Preparation method of semiconductor packaging piece, preparation method of copper powder, copper powder and copper powder reaction device

Abstract

The invention provides a preparation method of a semiconductor packaging piece, a preparation method of copper powder, the copper powder and a copper powder reaction device. The preparation method of the copper powder comprises the following steps: providing a mixed solution; the mixed solution comprises carboxylate ions, and the mixed solution is in an alkaline environment; adding a copper raw material into the mixed solution, and uniformly mixing the copper raw material and the mixed solution to obtain a target solution; the copper raw material comprises copper particles and copper oxide formed on the peripheries of the copper particles; the target solution is pumped into the flow guide channel, the target solution is kept in a flowing state in the flow guide channel, the target solution flowing in the flow guide channel is heated, carboxylate ions of the target solution react with copper oxide of the copper raw material to form copper carboxylate, and a product solution is obtained; and solid-liquid separation is conducted on the product solution, copper powder with copper particles as cores and copper carboxylate as shells is obtained, and part of the crystal face 111 in the copper powder is converted into a stable crystal face 220.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for preparing a semiconductor package, a method for preparing copper powder, copper powder and a copper powder reaction device. Background Art

[0002] In the past few decades, silicon has been the most widely used semiconductor material in power devices, but now it is approaching its physical limits. Recently, wide bandgap (WBG) semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) are replacing Si for power electronics due to favorable power density, switching speed, and operating temperature. For high-power applications, the junction temperature of WBG chips may reach above 250°C, and high temperatures will cause the failure of traditional chip connection materials. For example, the melting point of traditional tin-based solder is usually below 250°C, which is difficult to meet the needs of high-temperature electronic applications. Therefore, it is urgent to develop a new type of connection material that is resistant to high temperatures. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing a semiconductor package, a method for preparing copper powder, copper powder and a copper powder reaction device to solve the problems in the prior art.

[0004] In order to solve the above technical problems, the present invention provides a method for preparing copper powder, comprising the following steps:

[0005] Providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment;

[0006] Adding a copper raw material to the mixed solution and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles;

[0007] The target solution is pumped into the diversion channel, so that the target solution remains in a flowing state in the diversion channel, and the target solution flowing in the diversion channel is heated, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, thereby obtaining a product solution;

[0008] The product solution is subjected to solid-liquid separation to obtain copper powder with copper particles as cores and copper carboxylate as shells, and part of the crystal planes 111 in the copper powder are converted into stable crystal planes 220 .

[0009] In one embodiment, the method for preparing the copper raw material comprises the following steps:

[0010] Copper particles are provided, and the copper particles are subjected to an oxidation reaction to obtain the copper raw material having the copper particles as the core and copper oxide as the shell.

[0011] In one embodiment, the oxidation reaction steps are as follows:

[0012] The copper particles are mixed with deionized water and reacted at 150-250° C. for 5-20 minutes.

[0013] In one embodiment, the pH value of the mixed solution is 10 to 12;

[0014] The mixed solution includes an alkaline substance and a carboxylic acid-containing substance, and the carboxylic acid-containing substance includes at least one of a carboxylic acid and a carboxylate.

[0015] In one embodiment, the carboxylic acid includes at least one of formic acid, oxalic acid, citric acid and lactic acid, the carboxylate includes at least one of formates, oxalates, citrates and lactates, the mass percentage of the carboxylic acid-containing substance is 50-100%, and the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium formate, potassium formate, sodium oxalate, potassium oxalate, oleylamine, ethylenediamine, triethanolamine and isopropanolamine.

[0016] In one embodiment, in the target solution, the molar ratio of copper to the carboxylate ion is (0.1-1):1;

[0017] The copper particles have a particle size of 0.01-10 μm;

[0018] The copper particles include at least one of spherical copper, flake copper and dendritic copper.

[0019] In one embodiment, the reaction temperature of the target solution in the diversion channel is 120-200° C., and the reaction time is 10-60 min;

[0020] The inner diameter of the flow guiding channel is 0.25-0.6 mm.

[0021] The present invention also provides a copper powder, which is prepared by the preparation method as described above.

[0022] The present invention also provides a method for preparing a semiconductor package, comprising the following steps:

[0023] The copper powder prepared by the preparation method as described above is used as a raw material to prepare and obtain solder paste;

[0024] The two substrates are welded with the solder paste to obtain a semiconductor package.

[0025] In one embodiment, the solid content of the solder paste is 60%-90%;

[0026] The steps of welding two substrates to obtain a semiconductor package include: making a solder paste layer on one of the substrates by using the solder paste;

[0027] placing another substrate on the solder paste layer to obtain an intermediate part;

[0028] The semiconductor package is obtained by subjecting the intermediate piece to heat and pressure treatment under a protective gas atmosphere, wherein the heat preservation temperature is between 180° C. and 320° C., the pressure holding pressure is between 1 MPa and 20 MPa, and the heat and pressure preservation treatment time is between 1 min and 60 min.

[0029] The present invention also provides a copper powder reaction device, the device comprising:

[0030] A first container is used to contain reactants and mix the reactants evenly to obtain a target solution; the first container is corrosion-resistant;

[0031] One or more diversion channels, communicating with the first container;

[0032] A pumping assembly, used to draw the target solution in the first container into the diversion channel and keep the target solution in a flowing state;

[0033] a heating component, used for heating the target solution flowing in the flow guiding channel; and

[0034] The second container is connected to the flow guiding channel to accommodate the product solution outputted from the flow guiding channel.

[0035] It can be seen from the above technical solution that the advantages and positive effects of the present invention are:

[0036] The preparation method of the copper powder of the present invention uses carboxylate to react with copper to form copper powder with copper particles as the core and copper carboxylate as the shell. Since copper carboxylate has good thermal stability and good oxidation resistance, the oxidation resistance of the entire copper powder is good. At the same time, the sintering temperature of copper carboxylate is lower than the sintering temperature of copper, thereby reducing the overall sintering temperature of the copper powder, improving the sintering strength of the device, reducing the connection void rate of the device, and improving the long-term reliability of the device. The active crystal plane 111 of the copper particles in the copper powder is partially converted into a stable crystal plane 220, further improving the stability and oxidation resistance of the copper itself.

[0037] The semiconductor package of the present invention is prepared by using the copper powder as solder paste. Therefore, the semiconductor package has lower sintering strength, less connection void rate and higher long-term reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic flow diagram of the method for preparing copper powder in the present invention.

[0039] Figure 2 It is a schematic diagram of the formation principle of copper powder in the present invention.

[0040] Figure 3 It is a structural schematic diagram of a copper powder reaction device in one embodiment of the present invention.

[0041] Figure 4 It is the X-ray diffraction pattern of Example 1 and Comparative Example 1 in the present invention.

[0042] Figure 5 It is a transmission electron microscope image of Example 1 of the present invention.

[0043] Figure 6 It is a transmission electron microscope image of comparative example 1 in the present invention.

[0044] The following are the descriptions of the reference numerals:

[0045] 11. First container; 12. Guide channel; 13. Heating component; 14. Second container. DETAILED DESCRIPTION

[0046] Typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various changes in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations therein are essentially used for illustration purposes rather than for limiting the present invention.

[0047] In order to further illustrate the principle and structure of the present invention, preferred embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0048] It should be noted that the inventors of this application have discovered that existing nano-copper solders are at risk of being easily oxidized. Copper is oxidized to form copper oxide. Since the sintering temperature of copper oxide is higher than that of copper, this will increase the sintering temperature of the solder and increase the sintering voids, thereby leading to insufficient device connection strength and cold solder joints, greatly reducing the reliability of the device.

[0049] Previous nano copper sintering technology often uses high-end equipment and complex processes. For example, a xenon lamp is used to sinter copper conductive paste. The equipment required for this method is expensive and difficult to achieve large-scale industrial production. The prior art discloses adding imidazole compounds to coat nano copper particles during the preparation of nano copper to avoid the agglomeration and oxidation of nano copper particles. The prior art also discloses adding a short carbon chain (C3-C5) alcohol amine complexing agent during the preparation of nano copper particles to form a coordination bond between the complexing agent and the copper nano particles to inhibit the oxidation and agglomeration of copper nano particles. However, the above-mentioned prior art does not fundamentally solve the agglomeration and oxidation problems of nano copper particles, and the introduction of the coating will increase the sintering temperature and reduce the strength, electrical conductivity and thermal conductivity of the sintered body.

[0050] Therefore, the present application provides a method for preparing copper powder to prepare copper powder with good oxidation resistance.

[0051] The copper powder prepared by the preparation method has copper particles as the core and copper carboxylate as the shell. The copper carboxylate has good thermal stability and good oxidation resistance. Therefore, the copper carboxylate can prevent the copper particles from oxidizing. At the same time, the sintering temperature of the copper carboxylate is low, so the sintering temperature of the copper powder as a whole is reduced, the sintering strength of the device is improved, the connection void rate of the device is reduced, and the long-term reliability of the device is improved. Some crystal planes 111 of the copper particles in the copper powder are converted into stable crystal planes 220, which further improves the oxidation resistance of the copper itself.

[0052] The following is a detailed introduction to the preparation method of copper powder.

[0053] See also Figure 1 , the preparation method of copper powder comprises the following steps:

[0054] S100, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0055] Specifically, the carboxylate ion can be provided by carboxylic acid or carboxylate. The alkaline environment is provided by an alkaline substance. Therefore, the mixed solution includes an alkaline substance and a carboxylate-containing substance. The carboxylate-containing substance means that the substance contains carboxylate.

[0056] Wherein, the mass percentage of the carboxylic acid-containing substance is 50-100%. Exemplarily, when the carboxylic acid-containing substance is carboxylic acid, the mass percentage at this time refers to the mass percentage of the pure carboxylic acid to the mass sum of the pure carboxylic acid and water after the pure carboxylic acid and water are uniformly mixed.

[0057] Specifically, the carboxylic acid-containing substance includes at least one of a carboxylic acid and a carboxylate. That is, the mixed solution may include only carboxylic acid, only carboxylate, or both. At least one of the following can be understood as above, that is, it can be any one, a combination of any two, or a combination of any three. The combination of several substances is not limited and can be selected according to actual needs.

[0058] The carboxylic acid includes at least one of formic acid, oxalic acid, citric acid and lactic acid. The carboxylate includes at least one of formates, oxalates, citrates and lactates. That is, the mixed solution may contain only any one of the carboxylic acids, any two of the carboxylic acids, or one of the carboxylic acids and one of the carboxylates. The specific amount may be set according to actual needs.

[0059] The alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium formate, potassium formate, sodium oxalate, potassium oxalate, oleylamine, ethylenediamine, triethanolamine, and isopropanolamine.

[0060] The pH value of the mixed solution may be 8 to 12. The pH value of the mixed solution is preferably 10 to 12. Specifically, the pH value of the mixed solution can be achieved by adjusting the molar ratio of the alkaline substance and the carboxylic acid-containing substance.

[0061] S200, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution. The copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0062] Since copper particles are easily oxidized, various methods are used in related technologies to remove the oxide layer on the surface of copper particles or to form a protective layer on the surface of copper particles for protection. However, this solution takes a different approach and uses the property that copper particles are easily oxidized to generate copper oxide. It directly uses copper oxide to react with carboxylates to generate copper carboxylates that can prevent copper particles from oxidizing, eliminating the need for additional protective measures or reduction measures for copper. The sintering temperature of copper carboxylates is lower than that of copper, thereby reducing the sintering temperature of the target product copper powder and improving the sintering strength of the device.

[0063] In order to ensure that the periphery of the copper particles has sufficient copper oxide, it is preferred to subject the copper particles to an oxidation reaction in the present application.

[0064] Specifically, the preparation method of the copper raw material includes the following steps:

[0065] Copper particles are provided and subjected to oxidation reaction to obtain a copper raw material having the copper particles as a core and copper oxide as a shell.

[0066] The steps of the oxidation reaction are as follows:

[0067] The copper particles were mixed with deionized water and reacted at 150-250°C for 5-20 min.

[0068] The particle size of the copper particles is 0.01-10 μm.

[0069] The copper particles include at least one of spherical copper, flake copper and dendritic copper.

[0070] Specifically, when the copper particles are spherical copper, the particle size may be 0.1-1 μm. When the copper particles are flake copper, the particle size may be 0.2-10 μm.

[0071] The shape and size of the copper particles are selected according to the welding requirements.

[0072] Wherein, in the target solution, the molar ratio of copper to carboxylate ions is (0.1-1): 1. Here, it refers to the molar ratio of copper atoms to carboxylate ions.

[0073] S300, pumping the target solution into the diversion channel, keeping the target solution in a flowing state in the backflow channel, and heating the target solution flowing in the diversion channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0074] See also Figure 2 The carboxylate reacts with copper oxide to form copper carboxylate, which coats the periphery of the copper particles, forming a product with the copper particles as the core and the copper carboxylate as the shell. A uniform and dense copper carboxylate layer is formed on the periphery of the copper particles. And the copper carboxylate can prevent the copper particles from oxidizing.

[0075] Since the target solution is in an alkaline environment, copper oxide reacts with carboxylates in an alkaline environment to form copper carboxylates. The copper particles in the copper carboxylates are preferentially oriented, which changes the crystal phase of the copper surface and converts part of the 111 crystal plane into a 220 crystal plane.

[0076] Specifically, a peristaltic pump is used to extract the target solution, and the target solution is kept in a flowing state in the diversion channel. The flowing target solution is heated to allow the carboxylate ions to react with the copper raw material in a flowing state, thereby increasing the nucleation rate and the reaction rate.

[0077] The reaction temperature of the target solution in the diversion channel is 120-200° C., and the reaction time is 10-60 min.

[0078] Specifically, the guide channel portion may pass through a heating device, and the target solution flowing in the guide channel may be heated by the heating device.

[0079] The inner diameter of the flow guide channel is 0.25-0.6 mm.

[0080] S400 , performing solid-liquid separation on the product solution to obtain copper powder with copper particles as cores and copper carboxylate as shells, and part of the crystal planes 111 in the copper powder are converted into stable crystal planes 220 .

[0081] The solid-liquid separation can be carried out by filtering or centrifugation, and the solid-liquid separation method can be selected according to actual needs.

[0082] After solid-liquid separation, vacuum drying is performed to obtain copper powder.

[0083] In summary, the preparation method of the present application has the following advantages:

[0084] 1. Since the mixed solution is alkaline, the reaction environment of the copper raw material and the carboxylate is an alkaline environment, so that the carboxylic acid can be neutralized by the alkaline substance, and the strong corrosiveness of the carboxylic acid can be suppressed based on the alkaline environment, thereby avoiding changes in the morphology of the copper particles.

[0085] 2. Due to the alkaline environment of the mixed solution, the carboxylate-containing substances can be ionized to generate carboxylate ions, which then react with the copper oxide on the surface of the copper raw material. The carboxylate can directly react with the copper oxide on the surface of the copper nanoparticles to generate copper carboxylate, which is attached to the surface of the copper nanoparticles. Since the reaction is relatively direct, the reaction temperature is reduced and the reaction time is shortened.

[0086] 3. Since carboxylate reacts with copper oxide in the flow channel, the heat capacity is reduced by using the micron-sized channel of the flow channel, making it easier to heat up, shortening the heating time and increasing the reaction speed. That is, by using a small-diameter flow channel, the target reaction temperature can be reached in a very short time.

[0087] Moreover, the carboxylate reacts with copper oxide in a flowing state, which increases the nucleation rate of the particles and improves the reaction rate, thereby forming a more uniform and dense copper carboxylate modified layer on the surface of the copper particles.

[0088] 4. Copper oxide reacts with carboxylate in an alkaline environment to form copper carboxylate. The copper particles in the copper carboxylate are preferentially oriented, which changes the crystal phase of the copper surface, converting part of the crystal plane 111 into a stable crystal plane 220, thereby making the copper particles themselves more stable and improving oxidation resistance.

[0089] The present application also provides a copper powder, which is prepared by the above-mentioned preparation method.

[0090] See also Figure 3 The present application also provides a copper powder reaction device for preparing copper powder. Specifically, the copper powder reaction device includes a first container 11, a flow guide channel 12, a pumping component (not shown in the figure), a heating component 13 and a second container 14.

[0091] The first container 11 is used to hold reactants and mix the reactants to obtain a target solution. The first container 11 is corrosion-resistant. Specifically, the first container 11 is made of glass, which is acid-resistant and alkali-resistant. Exemplarily, the first container 11 can be a beaker or a flask.

[0092] The guide channel 12 is connected to the first container 11. The number of the guide channels 12 can be one or more. When the number of the guide channels 12 is multiple, the multiple guide channels 12 are all connected to the first container 11, which can be understood as multiple guide channels 12 are arranged in parallel.

[0093] The pumping assembly is used to draw the target solution in the first container 11 into the flow channel 12 and keep the target solution in a flowing state.

[0094] The heating component 13 is used to heat the target solution flowing in the guiding channel 12 .

[0095] The second container 14 is connected to the flow guiding channel 12 to accommodate the product solution outputted from the flow guiding channel 12 .

[0096] A solid-liquid separation device and a drying device are also provided downstream of the copper powder reaction device. The solid-liquid separation device is used to separate the copper powder in the product solution. The drying device is used to dry the copper powder.

[0097] The present application also provides a method for preparing a semiconductor package, comprising the following steps:

[0098] S600, preparing and obtaining solder paste using the copper powder prepared by the above preparation method as raw material.

[0099] Specifically, the solid content of the solder paste is 60%-90%.

[0100] S700, soldering two substrates with solder paste to obtain a semiconductor package.

[0101] Specifically, the steps of welding two substrates to obtain a semiconductor package include:

[0102] S710, forming a solder paste layer on one of the substrates using solder paste.

[0103] S720, placing another substrate on the solder paste layer to obtain an intermediate component.

[0104] S730. Under a protective gas atmosphere, the intermediate piece is subjected to heat and pressure treatment to obtain a semiconductor package, wherein the heat preservation temperature is between 180° C. and 320° C., the pressure is between 1 MPa and 20 MPa, and the heat and pressure treatment time is between 1 min and 60 min.

[0105] Protective gas atmosphere such as helium, nitrogen, etc.

[0106] Since the semiconductor package in the present application adopts the above copper powder, its sintering temperature of 180-320° C. is lower than 260-320° C. in the related art.

[0107] The inventors of the present application have achieved the preparation of copper powder by strictly designing the content of each component and the parameters in each step. The preparation method of copper powder is introduced below through various embodiments.

[0108] Example 1

[0109] The preparation method of the copper powder in this embodiment comprises the following steps:

[0110] S11, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0111] Specifically, the mixed solution includes oxalic acid and potassium hydroxide, and the mass percentage of oxalic acid is 85%.

[0112] The pH value of the mixed solution was 11.

[0113] S12, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0114] The copper particles have a particle size of 0.01 μm. The copper particles are spherical copper. The copper particles are mixed with deionized water and reacted at 150° C. for 20 minutes.

[0115] In the target solution, the molar ratio of copper to carboxylate ions is 0.5:1.

[0116] S13, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0117] The target solution has a temperature of 160° C. in the flow channel and remains in a flowing state for 20 minutes.

[0118] S14, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0119] The product solution is separated and dried to obtain copper powder.

[0120] Example 2

[0121] The preparation method of the copper powder in this embodiment comprises the following steps:

[0122] S21, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0123] Specifically, the mixed solution includes formic acid and sodium formate, and the mass percentage of formic acid is 100%.

[0124] The pH value of the mixed solution was 10.

[0125] S22, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0126] The copper particles have a particle size of 10 μm. The copper particles are flake copper. The copper particles are mixed with deionized water and reacted at 250° C. for 5 minutes.

[0127] In the target solution, the molar ratio of copper to carboxylate ions is 1:1.

[0128] S23, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0129] The target solution has a temperature of 200° C. in the flow channel and remains in a flowing state for 10 min.

[0130] S24, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0131] The product solution is separated and dried to obtain copper powder.

[0132] Example 3

[0133] The preparation method of the copper powder in this embodiment comprises the following steps:

[0134] S31, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0135] Specifically, the mixed solution includes formic acid and potassium formate, and the mass percentage of formic acid is 50%.

[0136] The pH value of the mixed solution was 8.

[0137] S32, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0138] The copper particles have a particle size of 0.2 μm. The copper particles are dendritic copper. The copper particles are mixed with deionized water and reacted at 200° C. for 10 min.

[0139] In the target solution, the molar ratio of copper to carboxylate ions is 0.1:1.

[0140] S33, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0141] The target solution has a temperature of 200° C. in the flow channel and remains in a flowing state for 10 min.

[0142] S34, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0143] The product solution is separated and dried to obtain copper powder.

[0144] Example 4

[0145] The preparation method of the copper powder in this embodiment comprises the following steps:

[0146] S41, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0147] Specifically, the mixed solution includes sodium oxalate and sodium carbonate, and the mass percentage of the sodium oxalate is 80%.

[0148] The pH value of the mixed solution was 9.

[0149] S42, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0150] The copper particles have a particle size of 1 μm. The copper particles are spherical copper. The copper particles are mixed with deionized water and reacted at 180° C. for 15 minutes.

[0151] In the target solution, the molar ratio of copper to carboxylate ions is 0.6:1.

[0152] S43, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0153] The target solution has a temperature of 120° C. in the flow channel and remains in a flowing state for 60 min.

[0154] S44, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0155] The product solution is separated and dried to obtain copper powder.

[0156] Example 5

[0157] The preparation method of the copper powder in this embodiment comprises the following steps:

[0158] S51, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0159] Specifically, the mixed solution includes sodium citrate and triethanolamine, and the mass percentage of citric acid is 70%.

[0160] The pH value of the mixed solution was 12.

[0161] S52, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0162] The copper particles have a particle size of 2 μm. The copper particles are spherical copper. The copper particles are mixed with deionized water and reacted at 220° C. for 8 minutes.

[0163] In the target solution, the molar ratio of copper to carboxylate ions is 0.8:1.

[0164] S53, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0165] The target solution has a temperature of 180° C. in the flow channel and remains in a flowing state for 15 min.

[0166] S54, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0167] The product solution is separated and dried to obtain copper powder.

[0168] Example 6

[0169] The preparation method of the copper powder in this embodiment comprises the following steps:

[0170] S61, providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment.

[0171] Specifically, the mixed solution includes lactic acid and sodium oxalate, and the mass percentage of sodium lactate is 50%.

[0172] The pH value of the mixed solution was 8.

[0173] S62, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0174] The copper particles have a particle size of 0.5 μm. The copper particles are spherical copper. The copper particles are mixed with deionized water and reacted at 160° C. for 16 minutes.

[0175] In the target solution, the molar ratio of copper to carboxylate ions is 0.4:1.

[0176] S63, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0177] The target solution has a temperature of 150° C. in the flow channel and remains in a flowing state for 30 minutes.

[0178] S64, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0179] The product solution is separated and dried to obtain copper powder.

[0180] Example 7

[0181] The preparation method of the copper powder in this embodiment comprises the following steps:

[0182] S71. Provide a mixed solution; the mixed solution includes carboxylate ions and the mixed solution is in an alkaline environment.

[0183] Specifically, the mixed solution includes oxalic acid, sodium oxalate and sodium hydroxide. Oxalic acid and sodium oxalate together constitute a carboxylic acid-containing substance, and the mass percentage is 90%.

[0184] The pH value of the mixed solution was 10.5.

[0185] S72, adding a copper raw material to the mixed solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0186] The copper particles have a particle size of 0.5 μm. The copper particles are spherical copper. The copper particles are mixed with deionized water and reacted at 170° C. for 14 minutes.

[0187] In the target solution, the molar ratio of copper to carboxylate ions is 0.7:1.

[0188] S73, pumping the target solution into the guide channel, keeping the target solution in a flowing state in the guide channel, and heating the target solution flowing in the guide channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0189] The target solution has a temperature of 190° C. in the flow channel and remains in a flowing state for 15 minutes.

[0190] S74, performing solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell, and part of the crystal plane 111 in the copper powder is converted into a stable crystal plane 220.

[0191] The product solution is separated and dried to obtain copper powder.

[0192] Comparative Example 1 (formic acid only, no alkaline environment)

[0193] The preparation method of the copper powder in this embodiment comprises the following steps:

[0194] S81. Provide a formic acid solution.

[0195] S82, adding a copper raw material to the formic acid solution, and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles.

[0196] The copper particles have a particle size of 0.01 μm. The copper particles are spherical copper. The copper particles are mixed with deionized water and reacted at 150° C. for 20 minutes.

[0197] In the target solution, the molar ratio of copper to formate ions is 0.5:1.

[0198] S83, pumping the target solution into the diversion channel, keeping the target solution in a flowing state in the diversion channel, and heating the target solution flowing in the diversion channel, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, and obtain a product solution.

[0199] The target solution has a temperature of 160° C. in the flow channel and remains in a flowing state for 20 minutes.

[0200] S84. Perform solid-liquid separation on the product solution to obtain copper powder with copper particles as core and copper carboxylate as shell.

[0201] The product solution is separated and dried to obtain copper powder.

[0202] Comparative Example 2

[0203] Copper powder from Guangzhou Hongwu New Materials.

[0204] The copper powders of Examples 1 to 7 and Comparative Example 1 were subjected to X-ray diffraction detection to obtain X-ray diffraction patterns, respectively. Figure 4The graphs of Example 1, Comparative Example 1 and standard copper are shown, wherein the graphs of Example 1, Comparative Example 1 and standard copper are represented from top to bottom. It can be seen from the graph that the graph of the copper powder of Comparative Example 1 is basically consistent with the graph of the standard copper in terms of diffraction angle and intensity, while the graph of the copper powder in Example 1 is basically consistent with the diffraction angle of the standard graph, except that the intensity is different. The crystal plane 220 of the copper powder in Example 1 is significantly increased, and the crystal plane 111 is significantly reduced. Therefore, the copper powder in Example 1 has more stable crystal planes 200, which increases the stability of the copper powder. The X-ray diffraction graphs of the copper powders of Examples 2 to 7 are basically consistent with the X-ray diffraction graph of Example 1.

[0205] After the copper powders of Examples 1 to 7 and Comparative Example 1 were treated, they were observed using a transmission electron microscope. Figure 5 and Figure 6 The transmission electron microscope images of the copper powder in Example 1 and Comparative Example 1 are shown respectively. Figure 6 It is obvious that there are crystal planes 111 and 220 on the periphery of the copper powder. Figure 5 The crystal planes are basically 220.

[0206] Therefore, combining the X-ray diffraction pattern and the transmission electron microscope image, it can be known that most or even all of the periphery of the copper powder in the present application is a stable crystal plane 220, thereby improving the oxidation resistance of the copper powder.

[0207] The copper powders of Examples 1 to 7 and Comparative Examples 1 to 2 were mixed with a solvent at a volume ratio of 90:10 to obtain a copper paste having certain fluidity and viscosity.

[0208] A 80μm nano solder paste layer was prepared on a copper substrate by screen printing. Another copper plate was then placed on top of the solder paste. After preheating at 80°C for 5 minutes and keeping warm at the same sintering temperature and 20MPa pressure for 5 minutes, a semiconductor package was obtained.

[0209] The sintering temperatures are 180°C and 250°C, respectively, that is, a group of semiconductor packages corresponding to Examples 1 to 7 and Comparative Examples 1 to 2 are obtained at a sintering temperature of 180°C, and a group of semiconductor packages corresponding to Examples 1 to 7 and Comparative Examples 1 to 2 are obtained at a sintering temperature of 250°C. The semiconductor packages prepared in Examples 1 to 7 and Comparative Examples 1 to 2 are tested respectively, and the test data are shown in Table 1.

[0210] Table 1 Performance of semiconductor packages

[0211]

[0212]

[0213] It can be seen from Table 1 that the connection strengths of the semiconductor packages corresponding to Examples 1 to 7 at both the low temperature of 180° C. and the high temperature of 250° C. are better than those of Comparative Examples 1 and 2.

[0214] Moreover, the copper powder in this solution can meet the interconnection requirements of semiconductor packages at a sintering temperature of 180° C. Therefore, the copper powder prepared by the preparation method of the present application can reduce the sintering temperature and improve the sintering strength of the device.

[0215] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A method for preparing copper powder, characterized in that: The following steps are involved: Providing a mixed solution; the mixed solution includes carboxylate ions, and the mixed solution is in an alkaline environment; Adding a copper raw material to the mixed solution and mixing the two evenly to obtain a target solution; the copper raw material includes copper particles and copper oxide formed on the periphery of the copper particles; The target solution is pumped into the diversion channel, so that the target solution remains in a flowing state in the diversion channel, and the target solution flowing in the diversion channel is heated, so that the carboxylate ions of the target solution react with the copper oxide of the copper raw material to form copper carboxylate, thereby obtaining a product solution; The product solution is subjected to solid-liquid separation to obtain copper powder with copper particles as cores and copper carboxylate as shells, and part of the crystal planes 111 in the copper powder are converted into stable crystal planes 220 .

2. The method for preparing copper powder according to claim 1, characterized in that: The preparation method of the copper raw material comprises the following steps: Copper particles are provided, and the copper particles are subjected to an oxidation reaction to obtain the copper raw material having the copper particles as the core and copper oxide as the shell.

3. The method for preparing copper powder according to claim 2, characterized in that: The steps of the oxidation reaction are as follows: The copper particles are mixed with deionized water and reacted at 150-250° C. for 5-20 minutes.

4. The method for preparing copper powder according to claim 1, characterized in that: The pH value of the mixed solution is 10 to 12; The mixed solution includes an alkaline substance and a carboxylic acid-containing substance, and the carboxylic acid-containing substance includes at least one of a carboxylic acid and a carboxylate.

5. The method for preparing copper powder according to claim 4, characterized in that: The carboxylic acid includes at least one of formic acid, oxalic acid, citric acid and lactic acid, the carboxylate includes at least one of formates, oxalates, citrates and lactates, the mass percentage of the carboxylic acid-containing substance is 50-100%, and the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium formate, potassium formate, sodium oxalate, potassium oxalate, oleylamine, ethylenediamine, triethanolamine and isopropanolamine.

6. The method for preparing copper powder according to claim 1, characterized in that: In the target solution, the molar ratio of copper to the carboxylate ion is (0.1-1):1; The copper particles have a particle size of 0.01-10 μm; The copper particles include at least one of spherical copper, flake copper and dendritic copper.

7. The method for preparing copper powder according to claim 1, characterized in that: The reaction temperature of the target solution in the diversion channel is 120-200° C., and the reaction time is 10-60 min; The inner diameter of the flow guiding channel is 0.25-0.6 mm.

8. A copper powder, characterized in that The copper powder is prepared by the preparation method described in any one of claims 1 to 7.

9. A method for preparing a semiconductor package, characterized in that: The following steps are involved: Using the copper powder prepared by the preparation method according to any one of claims 1 to 7 as a raw material to prepare a solder paste; The two substrates are welded with the solder paste to obtain a semiconductor package.

10. The method for preparing a semiconductor package according to claim 9, characterized in that: The solid content of the solder paste is 60%-90%; The steps of welding two substrates to obtain a semiconductor package include: making a solder paste layer on one of the substrates by using the solder paste; placing another substrate on the solder paste layer to obtain an intermediate part; The semiconductor package is obtained by subjecting the intermediate piece to heat and pressure treatment under a protective gas atmosphere, wherein the heat preservation temperature is between 180° C. and 320° C., the pressure holding pressure is between 1 MPa and 20 MPa, and the heat and pressure preservation treatment time is between 1 min and 60 min.

11. A copper powder reaction device, characterized in that: The device comprises: A first container is used to contain reactants and mix the reactants evenly to obtain a target solution; the first container is corrosion-resistant; One or more diversion channels, communicating with the first container; A pumping assembly, used to draw the target solution in the first container into the diversion channel and keep the target solution in a flowing state; a heating component, used for heating the target solution flowing in the flow guiding channel; and The second container is connected to the flow guiding channel to accommodate the product solution outputted from the flow guiding channel.

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