A composite ink, its preparation method and use in aerosol jet printing conformal circuits

Abstract

The application discloses a kind of composite ink and its preparation method and application in aerosol jet printing conformal circuit, belong to commonality circuit preparation technical field.The application provides a kind of composite ink, which can be sintered in situ at low post-processing temperature, realizes the preparation of conformal circuit on polymer substrate using aerosol jet printing method.The application uses silver nanoparticles and silver ion complex preparation for the preparation of composite ink for aerosol jet printing conformal circuit.The composite ink uses high solid content nano silver particle ink to deposit on the substrate, and the capillary action between the particles makes the ink containing silver ions fill the gap between the particles, and the silver ions are reduced in situ on the heated substrate, and the generated nano silver particles fill the gap in the original nano particles, which greatly improves the conductivity of conformal circuit.The conductivity of the prepared conformal circuit reaches 22.4 μΩ·cm at 100 DEG C post-processing temperature using the composite ink for aerosol jet printing.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite ink, a preparation method thereof and an application thereof in aerosol jet printing conformal circuit, and belongs to the technical field of common circuit preparation. BACKGROUND

[0002] Conformal electronics has become a hot topic in academia and industry due to its ability to integrate electronic systems on curved surfaces, bringing new characteristics and functions. On the one hand, conformal electronics can accurately respond to external stimuli on non-planar and dynamic surfaces, meeting the strong demand of the next generation of sensing devices in the field of safety, environment and health monitoring. On the other hand, conformal electronics is not limited by installation space, has the advantages of miniaturization and light weight, and has been applied in the fields of intelligent implants, conformal displays, conformal antennas, etc. The great advantages and wide application of conformal electronics urgently need high-resolution and high-conductivity conformal circuits.

[0003] Traditional circuit manufacturing techniques provide nanoscale resolution, but processes such as photolithography, etching, and doping are not compatible with curved surfaces. Existing transfer printing techniques can indirectly produce large-area curved patterns, but only provide millimeter-scale resolution. And assembling electronic products from a flat surface to a curved surface is another method, but the complex process and potential threat of residual stress limit its application. Other methods, such as non-planar photolithography and laser direct writing, can achieve fine patterns on curved substrates, but rely on expensive equipment and result in higher costs. In contrast, inkjet printing, as an additive manufacturing technique, provides wide material compatibility, high resolution, environmental protection, and cost-effectiveness.

[0004] Aerosol jet printing is one of the inkjet printing technologies, and due to the sheath gas focusing effect, its working distance exceeds 2mm, and the higher working distance enables it to adapt to various complex surface morphologies. In addition, due to the protection of sheath gas, aerosol jet printing can be compatible with inks with a solid content of up to 50% without nozzle clogging, and the high solid content of the ink ensures excellent adhesion of the printed pattern to three-dimensional substrates of various materials. Therefore, aerosol jet printing is considered to be the most promising conformal circuit preparation technology.

[0005] However, the aerosol jet printing ink currently used for conformal circuit preparation is mainly nano-silver ink, but its post-processing temperature often exceeds 150℃, which is not suitable for polymer substrates such as epoxy resin and PET, greatly limiting the application range of conformal circuits, so it is necessary to develop silver-based aerosol ink with low post-processing temperature and high conductivity to adapt to different types of substrate materials and promote the development of conformal electronics. SUMMARY

[0006] The present application aims at the above technical problems and development bottlenecks of the existing conformal circuit, and provides a composite ink which can be in-situ sintered at a low post-processing temperature, so that the conformal circuit is prepared on a polymer substrate by an aerosol jet printing method.

[0007] The technical scheme of the present application is as follows:

[0008] One of the purposes of the present application is to provide a composite ink which is prepared by mixing silver nanoparticle ink and silver ion ink; the silver nanoparticle ink comprises spherical silver nanoparticles, an additive, and a mixed solvent; and the silver ion ink comprises a silver source, a solvent, a complexing agent, and a reducing agent.

[0009] Further limitation, the particle size of the spherical silver nanoparticles ranges from 20 to 60 nm, and the surface coating agent is citrate.

[0010] Further limitation, the mixed solvent comprises isopropyl alcohol, ethylene glycol, terpineol, and deionized water.

[0011] Further limitation, the mixed solvent comprises 40 to 55 vol% isopropyl alcohol, 10 to 15 vol% ethylene glycol, 0.5 to 2 vol% terpineol, and the balance is deionized water.

[0012] Further limitation, the additive comprises a fluorocarbon surfactant and a leveling agent.

[0013] Further limitation, the content of the leveling agent in the silver nanoparticle ink is 1 to 3 wt%, the content of the fluorocarbon surfactant is 0.1 to 0.2 wt%, and the content of the spherical silver nanoparticles is 35 to 45 wt%.

[0014] Further limitation, the leveling agent is a 10% carboxymethyl cellulose aqueous solution, and the molecular weight of the carboxymethyl cellulose is 66000.

[0015] Further limitation, the silver source is one or a mixture of several of silver acetate, silver tartrate, silver citrate, silver oxalate, and silver carbonate.

[0016] Further limitation, the solvent is one or a mixture of several of methanol, ethanol, isopropyl alcohol, and ethylene glycol.

[0017] Further limitation, the complexing agent is one or a mixture of several of ethylamine, propylamine, ethylenediamine, and propylenediamine.

[0018] Further limitation, the reducing agent is formic acid and / or diethanolamine.

[0019] Further limitation, the molar content ratio of the amine group in the complexing agent to the silver ion in the silver source is 2:1.

[0020] The second purpose of the present application is to provide a preparation method of the above composite ink, which comprises the following steps:

[0021] First, spherical silver nanoparticles are dispersed in a mixed solvent, and after adding an additive, stirring is uniform to obtain silver nanoparticle ink;

[0022] Then, silver source is dispersed in a solvent, and after adding a complexing agent and a reducing agent, stirring is uniform to obtain silver ion ink;

[0023] Finally, the silver nanoparticle ink and the silver ion ink are mixed to obtain a composite ink.

[0024] Further limited, the volume ratio of the silver nanoparticle ink and the silver ion ink is 2:0.05-0.08.

[0025] The third object of the present application is to provide an application of the above composite ink, specifically for aerosol jet printing conformal circuit.

[0026] Further limited, the aerosol jet printing parameters are: atomization voltage 20-47V, carrier gas flow 0-100sccm, sheath gas flow 0-200sccm, carrier gas flow >1.5, printing speed 0.1-40mm / s, substrate temperature 50-150℃, after printing, stored in a constant temperature box at 50-150℃ for 15-60min to obtain a common circuit.

[0027] Beneficial effects:

[0028] (1) The present application provides a composite ink for aerosol jet printing to prepare a conformal circuit, which uses silver nanoparticles and silver ions in combination. Since the solid content of the ink is about 40%, and after being converted into aerosol, the solvent is further evaporated under the action of high-speed sheath gas, the aerosol droplets deposited on the substrate only contain a very small amount of liquid components. By using high-solid-content silver nanoparticle ink to deposit on the substrate, the capillary action between the particles makes the ink containing silver ions fill the gaps between the nanoparticles, and the high-viscosity deposit provides excellent adhesion and conformal performance for various material substrates. Moreover, the silver ions in the liquid components of the ink are rapidly reduced in situ under the combined action of a heated substrate and a reducing agent, forming new silver nanoparticles. As the reduction reaction continues, the generated silver nanoparticles continue to grow and fill the gaps of the original silver nanoparticles, realizing the interconnection between the nanoparticles, thereby improving the conductivity of the circuit. Using the composite ink for aerosol jet printing, the prepared conformal circuit has an electrical conductivity of 22.4μΩ·cm at a post-processing temperature of 100℃. The conformal conductive lines obtained by printing can realize high-density electrical interconnection on a curved substrate, thereby greatly reducing the weight of the equipment.

[0029] (2)The spherical silver nanoparticles used in the application are coated with citrate on the surface, and have hydrophilicity. Meanwhile, the amino complexing agent is used to form a coordination bond with metal ions, thereby reducing the binding force of anions to metal ions and greatly improving the solubility of silver, and reducing the post-treatment temperature.

[0030] (3)The ratio of the silver nanoparticle ink to the silver ion ink is a key parameter in the application. If the content of the silver ion ink is too high, the solid content of the composite ink is low, and the adhesion to the substrate cannot be good, which affects the performance of the conformal printing. If the content of the silver ion ink is too low, only a small amount of silver ions are reduced after the post-treatment, and high conductivity cannot be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A low-temperature post-treatment process schematic diagram of the composite ink provided in the application is shown in the figure.

[0032] In the figure, 1 is the liquid component of the composite ink, 2 is the silver nanoparticle in the composite ink, 3 is the reduced silver atom, 4 is the silver nanoparticle, and 5 is the substrate. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the embodiments of the application.

[0034] In the following description, many specific details are set forth in order to provide a thorough understanding of the application, but the application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the concept of the application, therefore the application is not limited to the specific embodiments disclosed below.

[0035] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or selected from other embodiments.

[0036] The experimental methods used in the following embodiments are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, which can be obtained by commercial channels by those skilled in the art, and the purity of the solid and liquid reagents used is analytical pure.

[0037] Example 1

[0038] The process of preparing the composite ink in this embodiment is as follows:

[0039] (1) Preparation of silver nanoparticle ink;

[0040] First, 1.0 g of spherical silver nanoparticles with an average particle size of 20 nm was weighed, and the spherical silver nanoparticles were coated with a surface coating agent of citrate and had hydrophilicity.

[0041] Then, isopropyl alcohol, ethylene glycol, terpineol, and deionized water were mixed in a volume ratio of 40:15:0.5:44.5 to obtain a mixed solvent.

[0042] Finally, the spherical silver nanoparticles were dispersed in 2 ml of the mixed solvent, 0.25 g of a carboxypropyl methyl cellulose aqueous solution with a mass fraction of 10% and a molecular weight of 66,000, and 3 mg of fluorocarbon surfactant (FS-50) were added, and stirring was performed at 600 r / min for 20 min to obtain silver nanoparticle ink.

[0043] (2) Preparation of silver ion ink

[0044] Silver acetate was selected as the silver source, ethanol was used as the solvent, isopropanolamine was used as the complexing agent, and formic acid was used as the reducing agent.

[0045] Silver acetate 0.5 g was weighed and dispersed in 1.5 ml of ethanol, isopropanolamine 0.9 g and formic acid 0.15 g were added, and stirring was performed at 600 r / min for 30 min. The obtained solution was filtered using a 5 μm needle filter to obtain silver ion ink.

[0046] (3) Preparation of silver nanoparticle / silver ion composite ink

[0047] 0.08 ml of silver ion ink was added to 2 ml of silver nanoparticle ink, stirring was performed at 600 r / min for 30 min and water bath ultrasonic was performed for 20 min to obtain the composite ink.

[0048] The composite ink prepared in this example was used to prepare a conformal circuit in an aerosol jet printing mode, and the specific process was as follows:

[0049] A spiral line was drawn on an arc surface with a radius of curvature of 1.5 cm using CAD software; G-code code for a five-axis machine tool was written according to the drawn spiral circuit, so that the nozzle was always located in the normal direction of the substrate during printing and the relative speed with the substrate surface remained constant.

[0050] The composite ink was loaded into the ink tank and ultrasonic atomization was used, and various printing parameters were adjusted, wherein the atomization voltage was 40 V, the carrier gas flow was 10 sccm, the sheath gas flow was 80 sccm, and the printing speed was 5 mm / s. The curved surface substrate was heated to 100°C. The G-code code was run for printing, and the aerosol beam was deposited on the substrate and in-situ sintering was achieved. After printing, it was stored in a constant temperature box at 100°C for 60 min, and the measured resistivity of the circuit was 22.4 μΩ·cm.

[0051] The printed conformal wire can achieve high-density electrical interconnection on a curved substrate, thereby greatly reducing the weight of equipment.

[0052] The principle of low-temperature post-processing realized by the present application is described as follows:

[0053] As shown in Figure 1 , the process of low-temperature post-processing realized by the composite ink is shown. Since the solid content of the composite ink is about 40%, the solvent will be further evaporated after being atomized into aerosol and subjected to the action of high-speed sheath gas. The aerosol droplets deposited on the substrate only contain a very small amount of liquid components. Due to capillary action, the liquid components 1 of the ink will fill the gaps between the silver nanoparticles 2 in the composite ink. The high-viscosity deposit provides excellent adhesion and conformal performance for various material substrates. The silver ions in the liquid components 1 of the composite ink are rapidly reduced under the combined action of a heated substrate 5 and a reducing agent, forming new silver nanoparticles 4. As the reduction reaction further proceeds, the generated silver nanoparticles 4 continuously grow and fill the gaps of the original silver nanoparticles, realizing the interconnection between the nanoparticles, thereby improving the conductivity of the circuit.

[0054] In addition, isopropanolamine is used as a complexing agent in the present embodiment. The amine group contained therein forms a coordination bond with silver ions, reducing the binding force of acetate ions on silver ions, thereby greatly improving the solubility of silver and reducing the post-processing temperature.

[0055] Example 2

[0056] The process of preparing the composite ink in the present embodiment is as follows:

[0057] (1) Preparation of silver nanoparticle ink;

[0058] First, 1.0 g of spherical silver nanoparticles with an average particle size of 50 nm is weighed. The spherical silver nanoparticles are coated with citrate, which is hydrophilic.

[0059] Then, isopropanol, ethylene glycol, terpineol, and deionized water are mixed in a volume ratio of 40:10:2:48 to obtain a mixed solvent.

[0060] Finally, the spherical silver nanoparticles are dispersed in 2 ml of the mixed solvent, 0.15 g of a carboxypropyl methyl cellulose aqueous solution with a mass fraction of 10% and a molecular weight of 66000, and 3 mg of fluorocarbon surfactant (FS-50) are added. The mixture is stirred at 600 r / min for 40 min to obtain silver nanoparticle ink.

[0061] (2) Preparation of silver ion ink;

[0062] Silver oxalate is selected as the silver source, methanol and ethylene glycol are selected as the solvent, propylene diamine is selected as the complexing agent, and diethanolamine is selected as the reducing agent.

[0063] Take silver oxalate 0.5 g, disperse in 1.2 ml of methanol and 0.6 ml of ethylene glycol mixed solvent, add propylene diamine 0.58 g, diethanolamine 0.25 g and stir at 600 r / min for 40 min. The obtained solution is filtered using a 5 μm needle filter to obtain a silver ion ink.

[0064] (3) Preparation of silver nanoparticle / silver ion composite ink

[0065] Add 0.05 ml of silver ion ink to 2 ml of silver nanoparticle ink, stir at 600 r / min for 30 min and water bath ultrasonic for 30 min to obtain a composite ink.

[0066] The composite ink prepared in this example is used to prepare a conformal temperature sensor by aerosol jet printing, and the specific process is as follows:

[0067] Draw a serpentine line on an arc surface with a radius of curvature of 35 cm using CAD software; according to the prepared common circuit, write the G-code code of the five-axis machine tool, so that the nozzle is always located in the normal direction of the substrate and the relative speed with the substrate surface remains constant during printing; adjust the printing parameters, among which the atomization voltage is 47 V, the carrier gas flow is 10 sccm, the sheath gas flow is 120 sccm, and the printing speed is 10 mm / s. Set the substrate temperature to 120℃. Run the G-code code for printing, and after printing, store in a constant temperature oven at 150℃ for 60 min. The temperature monitoring range of the prepared temperature sensor is 25-200℃, and the resistance temperature coefficient is >0.002.

[0068] Comparative Example 1

[0069] The difference between this comparative example and Example 1 is that no silver ion ink is added, only silver nanoparticle ink is used, and the rest of the process steps and parameter settings are the same as Example 1.

[0070] After printing the composite ink, store it in a constant temperature oven at 100℃, 150℃, and 200℃ for 60 min, respectively. The resistivity of the measured circuit is 1.2×10 5 μΩ·cm, 76.7 μΩ·cm, and 14.1 μΩ·cm, respectively.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Example 1 is that no complexing agent is added during the preparation of the silver ion ink, and the rest of the process steps and parameter settings are the same as Example 1.

[0073] After printing the composite ink, store it in a constant temperature oven at 100℃ for 60 min, and the resistivity of the measured circuit is 237.2 μΩ·cm.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that no reducing agent is added during the silver ion ink configuration process, and the remaining process steps and parameter settings are the same as those of Example 1.

[0076] After the composite ink printing is completed, the sample is stored in a constant temperature box at 100°C for 60 min, and the resistivity of the measured circuit is 5.6 x 10 3 μΩ·cm.

[0077] Although the present application has been disclosed in the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, and therefore the protection scope of the present application should be defined by the claims.

Claims

1. A composite ink for aerosol inkjet printing conformal circuits, characterized in that, The composite ink is made by mixing silver nanoparticle ink and silver ion ink; the silver nanoparticle ink includes spherical silver nanoparticles, additives and mixed solvents; the silver ion ink includes a silver source, solvent, complexing agent and reducing agent; The volume ratio of silver nanoparticle ink to silver ion ink is 2:0.05~0.08; The spherical silver nanoparticles have a particle size range of 20~60 nm, and the surface coating agent is citrate. Additives include fluorocarbon surfactants and leveling agents; mixed solvents include isopropanol, ethylene glycol, terpineol, and deionized water; The silver nanoparticle ink contains 1-3 wt% leveling agent, 0.1-0.2 wt% fluorocarbon surfactant, and 35-45 wt% spherical silver nanoparticles.

2. The composite ink according to claim 1, characterized in that, The mixed solvent comprises, by volume percentage, 40-55 vol% isopropanol, 10-15 vol% ethylene glycol, 0.5-2 vol% terpineol, with the balance being deionized water.

3. The composite ink according to claim 1, characterized in that, The leveling agent is a 10% (w / w) aqueous solution of carboxypropyl methylcellulose, which has a molecular weight of 66,000.

4. The composite ink according to claim 1, characterized in that, The silver source is one or a mixture of silver acetate, silver citrate, silver oxalate, and silver carbonate; the solvent is one or a mixture of methanol, ethanol, isopropanol, and ethylene glycol; the complexing agent is one or a mixture of ethylamine, propylamine, ethylenediamine, and propylenediamine; and the reducing agent is formic acid and / or diethanolamine.

5. The composite ink according to claim 1 or 4, characterized in that, The molar ratio of amino groups in the complexing agent to the molar ratio of silver ions in the silver source is 2:

1.

6. A method for preparing the composite ink according to any one of claims 1 to 5, characterized in that, First, spherical silver nanoparticles are dispersed in a mixed solvent, and after adding additives, the mixture is stirred evenly to obtain silver nanoparticle ink. Then, a silver source is dispersed in a solvent, and after adding a complexing agent and a reducing agent, the mixture is stirred evenly to obtain silver ion ink. Finally, the silver nanoparticle ink and the silver ion ink are mixed to obtain a composite ink.

7. An application of the composite ink according to any one of claims 1 to 5, characterized in that, Used for conformal circuits in aerosol printing.

8. The application of the composite ink according to claim 7, characterized in that, The aerosol printing parameters are: atomization voltage 20-47V, carrier gas flow rate 0-100sccm, sheath gas flow rate 0-200sccm, printing speed 0.1-40mm / s, substrate temperature 50-150℃, and after printing, the substrate is kept in a constant temperature chamber at 50-150℃ for 15-60 minutes to obtain the common circuit.

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