A method for manufacturing a micro-drill with a very small diameter

Abstract

The application discloses a preparation method of a micro drill with an extremely small diameter, relates to the technical field of micro drill preparation, and utilizes a high-pressure dielectrophoresis field to perform non-uniform electric field sorting on an intermediate III, promotes directional aggregation of a high-crystalline hard tungsten carbide region, performs dynamic flow state screening through a butyl / octyl functionalized porous ceramic medium bed, selectively adsorbs and removes a weakened region and a defect zone at a coating-substrate interface, guides microstructure ordered recombination of a drill tip region, obtains an intermediate IV, carves out a micro drill structure with an extremely small diameter from the intermediate IV, supplements electrolytic polishing treatment in a non-rake surface region, obtains a finished micro drill, performs annealing on the finished micro drill, and adopts oxygen plasma to perform passivation treatment on the surface of the finished micro drill, so that the finished micro drill with an extremely small diameter is obtained through a post-processing procedure. The preparation method significantly improves the comprehensive mechanical properties and service life of the micro drill with an extremely small diameter.

Description

Technical Field

[0001] This application relates to the field of micro-drill fabrication technology, specifically to a method for fabricating extremely small diameter micro-drills. Background Technology

[0002] With the rapid development of high-end industries such as 5G communication, artificial intelligence servers, automotive electronics, and aerospace, printed circuit boards (PCBs) and packaging substrates, as key components in the electronic information industry chain, are rapidly evolving towards higher density, higher precision, and higher hardness. A significant development trend in packaging substrates is smaller substrate size, finer holes, and denser component mounting. Simultaneously, to meet the demands of high-performance computing, substrate thickness is continuously increasing, resulting in a significant increase in the aspect ratio of microvias. Furthermore, to meet the requirements of high-frequency, high-speed signal transmission, packaging substrate materials typically prioritize high-hardness ceramic fillers, modified fiberglass cloth, and modified resins as their main components. These high proportions of hard fillers greatly exacerbate the wear of micro-drills, leading to a drastically shortened lifespan and severely impacting the quality and efficiency of micro-hole processing in packaging substrates. Therefore, micro-drills with diameters less than 1 mm, especially around 0.1 mm, have become crucial tools for meeting these processing requirements.

[0003] However, the fabrication and application of extremely small diameter micro-drills face a series of severe technical challenges.

[0004] 1. The miniaturization of drill bit diameter and the increase in length-to-diameter ratio lead to a significant reduction in the strength of the drill bit matrix itself, making it extremely prone to brittle fracture during high-speed drilling.

[0005] 2. To address the challenges of machining hard and brittle materials such as ceramic plates and improve drill bit life, diamond coatings are considered the most ideal coating choice due to their ultra-high hardness, high wear resistance, and low coefficient of friction. However, achieving uniform and firm adhesion of the diamond coating while maintaining the strength of the micro-diameter drill bit substrate remains the core challenge facing current coating technology.

[0006] Therefore, there is an urgent need for a novel method for preparing ultra-small diameter micro-drills. This method not only requires improving the intrinsic mechanical properties of the drill bit through material composites and matrix reinforcement, but also requires innovative interface engineering and microstructure control technologies to ensure the high strength of the matrix while achieving a perfect combination with the superhard coating. Finally, through precision machining and post-processing, a finished ultra-small diameter micro-drill with high rigidity, high wear resistance, excellent centering ability, and long life can be obtained to meet the demanding requirements of the future high-end electronics manufacturing industry. Summary of the Invention

[0007] The purpose of this application is to provide a method for preparing extremely small diameter micro-drills to address the shortcomings of the prior art.

[0008] To achieve the above objectives, this application provides the following technical solution: a method for preparing a very small diameter micro-drill, the method comprising the following steps: Step S1: Tungsten carbide powder, cobalt powder and chromium carbide powder are mixed and PDA-silane-bridged modified boron nitride dispersion is added. After the mixed powder is ball-milled, it is cold-pressed into a rod blank and then vacuum hot-pressed and sintered to obtain intermediate I. Step S2: Immerse intermediate I in sodium hydroxide solution for alkaline treatment, and then transfer it to hydrochloric acid solution for acid treatment to obtain intermediate II; Step S3: During the first coating, intermediate II is heated to the melting initiation temperature of the coating material and then uniformly coated. After drying, a porous rough layer is formed on the surface of intermediate II. The second coating is carried out on the porous rough layer to obtain intermediate III. Step S4: Use a high-voltage dielectric electrophoresis field to sort intermediate III under a non-uniform electric field, which promotes the directional aggregation of highly crystalline hard tungsten carbide regions. Dynamic flow screening is performed through a butyl / octyl functionalized porous ceramic medium bed to selectively adsorb and remove the weakened areas and defect bands at the coating-substrate interface, guide the orderly recombination of the microstructure in the drill tip region, and obtain intermediate IV. Step S5: Carve a very small diameter micro-drill structure into the intermediate body IV, and perform electrolytic polishing on the non-cutting surface area to obtain the finished micro-drill; Step S6: Anneal the finished micro-drill and passivate its surface using oxygen plasma. The finished micro-drill with extremely small diameter is obtained through post-processing.

[0009] In a preferred embodiment, step S4, guiding the orderly reorganization of the microstructure of the drill tip region, includes the following steps: Physical ultrafiltration is performed using ceramic membranes, and isoelectric focusing self-assembly technology is combined to regulate the ζ-potential distribution and guide the orderly reorganization of the microstructure in the drill tip region.

[0010] In a preferred embodiment, in step S4, the frequency of the high-voltage dielectric field is 1MHz, the electric field strength is 200V / cm, the pore size of the butyl / octyl functionalized porous ceramic dielectric bed is 50~100nm, and the ceramic film is on the 10kDa level.

[0011] In a preferred embodiment, in step S1, the mixing mass ratio of tungsten carbide powder, cobalt powder and chromium carbide powder is 94:5:1, the PDA-silane-bridged modified boron nitride dispersion accounts for 0.5 wt% of the total powder weight, the vacuum hot pressing sintering temperature is 1380℃~1430℃, the pressure is 25MPa~30MPa, and the holding time is 1.5~2 hours.

[0012] In a preferred embodiment, PDA-silane-bridged modified boron nitride is ultrasonically dispersed in N,N-dimethylformamide for 3-6 hours to obtain a PDA-silane-bridged modified boron nitride dispersion.

[0013] In a preferred embodiment, in step S3, the coating material is a fluoropolymer-based functional emulsion or a modified PEEK-based nanocomposite emulsion.

[0014] In a preferred embodiment, in step S3, the roughness Ra of the porous rough layer is greater than 0.35 μm. After the second coating is completed, the temperature of intermediate II is increased by 40~50°C to melt the coating material and achieve molecular rearrangement.

[0015] In a preferred embodiment, in step S2, the sodium hydroxide solution is 0.20 mol / L, the alkali treatment time is 55 minutes, the hydrochloric acid solution is 0.10~0.12 mol / L, the acid treatment time is 9 minutes, and after each treatment, the solution is rinsed with deionized water until neutral and then dried.

[0016] In a preferred embodiment, in step S5, the intermediate body IV is fixed to a five-axis micro-nano machining center and is engraved using a synergistic forming technology of femtosecond laser-induced ablation combined with magnetron sputtering-assisted grinding. The diameter of the micro-drill structure is less than or equal to 0.2 mm, the radius of curvature of the drill tip is less than or equal to 15 μm, and the helix angle error is within ±1°.

[0017] In a preferred embodiment, in step S6, the finished micro-drill is annealed at a temperature of 300°C to 350°C under an argon atmosphere, and the passivation treatment time is 30 to 60 seconds.

[0018] The technical effects and advantages provided by this application in the above technical solution are as follows: 1. This application preliminarily optimizes the microstructure and uniformity of the cemented carbide substrate by introducing a modified boron nitride dispersion from the material source and employing vacuum hot pressing sintering. More importantly, drawing on the essence of the concept of regional acid-base treatment, through alkali and acid treatments, surface cobalt elements are removed to enhance coating adhesion. Theoretically, by controlling the treatment time and area, a significant decrease in the overall strength of the substrate due to excessive corrosion can be avoided, thus achieving a balance between coating adhesion and substrate strength. The two coatings form a porous, rough layer, greatly increasing the contact area and mechanical interlocking between the coating and the substrate. This lays the microstructural foundation for the firm adhesion of subsequent high-performance coatings (such as diamond coatings), significantly improving the overall mechanical properties and service life of the micro-drill.

[0019] 2. This application utilizes microstructure sorting and recombination technology to achieve targeted enhancement of the drill tip region's performance. For ultra-small diameter micro-drills, the drill tip is the critical component bearing the greatest cutting force and wear. By employing a high-voltage dielectric electrophoresis field and a functionalized porous ceramic dielectric bed, the matrix material is microscopically screened and defect-removed, selectively removing interface weakening zones and defect bands, and guiding the directional aggregation of hard phases (such as highly crystalline tungsten carbide) in the drill tip region. This process is equivalent to optimizing and purifying the drill bit's cutting edge at the microscale, thereby significantly improving the drill tip's hardness, wear resistance, and anti-chipping ability, effectively addressing the problems of poor toughness and easy chipping of ultra-hard materials such as diamond.

[0020] 3. This application utilizes post-processing techniques to ensure the dimensional accuracy, surface quality, and long-term stability of the finished micro-drill. After engraving the extremely small diameter structure, electropolishing is performed on the non-cutting surfaces. This helps eliminate machining burrs, reduce surface roughness, and decrease stress concentration and frictional resistance during high-speed rotation (up to 100,000 RPM or more), which is crucial for high-precision PCB drilling. Annealing and oxygen plasma passivation release internal processing stress, stabilize the material structure, and form a dense oxide layer through surface passivation, improving the chemical stability and anti-adhesion ability of the drill bit. This reduces material adhesion when processing composite materials such as modified resins and fiberglass cloth, ensuring hole wall quality and drill bit life during long-term processing.

[0021] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0023] Figure 1 This is a flowchart of the preparation method of this application.

[0024] Figure 2 This is a schematic diagram of the micro-drill geometry parameters of this application.

[0025] Figure 3 Metallographic image of the surface coating of intermediate III in this application.

[0026] Figure 4 This is a schematic diagram of the covalent grafting of the silane coupling agent of this application onto the surface of boron nitride.

[0027] Figure 5 This is a histogram showing the diameter accuracy distribution of the micro-drills produced in this application. Detailed Implementation

[0028] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0029] Please see Figure 1 As shown, this embodiment provides a method for preparing a very small diameter micro-drill, which includes the following steps: Step S1: Partial modification of raw materials and preparation of reinforcing agents Tungsten carbide (WC) powder, cobalt (Co) powder, and chromium carbide (Cr3C2) powder were mixed in a mass ratio of 94:5:1, and 0.5 wt% of PDA-silane-bridged modified boron nitride was added. This modified boron nitride was first ultrasonically dispersed in N,N-dimethylformamide for 3–6 hours to obtain a stable dispersion. Subsequently, the mixed powder was thoroughly ball-milled to ensure uniform fusion. After ball milling, the powder was cold-pressed into rod blanks and then vacuum hot-pressed at 1380–1430 °C and 25–30 MPa for 1.5–2 hours to obtain a high-density, high-toughness cemented carbide matrix rod, which served as the initial structural intermediate I.

[0030] Step S2: Perform matrix surface orientation activation and anchor point construction on the original structural intermediate I. The original intermediate I was completely immersed in a 0.20 mol / L sodium hydroxide (NaOH) solution for 55 minutes to induce surface hydroxylation and produce a micro-etching effect. It was then transferred to a 0.10–0.12 mol / L hydrochloric acid (HCl) solution for 9 minutes to achieve surface protonation control and dangling bond passivation. After each chemical treatment, it was rinsed with deionized water until neutral and then dried at low temperature to obtain a pretreated matrix, intermediate II, with good wettability and abundant chemical anchoring sites.

[0031] Step S3: Construct a two-stage gradient functional coating system Fluoropolymer-based functional emulsions (e.g., perfluoroethylene propylene) or modified PEEK-based nanocomposite emulsions are prepared as coating materials. For the first coating, intermediate II is heated to the melting initiation temperature of the coating material and uniformly coated. After preliminary drying, a porous rough layer with a roughness Ra greater than 0.35 μm is formed on the surface of intermediate II. For the second coating, another layer is applied on top of the porous rough layer, and the temperature of intermediate II is increased by 40–50 °C to promote melting of the coating material and molecular rearrangement, thereby achieving structural densification and stress release. Subsequently, through gradient cooling and thorough drying, a surface functional film with strong adhesion, low friction coefficient, and high-temperature wear resistance is finally formed on the surface of intermediate II, yielding intermediate III.

[0032] Step S4: Domain optimization and interface regulation and recombination Intermediate III was sorted by a non-uniform electric field using a high-voltage dielectric electrophoresis field (1MHz, 200V / cm), which promoted the directional aggregation of highly crystalline hard tungsten carbide WC regions. Dynamic flow screening was then performed using a butyl / octyl functionalized porous ceramic media bed with a pore size of 50~100nm to selectively adsorb and remove weakened regions and defect zones at the coating-matrix interface, retaining only regions with complete structure and excellent rigidity. Physical ultrafiltration was performed using a 10kDa ceramic membrane, and isoelectric focusing self-assembly technology was combined to regulate the ζ-potential distribution and guide the orderly recombination of the microstructure (including the WC reinforcing phase and the polymer coating phase) in the drill tip region, ultimately forming a uniform, high-strength, and cohesive cutting edge precursor, namely intermediate IV.

[0033] Step S5, Micro-forming and Geometric Precision Locking like Figure 2 As shown, intermediate body IV is fixed on a five-axis micro / nano machining center. A synergistic forming technology combining femtosecond laser-induced ablation and magnetron sputtering-assisted grinding is employed to precisely sculpt an ultra-small diameter micro-drill structure with a diameter not exceeding 0.2 mm, a drill tip curvature radius not exceeding 15 μm, and a helix angle error controlled within ±1°. Electrolytic polishing is then applied to the non-cutting surface areas to reduce the surface roughness Ra to below 0.1 μm, thereby optimizing the smoothness of the chip removal channel and obtaining the finished micro-drill. An online laser confocal monitoring system is incorporated throughout the forming process to detect and correct geometric deviations in real time through closed-loop feedback, ensuring consistency between different batches of products.

[0034] Step S6, stress regulation and surface passivation final treatment The finished micro-drills are subjected to low-temperature annealing at 300-350℃ in an argon atmosphere to eliminate residual internal stress generated during processing. Oxygen plasma is then used for surface passivation treatment for 30-60 seconds, effectively sealing surface microcracks and improving the micro-drills' resistance to oxidation, element diffusion, and corrosion. Finally, ultrasonic cleaning, centrifugal dehydration, and vacuum cryogenic encapsulation processes yield structurally stable, high-performance micro-drills.

[0035] The preparation process of DA-silane-bridged modified boron nitride dispersion can be divided into three main stages: boron nitride surface modification, PDA bridging coating, and dispersion construction. The aim is to improve the dispersibility and interfacial compatibility of boron nitride in a cemented carbide matrix. Specifically, the process includes the following steps: The raw material selected is hexagonal boron nitride (h-BN), whose layered structure and low surface energy result in high chemical inertness. Direct dispersion easily leads to agglomeration, which is not conducive to uniform distribution in the composite powder system. Therefore, a two-step surface modification is required first.

[0036] The first step is hydroxylation treatment, in which h-BN powder is placed in a 10% sodium hydroxide (NaOH) solution and treated at 90°C for 60 minutes. The etching effect of the alkaline solution on the BN surface introduces hydroxyl (–OH) active sites, providing anchoring sites for subsequent coupling reactions.

[0037] like Figure 4 As shown, the second step involves silane coupling agent grafting. A silane coupling agent containing double bonds (such as KH-570, γ-methacryloyloxypropyltrimethoxysilane) is selected and dissolved in anhydrous ethanol to prepare an approximately 10% (w / v) solution. The pH is adjusted to approximately 4 with dilute hydrochloric acid, and the solution is allowed to stand for pre-hydrolysis. Simultaneously, the hydroxylated BN is dispersed in an organic solvent such as toluene and subjected to ultrasonic pretreatment. After mixing the two dispersion systems, the mixture is reacted at the reflux temperature of toluene for approximately 8 hours. This allows the silanol groups generated by the hydrolysis of the silane coupling agent to undergo a condensation reaction with the hydroxyl groups on the BN surface, achieving covalent grafting of silane molecules onto the BN surface. After the reaction, the mixture is sequentially centrifuged, dried, and purified by Soxhlet extraction to remove unreacted coupling agent and byproducts, yielding silane-modified BN powder.

[0038] PDA bridging coating was then performed. Polydopamine (PDA), rich in catechol and amino functional groups, can undergo oxidative self-polymerization under weakly alkaline conditions (such as TrⅠs-HCl buffer, pH≈8.5) to form a uniform coating layer on the silane-modified BN surface. This coating layer achieves stable bridging through multiple interactions between PDA and the silane layer (such as hydrogen bonding, π-π stacking, and electrostatic interactions), thereby enhancing the interfacial bonding between BN and the cemented carbide matrix and significantly improving its dispersion stability during subsequent ball milling.

[0039] To obtain a dispersion suitable for cemented carbide powder systems, PDA-silane-bridged modified boron nitride (BN) needs to be ultrasonically dispersed in a suitable solvent. N,N-dimethylformamide (DMF) exhibits excellent wetting and dispersing properties for h-BN, and is therefore selected as the dispersion medium. Modified BN powder is weighed according to the target addition ratio (e.g., 0.5 wt% of the total mass of the mixed powder) and added to DMF, then processed using a probe-type ultrasonic device. Ultrasonic parameters can be set to a frequency of 30–90 kHz and a power of 50–150 W. The time is adjusted according to particle size and concentration, generally requiring 3–6 hours to utilize cavitation to break up particle agglomeration and achieve uniform dispersion. The resulting PDA-silane-bridged modified boron nitride dispersion can be directly mixed with tungsten carbide (WC), cobalt (Co), and chromium carbide (Cr3C2) powders and then ball-milled to provide a raw material system with uniform composition and optimized interfacial properties for subsequent cold pressing and vacuum hot pressing sintering.

[0040] In one embodiment of this application, when constructing the dual-gradient functional coating system in step S3, the temperature difference between the second coating and the first coating is preferably 40℃-50℃, including but not limited to any value among 40℃, 42℃, 45℃, 48℃, and 50℃, or any range between the two. By controlling the temperature rise of the second coating to match the temperature of the first coating, a specific temperature difference is achieved between the two coating stages, further promoting the melting and molecular rearrangement of the coating material, thereby achieving structural densification and the release of internal stress, ultimately forming a surface functional film with strong adhesion, low friction coefficient, and high-temperature wear resistance.

[0041] In one embodiment disclosed in this application, when constructing the two-stage gradient functional coating system in step S3, the reaction temperature of the first coating (i.e., the heating temperature of intermediate II) is the melting initiation temperature of the coating material, and the reaction temperature of the second coating is increased by 40°C-50°C based on the first coating temperature. By precisely controlling the temperature difference between the two stages, it is beneficial to promote the orderly melting and densification of the coating material, thereby significantly optimizing the density and internal stress distribution of the functional film and improving the wear resistance and bonding strength of the micro-drill.

[0042] In one embodiment of this application, when constructing the two-stage gradient functional coating system in step S3, the total time for melt rearrangement and gradient cooling after the second coating is 2h to 3h, including but not limited to any one of 2h, 2.2h, 2.5h, 2.8h, 3h or any range between the two.

[0043] In one embodiment of this application, when constructing the dual-gradient functional coating system in step S3, the initial drying time after the first coating is 5h to 8h, including but not limited to any one of 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h or any range between two of them.

[0044] In one embodiment disclosed in this application, by adjusting the processing time after the second coating and the processing time after the first coating in step S3, it is beneficial to further optimize the melting rearrangement degree and pore structure evolution of the coating material, thereby significantly improving the structural stability of the functional film and reducing the risk of coating peeling during the use of the micro-drill. Preferably, the processing time after the second coating is 2h to 3h, and the processing time after the first coating is 5h to 8h.

[0045] In one embodiment disclosed in this application, during step S4, the structural domain optimization and interface regulation and recombination stage, there is a synergistic relationship between the electric field strength of the high-voltage dielectric field and the difference in pore size of the dielectric bed in the dynamic flow screening. The preferred frequency of the dielectric field is 1 MHz, and the preferred electric field strength is 200 V / cm; the preferred pore size of the functionalized porous ceramic dielectric bed is 50-100 nm. By adjusting the difference between the electric field parameters and the physical screening parameters, it is beneficial to promote the directional aggregation of highly crystalline regions and the selective removal of weakened regions, thereby significantly improving the structural uniformity and cohesion of the blade precursor.

[0046] In one embodiment of this application, in step S4, the domain optimization and interface regulation and recombination stage, the ceramic membrane used for physical ultrafiltration has a molecular weight cutoff of 10 kDa. By using a membrane with a specific molecular weight cutoff for ultrafiltration and combining it with isoelectric focusing self-assembly technology to regulate the ζ-potential distribution, it is beneficial to guide the orderly recombination of the microstructure, ultimately forming a uniform and high-strength blade precursor.

[0047] In one embodiment disclosed in this application, in step S5, the micro-forming and geometric precision locking stage, the time for the synergistic forming process of femtosecond laser-induced ablation and magnetron sputtering-assisted grinding is optimally matched with the subsequent electrolytic polishing time for non-edge areas. The synergistic forming process time is determined based on the specific structural dimensions, and the electrolytic polishing time is preferably sufficient to reduce the surface roughness Ra to below 0.1 μm. By controlling the time of different processing steps, it is beneficial to optimize surface quality while achieving precise geometric forming, thereby ensuring the smoothness of chip removal and batch consistency of the micro-drill.

[0048] In one embodiment of this application, in step S6, the stress regulation and surface passivation final treatment stage, the low-temperature annealing time and the oxygen plasma treatment time have a synergistic relationship. The low-temperature annealing is performed in an argon atmosphere at 300-350°C, and the time is determined according to the dimensions to eliminate internal stress; the oxygen plasma treatment time is preferably 30-60 seconds. By synergistically optimizing the annealing and passivation parameters, it is beneficial to effectively seal surface microcracks while eliminating residual stress, thereby improving the overall performance of the micro-drill, including its oxidation resistance, diffusion resistance, and corrosion resistance.

[0049] In one embodiment of this application, after the original structural intermediate I is subjected to substrate surface orientation activation and anchor point construction in step S2, and before the two-stage gradient functional coating system is constructed in step S3, thorough cleaning and low-temperature drying are performed as a system stabilization treatment step.

[0050] It is understood that the temperatures mentioned above all refer to the operating temperature of the equipment used to perform the above treatment or the ambient temperature.

[0051] In one embodiment of this application, the rinsing and low-temperature drying stage following alkali and acid treatment in step S2 is preferably characterized by a temperature ≤ 80°C and a time sufficient to completely remove surface moisture. By synergistically optimizing the temperature and time parameters, the moisture removal efficiency and surface active site retention of the substrate during post-treatment are optimally balanced. This not only facilitates obtaining a dry pre-treated substrate but also avoids excessive surface oxidation or anchor point deactivation caused by high temperatures. It also helps maintain good wettability of the substrate and provides a stable foundation for subsequent coating bonding.

[0052] In one embodiment disclosed in this application, the temperature of the low-temperature drying stage in step S2 is ≤80°C, including but not limited to any one of 60°C, 65°C, 70°C, 75°C, and 80°C or any range between two of them, and the drying time is based on ensuring that the substrate surface is completely dry.

[0053] In one embodiment disclosed in this application, by combining the precise surface treatment in step S2 with the gradient coating construction in step S3, and coordinating with the fine control in subsequent steps S4 to S6, the resulting micro-drill has the characteristics of stable structure, high wear resistance, high precision and excellent comprehensive performance, and can be widely used in the field of micro-processing and manufacturing of high-precision and high-reliability electronic components.

[0054] Example 1.1 Step S1: Tungsten carbide (WC), cobalt (Co), and chromium carbide (Cr3C2) powders were mixed at a mass ratio of 94:5:1. PDA-silane-bridged modified boron nitride (ultrasonically dispersed in N,N-dimethylformamide for 4 hours) was added at 0.5 wt% of the total powder weight. After ball milling, the mixture was vacuum hot-pressed and sintered at 1400℃ and 28 MPa for 1.8 hours to obtain intermediate I with the original structure.

[0055] Step S2: Immerse intermediate I in 0.20 mol / L NaOH solution for 55 minutes, then immerse it in 0.11 mol / L HCl solution for 9 minutes. After each treatment, wash thoroughly with water and dry to obtain intermediate II.

[0056] Step S3: A concentrated polyfluoroethylene propylene (FEP) emulsion is used as the coating material. Intermediate II is heated to 320°C for the first coating and dried to form a porous, rough layer. A second coating is then performed at 360°C and melted. After gradient cooling, a functional film is formed, yielding intermediate III. Figure 3 As shown.

[0057] Subsequent steps S4-S6: Performed according to the standard process described in this application.

[0058] Example 1.2 The difference from Example 1.1 is that in step S1, the vacuum hot pressing sintering temperature was adjusted to 1380°C, while the other parameters remained unchanged. The aim was to investigate the effect of a lower sintering temperature on the grain fineness and toughness of the matrix.

[0059] Example 1.3 The difference from Example 1.1 is that in step S1, the vacuum hot pressing sintering temperature was adjusted to 1430°C, while the other parameters remained unchanged. The aim was to investigate the effect of a higher sintering temperature on the density and hardness of the matrix.

[0060] Example 2.1 The difference from Example 1.1 is that in step S2, the concentration of NaOH solution and the concentration of HCl solution are adjusted to 0.10 mol / L, while the treatment time remains unchanged. The aim is to investigate the effect of mild activation conditions on the density of surface anchor points and the adhesion of the coating.

[0061] Example 2.2 The difference from Example 1.1 is that in step S2, the concentration of NaOH solution was adjusted to 0.30 mol / L, the concentration of HCl solution was adjusted to 0.12 mol / L, and the treatment time remained unchanged. The aim was to investigate the effect of stronger activation conditions on surface roughness and chemical activity.

[0062] Example 3.1 The difference from Example 1.1 is that in step S1, the mixing mass ratio of WC, Co, and Cr3C2 is adjusted to 92:7:1. This aims to investigate the effect of increasing the cobalt (Co) binder phase content on the flexural strength and toughness of the cemented carbide matrix.

[0063] Example 3.2 The difference from Example 1.1 is that in step S1, chromium carbide (Cr3C2) is replaced with an equal mass of vanadium carbide (VC). The aim is to investigate the effects of different grain growth inhibitors on suppressing WC grain growth during sintering and obtaining a finer grain structure.

[0064] Example 4.1 The difference from Example 1.1 is that in step S1, the amount of PDA-silane-bridged modified boron nitride added was adjusted to 0.3 wt% of the total powder weight. This was to investigate the contribution of lower reinforcement content to the overall performance of the matrix.

[0065] Example 4.2 The difference from Example 1.1 is that in step S1, the amount of PDA-silane-bridged modified boron nitride added was adjusted to 0.8 wt% of the total powder weight. The aim was to investigate the effect of a higher reinforcement content on the thermal conductivity, wear resistance, and toughening of the matrix.

[0066] Example 5.1 The difference from Example 1.1 is that in step S3, the perfluoroethylene propylene (FEP) emulsion was replaced with a modified polytetrafluoroethylene (PTFE) emulsion. The first coating temperature was 350°C, and the second coating melting temperature was 400°C. The aim was to compare the differences in temperature resistance, coefficient of friction, and film-forming properties between different fluoropolymers (PTFE vs FEP).

[0067] Example 5.2 The difference from Example 1.1 is that in step S3, a polyether ether ketone (PEEK) based nanocomposite emulsion is used as the coating material. The high strength, high temperature resistance and good adhesion to metal of PEEK itself are utilized to explore the possibility of non-fluorine high-performance coatings.

[0068] Example 6 The difference from Example 2.2 is that, before the acid-base activation in step S2, intermediate I is first subjected to oxygen plasma treatment (300W power, 60 seconds) to further clean the surface and introduce active groups, thereby enhancing the subsequent chemical anchoring effect.

[0069] Example 7 The difference from Example 1.1 is that in step S3, the two-stage coating is replaced with a three-stage gradient coating. The melting temperatures for the three coatings are set to 320°C, 340°C, and 360°C, respectively, and each coating is followed by a brief drying process. The aim is to construct a denser multilayer coating system with a gentler internal stress gradient.

[0070] Example 8 This embodiment aims to simulate the needs of high-end scenarios such as processing 5G / 6G communication PCB boards.

[0071] Step S1: Ultrafine tungsten carbide powder (particle size 0.3-2.0 μm) and cobalt powder are mixed at a mass ratio of 90:9:1 (WC:Co:VC), and 1.0 wt% of PDA-silane-bridged modified boron nitride is added. Sintering is performed at 1420℃ and 30 MPa to achieve ultra-high hardness and wear resistance.

[0072] Step S2: Use a milder treatment with 0.15 mol / L NaOH and 0.10 mol / L HCl to activate the surface while avoiding excessive etching that could affect the dimensional accuracy of the microstructure.

[0073] Step S3: Select an imported fluoropolymer emulsion with a high fluorine content (e.g., 45%) (e.g., AF2400S type) to utilize its superior hydrophobic and oleophobic properties, chemical stability, and temperature resistance to provide excellent anti-adhesion and protection for micro-drills when processing polymer copper-clad laminates.

[0074] Step S5: Set the final micro-drill diameter target to 0.15mm and strictly control the geometric accuracy, such as... Figure 5 As shown.

[0075] Comparative Example 1 Referring to step S1 of this application, an initial structural intermediate I (hard alloy matrix rod) is prepared. Intermediate I is treated with a 0.20 mol / L NaOH solution for 55 minutes, followed by washing and drying, omitting the acid treatment step. This treatment only produces preliminary hydroxylation, and the surface anchoring points are not fully constructed. After heating the simplified substrate to the melting temperature of the coating material, a single uniform coating is performed using a coating machine (using the same fluoropolymer or modified PEEK emulsion as in this application). After coating, it is directly dried and cooled for shaping, omitting the crucial step of secondary coating after forming a porous rough layer to achieve structural densification, as described in this application. The final coating is a single-layer structure, which may contain pores and stress concentrations. The fine interface control processes in step S4 of this application, such as high-voltage dielectric field sorting, porous media bed screening, ultrafiltration, and isoelectric focusing self-assembly, are completely skipped. The bonding between the coating and the substrate depends solely on the simplified surface treatment, and weakened areas and defect bands may exist at the interface. Referring to steps S5 and S6 of this application, the coated rod is subjected to micro-forming, stress relief and surface passivation treatment.

[0076] Comparative Example 2 WC powder (not ultrafine powder) with a Fisher particle size of approximately 1.2 μm and Co powder with a Fisher particle size of approximately 1.0 μm were selected and mixed at a mass ratio of 94:5:1, with 1 wt% Cr3C2 added as a grain inhibitor. The step of adding PDA-silane-bridged modified boron nitride reinforcement is omitted in this application. Conventional ball milling was used for mixing. The mixture was molded into rod blanks. Subsequently, sintering was carried out in an atmospheric pressure sintering furnace at a sintering temperature of approximately 1400°C, omitting the vacuum hot pressing sintering (25-30 MPa pressure) step in this application. After simple surface cleaning, the sintered rods (with relatively coarse grain size, expected to be above 0.5 μm) were directly subjected to steps S2 (alkali-acid treatment), S3 (two-stage coating), S4 (interface control), S5 (micro-forming), and S6 (post-treatment) of this application.

[0077] Performance testing items: The hardness (HRA) of the substrate is measured using a Rockwell hardness tester (HRA scale), which is a core indicator for evaluating the wear resistance of materials. The three-point bending method is used to assess the toughness and fracture resistance of the material. The average grain size (μm) of the WC is observed using a metallographic microscope or scanning electron microscope (SEM). Grain size directly affects the hardness, strength, and wear resistance of the material. The indentation method (HRA scale, 60 kgf load) is used to qualitatively evaluate the coating adhesion (qualitative grade). The indentation morphology is observed under a microscope and judged against the HF1-HF6 grade standard, with HF1-HF4 being acceptable, and HF1-HF3 indicating good adhesion. Simulated drilling tests are performed on a standard test board (such as FR-4), and the number of holes drilled until drill bit failure (such as chipping, excessive wear, or deterioration of hole wall quality) is recorded. Measurements are taken using a high-precision projector, image measuring instrument, or laser scanning diameter gauge. Diameter consistency is crucial for ensuring PCB hole diameter accuracy; the test results are shown in Table 1.

[0078]

[0079] Table 1: Test Results Table 1 shows that Examples 1.1-1.3 demonstrate that sintering temperature directly determines the balance between hardness and flexural strength by affecting grain size and density. Examples 3.1 (high cobalt content) and 8 (ultrafine grains) significantly improve flexural strength by increasing the binder phase and refining the grains, respectively, meeting the design goals of strength and toughness for cemented carbide. Comparative Example 2, due to its coarse grains and conventional sintering process, exhibits significantly lower hardness and strength, demonstrating the advanced nature of this application in matrix material preparation.

[0080] Examples 2.1-2.2 and Example 6 show that surface activation treatment needs to be precisely controlled to obtain optimal coating adhesion (HF2-HF1 level). Comparative Example 1, due to simplified surface treatment and coating process, had an adhesion level that dropped to HF5-HF6 (unacceptable), directly leading to a sharp drop in borehole life. This strongly demonstrates the indispensability of the two-stage gradient coating and interface control steps in this application for ensuring coating reliability.

[0081] Drilling life is the ultimate integrated manifestation of all the performance characteristics of a micro-drill. Example 8 achieves an ultra-long drilling life by integrating the optimal substrate (high hardness and high strength), surface treatment (precise activation), and top-level coating, fully meeting the processing requirements of high-end PCBs such as 5G / 6G. Comparative Examples 1 and 2, on the other hand, have extremely short lifespans due to coating failure and insufficient substrate performance, respectively, demonstrating the value of the full-chain process optimization in this application from two dimensions. The diameter accuracy of all examples meets the stringent requirements of PCB micro-drilling (within ±0.003mm), proving the effectiveness of the precision processing and real-time feedback technologies such as femtosecond laser-induced ablation combined with magnetron sputtering assisted grinding and online laser confocal monitoring in step S5 of this application. Example 8 further controls the diameter accuracy to ±0.001mm, demonstrating its ability to cope with the processing challenges of ultra-small diameter (0.15mm).

[0082] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

[0083] The preferred embodiments disclosed above are merely illustrative of this application. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. The selection and detailed description of these embodiments in this specification are intended to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application. This application is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a very small diameter micro-drill, characterized in that: The preparation method includes the following steps: Step S1: Tungsten carbide powder, cobalt powder and chromium carbide powder are mixed and PDA-silane-bridged modified boron nitride dispersion is added. After the mixed powder is ball-milled, it is cold-pressed into a rod blank and then vacuum hot-pressed and sintered to obtain intermediate I. Step S2: Immerse intermediate I in sodium hydroxide solution for alkaline treatment, and then transfer it to hydrochloric acid solution for acid treatment to obtain intermediate II; Step S3: During the first coating, intermediate II is heated to the melting initiation temperature of the coating material and then uniformly coated. After drying, a porous rough layer is formed on the surface of intermediate II. The second coating is carried out on the porous rough layer to obtain intermediate III. Step S4: Use a high-voltage dielectric electrophoresis field to sort intermediate III under a non-uniform electric field, which promotes the directional aggregation of highly crystalline hard tungsten carbide regions. Dynamic flow screening is performed through a butyl / octyl functionalized porous ceramic medium bed to selectively adsorb and remove the weakened areas and defect bands at the coating-substrate interface, guide the orderly recombination of the microstructure in the drill tip region, and obtain intermediate IV. Step S5: Carve a very small diameter micro-drill structure into the intermediate body IV, and perform electrolytic polishing on the non-cutting surface area to obtain the finished micro-drill; Step S6: Anneal the finished micro-drill and passivate its surface using oxygen plasma. The finished micro-drill with extremely small diameter is obtained through post-processing.

2. The method for preparing a very small diameter micro-drill according to claim 1, characterized in that: In step S4, the microstructure of the drill tip region is guided to reorganize in an orderly manner, including the following steps: Physical ultrafiltration is performed using ceramic membranes, and isoelectric focusing self-assembly technology is combined to regulate the ζ-potential distribution and guide the orderly reorganization of the microstructure in the drill tip region.

3. The method for preparing a very small diameter micro-drill according to claim 2, characterized in that: In step S4, the frequency of the high-voltage dielectric field is 1MHz and the electric field strength is 200V / cm. The pore size of the butyl / octyl functionalized porous ceramic dielectric bed is 50~100nm and the ceramic film is on the 10kDa level.

4. The method for preparing a very small diameter micro-drill according to claim 1, characterized in that: In step S1, the mixing mass ratio of tungsten carbide powder, cobalt powder and chromium carbide powder is 94:5:1, the PDA-silane bridged modified boron nitride dispersion accounts for 0.5 wt% of the total powder weight, the vacuum hot pressing sintering temperature is 1380℃~1430℃, the pressure is 25MPa~30MPa, and the holding time is 1.5~2 hours.

5. The method for preparing a very small diameter micro-drill according to claim 4, characterized in that: After ultrasonically dispersing the PDA-silane-bridged modified boron nitride in N,N-dimethylformamide for 3-6 hours, a PDA-silane-bridged modified boron nitride dispersion was obtained.

6. A method for preparing a very small diameter micro-drill according to claim 3 or 5, characterized in that: In step S3, the coating material is a fluoropolymer-based functional emulsion or a modified PEEK-based nanocomposite emulsion.

7. The method for preparing a very small diameter micro-drill according to claim 6, characterized in that: In step S3, the roughness Ra of the porous rough layer is greater than 0.35 μm. After the second coating is completed, the temperature of intermediate II is increased by 40~50℃ to melt the coating material and achieve molecular rearrangement.

8. The method for preparing a very small diameter micro-drill according to claim 2, characterized in that: In step S2, the sodium hydroxide solution is 0.20 mol / L, the alkali treatment time is 55 minutes, the hydrochloric acid solution is 0.10~0.12 mol / L, the acid treatment time is 9 minutes, and after each treatment, the solution is rinsed with deionized water until neutral and then dried.

9. The method for preparing a very small diameter micro-drill according to claim 7, characterized in that: In step S5, intermediate body IV is fixed on a five-axis micro-nano machining center and engraved using a synergistic forming technology of femtosecond laser-induced ablation combined with magnetron sputtering-assisted grinding. The diameter of the micro-drill structure is less than or equal to 0.2 mm, the radius of curvature of the drill tip is less than or equal to 15 μm, and the helix angle error is within ±1°.

10. The method for preparing a very small diameter micro-drill according to claim 9, characterized in that: In step S6, the finished micro-drill is annealed at a temperature of 300℃~350℃ in an argon atmosphere, and the passivation treatment time is 30~60 seconds.

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