Method and system for preparing flexible circuit by sintering metal nanoparticles through ultrafast laser

Abstract

The invention provides a method for preparing a flexible circuit through ultrafast laser sintering of metal nanoparticles, and the method comprises the following steps: S1, coating the surface of a flexible substrate with metal nanoparticle slurry, and drying the metal nanoparticle slurry to form a metal nanoparticle layer; s2, the flexible base material is preheated through a preheating device; s3, pulse laser generated by the ultrafast laser light source is focused on the surface of the metal nanoparticle layer, and a metal nanoparticle sintering area is formed through sintering; and S4, preparing a patterned flexible circuit. The metal nanoparticles are preheated and softened, so that the deformation resistance of the metal nanoparticles is reduced; low-temperature sintering of metal nanoparticles on the flexible substrate and preparation of a flexible circuit are realized through a thermal-mechanical composite effect introduced by ultrafast laser, the nanoparticles are fully coalesced, the conductivity of a conductive region is high, and the selection range of a flexible substrate material is wide; by introducing the bonding layer into the flexible substrate, the conductive area is semi-embedded into the substrate, and the mechanical deformation durability of the flexible circuit is good.

Description

Technical Field

[0001] The present invention relates to the new technical field of material sintering. Specifically, it relates to a method and system for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles. Background Art

[0002] With the continuous development of electronic devices towards miniaturization, light weight, flexibility and portability, the rapid and high-quality preparation of flexible circuits has become an important issue attracting much attention in the field of electronic component manufacturing. Traditional flexible circuit manufacturing processes require vacuum deposition of a copper layer on a polyimide substrate, followed by electronic component manufacturing processes such as lithography, etching, and post-treatment. These processes have defects such as high cost, complex processes, and generation of toxic waste. With the continuous development and application of modern nanotechnology, depositing functional patterns on a flexible substrate by means of screen printing, inkjet printing, laser direct writing, etc. using metal nanoparticle slurries is a current new method for preparing flexible circuits.

[0003] Since the metal nanoparticles in the slurry are wrapped by polymers, the functional patterns are not conductive. Removing the polymers around the nanoparticles and inducing the fusion and coalescence of metal nanoparticles through sintering technology is the key process to endow the flexible circuits with conductivity. Currently, common metal nanoparticle sintering methods include thermal sintering, pulsed intense light sintering, laser sintering, etc. The thermal sintering process has defects such as long sintering time and high heat load, which can cause serious damage to the flexible heat-sensitive substrate. Pulsed intense light sintering can significantly reduce the input heat load and has the advantage of large-area exposure, but has low spatial resolution. Laser sintering has high process resolution, small thermal damage to the substrate, and does not require a mask for patterning, and is a new and promising low-temperature sintering method for metal nanoparticles.

[0004] The patent with the application number CN201410472331.5 discloses a method for forming pure silver conductive graphics by laser low-temperature rapid sintering of printed nano silver paste. It uses laser low-temperature rapid sintering of silver paste on the surfaces of paper and plastic film by gravure printing or inkjet printing, and a porous pure silver sintered body is formed after sintering. During the sintering process of this process method, the substrate temperature does not exceed 150 °C, and the mechanical properties of the printed substrates of paper and plastic film are not deteriorated. However, the flexible conductive graphics formed by this preparation method show a uniform porous structure, and at the same time have problems of poor conductivity and difficulty in further improving the processing resolution. The patent with the application number CN201610896524.4 discloses a method for preparing a silver electrode with high bonding strength on a flexible substrate by using laser direct writing technology. It scans the laser beam incident from the back of the plastic and focuses on the contact interface between the plastic and the silver paste precursor solution to prepare a silver electrode with very high bonding strength. This process method is simple and fast, and can complete the in-situ reduction and sintering of silver nano materials in one step. However, the process of laser-induced reduction of the precursor solution takes a long time and the processing efficiency is low. In addition, the conductive microstructures prepared by in-situ reduction and sintering have a large porosity, poor electrical properties, and poor processing accuracy. Noh et al. (Noh, Jihun, and Dongsik Kim. "Femtosecond laser sintering of silver nanoparticles for conductive thin-film fabrication." Applied Physics A 126.2 (2020): 124.) directly irradiate a silver nanoparticle layer with a pulsed femtosecond laser, and use the local thermal effect introduced by the femtosecond laser to complete the aggregation and sintering of metal nanoparticles, and can achieve the high-efficiency and high-precision preparation of flexible conductive thin films. However, the electrical properties of the sintered area obtained by this process method are not good. In addition, this process method is only applicable to the preparation of conductive thin films with a sub-micron thickness, and its application range is greatly limited.

[0005] Existing processing methods cannot take into account the processing requirements of high conductivity, high resolution, high durability, high processing efficiency and high process flexibility in the preparation of flexible circuits. There is an urgent need for a method for sintering metal nanoparticles and preparing flexible circuits that takes into account the above requirements. Summary of the Invention

[0006] Aiming at the defects in the prior art, the purpose of the present invention is to provide a method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles.

[0007] According to a method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles provided by the present invention, it includes the following steps:

[0008] Step S1: Coat a metal nanoparticle slurry on the surface of a flexible substrate, and dry it to remove the slurry solvent to form a metal nanoparticle layer;

[0009] Step S2: Heat the flexible substrate to a set temperature through a preheating device to preheat the metal nanoparticle layer coated on the surface of the flexible substrate;

[0010] Step S3: Focus the pulsed laser generated by an ultrafast laser light source on the surface of the metal nanoparticle layer, and sinter the metal nanoparticles to form a conductive metal nanoparticle sintered area without thermal damage to the flexible substrate;

[0011] Step S4: Adjust the position of the metal nanoparticle sintered area through the relative movement of the pulsed laser beam and the flexible substrate to achieve the preparation of a patterned flexible circuit.

[0012] Preferably, in step S1, the flexible substrate includes: a bonding layer and a substrate, the bonding layer covers the substrate, and the metal nanoparticle paste is coated on the bonding layer.

[0013] Preferably, in step S2, the preheating temperature of the preheating device is lower than the melting point of the metal nanoparticles and lower than the glass transition temperature or thermal damage temperature of the flexible substrate.

[0014] Preferably, in step S2, the preheating device is arranged at the bottom of the flexible substrate, and a motion system is arranged at the bottom of the preheating device, and the motion system drives the preheating device to move in the horizontal direction.

[0015] Preferably, in step S3, the pulsed ultrafast laser beam generated by the ultrafast laser light source is incident into a shaping and scanning optical path device, and the shaping and scanning optical path device emits a focused laser beam downward.

[0016] Preferably, in step S3, the laser energy density of the focused laser beam is lower than the ablation removal threshold of the metal nanoparticle layer and can generate local melting thermal effect and impact densification force effect.

[0017] Preferably, the shaping and scanning optical path device is connected with a control device, and the shaping and scanning optical path device can move parallel to the flexible substrate.

[0018] Preferably, in step S3, the resistivity of the metal nanoparticle sintered area is 2.2×10 -8 Ω·m, and the thickness is between 1 - 3 μm.

[0019] A system for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles according to the present invention is applied to the method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles as described above, and includes: an ultrafast laser light source, a preheating device, and a flexible substrate. A metal nanoparticle layer is coated on the upper surface of the flexible substrate. The preheating device is arranged at the bottom of the flexible substrate. The pulsed laser generated by the ultrafast laser light source is focused on the surface of the metal nanoparticle layer to form a metal nanoparticle sintering region, and the pulsed laser beam and the flexible substrate can move relative to each other.

[0020] Preferably, the ultrafast laser light source and / or the preheating device are connected with a moving device.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In the present invention, the metal nanoparticles are preheated and softened by the flexible substrate to reduce their deformation resistance; the ultrafast laser irradiates point by point in a lap joint manner to generate a thermo-mechanical composite effect. The thermal effect drives the local melting of the metal nanoparticles, and the mechanical effect drives the atomic diffusion between the metal nanoparticles, jointly driving the nanoparticles to coalesce with each other; the low-temperature sintering of the metal nanoparticles on the flexible substrate and the preparation of the flexible circuit are realized through the thermo-mechanical composite effect introduced by the ultrafast laser. The nanoparticles coalesce sufficiently, the conductivity of the conductive region is high, and the selection range of the flexible substrate material is wide; the semi-embedding of the conductive region into the substrate is realized by introducing a bonding layer in the flexible substrate, and the mechanical deformation durability of the flexible circuit is good; the flexible circuit is prepared by laser direct writing without a mask, the process flow is simple, and the period is short; the adhesion of the conductive circuit on the flexible substrate after laser direct writing meets the requirements, realizing the preparation of a flexible circuit with high conductivity, fast speed and no pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present invention will become more obvious:

[0024] Figure 1 It is a schematic diagram of the method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles mainly embodied in the present invention;

[0025] Figure 2 It is a schematic flow diagram of the method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles mainly embodied in the present invention;

[0026] Figure 3 It is the morphology of the sintering region of metal nanoparticles irradiated by ultrafast laser under a scanning electron microscope mainly embodied in the present invention;

[0027] Figure 4 It is the result of the resistance change in the bending test of the flexible circuit prepared by ultrafast laser sintering of metal nanoparticles mainly embodied in the present invention.

[0028] As shown in the figure:

[0029] Shaping and scanning optical path 1 Bonding layer 9

[0030] Focused laser beam 2 Substrate 10

[0031] Flexible substrate 3 Ultrafast laser 11

[0032] Flexible circuit 4 Pulsed ultrafast laser beam 12

[0033] Preheating device 5 Glass container 13

[0034] Motion system 6 Organic solvent 14

[0035] Metal nanoparticle sintering region 7 High-energy focused laser beam 15

[0036] Metal nanoparticle layer 8 Specific embodiments

[0037] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0038] Embodiment 1

[0039] As Figure 1 and 2 shown, a method for preparing a flexible circuit by sintering metal nanoparticles with an ultrafast laser according to the present invention includes the following steps:

[0040] Step S1: Coat the surface of the flexible substrate 3 with a metal nanoparticle slurry, and dry it to remove the slurry solvent to form a metal nanoparticle layer 8;

[0041] Step S2: Lay the flexible substrate 3 flat on the preheating device 5, and heat the flexible substrate 3 to a set temperature through the preheating device 5 to preheat the metal nanoparticle layer 8 coated on the surface of the flexible substrate 3;

[0042] Step S3: Focus the pulsed laser generated by the ultrafast laser light source 11 on the surface of the metal nanoparticle layer 8, and sinter the metal nanoparticles to form a conductive metal nanoparticle sintering region 7 without thermal damage to the flexible substrate 3;

[0043] Step S4: Adjust the position of the metal nanoparticle sintering region 7 by the relative movement of the pulsed laser beam and the flexible substrate 3 to realize the preparation of the patterned flexible circuit 4.

[0044] In step S1, the metal nanoparticle slurry is a homogeneous mixture of metal nanoparticles and an organic solvent that is volatile upon heating. The metal nanoparticles are metal microspheres or microflakes with a nanoscale particle size. The solid content of the slurry is controlled to be higher than the critical value at which a continuous and uniform nanoparticle layer can be formed after coating and drying.

[0045] In step S1, the flexible substrate 3 includes: a bonding layer 9 and a substrate 10. The bonding layer 9 covers the substrate 10, and the metal nanoparticle slurry is coated on the bonding layer 9. The bonding layer 9 is used to enhance the bonding strength between the surface metal nanoparticle layer 8 and the underlying substrate 10, and the material is a polymer with a low elastic modulus; the substrate 10 is a rigid substrate or a flexible substrate.

[0046] The preheating device 5 is used to fully preheat the flexible substrate 3. In step S2, the preheating temperature of the preheating device 5 is lower than the melting point of the metal nanoparticles and lower than the glass transition temperature or the thermal damage temperature of the flexible substrate 3.

[0047] In step S2, the preheating device 5 is disposed at the bottom of the flexible substrate 3, and a motion system 6 is provided at the bottom of the preheating device 5. The motion system 6 drives the preheating device 5 to move in the horizontal direction. The motion system 6 is used to change the relative position between the pulsed laser beam and the flexible substrate 3, irradiate the metal nanoparticle layer 8 to sinter and densify it to form a conductive region, and realize the preparation of patterned flexible circuits 4 with different arrangements or shapes.

[0048] In step S3, the pulsed ultrafast laser beam 12 generated by the ultrafast laser light source 11 is incident on the shaping and scanning optical path device 1, and the shaping and scanning optical path device 1 emits a focused laser beam 2 downward. The focused laser beam 2 is used to irradiate the metal nanoparticles to sinter and densify them to form a conductive region.

[0049] In step S3, the laser energy density of the focused laser beam 2 is lower than the ablation removal threshold of the metal nanoparticle layer 8 and can generate local melting heat effects and impact densification force effects.

[0050] In a specific embodiment, the shaping and scanning optical path device 1 is connected to a control device, and the shaping and scanning optical path device 1 can move parallel to the flexible substrate 3 without the motion system 6 driving the preheating device 5 to drive the flexible substrate 3 to move. In another specific embodiment, two moving methods, namely, the control device connected to the shaping and scanning optical path device 1 and the driving of the motion system 6, can be adopted to realize the relative motion between the light beam and the flexible substrate 3.

[0051] In step S3, the resistivity of the metal nanoparticle sintering region 7 is about 2.2×10 -8 Ω·m, about 1.4 times that of bulk silver, and the thickness is between 1 - 3 μm. After 4000 bending tests, its resistivity remains basically unchanged.

[0052] This application is further elaborated through a specific embodiment. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles includes the following steps:

[0053] Step S1: Select appropriate materials for the bonding layer 9 and the substrate 10 according to the function, shape, and size of the flexible circuit to be fabricated. Cut them into small pieces of 25 mm × 50 mm, and sequentially place them in anhydrous ethanol and deionized water for ultrasonic cleaning of the surface. After cleaning, take them out and let them dry naturally; select an appropriate bonding process to bond the bonding layer 9 on the surface of the substrate 10; select an appropriate film-forming process to coat the metal nanoparticle slurry on the surface of the bonding layer 9, and after drying to evaporate most of the solvent, obtain a dry metal nanoparticle layer 8;

[0054] Step S2: Select appropriate preheating temperature of the preheating device 5 and parameters of the focused laser beam 2 according to the function, shape, and size of the flexible circuit to be fabricated;

[0055] Step S3: Irradiate the focused laser beam 2 on the surface of the metal nanoparticle layer 8 to perform the process of ultrafast laser sintering of metal nanoparticles. Through the two-dimensional planar movement of the motion platform 6, the metal nanoparticle sintering region 7 is arranged in a certain pattern, and the preparation of the flexible circuit 4 is completed;

[0056] Step S4: Immerse the conductive pattern 4 after ultrafast laser sintering in a glass container 13 filled with an organic solvent 14 to wash away the excess metal nanoparticles; or, irradiate the high-energy focused laser beam 15 on the surface of the excess metal nanoparticle layer 8 around the conductive pattern 4 to perform a laser ablation process, and remove the excess metal nanoparticles through the two-dimensional planar movement of the motion platform 6, then the flexible circuit 4 can be obtained.

[0057] The morphologies of the metal nanoparticle sintering region 7 and the flexible circuit 4 after processing under a scanning electron microscope are as Figure 3 shown, with a low porosity. The resistance change curve after the bending test is as Figure 4 shown. After 4000 bending tests, its resistance value remains basically unchanged, showing good bending durability.

[0058] In this application, the flexible substrate 3 preheats and softens the metal nanoparticles to reduce their deformation resistance; the ultrafast laser irradiates point by point and overlaps, generating a thermal-mechanical composite effect. The thermal effect drives the local melting of the metal nanoparticles, and the mechanical effect drives the atomic diffusion between the metal nanoparticles, jointly driving the nanoparticles to coalesce with each other. This application realizes the low-temperature sintering of metal nanoparticles on the flexible substrate 10 and the preparation of the flexible circuit 4 through the thermal-mechanical composite effect introduced by the ultrafast laser. The nanoparticles coalesce sufficiently, the conductivity of the conductive region is high, and the material selection range of the flexible substrate 10 is wide; by introducing the bonding layer 9 into the flexible substrate 3, the conductive region is semi-embedded in the substrate 10, and the mechanical deformation durability of the flexible circuit 4 is excellent; by preparing the flexible circuit 4 by laser direct writing, no mask is required, the process flow is simple, and the cycle is short; after laser direct writing, the adhesion of the conductive circuit on the flexible substrate 10 meets the requirements, realizing the preparation of a flexible circuit with high conductivity and no pollution quickly.

[0059] Compared with the existing laser sintering and direct writing technologies, this application realizes the comprehensive utilization of the thermal effect of local melting of the ultrafast laser and the impact densification mechanical effect through the preheating device 5, and can prepare a flexible circuit with excellent performance of high conductivity and low porosity.

[0060] This application increases the bonding strength between the circuit and the substrate 10 through the bonding layer 9 in the flexible substrate 3 and the shock wave mechanical effect introduced by the ultrafast laser, improving the mechanical bending durability of the flexible circuit.

[0061] This application manufactures the flexible circuit through the printing process of laser direct writing. There is no mask in the processing process, and one laser pulse can complete the manufacture of a dense sintering area, which has the advantages of simple process flow, large process flexibility, high processing resolution, and high processing efficiency.

[0062] Example 2

[0063] A system for preparing a flexible circuit by sintering metal nanoparticles with an ultrafast laser according to the present invention is applied to the method for preparing a flexible circuit by sintering metal nanoparticles with an ultrafast laser in Example 1, including: an ultrafast laser light source 11, a preheating device 5, and a flexible substrate 3. A metal nanoparticle layer 8 is coated on the upper surface of the flexible substrate 3. The preheating device 5 is arranged at the bottom of the flexible substrate 3. The pulsed laser generated by the ultrafast laser light source 11 is focused on the surface of the metal nanoparticle layer 8 to sinter and form a metal nanoparticle sintering area 7, and the pulsed laser beam and the flexible substrate 3 can move relative to each other.

[0064] The ultrafast laser light source 11 and / or the preheating device 5 is connected with a moving device. The relative movement is realized by controlling the deflection of the laser beam by a galvanometer to irradiate the metal nanoparticles point by point; or the relative movement trajectory of the light beam and the flexible substrate 3 is realized by controlling the planar movement of a two-dimensional movement platform.

[0065] The flexible substrate 3 with its surface coated with metal nanoparticle paste and dried to remove the solvent is placed on the preheating device 5 for sufficient heating. The focused laser beam 2 generated by the ultrafast laser light source 11 is focused on the surface of the metal nanoparticle layer 8, causing the metal nanoparticles to undergo local melting and simultaneously generating shock waves, thereby achieving low-temperature sintering of the metal nanoparticles on the flexible film. According to the shape and size required by the function of the conductive pattern, the position of the focused laser beam 2 or the motion system 6 is adjusted to achieve rapid and flexible preparation of the flexible circuit.

[0066] This application can achieve low-temperature sintering of metal nanoparticles and preparation of flexible circuits, and has the advantages of high conductivity, high resolution, high durability, high processing efficiency, and high process flexibility, meeting the circuit manufacturing requirements in the field of flexible electronics.

[0067] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application.

[0068] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of this application and the features in the embodiments can be arbitrarily combined with each other.

Claims

1. A method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles, characterized in that: The following steps are involved: Step S1: coating a metal nanoparticle slurry on the surface of a flexible substrate (3), and removing the slurry solvent through drying to form a metal nanoparticle layer (8); Step S2: heating the flexible substrate (3) to a set temperature by means of a preheating device (5) to preheat the metal nanoparticle layer (8) coated on the surface of the flexible substrate (3); Step S3: The pulsed laser generated by the ultrafast laser light source (11) is focused on the surface of the metal nanoparticle layer (8), and the metal nanoparticles are sintered to form a conductive metal nanoparticle sintered region (7) without causing thermal damage to the flexible substrate (3); Step S4: adjusting the position of the metal nanoparticle sintering region (7) through the relative movement of the pulsed laser beam and the flexible substrate (3) to achieve the preparation of the patterned flexible circuit (4).

2. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles according to claim 1, characterized in that: In the step S1, the flexible substrate (3) comprises: a bonding layer (9) and a base (10), the bonding layer (9) covers the base (10), and the metal nanoparticle slurry is coated on the bonding layer (9).

3. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles according to claim 1, characterized in that: In the step S2, the preheating temperature of the preheating device (5) is lower than the melting point of the metal nanoparticles and lower than the glass transition temperature or thermal damage temperature of the flexible substrate (3).

4. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles according to claim 1, characterized in that: In the step S2, the preheating device (5) is arranged at the bottom of the flexible substrate (3), and a motion system (6) is arranged at the bottom of the preheating device (5), and the motion system (6) drives the preheating device (5) to move in a horizontal direction.

5. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles according to claim 1, characterized in that: In the step S3, the pulsed ultrafast laser beam (12) generated by the ultrafast laser light source (11) is injected into the shaping and scanning optical path device (1), and the shaping and scanning optical path device (1) emits a focused laser beam (2) downward.

6. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles as claimed in claim 5, characterized in that: In the step S3, the laser energy density of the focused laser beam (2) is lower than the ablation removal threshold of the metal nanoparticle layer (8) and is capable of generating a local melting heat effect and an impact densification force effect.

7. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles as claimed in claim 5, characterized in that: The shaping and scanning optical path device (1) is connected to a control device, and the shaping and scanning optical path device (1) is capable of moving parallel to the flexible substrate (3).

8. The method for preparing a flexible circuit by ultrafast laser sintering of metal nanoparticles as claimed in claim 1, characterized in that: In the step S3, the resistivity of the metal nanoparticle sintering region (7) is 2.2×10 -8 Ω·m, thickness is between 1-3μm.

9. A system for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles, applied to the method for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles as claimed in any one of claims 1 to 8, characterized in that: include: An ultrafast laser light source (11), a preheating device (5), and a flexible substrate (3); the upper surface of the flexible substrate (3) is coated with a metal nanoparticle layer (8); the preheating device (5) is arranged at the bottom of the flexible substrate (3); the pulsed laser generated by the ultrafast laser light source (11) is focused on the surface of the metal nanoparticle layer (8) to sinter and form a metal nanoparticle sintering area (7); and the pulsed laser beam and the flexible substrate (3) are capable of relative movement.

10. The system for preparing flexible circuits by ultrafast laser sintering of metal nanoparticles as claimed in claim 9, characterized in that: The ultrafast laser light source (11) and / or the preheating device (5) are connected to a moving device.

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