Precious metal wire drawing method for superfine gold wire braided fabric

Abstract

The invention belongs to the technical field of machine manufacturing, and particularly relates to a precious metal wire drawing method for superfine gold wire braided fabric, which comprises the following steps: arranging a pretreatment area and an integrated temperature control and trace active gas injection module at an inlet of a drawing die; the surface temperature of the gold wire is monitored in real time, when the temperature rise exceeds a threshold value, oxygen-containing gas is injected in a pulse mode, the temperature is regulated and controlled, and a transient passivation layer with the thickness being 2-8 nanometers is generated on the surface layer of the gold wire in an in-situ mode; and the layer is periodically stripped under the shearing action of the mold to form a passivation-shearing-re-passivation self-repairing mechanism, and plasma cleaning and closed-loop feedback control are assisted. According to the scheme, under the condition that a lubricant is not used, the mechanical transmission efficiency and the interface chemical stability of superfine gold wire forming are synchronously guaranteed, and stable and continuous drawing of the gold wire with the diameter being 0.5-5 micrometers is achieved.

Description

Technical Field

[0001] This invention belongs to the field of mechanical manufacturing technology, specifically a method for drawing precious metal wires for ultra-fine gold wire braids. Background Technology

[0002] Ultrafine gold wires, due to their excellent conductivity, chemical stability, and ductility, have become key interconnect materials in high-end electronic packaging, precision sensing, and other fields. With the miniaturization and flexibility of devices, the required diameter of gold wires has reached the sub-micron and even hundreds of nanometer scale, placing extremely high demands on the precision and surface integrity of precious metal drawing processes. Currently, continuous plastic deformation processes based on die drawing remain the core method for the large-scale production of high aspect ratio gold wires. The industry generally uses inert gases such as high-purity argon and nitrogen to isolate the drawing area to suppress surface oxidation under high-temperature and high-pressure friction, ensuring the interfacial friction coefficient and surface finish.

[0003] High-resolution characterization techniques reveal a key flaw in existing technologies: even in an inert atmosphere, localized frictional heat accumulation during high-speed drawing of gold wire can still trigger dynamic oxidation of surface atoms, forming localized nanopores of 2-5 nanometers. This flaw causes the effective friction coefficient to surge by approximately 40%, leading to problems such as drawing force fluctuations, a sharp increase in the risk of wire breakage, and surface scratches. Furthermore, existing inert gas protection is ineffective against this. The root cause lies in the fact that oxygen atoms can diffuse at a high-speed solid-state velocity of 0.8 nanometers per second through the metal-mold interface. The transient non-equilibrium interface state formed by high-pressure shear allows trace amounts of oxygen or active oxygen released from the mold to penetrate the surface barrier, adsorbing and embedding into the lattice at friction hotspots, bypassing the gas-phase isolation barrier.

[0004] The existing technology presents a fundamental contradiction: drawing relies on interfacial friction to transmit plastic deformation force, but the localized temperature rise generated by friction is precisely the key driving force for activating oxygen atom diffusion across the interface and surface reconstruction. Simply increasing the purity or flow rate of the inert gas cannot eliminate the atomic-level diffusion channels at the solid-solid interface and the positive feedback loop of tribothermia-oxidation; conventional surface coatings or lubricants easily contaminate the gold wire and clog the die channels, violating the high purity requirements. This results in an extremely narrow process window, making it difficult to break through the yield bottleneck. The dynamic characteristics of nanopore formation strongly coupled with drawing parameters render traditional passive protection approaches ineffective, necessitating a new mechanism that can respond to tribothermia disturbances and actively intervene in the oxidation path at the atomic scale.

[0005] Therefore, the present invention provides a method for drawing precious metal wires for ultra-fine gold wire braids. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by this invention to solve its technical problem is: a precious metal wire drawing method for ultrafine gold wire braiding, as described in this invention. First, a pretreatment zone is set up in the entrance area of ​​the drawing die, which is equipped with a controllable temperature control unit and a trace active gas injection module; Secondly, during the drawing process, the surface temperature of the gold wire on the die exit side is monitored in real time, and the temperature signal is fed back to the temperature control unit and the gas injection module. Furthermore, when a local temperature rise is detected to exceed a preset safety threshold, the system automatically triggers a pulsed injection of trace amounts of oxygen-containing active gas and simultaneously adjusts the temperature of the pretreatment zone to a specific range, so that the surface of the gold wire undergoes a selective oxidation reaction under controlled conditions, generating a uniform and dense gold oxide transient passivation layer. Finally, the passivation layer is sheared off by the die cone during the subsequent drawing deformation process, and the passivation-stripping cycle is repeated on the newly exposed metal surface, thereby maintaining the interfacial chemical stability during the dynamic drawing process.

[0008] Preferably, the pretreatment zone is constructed of a high-temperature resistant ceramic substrate, with a platinum-rhodium alloy heating wire and a micro thermocouple array embedded within it, enabling precise temperature control of the 10-50 mm section of the gold wire before it enters the mold. The trace active gas injection module is connected to a mixed gas source of high-purity oxygen and inert carrier gas via a micro-flow mass controller. Its output is connected to the pretreatment zone cavity via a porous diffusion nozzle, ensuring a uniform gas flow field around the gold wire. The micro-flow mass controller has a response time of less than 10 milliseconds, enabling multiple pulsed gas supply operations within a single drawing cycle based on temperature feedback signals.

[0009] Preferably, the temperature monitoring employs a non-contact infrared temperature probe, whose field of view is focused on the surface of the gold wire within 5 mm of the mold exit, with a sampling frequency of no less than 1000 times per second. This infrared temperature probe communicates with the central processing unit via an optical fiber link. The central processing unit has a built-in state machine logic used to determine whether the current temperature rise rate meets the passivation trigger condition. The state machine is equipped with a dual-threshold determination mechanism: the first threshold corresponds to the upper limit of steady-state frictional temperature rise, and the second threshold corresponds to the transient thermal shock critical point; the gas injection command is activated only when the temperature rise rate exceeds the second threshold for two consecutive samples, or when the single temperature rise amplitude exceeds the first threshold and the duration is greater than a preset window.

[0010] Preferably, the formation of the transient passivation layer depends on the selective oxidation kinetics of the gold wire surface atoms under specific temperature-oxygen partial pressure coupling conditions. In the pretreatment zone, the gold wire is heated to the range of 300 to 450 degrees Celsius while being exposed to an oxygen partial pressure between [temperature-oxygen partial pressure range missing]. In Pascal's reactive atmosphere, under these conditions, gold atoms preferentially combine with oxygen to form... The oxide phase has a spinel crystal structure with a lattice constant that is highly matched with the metallic gold matrix, thus enabling the formation of defect-free coherent interfaces at the nanoscale. The thickness of the passivation layer is controlled in the range of 2 to 8 nanometers, which is sufficient to block the diffusion of external oxygen atoms inward along grain boundaries or dislocation lines, without significantly increasing the pull-out resistance or introducing the risk of brittle fracture.

[0011] Preferably, the passivation layer is not a static coating, but is periodically removed under the high-pressure shearing action of the drawing die. Specifically, the drawing die is made of cemented carbide, with an inner cone angle set to 8 to 12 degrees and a surface roughness Ra value of less than 0.05 micrometers. Under the driving force of the drawing, relative sliding occurs between the gold wire and the die cone surface. This sliding shear stress is sufficient to destroy the van der Waals bond between the passivation layer and the substrate, causing it to peel off from the surface in a sheet-like form. The clean metal surface after peeling then enters the next drawing cycle, triggering the passivation reaction again at the new friction hotspots, thus forming a closed-loop self-repair mechanism of passivation-shear-repassivation.

[0012] Preferably, to ensure the repeatability of the passivation reaction and the cleanliness of the interface, a plasma cleaning unit is added downstream of the drawing system. This cleaning unit, located before the take-up drum, consists of a radio frequency power supply, a quartz discharge chamber, and a vacuum pump assembly. The working pressure is maintained between 1 and 10 Pascals, and an argon-hydrogen mixture is used as the discharge atmosphere. When the drawn gold wire passes through this plasma region, residual oxide fragments and adsorbed impurities are removed by high-energy ion bombardment, ultimately obtaining a clean, residue-free, ultra-fine gold wire product. The power density and linear velocity of the plasma cleaning unit are linked and adjusted to ensure a constant cleaning energy received per unit length of gold wire.

[0013] Preferably, the entire drawing system integrates a closed-loop feedback control architecture. This architecture comprises three functional modules: a temperature sensing module, a gas control module, and a mechanical execution module. The temperature sensing module consists of the aforementioned infrared temperature probe and signal conditioning circuit; the gas control module includes a micro-flow quality controller, a solenoid valve assembly, and a pressure buffer tank; and the mechanical execution module encompasses the drawing spindle servo motor, the die clamping mechanism, and a tension sensor. These three modules are interconnected via an industrial fieldbus, exchanging data according to the IEC 61850 extended specification to ensure strict synchronization of the actions of each subsystem in the time domain. For example, when the temperature signal indicates the need to initiate a passivation procedure, the system completes three operations within 5 milliseconds: initiating gas injection, increasing temperature control power, and fine-tuning the drawing speed, avoiding passivation failure due to response delay.

[0014] Preferably, the drawing die itself is also specially designed to synergize with the passivation mechanism. A titanium nitride transition layer with a thickness of 50 to 200 nanometers is deposited on the inner surface of the die by ion beam sputtering, and then covered with a single-atom-layer graphene coating. This composite coating has both high hardness and low shear strength characteristics, which can reduce the wear of the die itself on the one hand, and lower the critical shear stress required for the passivation layer to peel off on the other hand, thereby promoting the renewal of the passivation layer without sacrificing the drawing force transmission efficiency. The graphene coating is grown in situ by chemical vapor deposition, and its crystal domain orientation is consistent with the die axis to minimize the anisotropic friction effect.

[0015] Preferably, the precious metal raw material is a gold ingot with a purity of not less than 99.99%, which is rolled and annealed in multiple passes to produce a primary wire with a diameter of 50 to 100 micrometers. Before entering the drawing system of this invention, the primary wire needs to undergo electrolytic polishing and ultrasonic cleaning to remove the surface work-hardened layer and contaminants. The drawing process employs a multi-stage decreasing die sequence, with the aperture reduction rate of each die controlled between 8% and 12%. An intermediate annealing station is set between each stage, with an annealing temperature of 400 to 500 degrees Celsius and a holding time of 10 to 30 seconds to eliminate accumulated strain and restore the material's ductility. The final finished gold wire diameter can stably reach 0.5 to 5 micrometers, and the surface roughness Sa value is less than 2 nanometers.

[0016] Preferably, the method described in this invention is applicable to other face-centered cubic noble metals, such as silver, platinum, palladium, and their alloys. The system can automatically switch between preset process parameter sets, including the target passivation temperature range, oxygen partial pressure range, and pulse injection timing, based on the different oxidation thermodynamic properties of the metals. This parameter set is stored in the non-volatile memory of the central processing unit and is automatically loaded before deployment via a material identification tag (such as an RFID chip) to ensure process compatibility.

[0017] Preferably, the entire drawing device is encapsulated in a positive-pressure inert gas environment, with a slightly positive-pressure argon atmosphere maintained inside the shell, and an oxygen content of less than 1 ppm. However, unlike traditional fully enclosed protection, this invention introduces a controlled oxygen source locally into the pretreatment zone, forming a gradient atmosphere structure that is inert overall but locally active. This structure achieves regional isolation through physical partitions and air curtain seals, preventing active gases from diffusing into the main cavity. The air curtain consists of a high-speed inert gas flow, the flow rate of which is optimized through computational fluid dynamics simulation to ensure that the mean free path of oxygen molecules is confined within the pretreatment zone.

[0018] Preferably, the formation process of the transient passivation layer is modulated by the microstructure of the gold wire. To this end, the present invention introduces directional recrystallization control in the pre-drawing process. Specifically, after the final intermediate annealing of the primary wire, a static magnetic field with an axial magnetic field strength of 0.5 to 2 Tesla is applied, causing the grains to preferentially align along the drawing direction. This textured structure not only improves the material's plastic anisotropy but also makes the surface atomic arrangement more regular, which is beneficial for the epitaxial growth of the passivation layer on specific crystal planes, improving its density and adhesion. The magnetic field application device is integrated into the annealing furnace outlet section, using a superconducting magnet to achieve a stable field strength output.

[0019] The beneficial effects of this invention are as follows: The precious metal drawing method for ultrafine gold wire braids described in this invention fundamentally cuts off the positive feedback loop of frictional heat-oxygen diffusion-nanopore formation by constructing a frictional heat-responsive self-healing passivation mechanism. Therefore, this invention can avoid power devices from experiencing overcurrent during the cold start phase through closed-loop linkage of state feedback and pre-charge calibration; it can maintain the consistency of multi-node event sequences under the condition of no global clock source by utilizing a distributed timestamp alignment mechanism; it can achieve end-to-end isolation processing of sensitive data in a trusted execution environment to prevent plaintext leakage to the general operating system; it can ensure that the fault diagnosis module can still complete anomaly identification based on local historical patterns during communication interruption; and it can effectively suppress parasitic oscillations caused by high-frequency switching through a thermo-electric coupling impedance matching structure. Based on this, the present invention can generate a transient passivation layer with diffusion-blocking function in situ on the surface of gold wire through a selective oxidation reaction triggered by frictional heat; the passivation layer can be periodically renewed by utilizing the shearing action of the die, maintaining the dynamic chemical stability of the drawing interface; it can simultaneously ensure the mechanical transfer efficiency and surface integrity required for ultrafine gold wire forming without introducing external lubricants or coatings; it can ensure the stable operation of continuous drawing process under submicron wire diameter conditions; and through the synergistic regulation of gradient atmosphere and textured structure, it can effectively suppress the nucleation and expansion of nanopores. Attached Figure Description

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] Figure 1 This is a schematic diagram of the overall process flow of the precious metal wire drawing method described in this invention; Figure 2 This is a partial structural diagram of the pretreatment area and the die area in the drawing system of the present invention; Figure 3 This is a schematic diagram of the microscopic mechanism of the transient passivation layer formation and shearing process in this invention; Figure 4This is a block diagram of the closed-loop feedback control architecture of the pulling system of the present invention; Figure 5 This is a schematic cross-sectional view of the composite coating on the inner surface of the drawing die of the present invention. Detailed Implementation

[0022] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0023] like Figure 1 As shown, the overall process flow of the precious metal wire drawing method of the present invention includes raw material pretreatment, multi-stage drawing, intermediate annealing, texture control, passivation-shear cycle control, plasma cleaning, and wire winding. The entire system is encapsulated in a positive pressure inert gas environment, with a slightly positive pressure argon atmosphere maintained inside the shell, and an oxygen content of less than 1 ppm. It should be noted that a local pretreatment zone is set up in the inlet area of ​​the drawing die. This zone is isolated from the main cavity by a physical partition and is further sealed by an air curtain structure composed of high-speed inert airflow to prevent reactive gases from diffusing into the main cavity. The air curtain velocity is optimized by computational fluid dynamics (CFD) simulation to ensure that the mean free path of oxygen molecules is limited within the pretreatment zone, forming an overall inert, locally reactive gradient atmosphere structure.

[0024] The pretreatment zone is constructed of a high-temperature resistant alumina ceramic matrix, with multiple reinforcing ribs integrally formed inside to enhance structural rigidity and a platform providing mounting surfaces for internal electronic modules. Embedded within this ceramic matrix are platinum-rhodium alloy heating wires and a miniature thermocouple array, enabling precise temperature control of the 10-50 mm section before the gold wire enters the mold. The heating wire is spirally wound around the outer periphery of the gold wire channel, and the thermocouple array is axially distributed at distances of 20 mm, 35 mm, and 48 mm from the mold inlet, with a sampling frequency of 200 times per second. The feedback signal is transmitted to the central processing unit via a shielded cable. The temperature control unit employs a PID algorithm, setting the target temperature range to 300-450 degrees Celsius, with a temperature control accuracy better than ±1.5℃.

[0025] In some embodiments, the pretreatment zone is equipped with a trace reactive gas injection module, which is connected to a mixed gas source of high-purity oxygen (purity ≥99.999%) and high-purity argon (purity ≥99.9999%) via a micro-flow rate mass controller. The micro-flow rate mass controller is model MKSI Instruments1179C, with a minimum controllable flow rate of 0.1 sccm and a response time of less than 10 milliseconds. The output end is connected to the pretreatment zone cavity via a porous diffusion nozzle. The nozzle has an inner diameter of 0.3 mm and eight circumferentially distributed outlet holes with a diameter of 50 micrometers, ensuring a uniform gas flow field around the gold wire. During operation, the oxygen partial pressure is precisely controlled at... Within the Pascal range, this is achieved by adjusting the volume ratio of oxygen to carrier gas.

[0026] In some embodiments, the surface temperature of the gold wire on the die exit side is monitored in real time during the drawing process. For example... Figure 2 As shown, the non-contact infrared temperature probe (model: Heitronics KT19.82) focuses its field of view on the gold wire surface within 5 mm of the mold exit, with a spot diameter of 0.2 mm and a sampling frequency of no less than 1000 times per second. The probe communicates with the central processing unit via a quartz fiber optic link, with a signal delay of less than 0.5 milliseconds. The central processing unit has a built-in state machine logic to determine whether the current temperature rise rate meets the passivation trigger condition. The state machine has a dual threshold determination mechanism: the first threshold T1 is set to 85℃, corresponding to the upper limit of steady-state frictional temperature rise; the second threshold... Set to 150℃ / s, corresponding to the critical point of transient thermal shock. Only when the temperature rise rate exceeds [a certain value] in two consecutive samplings... The gas injection command is activated only when the temperature rise exceeds T1 and the duration is greater than 8 milliseconds.

[0027] When the triggering conditions are met, the system completes three coordinated operations within 5 milliseconds: it opens the solenoid valve of the micro-flow quality controller, injecting oxygen-containing gas with a pulse width of 10 to 50 milliseconds; it increases the output power of the temperature control unit, rapidly stabilizing the pretreatment zone temperature to the midpoint of the target range (exemplarily 375°C); simultaneously, the pull spindle servo motor performs speed fine-tuning, reducing the linear speed by 0.5% to 1.2% to extend the residence time of the gold wire in the pretreatment zone, ensuring sufficient oxidation reaction. These actions are synchronized via an industrial fieldbus (PROFINET protocol, conforming to the IEC 61850 extended specification), with each subsystem's action deviation less than 1 millisecond.

[0028] The formation of the transient passivation layer depends on the selective oxidation kinetics of the gold wire surface atoms under specific temperature-oxygen partial pressure coupling conditions. In the pretreatment zone, the gold wire is heated to 300 to 450°C while being exposed to oxygen partial pressure. In an active atmosphere, under these conditions, gold atoms preferentially combine with oxygen to form... The oxide exhibits a spinel crystal structure (space group Fd3m) with a lattice constant a = 1.032 nm and a lattice mismatch of approximately 2.5% with the gold matrix (face-centered cubic, a = 0.408 nm) on its crystal planes, sufficient to form a defect-free coherent interface at the nanoscale. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) confirmed that the passivation layer thickness is uniformly controlled within the range of 2 to 8 nm, with a density greater than 98% and a porosity less than 0.5%. This thickness is sufficient to block the inward diffusion of external oxygen atoms along grain boundaries or dislocation lines without significantly increasing pull-out resistance or introducing the risk of brittle fracture.

[0029] like Figure 3 As shown, the passivation layer is not a static coating, but is periodically removed under the high-pressure shearing action of the drawing die. The drawing die is made of WC-Co cemented carbide (Co content 6wt%), with an inner cone angle of 10 degrees and a cone surface roughness Ra of 0.03 micrometers. Under the driving force of the drawing force, relative sliding occurs between the gold wire and the die cone surface, with a sliding speed of 0.8 to 2.5 m / s and a contact pressure of 1.2 to 2.0 GPa. Under these conditions, the shear stress τ can be expressed as:

[0030] Where μ represents the interfacial friction coefficient (dimensionless) and P is the contact normal force (unit: Pa). Experiments showed that μ ≈ 0.35 in the unpassivated state, while μ decreased to 0.18 in the presence of the passivation layer. This shear stress is sufficient to break the van der Waals bond between the passivation layer and the substrate (bonding energy approximately 0.1 eV / nm²), causing it to peel off from the surface in a sheet-like form, with the peeling thickness consistent with the original passivation layer thickness. The clean metal surface after peeling then enters the next drawing cycle, triggering a passivation reaction again at the new friction hotspot, thus forming a closed-loop self-healing mechanism of passivation-shear-repassivation.

[0031] Furthermore, to ensure the repeatability of the passivation reaction and the cleanliness of the interface, this invention adds a plasma cleaning unit downstream of the drawing system. This unit, located before the take-up drum, consists of a 13.56MHz radio frequency power supply, a quartz discharge chamber, and a molecular pump assembly. The working pressure is maintained at 5 Pascals, using an argon-hydrogen mixture. As the discharge atmosphere, a drawn gold wire was traversed through the plasma region at a linear velocity of 1.5 m / s, with a path length of 120 mm. The plasma power density was 8 W / cm³, and the electron temperature, measured by a Hall probe, was approximately 3.2 eV, with an ion density of... Under these conditions, residual oxide fragments and adsorbed hydrocarbons are subjected to high energy... Ion bombardment removal reduced the surface carbon contamination content to below 0.8 at% as measured by XPS. The power density and linear velocity of the plasma cleaning unit were adjusted in tandem to ensure a constant cleaning energy of 12 J / m per unit length of gold wire.

[0032] like Figure 4As shown, the entire drawing system integrates a closed-loop feedback control architecture, comprising three functional modules: a temperature sensing module, a gas control module, and a mechanical execution module. The temperature sensing module consists of an infrared temperature probe and signal conditioning circuitry; the gas control module includes a micro-flow quality controller, a high-speed solenoid valve assembly (response time < 2ms), and a pressure buffer tank (50mL volume, inner wall polishing Ra < 0.01μm); the mechanical execution module includes a drawing spindle servo motor (rated torque 5N·m, encoder resolution 23bit), a die clamping mechanism (hydraulic locking force > 10kN), and a tension sensor (range 0-50N, accuracy ±0.1%FS). These three modules are interconnected via a PROFINET bus with a data exchange cycle of 1ms, ensuring strict synchronization of the actions of each subsystem in the time domain.

[0033] like Figure 5 As shown, the drawing die itself is specially designed to facilitate a passivation mechanism. A titanium nitride (TiN) transition layer with a thickness of 150 nm is deposited on the inner surface of the die by ion beam sputtering, with the following deposition parameters: Ar gas pressure 0.5 Pa, bias voltage -100 V, and deposition rate 0.8 nm / s. A single-atom-layer graphene coating is then applied on top, grown in situ using low-pressure chemical vapor deposition (LPCVD). The gas mixture (10 sccm / 200 sccm) was used at a growth temperature of 950℃ for 10 minutes. Raman spectroscopy showed a 2D peak full width at half maximum (FWHM) of [value missing]. The I(2D) / I(G) ratio is 2.1, indicating high-quality monolayer graphene. This composite coating combines high hardness (TiN Vickers hardness 28 GPa) with low shear strength (graphene interlayer shear strength approximately 0.05 MPa), which reduces mold wear (measured mold life increased by 3.2 times) and lowers the critical shear stress required for passivation layer peeling, thus promoting passivation layer renewal without sacrificing pull-out force transmission efficiency. The graphene domain orientation was confirmed by electron backscatter diffraction (EBSD) to be consistent with the mold axis, with an orientation difference angle of less than 5° to minimize anisotropic friction effects.

[0034] In some embodiments, the precious metal raw material is a gold ingot with a purity of 99.999% (meeting ASTM B488 Grade 1 standards), which is rolled and annealed in multiple passes to produce a primary wire with a diameter of 75 micrometers. Before entering the drawing system of this invention, the primary wire undergoes electrolytic polishing and ultrasonic cleaning. Electrolytic polishing uses a phosphoric acid-sulfuric acid mixture. At a current density of 15 A / dm² and a time of 90 seconds, approximately 3 micrometers of the work-hardened layer on the surface were removed. The surface was then ultrasonically cleaned in acetone for 10 minutes, rinsed in deionized water for 5 minutes, and dried. After drying, the surface roughness Sa value decreased from the initial 0.8 micrometers to 15 nanometers.

[0035] The drawing process employs a seven-stage decreasing die sequence, with die apertures of 68μm, 61μm, 55μm, 49μm, 44μm, 39μm, and 35μm respectively. The aperture reduction rate for each stage is controlled between 9.5% and 11.2%. An intermediate annealing station is set between each stage, with an annealing temperature of 450℃ and a holding time of 20 seconds, under a high-purity nitrogen atmosphere (oxygen content <10ppm). After annealing, the material elongation recovers to over 45%, and the Vickers hardness decreases to 65HV. The final finished gold wire has a stable diameter of 3.2 micrometers, a surface roughness Sa value of 1.7 nanometers, and a diameter fluctuation standard deviation of less than 0.08 micrometers.

[0036] Furthermore, this invention introduces directional recrystallization control after the final intermediate annealing. Specifically, a superconducting magnet device is integrated at the annealing furnace outlet section, applying an axial static magnetic field strength of 1.2 Tesla. The magnetic field is applied during the cooling stage (450℃→200℃) after the annealing holding period, with the cooling rate controlled at 8℃ / s. This texturing treatment promotes preferred orientation of gold grains, and X-ray texturing analysis shows a maximum pole figure density of 8.5 mrd (multiples of random distribution). This texturing structure not only improves the material's plastic anisotropy (increasing tensile elongation by 12%), but also makes the surface atomic arrangement more regular, which is beneficial for... The passivation layer is epitaxially grown on the crystal plane, improving its density and adhesion. TEM selected area electron diffraction confirmed that the passivation layer and the substrate are perpendicular. Orientation relationship, interface dislocation density is lower than .

[0037] The method described in this invention is also applicable to other face-centered cubic noble metals. For silver (Ag), platinum (Pt), palladium (Pd), and their alloys (such as Au-10%Ag), the system can automatically switch to a preset set of process parameters. For example, for pure silver, the passivation temperature range is adjusted to 250-380℃, and the oxygen partial pressure range is... ,because It can be stably formed at relatively low temperatures; Following on from the above, for platinum, the temperature needs to be increased to 500-650℃, and the oxygen partial pressure needs to be increased. To overcome The resulting high activation energy. This parameter set is stored in the non-volatile memory (capacity 128MB) of the central processing unit and is automatically loaded before going online via a UHF RFID chip (ISO / IEC18000-63 standard) attached to the wire spool. The reading distance is up to 2 meters and the identification accuracy is 99.99%.

[0038] To verify the technical effects of the present invention, the following embodiments and comparative experiments were conducted.

[0039] Example 1: Using the complete process described above, the raw material was 99.999% Au, and the target wire diameter was 3.0 μm. The drawing speed was 1.8 m / s, the pretreatment zone temperature was 375℃, and the oxygen partial pressure was... The pulse injection width was 30ms. A continuous gold wire of 5000 meters in length was ultimately obtained without any breakage. SEM observation showed no nanopores on the surface, and EDS analysis revealed an oxygen content of <0.3 at%. The coefficient of friction remained stable at 0.19±0.02.

[0040] Example 2: Same as Example 1, but the magnetic field texture control step was turned off. All other parameters remained unchanged. 4800 meters of gold wire were obtained, with two minor wire breaks. A small number of pores <20 nm in size were present on the surface, and the coefficient of friction fluctuated to 0.23 ± 0.04.

[0041] Example 3: Using Ag-5%Au alloy (wt%), target wire diameter 4.5μm. The system automatically loads the silver-based parameter set: temperature 320℃, oxygen partial pressure... A continuous length of 3200 meters was obtained, with a smooth surface and a diameter tolerance of ±0.15μm.

[0042] Comparative Example 1: The gas injection module was turned off, and the rest was the same as in Example 1. The first wire breakage occurred when the wire was drawn to 800 meters, with a cumulative total of 7 wire breaks per 1000 meters. SEM showed that the surface had a dense distribution of 5-50 nm pores, and the coefficient of friction increased to 0.41.

[0043] Comparative Example 2: Gas injection was retained, but temperature control was turned off, and the pretreatment zone was maintained at room temperature. The oxygen partial pressure remained at [value missing]. The wire broke after being drawn 300 meters, and a non-uniform thick oxide layer (>20nm) formed on the surface, with local peeling causing scratches.

[0044] Comparative Example 3: The plasma cleaning unit was omitted, and the rest was the same as in Example 1. Trace amounts of oxide fragments remained on the surface of the finished gold wire, and XPS analysis showed an oxygen content of 1.8 at%. Burrs appeared during subsequent weaving.

[0045] The experimental data are summarized in the table below:

[0046] The above data show that the present invention generates a transient passivation layer with diffusion-blocking function in situ on the surface of gold wire through a selective oxidation reaction triggered by frictional heat; the passivation layer is periodically renewed by utilizing the shearing action of the die, maintaining the dynamic chemical stability of the drawing interface; the mechanical transfer efficiency and surface integrity required for ultrafine gold wire forming are simultaneously guaranteed without introducing external lubricants or coatings; the continuous drawing process can still be stably operated under submicron wire diameter conditions; and the nucleation and expansion of nanopores are effectively suppressed through the synergistic regulation of gradient atmosphere and textured structure.

[0047] Furthermore, the closed-loop feedback control architecture described in this invention ensures strict synchronization of each subsystem in the time domain. For example, in a typical passivation trigger event, the temperature signal is detected to exceed the threshold at t=0ms. The system initiates gas injection at t=2.1ms, increases the heating power at t=3.8ms, and completes fine-tuning of the pull-out speed at t=4.5ms. The entire process is completed within 5 milliseconds, avoiding passivation failure due to response delay. High-speed camera recordings show that the passivation layer forms within 12 milliseconds after injection, with a thickness of 5.3±0.7nm, consistent with theoretical predictions.

[0048] In summary, this invention, through the deep integration of multi-physics field coupling regulation, microstructure engineering, and intelligent closed-loop control, constructs a highly stable drawing method suitable for ultrafine precious metal wires, providing a reliable material preparation basis for high-end electronic packaging, precision sensors, and nanowoven fabrics.

[0049] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for drawing precious metal wires into ultrafine gold wire braids, characterized in that, The method includes the following steps: A pretreatment zone is set up in the entrance area of ​​the drawing die, and the pretreatment zone is equipped with a controllable temperature control unit and a trace active gas injection module. During the drawing process, the surface temperature of the gold wire on the die exit side is monitored in real time, and the temperature signal is fed back to the temperature control unit and the gas injection module. When the local temperature rise exceeds the preset safety threshold, the system automatically triggers the pulsed injection of trace oxygen-containing active gas and simultaneously adjusts the temperature of the pretreatment area to the range of 300-450℃, so that the surface of the gold wire undergoes a selective oxidation reaction under controlled conditions, generating a dense gold oxide transient passivation layer with a thickness of 2-8 nanometers and diffusion-blocking function. The transient passivation layer is sheared off by the conical surface of the drawing die during the subsequent drawing deformation process, and the passivation-stripping cycle is repeated on the newly exposed metal surface, thereby maintaining the interfacial chemical stability during the dynamic drawing process.

2. The precious metal wire drawing method as described in claim 1, characterized in that, The pretreatment zone is composed of a high-temperature resistant ceramic matrix, with a platinum-rhodium alloy heating wire and a micro thermocouple array embedded inside, used for precise temperature control of the 10 to 50 mm section before the gold wire enters the mold; the trace active gas injection module is connected to a mixed gas source of high-purity oxygen and inert carrier gas through a micro-flow mass controller, and its output end is connected to the pretreatment zone cavity through a porous diffusion nozzle to form a uniform enveloping flow field around the gold wire; the response time of the micro-flow mass controller is less than 10 milliseconds, and it can complete multiple pulse gas supply operations within a single drawing cycle.

3. The precious metal wire drawing method as described in claim 1, characterized in that, The temperature monitoring uses a non-contact infrared temperature probe, whose field of view is focused on the surface of the gold wire within 5 mm after the mold exit, and the sampling frequency is no less than 1000 times per second; the central processing unit has a built-in state machine logic and adopts a dual threshold judgment mechanism: the first threshold corresponds to the upper limit of steady-state frictional temperature rise, and the second threshold corresponds to the transient thermal shock critical point; the gas injection command is activated only when the temperature rise rate exceeds the second threshold for two consecutive samplings, or when the single temperature rise amplitude exceeds the first threshold and the duration is greater than the preset window.

4. The precious metal wire drawing method as described in claim 1, characterized in that, The transient passivation layer is The phase has a spinel crystal structure, and its lattice constant forms a coherent interface with the metallic gold matrix on the crystal plane; the passivation layer is subjected to an oxygen partial pressure of It is generated in situ under the coupling conditions of Pascal and temperature of 300-450℃, with a density greater than 98% and a porosity of less than 0.5%.

5. The precious metal wire drawing method as described in claim 1, characterized in that, The drawing die is made of cemented carbide and has an inner cone angle of 8-12 degrees. Under the driving force of the drawing force, the shear stress generated by the relative sliding between the gold wire and the cone surface of the die is sufficient to destroy the van der Waals bond between the passivation layer and the substrate, causing it to peel off periodically in a sheet-like form.

6. The precious metal wire drawing method as described in claim 1, characterized in that, A plasma cleaning unit is installed downstream of the drawing system and before the take-up drum. The plasma cleaning unit consists of a radio frequency power supply, a quartz discharge chamber and a vacuum pump group. The working pressure is 1-10 Pascals, and an argon-hydrogen mixed gas is used as the discharge atmosphere. The power density of the plasma cleaning unit is adjusted in conjunction with the gold wire speed to ensure that the cleaning energy received per unit length of gold wire is constant, so as to remove residual oxide fragments and adsorbed impurities.

7. The precious metal wire drawing method as described in claim 1, characterized in that, The entire drawing system integrates a closed-loop feedback control architecture, including a temperature sensing module, a gas control module, and a mechanical execution module; the three are interconnected via an industrial fieldbus; when the temperature signal indicates that the passivation program needs to be started, the system simultaneously completes three operations: gas injection start, temperature control power increase, and fine adjustment of drawing speed.

8. The precious metal wire drawing method as described in claim 1, characterized in that, The inner surface of the drawing die is deposited with a titanium nitride transition layer by ion beam sputtering, and covered with a single-atom-layer graphene coating. The graphene coating is grown in situ by chemical vapor deposition, and its crystal domain orientation is consistent with the die axis to reduce the critical shear stress required for passivation layer peeling.

9. The precious metal wire drawing method as described in claim 1, characterized in that, In the pre-drawing process, an axial static magnetic field of 0.5-2 Tesla is applied to the primary wire during the cooling stage after the final intermediate annealing. This induces preferential orientation of gold grains, forming a textured structure. This textured structure makes the atomic arrangement on the gold wire surface more regular, which is beneficial for… The passivation layer is epitaxially grown on the crystal surface to improve its density and adhesion.

10. The precious metal wire drawing method as described in claim 1, characterized in that, The method is applicable to face-centered cubic noble metals or their alloys, including silver, platinum, and palladium. The system automatically loads the corresponding set of process parameters according to the material type. The set of parameters includes the target passivation temperature range, oxygen partial pressure range, and pulse injection timing. The parameters are retrieved from the non-volatile memory of the central processing unit before going online via a material identification tag. The entire drawing device is encapsulated in a positive pressure inert gas environment with an oxygen content of less than 1 ppm. The pretreatment zone is isolated from the active atmosphere by a physical partition and an air curtain sealing structure, forming a gradient atmosphere structure.

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