Modified copper paste, preparation method and application thereof

Abstract

This application relates to the field of semiconductor packaging technology, and particularly to modified copper paste, its preparation method, and its application. The modified copper paste comprises a copper coordination compound, submicron-sized copper powder, micron-sized copper powder, resin, resin curing agent, and solvent. The copper coordination compound exhibits high dispersibility, and during the subsequent sintering process, nano-sized copper particles are generated in situ throughout the copper paste, leveraging the nanoscale effect to effectively reduce the required sintering temperature and pressure. Through the multi-scale particle size distribution of micron-sized, submicron-sized, and nano-sized copper powder, effective filling between particles is achieved during sintering, forming a gradient particle size distribution and achieving the densest packing. This not only significantly improves the density of the solder layer and the interfacial bonding strength, enhancing connection strength and reliability, but also optimizes the conductive path. As a semiconductor bonding material, this modified copper paste exhibits high bonding strength, lifespan, and conductivity after sintering, significantly improving the quality of power packaging.

Description

Technical Field

[0001] This application relates to the field of semiconductor packaging technology, and in particular to modified copper paste, its preparation method and application. Background Technology

[0002] Third-generation semiconductors such as silicon carbide and gallium nitride possess excellent electrical properties and have a wide range of applications, but they also face numerous challenges. For example, in semiconductor power devices, they face stringent electrical, thermal, and mechanical challenges. The interconnect materials of semiconductor chips are subjected to multiple tests, including mechanical vibration, thermomechanical stress, and high-density current. These interconnect materials need to possess properties such as the ability to carry large currents and high voltages, good heat dissipation, and reliable and stable connections. Furthermore, the performance of semiconductor devices is often negatively correlated with their packaging temperature; excessively high temperatures affect their current-carrying capacity (electrical performance) and also impact long-term reliability and lifespan.

[0003] Therefore, traditional soldering is rarely used in semiconductor packaging, especially power packaging. Instead, silver paste sintering or copper paste pressure sintering (welding) techniques are employed to form a dense solder layer on the semiconductor. This solder layer serves as the semiconductor's connection material to meet the application requirements in complex scenarios. When preparing silver or copper paste, corresponding nanoscale metal particles are often added. Their nanoscale size effect is utilized to lower the sintering temperature, thereby reducing the impact on semiconductor components. These nanoscale metal particles typically have a particle size of several nanometers to tens of nanometers, making them highly prone to agglomeration, which affects activity and the effectiveness of lowering the sintering temperature.

[0004] Furthermore, while silver paste exhibits good electrical and thermal conductivity after sintering, its high price limits its large-scale production and application. Copper paste, after sintering, offers only slightly inferior electrical and thermal conductivity compared to silver paste, and its lower cost facilitates large-scale production and application. However, copper is highly susceptible to oxidation in air, and the resulting copper oxides degrade interconnect performance, affecting conductivity, thermal conductivity, connection stability, reliability, and lifespan. In summary, copper paste still has several shortcomings as a sintering material for semiconductor interconnects. Summary of the Invention

[0005] The purpose of this application is to provide modified copper paste, its preparation method and application, in order to solve the technical problem that the copper paste for semiconductors does not perform well when sintered into a connecting material in the prior art.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a modified copper paste comprising the following components in parts by weight: 0.5 to 5 parts of copper coordination compound; 5 to 25 parts of submicron-sized copper powder; 55 to 95 parts of micron-sized copper powder; 1 to 15 parts of resin; 1 to 5 parts of resin curing agent; Solvent: 1 to 15 parts.

[0008] This modified copper paste incorporates three copper sources. Firstly, in existing copper pastes, directly adding extremely small nano-sized copper particles easily leads to agglomeration and oxidation. This modified copper paste, however, does not directly add such copper particles but instead uses copper coordination compounds. This not only improves the dispersibility of copper ions but also allows them to be reduced to nano-sized copper particles throughout the paste during subsequent sintering, further enhancing their dispersibility and reducing agglomeration. The high stability of the copper coordination compounds further inhibits oxidation. Secondly, during sintering, nano-sized copper particles are generated in situ throughout the paste, leveraging the nanoscale effect to effectively reduce the required sintering temperature and pressure, minimizing the impact on the semiconductor. Thirdly, through multi-scale particle gradation of micron-sized copper powder, submicron-sized copper powder, and nano-sized copper particles, effective filling between particles is achieved during sintering, forming a gradient particle size distribution for the densest packing. This significantly improves the density of the weld layer and the interfacial bonding strength, enhancing connection strength and reliability, and also optimizes the conductive pathway. The resin and resin curing agent cure during sintering, forming a dense welding layer with the copper powders, while the solvent can uniformly disperse the components. Therefore, this modified copper paste, as a semiconductor bonding material, exhibits high bonding strength, lifespan, and conductivity after sintering, significantly improving the quality of power packaging.

[0009] Secondly, this application provides a method for preparing modified copper paste, comprising the following steps: The components including the modified copper paste described above are mixed to obtain the modified copper paste.

[0010] The preparation method of this application involves mixing the components of the modified copper paste to ensure thorough dispersion and the formation of a homogeneous slurry system. During subsequent sintering, copper coordination compounds generate nanoscale copper particles, which then form a multi-scale particle size distribution with submicron and micron-sized copper powders, achieving the densest packing. This preparation method offers controllable processes, resulting in a modified copper paste with stable properties. After sintering, it forms a dense welding layer, improving connection strength and reliability, while also reducing sintering temperature and pressure.

[0011] Thirdly, this application provides the application of the above-mentioned modified copper paste, or the modified copper paste prepared by the above-mentioned method, in semiconductor packaging, including the following steps G10 to G20: G10. Form a wet film of sintering paste on the surface of the semiconductor device; G20. After drying the wet film, it is bonded to the parts to be connected and then sintered (welded).

[0012] Because the modified copper paste includes copper coordination compounds, submicron-sized copper powder, and micron-sized copper powder, the copper coordination compounds can generate nano-sized copper particles during sintering. These particles are not only well-dispersed but also resistant to oxidation. Furthermore, the particle size distribution across these three scales allows for the densest possible packing. Therefore, the application of this modified copper paste can sinter a wet film to form a dense solder layer, resulting in high bonding strength and stability between the semiconductor device and the components to be connected. In addition, it allows for the use of lower sintering temperatures and pressures, reducing the impact on semiconductor devices and improving packaging reliability. Compared to silver paste sintering materials, the application of modified copper paste offers a greater cost advantage, particularly in reducing the cost of power packaging technology and driving industry progress. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is an SEM image of the submicron-sized copper powder obtained in step S2 of Example 1 of this application; Figure 2 This is a side SEM image of the weld layer formed in step S5 of embodiment 1 of this application; Figure 3 This is a schematic diagram of the selected area for EDS testing in step S5 of embodiment 1 of this application, where a weld layer is formed. Figure 4 This is the EDS test result of the content of each element in the weld layer formed in step S5 of embodiment 1 of this application. Detailed Implementation

[0015] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0016] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0017] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions mean any combination of these items, including any combination of single or multiple items.

[0018] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0019] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, a first feature may also be referred to as a second feature, and similarly, a second feature may also be referred to as a first feature. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0020] The first aspect of this application provides a modified copper paste, comprising the following components in parts by weight: 0.5 to 5 parts of copper coordination compound; 5 to 25 parts of submicron copper powder; 55 to 95 parts of micron-sized copper powder; 1 to 15 parts of resin; 1 to 5 parts of resin curing agent; Solvent: 1 to 15 parts.

[0021] The modified copper paste in this application includes three copper sources. Firstly, in existing copper pastes, directly adding extremely small nano-sized copper particles easily leads to agglomeration and oxidation. In this application, the modified copper paste does not directly add such copper particles but instead uses copper coordination compounds. This not only improves the dispersibility of copper ions but also allows them to be reduced to nano-sized copper particles throughout the paste during subsequent sintering, further enhancing their dispersibility and reducing agglomeration. The high stability of the copper coordination compounds further inhibits oxidation. Secondly, during subsequent sintering, nano-sized copper particles are generated in situ throughout the paste, leveraging the nanoscale effect to effectively reduce the required sintering temperature and pressure, minimizing the impact on the semiconductor. Thirdly, through multi-scale particle gradation of micron-sized copper powder, submicron-sized copper powder, and nano-sized copper particles, effective filling between particles is achieved during sintering, forming a gradient particle size distribution for the densest packing. This significantly improves the density of the weld layer and the interfacial bonding strength, enhancing connection strength and reliability, and also optimizes the conductive path. The resin and resin curing agent cure during sintering, forming a dense welding layer with the copper powders, while the solvent can uniformly disperse the components. Therefore, this modified copper paste, as a semiconductor bonding material, exhibits high bonding strength, lifespan, and conductivity after sintering, significantly improving the quality of power packaging.

[0022] Regarding copper coordination compounds: Copper coordination compounds play several roles. First, they act as a copper source, subsequently being reduced to nanoscale copper particles, which then serve as part of the bonding material, providing electrical and thermal conductivity. Second, the formation of coordination compounds by copper ions improves dispersion, ensuring uniform distribution throughout the copper paste. During subsequent sintering, these ions are reduced in situ to nanoscale copper particles, preventing agglomeration. Third, the nanoscale copper particles formed are typically a few nanometers to tens of nanometers in size, which not only leverages the nanoscale effect to reduce sintering temperature and pressure but also, due to their uniform formation, effectively fills the pores between larger particles such as submicron and micron-sized particles, achieving the densest packing and increasing the compactness during sintering. Fourth, copper coordination compounds exhibit good stability, effectively avoiding the oxidation problems of existing nanoscale copper particles or copper paste containing them during storage. They are also not easily reduced at room temperature, allowing them to be stored in copper paste and undergo a reduction reaction during sintering. The mass fraction of the copper coordination compound is 0.5 to 5 parts, and can be any value or any two values ​​of 0.5, 1, 2, 3, 4, or 5 parts, which is beneficial to achieving the above-mentioned effects.

[0023] In some embodiments, the copper coordination compound comprises a copper salt and a ligand group, wherein the copper salt includes copper carboxylate; and / or, the ligand group includes at least one of an amino group, a nitrogen-containing heterocycle, and a phosphine group. Since copper salts such as copper chloride and copper sulfate readily introduce halogens and sulfur, posing a significant hazard to semiconductor electronic devices, copper carboxylate is more easily decomposed during sintering and leaves no harmful residues. In exemplary embodiments, copper carboxylate may include, but is not limited to, copper acetate and copper propionate. The ligand group, such as the amino group, can form stable coordination bonds with copper ions, further improving its dispersibility and chemical stability. When the ligand group includes an amino group, it may include C1-C5 alkylamines, including but not limited to alkylamine ligand groups such as methylamino, ethylamino, and propylamino. Optionally, three ligand groups can be used to form three copper coordination compounds, further enhancing the aforementioned effects.

[0024] Regarding micron-sized and submicron-sized copper powder: Micron-sized copper powder has the largest particle size and is used in the highest quantity among the three copper sources. Its function is to act as a skeleton during the copper paste sintering process, providing support in the formed dense weld layer, maintaining connection strength and structural stability, and providing the main conductive pathways. The mass fraction of micron-sized copper powder is 55 to 95 parts, including but not limited to any value or any two of 55, 60, 70, 80, 90, and 95 parts, which is beneficial for achieving the aforementioned effects. Submicron-sized copper powder, with a particle size between micron-sized and nano-sized copper powder, can initially fill the pores between micron-sized copper powder particles, improving the density of the weld layer. Submicron-sized copper powder can also reduce the sintering temperature and pressure to some extent. The mass fraction of submicron-sized copper powder is 5 to 25 parts, including but not limited to any value or any two of 5, 10, 15, 20, and 25 parts, which is beneficial for achieving the aforementioned effects.

[0025] The most important relationship between micron-sized and submicron-sized copper powder is their particle size and mass relationship. This relationship facilitates the densest packing, thereby further improving the density of the modified copper paste after sintering, enhancing connection strength and stability, and improving electrical performance. In some embodiments, the ratio of the Dv50 particle size of the micron-sized copper powder to that of the submicron-sized copper powder is 20:1 to 100:1, meaning the Dv50 particle size of the former is 20 to 100 times that of the latter. This ratio can include, but is not limited to, any ratio or any two ratios between 20:1, 25:1, 50:1, 75:1, and 100:1, with 25:1 being a preferred choice. This particle size ratio helps the submicron-sized copper powder better fill the pores between the micron-sized copper powders, forming a denser particle packing structure, significantly reducing porosity, and achieving a space utilization rate of over 74%.

[0026] Specifically, the particle size of micron-sized copper powder is on the scale of several micrometers or tens of micrometers. In some embodiments, the Dv50 particle size of micron-sized copper powder is 2 μm to 10 μm, which can include, but is not limited to, any value or any two values ​​of 2 μm, 4 μm, 5 μm, 8 μm, and 10 μm, and may be selected as 5 μm. The particle size of submicron-sized copper powder is on the scale of less than a few micrometers, but much larger than a few nanometers. In some embodiments, the Dv50 particle size of submicron-sized copper powder is 100 nm to 500 nm, which can include, but is not limited to, any value or any two values ​​of 100 nm, 150 nm, 200 nm, 300 nm, and 500 nm, and may be selected as 200 nm. These particle size ranges are beneficial for further achieving effective filling between particles and improving packing density.

[0027] In some embodiments, the mass ratio of micron-sized copper powder to submicron-sized copper powder is 2.2:1 to 5:1, which may include, but is not limited to, any ratio or any two ratios of 2.2:1, 7:3, 3:1, 4:1, 5:1. These mass ratios of the two copper powders are beneficial for further achieving effective filling between particles and improving packing density.

[0028] Furthermore, in some embodiments, the micron-sized copper powder includes flake-shaped copper powder; in other embodiments, the submicron-sized copper powder includes spherical copper powder. Flake-shaped copper powder has a larger specific surface area and is easier to stack, while spherical copper powder is more likely to fill the gaps between flake-shaped particles. The synergistic effect of the two can significantly improve the packing density and increase the density of the modified copper paste after sintering.

[0029] About resin: The resin primarily provides rheological properties for the copper paste and facilitates the dispersion of copper coordination compounds and the two copper powders. Furthermore, it cures with the curing agent during the subsequent sintering process to form a dense weld layer. The resin's mass fraction ranges from 1 to 15 parts, including but not limited to any value or any two of 1, 2, 5, 8, 10, 12, and 15 parts, to facilitate compatibility with the copper powder.

[0030] In some embodiments, the resin may include an epoxy resin containing active epoxy groups, which can be thermo-cured in conjunction with a resin curing agent. During sintering, a ring-opening addition reaction occurs to form a three-dimensional cross-linked network, tightly bonding the copper powders to form a dense weld layer as a connecting material. In an exemplary example, the epoxy resin may be formed by the condensation polymerization of bisphenol A and epichlorohydrin, possessing not only two terminal epoxy groups but also a certain degree of toughness, as shown in the following molecular structure: .

[0031] Optionally, the epoxy resin may be at least one of the following models from Mitsubishi Chemical: YX8000D, YX8034, YX8040, YX7760, YX7110B80, YX7105, YX7400N, YX7700, YL6810, YL1750, YL980, YL983U, YL630LSD, and YL6810; or two or more of these may be used in combination.

[0032] Regarding resin curing agents: The role of the resin curing agent is to initiate the cross-linking reaction of the epoxy resin under heating conditions, curing the resin to form a cross-linked network structure, which forms a dense welding layer with the copper powder, thus helping to improve the connection strength and stability as a bonding material. The resin curing agent is present in parts by weight of 1 to 5 parts, and may include, but is not limited to, any value or any two values ​​of 1, 2, 3, 4, or 5 parts, to facilitate the curing of the resin.

[0033] In some embodiments, the resin curing agent may include a latent curing agent, which, after being mixed with the resin at room temperature, can maintain a stable state for a relatively long time without immediately initiating a cross-linking curing reaction. Therefore, the latent curing agent is beneficial for the modified copper paste to have good chemical stability during storage and use, and can be activated under the heating conditions of sintering treatment, initiating a cross-linking reaction of the resin. In an exemplary embodiment, the latent curing agent may be selected from products of ADEKA, including but not limited to at least one of ADEKA's EH-3293S, EH-3842, EH-5031S, EH-4357S, EH-5030S, EH-5057PK, EH-5011S, EH-5046S, and EH-2110K, to further achieve the aforementioned effects of storage stability and cross-linking curing upon heating.

[0034] Regarding solvents: The main function of the solvent is to evenly disperse the copper powder and other components, while also giving the copper paste a certain degree of fluidity, viscosity, and workability. The solvent's mass fraction ranges from 1 to 15 parts, and can include, but is not limited to, any value or any range between two of 1, 5, 10, and 15 parts.

[0035] In some embodiments, alcohols may include at least one of alcohols, ketones, esters, and ethers, wherein alcohols include at least one of methanol, ethanol, 1-propanol, 2-propanol, n-propanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, ethylene glycol, 1,3-propanediol, 1,2-propanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, methyl glycol, menthol, terpineol, terpineol, diethylene glycol, butyl carbitol, diethylene glycol, and triethylene glycol; ketones include at least one of acetone, butanone, methyl ethyl ketone, and isophorone; esters include at least one of divalent esters (DBE), diethylene glycol butyl ether acetate, ethyl acetate, and butyl acetate; and ethers include at least one of monobutyl ether, methyl ethyl ether, and dipropylene glycol methyl ether.

[0036] In some embodiments, the solvent includes a reducing solvent. Besides the aforementioned solvent function, the reducing solvent can reduce the copper coordination compound to nanoscale copper particles during sintering. Furthermore, because the copper ions in the copper coordination compound form stable coordination bonds, they are less likely to react with the reducing solvent during storage. Alternatively, a non-reducing solvent can be used, with a reducing component added to the modified copper paste; or a reducing solvent can be used, with an additional reducing component added. In the example, the reducing solvent may include at least one of aldehydes and glycols. Taking the coordination compound formed by the aforementioned copper carboxylate and amine groups as an example, during sintering, aldehydes or glycols reduce copper ions to nanoscale copper particles, simultaneously generating products such as ammonia, carbon dioxide, and water. These products are easily volatilized at high temperatures and will not remain in the solder layer, affecting performance. Therefore, if the solvent includes a reducing solvent or an additional reducing component is added, the modified copper paste does not require a reducing atmosphere during sintering, only an inert atmosphere, eliminating the need to modify existing equipment and demonstrating good industrial adaptability.

[0037] Regarding other ingredients and parameters: In some embodiments, the modified copper paste comprises an additive, the additive being 0.01 to 1 part by weight, including but not limited to any value or range between any two of 0.01, 0.05, 0.1, 0.5, and 1 part. The additive typically improves the processing performance and paste quality of the modified copper paste, such as improving leveling, eliminating bubbles, and enhancing dispersibility. The additive may include at least one of defoaming agents, leveling agents, and dispersing agents. In an example, it may include dispersing agents from HIPLAAD, including but not limited to at least one of models such as ED116, ED120, ED152, ED251, ED350, ED360, and ED403, to improve the dispersibility of the modified copper paste.

[0038] In some embodiments, the viscosity of the modified copper paste can be 10 Pa·s to 25 Pa·s, and the thixotropic coefficient can be 2 to 5, so that it has good and moderate properties of thinning when stirred and thickening when left to stand, making it easy to process into a wet film to be sintered by processes such as dispensing and screen printing.

[0039] The second aspect of this application provides a method for preparing modified copper paste, comprising the following step S10: S10. The components including the modified copper paste of the above embodiment are mixed to obtain the modified copper paste.

[0040] The preparation method of this application involves mixing the components of the modified copper paste to ensure thorough dispersion and the formation of a homogeneous slurry system. During subsequent sintering, copper coordination compounds generate nanoscale copper particles, which then form a multi-scale particle size distribution with submicron and micron-sized copper powders, achieving the densest packing. This preparation method offers controllable processes, resulting in a modified copper paste with stable properties. After sintering, it forms a dense welding layer, improving connection strength and reliability, while also reducing sintering temperature and pressure.

[0041] The types, dosages, and functions of copper coordination compounds, submicron-sized copper powder, micron-sized copper powder, resin, resin curing agent, solvent, and optional additives can be found in the description of modified copper paste provided in the first aspect above, and will not be repeated here. The preparation methods for copper coordination compounds and submicron-sized copper powder can be found in the following description: In some embodiments, the preparation method of the copper coordination compound includes the following step S11: S11. Coordinate copper salt with a raw material containing a ligand group to obtain a copper coordination compound; The copper salt includes copper carboxylate, and the raw materials containing ligand groups include at least one of alkylamines, imidazoles, pyridines, and organophosphorus compounds.

[0042] Copper carboxylate can include, but is not limited to, alkyl copper carboxylate, such as copper acetate and copper propionate. Using copper carboxylate as a copper salt helps reduce the introduction of elements such as chlorine and sulfur, thus reducing the impact on semiconductor devices. Alkylamines, imidazoles, pyridines, organophosphorus compounds, and other raw materials can provide amine groups, nitrogen-containing heterocycles, phosphine groups, etc., to coordinate with copper ions, forming stable copper complex structures. In the example, when the raw material containing the ligand group is an alkylamine, three alkylamines can be selected in a mass ratio of 1:1:1. The stability of the complex is enhanced through the synergistic coordination of multiple alkylamines. In the example, step S11 can be performed in a fume hood. First, ethanol is added to a three-necked flask, then the copper salt is added and stirred evenly. Then, the raw material containing the ligand group is slowly added to allow a coordination reaction to occur between the raw materials, yielding a copper coordination compound.

[0043] In some embodiments, the method for preparing submicron-sized copper powder includes the following steps S12 to S14: S12. The raw materials, including inorganic copper salt, reducing organic acid, and control agent, are subjected to a reduction reaction; S13. The product of the reduction reaction and the dispersant are dispersed in an alcohol solvent to obtain a dispersion; S14. The dispersion was freeze-dried to obtain submicron-sized copper powder; The dispersant includes at least one of C8-C12 alkylamines, imidazoles, pyridines, and organophosphorus compounds.

[0044] Submicron-sized copper powder can be obtained through steps S12 to S14 above. Its SEM image can be found in the reference images. Figure 1 Step S12 is the step of reducing the inorganic copper source into copper particles. The inorganic copper source can be, but is not limited to, soluble copper salts such as copper sulfate pentahydrate, copper nitrate trihydrate, and copper chloride. The reducing organic acid can be, but is not limited to, ascorbic acid and citric acid. The control agent can include polyvinylpyrrolidone (PVP). The role of the control agent is to regulate the nucleation and growth process of copper crystals, control the morphology and particle size, and control the particle size of the copper particles generated by the reduction reaction to be in the submicron range. The reaction system can be an aqueous system. After the reaction is completed, solid-liquid separation can be performed, such as centrifugation, and the reduction product can be washed with solvents such as ethanol and water to remove excess raw materials or reaction byproducts.

[0045] In step S13, copper particles are thoroughly dispersed in an alcohol solvent using a dispersant to minimize agglomeration. The dispersant may include at least one of C8-C12 alkylamines, imidazoles, pyridines, and organophosphines; in an example, octylamine may be included. The alkyl segments in octylamine are relatively long, which can create a steric hindrance effect on the surface of the copper particles. Furthermore, the amino groups in octylamine can adsorb onto the copper surface, altering its charge distribution and increasing the electrostatic repulsion between particles. The combined effect of these two factors improves the dispersibility of the copper particles.

[0046] In the final step S14, the dispersion is freeze-dried to remove the solvent. The freeze-drying process also helps the copper particles maintain chemical stability, resulting in submicron-sized copper powder. Before freeze-drying, solid-liquid separation can be performed, such as centrifugation, to collect the wet copper particles before the freeze-drying process described above.

[0047] As an example of this application, steps S12 to S14 can be performed as follows: In step S12, ultrapure water is first added to a container, and after heating, polyvinylpyrrolidone (PVP) is added and magnetically stirred until completely dissolved; CuSO4·5H2O is added and magnetically stirred until completely dissolved, resulting in a blue transparent solution; after heating, ascorbic acid aqueous solution is slowly added dropwise to the container, and the solution color changes from blue to light yellow, and finally to brownish-red or dark red, indicating that copper ions have been converted into elemental copper; finally, centrifugation is performed to remove some solvent, and then the solution is washed clean with ethanol and water alternately. In step S13, copper particles are dispersed in ethanol to obtain a suspension, and then octylamine is added as a dispersant, and magnetically stirred until uniform to obtain a dispersion. In step S14, the above dispersion is centrifuged and freeze-dried to obtain submicron-sized copper powder; this submicron-sized copper powder needs to be stored in the absence of oxygen and can be stored under vacuum for later use.

[0048] In addition to the preparation methods described above, copper coordination compounds and submicron-sized copper powder can also be obtained by selecting commercially available ingredients or referring to other preparation methods. Micron-sized copper powder, resin, resin curing agent, solvent, and optional additives can also be prepared by selecting commercially available ingredients or referring to existing processes. Weigh the above components according to the mass proportions in the modified copper paste of the first aspect, mix and homogenize them to obtain a paste, and finally degas the paste in a degassing machine to obtain the modified copper paste.

[0049] The third aspect of this application provides an application of the modified copper paste of the above-described application embodiments, or the modified copper paste prepared by the preparation method of the above-described application embodiments, in semiconductor packaging, including the following steps G10 to G20: G10. Form a wet film of sintering paste on the surface of the semiconductor device; G20. After drying the wet film, it is bonded to the parts to be connected and then sintered (welded).

[0050] Because the modified copper paste includes copper coordination compounds, submicron-sized copper powder, and micron-sized copper powder, the copper coordination compounds can generate nano-sized copper particles during sintering. These particles are not only well-dispersed but also resistant to oxidation. Furthermore, the particle size distribution across these three scales allows for the densest possible packing. Therefore, the application of the modified copper paste in this embodiment can sinter a wet film to form a dense solder layer, resulting in high bonding strength and stability between the semiconductor device and the components to be connected. In addition, it allows for the use of lower sintering temperatures and pressures, reducing the impact on semiconductor devices and improving packaging reliability. Compared to silver paste sintering materials, the application of modified copper paste offers a greater cost advantage, particularly in reducing the cost of power packaging technology and driving industry progress.

[0051] In some embodiments, the drying and sintering processes are carried out in an inert atmosphere to reduce the influence of components such as oxygen on the modified copper paste. In exemplary cases, the processes can be performed in a vacuum environment or in an atmosphere such as nitrogen or argon.

[0052] Step G10 is the step of forming a wet film. In the example, processes such as dispensing, transfer printing, and screen printing can be used to form a wet film on the semiconductor device according to the specific requirements of the application. In the example, before the screen printing process, the modified copper paste can be thawed to 20°C to 25°C, stirred and mixed until the modified copper paste has a uniform appearance, and further stirred to remove bubbles. Finally, the printing parameters are set, and the modified copper paste is printed to form a wet film. In some embodiments, the thickness of the wet film is 100 μm to 350 μm, which may include, but is not limited to, any value or any two values ​​of 100 μm, 150 μm, 200 μm, 300 μm, and 350 μm. Wet films of these thicknesses are beneficial for the subsequent sintering process to form a solder layer with good density and mechanical strength.

[0053] Step G20 is the entire sintering process, achieving semiconductor connection and packaging. Specifically, it includes a drying process, followed by bonding the components to be connected, and finally sintering. The drying process removes some solvent, allowing the resin and resin curing agent to cross-link and solidify. It also reduces copper coordination compounds to nanoscale copper particles using reducing solvents or added reducing components, thus forming a cured wet film. This film is then sintered with the components to be bonded, forming a solder layer for connection.

[0054] The drying temperature can be 70℃~90℃, or 80℃, and the time can be 10 min~20 min. After drying, the modified copper paste will form a cured film. At this time, the parts to be connected can be attached to it. The parts can be attached at a temperature of 70℃~90℃ and appropriate pressure can be applied. Through van der Waals forces and other forces, the cured film and the parts to be connected will generate initial adhesion.

[0055] Finally, the semiconductor element and the initially bonded component to be connected are subjected to a sintering process. In some embodiments, the sintering temperature can be 230°C to 260°C, including but not limited to any value or any two of 230°C, 240°C, 250°C, and 260°C. In some embodiments, the pressure applied during sintering can be 10 MPa to 20 MPa, including but not limited to any value or any two of 10 MPa, 15 MPa, and 20 MPa, i.e., pressure sintering. During the sintering process, pressure is maintained on the semiconductor element and the component to be connected to improve the bonding strength of the sintered connection. The sintering time can be 5 min to 10 min. Within this sintering parameter range, the modified copper paste can achieve sufficient densification, effectively improving the bonding strength at the connection. Furthermore, due to the size effect of nano-sized and submicron-sized copper particles, the required sintering temperature and pressure are significantly lower than the parameters of the prior art, reducing the impact on the semiconductor element. After the sintering process is completed, the temperature can be slowly reduced to eliminate thermal stress.

[0056] The weld layer formed by the above method has high welding strength, reaching over 30 MPa, and a high brazing rate and low void rate, indicating high welding quality. Moreover, the oxygen content of the weld layer is very low, indicating that the copper powder was almost not oxidized during the sintering process and has high activity, which gives the connection part good electrical and thermal conductivity, improving the power packaging effect.

[0057] The following description is based on specific embodiments.

[0058] Example 1 This embodiment provides a modified copper paste, its preparation method, and its application. The modified copper paste comprises the following components in parts by weight: Five parts of copper coordination compounds were found; these were amino coordination compounds of copper acetate. 25 parts of submicron copper powder, with a Dv50 particle size of 200 nm; 65 parts of micron-sized copper powder, which is in the form of flake copper powder with a Dv50 particle size of 5 μm; Four parts of resin, epoxy resin, Mitsubishi Chemical's YX8000D model; One part of resin curing agent, a latent curing agent, is ADEKA's EH-3293S model; Solvent: 5 parts, ethylene glycol; 0.05 parts of dispersant, HIPLAAD's ED116 model.

[0059] Example 1: The preparation method of modified copper paste includes the following steps S1 to S3: S1: Preparation of copper coordination compounds. The procedure was performed in a fume hood. 300 mL of ethanol (treated with molecular sieves) was added to a 1 L three-necked flask, followed by 0.3 mol of copper acetate. The mixture was stirred and homogenized for 10 min. Separately, methylamine, ethylamine, and propylamine were mixed in a 1:1:1 mass ratio to obtain a mixed amine ligand solution. This amine ligand solution was slowly added to the three-necked flask to obtain the copper coordination compound.

[0060] S2: Preparation of submicron-sized copper powder.

[0061] Add 500 mL of ultrapure water to a 1 L three-necked flask and heat to 50 °C; weigh 1.0 g of PVP and add it to the flask, then stir magnetically until completely dissolved; add 5 g of CuSO4·5H2O and stir magnetically until completely dissolved to obtain a blue transparent solution. Weigh 2 g of ascorbic acid, dissolve it in 100 mL of deionized water, stir to dissolve, and obtain an ascorbic acid aqueous solution for later use; The temperature of the solution in the three-necked flask was raised to 70°C, and the temperature was kept constant while magnetic stirring was maintained. Add the ascorbic acid aqueous solution dropwise slowly into the three-necked flask using a graduated separatory funnel. As the ascorbic acid is added, the color of the solution will change from blue to light yellow, and finally to brownish-red or dark red, indicating that the copper ions have been reduced to elemental copper. The reaction product was centrifuged, washed three times with ethanol and water, dispersed in 100 g of ethanol to obtain a suspension, and then added to a 500 mL three-necked flask. 0.1 g of octylamine was added, and the mixture was magnetically stirred for 1 h to obtain a dispersion. The dispersion was centrifuged and then freeze-dried to obtain submicron-sized copper powder, which was spherical and stored under vacuum for later use.

[0062] S3: Mix the above-mentioned copper coordination compound, submicron-sized copper powder, micron-sized copper powder and other components and homogenize them to obtain a paste. Degas the paste in a degassing machine to obtain modified copper paste.

[0063] The modified copper paste is used for semiconductor power packaging, including the following steps S4 to S5: S4: Using stencil printing, the modified copper paste is thawed to 20℃~25℃ before printing, and then manually stirred until the modified copper paste has a uniform appearance; then mechanically stirred to remove bubbles at 1300 rpm for 180 s; finally, an automated printing equipment is used to set the printing parameters and print the modified copper paste on the semiconductor components.

[0064] S5: Sintering Process. First, the printed copper paste is dried in a nitrogen atmosphere at 80°C for 15 minutes. Then, the components to be connected are placed onto the dried modified copper paste using a pick-and-place machine. The nozzle is not heated, but the platform is heated to 80°C and slightly pressurized at 1 MPa. Finally, sintering is performed at 230°C, with the semiconductor components and the components to be connected sintered under pressure at 15 MPa for 5 minutes. After sintering, the temperature is slowly reduced to eliminate thermal stress, allowing the semiconductor components to connect with other components.

[0065] Example 2 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the Dv50 particle size of the micron-sized copper powder is 4 μm, which reduces the ratio of the Dv50 particle size of the micron-sized copper powder to the Dv50 particle size of the submicron-sized copper powder to 20:1; all other aspects are the same.

[0066] Example 3 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the Dv50 particle size of the micron-sized copper powder is 6 μm, which increases the ratio of the Dv50 particle size of the micron-sized copper powder to the Dv50 particle size of the submicron-sized copper powder to 30:1; all other aspects are the same.

[0067] Example 4 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the Dv50 particle size of the micron-sized copper powder is 8 μm, and the Dv50 particle size of the submicron-sized copper powder is changed to 160 nm, so that the ratio of the Dv50 particle size of the micron-sized copper powder to the Dv50 particle size of the submicron-sized copper powder is increased to 50:1; all other aspects are the same.

[0068] Example 5 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the mass part of the micron-sized copper powder is changed to 55 parts, so that the mass ratio of micron-sized copper powder to submicron-sized copper powder is reduced to 2.2:1; all other aspects are the same.

[0069] Example 6 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the mass part of the micron-sized copper powder is changed to 75 parts, so that the mass ratio of micron-sized copper powder to submicron-sized copper powder is increased to 3:1; all other aspects are the same.

[0070] Example 7 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the mass fraction of micron-sized copper powder is changed to 80 parts and the mass fraction of submicron-sized copper powder is changed to 20 parts, so that the mass ratio of micron-sized copper powder to submicron-sized copper powder is increased to 4:1; all other aspects are the same.

[0071] Example 8 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that methylamine, ethylamine, and propylamine in step S1 are replaced with 2-ethylimidazole; all other aspects are the same.

[0072] Example 9 This embodiment provides a modified copper paste and its preparation method. The only difference from Example 1 is that the mass part of the copper coordination compound is changed to 2 parts; everything else is the same.

[0073] Example 10 This embodiment provides a modified copper paste and its preparation method. The only difference from Embodiment 1 is that the sintering pressure in step S5 is changed to 10 MPa; all other aspects are the same.

[0074] Example 11 This embodiment provides a modified copper paste and its preparation method. The only difference from Embodiment 1 is that the sintering temperature in step S5 is changed to 260℃; all other aspects are the same.

[0075] Comparative Example 1 This comparative example provides a modified copper paste and its preparation method. The only difference from Example 1 is that copper coordination compounds are not added to the raw materials for preparing the modified copper paste, and this part by mass is replaced with submicron-sized copper powder; all other aspects are the same.

[0076] Comparative Example 2 This comparative example provides a modified copper paste and its preparation method. The only difference between this example and Example 1 is that the step S1 for preparing the copper coordination compound is omitted, and acetate is directly used as the raw material component of the modified copper paste; all other aspects are the same.

[0077] Comparative Example 3 This comparative example provides a modified copper paste and its preparation method. The only difference from Example 1 is that submicron-sized copper powder is not added to the raw materials for preparing the modified copper paste, and this part by weight is replaced with micron-sized copper powder; all other aspects are the same.

[0078] Comparative Example 4 This comparative example provides a modified copper paste and its preparation method. The only difference from Example 1 is that micron-sized copper powder is not added to the raw materials for preparing the modified copper paste; instead, this mass fraction is replaced with submicron-sized copper powder. All other aspects are the same.

[0079] The differences between Examples 1 to 11 and Comparative Examples 1 to 4 are shown in Table 1.

[0080]

[0081] Relevant performance tests and results analysis 1. Morphology and particle size analysis of submicron copper powder.

[0082] The submicron-sized copper powder obtained in step S2 of Example 1 was scanned by electron microscopy, and its SEM image is shown below. Figure 1 As shown, from Figure 1 As can be seen, the submicron-sized copper powder exhibits a uniform spherical morphology and has a similar particle size. Figure 1 The particle size of several particle samples is marked in the document.

[0083] 2. Morphological analysis of the weld layer.

[0084] The side of the solder layer formed by the semiconductor device power package in step S5 of Example 1 is scanned by electron microscopy, and its SEM image is shown below. Figure 2 As shown, it can be seen Figure 2 The welded layer is dense and firmly bonded to the upper and lower layers, with no obvious defects such as incomplete welding or voids.

[0085] 3. Elemental analysis of the weld layer.

[0086] Energy-dispersive X-ray spectroscopy (EDS) analysis was performed on the solder layer formed by the semiconductor device power package in step S5 of Example 1. The selected area of ​​the EDS sample is as follows: Figure 3 As shown, the content of each element is as follows: Figure 4 As shown, Figure 4 As can be seen, the oxygen content in the weld layer is less than 0.1%, indicating that the copper particles are almost completely oxidized. Therefore, the weld layer has good electrical and thermal conductivity.

[0087] 4. Welding quality analysis.

[0088] The solder layer formed by the semiconductor device power packaging in step S5 of Example 1 was analyzed by ultrasonic scanning to determine the solder adhesion rate and void rate. The sum of the solder adhesion rate and void rate was 100%.

[0089] Six samples were made for each case, and the weld layer in each sample was tested. The brazing rates were 99.88%, 98.71%, 99.87%, 99.96%, 99.88%, and 99.62%, respectively. The higher the brazing rate, the tighter and stronger the weld bond, and the better the weld quality.

[0090] 5. Welding strength analysis.

[0091] Four samples were prepared for each of the above cases, and the welding strength of the weld layer was measured by a push-pull tester. The results are recorded in Table 1.

[0092] Based on the contents of Table 1, Examples 2 to 4 adjusted the particle size of the micron-sized copper powder. The micron-sized copper powder in Example 2 was too small, while the micron-sized copper powder in Examples 3 and 4 was too large. This would affect the filling between copper particles of different sizes, affect the particle packing density, make it difficult to form the densest packing, and thus affect the density of the weld layer formed by sintering and the weld strength.

[0093] Similarly, the adjustment of the mass ratio of micron-sized copper powder to submicron-sized copper powder in Examples 5-7 also affected the filling between copper particles of different sizes. The amount of micron-sized copper powder used in Example 5 was too small, while the amount of micron-sized copper powder used in Examples 6 and 7 was too large, which would affect the particle packing density, making it difficult to form the densest packing, and thus affecting the density of the weld layer formed by sintering and the weld strength.

[0094] Example 8 prepared another copper coordination compound, which was further used to prepare modified copper paste and finally sintered to form a welding layer. The welding strength was also quite ideal, which shows the feasibility of using copper coordination compounds.

[0095] In Example 9, the mass fraction of the copper coordination compound was too small, resulting in too little mass of nanoscale copper particles. This also affected the filling between copper particles of different sizes, impacting the particle packing density and making it difficult to form the densest packing. Consequently, it affected the density of the weld layer formed during sintering and the weld strength.

[0096] In Example 10, the pressure applied during the sintering process was reduced to 10 MPa, but the welding strength was still over 40 MPa, which is greater than 30 MPa. This fully meets the strength requirements of power packaging, indicating that the modified copper paste still has good applicability at lower pressures.

[0097] In Example 11, the sintering temperature was further increased to 260°C, resulting in further improved welding strength. While higher temperatures could be considered for achieving even greater welding strength, this would increase the impact on semiconductor components. However, Example 1, at 230°C, already provided welding strengths of over 40 MPa or even 70 MPa, fully meeting the strength requirements of power packaging.

[0098] The primary problem with Comparative Examples 1 to 4 is that effective sintering is not possible under sintering conditions of 15 MPa / 230°C. The welding strength is significantly lower than that of the Examples and does not meet the requirements for use. Further increases in sintering temperature or pressure are needed, but this will increase the risk of damaging semiconductor components.

[0099] In Comparative Example 1, no copper coordination compound was used; the mass fraction of the sample was replaced with submicron-sized copper powder. Sintering relied solely on submicron and micron-sized copper powder, lacking a gradient particle size distribution. This resulted in loose particle packing and significantly reduced weld strength. Compared to the above examples, it can be seen that the copper coordination compound plays a crucial role in the in-situ reduction of nanoscale copper particles.

[0100] The copper salt in Comparative Example 2 was not treated with coordination, resulting in uneven dispersion in the copper paste. The nano-sized copper particles formed had limited effect, and the EDS spectrum also showed a significant increase in oxygen content. This indicates that if the copper salt is not treated with coordination, it may be oxidized during storage, batching, and other processes.

[0101] Comparative Example 3 did not contain submicron-sized copper powder; its mass fraction was replaced with micron-sized copper powder. Comparative Example 4 also did not contain micron-sized copper powder; its mass fraction was replaced with submicron-sized copper powder. Both of these comparative examples lacked a gradient particle size distribution, resulting in loose particle packing and significantly reduced welding strength. Compared with the above examples, it can be seen that the combination of copper particles of three different sizes plays a crucial role.

[0102] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A modified copper paste, characterized in that, The components include the following parts by weight: 0.5 to 5 parts of copper coordination compound; 5 to 25 parts of submicron-sized copper powder; 55 to 95 parts of micron-sized copper powder; 1 to 15 parts of resin; 1 to 5 parts of resin curing agent; Solvent: 1 to 15 parts.

2. The modified copper paste according to claim 1, characterized in that: The ratio of the Dv50 particle size of the micron-sized copper powder to the Dv50 particle size of the submicron-sized copper powder is 20:1 to 100:1; and / or, The mass ratio of the micron-sized copper powder to the submicron-sized copper powder is 2.2:1 to 5:

1.

3. The modified copper paste according to claim 1 or 2, characterized in that: The Dv50 particle size of the micron-sized copper powder is 2 μm to 10 μm; and / or, The submicron-sized copper powder has a Dv50 particle size of 100 nm to 500 nm; and / or, The micron-sized copper powder includes flake-shaped copper powder; and / or, The submicron-sized copper powder includes spherical copper powder.

4. The modified copper paste according to claim 1 or 2, characterized in that: The copper coordination compound comprises a copper salt and a ligand group; wherein... The copper salt includes copper carboxylate; and / or, The ligand group includes at least one of an amino group, a nitrogen-containing heterocycle, and a phosphine group.

5. The modified copper paste according to claim 1 or 2, characterized in that: The resin includes epoxy resin; and / or, The resin curing agent includes a latent curing agent; and / or, The solvent includes reducing solvents; and / or, The modified copper paste includes an additive, and the additive has a mass fraction of 0.01 to 1 part.

6. A method for preparing modified copper paste, characterized in that, Includes the following steps: The modified copper paste is obtained by mixing the components comprising any one of claims 1 to 5.

7. The preparation method according to claim 6, characterized in that, The preparation method of the copper coordination compound includes the following steps: The copper salt is subjected to a coordination reaction with a raw material containing a ligand group to obtain the copper coordination compound; The copper salt includes copper carboxylate, and the raw material containing the ligand group includes at least one of alkylamines, imidazoles, pyridines, and organophosphorus compounds.

8. The preparation method according to claim 6 or 7, characterized in that, The preparation method of the submicron-sized copper powder includes the following steps: The raw materials, including inorganic copper salt, reducing organic acid, and control agent, are subjected to a reduction reaction. The product of the reduction reaction and the dispersant are dispersed in an alcohol solvent to obtain a dispersion. The dispersion was freeze-dried to obtain the submicron-sized copper powder; The dispersant includes at least one of C8-C12 alkylamines, imidazoles, pyridines, and organophosphorus compounds.

9. The application of a modified copper paste as described in any one of claims 1 to 5, or a modified copper paste prepared by the preparation method described in any one of claims 6 to 8, in semiconductor packaging, characterized in that, Includes the following steps: The modified copper paste is used to form a wet film on the surface of the semiconductor device; After the wet film is dried, it is bonded to the component to be connected and then sintered.

10. The application according to claim 9, characterized in that: The thickness of the wet film is 100 μm to 350 μm; and / or, The atmosphere for the drying and sintering processes is an inert atmosphere; and / or, The sintering temperature is 230℃~260℃; and / or, The pressure applied during the sintering process is 10 MPa to 20 MPa.

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