High-precision multi-layer circuit board and its 3D printing manufacturing method

Abstract

The present invention relates to a high-precision multi-layer circuit board and its 3D printing manufacturing method, which includes: S1, forming a three-dimensional circuit layer on the upper surface of a substrate; S2, stacking metal pillars at a preset position of the current three-dimensional circuit layer; S3, forming an insulating layer on the upper surface of the current three-dimensional circuit layer, drilling holes in the insulating layer, and filling the drilled holes with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer; S4, if the current insulating layer is the top layer, forming a bonding pad layer on the upper surface of the current insulating layer and performing step S5; if not, repeating steps S1-S2 with the current insulating layer as a new substrate and performing step S6; S5, connecting the corresponding metal pillars to the bonding pad layer or by pre-drawing to complete the manufacturing of a multi-layer circuit board; S6, connecting the corresponding metal pillars to the current three-dimensional circuit layer or by pre-drawing, and returning to step S3. The present invention can manufacture a high-precision multi-layer circuit board with high interconnection accuracy.

Description

[Technical field]

[0001] The present invention belongs to the technical field of circuit board manufacturing, and specifically relates to a high-precision multi-layer circuit board and its 3D printing manufacturing method. [Background technology]

[0002] Multilayer circuit boards are commonly found in IC carriers, package substrates, printed circuit boards (PCBs), low temperature co-fired ceramic (LTCC) substrates, etc., and are the basic components of electronic applications and products. Active devices (e.g., power MOS, transistors, IC chips, etc.) and various other passive components (e.g., filters, transformers, resistors, capacitors, and inductors, etc.) need to be assembled or embedded into the multilayer circuit boards after a certain packaging process. These boards need to be subsequently assembled with the next stage of packaging to form a packaging system. Thus, the multilayer circuit board plays an important role in the electrical connection, assembly connection, and structural protection of various components. In the design and manufacture of the multilayer circuit board, the electrical, thermal, mechanical, etc. requirements brought by the device and package need to be fully considered. Over the years, the electronics industry has developed various multilayer circuit board manufacturing technologies to adapt to the design and application of the product.

[0003] Traditional processes for manufacturing multi-layer circuit boards mainly include thin film technology, thick film technology and organic laminate technology. According to different types of circuit boards (IC carriers, package substrates, printed circuit boards, ceramic substrates), different materials (e.g., organic, inorganic, etc.) and different requirements for interconnection precision, generally, the circuit pattern is transferred by photolithography + development + chemical plating / electroplating, deposition or screen printing, etc., the through-holes are formed by mechanical punching / drilling, laser drilling, chemical etching, plasma etching, etc., the holes are metallized by electroplating, screen printing, etc., and the single-layer superposition is combined into a multi-layer structure by deposition, spin coating, stack co-firing, lamination, etc. Although such processes are the most widely used in the industry, factors such as cumbersome process flow, multiple masks, expensive equipment, and large amounts of material waste greatly increase the manufacturing cost and time of multi-layer circuit boards.

[0004] In recent years, with the advancement of 3D printing processes, compared with traditional manufacturing processes for multilayer circuit boards, they have shown enormous potential in shortening the research and development and implementation cycles of new products, reducing NRE costs, etc. In some 3D printing processes based on inkjet or aerosol jet, the line width is large (ranging from tens of microns to hundreds of microns), the thickness of the insulating layer is large (minimum thickness is about 35 um), and the size of the vertical interconnect structure is too large (on the order of hundreds of microns), which limits the application of such technology in circuit boards with multilayer and high-density interconnect scenarios, and only printed circuit boards that do not require a large number of layers and interconnect accuracy can be manufactured. In some 3D printing processes based on fused deposition modeling (FDM), due to the limitations of line materials and melting technology, only insulating layers of certain materials can be manufactured, and the surface quality of the printing by FDM method is low, and the circuit layers and vertical interconnect structures need to be completed by other non-printing methods, resulting in low interconnect accuracy. Some 3D printing processes based on selective laser sintering (SLS), selective laser melting (SLM), electron beam selective melting (EBSM), direct metal laser sintering (DMLS), etc. require the use of high energy sources to sinter or melt the metal after scattering or spraying the powder, resulting in low metal processing precision and not suitable for the production of precision multi-layer circuit boards. In addition, some methods combine the extrusion 3D printing method with the corresponding paste to improve printing precision. For example, a Chinese patent with publication number CN109534767A discloses a paste for extrusion 3D white marble powder printing and its manufacturing method, in which the paste has a high solid content and good shear performance, which is suitable for the extrusion 3D printing process, and gradually dries and hardens during the 3D printing process under room temperature conditions, resulting in high-precision moldings without collapse phenomenon. Also, for example, Chinese patent publication number CN107365158A provides a paste with good stability and shear thinning properties, which can be smoothly extruded from a needle tip, and can still maintain the line shape and a certain span after being deposited on a substrate, and has good formability, thereby improving precision. Summary of the Invention

[0005] In response to the above problems existing in the prior art, the present invention provides a high-precision multi-layer circuit board 3D printing manufacturing method that can manufacture high-precision multi-layer circuit boards with high interconnection accuracy.

[0006] The present invention adopts the following technical solutions:

[0007] A high-precision multi-layer circuit board 3D printing manufacturing method, comprising:

[0008] S1: extruding a nanoscale metal paste having shear thinning properties from an extrusion port to form a three-dimensional circuit layer on a substrate;

[0009] S2, the nanoscale metal paste having shear thinning properties is extruded from the extrusion port to form a metal pillar at a preset position of the current three-dimensional circuit layer;

[0010] S3. forming an insulating layer on the top surface of the current three-dimensional circuit layer, drilling holes in the insulating layer, and filling the drilled holes with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer;

[0011] S4, determining whether the current insulating layer is the top insulating layer, and if so, forming a bonding pad layer on the top surface of the current insulating layer and executing step S5; if not, repeating steps S1 to S2 with the current insulating layer as a new substrate and executing step S6;

[0012] S5, the metal pillar of the corresponding three-dimensional circuit layer located directly under the current insulating layer is connected to the bonding pad layer or is connected by the pre-drawing, thereby completing the manufacture of the multi-layer circuit board;

[0013] S6, connecting the metal pillar of the corresponding three-dimensional circuit layer located immediately below the current three-dimensional circuit layer to the current three-dimensional circuit layer or connecting it by the previously drawn out step, and returning to step S3.

[0014] The present invention inventively utilizes extrusion 3D printing to manufacture high-precision multi-layer circuit boards with high interconnection accuracy, and overcomes many of the technical prejudices in the prior art when applying extrusion 3D printing to the manufacture of high-precision multi-layer circuit boards.

[0015] Compared with the manufacture of a single-layer circuit board, a multi-layer circuit board needs to add a vertical interconnect structure between circuit layers, and when the conventional technology is applied to a multi-layer circuit board, the size of the vertical interconnect structure is large, so it is difficult to meet the requirements for high-precision interconnection in a high-precision multi-layer circuit board. When the conventional technology is used to manufacture a multi-layer circuit board, it is necessary to scrape multiple insulating layers to form a multi-layer board on which each circuit layer is installed, so high-precision scraper coating is required, so that the thickness of each layer board formed thereby is consistent and the upper surface of each layer board is flat. However, if there is a slight deviation in the coating gap and coating inclination during the coating process, errors are likely to occur, and even if the accuracy is consistent when applying the insulating layer after each layer of the insulating layer is applied, it needs to be cured, and the accuracy of the formed board after curing cannot be guaranteed to be consistent, and the flatness of the upper surface of each board itself cannot be guaranteed, and the accumulation of the formation errors of each board will affect the manufacturing accuracy of the entire multi-layer circuit board. Since the flatness of the upper surface of each board itself cannot be guaranteed, the unevenness of the height and surface roughness of the upper surface of the board have a significant impact on the state of the printed circuit and the printing process window. Therefore, it is difficult for those skilled in the art to foresee the realization of the production of multi-layer circuit boards by extrusion printing, which will result in unevenness in the linearity and line width of the circuit, as well as breaks and pin strikes. In addition, the inventors have found during research and development that when lines are extruded by extrusion-type 3D printing methods, there will be problems of delayed discharge and unevenness at the start of the line, and problems of stacking and wire drawing will occur at the end of the line, which will have a significant impact on the pattern printing accuracy and uniformity of the line, and the impact will be more pronounced after stacking layers when producing multi-layer circuit boards. Both the circuit layer and the insulating layer need to be cured after formation, and each time they are cured, the previous circuit layer and insulating layer will repeatedly undergo thermal deformation, so the shape retention, adhesion, and shrinkage of the circuit layer and insulating layer after curing will affect the production of high-precision multi-layer circuit boards.

[0016] Therefore, the present invention overcomes the technical prejudice that those skilled in the art believe that the extrusion 3D printing method cannot manufacture a high-precision multi-layer circuit board with high interconnection accuracy by the above technical solution, and realizes the manufacture of a high-precision multi-layer circuit board by the extrusion 3D printing method. Usually, the high precision referred to in the present invention means that the line width of the wiring of the three-dimensional circuit layer reaches 1-150 um, the line spacing of the wiring reaches 1-150 um, the size of the vertical interconnection structure reaches 20-150 um, the spacing of the vertical interconnection structure reaches 20-150 um, the line width and the spacing can be significantly reduced to 10 um or less, and the size and spacing of the vertical interconnection structure can be significantly reduced to 150 um or less, so that there is high interconnection accuracy within and between the three-dimensional circuit layer, that is, the interconnection accuracy of the multi-layer circuit board. The three-dimensional circuit layer means that the extrusion head not only performs extrusion printing on the substrate in one plane, i.e., the extrusion plane, but also performs moving extrusion printing in a direction perpendicular to the extrusion plane, so that the formed circuit layer is three-dimensional, not flat as in the prior art. This structure not only solves the problems of collisions and needle breakage during the manufacturing process, but also allows the three-dimensional circuit layers to better adapt to the surface shape of the substrate and is less likely to cause damage to the substrate during various subsequent manufacturing processes, greatly improving the overall yield of multi-layer circuit boards.

[0017] As a preferred solution, in step S1, when forming a three-dimensional circuit layer on the upper surface of the substrate,

[0018] The method includes measuring the height of each point on the upper surface of the substrate to obtain a height dataset of the upper surface of the substrate, and relatively moving the extrusion nozzle along the Z-axis direction at the corresponding point on the upper surface of the substrate when extruding the nanoscale metal paste having shear thinning properties from the extrusion nozzle based on the height dataset of the upper surface of the substrate, so that the nanoscale metal paste having shear thinning properties extruded from the extrusion nozzle forms a three-dimensional circuit layer on the upper surface of the substrate.

[0019] As a preferred solution, in step S1, when forming a three-dimensional circuit layer on the upper surface of the substrate, a difference between an actual position of the three-dimensional circuit layer at a specific point on the upper surface of the substrate and a preset position is measured, and the extrusion head is calibrated based on the difference.

[0020] As a preferred solution, in step S1, before forming the starting ends of each circuit in the three-dimensional circuit layer by extruding the nanoscale metal paste having shear thinning properties from the extrusion port, a curved pre-extrusion motion is performed in a vertical plane perpendicular to the substrate, and the extrusion motion moves along the regular extrusion formation path of the circuit along the tangent direction of the curve;

[0021] In step S1, a predetermined excess material portion is provided at the end of the formal extrusion forming path of the circuit, and the operation of extruding the nanoscale metal paste having shear thinning properties is stopped when the extrusion outlet is located at the excess material portion.

[0022] As a preferred solution, in step S2, a nanoscale metal paste having shear thinning properties is extruded from an extrusion port to alternately form the outer frame lines and filling lines in each layer of the metal pillar, and then stacked at a preset position of the current three-dimensional circuit layer to form the metal pillar.

[0023] As a preferred solution, in step S3, forming the insulating layer includes:

[0024] The method includes forming an insulating layer on top of a current three-dimensional circuit layer by forcing a pre-applied insulating medium material onto the application surface with a scraper application head.

[0025] As a preferred solution, in step S3, forming the insulating layer includes:

[0026] The method includes extruding an insulating medium material through a slit in a slit coating head and coating the insulating medium material on the coating surface to form the insulating layer on the top surface of the current three-dimensional circuit layer.

[0027] As a preferred solution, in step S3, before applying the insulating layer,

[0028] a) controlling a Z-axis motor to lower the application head and bring both ends of the application head into contact with the touch sensor;

[0029] b) respectively recording the different heights of the Z-axis motor when the left and right ends of the coating head trigger touch sensor signals, and further obtaining the height difference between the left and right sides of the coating head;

[0030] c) calibrating the left and right heights of the left and right ends of the application head based on the left and right height difference.

[0031] As a preferred solution, in step S3, before applying the insulating layer,

[0032] A, measuring the height of the contact surface of the touch sensor using a laser displacement sensor to obtain the height of the touch sensor;

[0033] B. measuring the height of the coating start point on the coating surface using a laser displacement sensor to obtain the height of the coating start point;

[0034] C. calculating a relative height difference between the touch sensor and the application start point based on the height of the touch sensor and the height of the application start point;

[0035] D) contacting the center of the tilt-calibrated application head with the touch sensor and recording the Z-axis height of the application head at the time of contact;

[0036] E. Calibrating the Z-axis height of the coating head based on the relative height difference between the touch sensor and the coating start point, the Z-axis height when the coating head contacts the touch sensor, and a preset coating gap.

[0037] As a preferred solution, in step S3,

[0038] S3.1, forming an insulating layer on the top surface of the current three-dimensional circuit layer;

[0039] S3.2. According to the connection demand of each three-dimensional circuit layer and the height of the metal pillar in each three-dimensional circuit layer, the insulating layer is drilled, and the drilled holes are filled with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer.

[0040] As a preferred solution, the nanoscale metal paste with shear thinning properties includes nanoscale metal particles and a dispersion medium, the content of the nanoscale metal particles is 75% to 95%, the viscosity of the nanoscale metal paste with shear thinning properties is between 100,000 cps to 1,000,000 cps, the thixotropy index is 4 to 10, and the aspect ratio of the line formed by the nanoscale metal paste with shear thinning properties is ≧0.5. The aspect ratio of the line described in the present invention is obtained by dispensing the paste onto a glass substrate at a predetermined air pressure of 20 psi and a dispensing needle tip moving speed of 2 mm / s using a Musashi 300DS three-axis dispenser equipped with a Nordson Optimum (registered trademark) 100 um inner diameter general-purpose dispensing needle tip to form a line, and then observing the line under a microscope after leaving it for 10 minutes to calculate the ratio of the line height to the line width.

[0041] The dispersion medium of the nanoscale metal paste is used to disperse and protect the nanoscale metal particles, inhibit the aggregation of the nanoscale metal particles, improve the adhesion between the paste and the substrate, and provide a certain shape retention ability and thixotropy.

[0042] In a preferred solution, said nanoscale metal particles are nanoscale silver metal particles.

[0043] In a preferred solution, the dispersion medium includes a dispersion solvent and an adhesive, the dispersion solvent includes any one or more of an organic solvent and water, and the adhesive includes any one or more of polyacrylic acid, diethanolamine, and a complex of polyacrylic acid and diethanolamine.

[0044] As a preferred solution, the polyacrylic acid includes short-chain polyacrylic acid and long-chain polyacrylic acid.

[0045] As a preferred solution, the mass ratio of short-chain polyacrylic acid to long-chain polyacrylic acid is between 2:1 and 8:1.

[0046] In a preferred solution, the molar mass of the short-chain polyacrylic acid is between 1000 and 10000 g / mol and the molar mass of the long-chain polyacrylic acid is between 10000 and 100000 g / mol.

[0047] In a preferred solution, the organic solvent comprises one or more of ethylene glycol and glycerin.

[0048] In a preferred solution, said nanoscale metal particles are nanoscale copper metal particles.

[0049] In a preferred solution, the dispersion medium includes a dispersion solvent and an adhesive, the dispersion solvent includes one or more of an organic solvent and water, and the adhesive includes an epoxy resin, a curing agent, and a protective agent.

[0050] In a preferred solution, the epoxy resin is a heat-setting epoxy resin.

[0051] In a preferred solution, the heat-setting epoxy resin includes one or more of bisphenol A epoxy resin, E-44 epoxy resin, and biphenyl oxygen epoxy resin.

[0052] As a preferred solution, the curing agent is any one of a polythiol curing agent, a dicyandiamide curing agent, and an anhydride curing agent, so that the epoxy resin can be rapidly cured by exposure to heat.

[0053] In a preferred solution, the organic solvent comprises one or more of diethylene glycol monoethyl ether acetate, dibasic acid ester, isophorone, terpineol, or diethylene glycol monobutyl ether.

[0054] In a preferred solution, the nano-scale metal paste with shear thinning properties further comprises a protective agent.

[0055] As a preferred solution, the protective agent is formed by any one of triarylphosphine compounds, trialkylphosphine compounds, or a combination of multiple compounds, which coordinate with copper powder when the temperature is <100°C, and combine with oxygen atoms to form phosphine oxide compounds when the temperature is ≥100°C, thereby suppressing the oxidation problem of copper nanoparticles during the manufacturing and printing process.

[0056] In a preferred solution, the nano-scale metal paste with shear thinning properties further comprises a non-conductive filler.

[0057] As a preferred solution, the non-conductive filler is formed of any one of toner powder, nano graphene powder, bentonite and nano silica powder, or a combination of multiple types, and is mainly used to adjust the viscosity and thixotropy of the paste.

[0058] As a preferred solution, between steps S2 and S3,

[0059] performing a first pre-curing process on a current three-dimensional circuit layer and a metal pillar formed by stacking at a preset position of the current three-dimensional circuit layer;

[0060] Step S3 further includes performing a second pre-curing process on the insulating layer after forming an insulating layer on the upper surface of the current three-dimensional circuit layer;

[0061] In step S3, the insulating layer is perforated, and the perforated holes are filled with the nanoscale metal paste, and then the nanoscale metal paste is subjected to a third pre-curing treatment;

[0062] In step S5, the metal pillar of the corresponding three-dimensional circuit layer located directly under the current insulating layer is connected to the bonding pad layer or connected by the pre-drawing, and then the multi-layer circuit board is subjected to a full sintering hardening process to complete the manufacture of the multi-layer circuit board.

[0063] As a preferred solution, in the first preliminary curing treatment, the curing temperature is 100° C. to 150° C., and the curing time is 3 minutes to 10 minutes.

[0064] As a preferred solution, the second pre-curing process uses a stepwise pre-curing process.

[0065] As a preferred solution, the stepwise pre-curing treatment includes first curing at a curing temperature of 60°C to 95°C for 3 min to 10 min, and then curing at a curing temperature of 120°C to 200°C for 3 min to 10 min.

[0066] In a preferred solution, the insulating layer material is an organic medium.

[0067] As a preferred solution, in the overall sintering hardening treatment, the sintering temperature is 200° C. to 350° C., and the sintering time is 1 hour to 3 hours.

[0068] In a preferred solution, the insulating layer material is a ceramic medium.

[0069] As a preferred solution, in the overall sintering hardening treatment, the sintering temperature is 850° C. and the sintering time is 0.5 to 2 hours.

[0070] In order to ensure the efficiency and accuracy during the manufacturing process of the above-mentioned high-precision multi-layer circuit board, it is necessary to avoid the problems of the thermal influence on the precision equipment caused by the curing process and the repeated thermal deformation between the insulating medium and the circuit during the curing process. The present invention further provides a curing method in the manufacturing process of the high-precision multi-layer circuit board,

[0071] S1, forming a three-dimensional circuit layer on the upper surface of a substrate;

[0072] S2, forming a metal pillar at a preset position of the current three-dimensional circuit layer;

[0073] S3, performing a first pre-hardening process on the current three-dimensional circuit layer and the metal pillar formed by stacking at a preset position of the current three-dimensional circuit layer;

[0074] S4: forming an insulating layer on the upper surface of the current three-dimensional circuit layer, and performing a second pre-curing process on the current insulating layer;

[0075] S5, determining whether the current insulating layer is the top insulating layer, if so, forming a bonding pad layer on the top surface of the current insulating layer and performing step S6, if not, taking the current insulating layer as a new substrate and returning to step S1;

[0076] S6, performing a full sintering hardening process on the multi-layer circuit board.

[0077] As a preferred solution, in steps S1 and S2, nanoscale metal pastes, both of which have shear thinning properties, are extruded from an extrusion port to form a three-dimensional circuit layer and metal pillars.

[0078] The nanoscale metal paste with shear thinning properties includes nanoscale metal particles and a dispersion medium, the content of the nanoscale metal particles is 75% to 95%, the viscosity of the nanoscale metal paste with shear thinning properties is between 100,000 cps to 1,000,000 cps, the thixotropy index is 4 to 10, and the aspect ratio of the line formed by the nanoscale metal paste with shear thinning properties is ≧0.5.

[0079] As a preferred solution, between steps S4 and S5, the method further includes the steps of drilling holes in the insulating layer, filling the drilled holes with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer, and performing a third pre-curing process on the filled nanoscale metal paste.

[0080] As a preferred solution, in step S3, a first preliminary curing treatment is performed on the aforementioned current three-dimensional circuit layer and the metal pillar formed by stacking at a predetermined position on the current three-dimensional circuit layer, the curing temperature is 100°C to 150°C, and the curing time is 3 minutes to 10 minutes.

[0081] In a preferred solution, in step S4, the second pre-cure process for the current insulating layer uses a step-wise pre-cure process.

[0082] As a preferred solution, the stepwise pre-curing treatment includes first curing at a curing temperature of 60°C to 95°C for 3 min to 10 min, and then curing at a curing temperature of 120°C to 200°C for 3 min to 10 min.

[0083] In a preferred solution, the insulating layer material is an organic medium.

[0084] As a preferred solution, in step S6, the sintering temperature of the entire sintering hardening treatment is 200° C. to 350° C., and the sintering time is 1 hour to 3 hours.

[0085] In a preferred solution, the insulating layer material is a ceramic medium.

[0086] As a preferred solution, in step S6, the sintering temperature of the entire sintering hardening treatment is 850° C., and the sintering time is 0.5 to 2 hours.

[0087] In order to improve the shape retention of the metal pillar in the manufacturing process of the above-mentioned high-precision multi-layer circuit board, ensure the printing size of the metal pillar, and further ensure the overall size of the vertical interconnect structure to be small, and meet the requirements of high-precision interconnection in the high-precision multi-layer circuit board, the present invention further provides a manufacturing method for a metal pillar in a high-precision multi-layer circuit board,

[0088] S1: extruding a nanoscale metal paste having shear thinning properties from an extrusion port to form a three-dimensional circuit layer on a substrate;

[0089] S2. extruding a nanoscale metal paste having shear thinning properties at a preset position of the three-dimensional circuit layer to alternately form an outer frame line and a filling line in each layer of the metal pillar, and stacking them to form a metal pillar;

[0090] The nanoscale metal paste with shear thinning properties includes nanoscale metal particles and a dispersion medium, the content of the nanoscale metal particles is 75% to 95%, the viscosity of the nanoscale metal paste with shear thinning properties is between 100,000 cps to 1,000,000 cps, the thixotropy index is 4 to 10, and the aspect ratio of the line formed by the nanoscale metal paste with shear thinning properties is ≧0.5.

[0091] As a preferred solution, in step S2, the height of the metal pillar is higher than the insulating layer to be formed on the three-dimensional circuit layer.

[0092] A preferred solution further includes, after forming the insulating layer, extruding a nanoscale metal paste to form a leader line connected to the top surface of the metal pillar.

[0093] As a preferred solution, in step S2, the height of the metal pillar is lower than the insulating layer to be formed on the three-dimensional circuit layer.

[0094] A preferred solution further includes, after forming the insulating layer, forming micro-holes by laser drilling the insulating layer above the metal pillars.

[0095] In a preferred solution, the method further comprises the step of filling the micro-holes with a nano-scale metal paste after forming the micro-holes to form an extended column of a metal pillar.

[0096] A preferred solution further includes the step of extruding a nanoscale metal paste after forming the extended metal pillar to form a leader line connected to the top surface of the extended metal pillar.

[0097] As a preferred solution, in steps S1 and S2, when the three-dimensional circuit layer and the metal pillars are formed, the environmental humidity is 20% to 60%.

[0098] In a preferred solution, said nanoscale metal particles are nanoscale silver metal particles.

[0099] In a preferred solution, said nanoscale metal particles are nanoscale copper metal particles.

[0100] The present invention further provides a high-precision multi-layer circuit board obtained by using the above-mentioned high-precision multi-layer circuit board 3D printing manufacturing method.

[0101] The present invention further provides a flexible circuit using the above-mentioned high-precision multilayer circuit board.

[0102] The present invention further provides a wearable device that uses the above-mentioned high-precision multi-layer circuit board.

[0103] The present invention further provides a small passive electronic device that uses the above-mentioned high-precision multi-layer circuit board.

[0104] The beneficial effects of the present invention are as follows:

[0105] The present invention creatively utilizes an extrusion 3D printing method to manufacture high-precision multi-layer circuit boards with high interconnection accuracy, thereby improving the interconnection accuracy of multi-layer circuit boards.

[0106] The high-precision multi-layer circuit board 3D printing manufacturing method described in the present invention can be applied to various medium materials and pastes of various metal materials.

[0107] A nanoscale metal paste having shear thinning properties is extruded from an extrusion port to form a three-dimensional circuit layer on the upper surface of the substrate. Because the nanoscale metal paste has shear thinning properties, the printing precision of the three-dimensional circuit layer is high, the line width of the wiring in the three-dimensional circuit layer reaches 1-150 um, the line spacing of the wiring reaches 1-150 um, the size of the vertical interconnect structure reaches 20-150 um, and the spacing of the vertical interconnect structure reaches 20-150 um, and the line width and spacing can be significantly reduced to 10 um or less, and the size and spacing of the vertical interconnect structure can be significantly reduced to 150 um or less, so that there is high interconnection precision between the three-dimensional circuit layers, i.e., the interconnection precision of the multilayer circuit board.

[0108] At present, a connection can be realized by drilling a micro-hole with a small hole diameter in an insulating layer by laser drilling, and contacting a filled metal paste with the circuit, but in a scenario of printing a precise circuit, the size of the line width, line thickness, etc. of the circuit is smaller than the micro-hole (line width, line thickness is only a few microns), and the circuit at the bottom of the micro-hole is easily ablated by the laser, so that the filled paste does not contact the metal circuit during filling, or the contact area is very small, so that the conduction cannot be guaranteed. Therefore, in this application, a metal pillar is printed at a predetermined position of a three-dimensional circuit layer to increase the connection area, thereby ensuring the interconnection of the circuit and avoiding the circuit disconnection phenomenon.

[0109] In order to meet the precision requirements of the wiring line width, wiring line spacing, and insulating layer thickness, the present invention also extrudes a nanoscale metal paste with shear thinning properties and prints metal pillars, thereby ensuring the precision requirements of the printing size of the metal pillars and further ensuring the interconnection precision of high-precision multi-layer circuit boards.

[0110] Only by means of a preset metal pillar can the interconnection between the two most adjacent three-dimensional circuit layers be realized, and the present invention can realize the interconnection between any three-dimensional circuit layers by drilling holes in an insulating layer and filling the drilled holes with paste to draw out the metal pillar of the corresponding three-dimensional circuit layer located directly below the current three-dimensional circuit layer from at least one insulating layer.

[0111] Because the printing precision of the three-dimensional circuit layer is high and the volume is small, the covering can be achieved by only applying a very thin insulating layer. Since the vertical interconnect structure needs to be installed through the insulating layer, on this basis, the size of the vertical interconnect structure can be reduced and the interconnection precision of the high-precision multi-layer circuit board can be further guaranteed.

[0112] The flatness of the upper surface of each substrate itself cannot be guaranteed. In the present application, when a three-dimensional circuit layer is formed on the upper surface of the substrate, the height of each point on the upper surface of the substrate is measured to obtain a height data set of the upper surface of the substrate, and when the nanoscale metal paste having shear thinning properties is extruded from the extrusion nozzle according to the height data set of the upper surface of the substrate, the extrusion nozzle is relatively moved along the Z-axis direction at the corresponding point on the upper surface of the substrate, so that the nanoscale metal paste having shear thinning properties extruded from the extrusion nozzle forms a three-dimensional circuit layer on the upper surface of the substrate, and the uniformity of the linearity and line width of the circuit is ensured.

[0113] The jitter of the extrusion head during extrusion will cause deviation in the extrusion position, or if there is an error in the initial fixed position of the extrusion head, the same will cause deviation in the extrusion position, and the deviation in the extrusion position will have a significant impact on the position accuracy, line width, and linearity of the printed circuit in a high-precision printing scenario, resulting in non-uniform circuit linearity and line width, circuit deviation, and pin strike. Therefore, in the present application, when forming a three-dimensional circuit layer on the upper surface of a substrate, the difference between the actual position of the three-dimensional circuit layer at a specific point on the upper surface of the substrate and a preset position is measured, and the extrusion head is calibrated based on the difference, and the calibration may be to calibrate the stability of the extrusion head or to calibrate the fixed position of the extrusion head.

[0114] The present application avoids the problems of delayed discharge and uneven discharge at the start of the formal extrusion forming path of the extrusion outlet by presetting a curved pre-extrusion motion before the formal extrusion forming path of the circuit, and presetting an excess material portion at the end of the formal extrusion forming path of the circuit, and stopping the supply of extrusion power for extruding the nanoscale metal paste with shear thinning properties when the excess material portion is located, thereby avoiding the problems of pile-up and wire drawing at the end of the formal extrusion forming path of the circuit at the extrusion outlet.

[0115] In order for the surface profile and thickness uniformity of the insulating layer to meet the extremely high quality requirements in the present high precision printing scenario, the present invention calibrates the tilt degree at both the left and right ends of the application head before applying the insulating layer.

[0116] To ensure the coating thickness of the insulating layer, the present invention calibrates the coating gap between the coating head and the coating surface before coating the insulating layer.

[0117] The curing method provided by the present invention can ensure the manufacturing efficiency and precision of high-precision multi-layer circuit boards when using an extrusion 3D printing method to manufacture high-precision multi-layer circuit boards with high interconnection accuracy, and avoid the problems of the heat impact on precision equipment caused by the curing process and the repeated severe thermal deformation between insulating layers, metal pillars, and three-dimensional circuit layers during the curing process.

[0118] The metal paste with shear thinning properties selected according to the present invention can ensure the shape retention and adhesion of metal pillars and circuits during repeated curing processes, while simultaneously considering adhesion, shape retention, electrical conductivity, continuity of extrusion, and reduction of wire drawing phenomenon during discharge, when manufacturing high-precision multi-layer circuit boards with high interconnection accuracy using an extrusion 3D printing method, thereby improving the yield rate when manufacturing high-precision multi-layer circuit boards with high interconnection accuracy.

[0119] The metal pillar manufacturing method provided by the present invention can improve the shape retention of the metal pillar, ensure the printing size of the metal pillar, and further ensure the reduction of the overall size of the vertical interconnection structure when using an extrusion 3D printing method to manufacture high-precision multi-layer circuit boards with high interconnection accuracy, thereby meeting the high-precision interconnection requirements of high-precision multi-layer circuit boards. [Brief description of the drawings]

[0120] In order to more clearly describe the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative efforts. [Figure 1] 1 is a flowchart of a high-precision multi-layer circuit board 3D printing manufacturing method according to the present invention. [Diagram 2] 1 is a schematic diagram of a manufacturing process for a multilayer circuit board. [Diagram 3] 2 is a flow chart of a hardening method in the manufacturing process of a high-precision multi-layer circuit board according to the present invention. [Figure 4] 1 is a flow chart of a method for manufacturing metal pillars in a high-precision multilayer circuit board according to the present invention. [Diagram 5] FIG. 2 is a schematic diagram of a first vertical interconnect structure according to the present invention. [Figure 6] FIG. 2 is a schematic diagram of a first vertical interconnect structure unit according to the present invention; [Figure 7]FIG. 2 is a schematic diagram of a second vertical interconnect structure according to the present invention. [Figure 8] FIG. 2 is a schematic diagram of a second vertical interconnect structure unit according to the present invention; [Figure 9] FIG. 2 is a schematic diagram of an interconnection structure between two adjacent three-dimensional circuit layers. [Figure 10] FIG. 2 is a schematic diagram of an interconnection structure of multi-layer spaced three-dimensional circuit layers. [Figure 11] 1 is a schematic diagram of an interconnection structure between a bottom three-dimensional circuit layer and a surface three-dimensional circuit layer. FIG. [Figure 12] FIG. 2 is a schematic diagram of an interconnection structure of a multi-layer three-dimensional circuit layer on a vertical line where the same metal pillar is located. [Figure 13] This is an overall image of a high-precision multilayer circuit board.

[0121] Reference symbols in the figure: 1, substrate; 2, three-dimensional circuit layer; 3, insulating layer; 4, metal pillar; 5, extension column; 6, lead wire; 7, microhole; 8, vertical interconnection structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0122] Hereinafter, the embodiments of the present invention will be described by specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and each detail of this specification can be modified or changed in various ways based on different perspectives and applications without departing from the spirit of the present invention. It should be noted that the following examples and features of the examples can be combined with each other if not inconsistent.

[0123] Example 1:

[0124] Referring to FIG. 1 and FIG. 2, this embodiment provides a high-precision multi-layer circuit board 3D printing manufacturing method,

[0125] S1: extruding a nanoscale metal paste having shear thinning properties from an extrusion port to form a three-dimensional circuit layer on a substrate;

[0126] S2, the nanoscale metal paste having shear thinning properties is extruded from the extrusion port to form a metal pillar at a preset position of the current three-dimensional circuit layer;

[0127] S3: forming an insulating layer on the top surface of the current three-dimensional circuit layer, drilling holes in the insulating layer, and filling the holes with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer (specifically, according to the connection requirements of each three-dimensional circuit layer and the height of the metal pillars in each three-dimensional circuit layer, drilling holes in the insulating layer, and filling the holes with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer);

[0128] S4, determining whether the current insulating layer is the top insulating layer, and if so, forming a bonding pad layer on the top surface of the current insulating layer and executing step S5; if not, repeating steps S1 to S2 with the current insulating layer as a new substrate and executing step S6;

[0129] S5, the metal pillar of the corresponding three-dimensional circuit layer located directly under the current insulating layer is connected to the bonding pad layer or is connected by the pre-drawing, thereby completing the manufacture of the multi-layer circuit board;

[0130] S6, connecting the metal pillar of the corresponding three-dimensional circuit layer located directly below the current three-dimensional circuit layer to the current three-dimensional circuit layer or connecting by previously drawing out, and returning to step S3. S6, connecting the metal pillar of the corresponding three-dimensional circuit layer located directly below the current three-dimensional circuit layer to the current three-dimensional circuit layer or connecting by previously drawing out, and returning to step S3.

[0131] In this embodiment, the high-viscosity nanoscale metal paste can be discharged in a thread-like form from the extrusion port (inner diameter of extrusion port ≧1um, made of glass or ceramic material) at the tip of the precision printing needle by using a precision air pressure control propulsion and boosting structure.

[0132] As can be seen from the above:

[0133] The present invention creatively utilizes an extrusion 3D printing method to manufacture high-precision multi-layer circuit boards with high interconnection accuracy, thereby improving the interconnection accuracy of multi-layer circuit boards.

[0134] A nanoscale metal paste having shear thinning properties is extruded from an extrusion port to form a three-dimensional circuit layer on the upper surface of the substrate. Because the nanoscale metal paste has shear thinning properties, the printing precision of the three-dimensional circuit layer is high, the line width of the wiring in the three-dimensional circuit layer reaches 1-150 um, the line spacing of the wiring reaches 1-150 um, the size of the vertical interconnect structure reaches 20-150 um, and the spacing of the vertical interconnect structure reaches 20-150 um, and the line width and spacing can be significantly reduced to 10 um or less, and the size and spacing of the vertical interconnect structure can be significantly reduced to 150 um or less, so that there is high interconnection precision between the three-dimensional circuit layers, i.e., the interconnection precision of the multilayer circuit board.

[0135] At present, a connection can be realized by drilling a micro-hole with a small hole diameter in an insulating layer by laser drilling, and contacting a filled metal paste with the circuit, but in a scenario of printing a precise circuit, the size of the line width, line thickness, etc. of the circuit is smaller than the micro-hole (line width, line thickness is only a few microns), and the circuit at the bottom of the micro-hole is easily ablated by the laser, so that the filled paste does not contact the metal circuit during filling, or the contact area is very small, so that the conduction cannot be guaranteed. Therefore, in this application, a metal pillar is printed at a predetermined position of a three-dimensional circuit layer to increase the connection area, thereby ensuring the interconnection of the circuit and avoiding the circuit disconnection phenomenon.

[0136] In order to meet the precision requirements of the wiring line width, wiring line spacing, and insulating layer thickness, the present invention also extrudes a nanoscale metal paste with shear thinning properties and prints metal pillars, thereby ensuring the precision requirements of the printing size of the metal pillars and further ensuring the interconnection precision of high-precision multi-layer circuit boards.

[0137] Only by means of a preset metal pillar can the interconnection between the two most adjacent three-dimensional circuit layers be realized, and the present invention can realize the interconnection between any three-dimensional circuit layers by drilling holes in an insulating layer and filling the drilled holes with paste to draw out the metal pillar of the corresponding three-dimensional circuit layer located directly below the current three-dimensional circuit layer from at least one insulating layer.

[0138] Because the printing precision of the three-dimensional circuit layer is high and the volume is small, the covering can be achieved by only applying a very thin insulating layer. Since the vertical interconnect structure needs to be installed through the insulating layer, on this basis, the size of the vertical interconnect structure can be reduced and the interconnection precision of the high-precision multi-layer circuit board can be further guaranteed.

[0139] in particular:

[0140] When manufacturing a high-precision multi-layer circuit board, each layer of the three-dimensional circuit layer, each metal pillar corresponding to the three-dimensional circuit layer, or each layer of the insulating layer needs to be cured, so it is necessary to improve the circuit shape retention of the three-dimensional circuit layer and the metal pillar corresponding to the three-dimensional circuit layer. However, while improving the circuit shape retention, the adhesion of the circuit is reduced. Therefore, the nanoscale metal paste with the selected shear thinning properties must consider both shape retention and adhesion at the same time. Furthermore, in order to manufacture a high-precision multi-layer circuit board, the line disturbance phenomenon of the circuit in the process of forming each layer of the three-dimensional circuit layer has a significant impact on the accuracy of the entire multi-layer circuit board, so the nanoscale metal paste with the selected shear thinning properties must also consider the line disturbance effect at the same time. Furthermore, the nanoscale metal paste with the selected shear thinning properties must also guarantee the conductivity to ensure the normal use of the multi-layer circuit board. Furthermore, the nanoscale metal paste with the selected shear thinning properties must also further guarantee the continuity during extrusion and avoid the clogging of the extrusion port or the damage phenomenon of the material, thereby improving the yield when using the extrusion 3D printing method to manufacture high-precision multi-layer circuit boards with high interconnection accuracy.

[0141] The nanoscale metal paste having the above shear thinning properties can be selected as nanoscale silver metal paste or nanoscale copper metal paste.

[0142] Here, a nanoscale silver metal paste with shear thinning properties can be produced by the following method.

[0143] Take 1, 2 g of short-chain polyacrylic acid (PAA) solution (50 wt%, 5000 g / mol), 1 g of long-chain polyacrylic acid (PAA) solution (25 wt%, 50000 g / mol), and 40 g of DEA diethanolamine and dissolve them in 50 ml of deionized water.

[0144] 2. Stir at room temperature for 2 hours and adjust the pH value of the solution to 9.5, making it solution 1.

[0145] 3. Add silver nitrate solution (dissolve 20 g of silver nitrate in 20 ml of deionized water) dropwise to solution 1 and stir rapidly to obtain a dark yellow solution 2.

[0146] 4. Stir at room temperature for 24 hours, and the color of solution 2 will gradually change to dark black, forming nano silver particles with diameters of 2 nm to 8 nm.

[0147] 5. Stir in a hot water bath at 60°C for 2 hours to obtain solution 3. After this step, the size of the silver particles matures to 5nm to 50nm.

[0148] 6. Add 240 ml of ethanol to solution 3 at a rate of 10 ml / min, stir for 20 minutes, and obtain solution 4.

[0149] 7. Remove the supernatant of solution 4 and centrifuge the precipitate at 9000 rpm for 20 min to obtain a high-concentration dry nanosilver paste.

[0150] 8. Add 10wt% solvent (the solvent is a mixture of 30wt% ethylene glycol and 70wt% water, which dissolves polyacrylic acid and diethanolamine and keeps moisture) to the dried nano-silver paste, shake it evenly, and then degas it in a vacuum box at 50℃ and 25mbar for 30min to obtain the final nano-scale silver metal paste with shear thinning properties.

[0151] Here, a nanoscale copper metal paste with shear thinning properties can be produced by:

[0152] 8 g of bisphenol A epoxy resin is weighed, dissolved in 15 g of butyl acetate solvent, heated to 80 ° C, and held for 1 hour until completely dissolved to obtain a preliminary carrier. 1 g of anhydride hardener is weighed, added to the preliminary carrier, high-speed dispersed using a high-speed disperser, uniformly dispersed, heated to 30-35 ° C, and aged for 2 hours to obtain a dispersion medium. 70 g of 100-200 nm copper powder, 5 g of triphenylphosphine as a reducing agent, 0.2 g of nanographene powder as a non-conductive filler, and 0.8 g of 50 nm silica powder are weighed, thoroughly mixed with the dispersion medium in a mixer, and further high-speed dispersed using a high-speed disperser to obtain a uniform initial paste. The initial paste is rolled six times with a three-roll rolling machine until it reaches a fineness of less than 1 μm, and then filtered with a 10 μm filter to finally obtain a nanoscale copper metal paste. For a more specific manufacturing method of the nanoscale copper metal paste, reference can be made to the Chinese invention patent with publication number CN113362984A.

[0153] Based on the above, one skilled in the art can obtain a nanoscale metal paste with shear thinning properties that meets the requirements of the present invention by modifying various parameters such as concentration.

[0154] Typically, in step S1, the nanoscale metal paste having shear thinning properties is an organic dispersion system containing nanoscale metal particles, including nanoscale metal particles and a dispersion medium, the content of nanoscale metal particles is 75% to 95%, the viscosity of the paste is between 100000cps to 1,000,000cps, the thixotropy index is 4 to 10, and the aspect ratio of the formed line is ≧0.4. If the solid content of the metal is high, the shape retention is improved, the wire drawing of the printing needle tip is reduced, the shrinkage during sintering is reduced, and the conductivity is further improved, but the adhesion to the substrate such as glass, silicon wafer, polyimide, etc. is reduced. If the solid content of the metal is too low, the conductivity is reduced, and the shrinkage during sintering of the paste is too large, making it easy for the circuit to break. Nanoscale metal particles have high surface energy, and are easily aggregated and bonded to larger particles, which clog the extrusion port, so it is necessary to add dispersed nanoparticles, which are a dispersion medium corresponding to the paste, to suppress aggregation. For nanoscale metal particles of different materials, it is necessary to select a suitable dispersion medium and add other auxiliary materials according to the physical and chemical properties of the nanometal particles.

[0155] For nanoscale silver metal paste, the dispersion medium includes a dispersion solvent and an adhesive, the dispersion solvent includes any one or more of an organic solvent and water, and the adhesive includes any one or more of polyacrylic acid, diethanolamine, and a complex of polyacrylic acid and diethanolamine. The polyacrylic acid includes short-chain polyacrylic acid and long-chain polyacrylic acid, and the organic solvent includes any one or more of ethylene glycol and glycerin. The silver nanoparticles have good oxidation resistance, and the dispersion medium includes polyacrylic acid and diethanolamine components (polyacrylic acid and the substrate have good adhesion and can disperse metal particles, and diethanolamine gradually reduces metal ions to metal particles), so there is no need to add additional protective agents and curing agents. The mass ratio of short-chain to long-chain polyacrylic acid is between 2:1 and 8:1, the molar mass of short-chain polyacrylic acid is between 1000 and 10000 g / mol, and that of long-chain polyacrylic acid is between 10000 and 100000 g / mol. By adjusting the mass ratio, polymerization degree, silver nanoparticle content and water content of polyacrylic acid with various molecular weights, the printing effect of the paste, adhesion to the substrate and conductivity after sintering and hardening can be adjusted.

[0156] In the case of the nanoscale copper metal paste, the dispersion medium includes a dispersion solvent and an adhesive, the dispersion solvent includes any one or more of an organic solvent and water, and the adhesive includes an epoxy resin, a hardener, and a protective agent. The epoxy resin is a heat-setting epoxy resin, and the heat-setting epoxy resin includes any one or more of bisphenol A epoxy resin, E-44 epoxy resin, and biphenyl oxygen epoxy resin. The hardener is any one of a polythiol hardener, a dicyandiamide hardener, and an anhydride hardener. The organic solvent includes any one or more of diethylene glycol monoethyl ether acetate, a dibasic acid ester, isophorone, terpineol, and diethylene glycol monobutyl ether. The nanoscale metal paste with shear thinning properties further includes a protective agent, and the protective agent is formed of any one of a triarylphosphine compound and a trialkylphosphine compound, or is formed of a combination of a plurality of types. The nanoscale metal paste with shear thinning properties further includes a non-conductive filler, which is formed of any one of toner powder, nanographene powder, bentonite and nanosilica powder, or a combination of a plurality of kinds. Copper nanoparticles are easily oxidized by moisture and air, so the dispersion medium contains an epoxy resin component (epoxy resin is hydrophobic, can inhibit moisture penetration, and has good adhesion to the substrate after curing), so that the oxidation of copper nanoparticles is inhibited by adding a protective agent, and the epoxy resin is rapidly cured by adding a curing agent when exposed to heat, and the non-conductive filler is added according to the actual viscosity and thixotropy requirements.

[0157] The nanoscale metal paste nanoparticles with shear thinning properties have good dispersibility and can be smoothly extruded from a glass capillary with an inner diameter of 1um to 150um without clogging. The volumetric shrinkage rate of the paste after curing is less than 30%, and it has good adhesion to substrates such as glass, silicon wafers, and polyimides (when a paste with a thickness of about 20um is scraped onto a glass substrate with a scraper and sintered and cured at 200℃, and then peeled off with a 3M Scotch 600 adhesive tape, the material does not peel off). The viscosity and thixotropy index of the paste are characterized by a conventional Brookfield rotational viscometer. The paste has a water absorption rate of ≦5% under conditions of relative humidity 20% to 60% and 23±5℃ (affects the shape retention and shrinkage effect after sintering, test method: a paste with a thickness of about 100um is scraped onto a glass substrate with a scraper, the weight is measured on a precision electronic balance, and the mass increase after an interval of 1h is ≦5%).

[0158] The aspect ratio of the lines formed by the paste used in the production of existing single-layer high-precision circuit boards is generally about 0.2. In the present invention, vertical interconnection between multiple layers is required, and the aspect ratio of the paste is low, so that the important process of the present invention, such as printing of metal pillars, cannot be supported. At the same time, the use scenario of the multi-layer circuit board is more complicated than that of the single-layer circuit board (e.g., transmission of high-voltage signals, large currents, etc.), and the requirements for the thickness of the circuit are higher than those of the single-layer circuit board, so if a paste with a low aspect ratio of lines is used to produce a multi-layer board circuit, it is necessary to increase the thickness of the circuit at the expense of the accuracy of the line width and line spacing, so that a high-precision multi-layer circuit board with high interconnection accuracy cannot be produced.

[0159] When manufacturing a multi-layer circuit board, it is necessary to scrape-coat multiple insulating layers to form a multi-layer board on which each three-dimensional circuit layer is printed, so high-precision scraper coating is required, so that the thickness of each layer board formed is consistent, and the top surface of each layer board is flat. However, if there is a slight deviation in the coating gap and coating inclination during the coating process, it is easy to cause errors, and even if the precision is consistent when applying the insulating layer after each layer of the insulating layer is applied, it needs to be cured, and the precision of the formed board cannot be guaranteed to be consistent after curing, and the top surface of each board itself cannot be guaranteed to be flat. During printing, the extrusion head needs to approach the printing board to make the thread-like material contact the printing board, and in the high-precision printing scenario, the height variation and surface roughness of the printing board will have a significant impact on the state of the printed circuit, resulting in uneven circuit linearity, line width, disconnection, and pin strike.

[0160] Therefore, based on the fact that it is not possible to guarantee that the upper surface of each of the substrates themselves is flat, in step S1, when forming a three-dimensional circuit layer on the upper surface of the substrate, the height of each point on the upper surface of the substrate is measured to obtain a height data set of the upper surface of the substrate, and when the nanoscale metal paste with shear thinning properties is extruded from the extrusion nozzle based on the height data set of the upper surface of the substrate, the extrusion nozzle is moved relatively along the Z-axis direction at the corresponding point on the upper surface of the substrate, so as to match the height between each point on the upper surface of the substrate when the extrusion nozzle extrudes the nanoscale metal paste with shear thinning properties, that is, in this application, the printing of the three-dimensional circuit layer is three-dimensional printing, and in the printing process, the extrusion head moves relatively along the Z direction with respect to each point on the upper surface of the substrate, and finally forms a three-dimensional circuit layer on the upper surface of the substrate, thereby ensuring the uniformity of the linearity and line width of the circuit.

[0161] More specifically, in this embodiment, the height of each point on the upper surface of the substrate is measured by a laser displacement sensor to obtain a height data set on the upper surface of the substrate, and the resolution of the laser displacement sensor must be 0.3 um or less. If the resolution exceeds the standard, the compensation accuracy cannot be guaranteed in a large range scenario, and the height between the extrusion nozzle and the substrate cannot be accurately controlled during actual printing. During printing, the Z-axis movement of the substrate causes the extrusion nozzle to move relatively along the Z-axis direction at the corresponding point on the upper surface of the substrate.

[0162] Similarly, in the present invention, the needle tip needs to approach the substrate when the paste is extruded to bring the filamentous material into contact with the substrate, and the jitter generated during air pressure propulsion will have a significant impact on the positional accuracy, line width and linearity of the printed circuit in high-precision printing scenarios, resulting in non-uniform circuit linearity and line width, circuit misalignment and pin strike. Therefore, it is necessary to add a metal stabilizing mechanism to the needle tip base. At the same time, when forming a three-dimensional circuit layer on the upper surface of the substrate, the difference between the actual position of the three-dimensional circuit layer at a specific point on the upper surface of the substrate and the preset position is measured, and the stability of the needle tip is calibrated based on the difference, and the horizontal and vertical jitter difference of the needle tip after stabilization is controlled within 0.5 um, thereby avoiding the difference between the actual position and the preset position exceeding the preset threshold.

[0163] It should be noted that in some cases, the excessive deviation between the actual position and the preset position may be caused not by the jitter of the needle tip but by the deviation of the fixed position of the needle tip. In this embodiment, computer-aided manufacturing (CAM) technology is used to import a pre-designed circuit pattern to generate a numerically controlled path, and the printed needle tip moves along the numerically controlled path to form the required circuit pattern. Therefore, if there is a deviation in the fixed position of the needle tip, the deviation of the entire circuit pattern will occur. At this time, the fixed position of the needle tip can be calibrated based on the difference between the actual position and the preset position in the same way.

[0164] It should also be noted that if the deviation is caused by the effect of jitter, the deviation will change when printing is on or off, and if the deviation is caused by the effect of a fixed position, the deviation will not be affected by printing on or off.

[0165] Furthermore, since the present invention uses an extrusion-type 3D printing method, when extruding a line in the extrusion-type 3D printing method, problems of delayed discharge and unevenness will occur at the starting end of the line, and problems of pile-up and wire drawing will occur at the end of the line, which will have a significant impact on the printing accuracy of the line, and when manufacturing a multi-layer circuit board, the effect will be more pronounced after the layers are stacked.

[0166] In regard to the problem of delayed discharge and unevenness at the start of the line, the present invention uses the following solution: before forming the start of each circuit in the three-dimensional circuit layer by extruding the nanoscale metal paste with shear thinning properties from the extrusion port, a curved pre-extrusion motion is performed in a vertical plane perpendicular to the substrate, and the circuit is formally extruded along the tangential direction of the curve. That is, the curve is made into a pre-extrusion section, thereby avoiding the problems of delayed discharge and unevenness during formal extrusion.

[0167] Regarding the problem of pile-up or wire drawing at the end of the wire, the present invention uses the following solution: A surplus material portion is preset at the end of the regular extrusion forming path of the circuit, and the operation of extruding the nanoscale metal paste with shear thinning properties is stopped when the extrusion port is located at the surplus material portion, that is, when it is located at the surplus material portion, the supply of extrusion power for extruding the metal paste with shear thinning properties is stopped, and the surplus material portion occupies 5% to 30% of the total length of the last section of each circuit (Note: one circuit includes multiple printing paths of continuous printing, and the last section of the circuit is the last printing path in the circuit).

[0168] After the circuit is printed, it can maintain its pattern shape and cross-sectional shape, and has a specific aspect ratio. (When printing the circuit, the relative humidity of the environment must be controlled to 20% to 60%. If it is too low, the paste will not adhere to the substrate, and if it is too high, the paste will absorb water, reducing shape retention.)

[0169] Furthermore, since the multi-layer circuit board is composed of three-dimensional circuit layers and insulating layers alternately stacked, it is necessary to harden each three-dimensional circuit layer or insulating layer after its formation in order to form the next three-dimensional circuit layer or insulating layer. The present invention aims at manufacturing a high-precision multi-layer circuit board, and the manufacturing precision can reach 10um or less. When each layer of the three-dimensional circuit layer or insulating layer is fully hardened at high temperature, there will be repeated severe thermal deformation between the insulating medium and the circuit, and the thermal stress between the circuit and the medium, the thermal stress of the circuit and the medium itself will cause disconnection or failure during the process, and the repeated high-temperature heating will also cause the insulating medium to expand and contract severely, resulting in the oxidation of the insulating medium. Therefore, in the present invention, as shown in FIG. 3, a method of pre-hardening + full sintering hardening is used, which includes the following steps:

[0170] S1, forming a three-dimensional circuit layer on the upper surface of the substrate;

[0171] S2, stacking the current three-dimensional circuit layer at a preset position to form a metal pillar.

[0172] S3, a first pre-curing process is performed on the current three-dimensional circuit layer and the metal pillars formed by stacking at the preset positions of the current three-dimensional circuit layer.

[0173] S4: An insulating layer is formed on the top surface of the current three-dimensional circuit layer, and a second pre-curing process is performed on the current insulating layer.

[0174] S5, determining whether the current insulating layer is the top insulating layer, if so, forming a bonding pad layer on the top surface of the current insulating layer and performing step S6, if not, taking the current insulating layer as a new substrate and returning to step S1;

[0175] S6, the multi-layer circuit board is subjected to a total sintering hardening process.

[0176] in particular:

[0177] Regarding the formation of metal pillars by stacking the three-dimensional circuit layer formed on the upper surface of the substrate and the current three-dimensional circuit layer at a preset position, in the present invention, the curing temperature of the first pre-curing treatment is 100°C to 150°C, and the curing time is 3 minutes to 10 minutes, which removes moisture in the circuit material and at the same time defines the circuit, and increases the adhesion between the circuit and the substrate in preparation for the coating operation of the next insulating layer.

[0178] After the three-dimensional circuit layer and the metal pillar are cured, the insulating layer applied to the three-dimensional circuit layer is also cured by a pre-curing process. Specifically, after application, the insulating layer containing a solvent is first pre-cured to volatilize the solvent in the wet film (especially water, alcohol, dimethylacetamide, and other highly polar solvents) and prevent the thin film from fluctuating (liquid flow, uneven shrinkage, etc.) and the residual solvent that dissolves the circuit or reduces the adhesive strength between the circuit and the substrate. Furthermore, in order to prevent problems such as bubbles and wrinkles, the insulating layer is subjected to a second or higher stage of pre-curing, where the second stage of pre-curing is taken as an example and first cured at 60°C to 95°C for 3 min to 10 min, and then cured at 120°C to 200°C for 3 min to 10 min. The coating materials for the insulating layer usually contain a large amount of solvent. If they are directly cured at high temperatures, the solvent will evaporate rapidly and the skin effect (the surface of the coating layer is heated rapidly, drying and curing) will occur easily. This will cause air bubbles and residual solvent to be unable to be expelled in time, resulting in residual air bubbles and uneven wrinkles. At the same time, if the heating is too fast, strong thermal stress will be generated in the thin film, causing deformation of the circuit.

[0179] Between step S4 and step S5, the method further includes a step of pre-drawing corresponding metal pillars from the formed insulating layer by drilling holes in the insulating layer and filling the drilled holes with nanoscale metal paste, and performing a third pre-curing process on the filled nanoscale metal paste, where the third pre-curing process described here is similar to the first pre-curing process, and therefore its description is omitted.

[0180] After each three-dimensional circuit layer, insulating layer, and bonding pad layer (the bonding pad layer is a connection layer of the manufactured multilayer circuit board for connecting external electronic components, for more detailed explanation, see the interpretation section for the metal pillar below) are all completed, it is necessary to perform overall sintering and hardening (it should be noted that after the formation of the topmost bonding pad layer of the multilayer circuit board, there is no need to perform pre-hardening, and overall sintering and hardening can be performed directly). Specifically, when the insulating layer material is an organic medium and is thermally hardened in an air atmosphere, the overall sintering and hardening process is performed by muffle furnace sintering at a sintering temperature of 200°C to 300°C and a sintering time of 1h to 3h. The sintering conditions are also different depending on the nanoscale metal paste. For example, in the case of nanoscale copper metal paste, copper itself is easily oxidized, so generally, the overall sintering and hardening is performed in a nitrogen atmosphere (for details, see Example 7 below). When infrared, laser, photon sintering, etc. are used, the sintering time of the nanoscale metal paste can be further shortened. Conventional organic substrates such as FR-4 epoxy glass fiber substrates, organic insulating layer materials such as BT (Bismaleimide Triazine), PI (Polyimide), Epoxy resin, BCB (Benzocyclobutene), etc., have limited heat resistance, so in the invention, the whole sintering hardening is generally performed at 200℃ to 300℃. When the insulating layer material is a low-temperature co-sintering ceramic such as alumina-based or aluminum nitride-based low-temperature co-sintering ceramic, the whole sintering hardening process is performed by low-temperature ceramic co-sintering at a sintering temperature of 850℃ and a sintering time of 0.5h to 2h. Through the whole sintering hardening, the organic matter in the paste is partially or completely removed, the metal particles are mutually bonded, the crystal particles grow, the gaps (pores) and grain boundaries are reduced, and finally a metal circuit with good conductivity and a certain uniform linearity is formed. Through the whole sintering hardening, the insulating medium forms a stable insulating layer with certain electrical properties.

[0181] Here, compared with the full sintering hardening, the pre-hardening has the following advantages in terms of hardening parameters: lower temperature and shorter time. Pre-hardening can ensure that the medium is shaped in a timely manner, the circuit is filled in the subsequent process, the adhesion between the circuit and the medium is strengthened, and the efficiency is saved, and the thermal impact on the precision equipment is reduced.

[0182] If the curing conditions of the metal paste and the insulating medium are not compatible, it is necessary to give special explanation. If the insulating layer material is an organic medium and needs to be fully heat cured in a special atmosphere (for example, in the case of high-temperature curing polyimide in a nitrogen atmosphere, it generally needs to be fully cured at 350°C, and if it is directly cured at high temperature in an air atmosphere, the imine oxidation problem occurs, so the cured polyimide turns black and the mechanical strength is reduced). However, the silver metal paste prepared by the compounding method described in this application needs to be cured in an air atmosphere, and if the curing conditions of the metal paste and the insulating medium are not compatible, the curing method of mixed sintering is preferentially selected, that is, each layer metal circuit and metal pillar are directly fully cured by laser selection, and in the case of the entire multi-layer circuit board, it is fully cured at high temperature in an offline special atmosphere furnace. The laser used here is different from the ultraviolet picosecond laser used in the laser drilling described later, and the laser here can be a small infrared band continuous laser or a millisecond pulse laser. When hardening metal paste with laser, it should be noted that laser is a localized high energy input, so laser irradiation is likely to cause intense evaporation and decomposition of organic components in nanoscale metal paste. When hardening metal pillar and surface bonding pad layer with laser, if the energy input in a short time is too large, obvious bubbling problem will occur, and when hardening metal pillar and surface bonding pad layer with laser, it is also necessary to harden in stages, generally with pre-hardening at 5W~15W laser power first, and then fully hardening at high power of 20W~50W.

[0183] More specifically,

[0184] Regarding the coating of the insulating layer, in this embodiment, the coating head needs to be made of a metal material with a blade flatness of ≦2um. The coating process includes coating head tilt calibration and coating gap calibration.

[0185] Calibrating the inclination of the coating head: As can be seen from the above, the surface of the insulating layer is used as the substrate surface for circuit printing, so it needs to meet extremely high quality requirements to meet the surface morphology and thickness uniformity of the insulating layer in the high-precision printing scenario of this case. The coating head needs to calibrate the inclination of both the left and right ends of the head before coating. Specifically, the Z-axis motor is controlled to lower the coating head, and its left and right ends are respectively brought into contact with the high-precision touch sensor, and the touch sensor is subjected to the contact pressure of the coating head and reaches the sensor threshold, after which a contact signal is triggered, and the height of the Z-axis motor is recorded when both the left and right ends of the coating head trigger the touch sensor signal, and then fed back, thereby obtaining the left and right inclination of the coating head. Based on the inclination information, the precision screw ejector pins on both the left and right sides above the coating head are adjusted to control the left and right inclination, and the height deviation of both the left and right ends is repeatedly measured until it is ≦2um (it should be explained that here, the control of the left and right inclination situation of the entire head is not the same concept as the flatness of the blade plane ≦2um, and the flatness of the blade plane is the maximum variation difference of the blade plane).

[0186] Coating gap calibration: The height gap between the coating head and the substrate surface is an important coating parameter that has a significant effect on the thickness of the insulating layer. In this case, there is no mechanical connection structure between the coating head and the substrate, and the height gap between the two needs to be calibrated by a laser displacement sensor and a high-precision touch sensor. Before coating, first measure the height of the contact surface of the touch sensor using a laser displacement sensor to obtain the height of the touch sensor, then measure the height of the coating start point of the coating surface using a laser displacement sensor to obtain the height of the coating start point, and then calculate based on the height of the touch sensor and the height of the coating start point to obtain the relative height difference between the touch sensor and the coating start point, and bring the center of the inclination-calibrated coating head into contact with the touch sensor, record the Z-axis height of the coating head at the time of contact, and finally calibrate the Z-axis height of the coating head based on the relative height difference between the touch sensor and the coating start point, the Z-axis height when the coating head contacts the touch sensor, and the preset coating gap.

[0187] In this embodiment, regarding the coating of the insulating layer,

[0188] The basic structure of a multilayer circuit board is a stack of multiple insulating layers and three-dimensional circuit layers. The three-dimensional circuit layer is composed of a metal conductor pattern, and the insulating layer is composed of an organic resin or an inorganic ceramic. In the present invention, the stacking of multiple insulating layers is realized by scraper coating, slit coating, and stack coating, and each insulating layer is coated in situ by a coating head integrated into the equipment. The coating head is assembled on a Z axis controlled by a servo motor, and during coating, the coating head descends to a specific height above the substrate, and the coating head is held constant and the sample stage on which the substrate is placed is controlled to move forward, so that the coating head applies coating against the progress of the substrate surface, and can be precisely controlled by adjusting parameters such as the gap between the coating head and the substrate, the substrate advancement speed, and the amount of shrinkage of the insulating medium material. There are two types of coating heads: scraper coating heads and slit coating heads. The former is to add a certain amount of insulating medium material on the substrate by extrusion, and then the scraper coating head presses the insulating medium material against the substrate to form a thin film on the substrate. The latter is to adjust the slit gap, slit discharge amount and discharge speed, and then the slit head discharges the material along the substrate to form a thin film on the substrate. The above coating process can be repeated to obtain a thicker insulating layer. In particular, for some insulating medium materials with high solvent content (such as polyimide liquid materials), when applying a thicker thin film in one pass (generally, when the coating thickness is >100um), too much solvent is required to evaporate, which causes obvious shrinkage stress and is easy to cause bubbles or breakage of precision circuits. For such materials, multiple coating molding is recommended.If the coating thickness is too thin, there will be problems with surface variation, and the variation in the circuit of the previous layer will be reflected on the surface of the medium (because the circuit itself has a certain height). When the circuit of the next layer is printed above the circuit of the previous layer, there will be variation in height between the needle tip and the substrate surface. Furthermore, because the size of the circuit of the previous layer is small, the variation in height caused by the circuit only exists locally above the circuit, and cannot be solved by moving the substrate in the Z-axis direction as mentioned above. Therefore, when applying the insulating medium, the thickness of the medium needs to be at least twice the thickness of the circuit of the previous layer in order to reduce the influence of the height of the circuit of the previous layer.

[0189] The following describes a vertical interconnect structure in a high precision multi-layer circuit board.

[0190] As shown in Figures 5 to 8, the present invention relates to two types of vertical interconnection structures. The first one is composed of metal pillars 4, micro-holes 7 and nano-scale metal paste filled therein (it should be explained that the filled nano-scale metal paste can be regarded as the extension column 5 of the metal pillars 4), and lead wires 6 (the lead wires 6 are used to connect the metal pillars 4 and the three-dimensional circuit layer 2 or the extension column 5 and the three-dimensional circuit layer 2). The second one is directly composed of the metal pillars 4 and the lead wires 6. The former has low process requirements for the height of the metal pillars 4 and the thickness of the insulating layer 3, the insulating layer 3 completely covers the metal pillars 4, and the surface of the insulating layer 3 is flat, but it is necessary to add a laser-assisted process to form and fill the micro-holes 7 in the insulating layer 3. The latter can omit the auxiliary means, but the surface of the metal pillar 4 needs to pass through the pre-cured insulating layer 3 (i.e., the insulating layer 3 shrinks after pre-curing so that the surface of the metal pillar 4 can pass through the insulating layer 3), and due to surface tension, the surface of the insulating layer 3 will curve within a small area near the pillar, and the process control requirements such as material state, metal pillar height, coating thickness, etc. are high.

[0191] Specifically, the metal pillar is a key component of the vertical interconnect structure in the present invention. Referring to FIG. 4, the metal pillar needs to be printed and laminated on the vertical interconnect circuit by high-precision 3D printing according to the present invention, and the pillar is generally a cube or cylinder;

[0192] S1: extruding a nanoscale metal paste having shear thinning properties from an extrusion port to form a three-dimensional circuit layer on a substrate;

[0193] S2. extruding a nanoscale metal paste having shear thinning properties at a preset position of the three-dimensional circuit layer to alternately form an outer frame line and a filling line in each layer of the metal pillar, and stacking them to form a metal pillar;

[0194] The nanoscale metal paste with shear thinning properties includes nanoscale metal particles and a dispersion medium, the content of the nanoscale metal particles is 75% to 95%, the viscosity of the nanoscale metal paste with shear thinning properties is between 100,000 cps to 1,000,000 cps, the thixotropy index is 4 to 10, and the aspect ratio of the line formed by the nanoscale metal paste with shear thinning properties is ≧0.5.

[0195] The nanoscale metal paste with shear thinning properties prepared by the steps described in the present specification can meet the requirements of this step, and the nanoscale metal paste with shear thinning properties for printing with metal pillars is preferably one with higher shape retention ability and the aspect ratio of the formed line is ≧0.5, and the printing with metal pillars is preferably one in which the environmental humidity is controlled to 20%-60%. If the shape retention ability of the paste and the environmental relative humidity during printing (20%-60%) are not met, the metal pillars will be crushed or deformed during printing, resulting in non-standard sizes. During stack printing with metal pillars, each layer has an outer frame line and a filling line, and the overlap rate between the filling lines is 5%-15%. The deviation between the total discharge volume of metal pillar printing (metal pillar printing time * discharge mass per unit time at a given air pressure / paste density) and the design volume of the metal pillar is less than 10%. If the volume matching is incorrect, the metal pillars after pre-curing will have surface depressions or non-standard sizes. The metal pillar structure manufactured in this case generally has a diameter of 20um-150um, a height of 3um-150um, and the top surface of the metal pillar is flat (flatness≦1um). It should be noted that the bonding pad layer can include a plurality of bonding pads, and the process of forming the bonding pads is similar to the process of forming the metal pillars, which is also laminate printing, and each layer has an outer frame line and a filling line (the bonding pad in this case can also be understood as a metal pillar whose size in the X and Y directions is much larger than the height size in the Z direction to connect the multi-layer circuit board with external electronic components, and the description thereof is omitted here). The height and cross-sectional size of the metal pillar need to be determined according to the requirements of interconnection precision, the thickness requirements of the insulating layer, and the selection of the vertical interconnection structure. For the metal pillars of the first vertical interconnect structure, if the printing height is too low, the metal pillars will be pierced during the subsequent laser drilling, and if the printing height is too high, the process will be unstable when forming the subsequent leader line where the thin film of the upper insulating medium is raised, and the printed leader line will be prone to breakage. For the metal pillars of the second vertical interconnect structure, the height of the metal pillars needs to be printed high enough so that the top surface of the metal pillars is higher than the insulating layer after pre-curing.The insulating layer material used in this scenario needs to contain a certain solvent to ensure sufficient shrinkage in pre-cured thickness; if there is no shrinkage in the pre-cured thickness of the insulating layer, the metal pillars cannot be made taller than the insulating layer.

[0196] Forming microholes: the diameter of the microholes in the present invention is 15-150um. Forming and filling microholes is only applied to the first vertical interconnect structure. If the applied insulating layer is too thick, the metal pillars will be completely covered by the insulating layer. The insulating layer above the metal pillars is destroyed by laser drilling to form microholes. The laser drilling is preferably performed with an ultraviolet picosecond laser with a wavelength of 343nm or 355nm, an average output of 3-10W, a pulse width of <15ps, and a repetition rate of 200KHz-1MHz. The ultraviolet picosecond processing belongs to cold processing and has an excellent microhole forming effect on organic and ceramic insulating layers. Due to the ablation action of the ultraviolet picosecond laser, there are ablation marks on the surface of the metal pillars directly under the insulating layer, and the surface is in a depressed state. Microholes processed by infrared femtosecond laser, green picosecond laser, ultraviolet nanosecond laser, etc. have large hole diameters, poor compatibility with insulating layer materials, and are easy to penetrate metal pillars, so they are applied to certain insulating layers and microhole processing of 80um to 150um. The laser emission from the laser is focused on the surface of the sample through a vibrating mirror and a telecentric mirror, and scan drilling is performed line by line by line by visual positioning, and the diameter of the focused spot is 10 to 25um. The drilling path is an auger path. If the laser scanning deviation is large, the insulating layer above the metal pillar will not be completely ablated, and the metal circuit near the pillar will be damaged, affecting electrical conduction. In order to avoid the problem of laser scanning deviation, it is necessary to use visual positioning to identify the mark point during laser drilling, but in the scenario of some insulating layers with large thermal expansion coefficients, the risk of expansion and contraction brought about by the laminate pre-curing of the insulating layer in the present invention is increased, so when shrinkage occurs and the mark identification effect is low, it is necessary to identify it with a metal pillar template, that is, by visually capturing the outer contour of the corresponding metal pillar, single-point alignment is realized. This is one of the reasons why metal pillars are required to have a high degree of shape retention.

[0197] Filling of micropores: The filling of micropores can be done by precision pneumatic extrusion of nanoscale metal paste (it should be explained that the nanoscale metal paste does not have the thixotropic effect of shear thinning) or inkjet filling of nanoscale metal paste (it should be explained that the nanoscale metal paste is a low-viscosity paste material suitable for inkjet printing and does not have the effect of shear thinning). The former is suitable for micropore filling scenarios with a hole diameter of 15-150um and a hole spacing of >20um because of the high enough discharge precision, while the latter is only suitable for micropore filling scenarios with a hole diameter of 100-150um and a hole spacing of >100um because of the large droplet size. The bottom of the micropore is a metal pillar, so the filled paste can fully contact and wet the surface of the metal pillar. If the height of the metal pillar is too thin and the input of laser energy is too large, the metal pillar will penetrate into the micropore forming stage, and the filling paste will fill the lower three-dimensional circuit layer, causing an electrical short circuit. In addition, if the metal pillar is canceled and filled directly after the laser microhole formation, the above paste will be filled into the remaining three-dimensional circuit layer, which will cause the risk of short circuit. In addition, in the precision circuit printing scenario, the size of the circuit line width, line thickness, etc. is smaller than the microhole (for example, the line width and line thickness are only a few microns), so the circuit at the bottom of the microhole is completely ablated by the laser, so the filled paste will not contact the metal circuit when filling or the contact part is very small (it can be imagined that the laser drills above the thin metal line, the size of the hole is much larger than the width of the thin line, and the circuit at the bottom of the microhole is completely ablated by the laser, so the filled paste will not contact the metal circuit when filling or the contact part is very small), and the conduction cannot be guaranteed. The hole surface of the microhole after filling is filled with the filling paste, and the filling paste on the hole surface is basically flush with the hole to control the discharge amount. In the hole filling scenario using the precision air pressure extrusion method, the air pressure is between 5-80psi, the needle tip penetration depth into the hole is between 5-400um, and the needle tip pull speed is between 0.01-5mm / s. The post-processing of the micro-hole filling paste is similar to the post-processing of the three-dimensional circuit layer and metal pillar mentioned above, and requires pre-curing molding.

[0198] Leader:

[0199] The lead wire electrically connects the metal pillars of the bottom layer of the vertical interconnect structure to the upper three-dimensional circuit layer. For the first vertical interconnect structure, during the drawing operation, the precision pneumatic printing needle tip is moved to a certain height above the hole (this height is related to the requirements of interconnection precision, generally, when the line width of the lead wire needs to be 5um-10um and the hole diameter of the microhole needs to be 40um±5um, this height is 3um-5um), and after the thread-like discharge is fully in contact with the surface of the hole, the printing needle tip is moved to draw the lead wire out of the hole to interconnect the circuit of the upper three-dimensional circuit layer. The initial stage of the lead line is a critical step. In the initial stage, the printing path is displaced in the Z direction to compensate for the problem of local lifting of the insulating layer, and at the same time, in order to improve the reliability of the vertical conductive structure, the printing speed needs to be gradually increased to achieve a gradation effect of making the line width at the start of the lead line larger (almost the same as the difference in the micropores, see Figures 6 and 8) but smaller at the end of the lead line (almost the same as the difference in the circuit of the three-dimensional circuit layer). In the first vertical interconnect structure, there is a process adjustment process between the thickness of the insulating layer and the height of the metal pillar, so that the impact on the lifting of the upper insulating layer can be effectively controlled. The needle tip movement path during the lead line only needs a small displacement in the Z direction so that the distance between the needle tip and the substrate surface is within the normal printing range (for a metal pillar with a height of 10um and a sintered polyimide insulating layer with a thickness of 20um, the surface of the insulating layer above the metal pillar is generally 3um~5um higher than the surface of the insulating layer away from the metal pillar). The initial printing speed of the initial part of the lead line is generally 0.01 mm / s, and then gradually accelerates from this speed to perform a certain horizontal movement and Z-direction displacement, and in the first vertical conductive structure, the horizontal displacement of this part is generally 10-50 um. After the horizontal displacement and Z-direction displacement are completed, it can be rapidly accelerated to the speed of a normal printed circuit.

[0200] In the case of the second vertical interconnect structure, since there is no micropore and filling structure, the height of the metal pillar is higher than the insulating layer after curing, and the flatness of the upper surface of the metal pillar is ≦2um, and the printing needle tip can be moved directly to the upper surface of the metal pillar to form a leader line. Due to the influence of the height of the metal pillar and the surface tension of the coating liquid, the surface of the insulating layer is curved within a small area around the pillar (for a metal pillar with a diameter of 45um-55um, the radius is generally within 100um), and the surface height from near to far is obviously reduced. When the printing needle tip is drawn out from the surface of the metal pillar to print, it is necessary to ensure that the printing needle tip draws the leader line from the upper surface of the metal pillar to the insulating layer outside the small area around the metal pillar in one go to interconnect the circuit of the upper three-dimensional circuit layer according to the height difference between the upper surface of the metal pillar and the surface of the insulating layer away from the metal pillar in the Z direction. The initial printing speed of the initial portion of the lead line is generally 0.01 mm / s, and then gradually accelerates from this speed to perform a certain horizontal movement and Z-direction displacement, and in the second vertical conductive structure, the horizontal displacement of this portion is generally 20-100 um. After the horizontal displacement and Z-direction displacement are completed, it can be rapidly accelerated to the speed of a normal printed circuit.

[0201] The manufacturing process of the multi-layer circuit board and the vertical interconnect structure according to the present invention will be described in more detail below with reference to the corresponding drawings.

[0202] As shown in Figures 5 and 6, the first vertical interconnect structure is shown in which the metal pillar 4 is small in size and covered below the insulating layer 3. By filling the insulating layer 3 with micropores 7, an extension column 5 of the metal pillar 4 is formed, and the extension column 5 is connected to the circuit of the upper three-dimensional circuit layer 2 by a lead wire 6, thereby realizing the connection.

[0203] As shown in Figures 7 to 8, the second vertical interconnect structure is shown in which the size of the metal pillar 4 is large, and the insulating layer 3 shrinks after curing, so that the surface of the metal pillar 4 passes through the insulating layer 3, and the lead wire 6 directly connects the metal pillar 4 to the circuit of the three-dimensional circuit layer 2, thereby realizing the connection.

[0204] As shown in FIG. 9, the figure shows that the first vertical interconnection structure realizes the interconnection between two adjacent three-dimensional circuit layers 2. In this embodiment, the interconnection between two adjacent three-dimensional circuit layers 2 is used to explain the step S3 of "based on the connection requirements between each three-dimensional circuit layer and the height of the metal pillar in each three-dimensional circuit layer, drill holes in the insulating layer, and fill the drilled holes with nanoscale metal paste to pre-draw the corresponding metal pillar from the formed insulating layer". First, the first three-dimensional circuit layer 2 is printed, and based on the connection requirements of the first three-dimensional circuit layer 2, the metal pillar 4 is printed at a preset position, and the first insulating layer 3 is further formed on the first three-dimensional circuit layer 2. At this time, the first three-dimensional circuit layer 2 and the second three-dimensional circuit layer 2 to be formed subsequently have a connection requirement, and the height of the metal pillar 4 in the first three-dimensional circuit layer 2 is lower than the first insulating layer 3, so at this time, the first insulating layer 3 is drilled, and the drilled holes are filled with nanoscale metal paste (nanoscale metal paste) to form the extended pillar 5. (It should be noted that if the height of the metal pillar 4 in the first three-dimensional circuit layer 2 is higher than that of the first insulating layer 3, there is no need to drill and fill, and the lead wire 6 can be directly printed on the metal pillar 4.) Furthermore, the second three-dimensional circuit layer 2 can be formed on the first insulating layer 3, and then the lead wire 6 can be connected to the circuit of the second three-dimensional circuit layer 2 to realize interconnection.

[0205] It should be noted that in the present invention, instead of pulling out the metal pillars 4 that need to be connected to the three-dimensional circuit layer 2 after the three-dimensional circuit layer 2 is formed, the metal pillars 4 are pulled out in advance, which can avoid the impact on the three-dimensional circuit layer 2 during the drilling and filling processes, and thereby ensure the interconnection accuracy of the multi-layer circuit board.

[0206] As shown in FIGS. 10 to 11, the first vertical interconnection structure realizes interconnection between three-dimensional circuit layers 2 spaced apart from one another.

[0207] As shown in Figure 12, the interconnection of multiple three-dimensional circuit layers 2 on the same vertical line is shown in the figure. As shown in the figure, after the connection between the first and third three-dimensional circuit layers 2 is realized by printing the metal pillars 4, filling the extension columns 5, and printing the lead lines 6, when the connection needs to be connected to the fourth three-dimensional circuit layer 2, another extension column 5 can be formed at the position of the lead line 6 in the third three-dimensional circuit layer 2 by directly drilling the micro holes 7 and filling the paste without additionally presetting the metal pillars 4, and since the line width of the lead line 6 at the start point is large (about the same as the micro holes 7, as shown in Figures 6 and 8), the above-mentioned non-conductive phenomenon does not occur.

[0208] It should be noted here that in the manufacturing process of a multi-layer circuit board, the shape of the vertical interconnect structure can be selected according to the connection requirements. For example, when it is only necessary to realize the interconnection between two adjacent three-dimensional circuit layers 2, the second vertical interconnect structure can be directly selected, and when it is necessary to realize the interconnection between three-dimensional circuit layers 2 spaced apart from each other by multiple layers, the first vertical interconnect structure can be selected.

[0209] As shown in Figure 13, the figure shows the overall image of the high-precision multilayer circuit board after connection.

[0210] The specific manufacturing process of the high-precision multi-layer circuit board will be described below (for convenience of explanation, the manufacturing process of the bonding pad layer will be omitted in the following manufacturing process).

[0211] Phase 1: Multi-layer circuit board printing design:

[0212] Step 1. According to the design information of the multi-layer circuit board (such as line width and line spacing, stacking design, impedance design, position of vertical interconnect design, etc.), determine the type of needle tip, medium material, and printing material. Here, take a total of four three-layered circuit layers with line width 5um, line spacing 5um, and line height 3um and four polyimide insulation layers (insulation layer thickness is 18um) as an example.

[0213] Step 2. Import the DXF design drawing into the process matching CAM software, and the CAM software generates the printing path code for each circuit layer, and the CAM software generates the coating thickness and area of ​​each insulating medium layer, and determines the preset position of the vertical interconnection structure of each three-dimensional circuit layer according to the connection requirements of the multi-layer circuit board.

[0214] Step 3. Inspect and correct the print path and calibrate the application head (the calibration method is as described above).

[0215] Phase 2: Preparation of supplies and equipment:

[0216] Step 1. Select a nanoscale silver metal paste material with a viscosity of 580,000cps, a metal solid content of 85%, a thixotropy index of 9, a line aspect ratio of 0.5, and shear thinning properties that can withstand the peeling of 3M Scotch 600 adhesive tape; select a standard polyimide liquid material with a viscosity of 10,000cps and a solid content of 18% as the application medium material; select a glass needle with an inner diameter of 5um, an outer diameter of 10um, and an end face flatness of ≦1um; and select a metal scraper as the application head.

[0217] Step 2. Attach the barrel containing the nanoscale silver metal paste material to a precision pneumatic dispenser, and attach the barrel containing the application media material to a precision metering feeder.

[0218] Step 3. Automatically / manually feed the 200mm*200mm*0.25mm polyimide film substrate from the feeding area, start the CAM software, turn on the vacuum suction, the sample stage adsorbs the substrate, and the equipment mechanically returns to the origin.

[0219] Step 4. Use a laser displacement sensor (with a measurement resolution of 0.3um) to scan the entire substrate printing area and measure the height of each point on the substrate top surface, obtain a height dataset of the substrate top surface, and the CAM software records the height dataset of the substrate.

[0220] Step 5. In the pre-printing area, turn on the precision air pressure dispenser, set the output air pressure and printing movement speed in the CAM software, control the descent of the needle tip by the software so that the height between the needle tip and the silicon substrate in the pre-printing area is 3um, pre-print the wiring at various air pressures and movement speeds, record the pressure and speed parameters of the line width for 5±0.5um, in this embodiment, the pressure is 45psi and the speed is 0.5mm / s, then use the laser displacement sensor to measure and record the printing starting point on the polyimide substrate, and pre-print the relative height difference on the silicon substrate.

[0221] Phase 3: Manufacturing the multi-layer circuit board:

[0222] Step 1. After transferring to the printing starting point, based on the information of the relative height difference obtained in step 5 in the second stage, adjust the Z-axis height of the needle tip so that the distance between the needle tip and the polyimide substrate is the distance between the needle tip and the silicon substrate in the pre-printing area during pre-printing, and compensation needs to be turned on before printing, and at the same time, the laser displacement sensor has recorded the height data set of the substrate in the software, so that the height variation of the substrate surface is automatically compensated for by raising and lowering the sample stage, and the distance between the needle tip and the substrate is maintained at 3um in the printing process.

[0223] Step 2: Print a first three-dimensional circuit layer based on the printing path generated in the first step and the printing parameters obtained in the second step.

[0224] Step 3. Print metal pillars at the positions of vertical interconnects, and print cross marks at the marks. The metal pillars are fabricated by repeatedly filling the circuit layer by layer, with the hatch spacing of the filled lines in each layer being 5um, the hatch spacing of the layers being 3um, and the length, width and height of the final metal pillar after multi-layer stacking being 50um*50um*12um. The device-integrated heating ceramic suction cup is used to pre-cure the metal circuit and pillars at a temperature of 150℃ for 10min, and then cooled after pre-cure.

[0225] Step 4. Move the sample stage to the initial coating position, adjust the gap between the scraper and the substrate (the gap adjustment method is as described above) according to the coating thickness (100um) required for the current layer generated in the first step, and apply the polyimide liquid 5mm in front of the scraper by dispensing. Set the movement speed of the sample stage to 1mm / s. The scraper presses the polyimide material against the sample stage to form a wet film on the substrate, and leaves it for 60s.

[0226] Step 5. Cure the wet membrane by using the device-integrated heating ceramic suction cup, convert the wet membrane into a dry membrane, firstly cure at 70℃ for 10min, then cure at 150℃ for 10min, and cool after curing.

[0227] Step 6. The sample stage is transferred to the micro-hole forming station, and the relative positional relationship is calibrated by visually capturing the mark point, and then a laser is used to drill a micro-hole above the metal pillar and destroy the insulating layer above the metal pillar, the light source used is a 355nm ultraviolet picosecond laser with an average power of 4W, a pulse width of <15ps, a repetition frequency of 1MHz, a helical scan speed of 0.5mm / s, a jump speed of 100mm / s, and a spot diameter of 20um, and the resulting hole diameter is 40um and the hole depth is 20um.

[0228] Step 7. The sample stage returns to the printing station, and the printing needle tip uses precision air pressure extrusion to fill the micro-holes with metal paste, the metal paste used is also nanoscale silver metal paste (diluted to 400000cps viscosity), the penetration depth of the printing needle tip into the hole is 15um, the air pressure is 40psi, the pulling speed is 0.05mm / s, and then the drawing operation is performed, the initial speed of the drawing line is 0.01mm / s, the initial horizontal displacement of the drawing is 20um, and the Z-direction displacement is 3um.

[0229] Step 8. By visually capturing the mark points, calibrate the relative positional relationship, and based on the printing path generated in the first stage and the printing parameters obtained in the second stage, print the first layer circuit on the surface of the sintered polyimide insulation layer, and print metal pillars at the positions of the vertical interconnects.

[0230] Step 9. Repeat steps 3 to 8 until four layers of circuit printing and four layers of insulating layer coating and curing are completed.

[0231] Step 10. Using the device-integrated heating ceramic suction cup, the entire multi-layer circuit board is fully cured at a temperature of 250°C for 1 hour.

[0232] Step 11. Turn off the vacuum and drain.

[0233] Step 12. Inspection and cutting of multi-layer circuit board samples.

[0234] Example 2:

[0235] The difference between this embodiment and embodiment 1 is that a multi-layer circuit board is manufactured using a sacrificial material, and the specific improvements are as follows:

[0236] 1. The next step 3 of the second step described in Example 1 is modified to automatically / manually supply a 6-inch standard silicon wafer substrate (a sacrificial material is attached to the surface of the 6-inch standard silicon wafer substrate) to the supply area, start the CAM software, turn on vacuum suction, the sample stage suctions the substrate, and the equipment mechanically returns to the mechanical origin.

[0237] 2. The next step 11 of the third stage described in Example 1 is modified to turn off the vacuum suction and discharge, and desorb the sacrificial material by corresponding chemical reagent to obtain a free-standing multi-layer circuit board.

[0238] 3. Other process steps and their steps are the same as in Example 1.

[0239] Example 3:

[0240] The difference between this embodiment and embodiment 1 is that a slit coating method is used, and the specific improvements are as follows.

[0241] 1. Slit coating method: The next step 4 of the third step in Example 1 is modified to move the sample stage to the initial coating position after printing, adjust the gap between the slit coating head and the substrate to 100um according to the coating thickness of 100um required for the current layer generated in the first step in Example 1, set the discharge amount of the slit coating head to 2250uL and the discharge speed to 15uL / s, set the average moving speed of the coating head relative to the substrate to 1mm / s, slightly faster in the initial stage (5s at 1.2mm / s) and slightly slower in the final stage (5s at 0.7mm / s), and then start the coating process to complete the coating of the current insulating layer.

[0242] 2. Other process steps and their steps are the same as in Example 1.

[0243] Example 4:

[0244] The difference between this embodiment and the first embodiment is that the second vertical interconnect structure is used for manufacturing, and the specific improvements are as follows:

[0245] 1. Direct molding:

[0246] The next step 2 of the third stage in Example 1 is modified to print the first layer circuit based on the printing path generated in the first stage and the printing parameters obtained in the second stage, and print metal pillars at the positions of the vertical interconnects, and the metal pillars are manufactured by repeatedly filling the circuit layer by layer, with the hatch spacing of the filled lines in each layer being 5um, the layer distance being 3um, and the length, width and height of the final metal pillar after multi-layer stacking being 50um*50um*50um.

[0247] The next step 6 of the third stage in the first embodiment is cancelled.

[0248] The next step 7 of the third stage in Example 1 is modified so that the sample stage is transferred to the printing station, and the printing needle tip performs the drawing operation directly on the top surface of the pillar by precision pneumatic extrusion, the initial speed of the drawing line is 0.01 mm / s, the initial horizontal displacement of the drawing is 70 um, and the Z-direction displacement is 32 um.

[0249] 2. Other process steps and their steps are the same as in Example 1.

[0250] Example 5:

[0251] The difference between this embodiment and embodiment 1 is the hardening and sintering of the insulating medium material, and the specific improvements are as follows.

[0252] (1) Organic thermosetting polyimides:

[0253] 1. The next step 5 of the third step in Example 1 is modified to pre-cure the medium using a device-integrated infrared lamp at a power of 600 w and a time of 30 s.

[0254] 2. The next step 10 of the third stage in Example 1 is modified to completely harden and sinter the entire multi-layer circuit board using a device-integrated infrared lamp at a power of 3000W for a time of 20 seconds.

[0255] 3. The next step 10 of the third stage in Example 1 may be modified to turn off the vacuum suction, eject the substrate, and completely cure the entire multilayer circuit board at 250°C for 1 hour using an offline muffle furnace.

[0256] 4. Other process steps and their steps are the same as in Example 1.

[0257] (2) Organic light-curing photosensitive epoxy resin:

[0258] 1. Modify step 5 of step 3 in Example 1 below to pre-cure the media using a device integrated UV curing lamp.

[0259] 2. Modify step 10 of the third stage in Example 1 to fully cure the media using a device integrated UV curing lamp and fully cure the circuit using a device integrated IR lamp or heated ceramic suction cup.

[0260] 3. The next step 10 of the third stage in Example 1 may be modified to turn off the vacuum suction, eject the substrate, fully cure the medium using an offline UV curing lamp, and fully cure the circuit using an offline muffle furnace and infrared lamp.

[0261] 4. Other process steps and their steps are the same as in Example 1.

[0262] (3) Sintered ceramics Alumina ceramics:

[0263] 1. The next step 5 of the third step in Example 1 is modified to perform media pre-sintering at a temperature of 200° C. for 5 min using a device-integrated heating ceramic suction cup.

[0264] 2. The next step 10 of the third stage in Example 1 is modified to turn off the vacuum suction, discharge the sample, and perform low-temperature co-sintering of the entire ceramic sample (temperature 850° C., time 2 h) using an offline muffle furnace.

[0265] 3. Other process steps and their steps are the same as in Example 1.

[0266] Example 6:

[0267] The difference between this embodiment and embodiment 1 is that the metal circuit and the metal pillars are sintered by laser, and the insulating medium is completely cured in a protective atmosphere, and the specific improvements are as follows:

[0268] (1) Polyimides that require high temperature curing in a nitrogen environment:

[0269] 1. The next step 3 of the third step in the embodiment 1 is changed as follows: Print metal pillars at the position of vertical interconnection, and print cross mark points at the mark points. The metal pillars are manufactured by repeatedly filling the circuit layer by layer, with the hatch spacing of the filling lines in each layer being 5um, the hatch spacing of the layers being 3um, and the length, width and height of the last metal pillar after multi-layer stacking being 50um*50um*12um; the device-integrated optical fiber output semiconductor laser is used to select and sinter the metal circuit and pillars, the laser wavelength emitted by the laser is 915nm, the maximum power is 50W, and the minimum spot diameter is 200um, in the metal circuit area, the spot moves along the circuit path at a speed of 1mm / s, and in the pillar area, the spot first moves along the pillar outer frame line at a power of 5W and a speed of 1mm / s, and then moves back and forth along the pillar filling path at a power of 25W and a speed of 2mm / s, and the metal circuit and pillars after laser sintering are already conductive.

[0270] 2. The next step 10 of the third step in Example 1 is modified as follows: turn off the vacuum suction, eject the substrate, and fully cure the insulating medium of the multi-layer circuit board in an offline nitrogen sintering furnace, with oxygen content ≦20ppm, temperature 350℃ for 1h, and heating rate 5℃ / min.

[0271] 3. Other process steps and their steps are the same as in Example 1.

[0272] Example 7:

[0273] The difference between this embodiment and embodiment 1 is that the printing material is changed to nanoscale copper metal paste, and the specific improvements are as follows:

[0274] 1. Modify the next step 1 of the second step in Example 1 to select a nanoscale copper metal paste material with shear thinning properties, with a viscosity of 580000cps, a metal solid content of 80%, a thixotropic index of 9, a line aspect ratio of 0.5, and the ability to withstand peeling of 3M Scotch 600 adhesive tape; select a standard polyimide liquid material with a viscosity of 10000cps and an effective content of 18% as the application medium material; select a glass needle with an inner diameter of 5um, an outer diameter of 10um, and an end surface flatness of ≦1um; and select a metal scraper as the application head.

[0275] 2. The next step 3 of the third stage in Example 1 is changed as follows: Print metal pillars at the positions of vertical interconnects, and print cross marks at the marks. The metal pillars are manufactured by repeatedly filling the circuit layer by layer, with the hatch spacing of the filled lines in each layer being 5um, the hatch spacing of the layers being 3um, and the length, width and height of the final metal pillar after multi-layer stacking being 50um*50um*12um. The device-integrated heated ceramic suction cup is used to pre-cure the metal circuit and pillars at a temperature of 100°C for 8 minutes, and then cooled after pre-cure.

[0276] 3. The next step 7 of the third stage in Example 1 is changed so that the sample stage returns to the printing station, the printing needle tip fills the micro-holes with metal paste through precision pneumatic extrusion, the metal paste used is similarly nanoscale copper metal paste (diluted to a viscosity of 400,000cps), the penetration depth of the printing needle tip into the hole is 15um, the air pressure is 40psi, the pull-out speed is 0.05mm / s, and then the pull-out operation is performed, the initial speed of the pull-out is 0.01mm / s, the initial horizontal displacement of the pull-out is 20um, and the Z-direction displacement is 3um.

[0277] 4. The next step 10 of the third step in Example 1 is modified as follows: turn off the vacuum suction, eject the substrate, and fully cure the entire multi-layer circuit board in an offline nitrogen sintering furnace, with oxygen content ≦20ppm, temperature 300℃ for 1h, and heating rate 5℃ / min.

[0278] 3. Other process steps and their steps are the same as in Example 1.

[0279] Example 8:

[0280] This embodiment provides a high-precision multilayer circuit board obtained using the above-mentioned high-precision multilayer circuit board 3D printing manufacturing method.

[0281] Example 9:

[0282] This embodiment provides applications based on the high-precision multi-layer circuit board, and by using different material substrates, insulating media, and metal wiring printed with specific patterns, different types of high-precision multi-layer circuit boards can be manufactured, which can be applied to flexible circuits, wearable devices, small passive electronic devices, and SIP package interposer boards.

[0283] The above-described examples are merely illustrative of preferred embodiments of the present invention, and do not limit the scope of the present invention. Any modifications or improvements to the technical solutions of the present invention made by those skilled in the art without departing from the design spirit of the present invention are included in the protection scope of the present invention.

Claims

1. S1: extruding a nanoscale metal paste having shear thinning properties from an extrusion port to form a three-dimensional circuit layer on a substrate; S2, the nanoscale metal paste having shear thinning properties is extruded from the extrusion port to stack at the preset position of the current three-dimensional circuit layer to form a metal pillar; S3. forming an insulating layer on the top surface of the current three-dimensional circuit layer, drilling holes in the insulating layer, and filling the drilled holes with nanoscale metal paste to pre-draw corresponding metal pillars from the formed insulating layer; S4, determining whether the current insulating layer is the top insulating layer, and if so, forming a bonding pad layer on the top surface of the current insulating layer and performing step S5; if not, repeating steps S1 to S2 with the current insulating layer as a new substrate and performing step S6; S5, the metal pillar of the corresponding three-dimensional circuit layer located directly under the current insulating layer is connected to the bonding pad layer or is connected by the pre-drawing, thereby completing the manufacture of the multi-layer circuit board; S6, connecting the metal pillar of the corresponding three-dimensional circuit layer located directly below the current three-dimensional circuit layer to the current three-dimensional circuit layer or connecting it by pulling out in advance, and returning to step S3; A high-precision multilayer circuit board 3D printing manufacturing method characterized by:

2. In step S1, when a three-dimensional circuit layer is formed on the upper surface of the substrate, measuring the height of each point on the upper surface of the substrate to obtain a height data set of the upper surface of the substrate; and, based on the height data set of the upper surface of the substrate, relatively moving the extrusion nozzle along the Z-axis direction at the corresponding point on the upper surface of the substrate when the nanoscale metal paste having shear thinning properties is extruded from the extrusion nozzle based on the height data set of the upper surface of the substrate, thereby forming a three-dimensional circuit layer on the upper surface of the substrate with the nanoscale metal paste having shear thinning properties extruded from the extrusion nozzle. The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

3. In step S1, the extrusion nozzle performs a curved pre-extrusion movement in a vertical plane perpendicular to the substrate before forming a starting end of each circuit in a three-dimensional circuit layer by extruding a nanoscale metal paste having shear thinning properties from the extrusion nozzle, and the extrusion nozzle moves along a formal extrusion formation path of the circuit along a tangent direction of the curve; In step S1, a surplus material portion is preset at the end of the regular extrusion forming path of the circuit, and the operation of extruding the nanoscale metal paste having shear thinning properties is stopped when the extrusion port is located at the surplus material portion; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

4. In step S2, the nanoscale metal paste having shear thinning properties is extruded from the extrusion port to alternately form the outer frame line and the filling line in each layer of the metal pillar, and then stacked at the preset position of the current three-dimensional circuit layer to form the metal pillar; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

5. In step S3, forming the insulating layer includes: forming the insulating layer on the top surface of the current three-dimensional circuit layer by pressing the insulating medium material previously applied to the coating surface with a scraper coating head or extruding the insulating medium material onto the coating surface with a slit coating head; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

6. In step S3, before applying the insulating layer, a) controlling a Z-axis motor to lower the application head and bring both ends of the application head into contact with the touch sensor; b) respectively recording the different heights of the Z-axis motor when the left and right ends of the coating head trigger touch sensor signals, and further obtaining the height difference between the left and right sides of the coating head; c) calibrating the left and right heights of the left and right ends of the application head based on the left and right height difference; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 5.

7. In step S3, before applying the insulating layer, A, measuring the height of the contact surface of the touch sensor using a laser displacement sensor to obtain the height of the touch sensor; B. measuring the height of the coating start point on the coating surface using a laser displacement sensor to obtain the height of the coating start point; C. calculating a relative height difference between the touch sensor and the application start point based on the height of the touch sensor and the height of the application start point; D) contacting the center of the tilt-calibrated application head with the touch sensor and recording the Z-axis height of the application head at the time of contact; E. Calibrating the Z-axis height of the coating head based on the relative height difference between the touch sensor and the coating start point, the Z-axis height when the coating head contacts the touch sensor, and the preset coating gap; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 5.

8. In step S3, S3.1, forming an insulating layer on the top surface of the current three-dimensional circuit layer; S3.

2. According to the connection demand of each three-dimensional circuit layer and the height of the metal pillar in each three-dimensional circuit layer, the insulating layer is drilled, and the drilled hole is filled with nanoscale metal paste to pre-draw the corresponding metal pillar from the formed insulating layer; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

9. The shear thinning nanoscale metal paste comprises nanoscale silver or nanoscale copper metal particles and a dispersion medium, the content of the nanoscale metal particles is 75%-95%, the viscosity of the shear thinning nanoscale metal paste is between 100000cps-1,000,000cps, the thixotropy index is 4-10, and the aspect ratio of the line formed by the shear thinning nanoscale metal paste is ≧0.5; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

10. The dispersion medium includes a dispersion solvent and an adhesive, and the dispersion solvent includes one or more of an organic solvent and water; The adhesive includes any one or more of polyacrylic acid, diethanolamine, and a complex of polyacrylic acid and diethanolamine; Alternatively, the adhesive includes an epoxy resin, a hardener, and a protective agent. The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 9.

11. The organic solvent includes any one or more of ethylene glycol, glycerin, diethylene glycol monoethyl ether acetate, dibasic acid ester, isophorone, terpineol, and diethylene glycol monobutyl ether; the protective agent is formed of any one or a combination of a triarylphosphine compound and a trialkylphosphine compound; the epoxy resin includes any one or more of bisphenol A epoxy resin, E-44 epoxy resin, and biphenyl oxygen epoxy resin; and the curing agent is any one of a polythiol curing agent, a dicyandiamide curing agent, and an anhydride curing agent. The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 10.

12. Between step S2 and step S3, performing a first pre-curing process on a current three-dimensional circuit layer and a metal pillar formed by stacking at a preset position of the current three-dimensional circuit layer; Step S3 further includes performing a second pre-curing process on the insulating layer after forming an insulating layer on the upper surface of the current three-dimensional circuit layer; In step S3, after drilling holes in the insulating layer and filling the drilled holes with the nanoscale metal paste, the nanoscale metal paste is subjected to a third pre-curing treatment; In step S5, the metal pillar of the corresponding three-dimensional circuit layer located directly under the current insulating layer is connected to the bonding pad layer or is connected by the pre-drawing, and then the multi-layer circuit board is subjected to a total sintering hardening process to complete the manufacture of the multi-layer circuit board; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 1.

13. The material of the insulating layer is an organic or ceramic medium; The high-precision multi-layer circuit board 3D printing manufacturing method according to claim 12.

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