A coaxial electrostatic printing method for fabricating microscale electronic structures on rough surfaces

Abstract

A coaxial electrostatic printing method for manufacturing microscale electronic structures on a rough surface comprises the following steps: first, conductive material and insulating material are respectively injected into a printing syringe, and the syringes are assembled with a coaxial needle and a printing platform; then, according to the geometric pattern of the conductive structure, an electric field-driven coaxial electrostatic printing process is adopted to print a preset microscale electronic structure on the rough substrate surface; finally, a high-temperature sintering process is used to perform a sintering post-treatment on the conductive material in the conductive structure to improve its conductivity, and the insulating packaging material in the microscale electronic structure and the liquid filling material on the rough substrate surface are solidified, and the interfacial adhesion between the insulating packaging material in the microscale electronic structure and the liquid filling material on the rough substrate surface is enhanced; during the printing process, the present invention utilizes the characteristic that the outer layer of the insulating material of the coaxial needle diffuses and fills the rough surface rapidly, thereby realizing efficient and rapid manufacturing of high-resolution microscale electronic structures on rough surfaces, and has the advantages of low cost, high efficiency, environmental protection and non-toxicity.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing of microscale electronic structures, and in particular relates to a coaxial electrostatic printing method for manufacturing microscale electronic structures on a rough surface. Background Art

[0002] Micro-nano electronic circuits have broad application prospects in aerospace, bio-detection, and wearable electronic devices, and have enormous market potential. As an emerging micro-nano 3D printing technology, electric field-driven electrostatic printing has outstanding advantages in manufacturing high-precision micro-nano electronic structures, complex three-dimensional micro-nano electronic structures, flexible electronics, and sensors. It also has the advantages of simple equipment, low cost, a wide variety of usable materials, no need for masks or molds, and direct forming (Lan Hongbo, Li Dichen, Lu Bingheng. Micro-nano scale 3D printing [J]. Science China: Technological Sciences, 2015(9):22. DOI:CNKI:SUN:JEXK.0.2015-09-002).

[0003] At present, when electrostatic printing is used to manufacture micro-nano electronic structures, ordinary glass with smooth surface, conductive glass, photocurable resin templates, extrusion-printed polylactic acid templates and various flexible films (such as silicone film, polyimide film, polyester film and polyvinyl alcohol film, etc.) are mainly used as printing substrates to ensure the uniform distribution of electric field charge and the stability of cone jet during the printing process, thereby improving the printing accuracy and conductivity of micro-nano electronic structures.

[0004] However, in actual engineering applications, when printing micro-scale electronic structures on rough ceramic, wood, and polymer surfaces, the electrostatic printing process will cause uneven charge distribution during the printing process due to the rough surface, resulting in unstable cone jets, which in turn affects the printing accuracy and connectivity of the micro-nano electronic structures. On the other hand, when using multi-material 3D printing processes (such as extrusion printing and electrostatic printing) to manufacture functional structural electronic devices, the required polymer substrate is first printed through an extrusion process. For example, samples made of polylactic acid and polyetheretherketone (PEEK) are generally rough due to the multi-layer printing process. There are small grooves and holes. In the electrostatic printing process, the rough surface will also affect the stability of the cone jet, thereby reducing the printing accuracy and connectivity of the micro-nano electronic structure.

[0005] To address these issues, physical polishing and chemical coating are typically used to treat rough surfaces, reducing surface roughness and making the surface topography more uniform and the charge distribution more uniform, which is beneficial for a more stable conductive material jetting process during electrostatic printing. However, physical polishing often relies on manual experience to control the polishing time and position, resulting in poor consistency in surface roughness across multiple samples. Chemical coating (R. Singh, S. Singh, IPS Singh, F. Fabbrocino, F. Fraternali, Investigation for surface finish improvement of FDM parts by vapor smoothing process, Compos. Part BEng. 111 (2017) 228–234.) requires different organic solvents for treating rough surfaces of different materials, and some organic solvents require spin coating and post-processing, making the entire manufacturing process complex, inefficient, and prone to environmental pollution. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a coaxial electrostatic printing method for manufacturing microscale electronic structures on rough surfaces. During the printing process, the characteristic of the outer layer insulating material of the coaxial needle rapidly diffuses and fills the rough surface, thereby overcoming the problems such as jet instability caused by uneven charge distribution during electrostatic printing due to the rough surface of the substrate, and realizing efficient and rapid manufacturing of high-resolution microscale electronic structures on rough surfaces, and further realizing the integrated preparation of curved conformal microscale electronic structures and interlayer embedded microscale electronic structures; this method does not require photolithography and sputtering equipment, does not have a complex multi-step process, and will not cause a large amount of conductive / insulating material waste, and has the advantages of low cost, high efficiency, environmental protection and non-toxicity.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A coaxial electrostatic printing method for manufacturing microscale electronic structures on a rough surface comprises the following steps:

[0009] Step 1: Select conductive materials and insulating materials as printing inks for rough surface micro-scale conductive structures, inject the conductive materials and insulating materials into the printing syringes respectively, and assemble them with the coaxial needle and the printing platform;

[0010] Step 2: Based on the designed conductive structure geometry, a coaxial electrostatic printing process driven by an electric field is used to print the preset microscale electronic structure on the rough substrate surface;

[0011] During the coaxial electrostatic printing process, a coaxial conical jet with an outer layer of insulating material enveloping an inner layer of conductive material is formed at the outlet of the coaxial needle. As the printing platform moves, part of the insulating material on the outer layer of the coaxial needle first contacts the rough substrate surface. Part of the insulating material instantly diffuses on the rough surface and fills and covers the printing area, forming a dense liquid protective layer on the rough surface, reducing the surface roughness.

[0012] While a liquid protective layer is formed on the rough substrate surface, a microscale conductive structure with an encapsulation layer is fabricated on the liquid protective layer on the rough substrate surface by coaxial electrostatic printing. During the printing process, the insulating material diffuses and fills the rough surface near the coaxial needle while printing the microscale conductive structure with the encapsulation layer on the filled surface until printing is complete.

[0013] Step 3: Using a high-temperature sintering process, according to the set sintering temperature, sintering time and sintering curve, the conductive material in the conductive structure is sintered to improve its conductivity and the insulating material in the micro-scale conductive structure is solidified;

[0014] Step 4: Using a high-temperature sintering process, according to the set sintering temperature, sintering time and sintering curve, the liquid protective layer on the surface of the rough substrate is solidified and the interface adhesion between the liquid protective layer and the rough surface substrate is enhanced.

[0015] The conductive material and the insulating material in step 1 are two mutually immiscible materials with greatly different fluidity, and their electrical conductivities are similar or greatly different, ensuring that at least one of the materials is sensitive to the electric field.

[0016] The conductive material in step 1 is a conductive paste containing 10-1000nm metal particles, including micro / nano conductive silver paste, micro / nano conductive copper paste, micro / nano conductive platinum paste and micro / nano conductive gold paste, and also includes resistor pastes, sensor pastes and other micro / nano metal or non-metal electronic materials of various models and various raw materials.

[0017] The insulating material in step 1 is polydimethylsiloxane (PDMS), polyimide solution (PI), polyurethane solution, Ecoflex series silicone, silicone oil of different viscosities and other insulating materials.

[0018] The printing syringes in step 1 are 5ml and 10ml plastic dispensing syringes respectively.

[0019] The coaxial needle in step 1 is a combination of an inner needle size of 18G-28G and an outer needle size of 16G-28G, and the coaxial needle is made of stainless steel.

[0020] The rough substrate surface in step 2 includes a planar / curved rough surface manufactured by machining, extrusion 3D printing, laser cutting, or other processing techniques.

[0021] The rough substrate surface material in step 2 includes various types of ceramic materials, foam materials, wood materials, nylon materials, and light-curing resin materials suitable for extrusion 3D printing, ABS resin materials, polylactic acid (PLC) materials, polycaprolactone (PCL), polyetheretherketone (PEEK) materials and various polyetheretherketone composite materials.

[0022] The microscale conductive structure in step 2 is a microscale electronic structure having an encapsulation layer, or a microscale electronic structure having interlayer or intralayer connections.

[0023] The process parameters of the electric field driven coaxial electrostatic printing in step 2 include: inner and outer diameters of the coaxial needle, printing voltage, printing speed, receiving distance between the needle and the substrate, and extrusion pressure of the two materials.

[0024] The printing voltage used in step 2 is 1000-3000V; the printing speed is 10-100mm / s; the receiving distance between the needle and the substrate is 50μm-350μm, the extrusion pressure of the inner conductive material is 500mbar-6500mbar, and the extrusion pressure of the outer insulating material is 10mbar-1000mbar.

[0025] The thickness of the liquid protective layer in step 2 is 100 nm to 100 μm.

[0026] In step 2, the line width of the microscale electronic structure is 10 μm to 1000 μm, and the thickness is 2 μm to 50 μm; the thickness of the insulating material is 1 μm to 1000 μm, and the line width of the insulating material is 10 μm to 2000 μm.

[0027] In step 2, the microscale conductive structure is printed by a coaxial electrostatic printing method to realize the printing of a single-layer microscale conductive structure with a rough surface, or a multi-layer superposition printing method to realize the manufacture of a multi-level three-dimensional microscale circuit structure with interlayer insulation, depending on the size and requirements of the conductive structure; the number of layers, line width and thickness of the multi-level three-dimensional microscale electronic structure with interlayer insulation increases with the increase of the number of printed layers.

[0028] The high-temperature sintering process in step 3 and step 4 is one or more of air sintering, vacuum sintering and inert gas sintering; vacuum sintering is selected, the sintering temperature is 100° C.-320° C., and the sintering time is 45 minutes-180 minutes.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention proposes a coaxial electrostatic printing method for manufacturing microscale electronic structures on rough surfaces. At the moment of printing the microscale electronic structure on the rough surface, part of the insulating material first quickly diffuses on the rough surface and fills the local printing area to form a dense liquid protective layer, which helps to uniformly distribute the charge and stabilize the cone jet, greatly improves the morphology and connectivity of the microscale electronic structure on the rough surface, and helps to achieve efficient and rapid manufacturing of high-resolution microscale electronic structures on rough surfaces.

[0031] Compared with the complex process of existing traditional technologies that require physical polishing of the rough surface or spin coating of chemical reagents on the rough surface and then depositing the microscale electronic structure on its surface, the process of the present invention is simple and has high manufacturing efficiency. It does not require pretreatment of the rough surface. The accuracy of the microscale electronic structure is not affected by the surface roughness of the substrate structure. It can realize the simple and efficient manufacturing of conformal / embedded microscale conductive structures on rough surfaces of various materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of a method according to an embodiment of the present invention.

[0033] Figure 2 This is a SEM morphology characterization of the rough surface of the extrusion-printed PEEK structure in an embodiment of the present invention.

[0034] Figure 3 This is a physical image and a partially enlarged microscopic image of the microscale electronic structure produced by coaxial electrostatic printing on the rough surface of PEEK according to an embodiment of the present invention.

[0035] Figure 4 This is a real picture and a partially enlarged picture of the printed curved conformal microscale electronic structure on the surface of a PEEK rough curved substrate according to an embodiment of the present invention.

[0036] Figure 5 These are actual photos of the microscale electronic structure embedded between PEEK layers and CT characterization images of the three-dimensional morphology of the interlayer conductive structure in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the embodiments and accompanying drawings.

[0038] Reference Figure 1 , a coaxial electrostatic printing method for manufacturing microscale electronic structures on a rough surface, comprising the following steps:

[0039] Step 1: Select conductive materials and insulating materials as printing inks for rough surface microscale electronic structures, inject the conductive materials and insulating materials into the printing syringes respectively, and assemble them with the coaxial needle and the printing platform;

[0040] In this embodiment, the conductive material and the insulating material are two mutually immiscible materials with greatly different fluidity. Their conductivity is similar or greatly different, ensuring that at least one material is more sensitive to the electric field, which is conducive to the formation of the coaxial cone jet. The conductive material is a conductive paste containing 100nm metal particles, which is a micro / nano conductive silver paste; the insulating material is polydimethylsiloxane (PDMS); the printing syringes are 5ml plastic dispensing syringes; the coaxial needle is a combination of an inner needle with a size of 18G-28G and an outer needle with a size of 16G-28G, and the coaxial needle material is stainless steel;

[0041] Step 2: Based on the designed conductive structure geometry, a coaxial electrostatic printing process driven by an electric field is used to print the preset microscale electronic structure on the rough substrate surface;

[0042] During the coaxial electrostatic printing process, a coaxial conical jet with an outer layer of insulating material wrapped around an inner layer of conductive material is formed at the outlet of the coaxial needle. In conjunction with the movement of the printing platform, part of the insulating material on the outer layer of the coaxial needle first contacts the rough substrate surface. Part of the insulating material instantly diffuses on the rough surface and fills and covers the printing area, forming a dense liquid protective layer on the rough surface to reduce the surface roughness. While the liquid protective layer is forming on the rough substrate surface, a microscale conductive structure with an encapsulation layer is manufactured on the liquid protective layer on the rough substrate surface through coaxial electrostatic printing. During the printing process, the insulating material diffuses and fills the rough surface near the coaxial needle, while printing the microscale electronic structure with an encapsulation layer on the filled surface until printing is completed.

[0043] In this embodiment, the rough substrate surface is a planar / curved rough surface processed by extrusion 3D printing. The rough substrate surface is made of polyetheretherketone (PEEK) material with a surface roughness of ≥10 μm. The microscale electronic structure is a microscale electronic structure with an encapsulation layer. The process parameters of the electric field-driven coaxial electrostatic printing include: inner and outer diameters of the coaxial needle, printing voltage, printing speed, receiving distance between the needle and the substrate, and extrusion pressure of the two materials. The printing voltage is 2000 V; the printing speed is 50 mm / s; the receiving distance between the needle and the substrate is 200 μm; the extrusion pressure of the inner conductive material is 1000 mbar. The outer insulating material is extruded at a pressure of 500 mbar. The liquid protective layer is 100 μm thick, which helps to evenly distribute the charge and stabilize the conical jet, enabling stable and efficient fabrication of microscale circuits on rough surfaces. The line width of the microscale electronic structure is 50 μm and the thickness is 3 μm. The thickness of the insulating material is 10 μm, and the line width of the insulating material is 150 μm. The microscale electronic structure is printed in a multi-layer stacked manner, based on the size and requirements of the conductive structure, to achieve the fabrication of multi-level three-dimensional microscale circuit structures with interlayer insulation. The number of layers, line width, and thickness of the multi-level three-dimensional microscale electronic structure with interlayer insulation increase with the number of printed layers.

[0044] Step 3: Using a high-temperature sintering process, according to the set sintering temperature, sintering time and sintering curve, the conductive material in the conductive structure is sintered to improve its conductivity and the insulating material in the micro-scale conductive structure is solidified;

[0045] Step 4: Using a high-temperature sintering process, according to the set sintering temperature, sintering time and sintering curve, the liquid protective layer on the surface of the rough substrate is solidified and the interface adhesion between the liquid protective layer and the rough surface substrate is enhanced.

[0046] The high-temperature sintering process in step 3 and step 4 of this embodiment is vacuum sintering, the sintering temperature is 100° C.-320° C., and the sintering time is 45 minutes-180 minutes.

[0047] Reference Figure 2 , Figure 2 The SEM morphology characterization image and three-dimensional morphology characterization image of the rough surface of the extruded 3D printed PEEK structure in the embodiment show that the surface of the extruded printed PEEK structure is uneven, with obvious protrusions and depressions, which seriously affect the continuity and consistency of the microscale electronic structure during the printing process.

[0048] Reference Figure 3 , Figure 3 The actual picture and the locally enlarged microscopic picture of the microscale electronic structure of the coaxial electrostatic printing on the rough surface of PEEK in the embodiment show that the morphology of the microscale electronic structure of the coaxial electrostatic printing on the rough surface of PEEK is uniform and consistent, with good continuity, and it can be seen that the insulating material has obvious diffusion phenomenon in the electronic structure. It can be seen that the coaxial electrostatic printing method of the present invention can effectively solve the problems such as jet instability caused by uneven charge distribution during electrostatic printing due to the rough surface, and realize the efficient and rapid manufacturing of high-resolution microscale electronic structures on rough surfaces.

[0049] Reference Figure 4 , Figure 4 The actual picture and local magnified picture of the printed curved conformal microscale electronic structure on the surface of the rough curved surface PEEK substrate in the embodiment show that the array of conformal microscale electronic structures on the surface of the rough curved surface PEEK substrate has a complete and continuous morphology and good structural consistency. It can be seen that the coaxial electrostatic printing method of the present invention can be extended to the manufacture of conformal microscale electronic structures on the surface of rough curved surface substrates.

[0050] Reference Figure 5 , Figure 5These are actual photos of the microscale electronic structure embedded between PEEK layers in the embodiment and a CT characterization of the three-dimensional morphology of the interlayer conductive structure. From the CT characterization side view, it can be clearly seen that there are three layers of microscale electronic structures inside the PEEK structure. From the CT characterization top view, it can be clearly seen that the morphology of the three layers of microscale electronic structures inside the PEEK structure is complete and continuous. It can be seen that the coaxial electrostatic printing method of the present invention can be combined with other printing methods, such as extrusion 3D printing, to achieve integrated manufacturing of interlayer embedded microscale electronic structures.

Claims

1. A coaxial electrostatic printing method for manufacturing microscale electronic structures on rough surfaces, characterized in that: The following steps are involved: Step 1: Select conductive materials and insulating materials as printing inks for rough surface micro-scale conductive structures, inject the conductive materials and insulating materials into the printing syringes respectively, and assemble them with the coaxial needle and the printing platform; Step 2: Based on the designed conductive structure geometry, a coaxial electrostatic printing process driven by an electric field is used to print the preset microscale electronic structure on the rough substrate surface; During the coaxial electrostatic printing process, a coaxial conical jet with an outer layer of insulating material enveloping an inner layer of conductive material is formed at the outlet of the coaxial needle. As the printing platform moves, part of the insulating material on the outer layer of the coaxial needle first contacts the rough substrate surface. Part of the insulating material instantly diffuses on the rough surface and fills and covers the printing area, forming a dense liquid protective layer on the rough surface, reducing the surface roughness. While forming a liquid protective layer on the surface of the rough substrate, a microscale conductive structure having an encapsulation layer is manufactured on the liquid protective layer on the surface of the rough substrate by coaxial electrostatic printing; During the printing process, the insulating material diffuses and fills the rough surface near the coaxial needle, while printing the microscale electronic structure with the encapsulation layer on the filled surface until the printing is completed; Step 3: Using a high-temperature sintering process, according to the set sintering temperature, sintering time and sintering curve, the conductive material in the conductive structure is sintered to improve its conductivity and the insulating material in the microscale electronic structure is solidified; Step 4: Using a high-temperature sintering process, according to the set sintering temperature, sintering time and sintering curve, the liquid protective layer on the surface of the rough substrate is solidified and the interface adhesion between the liquid protective layer and the rough surface substrate is enhanced.

2. The method according to claim 1, wherein: The conductive material and the insulating material in step 1 are two mutually immiscible materials with greatly different fluidity, and their electrical conductivities are similar or greatly different, ensuring that at least one of the materials is sensitive to the electric field.

3. The method according to claim 1, wherein: The conductive material in step 1 is a conductive paste containing 10-1000nm metal particles, including micro / nano conductive silver paste, micro / nano conductive copper paste, micro / nano conductive platinum paste and micro / nano conductive gold paste, and also includes resistor pastes, sensor pastes and other micro / nano metal or non-metal electronic materials of various models and various raw materials.

4. The method according to claim 1, wherein: The insulating material in step 1 is polydimethylsiloxane (PDMS), polyimide solution (PI), polyurethane solution, Ecoflex series silicone or silicone oil of different viscosities.

5. The method according to claim 1, wherein: The rough substrate surface material in step 2 includes various types of ceramic materials, foam materials, wood materials, nylon materials, and light-curing resin materials suitable for extrusion 3D printing, ABS resin materials, polylactic acid (PLC) materials, polycaprolactone (PCL), polyetheretherketone (PEEK) materials and various polyetheretherketone composite materials.

6. The method according to claim 1, wherein: The electric field-driven coaxial electrostatic printing process parameters in step 2 include: inner and outer diameter dimensions of the coaxial needle, printing voltage, printing speed, receiving distance between the needle and the substrate, and extrusion pressure of the two materials; printing voltage 1000-3000V; printing speed 10-100mm / s; receiving distance between the needle and the substrate 50μm-350μm, inner conductive material extrusion pressure 500mbar-6500mbar, outer insulating material extrusion pressure 10mbar-1000mbar.

7. The method according to claim 1, wherein: The thickness of the liquid protective layer in step 2 is 100 nm to 100 μm.

8. The method according to claim 1, wherein: In step 2, the line width of the microscale electronic structure is 10 μm to 1000 μm, and the thickness is 2 μm to 50 μm; the thickness of the insulating material is 1 μm to 1000 μm, and the line width of the insulating material is 10 μm to 2000 μm.

9. The method according to claim 1, wherein: In step 2, the microscale electronic structure is selected to print a single-layer microscale electronic structure with a rough surface by a coaxial electrostatic printing method, or to manufacture a multi-layer three-dimensional microscale electronic structure with interlayer insulation by a multi-layer superposition printing method, depending on the size and requirements of the conductive structure; the number of layers, line width and thickness of the multi-layer three-dimensional microscale electronic structure with interlayer insulation increases with the increase in the number of printed layers.

10. The method according to claim 1, wherein: The high-temperature sintering process in step 3 and step 4 is one or more of air sintering, vacuum sintering and inert gas sintering; vacuum sintering is selected, the sintering temperature is 100° C.-320° C., and the sintering time is 45 minutes-180 minutes.

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