CN109280424B

CN109280424B - Room-temperature sintering method of nano-silver-coated copper conductive ink

Info

Publication number: CN109280424B
Application number: CN201811028936.XA
Authority: CN
Inventors: 王涛; 戴小凤
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2018-09-05
Filing date: 2018-09-05
Publication date: 2020-09-22
Anticipated expiration: 2038-09-05
Also published as: CN109280424A

Abstract

The invention discloses a room temperature sintering method of nano silver-coated copper conductive ink, belonging to the field of conductive ink. The method comprises the following steps: a. printing or coating the ink on the flexible film base material by using a printer or a film coating machine and the like; b. soaking the membrane obtained in the step a in 0-50 v% of alcohol amine solution for 0-1h, then cleaning for 2-4 times by using a hydrophilic solvent, and wiping to dry; c. repeating the step a and the step b to repeatedly print or coat the printed layer to reach the thickness of the required printed layer; d. and c, soaking the membrane in the step c in a reducing agent solution with the concentration of 0-40 w% for 0-30min, washing for 2-4 times by using water, and wiping to dry. The metal thin layer prepared by the chemical sintering method has low resistivity, realizes the sintering of the nano copper-silver-coated ink in the air at room temperature, and can be used for various thermosensitive and flexible substrates.

Description

Room-temperature sintering method of nano-silver-coated copper conductive ink

Technical Field

The invention belongs to the field of conductive ink, and particularly relates to a room-temperature sintering method of nano silver-coated copper conductive ink.

Background

In recent years, metal nano materials in electronic functional materials have the characteristics of easy flexible connection, convenient realization of low-temperature sintering, active chemical properties and the like, and gradually become a research hotspot in the field of microelectronics. The nano silver-coated copper not only maintains the high conductivity of copper and silver, but also can reduce the oxidability of copper and the electromigration of silver, and is an ideal conductive filler. However, the stabilizer on the surface of the nanoparticles may prevent the formation of conductive paths between the particles. It is necessary to perform a subsequent sintering process for the printed pattern.

At present, the sintering of the nano silver-coated copper conductive ink is mostly carried out in a heating mode. The traditional heating sintering is simple and easy to implement, but is often required to be carried out in an inert atmosphere, so that the silver shell layer is prevented from being damaged by heat and the copper core is prevented from being oxidized after being exposed. Michael Grouchko et al (j. mater. chem.2009,19,3057.) found that the silver shell was destroyed at 200 ℃, resulting in oxidation of the copper core. In addition, high-temperature sintering is required to form a continuous conductive phase. However, heat sintering has the following drawbacks: firstly, high-temperature sintering has high energy consumption and high requirement on equipment; secondly, the inert atmosphere protects, so that the production cost and the operation difficulty are increased; third, higher heating temperatures limit the choice of substrates, especially heat sensitive substrates such as paper, plastic, fabric, etc., which cannot withstand high temperatures in excess of 150 ℃. Therefore, researchers have turned their eyes to new sintering methods such as microwave sintering, laser sintering, infrared sintering, and plasma sintering, and have reduced damage to the substrate by locally rapid heating. The underlying principle is still heat sintering, limited protection of the substrate and the need for expensive equipment support. Therefore, the realization of sintering in air at low temperature is still a big difficulty for printing electronics.

Disclosure of Invention

The invention aims to provide a room-temperature sintering method of nano silver-coated copper conductive ink, which is characterized in that a reductive electrolyte solution is adopted to inhibit the corrosion of a galvanic cell of a silver-coated copper nano material, the sintering in the air at room temperature is realized according to the self-agglomeration effect of nano particles in the electrolyte solution, and the defects caused by the traditional high-temperature sintering are overcome. The method comprises the following steps:

(1) dispersing the nano silver-coated copper in a solvent to prepare ink with solid content of 10-80 w%, and putting the ink into an ultrasonic cleaner for ultrasonic treatment for 2 hours to obtain the conductive ink.

Wherein the nano silver-coated copper comprises silver-coated copper nanoparticles with the diameter less than 100nm and nanowires.

Wherein the solvent comprises a hydrophilic solvent and a hydrophobic solvent. The hydrophilic solvent is one or more of water, methanol, ethanol and ethylene glycol, and the hydrophobic solvent is hexane, octane or toluene.

(2) And (2) printing or coating the conductive ink prepared in the step (1) on a flexible film substrate to form a pattern or a coating.

(3) And (3) soaking the film prepared in the step (2) in an alcohol solvent solution of 0-50 v% of alcohol amine for 0-1h, and replacing the hydrophobic stabilizer on the surface of the nano silver-coated copper material with the alcohol amine to change the hydrophobic property of the surface of the printed or coated graph into hydrophilic property. And cleaning for 2-4 times by using an alcohol solvent, and wiping to dry.

Wherein the alcohol amine is ethanolamine, 1-amino-2-propanol or 2-amino n-butanol, and the alcohol solvent is methanol, ethanol or isopropanol.

(4) Repeating the steps (2) and (3) to reach the required thickness of the printing layer;

(5) and (3) soaking the membrane obtained in the step (4) in 0-40 w% of reducing agent water solution for 0-30min, washing with water for 2-4 times, and wiping to dry.

Wherein the reducing agent is sodium borohydride, hydrazine hydrate or formaldehyde.

(6) The sheet resistance of the film was measured by a four-probe tester, and the film thickness was measured by a Scanning Electron Microscope (SEM), and the resistivity of the film was calculated.

The invention has the beneficial effects that:

(1) provides a room temperature sintering method of the nano silver-coated copper conductive ink, and effectively realizes the sintering of the economically dominant nano silver-coated copper conductive ink in the room temperature air.

(2) The method can be used for flexible substrates that are heat sensitive.

(3) The method has simple process and is beneficial to large-scale production.

Drawings

FIG. 1 is an XPS plot for example 1 (FIG. 1a) and example 2 (FIG. 1 b);

FIG. 2 is a SEM cross-sectional view of the sintered membrane prepared in example 2;

fig. 3 is a graph showing the contact angle with water before (fig. 3a) and after (fig. 3b) the film prepared in example 2 was soaked in the 1-amino-2-propanol solution.

Detailed Description

The invention provides a room temperature sintering method of nano silver-coated copper conductive ink, which is further described with reference to the accompanying drawings and examples.

Example 1:

(1) dispersing silver-coated copper nanoparticles (prepared by ZL201611072652.1 method) with the diameter of 11nm in n-octane to prepare ink with the solid content of 30 w%, and putting the ink into an ultrasonic cleaner for ultrasonic treatment for 2h to obtain yellow-brown ink.

(2) An appropriate amount of ink was applied to a polyethylene terephthalate (PET) film, and the film was coated using a preparation apparatus.

(3) And (3) soaking the membrane prepared in the step (2) in 10 v% of 1-amino-2-propanol methanol solution for 1min, and replacing oleylamine on the particle surface with alcohol amine to change the surface of the membrane from hydrophobicity to hydrophilicity. Then washing with methanol for 3 times, and wiping to dry.

(4) Repeating the steps (2) and (3) for 3 times to carry out film coating;

(5) and (3) soaking the membrane obtained in the step (4) in a 2 w% NaCl solution for 3min, washing for 3 times by using water, and wiping to dry.

(6) The sheet resistance of the film was 10. omega./□ as measured by a four-probe tester, the film thickness was 500nm as measured by SEM, and the resistivity of the film was calculated to be 500.0. mu. omega. cm.

And (3) carrying out X-ray photoelectron spectroscopy (XPS) on the metal film in the step (5), and as shown in figure 1a, a satellite peak of + 2-valent copper appears at 940-950 eV, which shows that the electrolyte NaCl solution without the reducing agent has copper core galvanic cell corrosion. The resistivity of the metal film increases due to the presence of copper oxide, and is as high as 500.0 μ Ω.

Example 2:

(1) dispersing silver-coated copper nanoparticles (ZL201611072652.1) with the diameter of 11nm in n-octane to prepare ink with the solid content of 30 w%, and putting the ink into an ultrasonic cleaner for ultrasonic treatment for 2h to obtain yellow-brown ink.

(4) Repeating the steps (2) and (3) for 2 times to carry out film coating;

(5) NaBH4 was dissolved in NaOH solution at pH 12 to obtain a 2 w% mass fraction NaBH4 solution.

(6) And (3) soaking the membrane in the step (4) in the NaBH4 solution in the step (5) for 3min, washing for 3 times by using water, and wiping to dry.

(7) The sheet resistance of the film was 1.21. mu. OMEGA/□ as determined by a four-probe tester, and the film thickness was 300nm as determined by SEM (FIG. 2), and the resistivity of the film was calculated to be 36.3. mu. OMEGA. cm.

The contact angle test was performed on the membranes of steps (2) and (3) and, as shown in fig. 3, resulted in a change in the contact angle of the treated membrane from 111.3 ° (shown in fig. 3a) to 77.3 ° (shown in fig. 3b), from hydrophobic to hydrophilic, indicating successful oleylamine substitution by 1-amino-2-propanol.

The XPS test on the metal film of step (6) showed that +2 valent copper was not present on the film surface, as shown in fig. 1b, indicating that the NaBH4 solution successfully inhibited galvanic corrosion of the copper core. The resistivity of the film was thus significantly reduced to 36.3 μ Ω · cm compared to example 1.

Example 3:

(1) silver-coated copper nanoparticles (ZL201611072652.1) with the diameter of 11nm are dispersed in n-octane to prepare ink with the solid content of 30 w%, and the ink is placed in an ultrasonic cleaner for ultrasonic treatment for 2h to obtain yellow-brown ink.

(2) And (3) taking a proper amount of ink on the PET film, and coating the PET film by using a preparation device.

(4) Repeating the steps (2) and (3) for 3 times to carry out film coating;

(6) And (3) soaking the membrane in the step (4) in the NaBH4 solution in the step (5) for 2min, washing for 3 times by using water, and wiping to dry.

(7) The sheet resistance of the film measured by the four-probe tester was 0.8. omega./□, and the film thickness measured by SEM was 500nm, and the resistivity of the film calculated to be 40.0. mu. omega. cm was significantly reduced as compared with example 1.

Claims

1. A room temperature sintering method of nano silver-coated copper conductive ink is characterized by comprising the following steps:

(1) dispersing nano silver-coated copper in a solvent to prepare ink with solid content of 10-80 w%, and putting the ink into an ultrasonic cleaner for ultrasonic treatment for 2 hours to obtain conductive ink;

(2) printing or coating the conductive ink prepared in the step (1) on a flexible film substrate to form a pattern or a coating;

(3) soaking the film prepared in the step (2) in an alcohol solvent solution of 10-50 v% of alcohol amine for 1min-1h, replacing a hydrophobic stabilizer on the surface of the nano silver-coated copper material by using the alcohol amine to change the hydrophobicity of the surface of the printed or coated pattern into hydrophilicity, cleaning for 2-4 times by using the alcohol solvent, and wiping to dry;

(4) repeating the steps (2) and (3) to achieve the required thickness of the printing layer;

(5) soaking the membrane prepared in the step (4) in 2-40 w% of reducing agent water solution for 2-30min, washing with water for 2-4 times, and wiping;

the alcohol amine in the step (3) is ethanolamine, 1-amino-2-propanol or 2-amino n-butanol;

and the conductive ink is sintered at room temperature.

2. The room temperature sintering method of conductive ink of claim 1, wherein the nano silver-coated copper in step (1) comprises nano silver-coated copper particles and nano wires with a diameter of less than 100 nm.

3. The room temperature sintering method of conductive ink coated with nano-silver and copper according to claim 1, wherein the solvent in step (1) comprises a hydrophilic solvent and a hydrophobic solvent, wherein the hydrophilic solvent is one or more of water, methanol, ethanol and ethylene glycol; the hydrophobic solvent is hexane, octane or toluene.

4. The room temperature sintering method of nano-silver-coated copper conductive ink according to claim 1, wherein the alcohol solvent in step (3) is methanol, ethanol or isopropanol.

5. The room temperature sintering method of nano-silver-coated copper conductive ink according to claim 1, wherein the reducing agent in the step (5) is sodium borohydride, hydrazine hydrate or formaldehyde.