A method for forming a 3D printed curved multilayer circuit vertical interconnect structure

Abstract

This invention provides a method for forming vertical interconnect structures of curved multilayer circuits using 3D printing. This method enables the integrated forming of highly conductive interconnect structures with different features and smooth surfaces during the additive manufacturing of multilayer circuits. It also allows for the additive forming of arbitrary spatial structures on curved surfaces. This method offers high flexibility and is easily integrated into the additive manufacturing process of multilayer circuits. It can integrally form interconnect structures of various diameters and types, avoiding the problems of existing technologies that require switching between multiple methods and the inability to form certain features. Furthermore, the printing method allows for the formation of spatially irregular metal structures on existing curved circuit boards, further expanding circuit functionality and enabling the fabrication of miniature antennas and sensors.

Description

Technical Field

[0001] This invention belongs to the field of conformal circuit manufacturing technology, specifically relating to a method for forming a 3D printed curved multilayer circuit vertical interconnect structure. This method is an additive manufacturing method for curved multilayer vertical interconnect structures, mainly used to realize vertical interconnection between curved multilayer circuits and ensure the integrity of electrical signals between curved multilayer circuits. Background Technology

[0002] Vertical interconnect vias are a crucial step in transitioning from discrete multilayer circuits to integrated circuits. In PCB manufacturing, various types of vias are designed to ensure the interconnection of electrical signals between multilayer circuits, such as buried blind vias and metallized through-hole structures. These vias are typically fabricated using electroless plating and via plugging processes. Specifically, after forming through-holes in the core board through mechanical drilling or laser etching, electroless plating is used to metallize the hole walls, or a metal paste (copper paste, silver paste, etc.) is poured in and cured to achieve conductivity between the upper and lower layers, followed by lamination with other metal layers. However, in engineering applications, electroless plating and via plugging for blind vias are not recommended because the plating solution or plugging paste cannot fully penetrate the hole due to limitations in hole diameter and depth, resulting in poor interconnectivity.

[0003] Most existing interconnect structures in curved multilayer circuits still borrow from the implementation ideas of interconnect holes in traditional PCBs, using electroless plating, metal paste filling, and mechanical interconnection methods (such as pins, springs, etc.) to achieve interconnection in curved multilayer circuits. For example, Chinese patent CN114552200B uses electroless plating or sputtering processes to achieve interconnection between upper and lower layer circuits in a multilayer shell; Chinese patent CN111613888B discloses that interconnect holes are formed by mechanical drilling and laser drilling, followed by laser activation-assisted electroless plating, which is essentially still an electroless plating process; Chinese patent CN109755760B discloses the use of laser drilling + metal paste filling to achieve connection between upper and lower layer circuits; Chinese patent applications CN117096596A, CN117276879A, and CN117525873A disclose the use of spring pins, springs, and rivets for mechanical interconnection between curved multilayer circuits. In the process of integrating the dielectric and conductor layers through additive manufacturing, the above process will face the following problems: secondary positioning errors caused by drilling and chemical plating, inability to achieve chemical plating and slurry plugging of micro blind holes, inability to remove debris at the bottom of blind holes due to online drilling, and easy formation of conical structures by laser drilling, and varying degrees of resin residue at the bottom of the holes due to focal length deviation on curved surfaces, all of which will affect the connectivity effect.

[0004] Chinese patent application CN117712031A discloses the use of nano-silver paste (silver powder: epoxy resin = 90:10) for 3D printing to create vertical interconnect pillars. After positioning, the conductivity between upper and lower layers is achieved by the curing of conductive adhesive. However, the specific implementation details and effects are not discussed in detail. It is inferred that a certain pillar height is achieved through the self-supporting properties of the paste, but the printable height of the vertical pillars is limited and easily tilted due to gravity. The end faces of the pillars are easily affected by extrusion-induced adhesive breakage, resulting in different stringing effects and making it impossible to form regular cones or flat end faces. Chinese patent CN112123950B discloses the use of alternating printing of ceramic ink and conductive ink to form metal pillars or conductive rings, thereby achieving conductive interconnection. However, the flow of conductive ink and the surface tension climbing phenomenon of the dielectric material result in pillars resembling a "pagoda-shaped" stacked interface. The smaller the alternating layers in the printing, the more the "pagoda-shaped" stacked interface evolves into a "hairy" edge, resulting in a rough interconnect pillar surface, which significantly affects high-frequency signal transmission.

[0005] Additive manufacturing of conformal integrated circuits is one of the important trends in the development of heterogeneous integrated circuits. How to achieve a smooth surface and reliable conductivity interconnect structure in the integrated manufacturing process of heterogeneous materials has become the key to improving the performance of additive manufacturing electronic devices. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of current additive manufacturing methods for forming interconnect structures in curved multilayer circuits, and to provide a method for forming vertical interconnect structures in 3D printed curved multilayer circuits. This method enables the integrated forming of highly conductive interconnect structures with different features and smooth surfaces during the additive manufacturing process of multilayer circuits, and can also additively form arbitrary spatial structures on curved surfaces. This method is highly flexible and easily integrated into the additive manufacturing process of multilayer circuits. It can integrally form various interconnect structure features of different diameters and types, avoiding the problems of existing technologies requiring switching between multiple methods and the inability to form certain features. Furthermore, by printing, spatial irregular metal structures can be formed on existing curved circuit boards, further expanding circuit functionality and enabling the manufacture of miniature antennas and sensors.

[0007] To achieve the above objectives, the technical solution provided by this invention is:

[0008] A method for forming a 3D printed curved multilayer circuit vertical interconnect structure, characterized by the following steps:

[0009] Step 1: Mount the substrate onto a work platform that can rotate and move. Heat the substrate to keep its surface temperature above 120°C throughout the interconnect structure forming process. At the same time, ensure that the axis of the 3D printing head is always aligned with the direction of gravity.

[0010] The aforementioned working platform allows the substrate to rotate or translate at various angles, facilitating control of the angle between the normal of the deposited surface and the printhead axis. The aforementioned control of the substrate surface temperature is primarily to facilitate the rapid solidification of the deposited nanomaterials. The solidified metal layer can conduct heat quickly, ensuring that subsequent deposited materials can solidify rapidly, thereby ensuring the continuous growth of the interconnect structure. The main purpose of ensuring that the printhead axis always remains in the direction of gravity is to ensure that the ink droplets fall vertically in the direction of gravity during the jet deposition process in order to control the deposition accuracy of the ink droplet landing point. Otherwise, even a slight deflection of the printhead will cause the ink droplet flight trajectory to become uncontrollable due to gravity.

[0011] Step 2: Adjust the position of the substrate using the work platform so that the angle between the print head axis and the normal of the substrate surface to be deposited meets the printing requirements; use the 3D printing equipment to deposit metal layer by layer on the substrate according to the interconnect structure characteristics to the specified height, forming the interconnect structure;

[0012] Step 3: Using 3D printing equipment, a dielectric layer is printed around the interconnect structure formed in step 2 using dielectric resin and then cured and shaped; wherein, an isolation strip is provided between the dielectric layer and the interconnect structure;

[0013] When printing a dielectric layer on a curved surface using low-viscosity dielectric resin, the dielectric layer filling efficiency is very low. If the printed layer is too thick, it is prone to flow and spread under gravity, resulting in uncontrollable dielectric layer thickness. If the printed layer is too thin, the dielectric layer forming efficiency is too low, making it impossible to achieve efficient engineering applications. Therefore, to avoid this situation, dielectric resin with a higher viscosity (greater than or equal to 100 cP) is usually used to print the dielectric layer. However, when the viscosity of the printed dielectric layer material is high, it will cause column climbing on the interconnect structure body, resulting in a "figure-eight" shaped encapsulation of dielectric resin near the end face of the interconnect structure. The ink subsequently deposited on the interconnect structure or connecting the interconnect structure wires will spread at the interface of the dielectric resin, resulting in a "figure-eight" shaped protruding connection structure at the connection when printing the line connected to the interconnect structure, affecting the quality and reliability of the connection. Therefore, in this invention, an isolation strip is first set between the interconnect structure and the dielectric layer, and then a low-viscosity, low-surface-tension dielectric resin is used to fill the isolation strip. At this time, the climbing phenomenon will be greatly improved due to the low surface tension of the dielectric resin in the isolation strip. At the same time, the dielectric layer printed with a higher viscosity dielectric resin will also form a fence after curing, which also overcomes the spreading problem faced by printing low-viscosity dielectric resin on curved surfaces.

[0014] Of course, in practice, if it is necessary to use a dielectric resin with a lower viscosity (less than 100 cP) to print the dielectric layer due to certain requirements, and if the dielectric layer thickness can be printed in a way that meets the molding efficiency and allows the surface tension of the dielectric layer to overcome gravity and prevent flow and spread through process design and other means, then it is not necessary to set up an isolation strip.

[0015] Step 4: Use 3D printing equipment to fully fill the insulating strip area with dielectric resin and cure it to achieve the specified height;

[0016] The dielectric resin used in the insulating strip and the dielectric resin used in the dielectric layer are the same type of resin or compatible resin types, but the surface tension and viscosity of the dielectric resin used in the insulating strip are lower than those of the dielectric resin used in the dielectric layer.

[0017] When filling the isolation strip, in order to prevent the uncured filling material from flowing during the substrate flipping and moving, the medium substrate is usually moved or flipped to the next isolation strip of the interconnect structure for filling and curing after one isolation strip is filled and cured.

[0018] Step 5: In order to increase the interlocking area of ​​the interconnect structure and make it reliably connected to the circuit, a metal ring strip sheet layer needs to be printed circumferentially along the upper and lower ends of the interconnect structure, and then the same layer of circuit layer is printed and connected to the metal ring strip sheet layer.

[0019] Step 6: Repeat steps 2 to 5 to form other interconnect structures on the surface of the dielectric substrate, completing the formation of the curved multilayer circuit vertical interconnect structure. During the repetition process, the surface temperature of the dielectric substrate must always be kept above 120°C. This is because the filling of the insulating strip may affect the thermal conductivity of the dielectric substrate for spreading the resin. As the resin thickens, the surface temperature will decrease. If the surface temperature is too low, the metal ink will collapse and fail to spread effectively to form a solid structure. Therefore, it is necessary to keep the temperature above 120°C to ensure the curing and spreading of the metal ink.

[0020] Further, in step 2, piezoelectric inkjet is used to spray nano metal ink, aerosol jet is used to spray nano metal ink, or ion particle atomization jet deposition is used to deposit plasma atomized metal particles to form an interconnect structure on the dielectric substrate. Specifically, piezoelectric inkjet and aerosol are mainly used to spray nano-scale metal inks (such as nano gold, nano nickel, nano copper, nano silver, etc. In actual operation, metalized inks with higher thermal conductivity are preferably used), while ion particle atomization jet deposition is used to deposit plasma atomized metal particles. When the metal particles are ejected, a laser is attached to the nozzle for micro-melting treatment, and after falling onto the substrate, they are solidified and deposited. Of course, micro direct writing technology can also be selected to print low melting point or eutectic metal materials (such as eutectics composed of monomers or multiple of metals such as tin, bismuth, and indium). By heating and extruding the molten material, a self-supporting interconnect structure is formed relying on surface tension and air cooling after extrusion. However, the size of the formed interconnect structure is relatively single in this way;

[0021] The interconnect structure is a solid core, thin-walled structure such as a cylinder, a tubular body, or any other arbitrary shape. Among them, the size of a solid interconnect structure such as a cylinder is not less than 50μm, and for a tubular or thin-walled interconnect structure, the wall thickness is not less than 100μm. The formed interconnect structure can grow into any spatial structure in cooperation with the bottom working platform. For example, special structures such as a spatial cone and a spiral can be formed. And laser irradiation heat transfer can be used to assist the growth of structural features on the formed interconnect structure. This is because as the height of the interconnect structure feature body increases, the area of its interaction with air will gradually increase, and the heat transfer efficiency to the growth surface will become lower and lower, thus reducing the effect of ink droplet accumulation or possibly causing inability to stack and form. Therefore, in order to ensure that the growth surface of the interconnect structure maintains a certain temperature, the heat input of the printed structure can be increased by laser irradiation on the already printed interconnect structure to increase the temperature of the printing surface and compensate for the heat loss caused by its interaction with air.

[0022] Further, in step 2, the angle between the axis of the print head and the normal direction of the deposited surface of the dielectric substrate is 0 to ±45°. The axis of the print head always remains in the direction of gravity. Usually, the axis of the print head coincides with the normal direction of the deposited surface, that is, the angle is 0°. However, in some interference scenarios, this cannot be satisfied. At this time, the maximum angle between the axis of the print head and the normal direction of the deposited surface can be controlled within the range of ±45°. This is mainly achieved by adjusting the position of the deposited surface through the working platform.

[0023] Further, different from linear filling, in order to avoid the edge from becoming rough, in step 2, the trajectory of depositing layer by layer to the specified height according to the interconnect structure features is filled from the outside to the inside in a "return" shape;

[0024] For solid interconnect structures, a minimum diameter of 60-100μm should be reserved in the central area as a non-printable fill area (no further processing is required for the non-printable fill area, as the printing ink will automatically level out). This is because when the central area is filled in a spiral pattern, the printing line speed will gradually produce an accumulation phenomenon. If the diameter is less than 60μm, the central area will tend to be too high. Setting an upper limit for the reserved diameter is because if it is greater than 100μm, the central area will cause a depression later.

[0025] The specified height of the interconnect structure should be greater than or equal to the thickness of the dielectric material penetrating between the two connected circuit layers. Without interfering with the filling of the surrounding dielectric resin (i.e., the filling isolation strip), the height of the interconnect structure can be printed in one step according to the dielectric height of the connected circuit layer. This is to avoid multiple stacking printing during the deposition process, which can cause seams (for example, if the dielectric thickness between two circuit layers is 0.3mm, and the first printed interconnect height is 0.14mm, a second printing of the interconnect is required until it penetrates the 0.3mm dielectric between the two circuit layers; in this process, the printing of the interconnect is split into two steps, thus forming a seam on the interconnect body. Although filling with dielectric resin can improve this, the seam is still clearly visible in the cross-sectional structure, so it is best to print to the specified height in one step). Of course, the height of the interconnect structure should ideally be higher than the dielectric thickness between the two connected circuit layers to ensure the connectivity between subsequent circuits.

[0026] Furthermore, in step 3, the width of the isolation strip is less than or equal to 200 μm.

[0027] Furthermore, in step 4, under heating conditions, the surface tension of the dielectric resin used to fill the isolation strip is less than 15 dyn / cm and the viscosity is less than 12 cP, so as to ensure that it naturally levels and fully fills the isolation strip. It is also applicable to use the method of heating the material by the print head to meet this requirement in terms of surface tension and viscosity. The coefficient of thermal expansion after curing is less than 60 ppm to prevent the interconnect structure from cracking due to the mismatch between the expansion and contraction of the interconnect structure in the later thermal service environment.

[0028] To prevent the low-viscosity dielectric resin from wetting and covering the end face of the interconnect structure and affecting the conductivity of subsequent segments, the filled isolation strip is 30-70 μm lower than the upper end face of the interconnect structure. In addition, for the central area of ​​thin-walled or tubular interconnect structures, the printed low-viscosity dielectric resin is used for filling, and the end face of the central area is 30-70 μm lower than the upper end face of the interconnect structure after filling, and is basically flush with the upper end face of the isolation strip.

[0029] Furthermore, in order to effectively ensure the stability of the interconnect structure, in step 5, the thickness of the metal ring strip layer is consistent with the thickness of the same layer of circuit, and the width of the metal ring strip is not less than 150μm. The specific width can be designed according to the actual multilayer circuit.

[0030] Furthermore, the curing and shaping in steps 3 and 4 are both achieved by ultraviolet light irradiation.

[0031] Meanwhile, the present invention also provides a curved multilayer circuit board, which is special in that: the vertical interconnect structure on it is formed by the above method. In addition, secondary additive manufacturing can be performed on the existing curved multilayer structure. The curved multilayer circuit board can ultimately be used for micro antennas, sensors, waveguides, inductors and radio frequency shielding, etc.

[0032] The advantages of this invention are:

[0033] 1. The molding method for 3D printing curved multilayer circuit interconnect structures provided by this invention is simpler than existing processes. It eliminates the need for switching between multiple cutting tools of different diameters and for grouting and filling processes. It can not only mold interconnect structures of different diameters and features on curved substrates in one step, such as forming interconnect feature structures with different diameters (φ150μm, φ250μm, φ320μm, etc.) and different shapes (elliptical, square, ring-shaped cylinders, etc.) and even some irregular structures on curved substrates in one step, but also digitally control the size of the printed pattern to grow into conductive pillars of different sizes, making it easier to integrate into the additive manufacturing process of multilayer circuits.

[0034] 2. The interconnect structure forming method of the present invention can grow and form a micro-metal interconnect structure in arbitrary space in cooperation with the bottom working platform under unsupported conditions, solving the problem that existing processes cannot manufacture it.

[0035] 3. The interconnect structure forming method of the present invention can efficiently and with high quality realize the interconnection between curved multilayer circuits. The formed interconnect structure has a smooth surface and high conductivity, which can effectively reduce the loss caused by the electrical interconnection between layers due to processes such as via plugging, realize higher frequency applications, and has high compatibility with integrated manufacturing processes and is easy to integrate, which can further promote the development of additive manufacturing multilayer circuits.

[0036] 4. The interconnect structure forming method of the present invention, through the working platform and the control of the angle between the print head and the normal of the substrate surface, always keeps the printing direction in the direction of gravity. Not only can interconnect structures of arbitrary angles be grown on the curved surface (interconnect structures can be along any surface normal), but different branch structures can also be generated by secondary printing on the basis of the already printed interconnect structure. It can be applied to devices such as micro antennas, sensors and inductors. It can expand the functionality based on the existing circuit board structure through secondary manufacturing and has great application potential. Attached Figure Description

[0037] Figure 1The conventional interconnect structures shown in this invention are as follows: a is a metal pillar interconnect structure without a metal substrate, b is a metal pillar interconnect structure with a metal substrate, c is a metal tubular interconnect structure without a metal substrate, and d is a metal tubular interconnect structure with a metal substrate.

[0038] Figure 2 This is a schematic diagram of the printing of ring-shaped layers at the top and bottom of the interconnect pillars in this invention;

[0039] Figure 3(a) is a schematic diagram of the metal interconnect structure printed on the curved substrate;

[0040] Figure 3(b) shows the process of filling the dielectric material around the interconnect structure of the curved substrate;

[0041] Figure 3(c) is a schematic diagram of the secondary printing interconnect structure on the curved medium surface;

[0042] Figure 4 This is a schematic diagram of a non-linear interconnect structure for printing on a curved surface.

[0043] Figure 5 Print interconnected column morphologies with different numbers of layers on curved surfaces;

[0044] Figure 6 For printing curved multilayer circuit vertical interconnect structure;

[0045] Figure 7 X-ray scanning for printing curved multilayer circuit interconnect structures;

[0046] Figure 8 Filling dielectric material for printing multilayer circuit interconnect structures on curved surfaces;

[0047] Figure 9 This is a cross-sectional view of a vertical interconnecting column;

[0048] Figure 10 A schematic diagram of resin filling inside and outside a wall-tube interconnect structure;

[0049] Figure label:

[0050] 100-Substrate; 101-Metal substrate; 102-Metal pillar; 103-Metal wall tube; 104-Metal ring sheet layer; 201-Print head; 301-Media layer; 302-Isolation strip; 401-Main pillar; 402-Denial pillar I; 403-Denial pillar II. Detailed Implementation

[0051] This invention relates to a method for fabricating typical characteristic structures of curved conformal multilayer circuits, specifically a method for fabricating vertical interconnect structures of curved multilayer circuits using 3D printing technology. The method employs piezoelectric inkjet printing, aerosol, or ion particle atomization jet deposition to print and grow metal pillars or metal tubes along the normal direction on the surface of a curved dielectric substrate. The printing height is as high as possible, exceeding the dielectric thickness between the two interconnected circuit layers. During the printing of the dielectric layer, an isolation band is reserved around the metal pillars or metal tubes. Then, a low-surface-tension, low-viscosity photocurable dielectric resin material is used to print and fill the isolation band and the interior of the metal tube (for large-sized tube types, resin slurry is required to ensure that the thickness of the inner and outer resin layers is as consistent as possible, e.g., ...). Figure 10 As shown, otherwise the subsequent resin layers cannot be stacked and formed, ensuring that the height of the isolation band and the internal filling is 30-70 μm lower than the end face of the interconnect structure; print metal ring strip sheet layers around the outer sides of the upper and lower ends of the formed metal pillar / metal wall tube to ensure the reliability of the connection between the interconnect structure and the circuit layer.

[0052] To further illustrate the specific content of this invention, the following detailed description of the forming process of the curved multilayer circuit vertical interconnect structure, in conjunction with the accompanying drawings and embodiments, is provided. The specific process is detailed in the following embodiments.

[0053] Example 1:

[0054] This embodiment mainly elaborates on the process of printing interconnected pillars and filling media involved in the present invention.

[0055] The printing equipment is a five-axis electronic device additive manufacturing system (5X-3DPES) produced by Xi'an Ruite 3D Technology Co., Ltd.; the print head is a 50μm piezoelectric inkjet head produced by Xi'an Ruite 3D; the printing material is nano-silver conductive ink (d50 < 60nm); the resin material of the printing medium layer is acrylic resin (viscosity 18000cP), and the resin material of the filling isolation strip is also acrylic resin (viscosity: 10cP, surface tension 23dyn / cm); the designed interconnect pillars have a diameter of 300μm and a height of 2mm; the planar substrate is a polyimide film, and the curved substrate is an anodized and insulated aluminum alloy metal block. The specific steps are as follows:

[0056] Step 1: Install and fix the polyimide film or aluminum alloy metal block on the turntable of the five-axis printing equipment. By controlling the heating program and infrared temperature measurement feedback, the surface temperature of the substrate is heated to 130℃±2℃. After maintaining the surface temperature of the substrate, control the movement of the turntable so that the deposition surface is perpendicular to the axis of the print head (the angle between the normal of the curved surface and the axis of the print head is 0°), while ensuring that the axis of the print head is always kept in the direction of gravity.

[0057] Step 2: After adjusting the inkjet parameters of the nano-silver ink with the piezoelectric inkjet used, the printing trajectory of the interconnecting metal pillars is processed. Among them, no filling treatment is performed within 60 μm of the center of the interconnecting metal pillars, and the overall trajectory is filled in a "hui" character shape. The interconnecting metal pillars are printed on a planar polyimide film and a curved metal substrate respectively, and different numbers of layers are printed; the printing schematic is shown in Figure 1 and Figure 3(a). The actual situation of printing the interconnecting metal pillars is specifically shown in Figure 5 and Figure 6 . Among them, Figure 5 The printing and growth conditions of the interconnecting metal pillars are respectively tested with and without a metal substrate chassis. For the case with a metal substrate, the root of the conductive interconnecting pillar is smaller, and the height is higher than that of the growth without a metal substrate under the same number of printed layers.

[0058] Step 3: Print acrylic dielectric resin (viscosity 18000 cP) around the structure of the interconnecting metal pillars, control the width of the isolation belt to be 300 μm, and the isolation belt is only about 100 μm wide after the resin spreads and flows. After curing and shaping the dielectric resin by ultraviolet irradiation at 365 nm;

[0059] Step 4: Fill the isolation belt with acrylic resin (viscosity: 10 cP, surface tension 23 dyn / cm), ensure that it fully fills the isolation belt, and immediately cure it by ultraviolet irradiation after filling each isolation belt, and then switch to the next isolation belt through a turntable to print and fill the resin for filling and then curing;

[0060] Step 5: After measuring the height of the isolation belt printing through a vision camera to reach 1.95 mm, it is 50 μm lower than the metal pillar surface; print a metal ring strip layer with a diameter of 500 μm around the end face of the interconnecting structure (as shown in Figure 2 ), among which, the printing thickness is 10 μm, and a 10-μm conductive circuit of this layer is printed around the printed metal ring; specifically shown in Figure 7 and Figure 8 .

[0061] Step 6: Repeat Steps 2 to Step 5 to form a new interconnecting structure on the surface of the dielectric substrate. The specific schematic is shown in Figure 3(c). Control the heating program to make the surface temperature reach the requirement of 130 °C after filling the acrylic resin. Through Figure 9 It can be seen the cross-section sampling situation of the overall interconnecting metal pillars. The edge of the interconnecting metal pillars is relatively smooth, the internal structure formed by the sampling is relatively dense, and the formed interconnecting metal pillars can reach about 260 μm.

[0062] Example 2:

[0063] This embodiment is mainly to further illustrate that any metal interconnecting structure can be printed and grown on the surface of a curved substrate by using the forming method of the present invention.

[0064] The printing device is a five-axis electronic device additive manufacturing system (5X-3DPES) produced by Xi'an Reiter 3D Technology Co., Ltd.; the print head selected is a piezoelectric inkjet head with a 30-μm nozzle hole produced by Xi'an Reiter 3D; the printing material selected is nano silver conductive ink (d50 < 20 nm); the designed interconnect structure is in the shape of a spatial tree, with the main column having a diameter of 600 μm and a height of 1.2 mm; the branched column has a diameter of 250 μm and a branch length of 0.6 mm. The selected substrate is an aluminum alloy block with an anodic oxidation surface insulation treatment; the specific steps are as follows:

[0065] Step 1: Fix the aluminum alloy metal block 100 on the turntable of the five-axis printing device. By controlling the heating program and infrared temperature measurement feedback, the surface temperature of the substrate is raised to 150°C ± 5°C. After maintaining the surface temperature of the substrate stable, control the movement of the turntable to make the deposited surface perpendicular to the axis of the print head (i.e., the angle between the surface normal of the curved surface and the axial direction of the print head is 0°), and at the same time ensure that the axis of the print head always remains in the gravity direction;

[0066] Step 2: After adjusting the inkjet parameters of the nano silver ink with the piezoelectric inkjet used, perform the printing trajectory processing of the interconnect structure. Among them, no filling is performed within 60 μm of the center of the main column, and the overall trajectory is a "return" - shaped filling. Print the interconnect metal columns on the curved surface metal substrate, and print the main column 401 to a height of 1.2 mm;

[0067] Step 3: By adjusting the turntable, make the axis of the main column 401 form a 90° angle with the printing axis. Use inkjet printing to deposit the branched column I 402 on the surface of the main column 401 until a height of 600 μm. Then adjust the turntable to print a strut every time the main column 401 rotates 60° until all the branched columns I 402 are printed;

[0068] Step 4: Continue to adjust the turntable to make the angle between the axis of the print head and the axis of the main column 401 45°. In addition, use a 1064-nm laser with a power of 0.1 w on the main column 401, and control the defocused spot to irradiate at 200 μm; test that the surface temperature of the branched column I 402 has reached 165°C. Continue to use piezoelectric inkjet to print the branched column II 403 on the branched column I 402. After each printing, adjust the turntable to the next branched column I 402 to print the branched column II 403 until all the branched columns II 403 are printed; the overall schematic diagram of the completed dendritic interconnect structure is as Figure 4 shown.

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for forming a 3D printed curved multilayer circuit vertical interconnect structure, characterized in that, It includes the following steps: Step 1: Mount the dielectric substrate on a working platform with rotatable and movable functions, heat the dielectric substrate to keep its surface temperature above 120°C during the formation process of the interconnect structure. At the same time, ensure that the axis of the print head of the 3D printing device always remains in the direction of gravity; Step 2: Adjust the position of the dielectric substrate through the working platform to make the angle between the axis of the print head and the normal of the deposited surface of the dielectric substrate meet the printing requirements; Use the 3D printing device to deposit metal layer by layer on the dielectric substrate according to the characteristics of the interconnect structure to a specified height to form an interconnect structure; Step 3: Use the 3D printing device to print a dielectric layer around the interconnect structure formed in Step 2 and cure and shape it; Among them, an isolation belt is provided between the dielectric layer and the interconnect structure; Step 4: Use the 3D printing device to fully fill the isolation belt area with dielectric resin and cure and shape it to make the isolation belt reach the specified height; The dielectric resin used for the isolation belt and the dielectric resin used for the dielectric layer are of the same type of resin or mutually compatible resin types, and the surface tension and viscosity of the dielectric resin used for the isolation belt are both lower than the surface tension and viscosity of the dielectric resin used for the dielectric layer; Step 5: Print a metal ring sheet layer along the circumferences of the upper and lower ends of the interconnect structure, and then print the same-layer circuit layer to connect with the metal ring sheet layer; Step 6: Repeat Step 2 to Step 5 to form other interconnect structures on the surface of the dielectric substrate, and complete the formation of the curved multi-layer circuit vertical interconnect structure.

2. The method for forming a 3D printed curved multi-layer circuit vertical interconnect structure according to claim 1, wherein: In Step 2, piezoelectric inkjet spraying of nano metal ink, aerosol spraying of nano metal ink, or ion particle atomization spraying and deposition of plasma atomized metal particles are used to form an interconnect structure on the dielectric substrate; The interconnect structure is a solid core, thin-walled structure in the shape of a cylinder, tubular body or other shapes.

3. The method for forming a 3D printed curved multi-layer circuit vertical interconnect structure according to claim 1 or 2, wherein: In Step 2, the angle between the axis of the print head and the normal of the deposited surface of the dielectric substrate is 0 to ±45°; 4. The method for forming a 3D printed curved multi-layer circuit vertical interconnect structure according to claim 3, wherein: In Step 2, the trajectory of depositing layer by layer to the specified height according to the characteristics of the interconnect structure is filled from the outside to the inside in a "return" shape; For a solid interconnect structure, at least a diameter of 60 - 100μm is reserved in the central area as a non-printing filling area; The specified height of the interconnect structure is greater than or equal to the thickness of the dielectric between two connected layers of circuits; 5. The method for forming a 3D printed curved multi-layer circuit vertical interconnect structure according to claim 4, wherein: In Step 3, the width of the isolation belt is less than or equal to 200μm; 6. The method for forming a 3D printed curved multi-layer circuit vertical interconnect structure according to claim 5, wherein: In Step 4, under heating conditions, the surface tension of the dielectric resin used to fill the isolation belt is less than 15 dyn / cm, the viscosity is less than 12 cP, and the expansion coefficient after curing is less than 60 ppm; The filled isolation band is 30–70 μm below the top surface of the interconnect structure.

7. The method for forming a 3D printed curved surface multilayer circuit vertical interconnect structure according to claim 6, characterized in that: In step 5, the thickness of the metal ring strip layer is consistent with the thickness of the same circuit layer, and the width of the metal ring strip is not less than 150μm.

8. The method for forming a 3D printed curved multilayer circuit vertical interconnect structure according to claim 7, characterized in that: The curing and shaping in steps 3 and 4 are both achieved by ultraviolet light irradiation.

9. A curved multilayer circuit board, characterized in that: The vertical interconnect structure thereon is formed using the method described in any one of claims 1-8.

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