Composite copper powder, its preparation method, semiconductor package and its preparation method

Abstract

The present invention relates to the field of semiconductor technology. To solve the problems of nano-copper oxidation and sintering shrinkage in the prior art, a composite copper powder, a preparation method thereof, a semiconductor package, and a preparation method thereof are provided. The preparation method of the composite copper powder comprises the following steps: weighing soluble copper salt and a pore-forming agent, dissolving them in a first alkaline solution, and mixing uniformly to obtain a first solution; weighing a reducing agent and a dispersant, dissolving them in a second alkaline solution to obtain a second solution; quickly mixing the first solution and the second solution under stirring and reacting, cooling to room temperature after the reaction ends, performing solid-liquid separation to obtain copper particles; adding the copper particles into a solvent, mixing uniformly, adding a coating agent, and stirring, performing solid-liquid separation and vacuum drying to obtain micron copper; weighing micron copper and nano copper, the mass ratio of micron copper to nano copper being (1 to 81):9, mixing the micron copper and the nano copper, and embedding the nano copper into the concave points of the micron copper to obtain the composite copper powder.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly relates to a composite copper powder and a preparation method thereof, a semiconductor package and a preparation method thereof. Background Art

[0002] With the requirements of semiconductor devices in the fields of new energy, electronic information, etc. for serving under conditions such as high temperature and high pressure, higher requirements are put forward for the high heat dissipation and high reliability of packaging materials for power devices and chips. Although the commonly used nano-silver materials are widely used in the packaging field at present, during the service process, there is an electromigration phenomenon in the nano-silver materials, and the high cost of the nano-silver materials restricts their development. The resistivity and thermal conductivity of metallic copper are both close to those of silver, and at the same time, the cost is only one-tenth of that of silver, with a low price, and it has been widely used in the field of packaging interconnection. However, problems such as oxidation of nano-copper and large sintering shrinkage are still difficult problems to overcome. Summary of the Invention

[0003] The purpose of the present invention is to provide a composite copper powder and a preparation method thereof, a semiconductor package and a preparation method thereof to solve the problems in the prior art.

[0004] To solve the above technical problems, the present invention provides a preparation method of a composite copper powder, including the following steps:

[0005] Weigh soluble copper salt and a pore-forming agent, dissolve them in a first alkaline solution, and mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is (12~1):6; the pore-forming agent is an ammonium salt;

[0006] Weigh a reducing agent and a dispersant, dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is (10~1):1;

[0007] Rapidly mix the first solution and the second solution under stirring, and react at 80 - 160 °C for 15 min - 120 min. After the reaction ends, cool to room temperature, perform solid-liquid separation to obtain copper particles; the copper particles are in a fluffy shape;

[0008] Add the copper particles to a solvent, mix evenly, then add a coating agent, and stir for 30 - 60 min. Perform solid-liquid separation and vacuum drying, and then pass through a sieve with 80 - 800 meshes to obtain fluffy micron-sized copper with a particle size of 1 - 6 μm and a specific surface area of 0.2 - 8 m 2 / g;

[0009] Weigh the micron copper and nano copper with a particle size of 10 - 100 nm. The mass ratio of the micron copper to the nano copper is (1 - 81):9. Mix the micron copper and the nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0010] In one embodiment, the size of the concave points ≤ 100 nm, and the particle size of the nano copper is not greater than the size of the concave points;

[0011] The mixing time of the first solution and the second solution < 3 min.

[0012] In one embodiment, the step of mixing the micron copper and the nano copper and embedding the nano copper into the concave points of the micron copper to obtain composite copper powder includes:

[0013] Premix the micron copper and the nano copper for 30 - 60 min to obtain a premix, then add ball milling beads with a diameter of 2 - 10 mm. The mass ratio of the ball milling beads to the premix is (3 - 20):1. After ball milling for 4 - 20 h, composite copper powder is obtained.

[0014] In one embodiment, the ball milling beads are ceramic beads;

[0015] After ball milling, pass through a sieve with 80 - 800 meshes to obtain composite copper powder with a particle size of 1 - 10 μm.

[0016] In one embodiment, the soluble copper salt includes at least one of copper sulfate, copper nitrate, copper chloride, copper acetate, copper citrate and their hydrates;

[0017] The pore - forming agent includes at least one of ammonium chloride, ammonium bromide, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, urea, ethylenediamine, triethanolamine, triethylamine.

[0018] In one embodiment, both the first basic solution and the second basic solution include a base and a solvent. The base includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ethylenediamine, ammonia water, and the solvent includes at least one of pure water, ethanol, ethylene glycol, glycerol, isopropanol and polyethylene glycol;

[0019] The proportion of the base in the first basic solution is 5 - 30%, and the proportion of the base in the second basic solution is 2 - 20%.

[0020] In one embodiment, the mass ratio of the dispersant to the copper particles is (0.001 - 0.05):1;

[0021] The dispersant includes at least one of gelatin, polyvinylpyrrolidone, gum arabic, benzimidazole, 2-methylimidazole, 2-phenylimidazole, imidazole, and cetyltrimethylammonium bromide;

[0022] The reducing agent includes at least one of sodium hypophosphite, sodium ascorbate, ascorbic acid, hydrazine hydrate, glucose, sodium borohydride, and glycerol.

[0023] In one embodiment, the coating agent includes at least one of stearic acid, oleic acid, benzimidazole, 2-methylimidazole, 2-phenylimidazole, and imidazole, and the solvent includes at least one of absolute ethanol, ethylene glycol, pure water, acetone, ether, glycerol, and acetone; the mass ratio of the coating agent to the copper particles is (0.005 - 0.1):1.

[0024] The present invention also provides a composite copper powder prepared by the preparation method as described above.

[0025] The present invention also provides a preparation method for a semiconductor package, including the following steps:

[0026] Using the composite copper powder prepared by the preparation method as a raw material to prepare and obtain solder paste;

[0027] Using the solder paste to weld two substrates to obtain a semiconductor package.

[0028] The present invention also provides a semiconductor package, including two substrates and a solder paste layer located between the two substrates, and the solder paste layer is prepared using the composite copper powder prepared by the above preparation method as a raw material.

[0029] As can be seen from the above technical solutions, the advantages and positive effects of the present invention are as follows:

[0030] In the preparation method of the present invention, micron copper in the shape of fluff is first prepared, then concave points are formed on the outer periphery of the micron copper in the shape of fluff, and then nano copper is dispersed and attached to the concave points of the micron copper to obtain composite copper powder. This composite copper powder combines the advantages of both nano copper and micron copper, that is, nano copper provides sintering active sites, ensuring high activity of the composite copper powder during low-temperature sintering, and micron copper inhibits sintering shrinkage. The micron copper is in the shape of fluff, providing a high specific surface area, and the nano copper is attached to the concave points formed by the micron copper during ball milling, making the composite copper powder densely packed. By mixing nano copper and micron copper, the cost is reduced. Description of the Drawings

[0031] Figure 1 It is a process schematic diagram of the preparation method of the composite copper powder in the present invention.

[0032] Figure 2 It is a schematic diagram of the principle of nano copper embedded in the concave points of micron copper in the present invention.

[0033] Figure 3 It is the scanning electron microscope image of Example 2 in the present invention.

[0034] Figure 4 It is the sintering schematic diagram of the solder paste prepared from the composite copper powder of Example 2 in the present invention.

[0035] Figure 5 It is the sintering schematic diagram of the solder paste prepared from the composite copper powder of Comparative Example 1.

[0036] Figure 6 It is the sintering schematic diagram of the solder paste prepared from the copper powder of Comparative Example 2. Detailed implementation manners

[0037] Typical implementation manners reflecting 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 implementation manners, all of which do not depart from the scope of the present invention, and the descriptions and illustrations therein are essentially for illustrative purposes rather than for limiting the present invention.

[0038] To further illustrate the principle and structure of the present invention, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0039] It should be noted that in low-temperature interconnection, copper paste prepared from pure nano-copper powder is usually used. However, the pure nano-copper powder has poor oxidation resistance, large sintering shrinkage resulting in cracks, and high cost of nano-copper powder.

[0040] Therefore, the present invention provides a preparation method of composite copper powder, which can prepare composite copper powder with lower cost and suitable for low-temperature sintering.

[0041] In the preparation method of the composite copper powder, micron copper in the shape of fluff is first prepared, then concave points are formed on the outer periphery of the micron copper in the shape of fluff, and then nano-copper is dispersed and attached to the concave points of the micron copper to obtain the composite copper powder. The composite copper powder combines the advantages of both nano-copper and micron copper, that is, nano-copper provides sintering active sites, ensuring high activity of the composite copper powder during low-temperature sintering, and micron copper inhibits sintering shrinkage. The micron copper is in the shape of fluff, providing a high specific surface area, and the nano-copper is attached to the concave points formed by the micron copper during ball milling, making the composite copper powder densely packed. By mixing nano-copper and micron copper, the cost is reduced.

[0042] The following specifically introduces the preparation method of the composite copper powder.

[0043] Refer to Figure 1 , the preparation method of the composite copper powder includes the following steps:

[0044] S100. Weigh soluble copper salts and a pore former, dissolve them in a first alkaline solution, and mix them evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salts to the pore former is (12~1):6. The pore former is an ammonium salt.

[0045] Specifically, the soluble copper salts include at least one of copper sulfate, copper nitrate, copper chloride, copper acetate, copper citrate, and their hydrates. Here, "soluble" includes both readily soluble and slightly soluble.

[0046] The soluble copper salts can be any one of the above, or a mixture of two, three, or several of them.

[0047] The pore former is an ammonium salt. Specifically, the pore former includes at least one of ammonium chloride, ammonium bromide, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, urea, ethylenediamine, triethanolamine, and triethylamine. That is, the pore former can be any one of the above, or a mixture of two, three, or several of them.

[0048] The pore former is used to generate gas and escape during the reduction of copper ions to copper, thereby forming pores on the outer periphery of the copper.

[0049] Specifically, the molar ratio of copper ions in the soluble copper salts to the pore former is (12~1):6. Using this ratio can form pores on the surface of the copper particles.

[0050] The first alkaline solution includes an alkaline substance and a solvent. The alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ethylenediamine, and ammonia water. The alkaline substance can be any one of the above, or any two or more of them.

[0051] The solvent includes at least one of pure water, ethanol, ethylene glycol, glycerol, isopropanol, and polyethylene glycol. The solvent can be any one of the above, or any two or more of them.

[0052] In the first alkaline solution, the mass percentage of the alkaline substance is 5~30%. Here, the mass percentage refers to the percentage of the mass of the alkaline substance in the total mass of the first alkaline solution.

[0053] Exemplarily, the first alkaline solution includes sodium hydroxide and pure water, and the mass percentage of sodium hydroxide is 5%. Or, the first alkaline solution includes sodium hydroxide, potassium hydroxide, and pure water, and the percentage of the sum of the masses of sodium hydroxide and potassium hydroxide is 5%.

[0054] S200. Weigh a reducing agent and a dispersant, dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salts is (10~1):1.

[0055] The mass ratio of the dispersant to the copper particles is (0.001-0.05): 1. The copper particles are theoretically prepared products from the reaction of soluble copper salts and reducing agents.

[0056] The reducing agent includes at least one of sodium hypophosphite, sodium ascorbate, ascorbic acid, hydrazine hydrate, glucose, sodium borohydride and glycerol. The reducing agent can be any one of the above, or any two or more.

[0057] The dispersant includes at least one of gelatin, polyvinyl pyrrolidone, gum arabic, benzimidazole, 2-methylimidazole, 2-phenylimidazole, imidazole, and hexadecyltrimethylammonium bromide. The dispersant can be any one of the above, or any two or more.

[0058] The second alkaline solution includes an alkaline substance and a solvent. The alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ethylenediamine, and ammonia water. The solvent includes at least one of pure water, ethanol, ethylene glycol, glycerol, isopropanol, and polyethylene glycol. In the second alkaline solution, the mass proportion of the alkaline substance is 2-20%. The second alkaline solution can refer to the description of the first alkaline solution.

[0059] In the above two steps, the soluble copper salt and the reducing agent are respectively prepared as the first solution and the second solution, which can avoid the reaction between the two during the mixing process. At the same time, the soluble copper salt and the pore-forming agent are dispersed in the first alkaline solution, which is conducive to the pore-forming agent and the soluble copper salt to form a complex first and disperse evenly. Mixing the reducing agent with the second alkaline solution in advance is conducive to the activation of the reducing agent.

[0060] S300, the first solution and the second solution are mixed rapidly under stirring, and reacted at 80-160°C for 15-120 minutes. After the reaction is completed, the mixture is cooled to room temperature, and the solid and liquid are separated to obtain copper particles. The copper particles are in a plush state.

[0061] Specifically, the mixing time of the first solution and the second solution is less than 3 min. The specific time varies depending on the volume. For example, during the experiment, the first solution can be directly poured into the second solution while stirring.

[0062] The first solution and the second solution undergo a reduction reaction at 80-160° C., that is, the copper ions are reduced to copper element.

[0063] In an alkaline environment, copper ions undergo an oxidation-reduction reaction with a reducing agent, and the copper ions are reduced to copper. In the process of copper ions being reduced to copper, copper nuclei are formed and aggregated, and the pore-forming agent ammonium salt reacts with hydroxide ions in an alkaline environment to produce ammonia gas and overflow. Ammonia gas is corrosive, so when ammonia gas overflows from the surface of copper particles, fuzzy holes are generated on the surface of copper particles. Therefore, the periphery of the copper particles finally formed after the reaction is completed has multiple fuzzy holes.

[0064] In the above reaction process, the pore-forming agent ammonium salt can also form a complex with copper ions, and the complex gradually dissociates during the reduction reaction of copper ions. After the ammonium salt combines with copper ions, hydroxide ions are dissociated, which increases the alkalinity of the solution, increases the reaction rate of oxidation-reduction, and increases the growth rate of copper crystal nuclei.

[0065] Therefore, the preparation method of the present application adjusts the redox reaction rate by controlling the alkaline concentration of the first alkaline solution and the second alkaline solution, uses ammonium salt as a pore-forming agent and controls the molar ratio of the pore-forming agent to copper to control the morphology and porosity of the prepared copper, and controls the size of the prepared copper by selecting the above-mentioned reducing agent and controlling the dosage. By selecting the type of ammonium salt and controlling the concentration of the alkali solution, the reaction rate is increased, the copper microcrystals maintain a high growth rate, and plush holes are formed during the overflow of the strong alkaline gas.

[0066] The purpose of adding the dispersant is to inhibit the agglomeration of the formed copper particles due to the fast reaction rate and to improve the dispersibility.

[0067] In this embodiment, the solid-liquid separation adopts the method of centrifugal washing. In other embodiments, other methods such as filtration can also be adopted. The specific method can be selected according to actual needs.

[0068] S400, add copper particles to the solvent, mix well, add coating agent, stir for 30-60 minutes, separate solid and liquid, and vacuum dry to obtain micron copper, and then pass through a 80-800 mesh sieve to obtain a particle size of 1-6μm and a specific surface area of ​​0.2-8m 2 / g of plush micron copper.

[0069] The coating agent includes at least one of stearic acid, oleic acid, benzimidazole, 2-methylimidazole, 2-phenylimidazole and imidazole. The solvent includes at least one of anhydrous ethanol, ethylene glycol, pure water, acetone, ether, glycerol and acetone.

[0070] The mass ratio of the coating agent to the copper particles is (0.005-0.1): 1. That is, the coating agent and the copper particles are mixed in the above ratio.

[0071] The copper particles are subjected to an anti-oxidation treatment by using a coating agent to prevent the surface of the copper particles from being oxidized to form copper oxide.

[0072] Since the outer periphery of the copper particles has concave points, the outer periphery of the micron copper also has a plurality of concave points.

[0073] S500: Weigh micron copper and nano copper with a particle size of 10 - 100 nm. The mass ratio of micron copper to nano copper is (1 - 81):9. Mix the micron copper and nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0074] Among them, the size of the concave points ≤ 100 nm. The particle size of the nano copper is not greater than the size of the concave points so that the nano copper can be embedded into the concave points.

[0075] Specifically, the steps of mixing the micron copper and nano copper and embedding the nano copper into the concave points of the micron copper to obtain composite copper powder include:

[0076] Premix the micron copper and nano copper for 30 - 60 min to obtain a premix, then add ball - milling beads with a diameter of 2 - 10 mm. The mass ratio of the ball - milling beads to the premix is (3 - 20):1, and composite copper powder is obtained after ball - milling for 4 - 20 h.

[0077] The function of premixing is to make the nano copper fully contact the micron copper so that the nano copper can enter the concave points during subsequent ball - milling.

[0078] The ball - milling beads are ceramic beads. Specifically, the material of the ceramic beads is zirconia or alumina.

[0079] The ball - milling is carried out in a ball mill. During the ball - milling process, the rotation speed can also be adjusted. Exemplarily, such as a rotation speed of 200 r / min. The specific rotation speed can be set according to actual needs.

[0080] Furthermore, after ball - milling, pass through a sieve with 80 - 800 meshes to obtain composite copper powder with a particle size of 1 - 10 μm. The composite copper powder within this particle size range has a higher specific surface area compared to ball copper of the same size, making the sintering activity higher. The composite copper powder within this specific surface area range is larger in size compared to ball copper with the same specific surface area, thus being able to inhibit shrinkage cracking during drying and sintering.

[0081] That is, through the function of the sieve, the ball - milling beads and the composite copper powder are separated.

[0082] During the ball - milling process, the ceramic balls and the copper powder come into contact repeatedly, and the contact part has a higher activity. During the ball - milling process, the nano balls are mixed with the fluffy micron balls, and some nano balls enter the fluffy holes on the surface of the micron balls or are semi - embedded in the fluffy fibers. Through ball - milling and micro - fragmentation, the nano - ball copper can be further pounded into the concave points of the surface fluffy fibers, as Figure 2 shown.

[0083] The fluffy micron copper powder first undergoes microflaking, and concave points are formed on the surface fluffy holes. The nano copper powder is pounded into the concave points, making the combination of nano copper powder and micron copper powder closer. The nano copper adheres to the concave parts on the surface of the microflaked fluffy copper, forming composite copper powder.

[0084] In this embodiment, the above mechanical grinding, i.e., physical method, is used to embed nano copper into the concave points of micron copper. In other embodiments, a chemical method can also be used to exactly combine nano copper into the concave points of micron copper.

[0085] In summary, the preparation method of this application has the following advantages:

[0086] 1. In the composite copper powder of this application, the nano powder is dispersed and connected in the concave points of micron copper. By ensuring the provision of sintering active points through nano copper, the high sintering activity of the composite copper powder is guaranteed. By suppressing sintering shrinkage through micron copper, the problem of cracking during drying and sintering is solved.

[0087] 2. The micron copper prepared in this application has a fluffy morphology. At the same scale, the copper powder with a fluffy morphology has higher sintering activity. And the preparation method of the fluffy copper powder is simple, and the equipment is simple, which is conducive to mass production.

[0088] 3. The mixing of micron copper and nano copper reduces the proportion of nano copper and reduces the cost. Therefore, the economic benefit is higher.

[0089] 4. This application uses a physical method to embed nano copper into the concave points of micron copper, without introducing a large amount of organic solvents, which is relatively environmentally friendly and convenient for mass production.

[0090] This application also provides a composite copper powder. This composite copper powder is prepared by the above preparation method.

[0091] This application also provides a preparation method of a semiconductor package, including the following steps:

[0092] S600. Using the copper powder prepared by the above preparation method as a raw material to prepare and obtain solder paste.

[0093] Specifically, the solid content of the solder paste is 60% - 90%.

[0094] S700. Using the solder paste to weld two substrates to obtain a semiconductor package.

[0095] Specifically, the step of welding two substrates to obtain a semiconductor package includes:

[0096] S710. Making a solder paste layer on one of the substrates through the solder paste.

[0097] S720. Placing the other substrate on the solder paste layer to obtain an intermediate.

[0098] S730. After heat preservation and pressure maintenance treatment of the interposer in a protective gas atmosphere, a semiconductor package is obtained, where the heat preservation temperature is between 180°C and 320°C, the pressure maintenance pressure is between 1 Mpa and 20 Mpa, and the time of heat preservation and pressure maintenance treatment is between 1 minute and 60 minutes.

[0099] The protective gas is an atmosphere such as helium, nitrogen, etc.

[0100] This application also provides a semiconductor package, including two substrates and a solder paste layer located between the two substrates. The solder paste layer is prepared with the composite copper powder obtained by the above preparation method as the raw material.

[0101] The inventors of this application realized the preparation of the composite copper powder by strictly designing the content of each component and the parameters in each step. The preparation method of the composite copper powder is introduced through the following examples.

[0102] Example 1

[0103] The preparation method of the composite copper powder in this example includes the following steps:

[0104] S11. Weigh soluble copper salt and pore former, and dissolve them in the first alkaline solution, and mix evenly to obtain the first solution. The molar ratio of copper ions in the soluble copper salt to the pore former is 1:2.

[0105] Specifically, the soluble copper salt is copper acetate monohydrate. The pore former is ammonium chloride. The first alkaline solution includes sodium hydroxide and pure water, and the mass proportion of sodium hydroxide is 5%.

[0106] S12. Weigh reducing agent and dispersant, and dissolve them in the second alkaline solution to obtain the second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 10:1.

[0107] The reducing agent is sodium hypophosphite monohydrate. The dispersant is gelatin. The mass ratio of the dispersant to the copper particles is 0.05:1.

[0108] The second alkaline solution includes sodium hydroxide and pure water, and the mass proportion of sodium hydroxide is 2%.

[0109] S13. Rapidly mix the first solution and the second solution under stirring, and react at 80°C for 120 minutes. After the reaction, cool to room temperature, and perform solid-liquid separation to obtain copper particles. The copper particles are in a fluffy shape.

[0110] Specifically, the mixing time of the first solution and the second solution is 30 s.

[0111] S14. Add the copper particles to the solvent, mix evenly, then add the coating agent, and stir for 50 minutes. Perform solid-liquid separation and vacuum drying to obtain micron copper.

[0112] The coating agent is benzimidazole. The solvent is absolute ethanol. Among them, the mass ratio of the coating agent to the copper particles is 0.005:1.

[0113] In this embodiment, the specific surface area of the micron copper is 0.21 m 2 / g, and the average particle size is 6 μm.

[0114] S15. Weigh micron copper and nano copper with a particle size of 10 nm. The mass ratio of micron copper to nano copper is 1:9. Mix the micron copper and nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0115] Specifically, premix the micron copper and nano copper for 30 min to obtain a premix, then add zirconium beads with a diameter of 5 mm. The mass ratio of the premix to the zirconium beads is 1:20, and the composite copper powder is obtained after ball milling for 4 h.

[0116] In the composite copper powder, the nano powder adheres to the micro-fragmented fluffy concave points.

[0117] Example 2

[0118] The preparation method of the composite copper powder in this embodiment includes the following steps:

[0119] S21. Weigh soluble copper salt and pore-forming agent, and dissolve them in the first alkaline solution, and mix evenly to obtain the first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 1:6.

[0120] Specifically, the soluble copper salt is copper acetate monohydrate. The pore-forming agent is ammonium chloride. The first alkaline solution includes sodium hydroxide and pure water, and the mass proportion of sodium hydroxide is 30%.

[0121] S22. Weigh the reducing agent and dispersant, and dissolve them in the second alkaline solution to obtain the second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 5:1.

[0122] The reducing agent is sodium ascorbate and glycerol. The dispersant is gelatin. The mass ratio of the dispersant to the copper particles is 0.001:1.

[0123] The second alkaline solution includes sodium hydroxide and pure water. The mass proportion of sodium hydroxide is 10%.

[0124] S23. Rapidly mix the first solution and the second solution under stirring, and react at 80 °C for 60 min. After the reaction is completed, cool to room temperature, and perform solid-liquid separation to obtain copper particles. The copper particles are fluffy.

[0125] Specifically, the mixing time of the first solution and the second solution is 50 s.

[0126] S24. Add copper particles to a solvent. After mixing evenly, add a coating agent and stir for 40 min. Then, perform solid-liquid separation and vacuum drying to obtain micron copper.

[0127] The coating agent is oleic acid. The solvent is ethanol. Among them, the mass ratio of the coating agent to the copper particles is 0.005:1.

[0128] In this example, the specific surface area of the micron copper is 3.63 m 2 / g, and the average particle size is 1.94 μm.

[0129] S25. Weigh micron copper and nano copper with a particle size of 30 nm. The mass ratio of micron copper to nano copper is 7:3. Mix the micron copper and nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0130] Specifically, premix the micron copper and nano copper for 60 min to obtain a premix. Then, add zirconium beads with a diameter of 10 mm. The mass ratio of zirconium beads to the premix is 5:1. After ball milling for 12 h, composite copper powder is obtained.

[0131] In the composite copper powder, the nano powder adheres to the micro-flaky and fluffy concave points.

[0132] Example 3

[0133] The preparation method of the composite copper powder in this example includes the following steps:

[0134] S31. Weigh a soluble copper salt and a pore-forming agent, and dissolve them in a first alkaline solution. Mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 1:6.

[0135] Specifically, the soluble copper salt is copper acetate monohydrate. The pore-forming agent is ammonium sulfate. The first alkaline solution includes sodium hydroxide, pure water, and absolute ethanol, and the mass fraction of sodium hydroxide is 25%.

[0136] S32. Weigh a reducing agent and a dispersant, and dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 5:1.

[0137] The reducing agent is ascorbic acid and glycerol. The dispersant is gum arabic. The mass ratio of the dispersant to the copper particles is 0.05:1.

[0138] The second alkaline solution includes sodium hydroxide, pure water, and absolute ethanol, and the mass fraction of sodium hydroxide is 20%.

[0139] S33. Rapidly mix the first solution and the second solution under stirring, and react at 160 °C for 60 min. After the reaction, cool to room temperature and perform solid-liquid separation to obtain copper particles. The copper particles are in a fluffy shape.

[0140] Specifically, the mixing time of the first solution and the second solution is 58 s.

[0141] S34. Add copper particulate matter to the solvent, mix evenly, add a coating agent, and stir for 60 min. Separate the solid from the liquid and dry it under vacuum to obtain micron copper.

[0142] The coating agent is methylimidazole. The solvent is anhydrous ethanol. Among them, the mass ratio of the coating agent to the copper particulate matter is 0.01:1.

[0143] In this example, the specific surface area of the micron copper is 7.98 m 2 / g, and the average particle size is 1 μm.

[0144] S35. Weigh micron copper and nano copper with a particle size of 100 nm. The mass ratio of micron copper to nano copper is 9:1. Mix the micron copper and nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0145] Specifically, premix the micron copper and nano copper for 40 min to obtain a premix, then add zirconium beads with a diameter of 2 mm. The mass ratio of the zirconium beads to the premix is 10:1. After ball milling for 4 h, composite copper powder is obtained.

[0146] Example 4

[0147] The preparation method of the composite copper powder in this example includes the following steps:

[0148] S41. Weigh a soluble copper salt and a pore-forming agent, and dissolve them in a first alkaline solution, mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 1:4.

[0149] Specifically, the soluble copper salt is copper chloride. The pore-forming agent is ammonium chloride. The first alkaline solution includes sodium hydroxide and pure water, and the mass fraction of sodium hydroxide is 15%.

[0150] S42. Weigh a reducing agent and a dispersant, and dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 5:1.

[0151] The reducing agent is sodium hypophosphite. The dispersant is polyvinylpyrrolidone. The mass ratio of the dispersant polyvinylpyrrolidone to the copper particulate matter is 0.001:1.

[0152] The second alkaline solution includes sodium hydroxide and pure water, and the mass fraction of sodium hydroxide is 5%.

[0153] S43. Rapidly mix the first solution and the second solution under stirring, and react at 90 °C for 120 min. After the reaction, cool to room temperature, separate the solid from the liquid, and obtain copper particulate matter. The copper particulate matter is in a fluffy shape.

[0154] Specifically, the mixing time of the first solution and the second solution is 58 s.

[0155] S44. Add copper particulate matter into a solvent. After mixing evenly, add a coating agent and stir for 35 min. Perform solid-liquid separation and vacuum drying to obtain micron copper.

[0156] The coating agent is stearic acid. The solvent is ethanol. Among them, the mass ratio of the coating agent to the copper particulate matter is 0.01:1.

[0157] In this embodiment, the specific surface area of the micron copper is 0.98 m 2 / g, and the average particle size is 3.01 μm.

[0158] S45. Weigh micron copper and nano copper with a particle size of 50 nm. The mass ratio of micron copper to nano copper is 1:1. Mix the micron copper and the nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0159] Specifically, premix the micron copper and the nano copper for 50 min to obtain a premix. Then add zirconium beads with a diameter of 3 mm. The mass ratio of the zirconium beads to the premix is 3:1. After ball milling for 20 h, composite copper powder is obtained.

[0160] Example 5

[0161] The preparation method of the composite copper powder in this embodiment includes the following steps:

[0162] S51. Weigh a soluble copper salt and a pore-forming agent, and dissolve them in a first alkaline solution. Mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 1:6.

[0163] Specifically, the soluble copper salt is copper sulfate. The pore-forming agent is ammonium sulfate and ethylenediamine. The first alkaline solution includes ammonia water, potassium hydroxide and pure water. The total mass ratio of ammonia water and potassium hydroxide is 20%.

[0164] S52. Weigh a reducing agent and a dispersant, and dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 2:1.

[0165] The reducing agent is hydrazine hydrate. The dispersant is cetyltrimethylammonium bromide. The mass ratio of the dispersant to the copper particulate matter is 0.05:1.

[0166] The second alkaline solution includes potassium hydroxide and pure water. The mass ratio of potassium hydroxide is 10%.

[0167] S53. Rapidly mix the first solution and the second solution under stirring, and react at 80 °C for 120 min. After the reaction, cool to room temperature, perform solid-liquid separation to obtain copper particles. The copper particles are in a fluffy shape.

[0168] Specifically, the mixing time of the first solution and the second solution is 18 s.

[0169] S54. Add the copper particles to a solvent, mix evenly, add a coating agent, and stir for 30 min. Perform solid-liquid separation and vacuum drying to obtain micron copper.

[0170] The coating agent is imidazole. The solvent is pure water. Among them, the mass ratio of the coating agent to the copper particles is 0.005:1.

[0171] In this example, the specific surface area of the micron copper is 2.33 m 2 / g, and the average particle size is 1.1 μm.

[0172] S55. Weigh micron copper and nano copper with a particle size of 50 nm. The mass ratio of micron copper to nano copper is 3:1. Mix the micron copper and nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0173] Specifically, premix the micron copper and nano copper for 40 min to obtain a premix, then add zirconium beads with a diameter of 6 mm. The mass ratio of zirconium beads to the premix is 7:1. After ball milling for 10 h, composite copper powder is obtained.

[0174] Example 6

[0175] The preparation method of the composite copper powder in this example includes the following steps:

[0176] S61. Weigh a soluble copper salt and a pore-forming agent, dissolve them in a first alkaline solution, and mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 1:6.

[0177] Specifically, the soluble copper salt is copper sulfate. The pore-forming agents are ammonium chloride and ammonium sulfate. The first alkaline solution includes sodium hydroxide and pure water, and the mass fraction of sodium hydroxide is 30%.

[0178] S62. Weigh a reducing agent and a dispersant, dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 8:1.

[0179] The reducing agent is hydrazine hydrate. The dispersant is gum arabic. The mass ratio of the dispersant to the copper particles is 0.001:1.

[0180] The second alkaline solution includes sodium hydroxide and pure water, and the mass fraction of sodium hydroxide is 2%.

[0181] S63. Rapidly mix the first solution and the second solution under stirring, and react at 80 °C for 15 min. After the reaction, cool to room temperature, separate the solid from the liquid to obtain copper particles. The copper particles are in a fluffy shape.

[0182] Specifically, the mixing time of the first solution and the second solution is 45 s.

[0183] S64. Add the copper particles to a solvent, mix evenly, add a coating agent, and stir for 30 - 60 min. Separate the solid from the liquid and dry in vacuum to obtain micron-sized copper.

[0184] The coating agent is oleic acid. The solvent is anhydrous ethanol. Among them, the mass ratio of the coating agent to the copper particles is 0.01:1.

[0185] In this example, the specific surface area of the micron-sized copper is 2.89 m 2 / g, and the average particle size is 1.5 μm.

[0186] S65. Weigh the micron-sized copper and the nano-sized copper with a particle size of 30 nm. The mass ratio of the micron-sized copper to the nano-sized copper is 3:1. Mix the micron-sized copper and the nano-sized copper and embed the nano-sized copper into the concave points of the micron-sized copper to obtain composite copper powder.

[0187] Specifically, premix the micron-sized copper and the nano-sized copper for 45 min to obtain a premix, then add zirconium beads with a diameter of 7 mm. The mass ratio of the zirconium beads to the premix is 7:1, and composite copper powder is obtained after ball milling for 10 h.

[0188] Example 7

[0189] The preparation method of the composite copper powder in this example includes the following steps:

[0190] S71. Weigh a soluble copper salt and a pore-forming agent, dissolve them in a first basic solution, and mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 2:1.

[0191] Specifically, the soluble copper salt is copper acetate monohydrate. The pore-forming agent is ammonium sulfate. The first basic solution includes sodium hydroxide, glycerol, and ethylene glycol, and the mass proportion of sodium hydroxide and glycerol is 5%.

[0192] S72. Weigh a reducing agent and a dispersant, dissolve them in a second basic solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 1:1.

[0193] The reducing agent is ascorbic acid. The dispersant is gelatin. The mass ratio of the dispersant to the copper particles is 0.001:1.

[0194] The second basic solution includes sodium hydroxide, glycerol, and ethylene glycol, and the mass proportion of sodium hydroxide and glycerol is 2%.

[0195] S73. Rapidly mix the first solution and the second solution under stirring, and react at 130 °C for 130 min. After the reaction is completed, cool to room temperature, separate the solid from the liquid to obtain copper particles. The copper particles are in a fluffy shape.

[0196] Specifically, the mixing time of the first solution and the second solution is 25 s.

[0197] S74. Add the copper particles to a solvent, mix evenly, add a coating agent, and stir for 35 min. Separate the solid from the liquid and dry in vacuum to obtain micron copper.

[0198] The coating agent is stearic acid. The solvent is absolute ethanol. Among them, the mass ratio of the coating agent to the copper particles is 0.005:1.

[0199] In this example, the specific surface area of the micron copper is 2.7 m 2 / g, and the average particle size is 1.03 μm.

[0200] S75. Weigh micron copper and nano copper with a particle size of 30 nm. The mass ratio of micron copper to nano copper is 3:1. Mix the micron copper and nano copper and embed the nano copper into the concave points of the micron copper to obtain composite copper powder.

[0201] Specifically, premix the micron copper and nano copper for 55 min to obtain a premix, then add zirconium beads with a diameter of 8 mm. The mass ratio of zirconium beads to the premix is 7:1. After ball milling for 10 h, composite copper powder is obtained.

[0202] Comparative Example 1 (simple mixing of micron copper and nano copper)

[0203] The preparation method of the composite copper powder in this example includes the following steps:

[0204] S81. Weigh a soluble copper salt and a pore-forming agent, dissolve them in a first alkaline solution, and mix evenly to obtain a first solution. The molar ratio of copper ions in the soluble copper salt to the pore-forming agent is 1:6.

[0205] Specifically, the soluble copper salt is copper acetate monohydrate. The pore-forming agent is ammonium chloride. The first alkaline solution includes sodium hydroxide and pure water, and the mass fraction of sodium hydroxide is 30%.

[0206] S82. Weigh a reducing agent and a dispersant, dissolve them in a second alkaline solution to obtain a second solution. The molar ratio of the reducing agent to the copper ions in the soluble copper salt is 5:1.

[0207] The reducing agent is sodium ascorbate and glycerol. The dispersant is gelatin. The mass ratio of the dispersant to the copper particles is 0.001:1.

[0208] The second alkaline solution includes sodium hydroxide and pure water. The mass ratio of sodium hydroxide is 10%.

[0209] S83. Rapidly mix the first solution and the second solution under stirring, and react at 80 °C for 60 min. After the reaction, cool to room temperature, and perform solid-liquid separation to obtain copper particles. The copper particles are in a fluffy shape.

[0210] Specifically, the mixing time of the first solution and the second solution is 50 s.

[0211] S84. Add the copper particles to a solvent, mix evenly, add a coating agent, and stir for 40 min. Perform solid-liquid separation and vacuum drying to obtain micron copper.

[0212] The coating agent is oleic acid. The solvent is ethanol. Among them, the mass ratio of the coating agent to the copper particles is 0.005:1.

[0213] In this example, the specific surface area of the micron copper is 3.63 m 2 / g, and the average particle size is 1.94 μm.

[0214] S85. Weigh micron copper and nano copper with a particle size of 30 nm. The mass ratio of micron copper to nano copper is 7:3. Simply mix the two to obtain composite copper powder.

[0215] Comparative Example 2

[0216] Commercially available copper powder with a particle size of 50 nm.

[0217] The micron copper in Examples 1-7 was observed by scanning electron microscopy, and it was found that the micron copper in Examples 1-7 was all in a fluffy shape. This application only shows the scanning electron microscopy pattern of the micron copper in Example 2, as Figure 3 shown. It can be clearly seen from Figure 3 that the micron copper is in a fluffy shape.

[0218] Add an organic solvent with a volume ratio of 16% to the copper powder in Examples 1-7 and Comparative Examples 1-2 respectively, and mix to obtain a solder paste with certain fluidity and viscosity.

[0219] Using the screen printing method, prepare a 80-μm nano solder paste layer on a copper substrate, then add another copper plate on top of the solder paste, preheat at 70 °C for 20 min, and keep it at 260 °C under a pressure of 10 MPa for 2 min, then a semiconductor package can be obtained.

[0220] The semiconductor packages prepared in Examples 1-7 and Comparative Examples 1-2 were detected respectively, and the detection data are shown in Table 1.

[0221] Table 1 Performance of semiconductor packages

[0222]

[0223] As can be seen from Table 1, the connection strength of the semiconductor packages in Examples 1 to 7 is better than that in Comparative Example 1 and Comparative Example 2. There are no cracks on the surfaces of the semiconductor packages in Examples 1 to 7, while obvious cracks can be seen in the semiconductor packages corresponding to Comparative Example 1 and Comparative Example 2.

[0224] Figure 4 、 Figure 5 、 Figure 6 The appearance diagrams of the semiconductor packages corresponding to Example 2, Comparative Example 1, and Comparative Example 2 after sintering are shown respectively. It can be seen from the figures that there are no obvious cracks in the semiconductor package corresponding to Example 2, while the cracks in the semiconductor packages corresponding to Comparative Example 1 and Comparative Example 2 are not only obvious but also numerous.

[0225] Although the present invention has been described with reference to several exemplary embodiments, it should be understood that the terms used are descriptive and exemplary, rather than restrictive. Since the present invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above-described embodiments are not limited to any of the foregoing details, but should be broadly construed within the spirit and scope defined by the appended claims. Therefore, 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 a composite copper powder, characterized in that: The following steps are involved: Weighing a soluble copper salt and a pore-forming agent, dissolving them in a first alkaline solution, and mixing them evenly to obtain a first solution, wherein the molar ratio of copper ions in the soluble copper salt to the pore-forming agent is (12-1):6; Weighing a reducing agent and a dispersing agent, and dissolving them in a second alkaline solution to obtain a second solution, wherein the molar ratio of the reducing agent to the copper ions in the soluble copper salt is (10-1):1; The first solution and the second solution are quickly mixed under stirring, and reacted at 80-160° C. for 15-120 minutes. After the reaction is completed, the mixture is cooled to room temperature, and solid-liquid separation is performed to obtain copper particles; the copper particles are in a plush state; The copper particles are added to the solvent, mixed evenly, and then the coating agent is added and stirred for 30-60 minutes, the solid-liquid separation is carried out, and the particles are vacuum dried, and then passed through a 80-800 mesh sieve to obtain particles with a diameter of 1-6 μm and a specific surface area of ​​0.2-8 m 2 / g of plush micron copper; Weighing the micron copper and nano copper with a particle size of 10-100 nm, wherein the mass ratio of the micron copper to the nano copper is (1-81):9, mixing the micron copper and the nano copper and embedding the nano copper into the concave points of the micron copper to obtain a composite copper powder; The soluble copper salt includes at least one of copper sulfate, copper nitrate, copper chloride, copper acetate, copper citrate and hydrates thereof; The pore-forming agent includes at least one of ammonium chloride, ammonium bromide, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, urea, ethylenediamine, triethanolamine, and triethylamine; The first alkaline solution and the second alkaline solution both include an alkaline substance and a solvent, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ethylenediamine, and ammonia water, and the solvent includes at least one of pure water, ethanol, ethylene glycol, glycerol, isopropanol, and polyethylene glycol; the proportion of the alkaline substance in the first alkaline solution is 5-30%, and the proportion of the alkaline substance in the second alkaline solution is 2-20%; The dispersant includes at least one of gelatin, polyvinyl pyrrolidone, gum arabic, benzimidazole, 2-methylimidazole, 2-phenylimidazole, imidazole, and hexadecyltrimethylammonium bromide; the mass ratio of the dispersant to the copper particles is (0.001-0.05): 1; The reducing agent includes at least one of sodium hypophosphite, sodium ascorbate, ascorbic acid, hydrazine hydrate, glucose, sodium borohydride and glycerol.

2. The method for preparing the composite copper powder according to claim 1, characterized in that: The size of the pits is ≤100 nm, and the particle size of the nano copper is not greater than the size of the pits; The mixing time of the first solution and the second solution is less than 3 min.

3. The method for preparing the composite copper powder according to claim 1, characterized in that: The step of mixing the micron copper and the nano copper and embedding the nano copper into the pits of the micron copper to obtain the composite copper powder comprises: The micron copper and the nano copper are premixed for 30-60 minutes to obtain a premix, and then ball milling beads with a diameter of 2-10 mm are added, the mass ratio of the ball milling beads to the premix is ​​(3-20):1, and composite copper powder is obtained after ball milling for 4-20 hours.

4. The method for preparing the composite copper powder according to claim 3, characterized in that: The ball milling beads are ceramic beads; After ball milling, the powder is passed through a 80-800 mesh sieve to obtain a composite copper powder with a particle size of 1-10 μm.

5. The method for preparing the composite copper powder according to claim 1, characterized in that: The coating agent includes at least one of stearic acid, oleic acid, benzimidazole, 2-methylimidazole, 2-phenylimidazole and imidazole, and the solvent includes at least one of anhydrous ethanol, ethylene glycol, pure water, acetone, ether, glycerol and acetone; the mass ratio of the coating agent to the copper particles is (0.005-0.1):

1.

6. A composite copper powder, characterized in that: The composite copper powder is prepared by the preparation method according to any one of claims 1 to 5.

7. A method for preparing a semiconductor package, characterized in that: The following steps are involved: Using the composite copper powder prepared by the preparation method according to any one of claims 1 to 5 as a raw material to prepare and obtain a solder paste; The two substrates are welded with the solder paste to obtain a semiconductor package.

8. A semiconductor package, characterized in that: The invention comprises two substrates and a solder paste layer located between the two substrates, wherein the solder paste layer is prepared using the composite copper powder prepared by the preparation method according to any one of claims 1 to 5 as a raw material.

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