CN106928775A - A kind of low temperature sintering nano-copper conductive ink, preparation method and printing application - Google Patents

Abstract

The invention provides a low-temperature sinterable nano-copper conductive ink and its preparation method and printing application; through the method of organic acid treatment on the surface of copper nanoparticles, copper nanoparticles with no oxidation on the surface are synthesized, and based on the copper nanoparticles The nano-copper conductive ink is prepared by the particles, and the low-temperature sintering of the nano-copper conductive ink is realized; the nano-copper conductive ink prepared by the present invention has good stability, simple method, easy-to-obtain equipment, and the obtained sintered film has good conductivity and is easy to obtain. It solves the common problems of oxidation and high sintering temperature in the application process of nano-copper conductive ink.

Description

A kind of low-temperature sinterable nano-copper conductive ink, preparation method and printing application

technical field

The invention belongs to the field of electronic printing materials, and relates to a low-temperature sinterable nano-copper conductive ink, a preparation method thereof and a printing application.

Background technique

The traditional printed circuit board is not really made by printing technology, but by a method similar to integrated circuit processing, which is basically formed on a pre-copper-plated substrate through photolithography, corrosion and other processes. This processing technology has two serious problems: one is that a large amount of corrosion waste liquid produced during the corrosion process of the substrate will cause serious environmental pollution; the other is that a large amount of copper is removed by corrosion during the process of corrosion forming, resulting A lot of waste. As the world's largest producer of printed circuit boards, my country's adverse effects of pollution and waste on our country are self-evident. In response to these unfavorable factors, scientific researchers began to focus on developing new technologies and processes to solve the problems encountered in actual production. In recent years, the rapid development of printed electronic technology has put forward new ideas for the production process of printed circuit boards. Printed electronics technology has the advantages of batch capacity and low cost, and also avoids environmental pollution caused by photolithography and corrosion, and has a high utilization rate of raw materials, so it has broad market prospects. At present, in liquid crystal flat panel displays In the manufacturing industry, some traditional photolithography processing techniques have been replaced by inkjet printing technology.

The key to why printed circuit boards can be made by printing lies in the preparation of printable electronic materials. The main component of conductive ink is generally metal nanoparticles, such as gold, silver, copper and so on. Although gold and silver have good electrical conductivity, they are expensive and not suitable for large-scale actual production.

Copper has a conductivity comparable to that of gold and silver, and its cost is low, so it has the prospect of large-scale application. The problem is that it is easy to oxidize. It is difficult to prepare copper nanoparticles with no oxidation on the surface by conventional methods. The surface of copper nanoparticles on the market is covered with an oxide layer. The existence of this oxide layer will lead to an increase in the sintering temperature of copper nanoparticles. , reducing the conductivity of the sintered body. It has been reported that sintering copper nanoparticles in organic acid vapor can obtain sintered copper film with excellent conductivity at a lower sintering temperature. The problem is that organic acid vapor will corrode electronic functional devices and cause a series of reliability problems. To be avoided in the electronics manufacturing industry.

Contents of the invention

In order to solve the shortcomings of the above-mentioned existing conductive inks, the present invention provides a low-temperature sinterable nano-copper conductive ink, which overcomes the problem of high cost of the existing conductive inks.

A low-temperature sinterable nano-copper conductive ink, comprising 10-30 parts of copper nanoparticles, 10-20 parts of absolute ethanol and 30-60 parts of an organic solvent, wherein the organic solvent is miscible with the absolute alcohol; The copper nanoparticles are uniformly dispersed in the low-temperature sinterable nano-copper conductive ink, and the surface of the copper nanoparticles is free of oxides. The conductive ink adopts copper as the main conductive medium, and has low cost, safety and reliability.

The further improvement of the present invention is that: the particle size of the copper nanoparticles is 30nm-50nm. The performance of the conductive ink obtained under this particle size is the best.

A further improvement of the present invention is that: the organic solvent is one or more of ethylene glycol, toluene, isopropanol, and xylene. The above-mentioned organic solvents are more conducive to the dispersion of copper nanoparticles.

The further improvement of the present invention is: it also contains a dispersant, and the dispersant is one of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and dodecylmercaptan. one or more species. The above-mentioned dispersant can obtain a better dispersion effect.

Another object of the present invention is to provide a method for preparing a low-temperature sinterable nano-copper conductive ink. The method includes the following steps:

Step A: preparing copper nanoparticles, which are obtained after reduction reaction of copper-containing compounds.

Wherein, the step A includes the following sub-steps:

Step A1: Prepare initial nano-copper particles, which are obtained by centrifuging and washing the copper-containing compound after reduction.

Further, the step A1 includes the following sub-steps:

Step A11: preparing a reduction solution, the concentration of the reduction solution is 100-300 g/L, the temperature of the reduction solution is 80-120 ° C, wherein the reducing agent is sodium hypophosphite monohydrate, sodium borohydride, hydrazine hydrate One or more of them, the solvent is diethylene glycol and/or ethylene glycol;

Step A12: Prepare the reaction solution, which contains 10-30 g/L copper source and 20-40 g/L dispersant, wherein the copper source adopts copper chloride dihydrate, copper nitrate trihydrate, pentahydrate One or more of copper sulfate in water, the dispersant adopts one of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and dodecylmercaptan or more, the solvent is diethylene glycol and/or ethylene glycol, and the temperature of the reaction solution is 80-120°C;

Step A13: a reaction step, the reaction step is to add the reducing solution to the reaction solution at a rate of 10-30 ml/s;

Step A14: post-processing step, the post-processing step is to add 200-400ml of deionized water to the reaction system obtained after 5-20 min after the dropwise addition in the reaction step, and centrifuge and wash it several times.

Step A2: Prepare copper nanoparticles, the copper nanoparticles are dispersed in the initial nano-copper particles in an absolute ethanol solution containing 1-10 wt% organic acid, soaked for 5-15 min, then add absolute ethanol to wash for several times obtained, the organic acid is one or more of monobasic saturated carboxylic acids.

Step B: preparing conductive ink, the conductive ink is obtained after ultrasonication and stirring of the copper nanoparticles, absolute ethanol and organic solvent, and the conductive ink contains 10-30 parts of copper nanoparticles, 10-20 parts absolute ethanol and 30-60 parts of organic solvent, the organic solvent is miscible with the absolute ethanol; the organic solvent is one or more of ethylene glycol, toluene, isopropanol, xylene; the The copper nanoparticles are uniformly dispersed in the low-temperature sinterable nano-copper conductive ink.

A conductive ink can be prepared by the above method. The conductive ink has low cost and good conductive effect. The method is easy to implement and is conducive to wide-scale promotion.

The further improvement of the present invention is that: when preparing the reaction solution in the step A12, mechanical stirring is also required, and the stirring speed is 200-400 r/min. Mechanical stirring is more conducive to the combination of dispersant and nano-copper particles, which is more conducive to dispersion.

The third object of the present invention is to provide a method for making a conductive circuit, the method comprising the following steps:

Step A: Prepare a conductive substrate; the conductive substrate is to print the above-mentioned conductive ink on the substrate by screen printing, and print it into a certain pattern;

Step B: Prepare a conductive circuit, the conductive circuit is sintered to the conductive substrate until the resistivity of the conductive layer is finally 5.67μΩ·cm-6.59μΩ·cm, and the sintering temperature is 160-260°C, and the sintering time is 5-60min.

A further improvement of the present invention is that: the substrate is a rigid substrate or a flexible film. The rigid substrate can be glass or ceramics, and the flexible film can be polyimide film, high temperature resistant polyester film, etc.

Compared with the prior art, the present invention has the advantages of:

(1). The preparation method of raw copper nanoparticles in the present invention is simple, the preparation process is time-saving, the required equipment is simple and easy to obtain, and the cost is low. The method for removing the oxide layer on the surface of copper nanoparticles is convenient and quick, and the removal is thorough, without subsequent adverse effects such as corrosion.

(2). Compared with the copper nanoparticles on the market, the sintering temperature of the organic acid-treated copper nanoparticles is significantly lowered, and the conductivity of the sintered body is significantly improved. The resistivity can be obtained at 260°C under low-temperature sintering. The resistivity is 5.67μΩ ·cm -6.59μΩ·cm conductive copper film is more suitable for the preparation of high-performance metal conductive ink.

(3). In the process of the present invention, the forming process of the conductive structure is simple, the requirements for the equipment used are low, and the components of the ink are non-toxic and non-polluting. In industrial production, the production of conductive structures can be carried out in large quantities at the same time, with high production efficiency and low cost.

Description of drawings

Accompanying drawing 1 is the SEM image of the microstructure of the low-temperature sinterable nano-copper conductive ink prepared by the present invention, silk screen printing and sintering.

detailed description

The present invention firstly provides a low-temperature sinterable nano-copper conductive ink, comprising 10-30 parts of copper nanoparticles, 10-20 parts of absolute ethanol and 30-60 parts of an organic solvent, the organic solvent and the Anhydrous ethanol is mutually soluble; the copper nanoparticles are uniformly dispersed in the low-temperature sinterable nano-copper conductive ink, and the surface of the copper nanoparticles is free of oxides. The particle size of the copper nanoparticles is 30nm-50nm. The organic solvent is one or more of ethylene glycol, toluene, isopropanol and xylene. The above-mentioned organic solvents are more conducive to the dispersion of copper nanoparticles. It also contains a dispersant, and the dispersant is one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and dodecylmercaptan. The above-mentioned dispersant can obtain a better dispersion effect. The conductive ink adopts copper as the main conductive medium, and has low cost, safety and reliability.

Secondly, the present invention provides a preparation method of nano-copper conductive ink that can be sintered at low temperature. The obtained conductive ink has good stability and can be sintered at a relatively low temperature. The sintered film has low resistivity and excellent conductivity.

A preparation method of low-temperature sinterable nano-copper conductive ink, comprising the following steps:

(1) Prepare alcohol solution of copper source + dispersant.

(2) Alcohol solution of reducing agent.

(3) Copper nanoparticles were synthesized by the improved polyol method.

(4) Prepare an anhydrous ethanol solution of an organic acid.

(5) The synthesized copper nanoparticles were placed in an anhydrous ethanol solution of an organic acid to remove the oxide layer on the surface of the particles.

(6) Mix the surface-free copper nanoparticles with absolute ethanol and an organic solvent, and obtain nano-copper conductive ink after ultrasonic dispersion.

The copper source is one of copper chloride dihydrate, copper nitrate trihydrate and copper sulfate pentahydrate, or a mixture of at least two of them.

The base of the alcohol solution is diethylene glycol, ethylene glycol, or a mixture of the two.

On the one hand, the role of the dispersant is to prevent the agglomeration of copper nanoparticles and increase the dispersion of the particles; on the other hand, it is to form a coating layer on the surface of the copper nanoparticles to prevent further oxidation of the particles. One of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and dodecylmercaptan, or a mixture of at least two of them, is used.

The reducing agent is one of sodium hypophosphite monohydrate, sodium borohydride, and hydrazine hydrate, or a mixture of at least two of them.

The function of the organic acid is to react with the oxide layer on the surface of the copper nanoparticles to generate an organic acid salt, so as to completely remove the oxide layer and obtain copper nanoparticles without oxidation on the surface. One of monobasic saturated carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, or a mixture of at least two kinds is used.

The organic solvent in the conductive ink is ethylene glycol, toluene, isopropanol, xylene, it can be one of them, or a mixture of at least two

More specific steps are detailed as follows:

(1) Prepare 200ml-600ml of a solution containing 10g/L-30g/L copper source and 20g/L-40g/L dispersant, heat and stir to 80°C-120°C, and the stirring speed is 200r/min-400r/min. Then add the 100g/L-300g/L reducing agent solution heated to 80°C-120°C to the copper source solution at a dropping rate of 10ml/s-30ml/s, and react for 5min-20min after the dropping is completed, and the reaction is over Finally, 200ml-400ml deionized water was added, and the copper nanoparticles were washed by centrifugation several times.

(2) The removal method of the oxide layer on the surface of copper nanoparticles: redisperse the prepared copper nanoparticles into an anhydrous ethanol solution containing 1%-10% organic acid, soak for 5min-15min, then add anhydrous ethanol to clean Once, copper nanoparticles with no oxide layer on the surface were obtained.

(3) Take copper nanoparticles with no oxide layer on the surface, add absolute ethanol and organic solvent, and use ultrasonic and mechanical stirring to uniformly disperse copper nanoparticles in the solvent to obtain nano-copper conductive ink with uniform composition.

Another object of the present invention is to provide a method of manufacturing a conductive circuit,

(1) Print the aforementioned nano-copper conductive ink on the substrate by screen printing to form a certain pattern.

(2) Take a substrate printed with a certain pattern, select a sintering temperature of 160°C-260°C, and a sintering time of 5min-60min, and form a conductive structure after sintering.

Wherein, the resistivity of the conductive layer is finally 5.67 μΩ·cm-6.59 μΩ·cm. By comparing with the nano-copper conductive ink without organic acid treatment, the sintering temperature of the conductive ink in the present invention is obviously lowered, and the conductivity is obviously improved. The selected printed substrates can be rigid substrates such as ceramics and glass, or flexible films such as polyimide films and high-temperature resistant polyester films.

The present invention will be further described below in conjunction with specific embodiments and accompanying drawings. It should be understood that the embodiments are only for illustrating the present invention rather than limiting the scope of the present invention.

Implementation example 1 A kind of low-temperature sinterable nano-copper conductive ink and its preparation method and printing application

Take 2 g of copper nanoparticles prepared by the polyol method, ultrasonically disperse them into an anhydrous ethanol solution containing 10% formic acid, soak for 5 min, and then centrifuge. The separated copper nanoparticles were washed several times with absolute ethanol and then used for later use.

Mix the formic acid-treated copper nanoparticles with ethylene glycol and absolute ethanol at a mass ratio of 1:3:1 to prepare a low-temperature sinterable nano-copper conductive ink, and ultrasonically disperse it for 20 minutes to uniformly disperse the nanoparticles in the ink. The conductive ink was printed on the polyimide film using screen printing technology, and sintered at 260°C for 60 minutes to obtain a sintered film. The sintering atmosphere was 95% nitrogen + 5% hydrogen.

Implementation Example 2 A low-temperature sinterable nano-copper conductive ink and its preparation method and printing application

Take 2 g of copper nanoparticles prepared by the polyol method, ultrasonically disperse them into an anhydrous ethanol solution containing 5% formic acid, soak for 5 min, and then centrifuge. The separated copper nanoparticles were washed several times with absolute ethanol and then used for later use.

Mix the formic acid-treated copper nanoparticles with toluene and absolute ethanol at a mass ratio of 1:3:1 to prepare a low-temperature sinterable copper nanoconductive ink, and ultrasonically disperse it for 20 minutes to uniformly disperse the nanoparticles in the ink. The conductive ink was printed on the polyimide film using screen printing technology, and sintered at 260°C for 60 minutes to obtain a sintered film. The sintering atmosphere was 95% nitrogen + 5% hydrogen.

Implementation Example 3 A low-temperature sinterable nano-copper conductive ink and its preparation method and printing application

Take 2 g of copper nanoparticles prepared by the polyol method, ultrasonically disperse them into an anhydrous ethanol solution containing 10% formic acid, soak for 5 min, and then centrifuge. The separated copper nanoparticles were washed twice with deionized water, and then washed twice with absolute ethanol before use.

Mix the formic acid-treated copper nanoparticles with toluene and absolute ethanol at a mass ratio of 1:4:1 to prepare a low-temperature sinterable copper nanoconductive ink, and ultrasonically disperse it for 20 minutes to uniformly disperse the nanoparticles in the ink. The conductive ink was printed on the polyimide film using screen printing technology, and sintered at 260°C for 60 minutes to obtain a sintered film. The sintering atmosphere was 95% nitrogen + 5% hydrogen.

Implementation Example 4 A low-temperature sinterable nano-copper conductive ink and its preparation method and printing application

Take 2 g of copper nanoparticles prepared by the polyol method, ultrasonically disperse them into an anhydrous ethanol solution containing 15% formic acid, soak for 5 min, and then centrifuge. The separated copper nanoparticles were washed several times with absolute ethanol and then used for later use.

Mix the formic acid-treated copper nanoparticles with toluene and absolute ethanol at a mass ratio of 1:4:1 to prepare a low-temperature sinterable copper nanoconductive ink, and ultrasonically disperse it for 20 minutes to uniformly disperse the nanoparticles in the ink. The conductive ink was printed on the polyimide film using screen printing technology, and sintered at 260°C for 60 minutes to obtain a sintered film. The sintering atmosphere was 95% nitrogen + 5% hydrogen.

Implementation Example 5 A low-temperature sinterable nano-copper conductive ink and its preparation method and printing application

Take 2 g of copper nanoparticles prepared by the polyol method, ultrasonically disperse them into an anhydrous ethanol solution containing 15% acetic acid, soak for 5 min, and then centrifuge. The separated copper nanoparticles were washed several times with absolute ethanol and then used for later use.

Mix the formic acid-treated copper nanoparticles with toluene and absolute ethanol at a mass ratio of 1:4:1 to prepare a low-temperature sinterable copper nanoconductive ink, and ultrasonically disperse it for 20 minutes to uniformly disperse the nanoparticles in the ink. The conductive ink was printed on the polyimide film using screen printing technology, and sintered at 260°C for 60 minutes to obtain a sintered film. The sintering atmosphere was 95% nitrogen + 5% hydrogen.

Accompanying drawing 1 is the SEM picture of the microstructure of the low-temperature sinterable nano-copper conductive ink prepared by the present invention after screen printing and sintering. The structure of the conductive ink and its distribution can be seen from it.

Compared with the prior art, the present invention has the advantages of:

(1). The preparation method of raw copper nanoparticles in the present invention is simple, the preparation process is time-saving, the required equipment is simple and easy to obtain, and the cost is low. The method for removing the oxide layer on the surface of copper nanoparticles is convenient and quick, and the removal is thorough, without subsequent adverse effects such as corrosion.

(2). Compared with the copper nanoparticles on the market, the sintering temperature of the organic acid-treated copper nanoparticles is significantly lowered, and the conductivity of the sintered body is significantly improved. The resistivity can be obtained at 260°C under low-temperature sintering. The resistivity is 5.67μΩ ·cm -6.59μΩ·cm conductive copper film is more suitable for the preparation of high-performance metal conductive ink.

(3). In the process of the present invention, the forming process of the conductive structure is simple, the requirements for the equipment used are low, and the components of the ink are non-toxic and non-polluting. In industrial production, the production of conductive structures can be carried out in large quantities at the same time, with high production efficiency and low cost.

The above content is a further detailed description of the present invention in combination with specific preferred modes, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (10)

1. a nano-copper conductive ink that can be sintered at low temperature is characterized in that: the copper nanoparticles comprising 10-30 parts, the dehydrated alcohol of 10-20 parts and the organic solvent of 30-60 parts, said organic solvent and said organic solvent The anhydrous ethanol is mutually soluble; the copper nanoparticles are uniformly dispersed in the low-temperature sinterable nano-copper conductive ink, and the surface of the copper nanoparticles is free of oxides. 2. The low-temperature sinterable nano-copper conductive ink according to claim 1, characterized in that: the particle diameter of the copper nanoparticles is 30nm-50nm. 3. The low-temperature sinterable nano-copper conductive ink according to claim 1 or 2, characterized in that: the organic solvent is one or more of ethylene glycol, toluene, isopropanol, and xylene. 4. according to claim 1 and 2 described nano-copper conductive inks that can be sintered at low temperature, it is characterized in that: also contain dispersant, described dispersant is polyvinylpyrrolidone, cetyltrimethylammonium bromide, cetyl trimethylammonium bromide, One or more of sodium dialkylbenzenesulfonate and dodecylmercaptan. 5. A preparation method of nano-copper conductive ink capable of low-temperature sintering, characterized in that, comprising the following steps: Step A: preparing copper nanoparticles, which are obtained after a reduction reaction of a copper-containing compound; Step B: preparing conductive ink, the conductive ink is obtained after ultrasonication and stirring of the copper nanoparticles, absolute ethanol and organic solvent, and the conductive ink contains 10-30 parts of copper nanoparticles, 10-20 parts absolute ethanol and 30-60 parts of organic solvent, the organic solvent is miscible with the absolute ethanol; the organic solvent is one or more of ethylene glycol, toluene, isopropanol, xylene; the The copper nanoparticles are uniformly dispersed in the low-temperature sinterable nano-copper conductive ink. 6. the preparation method of the nano-copper conductive ink that can be sintered at low temperature according to claim 5, is characterized in that, described step A comprises following sub-steps: Step A1: preparing initial nano-copper particles, the initial nano-copper particles are obtained by centrifuging and cleaning the copper-containing compound after reduction; Step A2: Prepare copper nanoparticles, the copper nanoparticles are obtained by dispersing the initial copper nanoparticles into an absolute ethanol solution containing 1-10wt% organic acid, soaking for 5-15 min, adding absolute ethanol and washing for several times , the organic acid is one or more of monobasic saturated carboxylic acids. 7. the preparation method of the nano-copper conductive ink that can be sintered at low temperature according to claim 6, is characterized in that, described step A1 comprises following sub-steps: Step A11: preparing a reduction solution, the concentration of the reduction solution is 100-300 g/L, the temperature of the reduction solution is 80-120 ° C, wherein the reducing agent is sodium hypophosphite monohydrate, sodium borohydride, hydrazine hydrate One or more of them, the solvent is diethylene glycol and/or ethylene glycol; Step A12: Prepare the reaction solution, which contains 10-30 g/L copper source and 20-40 g/L dispersant, wherein the copper source adopts copper chloride dihydrate, copper nitrate trihydrate, pentahydrate One or more of copper sulfate in water, the dispersant adopts one of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and dodecylmercaptan or more, the solvent is diethylene glycol and/or ethylene glycol, and the temperature of the reaction solution is 80-120°C; Step A13: a reaction step, the reaction step is to add the reducing solution to the reaction solution at a rate of 10-30 ml/s; Step A14: post-processing step, the post-processing step is to add 200-400ml of deionized water to the reaction system obtained after 5-20 min after the dropwise addition in the reaction step, and centrifuge and wash it several times. 8. The method for preparing low-temperature sinterable nano-copper conductive ink according to claim 7, characterized in that, when preparing the reaction solution in step A12, mechanical stirring is also required, and the stirring speed is 200-400 r/min. 9. A method for making a conductive circuit, comprising the following steps: Step A: preparing a conductive substrate; the conductive substrate is to print the conductive ink described in any one of claims 1-4 on the substrate by screen printing, and print it into a certain pattern; Step B: Prepare a conductive circuit, the conductive circuit is sintered to the conductive substrate until the resistivity of the conductive layer is finally 5.67μΩ·cm-6.59μΩ·cm, and the sintering temperature is 160-260°C, and the sintering time is 5-60min. 10. The method for manufacturing a conductive circuit according to claim 9, wherein the substrate is a rigid substrate or a flexible film.