric acid, tartaric acid, lactic acid, propionic acid and oleic acid;

The amine compound is one or more of oleylamine, ethylenediamine, methanolamine, triethanolamine, N-dimethylethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine and diethylenetriamine;

the polyalcohol solvent is one or more of ethylene glycol, diethylene glycol, propylene glycol, glycerol, isopropanol and n-propanol;

The organic copper salt is one or more of copper acetate, copper amino acid, copper rosinate, copper citrate and copper ammine.

4. The method for preparing copper powder densely coated with copper powder with micron particle size according to claim 2 or 3, wherein the concentration of the inorganic copper salt in the first preformed liquid is 30-80g/L, the total concentration of the organic acid and the amine compound is 300-600g/L, and the mass concentration ratio of the organic acid to the amine compound is 1:1-5:1;

In the second prefabricated liquid, the concentration of the organic copper salt is 30-80g/L, and the concentration of the organic copper salt is 400-1200g/L.

5. The method for preparing copper powder densely coated with copper powder with two nanometer particle sizes and copper powder with a micrometer copper sheet according to claim 2, wherein the weak reducing agent is one or more of sodium citrate, sodium hypophosphite, sodium phosphite, potassium tartrate, hydrogen peroxide and glucose;

the strong reducing agent is one or more of hydrazine hydrate, hydrazine sulfate, sodium borohydride, ascorbic acid and tetrabutylammonium borohydride.

6. The method for preparing copper powder densely coated with copper powder with micron particle size according to claim 2 or 5, wherein the concentration of the weak reducing agent in the initial reaction solution is 400-800g/L; the concentration of the strong reducing agent in the final reaction solution is 200-500g/L.

7. The method for preparing copper powder densely coated with copper powder with two nanometer particle sizes and copper powder with a micrometer copper sheet according to claim 2, wherein in the preparation of the flaky copper powder suspension, the three copper powder suspensions with different particle sizes, the first prefabricated liquid and the second prefabricated liquid, the continuous stirring speed is 400-600r/min, the stirring time in the preparation of the first prefabricated liquid and the second prefabricated liquid is 5-20min, the stirring time in the preparation of the flaky copper powder suspension is 10-60min, and the stirring time in the preparation of the copper powder suspensions with different particle sizes is 10-30min;

The cooling is to cool to room temperature;

Centrifuging the cooled reaction product by adopting a centrifuge at a rotating speed of 3000-6000r/min for 3-10 minutes;

The washing is carried out by repeatedly washing with one or more of ethanol, deionized water and acetone for 2-5 times.

8. The use of copper powder densely coated with copper powder with micron copper flakes with two nanometer particle size according to claim 1 for preparing copper paste.

9. The application of the copper powder densely coated with the copper powder with the nanometer particle size and the copper powder with the micrometer copper powder to preparing copper paste, according to the claim 8, is characterized in that the copper powder densely coated with the copper powder with the nanometer particle size and the copper powder with the micrometer copper powder are uniformly stirred and defoamed to prepare the copper paste; the organic solvent is one or more of ethylene glycol, propylene glycol, glycerol, diethylene glycol, terpineol and polyethylene glycol.

10. The use of copper powder densely coated with copper powder with micron copper sheets with two nanometer particle size according to claim 9, wherein the uniform stirring is mixing by a planetary gravity stirrer;

the copper powder of the two nanometer particle size copper powders densely coated with the micrometer copper sheet accounts for 75-90% by mass percent, and the organic solvent accounts for 25-10%;

The application of the copper paste in preparing the sintered joint comprises the following steps: printing on the surface of a lower pure copper substrate by adopting a screen printing method, wherein the thickness of copper paste is 10-400 mu m, placing a power chip or a power device on the printed copper paste surface, applying patch pressure of 0-0.5MPa, and keeping the pressure for 1-5min to obtain a chip/copper paste/copper substrate sandwich structure to-be-sintered assembly; sintering at 160-240 deg.c for 10-40min in nitrogen atmosphere without pressure assistance to form sintered joint.