Ink-jet printing method and device for conductive circuit with large height-width ratio

Abstract

The invention provides a large aspect ratio conductive circuit ink-jet printing method, which specifically comprises the following steps: in an ink-jet printing process, controlling an emission angle of an infrared laser, keeping an intersection point of laser emitted by the infrared laser and an ink droplet falling track of a printing head above a printing substrate, and presintering and curing ink droplets before the ink droplets fall on the surface of the printing substrate; the invention further provides an ink-jet printing device for the conductive circuit with the large height-width ratio and an application method of the ink-jet printing device. The nano-silver ink for ink-jet printing is rapidly sintered through laser in the flying process, the high-performance conductive trace can be directly manufactured on the substrate, and the manufacturing efficiency and the quality of the final electronic trace are remarkably improved through the collaborative process of presintering in the ink droplet flying process and synchronously preheating the substrate; the large-aspect-ratio conductive circuit ink-jet printing device for achieving the method is simple in structure, flexible and convenient to operate and high in practicability, and the focusing accuracy of laser and ink droplets is improved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology for structural circuits, specifically relating to a method and apparatus for inkjet printing conductive lines with a large aspect ratio. Background Technology

[0002] Among numerous additive manufacturing technologies, piezoelectric inkjet printing (IJP) has garnered significant attention in the printed electronics field due to its advantages such as high precision, non-contact operation, high material utilization, and digital drive. This technology forms pre-defined circuit patterns on a substrate by spraying conductive ink containing nano-metal particles (such as nano-silver and nano-copper) on demand. However, to ensure that the printed patterns possess excellent conductivity to meet practical application requirements, a series of process challenges must be overcome.

[0003] The geometry of inkjet-printed conductive lines is crucial to their performance. A higher aspect ratio means a larger conductive cross-sectional area can be obtained with the same linewidth, effectively reducing the adverse effects of the skin effect during high-frequency operation. To improve the aspect ratio, existing technologies typically employ multi-layer stacking printing. Although repeated deposition can increase the conductor cross-sectional area, the improvement in conductivity and the increase in layer thickness are not unlimited. As the number of stacked layers gradually increases, further increases in the number of layers tend to level off, resulting in significant diminishing marginal benefits. Secondly, this method sacrifices the lateral accuracy of the pattern; repeated printing leads to significant diffusion at the conductor edges and an uncontrolled increase in linewidth, which contradicts the requirements for pattern fidelity in precision machining.

[0004] After ink is deposited on the substrate, the presence of stabilizers and solvents often prevents metal nanoparticles from immediately exhibiting optimal electrical properties. Currently, the mainstream sintering methods include oven sintering and laser-assisted sintering. Oven sintering involves heating the entire workpiece for an extended period, but its long heating cycle severely restricts manufacturing efficiency; it also suffers from a significant coffee ring effect, affecting the consistency of the conductor morphology. Laser-assisted sintering involves heating the conductor after printing using a laser scan. While this improves the electrical properties of the conductor to some extent, it still belongs to a two-step "printing-sintering" process, which is complex and lengthy, and does not fundamentally improve efficiency.

[0005] In summary, existing conductive line inkjet printing technology has many shortcomings in terms of manufacturing process, production efficiency, and image quality, making it difficult to simultaneously meet the integrated manufacturing requirements of high efficiency, high performance, and high precision. Therefore, there is an urgent need to develop a new conductive line printing method and printing device to solve the above problems. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a method and apparatus for inkjet printing conductive lines with a large aspect ratio. The aim is to rapidly sinter the inkjet-printed nano-silver ink during flight using a laser during the piezoelectric inkjet printing process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: (i) The present invention provides an inkjet printing method for conductive lines with a large aspect ratio, including controlling the emission angle of an infrared laser during the inkjet printing process, keeping the intersection point of the emitted laser and the ink droplet falling trajectory of the print head above the printing substrate, so that the ink droplets are pre-sintered and cured before falling onto the surface of the printing substrate.

[0008] Furthermore, the vertical distance between the intersection point of the laser emitted by the infrared laser and the trajectory of the falling ink droplets and the printing substrate is 0.2~0.5mm; the printing substrate is preheated before the printing operation.

[0009] (II) The present invention also provides an inkjet printing apparatus for conductive lines with a large aspect ratio, comprising a printing substrate, a back plate, a laser assembly, and a printing assembly; the back plate is vertically distributed above the printing substrate, and the laser assembly and the printing assembly are mounted on the same side of the back plate; the laser assembly includes an infrared laser and a turntable, the turntable is mounted on the back plate, and the infrared laser is disposed on the mounting surface of the turntable and can rotate with the turntable on a vertical plane; the printing assembly includes a fixed stage, a slide stage, and an inkjet printhead, the fixed stage is fixedly mounted on the back plate, and the slide stage is slidably connected to the fixed stage and can move linearly along the direction perpendicular to the back plate; the inkjet printhead is disposed on the side of the slide stage facing the infrared laser, and the inkjet printheads are vertically distributed.

[0010] Furthermore, the laser assembly also includes a laser fixture, which is fixed to the mounting surface of the turntable, and the infrared laser is clamped and fixed inside the laser fixture.

[0011] Furthermore, the printing assembly also includes a printhead clamp, which is fixedly connected to the slide, and the inkjet printhead is clamped and fixed within the printhead clamp.

[0012] Furthermore, the printing assembly also includes an ink bottle clamp, an ink bottle, and an ink supply line; the ink bottle clamp is fixedly mounted on the back plate, the ink bottle is clamped and fixed inside the ink bottle clamp, one end of the ink supply line is connected to the ink bottle, and the other end is connected to the inkjet printhead.

[0013] Furthermore, the printing substrate is capable of moving along the X-axis; the backplate is capable of moving along the Y and Z axes.

[0014] Furthermore, the printing substrate is sanded before application, and the surface roughness is 1~3μm.

[0015] Furthermore, the ink bottle contains nano-silver ink with a viscosity of 8~25 cPs, a solid content of 30%~45%, and a resistivity of 12~28 μΩ·cm.

[0016] Furthermore, the infrared laser is a 10W laser with adjustable power and a wavelength of 808nm.

[0017] Furthermore, the turntable is a manual turntable with a concentricity of 0.02 mm and a minimum angle of 1.23 minutes.

[0018] Furthermore, the slide is a manual slide with a length of 50mm.

[0019] (III) The present invention also provides a method for applying the inkjet printing device with high aspect ratio conductive lines described above, including: Move the backplate so that the laser assembly and printing assembly mounted on the side of the backplate are moved above the printing substrate, so that the vertical distance between the inkjet printhead and the surface of the printing substrate meets the design requirements. Control the inkjet printhead to spray ink droplets onto the substrate surface. By controlling the rotation of the turntable and the translation of the slide, the laser emitted by the infrared laser intersects with the sprayed ink droplets on the substrate surface. Translate the backplate and spray ink droplets onto the substrate surface again from the inkjet printhead. Observe whether the laser emitted by the infrared laser intersects with the sprayed ink droplets this time. If it does, the adjustment is complete; if not, continue adjusting until the near-infrared laser focus completely coincides with the sprayed ink droplets. After adjustment, the backplate, laser assembly, and printing assembly are vertically lifted upwards by 0.2~0.5mm using the Z-axis motion system, so that the intersection of the laser focus and the ink droplet trajectory is transferred from the surface of the printing substrate to mid-air. Start the automatic printing program, activate the X-axis motion system to control the movement of the printing substrate, and complete the printing job according to the preset circuit pattern.

[0020] Furthermore, the infrared laser emits a laser power of 2.00 mA to 2.22 mA; Furthermore, the printing substrate moves at a speed of 30 mm / min along the X-axis.

[0021] The beneficial effects of this invention are: (1) The present invention aims to rapidly sinter the nano-silver ink printed by the laser during the flight of the piezoelectric inkjet printing process, thereby enabling the direct fabrication of high-performance conductive traces on the substrate. This technology significantly improves the manufacturing efficiency and the quality of the final electronic traces through the synergistic process of pre-sintering and simultaneously preheating the substrate during ink droplet flight. (2) Compared with traditional curing treatment, the method of the present invention can not only improve the conductivity and aspect ratio of the conductive lines, but also suppress the coffee ring effect and obtain conductive lines with uniform cross-sectional profile. This ensures the uniform distribution of current density and reduces conductor resistance, thereby improving the electrical performance and reliability of the device. (3) The present invention simplifies the processing flow, transforming the traditional two-step process of ink deposition + oven sintering or ink deposition + laser sintering into a single process in which deposition and sintering are carried out simultaneously. Compared with the traditional oven or laser sintering method, it significantly improves production efficiency.

[0022] (4) This invention improves the geometric profile of the conductive lines, achieving a larger conductive cross-sectional area with the same linewidth. This structure not only reduces DC resistance but also significantly reduces the adverse effects of the skin effect during high-frequency operation, thereby effectively improving the high-frequency performance of devices such as antennas; (5) The present invention also provides an inkjet printing device with a high aspect ratio conductive line that implements the above method. It has a simple structure, is flexible and convenient to operate, improves the focusing accuracy of laser and ink droplets, and is highly practical. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the inkjet printing device for high aspect ratio conductive lines of the present invention. Figure 2 This is a schematic diagram of inkjet printing of high aspect ratio conductive lines according to the present invention; Figure 3 This is a flowchart of the printing process of the present invention; Figure 4 This is a comparison diagram of the resistivity of the method of the present invention and that of oven sintering; Figure 5 A comparison chart of return loss of microstrip patch antenna samples fabricated by the method of the present invention and microstrip patch samples fabricated by traditional copper film patch and inkjet printing oven sintering methods is shown. Figure 6 A photograph of a patch microstrip antenna fabricated using this method; The labels in the attached diagram are: 1. Infrared laser; 2. Laser fixture; 3. Turntable; 4. Inkjet printhead; 5. Printhead fixture; 6. Mounting table; 7. Ink bottle fixture; 8. Ink bottle; 9. Ink supply line; 10. Slide table. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 This invention provides a method for inkjet printing conductive lines with a high aspect ratio.

[0026] Specifically, before printing, the printing substrate is preheated. During inkjet printing, the emission angle of the infrared laser is controlled to ensure that the intersection point of the emitted laser and the ink droplet trajectory of the printhead is 0.3 mm above the printing substrate, allowing the ink droplets to pre-sinter and solidify before falling onto the substrate surface. See [link to relevant documentation]. Figure 2 .

[0027] This invention aims to rapidly sinter nano-silver ink printed in piezoelectric inkjet printing using a laser during the inkjet printing process. Compared to traditional curing methods, this method not only improves the conductivity and aspect ratio of conductive circuits and suppresses the coffee ring effect, but also simplifies the workflow and improves overall work efficiency.

[0028] Example 2 like Figure 1 As shown, this embodiment of the invention provides a printing apparatus for implementing the above-described printing method, including a printing substrate, a backplate, a laser assembly, and a printing assembly. The backplate is vertically distributed above the printing substrate, and the laser assembly and the printing assembly are mounted on the same side of the backplate. The printing substrate is movable along the X-axis, and the backplate is movable along the Y and Z axes.

[0029] The laser assembly includes an infrared laser 1, a laser fixture 2, and a turntable 3. The turntable 3 is mounted on a backplate, and the laser fixture 2 is fixed to the mounting surface of the turntable 3. The infrared laser 1 is clamped and fixed within the laser fixture 2 and can rotate with the turntable 3 on a vertical plane. The infrared laser 1 is a 10W laser with adjustable power and a wavelength of 808nm. The turntable 3 is a manual turntable with a concentricity of 0.02mm and a minimum angle of 1.23 minutes.

[0030] The printing assembly includes a fixed stage 6, a slide 10, a printhead clamp 5, an inkjet printhead 4, an ink bottle clamp 7, an ink bottle 8, and an ink supply line 9. The fixed stage 6 is fixedly mounted on the back panel. The slide 10 is slidably connected to the fixed stage 6 and can move linearly along the direction perpendicular to the back panel (X-axis direction). The slide 10 is a manual slide with a length of 50mm. The printhead clamp 5 is located on the side of the slide 10 facing the infrared laser 1. The inkjet printhead 4 is clamped and fixed within the printhead clamp 5, and the inkjet printhead 4 is vertically distributed. The ink bottle clamp 7 is fixedly mounted on the back panel. The ink bottle 8 is clamped and fixed within the ink bottle clamp 7. One end of the ink supply line 9 is connected to the ink bottle 8, and the other end is connected to the inkjet printhead 4. Ink from the ink bottle 8 enters the inkjet printhead 4 through the ink supply line 9. The ink bottle 8 contains nano silver ink with a viscosity of 8~25 cPs, a solid content of 30%~45%, and a resistivity of 12~28 μΩ.cm.

[0031] The application methods of the above high aspect ratio conductive line inkjet printers are described in [link to documentation]. Figure 3 ,include: Step 1: Clean the inkjet printhead 4 with an ultrasonic cleaner and a lint-free cloth to ensure that there is no obvious ink solidification inside and around it; firmly install the printing substrate, which has been sanded with 800-grit sandpaper and has a surface roughness in the range of 1~3μm, on the printing platform; check and fill with nano silver metallic ink, and control the air pressure at -1.0kpa to form a meniscus.

[0032] Step 2: Start the printing control system and the synchronous near-infrared laser system. Move the back panel so that the laser assembly and printing assembly mounted on the side of the back panel are above the printing substrate, so that the vertical distance between the inkjet printhead 4 and the surface of the printing substrate is 3mm.

[0033] Step 3: Control the inkjet printhead 4 to spray ink droplets onto the substrate surface. By controlling the rotation of the turntable 3 and the translation of the slide 10, make the laser emitted by the infrared laser 1 (the laser power should be set to about 1mA so that the laser focus can be clearly observed and the substrate and printhead will not be damaged during the adjustment process) intersect with the ink droplets on the substrate surface; translate the back plate and make the inkjet printhead 4 spray ink droplets onto the substrate surface again. Observe whether the laser emitted by the infrared laser 1 intersects with the ink droplets this time. If so, the adjustment is complete; if not, continue to adjust until the near-infrared laser focus and the ink droplets are completely aligned.

[0034] Step 4: After completing the focus alignment calibration in Step 3, lock the positions of the inkjet printhead 4 and the infrared laser 1, and lift the back plate, laser assembly and printing assembly vertically upward by 0.3mm using only the Z-axis motion system, so that the intersection of the laser focus and the ink droplet falling trajectory is transferred from the surface of the printing substrate to mid-air. Step 5: Limit the laser power to the range of 2.00mA~2.22mA, start the automatic printing program, and activate the X-axis motion system to control the movement of the printing substrate. Complete the printing job according to the preset circuit pattern. The movement speed of the motion platform is limited to 30mm / min. After the printing job is completed, turn off the laser and remove the substrate from the fixture. See the image for the completed print. Figure 6 .

[0035] The resistivity of the printed parts prepared by the method of this invention and the printed parts obtained by inkjet printing-oven sintering were tested, and the results are as follows: Figure 4 As shown. By Figure 4 It can be seen that the resistivity of the printed parts prepared by the method of the present invention is significantly lower than that of the printed parts obtained by printing-oven sintering.

[0036] Return loss tests were conducted on the printed parts prepared by the method of this invention, traditional copper film patches, and microstrip patch samples prepared by traditional inkjet printing oven sintering. The results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the return loss of the sample prepared by the method of the present invention is significantly lower than that of the microstrip patch sample prepared by the traditional copper film patch and the traditional inkjet printing oven sintering method.

[0037] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for inkjet printing conductive lines with a large aspect ratio, characterized in that, include During inkjet printing, the intersection point of the laser emitted by the infrared laser and the trajectory of the ink droplets falling from the printhead is kept above the printing substrate, so that the ink droplets are pre-sintered and cured before falling onto the surface of the printing substrate.

2. The inkjet printing method for high aspect ratio conductive lines according to claim 1, characterized in that, The vertical distance between the intersection point of the laser emitted by the infrared laser and the trajectory of the falling ink droplets and the printing substrate is 0.2~0.5mm; the printing substrate is preheated before the printing operation.

3. A high aspect ratio conductive line inkjet printing device, characterized in that, Includes printing substrate, backplane, laser assembly, and printing assembly; The backplate is vertically distributed above the printing substrate, and the laser assembly and the printing assembly are mounted on the same side of the backplate; The laser assembly includes an infrared laser (1) and a turntable (3). The turntable (3) is mounted on a back plate, and the infrared laser (1) is disposed on the mounting surface of the turntable (3) and can rotate with the turntable (3) on a vertical plane. The printing assembly includes a fixed stage (6), a slide (10), and an inkjet printhead (4). The fixed stage (6) is fixedly mounted on the back plate, and the slide (10) is slidably connected to the fixed stage (6) and can move linearly along the direction perpendicular to the back plate. The inkjet printhead (4) is located on the side of the slide (10) facing the infrared laser (1) and is vertically distributed.

4. The inkjet printing device for high aspect ratio conductive lines according to claim 3, characterized in that, The laser assembly also includes a laser fixture (2), which is fixed on the mounting surface of the turntable (3), and the infrared laser (1) is clamped and fixed in the laser fixture (2).

5. The inkjet printing device for high aspect ratio conductive lines according to claim 3, characterized in that, The printing assembly also includes a printhead clamp (5), which is fixedly connected to the slide (10), and the inkjet printhead (4) is clamped and fixed in the printhead clamp (5).

6. The inkjet printing device for high aspect ratio conductive lines according to claim 3, characterized in that, The printing assembly also includes an ink bottle clamp (7), an ink bottle (8), and an ink supply line (9). The ink bottle clamp (7) is fixedly mounted on the back plate, and the ink bottle (8) is clamped and fixed in the ink bottle clamp (7). One end of the ink supply line (9) is connected to the ink bottle (8), and the other end is connected to the inkjet print head (4).

7. The inkjet printing device for high aspect ratio conductive lines according to claim 3, characterized in that, The printing substrate can move along the X-axis; the back plate can move along the Y and Z axes.

8. The inkjet printing device for high aspect ratio conductive lines according to claim 3, characterized in that, The printing substrate is sanded before application, and the surface roughness is 1~3μm.

9. The method of using the inkjet printing apparatus for high aspect ratio conductive lines according to any one of claims 3 to 8, characterized in that, include: Move the backplate so that the laser assembly and printing assembly mounted on the side of the backplate are moved above the printing substrate so that the vertical distance between the inkjet printhead (4) and the surface of the printing substrate meets the design requirements. Control the inkjet printhead (4) to spray ink droplets onto the substrate surface. By controlling the rotation of the turntable (3) and the translation of the slide (10), the laser emitted by the infrared laser (1) intersects with the ink droplets on the substrate surface. Translate the back plate and make the inkjet printhead (4) spray ink droplets onto the substrate surface again. Observe whether the laser emitted by the infrared laser (1) intersects with the ink droplets sprayed this time. If yes, the adjustment is complete. If no, continue to adjust until the near-infrared laser focus completely coincides with the ink droplets. After adjustment, the backplate, laser assembly, and printing assembly are vertically lifted upwards by 0.2~0.5mm using the Z-axis motion system, so that the intersection of the laser focus and the ink droplet trajectory is transferred from the surface of the printing substrate to mid-air. Start the automatic printing program, activate the X-axis motion system to control the movement of the printing substrate, and complete the printing job according to the preset circuit pattern.

10. The application method of the inkjet printing device for high aspect ratio conductive lines according to claim 9, characterized in that, The infrared laser (1) emits a laser power of 2.00 mA to 2.22 mA; The printing substrate moves at a speed of 30 mm / min along the X-axis.

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