Electrostatic spray filling metallization method and device for group hole vertical interconnection

Abstract

The invention belongs to the field of micro-nano manufacturing, and discloses an electrostatic spray filling metallization method and device for group hole vertical interconnection. The method comprises the following steps: (1) carrying out modification treatment on the inner wall surface of a micropore in a substrate by adopting plasma; and (2) electrostatic spraying is carried out on the micropores in the upper area and the lower area of the substrate, along with accumulation of charges on the outer surfaces of the micropores, the electric potential of the outer surfaces of the micropores is higher than that in the micropores, meanwhile, electric field lines are focused into the micropores, then particles generated by electrostatic spraying are deposited into the micropores, and metal conductive layers are formed on the inner walls of the micropores. According to the invention, the electrofluid spray surface is used for depositing charged particles before and after the electrofluid spray surface is deposited, and the electrofluid spray surface is used for depositing charged particles, so that a non-uniform self-focusing electric field is constructed through droplet charge accumulation to realize rapid metallization of the micropores.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-nano manufacturing, and more particularly, to a method and device for electrostatic spray filling metallization oriented to group-hole vertical interconnection. BACKGROUND

[0002] In the field of aerospace and weapon equipment manufacturing, products and their parts and components tend to be small, light, multi-functional and high-reliability, and higher and higher requirements are put forward for the structure and function integration technology of electronic products. The integrated manufacturing technology of multi-layer three-dimensional circuit is an important guarantee for products and their parts and components to meet the above requirements. For the manufacturing of large multi-layer three-dimensional circuit such as multi-layer active frequency selection surface, the related three-dimensional circuit manufacturing and packaging technology should meet the high-density vertical interconnection and conductive pattern preparation of three-dimensional circuit. Therefore, the vertical interconnection technology and patterned circuit preparation technology are important ways to break through the bottleneck of the development of component integration, miniaturization and light weight under the limitation of installation space of aircraft carrier, and have wide application in the field of military and national defense such as radar antenna cover, conformal antenna and intelligent skin.

[0003] Currently, functional electronic circuits have evolved from single-layer structure circuits to multi-layer three-dimensional system circuit, and the vertical interconnection structure plays an irreplaceable role in the integration of 3D packaging and system integration. At present, there are vacuum / pressure filling, electroplating, printing, inkjet printing and other ways for through-hole metallization. Vacuum / pressure filling fills the conductive slurry into the vertical interconnection micro-hole through the pressure difference between the two sides of the substrate through-hole. It is mainly used for through-hole filling of planar substrates. Vacuum / pressure filling method faces challenges such as filling uniformity, material compatibility, bubble problems and other challenges in the process of micro-hole metallization, and further optimization of process control and material selection is needed. Electroplating technology is a kind of metal deposition process, which converts copper ions into metal form by providing electrons to the solution. Because it does not require complex vacuum process equipment and works at normal temperature and pressure, it is widely used. However, during the electroplating process, due to the difference in current density, a thin metal layer may be formed on the wall of the micro-hole, resulting in insufficient strength of the metal layer on the wall of the micro-hole and environmental pollution. In addition, there are many factors affecting the quality of electroplated copper, and the internal mechanism is complex, and the process is very time-consuming (usually several hours). The way of filling holes by screen printing is to press the slurry into the micro-hole through the movement of the squeegee. The filling workbench is made of porous ceramic, and the workbench is under vacuum when working. However, as the thickness of the substrate increases and the diameter of the micro-hole decreases, the filling uniformity of the screen printing method becomes worse, and the filling completeness of the slurry is uneven, and the slurry is left. Inkjet printing technology uses different printing processes to inject conductive slurry into micro-holes, and then realizes the conductive sintering of the conductive slurry through drying and sintering processes to realize the metallization of the micro-holes. However, the inkjet printing technology still has problems such as unsystematic sintering process and many defects in the sintered micro-holes.

[0004] In summary, the existing technology faces great challenges in realizing high-density group-hole interconnection, and it is urgent to develop a new method that can efficiently and high-quality complete group-hole metallization. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a static spray filling metallization method and device for group-hole vertical interconnection, which aims to realize rapid metallization of micro-holes by changing the surface potential and electric field direction of charged particles before and after surface deposition by electrohydrodynamic spraying, thereby solving the problem of low efficiency and quality of existing micro-hole metallization.

[0006] To achieve the purpose of the present application, according to the first aspect of the present application, a static spray filling metallization method for group-hole vertical interconnection is provided, comprising the following steps:

[0007] (1) The inner wall surface of the micro-hole on the substrate is modified by plasma; wherein the micro-hole is a vertical interconnection hole penetrating through the substrate;

[0008] (2) above the substrate, electrostatic spray to the lower area of the micropore, as the micropore surface charge accumulation, the micropore surface potential is higher than the potential inside the micropore, while the electric field lines focus inside the hole, then the particles produced by the electrostatic spray is deposited in the micropore, forming a metal conductive layer on the inner wall of the micropore.

[0009] As a preferred embodiment of the present application, the voltage of the electrostatic spray is 2000V-4000V.

[0010] As a preferred embodiment of the present application, the distance between the electrostatic spray nozzle and the substrate is 10-20mm.

[0011] As a preferred embodiment of the present application, the radius of the area covered by the charged particles produced by the electrostatic spray on the substrate is not more than 10mm.

[0012] As a preferred embodiment of the present application, the radius of the area covered by the charged particles produced by the electrostatic spray on the substrate is not more than 5mm.

[0013] As a preferred embodiment of the present application, the inner wall surface of the micropore on the substrate is modified by low pressure plasma or atmospheric pressure plasma; the plasma treatment power is 25-400W, and the treatment time is 25s-150s.

[0014] As a preferred embodiment of the present application, the operation of step (2) is repeated, and the substrate is heated after each execution of step (2); the number of repetitions is 3-5 times; the heating temperature is 60-80℃.

[0015] As a preferred embodiment of the present application, after forming a metal conductive layer of target thickness on the inner wall of the micropore of the substrate, the substrate is subjected to conductive heat sintering and annealing.

[0016] As a preferred embodiment of the present application, the substrate is a planar substrate or a curved substrate.

[0017] According to the second aspect of the present application, an electrostatic spray filling and metallization device for group hole vertical interconnection is provided for performing the above method, comprising an electrostatic spray module and a multi-axis motion platform, the electrostatic spray module is installed on the multi-axis motion platform;

[0018] The electrostatic spray module comprises a gas supply unit, an electrostatic spray nozzle and a high voltage power supply; wherein the electrostatic spray nozzle is connected to the high voltage power supply; the gas supply unit is connected to the electrostatic spray nozzle through a flow meter, for controlling the amount of spray from the electrostatic spray nozzle;

[0019] The multi-axis motion platform includes a robotic arm, a rotating base, an electrostatic spraying end, and fixing bolts; wherein, the rotating base is used to fix the substrate by the fixing bolts, and the end of the robotic arm is connected to the electrostatic spraying module, and is used to drive the electrostatic spraying module to move relative to the substrate by the movement of the multi-axis motion platform.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0021] 1. Compared to traditional electroplating for depositing metal layers on the surface of vertically interconnected micropores, this application first modifies the micro / nanostructure and hydrophilicity / hydrophobicity of the micropore inner wall surface through plasma treatment. Then, electrostatic spraying of the micropores rapidly prepares a high-quality metal layer on the inner wall surface, eliminating the need for the complex pretreatment process of electroplating. Specifically, the plasma modification of the micropore inner wall surface improves the micro / nanostructure and hydrophilicity / hydrophobicity, enhancing the continuity, uniformity, and interfacial adhesion of the metal layer filling the micropores. Electrostatic spraying is performed on the micropores directly below the substrate. As charge accumulates on the outer surface of the micropores, the potential on the outer surface becomes higher than the potential inside the micropores. Subsequently, particles generated by electrostatic spraying deposit into the micropores, thereby rapidly achieving the metallization of highly conductive vertically interconnected micropores.

[0022] 2. Due to the electric field-dominated spatial guiding mechanism, it exhibits a significant "self-focusing deposition" capability in microporous structures. Different electrostatic atomization process parameters affect the self-focusing electric field construction effect in micropores. Regarding the spray voltage, as the voltage increases, exceeding 4000V, the radial component of the electric field changes direction, shifting from pointing inwards towards the focusing component to pointing outwards towards the diffusion component. Therefore, excessively high voltage can weaken or even eliminate the self-focusing effect. When the voltage is below 2000V, the electric field force is insufficient to form a Taylor cone and break up droplets, resulting in increased droplet size and random drift. Therefore, to prevent atomization failure and ensure focusing effect, the DC voltage of the power supply connected to the nozzle is preferably between 2000V and 4000V.

[0023] 3. Still referring to the influence of the above-mentioned "self-focusing deposition" capability, as the nozzle height increases, the influence of the nozzle potential component in the electric field weakens, the radial component of the electric field in the orifice area becomes negative and the absolute value increases, resulting in a better focusing effect. At the same time, considering that excessive height will lead to excessive solvent evaporation and charge decay runaway problems, the distance from the nozzle to the multilayer circuit board is preferably selected to be 10mm to 20mm to enhance the focusing effect dominated by surface charge.

[0024] 4、Similarly, the alignment accuracy of the nozzle to the micro-hole has certain influence on the focusing effect, when the offset distance increases, the radial electric field will be weakened, in order to ensure the focusing effect, the radial alignment accuracy of the nozzle to the center of the micro-hole is not more than 5mm.

[0025] 5、The present application preferably realizes the deposition of a metal layer with large thickness by multiple electrohydrodynamic spraying micro-hole filling and heating, and realizes vertical interconnection with high strength.

[0026] 6、The annealing method of the present application is preferably slow cooling in the furnace, and the metal layer on the inner wall of the vertical interconnection micro-hole can be solidified through sintering annealing, and slow cooling can prevent the generation of cracks.

[0027] 7、The present application has strong applicability, is suitable for large-area metal pattern preparation and a large number of micro-hole filling, and compared with traditional electroplating film preparation and micro-hole filling, the efficiency is significantly improved. In addition, by installing the electrohydrodynamic spraying nozzle at the end of the multi-axis motion platform mechanical arm, the filling and metallization of a large number of micro-holes on a plane or a curved surface can be realized, and the speed of micro-hole metallization is improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a structure schematic view of an electrostatic spraying filling and metallization device for group-hole vertical interconnection in the present application.

[0029] Figure 2 It is a flowchart of an electrostatic spraying filling and metallization method for group-hole vertical interconnection in the present application.

[0030] Figure 3 It is a cross-sectional view of metallization of a micro-hole by electrostatic spraying in the present application. Figure 3 The left view in FIG. 4 is a cross-sectional view under the size of 400μm, and the right view is a cross-sectional view under the size of 200μm.

[0031] Figure 4 It is a cross-sectional view of metallization and filling of a micro-hole by electrostatic spraying in the present application. Figure 4 The left view in FIG. 5 is a metallization cross-sectional view without plasma pretreatment, and the right view is a metallization cross-sectional view with plasma pretreatment.

[0032] Figure 5 It is the potential distribution of the inside and outside of a micro-hole before and after deposition of charged particles on the outer surface of the micro-hole obtained by simulation in the present application. Figure 5 In FIG. 6, a is the potential distribution of the inside and outside of the hole when the surface has not deposited charged particles, and b is the potential distribution of the inside and outside of the hole after electrostatic spraying.

[0033] Figure 6 It is the cross-sectional electric field line distribution of the inside and outside of a micro-hole before and after deposition of charged particles on the outer surface of the micro-hole obtained by simulation in the present application.Figure 6 a is the cross-sectional electric field line distribution of the surface before the charged particles are deposited in the micropores, and b is the cross-sectional electric field line distribution after electrostatic spraying.

[0034] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein 1 is a lower dielectric layer, 2 is a conductive metal layer, 3 is an upper dielectric layer, 4 is conductive ink, 5 is an electrostatic spraying nozzle, 6 is a gas supply unit, 7 is a high-voltage power supply, 8 is an upper composite material, 9 is a copper layer, 10 is a lower composite material, 11 is a heat release tape, 12 is a nano silver particle, 13 is a heating plate, 14 is a metal layer with uneven thickness, and 15 is a uniform and continuous metal layer. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0036] In the method for electrostatic spraying filling and metallization of the group-hole vertical interconnection of the present application, first, the inner wall surface of the micropore is modified by plasma treatment to improve the charge dissipation speed and hydrophilic and hydrophobic properties of the inner wall surface of the micropore and to improve the performance of the electrohydrodynamic spraying of the inner wall surface. Then, by using the change of the surface potential and the electric field direction of the micropore before and after the electrohydrodynamic spraying surface deposition of the charged particles, the rapid metallization of the micropore can be realized. Thus, the method of the present application can rapidly realize the metallization of a large number of micropores of a multilayer circuit, and a continuous, dense and large-wall-thickness micropore metal conductive layer is obtained.

[0037] In order to achieve the above-mentioned purpose, in a first aspect, a method for electrostatic spraying filling and metallization of group-hole vertical interconnection is provided, comprising the following steps:

[0038] (1) The inner wall surface of the micropore on the substrate is modified by plasma treatment; wherein the micropore is a vertical interconnection hole penetrating through the substrate, and the pore size is 0.02-1 mm.

[0039] Specifically, a substrate with a conductive layer is selected, and a micropore penetrating through the thickness of the substrate is formed thereon. For example, in a composite multilayer circuit substrate, the upper and lower layers are dielectric layers, and the middle layer is a metal layer, and the surface of the metal layer is cleaned. A heat release tape is attached to the upper surface of the upper dielectric layer. The composite multilayer circuit substrate is processed to form micropores penetrating through the first dielectric layer and the conductive layer. The inner wall surface of the micropore prepared in the above step is modified by plasma treatment.

[0040] (2) Move the electrospray nozzle to directly above the micro-hole, adjust the position of the nozzle to the substrate, and spray the electrospray to cover the substrate in the area directly below. The micro-hole after plasma modification is filled by electrospray method, and the micro-hole is metallized.

[0041] Specifically, during the electrospray process, the multilayer circuit substrate after plasma treatment is placed on the grounded platform, the electrospray nozzle is connected to the high-voltage DC power supply, and Taylor cone electrospray is formed by spraying. When the surface of the substrate has not yet deposited charged particles, i.e., before electrostatic spraying, the potential of the outer surface of the hole is lower than that of the inner surface, and the electric field lines at this time are in a state of outward diffusion. The positively charged particles generated by electrospray will preferentially deposit on the outer surface of the hole. During the electrostatic spraying process, as the charge on the outer surface of the micro-hole accumulates, the potential of the outer surface of the hole gradually increases, forming a surface charge barrier. At this time, the potential inside the hole will be lower than that outside the hole, and the electric field lines will focus towards the inside of the hole. At this time, the subsequent particles generated by electrospray are repelled and no longer preferentially deposit on the surface, but instead focus on the inside of the hole, thereby forming a metal layer inside the hole and completing the rapid metallization of the micro-hole.

[0042] In some embodiments, during the modification process of the inner wall surface of the micro-hole using low-pressure plasma or atmospheric pressure plasma, oxygen plasma is used, and the plasma treatment power is 25-400 W, and the treatment time is 25-150 s. In this process, the inner wall surface of the micro-hole is modified to improve the charge dissipation speed and hydrophilic / hydrophobic properties of the inner wall surface, and to improve the performance of electrospray on the inner wall surface, so as to help obtain a continuous, uniform, dense and defect-free metal layer on the inner wall surface of the micro-hole during the subsequent electrostatic spraying process. In addition, through plasma treatment, the micro-nano structure of the inner wall surface of the micro-hole changes, and after plasma treatment, irregular nano-sized particles appear on the inner wall surface of the micro-hole, which allows the conductive functional ink to better contact the micro-hole wall, thereby enhancing the conductivity and adhesion of vertical interconnection.

[0043] In the present application, due to the space orientation mechanism dominated by electric field, it shows significant "self-focusing deposition" ability in the micro-porous structure, and different electrostatic atomization process parameters will affect the self-focusing electric field construction effect of the micro-porous structure. The preferred electrostatic spraying nozzle of the present application is a disc nozzle, the direct current voltage of the power supply connected to the nozzle is 2000V-4000V, the distance from the nozzle to the multi-layer circuit substrate is 10mm-20mm, and the air pressure is 50kpa-70kpa. The coverage area of the charged particles generated by electrostatic spraying on the substrate is not more than 10mm in radius, and is preferably not more than 5mm. For the spraying voltage, as the voltage increases, the direction of the radial component of the electric field changes, and if the voltage is too high, the self-focusing effect will be weakened or even disappear, so the direct current voltage of the power supply connected to the nozzle is selected in the range of 2000V-4000V. As the nozzle height increases, the radial component of the electric field becomes larger, and the focusing effect is better, so the distance from the nozzle to the multi-layer circuit substrate is selected to be 10mm-20mm to strengthen the focusing effect of the surface charge. The alignment accuracy of the nozzle to the micro-pore has a certain influence on the focusing effect, and when the offset distance increases, the radial electric field will be weakened. In order to ensure the focusing effect, the radial alignment accuracy of the nozzle relative to the center of the micro-pore needs to be better than ±5mm.

[0044] In some embodiments, the operation of step (2) is repeatedly performed, and the substrate is heated after each execution of step (2); the number of repetitions is 3-5 times.

[0045] Specifically, after performing step (2), the multi-layer circuit substrate is placed on a heating plate for heating to dry the droplets deposited by electrostatic spraying, and the heating temperature is 60-80℃. Specifically, after the electrofluidic spray micro-pore filling, the multi-layer circuit substrate is placed on a heating plate for heating, and the heating temperature is 60-80℃. Since the shrinkage rate of the conductive ink after drying is very large, the steps of electrofluidic spray micro-pore filling and heating are repeated 3-5 times, thereby increasing the ink filling amount, increasing the thickness of the wall metal layer, and improving the strength of the hole wall metallization layer.

[0046] In some embodiments, after forming a metal conductive layer of a target thickness on the inner wall of the micro-pore of the substrate, the substrate is subjected to conductive heat sintering and annealing. Specifically, the multi-layer circuit substrate subjected to electrofluidic spray micro-pore filling is subjected to conductive heat sintering, the sintering temperature is 200℃-230℃, and the sintering time is 20-30 minutes. Further, the multi-layer circuit substrate after sintering is subjected to annealing treatment. For example, for a composite multi-layer circuit substrate, due to the different thermal expansion coefficients of the intermediate metal layer, the upper and lower dielectric layers, and the filled metal layer, if the cooling speed is too fast, thermal stress will be generated, thereby causing cracks. Therefore, the annealing method is slow cooling in the furnace, and sintering annealing can solidify the metal layer on the vertical interconnection micro-pore inner wall, and slow cooling can prevent the generation of cracks.

[0047] In some embodiments, the substrate is a planar substrate or a curved substrate.

[0048] In some embodiments, the substrate is a multilayer circuit board, and the method has excellent application effect in micro-hole metallization of the multilayer circuit board.

[0049] The application provides a device for filling metallization by using electrostatic spraying of group holes. Figure 1 As shown in the figure, the electrostatic spraying device comprises an electrostatic spraying module and a multi-axis motion platform on which the electrostatic spraying module is installed.

[0050] The electrostatic spraying module comprises a gas supply unit 6, a high-voltage power supply 7 and an electrostatic spraying nozzle 5, wherein the electrostatic spraying nozzle is connected to the high-voltage DC power supply.

[0051] The gas supply unit 6 is connected to the electrostatic spraying nozzle 5 through a flow meter to control the size of the gas pressure and the amount of ink 4 sprayed at the nozzle.

[0052] The multi-axis motion platform is composed of a mechanical arm, a rotating base, an electrostatic spraying end, a multilayer circuit substrate and fixing bolts, wherein the multilayer circuit substrate is connected and fixed to the rotating base of the multi-axis motion platform through the fixing bolts, and the electrostatic spraying end is connected to the end of the mechanical arm.

[0053] Further, the multilayer circuit substrate after plasma treatment is placed on a grounding platform, wherein the conductive metal layer is connected to the grounding wire. The electrostatic spraying nozzle is connected to the high-voltage DC power supply. When the high-voltage power supply applies high-voltage DC power, an electric field is formed between the nozzle and the grounded multilayer substrate to be filled with micro-holes, so that the electric field intensity of the ink liquid surface breaks through the Taylor cone limit to form a Taylor cone spray.

[0054] Further, by integrating the electrostatic spraying module on the multi-axis motion platform, the multilayer planar or curved circuit substrate can be directly and quickly micro-holed and metallized, the speed of high-density group hole vertical interconnection is improved, and the method is suitable for rapid filling of high-density micro-holes of large multilayer planar or curved circuit substrates.

[0055] The method of the application will be further described below in conjunction with more specific embodiments.

[0056] Example 1

[0057] Please refer to the accompanying Figures 1-2 , combined with the schematic diagram of the device for vertical interconnection micro-hole metallization, the application uses the electrostatic spraying micro-hole metallization process to prepare a multilayer circuit micro-hole metal conductive layer, and the specific steps are as follows:

[0058] Step S1: please refer to Figure 2In section a, a multilayer composite material circuit board is provided, comprising an upper composite material layer 8, a copper layer 9, and a lower composite material layer 10. The upper composite material layer 8 has a thickness of 0.3 mm, the lower composite material layer 10 has a thickness of 1 mm, and the middle copper layer 9 has a thickness of 3 μm. The surface of the multilayer composite material circuit board is cleaned.

[0059] Step S2: Please refer to Figure 2 In step b, a heat-release adhesive tape layer 11 is attached to the upper surface of the upper composite material layer 8, and the thickness of the heat-release adhesive tape layer 11 is 0.1 mm.

[0060] Step S3: Please refer to Figure 2 In step c, micro-holes are machined on the multilayer circuit board of composite material by mechanical processing. The micro-holes penetrate the upper composite material layer 8 and the copper layer 9 and terminate in the lower composite material layer 10. The diameter of the hole is 0.4 mm. Then, the debris and dust generated during the hole making process are cleaned.

[0061] Step S4: Please refer to Figure 2 In step d, the surface of the micropore inner wall prepared in the above steps is modified by low-pressure plasma. The multilayer circuit substrate is then subjected to plasma modification treatment by reactive ion etching machine using oxygen plasma at a power of 50W for 50s.

[0062] Specifically, turn on the power to the equipment and the cooling device, then fill the vacuum chamber with air to restore the pressure inside to atmospheric pressure. Open the vacuum chamber, place the insulating glass substrate on the lower substrate liner, and close the vacuum chamber. Evacuate the vacuum chamber to reduce the pressure inside to 10... -3 Pa. Activate the plasma processing program to perform plasma modification treatment on the composite multilayer circuit board after hole fabrication. Treat the multilayer circuit board with oxygen plasma at a power of 50W for 50 seconds. Fill the vacuum chamber with air to restore the pressure inside to atmospheric pressure. Open the vacuum chamber and remove the plasma-modified insulating glass substrate. Close the vacuum chamber and apply vacuum protection. Turn off the power to the device and the cooling device.

[0063] Step S5: Please refer to Figure 2 In the middle e, the plasma-modified micropores are filled using an electrostatic spray micropore metallization process to metallize the micropores;

[0064] Specifically, the multi-layer circuit board after plasma treatment is placed on the rotating base of the multi-axis motion platform and positioned and fixed by bolts, the mechanical arm of the multi-axis motion platform is controlled by the teach pendant, and the electro-fluid spray tip is vertically aligned with the multi-layer circuit board. The electro-fluid spray tip is connected to a high-voltage DC power supply, and a Taylor cone spray is formed by spraying. Specifically, the DC voltage of the power supply connected to the spray tip is 3000V, the distance between the spray tip and the multi-layer circuit board is 10mm, and the air pressure is 50kpa.

[0065] Step S6: Place the composite multi-layer circuit board on the heating plate 13 to heat and dry the droplets deposited by electrostatic spraying, and the heating temperature is 80℃.

[0066] Step S7: Repeat the micro-hole filling step and the heating step 3 times.

[0067] Specifically, after the electro-fluid spray micro-hole filling, the multi-layer circuit board is placed on the heating plate to heat, and the heating temperature is 80℃. Since the conductive ink shrinks greatly after drying, the electro-fluid spray micro-hole filling and heating steps are repeated 3 times to increase the ink filling amount, increase the wall metal layer thickness, and improve the strength of the hole wall metal layer.

[0068] Step S8: Please refer to f in Figure 2 , place the composite multi-layer circuit board on the heating plate 13 to heat to a temperature of 120℃, and remove the heat release tape 11.

[0069] Step S9: Please refer to g in Figure 2 , conductive sintering and curing are performed on the micro-hole inner wall metal layer, and annealing treatment is performed after slow cooling in the furnace after sintering. Specifically, the multi-layer circuit board after electro-fluid spray micro-hole filling is subjected to conductive sintering, the sintering temperature is 220℃, and the sintering time is 30 minutes.

[0070] Please refer to Figure 3 , it can be seen from the cross-sectional view that the micro-hole metal conductive layer obtained by the present application is continuous, dense, and has a large wall thickness.

[0071] Further, for the operation of modifying the surface of the micro-hole inner wall by low-pressure plasma in step S4, please refer to Figure 4The micro-pore wall metallization cross-sectional view without plasma treatment (left) and the micro-pore wall metallization cross-sectional view with plasma modification treatment (right) are compared. It can be seen that the micro-pore wall conductive metal layer without plasma modification treatment is a metal layer 14 with uneven thickness, and the micro-pore wall conductive metal layer with plasma modification treatment is a uniform and continuous metal layer 15. The plasma modification treatment improves the charge dissipation speed and hydrophilic and hydrophobic properties of the micro-pore inner wall surface, changes the micro-nano structure of the micro-pore inner wall surface, so that the conductive functional ink and the micro-pore wall better contact, and the conductivity and adhesion of the vertical interconnection are enhanced.

[0072] Example Two

[0073] According to the parameters of the example in Example 1, simulation is performed.

[0074] Please refer to Figure 5 , which is a simulation of the potential distribution of the inside and outside of the micro-pore before and after the deposition of charged particles on the outer surface of the micro-pore. Figure 5 In a, when the surface has not yet deposited charged particles, i.e. before electrostatic spraying, the potential distribution inside and outside the hole is shown. At this time, the potential of the outer surface of the hole is lower than that of the inside. Figure 5 In b, as the electrostatic spraying proceeds, the potential distribution inside and outside the hole is shown. At this time, the potential inside the hole becomes lower than that outside the hole.

[0075] Please refer to Figure 6 , which is a simulation of the cross-sectional electric field line distribution of the inside and outside of the micro-pore before and after the deposition of charged particles on the outer surface of the micro-pore. Figure 6 In a, when the surface has not yet deposited charged particles, i.e. before electrostatic spraying, the cross-sectional electric field line distribution is shown. At this time, the electric field lines are in a state of outward diffusion. Figure 6 In b, as the electrostatic spraying proceeds, the cross-sectional electric field line distribution is shown. At this time, the electric field lines will focus towards the inside of the hole. The whole process and principle of realizing micro-pore metallization by electrostatic spraying are as follows: when the surface has not yet deposited charged particles, i.e. before electrostatic spraying, the potential of the outer surface of the hole is lower than that of the inside, and the electric field lines are in a state of outward diffusion. The positively charged particles produced by electrofluidic spraying will preferentially deposit on the outer surface of the hole. During the electrostatic spraying process, as the charge on the outer surface of the hole accumulates, the potential of the outer surface of the hole gradually increases. At this time, the potential inside the hole becomes lower than that outside the hole, and the electric field lines will focus towards the inside of the hole. At this time, the particles produced by electrofluidic spraying will focus and deposit inside the hole, thereby producing a continuous and uniform dense metal layer inside the hole, realizing rapid metallization of the micro-pore.

[0076] Example Three

[0077] The application provides a device for electrostatic atomization high-efficiency filling for high-density group-hole vertical interconnection, which is also suitable for film preparation on a large-area substrate surface and micro-hole metallization, and through a mask, vertical interconnection of a large-area multilayer circuit and patterned circuit preparation can be realized.

[0078] The present example is based on a proposed electrostatic atomization high-efficiency filling method and device for high-density group-hole vertical interconnection to realize preparation of a large-area multilayer active frequency selective surface. The multilayer active frequency selective surface includes a plurality of array units with the same structure and periodic arrangement, each array unit is provided with a dielectric layer, a first metal layer arranged on the top surface of the dielectric layer, and a second metal layer arranged on the bottom surface of the dielectric layer, each layer is arranged opposite to each other, and a through hole is arranged in the center of the dielectric layer. The upper and lower metal layers include a square metal layer in the center and a square ring metal layer at the edge, and a square ring gap is formed between the square metal layer and the square ring metal layer. The substrate has a periodic array of micro-holes with a hole diameter of 0.4 mm arranged in a rectangular grid, and the number of holes is 225.

[0079] By integrating an electrofluidic spray tip into the end of a multi-axis motion platform mechanical arm, preparation of a large-area multilayer active frequency selective surface can be realized. The multilayer circuit substrate that needs to realize micro-hole interconnection is fixed on the rotating base by bolts, the path is planned according to the distribution of the holes on the substrate, and the high-density group holes on the substrate are quickly metallized by the movement of the mechanical arm and the platform. The following is the detailed preparation process.

[0080] S1 provides a dielectric layer substrate, and FR-4 with a dielectric constant of 4.4 and a loss tangent angle value of 0.02 is selected as the material thereof. A thermal release tape is attached to the upper surface of the substrate, the thickness of the RF-4 substrate is 1.6 mm, the thickness of the thermal release tape layer is 0.1 mm, and a vertical micro-hole is drilled by mechanical processing, and the micro-hole diameter is 0.4 mm.

[0081] S2 uses anhydrous ethanol and dust-free paper to clean the surface of the RF-4 substrate to remove debris and dust generated during the hole drilling process, and to ensure the cleanliness of the substrate surface. A thermal release tape is attached to the lower surface of the substrate.

[0082] S3 places the substrate with the attached thermal release tape on a grounded metal platform, and fills the micro-holes by an electrostatic spray metallization process.

[0083] Specifically, first, in the process of modifying the inner wall surface of the micropore, oxygen plasma is used to treat the inner wall surface of the micropore for 50 s at a power of 50 W, so as to improve the charge dissipation speed and hydrophilic and hydrophobic properties of the inner wall surface of the micropore, and improve the performance of the electrohydrodynamic spraying of the inner wall surface, so that the nano-silver paste can better contact the micropore wall. Then, the RF-4 substrate treated by the plasma is placed on a grounding platform and fixed on a rotating base of a multi-axis motion platform by bolts. The multi-axis motion platform mechanical arm is controlled by a teach pendant, and the electrohydrodynamic spraying end is vertically aligned with the multi-layer circuit substrate. According to the hole distribution and the single-time spray filling angle, the workpiece printing area is divided into several equal parts, and then the printing path is planned according to the divided area and compensation and the distribution of the holes on the multi-layer circuit substrate.

[0084] Further, the electrohydrodynamic spraying nozzle is connected to a high-voltage direct current power supply, and the nano-silver paste is formed into a Taylor cone spray in a spraying manner. The direct current voltage of the power supply connected to the nozzle is 3000 V, the distance between the nozzle and the multi-layer circuit substrate is 10 mm, and the air pressure is 50 kpa. After the electrohydrodynamic spraying micropore filling, the substrate is placed on a heating plate for heating, and the heating temperature is 80℃. The two steps of electrostatic spraying micropore filling and heating are repeated for 3 times, so as to increase the filling amount of the nano-silver paste and increase the thickness of the wall surface metal layer.

[0085] S4, the substrate is placed on a heating plate and heated to a temperature of about 120℃ to make the heat release tape fall off, and the heat release tape is removed. The substrate is subjected to conductive sintering, the sintering temperature is 220℃, and the sintering time is 30 minutes. Finally, the furnace is slowly cooled to prevent cracks.

[0086] S5, the heat release tape is attached to the upper and lower surfaces of the substrate after the electrostatic spraying metallization process.

[0087] S7, the excess heat release tape on the upper and lower surfaces is cut off by laser cutting to obtain a mask.

[0088] S8, the multi-axis motion platform with the electrohydrodynamic spraying end is used to perform electrostatic spraying film deposition on the surface of the RF-4 substrate with the mask to prepare a conductive pattern, and a square metal layer and a square ring metal layer are obtained. The side length of the square metal layer is 4.8 mm, the inner side length of the square ring metal layer is 6.4 mm, and the outer side length is 10 mm. The substrate with the mask is placed on the motion platform, 100cp viscosity 75% solid content nano-silver paste is used as the printing ink, a 34G metal needle is used as the nozzle, the spraying height is 20 mm, the ink back pressure is 50Kpa or the flow pump control flow is 15μL / min, the nozzle is connected to a 6600V direct current voltage, and the substrate moving speed is 4mm / s.

[0089] S9 places the substrate on the hot plate, heats to a temperature of about 120℃ to make the heat release tape fall off, and removes the heat release tape. The surface patterned and microporous metallized substrate is conductive heat sintered, the sintering temperature is 220℃, and the sintering time is 30 minutes. Finally, the furnace is slowly cooled for annealing.

[0090] The embodiment realizes large-area multilayer circuit vertical interconnection and patterned circuit preparation by the above method, which is more efficient and better in effect than the existing vertical interconnection and patterned circuit preparation.

[0091] Obviously, various modifications and variations of the present application can be made by those skilled in the art without departing from the spirit and scope of the application. Thus, it is intended that the present application cover modifications and variations of this application provided they come within the scope of the appended claims and their equivalents. The above-described embodiments are merely preferred embodiments of the application, but the scope of protection of the application is not limited thereto. Any equivalent replacement and transformation made by those skilled in the art based on the application shall fall within the scope of protection of the application.

Claims

1. A method for electrostatic spray filling and metallization for vertical interconnection of multiple apertures, characterized in that, Includes the following steps: (1) The inner wall surface of the micropores on the substrate is modified by plasma; wherein the micropores are vertical interconnecting holes that penetrate the substrate. (2) Electrostatic spraying is performed on the micropores in the lower region above the substrate. As the charge accumulates on the outer surface of the micropores, the potential of the outer surface of the micropores is higher than the potential inside the micropores. At the same time, the electric field lines focus into the hole. Subsequently, the particles generated by the electrostatic spraying are deposited into the micropores, forming a metal conductive layer on the inner wall of the micropores.

2. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 1, characterized in that, The voltage of the electrostatic spray is 2000V to 4000V.

3. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 1, characterized in that, The distance between the nozzle of the electrostatic spray and the substrate is 10-20 mm.

4. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 1, characterized in that, The charged particles generated by the electrostatic spray cover an area with a radius not exceeding 10 mm on the substrate.

5. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 4, characterized in that, The charged particles generated by the electrostatic spray cover an area with a radius of no more than 5 mm on the substrate.

6. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 5, characterized in that, The inner wall surface of the micropores on the substrate is modified by low-pressure plasma or atmospheric-pressure plasma; the plasma treatment power is 25-400W and the treatment time is 25s-150s.

7. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 1, characterized in that, The operation of step (2) is repeated, and the substrate is heated after each execution of step (2); the number of repetitions is 3 to 5 times; the heating temperature is 60 to 80°C.

8. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 1, characterized in that, After forming a metal conductive layer of the target thickness on the inner wall of the micropores of the substrate, the substrate is subjected to conductive thermal sintering and annealing.

9. The electrostatic spray filling metallization method for vertical interconnection of multiple holes according to claim 1, characterized in that, The substrate is a planar substrate or a curved substrate.

10. An apparatus for electrostatic spray filling metallization for vertical interconnection of multiple apertures, for performing the method as described in any one of claims 1-8, comprising an electrostatic spray module and a multi-axis motion platform, the electrostatic spray module being mounted on the multi-axis motion platform; The electrostatic spray module includes an air supply unit, an electrostatic spray nozzle, and a high-voltage power supply; wherein... The electrostatic spray nozzle is connected to a high-voltage power supply; the air supply unit is connected to the electrostatic spray nozzle through a flow meter to control the spray volume of the electrostatic spray nozzle. The multi-axis motion platform includes a robotic arm, a rotating base, an electrostatic spraying end, and fixing bolts; wherein, the rotating base is used to fix the substrate by the fixing bolts, and the end of the robotic arm is connected to the electrostatic spraying module, and is used to drive the electrostatic spraying module to move relative to the substrate by the movement of the multi-axis motion platform.

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