Method for manufacturing a micro-drill with a cvd diamond coating and micro-drill manufactured by this method

Abstract

This application relates to the field of hard tool manufacturing technology, and discloses a method for preparing CVD diamond-coated micro-drills and the micro-drills prepared by this method. The preparation method includes the following steps: processing a rod raw material into a micro-drill substrate; transferring the cleaned and dried micro-drill substrate into a PVD magnetron sputtering chamber for plasma cleaning; sequentially depositing a Ti transition layer, a TiC transition layer, and an amorphous carbon sacrificial layer on the surface of the micro-drill substrate; transferring it across the chamber to a hot-filament chemical vapor deposition chamber; using plasma to etch and volatilize the amorphous carbon sacrificial layer and its surface oxides to expose the unoxidized TiC transition layer; introducing carbon source gas and hydrogen in situ; epitaxially growing a CVD diamond coating; and using a femtosecond laser to remove the deposited passivated crystal clusters. This preparation method eliminates the need for acid leaching to remove cobalt, and utilizes the preferential oxidation of the amorphous carbon sacrificial layer during the transfer process to protect the underlying TiC transition layer, thus solving the problem of transition layer oxidation failure.

Description

Technical Field

[0001] This application relates to the field of hard tool manufacturing technology, and in particular to a method for preparing CVD diamond-coated micro-drills and the micro-drills prepared by the method. Background Technology

[0002] In the high-precision micro-hole machining of printed circuit boards and integrated circuit packaging substrates, micro-drills are often used. CVD (Chemical Vapor Deposition) diamond-coated micro-drills offer advantages over traditional PCD (Polycrystalline Diamond) micro-drills, including higher hardness and lower risk of tip breakage, and have broader application prospects. However, when preparing CVD diamond coatings on cemented carbide, cobalt in the cemented carbide matrix diffuses to the surface at high temperatures, catalyzing the transformation of diamond into the graphite phase, leading to decreased coating adhesion. Existing technologies typically employ chemical acid etching for cobalt removal to form a porous framework for mechanical locking. However, this cobalt removal process can damage the microstructural integrity of the micro-drill cutting edge, reducing edge strength and making it prone to micro-chipping when machining hard composite materials.

[0003] To avoid damage to the substrate caused by cobalt removal during acid pickling, a physical transition layer can be introduced between the substrate and the coating. However, due to equipment limitations, after depositing the transition layer in a PVD (Physical Vapor Deposition) machine, the micro-drill usually needs to be transferred through an atmospheric environment to a CVD (Chemical Vapor Deposition) machine for diamond deposition. During this cross-cavity transfer, the surface of the transition layer readily reacts with oxygen in the air, forming a thermodynamically stable oxide passivation film. This oxidation failure caused by the cross-cavity transfer hinders the chemical bonding during subsequent diamond growth, resulting in poor coating adhesion. Furthermore, due to the grain clustering effect during the deposition of thick CVD diamond coatings, the surface of the micro-drill cutting edge and chip flute coating after deposition often exhibits passivation and roughness, increasing the cutting resistance during micro-hole machining. Summary of the Invention

[0004] This application provides a method for preparing CVD diamond-coated micro-drills and a micro-drill prepared by the method, aiming to at least solve the problems of transition layer oxidation failure caused by cross-cavity transfer during the preparation of existing CVD diamond-coated micro-drills, as well as cutting edge blunting and increased cutting resistance due to surface roughness after CVD thick coating deposition.

[0005] The method for preparing CVD diamond-coated micro-drills according to the first aspect of this application includes the following steps: processing a rod raw material into a micro-drill substrate; transferring the cleaned and dried micro-drill substrate into a PVD magnetron sputtering chamber to perform plasma cleaning on the micro-drill substrate; sequentially depositing a Ti transition layer, a TiC transition layer, and an amorphous carbon sacrificial layer on the surface of the micro-drill substrate to obtain a micro-drill to be etched; transferring the micro-drill to be etched from the PVD magnetron sputtering chamber to a hot filament chemical vapor deposition chamber, and using plasma to clean the amorphous carbon sacrificial layer and its surface oxides. Etching and volatilization are performed, and the etching process is monitored by plasma atomic emission spectrometry. When the intensity of the characteristic emission peak of excited-state CH radicals, which characterizes hydrocarbon reactions, drops back to a preset intensity, it is determined that the amorphous carbon sacrificial layer has been removed, exposing the unoxidized TiC transition layer. A mixed gas containing carbon source gas and hydrogen is introduced in situ, and a CVD diamond coating is epitaxially grown on the surface of the unoxidized TiC transition layer. The micro-drill with the CVD diamond coating is clamped onto a femtosecond laser processing platform, and the deposited passivation crystal clusters formed on the surface of the micro-drill are removed by femtosecond laser.

[0006] The method for preparing CVD diamond-coated micro-drills according to the embodiments of this application has at least the following beneficial effects: This method eliminates the need for acid etching to remove cobalt, avoiding the damage to the micro-drill cutting edge strength caused by traditional acid etching. Furthermore, the use of a Ti transition layer and a TiC transition layer preserves the original impact and fracture resistance of the cemented carbide substrate. Secondly, the in-situ deposited amorphous carbon, acting as a sacrificial layer, preferentially reacts with oxygen during cross-cavity transfer, effectively protecting the underlying TiC transition layer from oxidation. Combined with subsequent plasma etching, the oxidized sacrificial layer is removed, thereby improving the coating failure problem caused by transfer oxidation. During the etching process, plasma... Emission spectroscopy monitors the etching process, utilizing the self-confined effect of hydrogen plasma, which etches amorphous carbon quickly but TiC slowly, to accurately identify the endpoint of amorphous carbon layer removal. This avoids etching residue and prevents over-etching of the TiC transition layer. Removing the sacrificial layer exposes the unoxidized TiC transition layer interface, which facilitates the formation of strong chemical bonds between subsequently deposited carbon atoms and the layer, improving the adhesion of the diamond coating. Finally, a femtosecond laser is used to finish the deposited coating surface and cutting edge, utilizing its cold ablation characteristics to remove the passivation clusters and surface roughness caused by the grain clustering effect in the thick coating, effectively reducing the cutting edge radius.

[0007] According to some embodiments of this application, the thickness of the Ti transition layer is defined as h1, 0.1μm≤h1≤0.3μm; the thickness of the TiC transition layer is defined as h2, 0.5μm≤h2≤1.0μm; the thickness of the amorphous carbon sacrificial layer is defined as h3, 0.02μm≤h3≤0.1μm; and the thickness of the CVD diamond coating is defined as h4, 3μm≤h4≤5μm.

[0008] According to some embodiments of this application, the steps of cleaning and drying the micro-drill substrate include: placing the micro-drill substrate in a degreasing agent, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaning it for 10 to 15 minutes respectively; drying it with high-purity nitrogen gas and then drying it in a vacuum drying oven.

[0009] According to some embodiments of this application, the step of plasma cleaning the micro-drill substrate includes: cleaning the substrate under a vacuum degree lower than 3.0 × 10⁻⁶. -3 Argon gas is introduced under the condition of Pa, and the chamber pressure is maintained between 0.5 Pa and 1.0 Pa. A pulsed negative bias voltage of -400 V to -600 V is applied to perform reverse sputtering cleaning on the micro-drill substrate for at least 30 minutes.

[0010] According to some embodiments of this application, the step of sequentially depositing a Ti transition layer, a TiC transition layer, and an amorphous carbon sacrificial layer on the surface of the micro-drill substrate includes: applying a first pulse negative bias voltage to the substrate stage supporting the micro-drill substrate, turning on the titanium target power supply, setting the peak power density of the target to 1.0 kW / cm²~2.0 kW / cm², and setting the duty cycle to 1%~5%, depositing a Ti transition layer on the surface of the micro-drill substrate; gradually introducing hydrocarbon reactive gas, uniformly increasing the flow rate of the hydrocarbon reactive gas to a first preset flow rate within 45 minutes, depositing a TiC transition layer on the surface of the Ti transition layer; turning off the titanium target power supply, increasing the flow rate of the hydrocarbon reactive gas from the first preset flow rate to a second preset flow rate, adjusting the pulse negative bias voltage of the substrate stage to a second pulse negative bias voltage and maintaining it for a set duration, using high-voltage bias to excite glow discharge for pyrolysis deposition, depositing an amorphous carbon sacrificial layer on the surface of the TiC transition layer.

[0011] According to some embodiments of this application, when etching and volatilizing the amorphous carbon sacrificial layer and its surface oxides, the cavity pressure is 2kPa~4kPa, and the temperature of the micro-drill substrate is 800℃~900℃.

[0012] According to some embodiments of this application, during the monitoring of the etching process by a plasma emission spectrometer, the monitored target emission characteristic peak is the emission spectral peak of excited-state CH radicals in the wavelength range of 431nm~432nm.

[0013] According to some embodiments of this application, the femtosecond laser has a wavelength of 515nm~532nm, a pulse width of no more than 800fs, a single pulse energy of 5μJ~20μJ, a repetition frequency of 100kHz~300kHz, and a scanning speed of 30mm / s~80mm / s.

[0014] According to the second aspect of this application, the CVD diamond-coated micro-drill is made by the above-described method for preparing CVD diamond-coated micro-drills. The CVD diamond-coated micro-drill includes a cemented carbide micro-drill substrate, a Ti transition layer, a TiC transition layer, and a CVD diamond coating sequentially deposited on the surface of the micro-drill substrate.

[0015] The CVD diamond-coated micro-drills according to embodiments of this application have at least the following beneficial effects: During the preparation process, acid etching for cobalt removal is eliminated, avoiding damage to the micro-drill edge strength caused by traditional acid etching for cobalt removal. Furthermore, the use of Ti and TiC transition layers preserves the original impact and fracture resistance of the cemented carbide substrate. Secondly, the in-situ deposited amorphous carbon, acting as a sacrificial layer, preferentially reacts with oxygen during cross-cavity transfer, effectively protecting the underlying TiC transition layer from oxidation. Combined with subsequent plasma etching, the oxidized sacrificial layer is removed, thereby improving the coating failure problem caused by transfer oxidation. During the etching process, plasma... The etching process is monitored by a photoluminescence spectrometer. Utilizing the self-confining effect of hydrogen plasma, which etches amorphous carbon quickly but TiC slowly, the endpoint of amorphous carbon layer removal is accurately identified, avoiding etching residue and preventing over-etching of the TiC transition layer. After removing the sacrificial layer, the unoxidized TiC transition layer interface is exposed, which is conducive to the formation of strong chemical bonds between the subsequently deposited carbon atoms and the interface, improving the adhesion of the diamond coating. Finally, a femtosecond laser is used to finish the surface of the deposited coating and the cutting edge. Its cold ablation characteristics remove the passivation clusters and surface roughness caused by the grain clustering effect in the thick coating, effectively reducing the cutting edge radius.

[0016] According to some embodiments of this application, the cutting edge radius of the CVD diamond-coated micro-drill is less than 2 μm.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The present application will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a flowchart illustrating a method for preparing CVD diamond-coated micro-drills according to an embodiment of this application; Figure 2 This is a process flow diagram of a method for preparing CVD diamond-coated micro-drills according to an embodiment of this application; Figure 3 This is a schematic diagram illustrating the coating structure changes during the fabrication process of a CVD diamond-coated microdrill according to an embodiment of this application. Figure 4This is a schematic diagram of the femtosecond laser processing principle in the preparation method of CVD diamond-coated micro-drills according to an embodiment of this application.

[0019] Icon labels: 11. Rod material; 12. Micro-drill substrate; 13. Spiral chip removal groove; 21. Ti transition layer; 22. TiC transition layer; 23. Amorphous carbon sacrificial layer; 24. CVD diamond coating; 31. Rake face; 32. Flank face; 33. Deposited passivated crystal cluster; 40. Femtosecond laser beam; 50. PVD magnetron sputtering chamber; 60. HFCVD chamber; 70. Plasma emission spectrometer. Detailed Implementation

[0020] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0021] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, features defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] This invention provides a method for preparing CVD diamond-coated micro-drills, aiming to at least solve the problems of transition layer oxidation failure caused by cross-cavity transfer during the preparation of existing CVD diamond-coated micro-drills, as well as cutting edge dulling and increased cutting resistance due to surface roughness after CVD thick coating deposition.

[0024] Reference Figures 1 to 4 The method for preparing CVD diamond-coated micro-drills provided by this invention includes the following steps: S1: Process the rod raw material 11 into a micro-drill matrix 12; S2: Transfer the cleaned and dried micro-drill substrate 12 into the PVD magnetron sputtering chamber 50 for plasma cleaning of the micro-drill substrate 12; S3: A Ti transition layer 21, a TiC transition layer 22, and an amorphous carbon sacrificial layer 23 are sequentially deposited on the surface of the micro-drill substrate 12 to obtain the micro-drill to be etched; S4: The micro-drill to be etched is transferred from the PVD magnetron sputtering chamber 50 across the chamber to the hot filament chemical vapor deposition (HFCVD) chamber. Plasma is used to etch and volatilize the amorphous carbon sacrificial layer and its surface oxides. The etching process is monitored by a plasma emission spectrometer 70. When the intensity of the characteristic emission peak of the excited state CH free radical, which characterizes the hydrocarbon reaction, drops back to the preset intensity, it is determined that the amorphous carbon sacrificial layer 23 has been removed, exposing the unoxidized TiC transition layer 22. S5: In-situ introduction of a mixed gas containing carbon source gas and hydrogen to epitaxially grow a CVD diamond coating 24 on the surface of the unoxidized TiC transition layer 22. S6: The micro-drill with CVD diamond coating 24 deposited is clamped onto the femtosecond laser processing platform and the deposited passivated crystal clusters 33 formed on the surface of the micro-drill are removed by femtosecond laser.

[0025] In this method for preparing CVD diamond-coated micro-drills, the rod material 11 can be formed by grinding cobalt-containing cemented carbide such as tungsten carbide-cobalt cemented carbide or tungsten carbide-cobalt-nickel cemented carbide with a cobalt content of 6%~10% using a high-precision grinding machine, thus machining a micro-drill substrate 12 with a spiral chip removal groove 13. The cobalt element in this type of cemented carbide acts as a binder phase, imparting high bending strength and high fracture toughness to the substrate to meet the impact and fracture resistance requirements of the micro-drill during high-speed drilling. To allow for a thickness margin for the subsequent coating deposition, the outer diameter of the working part is machined to the net dimension, ensuring that the surface roughness Ra after machining is less than 0.1 μm to obtain a smooth deposition substrate. Subsequently, the ground micro-drill substrate 12 is cleaned and dried.

[0026] After cleaning and drying, the micro-drill substrate 12 is transferred into the PVD magnetron sputtering chamber 50 for plasma cleaning. Plasma cleaning is a cleaning technology that uses gaseous plasma to remove contaminants from the surface of an object. Its basic principle is as follows: a small amount of gas (such as argon, oxygen, nitrogen, etc.) is introduced into a vacuum chamber, and a high-voltage electric field is applied to ionize the gas, generating plasma composed of ions, electrons, free radicals, and excited-state molecules. The active particles in the plasma physically bombard or chemically react with the surface contaminants, thereby removing them. Through plasma cleaning, the natural oxide layer and atomically adsorbed contaminants on the surface of cemented carbide can be effectively removed, resulting in a clean, activated substrate surface with high surface energy, providing ideal interface conditions for the subsequent deposition of transition layers.

[0027] Subsequently, using high-power pulsed magnetron sputtering technology, a Ti transition layer 21, a TiC transition layer 22, and an amorphous carbon sacrificial layer 23 were sequentially deposited on the surface of the micro-drill substrate 12, such as... Figure 3 As shown. High-power pulsed magnetron sputtering is a pulsed sputtering technology with a peak power density reaching the kW / cm² level and a duty cycle typically below 10%. It has a high ionization rate, which can generate high-density metal ions, thereby depositing a dense and strongly bonded coating. In this technical solution, the Ti transition layer 21 is directly deposited on the surface of the cemented carbide substrate, forming a metallurgical bond with the substrate, mainly serving to bond the substrate and subsequent coatings; the TiC transition layer 22 is deposited on top of the Ti transition layer 21, with a hardness between the Ti layer and the diamond coating, used to form a hardness gradient and relieve internal stress in the coating; the amorphous carbon sacrificial layer 23 is deposited on the surface of the TiC transition layer 22, and its function is to preferentially react with oxygen in the air during subsequent cross-cavity transfer, so as to protect the underlying TiC transition layer 22 from oxidation.

[0028] After deposition, the micro-drill substrate 12 is removed from the PVD magnetron sputtering chamber 50 and transferred to the HFCVD chamber 60 via atmospheric conditions. During the transfer, the amorphous carbon sacrificial layer 23 on the micro-drill surface adsorbs and reacts with oxygen in the air, thereby preventing oxidation of the underlying TiC transition layer 22. After the micro-drill substrate 12 is transferred into the HFCVD chamber 60, hydrogen gas is introduced to excite hydrogen plasma to etch and vaporize the amorphous carbon sacrificial layer 23. During the etching process, the etching process is monitored by a plasma emission spectrometer 70. When the intensity of the characteristic peak (wavelength 431 nm) of the excited-state CH radical, which characterizes the hydrocarbon reaction, drops and stabilizes at a preset intensity, it is determined that the amorphous carbon sacrificial layer 23 has been removed. The preset intensity refers to the intensity value at which the characteristic peak intensity tends to stabilize in the later stage of etching and no longer decreases significantly with the extension of etching time. Since the etching rate of active hydrogen atoms on the amorphous carbon sacrificial layer 23 is greater than that on the TiC transition layer 22, the etching process will stop in a self-limited manner on the surface of the TiC transition layer 22, which can avoid etching damage to the TiC transition layer 22 and expose the unoxidized pure TiC interface.

[0029] After etching, a mixture of carbon source gas and hydrogen (e.g., a mixture of methane and hydrogen, with a methane volume ratio of 1.0%–2.0%) is introduced in situ. Deposition takes approximately 10 hours, allowing for the epitaxial growth of a 4 μm thick CVD diamond coating 24 on the exposed, unoxidized TiC transition layer 22 interface. Due to the grain clustering effect during the deposition of the CVD diamond coating 24, deposited passivated crystal clusters 33 form on the cutting edge and chip flute surface of the micro-drill after deposition. These passivated crystal clusters typically have a cutting edge radius greater than 8 μm, increasing the cutting resistance in subsequent micro-hole machining.

[0030] Then, the micro-drill with the CVD diamond coating 24 deposited is clamped onto a femtosecond laser processing platform. The femtosecond laser beam 40 is controlled to scan and ablate along the cutting edge trajectory of the micro-drill and the surface of the spiral chip removal groove 13, removing the passivated crystal clusters at the junction of the rake face 31 and the flank face 32 and reducing the surface roughness. Femtosecond lasers have extremely short pulse widths and extremely high peak power densities. The laser energy is absorbed by the material in a very short time, directly achieving a solid-gas transition with a small heat-affected zone. Therefore, femtosecond laser finishing does not introduce microcracks or thermally altered layers into the coating, and can remove redundant coatings and restore the sharpness of the cutting edge. After femtosecond laser finishing, the cutting edge radius of the micro-drill can be reduced to less than 2 μm.

[0031] In summary, the preparation method of this CVD diamond-coated micro-drill includes the following steps: processing the rod material 11 into a micro-drill substrate 12; transferring the cleaned and dried micro-drill substrate into a PVD magnetron sputtering chamber 50 for plasma cleaning; sequentially depositing a Ti transition layer 21, a TiC transition layer 22, and an amorphous carbon sacrificial layer 23 on the substrate surface to obtain the micro-drill to be etched; transferring the micro-drill to be etched across the chamber to a hot filament chemical vapor deposition chamber; using plasma to etch and volatilize the amorphous carbon sacrificial layer and its surface oxides; monitoring the etching process using a plasma emission spectrometer 70; determining that the amorphous carbon sacrificial layer has been removed when the intensity of the characteristic emission peak of the excited-state CH free radical, which characterizes the hydrocarbon reaction, drops back to the preset intensity, thereby exposing the unoxidized TiC transition layer; then introducing a mixed gas containing carbon source gas and hydrogen to epitaxially grow a CVD diamond coating 24; and finally using a femtosecond laser beam 40 to ablate the coating surface and cutting edge to remove the deposited passivated crystal clusters 33. This method eliminates the need for acid pickling to remove cobalt, avoiding the damage to the micro-drill edge strength caused by traditional acid pickling. It also utilizes a Ti transition layer 21 and a TiC transition layer 22, preserving the original impact and fracture resistance of the cemented carbide substrate. Secondly, in-situ deposited amorphous carbon is used as a sacrificial layer, preferentially reacting with oxygen during cross-cavity transfer, effectively protecting the underlying TiC transition layer 22 from oxidation. Subsequent plasma etching removes the oxidized sacrificial layer, thus improving the coating failure problem caused by transfer oxidation. During etching, the process is monitored using a plasma emission spectrometer 70. The self-confined effect of hydrogen plasma, which etches amorphous carbon quickly but TiC slowly, allows for precise identification of the endpoint of amorphous carbon layer removal. This avoids etching residue and prevents over-etching of the TiC transition layer 22. Removing the sacrificial layer exposes the unoxidized TiC transition layer 22 interface, which facilitates the formation of strong chemical bonds between subsequently deposited carbon atoms and the layer, improving the adhesion of the diamond coating. Finally, a femtosecond laser is used to finish the deposited coating surface and cutting edge. Its cold ablation characteristics remove the passivation clusters and surface roughness caused by the grain clustering effect in the thick coating, effectively reducing the cutting edge radius.

[0032] The thickness of the Ti transition layer 21 is defined as h1, the thickness of the TiC transition layer 22 is defined as h2, the thickness of the amorphous carbon sacrificial layer 23 is defined as h3, and the thickness of the CVD diamond coating 24 is defined as h4. In some embodiments, 0.1μm≤h1≤0.3μm, 0.5μm≤h2≤1.0μm, 0.02μm≤h3≤0.1μm, and 3μm≤h4≤5μm.

[0033] The main function of the Ti transition layer 21 is to act as a bonding layer, forming a metallurgical bond with the cemented carbide substrate. If the thickness is too thin (<0.1μm), it is difficult to form a continuous and dense covering layer, and cobalt elements in the substrate may still diffuse to the surface; if the thickness is too thick (>0.3μm), it will increase the overall thickness of the coating, and since the Ti layer has low hardness, excessive thickness may cause the cutting edge to undergo plastic deformation under stress. h1 is preferably 0.2μm to ensure the barrier effect without weakening the cutting edge strength.

[0034] The TiC transition layer 22 is used to form a hardness gradient and alleviate the internal stress between the diamond coating and the Ti layer. If the thickness is too thin (<0.5μm), the hardness gradient transition is insufficient, and stress concentration can easily lead to coating peeling; if the thickness is too thick (>1.0μm), it will occupy the radial space of the micro-drilling working part, and the accumulation of TiC deposition stress may actually reduce the adhesion. h2 is preferably 0.8μm to achieve a balance between stress buffering and space utilization.

[0035] The function of the amorphous carbon sacrificial layer 23 is to preferentially oxidize during cross-cavity transfer to protect the underlying TiC transition layer 22. If the thickness is too thin (<0.02μm), a complete protective layer cannot be formed, and it may be completely oxidized and depleted during atmospheric transfer, causing the underlying TiC to be exposed to oxygen. If the thickness is too thick (>0.1μm), it will lead to a prolonged subsequent hydrogen plasma etching time. H3 is preferably 0.04μm to achieve a balance between sufficient protection and rapid removal.

[0036] The CVD diamond coating 24 is the working layer of the micro-drill, directly responsible for cutting and wear resistance. If the thickness is too thin (<3μm), the wear life is insufficient, and the micro-drill wears out too quickly when machining high-hardness PCB boards; if the thickness is too thick (>5μm), the grain clustering effect is aggravated, the cutting edge is more severely dulled, resulting in increased removal in subsequent femtosecond laser finishing. An optimal thickness of 4μm (h4) achieves a balance between wear life and cutting edge sharpness.

[0037] In some embodiments, the step of cleaning and drying the micro-drill substrate 12 includes: S21: Place the micro-drill substrate 12 in degreasing agent, deionized water and anhydrous ethanol in sequence, and perform ultrasonic cleaning for 10-15 minutes respectively. S22: After being dried by blowing with high-purity nitrogen, it is placed in a vacuum drying oven for further drying.

[0038] Specifically, the micro-drill substrate 12, after being ground and shaped, is sequentially placed in a degreasing agent, deionized water, and anhydrous ethanol, and ultrasonically cleaned for 10–15 minutes (including 10 minutes and 15 minutes) respectively. This thoroughly removes grinding fluid residue, oil, and solid debris from the substrate surface. After cleaning, the micro-drill substrate 12 is dried using high-purity nitrogen gas and then placed in a vacuum drying oven for baking to remove moisture.

[0039] In some embodiments, plasma cleaning of the micro-drill substrate 12 specifically includes the following steps: cleaning under a vacuum level below 3.0 × 10⁻⁶. -3 Argon gas is introduced under the condition of Pa, and the chamber pressure is maintained between 0.5 Pa and 1.0 Pa. A pulsed negative bias voltage of -400 V to -600 V is applied to perform reverse sputtering cleaning on the micro-drill substrate 12 for at least 30 minutes.

[0040] Specifically, the vacuum level is below 3.0 × 10⁻⁶. -3 The pressure of 0.5 Pa ensures a clean chamber background, preventing residual gas contamination; maintaining a pressure between 0.5 Pa and 1.0 Pa provides sufficient argon ion density while ensuring the ions have a sufficient mean free path to accelerate bombardment; the bias voltage is controlled between -400 V and -600 V, generating sufficiently high bombardment energy to effectively remove natural oxide layers (such as tungsten oxide, cobalt monoxide, etc.) and atomically adsorbed contaminants, without excessively damaging the substrate surface due to excessive energy. Through plasma cleaning, a clean, activated, and high-surface-energy substrate surface can be obtained, providing ideal interface conditions for the subsequent deposition of the transition layer.

[0041] In some embodiments, step S3: sequentially depositing a Ti transition layer 21, a TiC transition layer 22, and an amorphous carbon sacrificial layer 23 on the surface of the micro-drill substrate 12, specifically includes the following steps: S31: Apply a first pulse negative bias voltage to the substrate stage supporting the micro-drill substrate 12, turn on the titanium target power supply, set the peak power density of the target to 1.0kW / cm²~2.0kW / cm², set the duty cycle to 1%~5%, and deposit a Ti transition layer 21 on the surface of the micro-drill substrate 12. S32: Gradually introduce hydrocarbon reaction gas, and increase the flow rate of hydrocarbon reaction gas to the first preset flow rate at a constant rate within 45 minutes to deposit TiC transition layer 22 on the surface of Ti transition layer 21. S33: Turn off the power supply of the titanium target, increase the flow rate of the hydrocarbon reaction gas from the first preset flow rate to the second preset flow rate, and increase the pulse negative bias voltage of the substrate stage to the second pulse negative bias voltage and maintain it for a set duration. Use the high-voltage bias voltage to excite glow discharge for pyrolysis deposition, and deposit an amorphous carbon sacrificial layer 23 on the surface of the TiC transition layer 22.

[0042] Specifically, in step S31, high-power pulsed magnetron sputtering technology is used to apply a first pulse negative bias voltage to the substrate stage supporting the micro-drill substrate 12. The value of the first pulse negative bias voltage can be between -80V and -120V. Under the action of the first pulse negative bias voltage, a Ti transition layer 21 is deposited on the micro-drill substrate 12. The Ti transition layer 21 is deposited on the surface of the micro-drill substrate 12 and forms a metallurgical bond with the micro-drill substrate 12, which plays the role of bonding the micro-drill substrate 12 to the subsequent coating.

[0043] In step S32, hydrocarbon reactive gases such as acetylene or methane are introduced into the cavity to provide a carbon source. The flow rate of the hydrocarbon reactive gas is uniformly increased from 0 to a first preset flow rate within 45 minutes. The first preset flow rate can be between 40 sccm and 50 sccm. During this process, titanium ions sputtered from the titanium target react with the active carbon groups generated by the cracking of the hydrocarbon reactive gas on the substrate surface, forming a TiC transition layer 22. The TiC transition layer 22 is deposited on top of the Ti transition layer 21, and its hardness is between that of the Ti layer and the diamond coating, serving to create a hardness gradient and alleviate internal stress in the coating.

[0044] In step S33, after the titanium target power supply is turned off, the source of titanium ions in the plasma is cut off. At this time, the flow rate of hydrocarbon reactive gas is increased from the first preset flow rate to the second preset flow rate. For example, increasing the flow rate of hydrocarbon reactive gas from 45 sccm to between 60 sccm and 100 sccm is to increase the concentration of hydrocarbon gas in the cavity, so as to significantly increase the density of carbon active groups in the plasma, thereby meeting the carbon source supply required for the deposition of amorphous carbon layer. At the same time, the pulse negative bias voltage of the substrate stage is increased to the second pulse negative bias voltage and maintained for a set duration. For example, increasing the pulse negative bias voltage of the substrate stage from -100V to between -500V and -800V and maintaining for a set duration can enhance the cracking efficiency of hydrocarbon gas and promote the deposition of amorphous carbon sacrificial layer 23. High-voltage bias voltage is used to directly excite glow discharge to crack high-concentration hydrocarbon reactive gas, so as to achieve in-situ deposition of amorphous carbon sacrificial layer 23 without relying on metal target material.

[0045] In some embodiments of this preparation method, when etching and volatilizing the amorphous carbon sacrificial layer 23 and its surface oxides, the cavity pressure is 2 kPa to 4 kPa, and the temperature of the micro-drill substrate is 800°C to 900°C.

[0046] If the chamber pressure in HFCVD chamber 60 is too low (<2kPa), the hydrogen atom density is insufficient, resulting in a reduced etching rate and prolonged process time. If the chamber pressure is too high (>4kPa), the hydrogen atom collision frequency increases, the mean free path decreases, and the etching uniformity declines. Maintaining the substrate temperature between 800℃ and 900℃ activates the chemical reaction between hydrogen atoms and amorphous carbon, ensuring smooth etching, while preventing excessive diffusion of cobalt from the cemented carbide matrix due to excessive temperature. Under these temperature and pressure conditions, the etching rate of active hydrogen atoms on the amorphous carbon sacrificial layer 23 is much greater than that on the TiC transition layer 22. Therefore, the etching process self-confined stops on the surface of the TiC transition layer 22, preventing etching damage to the TiC transition layer 22 and exposing the unoxidized, pure TiC interface.

[0047] In some embodiments of this preparation method, during the monitoring of the etching process by the plasma emission spectrometer 70, the monitored target emission characteristic peak is the emission spectrum peak of excited-state CH radical in the wavelength range of 431nm~432nm.

[0048] CH radicals are typical reactive groups of hydrocarbons in plasma, with their emission spectrum characteristic peaks located between 431 nm and 432 nm. In the initial stage of etching, the amorphous carbon sacrificial layer 23 reacts with hydrogen atoms to generate a large amount of gaseous hydrocarbons, resulting in a high CH concentration in the plasma and a significant characteristic peak intensity. As the amorphous carbon sacrificial layer 23 is gradually removed, the carbon source is exhausted, and the characteristic peak intensity of the CH radicals continuously decreases. When the amorphous carbon sacrificial layer 23 is completely removed, the etching reaction shifts to the surface of the TiC transition layer 22. Because the carbon atoms in TiC are bound by titanium atoms, the etching rate of hydrogen atoms on TiC is extremely low. At this point, the characteristic peak intensity of the CH radicals drops back and stabilizes at a preset intensity. Therefore, by monitoring the intensity change of the CH radical characteristic peak at 431 nm to 432 nm in real time using a plasma emission spectrometer 70, the removal endpoint of the amorphous carbon sacrificial layer 23 can be accurately determined. This online monitoring method does not rely on empirical time control, avoiding etching residues or over-etching of the TiC transition layer 22, and improving the consistency and reliability of the process.

[0049] In some embodiments of this preparation method, a femtosecond laser is used to remove the deposited passivated crystal cluster 33 formed on the surface of the micro-drill. The femtosecond laser parameters are set as follows: wavelength is 515nm~532nm, pulse width is not greater than 800fs, single pulse energy is 5μJ~20μJ, repetition frequency is 100kHz~300kHz, and scanning speed is 30mm / s~80mm / s.

[0050] The above-mentioned femtosecond laser parameters are determined based on the material properties of the CVD diamond coating 24 and the geometry of the micro-drill. For example, in one embodiment, the femtosecond laser parameters are set as follows: wavelength 515nm, pulse width 400fs, single pulse energy 10μJ, repetition frequency 200kHz, and scanning speed 50mm / s.

[0051] Visible light lasers with wavelengths of 515nm to 532nm have good absorption rates for diamond coatings and are in the output band of common femtosecond lasers. Lasers with pulse widths no greater than 800fs fall into the femtosecond range, allowing laser energy to be absorbed by the material in a very short time, directly achieving solid-gas transformation with a very small heat-affected zone, preventing the introduction of microcracks or thermally altered layers into the coating. The single-pulse energy is 5μJ to 20μJ; too low an energy will result in insufficient ablation efficiency, while too high an energy may damage the coating or substrate. The repetition frequency is 100kHz to 300kHz, ensuring sufficient processing efficiency while avoiding heat accumulation. The scanning speed is 30mm / s to 80mm / s, matching the aforementioned parameters, enabling precise scanning and ablation along the cutting edge trajectory of the micro-drill and the surface of the helical chip groove 13, removing the passivated crystal clusters at the junction of the rake face 31 and the flank face 32 and reducing surface roughness, thus reducing the micro-drill's cutting edge radius to less than 2μm.

[0052] The present invention also provides a CVD diamond-coated microdrill prepared by the above preparation method, the CVD diamond-coated microdrill comprising a cemented carbide microdrill substrate 12, and a Ti transition layer 21, a TiC transition layer 22 and a CVD diamond coating 24 sequentially deposited on the surface of the microdrill substrate 12.

[0053] This CVD diamond-coated micro-drill eliminates the need for acid leaching to remove cobalt, avoiding the damage to the micro-drill's cutting edge strength caused by traditional acid leaching. It also utilizes a Ti transition layer 21 and a TiC transition layer 22 to preserve the original impact and fracture resistance of the cemented carbide substrate. Secondly, in-situ deposited amorphous carbon is used as a sacrificial layer, preferentially reacting with oxygen during cross-cavity transfer, effectively protecting the underlying TiC transition layer 22 from oxidation. Subsequent plasma etching removes the oxidized sacrificial layer, thus mitigating coating failure caused by transfer oxidation. During etching, plasma emission spectrometry 70 is used to monitor the etched surface. The process is monitored, utilizing the self-confined effect of hydrogen plasma—fast etching of amorphous carbon and slow etching of TiC—to accurately identify the endpoint of amorphous carbon layer removal. This avoids etching residue and prevents over-etching of the TiC transition layer 22. Removing the sacrificial layer exposes the unoxidized TiC transition layer 22 interface, which facilitates the formation of strong chemical bonds between subsequently deposited carbon atoms and the layer, improving the adhesion of the diamond coating. Finally, a femtosecond laser is used to finish the deposited coating surface and cutting edge. Its cold ablation characteristics remove passivated grain clusters and surface roughness caused by grain clustering in the thick coating, effectively reducing the cutting edge radius. After femtosecond laser finishing, the micro-drill's cutting edge radius is less than 2μm, exhibiting excellent cutting performance and service life.

[0054] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0055] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing CVD diamond-coated micro-drills, characterized in that, Includes the following steps: Process the rod raw material into a micro-drill matrix; The cleaned and dried micro-drill substrate is transferred into the PVD magnetron sputtering chamber for plasma cleaning. A Ti transition layer, a TiC transition layer, and an amorphous carbon sacrificial layer are sequentially deposited on the surface of the micro-drill substrate to obtain the micro-drill to be etched. The micro-drill to be etched is transferred from the PVD magnetron sputtering chamber to the hot filament chemical vapor deposition chamber. Plasma is used to etch and volatilize the amorphous carbon sacrificial layer and its surface oxides. The etching process is monitored by a plasma emission spectrometer. When the intensity of the characteristic emission peak of excited-state CH free radicals, which characterizes hydrocarbon reactions, drops back to a preset intensity, it is determined that the amorphous carbon sacrificial layer has been removed, exposing the unoxidized TiC transition layer. A mixture of carbon source gas and hydrogen is introduced in situ to epitaxially grow a CVD diamond coating on the surface of the unoxidized TiC transition layer. The micro-drill with a CVD diamond coating is clamped onto a femtosecond laser processing platform, and the deposited passivated crystal clusters formed on the surface of the micro-drill are removed by the femtosecond laser.

2. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, The thickness of the Ti transition layer is defined as h1, where 0.1 μm ≤ h1 ≤ 0.3 μm; The thickness of the TiC transition layer is defined as h2, where 0.5 μm ≤ h2 ≤ 1.0 μm; The thickness of the amorphous carbon sacrificial layer is defined as h3, where 0.02 μm ≤ h3 ≤ 0.1 μm; The thickness of the CVD diamond coating is defined as h4, where 3μm≤h4≤5μm.

3. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, The steps of cleaning and drying the micro-drill substrate include: The micro-drill substrate was placed in degreasing agent, deionized water and anhydrous ethanol in sequence, and ultrasonically cleaned for 10-15 minutes respectively. After being dried by blowing with high-purity nitrogen, it is placed in a vacuum drying oven for further drying.

4. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, The plasma cleaning step of the micro-drill substrate includes: cleaning the substrate under a vacuum level below 3.0 × 10⁻⁶. -3 Argon gas is introduced under the condition of Pa, and the chamber pressure is maintained between 0.5 Pa and 1.0 Pa. A pulsed negative bias voltage of -400 V to -600 V is applied to perform reverse sputtering cleaning on the micro-drill substrate for at least 30 minutes.

5. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, The step of sequentially depositing a Ti transition layer, a TiC transition layer, and an amorphous carbon sacrificial layer on the surface of the micro-drill substrate includes: A first pulse negative bias voltage is applied to the substrate stage supporting the micro-drill substrate, the titanium target power supply is turned on, the peak power density of the target is set to 1.0kW / cm²~2.0kW / cm², the duty cycle is set to 1%~5%, and a Ti transition layer is deposited on the surface of the micro-drill substrate. Hydrocarbon reaction gas is gradually introduced, and the flow rate of the hydrocarbon reaction gas is uniformly increased to the first preset flow rate within 45 minutes, so as to deposit a TiC transition layer on the surface of the Ti transition layer. Turn off the power supply to the titanium target, increase the flow rate of hydrocarbon reaction gas from the first preset flow rate to the second preset flow rate, and increase the pulse negative bias voltage of the substrate stage to the second pulse negative bias voltage and maintain it for a set duration. Use the high-voltage bias voltage to excite glow discharge for pyrolysis deposition, and deposit an amorphous carbon sacrificial layer on the surface of the TiC transition layer.

6. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, When etching and volatilizing the amorphous carbon sacrificial layer and its surface oxides, the cavity pressure is 2 kPa to 4 kPa, and the temperature of the micro-drill substrate is 800°C to 900°C.

7. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, During the monitoring of the etching process using a plasma emission spectrometer, the target emission characteristic peaks monitored were the emission spectral peaks of excited-state CH radicals in the wavelength range of 431 nm to 432 nm.

8. The method for preparing CVD diamond-coated micro-drills according to claim 1, characterized in that, The femtosecond laser has a wavelength of 515nm~532nm, a pulse width of no more than 800fs, a single pulse energy of 5μJ~20μJ, a repetition frequency of 100kHz~300kHz, and a scanning speed of 30mm / s~80mm / s.

9. A CVD diamond-coated microdrill, characterized in that, The micro-drill is prepared by the method described in any one of claims 1 to 8, wherein the micro-drill comprises a cemented carbide micro-drill substrate, a Ti transition layer, a TiC transition layer and a CVD diamond coating sequentially deposited on the surface of the micro-drill substrate.

10. The CVD diamond-coated micro-drill according to claim 9, characterized in that, The cutting edge radius of the CVD diamond-coated micro-drill is less than 2μm.

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