A nano-copper paste for pressureless sintering of chip interconnection and a preparation method thereof
By preparing a combination of formate composite shell nano-copper powder and modified organic carrier with nitrogen-doped carbon dots, the problem of copper paste being difficult to sinter densely under low temperature and pressureless conditions was solved, and a copper interconnect layer with high electrical conductivity, high thermal conductivity and mechanical strength was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 深圳市晨日科技股份有限公司
- Filing Date
- 2026-03-06
- Publication Date
- 2026-05-19
AI Technical Summary
Existing copper pastes are difficult to sinter densely under low-temperature and pressureless conditions, and their electrical conductivity and mechanical properties need to be improved. Furthermore, traditional modification methods are costly or have limited effectiveness.
A combination of formate composite shell nano-copper powder, modified organic carrier, and nitrogen-doped carbon dots is used to prepare nano-copper slurry through a specific process. Low-temperature pressureless sintering is achieved by utilizing the decomposition active substances of the composite shell and the synergistic effect of the modified carrier.
A high-density copper interconnect layer was achieved under low-temperature and pressureless conditions, which improved conductivity, thermal conductivity and mechanical strength, and reduced sintering temperature and material cost.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of copper paste preparation technology, specifically to a pressureless sintering type nano-copper paste for chip interconnection and its preparation method. Background Technology
[0002] In recent years, with the increasing demands for reliability, thermal conductivity, electrical conductivity, and lifespan of packaged interconnects from power devices and third-generation semiconductors, low-temperature, low-pressure sintering interconnect technology based on nano- and micro-sized copper powder has gradually been regarded as a cost-effective solution. Compared with traditional high-temperature solders, nano-copper paste can achieve copper-copper bonding at lower temperatures, endowing the packaged structure with high electrical conductivity, high thermal conductivity, and good anti-electromigration properties, while reducing material costs. It is an important development direction for achieving large-scale, reliable, and efficient packaged interconnects. Currently, there are many mainstream materials and modification methods used for low-temperature sintering interconnects. Common practices include: using pure nano-copper particles as the base material, improving its oxidation resistance and dispersibility through oxidation-reduction pretreatment, surface activator treatment, etc.; or using mixed metal systems, such as silver-copper alloy nanoparticles, to improve the conductivity and stability after sintering; and using different solvent systems, adding reducing agents or activators, adjusting the sintering atmosphere, gas pressure, or applying a certain pressure to promote sintering.
[0003] In existing technologies, these common materials and modification methods still have shortcomings. If precious metals or Ag-Cu mixed systems are used, the cost increases significantly, which is not conducive to large-scale industrialization. Moreover, relying solely on traditional oxidation-reduction pretreatment can partially improve the oxidation resistance of copper particles, but it is still difficult to eliminate the oxide layer. Especially during sintering, storage, or long-term use, copper is prone to re-oxidation, which hinders metal-metal contact between particles, resulting in low sintering density, large porosity, and decreased electrical and thermal conductivity. In addition, higher sintering temperatures, inert / reducing atmospheres, and pressures are still required to ensure densification.
[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention
[0005] The purpose of this invention is to provide a pressureless sintering type of nano-copper paste for chip interconnect and its preparation method, which solves the technical problems in the prior art where it is difficult to achieve dense sintering of copper paste under low temperature and pressureless conditions, and the conductivity and mechanical properties need to be further improved.
[0006] The objective of this invention can be achieved through the following technical solutions:
[0007] A pressureless sintering type nano-copper paste for chip interconnection comprises the following components by weight: 75-80 parts formate composite shell nano-copper powder, 20-25 parts modified organic carrier and 0.5-1 parts nitrogen-doped carbon dots;
[0008] The formate composite shell nano-copper powder is prepared by the following steps:
[0009] A1. Place copper nitrate, deionized water, polyvinylpyrrolidone and ethanolamine in a reaction vessel and stir. Heat the reaction vessel to 80-90℃, add a reducing agent, keep the reaction at the temperature for 2-4 hours, and then process to obtain nano copper powder.
[0010] A2. Place ethylene glycol, sodium formate, ammonium formate and formic acid in a reaction vessel under nitrogen atmosphere protection, stir at room temperature for 10-15 min, add nano copper powder, heat the reaction vessel to 120-130℃, keep the temperature for 1-2 h, and then process to obtain crude formate composite shell nano copper powder.
[0011] A3. Place crude formate composite shell copper nanopowder and methanol in a reaction vessel and stir. Add ammonium formate methanol solution and copper chloride methanol solution dropwise in sequence. React at room temperature for 15-30 min. Post-process to obtain formate composite shell copper nanopowder.
[0012] The reaction principle for preparing formate composite shell nano-copper powder is as follows:
[0013] In step A1, copper nitrate is reduced to a metallic copper core by ascorbic acid and hydrazine hydrate under the coordination of polyvinylpyrrolidone and ethanolamine. In step A2, the nano-copper powder reacts with the formate system in ethylene glycol medium and nitrogen protection. The copper surface coordinates and exchanges ions with formate, ammonium and other ions to form a composite shell mainly composed of formate. In step A3, the crude nano-copper powder reacts with ammonium formate and a small amount of copper chloride solution in methanol. Through surface coordination balance adjustment and shell reconstruction, the formate layer becomes more dense and uniform, and finally a stable formate composite shell nano-copper powder is formed.
[0014] Further, in step A1, the ratio of copper nitrate, deionized water, polyvinylpyrrolidone, ethanolamine, and reducing agent is 4-6g:10-15mL:0.02-0.04g:0.05-0.1g:4-6mL. The reducing agent is composed of ascorbic acid, hydrazine hydrate, and deionized water in a ratio of 0.3-0.9g:4-6g:45-50mL. The post-processing steps include: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed 2-4 times with deionized water and ethanol, transferred to an oven at 50-60℃, and dried to constant weight to obtain nano-copper powder.
[0015] Further, in step A2, the ratio of ethylene glycol, sodium formate, ammonium formate, formic acid, and nano-copper powder is 80-100mL:4-6g:0.5-1g:0.2-0.4g:8-10g. The post-processing steps include: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed 2-4 times with deionized water and ethanol, transferred to an oven at 50-60℃, and dried to constant weight to obtain crude formate composite shell nano-copper powder.
[0016] Further, in step A3, the ratio of crude formate composite shell copper nanopowder, methanol, ammonium formate methanol solution, and copper chloride methanol solution is 8-10g:14-16mL:14-16mL:14-16mL, the concentration of ammonium formate methanol solution is 0.6-0.8mol / L, and the concentration of copper chloride methanol solution is 0.05-0.1mol / L. The post-processing steps include: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed with methanol 2-4 times, transferred to an oven at 50-60℃, and dried to constant weight to obtain formate composite shell copper nanopowder.
[0017] Furthermore, the modified organic carrier is prepared by the following steps:
[0018] B1. Place copper formate tetrahydrate, n-pentylamine and ethylene glycol in a reaction vessel and stir. Heat the reaction vessel to 45-55℃ and stir for 15-30 minutes to obtain copper amine pre-complexed solution.
[0019] B2. Place ethylene glycol, α-terpineol and ethyl cellulose in a reaction vessel and stir. Heat the reaction vessel to 60-70℃ and stir for 30-60 min. Cool the reaction vessel to room temperature, add formic acid, ascorbic acid and bis(2-ethylhexyl) phosphate, and stir for 10-15 min to obtain the organic carrier mother liquor.
[0020] B3. Place the copper amine pre-complexed solution and the organic carrier mother liquor in a reaction vessel and stir at room temperature for 20-30 minutes to obtain the modified organic carrier.
[0021] The reaction principle for the preparation of modified organic carriers is as follows:
[0022] During the reaction, copper ions coordinate with amine groups to form a stable copper-amine complex solution. Further, ethyl cellulose is dissolved in ethylene glycol and α-terpineol by heating, and then combined with formic acid, ascorbic acid and bis(2-ethylhexyl) phosphate to construct a carrier system containing multiple organic functional components. In step B3, the copper-amine pre-complexed solution is mixed with the organic carrier mother liquor, and the two are uniformly combined through coordination interaction and intermolecular forces to form a component-stable modified organic carrier.
[0023] Further, in step B1, the ratio of copper formate tetrahydrate, n-pentylamine, and ethylene glycol is 3-6 g: 2-4 mL: 1-3 mL; in step B2, the ratio of ethylene glycol, α-terpineol, ethyl cellulose, formic acid, ascorbic acid, and bis(2-ethylhexyl) phosphate is 1-3 mL: 2-4 g: 0.5-1 g: 0.2-0.4 g: 0.1-0.2 g: 0.1-0.2 g; in step B3, the volume ratio of the copper amine pre-complexing solution to the organic carrier mother liquor is 10-15: 8-12.
[0024] Furthermore, the method for preparing the nitrogen-doped carbon dots is as follows: citric acid, urea, deionized water and ethylene glycol are placed in a closed reaction vessel, the reaction vessel is heated to 150-170℃, and the reaction is maintained at this temperature for 4-6 hours. The nitrogen-doped carbon dots are then obtained through post-treatment.
[0025] The reaction principle for preparing nitrogen-doped carbon dots is as follows:
[0026] During the reaction, citric acid undergoes dehydration and condensation to form a carbonization precursor. Urea decomposes at this temperature to generate an amino-based nitrogen-containing intermediate, which, together with the citric acid condensation product, participates in the formation of the carbon skeleton, incorporating nitrogen into the carbon structure. As the reaction continues, the condensate further carbonizes and nucleates, forming small carbon core particles, thus preparing nitrogen-doped carbon dots.
[0027] Furthermore, the ratio of citric acid, urea, deionized water, and ethylene glycol is 8-10g:5-7g:100-150mL:3-5mL. The post-processing steps include: after the reaction is completed, wait for the reaction vessel to cool to room temperature, add ethanol to the reaction solution to precipitate the precipitate, filter, transfer the filtrate to a rotary evaporator at a temperature of 80-90℃, and evaporate until no liquid is collected to obtain nitrogen-doped carbon dots.
[0028] This invention also proposes a method for preparing a pressureless sintering type nano-copper paste for chip interconnect, comprising the following steps:
[0029] S1. Place the formate composite shell nano-copper powder, modified organic carrier and nitrogen-doped carbon dots in a high-speed homogenizer and stir at high speed until uniform to obtain a mixed slurry.
[0030] S2. Place the mixed slurry in a three-roll mill and grind for 15-30 minutes to obtain nano copper slurry.
[0031] Furthermore, in step S1, the high-speed stirring speed is 800-1000 r / min; in step S2, the roller gap is 5-8 μm.
[0032] The present invention has the following beneficial effects:
[0033] 1. In the formate composite shell nano-copper powder of the present invention, the formate composite shell can decompose under medium and low temperature conditions and release active substances such as formate, amino, and copper ions in situ. This allows for in-situ reduction and activation of the surface of the nano-copper particles during sintering, effectively removing the oxide layer on the surface of the nano-copper particles, improving the contact quality between particles, lowering the sintering start-up temperature, and enabling the copper particles to rapidly neck and densify at lower temperatures without external pressure. Furthermore, the composite shell structure provides a certain degree of spatial barrier for the nano-copper powder, inhibiting storage... The oxidation during the slurry dispersion process improves the chemical stability of the material. At the same time, the composite shell contains easily decomposable and volatile components such as formate, ammonium salt and organic copper complexes, which can be uniformly removed during heating without producing difficult-to-remove carbon residues. This helps to obtain a sintered copper interconnect layer with low porosity, high density and high metal purity. The clean interface and high density structure not only improve the electrical conductivity and thermal conductivity of the sintered body, but also significantly enhance the mechanical strength of the interconnect interface, so that the final copper interconnect layer has excellent electrical conductivity, thermal conductivity and mechanical properties.
[0034] 2. The modified organic carrier prepared in this invention, by introducing a copper amine pre-complexing liquid, constructs a synergistic densification system of molecular-level filling and particle-level stacking. This copper amine pre-complexing liquid not only forms a weak coordination structure with the formate composite shell layer of nano-copper powder, ensuring high dispersibility and rheological stability of the slurry, but more importantly, this complex structure acts as a liquid-phase molecular solder during the sintering heating process. That is, the atomic-level active copper species generated by its in-situ decomposition can accurately fill the micropores and grain boundary gaps left by the physical stacking of nano-copper particles, significantly repairing the geometric defects of the sintering neck. This in-situ filling effect effectively reduces the porosity of the sintered layer, greatly reduces the electron scattering and phonon scattering interfaces caused by pores, and reduces the interfacial thermal resistance. At the same time, the reducing atmosphere constructed by the components such as ethylene glycol, α-terpineol, and ethyl cellulose in the carrier ensures that there is no carbon residue in the decomposition products. Under low temperature and pressureless conditions, a continuous, dense, and high-purity metal thermal conduction network is constructed, giving the sintered interconnect layer excellent thermal conductivity and mechanical properties.
[0035] 3. The nitrogen-doped carbon dots prepared by this invention can be used as a highly efficient dispersing agent. Their surface functional groups can weakly interact with the formate composite shell on the surface of copper powder to form a stable spatial barrier structure, which inhibits the agglomeration of nano-copper particles during storage and dispersion, and improves the long-term stability of the slurry. Moreover, the nitrogen-doped carbon dots have good electron transfer and local reduction capabilities. During the heating stage, they can participate in the in-situ reduction of residual oxides on the surface of copper powder, further reducing the activation energy of copper powder, so that sintering can occur at a lower temperature. At the same time, the network structure composed of ethylene glycol, α-terpineol and ethyl cellulose in the carrier can fully disperse the carbon dots and make them uniformly distributed in the slurry system. The formic acid, ascorbic acid and copper amine complex in the carrier gradually release mild reducing properties during heating, providing a reaction environment for the carbon dots to participate in electron transfer. Together, they form a continuous low-temperature reduction system, which promotes close contact and neck growth between copper particles. The synergistic effect of the three enables the nano-copper slurry of this invention to obtain a sintered copper layer with high thermal conductivity and high electrical conductivity under low temperature and pressureless conditions. Detailed Implementation
[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0037] The polyvinylpyrrolidone used in this application was purchased from Jinan Zhengkang Chemical Co., Ltd., model K30, product grade is superior, brand is Jinan Zhengkang;
[0038] The ethyl cellulose used in this application was purchased from Hebei Chaoyan New Material Technology Co., Ltd., with a density of 1.15 g / mL, a particle size of 11 mm, and the brand name was Jinan Zhengkang.
[0039] Example 1
[0040] This embodiment provides a method for preparing formate composite shell nano-copper powder, including the following steps:
[0041] Step I: Preparation of nano-copper powder
[0042] Weigh out 3g of ascorbic acid, 40g of hydrazine hydrate and 450mL of deionized water and place them in a reaction vessel. Mix them thoroughly to obtain a reducing agent for later use.
[0043] Weigh out 40g of copper nitrate, 100mL of deionized water, 0.2g of polyvinylpyrrolidone, and 0.5g of ethanolamine and place them in a reaction vessel. Stir the mixture and heat the reaction vessel to 80℃. Add 40mL of reducing agent and keep the mixture at this temperature for 2 hours. After the reaction is complete, wait for the reaction system to cool to room temperature, filter the mixture, wash the filter cake twice with deionized water and ethanol, transfer it to an oven at 50℃, and dry it to constant weight to obtain nano-copper powder.
[0044] Step II: Preparation of crude formate composite shell nano-copper powder
[0045] Weigh out 800 mL of ethylene glycol, 40 g of sodium formate, 5 g of ammonium formate, and 2 g of formic acid and place them in a reaction vessel under a nitrogen atmosphere. Stir at room temperature for 10 min, add 80 g of nano copper powder, heat the reaction vessel to 120 °C, and keep it at that temperature for 1 h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, wash the filter cake twice with deionized water and ethanol, transfer it to an oven at 50 °C, and dry it to constant weight to obtain crude formate composite shell nano copper powder.
[0046] Step III: Preparation of formate composite shell nano-copper powder
[0047] Weigh 80g of crude formate composite shell nano-copper powder and 140mL of methanol and place them in a reaction vessel and stir. Add 140mL of 0.6mol / L ammonium formate methanol solution and 140mL of 0.5mol / L copper chloride methanol solution dropwise in sequence. React at room temperature for 15min. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, wash the filter cake twice with methanol, transfer it to an oven at 50℃ and dry it to constant weight to obtain formate composite shell nano-copper powder.
[0048] Example 2
[0049] This embodiment provides a method for preparing formate composite shell nano-copper powder, including the following steps:
[0050] Step I: Preparation of nano-copper powder
[0051] Weigh out 6g of ascorbic acid, 50g of hydrazine hydrate and 475mL of deionized water and place them in a reaction vessel. Mix them thoroughly to obtain a reducing agent for later use.
[0052] Weigh out 50g of copper nitrate, 125mL of deionized water, 0.3g of polyvinylpyrrolidone, and 0.75g of ethanolamine and place them in a reaction vessel. Stir the mixture and heat the reaction vessel to 85℃. Add 50mL of reducing agent and keep the mixture at this temperature for 3 hours. After the reaction is complete, wait for the reaction system to cool to room temperature, filter the mixture, wash the filter cake three times with deionized water and ethanol, transfer it to an oven at 55℃, and dry it to constant weight to obtain nano-copper powder.
[0053] Step II: Preparation of crude formate composite shell nano-copper powder
[0054] Weigh out 900 mL of ethylene glycol, 50 g of sodium formate, 7.5 g of ammonium formate, and 3 g of formic acid and place them in a reaction vessel under a nitrogen atmosphere. Stir at room temperature for 12 min, then add 90 g of nano copper powder. Heat the reaction vessel to 125 °C and keep it at that temperature for 1.5 h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter it, wash the filter cake three times with deionized water and ethanol, transfer it to an oven at 55 °C, and dry it to constant weight to obtain crude formate composite shell nano copper powder.
[0055] Step III: Preparation of formate composite shell nano-copper powder
[0056] Weigh 90g of crude formate composite shell nano-copper powder and 150mL of methanol and place them in a reaction vessel and stir. Add 150mL of 0.7mol / L ammonium formate methanol solution and 150mL of 0.75mol / L copper chloride methanol solution dropwise in sequence. React at room temperature for 20min. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, wash the filter cake three times with methanol, transfer it to an oven at 55℃ and dry it to constant weight to obtain formate composite shell nano-copper powder.
[0057] Example 3
[0058] This embodiment provides a method for preparing formate composite shell nano-copper powder, including the following steps:
[0059] Step I: Preparation of nano-copper powder
[0060] Weigh out 9g of ascorbic acid, 60g of hydrazine hydrate and 500mL of deionized water and place them in a reaction vessel. Mix them thoroughly to obtain a reducing agent for later use.
[0061] Weigh out 60g of copper nitrate, 150mL of deionized water, 0.4g of polyvinylpyrrolidone and 1g of ethanolamine and place them in a reaction vessel. Stir the mixture and heat the reaction vessel to 90℃. Add 60mL of reducing agent and keep the mixture at this temperature for 4 hours. After the reaction is complete, wait for the reaction system to cool to room temperature, filter the mixture, wash the filter cake four times with deionized water and ethanol, transfer it to an oven at 60℃, and dry it to constant weight to obtain nano-copper powder.
[0062] Step II: Preparation of crude formate composite shell nano-copper powder
[0063] Weigh out 1000 mL of ethylene glycol, 60 g of sodium formate, 10 g of ammonium formate, and 4 g of formic acid and place them in a reaction vessel under a nitrogen atmosphere. Stir at room temperature for 15 min, add 100 g of nano copper powder, heat the reaction vessel to 130 °C, and keep it at that temperature for 2 h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, wash the filter cake four times with deionized water and ethanol, transfer it to an oven at 60 °C, and dry it to constant weight to obtain crude formate composite shell nano copper powder.
[0064] Step III: Preparation of formate composite shell nano-copper powder
[0065] Weigh 100g of crude formate composite shell nano-copper powder and 160mL of methanol and place them in a reaction vessel and stir. Add 160mL of 0.8mol / L ammonium formate methanol solution and 160mL of 0.1mol / L copper chloride methanol solution dropwise in sequence. React at room temperature for 30min. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, wash the filter cake 4 times with methanol, transfer it to an oven at 60℃ and dry it to constant weight to obtain formate composite shell nano-copper powder.
[0066] Example 4
[0067] This embodiment provides a method for preparing a modified organic support, including the following steps:
[0068] Step ①: Preparation of copper amine pre-complexed solution
[0069] Weigh out 30g of copper formate tetrahydrate, 20mL of n-pentylamine and 10mL of ethylene glycol and place them in a reaction vessel. Stir the reaction vessel and heat it to 45℃. Keep it warm and stir for 15min to obtain a copper amine pre-complexed solution.
[0070] Step 2: Preparation of organic carrier mother liquor
[0071] Weigh out 10 mL of ethylene glycol, 20 g of α-terpineol and 5 g of ethyl cellulose and place them in a reaction vessel and stir. Heat the reaction vessel to 60 °C and stir for 30 min. Cool the reaction vessel to room temperature and add 2 g of formic acid, 1 g of ascorbic acid and 1 g of bis(2-ethylhexyl) phosphate. Stir for 10 min to obtain the organic carrier mother liquor.
[0072] Step ③: Preparation of modified organic carrier
[0073] Weigh 100 mL of copper amine pre-complexing solution and 80 mL of organic carrier mother liquor and place them in a reaction vessel. Stir at room temperature for 20 min to obtain the modified organic carrier.
[0074] Example 5
[0075] This embodiment provides a method for preparing a modified organic support, including the following steps:
[0076] Step ①: Preparation of copper amine pre-complexed solution
[0077] Weigh out 40g of copper formate tetrahydrate, 30mL of n-pentylamine and 20mL of ethylene glycol and place them in a reaction vessel. Stir the reaction vessel and heat it to 50℃. Keep it warm and stir for 22min to obtain a copper amine pre-complexed solution.
[0078] Step 2: Preparation of organic carrier mother liquor
[0079] Weigh out 20 mL of ethylene glycol, 30 g of α-terpineol and 7.5 g of ethyl cellulose and place them in a reaction vessel and stir. Heat the reaction vessel to 65 °C and stir for 45 min. Cool the reaction vessel to room temperature, add 3 g of formic acid, 1.5 g of ascorbic acid and 1.5 g of bis(2-ethylhexyl) phosphate, and stir for 13 min to obtain the organic carrier mother liquor.
[0080] Step ③: Preparation of modified organic carrier
[0081] Weigh 125 mL of copper amine pre-complexing solution and 100 mL of organic carrier mother liquor and place them in a reaction vessel. Stir at room temperature for 25 min to obtain the modified organic carrier.
[0082] Example 6
[0083] This embodiment provides a method for preparing a modified organic support, including the following steps:
[0084] Step ①: Preparation of copper amine pre-complexed solution
[0085] Weigh out 60g of copper formate tetrahydrate, 40mL of n-pentylamine and 30mL of ethylene glycol and place them in a reaction vessel. Stir the reaction vessel and heat it to 55℃. Keep it warm and stir for 30min to obtain a copper amine pre-complexed solution.
[0086] Step 2: Preparation of organic carrier mother liquor
[0087] Weigh out 30 mL of ethylene glycol, 40 g of α-terpineol and 10 g of ethyl cellulose and place them in a reaction vessel and stir. Heat the reaction vessel to 70 °C and stir for 60 min. Cool the reaction vessel to room temperature and add 4 g of formic acid, 2 g of ascorbic acid and 2 g of bis(2-ethylhexyl) phosphate. Stir for 15 min to obtain the organic carrier mother liquor.
[0088] Step ③: Preparation of modified organic carrier
[0089] Weigh 150 mL of copper amine pre-complexing solution and 120 mL of organic carrier mother liquor and place them in a reaction vessel. Stir at room temperature for 30 min to obtain the modified organic carrier.
[0090] Example 7
[0091] This embodiment provides a method for preparing a pressureless sintering type nano-copper paste for chip interconnect, including the following steps:
[0092] Step (1): Preparation of nitrogen-doped carbon dots
[0093] Weigh out 80g of citric acid, 50g of urea, 1000mL of deionized water and 30mL of ethylene glycol and place them in a sealed reaction vessel. Heat the reaction vessel to 150℃ and keep it at that temperature for 4 hours. After the reaction is complete, wait for the reaction vessel to cool to room temperature, add ethanol to the reaction solution to precipitate the precipitate, filter it, and transfer the filtrate to a rotary evaporator at 80℃. Evaporate until no liquid is collected to obtain nitrogen-doped carbon dots.
[0094] Step 2: Preparation of mixed slurry
[0095] Weigh out the following by weight: 75 parts of formate composite shell nano-copper powder prepared in Example 1, 20 parts of modified organic carrier prepared in Example 4, and 0.5 parts of nitrogen-doped carbon dots. Place them in a high-speed homogenizer and stir at 800 r / min to obtain a mixed slurry.
[0096] Step 3: Preparation of nano-copper paste
[0097] The mixed slurry was placed in a three-roll mill and milled for 15 minutes with a roller gap of 5 μm to obtain nano copper slurry.
[0098] Example 8
[0099] This embodiment provides a method for preparing a pressureless sintering type nano-copper paste for chip interconnect, including the following steps:
[0100] Step (1): Preparation of nitrogen-doped carbon dots
[0101] Weigh out 90g of citric acid, 60g of urea, 1250mL of deionized water and 40mL of ethylene glycol and place them in a sealed reaction vessel. Heat the reaction vessel to 160℃ and keep it at that temperature for 5 hours. After the reaction is complete, wait for the reaction vessel to cool to room temperature, add ethanol to the reaction solution to precipitate the precipitate, filter it, and transfer the filtrate to a rotary evaporator at 85℃. Evaporate until no liquid is collected to obtain nitrogen-doped carbon dots.
[0102] Step 2: Preparation of mixed slurry
[0103] Weigh out the following by weight: 77.5 parts of formate composite shell nano-copper powder prepared in Example 2, 22.5 parts of modified organic carrier prepared in Example 5, and 0.75 parts of nitrogen-doped carbon dots. Place them in a high-speed homogenizer and stir at 900 r / min to obtain a mixed slurry.
[0104] Step 3: Preparation of nano-copper paste
[0105] The mixed slurry was placed in a three-roll mill and milled for 22 minutes with a roller gap of 6.5 μm to obtain nano copper slurry.
[0106] Example 9
[0107] This embodiment provides a method for preparing a pressureless sintering type nano-copper paste for chip interconnect, including the following steps:
[0108] Step (1): Preparation of nitrogen-doped carbon dots
[0109] Weigh out 100g of citric acid, 70g of urea, 1500mL of deionized water and 50mL of ethylene glycol and place them in a sealed reaction vessel. Heat the reaction vessel to 170℃ and keep it at that temperature for 6 hours. After the reaction is complete, wait for the reaction vessel to cool to room temperature, add ethanol to the reaction solution to precipitate the precipitate, filter it, and transfer the filtrate to a rotary evaporator at 90℃. Evaporate until no liquid is collected to obtain nitrogen-doped carbon dots.
[0110] Step 2: Preparation of mixed slurry
[0111] Weigh out the following by weight: 80 parts of formate composite shell nano-copper powder prepared in Example 3, 25 parts of modified organic carrier prepared in Example 6, and 1 part of nitrogen-doped carbon dots. Place them in a high-speed homogenizer and stir at 1000 r / min to obtain a mixed slurry.
[0112] Step 3: Preparation of nano-copper paste
[0113] The mixed slurry was placed in a three-roll mill and milled for 30 minutes with a roller gap of 8 μm to obtain nano copper slurry.
[0114] Comparative Example 1
[0115] The difference between this comparative example and Example 9 is that, in step (2) when preparing the mixed slurry, nano-copper powder is used in an equal amount to replace the formate composite shell nano-copper powder.
[0116] Comparative Example 2
[0117] The difference between this comparative example and Example 9 is that, in step (2) when preparing the mixed slurry, an equal amount of copper amine pre-complexed liquid is used instead of the modified organic carrier.
[0118] Comparative Example 3
[0119] The difference between this comparative example and Example 9 is that, in step (2) when preparing the mixed slurry, the addition of nitrogen-doped carbon dots is omitted.
[0120] Performance testing:
[0121] The density of the nano-copper pastes prepared in Examples 7-9 and Comparative Examples 1-3 after sintering at 200℃ was tested in accordance with the standard GB / T 3850-2015 "Method for Determination of Density of Dense Sintered Metallic Materials and Hard Alloys".
[0122] The sheet resistance of the nano-copper pastes prepared in Examples 7-9 and Comparative Examples 1-3 was tested in accordance with the standard SJ / T 10455-2020 "Copper Conductor Paste for Thick Film Hybrid Integrated Circuits".
[0123] Referring to standard GB / T 22588-2008 "Measuring Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method", the nano-copper paste prepared in Examples 7-9 and Comparative Examples 1-3 was coated onto the surface of a clean high-temperature resistant quartz substrate to form a uniform wet film. After drying in an oven at 125℃-150℃ for 10-15 minutes, the film was transferred to a nitrogen furnace and heated to 200℃ at a rate of 10℃ / min. The film was then held at this temperature for 30 minutes. After cooling, the nano-copper sintered layer on the substrate surface was peeled off, and the film was cut and ground to form sheet-like samples that meet the requirements of the laser flash method. After vacuum drying pretreatment, the thermal conductivity of the samples was tested using the laser flash method.
[0124] According to standard SJ / T 10455-2020, the nano-copper paste prepared in Examples 7-9 and Comparative Examples 1-3 was dotted on a copper substrate with an area of 3×3 mm. A 3×3 mm Si chip with Cu as the back metal was placed on the substrate using a vacuum pen, ensuring that the chip and the paste were in full contact without applying additional pressure. The substrate was dried in an oven at 125℃-150℃ for 10-15 min, and then transferred to a nitrogen furnace. The temperature was increased at 10℃ / min to 200℃, 220℃, 240℃ and 260℃ for 30 min respectively. The shear strength of the specimen was tested according to GB / T4937.19-2018 "Mechanical and Climatic Test Methods for Semiconductor Devices - Part 19: Chip Shear Strength".
[0125] See Table 1 for specific data.
[0126] Table 1 - Performance Test Data for Each Sample
[0127]
[0128] Data Analysis:
[0129] Comparative analysis of the data in Table 1 revealed that the sheet resistance of the nano-copper paste prepared in this invention is 3.21 mΩ / □, and the density after sintering at 200℃ is 8.30 g / cm³. 3 The thermal conductivity is 205.28 W / m·K, and the shear strengths after sintering at 200℃, 220℃, 240℃ and 260℃ for 30 min are 37.62 MPa, 46.88 MPa, 56.95 MPa and 59.72 MPa, respectively. All data are better than the comparative example.
[0130] The nano-copper paste prepared by this invention first reacts copper salt with a complexing agent to generate a copper amine complex, and then introduces formate compounds to construct a thermally decomposable shell at low temperatures, promoting the sintering of copper particles in the range of 200-240℃. To improve dispersibility and oxidation resistance, nitrogen-doped carbon dots are further added to the system as a stabilizer to inhibit copper powder agglomeration and oxidation. Subsequently, a modified organic carrier is added to regulate the rheological properties of the paste, and finally a stable and uniform nano-copper paste is obtained, which improves the conductivity and thermal conductivity of the copper interconnect layer under low temperature and pressureless conditions.
[0131] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.
[0132] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0133] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A pressureless sintering type nano-copper paste for chip interconnection, characterized in that, It comprises the following components by weight: 75-80 parts formate composite shell nano-copper powder, 20-25 parts modified organic carrier and 0.5-1 parts nitrogen-doped carbon dots; The formate composite shell nano-copper powder is prepared by the following steps: A1. Place copper nitrate, deionized water, polyvinylpyrrolidone and ethanolamine in a reaction vessel and stir. Heat the reaction vessel to 80-90℃, add a reducing agent, keep the reaction at this temperature for 2-4 hours, and then process to obtain nano copper powder. A2. Place ethylene glycol, sodium formate, ammonium formate and formic acid in a reaction vessel under nitrogen atmosphere protection, stir at room temperature for 10-15 min, add nano copper powder, heat the reaction vessel to 120-130℃, keep the temperature for 1-2 h, and then process to obtain crude formate composite shell nano copper powder. A3. Place crude formate composite shell copper nanopowder and methanol in a reaction vessel and stir. Add ammonium formate methanol solution and copper chloride methanol solution dropwise in sequence. React at room temperature for 15-30 min. Post-process to obtain formate composite shell copper nanopowder.
2. The pressureless sintering type nano-copper paste for chip interconnection according to claim 1, characterized in that, In step A1, the ratio of copper nitrate, deionized water, polyvinylpyrrolidone, ethanolamine, and reducing agent is 4-6g:10-15mL:0.02-0.04g:0.05-0.1g:4-6mL. The reducing agent is composed of ascorbic acid, hydrazine hydrate, and deionized water in a ratio of 0.3-0.9g:4-6g:45-50mL.
3. The pressureless sintering type nano-copper paste for chip interconnection according to claim 1, characterized in that, In step A2, the ratio of ethylene glycol, sodium formate, ammonium formate, formic acid and nano copper powder is 80-100mL:4-6g:0.5-1g:0.2-0.4g:8-10g.
4. The pressureless sintering type nano-copper paste for chip interconnection according to claim 1, characterized in that, In step A3, the ratio of crude formate composite shell nano-copper powder, methanol, ammonium formate methanol solution, and copper chloride methanol solution is 8-10g:14-16mL:14-16mL:14-16mL, the concentration of ammonium formate methanol solution is 0.6-0.8mol / L, and the concentration of copper chloride methanol solution is 0.05-0.1mol / L.
5. The pressureless sintering type nano-copper paste for chip interconnection according to claim 1, characterized in that, The modified organic carrier is prepared by the following steps: B1. Place copper tetrahydrate, n-pentylamine and ethylene glycol in a reaction vessel and stir. Heat the reaction vessel to 45-55℃ and stir for 15-30 minutes to obtain a copper amine pre-complexed solution. B2. Place ethylene glycol, α-terpineol and ethyl cellulose in a reaction vessel and stir. Heat the reaction vessel to 60-70℃ and stir for 30-60 min. Cool the reaction vessel to room temperature, add formic acid, ascorbic acid and bis(2-ethylhexyl) phosphate, and stir for 10-15 min to obtain the organic carrier mother liquor. B3. Place the copper amine pre-complexed solution and the organic carrier mother liquor in a reaction vessel and stir at room temperature for 20-30 minutes to obtain the modified organic carrier.
6. The pressureless sintering type nano-copper paste for chip interconnection according to claim 5, characterized in that, In step B1, the ratio of copper formate tetrahydrate, n-pentylamine, and ethylene glycol is 3-6 g: 2-4 mL: 1-3 mL; in step B2, the ratio of ethylene glycol, α-terpineol, ethyl cellulose, formic acid, ascorbic acid, and bis(2-ethylhexyl) phosphate is 1-3 mL: 2-4 g: 0.5-1 g: 0.2-0.4 g: 0.1-0.2 g: 0.1-0.2 g; in step B3, the volume ratio of the copper amine pre-complexing solution to the organic carrier mother liquor is 10-15: 8-12.
7. The pressureless sintering type nano-copper paste for chip interconnection according to claim 1, characterized in that, The method for preparing the nitrogen-doped carbon dots is as follows: citric acid, urea, deionized water and ethylene glycol are placed in a closed reaction vessel, the reaction vessel is heated to 150-170℃, and the reaction is maintained for 4-6 hours. The nitrogen-doped carbon dots are then obtained through post-treatment.
8. The pressureless sintering type nano-copper paste for chip interconnection according to claim 7, characterized in that, The ratio of citric acid, urea, deionized water and ethylene glycol is 8-10g:5-7g:100-150mL:3-5mL.
9. A method for preparing a pressureless sintering type chip interconnect nano-copper paste as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Place the formate composite shell nano-copper powder, modified organic carrier and nitrogen-doped carbon dots in a high-speed homogenizer and stir at high speed until uniform to obtain a mixed slurry. S2. Place the mixed slurry in a three-roll mill and grind for 15-30 minutes to obtain nano copper slurry.
10. The method for preparing a pressureless sintering type chip interconnect nano-copper paste according to claim 9, characterized in that, In step S1, the speed of the high-speed stirrer is 800-1000 r / min; in step S2, the roller gap is 5-8 μm.