Sintered copper paste for interconnection of power module chips and preparation method of sintered copper paste

Abstract

The invention provides a power module chip interconnection copper paste and a preparation method thereof. The copper paste comprises the following raw materials in parts by weight: 70-75 parts of copper powder, 5-10 parts of a metal salt solution and 25-30 parts of an organic solvent system. According to the copper paste obtained through the preparation method and the preparation method thereof, the oxidation resistance is high, the sintering temperature is low, agglomeration is effectively inhibited, the low-temperature curing speed is high, and the sintering shrinkage rate is low, it is ensured that particles are evenly dispersed, the agglomeration phenomenon of nano-copper particles is effectively inhibited, the uniformity and rheological property of the copper paste are improved, and the service life of the copper paste is prolonged. The copper paste can be uniformly distributed in the chip interconnection process, the interconnection quality is improved, the long-term stability of interconnection is improved, the requirement for production efficiency in large-scale production is met, the production period is shortened, and the cost is reduced.

Description

Technical Field

[0001] This application relates to the field of electronic materials technology, and in particular to a sintered copper paste for power module chip interconnection and its preparation method. Background Technology

[0002] In the development of power modules, chip interconnect technology is crucial, and copper paste, as a key material for realizing chip interconnect, directly affects the overall performance of the power module.

[0003] Currently, traditional sintered copper paste suffers from at least one of the following problems in practical applications. Firstly, insufficient oxidation resistance is a prominent issue. Due to the inherent reactivity of copper, copper particles readily react with oxygen in the air during preparation, storage, and use, generating oxides such as copper oxide. The presence of these oxides severely affects the electrical and thermal conductivity of the copper paste, thereby reducing the performance of the power module. For example, in harsh working environments with high temperature and high humidity, the oxidation rate of copper particles in ordinary copper paste accelerates, leading to increased resistance in chip interconnects, signal transmission delays and attenuation, and potentially even localized overheating, affecting the stability and reliability of the power module.

[0004] Secondly, the sintering temperature of existing copper pastes is relatively high. Good sintering results are typically achieved at temperatures above 300°C, posing a significant challenge to other heat-sensitive components in power modules. High-temperature sintering can not only degrade the performance and shorten the lifespan of heat-sensitive components but also increase process complexity and cost. For example, in some power modules integrating multiple functional components, excessively high sintering temperatures may cause parameter drift in some temperature-sensitive semiconductor devices, affecting the overall functionality and accuracy of the module.

[0005] Thirdly, the agglomeration of copper particles cannot be ignored. During the preparation and storage of copper paste, nano-copper particles, due to their large specific surface area and surface energy, are prone to agglomeration. Agglomerated copper particles affect the uniformity and rheological properties of the copper paste, making it difficult to achieve uniform distribution during coating and sintering, thus leading to unstable quality of chip interconnects. For example, when coating copper paste on printed circuit boards, agglomerated copper particles may cause uneven local copper paste thickness, forming weak points in the connection after sintering, reducing the mechanical strength and electrical performance of the interconnect.

[0006] Fourth, existing copper pastes have a slow curing speed at low temperatures, which cannot meet the needs of rapid production. This makes it difficult to meet the demands of large-scale power module production, which requires copper pastes to cure in a short time to improve production efficiency; however, slow curing at low temperatures leads to longer production cycles and increased production costs.

[0007] Fifth, copper paste exhibits significant shrinkage after sintering, which can lead to stress between the chip and the substrate, affecting the long-term stability of the interconnect. For example, during thermal cycling tests, the shrinkage and expansion of the sintered copper paste may gradually loosen the connection between the chip and the substrate, ultimately causing interconnect failure. Summary of the Invention

[0008] This application is made in view of the above-mentioned issues, and its purpose is to provide a sintering copper paste for power module chip interconnection and a method for preparing the same.

[0009] To achieve the above objectives, this application provides a copper paste with strong antioxidant properties, low sintering temperature, effective inhibition of agglomeration, fast low-temperature curing speed, and low sintering shrinkage, as well as a method for its preparation. This ensures uniform particle dispersion, effectively inhibits the agglomeration of nano-copper particles, improves the uniformity and rheological properties of the copper paste, ensures uniform distribution of the copper paste during chip interconnection, improves interconnection quality, enhances the long-term stability of interconnection, and meets the requirements for production efficiency in large-scale production, shortens the production cycle, and reduces costs.

[0010] The first aspect of this application provides a copper paste for interconnecting power module chips, comprising the following raw materials in parts by weight: 70-75 parts by weight of copper powder, 5-10 parts by weight of metal salt, and 25-30 parts by weight of organic solvent system.

[0011] In any embodiment, the organic solvent system comprises 5-10 parts by weight of dispersant, 1-3 parts by weight of antioxidant, 10-20 parts by weight of binder, and 60-80 parts by weight of solvent.

[0012] In any embodiment, the metal salt is one or more of nickel nitrate, nickel acetate, and nickel chloride.

[0013] In any embodiment, the dispersant is at least one of n-decaol or acrylic acid, the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT), the binder is at least one of ethyl cellulose or methyl cellulose, and the solvent is terpineol.

[0014] A second aspect of this application also provides a method for preparing interconnect copper paste for power module chips, comprising the following steps:

[0015] 1) Copper powder pretreatment

[0016] Copper powder is added to a sulfuric acid solution, stirred, and centrifuged. The resulting copper powder is then added to an α-hydroxy acid solution, stirred, and centrifuged to obtain pure copper powder.

[0017] 2) Drying and grinding

[0018] The copper powder obtained above is transferred to an oven and dried at 45-50℃ for 4-6 hours. The dried powder is then transferred to a mortar or grinder for grinding.

[0019] 3) Preparation of organic solvent system

[0020] An organic solvent system is obtained by mixing dispersant, antioxidant, binder and solvent in a weight ratio of 5-10:1-3:10-20:60-80; the above-ground powder and organic solvent system are added to a container with a stirring paddle and stirred at a speed of 200-500 rpm for 1-2 hours to form a uniform copper-based solder paste mixture.

[0021] 4) Secondary grinding and homogenization

[0022] The copper-based solder paste mixture is transferred into a three-roll mill. The three rollers of the three-roll mill rotate at different speeds. The copper powder particles are further refined by the squeezing and shearing forces between the rollers, and finally a uniform, fine and stable sintered copper paste is obtained.

[0023] In any embodiment, the weight ratio of copper powder to α-hydroxy acid added in step 1) is 70-75:3-5; the weight ratio of powder to organic solvent system added in step 3) is 70-85:25-30, with a preferred ratio of 75-80:25-30.

[0024] Too low a solvent ratio will result in insufficient mixing of the paste, while too high a solvent ratio will result in solid-liquid separation.

[0025] In any embodiment, the purified copper powder from step 1) is added to 5-10 parts by weight of a metal salt solution and mixed evenly, wherein the metal salt is one or more of nickel nitrate, nickel acetate, and nickel chloride.

[0026] In any embodiment, the copper powder is electrolytic copper powder with an average particle size of 0.1-10 μm.

[0027] In any embodiment, the sulfuric acid solution has a mass fraction of 5%-10%; copper powder is slowly added to the sulfuric acid solution, and the stirring speed is 300-500 rpm for 30-60 minutes; after stirring, the copper powder suspension is centrifuged at 3000-5000 rpm for 10-15 minutes.

[0028] In any embodiment, the α-hydroxy acid is at least one of citric acid and malic acid. Copper powder is added to the α-hydroxy acid solution, and the stirring speed is 200-400 rpm for 20-40 minutes.

[0029] In any embodiment, the dispersant is at least one of n-decaol or acrylic acid, the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT), the binder is at least one of ethyl cellulose or methyl cellulose, and the solvent is terpineol.

[0030] In any embodiment, the distance between the three rollers is first adjusted to 0.5-1mm for coarse grinding, which is performed 2-3 times; then the distance between the three rollers is gradually reduced to 0.1-0.3mm for fine grinding and homogenization, which is performed 3-5 times; during the roller passing process, the roller passing speed is controlled at 10-20 rpm; the entire secondary grinding and homogenization process lasts for 30-60 minutes, and finally a uniform, fine, and stable sintered copper paste is obtained.

[0031] The beneficial effects of this application are:

[0032] 1. Performance improvements

[0033] Antioxidant properties: The improved antioxidant properties enable the copper paste to maintain stable performance during storage and use. Tests have shown that the copper paste prepared using this method retains good electrical and thermal conductivity even after being exposed to air for over 120 days. Compared to traditional copper paste, this significantly extends its service life, reduces performance degradation and failure risks caused by oxidation, and improves the reliability and stability of power modules.

[0034] Lowering the sintering temperature to around 200℃ not only avoids damage to heat-sensitive components in the power module but also expands its applicability in various application scenarios. For example, it can be used in electronic devices with strict temperature requirements, such as portable electronic products and aerospace electronic equipment, thereby improving product performance and competitiveness.

[0035] Effective suppression of agglomeration: Suppressing agglomeration ensures the uniformity and rheological properties of the copper paste, enabling uniform coating and sintering during chip interconnection, thus improving the quality and reliability of the interconnection. Testing shows that using this copper paste for chip interconnection significantly improves the resistance uniformity of the connection points, resulting in more stable signal transmission and reducing signal interference and transmission errors caused by poor connections.

[0036] 2. Improved production efficiency

[0037] Improving the low-temperature curing speed enables shorter production cycles in large-scale manufacturing. Under low-temperature conditions, copper paste can cure in a shorter time, increasing production efficiency by more than 10% compared to traditional copper paste. This effectively reduces production costs, improves production efficiency, and meets market demand for large-scale, high-efficiency power module production.

[0038] 3. Control production costs

[0039] Compared to complex processes such as silver-coated copper nanoparticles used to improve performance, this invention significantly reduces costs while maintaining performance by optimizing the copper powder composition and preparation process. For example, raw material costs are reduced by approximately 50%, and the simplified preparation process also reduces equipment investment and energy consumption, further lowering production costs and enhancing the product's market competitiveness.

[0040] Reducing sintering shrinkage lowers the stress between the chip and the substrate, improving the long-term stability of the interconnect. In thermal cycling and long-term use tests, the chip interconnect structure using this copper paste can withstand more thermal cycles without loosening or failure, reducing after-sales maintenance and replacement costs, and improving product quality and user satisfaction. Detailed Implementation

[0041] The following describes a specific embodiment of a sintered copper paste for power module chip interconnection and its preparation method. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] A copper paste for interconnecting power module chips comprises the following raw materials in parts by weight: 70-75 parts copper powder, 5-10 parts metal salt solution, and 25-30 parts organic solvent system.

[0049] In some embodiments, the organic solvent system comprises 5-10 parts by weight of dispersant, 1-3 parts by weight of antioxidant, 10-20 parts by weight of binder, and 60-80 parts by weight of solvent.

[0050] The composition and formulation of copper powder are optimized by using multi-peak copper powder, such as a tri-peak copper material composed of submicron particles and micron copper flakes, along with the addition of appropriate amounts of metal salts. This combination effectively increases the packing density during sintering and lowers the sintering temperature. For example, by adding nickel salts, the nickel or nickel oxide particles decomposed during sintering can form a strong metallurgical bond with copper, enabling the copper paste to achieve good sintering at around 200℃. This solves the problem of excessively high sintering temperatures in traditional copper paste causing damage to heat-sensitive components and expands the application scenarios of power modules.

[0051] In the preparation process, n-decaol and acrylic acid are selected as dispersants and thoroughly ultrasonically mixed with the corrosion inhibitor-coated copper nanoparticles to ensure uniform particle dispersion, effectively inhibit the agglomeration of copper nanoparticles, improve the uniformity and rheological properties of copper paste, and ensure that the copper paste can be uniformly distributed during the chip interconnection process, thereby improving the interconnection quality.

[0052] Adjusting the proportions and types of components in the organic solvent system, increasing the binder content, and selecting appropriate solvents are all beneficial. For example, appropriately increasing the proportion of binders such as polyvinyl alcohol and polymethyl methacrylate, while using solvents with moderate volatility, allows the copper paste to cure rapidly at low temperatures, meeting the production efficiency requirements of large-scale production, shortening the production cycle, and reducing costs.

[0053] Shrinkage during sintering can be controlled by pretreating copper powder and adding specific additives. For example, in the copper powder pretreatment process, the copper powder is ultrasonically treated with acid to remove surface impurities and optimize the surface properties of the copper powder. At the same time, some additives with expansion properties, such as certain organosilicon compounds, are added. These additives interact with copper during sintering to compensate for copper shrinkage, thereby reducing the sintering shrinkage rate, lowering the stress between the chip and the substrate, and improving the long-term stability of the interconnect.

[0054] In some embodiments, the copper powder is a trimodal copper material composed of nanoparticles, submicron particles, and micron-sized copper flakes. The diameter of the nanoparticle copper powder is 120–500 nm, the diameter of the submicron particle copper powder is 500–1000 nm, and the diameter of the micron-sized copper flakes is 1–10 μm. This multi-scale particle size distribution gives the material a unique microstructure; the small nanoparticles can fill the pores of the submicron particles and micron-sized flakes, forming a tightly packed structure and effectively increasing the packing density.

[0055] In some embodiments, the dispersant is at least one of n-decaol or acrylic acid, the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT), the binder is at least one of ethyl cellulose or methyl cellulose, and the solvent is terpineol.

[0056] The dispersant's role is to reduce the surface tension between copper powder particles, prevent agglomeration, and ensure uniform dispersion of the copper powder in the organic solvent. For example, for 100g of dry, ground powder, add 5-10g of n-decaol or acrylic acid. The antioxidant is an organic compound with good antioxidant properties, such as 2,6-di-tert-butyl-p-cresol (BHT). The antioxidant forms a protective film on the surface of the copper powder, inhibiting oxidation during preparation and storage. The binder enables the copper powder particles to bond together during sintering, forming a stable structure. Terpineol is chosen as the solvent because it has moderate volatility and good solubility.

[0057] A second aspect of this application also provides a method for preparing interconnect copper paste for power module chips, comprising the following steps:

[0058] 1) Copper powder pretreatment

[0059] Copper powder is added to a sulfuric acid solution, stirred, and centrifuged. The resulting copper powder is then added to an α-hydroxy acid solution, stirred, and centrifuged to obtain pure copper powder.

[0060] 2) Drying and grinding

[0061] The copper powder obtained above is transferred to an oven and dried at 45-50℃ for 4-6 hours. The dried powder is then transferred to a mortar or grinder for grinding.

[0062] 3) Preparation of organic solvent system

[0063] An organic solvent system is obtained by mixing dispersant, antioxidant, binder and solvent in a weight ratio of 5-10:1-3:10-20:60-80; the above-ground powder and organic solvent system are added to a container with a stirring paddle and stirred at a speed of 200-500 rpm for 1-2 hours to form a uniform copper-based solder paste mixture.

[0064] 4) Secondary grinding and homogenization

[0065] The copper-based solder paste mixture is transferred into a three-roll mill. The three rollers of the three-roll mill rotate at different speeds. The copper powder particles are further refined by the squeezing and shearing forces between the rollers, and finally a uniform, fine and stable sintered copper paste is obtained.

[0066] The composition and formulation of copper powder are optimized by using multi-peak copper powder, such as a tri-peak copper material composed of submicron particles and micron copper flakes, along with the addition of appropriate amounts of metal salts. This combination effectively increases the packing density during sintering and lowers the sintering temperature. For example, by adding nickel salts, the nickel or nickel oxide particles decomposed during sintering can form a strong metallurgical bond with copper, enabling the copper paste to achieve good sintering at around 200℃. This solves the problem of excessively high sintering temperatures in traditional copper paste causing damage to heat-sensitive components and expands the application scenarios of power modules.

[0067] In the preparation process, n-decaol and acrylic acid are selected as dispersants and thoroughly ultrasonically mixed with the corrosion inhibitor-coated copper nanoparticles to ensure uniform particle dispersion, effectively inhibit the agglomeration of copper nanoparticles, improve the uniformity and rheological properties of copper paste, and ensure that the copper paste can be uniformly distributed during the chip interconnection process, thereby improving the interconnection quality.

[0068] Adjusting the proportions and types of components in the organic solvent system, increasing the binder content, and selecting appropriate solvents are all beneficial. For example, appropriately increasing the proportion of ethyl cellulose or methyl cellulose, while using solvents with moderate volatility, allows the copper paste to cure rapidly at low temperatures, meeting the efficiency requirements of large-scale production, shortening the production cycle, and reducing costs.

[0069] Shrinkage during sintering can be controlled by pretreating copper powder and adding specific additives. For example, in the copper powder pretreatment process, acid is used to ultrasonically treat the copper powder to remove surface impurities and optimize the surface properties of the copper powder.

[0070] In any embodiment, in step 1), 70-75 parts by weight of copper powder and 3-5 parts by weight of α-hydroxy acid are added; in step 3), the weight ratio of powder to organic solvent system is 70-85:25-30, with a preferred ratio of 75-80:25-30.

[0071] Too low a solvent ratio will result in insufficient mixing of the paste, while too high a solvent ratio will result in solid-liquid separation.

[0072] In any embodiment, the purified copper powder from step 1) is added to 5-10 parts by weight of a metal salt solution and mixed evenly, wherein the metal salt is one or more of nickel nitrate, nickel acetate, and nickel chloride.

[0073] During sintering, metal salts can form alloys with copper, which helps to lower the sintering temperature and improve the performance of the sintered body. Nickel salts decompose during sintering, releasing nickel or nickel oxide particles that are uniformly distributed in the bonding layer, effectively improving the oxidation resistance of the sintered interconnect structure. If the proportion of nickel salts is too low, the number of nickel or nickel oxide particles formed will be insufficient to form a sufficiently dense anti-oxidation protective layer around the copper powder. If the proportion of nickel salts is too high, it may disrupt the balance of the paste system, leading to decreased stability. For example, nickel salts may interact with the binder, altering its properties and causing abnormal changes in the paste's viscosity and flowability, affecting the printability of the copper paste.

[0074] In any embodiment, the metal salt is one or more of nickel nitrate, nickel acetate, and nickel chloride.

[0075] When nickel salt solution comes into contact with copper powder, nickel ions will be adsorbed and deposited on the surface of the copper powder. During the sintering process, nickel salt can also decompose to release nickel or nickel oxide particles, which can enhance the performance of the sintered interconnect structure.

[0076] In some embodiments, the copper powder is electrolytic copper powder with an average particle size of 0.1-10 μm.

[0077] Copper powders within this particle size range can bond well together during subsequent sintering to form a dense structure, ensuring the electrical and thermal conductivity of the sintered copper paste.

[0078] In some embodiments, the mass fraction of the sulfuric acid solution is 5%-10%; copper powder is slowly added to the sulfuric acid solution, and the stirring speed is 300-500 rpm for 30-60 minutes; after stirring, the copper powder suspension is centrifuged at 3000-5000 rpm for 10-15 minutes.

[0079] This concentration of sulfuric acid solution effectively removes impurities from the surface of copper powder without excessively corroding it. During stirring, the sulfuric acid reacts chemically with oxides and other impurities on the surface of the copper powder, producing a water-soluble substance.

[0080] In some embodiments, the α-hydroxy acid is at least one of citric acid and malic acid. Copper powder is added to the α-hydroxy acid solution, and the stirring speed is 200-400 rpm for 20-40 minutes.

[0081] By coating nano-copper particles with specific corrosion inhibitors, a protective film is formed on the surface of the copper particles, effectively preventing oxygen from contacting the copper and thus improving the oxidation resistance of the copper paste. For example, using α-hydroxy acids such as citric acid and malic acid as corrosion inhibitors and coating them onto the surface of nano-copper particles using a high-speed airflow impact method allows the copper paste to be stored in air for extended periods without easily oxidizing, solving the problem of easy oxidation of existing copper pastes during storage and use, and ensuring the stability of the electrical and thermal conductivity of the power module during long-term operation.

[0082] Citric acid has a good complexing ability and can react with impurities on the surface of copper powder to further remove residual impurities, making it easy to remove impurities; and it can also modify the surface of copper powder.

[0083] Most α-hydroxy acids are removed during centrifugation, with trace amounts remaining on the surface of the copper powder particles, which are not controlled. The carboxyl acids, however, not only remove impurities but also modify the copper powder surface when interacting with it. Carboxyl acid molecules can adhere to the copper powder surface through chemisorption, altering its chemical state. Because carboxyl acid molecules contain multiple polar groups, the copper powder surface possesses both hydrophilicity and polarity, thus improving its compatibility with other components (such as organic solvents and additives) during subsequent mixing. For example, when adding organic solvents, copper powder with a hydrophilic surface is more easily and evenly dispersed in the organic solvent, contributing to the formation of a stable and homogeneous copper paste system.

[0084] Citric acid molecules contain three carboxyl groups and one hydroxyl group. Their unique molecular structure allows them to form a stable polydentate coordination structure with copper atoms on the surface of copper powder. This structure tightly encapsulates the copper powder, effectively isolating it from oxygen and thus providing excellent antioxidant properties. If the citric acid solution is too weak, it will not protect the copper powder; if it is too strong, it will disrupt the solvent system.

[0085] Citric acid has a good complexing ability and can react with impurities on the surface of copper powder to further remove residual impurities, making it easy to remove impurities; and it can also modify the surface of copper powder.

[0086] β, γ, δ, ε and above hydroxy acids: Although these hydroxy acids also contain carboxyl and hydroxyl groups, the relative positions, numbers and spatial distribution of carboxyl and hydroxyl groups in their molecular structures are different from those of citric acid, resulting in poor stability of the coordination structure formed with the copper powder surface.

[0087] In some embodiments, the dispersant is at least one of n-decaol or acrylic acid, the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT), the binder is at least one of ethyl cellulose or methyl cellulose, and the solvent is terpineol.

[0088] The dispersant's role is to reduce the surface tension between copper powder particles, prevent agglomeration, and ensure uniform dispersion of the copper powder in the organic solvent. For example, for 100g of dry, ground powder, add 5-10g of n-decaol or acrylic acid. The antioxidant is an organic compound with good antioxidant properties, such as 2,6-di-tert-butyl-p-cresol (BHT). The antioxidant forms a protective film on the surface of the copper powder, inhibiting oxidation during preparation and storage. The binder enables the copper powder particles to bond together during sintering, forming a stable structure. Terpineol is chosen as the solvent because it has moderate volatility and good solubility.

[0089] In some embodiments, the distance between the three rollers is first adjusted to 0.5-1mm for coarse grinding, which is performed 2-3 times; then the distance between the three rollers is gradually reduced to 0.1-0.3mm for fine grinding and homogenization, which is performed 3-5 times; during the roller passing process, the roller passing speed is controlled at 10-20 rpm; the entire secondary grinding and homogenization process lasts for 30-60 minutes, and finally a uniform, fine, and stable sintered copper paste is obtained.

[0090] Example

[0091] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0092] Example 1

[0093] A method for preparing copper paste for interconnecting power module chips includes the following steps:

[0094] (1) Copper powder pretreatment

[0095] 1) Sulfuric acid solution treatment

[0096] Copper powder selection: Select electrolytic copper powder with an average particle size of 0.1-10μm. Slowly add 73g of copper powder to a 6% sulfuric acid solution (the mass of the sulfuric acid solution should be twice the mass of the copper powder). Simultaneously turn on a magnetic stirrer at a speed of 300-500 rpm for 30-60 minutes. After stirring, transfer the copper powder suspension to a centrifuge and centrifuge at 3000-5000 rpm for 10-15 minutes. Centrifugation causes the copper powder to precipitate at the bottom of the centrifuge tube. The supernatant contains dissolved impurities. Carefully pour off the supernatant and collect the precipitate to obtain the copper powder precipitate.

[0097] 2) Organic acid solution treatment

[0098] Add the copper powder precipitate obtained in step 1) to 4g of citric acid solution, and turn on the magnetic stirrer again. Adjust the stirring speed to 200-400 rpm and stir for 20-40 minutes. During stirring, the citric acid reacts with the impurities on the surface of the copper powder, making the impurities easier to remove. After stirring, repeat the centrifugation operation at 3000-5000 rpm for 10-15 minutes. Discard the supernatant to obtain a relatively pure copper powder precipitate again.

[0099] (2) Preparation of metal salt solution

[0100] Slowly add 8g of nickel nitrate solution to the copper powder precipitate treated with citric acid, while stirring with a glass rod or magnetic stirrer at a speed of 100-300 rpm for 15-30 minutes to ensure thorough mixing of the nickel nitrate solution and copper powder precipitate, resulting in a homogeneous copper-nickel mixture.

[0101] (3) Drying and grinding

[0102] The copper-nickel mixture obtained above was transferred to an oven, and the oven temperature was set to 45-50℃ for 4-6 hours. During the drying process, the material was turned over every 1-2 hours to ensure uniform drying.

[0103] Transfer the dried powder to a mortar and pestle or grinder for grinding. If using a mortar and pestle, grind slowly and evenly for approximately 15-30 minutes, turning the powder constantly to ensure even grinding. If using a grinder, set the speed to 200-400 rpm and grind for 10-20 minutes. Grinding will make the powder particle size more uniform, which is beneficial for subsequent mixing and sintering.

[0104] (4) Mixing and stirring

[0105] Composition and proportions of organic solvent system:

[0106] Mix 2g of n-decaol or acrylic acid, 0.6g of 2,6-di-tert-butyl-p-cresol (BHT), 4.3g of ethyl cellulose or methyl cellulose, and 20g of terpineol to obtain an organic solvent system. Add the ground powder and the prepared organic solvent system to a container equipped with a stirrer. Turn on the stirrer and set the stirring speed to 200-500 rpm for 1-2 hours. During the stirring process, ensure that all components are fully mixed to form a homogeneous copper-based solder paste mixture.

[0107] (5) Grinding and homogenization

[0108] The copper-based solder paste mixture is transferred to the feed inlet of a three-roll mill. The three rollers of the three-roll mill rotate at different speeds, further refining the copper powder particles and making the components more evenly distributed through the squeezing and shearing forces between the rollers. First, adjust the distance between the three rollers to a relatively large value of 0.5-1mm, allowing the mixture to initially pass through the rollers for coarse grinding, repeating 2-3 times.

[0109] Homogenization process: Gradually reduce the gap between the three rollers to 0.1-0.3mm for fine grinding and homogenization, grinding 3-5 times. During the roller passing process, control the roller speed at 10-20 rpm, while carefully observing the state of the paste to ensure uniformity. The entire process lasts approximately 30-60 minutes, ultimately yielding a uniform, fine, and stable sintered copper paste.

[0110] The preparation conditions of Example 1 were modified as follows to obtain sintered copper paste for Examples 2-4 and Comparative Examples 1-3. The relevant parameters such as viscosity, thixotropy, oxidation resistance, resistivity, and mechanical strength were measured, as shown in Table 1 below.

[0111] Table 1: Parameter results of Examples 1-4 and Comparative Examples 1-3

[0112]

[0113] Note: In Example 1, 350-750, 1.2-4.5 (mass ratio 4:6) means that the mass ratio of 350-750nm submicron copper powder to 1.2-4.5μm micron copper sheet is 4:6. The same applies to other examples and comparative examples.

[0114] Based on the above results, it can be seen that the particle size distribution is detected by a laser particle size analyzer to ensure that the particle size of the copper particles meets the requirements; the viscosity is measured by a viscometer to ensure that the copper paste has good rheological properties, which is convenient for coating and printing; the oxidation test is used to evaluate the anti-oxidation performance and observe the degree of oxidation of the copper paste under certain time and environmental conditions; and the sintering test is carried out to detect the sintering effect under different temperature and time conditions, such as the resistivity and mechanical strength of the sintered body.

[0115] This application improves the low-temperature curing speed, enabling shorter production cycles in large-scale production. Under low-temperature conditions, the copper paste can cure in a shorter time. Compared to traditional copper paste, it effectively produces a sintering effect at a sintering temperature of 200°C. In actual mass production, increasing the sintering temperature to 250°C is expected to reduce sintering time by 10%, increasing production efficiency by more than 10%, effectively reducing production costs, improving production efficiency, and meeting market demand for large-scale, high-efficiency power module production.

[0116] Compared to complex processes such as silver-coated copper nanoparticles used to improve performance, this invention significantly reduces costs while maintaining performance by optimizing the composition and preparation process of copper powder. For example, the unit price of silver is approximately 80–100 times that of copper. If we take the laboratory-prepared cost of 3600 yuan / kg for nano-copper powder as a reference, the cost of 200,000 yuan / kg for nano-silver powder is approximately 55 times that of copper powder. If we calculate based on the upper limit of 180 yuan / kg for nano-copper powder prepared by atomization, the cost of nano-silver powder is approximately 1100 times that of copper powder. This represents a reduction of approximately 50% in raw material costs. The simplified preparation process also reduces equipment investment and energy consumption, further lowering production costs and enhancing the product's market competitiveness.

[0117] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A copper paste for interconnecting power module chips, characterized in that, It comprises the following raw materials in parts by weight: 70-75 parts copper powder, 5-10 parts metal salt solution, 5-10 parts dispersant, and 25-30 parts organic solvent system.

2. The copper paste for interconnecting power module chips according to claim 1, characterized in that, The organic solvent system consists of 5-10 parts by weight of dispersant, 1-3 parts by weight of antioxidant, 10-20 parts by weight of binder, and 60-80 parts by weight of solvent.

3. The copper paste for interconnecting power module chips according to claim 1, characterized in that, The metal salt is one or more of nickel nitrate, nickel acetate, and nickel chloride; the dispersant is at least one of n-decaol or acrylic acid; the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT); the binder is at least one of ethyl cellulose or methyl cellulose; and the solvent is terpineol.

4. A method for preparing copper paste for interconnecting power module chips, comprising the following steps: 1) Copper powder pretreatment Copper powder is added to a sulfuric acid solution, stirred, and centrifuged. The resulting copper powder is then added to an α-hydroxy acid solution, stirred, and centrifuged to obtain pure copper powder. 2) Drying and grinding The copper powder obtained above is transferred to an oven to dry, and the dried powder is then transferred to a mortar or grinder for grinding. 3) Preparation of organic solvent system An organic solvent system is obtained by mixing dispersant, antioxidant, binder and solvent in a weight ratio of 5-10:1-3:10-20:60-80; the above-ground powder and organic solvent system are added to a stirrer and stirred to form a uniform copper-based solder paste mixture. 4) Secondary grinding and homogenization The copper-based solder paste mixture is transferred into a three-roll mill to obtain a uniform, fine, and stable sintered copper paste.

5. The method for preparing copper paste for interconnecting power module chips according to claim 4, characterized in that, In step 1), add 70-75 parts by weight of copper powder and 3-5 parts by weight of α-hydroxy acid; in step 3), the weight ratio of powder to organic solvent system is 70-85:25-30.

6. The method for preparing copper paste for interconnecting power module chips according to claim 4, characterized in that, Add the purified copper powder from step 1) to 5-10 parts by weight of a metal salt solution and mix thoroughly. The metal salt is one or more of nickel nitrate, nickel acetate, and nickel chloride.

7. The method for preparing copper paste for interconnecting power module chips according to claim 4, characterized in that, The copper powder is electrolytic copper powder with an average particle size of 0.1-10 μm; the sulfuric acid solution has a mass fraction of 5%-10%; the copper powder is slowly added to the sulfuric acid solution and stirred; after stirring, the copper powder suspension is centrifuged at a speed of 3000-5000 rpm.

8. The method for preparing copper paste for interconnecting power module chips according to claim 4, characterized in that, The α-hydroxy acid is at least one of citric acid and malic acid, and copper powder is added to the α-hydroxy acid solution and stirred.

9. The method for preparing copper paste for interconnecting power module chips according to claim 4, characterized in that, The dispersant is at least one of n-decaol or acrylic acid, the antioxidant is 2,6-di-tert-butyl-p-cresol (BHT), the binder is at least one of ethyl cellulose or methyl cellulose, and the solvent is terpineol.

10. The method for preparing copper paste for interconnecting power module chips according to claim 4, characterized in that, In step 4), the distance between the three rollers is first adjusted to 0.5-1mm for coarse grinding, which is repeated 2-3 times. Then, the distance between the three rollers is gradually reduced to 0.1-0.3mm for fine grinding and homogenization, which is repeated 3-5 times. During the roller passing process, the roller passing speed is controlled at 10-20 rpm. The entire secondary grinding and homogenization process lasts for 30-60 minutes, and finally a uniform, fine, and stable sintered copper paste is obtained.

Images