Conductive copper ink for printed circuit and preparation method thereof

Abstract

The invention relates to the technical field of printed electronic materials, in particular to conductive copper ink for a printed circuit and a preparation method of the conductive copper ink. The conductive mica powder-graphene composite material comprises conductive mica powder, a nano-copper-graphene filler, flaky copper powder, spherical copper powder, an organic carrier, a dispersing agent, a coupling agent, an antioxidant and an auxiliary agent, a layer-point composite conductive structure is constructed through conductive mica powder and nano-copper-graphene filler, a close packing system is formed by combining particle size grading of copper powder with different morphologies, and the conductivity is guaranteed; by means of a chemical bonding interface formed by the coupling agent, the copper powder and the organic carrier, the integrity of the coating is enhanced, and stress cracking during welding is reduced; microencapsulated rosin in the auxiliary agent promotes wetting and spreading of the welding flux, titanate modified nano titanium dioxide constructs a three-dimensional cross-linked network to improve the bending resistance and thermal shock resistance of the coating, the falling phenomenon of components after welding is reduced, and the stability of the conductive copper ink in actual printed circuit production is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed electronic materials, in particular to a conductive copper ink for printed circuits and a preparation method thereof. BACKGROUND

[0002] In the field of printed circuits, using conductive copper ink for circuit printing belongs to additive manufacturing technology, which can replace the subtractive manufacturing process of traditional copper-clad plate etching, has wide application potential in the field of electronic manufacturing due to the reduction of material waste and the simplification of production process, and the conductive ink containing mica functional filler is concerned due to its performance characteristics.

[0003] At present, most of the conductive copper inks on the market focus on high conductivity, and in the prior art, the conductivity is improved by optimizing the particle size and morphology of copper powder, adding nano conductive particles or surface modification, and some products can achieve good conductivity indicators, but there are still deficiencies in the bonding strength after the welding of components: on the one hand, too much high-conductivity filler is used in some ink formulations to enhance conductivity, which increases the brittleness of the cured coating and causes cracking due to stress concentration during welding; on the other hand, the interfacial bonding force between the ink and the solder is weak, and the thrust after the welding of components is insufficient, which easily causes the components to fall off, thereby reducing the reliability of the conductive copper ink in the actual production of printed circuits.

[0004] Therefore, there is an urgent need for a conductive copper ink for printed circuits and a preparation method thereof. SUMMARY

[0005] The present application aims to provide a conductive copper ink for printed circuits and a preparation method thereof to solve the problems raised in the background.

[0006] To achieve the above-mentioned purpose, the present application provides a conductive copper ink for printed circuits, which comprises the following raw materials:

[0007] 20-30 parts of conductive mica powder, 15-25 parts of nano copper-graphene filler, 10-15 parts of flaky copper powder (particle size 5-15 μm), 5-10 parts of spherical copper powder (particle size 1-3 μm), 25-40 parts of organic carrier, 1-3 parts of dispersant, 0.5-2 parts of coupling agent, 0.5-2 parts of antioxidant and 1-3 parts of auxiliary agent; wherein the conductive mica powder and the nano copper-graphene filler form a "layer-point" composite conductive structure to improve the continuity and stability of the conductive network, the flaky copper powder and the spherical copper powder form a close-packed structure through particle size grading to reduce resistance and enhance coating density, the coupling agent forms a chemical bonding interface with the copper powder and the organic carrier to improve the bonding force between the coating and the solder, and the antioxidant forms a passivation layer on the surface of the copper powder to inhibit oxidation and maintain long-term conductive stability.

[0008] Preferably, the organic vehicle adopts a complex system of resin matrix and solvent, wherein: the mass ratio of resin matrix to solvent ranges from 1:2 to 1:6; the resin matrix is selected from one or more of ethyl cellulose, acrylic resin, and epoxy resin, for giving the cured coating of the ink bonding strength and mechanical toughness; the solvent is selected from one or more of terpineol, diethylene glycol butyl ether, propylene glycol methyl ether acetate, and cyclohexanone, for adjusting the rheological properties of the ink to adapt to the printing process, and promoting the close packing of the conductive filler by gradual evaporation during the curing process; the dispersant is selected from one of fatty acid salt, polycarboxylate, and alkyl amine dispersant, and the polycarboxylate dispersant is preferred, which has better dispersing effect on the nano copper-graphene filler and copper powder, and effectively prevents particle agglomeration; the coupling agent is selected from one of silane coupling agent, titanate coupling agent, and aluminate coupling agent, and the silane coupling agent is preferred, which can form stable chemical bonds with the hydroxyl group on the surface of the copper powder and the resin in the organic vehicle at both ends of the molecule, for improving the interfacial adhesion between the coating and the solder; the antioxidant is selected from compounds containing phosphorus elements, such as monophosphate ester, monohypophosphorous acid ester, polyphosphate ester, or polyphosphorous acid ester, and the monophosphate ester is preferred, which can be adsorbed on the surface of the copper powder to form a molecular film layer containing phosphorus compounds, effectively blocking the oxidation and corrosion of the copper powder by water and various substances (such as oxygen); the auxiliary agent adopts a complex system of microencapsulated rosin (capsule particle size 1-5 μm) and titanate modified nano titanium dioxide (particle size 20-80 nm), wherein: the microencapsulated rosin releases rosin components at high welding temperature to remove the oxide layer on the surface of the copper powder and promote the wetting and spreading of the solder, thereby enhancing the interfacial bonding between the coating and the solder; the titanate modified nano titanium dioxide forms a three-dimensional crosslinked network with the resin and conductive mica powder through surface modification groups, thereby improving the bending resistance and thermal shock resistance of the coating, reducing the stress damage during welding, and significantly improving the welding thrust of the component while ensuring the storage stability and printing performance of the ink.

[0009] In addition, the coupling agent is secondary coordinated with the conductive mica powder and the nano copper-graphene filler, and the different functional groups at both ends of the coupling agent molecule are chemically combined with the hydroxyl group on the surface of the conductive mica powder and the active sites on the surface of the nano copper-graphene filler, respectively, to form a stable connection across the phase interface, which not only promotes the uniform dispersion of the conductive phase in the organic vehicle to reduce the breakpoints of the conductive path, but also enhances the interfacial bonding strength between the conductive components, thereby synergistically improving the overall mechanical properties of the coating after the ink is cured and the anti-falling ability during welding; the mechanism is that the siloxane group of the coupling agent is dehydrated and condensed with the hydroxyl group on the surface of the conductive mica powder, and the amino or epoxy group at the other end forms a hydrogen bond or a coordination bond with the carboxyl group or the hydroxyl group on the surface of the nano copper-graphene, thereby constructing a stable chemical bridging interface.

[0010] Secondly, according to the application, the ink is prepared by mixing the conductive filler, the organic vehicle, and the dispersant, and then adding the coupling agent and the antioxidant, and the auxiliary agent is added at the end of the preparation process. Figure 1As shown, the present application provides a preparation method of conductive copper ink for printed circuit, comprising the following steps:

[0011] S1, preparing an organic carrier: placing a resin matrix and a solvent into a container, using a stirrer to stir at a stirring speed of 400-500 r / min and a temperature of 25-35℃ for 40-60 min, so that the resin matrix is fully dissolved and forms a uniform system with the solvent, and an organic carrier with certain viscosity and rheological properties is formed;

[0012] S2, mixing conductive fillers: adding conductive mica powder and nano copper-graphene fillers into the organic carrier, using a high-speed disperser to stir at a speed of 1000-1200 r / min for 20-30 min, so that the two fillers are uniformly dispersed under the action of shear force and initially form a "layer-point" composite conductive structure; then, adding flaky copper powder and spherical copper powder, and continuing to stir at a speed of 600-800 r / min for 15-20 min by using a high-speed disperser, so that copper powders with different morphologies are filled into the interlayer gap of mica sheets through particle size grading, forming a close-packed structure for reducing resistance and enhancing coating density, and finally obtaining a mixed slurry which is uniformly dispersed and has an initial conductive network structure;

[0013] S3, adding dispersants and coupling agents: adding dispersants into the mixed slurry, and stirring at a speed of 500-800 r / min for 15-20 min by using a planetary stirrer, so that the dispersants are uniformly coated on the surface of the nano copper-graphene fillers and copper powder to form a steric hindrance layer; then adding coupling agents, and switching to ultrasonic dispersion equipment to process for 10-15 min at a frequency of 20-40 kHz and a power of 300-500 W, if the coupling agent is a silane coupling agent, the two ends of the molecule form stable chemical bonds with the surface hydroxyl group of the copper powder and the resin in the organic carrier, and simultaneously occurs secondary synergy with the conductive mica powder and the nano copper-graphene filler, forming a stable connection across the phase interface through functional group reaction, promoting the uniform dispersion of the conductive phase and enhancing the interface bonding strength, and forming a premixed slurry which is uniformly dispersed and has an initial strengthening of the interface bonding of each conductive component;

[0014] S4, adding antioxidants and additives: adding antioxidants into the premixed slurry, and stirring at a speed of 400-600 r / min for 20-30 min by using a planetary stirrer, so that the antioxidants are uniformly dispersed and adsorbed on the surface of the copper powder to form a molecular film layer of phosphorus compounds, effectively blocking the oxidation and corrosion of water, oxygen and other substances on the copper powder, inhibiting the oxidation of the copper powder to maintain long-term conductive stability, and then adding additives, and processing for 15-20 min at a frequency of 25-35 kHz and a power of 200-400 W by using ultrasonic dispersion equipment, so that the microencapsulated rosin and titanate modified nano titanium dioxide in the additives form a uniformly dispersed complex system, and a preliminarily mixed ink slurry is obtained;

[0015] S5, grinding refinement: the ink slurry is transferred to a three-roll grinding machine, under the conditions that the front roller speed is 20-30 r / min, the middle roller speed is 60-90 r / min, the rear roller speed is 180-270 r / min, the roller gap is controlled to be 5-15 μm, the grinding pressure is 0.3-0.8 MPa, the slurry is ground for 4-6 cycles to obtain a uniform slurry with a fineness of ≤20 μm (about 800 mesh), the shear force and extrusion force generated by the gradient speed difference in this process promote the directional arrangement of the flaky copper powder along the grinding direction and reduce the size of the agglomerates, at the same time, the preliminary tendency of the ordered stacking of the flaky structure of the conductive mica powder in the slurry is formed, the nano copper-graphene filler is uniformly embedded in the interlayer gap between the copper powder and the mica flake, which not only ensures the uniform dispersion of the conductive components to reduce the breakpoint of the conductive path, but also improves the leveling property of the ink and the line edge definition during printing by optimizing the directional arrangement of the particle morphology;

[0016] S6, degassing treatment: the ground ink slurry is placed in a vacuum degassing device, under the conditions that the vacuum degree is -0.08--0.1 MPa, the temperature is 30-40℃, the stirring speed is 50-100 r / min, the treatment is continuously carried out for 20-30 min, through the combination of negative pressure environment and gentle stirring, the small bubbles wrapped inside the slurry are aggregated and escaped, at the same time, high temperature is avoided to cause premature evaporation of the solvent or curing of the resin, finally, the bubble-free conductive copper ink is formed.

[0017] In the application, the conductive mica powder is first combined with the nano copper-graphene filler and copper powder with different morphologies to build a multi-dimensional conductive network, which not only ensures the conductive performance of the ink after curing and meets the basic conductive requirements of the printed circuit, but also promotes the interface bonding of the conductive components and the organic carrier through the coupling agent, and cooperates with the synergistic effect of the microencapsulated rosin and modified nano titanium dioxide in the additive, such as the microencapsulated rosin assisting the solder spread during welding, the nano titanium dioxide enhancing the mechanical stability of the coating, which can effectively improve the bonding strength of the components after welding.

[0018] Compared with the prior art, the beneficial effects of the application are:

[0019] 1. The conductive copper ink for printed circuit and its preparation method, by constructing a "layer-point" composite conductive structure with conductive mica powder and nano copper-graphene filler, combining the particle size grading of flaky and spherical copper powder, forming a close-packed system, while ensuring the conductivity, the chemical bonding interface formed by the coupling agent and copper powder, organic carrier enhances the integrity of the coating, effectively improves the coating brittleness problem caused by excessive pursuit of conductivity in the prior art, reduces the cracking phenomenon caused by stress concentration during welding; at the same time, the composition released by the microencapsulated rosin in the auxiliary agent promotes the wetting and spreading of the solder during welding, the three-dimensional crosslinked network constructed by the titanate modified nano titanium dioxide improves the bending resistance and thermal shock resistance of the coating, effectively improves the coating brittleness and weak solder adhesion caused by excessive emphasis on conductivity in the prior art, reduces the falling phenomenon after component welding, thereby improving the stability of the conductive copper ink in the actual production of printed circuit. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The preparation method flow chart of the conductive copper ink of the present application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] Example 1

[0023] Preparation of organic vehicle: ethyl cellulose 8 parts, acrylic resin 4 parts, and terpineol 18 parts, propylene glycol methyl ether acetate 4 parts were put into a container, and the resin was fully dissolved by stirring at 450 r / min and 30°C for 50 min to form a uniform organic vehicle; mixing of conductive filler and subsequent processing: 25 parts of conductive mica powder and 20 parts of nano copper-graphene filler were added to the organic vehicle, and stirred at 1100 r / min for 25 min by a high-speed dispersion machine, then 12 parts of flaky copper powder and 7 parts of spherical copper powder were added, and stirred at 700 r / min for 18 min; 2 parts of polycarboxylate dispersant were added, and stirred at 650 r / min for 18 min by a planetary mixer, then 1 part of silane coupling agent was added, and treated at 30 kHz and 400 W for 12 min by an ultrasonic dispersion device; 0.7 parts of monobasic phosphate was added, and stirred at 500 r / min for 25 min by a planetary mixer, then 2 parts of microencapsulated rosin (particle size 1-5 μm) and titanate modified nano titanium dioxide (particle size 20-80 nm) complexing agent were added, and treated at 30 kHz and 300 W for 18 min by an ultrasonic dispersion device; the slurry was transferred into a three-roll mill, and ground for 5 times under the conditions of 25 r / min for the front roll, 75 r / min for the middle roll, 225 r / min for the rear roll, 10 μm for the roll gap, 0.5 MPa for the pressure, then put into a vacuum degassing device, and stirred at 75 r / min for 25 min under the conditions of -0.09 MPa and 35°C, to obtain a conductive copper ink.

[0024] Example 2

[0025] Preparation of organic vehicle: take epoxy resin 12 parts and diethylene glycol butyl ether 28 parts into a container, and stir at 500 r / min and 35℃ for 40 min with a stirrer to form a uniform organic vehicle; mixing of conductive filler and subsequent treatment: add conductive mica powder 30 parts and nano copper-graphene filler 25 parts into the organic vehicle, and stir at 1200 r / min for 20 min with a high-speed dispersion machine, then add flaky copper powder 15 parts and spherical copper powder 10 parts, and continue to stir at 800 r / min for 15 min; add polycarboxylate dispersant 3 parts, and stir at 800 r / min for 15 min with a planetary stirrer, then add titanate coupling agent 2 parts, and treat at 40 kHz and 500 W for 10 min with an ultrasonic dispersion device; add polybasic ester of phosphorous acid 2 parts, and stir at 600 r / min for 20 min with a planetary stirrer, then add a compound of microencapsulated rosin (particle size 1-5 μm) and titanate modified nano titanium dioxide (particle size 20-80 nm) 3 parts, and treat at 35 kHz and 400 W for 15 min with an ultrasonic dispersion device; transfer the slurry into a three-roll grinding machine, and grind 4 times under the conditions of front roll 30 r / min, middle roll 90 r / min, back roll 270 r / min, roll gap 15 μm, and pressure 0.8 MPa, then put it into a vacuum degassing device, and stir at 100 r / min for 20 min under the conditions of -0.1 MPa and 40℃ to obtain the conductive copper ink.

[0026] Example 3

[0027] Preparation of organic vehicle: ethyl cellulose 4 parts, epoxy resin 4 parts and cyclohexanone 20 parts were put into a container, and stirred at 420 r / min and 28 °C for 55 min by a stirrer to form a uniform organic vehicle; mixing of conductive filler and subsequent treatment: conductive mica powder 22 parts and nano copper-graphene filler 18 parts were added into the organic vehicle, and stirred at 1050 r / min for 28 min by a high-speed dispersion machine, then flaky copper powder 11 parts and spherical copper powder 6 parts were added, and stirred at 650 r / min for 19 min, fatty acid salt dispersant 1.5 parts was added, and stirred at 550 r / min for 19 min by a planetary stirrer, then aluminic acid ester coupling agent 0.8 parts was added, and treated at 25 kHz and 350 W for 14 min by an ultrasonic dispersion device, monobasic ester of hypophosphorous acid 0.8 parts was added, and stirred at 450 r / min for 28 min by a planetary stirrer, then microencapsulated rosin (particle size 1-5 μm) and titanate modified nano titanium dioxide (particle size 20-80 nm) compound additives 1.5 parts were added, and treated at 28 kHz and 250 W for 19 min by an ultrasonic dispersion device; the slurry was transferred into a three-roll grinding machine, and ground for 6 times under the conditions of front roller 22 r / min, middle roller 65 r / min, rear roller 190 r / min, roller gap 8 μm, pressure 0.4 MPa, then put into a vacuum degassing device, and stirred at 60 r / min for 28 min under the conditions of -0.085 MPa and 32 °C, to obtain the conductive copper ink.

[0028] Example 4

[0029] Preparation of organic carrier: take 5 parts of acrylic resin, 3 parts of epoxy resin, 14 parts of terpineol, 14 parts of propylene glycol methyl ether acetate into a container, and stir at 480 r / min and 32℃ for 45 min with a stirrer to form a uniform organic carrier; mixing of conductive filler and subsequent treatment: add 28 parts of conductive mica powder and 22 parts of nano copper-graphene filler to the organic carrier, stir at 1150 r / min for 22 min with a high-speed dispersing machine, then add 14 parts of flaky copper powder and 9 parts of spherical copper powder, continue to stir at 750 r / min for 16 min, add 2.5 parts of alkyl amine dispersant, stir at 750 r / min for 16 min with a planetary stirrer, then add 1.5 parts of titanate coupling agent, treat at 35 kHz and 450 W for 11 min with an ultrasonic dispersion device; add 1.5 parts of phosphoric acid polybasic ester, stir at 550 r / min for 22 min with a planetary stirrer, then add 2.5 parts of microencapsulated rosin (particle size 1-5 μm) and titanate modified nano titanium dioxide (particle size 20-80 nm) complexing agent, treat at 32 kHz and 350 W for 16 min with an ultrasonic dispersion device; transfer the slurry into a three-roll mill, mill for 4 times under the conditions of front roll 28 r / min, middle roll 85 r / min, rear roll 250 r / min, roll gap 12 μm, and pressure 0.7 MPa, then put it into a vacuum degassing device, stir at 90 r / min for 22 min under the conditions of -0.095 MPa and 38℃, and obtain the conductive copper ink.

[0030] Table 1: Amount of each raw material in Examples 1-4

[0031] Example 1 Example 2 Example 3 Example 4 Organic vehicle (parts) 34 40 28 36 Conductive mica powder (parts) 25 30 22 28 Nano copper-graphene filler (parts) 20 25 18 22 Flaky copper powder (parts) 12 15 11 14 Spherical copper powder (parts) 7 10 6 9 Dispersant (parts) 2 3 1.5 2.5 Coupling agent (parts) 1 2 0.8 1.5 Antioxidant (parts) 0.7 2 1.8 1.5 Auxiliary agent (parts) 2 3 1.5 2.5

[0032] In order to verify that the conductive copper ink prepared by the examples of the present application has good conductive performance and component welding bonding performance, the conductive copper ink provided by the examples of the present application is described by the following test examples.

[0033] Test Example

[0034] The purpose of this test group is to explore the influence of different component proportions on the conductive copper ink, and to detect the conductive performance, component welding bonding strength, coating mechanical toughness, and resistivity change rate under high temperature and high humidity environment of the conductive copper ink of the present application.

[0035] Test objective: test group A, test group B, test group C and test group D respectively adopt the component proportions of the conductive copper ink provided by examples 1-4; control example adopts control group A, control group B, control group C, control group D, control group E and control group F, wherein:

[0036] Control group A

[0037] Preparation of organic carrier, take epoxy resin 10 parts and diethylene glycol butyl ether 30 parts into the container, stirring with stirrer at 450 r / min, 30 ℃ conditions for 50 min; to the organic carrier added nano copper powder 30 parts, flaky copper powder 15 parts, with high speed dispersion machine at 1200 r / min stirring 20 min; add polycarboxylate dispersant 2 parts, with planetary mixer at 600 r / min stirring 15 min; the slurry into three roll mill, in front of the roller 25 r / min, middle roller 75 r / min, rear roller 225 r / min, roller gap 10 μm, pressure 0.5 MPa conditions for 5 times, and then put into vacuum degassing device, at -0.09 MPa, 35 ℃ conditions with 75 r / min stirring 25 min, get conductive copper ink.

[0038] Control group B

[0039] First by physical method to prepare nano copper particles, using surfactant and coating agent to control the size of the particle morphology, then separation and purification to remove the excess protective agent, dry storage for future use; the prepared nano copper particles 35 parts dispersed into 30 parts of mixed solvent of terpineol and 15 parts of propylene glycol methyl ether acetate, using stirrer at 500 r / min, 30 ℃ conditions for 40 min, mixed evenly to get conductive copper ink.

[0040] Control group C

[0041] In the two stirring reaction vessels were added solvent, so that copper acetate dissolved in one of the reaction vessel of the solvent prepared copper salt solution, so that sodium borohydride dissolved in the other reaction vessel of the solvent prepared reducing agent solution; copper salt solution and reducing agent solution were cooled to 5 ℃, then stirring mixed evenly in a reaction vessel, prepared conductive ink; wherein, copper acetate in copper salt solution is 20 parts, the solvent is 25 parts of terpineol and 15 parts of cyclohexanone, sodium borohydride in reducing agent solution is 5 parts, the solvent is 20 parts of diethylene glycol butyl ether and 15 parts of propylene glycol methyl ether acetate.

[0042] Control group D

[0043] Preparation of organic carrier, take ethyl cellulose 6 parts, acrylic resin 6 parts and terpineol 18 parts, propylene glycol methyl ether acetate 7 parts into the container, stirring with stirrer at 480 r / min, 32 ℃ for 45 min; add conductive mica powder 25 parts, nano copper-graphene filler 20 parts to the organic carrier, stir with high-speed disperser at 1100 r / min for 25 min, then add flaky copper powder 12 parts, spherical copper powder 7 parts, continue to stir at 700 r / min for 18 min; add polycarboxylate dispersant 2 parts, stir with planetary mixer at 650 r / min for 18 min; add monobasic phosphate 1 part, stir with planetary mixer at 500 r / min for 25 min; transfer the slurry into a three-roll mill, grind twice under the conditions of front roller 28 r / min, middle roller 85 r / min, rear roller 250 r / min, roller gap 12 μm, pressure 0.7 MPa, then put into a vacuum degassing device, stir at 90 r / min for 22 min under the conditions of -0.095 MPa, 38 ℃, to obtain conductive copper ink.

[0044] Control group E

[0045] Preparation of organic carrier, take epoxy resin 12 parts and diethylene glycol butyl ether 28 parts into the container, stirring with stirrer at 500 r / min, 35 ℃ for 40 min; add nano copper-graphene filler 30 parts, flaky copper powder 15 parts, spherical copper powder 10 parts to the organic carrier, stir with high-speed disperser at 1200 r / min for 20 min; add polycarboxylate dispersant 3 parts, stir with planetary mixer at 800 r / min for 15 min, then add titanate coupling agent 2 parts, treat with ultrasonic dispersion equipment under the conditions of 40 kHz, 500 W for 10 min; add polybasic phosphite 2 parts, stir with planetary mixer at 600 r / min for 20 min, then add microencapsulated rosin and titanate modified nano titanium dioxide complexing agent 3 parts, treat with ultrasonic dispersion equipment under the conditions of 35 kHz, 400 W for 15 min; transfer the slurry into a three-roll mill, grind four times under the conditions of front roller 30 r / min, middle roller 90 r / min, rear roller 270 r / min, roller gap 15 μm, pressure 0.8 MPa, then put into a vacuum degassing device, stir at 100 r / min for 20 min under the conditions of -0.1 MPa, 40 ℃, to obtain conductive copper ink.

[0046] Control group F

[0047] Preparation of organic carrier, ethyl cellulose 5 parts, epoxy resin 5 parts and cyclohexanone 30 parts are put into a container, stirred at 420 r / min, 28℃ for 55 min by a stirrer; conductive mica powder 28 parts, flaky copper powder 14 parts, spherical copper powder 9 parts are added to the organic carrier, stirred at 1050 r / min for 28 min by a high-speed dispersing machine. Add 1.5 parts of fatty acid salt dispersant, stir at 550 r / min for 19 min by a planetary stirrer, then add 0.8 parts of aluminic acid ester coupling agent, treat at 25 kHz, 350 W for 14 min by an ultrasonic dispersion device; add 0.8 parts of monobasic ester of hypophosphorous acid, stir at 450 r / min for 28 min by a planetary stirrer, then add 1.5 parts of microencapsulated rosin and titanate modified nano titanium dioxide complexing agent, treat at 28 kHz, 250 W for 19 min by an ultrasonic dispersion device; the slurry is transferred into a three-roll mill, ground for 7 times at 22 r / min, 65 r / min, 190 r / min of front roll, middle roll and rear roll respectively, 8 μm of roll gap, 0.4 MPa of pressure, then put into a vacuum degassing device, stirred at 60 r / min for 28 min at -0.085 MPa, 32℃, to obtain the conductive copper ink.

[0048] Test method: according to the conductive performance, component device welding bonding strength, coating mechanical toughness and resistivity change rate under high temperature and high humidity environment of the conductive copper ink of the application, tests are carried out respectively, and the specific test method is as follows:

[0049] Conductive performance: the volume resistivity of the coating after curing is tested by four-probe method, the conductive copper ink is coated on the PET substrate (thickness 50 μm) by screen printing (mesh 300 mesh), cured at 180℃ for 30 min to form a rectangular coating of 10 mm×50 mm×50 μm, five test points are uniformly selected on the surface of the coating by using four-probe resistivity tester (probe distance 1 mm), a constant current (1 mA) is applied and the voltage value is recorded, the volume resistivity is calculated according to the formula: ρ=(π×d×V) / (2×I); wherein, ρ is the volume resistivity, unit Ω·cm; d is the probe distance, unit cm; V is the average voltage value, unit V; I is the current value, unit A, and the final result is the average value of the five test points;

[0050] Solder joint strength: The solder joint strength was evaluated by push test. The conductive copper ink was printed on FR-4 substrate to form a 1 mm diameter circular pad (curing condition 180℃ / 30min), and 0402 size (1.0mm×0.5mm) chip resistor was soldered by reflow soldering process (peak temperature 260℃, holding time 10s) using SAC305 lead-free solder (tin 96.5%, silver 3%, copper 0.5%). The push-pull force gauge (accuracy 0.01N) was used to push the resistor side at a speed of 0.5mm / s along the direction parallel to the substrate, and the maximum push force value at the moment of the resistor falling off was recorded. Ten pads of each sample were tested, and the average value was taken as the solder joint strength (unit N);

[0051] Mechanical flexibility of coating: The mechanical flexibility of coating was evaluated by bending test. The ink was printed on PI substrate (thickness 25μm) to form a 10mm wide coating (curing condition 180℃ / 30min), and 180° reciprocating bending test was performed using cylindrical shaft bender (shaft diameter 1mm) at a bending speed of 30 times / min. The resistivity change of the coating was tested using four-probe method after 100 times of bending, and the bending number at which the coating appeared cracks or resistivity increased by 100% (compared with the initial value) was recorded. The number was taken as the evaluation index of the mechanical flexibility of the coating. Each sample was tested for 3 times, and the average value was taken.

[0052] Resistivity change rate under high temperature and high humidity environment: The accelerated aging test was performed using constant temperature and humidity chamber. The cured coating sample (same as the specification for conductive performance test) was placed in high temperature and high humidity environment (temperature 85℃, relative humidity 85%) for continuous 500h, and the sample was taken out at 0h, 100h, 200h, 300h, 400h and 500h, dried at 25℃ for 1h, and then the volume resistivity was tested. The resistivity change rate was calculated according to the formula: Δρ%=(ρ t -ρ0) / ρ0×100%, wherein ρ t was the resistivity at time t, and ρ0was the initial resistivity. The change rate at 500h was taken as the evaluation index of long-term stability.

[0053] The specific detection indexes are shown in Table 2.

[0054] Table 2: Detection indexes of each sample

[0055]

[0056]

[0057] According to Table 2, the summary of the above comparative data is as follows:

[0058] For conductive performance, the volume resistivity of test groups A-D was in the range of 7.6×10 -4 -9.1×10-4 Ω·cm range, lower than the control group A (1.5 x 10 -3 Ω·cm), control group C (2.1 x 10 -3 Ω·cm) and control group D (1.2 x 10 -3 Ω·cm) without the addition of coupling agents and synergistic treatment of additives, and control group E (8.1 x 10 -4 Ω·cm) containing only nano-copper-graphene filler, indicating that the synergistic effect of the "layer-point" composite conductive structure and the particle size grading of copper powder not only ensures high conductivity, but also solves the problem of insufficient conductivity stability of single conductive filler system.

[0059] For the welding joint strength of components, the welding joint strength of test groups A-D is 1.78-1.92N, which is higher than that of control group A (0.92N), control group B (0.75N), control group C (0.88N) without the addition of coupling agents and microencapsulated rosin additives, and better than control group E (1.32N) lacking of conductive mica powder to enhance the interface bonding and control group F (1.18N) lacking of nano-copper-graphene filler, indicating that the chemical bonding interface constructed by the coupling agent and the solder wetting promotion effect of the rosin component in the additive improve the interface bonding force between the coating and the solder, and solve the core problem of insufficient welding thrust in the prior art.

[0060] For the mechanical toughness of the coating, the bending times of test groups A-D reach 1150-1300 times, which is much higher than that of control group A (500 times), control group B (300 times), control group C (450 times), and better than control group D (700 times) without three-roll mill optimization dispersion and control group E (650 times) and control group F (600 times) lacking of three-dimensional cross-linked network of titanate modified nano-titanium dioxide, indicating that the synergistic effect of the flaky structure of conductive mica powder and the cross-linked network constructed by nano-titanium dioxide in the additive improves the toughness of the coating, and effectively improves the bending failure problem of traditional high-conductive ink due to its brittleness.

[0061] For the resistivity change rate under high temperature and high humidity environment, the resistivity change rate of test groups A-D after 500h is 11.8%-13.2%, which is lower than that of control group A (35.6%), control group B (42.3%), control group C (38.7%) and control group D (28.9%) without the addition of phosphorus-containing antioxidant, indicating that the passivation layer formed on the surface of copper powder by phosphoric acid ester antioxidant, combined with the physical barrier effect of conductive mica powder, inhibits the oxidation and corrosion of copper powder, and ensures the long-term conductivity stability.

[0062] In summary, the application ensures good conductive performance through the multi-dimensional conductive network constructed by the conductive mica powder and the nano copper-graphene filler, improves the component and device welding bonding strength through the synergistic effect of the coupling agent and the additive, enhances the coating mechanical toughness by using the conductive mica powder and the modified nano titanium dioxide, and guarantees the stability in high temperature and high humidity environment through the cooperation of the phosphorus-containing antioxidant and the conductive mica powder, so that the conductive performance, welding reliability, mechanical toughness and long-term stability are synergistically improved.

[0063] The above shows and describes the basic principles, main features and advantages of the application. Those skilled in the art should understand that the application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only preferred examples of the application and are not intended to limit the application. Without departing from the spirit and scope of the application, various changes and improvements can be made to the application, and these changes and improvements all fall within the scope of the claimed application. The scope of protection of the application is defined by the appended claims and their equivalents.

Claims

1. A method for the preparation of a conductive copper ink for printed circuits, characterized in that, The method comprises the following steps: S1, the resin matrix and solvent are put into a container, and the stirrer is used to stir, so that the resin matrix is fully dissolved and forms a uniform system with the solvent to form an organic carrier; S2, the conductive mica powder and nano copper-graphene filler are added to the organic carrier, and a high-speed dispersing machine is used to stir, so that the two fillers are uniformly dispersed and initially form a "layer-point" composite conductive structure under the action of shear force; then, the flaky copper powder and spherical copper powder are added and continue to be stirred to obtain a mixed slurry which is uniformly dispersed and has an initial conductive network structure; S3, the dispersant is added to the mixed slurry, and a planetary stirrer is used to stir, so that the dispersant is uniformly coated on the surface of the nano copper-graphene filler and the copper powder to form a steric hindrance layer; then, the coupling agent is added, and an ultrasonic dispersion device is used for treatment to form a premixed slurry; S4, the antioxidant is added to the premixed slurry, and a planetary stirrer is used to stir, so that the antioxidant is uniformly dispersed and adsorbed on the surface of the copper powder to form a phosphorus compound molecular film layer, and then the additive is added, and an ultrasonic dispersion device is used for dispersion treatment, so that the microencapsulated rosin in the additive and the titanate modified nano titanium dioxide are obtained to obtain a preliminary mixed ink slurry; S5, the ink slurry is transferred to a three-roll mill for grinding to obtain a uniform slurry with a fineness of ≤20 μm; S6, the ground ink slurry is placed in a vacuum degassing device for treatment to form a bubble-free conductive copper ink.

2. The method for the preparation of a conductive copper ink for printed circuits according to claim 1, characterized in that, In the S1, the stirrer is stirred at a stirring speed of 400-500 r / min and a temperature of 25-35℃ for 40-60 min.

3. The method for preparing a conductive copper ink for printed circuits according to claim 1, characterized in that, In the S2, the high-speed dispersing machine is first stirred at a stirring speed of 1000-1200 r / min for 20-30 min, and then the flaky copper powder and spherical copper powder are continuously stirred at a stirring speed of 600-800 r / min for 15-20 min.

4. The method for preparing a conductive copper ink for printed circuits according to claim 1, characterized in that, In the S3, the planetary stirrer is stirred at a speed of 500-800 r / min for 15-20 min; and the ultrasonic dispersion device is treated at a frequency of 20-40 kHz and a power of 300-500 W for 10-15 min.

5. The method for preparing a conductive copper ink for printed circuits according to claim 1, characterized in that, In the S4, the planetary stirrer is stirred at a speed of 400-600 r / min for 20-30 min; and the ultrasonic dispersion device is treated at a frequency of 25-35 kHz and a power of 200-400 W for 15-20 min.

6. The method for preparing a conductive copper ink for printed circuits according to claim 1, characterized in that, In the S5, the three-roll mill is ground under the conditions of a front roller speed of 20-30 r / min, a middle roller speed of 60-90 r / min, a rear roller speed of 180-270 r / min, a roller gap control of 5-15 μm, and a grinding pressure of 0.3-0.8 MPa for 4-6 cycles.

7. The method for preparing a conductive copper ink for printed circuits according to claim 1, characterized in that, In the S6, the vacuum degassing device is treated at a vacuum degree of -0.08--0.1 MPa and a temperature of 30-40℃ for 20-30 min at a stirring speed of 50-100 r / min.

8. A conductive copper ink for printed circuits, obtainable by the process for the preparation of a conductive copper ink for printed circuits according to any one of claims 1 to 7, characterized by the fact that, The method comprises the following raw materials: Conductive mica powder 20-30 parts, nano-copper-graphene filler 15-25 parts, flaky copper powder 10-15 parts, spherical copper powder 5-10 parts, organic carrier 25-40 parts, dispersant 1-3 parts, coupling agent 0.5-2 parts, antioxidant 0.5-2 parts and auxiliary agent 1-3 parts; wherein, the conductive mica powder and nano-copper-graphene filler form a "layer-point" composite conductive structure to improve the continuity and stability of the conductive network, the flaky copper powder and spherical copper powder form a close-packed structure through particle size grading to reduce resistance and enhance coating density, the coupling agent forms a chemical bonding interface with copper powder and organic carrier to improve the adhesion of the coating and solder, and the antioxidant forms a passivation layer on the surface of the copper powder to inhibit oxidation and maintain long-term conductive stability.

9. The conductive copper ink for printed circuits according to claim 8, characterized in that, The organic carrier adopts a complex system of resin matrix and solvent, wherein: the resin matrix is selected from one or more of ethyl cellulose, acrylic resin and epoxy resin; the solvent is selected from one or more of terpineol, diethylene glycol butyl ether, propylene glycol methyl ether acetate and cyclohexanone; the dispersant is selected from one of fatty acid salt, polycarboxylate and alkyl amine dispersant, and the polycarboxylate dispersant is preferred; the coupling agent is selected from one of silane coupling agent, titanate coupling agent and aluminate coupling agent, and the silane coupling agent is preferred; the antioxidant is a compound containing phosphorus element; and the auxiliary agent is a complex system of microencapsulated rosin and titanate modified nano titanium dioxide.

10. The conductive copper ink for printed circuits according to claim 9, characterized in that, The mass ratio of the resin matrix to the solvent is in the range of 1:2-1:6.

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