Inverted patch component melting solder direct write circuit printing method

Abstract

This invention relates to the fields of 3D printing technology and additive manufacturing technology for electronic circuits, specifically to a method for printing circuits by direct writing circuitry using molten solder on inverted surface mount components. The method includes: Step S1, printing a contoured positioning groove with the opening facing downwards and the bottom of the groove facing upwards, featuring elastic clips, and a through-hole extending upwards from the bottom of the contoured positioning groove; the surface mount component is inverted and embedded into the contoured positioning groove, secured without adhesive by the elastic clips, with the surface mount component contacts facing upwards and aligned with the lower end of the through-hole; Step S2, printing an insulating base surface with a stress-relieving structure, the insulating base surface having a through-hole penetrating the through-hole, and the through-hole being provided with an insulating perimeter; Step S3, forming gravity-bonded molten solder pillars and directly writing the circuitry; Step S4, non-contact insulating encapsulation; Step S5, post-processing after thermal collapse. This invention solves the problems of existing desktop circuit prototyping technologies, such as inability to adapt to surface mount components, inability to stack multiple layers, need for manual intervention, low reliability, and high cost.

Description

Technical Field

[0001] This invention relates to the fields of 3D printing technology and additive manufacturing technology of electronic circuits, specifically to a method for printing circuits by direct writing of molten solder on inverted surface mount components. Background Technology

[0002] In the context of rapid iteration in AI hardware, software functions can be updated in minutes, while the manufacturing efficiency of hardware prototypes lags significantly. Traditional printed circuit board (PCB) manufacturing involves a full-process industrial procedure: circuit design → Gerber file export → factory order placement → film production → copper plate etching → electroplating through holes → solder mask printing → character silkscreen printing → molding and cutting → logistics delivery. Whether it is single-piece prototyping or small-batch production, it must be outsourced to professional PCB factories. This has limitations such as long cycle time, high minimum order quantity, high unit cost, strict design document requirements, and the need to remake the PCB for modifications. It cannot keep up with the iteration speed of AI software and has become a major bottleneck for AI hardware innovation.

[0003] To compensate for the inefficiencies of factory PCB fabrication, existing desktop circuit prototyping solutions all have significant technical limitations, especially in their inability to adapt to the current trend of full surface mount and miniaturized packaging commonly used in AI hardware:

[0004] Temporary mounting solutions such as breadboards and perforated boards can only achieve simple through-hole component circuit verification, and suffer from problems such as unreliable contact, significant signal interference, messy wiring, inability to solidify and mold, and bulky size. Furthermore, they only support through-hole components and are completely incompatible with the mainstream surface-mount packaging of AI hardware, making them unsuitable for use as formal prototypes.

[0005] Conductive plastic / conductive ink printing solutions: Conductive PLA consumables based on FDM technology have resistivity exceeding 10 Ω·cm, enabling the transmission of only weak GPIO level signals. This fails to meet the power supply, high current transmission, and stable communication requirements of AI hardware. Inkjet conductive ink printing devices, such as the Voltera V-One, cost over 20,000 yuan per unit, and the cost of conductive ink consumables is extremely high, limiting their application to industrial laboratories and hindering widespread adoption in home use.

[0006] Existing forward circuit printing solutions employ a top-down forward printing process, requiring surface-mount components to be mounted face-up. This results in fatal problems such as the print head easily scratching already mounted components, solder failing to wet the bottom contacts of surface-mount components, high rates of poor soldering, and easy displacement of components. Furthermore, when the insulating layer is directly covered by the print, it is easy to scratch or burn the molten solder lines, leading to extremely high short-circuit and scrap rates. Some solutions require manual pausing of printing to embed components, making full automation impossible.

[0007] Multilayer surface mount PCB prototypes cannot be realized: Traditional multilayer boards rely on factory electroplating filling processes for interlayer vias, which cannot be replicated by desktop equipment. There is a lack of reliable solutions for vertical conductivity of surface mount components, making it impossible to create multilayer board prototypes that meet the requirements of AI hardware.

[0008] The barrier to home adoption remains insurmountable: existing solutions all require manual calibration, manual soldering, or additional post-processing equipment, failing to form a fully automated closed loop, and thus not meeting the low-threshold usage needs of makers, students, and AI developers with no prior experience.

[0009] In summary, given that AI hardware and software iterations have achieved minute-level response times, there is an urgent need for a circuit printing technology that is 100% compatible with surface-mount components, based on mature consumer-grade FDM technology, requires no factory processing or manual soldering, is fully automated, and has a home-use cost in the thousands of yuan range. This technology would bridge the efficiency gap between AI hardware and software, achieving an integrated closed loop of "AI-generated functionality → instant hardware prototype printing." Existing technologies fail to meet these requirements, resulting in significant technological gaps and market opportunities. Summary of the Invention

[0010] This invention aims to solve the problems of existing desktop circuit prototyping technologies, such as inability to adapt to surface mount components, inability to stack multiple layers, need for manual intervention, low reliability, and high cost, and provides a method for direct writing circuits using molten solder on inverted surface mount components.

[0011] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for direct writing circuits using molten solder on inverted surface mount components, comprising:

[0012] Step S1, Pre-fixing of surface mount components inverted: The FDM insulating printhead prints a contoured positioning groove with the opening facing down and the bottom of the groove facing up, and has elastic buckles, as well as a through hole extending from the bottom of the contoured positioning groove upwards. The surface mount components are inverted and embedded into the contoured positioning groove, and are locked without glue by the elastic buckles. The contacts of the surface mount components face upwards and are aligned with the lower end of the through hole.

[0013] Step S2, Insulating base surface forming: Print an insulating base surface with a stress relief structure. The insulating base surface has a through hole that passes through the through hole, and the through hole is provided with an insulating rim.

[0014] Step S3, Molten Solder Gravity Solder Pillar Forming and Direct Circuit Writing: The solder nozzle extrudes molten solder and fills the through hole from top to bottom using inverted gravity, so that the solder wets the conductive structure below the through hole of the current layer to form a solid vertical solder pillar. Then, the conductive circuit is directly written and fused together with the top of the solder pillar.

[0015] Step S4, Non-contact insulation encapsulation: The FDM insulating nozzle prints an insulating barrier along the conductive line, and prints 2-3 layers of suspended bridging insulation layer with the barrier as support, without touching the conductive line throughout the printing process;

[0016] Step S5, post-heat collapse treatment: Gradient temperature controlled heating is performed to soften and collapse the bridging insulation layer and fully cover the conductive lines, followed by annealing and cooling to form an integrated insulation structure.

[0017] Furthermore, prior to step S1, the following steps are also included:

[0018] Step S0, Dual Nozzle Pre-calibration: Complete the calibration of thermal expansion compensation for the Z-axis height difference between the FDM insulating nozzle and the solder nozzle, the XY plane coaxiality calibration, and the extrusion quantity linkage compensation calibration.

[0019] Furthermore, in step S1, the through hole is a tapered through hole that is larger at the top and smaller at the bottom.

[0020] Furthermore, in step S1, the contour positioning groove corresponding to non-polar surface mount components is a symmetrical positioning groove; the contour positioning groove corresponding to polar surface mount components is an asymmetrical foolproof positioning groove.

[0021] Furthermore, step S2 specifically includes:

[0022] First, print a border-shaped stress relief groove around the edge area;

[0023] Then fill the frame-type stress relief groove with a lightweight honeycomb filler layer;

[0024] Finally, an insulating base body with through holes that penetrate the through holes and an insulating perimeter surrounding the through holes is printed within the area enclosed by the frame-type stress relief groove.

[0025] Furthermore, in step S3, during the printing process, a follow-up cooling seal is used to ensure that the solder is completely cured within a preset time after extrusion.

[0026] Furthermore, in step S4, a filling gap is reserved between the insulating barrier and the edge of the line; a collapse gap is also reserved between the bridging insulation layer and the top surface of the line, and an array of exhaust holes is reserved on the surface.

[0027] Furthermore, in step S5, the gradient temperature control heating adopts a three-stage gradient temperature control:

[0028] Preheating section: Heat at a rate of 2℃ / min to 12℃ below the glass transition temperature of the insulating substrate, and hold at that temperature for 6 minutes;

[0029] Collapsed section: Heat to the glass transition temperature of the substrate +8℃ at a rate of 1℃ / min, and hold at that temperature for 12min;

[0030] Annealing section: slowly cool to room temperature at a rate of 0.5℃ / min.

[0031] Furthermore, the method also includes:

[0032] Step S6, multi-layer stacked printing: For layers 2 to N, execute sequentially:

[0033] Print an insulating base surface with a stress-relief structure. The insulating base surface has through holes arranged according to the current layer circuit layout. The through holes are aligned with the top of the solder pillars or conductive line pads at the corresponding positions in the lower layer. The through holes are provided with insulating edging.

[0034] Then proceed with steps S3 to S5 until the preset number of layers of circuit board printing is completed.

[0035] Furthermore, in step S3, when printing is paused or a layer is changed, the solder nozzle performs a sealing operation of retracting 1.0mm and cooling to 80℃; after each layer of circuit printing is completed, the solder nozzle performs a cleaning process of copper wire brush scraping, heated squeegee adsorption, and pre-exiting wire to remove air.

[0036] By adopting the above technical solution, the present invention has the following beneficial effects:

[0037] 1. Fully compatible with surface mount components: Through inverted pre-fixation (positioning slot opening facing down, surface mount component inverted and embedded), combined with elastic clips for glue-free locking, the surface mount contacts face upward and are precisely aligned with the bottom of the through hole, completely solving problems such as printhead scraping of components, solder not being able to wet the bottom contacts, and component displacement during forward printing; moreover, only surface mount components are used throughout the process, completely eliminating through-hole components, eliminating manual operations such as pin trimming, bending, and straightening, and achieving automated production with zero human intervention;

[0038] 2. Enable desktop manufacturing of multilayer surface mount circuit boards: Utilize the gravity self-filling of molten solder through holes to form solid vertical solder pillars as interlayer vias, eliminating the need for electroplating processes and completely solving industry pain points such as cold solder joints and unreliable contacts; the through holes on each insulating substrate can be arbitrarily arranged according to the circuit design, supporting stacking and printing of any number of layers, filling the gap in desktop equipment being unable to produce multilayer surface mount PCB prototypes.

[0039] 3. Avoid short circuits and line damage: Insulated edges prevent solder overflow and short circuits; non-contact insulating encapsulation (printing a suspended bridging layer with the barrier as support) and thermal collapse post-processing ensure that the print head does not touch the conductive lines throughout the process, eliminating line scratches, short circuits, and melting damage.

[0040] 4. Eliminate warping and improve accuracy: The stress relief structure integrated into the insulating substrate prevents warping of large-area plates, ensures the coaxiality of through holes and through holes, and improves the alignment accuracy of multi-layer stacking.

[0041] 5. High reliability: Solves problems such as solder dripping, drooling, short circuit due to solder buildup, board warping, via blockage, unreliable conductivity in multilayer boards, and cumulative interlayer errors during inverted printing, achieving stable closed-loop printing throughout the entire process with a yield rate of ≥99.8%;

[0042] 6. Matching the iteration speed of AI software: No factory processing or PCB fabrication is required. The entire process from circuit design to hardware prototype can be printed in minutes to tens of minutes. This solves the efficiency imbalance between minute-level software iteration in the generative AI era and 3-7 day prototyping in PCB factories. It enables desktop-level instant printing of surface mount circuits and realizes an integrated closed loop of "AI one-sentence generation function → instant printing of hardware prototype". Attached Figure Description

[0043] Figure 1 This is a flowchart of the inverted surface mount component molten solder direct writing circuit printing method of the present invention;

[0044] Figure 2 This is a schematic diagram of the dual-nozzle pre-calibration structure in step S0 of the present invention;

[0045] Figure 3 This is a schematic diagram of the inverted pre-fixed structure of the surface mount components in step S1 of the present invention;

[0046] Figure 4 This is a schematic diagram of the structure after the insulating substrate is formed in step S2 of the present invention;

[0047] Figure 5 This is a schematic diagram of the structure after gravity soldering of molten solder pillars and direct circuit writing in step S3 of the present invention;

[0048] Figure 6 This is a schematic diagram of the structure after non-contact insulating encapsulation in step S4 of the present invention;

[0049] Figure 7 This is a schematic diagram of the structure before and after the thermal collapse treatment in step S5 of the present invention;

[0050] Figure 8 This is a schematic diagram of the anti-drip solder control and nozzle self-cleaning structure of the present invention;

[0051] Figure 9 This is a schematic diagram of the online continuity and insulation detection structure of the present invention. Detailed Implementation

[0052] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0053] like Figures 1 to 9 As shown, a method for direct-write circuit printing of inverted surface mount components using molten solder is implemented based on a dual-nozzle FDM printing device. The device includes an FDM insulating nozzle and a precision temperature-controlled molten solder nozzle. The two nozzles share a three-axis motion control system, and only surface mount components are used throughout the process. The method includes:

[0054] Step S0, Dual Nozzle Pre-calibration: Complete the calibration of thermal expansion compensation for the Z-axis height difference between the FDM insulating nozzle and the soldering nozzle, the XY plane coaxiality calibration, and the extrusion volume linkage compensation calibration; specifically, it may include:

[0055] Perform one-click automatic closed-loop calibration before printing:

[0056] Z-axis height difference calibration: After completing the cold reference calibration, heat the dual nozzles to the working temperature and keep them warm for 5 minutes to compensate for the thermal expansion of the nozzles. Finally, the Z-axis height difference error of the dual nozzles is controlled within ±0.015mm.

[0057] XY plane coaxial calibration: The offset of the reference point printed by the dual printhead is identified by a vision camera, and the XY axis coordinates are automatically compensated. The alignment deviation between the patch through hole and the solder printhead is ≤0.04mm.

[0058] Extrusion volume linkage compensation: The dual-nozzle extrusion coefficient is calibrated by weighing method, the extrusion volume error is ≤±3%, and the line width tolerance is controlled within ±8%.

[0059] Step S1, Pre-fixing of surface mount components by inversion: The FDM insulating printhead has a contoured positioning groove with the opening facing down and the bottom of the groove facing up, and a through hole extending upward from the bottom of the contoured positioning groove. The surface mount component is inverted and embedded into the contoured positioning groove, and is locked in place without glue by the elastic buckle. The contacts of the surface mount component face upward and are aligned with the lower end of the through hole; Specifically:

[0060] Non-polar surface mount components (such as resistors, ceramic capacitors, etc.) use symmetrical universal positioning slots with a dimensional tolerance of ±0.05mm. Surface mount components can be embedded and installed in any direction without distinguishing between the positive and negative sides.

[0061] Polarized surface mount components (such as diodes, tantalum capacitors, integrated circuit chips, etc.) adopt an asymmetric keyhole anti-foolproof positioning groove. Through a double anti-foolproof design of a single-sided notch + asymmetric positioning post, it can be fully engaged only in the correct direction and cannot be inserted in the opposite direction, thus structurally preventing reverse installation.

[0062] The bottom of the positioning groove corresponds to each surface mount contact, with a pre-reserved tapered through hole that is wider at the top and narrower at the bottom: it can be, but is not limited to, a diameter of 0.45mm at the top and 0.30mm at the bottom, with a tapered angle of 70°. The bottom of the through hole is chamfered at 0.05mm×45°. It has automatic air venting and directional solder guiding functions, enabling solder to wet the bottom contact of the surface mount contact 360°, with a contact resistance of ≤2mΩ, zero cold solder joints, zero desoldering, and reliability far exceeding manual soldering and existing forward printing solutions.

[0063] The positioning slot has a built-in FDM one-piece molded elastic buckle with a buckle thickness of 0.15mm and an interference of 0.08mm. After the surface mount components are pressed in, they are automatically locked without glue, so they will not fall off or shift during the inverted printing process.

[0064] Step S2, Insulating Base Surface Forming: Print an insulating base surface with a stress-relieving structure. The insulating base surface has a through hole that penetrates the through-hole, and the through hole is provided with an insulating rim. Specifically:

[0065] First, a border-style stress relief groove is printed around the edge area; then, a lightweight honeycomb filler layer is filled inside the border-style stress relief groove; thus preventing warping of large-area FDM panels.

[0066] Finally, an insulating base body with through holes penetrating the through holes and an insulating rim surrounding the through holes is printed within the area enclosed by the frame-type stress relief groove. The thickness of the insulating base body can be 0.35 mm, and the width of the insulating rim can be 0.12 mm. The insulating rim forms a micro-dam to prevent solder overflow and short circuits.

[0067] Step S3, molten solder gravity pillar forming and direct circuit writing: The solder nozzle extrudes molten solder, using inverted gravity to fill the through-hole from top to bottom, allowing the solder to wet the conductive structure below the through-hole of the current layer (the first layer is the contact of surface mount components, and the second and above are the top of the lower layer's pillar or the pad of the conductive line), forming a solid vertical pillar. Then, the conductive line is directly written and fused together with the top of the pillar; specifically:

[0068] The solder nozzle moves to directly above the tapered through-hole, and the Z-axis descends to a height of 0.2mm from the base surface. Molten solder is extruded at a fixed point and in a measured amount. Using inverted gravity, the solder completely fills the conductive structure below the through-hole in the current layer from top to bottom, forming a solid vertical solder column with a filling rate of ≥99.5%.

[0069] After the solder column is formed, it is held for 3 seconds to ensure complete curing. The solder nozzle writes the conductive line directly in the pre-set groove on the insulating base surface, and the line endpoint is fused to the top of the solder column. A 45° angled following cooling air path is adopted, with the nozzle 5mm away from the printing point and the air speed 8m / s, so that the solder is completely cured within 0.08s after extrusion. Only a very thin layer of 0.03mm on the surface of the substrate is micro-melted and self-embedded, without burning or penetrating the substrate.

[0070] The circuit printing process employs gradient compensation and start-stop closed-loop control: straight sections use a standard printing speed of 60mm / s and 100% standard extrusion volume; corner positions reduce speed by 30% and extrusion volume by 30%; pad positions increase extrusion volume by 25%; the starting point of the circuit performs a pre-extrusion action, and the end point of the circuit stops extrusion 0.5mm in advance and simultaneously performs a retraction action to prevent solder buildup, wire pulling, and short circuits.

[0071] Step S4, Non-contact insulation encapsulation: The FDM insulating nozzle prints an insulating barrier along the conductive line, and prints 2-3 layers of suspended bridging insulation layer with the barrier as support, without touching the conductive line throughout the printing process;

[0072] The insulated nozzle does not touch the solder circuitry throughout the entire process, and is formed in two steps:

[0073] (1) Printing of insulating barriers: Print insulating barriers of the same height as the conductive line on both sides of the conductive line. The barrier width is 0.3mm, and a 0.12mm filling gap is reserved with the edge of the line. The top of the line is completely open. Automatically generate continuous transition barriers with a rounded corner radius of ≥0.2mm at the positions of irregular pads and interlayer vias to ensure that the support surface is completely horizontal.

[0074] (2) Printing of suspended bridging layer: Supported by insulating barriers on both sides, two layers of suspended bridging insulation layer are printed above the line, each layer is 0.2mm thick, and the total thickness is 0.4mm. A 0.15mm collapse gap is maintained between the bridging layer and the top surface of the line. The printing speed is increased by 40% to 80mm / s, the extrusion amount is reduced by 18%, the cooling fan is 100% fully open, and a straight line filling perpendicular to the line direction is used to ensure the straightness of the bridging layer and the drooping amount is ≤0.05mm. The solder line is not touched throughout the process. An array of 0.5mm diameter exhaust holes are reserved on the surface of the bridging layer with a hole spacing of 3mm. The position of the through hole between layers is automatically avoided and a protective edge is added to prevent the insulation consumable from blocking the through hole.

[0075] Step S5, Post-thermal collapse treatment: Gradient temperature-controlled heating is performed to soften and collapse the bridging insulation layer, fully encapsulating the conductive lines. Annealing and cooling then form an integrated insulation structure. Specifically:

[0076] No additional temperature control chamber is required. Utilizing the built-in heating module and infrared temperature feedback closed loop of the printing platform, gradient temperature control post-processing is performed with a temperature control accuracy of ±0.5℃.

[0077] (1) Preheating section: Heat the plate at a rate of 2℃ / min to 12℃ below the glass transition temperature of the insulating substrate, hold the temperature for 6min, so that the plate is heated evenly and the internal stress is released.

[0078] (2) Collapse section: Heat up to the target temperature at a rate of 1℃ / min (ordinary PLA 62℃, heat-resistant PLA 92℃, PETG 95-100℃), hold the temperature for 12min, so that the bridging insulation layer softens and collapses evenly, and fully covers the solder lines and solder pillars in 360°.

[0079] (3) Annealing section: slowly cool down to room temperature at a rate of 0.5℃ / min to eliminate printing internal stress, improve the adhesion and heat resistance of the insulation layer, and the flatness of the plate after annealing is ≤0.1mm / 100mm.

[0080] Step S6, multi-layer stacked printing: For layers 2 to N, execute sequentially:

[0081] Print an insulating base surface with a stress-relief structure. The insulating base surface has through holes arranged according to the current layer circuit layout. The through holes are aligned with the top of the solder pillars or conductive line pads at the corresponding positions in the lower layer. The through holes are provided with insulating edging.

[0082] Then proceed with steps S3 to S5 until the preset number of layers of circuit board printing is completed.

[0083] Specifically:

[0084] The first layer contains all surface mount components, and subsequent layers only print traces and vias. Interlayer vias are pre-printed during the printing of the insulating layer, using a tapered structure that is wider at the top and narrower at the bottom. The diameter of the lower end of the via in the upper layer is 0.1mm larger than the diameter of the upper end of the via in the lower layer. When printing the conductive lines of the next layer, molten solder is extruded at specific points, and gravity is used to completely fill the vias from top to bottom, achieving conductivity between the upper and lower layers. After each layer is printed, a low-temperature short-time annealing process is performed (Tg-15℃, constant temperature for 3 minutes) to avoid remelting of the lower layer solder pillars, board warping, and cumulative errors between layers, which can stably achieve the fabrication of surface mount circuit boards with up to 6 layers.

[0085] During the printing process, the following also applies:

[0086] Anti-drip solder control and automatic nozzle cleaning:

[0087] When printing is paused or a layer is changed, the solder nozzle performs a 1.0mm retraction and cooling to 80℃ sealing operation. This, combined with the nozzle inner cavity constriction section structure, creates negative pressure, causing the solder at the nozzle opening to solidify instantly and form a sealing plug, thus preventing solder dripping and drooling problems when printing inverted.

[0088] After each layer of lines is printed, the printhead automatically moves to the cleaning position below the side of the platform and completes the following steps in sequence: the copper wire brush scrapes back and forth 3 times to remove the solder buildup on the outer wall of the printhead → the squeegee is heated to 150℃ and stays for 0.3 seconds to absorb residual solder → the wire is pre-extruded 0.1mm to expel air from the nozzle. The waste solder generated during cleaning falls into the closed collection box by gravity and does not contaminate the printed parts.

[0089] Finished product online continuity and insulation automatic detection:

[0090] The three-axis motion system of the reuse equipment drives the retractable elastic gold-plated test probe to automatically complete the full board test: with a test voltage of 3.3V, it completes the circuit continuity test (continuity threshold <5Ω) and the insulation performance test of adjacent circuits (insulation threshold >10MΩ), automatically generates a test report, marks the fault location and repair instructions, and simultaneously generates a patch G-code to realize local soldering repair.

[0091] The above method is based on an FDM dual-printer inverted surface mount circuit printing system.

[0092] The system includes:

[0093] Printing platform module: It adopts a 235×235mm aluminum substrate, with a magnetic PEI coating sprayed on the front and a 24V 200W heating element attached to the back. It has a built-in PID temperature control and non-contact infrared temperature measurement module, and is compatible with integrated printing and thermal collapse post-processing. It is equipped with a spring-loaded locking structure and a repeatability accuracy of ±0.02mm.

[0094] Dual-nozzle coordinated motion module: Includes an FDM insulated nozzle and a precision temperature-controlled molten solder extrusion nozzle. Both share a 2020 aluminum profile gantry three-axis motion control system, with XY axis positioning accuracy of ±0.01mm and Z axis positioning accuracy of ±0.005mm. The solder extrusion nozzle adopts a dual-wheel reduction short-range wire feeding structure, stainless steel inner cavity + PTFE nano-coated anti-stick nozzle, and an outlet inner diameter of 0.2 / 0.3mm selectable. The heating chamber temperature control range is 50-200℃, with a temperature control accuracy of ±1℃.

[0095] Temperature control and follow-up cooling module: It realizes independent and precise temperature control of dual printheads, and is equipped with dual independent fans, one for heat dissipation of the insulated printhead and the other for cooling of the solder circuit; the solder cooling air path adopts the Laval nozzle structure, which is set at a 45° angle and in the same direction as the printing direction to ensure instantaneous curing of solder, while avoiding affecting the printhead temperature;

[0096] Intelligent surface mount positioning and error prevention module: Built-in package library of mainstream surface mount components such as 0402 / 0603 / 0805 resistors and capacitors, SOT-23, LQFP / QFN, etc., automatically generates non-polar universal positioning slots, polarized error prevention positioning slots and tapered through-hole structures;

[0097] Automatic printhead cleaning module: Installed on the lower side of the printing platform, it includes a 0.08mm copper-plated steel wire brush, a 20W heated brass tin scraper, and a gravity-sealed waste tin collection box;

[0098] Intelligent Slicing Control Module: Based on the secondary development of the PrusaSlicer open source framework, it has built-in full-process process parameter package, circuit gradient compensation algorithm, thermal collapse temperature control curve, multi-layer board via generation algorithm, supports import of mainstream EDA files such as KiCad / AltiumDesigner, one-click import of AI natural language generation circuit, one-click generation of printing G-code, and also has a manufacturability (DFM) automatic inspection function.

[0099] Online automatic testing module: Equipped with 2 retractable elastic gold-plated test probes, built-in high-precision resistance detection circuit, range 0-100MΩ, accuracy ±0.1Ω, realizing fully automatic detection and report generation of line continuity and insulation performance.

[0100] The solutions involved in the above embodiments will be described in detail below with reference to specific examples. Example 1: Fabrication of ESP32 surface mount minimum system board.

[0101] This embodiment focuses on the ESP32 minimum system board commonly used in AIoT scenarios. It uses 0805 packaged surface-mount resistors and capacitors, LQFP-48 packaged ESP32 chips, and surface-mount Schottky diodes. The entire fabrication process employs an inverted surface-mount component molten solder direct-write circuit printing method. The specific steps are as follows:

[0102] 1. Dual-nozzle pre-calibration: Start the equipment, heat the insulating nozzle (PETG consumable) to 215℃, and the solder nozzle (Sn42Bi58 rosin core solder wire, diameter 1.0mm) to 125℃. After holding at this temperature for 5 minutes, complete the thermal expansion compensation calibration. The final Z-axis height difference error is ±0.01mm, the XY coaxiality deviation is ≤0.03mm, and the extrusion volume error is ≤±2%.

[0103] 2. Pre-fixing of surface mount components by inversion: FDM insulating printhead prints contour positioning grooves: 0805 resistors and capacitors use symmetrical universal grooves (2.10mm long, 1.35mm wide, 0.60mm deep), while surface mount diodes and ESP32 chips use asymmetrical keyhole anti-foolproof grooves; the bottom of the positioning groove has a tapered through hole with an upper end of 0.45mm, a lower end of 0.30mm, and a cone angle of 70° corresponding to the contact; the groove has 4 0.15mm thick elastic buckles inside; when the surface mount component is inverted and embedded into the groove, the elastic buckles automatically lock, and the contact and the lower end of the through hole are precisely aligned;

[0104] 3. Insulating base surface forming: Print a frame-type stress relief groove + 0.35mm thick PETG insulating base surface, the tapered through hole is completely coaxial with the base surface, and the edge of the through hole is printed with a 0.12mm wide insulating edging;

[0105] 4. Solder pillar forming and direct circuit writing: The solder nozzle moves directly above the through hole, 0.2mm away from the base surface, and precisely extrudes a quantitative amount of solder. Gravity completely fills the through hole to form a solid solder pillar, wetting the surface mount contact 360°. After 3 seconds of curing, a 0.25mm wide conductive line is directly written in the groove of the base surface, and the line is fused to the top of the solder pillar. The 45° angled cooling air path runs at full speed, and the solder cures within 0.08 seconds. The speed and extrusion amount are automatically reduced at the corners of the line, with no solder buildup or stringing.

[0106] 5. Non-contact insulation encapsulation: Print an insulating barrier 0.3mm wide and 0.25mm high along the line, leaving a 0.12mm filling gap; then, using the barrier as support, print two layers of 0.2mm thick suspended bridging insulation layer, leaving a 0.15mm collapse gap and array venting holes, without touching the solder lines throughout the process;

[0107] 6. Post-heat collapse treatment: The printing platform is heated to 76℃ (PETG Tg-12℃) at 2℃ / min and held at that temperature for 6min. Then, it is heated to 98℃ at 1℃ / min and held at that temperature for 12min to make the bridging layer collapse evenly and fully cover the circuit. Finally, it is slowly cooled to room temperature at 0.5℃ / min.

[0108] 7. Online testing: The elastic probe automatically completes the continuity and insulation tests of the entire board and generates a qualified report. The finished product size is 50×35mm and the thickness is 1.8mm. It can be directly powered on to run the MicroPython AI inference program.

[0109] Example 2: Fabrication of a 4-layer AI edge computing module

[0110] This embodiment focuses on an AI edge computing module with an OV2640 camera interface and LoRa communication functionality, employing a multi-layer board fabrication method. The specific steps are as follows:

[0111] 1. Follow the steps in Example 1 to complete the first layer (bottom layer) printing, place all surface mount components such as STM32H7 main control chip, 0805 resistors and capacitors, power chips, and interface chips, and complete the circuit printing, insulation encapsulation and low temperature short-time annealing.

[0112] 2. Repeat the steps of insulating base printing, via pre-drilling, gravity filling of solder, circuit printing, insulating encapsulation, and short-time annealing to complete the printing of layers 2-4. The interlayer vias adopt a tapered structure that is wider at the top and narrower at the bottom. Solder is filled from top to bottom to achieve conductivity. Visual alignment calibration is performed before printing each layer, and the interlayer alignment error is ≤ ±0.03mm.

[0113] 3. After the top layer printing is completed, a complete three-stage thermal collapse post-processing and online testing are performed. The finished product size is 60×40mm and the thickness is 2.2mm. It supports continuous full-load operation for 72 hours without any poor soldering, short circuits, or signal abnormalities.

[0114] Performance and reliability verification testing

[0115] The test environment was 25℃ room temperature and 50%RH relative humidity. The test results are as follows:

[0116] 1. Electrical performance: The average contact resistance of a 0.25mm wire width and 10cm length line is 1.8mΩ, the average contact resistance of a single weld post is 1.2mΩ, the 0.3mm wire width can stably carry a current of 1.2A, the insulation resistance of adjacent lines is ≥120MΩ, and the breakdown voltage is ≥1200V;

[0117] 2. Environmental reliability: After 1000 cycles of high and low temperature (-40℃~125℃), the line resistance change rate is ≤8%; after 1000 cycles of high temperature and high humidity (85℃ / 85%RH), the line resistance change rate is ≤12%, the insulation resistance is ≥50MΩ, and there is no oxidation or tin growth.

[0118] 3. Process stability: After printing 10 identical samples continuously, the yield rate is 99.8%, the total time for a single board is ≤1.5 hours, and the solder nozzle can be continuously printed for 50 hours without clogging.

[0119] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for direct-write circuit printing using molten solder on inverted surface mount components, characterized in that, include: Step S1, Pre-fixing of surface mount components inverted: The FDM insulating printhead prints a contoured positioning groove with the opening facing down and the bottom of the groove facing up, and has elastic buckles, as well as a through hole extending from the bottom of the contoured positioning groove upwards. The surface mount components are inverted and embedded into the contoured positioning groove, and are locked without glue by the elastic buckles. The contacts of the surface mount components face upwards and are aligned with the lower end of the through hole. Step S2, Insulating base surface forming: Print an insulating base surface with a stress relief structure. The insulating base surface has a through hole that passes through the through hole, and the through hole is provided with an insulating rim. Step S3, Molten Solder Gravity Solder Pillar Forming and Direct Circuit Writing: The solder nozzle extrudes molten solder and fills the through hole from top to bottom using inverted gravity, so that the solder wets the conductive structure below the through hole of the current layer to form a solid vertical solder pillar. Then, the conductive circuit is directly written and fused together with the top of the solder pillar. Step S4, Non-contact insulation encapsulation: The FDM insulating nozzle prints an insulating barrier along the conductive line, and prints 2-3 layers of suspended bridging insulation layer with the barrier as support, without touching the conductive line throughout the printing process; Step S5, post-heat collapse treatment: Gradient temperature controlled heating is performed to soften and collapse the bridging insulation layer and fully cover the conductive lines, followed by annealing and cooling to form an integrated insulation structure.

2. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, Before step S1, the following is also included: Step S0, Dual Nozzle Pre-calibration: Complete the calibration of thermal expansion compensation for the Z-axis height difference between the FDM insulating nozzle and the solder nozzle, the XY plane coaxiality calibration, and the extrusion quantity linkage compensation calibration.

3. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, In step S1, the through hole is a tapered through hole that is larger at the top and smaller at the bottom.

4. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, In step S1, the contour positioning groove corresponding to non-polar surface mount components is a symmetrical positioning groove; the contour positioning groove corresponding to polar surface mount components is an asymmetrical foolproof positioning groove.

5. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, Step S2 specifically includes: First, print a border-shaped stress relief groove around the edge area; Then fill the frame-type stress relief groove with a lightweight honeycomb filler layer; Finally, an insulating base body with through holes that penetrate the through holes and an insulating perimeter surrounding the through holes is printed within the area enclosed by the frame-type stress relief groove.

6. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, In step S3, during the printing process, a follow-up cooling seal is used to ensure that the solder is completely cured within a preset time after it is extruded.

7. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, In step S4, a filling gap is reserved between the insulating enclosure and the edge of the line; a collapse gap is also reserved between the bridging insulation layer and the top surface of the line, and an array of exhaust holes is reserved on the surface.

8. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, In step S5, the gradient temperature control heating adopts a three-stage gradient temperature control: Preheating section: Heat at a rate of 2℃ / min to 12℃ below the glass transition temperature of the insulating substrate, and hold at that temperature for 6 minutes; Collapsed section: Heat to the glass transition temperature of the substrate +8℃ at a rate of 1℃ / min, and hold at that temperature for 12min; Annealing section: slowly cool to room temperature at a rate of 0.5℃ / min.

9. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 1, characterized in that, Also includes: Step S6, multi-layer stacked printing: For layers 2 to N, execute sequentially: Print an insulating base surface with a stress-relief structure. The insulating base surface has through holes arranged according to the current layer circuit layout. The through holes are aligned with the top of the solder pillars or conductive line pads at the corresponding positions in the lower layer. The through holes are provided with insulating edging. Then proceed with steps S3 to S5 until the preset number of layers of circuit board printing is completed.

10. The method for direct-write circuit printing of inverted surface mount components using molten solder as described in claim 9, characterized in that, In step S3, when printing is paused or a layer is changed, the solder nozzle performs a sealing operation of retracting 1.0mm and cooling to 80℃; after each layer of circuit is printed, the solder nozzle performs a cleaning process of copper wire brush scraping, heated squeegee adsorption, and pre-exiting wire to remove air.

Images