Method and apparatus for additive manufacturing of electronic circuits

Abstract

The invention relates to a method of additive manufacturing of an electronic circuit. The method comprises the steps of providing a printing device comprising a build plate, a first print head configured for printing of a molten conductive metal, and a second print head configured for printing of a non-conductive material. The method further comprises printing of an electronic circuit by printing of a conductive element from a molten conductive metal using the first print head and printing of a non-conductive structure using the second print head of the printing device. In another aspect, the invention relates to a printing device for additive manufacturing of an electronic circuit. The printing device comprises a build plate, a first print head configured for printing of a conductive element from a molten conductive metal, and a second print head configured for printing of a non-conductive structure from a dielectric material.

Description

Technical Field

[0001] This invention enables the direct fabrication of electronic circuits, such as printed circuit boards (PCBs), through additive manufacturing.

[0002] The present invention preferably relates to a method for additive manufacturing of electronic circuits. The method preferably includes the step of providing a printing apparatus comprising: a build plate; a first printhead configured to print molten conductive metal; and a second printhead configured to print a non-conductive material; and preferably means for independently moving the first and second printheads relative to the build plate in the xy plane and / or for moving the build plate relative to the first and / or second printheads in the xy plane. The method further includes printing electronic circuits by using the first printhead to print conductive elements from the molten conductive metal and using the second printhead of the printing apparatus to print non-conductive structures. Alternatively, the present invention preferably relates to a printing apparatus for additively manufacturing electronic circuits by the method of the present invention. This printing apparatus preferably includes: a build plate and an optional heater configured to melt conductive metal provided in block form. The printing apparatus further includes: a first printhead configured to print conductive elements from the molten conductive metal, and a second printhead configured to print non-conductive structures from a dielectric material. Optionally, the printing apparatus includes means for moving the first print head and the second print head relative to the build plate in the xy plane and / or for moving the build plate relative to the first print head and the second print head in the xy plane. Background Technology

[0003] Additive manufacturing (AM) – also known as 3D printing – is reshaping traditional centralized subtractive mass production technologies as an attractive alternative. More capabilities, such as Multi-Material Additive Manufacturing (MMAM), are critical to mainstream manufacturing. Additive manufacturing is revolutionizing how we create and manufacture items across a wide range of industries. This transformative technology opens new avenues for design, production, and innovation by building intricate and complex structures layer by layer. Additive manufacturing offers numerous advantages, such as customization and personalization at lower costs, and rapid delivery [P1]; decentralized and on-demand manufacturing [P2]; material savings and minimizing waste [P3], and more. Particularly during the Covid pandemic, the localized on-demand production of personal protective equipment (PPE) and critical medical components demonstrated the advantages of additive manufacturing in the context of logistical and supply chain disruptions and high demand for rapid delivery [P4]. However, the widespread application of additive manufacturing remains limited to single-type materials, such as polymers or metals, and most of these additively manufactured products are used for purely mechanical functions, such as bicycle frames [P5], car jet engines, custom car bodies [P6], and personalized eyeglass frames [P7]. Despite numerous efforts, particularly in the development of multi-material 3D printing over the last decade, the industry remains heavily focused on researching new materials and investigating purely mechanical properties, with a lack of attention to the development of new technologies [P8]. Conversely, adding more functionalities is crucial to driving the development of additive manufacturing technology for wider application in mainstream manufacturing [P9]. Consequently, the application of additive manufacturing technology in multi-material devices, such as electronic circuits, is limited.

[0004] After decades of development, the production of printed circuit boards via complex subtractive manufacturing processes has become mature and large-scale, as summarized in the cited review articles [1, 2]. Generally, this traditional process involves a series of steps performed on a planar substrate (e.g., so-called FR4 board): brushing, curing of etched resistors, etching, resistor stripping, black oxidation, drilling, cleaning, via plating, curing of plated resistors, circuit plating, solder plating, stripping of plated resistors and copper etching, solder stripping, solder mask printing, and hot air leveling. Due to the complexity of this process, it is primarily carried out in large factories equipped with highly automated specialized equipment. Consequently, this traditional approach results in long design-to-product cycles, high costs, and low design flexibility. Large quantities of (toxic) chemicals are involved throughout the process, and contaminated wastewater is generated. Therefore, additive manufacturing offers several general advantages over this established method, particularly in terms of reduced turnaround time, capital costs, design freedom, and material consumption.

[0005] Numerous attempts have been made to use additive manufacturing to print two-dimensional (2D) and even three-dimensional (3D) electronic circuits. These have been summarized in references [3, 4]. Most methods combine multiple manufacturing techniques to integrate electronic circuits into 3D objects. Conductive inks or pastes are typically used to print conductive structures. However, this leads to drawbacks such as very limited layer thickness (hundreds of nanometers to two micrometers), the release of toxic solvents during the drying process, and the need for sintering / curing steps after printing. Conductive inks result in high resistance, compatibility issues with polymer substrates, and are often impossible to manufacture on a single machine due to process complexity, as well as high costs due to the expense of nanoparticle inks. It is also known that conductive inks suffer from poor long-term stability, the "coffee ring" effect during printing, and first-drop problems (inconsistent droplet size and quality). Furthermore, while the substrates are mostly 3D in shape, the circuits can only be placed on the outer surface of a 2D substrate or 3D object.

[0006] In addition to manufacturing 3D objects with conductive features through 3D printing, the direct integration of electronic components to form fully functional electronic devices has also attracted much attention. Reference [5] summarizes typical methods for the conductive features and electrode interconnection of integrated circuits (ICs) such as microchips and SMDs. The most common method is to use low-melting-point solder or solder paste to electrically connect electronic components to conductive tracks, but this requires additional reflow processes, which limits the choice of substrate and 3D integration [6]. Another option is to use a combination of conductive inks / adhesives with non-conductive adhesives, which leads to increased process complexity and reduced mechanical stability [5].

[0007] Once the PCB is manufactured, electronic components need to be placed and interconnected with each other (e.g., transistors, resistors, and capacitors). Screen printing is a mature and traditional solder printing process that has been widely used to solder devices onto electronic circuits. However, screen printing has limitations depending on the size of the electrical and electronic components used. Furthermore, because screen printing is based on a mask principle, it can only be applied to flat surfaces such as PCBs and cannot be combined with 3D soldering printing. The known concepts for soldering electronic components onto PCBs have been summarized in the cited references [7, 8, 9].

[0008] Min-Saeng Kim et al. [7] proposed a method for directly connecting all electrical connections through rapid prototyping. Solder was used to form interconnects and polycaprolactone (PCL) was used to form polymer insulators. However, this method is limited to 2D interconnects on the back of general PCBs and is not suitable for microchips with SMD / SMT layouts. In another study, Wang L et al. [8] solved the problem of arranging electronic and electrical components on PCBs by first indirectly soldering components to form an intermetallic compound layer and then placing conductive ink for interconnects on the intermetallic compound layer. While this method improves the reliability of the connection, it introduces indirect soldering, which is prone to various errors and reduces the automation of printed electronics production. In addition, this method is highly dependent on special low-melting-point solder and silicone. Each silicone layer needs to be cured for 24 hours before depositing the metal layer. Goh, Guo Liang et al. [9] used carbon conductive coatings to connect electronic components because carbon conductive coatings have good adhesion to the underlying substrate and form continuous conductive tracks. However, carbon conductive coatings have high resistivity and are therefore not suitable for large three-dimensional functional electronic devices.

[0009] Research combining additive manufacturing of conductive and non-conductive materials currently focuses primarily on using metal-polymer hybrid filaments to enhance the properties of polymer materials, as the bonding strength between polymers and metals achieved through fused wire deposition (FFF) is insufficient. Therefore, greater efforts are being made to combine various printing technologies to achieve co-printing of metals and polymers. DeNava et al. reported the fabrication of a 3D flux sensor by combining stereolithography (SL) 3D printing of dielectric materials, off-axis direct writing of 3D conductive paths, and off-axis placement of electronic components [P15], with improvements made in subsequent designs [P16]. However, this multi-material additive manufacturing is performed step-by-step, so conductive features are deposited only on flat surfaces of the product or at most on curved edges. Espalin et al. reported another multi-material additive manufacturing process in which copper wires are embedded in a polymer produced by two FFF operations and one CNC machining to reduce resistance. Again, these processes are performed sequentially. While embedding copper wires results in significantly improved electrical conductivity, the geometric design freedom is greatly limited, and interconnects and contact components require additional soldering or brazing. Similarly, there are also reports of examples that combine multiple technologies, such as polymer injection molding and direct writing of conductive inks [P17], dielectric inkjet printing (polyJet) and conductive ink distribution [P18], in which the printed circuits are either located on the PCB surface or embedded through additional assembly steps.

[0010] To achieve maximum design freedom in multi-material additive manufacturing with electrical functions—where the desired form and shape of the electrical functions for the PCB are customizable—a hybrid printing platform combining additive manufacturing of dielectric and conductive materials is needed. The Lewis team at Harvard University [P19] is a pioneer in this field and has founded a startup dedicated to commercializing a low-cost hybrid 3D printer that combines direct ink writing for conductive interconnects with 3D printing polymers via FFF. Using this hybrid printing system, complex, free-form designs with embedded electronics, such as quadcopter drones, can be 3D printed. The technology employs room-temperature curing silver ink (containing silver in dispersed particles rather than in bulk form), thus avoiding the high-temperature curing problems of typical nanoparticle or flake metallic inks [P10] used in hybrid printing, and producing conductive lines with a wire resolution of 50 × 10 at 250 µm. -8 The conductivity in Ωm [P9]. However, as of the time of writing, this product has been discontinued, most likely due to the high cost of silver ink [P20]. Nano-dimension's DragonFly 2020 Pro 3D printer can directly manufacture multilayer PCBs by 3D inkjet printing dielectric and conductive materials [P21, P22]. It provides high conductivity (5.73 × 10⁻⁶ Ωm). -8 It can print conductors with a diameter of Ωm (approximately 30% of copper) and vertical vias with small heights. Due to the long build-up time of inkjet printing, this technology is currently limited to thin additive manufacturing of 2.5D (two-and-a-half-dimensional) PCBs. Other research on hybrid printed electronics includes combining polymer fused wire deposition (FFF) with intense pulsed light sintering (IPL) of silver nanoparticles [P23]. The nanoparticles are printed via syringe and then sintered using a xenon lamp light source. While this technology demonstrates excellent hybrid printing capabilities for functional electronics, the sintering process may limit the range of polymer materials that can be used in conjunction with this technology.

[0011] In state-of-the-art multimaterial additive manufacturing of conductive materials, nanoparticle-based metallic inks or silver pastes are commonly used. Printed features require drying steps to evaporate the solvent and several sintering steps to functionalize the printed ink [P24]. The solvents used can cause ink to seep between printed polymer layers, resulting in short circuits [P13]. Furthermore, ink diffusion is difficult to control, which is critical when printing conductive features with small line spacing (e.g., interdigitated circuits) [P25]. Another problem is the resolution difference between the polymer and ink-printed features, which can lead to print failures or require additional repairs or specific design constraints [P13]. The use of specific design guidelines limits the inherent design freedom of additive manufacturing technologies. While these inks are widely used for printing polymer-reinforced materials (PE), they are limited to two-dimensional applications and are not suitable for printing three-dimensional freeform electronic components. Moreover, inks are not only a limiting factor in the production of high-power electronics but also a bottleneck to current trends in green electronics development, as inks require chemically treated substrates to achieve good adhesion, meaning increasing amounts of chemical waste are released into the environment [P26].

[0012] US2020 / 0315024 discloses a method for designing and manufacturing electronic devices using a 3D printer and a pick-and-place machine. First, a non-conductive material layer is extruded to form the shape of a product with cavities in which electronic components are embedded. Flux is applied to the contacts of the electronic components to clean the surfaces and form better solderable contacts. Molten conductive material is extruded to form conductive traces, and the various components are electrically connected by stacked 3D signal traces. Another non-conductive layer can then be extruded to support the embedded components or electronic devices. The apparatus includes conductive and non-conductive material extruders disposed within the same moving head. The extrusion process is a contact printing process. Therefore, at any given time, only the nozzle in use is at the lowest point of the moving head, while other nozzles are raised.

[0013] US2016 / 0316556A1 discloses a 3D printing method for producing electronic components, such as rigid printed circuit boards. Pure ultra-high molecular weight polyethylene (UHMWPE) filaments on a spool are fed into a first extruder head of a dual-extrusion head, while suitable Indalloy solder wire, including conductive material, on the spool is fed into a second extruder head for assembly. In the fused deposition modeling (FDM) method used, molten material is ejected through a nozzle and deposited in a controlled manner onto a moving platform to form the desired shape.

[0014] US2007 / 0030326A1 describes a voxel-based method for manufacturing electroactive and / or mechanoactive objects. Multiple printheads are arranged along a production line, and one or more substrates move past these printheads. Each printhead nozzle ejects a droplet, which, after freezing, drying, or curing, forms a volumetric element (voxel) with a height of approximately 10 micrometers. Materials considered printable include hot melt adhesives, various polymers, metals, or metal alloys. Each layer is printed by one or more printheads, which are grouped into "layer groups." The printheads operate simultaneously, with the substrate movement speed adjusted accordingly, and different printheads used to print different materials. For example, if a product requires 1000 layers, it is preferable to use 1000 different subsystems, each corresponding to one layer, with 1000 subsystems operating simultaneously to produce 1000 sets of 1000 different layers. However, the personalized production of electronic circuits or the integration of electronic components is more challenging.

[0015] Given the existing technology, there is a need to develop alternative methods for manufacturing printed circuits, particularly those with improved conductivity, resolution, and design freedom, especially allowing for three-dimensional fabrication. Furthermore, there is a need to develop environmentally friendly and safe manufacturing methods. There is a need to increase the design freedom of distributing circuits in three-dimensional polymer models that can be easily printed on minimal equipment or production workstations, thereby promoting decentralized production. There is also a need to provide a method for green manufacturing of circuit boards, preferably involving layer-by-layer printing of polymers and conductive features without using any subtractive methods and without generating any residual waste. In addition, there is a need to further develop high-power multi-material additive manufacturing (MMAM) and printed electronics (PE) in the form of robust and reliable electrically conductive features. Summary of the Invention

[0016] Purpose of the invention The object of this invention is to provide printing equipment and methods for additive manufacturing electronic circuits, overcoming the shortcomings of existing technologies. In particular, the object of this invention is to provide improved circuit printing methods and equipment, which provide improved conductivity, resolution, and design freedom, especially enabling the fabrication of multilayer printed circuit boards with three-dimensional electronic circuits. Another object of this invention is to improve manufacturing safety and reduce waste, particularly toxic waste. Yet another object of this invention is to shorten the turnaround time for circuit boards from design to manufacturing, and to efficiently produce prototypes and small-batch products.

[0017] In a first aspect, the present invention relates to a method for additive manufacturing electronic circuits. The method includes the steps of: providing a printing apparatus comprising a build plate, a first printhead, and a second printhead, the first printhead being configured to print molten conductive metal and the second printhead being configured to print non-conductive material; and printing an electronic circuit by using the first printhead of the printing apparatus to print conductive elements through molten conductive metal and by using the second printhead to print non-conductive structures.

[0018] The function of the first printhead can be performed by one or more printheads, or by at least one printhead including one or more nozzles. Similarly, the function of the second printhead can be performed by one or more printheads, or by at least one printhead including one or more nozzles. Additional printheads with other functions may also exist on the same printing device or other printing devices.

[0019] The molten conductive metal can be solid or liquid at room temperature. The molten conductive metal can be provided to the printer and / or the first printhead in solid or liquid form. In some embodiments, the molten conductive metal is provided in solid form and melted in situ within the printing apparatus (or "printer"), for example, deposited in liquid form. In other embodiments, the molten conductive metal is deposited as metal powder and melted during or after deposition, preferably by selective laser melting (SLM) technology. In other embodiments, a metal that is liquid at room temperature (e.g., indium gallium alloys, particularly gallium indium tin alloys) can be used, which do not require additional heating for melting. Instead, this metal is liquid at room temperature.

[0020] The technology described herein is preferably referred to as "hybrid 3D printing" because it allows the combination of conductive materials (e.g., conductive metals used as electrical traces) and non-conductive support materials (e.g., polymer bases used as substrates) in a preferred fully automated process. This invention preferably constitutes a rapid prototyping and / or manufacturing method for PCB production, addressing issues such as long design-to-product lifecycles, high design and development costs, and time-consuming and labor-intensive small-batch prototyping / production. Furthermore, compared to traditional subtractive and centralized PCB manufacturing technologies based on photolithography, this hybrid 3D printing apparatus and method preferably offer greater data and design protection, decentralized "in-house" manufacturing, and reduced toxic waste and wastewater through additive manufacturing processes.

[0021] This invention specifically addresses the problem of poor conductivity in components printed using printable inks via molten metal printing conductive elements, as described in existing technologies. Compared to printable inks, this metal exhibits higher conductivity and lower resistance, which can be further improved by using larger cross-sectional dimensions of the conductive elements achievable through printing molten metal. Therefore, the performance of printed PCBs is enhanced compared to existing technologies.

[0022] In contrast, prior art printable conductive inks typically only allow for printing small layer thicknesses due to their low viscosity (particularly due to low metal concentration in the solution) and high cost. For example, the height of ink-based conductive elements can range from 100 nm to a few micrometers, with a linewidth of approximately 100 µm. While this may result in lower conductivity of ink-based conductive elements, it can also introduce mechanical problems, such as durability issues. Thin-layer electrical traces may also be unsuitable for all non-conductive printing processes, such as FDM, due to significant resolution differences. To improve the conductivity of conductive traces with small thicknesses, multiple layers may need to be deposited, leading to increased overall production time and / or the need for additional equipment, such as curing equipment. Therefore, conductive elements formed from printable inks are positioned on the surface of the material, and, for example, cannot be effectively partially embedded in non-conductive materials due to the difficulty in precisely stacking ink layers. The present invention overcomes this challenge by allowing the printing of conductive elements using bulk materials (molten metal) with similar rheological properties, thereby achieving thicknesses similar to or the same as dielectric materials. Thus, conductive elements can be at least partially embedded in dielectric material layers of similar thickness. Thus, conductive elements can be configured with a high aspect ratio (e.g., linewidth and height of approximately 100 µm, but length up to the millimeter level) to achieve high conductivity while maintaining mechanical stability.

[0023] This invention further improves the manufacturing speed of prototypes and small-batch products because it can simultaneously print both conductive and non-conductive material types on a printed circuit board using the same printer. The printer includes both a first printhead and a second printhead. Specifically, this means that both types of components can be built onto the same build board (particularly the print bed) without needing to be moved to different build boards between printing steps. Therefore, one-time manufacturing of both conductive and non-conductive parts of the PCB can be achieved. This is particularly economical because it avoids the capital costs of equipping multiple workstations with different manufacturing equipment according to existing technologies. Instead, only one printing device is needed, which does not have to be dedicated to manufacturing a specific prototype or series of products. Instead, this printing device can be used to produce PCBs of different designs without requiring significant hardware changes. Furthermore, this one-time printing device improves the manufacturing accuracy and quality of the PCB. In particular, since there is no need to move the printed components from the build board between printing steps, the introduction of errors is reduced. Subsequent components or layers printed on intermediate products do not require precise calibration based on existing intermediate products with known positions. Therefore, alignment problems are avoided.

[0024] Another advantage of using a single printing press to print both conductive and non-conductive materials is that there is no need to share confidential PCB design-related information with multiple facilities. Instead, sensitive data can be stored locally.

[0025] This invention also solves the compatibility problem between conductive elements and non-conductive materials, resulting in extremely high stability of the manufactured circuit board. A good fit is achieved between the non-conductive material and the conductive element. The fit is further enhanced when both conductive and non-conductive materials are printed using the same printing equipment, because one or more materials may still be flexible while the other is being deposited. This allows the flexible material to fill gaps and / or deform to accommodate the newly deposited material, thereby eliminating unwanted gaps. Therefore, the final PCB circuit board has extremely high strength.

[0026] Furthermore, since it lacks the volatile components commonly found in printable conductive inks, this invention provides a safer and more environmentally friendly method for manufacturing printed circuit boards. It avoids the toxic chemicals, flammable materials, or dust involved in traditional etching, stripping, and hot air leveling processes, thus allowing it to be implemented in virtually any environment. Additionally, it reduces or eliminates the need for large amounts of water to remove materials or toxic waste.

[0027] This invention also provides a high degree of design freedom because both the first and second printheads are preferably movable in the xy-plane. The movement of the printheads can be independent of each other. This allows for rapid fabrication of complex designs. Surprisingly, the first and second printheads can be configured to have substantially the same layer thickness. This is typically impossible when conductive inks are used in conjunction with printed non-conductive materials, as conductive inks are usually very thin. Therefore, the method of this invention can rapidly provide very stable layered structures. These layered structures can be configured as substantially two-dimensional, two-and-a-half-dimensional, or three-dimensional, as needed.

[0028] This method also eliminates the need for post-printing processing, as hybrid printed products achieve excellent surface finish and quality, as will be detailed in subsequent equipment and specific examples. Furthermore, this method preferably requires no advanced processing techniques or high costs.

[0029] As will be further explained below with reference to the accompanying drawings and examples, the preferred embodiment of the method of the present invention uses an internally developed technology called "Synkr". The "tima" printer uses on-demand inkjet printing to print molten metal in a single pass, creating 3D dielectric sections with fully embedded and structured conductive features. The printed conductive traces, with a linewidth of 230 µm, exhibit a resistance of only 5.7 mΩmm, which is 1 / 12th the resistance of wires printed with conductive inks in the prior art. - ¹. Printed traces with a dot pitch of 100 µm exhibit excellent shape fidelity with a standard deviation of only 7 µm. Quantitative evaluation of the adhesion between the metal traces and the dielectric material shows an average shear force of 7.2 N, only half that of reflow soldered electronic devices. (Synkr) Tima prints a demonstrator with embedded functional circuitry, directly interconnected components, and 3D out-of-plane metal structures (see further elaboration in the detailed description, where experiments conducted with reference to preferred embodiments of the printing apparatus and printing method outline other technical advantages of the invention).

[0030] In principle, this invention can use any additive manufacturing technology (e.g., FFF, FDM, Polyjet, etc.) for 3D material deposition to print insulating / dielectric layers as non-conductive structures constituting the PCB body. Electrical features (conductive elements) are preferably printed using one or more print heads integrated on the same 3D printing apparatus via bulk conductive metal, thus achieving a "hybrid printing" method. The size and density of the electrical traces depend primarily on the printing resolution and performance of the metal printing technology used to print the conductive metal traces.

[0031] When printing PCBs with flat-top conductive metal traces (or "traces"), in some embodiments, regardless of the width and aspect ratio of the conductive metal traces, the conductive metal traces are preferably etched onto the first layer of the printed circuit board. This does not necessarily mean using a (subtractive) etching process, but rather that the conductive metal traces are printed in a manner that appears to be etched. Specifically, the surface of the "etched" conductive metal traces is preferably substantially flush with the surface of a non-conductive structure, the shape of which is formed to accommodate the conductive metal traces. Therefore, this invention is applicable to any type of printable PCB, its applicability depending on the size, shape, and density of the electronic components on the PCB.

[0032] Furthermore, this invention preferably provides a method for further processing a printed PCB into 3D electronic circuits by printing layer by layer on a pre-printed PCB. This cannot be achieved using techniques that require reflow soldering after printing. By placing electronic components such as integrated circuits (ICs), microchips, and surface mount devices (SMDs) directly onto / within the 3D printed structure during the 3D printing process, and using the same molten metal printing method as the printing path to electrically connect them to the metal traces forming the circuit, it is possible to preferably print fully functional electronic devices with integrated 3D electronic circuits in a fully automated manner. Existing technologies have failed to achieve this.

[0033] For the purposes of this invention, the "additive manufacturing" method is preferably a method of manufacturing an object by adding material incrementally or stepwise. The incremental addition of material preferably includes the deposition of material droplets. The additive manufacturing process preferably uses computer-aided design or computer-aided manufacturing to control the addition of material. The material is preferably deposited incrementally, the increments preferably corresponding to droplets on layers on a first plane and on different orthogonal planes. Droplets of the same material or other increments applied to the same plane (preferably the xy plane) are preferably configured to fuse. Layers of the same or different materials can be configured not to fuse, thereby forming a vertical structure of a predetermined height in the third dimension, although interlayer adhesion may be desirable. Subtractive manufacturing steps are not excluded from the additive manufacturing methods disclosed herein.

[0034] For the purposes of this invention, a "circuit" is preferably a path through which current can flow, in whole or in part. This path preferably comprises a conductive material. The circuit preferably comprises a closed conductive path. Alternatively, the path may be open and can be configured to be integrated into other circuits. The circuit may optionally include electronic components such as power supplies, resistors, capacitors, light-emitting diodes (LEDs), microchips, sensors, etc., to form a complete electronic circuit.

[0035] For the purposes of this invention, the "build board" is preferably a rigid structure on which one or more materials can be printed. The surface of the "build board" preferably determines the shape of the lower surface of the circuit and preferably extends in the xy plane. Preferably, the build board is a printer platform. Alternatively, the build board can be a component other than a printer, such as a table. The build board can also be other components having rigid surfaces in the xy plane, on which materials can be printed directly or indirectly, such as by adhering to or removing from the build board. For example, the build board can be part of a rigid housing on which a PCB is printed. Printing of material on the build board can be achieved by one or more layers of material (e.g., a base sheet or a previously printed layer).

[0036] For the purposes of this invention, the "first printhead" is preferably a printhead configured to selectively deposit molten conductive metal. This first printhead preferably includes nozzles / more nozzles for this purpose and is preferably configured to withstand the melting temperature of at least the molten metal. The first printhead may optionally include a heater, particularly in cases where the metal is molten in situ, for example, when the metal is present in a solid form. Depending on the application, the first printhead is preferably used for different operating modes, such as on-demand inkjet printing or jet printing. To generate droplets, the molten material can be accelerated, for example, by (short) pressure pulses. To generate longer jets, the same technique is used, but the pressure is held for a longer time to produce a stable flow of molten material, thus forming a (continuous) jet (rather than substantially spherical droplets), the length of which can be controlled by the pressure holding time.

[0037] For the purposes of this invention, "metal" is preferably any substance that can conduct electricity at a temperature of absolute zero. The metal may belong to any of the following groups: alkali metals, alkaline earth metals, transition metals, post-transition lanthanides, and actinides. Transition metals are particularly preferred. The metal may be provided in elemental or alloy form.

[0038] For the purposes of this invention, the term "molten conductive metal" preferably refers to a conductive printing material in a liquid state, primarily composed of a liquid metal. If the liquid material includes other phases or dispersed phases, the metal is preferably a continuous phase in the liquid form. The metal can be present in a solid state at room temperature and melted in-situ to provide molten conductive metal. Similarly, metals that are liquid at room temperature can also be used.

[0039] The molten conductive metal may include non-metallic additives. However, it is preferable that the molten conductive metal is substantially free of non-metallic additives.

[0040] In a preferred embodiment of the invention, the conductive metal molten during printing comprises more than 80% by weight, preferably more than 90% by weight, more than 95% by weight, or more than 99% by weight. In a preferred embodiment, the conductive metal molten during printing comprises less than 20% by weight of non-metallic additives, preferably less than 10% by weight, less than 5% by weight, or less than 1% by weight.

[0041] Therefore, preferably, the molten conductive metal is substantially different from the conductive ink or silver paste, which includes silver in solid (e.g., spherical) form dispersed in non-metallic additives (e.g., resins, dispersants, solvents) for printing the conductive paste.

[0042] Advantageously, by printing molten conductive metal, pure metals or alloys optimized for desired functions can be printed without the need for large amounts of non-metallic additives, such as dispersants or solvents, as is done with printing inks or pastes. This results in lower resistance and improved electrical performance of the printed circuit. Furthermore, printed inks or pastes do not immediately possess conductive properties; they require typical sintering / post-processing to remove non-conductive materials and form a conductive metal structure through physical (fusion) or chemical reactions.

[0043] Furthermore, non-metallic additives (such as fluxes, or organic materials) preferably do not require cleaning or improvement of the spreadability of the conductive material printing layer. Instead, molten conductive metal can be deposited directly onto the surface (to be printed). Avoiding the use of non-metallic additives such as fluxes is particularly advantageous when integrating electronic components, as these additives can interfere with the stable performance of electronic components, create corrosion risks, or potentially affect electrical insulation. From an environmental perspective, pure metals may also be more preferred because they are easier to recycle, generally require simpler processing, do not involve harmful chemicals, and typically have a longer lifespan, thus reducing waste.

[0044] For the purposes of this invention, the "second printhead" is preferably a printhead configured to selectively deposit non-conductive materials (especially dielectric materials, preferably dielectric polymer materials). The dielectric polymer material is preferably deposited by the second printhead in the form of a molten liquid / gel. Such printheads preferably include nozzles for this purpose and are preferably configured to withstand at least the melting temperature of the dielectric material, but not necessarily the melting temperature of metals supplied in bulk form. The second printhead can also preferably be used in different operating modes. For some applications, on-demand inkjet printing or jetting non-contact deposition is preferred. To generate droplets, the molten material can be accelerated, for example, by a (short) pressure pulse. To generate a (longer) jet, the same technique can be used, but pressure needs to be maintained for a longer period to produce a stable flow of molten material, resulting in a (continuous) jet (rather than approximately spherical droplets), the length of which can be adjusted by controlling the pressure holding time. However, in some applications, a second printhead using a contact printing mode is also preferred, for example, by moving the nozzle close to a surface.

[0045] In a preferred embodiment, the printing apparatus includes a control unit configured to control a first printhead to print molten conductive metal and a second printhead to print non-conductive material. Preferably, the control unit is configured to control the first and second printheads respectively, for example, according to the desired portion of the electronic circuit to be printed and / or the deposition technique.

[0046] For the purposes of this invention, the "control unit" preferably refers to any computing device or system having a processor, processor chip, microprocessor, or microcontroller for the automatic control of printing apparatus components, particularly for controlling a first and second printhead for printing conductive and non-conductive materials. The components of the computer system can be conventional or custom-constructed for a particular implementation. Preferably, the computer system has a processor, input devices (e.g., a keyboard or mouse), memory (e.g., hard disk drives and volatile or non-volatile memory), and computer code (software) for controlling the first and second printheads.

[0047] The control unit may also include a programmable printed circuit board, a microcontroller, or other device for receiving and processing data signals from system components, such as the position of the printhead or nozzle relative to a surface, or other information related to the printing process. The control unit preferably also includes computer-usable or computer-readable media, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software used to execute the control components of the printing apparatus (particularly the first and second printheads) can be written in any programming language or model-based development environment, such as, but not limited to, C / C++, C#, Objective-C, Java, Basic / Visual Basic, MATLAB, Simulink, StateFlow, LabVIEW, or assembly language.

[0048] The computer software described herein and any functional descriptions thereof (including descriptions of control over aspects of a particular device or system) are considered technical features because they directly produce physical outputs to the manufacturing system. Therefore, the functional descriptions of the software can be considered as preferred and defining embodiments of the invention. The specific computer code employed is available to those skilled in the art and can be constructed using standard knowledge.

[0049] Those skilled in the art will understand that preferred method steps associated with the method of additive manufacturing of electronic circuits using printing equipment are preferably executed by a control unit, which is preferably configured to execute the method or operation steps.

[0050] The term "control unit is configured to" perform certain operational steps, such as printing molten metal using a first printhead, printing non-conductive material using a second printhead, or preferably, performing non-contact deposition of conductive material using the first printhead, and performing non-contact or contact deposition of non-conductive material using the second printhead. This may include custom-designed or standard software mounted on the control unit that initiates and regulates these operational steps.

[0051] According to the present invention, the control unit is configured to print or deposit molten conductive metal or non-conductive material using a first printhead and a second printhead, respectively. As described above, for this purpose, the control unit may include computer software that, in conjunction with the physical devices required to achieve this function, performs the necessary steps. Depending on the design of the molding system, these steps may include offsetting the printhead or nozzle in the xy plane or adjusting the height of the printhead or nozzle (i.e., movement in the z-direction).

[0052] To improve the accuracy and functionality of the printing system, the printing apparatus preferably includes one or more actuators (preferably electric motors) for moving the printhead and / or base sheet along the X, Y, and / or Z axes to achieve precise positioning. The printhead may also preferably use pneumatic actuators to generate and deposit (micro)droplets or jets of molten metal or non-conductive material, wherein pneumatic valves regulate the required airflow and pressure (preferably using a compressed air system, such as a compressor or pump) to regulate the air pressure required for pneumatic actuation. In another preferred embodiment, a detector (e.g., a top-view camera) may be used in conjunction with the actuator (e.g., an electric motor) to position the printhead, thereby achieving precise movement. Those skilled in the art will understand that the aforementioned components (e.g., actuators or valves) are also preferably controlled by a control unit.

[0053] For the purposes of this invention, the xy plane is preferably substantially parallel to the surface of the material to be printed on the building board.

[0054] In accordance with the present invention, the printing step preferably includes the directional and selective deposition of material onto a surface, particularly onto a build plate. Specifically, the deposition of the material is preferably directional in location on the xy plane. The deposition of the material is preferably selective in the amount of material deposited, and the deposition preferably occurs in the form of droplets, so that no material is deposited at certain locations. Preferably, depending on the structure to be printed, a first printhead or a second printhead can be used to selectively print dielectric material or molten conductive metal into selected locations in the form of droplets. Preferably, the control unit is configured to perform non-contact or contact deposition using the first printhead or the second printhead to selectively print dielectric material or molten conductive metal into selected locations in the form of droplets or jets.

[0055] For the purposes of this invention, the "conductive material" is preferably a material having high electrical conductivity and therefore low electrical resistance. Preferably, the material has a volume resistivity (ρ) less than 1 × 10⁻⁶ when measured at 20°C. -4 More preferably, when the volume resistivity (ρ) of the material measured at 20°C is less than 1 × 10 Ω·m. -6 At Ω·m, or even more preferably when the volume resistivity (ρ) of the material measured at 20°C is less than 1×10⁻⁶. -7 At Ω·m, the material is considered conductive, including most metallic substances.

[0056] For the purposes of this invention, the "conductive element" is preferably a printed feature configured for electrical conduction in a circuit and comprising a conductive material. The conductive element can have any size or shape, and preferably, it has a conductivity of no more than 1 × 10⁻⁶ measured at 20°C. -4 The resistivity in Ω·m, which is preferably determined based on the cross-section of the printed droplet.

[0057] For the purposes of this invention, the "dielectric material" is preferably a material with low conductivity, such that virtually no current can flow through it. Simultaneously, the dielectric material is preferably capable of supporting an electrostatic field; that is, the material is preferably polarized by applying an electric field. Preferably, the force (dielectric constant) between two charges in the dielectric is less than its force in a vacuum, while the energy stored in the electric field per unit volume of the dielectric is greater.

[0058] The ability of a dielectric material to store an electrostatic field is preferably expressed by its relative permittivity (εr), which is a measurement of the dielectric constant of the dielectric material relative to vacuum. For the purposes of this invention, the dielectric material preferably has a relative permittivity greater than 1. The relative permittivity is preferably less than 100, more preferably less than 50, and even more preferably less than 10.

[0059] Dielectric materials can also be characterized by their volume resistivity (ρ), where ρ = R × (A / L). Preferably, the dielectric material has a resistivity of at least 0.1 × 10¹ measured at 20°C. 5 More preferably, the dielectric material has a volume resistivity of at least 1 × 10 Ω·cm, as measured at 20°C. 15 The volume resistivity is Ω·cm, and even more preferably, the dielectric material has a volume resistivity of at least 5 × 10⁻⁶ Ω·cm measured at 20°C. 15 Volume resistivity in Ω·cm.

[0060] For the purposes of this invention, when a printed circuit board comprises only a single functional layer, for example, when conductive elements are located in the same plane and surrounded by non-conductive material within that plane, and the overall thickness is substantially constant, less than 3 mm, more preferably less than 1 mm, then the printed circuit board (PCB) is described as "two-dimensional" or "2D". Such a printed circuit board can be flexible, for example, constructed as a polymer foil, which can be laminated onto other structures.

[0061] For the purposes of this invention, a printed circuit board (PCB) comprising one or more functional layers (e.g., conductive elements on one or both surfaces of the PCB) and with a significant variation in thickness and / or a total thickness greater than 0.4 mm (preferably greater than 1 mm or greater than 2 mm) is described as “2.5D” or “2.5D”. For example, in a preferred embodiment, a 2.5D PCB may comprise 10 layers and have a thickness of 2.4 mm. Compared to a 2D PCB, such a 2.5D PCB has greater complexity because the varying layer thicknesses or thicker structures may include built-in mechanical features, and / or more functional layers can reduce the need to assemble PCB components on different devices.

[0062] For the purposes of this invention, a printed circuit board (PCB) comprising multiple functional layers, such as multilayer conductive elements encased between multiple layers of non-conductive material, and having a thickness greater than 3 mm (more preferably greater than 5 mm), is referred to as "three-dimensional" or 3D. A 3D PCB may comprise a complete product (including a housing) or a standardized port for connecting the PCB to a power supply.

[0063] For the purposes of this invention, the "droplet" is preferably a discrete unit composed of a liquid or gel material, with an interface between the discrete unit and the environment. Preferably, the droplet is not in contact with the associated printhead and / or the surface on which it is deposited at least at some point; therefore, droplet deposition is preferably a non-contact deposition technique. In contrast, extrusion is a contact deposition technique. The maximum diameter of the droplet is preferably 1 mm, and more preferably, the maximum diameter is 500 micrometers when measured in any direction.

[0064] For the purposes of this invention, the "jet" is preferably also a discrete unit of liquid or gel material. Unlike droplets, this discrete unit of liquid or gel material is preferably not substantially spherical, but has a relatively long length relative to its cross-sectional dimensions. In a preferred embodiment, the length of the jet can be, for example, 2, 4, 5, 10, 20, or more times the diameter of the jet's cross-section. Preferably, the jet does not contact the associated printhead and / or the surface to which it is deposited, at least momentarily, making jet deposition a non-contact deposition technique. The jet can have a diameter preferably less than 200 µm, preferably less than 100 µm, 50 µm, 30 µm, or smaller, and / or, the jet can have a length preferably greater than 100 µm, 500 µm, 1 mm, or longer.

[0065] In a preferred embodiment, the method includes providing conductive metal to a first printhead in bulk form (preferably in a solid state at room temperature). Conductive elements printed from molten conductive metal provided in bulk form exhibit lower resistance and higher electrical performance compared to prior art conductive inks. Preferably, the metal is melted in situ simultaneously with the provision of the molten metal in bulk solid form, for example, using a heater in the first printhead. This allows for safe and compact storage and provision of the conductive metal, while also enabling the regulation of the temperature and viscosity of the deposited metal. Control of these parameters can further regulate droplet size and the solidification of the droplets between the first printhead and the molten metal droplet deposition surface, thereby allowing the droplets to fuse together without altering the geometry of the underlying metal.

[0066] For the purposes of this invention, "bulk form" preferably refers to the material existing in sufficiently large continuous units so that it can be observed, touched, or weighed. Specifically, a solid material is considered to exist in bulk form when the smallest unit (e.g., wire, sheet, particle, briquette, bead, etc.) has a minimum size of at least 50 µm. Liquid materials can also be considered to exist in bulk form when they have sufficient volume and / or form a continuous phase of suspension or solution. Therefore, materials provided in bulk form are preferably not provided in the form of nanoparticles or in the form of a highly dispersed discontinuous phase in a suspension. Thus, conductive metals provided in bulk form are distinctly different from conductive inks containing metal nanoparticles dispersed in a continuous phase.

[0067] The metal provided in "bulk" form is preferably provided in a solid or liquid state, and preferably comprises pure metallic materials (e.g., tin) or alloys thereof (e.g., tin-silver-copper alloys). Preferably, the bulk metal contains substantially no substances other than metallic or alloying components. In addition to the above forms, the bulk metal may also be provided in powder form. The bulk form of the metal preferably contains substantially no liquid additives, such as solvents or carriers. If such liquid additives are present, they preferably do not serve as a continuous phase in the suspension of the metal particles.

[0068] In a preferred embodiment of the present invention, the method includes the following steps: a) Printing a non-conductive structure using the second printhead of the printing device; and printing a conductive element onto the non-conductive structure using the first printhead of the printing device, or b) The conductive element is printed using the first print head of the printing device, and then the non-conductive structure is printed onto the conductive element using the second print head of the printing device.

[0069] Non-conductive structures and conductive elements can be printed overlapping each other in any order. In the alternative embodiments disclosed herein, non-conductive structures and conductive elements can be printed side-by-side simultaneously or in any order.

[0070] By printing conductive elements onto a non-conductive structure, these conductive elements can be applied to a plane or inserted into pre-fabricated channels or recesses within the non-conductive structure. This method can be used to build electronic circuits on a non-conductive layer, which can form part of a multilayer or three-dimensional product. Therefore, conductive elements can be added to existing circuits or portions thereof to form additional layers of the circuit. Furthermore, printing conductive elements onto a non-conductive structure allows for the placement of additional components between the conductive elements and the non-conductive structure, with these additional components stabilized by the conductive elements.

[0071] Step b) provides an alternative to known methods of embedding conductive elements in a PCB, achieving the effect of "etching" the conductive element into a non-conductive structure. Preferably, this means that the conductive element is positioned to be exposed on the surface of the PCB such that the exposed surface of the conductive element is substantially flush with the exposed surface of the non-conductive material, thereby partially surrounding and securing the conductive material to the non-conductive material. However, this avoids the dust and waste generated by subtractive etching (i.e., removing material from the surface of the non-conductive structure). This implementation is significant because, when used in conjunction with other implementations, it enables the fabrication of double-sided and multilayer PCBs.

[0072] Multilayer structures can be further constructed by printing non-conductive structures onto conductive elements, for example, when step b) is performed after step a). In this case, the non-conductive structure can form a cover on the same PCB or on another PCB. Step b) can also be performed independently of step a), for example, when the printed conductive elements are configured to form part of the surface of a printed circuit board. Printing the conductive elements first allows them to solidify from a molten state before the non-conductive structure is printed on (optionally adjacent to) the conductive elements. The melting point of the conductive material can be higher than that of the non-conductive material, so that the non-conductive material remains soft or liquid when applied to solid conductive elements without remelting or changing the shape of these elements. Therefore, the non-conductive material can fill the gaps between the conductive elements. The non-conductive structures and conductive elements can also have surface quality or texture on their printed surfaces, such that they preferably have smoothed portions. The shape and diffusion of the deposited conductive material can also be controlled by the surface, based on the wetting behavior of the conductive material on the surface to which the conductive material is printed.

[0073] In another preferred embodiment of the invention, the method includes melting bulk metal using a heater to print conductive elements. The heater is preferably located in the printing apparatus, particularly preferably in the first printhead. Preferably, the heater is configured as a resistance coil or inductance coil, generally surrounding a reservoir in the printhead for storing the molten conductive metal material. In a preferred embodiment, the material (e.g., bulk metal) can be supplied to the printing apparatus in solid form (particularly in filament or granular form) and can be melted in situ. The heater is preferably configured to heat the material to a temperature equal to or above its melting point, such that the temperature of the contents in the reservoir reaches between 200°C and 2000°C, more preferably between 200°C and 1000°C, and even more preferably between 300°C and 800°C. The preferred heating temperature depends on the melting characteristics of the metal or alloy used. Preferably, the heater reaches a maximum temperature of 450°C, which has been tested to provide a high level of mechanical durability and can process a variety of metal materials. However, higher heater temperatures can be achieved by selecting suitable materials for the reservoir and / or any heating element of the printing apparatus.

[0074] The bulk metal provided in solid form can be precisely metered, for example, by wire length, particle mass, or droplet number, and can be melted in situ to control the temperature and rheology of the metal. This allows for control of the deposition process, such as forming uniform droplets and substantially consistent cross-sections of conductive elements (especially conductive traces). Advantageously, the first printhead does not emit hazardous or toxic dust when the molten metal melts from the bulk metal. The risk of upstream leakage to the first printhead is eliminated when melting is performed in situ. This can be achieved by using an inert gas (preferably nitrogen). Using bulk metal, especially solid metal, allows for the use of a wider range of materials to fabricate conductive elements and non-conductive structures. Materials with significantly different melting points can be selected for fabricating conductive elements and non-conductive structures. In this way, non-conductive structures can remain in a liquid or gel state during printing without causing accidental melting of conductive elements. Therefore, adding additional layers of non-conductive material does not affect the shape and distribution of the printed conductive elements. Furthermore, different conductive elements can use bulk metals with different melting points. For example, bulk metals used for soldering can have relatively low melting temperatures to avoid melting metals in adjacent conductive traces and / or electronic components.

[0075] In another preferred embodiment of the invention, the method includes melting metal using a remote heater, particularly melting metal particles during or after fused deposition. The remote heater preferably does not directly contact the metal particles. Preferably, one or more lasers can be used as remote heaters. This can raise the temperature of the metal particles, causing them to melt together to form a continuous conductive element.

[0076] In another preferred embodiment of the invention, the conductive element includes conductive traces, conductive pads, conductive solder, and / or conductive interconnects. Such conductive elements can be used to allow current to flow through circuits of any complexity. The conductive element can be sized to provide suitable resistance.

[0077] The conductive trace (or "track") preferably comprises a substantially uniform cross section that is much smaller than the length of the conductive trace. For example, the diameter or width of the conductive trace may be less than 1000 µm, preferably less than 500 µm, less than 100 µm, or even less than 10 µm, while the length of the conductive trace may be several millimeters, for example greater than 1 mm, greater than 3 mm, or greater than 10 mm.

[0078] Conductive traces are particularly preferred for connecting electronic features to each other. Conductive traces are configured to connect electronic features, which may include nodes, junctions, SMDs (surface mount devices), and / or additional conductive elements. For example, conductive traces can be printed to connect conductive pads to each other. In another preferred embodiment of the invention, conductive traces are used to create passive components, such as capacitors or resistors, in circuits. These can preferably be constructed in a three-dimensional manner, for example, for constructing three-dimensional capacitors. Furthermore, when conductive material is printed before non-conductive material, this provides an opportunity to print RF structures with a smooth metallic surface treatment, preferably having a surface roughness of less than 300 nm, or preferably less than 200 nm. The smoothness of the surface treatment can be improved by providing a suitable build plate (print bed) with a suitable surface treatment. Surface roughness is characterized by deviation from the centerline. A preferred measure of surface roughness is the Rz value, which represents the maximum height of the profile. The Rz value is measured as the vertical distance between the highest peak and the lowest valley within the measurement path (preferably along the printed conductive material).

[0079] Conductive pads are particularly preferred for mounting SMDs onto a PCB. This allows the SMD to draw current from conductive elements. Conductive soldering and / or conductive interconnects can further mechanically stabilize and / or connect the SMD to the conductive elements, enabling current to be drawn during PCB use. Additionally, conductive elements can also serve as electrical communication paths, i.e., for transmitting information and control signals.

[0080] By printing these conductive elements using molten metal, they can have sufficient diameter, width, and / or thickness to provide high current to the electronic features they are connected to. This significantly improves PCB printing performance compared to thin layers using high-resistivity conductive inks in existing technologies. Furthermore, conductive elements can be formed with precise and uniform dimensions when printed on the same printing apparatus as non-conductive structures. This is because similar layer thicknesses can be achieved for both conductive and non-conductive materials, and both materials can be constructed without moving the PCB.

[0081] In another preferred embodiment of the invention, the method includes using a heater to melt a dielectric material to print a non-conductive structure. The heater is preferably located in the printing apparatus, particularly preferably in a second printhead. Preferably, the heater is configured to melt filaments, powders, and / or particles of the dielectric material according to the printing method. This preferably includes fused deposition modeling (FFF). The dielectric material may be provided in a reinforced form, such that the dielectric material includes, for example, reinforcing fibers. Preferably, melting the dielectric material includes heating the material using the heater to a temperature equal to or above its melting point, but preferably below the melting point of any reinforcing fibers. Thus, the heater preferably heats the dielectric material to a temperature between 50°C and 600°C, more preferably between 60°C and 300°C, and even more preferably between 100°C and 250°C.

[0082] In-situ melting of dielectric materials allows for precise, quantitative material supply. It also allows for material deposition via non-contact methods—such as in the form of droplets resembling molten metal—which further contributes to uniformity and layer thickness control. Furthermore, melting the dielectric material during or at the time of deposition allows for good compatibility between conductive and non-conductive materials in the PCB.

[0083] In another preferred embodiment of the invention, the method further includes the steps of: providing a base sheet on a build plate, then printing a conductive element onto the base sheet, subsequently printing a non-conductive structure onto the conductive element to enclose the conductive element between the non-conductive structure and the base sheet, and optionally, removing the base sheet after printing the non-conductive structure is completed. (References herein) Figures 1-4 This will be explained separately.

[0084] In this way, conductive elements can be positioned on the surface of the PCB for exposure. Simultaneously, the non-conductive structure can be thick enough to provide sufficient mechanical strength for the PCB. In some embodiments, the non-conductive structure can be configured as a combination of a flexible layer and a flexible conductive element—e.g., formed from SAC305—to form a flexible PCB. Enclosing the conductive element between the non-conductive structure and the base sheet provides mechanical stability and electrical isolation. Furthermore, both the conductive element and the non-conductive structure can achieve the surface quality of the base sheet or the surface on which the conductive element and non-conductive structure are printed, preferably a smooth surface. Therefore, the resulting PCB can have a very smooth surface, reducing the risk of damage from abrasion. For example, conductive traces do not need to protrude from the PCB surface and are therefore less likely to be accidentally scratched off. Furthermore, one or more conductive elements can be perfectly flush with the non-conductive structure without prior art polishing methods or other subtractive methods. This improves the PCB's corrosion resistance and enhances the electrical insulation of the conductive elements.

[0085] The base sheet is preferably a solid material layer configured to separate the printing material from the build board and / or provide surface quality for the printed electronic circuitry. Separating the printing material from the build board preferably prevents undesirable adhesion of material to the build board. Adhesion of the printing material to the base sheet is also preferably limited, allowing the base sheet to be removed from the solidified printed circuit board without damage. Preferably, the material of the base sheet and, optionally, any surface treatment of the base sheet are selected accordingly. While the base sheet is preferably smooth, it can alternatively be textured, for example, as a watermark. The base sheet is preferably a single-use component to maintain high smoothness and prevent contamination.

[0086] The use of a base sheet is optional and can be omitted. Conductive elements can be printed directly onto the build plate, especially when the conductive elements and non-conductive structures are not adhered to the build plate. The non-conductive structures can then be printed onto the conductive elements to enclose the conductive elements between the non-conductive structures and the build plate. The printed circuit board including the non-conductive structures and conductive elements can be peeled off from the build plate or otherwise removed after solidification. In this way, the use of consumable materials such as base sheet rolls can be omitted, making the manufacturing process more environmentally friendly. This is achieved by using suitable materials in… Figure 20 Examples are shown below, and further explanations will be provided in the detailed description.

[0087] In another preferred embodiment of the invention, the printer's build plate, build plate, and / or base sheet are preheated before printing the non-conductive structure and / or conductive element. Preferably, the base sheet is heated to a temperature below the melting point of the molten metal, so that the metal is still solidified upon contact with the base sheet. Surprisingly, heating the base sheet has been found to further improve the surface quality of the printed circuit board, for example, by slowing down the solidification of the printed material and preventing crystallization due to rapid cooling. Preheating the base sheet also improves the flow of the non-conductive material when it is printed onto the conductive element in a liquid or gel state, thereby producing a continuous structure. In a preferred embodiment, the base sheet is heated to a temperature between 40°C and 250°C, preferably between 40°C and 100°C, and even more preferably between 40°C and 70°C.

[0088] In another preferred embodiment of the invention, the method further includes the steps of placing an electronic component at a predetermined location on a conductive element and / or (using a second printhead) at a predetermined location on a printed non-conductive structure, wherein this placement is performed manually or by a pick-and-place robot head, preferably forming part of the printing apparatus, wherein optionally, an adhesive is applied to the electronic component or the predetermined location before placing the electronic component at the predetermined location. The electronic component is preferably a surface-mount device. Non-limiting examples of preferred electronic components include transistors, diodes, resistors, capacitors, integrated circuits, power supplies, LEDs, sensors, etc. The adhesive is preferably applied by an additional printhead.

[0089] Therefore, a fully functional PCB can be manufactured on a single workstation—i.e., on the build board—without having to move the printed non-conductive structures. This allows electronic components to be positioned very precisely. Furthermore, the placement of electronic components can occur during or between printing steps, such that one or more materials on which the electronic components are placed, or the materials printed onto the electronic components, remain in a liquid or deformable state. This results in high mechanical stability for the electronic components on the solidified PCB.

[0090] In another preferred embodiment of the invention, the method further includes using the shrinkage of one or more printed materials to create holes, particularly slots, for placing the SMD. The holes are preferably located within a non-conductive structure. Surprisingly, the shrinkage of multiple printed dielectric materials provides cavities particularly suitable for enclosing an SMD or a portion thereof. Furthermore, when the SMD is attached to traces printed on a dielectric substrate, tightly enclosing the SMD within the dielectric material provides sufficient heat energy to the conductive material.

[0091] When the complexity of a PCB makes it difficult to place such components after the non-conductive structures and / or conductive components have been fully manufactured, it is particularly advantageous to place electronic components at predetermined locations on the non-conductive structures and / or conductive components as an intermediate step in PCB manufacturing. Therefore, it is advantageous to add electronic components before adding further complexity to the circuit structure. This increases the design freedom of the PCB. Furthermore, when adding additional material layers to the PCB, it is advantageous to place the electronic components on the lower layers before printing the additional layers on top. The same printing apparatus can then be advantageously used to print the additional layers.

[0092] In another preferred embodiment of the invention, non-conductive structures are provided with vias, specifically, the non-conductive structures are configured to have vias vias through a suitable printing process. The vias can be internally coated with a conductive material and used for routing electronic components onto the PCB from both sides and / or from other layers. The vias preferably represent vertical electrical connections extending substantially orthogonal to conductive elements arranged in the xy-plane. Preferably, these vias are not provided by drilling or other subtractive processes, but by configuring the printing method such that material is omitted from the cavities to be used as vias. The internal coating of the vias is also preferably achieved by selectively depositing conductive material at locations corresponding to the inner surface of the via. In this way, waste and dust can be avoided, while allowing for high PCB complexity. The vias also allow multiple layers or wafers of the PCB to be electrically connected to each other, supporting the manufacture of complex and three-dimensional PCBs.

[0093] In another preferred embodiment of the invention, at least a portion of a conductive element is printed onto a non-conductive structure including the positioned electronic component by molten metal to weld, and / or electrically contact, and / or mechanically stabilize the electronic component onto the electronic circuit.

[0094] Therefore, soldering can be performed precisely and on the same worktable. It has also been surprisingly found that soldering can be performed with precisely measured molten metal—preferably determined by the size of the droplets emitted by the first printhead—and in a very uniform manner, avoiding the large solder balls often seen in known soldering techniques. Another advantage of this preferred embodiment is that post-processing of the printed PCB can be reduced or eliminated, further shortening the turnaround time for producing fully laid-out and functional PCBs. Preferably, the temperature of the supporting PCB's build board and / or base sheet is adjusted during soldering to achieve rapid solidification of the solder material.

[0095] In another preferred embodiment of the invention, the non-conductive structure is printed such that grooves and / or recesses are formed on the surface of the non-conductive structure, the grooves and / or recesses being configured to accommodate conductive elements and / or electronic components, the conductive elements being, for example, conductive traces, and preferably, the conductive elements are printed at least partially such that the conductive elements are inserted into the grooves and / or recesses.

[0096] This technology preferably allows the printing of conductive elements such that the exposed (upper) surface of the conductive element is flush with the exposed (upper) surface of the non-conductive structure. Simultaneously, the conductive element is exposed, and electronic components can be placed using, for example, a pick-and-place robot head, without having to move the printing device and / or flip it to expose the conductive element. This technology also provides additional flexibility regarding the rheological properties of the molten metal used to form the conductive element. For example, molten conductive metal can be printed into the groove and solidified by lowering the temperature. Also preferably, a metal that is liquid at room temperature can be used to fill the groove without undesirably melting the non-conductive material. The metal can then be solidified or otherwise solidified. Alternatively, preferably, sufficient heat energy is dissipated from the molten metal during deposition so that the molten metal adheres to the non-conductive material in the groove without melting it. Preferably, melting of non-conductive materials is avoided by using a non-contact deposition method to deposit molten metal in the form of droplets, and adjusting the size and trajectory of the droplets so that the droplets have only enough thermal energy to adhere to the non-conductive material upon arrival, without deforming the shape of the groove on a macroscopic scale.

[0097] In another preferred embodiment of the invention, printing the non-conductive structure includes adding mechanical features such as housings, covers, mounting holes, hinges, and latches. In this way, complete devices, including both electronic and mechanical aspects, can be rapidly produced in a single workstation.

[0098] In another preferred embodiment of the invention, the method includes repeating the steps of printing conductive elements from molten conductive metal using a first printhead and printing non-conductive structures using a second printhead of a printing device to enclose one or more layers of conductive elements between any number of non-conductive structures, wherein optionally, electronic components are placed at predetermined positions between successive non-conductive structures.

[0099] To date, the use of multiple layers of conductive elements and non-conductive structures in the production of printed circuit boards has been considered impractical. This is because known techniques can cause undesirable reflow (melting and deformation) in the underlying layers, at least in part due to the thinness of the conductive ink and the proximity of the melting points of the materials used. Conversely, the preferred embodiment of layering conductive elements and / or non-conductive structures allows for the precise and efficient production of complex three-dimensional structures using a single printing device. By layering materials, complex electronic and mechanical structures can be formed. These layers can be configured to completely enclose conductive elements within non-conductive structures, thereby extending the lifespan of the circuit.

[0100] In another preferred embodiment of the invention, non-conductive structures are printed using a molten dielectric material via any of the following techniques: fused deposition modeling (FFF), direct material jetting, or a combination thereof, with FFF being preferred. These techniques have been found to provide good resolution and feature size for non-conductive structures and are particularly suitable for printing both non-conductive and conductive elements with appropriate layer thickness and uniformity. These techniques also provide good surface quality. Particularly preferred methods, such as FFF, can be applied by extruding filaments of a defined diameter, thereby controlling the size and shape of the printed parts.

[0101] In another preferred embodiment of the invention, the method is configured such that the layer thickness of the printed non-conductive material is substantially the same as the layer thickness of the printed conductive material. This can be achieved by adjusting the nozzle exit diameters of the first and second print heads, taking into account the rheological properties of each material used, so that the printed feature sizes of the two materials are substantially the same. The similarity between the layer thicknesses of the two materials allows for the printing of particularly smooth and mechanically stable PCBs with fewer production steps. Simultaneously, the conductive traces can be relatively thick and have low resistance.

[0102] In another preferred embodiment of the invention, the non-conductive material is a dielectric material, preferably selected from the following: PLA, PET, PTFE, PP, PMMA, nylon, polyimide or polycarbonate, wherein PET-g (polyethylene terephthalate-glucose) is particularly preferred.

[0103] In another preferred embodiment of the invention, the molten metal is selected from silver, copper alloys, zinc alloys, aluminum alloys, or tin alloys, wherein SAC305 (Sn96.5Ag3Cu0.5) is particularly preferred because SAC305 is a primary lead-free solder [P47] used for attaching electronic devices to printed circuit boards and has a melting point of 217°C, which is far from the melting point of the preferred dielectric polymer. Furthermore, using a molten metal with a melting point exceeding 200°C or higher, such as SAC305, allows the molten metal to be deposited as a metal droplet with sufficient heat energy to bond with the non-conductive polymer material, and this can be done economically. The melting temperature of the metal is preferably between 200°C and 500°C, more preferably between 200°C and 400°C, and even more preferably between 300°C and 350°C. Preferably, the melting point of the molten metal is not higher than 450°C so that it can be melted and dispensed in an economical and durable manner. Surprisingly, these materials can be printed in uniform droplet sizes while providing low resistance.

[0104] In a particularly preferred embodiment of the invention, the molten metal is SAC305, and the dielectric material is polyethylene terephthalate-glucose (PET-g). This combination provides sufficiently different melting points such that applying molten PET-g to the conductive element printed from SAC305 does not melt the conductive element, which retains its originally printed shape.

[0105] In another preferred embodiment of the invention, the melting point of the conductive metal (or metal alloy) used for melting is at least 20°C higher, preferably at least 50°C higher, and more preferably at least 100°C or more higher than the melting point of the non-conductive dielectric material to be printed. This ensures that the risk of partial melting or deterioration of the conductive element is minimized when a non-conductive structure is printed on top of a conductive element using a dielectric material.

[0106] In another preferred embodiment of the invention, the melting point of the metal (or metal alloy) used for the molten conductive metal is no more than 2000°C higher than the melting point of the non-conductive dielectric material to be printed, preferably no more than 1000°C higher. This minimizes the risk of deformation of the non-conductive element when using molten conductive metal droplets to print conductive elements, because sufficient heat energy can be easily dissipated from the molten metal droplets during deposition. As further explained herein, this risk is further minimized by adjusting the build board temperature, local air temperature, and droplet size to cause the deposited metal to cool down before reaching the existing layers of the PCB and to promote rapid solidification of the deposited metal.

[0107] In another preferred embodiment of the invention, the melting point of the conductive metal (or metal alloy) used for melting is 20°C to 250°C higher than the melting point or glass transition temperature of the non-conductive dielectric material to be printed, preferably 50°C to 150°C higher. Under these conditions, multilayer structures can be advantageously provided, wherein conductive elements are subsequently printed on top of the non-conductive structure or in reverse order, without the risk of interfering with the functional integrity of the printed structure.

[0108] Those skilled in the art can accordingly select metals and / or dielectric materials.

[0109] In another preferred embodiment of the invention, printing the non-conductive structure includes the step of solidifying a molten dielectric material, which preferably includes a thermal phase change and / or curing by heat and / or ultraviolet radiation. Other methods, such as high-intensity light—e.g., lasers—can also be used to achieve solidification. Electromagnetic radiation in other spectral regions can also be used at appropriate intensities to solidify the material. Therefore, the produced PCB is completely robust and resistant to unwanted deformation.

[0110] In another preferred embodiment of the invention, the conductive elements are printed using any of the following techniques: drop-on-demand deposition, continuous droplet generation (e.g., continuous jetting), extrusion, molten metal jet deposition, or a combination thereof, wherein drop-on-demand deposition is preferred. These techniques have been found particularly suitable for printing molten metal with high precision, uniformity, and high resolution. In particular, drop-on-demand deposition allows for fine-tuning of the temperature profile of the molten metal between the printhead and the build board or PCB, so that adjacent droplets in the same layer can merge with each other without causing reflow in the lower layer. For some soldering applications, continuous jetting is also preferred for providing continuous electrical connections between components. Furthermore, in a preferred embodiment using the continuous jetting printing method, homogeneous structures can be printed. This method preferably allows for printing uniform and convex lines, wherein the length of the lines is limited only by the distance the substrate can move.

[0111] In a preferred embodiment, the conductive element is printed using a non-contact deposition method, particularly a drop-on-demand or jet-on method. In some embodiments, the non-conductive material is also printed using a non-contact deposition method, such as drop-on-demand or jet-on. However, in some embodiments, the non-conductive material may preferably be printed using a contact method.

[0112] In embodiments where conductive materials, such as molten metal, are deposited non-contactly via droplet or jet deposition, the volume of the molten material can be precisely adjusted and controlled to ensure an adequate supply of heat energy. This level of control constitutes a significant advantage of preferred non-contact deposition methods compared to contact deposition methods—such as extrusion, where the transferred heat energy is more difficult to control due to the heat capacity of the nozzle and / or equipment. Thermal control can be particularly valuable when integrating electronic components that are especially sensitive to temperature rise. For example, electronic components may have a safe temperature that, if exceeded, could impair their function. Using non-contact deposition on conductive materials to contact electronic components advantageously allows for precise limitation of potential temperature rise at the location of the electronic component, thereby ensuring its reliable function. Furthermore, non-contact deposition methods—for both conductive elements and non-contact structures—allow for higher precision because possible vibrations or relative movement between the nozzle and the base sheet or print bed are less likely to compromise print accuracy.

[0113] In another preferred embodiment of the invention, printing the conductive element includes the step of solidifying the conductive element from a molten state. This solidification is preferably achieved by ensuring that the temperature of the surface on which the conductive element is printed is below the melting point of the bulk metal, preferably at least 20°C lower, more preferably at least 50°C, 100°C, or more lower. Preferably, for bulk metal with a melting point between 200°C and 250°C, the bulk metal is heated in the printing apparatus to a temperature between 200°C and 500°C, preferably to a temperature between 250°C and 400°C, and even more preferably to a temperature between 300°C and 350°C. The solidification of the conductive element provides a stable structure, thereby maintaining the shape of the conductive element during subsequent steps—such as laminating additional material onto the conductive element, peeling the base sheet from the PCB, and / or placing and soldering electronic components.

[0114] In another preferred embodiment of the invention, printing the conductive element includes the step of releasing molten metal droplets from a first printhead onto a surface, wherein the droplet diameter and / or the distance from the nozzle of the first printhead to the surface is selected such that the molten metal droplet is at a temperature higher than its melting point at the nozzle, and the molten metal droplet reaches the surface at a temperature substantially equal to or lower than its melting point, for example, at least 10°C, 20°C, or more lower. Preferably, the distance between the nozzle and the surface is at least 1 mm, preferably at least 2 mm, and more preferably at least 5 mm. In a preferred embodiment, the distance between the nozzle and the surface is between 1 mm and 50 mm, more preferably between 1 mm and 30 mm, and particularly preferably between 5 mm and 30 mm.

[0115] This allows droplets to initially be in a liquid state upon deposition. This state allows for the formation of very round and uniform discrete droplets through surface tension. Upon reaching the surface on which they are deposited—such as a building plate, base sheet, non-conductive structure, or underlying conductive material—droplets may be temporarily in a liquid or gel state, which allows adjacent droplets to fuse before rapid solidification, resulting in a smooth, robust structure that will not be deformed by subsequent process steps.

[0116] Preferably, this is achieved by adjusting the droplet size, particularly using known methods for adjusting the pressure and / or flow rate at the nozzle and the exit diameter of the nozzle of the first printhead. Preferably, the nozzle exit diameter is between 30 µm and 1000 µm, more preferably between 30 µm and 700 µm, between 40 µm and 700 µm, or between 70 µm and 500 µm, and even more preferably between 80 µm and 300 µm. Conductive elements formed in this way can have high resolution and uniformity because of the uniform droplet size. The fusion of droplets placed at precise locations with precise droplet spacing also allows the conductive trace to have a uniform cross-section, and therefore uniform resistance, improving electrical performance.

[0117] In another preferred embodiment of the invention, printing the conductive element includes the step of releasing molten metal droplets from a first printhead onto a surface, wherein a cooling mechanism is provided at the first printhead for actively cooling the molten metal droplets along a trajectory between the first printhead and the surface. This cooling mechanism is preferably based on an inert gas, such as liquid or gaseous nitrogen. For example, the cooling mechanism can ensure that the droplets are cooled by at least 20°C, 50°C, 100°C, or more during their trajectory between the first printhead and the surface. Furthermore, the use of an inert gas—preferably nitrogen—can advantageously help prevent oxidation of the molten metal droplets.

[0118] Preferably, liquid or gaseous nitrogen is supplied to the cooling equipment to accelerate the cooling of the molten metal droplets. This is particularly advantageous when the temperature of the molten metal in the first printhead is so high that the droplets do not immediately solidify upon reaching their deposition surface. Active cooling allows the use of a wider range of metals with different melting points. Additionally, reflow of existing material layers in the PCB can be avoided, especially when these layers are composed of the same material or of materials with similar melting points. Therefore, PCBs with high complexity and mechanical stability, utilizing multilayer and three-dimensional structures, can be manufactured.

[0119] In another preferred embodiment of the invention, the conductive element is printed by on-demand droplet deposition, wherein the spacing between droplets is less than the average droplet diameter and is configured such that successive droplets merge. Preferably, the spacing between the average droplets is between 10% and 90% of the average droplet diameter, more preferably between 20% and 80% of the average droplet diameter, between 30% and 60% of the average droplet diameter, between 40% and 60% of the average droplet diameter, and most preferably about 50% of the average droplet diameter. The average droplet diameter is preferably between 30 µm and 1500 µm, more preferably between 30 µm and 1000 µm, between 40 µm and 700 µm, even more preferably between 50 µm and 600 µm, more preferably between 100 µm and 500 µm, and particularly preferably between 250 µm and 300 µm. Preferably, the distance between droplets is between 20 µm and 500 µm, more preferably between 80 µm and 250 µm, and particularly preferably between 100 µm and 200 µm. Surprisingly, this droplet fusion has been found to improve the mechanical strength and electrical performance of the conductive element. The preferred droplet diameter and droplet-to-droplet distance also enable an optimized cooling profile from the first printhead to the surface where the droplets are deposited, as well as rapid droplet fusion and solidification.

[0120] In another preferred embodiment of the invention, the method includes fabricating a three-dimensional structure with embedded electrical features. The embedded electrical features can prevent damage or corrosion of these features and improve electrical isolation. It also allows for the production of complete electronic products in a single workstation. The method preferably includes the selective deposition of at least one dielectric material. Furthermore, the method preferably includes solidifying the dielectric material by thermal phase change, UV curing, or other suitable methods.

[0121] In another preferred embodiment of the invention, the method includes creating holes, void volumes, or other cavities during the fabrication of the non-conductive structure. Such cavities can advantageously save material, reduce PCB weight, and increase manufacturing speed.

[0122] Preferably, the method includes selectively depositing at least one molten metal in a liquid state to form conductive traces on top of the build plate and / or a previously printed layer. The conductive metal material can be printed / dispensed in the form of droplets, jets, or other forms. As described above, droplets preferably have a diameter between 30 µm and 1500 µm, preferably between 50 µm and 600 µm, more preferably between 100 µm and 500 µm, and are characterized by being substantially spherical. Jets are preferably characterized by a length greater than a cross-sectional parameter (e.g., diameter), and for example, may preferably have a cross-sectional diameter of less than 200 µm, preferably less than 100 µm, 50 µm, 30 µm or smaller, and / or preferably have a length greater than 100 µm, 500 µm, 1 mm or longer.

[0123] Preferably, the solidification of the molten metal occurs via a thermal phase transition, which is achieved by maintaining the build plate and / or the previously printed layer at a temperature below the solidification point of the metallic material. The three-dimensional structure can be fully constructed by repeatedly selectively depositing the dielectric material and at least one molten metal.

[0124] The conductive material deposition method preferably employs a pneumatically driven printhead, such as the StarJet technology described in more detail below.

[0125] The dielectric material deposition method is preferably a direct polymer deposition method, which supplies the thermoplastic material in its molten state, such as fused deposition modeling (FFF) or molten polymer spraying.

[0126] The temperature of the molten metal printhead is preferably higher than the melting temperature of the metal. The temperature of the non-conductive material printhead is preferably lower than the solidification temperature of the metal. Direct injection of metal droplets or jets is preferably used to create an electrically conductive connection between the electrodes of the electronic component and / or previously printed metal traces. For example, droplets can be used to form conductive traces. Similarly, metal jets can be deposited, the length of which can be precisely controlled by a nozzle, as described herein. Advantageously, both droplet and jet deposition methods produce particularly precise and homogeneous conductive structures, such as traces.

[0127] Additive manufacturing of fully printed circuits, including pre-laid electronic components, using simple, fully automated equipment preferably eliminates the need for centralized PCB production in factories, where various setups are typically required for sequential processes such as etching, resist stripping, drilling, soldering, etc. Furthermore, it significantly reduces manufacturing complexity and subsequent manufacturing steps.

[0128] First, conductive metal traces are printed on the build board, and then the conductive metal traces are covered with a non-conductive material. Preferably, a fully printed PCB is provided, in which both the conductive metal traces and the non-conductive structure have a smooth top surface. This PCB can be easily handled using conventional downstream soldering techniques such as SMT or any other technique.

[0129] Preferably, no post-processing is required to improve the conductivity of the metal traces. The high conductivity of the metal traces is ensured by using bulk metal for deposition and the high aspect ratio of the printed conductive metal traces.

[0130] Printing bulk metal, such as solder, is preferably used to directly solder ICs, SMDs, and other electronic components as part of a fully automated hybrid 3D printing process. Using hot liquid metal jets to directly solder electronic components is highly novel and innovative, while also significantly reducing manufacturing processes and improving the compatibility and flexibility of placing electronic components inside / on the surface of 3D-printed PCBs.

[0131] This invention preferably also provides user-specific PCB design flexibility, PCB material freedom, and the possibility of manufacturing complete end-user electronic devices. Electronic devices can be grown on the printed PCB. The materials used for the electronic devices can differ from the materials used for the printed PCB.

[0132] In another preferred embodiment of the invention, printing is performed based on CAD data provided to the printing apparatus and / or to a processor communicating with the printing apparatus. The CAD data can be suitable for directly printing 3D electronics or multilayer PCBs, optionally including 3D designs of mechanical structures with embedded 3D circuitry, with or without electronic components. This can include multilayer metal and / or non-conductive structures. The CAD can be processed by the processor to provide individual layer designs, which can also be broken down into designs for each material type.

[0133] For example: First, the CAD design file of the 3D object will preferably be sliced ​​into multiple 2D layers in the horizontal direction. A series of 2D designs will be printed layer by layer using appropriate infill patterns, as is typically done in 3D printing. For each layer, if applicable, the design will be broken down into: 1. a design for non-conductive materials; 2. a design for conductive materials; and 3. a design for placing electronic components. These designs preferably include information about where non-conductive materials, conductive materials, or electronic components (e.g., SMD devices) should be placed within a particular layer. All printing and / or placement processes will be performed sequentially before moving to the next layer. An exemplary sequence is: 1. Printing non-conductive materials; 2. Placing electronic components, if applicable; and 3. Printing conductive materials, if applicable. However, the process is not limited to this particular sequence, and other sequences may be used if deemed beneficial.

[0134] The processes proposed according to the present invention preferably do not require post-processing of the printed conductive metal traces, which is a significant improvement over the prior art. Since no post-processing via heat treatment is required, and bulk materials are used for both conductive and non-conductive portions of the printed object, a wider range of materials can be selected for electrical connections and insulating layers compared to the prior art. The process can preferably be performed on any additive manufacturing equipment capable of laying the conductive metal traces and insulating layers in a molten / liquid state (solidifying immediately after printing the lines / layers). Several additional possible implementations and application examples, demonstrating good consistency between conductive metal traces and insulating materials in the form of 3D printed PCBs and other electronic circuits, are described for clarity only without departing from this general statement.

[0135] By way of example only, the method of the present invention can be used for rapid prototyping of printed circuit boards (PCBs). This method preferably includes the following steps: 1) Deposit conductive material onto a flat surface to form at least one layer of conductive metallic traces; 2) Depositing dielectric material to cover metal traces using contact or semi-contact methods to form a supporting dielectric structure; and 3) After the dielectric material solidifies, remove the printed PCB from the surface.

[0136] Preferably, the solidification of the conductive metal traces occurs between steps 1) and 2).

[0137] The resulting printed circuit board preferably has a flat and smooth surface, with electrically conductive wiring and pads on the top surface. Electronic components can be laid on it using conventional soldering methods (such as SMT), just like any other standard PCB known in the art.

[0138] Printed circuit boards can have multilayer conductive features, 3D freeform wiring, vertical vias, and embedded electronic components.

[0139] In a second aspect, the present invention relates to a printing apparatus for additively manufacturing electronic circuits by means of the method according to any one of the preceding claims. The printing apparatus includes: a build plate; a first printhead configured to print conductive elements from molten conductive metal; and a second printhead configured to print non-conductive structures from a dielectric material.

[0140] Preferably, the printing apparatus further includes a heater configured to melt conductive metal provided in block form. Preferably, the first printhead is configured to print conductive elements from the molten conductive metal provided by the heater. Preferably, the printer includes means for moving the first and second printheads relative to the build plate in the xy plane. The printheads and the second printhead can move simultaneously and / or independently of each other. Additionally or alternatively, the printer includes means for moving the build plate relative to the first and second printheads in the xy plane. Preferably, the first printhead, the second printhead, and / or the build plate can also move relative to each other in the z plane. This is particularly advantageous for producing three-dimensional PCBs with fine control over the distance between the printheads and the surfaces on which the relevant material is deposited.

[0141] The printing apparatus of the present invention advantageously allows for "hybrid 3D printing" of conductive materials (e.g., conductive metals as electrical traces) and non-conductive support materials (e.g., polymer substrates as substrates) in a preferably fully automated process. This apparatus enables rapid prototyping and small-batch production of PCBs and addresses the problems of long design-to-product cycles, high design and development costs, and the high time and cost associated with small-batch PCB and prototype production.

[0142] Providing both a first and a second printhead on the same printing device improves PCB quality, complexity, and design freedom. For example, because two materials are printed from different printheads on the same printer, intermediate products in the PCB manufacturing process do not need to be fully solidified before adding more materials or components. This supports good fit between materials, which is impossible in existing processes. Electronic components can be added and soldered in situ before adding more layers or components. Therefore, PCBs can be built step-by-step without transferring them to different workstations. Furthermore, the possibility of keeping all intermediate products stationary before adding more layers or components allows for precise alignment of the layers. This printing device also provides greater data and design protection, decentralized "in-house" manufacturing, and reduces toxic waste and wastewater through the additive manufacturing process.

[0143] The printer of the present invention provides the possibility of directly printing freeform 3D objects in a fully digital form, with conductive features on both the interior and the surface, without the need for any tools (e.g., masks or molds).

[0144] In the context of this invention, a "heater" is preferably a device configured to directly or indirectly raise the temperature of a material. The heater preferably includes one or more resistance coils. Indirectly raising the material temperature may include heating elements such as a printhead, particularly a material reservoir for heating the printhead, which is configured to be in direct contact with the material.

[0145] In another preferred embodiment of the invention, the first printhead is configured to produce single droplets of molten metal of uniform diameter. Preferably, the first printhead is also configured for non-contact deposition of the molten metal. This preferably means that the deposited material is completely separated from the printhead before reaching the surface to which it is deposited. Non-contact deposition of the molten metal can advantageously be performed under ambient conditions rather than under a protected argon atmosphere, thereby allowing the droplets to have greater compatibility with non-conductive structures compared to ink. Non-contact deposition also advantageously ensures stable structures without undesirable relative movement of individual components, as there is no simultaneous contact with the (to be printed) surface and the printhead and / or nozzle. The non-contact deposition method is also particularly safe when embedding (temperature) sensitive or delicate electronic components and / or semiconductors, as it provides very precise control over heat transfer.

[0146] The generation of single droplets of molten metal allows for high resolution and uniformity in the conductive elements, resulting in constant resistance along their length. The droplets can initially be released in a liquid state. This state allows for the formation of highly spherical and uniform discrete droplets through surface tension. Those skilled in the art know how to adjust the nozzles of the printhead to achieve this droplet deposition. Adjacent droplets can then fuse before rapid solidification, forming a smooth, robust structure that will not be deformed by subsequent process steps. Furthermore, the fused droplets advantageously lack an internal porous structure.

[0147] The first printhead preferably includes or is connected to a reservoir for containing molten metal. Preferably, means for moving the molten metal into a nozzle of the printhead is provided, wherein the means is preferably based on pneumatic pressure, hydraulic pressure, gravity, capillary action, and / or a pump. Preferably, the first printhead is configured for generating pneumatic or hydraulic droplets or jets, wherein the pneumatic or hydraulic pressure of a second-stage fluid is applied to the molten metal in the reservoir to force the molten metal into the nozzle outlet. For this purpose, the first printhead preferably includes a pressure generating means for regulating the pressure of the second-stage fluid, wherein the second-stage fluid preferably flows into a front chamber above the liquid level in the reservoir and laterally flows into the nozzle outlet. The front chamber is preferably a volume located above the liquid level of the molten metal in the reservoir. The front chamber is preferably fluidly connected to other channels through which the second-stage fluid will flow.

[0148] The nozzle outlet of the first printhead is preferably made of a material selected such that the molten metal has sufficiently low wettability relative to the channel, allowing it to flow through the nozzle outlet without spreading on the nozzle. The inner wall of the nozzle outlet preferably has higher wettability to the secondary fluid than to the molten metal. The cross-sectional shape of the nozzle can also be configured to further reduce capillary action and contact between the molten metal and the nozzle outlet wall, wherein a star-shaped cross-section with two, three, four, five, or more spokes is preferred. Preferably, the secondary fluid flows through the spokes of the star-shaped cross-section parallel to the flow direction of the molten metal. This configuration allows the molten metal to remain within the central portion of the star-shaped cross-section of the nozzle outlet, where the contact surface area with the flowing molten metal is reduced. The side channel is preferably arranged to open into the sidewall of the nozzle outlet to deliver the secondary fluid to the nozzle outlet. Preferably, the secondary fluid is a flushing gas. The molten metal enters the nozzle outlet from the reservoir due to the gas pressure of the secondary gas in the front chamber and due to gravity. Droplets of partially molten metal enter the nozzle outlet, which preferably increases the pressure of the flushing gas entering the nozzle outlet from the side channel, thereby releasing (or "tearing off") the discrete droplets, while the remaining molten metal returns to the reservoir via capillary action. This process is preferably repeated sequentially, so that the droplets are released in a regular and consistent manner. In a preferred embodiment, the gas pressure can be selected to perform continuous release of molten material as a jet, wherein the duration of pressure application preferably allows for control of the jet.

[0149] The flushing gas preferably also acts as a sheath to prevent oxidation of the molten metal microdroplets. The flushing gas is preferably inert. Preferably (and in embodiments further described herein), the flushing gas is nitrogen.

[0150] This is a particularly advantageous technique for producing droplets of uniform size and is especially safe when using molten metal. It is particularly effective for generating uniform droplets from molten metal without contact with the surface to which the droplets are to be deposited. This not only allows for uniform droplet size but also allows for cooling during deposition.

[0151] In a preferred embodiment of the invention, the first printhead is the StarJet printhead disclosed in US8877145B2. This printhead has been found to be particularly suitable for the printing apparatus according to the invention.

[0152] In another preferred embodiment of the invention, the printing apparatus further includes a pick-and-place robot head, preferably configured to place electronic components at predetermined locations on the printed non-conductive structure and / or the printed conductive element and / or on the build board. The printing apparatus preferably also includes an in-line camera configured to verify the pickup and placement of the electronic components and / or monitor print quality. The pick-and-place robot head is, for example, a pneumatic gripper or similar device. Providing a pick-and-place robot head on the same printing apparatus as the first and second print heads allows for rapid, one-stop PCB production without post-processing. Therefore, electronic components can be applied between layers or in a stepwise manner to avoid mechanical interference, particularly in highly complex PCBs.

[0153] The second printhead is preferably configured to print non-conductive materials in a liquid and / or gel state to form non-conductive isolation regions on the 3D printed object. Any other non-solid form may be suitable. The second printhead can be configured in a similar or different manner to the first printhead. For example, the second printhead may correspond to the printhead of the Prusa i3 MK3 device.

[0154] Preferably, the second printhead includes a filament supply unit. This preferably includes an inlet for polymer filaments—which can be supplied from a spool—a motor, and optionally one or more gears. Alternatively, the second printhead may include a hopper and an extruder configured to supply polymer granules. The filament supply unit or hopper can supply polymer filaments or granules to a "hot end." This is preferably the heating portion of the printhead and may include a heater in the form of a coil. The hot end preferably includes a cavity for containing molten polymer and a nozzle for releasing the molten polymer. Depending on the type of polymer deposition to be performed through the second printhead, additional features may also be provided, such as a side inlet for a second-stage fluid—e.g., a pulsating pressure inert gas.

[0155] The heater of the second printhead is preferably different from the heater of the first printhead because the heater of the second printhead is configured to reach a lower maximum heating temperature. This is because the dielectric material used preferably has a lower melting point than molten metal. Preferably, the heater of the second printhead is configured to reach a maximum temperature not exceeding 300°C, more preferably not exceeding 150°C. Preferably, the heater of the first printhead is configured to reach a maximum temperature not exceeding 450°C.

[0156] In another preferred embodiment of the invention, the first printhead and / or the second printhead can be moved relative to the build plate in the z-direction, and / or the build plate can be moved relative to the first printhead and / or the second printhead in the z-direction. Therefore, the printing apparatus can be used to adjust and set the distance between each printhead and the surface where the material is to be deposited, which allows for the use of different cooling profiles for different materials. Simultaneously, the printheads can be adjusted relative to the build plate to maintain a constant distance between the relevant printhead and the intermediate PCB product when generating different layers.

[0157] In another preferred embodiment of the invention, the printer includes at least two printheads for printing two different materials. These may include all the typical mechanical and control features required to operate the printheads. The printheads may operate simultaneously or sequentially. Therefore, additional post-processing steps such as brushing, cleaning, or coating can be performed at a single site, further increasing PCB production speed and reducing the need to share data across different manufacturing facilities. Thus, this printing apparatus is particularly suitable for rapid prototyping without data security risks.

[0158] In another preferred embodiment, the first printhead is configured to print conductive materials using a non-contact method—e.g., on-demand dripping or jetting—while non-conductive materials are deposited using a contact method. In yet another preferred embodiment, the first printhead is configured to print conductive materials using a non-contact method, and the second printhead is configured to print non-conductive materials using a non-contact deposition method. In a preferred embodiment, printing is controlled by a control unit configured to control relevant components of the printing apparatus for this purpose. Preferably, the control unit is configured to control the first printhead (e.g., via one or more actuators) to print conductive materials using a non-contact method, and the control unit is additionally configured to control the second printhead (e.g., via one or more actuators) to print non-conductive materials using either a contact or non-contact method. These preferred embodiments and the printing flexibility described below are advantageously achieved due to the high flexibility of individually controllable printheads: printing both conductive and non-conductive materials in a non-contact deposition mode, or printing conductive materials in a non-contact manner while printing non-conductive materials in a contact manner, such as by extrusion.

[0159] In particular, preferably, the printing apparatus is configured to allow individual adjustment of the distance between one of the printheads and the surface of the substrate material. For example, in contact mode, the nozzles of the printheads are preferably controlled by a control unit to a distance of less than 1 mm, preferably less than 200 µm, so that the material is deposited directly onto the substrate. In non-contact deposition mode, the nozzles of the printheads can be controlled to be positioned at a distance greater than 1 mm, preferably greater than 2 mm, 5 mm, 10 mm, or more.

[0160] Therefore, depending on the desired application, for example, when printing near electronic components to provide high precision and avoid any interference with the device, non-contact deposition methods may be preferred for non-conductive materials. On the other hand, for printing larger non-conductive structures, contact deposition methods may be preferred for depositing large volumes of non-conductive material. Thus, the printing apparatus according to the invention, with two independently controllable printheads, provides a high degree of flexibility to optimize the printing process for the desired electronic circuitry. Terms such as substantially, about, approximately, etc., preferably describe tolerance ranges of less than ±20%, preferably less than ±10%, particularly preferably less than ±5%, and especially less than ±1%, and include precise values.

[0161] Those skilled in the art will understand that the technical features and advantages disclosed with respect to the methods described herein also apply to the printing apparatus, and vice versa. Attached Figure Description

[0162] Without intending to limit, the invention will be explained in more detail with reference to exemplary embodiments and the following figures: Figure 1 According to an embodiment of the present invention, conductive metal traces are printed in a schematic diagram that appears to be embedded in the surface of a polymer PCB substrate.

[0163] Figure 2 According to another embodiment of the present invention, a real printed sample in which conductive metal traces are printed onto a polymer.

[0164] Figure 3 According to another embodiment of the present invention, a real printed sample of a circuit including conductive metal traces printed onto a polymer.

[0165] Figure 4 According to an embodiment of the present invention, a scanning electron microscope image of the conductive metal traces printed on the base sheet before the polymer structure is printed onto and around the conductive metal traces and the base sheet is removed.

[0166] Figure 5 Scanning electron microscope images of metal conductive traces printed onto a build plate before printing dielectric material without a base sheet to provide a smooth surface.

[0167] Figure 6 A schematic illustration of a partially laid-out circuit according to another embodiment of the present invention, the circuit comprising conductive metal traces and conductive pads printed onto a polymer having grooves / recesses.

[0168] Figure 7 : A schematic illustration of a method for manufacturing an electronic circuit according to a preferred embodiment of the present invention, wherein grooves / recesses are formed in a non-conductive structure and conductive elements are printed in the grooves.

[0169] Figure 8 Schematic illustration and micrograph of a cross-section of an electronic circuit printed according to a preferred embodiment of the present invention, wherein conductive elements are printed in grooves / recesses and enclosed between polymer layers.

[0170] Figure 9 : A schematic diagram and micrograph of a cross-section of an electronic circuit printed according to another preferred embodiment of the invention, wherein conductive elements are printed on the surface of a polymer layer and enclosed by another polymer layer.

[0171] Figure 10 : An exploded schematic illustration of a three-dimensional electronic device as a computer-aided model, manufactured using a method according to another preferred embodiment of the present invention.

[0172] Figure 11Photographs of three-dimensional electronic devices manufactured using a method according to another preferred embodiment of the present invention.

[0173] Figure 12 : Confined in Figure 11 A schematic diagram of a circuit in a three-dimensional electronic device.

[0174] Figure 13 (a) A computer-aided design (CAD) model of the open-source Prusa i3MK3 3D printer with a single extruder for printing polymers. (b) A CAD model of the proposed hybrid 3D printer with a StarJet printhead integrated into the Prusa i3 MK3 printer. (c) An exploded view of the CAD model showing the different fixtures and thermal break elements (made of aluminum) for dissipating heat from the StarJet printhead. (d) A new control board with dual extruders, capable of replacing the single extruder control board. The control sequence is shown to illustrate the communication between the printer control board and the StarJet printhead.

[0175] Figure 14 (a) A photograph of the Synkrotima hybrid printer developed as part of this study. (b) A model printed by the Original Prusa i3 MK3 printer. (c) A model with the same CAD design as (b) but printed by Synkrotima, demonstrating unimpeded FFF printing performance after integration with StarJet.

[0176] Figure 15 The process flow of hybrid printing via Synkrotima is as follows: (a) An example of a 3D-CAD model of an assembly with a polymer structure and a conductive metal structure. (b) Creating a slicing model on a hybrid slicer profile, thereby assigning extruder 1 (print head 2) to the dielectric portion and extruder 2 (print head 1) to the electrically conductive portion. Furthermore, the G-code generated from this model is supplied to Synkrotima. (c) A photograph of the final hybrid printed sample, generated without human intervention.

[0177] Figure 16(a) Molten metal microdroplets printed by the StarJet printhead and captured in flight by a stroboscopic camera; (b) Scanning electron micrograph of molten metal microdroplets printed into water; (c) Solidified molten metal microdroplets on an FFF-printed PETG substrate with a contact angle of approximately 93 degrees; (d) Cross-sectional view of solder lines printed on a PETG substrate with a contact angle of approximately 96.5 degrees; (e) Focused ion beam (FIB) cross-section of electrically conductive traces printed on a PETG substrate; (f) SEM micrograph of electrically conductive traces (solder lines) printed with a dot pitch of 100 µm.

[0178] Figure 17: (a) Single solder lines and (b) double solder lines printed on PETG substrates with different linewidths of 80µm, 100µm, 150µm, 200µm, and 250µm; (c) Linewidths measured for single and double solder lines printed with different dot pitches. The minimum dot pitch considered for the printed samples is 80µm, while the maximum dot pitch is considered to be 250µm; (d) Conductivity measured for single and double solder lines with different dot pitches, where the conductivity of SAC305 solder is 7.69 × 10⁶ S / m, marked with a dashed line for reference; (e) Shear forces for single and double solder lines printed with different dot pitches. The double solder lines show higher shear forces due to the larger linewidth. The measured shear forces for single and double solder lines range from 6N to 16N.

[0179] Figure 18 Linewidth and resistance of electrically conductive traces printed with respect to different orientations of the polymer (0°, 45° and 90°).

[0180] Figure 19 The fabricated hybrid 3D printed structure with embedded electronic components: (a) the middle layer of the hybrid printing demonstrator, in which two electronic components (resistors and blue LEDs) are placed in the printed slots and conductive metal traces are printed into the grooves / recesses; (b) the fully hybrid printed demonstrator, in which the printed conductive traces are covered by a 3D printed polymer layer; (c) a demonstration of the lighting function of the blue LED embedded in the polymer substrate in image (b), which is driven at a voltage of 2.9V, with a measured current of 20 mA; image (d) shows a close-up of the aforementioned LED, showing solder printed onto the contact pads of the LED by molten droplets from the StarJet printhead.

[0181] Figure 20Fabrication of a hybrid structure with embedded electronic components on different layers. (a) A slice model with a layer height of 1.7 mm and fabricated polymer grooves; (b) A slice model with a layer height of 2.7 mm, where solder traces and LEDs are covered by polymer; (c) and (d) Slice 3D structures printed by StarJet in DoD (Drop-on-Demand) mode. (e) Top view and (f) rear view of the hybrid printed 3D model, where electrically conductive printed traces are fully embedded within the transparent green PETG polymer extruded by FFF. Off-surface 3D metallic characters (P, 3, and D) with a wall thickness of 530 µm were printed from SAC305 solder using StarJet. Detailed Implementation

[0182] The following disclosure is intended to explain and illustrate the invention by way of example, and is not intended to limit the scope of protection.

[0183] The present invention is preferably based on layer-by-layer additive manufacturing, or so-called 3D printing technology, for printing printed circuit boards (PCBs) and electronic circuits with integrated functional electronic components distributed within and / or on 3D structures / housings.

[0184] Figure 1 An example of a PCB printed according to an embodiment of the present invention is shown, in which the conductive metal traces 2 are printed first before the dielectric polymer layer is printed between the conductive metal traces. The dielectric polymer is additionally printed above the conductive metal traces. This embodiment provides a smooth PCB surface in which the metal traces 2 are presented as being etched within the dielectric polymer body 4 (a non-conductive structure).

[0185] To fabricate a flat 2D PCB with a layer of conductive traces 2, firstly, preferably, the conductive metal traces 2 are printed onto a heated base sheet (not shown) using a direct metal printing technology such as a StarJet printhead (patent US8877145B2). The temperature of the base sheet is preferably below the melting point of the conductive material used to print the conductive metal traces 2. These conductive traces 2 are laid out in a desired PCB circuit layout. Next, these conductive traces 2 are preferably "imprinted" into and simultaneously covered by a first dielectric material by printing a dielectric layer 4 on top. Since a non-conductive material printhead configured for printing an insulating layer in a liquid / gel state, such as a fused wire fabrication (FFF) technology, is used, the insulating layer preferably flows around the conductive metal traces 2 without interfering with their properties. In this way, the material properties and shape of the conductive metal traces 2 are not affected by the method, and the metal traces 2 preferably retain their initial printed shape. In subsequent steps, an additional layer of non-conductive material 4 can preferably be printed on top of the first layer to provide greater mechanical stability and / or add mechanical features such as mounting holes, hinges, snaps, etc., or even provide a complete outer housing for the electrical device. A significant advantage of this method of first printing the metal traces 2 onto a preheated substrate (“base sheet”) and then fully embedding it within the layer of non-conductive material 4 is that the surface presenting the metal traces is perfectly flat and very smooth (provided the base sheet is sufficiently flat and smooth). Therefore, after the PCB printing is complete, the PCB can be peeled off from the base sheet, flipped, and easily populated using conventional soldering. Figure 2 The image, based on post-processing, shows a PCB manufactured according to this method, using a base sheet that has been peeled off from the finished PCB. It can be seen that the printed PCB closely reflects... Figure 1 The design shown.

[0186] The PCB manufactured according to this embodiment has a thin surface, wherein conductive metal traces are etched on a dielectric layer, such as... Figure 2 As shown. The result is a PCB board with embossed conductive metal traces, which provides a smooth surface finish. The layout of the substrate 4 and the electrically conductive metal traces 2 depends on the creativity and design capabilities of the party wishing to use the invention. Therefore, the invention is not limited to a single embodiment.

[0187] In this specific example, the non-conductive material used is polyethylene terephthalate-glucose (PET-g). The conductive metal traces are formed using solder alloy SAC305 (Sn96.5Ag3Cu0.5). The overall dimensions of the printed PCB are 35mm x 60mm x 0.60mm.

[0188] Soldering of electronic component 6 is accomplished using solder with a lower melting point than the metal used to generate the metal traces 2 via printing, to avoid remelting of the traces during the soldering of electronic components. Depending on the PCB size, the production cycle from design to a printed PCB prototype ready for component assembly can be as short as a few minutes to an hour. This is significantly faster than any 24-hour PCB express delivery service.

[0189] Figure 3 It shows Figure 2 The image shows the PCB after it has been assembled with electronic component 6. The image illustrates that the PCB has vias 12 (through-holes), which allow connections from electronic component 6, such as LEDs and resistors, to reach the back of the PCB. In this example, the back 8 of the PCB has metal traces that can then be connected to the electronic component 6 on the front side 10 of the PCB. This PCB offers advantages such as smoothness, compactness, and high design fidelity. Another assembly method for the PCB disclosed herein involves placing electronic components, particularly surface-mount elements, on the front side and soldering these components to conductive elements 2.

[0190] The quality of the printed PCB is achieved, at least in part, by the significant rheological properties of the printed conductive element 2. A profilometer with a 12µm diamond probe was used to measure the height difference between the top surface of the conductive metal trace 2 and the top surface of the non-conductive polymer layer 4. The measured value was 130nm, indicating that the conductive metal trace is completely imprinted in and flush with the non-conductive polymer surface, thus providing a smooth PCB surface. Furthermore, this PCB is advantageous for component assembly, and the entire assembly can be printed on top of the printed planar PCB.

[0191] Figure 4 It shows Figure 2 and Figure 3 The image shows a scanning electron microscope (SEM) image of the surface of the device after the base sheet has been removed. The image reveals that the conductive trace 2 comprises multiple discrete droplets that merge together to provide a continuous material "path" with a substantially constant cross-section. The non-conductive structure 4 comprises substantially continuous material "paths" that conform to the contour of the conductive trace 2, thus firmly holding the conductive trace 2 in place. Furthermore, the upper surfaces of both the conductive element 2 and the non-conductive structure 4 are completely flat and flush with each other, resulting in a single, perfectly flat surface. This makes the PCB exceptionally smooth and less prone to damage.

[0192] In some other implementations, it is used for production Figure 1 and Figure 2The base sheet of the PCB can be omitted. For this implementation, suitable materials can be selected that can be removed from the building board without damage.

[0193] Figure 5 It shows a method similar to Figures 1 to 3 A scanning electron microscope image of the upper surface of another PCB produced using the same technique. However, both the conductive element 2 and the non-conductive structure 4 are printed directly onto the smooth surface of the build board without using an intermediate base sheet. Subsequently, after curing, the PCB is removed from the build board to expose the surfaces in contact with the build board. It can be seen that a tight fit is achieved between the non-conductive structure 4 and the conductive element 2, resulting in a smooth surface quality.

[0194] Another embodiment of the present invention is in Figure 6 As shown in the image. (and) Figures 1 to 4 Unlike other PCBs, this PCB is printed by first printing a first layer of non-conductive structure 4 onto a build board. This non-conductive structure is then shaped to create channels and recesses, which are subsequently filled with conductive elements 2. In this embodiment, the conductive elements 2 include metal traces and various conductive contact pads 16. Such a PCB is configured for in-situ assembly of electronic components 6 by applying them to their front and side surfaces without lifting and flipping the PCB from the build board. Therefore, electronic components 6 can be placed on the surface of the PCB without moving it. Alternatively, the same printing apparatus is used to place and / or solder the electronic components 6.

[0195] Figure 7 The diagram illustrates the construction process. Figure 6 A PCB printing apparatus and method are disclosed. The apparatus includes at least two movable dispensers (i.e., a first print head 22 for printing molten metal and a second print head 24 for printing non-conductive materials) for initial direct prototyping of PCBs in two-dimensional and / or 2.5-dimensional form, thereby allowing electronic components to be directly mounted onto the PCB during the printing process. The second print head 24 supplies a non-conductive material 4, such as a dielectric polymer, and can construct three-dimensional objects via continuous movement along the x, y, and z axes. In this embodiment, the non-conductive material 4 is a dielectric polymer provided in the form of a filament feed 18, which is melted and extruded by the second print head 24. A good example of a printing technique suitable for the second print head 24 is found in an FFF-based 3D printer.

[0196] Parallel to the FFF dispenser, a first printhead 22 is mounted on the same axis system adjacent to the FFF dispenser. The first printhead 22 supplies conductive material and forms electrical features 2, such as electrical interconnects / wiring, contact pads, vertical interconnects, etc. on a PCB board. A good example suitable for this printing technology is a metal printer based on StarJet (see patent US 8877145B2). A suitable example of an FFF dispenser is described in Krishnanand et al.

[10] . The two printheads can subsequently and independently deposit the two materials layer by layer as described above.

[0197] like Figure 7 As shown, the non-conductive structure 4 is first laid on the building board 20 and configured to create grooves and recesses on its upward-facing surface. These grooves and recesses are then filled with molten metal to form the conductive element 2, which is adapted to the shape of the grooves and recesses, as shown in another figure, thereby forming a stable integral structure. The non-conductive structure 4 preferably encloses and isolates the conductive element 2 from at least three sides, preferably leaving only the initially exposed upper side for electrical connection. Subsequently, the conductive element 2 can be completely enclosed by adding another layer of non-conductive material, thereby completely isolating the conductive element 2. This embodiment is suitable for rapid prototyping of PCB boards for subsequent assembly of electronic components.

[0198] Figure 7 Variations of the printing apparatus include an additional pick-and-place head (e.g., a pneumatic gripper) mounted on the same or a different x, y, or z-axis platform as the print head. The pick-and-place head picks up SMD components from a tray and places them on the printed surface (adhesive can be applied before placement to improve SMD component adhesion). Using such an apparatus, 2.5D printed PCBs or any other 3D printed electronic models with SMD components directly integrated internally can be manufactured fully automatically. This embodiment requires neither post-processing of the printed sample nor assembly of any electronic components after the printing run. Furthermore, this embodiment is suitable for situations where the complexity of the design and / or the limited available space due to component enclosure density prevents the formation of electronic interconnects after the printing apparatus has been manufactured.

[0199] Following placement, the SMD components are directly soldered fully automatically during conductive metal trace printing. The non-conductive structures of the printed (3D) electronics can be fabricated using FFF, direct polymer jetting, or any polymer dispensing technique that provides good resolution and feature size for non-conductive components. In the embodiment shown, FFF printing is used. The conductive metal traces are preferably printed via bulk metal printing to ensure direct soldering of the SMD components. Bulk metal printing can take the form of metal droplets or metal jets.

[0200] An advantageous feature of this embodiment is that the metal traces printed directly onto the contact pads require no additional soldering or post-processing steps. In this case, the conductive metal traces form a direct electrical interconnect with the contact pads and SMD components. Experiments have demonstrated that metal traces printed with SAC solder can achieve low-resistance, high-quality electrical connections. The contact pads can be placed anywhere on the printed electronics as needed by the designer. The contact pads can then be connected via the printed metal traces according to the digital design and can be covered with a non-conductive material for protection, or left open for further downstream processing.

[0201] Another feature of this embodiment is that the pick-and-place device includes an in-line camera located on the machine, enabling electronic components to be automatically picked up, aligned, and placed during the layer-by-layer printing sequence. The in-line camera can be used to verify the picked-up objects and their correct placement on the printing platform. The in-line camera can also be used to monitor the printing status to ensure the quality of the printed structure.

[0202] The present invention, and particularly the foregoing embodiments, offers a variety of unexpected advantages. The present invention preferably allows for the fully automated printing of complete and functional electronic components, even those with 3D shapes, arbitrary arrangements of electronic parts inside and outside an object, and multi-layered circuits and interlayer connections. No post-processing of any kind may be required after printing.

[0203] This invention also allows for fully automated prototyping of PCBs with ultra-smooth surfaces, which can then be assembled using SMT technology. Furthermore, the design flexibility of the PCB circuitry includes the possibility of providing multilayer PCBs with locations for contact pads and vias, electronic circuitry on curved surfaces, and more. Manufacturing can be carried out without the use of toxic chemicals known in the prior art. Post-processing of the PCB through heat treatment or electroplating may also become redundant.

[0204] This invention also significantly shortens the production cycle of customer-specific PCBs. Once a concept is ready for the design phase, manufacturing time is preferably unaffected by design complexity. This invention preferably eliminates the need for centralized, large-scale factories for small-scale PCB manufacturing, making it an economical solution. Distributed manufacturing provides additional hardware security and prevents the insertion of malicious chips during electronics manufacturing and transportation, and is sustainable due to shorter transportation distances. Distributed manufacturing also provides additional design and knowledge protection for the circuitry.

[0205] The solution of this invention also allows the entire electronic device—including any housing—to be printed on top of a printed PCB in a single run, thereby reducing the overall production time required to manufacture functional electronic devices. Preferably, lasers or other chemical adhesives are not required to solder SMD components to the printed electronics, as the SMD components can be directly soldered during printing using bulk metal printing technology.

[0206] Figure 8 It schematically shows the following based on Figure 7 The cross-section of the PCB produced using this technology is shown. It can be seen that the metal conductive element 2 is located within a channel sandwiched between layers of the non-conductive structure 4. Therefore, the conductive element 2 is completely electrically isolated. The entire PCB is printed on top of the build board 20 of the printing apparatus, preferably without requiring the PCB to be moved from its initial position on the build board.

[0207] Figure 8 It also shows according to Figure 7 A microscopic scanning image of the cross-section of a PCB produced using this technology. The cross-section of the conductive trace 30 can be clearly distinguished from the surrounding printed polymer 32. In this embodiment, it can be seen that the lower portion of the conductive trace material 30 is relatively flat, thus suited to the shape of the channel bottom formed in the non-conductive structure 4. The upper portion of the conductive trace material 30 is rounded, thus corresponding to a droplet that has solidified before deformation due to the addition of other materials. Therefore, the cross-section of the conductive trace is particularly uniform. Furthermore, it can be seen that there is a tight fit between the conductive trace and the droplet of polymer material printed on top of it, resulting in good isolation of the conductive trace.

[0208] Figure 9 The illustration schematically shows a slightly modified technique and uses... Figure 7The cross-section of the PCB produced by the printing apparatus. In this embodiment, the initial layer of the non-conductive structure 4 is constructed to be generally flat and without channels. Conductive traces 2 are printed on the flat structure of the initial layer of the non-conductive structure 4 located on the build board 20. Optionally, the conductive traces 2 are then connected and / or soldered to the electronic components 6. A layer of additional non-conductive material can then be deposited on top to isolate the conductive traces 2. This technique omits the setting of channels and is therefore potentially faster and / or simpler. From the same diagram shown Figure 9 As can be seen from the cross-sectional scan image, the cross-section of the conduction trace 30 remains consistent with... Figure 8 A similar form is shown. However, the non-conductive material paths are more densely packed around the conductive traces.

[0209] Figures 10 to 12 Another example of a PCB manufactured according to another preferred embodiment of the present invention is shown. Figure 10 An exploded view of the different layers of a multilayer electronic device housed within a printed structure is shown schematically. Figure 11 A photograph of the same device produced experimentally is shown. Figure 12 It shows the built-in Figure 10 and Figure 11 The electronic circuitry within the device. The entire device is printed "at once" on a single build plate 20 of the printing device.

[0210] like Figure 10 As shown, the electronic device includes a first dielectric layer 42 configured as the base of the device. The first dielectric layer 42 has channels and recesses configured to accommodate first-layer conductive traces 40. The first dielectric layer 42 is first printed, and then molten metal is deposited as droplets into the channels to form the conductive traces 40. Vias 12 are also provided in the first dielectric layer 42 and remain free of molten metal. The molten metal deposition process is configured such that the droplets are cooled between release from the first printhead 22 and deposition on the first dielectric layer 42. This prevents deformation of the first dielectric layer 42. Electronic components, such as LED 78, are then placed in the recesses of the first dielectric layer 42 to contact the conductive traces 40. Additional conductive materials can be added to increase the mechanical stability and connectivity of the electronic components. The conductive traces are arranged to be accessible at one end of the device, which is configured to receive power via a USB A connector.

[0211] This process is then repeated by printing an additional dielectric layer 38, including additional channels, followed by printing additional conductive elements 36. The cured dielectric layer 38 and conductive elements 36 are then covered with an upper cover 34 of the device, which in this example is printed from the same polymer material as the dielectric layer. Thus, the circuitry is completely enclosed within a fully assembled device having its final shape.

[0212] The device was produced experimentally, such as Figure 11 As shown, it is connected to a power source via a USB cable. The operation of the circuit can be observed.

[0213] Example The present invention is further described by way of the following examples. These examples are not intended to limit the scope of the invention, but rather represent preferred embodiments of various aspects of the invention to provide a more complete description of the invention as described herein.

[0214] Example 1: Printing device "Synkrótima" — Figure 13 As an exemplary embodiment of the present invention, a printing device has been developed. This printing device is named "Synkrotima" and is shown in [the image / description]. Figure 13 And will be described below.

[0215] The open-source desktop printer Original Prusa i3 MK3 (Prusa Research, Czech Republic) was chosen as the base for the Synkrótima, to integrate StarJet printheads for hybrid printing. See [link to Synkrótima]. Figure 13 The Original Prusa i3 MK3 offers advantages such as low cost, mature technology, ease of operation, good spare parts availability, and an open and customizable system. For printer customization, computer-aided design (CAD) models and controller board schematics are available from an online repository [P37].

[0216] Figure 13 (a) shows a CAD model (top view) of the initial desktop printer before the integration of additional StarJet printheads. Figure 13 (b) shows the CAD model after mechanical integration of the StarJet printhead 22. The hardware is designed to ensure that the StarJet printhead 22 moves along the x and z axes, while the build plate moves along the y axis. The StarJet printhead 22 is integrated alongside the FFF printhead 24 by modifying the single default x-axis 3D printer setting to a dual x-axis setting.

[0217] The FFF extruder has a main body, primarily constructed from 3D-printed plastic parts, making it lightweight. In contrast, the StarJet printhead 22's main body is made entirely of stainless steel, and after a lightweight redesign, its main body weighs only 786g. Therefore, Figure 1 The dual x-axis design shown in (c) redistributes the weight of the additional StarJet printhead 22 and stabilizes movement along the x and z axes. This improves controllability and shape fidelity.

[0218] The 3D-printed parts (made of PETG) from the Prusa printer have a heat distortion temperature (HDT) of 68°C at 0.46 MPa [P38], while the StarJet 22's operating temperature is fixed at 320°C. Therefore, in addition to mechanical stability, thermal management is also preferred for hybrid integration; see [link to relevant documentation]. Figure 1 (c) The materials used to attach the StarJet printhead 22 to the 3D printer were appropriately selected to dissipate the heat of the StarJet printhead to a temperature below its heat distortion temperature of 68°C before the heat from the StarJet printhead reaches the plastic part of the Prusa printer. These attachment materials include a PEEK sheet 48 and 3D-printed glass fiber-filled polyamide-6, as well as a thermal break component 46. The effectiveness of the thermal management was tested by heating the StarJet printhead 22 to 450°C for over 8 hours. The temperature at the plastic part of the Prusa printer was then measured, and it was found to be below the heat distortion temperature of the material.

[0219] Figure 13(d) further illustrates the control mechanism of the Synkrótima printer, which should be understood in conjunction with the reference numerals further elaborated herein. Since the Synkrótima operates as a single platform with two extruders (or simply printheads) for printing, an upgrade from the Prusa single extruder microcontroller board EinsyRambo 1a was provided to integrate the StarJet printhead 22 as an additional extruder (printhead). For this purpose, the new open-source microcontroller board RUMBA+ [P39] 62 was chosen because it supports multiple extruders and is fully open-source for easy customization. The FFF printhead is assigned "Extruder 1," while the StarJet is assigned "Extruder 2." Although the two printheads 22, 24 integrated into the Synkrótima have different printing principles, the control of the two printheads 22, 24 is accomplished through a single RUMBA+ motherboard 62 to keep the slicing method of the 3D printer simple in the future and without requiring any additional user intervention. To integrate the StarJet printhead 22 and enable it to function as an extruder 2, an Arduino 64 and a MOSFET-based control device 58 are positioned between the RUMBA+ 62 and the pneumatic valve of the StarJet printhead. The Arduino board 64 controls the operating parameters of the StarJet printhead 22 and also converts the extrusion signals from the RUMBA+ board 62 to turn the StarJet printhead on and off accordingly.

[0220] As a result, the Synkrótima hybrid printer was developed, which includes two printheads 22 and 24 with two different additive manufacturing operating principles, thereby printing two materials sequentially layer by layer. The maximum print volume for hybrid printing of electronics in all directions (x-axis, y-axis, and z-axis) is 50 mm x 200 mm x 200 mm in this prototype.

[0221] After integration, the offset between the FFF polymer extruder 24 and the StarJet molten metal printhead 22 is calibrated. The calibration method involves printing metal onto the edge of an L-shaped polymer frame that has previously been printed by the FFF extruder.

[0222] Example 2: Hybrid Printing Calibration — Figure 14 Before adding the StarJet printhead 22 and after setting up the printing apparatus to create Synkrótima, the printing apparatus was used to print a non-conductive model to study the impact of the changes on the non-conductive printing performance.

[0223] The resulting device was characterized by evaluating any changes in the printing performance of the FFF printer caused by the addition of the StarJet printhead 22. Figure 14 The results show that the polymer printing, characterized by optical methods, exhibits almost no change, while the values ​​measured by vernier calipers show a standard deviation of 258 µm in the x and y axes compared to the model printed by the Original Prusa i3 MK3. For small feature models printed on Synkrótima using FFF, no loss of print quality was observed due to the additional weight of the StarJet 22 and its fasteners.

[0224] Example 3: Layer height printed using Synkrótima — Figure 15 One of the main challenges of using two different printing methods on a single platform is the difference in resolution, either in the height of printable layers or in the vertical direction. Roach [P13] observed this resolution difference when using aerosol printing for conductive traces, where the line thickness was approximately 10 µm. For each layer printed from the polymer (with FFF layer heights ranging from 150 µm to 250 µm for a standard 400 µm nozzle), more than 20 runs were required to eliminate the layer height difference between the conductive and non-conductive materials.

[0225] However, using Synkrótima, the conductive traces are printed at a layer height comparable to that of the polymer. Therefore, the conductive traces and polymer can be printed layer by layer without requiring multiple runs to compensate for the layer height differences, as seen in Roach [P13]. This allows for sequential printing of the polymer and conductive traces, similar to multimaterial printing on FFF via polymer filaments, without any modification to the machine code. An example of a hybrid model printed with the IMTEK logo (see...) Figure 15 (c) in which the IMTEK characters are printed via the StarJet printhead. This allows for a roughly uniform article thickness without the need for multiple layer runs as in existing technologies.

[0226] Example 4: Droplet deposition The StarJet printhead 22 was further characterized using a stroboscopic setting that captured images of molten metal droplets 76 to determine volume and positional deviations. Stroboscopic characterization was used for drop-on-demand (DoD) to investigate the range of parameters within which the StarJet printhead was most stable and capable of producing stable solder droplets with repeatable results. This method and the corresponding settings can be further understood in conjunction with previous publications [P36, P49].

[0227] On-demand droplet printing was observed at frequencies of 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 40, and 50 Hz to characterize droplet stability. Droplets were considered stable when their positions remained consistent and no satellite droplets were present. For each frequency, the operating parameters of the StarJet printhead 22 (i.e., flushing pressure, actuation pressure, and valve opening time) were adjusted to achieve the minimum coefficient of variation (CV) of droplet volume, zero satellite droplets, and no missing droplets in over 5000 consecutive droplet ejections. The results clearly demonstrate the high stability of the StarJet printhead 22 in printing single molten metal droplets. For speed and stability, an operating frequency of 18 Hz was selected for conduction feature printing using a pulsed pneumatic technique. Pulsation was achieved by opening a solenoid valve to release nitrogen. The final parameters for the StarJet system included: actuation pressure 94 mBar, flushing pressure 108 mBar, valve opening time 14 ms, and reservoir temperature 320°C.

[0228] Experiments show that the droplet size is highly uniform and the droplets solidify rapidly after merging to form continuous conductive traces 2 on the non-conductive structure 4.

[0229] The accuracy and repeatability of Synkrótima's molten metal printing were further evaluated using five parameters: 1. Consistency of fixed droplet placement measured by means of consistent droplet spacing between droplets; 2. The uniformity of the diameter of the fixed droplets; 3. The droplet's deviation along the x-axis and y-axis; 4. Shear resistance of a single fixed droplet.

[0230] Example 5: Droplet spacing, uniformity, deviations on the x and y axes, shear resistance To evaluate the consistency of droplet spacing in the printed droplets, a series of individual solder droplets were printed with a set droplet spacing of 1500 µm. Furthermore, the adhered droplets were spaced sufficiently apart to be necessary for evaluating deviations along the x and y axes. The aforementioned parameters (parameters 1 to 4 in Example 4) were evaluated on the printed droplets using the imaging software ImageJ. For image analysis, a set of two droplets was selected in an image frame, and the diameter of the printed droplets, the droplet spacing between the droplets, and the deviations of the droplets from each other in the x and y planes were measured.

[0231]

[0232] Table 1: Printing accuracy of StarJet printing 50 droplets with a droplet spacing of 1500µm. The values ​​shown in the table are the average measurements of the 50 printed droplets. An uncertainty of ±10µm in the measurement must be considered. The percentage deviation on the x-axis is a small 0.02%, while the relative percentage deviation on the y-axis is 1.9%.

[0233] Table 1 shows the average values ​​of droplet diameter, droplet spacing, and deviations in the x and y planes obtained from image analysis of 50 bonded solder droplets. The average diameter of droplets printed using a 183µm nozzle chip was 288µm. The coefficient of variation (CV) for the measured droplet diameter was 0.05%. The percentage deviation in the y-plane was a mere 0.02%, while the relative percentage deviation observed in the x-plane was 1.9%. The print accuracy measured based on the set droplet spacing and the measured droplet spacing was a perfect 99.86%. Therefore, the first three parameters used to evaluate the performance of the StarJet printhead present promising results.

[0234] To evaluate the fourth parameter, shear strength was assessed on individual solder droplets to provide a preliminary understanding of their adhesion to the polymer surface. For this analysis, samples with 40 solder droplets printed on them were prepared. This quantification was performed using a Dage4000 adhesion tester. A chisel-shaped tool was placed at a shear height of 20 µm relative to the substrate. A DS100KG cartridge module measured the force at the tool at a speed of 250 µm·s. - ¹Speed ​​movement. The average shear strength obtained by printing a single solder droplet on a polymer substrate is 1800 mN.

[0235] Example 6: Cross-sectional area and aspect ratio — Figure 16 For conductive traces in additive manufacturing, achieving low resistance is advantageous for applications in printed electronics (PE) and 3D electronics. One approach is to use metals with inherently high conductivity, such as silver (1.59 × 10⁻⁶). -8 Ωm) and copper (1.72×10 -8 One approach is to additively fabricate electrical traces with high cross-sectional areas (Ωm), thereby reducing overall resistance. This section details how to form high aspect ratio lines with high cross-sectional areas (linewidths similar to "Voxel8," see p. 20), which offer significant advantages in terms of low resistance and layer height compatibility with FFF technology. The ability to fabricate high aspect ratio (width / height) electrical traces opens up possibilities for printing large-area 3D electronics.

[0236] For in-flight solder droplets released non-contactly from StarJet printhead 22 (see...) Figure 16 (a) in the aqueous medium (see Figure 16 (b) of the above, printed on a PET-G substrate via FFF printhead 24 (see [reference]). Figure 16 (c) in the middle), and as a cross-section of the metal traces printed on the PETG substrate (see Figure 16 (d) in the evaluation assessed the shape fidelity of the molten metal droplets. The droplet diameter varied by approximately 12 µm in air and water. When printed on a PET-G substrate, the droplets spread across the surface with a contact angle of approximately 93 degrees. The aspect ratio of a single droplet printed on the PET-G substrate was approximately 0.7. Therefore, the molten metal droplets printed on the PET-G substrate exhibited an aspect ratio (greater than 0.1) while maintaining a contact angle close to 90 degrees (a contact angle below 90 degrees is considered a good wetting angle); see [reference needed]. Figure 16 (c) The cross-section of the metal trace printed on PETG shows a height-to-width ratio of 0.8, see (c). Figure 16 (d) in the middle.

[0237] The high cross-sectional area of ​​conductive traces helps to understand how closely they resemble bulk materials in terms of internal structural density, which can be observed from FIB cuts performed on electrically conductive metal traces printed on a PET-G substrate. The lateral dimension of the FIB cuts is kept greater than 280 µm (the diameter of the molten metal droplets) to examine the internal structure at the intersection of two molten metal droplets.

[0238] Example 7: Resistance and morphology of conduction traces – Figure 17 The seamless merging of molten metal droplets—see Figure 17—leads to conformal conduction pathways.

[0239] Electrically conductive traces preferably have low resistance to ensure the application of multimaterial additive manufacturing in 3D electronics. Synkrótima has ingeniously facilitated this transition by printing conductive traces with a resistance 12 times lower than existing techniques using nanoparticle-based inks [P40].

[0240] To print conductive traces, the molten metal droplets dispensed from StarJet preferably coalesce to form straight lines with smooth edges. Any bumps or necking will result in a sudden decrease or increase in the cross-sectional area of ​​the line, thus affecting the resistance.

[0241] To evaluate the effect of droplet spacing, samples of solder droplets printed on polymer substrates with different droplet spacings were prepared. Since the average droplet diameter achieved was 288 µm, droplet merging began at a droplet spacing of approximately 250 µm, smaller than the droplet diameter, allowing droplets to overlap and form lines. Therefore, the maximum droplet spacing was experimentally set at 250 µm, while the minimum was kept at an exaggerated value of 80 µm. The different droplet spacing values ​​used in this section are: 250 µm, 200 µm, 150 µm, 100 µm, and 80 µm. The printed samples included solder structures with different droplet spacings in both single-solder-line and dual-solder-line configurations (one line stacked on top of another). A dual-solder-line evaluation was performed by comparing the results of single-solder-line and dual-solder-line configurations, thus assessing the enhancements that could be provided to the solder structure's performance. This evaluation was based on morphology, adhesion, and electrical properties. Each variant included a group of 20 samples. Subsequently, each sample was measured three times, resulting in a total of 60 measurements for each box plot. Shear strength and electrical resistance were then performed on the same sample group.

[0242] Figures 17(a) and (b) show microscopic top views of the printed circuit structures with the aforementioned droplet spacing for both single-line and dual-line applications. It can be observed that the smaller the droplet spacing, the less irregular the shape of the printed circuit. Therefore, a smaller droplet spacing is preferred for printing well-formed solder lines. The minimum droplet spacing is preferably 100 µm. At droplet spacings greater than 100 µm, the printed metal traces do not form self-supporting structures because the droplets remain sufficiently close to each other.

[0243] The solder linewidths of single and dual solder lines printed on polymer substrates with different droplet spacings were examined, and the results are plotted in Figure 17(c). For linewidth measurements, microscopic images captured at six different cross-sections of the printed solder lines were evaluated by performing 10 measurements on each image. Therefore, each data point below corresponds to 60 measurements. For both single and dual solder lines, a linear decrease in linewidth was observed. The smaller the droplet spacing of the solder lines, the closer the printed droplets are to each other, resulting in greater fusion between the droplets and wider, smoother printed lines.

[0244] The resistance of conductive lines was measured using a 4-wire resistance measurement method with an Agilent 34401A instrument. All measurements were performed at room temperature. To reduce noise during measurements, the 4-wire measurements were performed at a high current of 3 amps. A standard electrical probe with square pads was used to contact the printed metal traces.

[0245] The resistance variation of the printed conductive traces was affected by the droplet spacing variation, starting from 250 µm, as shown in Figure 17(d). Excellent conductivity was also observed for lines printed with droplet spacings of 80 µm and 100 µm. As expected, conductivity decreased linearly with increasing droplet spacing value. Since it was determined that lines printed with a droplet spacing of 80 µm could form suspended structures, a droplet spacing of 100 µm was the preferred value for sample production, showing 70% higher conductivity compared to the bulk solder material SAC305.

[0246] As a further evaluation, the adhesion performance of lines printed at different droplet spacings was analyzed, which was assessed by shear resistance testing. Figure 17(e) shows the shear resistance measured for single-solder and dual-solder lines at the aforementioned droplet spacings. The obtained shear resistance ranged from 6 N to 16 N. Higher shear resistance was observed for dual-solder lines. The linewidth of dual-solder lines is larger than that of single-solder lines, so it is reasonable that the shear resistance required to break a portion of a dual-solder line is higher than that of a single-solder line. However, for dual-solder lines, the shear resistance remained approximately the same across all droplet spacings, while a decreasing trend in shear resistance was observed for single-solder lines. In conclusion, since the variation in shear resistance was minimal in both single-solder and dual-solder lines, shear resistance measurement does not appear to play a significant role in the selection of droplet spacing for line printing experiments.

[0247] For single solder lines, lines with a droplet spacing of 100 µm exhibited an average shear strength of 7.20 N, which is higher than the shear strength obtained by other droplet spacing variations. Overall, based on experience, lines with a droplet spacing of 100 µm are considered to provide the most suitable results in terms of solder line morphology, adhesion, and electrical properties. Therefore, a droplet spacing of approximately 100 µm is preferred for further hybrid printing experiments.

[0248] Example 8: Conductive traces are independent of non-conductive construction orientations — Figure 18 To keep the process as simple as possible in multi-material additive manufacturing, thereby enabling greater design freedom and applications, preferably, the printed polymer layer does not affect the printing of conductive metal.

[0249] Figure 18The illustrations of the polymer paths and electrically conductive traces define the different build orientations (0°, 45°, and 90°) examined in this example. Each variant includes a population of 20 samples. Subsequently, each sample underwent three measurements, resulting in a total of 60 measurements per box plot. Here, build orientation refers to the different orientations of the electrically conductive traces built onto the printed polymer layer. The effects of electrically conductive traces printed on a polymer substrate with different build orientations can impose design or slicing constraints on the 3D model. Therefore, the effects of different build orientations on the shape fidelity and resistance of the electrically conductive traces were tested by measuring linewidth and resistance per millimeter. The 3D model was fabricated by placing the electrically conductive traces at different polymer grating angles (see [link to 3D model]). Figure 18 The illustration (blue) is shown in the image. For clarity, an illustration of the construction orientation between polymer 4 and electrical conductivity trace 2, along with an image of the actual sample, is added. Figure 18 The graph shows the resistance per millimeter and linewidth (N=60) at different build orientations.

[0250] The standard deviations of the linewidths at 0°, 45°, and 90° are 19.0µm, 14.9µm, 10.3µm, and 12.9µm, respectively. Simultaneously, the standard deviations of the resistance per millimeter at 0°, 45°, and 90° are 1.1mΩ, 1.5mΩ, 1.0mΩ, and 0.96mΩ, respectively. Therefore, based on the above results, the influence of build orientation on the shape fidelity and resistance of the electrically conductive traces is less than 10% and has minimal impact on the additive manufacturing of conductive metal traces. One possible reason for this result is that the metal droplets at least partially melt the polymer path, resulting in a less corrugated structure. The observed deviations can be further minimized by using a higher resolution polymer printer, thereby reducing surface roughness. The independence of the electrically conductive traces on the build orientation of the polymer path makes this method robust for any free-form 3D printing of electrically conductive traces embedded in polymer substrates in the future.

[0251] Example 9: Mixed print code generation Another aspect of the one-stop printing method involves generating a single machine code—often called G-code—for hybrid 3D printing. The G-code file for a 3D printer consists of the position of the model to be printed and extrusion parameters, as well as control segments for heating and cooling operations. The G-code file is generated by slicing the standard trigonometric language (STL) file of the desired 3D CAD model into different layers using software (in this case, Prusa Slicer Edition v1.40.1, Prusa Research, Czech Republic). However, to enable the machine to distinguish between the parts of the model to be printed by the FFF 24 and those to be printed by the StarJet printhead 22, the printheads for the different printing parts are declared in the slicing software. This declaration process includes the following steps: • Step 1: Design the CAD model of the hybrid part as a CAD component containing the polymer part and the electrically conductive part. Then save these two parts as two different STL files, namely, polymer and metal, see [link to documentation]. Figure 15 (a) in the diagram. This is indicated by the separate non-conductive structure shown in the CAD interface.

[0252] • Step 2: Create a hybrid slicing file simulating multi-material printing on the Prusa slicing software, where the FFF printing parameters are saved as Extruder 1 and the StarJet printing parameters are saved as Extruder 2.

[0253] • Step 3: Import the two STL files into the hybrid slice file, where Extruder 1 is assigned to print the polymer portion and Extruder 2 is assigned to print the conductive portion. See [link to relevant documentation]. Figure 15 (b) in the middle.

[0254] The input hybrid model is then sliced, and the generated G-code is sent to Synkrótima. To ensure reliable results, an active step of preparing both printheads is taken before the first print. This preparation involves moving the printheads outside the designated printing area so that they can dispense a certain amount of material; this is known as pre-filling the printheads. Therefore, through this integration and method, hybrid 3D models can be printed directly without any post-processing of either the polymer or conductive materials.

[0255] In the following example, a sample is printed on a Synkrótima using multimaterial additive manufacturing. The print height between the StarJet printhead nozzle 22 and the build plate 20 or substrate surface is 4 mm.

[0256] Example 10: Sample circuit including LEDs — Figure 19 Examples of hybrid 3D models were printed to demonstrate the potential of the developed Synkrótima platform. First example – see [link / reference]. Figure 19 (a) and (b) in the diagram illustrate a hybrid model where, using a method targeting... Figure 7 The described concept involves printing meandering conductive traces 2 with contact pads 16 in polymer grooves, which are then covered by a polymer layer. In this hybrid model, five sections (two contact pads, two grooves for electronic components, and one groove for the curved trace) are left uncovered for performance evaluation.

[0257] In this test model (30×40×4 mm), a loop for the conductive traces was designed, which included bending the solder traces into bends with a radius of curvature of 2250 µm. The printed solder lines had a linewidth of 350 µm and a conductivity of 2.25 × 10⁻⁶. 6 Sm - ¹. The traces were printed in a grooved polymer structure and further covered with polymer to form a sealed hybrid structure. Two electronic components—a 1000Ω SMD resistor (size 0603) and an SMD blue LED 78 (ROHM Semiconductor, size 0603, 470 nm)—are directly interconnected via the printed solder lines (see [link to documentation]). Figure 19 (d) in the middle.

[0258] The workflow for hybrid printing of this test model is described below: 1. Using the slicing software as described in Example 9, generate G-code for dual extruder printing.

[0259] 2. Insert a delay in the G-code to manually place the electronic components before printing conduction trace 2 to the intended layer.

[0260] 3. When Synkrótima is in pause mode, pick up and place electronic component 6 at the designated location.

[0261] 4. Printing is resumed via software, the second extruder (StarJet printhead 22) is activated and prints the conduction traces, and the electronic components 6 are directly interconnected to the rest of the circuit.

[0262] 5. Switch to the first extruder (FFF) 24 to print polymer and cover the printed conductive solder traces 2.

[0263] This example demonstrates the rapid production of fully functional electronic devices in a single printing unit.

[0264] Example 11: Sample circuit containing LEDs and surface traces — Figure 20 See Figure 20 Another example illustrates the following hybrid 3D model: conductive traces and a blue LED 78 are fully embedded within polymer layer 4, while contact pad 16 is exposed for power input. A CAD model was fabricated where grooves are provided in the initial layer, and the SMD LED 78 is embedded in polymer layer 4, allowing the conductive traces 2 to extend and contact the pad 16, thereby increasing the ability to test LED functionality. After several layers of polymer 4, an attempt was made to print a 3D structure via the StarJet printhead 22 to demonstrate StarJet's printing performance in printing 3D metal structures. A step-by-step description of the printing process is provided below. Figure 20 As shown in (a) to (d), the order of the parts printed on Synkrótima is displayed layer by layer via slicing software. Figure 20 (a) shows a model with a layer height of 1.7 mm, where the polymer grooves have been fabricated and molten solder droplets are being printed at this layer height. The lines formed by the aggregation of molten solder droplets are highlighted in blue and printed by extruder 2 (StarJet), while the polymer is rendered in yellow and printed by extruder 1 (FFF). After this layer, a delay is provided in the G-code, at which point the machine stops printing and pauses. An LED is placed... Figure 20 At the location marked by the red circle in (a) in the image, then resume printing. Figure 20 (b) shows a model with a layer height of 2.7 mm, where solder traces and LEDs are covered by a polymer layer. A small opening is left at the base of the structure for the contact pad 16. The StarJet printhead 22's ability to print 3D structures via molten solder droplets is... Figure 20 This is reflected in (c) to (e).

[0265] Figure 20 (e) shows a fully functional hybrid print model featuring working LED78 and a three-dimensional structure printed from molten solder droplets. Because the PETG polymer is translucent, the LEDs and solder traces embedded within the polymer structure are clearly visible under light, as shown in Figure (e). Figure 20 As shown in (f), the LED is positioned at a height of 1 mm above the top surface of the polymer. When power is applied to the contact pad, the embedded LED 78 exhibits full functionality, as can be seen in… Figure 20 (e) in the middle. Figure 20The 3D protruding letters printed on top of the model in (e) demonstrate the printer's ability to extend in the third dimension. Advantageously, surface mount devices can also be integrated with semiconductor electronics to create fully printed functional electronics, thereby eliminating any assembly or enclosure steps. Furthermore, since the devices in Examples 10 and 11 are printed using bulk metal, post-processing steps such as sintering to fix the conductive traces are not required.

[0266] Figure label: 2. Conduction trace 4. Non-conductive structure 6. Electronic components 8. Back side of the PCB 10. Front and side views of the PCB 12. Vias 14. Fixtures used for scanning electron microscopy imaging 16. Conductive contact pad 18. Silk material 20. Printing bed / build board 22. First printhead 24. Second printhead 26. Toolpath 28. Passage 30. Cross-section of printed conductive traces 32. Cross-section of the printed polymer 34. Top cover of a 3D PCB assembly 36. Second layer of conduction traces 38. Second dielectric layer 40. First layer of conduction trace 42. First dielectric layer 44. Fasteners used for thermal management 46. ​​Thermal fracture element 48. PEEK board 50. Install fasteners 52. Trigger for valves 56. Flyback diode 58. MOSFET switching module 60. Optical coupler 62. Rumba+ Microcontroller Board 64. Arduino UNO board 66. Output from the extruder 68. Grounding wire 70. The Line of Fire 72. Lead spool 74. Solenoid valve 76. 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Claims

1. A method for additive manufacturing of electronic circuits, Its features are, The method includes the following steps: A printing apparatus is provided, the printing apparatus comprising: a construction plate (20); a first print head (22) configured to print molten conductive metal; and a second print head (24) configured to print non-conductive material; The electronic circuit is printed by using the first printhead (22) to print the conductive element (2) from the molten conductive metal and by using the second printhead (24) of the printing device to print the non-conductive structure (4).

2. The additive manufacturing method for the electronic circuit according to the preceding claim, Its features are, The method includes the following steps: a.) Printing a non-conductive structure (4) using the second printhead (24) of the printing device; and printing a conductive element (2) onto the non-conductive structure (4) using the first printhead (22) of the printing device, or b.) The conductive element (2) is printed using the first print head (22), and the non-conductive structure (4) is printed onto the top of the conductive element (2) using the second print head (24) of the printing device.

3. The additive manufacturing method for the electronic circuit according to any one of the preceding two claims, Its features are, The conductive element (2) includes conductive traces, conductive pads, conductive solder, and / or conductive interconnects.

4. The method according to any one of the preceding claims, Its features are, The method further includes the following steps: A base sheet is provided on the construction board (20), and then the conductive element (2) is printed onto the base sheet. The non-conductive structure (4) is then printed onto the conductive element (2) to enclose the conductive element (2) between the non-conductive structure (4) and the base sheet, and Optionally, the base sheet may be removed after the non-conductive structure (4) has been printed.

5. The method according to any one of the preceding claims, Its features are, Before printing the non-conductive structure (4) and / or the conductive element (2), the printer's build plate (20), print bed, and / or base sheet are preheated.

6. The method according to any one of the preceding claims, Its features are, The method further includes the step of placing an electronic component (6) at a predetermined position on the conductive element (2) and / or the non-conductive structure (4) printed using the second printhead (24), wherein the placement is performed manually or by means of a pick-and-place robot head, preferably the pick-and-place robot head being part of the printing apparatus. Optionally, adhesive is applied to the electronic component (6) or to the predetermined location before the electronic component (6) is placed at the predetermined location.

7. The method according to any one of the preceding claims, Its features are, At least a portion of the conductive element (2) is printed onto a non-conductive structure (4) including the positioned electronic component (6) by molten metal to weld, and / or electrically contact, and / or mechanically stabilize the electronic component (6) onto the electronic circuit.

8. The method according to any one of the preceding claims, Its features are, The non-conductive structure (4) is printed such that grooves (28) and / or recesses are formed on the surface of the non-conductive structure, the grooves (28) and / or recesses being configured to accommodate conductive elements (2) and / or electronic components (6), for example, the conductive element (2) being a conductive trace, and Preferably, the conductive element (2) is printed at least partially such that the conductive element (2) is inserted into the groove (28) and / or the recess.

9. The method according to any one of the preceding claims, Its features are, The method includes repeating the following steps: printing the conductive element (2) from the molten conductive metal using the first printhead (22), and printing the non-conductive structure (4) using the second printhead (24) of the printing device to enclose one or more layers of conductive elements in the conductive element (2) between any number of non-conductive structures (4), wherein, optionally, electronic components (6) are placed at predetermined positions between consecutive non-conductive structures (4).

10. The method according to any one of the preceding claims, Its features are, Printing the conductive element (2) includes the following steps: releasing molten metal droplets (76) from the first printhead (22) onto a surface, wherein the droplet diameter and / or the distance from the nozzle of the first printhead (22) to the surface is selected such that: the molten metal droplets (76) are at the nozzle at a temperature higher than the melting point of the molten metal droplets (76), and the molten metal droplets (76) are at a temperature approximately equal to or less than the melting point of the molten metal droplets (76) when they reach the surface.

11. The method according to any one of the preceding claims, Its features are, Printing the conductive element (2) includes the following steps: releasing molten metal droplets (76) from the first print head (22) onto the surface, wherein a cooling mechanism is provided for actively cooling the molten metal droplets located on a trajectory between the first print head (22) and the surface, preferably the cooling mechanism is based on nitrogen.

12. The method according to any one of the preceding claims, Its features are, The conductive element (2) is printed by on-demand droplet deposition, wherein the distance between droplets is less than the average droplet diameter, and the distance between droplets is configured such that consecutive droplets fuse together. Preferably, the average droplet diameter is between 50µm and 400µm, more preferably, the average droplet diameter is between 250µm and 300µm, and the droplet-to-droplet spacing is between 80µm and 250µm.

13. A printing apparatus for additive manufacturing of electronic circuits by the method described in any one of the preceding claims. Its features are, The printing device includes: Construction board (20); A first printhead (22) is configured to print a conductive element (2) from a provided molten conductive metal. The second printhead (24) is configured to print a non-conductive structure (4) from a dielectric material.

14. The printing apparatus according to the preceding claim, Its features are, The printing apparatus further includes a pick-and-place robot head, preferably configured to place electronic components (6) at predetermined locations on the printed non-conductive structure (4) and / or the printed conductive element (2) and / or the build plate (20). Preferably, the printing device further includes an online camera configured to verify the pickup and placement of the electronic component (6), and / or the online camera is configured to monitor print quality.

15. The printing apparatus according to any one of the preceding two claims, Its features are, The first print head (22) and / or the second print head (24) are movable relative to the build plate (20) in the z-direction, and / or The build plate (20) is movable in the z-direction relative to the first print head (22) and / or the second print head (24).

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