Method for printing circuit board by using graphene conductive composite ink

Abstract

The invention discloses a method for printing a circuit board by using graphene conductive composite ink, which comprises the following steps of: printing a circuit diagram on heat transfer paper by using the graphene conductive composite ink, then carrying out heat transfer printing on a substrate, and carrying out ultraviolet curing. The ink-jet printing technology is combined with the heat transfer printing and ultraviolet light curing technology, the printing precision of a circuit diagram and the applicability of a substrate are remarkably improved, the conductive ink provided by the invention constructs an ink layer with high conductivity and mechanical strength by utilizing the synergistic effect of graphene and conductive macromolecules, traditional conductive metal particles are not needed, and the cost is low. And the circuit bearing capacity is obviously improved. Through optimization of heat transfer printing and ultraviolet curing conditions, stable combination of the ink layer and the substrate is ensured, meanwhile, the production period is greatly shortened, and the environmental protection property is enhanced. The production efficiency and the performance consistency of the circuit board are improved, the application range of the substrate is expanded, and an efficient and flexible solution is provided for complex circuit design.

Description

Technical Field

[0001] The invention relates to a method for printing a circuit board by using graphene conductive composite ink, and belongs to the technical field of printed circuits. Background Art

[0002] In recent years, the trend of miniaturization and multifunctionality of electronic devices has led the technological trend, and the demand for printed circuit boards (PCBs), which are the core components of electronic devices, has surged. With the popularization of 5G communications, the Internet of Things, and smart wearable devices, the market demand for high-density, high-performance PCBs continues to rise. This trend has not only promoted the innovation of PCB technology, but also spawned the exploration of more efficient and environmentally friendly preparation processes.

[0003] Traditional PCB preparation processes mainly include etching, photolithography and electroplating. The etching method is simple to operate and low in cost, but there are serious environmental pollution problems and the circuit accuracy is limited. The photolithography method is known for its high precision and high density, and is suitable for the manufacture of complex circuits, but the equipment cost and process complexity are high, and the environmental conditions are strict. The electroplating method can produce circuits with good conductivity, but the equipment investment is large, the process control requirements are high, and the production cycle is long. While these methods meet high performance requirements, they also expose inefficiencies in efficiency and cost.

[0004] In recent years, direct writing and inkjet printing technologies have shown great potential in the field of PCB preparation. For example, patent application CN104183335A discloses a method for forming pure silver conductive graphics by laser low-temperature rapid sintering of printed nanosilver paste. It proposes a method of using silver nanoparticle conductive ink combined with laser sintering. Although it can achieve rapid preparation, the additional sintering step increases energy consumption. Patent application CN108323023A discloses a printing method based on thermal curing graphene conductive ink. This method improves the conductivity of the ink by adding conductive fillers such as graphene and other technologies. It can directly perform inkjet printing on circuit boards. Although the operation is simple and no sintering is required, in order to improve the resolution and curing requirements of the PCB, this method requires the inkjet process to be always carried out at 80 to 150°C, which has high energy consumption and is not suitable for temperature-sensitive substrates, such as certain polymer films, which limits its application in the field of flexible electronics. For example, patent application CN110337191A discloses A method for 3D printing high-power LED printed circuit boards based on graphene conductive ink has been developed. The method prepares ink by preparing materials such as photosensitive resin and nano-silver conductive particles. After 3D inkjet printing, the ink can be cured by ultraviolet light, which can solve the problem of high energy consumption of methods such as thermal curing or sintering, and also reduces the curing time to a certain extent, and has no requirements for the high temperature resistance of the substrate. However, the printed circuit board prepared by only using nano-silver conductive particles and graphene as conductive media has poor conductivity. Although the continuous production mode of inkjet and UV curing improves the curing efficiency, the point-by-point construction characteristics of 3D printing itself result in poor overall manufacturing speed and difficulty in mass production. At the same time, this technology has high requirements on the accuracy and stability of the equipment, the operation process is complicated, and it is difficult to control the accuracy of printing complex design circuits. Summary of the invention

[0005] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for printing circuit boards using graphene conductive composite ink. The printed circuit board prepared by this method not only has high conductivity and excellent mechanical properties, but also achieves production efficiency and circuit board performance stability.

[0006] In order to achieve the above technical purpose, the present invention provides a method for printing a circuit board using graphene conductive composite ink, wherein a circuit diagram is printed on thermal transfer paper using the graphene conductive composite ink, and then thermally transferred to a substrate and cured by ultraviolet light; the graphene conductive composite ink is composed of the following components by weight: 10 to 30 parts of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), 5 to 20 parts of hydroxyethyl acrylate, 8 to 15 parts of waterborne polyurethane resin, 5 to 10 parts of graphene, 1 to 5 parts of a photoinitiator, 1 to 5 parts of a coupling agent, and 5 to 10 parts of an additive.

[0007] The present invention proposes a method for preparing a circuit diagram using commercial inkjet printing technology combined with thermal transfer and ultraviolet light curing processes, which significantly improves the resolution of circuit diagram printing and the applicability of substrates. This method can achieve delicate and high-resolution printing effects by using an ordinary inkjet printer to output high-precision circuit diagrams, and then use thermal transfer technology to accurately transfer the circuit diagram to a variety of substrates, greatly broadening the adaptability range of substrate materials, reducing restrictions on substrate materials, and enhancing the flexibility and versatility of the process. The present invention also introduces ultraviolet light curing technology to replace traditional sintering and thermal curing processes, achieving rapid curing, significantly shortening the process cycle, and greatly improving production efficiency and response speed. The above process can be realized mainly because the graphene conductive composite ink provided by the present invention, the hydroxyethyl acrylate in the ink is polymerized and cross-linked under the initiation of ultraviolet light, and the photocurable double bonds of polyurethane acrylate jointly construct a three-dimensional network, and the poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) conductive polymer can partially participate in cross-linking under the action of free radicals, and its poly(3,4-ethylenedioxythiophene) part forms a continuous conductive channel with graphene, and the high conductivity of graphene is combined with the conductive network of the conductive polymer, and the mechanical stability and bonding performance of the polyurethane resin to the system, so that the cured ink shows high conductivity while maintaining excellent mechanical properties, and then the high current carrying capacity of the circuit board can be achieved without using conductive metal particles such as nano silver. Due to the high conductivity, high stability and wide adaptability of the conductive ink, it is suitable for the efficient and flexible application of the process.

[0008] As a preferred solution, the conditions for thermal transfer are: temperature of 120-180°C, time of 30-60s, and pressure of 0.5-1.5MPa. If the temperature of the thermal transfer of the present invention is too low or the time is too short, the ink cannot be fully melted, resulting in poor contact with the substrate, affecting the formation of the conductive network, increasing the square resistance, reducing the adhesion, and impairing the stability and conductivity of the circuit. On the contrary, if the temperature is too high or the time is too long, it will affect the activity of the ink components, destroy the graphene network, increase the square resistance, and the substrate may be affected by thermal deformation, affecting the overall dimensional stability. If the pressure is insufficient, bubbles or gaps will exist between the ink layer and the substrate, affecting the conductivity and reliability of the circuit; if the pressure is too high, it may compress and destroy the graphene network, increase the square resistance, and reduce the circuit performance.

[0009] As a preferred solution, the conditions for UV curing are: UV wavelength of 250~400nm, energy density of 500~2000mJ / cm², and exposure time of 2~10s. The wavelength of the present invention is not suitable, the photoinitiator cannot be effectively excited, the curing reaction is insufficient, the mechanical strength of the ink layer is poor, the conductive network is incomplete, the square resistance is increased, and the adhesion is reduced. Too low energy density leads to incomplete curing, poor performance of the ink layer, and susceptibility to external damage; while too high energy density may cause excessive cross-linking of the ink components, brittleness of the material, reduced impact resistance and bending performance, and may destroy the graphene conductive network and increase square resistance. Too short exposure time leads to low curing degree and poor performance; too long exposure time may cause material embrittlement, affect conductivity, and increase square resistance.

[0010] As a preferred solution, the substrate is a FR-4 board, an FPC board, a glass fiber board or a paper substrate.

[0011] As a preferred solution, the thermal transfer paper is quick-drying or adhesive thermal transfer paper.

[0012] As a preferred solution, the number of graphene layers is 3 to 6 layers.

[0013] As a preferred solution, the waterborne polyurethane resin is one of HEBEN S-300, HK718 and waterborne polyurethane 1526.

[0014] As a preferred solution, the additive is at least one of a defoamer, a leveling agent and an antioxidant.

[0015] As a preferred solution, the defoamer is one of BYK-016, BYK-011 and BYK-012; the leveling agent is one of DC57, DC51 and DC56; and the antioxidant is one of Irganox 168, Irganox 1010 and Irganox L135.

[0016] As a preferred solution, the photoinitiator is Irgacure 2959 or Irgacure 500; and the coupling agent is a titanate coupling agent.

[0017] As a preferred solution, the viscosity of the graphene conductive composite ink is 50~300mPa·s.

[0018] Compared with the prior art, the technical solution of the present invention brings about the following innovative and beneficial technical effects: 1) The present invention utilizes the high precision of inkjet printing and combines it with the thermal transfer process, which not only significantly improves the printing accuracy and resolution of the circuit diagram, but also realizes a fine circuit pattern, meets the layout requirements of high-density and high-precision electronic components, and provides the possibility for complex circuit design. At the same time, the thermal transfer process is adopted, which is suitable for substrates of various materials, thus broadening the scope of application.

[0019] 2) The conductive ink provided by the present invention is cured by ultraviolet light curing. Compared with thermal curing or sintering, it is easier to operate, has a shorter curing time, is more environmentally friendly, and greatly improves production efficiency, reduces energy consumption and costs.

[0020] 3) The ink provided by the present invention uses a conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), wherein the conductive properties of poly(3,4-ethylenedioxythiophene) are combined with the thermal conductive properties of graphene, which can be combined with a three-dimensional continuous coating formed by curing hydroxyethyl acrylate and water-based polyurethane resin to construct a highly conductive and high mechanical property ink layer, which can be beneficial to the high current carrying capacity of the printed circuit board. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be further described below in conjunction with specific embodiments of the present invention. It should be noted that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments; these embodiments are only for a better understanding of the present invention, rather than limiting the scope of protection of the present invention.

[0022] Unless otherwise specified, all reagents and raw materials used in the present invention are commercially available products or products that can be prepared by known methods.

[0023] The graphene used in the present invention is graphene powder JY-GP01 produced by Hunan Jinyang Encarbon New Materials Co., Ltd.

[0024] The poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) used in the present invention was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., model number P191136. Example 1

[0025] First, weigh 20 parts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), then add 15 parts of hydroxyethyl acrylate and 10 parts of waterborne polyurethane resin HEBEN S-300, use a high-speed disperser to premix for 10 minutes at a speed of 1000 rpm, slowly add 8 parts of graphene and continue stirring at a speed of 500 rpm for 30 minutes to ensure that the graphene is evenly dispersed, add an appropriate amount of water in the middle to control the final ink viscosity at about 200 mPa·s, then slowly add 3 parts of photoinitiator Irgacure 2959, 2 parts of titanate coupling agent ZJ-318, 3 parts of leveling agent DC57, 1 part of defoamer BYK-016, 2 parts of antioxidant Irganox 168, continue stirring at a speed of 300 rpm for 20 minutes until all ingredients are completely evenly dispersed, and then store in a dark place.

[0026] Use an inkjet printer to print the designed circuit diagram with the prepared graphene conductive ink onto quick-drying thermal transfer paper. The printing speed is set to 200 mm / s and the ink layer thickness is controlled at 10 μm. After the ink is slightly dry, use a small thermal transfer machine to thermally transfer the printed circuit pattern. The FPC board is selected as the substrate, the thermal transfer temperature is set to 150°C, the pressure is 1.2 MPa, and the pressing time is 30 seconds. The transferred circuit board is placed in a UV curing machine and irradiated with UV light with a wavelength of 365 nm, an energy density of 800 mJ / cm², and an exposure time of 8 seconds to complete the curing to obtain a printed circuit board. Example 2

[0027] Compared with Example 1, the only difference is that the weight parts of the components of the graphene conductive composite ink are different, and the other conditions and steps are the same. The weight parts of the components of the graphene conductive composite ink in this embodiment are as follows: 10 parts of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), 20 parts of hydroxyethyl acrylate, 15 parts of water-based polyurethane resin HEBEN S-300, 5 parts of graphene, 3 parts of photoinitiator Irgacure 2959, 2 parts of titanate coupling agent ZJ-318, 3 parts of leveling agent DC57, 1 part of defoaming agent BYK-016, and 2 parts of antioxidant Irganox 168. Example 3

[0028] Compared with Example 1, the only difference is that the ultraviolet light energy density is set to 1500mJ / cm² and the exposure time is set to 5s, and the other conditions and steps are the same. Example 4

[0029] Compared with Example 1, the only difference is that the substrate is replaced by FR-4 board, and the other conditions and steps are the same.

[0030] Comparative Example 1 Compared with Example 1, the only difference is that the components of the conductive ink are different, and the other conditions and steps are the same. The components of the conductive ink in this comparative example are as follows: 20 parts of hydroxyethyl acrylate, 25 parts of waterborne polyurethane resin HEBEN S-300, 5 parts of carbon powder, 3 parts of photoinitiator Irgacure 2959, 2 parts of titanate coupling agent ZJ-318, 3 parts of leveling agent DC57, 1 part of defoaming agent BYK-016, and 2 parts of antioxidant Irganox 168.

[0031] Comparative Example 2 Compared with Example 1, the only difference is that the components of the conductive ink are different, and the other conditions and steps are the same. The components of the conductive ink in this comparative example are as follows: 10 parts of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), 25 parts of hydroxyethyl acrylate, 5 parts of water-based polyurethane resin JT-3015, 5 parts of graphene, 3 parts of photoinitiator Irgacure 2959, 2 parts of titanate coupling agent ZJ-318, 3 parts of leveling agent DC57, 1 part of defoaming agent BYK-016, and 2 parts of antioxidant Irganox 168.

[0032] Comparative Example 3 Compared with Example 1, the only difference is that the temperature during thermal transfer is 200° C. and the pressing time is 90 s, and the other conditions and steps are the same.

[0033] The circuit boards prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to performance tests. The results are shown in Table 1. The square resistance values ​​in the table are measured by a four-probe tester when the film thickness is 10 μm for each sample. The adhesion is measured by the cross-cut method in GB / T 13217.7-2023. The hardness is measured by a pencil hardness tester.

[0034]

[0035] As shown in Table 1, the present invention adopts the graphene conductive ink combined with thermal transfer and other processes to print circuit boards, and a circuit board with excellent conductive properties and mechanical properties can be obtained; from the data of Example 4, it can be seen that the test indicators after the substrate is changed from a flexible board to a rigid board are equivalent to those in the embodiment, which shows that on different substrates, the technology can still maintain good comprehensive performance and has a wide range of applications; from Comparative Example 2, it can be seen that the reduction of water-based polyurethane resin in the ink can greatly affect the adhesion and mechanical strength of the ink; and from Example 2 and Comparative Example 1, it can be seen that graphene and conductive polymer poly (3,4-ethylenedioxythiophene) -Poly(styrene sulfonic acid) not only affects the conductive properties, but also, even when the water-based polyurethane resin is not reduced, the hardness and adhesion of Comparative Example 1 are worse than those of Example 1, indicating that the graphene and conductive polymer resin in the ink will also affect the mechanical properties of the ink coating. The possible reason is that the graphene and conductive polymer resin participate in the film-forming reaction when the ink is cured, making the three-dimensional structure after curing more stable. It can be seen from Example 3 and Comparative Example 3 that both the transfer conditions and the curing conditions will affect the performance of the final conductive ink layer, and the ink needs to achieve the best performance under a suitable preparation process.

[0036] The above embodiments are only for better explanation of the principles and practical applications of the present invention, so that those skilled in the relevant technical field can better understand and utilize the present invention, but they are not intended to limit the patent scope of the present invention. All equivalent changes made using the contents of the present invention are within the patent protection scope of the present invention.

Claims

1. A method for printing a circuit board using graphene conductive composite ink, characterized in that: The circuit diagram is printed on thermal transfer paper using graphene conductive composite ink, and then thermally transferred to a substrate and cured by ultraviolet light; the graphene conductive composite ink is composed of the following components by weight: 10 to 30 parts of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), 5 to 20 parts of hydroxyethyl acrylate, 8 to 15 parts of waterborne polyurethane resin, 5 to 10 parts of graphene, 1 to 5 parts of a photoinitiator, 1 to 5 parts of a coupling agent, and 5 to 10 parts of an additive.

2. The method for printing a circuit board using graphene conductive composite ink according to claim 1, characterized in that: The conditions of the thermal transfer are: temperature of 120-180° C., time of 30-60 s, and pressure of 0.5-1.5 MPa.

3. The method for printing a circuit board using graphene conductive composite ink according to claim 2, characterized in that: The conditions of UV curing are: UV wavelength of 250-400nm, energy density of 500-2000mJ / cm², and exposure time of 2-10s.

4. The method for printing a circuit board using graphene conductive composite ink according to claim 2, characterized in that: The substrate is a FR-4 board, an FPC board, a glass fiber board or a paper substrate.

5. The method for printing a circuit board using graphene conductive composite ink according to claim 1, characterized in that: The thermal transfer paper is quick-drying or adhesive thermal transfer paper.

6. The method for printing a circuit board using graphene conductive composite ink according to claim 5, characterized in that: The number of graphene layers is 3 to 6.

7. The method for printing a circuit board using graphene conductive composite ink according to claim 1, characterized in that: The additive is at least one of a defoamer, a leveling agent and an antioxidant.

8. The method for printing a circuit board using graphene conductive composite ink according to claim 7, characterized in that: The defoamer is one of BYK-016, BYK-011 and BYK-012; the leveling agent is one of DC57, DC51 and DC56; and the antioxidant is one of Irganox 168, Irganox 1010 and Irganox L135.

9. The method for printing a circuit board using graphene conductive composite ink according to claim 1, characterized in that: The photoinitiator is Irgacure 2959 or Irgacure 500; the coupling agent is a titanate coupling agent.

10. The method for printing a circuit board using graphene conductive composite ink according to claim 1, characterized in that: The viscosity of the graphene conductive composite ink is 50~300mPa·s.

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