WO2024012611A1

WO2024012611A1 - Diamond coating micro drill bit, and preparation method therefor and use thereof

Info

Publication number: WO2024012611A1
Application number: PCT/CN2023/123688
Authority: WO
Inventors: 石倩; 张聿铭; 苏一凡; 林松盛; 张程; 唐鹏; 代明江; 黄淑琪
Original assignee: 广东省科学院新材料研究所
Priority date: 2022-11-16
Filing date: 2023-10-10
Publication date: 2024-01-18
Also published as: CN115896736A

Abstract

A diamond coating micro drill bit, and a preparation method therefor and the use thereof, which belong to the technical field of micro drill bits. The method comprises: before a diamond coating is deposited, subjecting a micro drill bit to chemical pretreatment, wherein the diameter of the micro drill bit is 0.35-0.75 mm, the grain size is 0.3-1.0 μm, and the cobalt content is 4-8 wt%; the chemical pretreatment comprises a first acid etching, an alkali etching and a second acid etching; an acid etching liquid comprises nitric acid, hydrochloric acid and water in a volume ratio of 1 : 2-4 : 10-15; an alkali etching liquid comprises potassium ferricyanide, potassium nitrate and water in a volume ratio of 1 : 1 : 10; and the time taken for the three instances of etching is respectively 10-30 s, 2-6 min and 10-50 s. The method can significantly reduce the influence of the chemical pretreatment on the breaking strength of the micro drill bit and the preparation effect of the diamond coating, the Co removal effect is good, the etching efficiency is high, and the micro drill bit obtained can be used for machining circuit boards.

Description

A diamond-coated micro drill bit and its preparation method and application

Technical areas:

The present invention relates to the technical field of micro drill bits, and specifically to a diamond-coated micro drill bit and its preparation method and application.

Background technique:

With the advent of the 5G communication era, base stations are developing towards miniaturization, lightweight and high integration. Among them, the 5G cavity filter generally requires a 1PCS microstrip PCB (Printed Circuit Board) circuit due to volume and performance requirements. PCBs for 5G are laminated composite materials composed of copper foil, resin, ceramic fillers or a variety of special woven glass fiber cloths. One of the key processing steps in manufacturing PCB circuit boards is drilling through holes. During the processing process, a large number of through holes with a diameter of 0.2-0.8mm need to be processed using carbide micro drills. Since PCB is a fiber-reinforced composite material containing multiple layers of copper foil, after a short drilling cycle, the micro drill bit will easily wear out and fail quickly. The short working life of the micro drill bit and frequent replacement of the micro drill bit have become a problem for PCB. Difficulties faced by the industry in efficient manufacturing.

In order to extend the working life of PCB board micro-drills, it is an effective solution to use chemical vapor deposition (CVD) to deposit a diamond coating on its surface. Diamond has extremely high hardness, excellent wear resistance and low friction coefficient, which can improve its chip removal ability and effectively protect the cutting edge. Diamond-coated micro drill bits can exponentially extend tool life when applied to ceramic-based PCBs, and their drilling quality is also greatly improved compared to the same type of uncoated tools.

However, the presence of Co as a binder in the tungsten-cobalt cemented carbide in micro drill bits promotes the formation of graphite phase during the deposition of diamond, greatly reducing the adhesion of the diamond coating. Therefore, specific pretreatment of the cemented carbide surface is required before depositing a diamond coating.

The relevant pretreatment methods in the existing technology will lead to the presence of a large number of pores and cavities on the substrate surface, causing damage to the substrate surface. Damage, and the Co removal effect is poor, which leads to a decrease in the fracture strength of the micro drill bit, which may easily lead to tool breakage during the drilling process.

In view of this, the present invention is proposed.

Contents of the invention:

One object of the present invention is to provide a method for preparing a diamond-coated micro drill bit to solve the above technical problems.

The second object of the present invention is to provide a diamond-coated micro drill bit prepared by the above preparation method.

The third object of the present invention is to provide an application of the above-mentioned diamond-coated micro drill bit.

This application can be implemented as follows:

In a first aspect, this application provides a method for preparing a diamond-coated micro drill bit, which includes the following steps:

Chemically pretreating micro-fine drill bits before depositing the diamond coating;

The diameter of the micro drill is 0.35-0.75mm, the grain size is 0.3-1.0μm, and the cobalt content is 4-8wt%;

Chemical pretreatment includes the first acid etching, alkali etching and the second acid etching in sequence;

Wherein, the acid etching liquid used for the first acid etching and the acid etching liquid used for the second acid etching independently include nitric acid, hydrochloric acid and water in a volume ratio of 1:2-4:10-15; The alkali etching solution used in alkali etching includes potassium ferricyanide, potassium nitrate and water in a volume ratio of 1:1:10;

The first acid etching time is 10-30s; the alkali etching time is 2-6min; the second acid etching time is 10-50s.

In an optional embodiment, the material of the micro drill bit is cemented carbide, preferably WC cemented carbide;

And/or, the diamond grains contained in the diamond coating include micron crystals, nanocrystals or gradient crystals composed of micron crystals and nanocrystals.

In an optional embodiment, before the chemical pretreatment, the micro drill bit is also cleaned.

In an optional embodiment, the micro drill bit is placed in an organic solvent for ultrasonic cleaning.

In an optional embodiment, the organic solvent includes at least one of absolute ethanol, acetone and isopropyl alcohol.

In an optional embodiment, ultrasonic cleaning is performed at 40-60°C for 20-40 minutes.

In an optional embodiment, before the chemical pretreatment, the ultrasonic cleaned micro drill bit is also dried.

In an optional embodiment, drying is performed under a nitrogen atmosphere with a purity of not less than 99.99%.

In an optional embodiment, before depositing the diamond coating, the method further includes seeding the chemically pretreated micro drill bit.

In an optional embodiment, the seed crystal planting treatment includes subjecting the chemically pretreated micro drill bit to ultrasonic vibration treatment in a treatment solution containing diamond powder.

In an optional embodiment, the treatment solution is prepared from absolute alcohol and nanodiamond powder in a ratio of 1 L: 0.3-0.5 g.

In an optional embodiment, the particle size of nanodiamond powder is 1-4 μm.

In an optional embodiment, the time for planting seed crystals is 10-15 minutes.

In an alternative embodiment, the diamond coating is deposited using chemical vapor deposition.

In an optional embodiment, when the grains of the diamond coating to be deposited are micron crystals, the deposition conditions include: the hot wire temperature is 2000-2200°C, the hot wire-substrate distance is 18-22 mm, and the substrate temperature The temperature is 800-850℃, the flow rate of CH4 is 50-70sccm, the flow rate of H2 is 17000-19000sccm, the air pressure is 5-10mbar, and the deposition time is 8-20h.

In an optional embodiment, when the grains of the diamond coating to be deposited are nanocrystals, the deposition conditions include: the hot wire temperature is 2000-2200°C, the hot wire-substrate distance is 18-22 mm, and the substrate temperature The temperature is 800-850℃, the flow rate of CH4 is 20-40sccm, the flow rate of H2 is 8000-10000sccm, the air pressure is 1-5mbar, and the deposition time is 8-20h.

In an optional embodiment, when the grains of the diamond coating to be deposited are gradient crystals, the deposition conditions include: the hot wire temperature is 2000-2200°C, the hot wire-substrate distance is 18-22 mm, and the substrate temperature The temperature is 800-850℃, the flow rate of CH4 is 30-165sccm, the flow rate of H2 is 8000-10000sccm, the air pressure is 1-5mbar, and the deposition time is 8-20h.

In a second aspect, the present application provides a diamond-coated micro drill bit, which is prepared by the preparation method of any one of the preceding embodiments.

In a third aspect, the present application provides the application of the diamond-coated micro drill bit as in the aforementioned embodiment, and the diamond-coated micro drill bit is used for circuit board processing.

In an optional embodiment, the circuit board is a 5G communication PCB circuit board containing copper foil and/or PTFE and/or ceramic filler.

The beneficial effects of this application include:

The above chemical pretreatment method provided by this application can achieve the effect of not significantly weakening the fracture strength of the micro drill bit on the basis of effectively shortening the etching time of the acid solution (improving the etching efficiency). Moreover, this method can improve the surface roughness of the substrate, improve the adhesion between the substrate and the coating, strengthen the mechanical locking effect between the substrate and the diamond coating, and improve the film-base bonding force. In addition, this method has good Co removal effect and high etching efficiency. The obtained diamond-coated micro drill bit has high fracture strength, good bonding between the coating and the substrate, is not prone to tool breakage during the drilling process, and can be used for circuit board processing.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and therefore do not should be regarded as a limitation of the scope. For those of ordinary skill in the art, without exerting creative efforts, they can also make reference to these drawings. Get other relevant drawings.

Figure 1 is a surface morphology diagram of a micro drill bit after chemical pretreatment in Example 1 of the present application;

Figure 2 is an enlarged view corresponding to the boxed area in Figure 1;

Figure 3 is a scanning electron microscope image of the diamond-coated micro drill bit after drilling testing in Example 1 of the present application.

Figure 4 is a scanning electron microscope image of the diamond-coated micro drill bit in Comparative Example 2 of the present application after drilling testing.

Detailed ways:

In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

The following is a detailed description of the diamond-coated micro drill bit provided by this application and its preparation method and application.

This application proposes a method for preparing a diamond-coated micro drill bit, which includes the following steps:

The micro drill bits are chemically pre-treated before the diamond coating is deposited on the surface of the micro drill bits.

It should be noted that the chemical pretreatment conditions applicable to different micro drill bits are different. The diameter of the micro drill bit targeted by this application is 0.35-0.75 mm, the grain size is 0.3-1.0 μm, and the cobalt content is 4- 8wt%.

For example, the diameter of the micro drill bit can be 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm or 0.75mm, etc., or other diameters within the range of 0.35-0.75mm. Any value.

The grain size may be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, etc., or any other value within the range of 0.3-1.0 μm.

The cobalt content can be 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt% or 8wt%, etc., or any other value within the range of 4-8wt% .

The material of the above-mentioned micro drill bit is cemented carbide, for example, WC cemented carbide.

In this application, the chemical pretreatment includes sequentially performing the first acid etching, the alkali etching and the second acid etching.

Wherein, the acid etching liquid used for the first acid etching and the acid etching liquid used for the second acid etching independently include nitric acid, hydrochloric acid and water in a volume ratio of 1:2-4:10-15. The alkali etching solution used in alkali etching includes potassium ferricyanide, potassium nitrate and water in a volume ratio of 1:1:10.

Among them, the volume ratio of nitric acid, hydrochloric acid and water in the acid etching solution can be 1:2:10, 1:2:11, 1:2:12, 1:2:13, 1:2:14, 1:2 :15, 1:3:10, 1:3:11, 1:3:12, 1:3:13, 1:3:14, 1:3:15, 1:4:10, 1:4:11 , 1:4:12, 1:4:13, 1:4:14 or 1:4:15, etc., or any other value in the range of 1:2-4:10-15.

For reference, the above etching can be performed by immersing a fine drill bit in the etching liquid.

The function of the above-mentioned first acid etching is to remove Co from the surface of the micro drill bit; the function of alkali etching is to remove the WC particles in the matrix (WC-Co matrix), exposing the Co element in the matrix and making the surface of the cemented carbide Roughening to enhance the contact area of the coating to the substrate material and improve the adhesion of the coating; the second acid etching is used to remove Co to a certain depth in the matrix to avoid Co in the process of depositing the diamond coating. adverse effects.

In this application, the first acid etching time can be 10-30s, such as 10s, 12s, 15s, 18s, 20s, 22s, 25s, 28s or 30s, etc., or it can be any other value within the range of 10-30s.

If the first acid etching time is shorter than 10s, it will easily lead to too little Co removal, which is not conducive to subsequent etching of WC; if it is longer than 30s, it will easily lead to a greater decrease in the fracture strength of the matrix.

The alkali etching time can be 2-6min, such as 2min, 2.5min, 3min, 3.5min, 4min, 4.5min, 5min, 5.5min or 6min, etc., or it can be any other value within the range of 2-6min.

If the alkali etching time is shorter than 2 minutes, the Co on the surface layer is not fully exposed, which may lead to incomplete removal; if it is longer than 6min, the matrix is corroded deeply, which can easily lead to a greater decrease in fracture strength.

The second acid etching time can be 10-50s, such as 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s or 50s, etc., or it can be any other value within the range of 10-50s.

If the second acid etching time is shorter than 10s, it is easy to cause Co to remain on the surface of the substrate, resulting in poor quality of the subsequent diamond coating; if it is longer than 50s, it is easy to produce a brittle layer, resulting in poor bonding between the coating and the substrate.

After the first acid etching, the cleaned micro drill bit is first soaked in deionized water, and then alkali etched. After alkali etching, the treated micro drill bit is first soaked in deionized water to remove suspended ions on the surface of the substrate, and then soaked and cleaned in deionized water before performing a second acid etching. After the second acid etching, the processed micro drill bits were soaked and cleaned in deionized water before subsequent processing.

It should be noted that due to the small size of the micro drill bit targeted by this application, excessive acid and alkali pretreatment can easily significantly reduce the fracture strength of the drill bit, resulting in easy tool breakage during the drilling process.

The above chemical pretreatment method provided by this application can effectively shorten the acid solution etching time (increase etching efficiency) without significantly weakening the fracture strength of the micro drill bit. Moreover, this method can improve the surface roughness of the substrate, improve the adhesion between the substrate and the coating, strengthen the mechanical locking effect between the substrate and the diamond coating, and improve the film-base bonding force. In addition, this method can greatly reduce the presence of pores and cavities on the substrate surface and reduce damage to the substrate surface compared with existing pretreatment methods.

In some embodiments, before the chemical pretreatment, the micro drill bit is also cleaned.

For example, micro drill bits can be placed in organic solvents for ultrasonic cleaning.

For reference, the above-mentioned organic solvent may include at least one of absolute ethanol, acetone and isopropyl alcohol.

Ultrasonic cleaning can be carried out at 40-60℃ (such as 40℃, 45℃, 50℃, 55℃ or 60℃, etc.) for 20-40min (Such as 20min, 25min, 30min, 35min or 40min, etc.).

Through the above cleaning process, some impurities and oil stains on the surface of the fine drill bit can be removed, which is beneficial to improving the subsequent etching effect.

Furthermore, before the chemical pretreatment, the ultrasonic cleaned micro drill bits are dried.

For reference, drying can be performed in a nitrogen atmosphere with a purity of not less than 99.99% to avoid water stains left by natural drying from affecting the subsequent etching effect.

Further, before depositing the diamond coating, it also includes seeding the chemically pretreated micro drill bit.

For reference, the seed crystal planting treatment includes: subjecting the chemically pretreated micro drill bit to ultrasonic vibration treatment in a treatment solution containing diamond powder.

The above treatment solution is composed of anhydrous alcohol and nano-diamond powder (particle size is about 1-4 μm) according to 1L: 0.3-0.5g (such as 1L: 0.3g, 1L: 0.35g, 1L: 0.4g, 1L: 0.45g or 1L :0.5g, etc.).

The time for planting seed crystals is 10-15min, such as 10min, 10.5min, 11min, 11.5min, 12min,

12.5min, 13min, 13.5min, 14min, 14.5min or 15min, etc., or any other value within the range of 10-15min.

Through the above seed crystal planting process, diamond seeds can be evenly distributed on the surface of the substrate, making it easier to generate a diamond phase during subsequent deposition of a diamond coating.

In this application, the diamond grains contained in the diamond coating include micron crystals, nanocrystals or gradient crystals composed of micron crystals and nanocrystals.

Among them, from the side close to the matrix to the side far away from the matrix, the gradient crystal shows a decreasing micron crystal gradient and a nanocrystal gradient. Increased form.

In this application, the diamond coating can be only a single layer or multiple layers (such as 2 layers, 3 layers or 4 layers, etc.). The total thickness of the diamond coating may be 2-20 μm, such as 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, or any other value within the range of 2-20 μm.

When the diamond coating is a single layer, the diamond grains contained in the diamond coating are preferably only nanocrystals or micron crystals. When the diamond coating is multi-layered, it can alternate between nanocrystalline layers (that is, the diamond grains contained in the diamond coating are nanocrystals) and micron crystal layers (that is, the diamond grains contained in the diamond coating are micron crystals). composition.

In this application, the diamond coating is deposited using chemical vapor deposition.

When the grains of the diamond coating to be deposited are micron crystals, the deposition conditions include: the hot wire temperature is 2000-2200℃ (such as 2000℃, 2020℃, 2050℃, 2080℃, 2100℃, 2120℃, 2150℃ , 2180℃ or 2200℃, etc.), the hot wire-substrate distance is 18-22mm (such as 18mm, 18.5mm, 19mm, 19.5mm, 20mm, 20.5mm, 21mm, 21.5mm or 22mm, etc.), and the substrate temperature is 800- 850℃ (such as 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃, etc.), the flow rate of CH4 is (such as 50sccm, 52sccm, 55sccm, 58sccm, 60sccm, 62sccm, 65sccm, 68sccm or 70sccm, etc.), The flow rate of H2 is 17000-19000sccm (such as 17000sccm, 17200sccm, 17500sccm, 17800sccm, 18000sccm, 18200sccm, 18500sccm, 18800sccm or 19000sccm, etc.), and the air pressure is 5-10mbar (such as 5mbar, 6mbar, 7 mbar, 8mbar, 9mbar or 10mbar, etc.), The deposition time is 8-20h (such as 8h, 10h, 12h, 15h, 18h or 20h, etc.).

When the grains of the diamond coating to be deposited are nanocrystals, the deposition conditions include: the hot wire temperature is 2000-2200℃ (such as 2000℃, 2020℃, 2050℃, 2080℃, 2100℃, 2120℃, 2150℃ , 2180℃ or 2200℃, etc.), the hot wire-substrate distance is 18-22mm (such as 18mm, 18.5mm, 19mm, 19.5mm, 20mm, 20.5mm, 21mm, 21.5mm or 22mm, etc.), the substrate temperature is 800-850℃ (such as 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃, etc.), the flow rate of CH4 is 20-40sccm (20sccm, 22sccm, 25sccm , 28sccm, 30sccm, 32sccm, 35sccm, 38sccm or 40sccm, etc.), the flow rate of H2 is 8000-10000sccm (such as 8000sccm, 8200sccm, 8500sccm, 8800sccm, 9000sccm, 9200sccm, 9500sccm, 9800sccm or 10000sccm, etc.), air pressure is 1-5mbar ( Such as 1mbar, 2mbar, 3mbar, 4mbar or 5mbar, etc.), the deposition time is 8-20h (such as 8h, 10h, 12h, 15h, 18h or 20h, etc.).

When the grains of the diamond coating to be deposited are gradient crystals, the deposition conditions include: the hot wire temperature is 2000-2200℃ (such as 2000℃, 2020℃, 2050℃, 2080℃, 2100℃, 2120℃, 2150℃ , 2180℃ or 2200℃, etc.), the hot wire-substrate distance is 18-22mm (such as 18mm, 18.5mm, 19mm, 19.5mm, 20mm, 20.5mm, 21mm, 21.5mm or 22mm, etc.), and the substrate temperature is 800- 850℃ (such as 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃, etc.), the flow rate of CH4 is 30-165sccm (such as 30sccm, 50sccm, 80sccm, 100sccm, 120sccm, 150sccm or 165sccm, etc.), H2 The flow rate is 8000-10000sccm (such as 8000sccm, 8200sccm, 8500sccm, 8800sccm, 9000sccm, 9200sccm, 9500sccm, 9800sccm or 10000sccm, etc.), and the air pressure is 1-5mbar (such as 1mbar, 2mbar, 3mbar, 4mbar or 5mbar, etc.) ), the deposition time is 8-20h (such as 8h, 10h, 12h, 15h, 18h or 20h, etc.).

In other words, changes in the flow rates of CH4 and H2 and gas pressure will cause changes in the grains.

Through the above method, the diamond coating can be uniformly deposited on the surface of the fine drill bit. The diamond coating has good crystallinity and has diamond crystals with clear edges and corners.

Correspondingly, this application also provides a diamond-coated micro drill bit, which is prepared by the above preparation method.

The diamond-coated micro-drill bit has high fracture strength, good bonding between the coating and the base, and does not need to be drilled during the drilling process. Knife breakage is prone to occur.

In addition, this application also provides the application of the above-mentioned diamond-coated micro drill bit, which can be used for circuit board processing, for example.

For example, the above-mentioned circuit board may be a 5G communication PCB circuit board containing copper foil and/or PTFE and/or ceramic filler.

The features and performance of the present invention will be described in further detail below with reference to examples.

Example 1

Step (1): Soak the micro drill bit (WC-6wt%Co, drill diameter is 0.5mm, grain size is 0.3-0.5μm) in absolute ethanol, ultrasonically clean it at 50°C for 30 minutes; then use a drill with a purity of 99.99 % nitrogen for drying.

Step (2): Soak the micro drill bit processed in step (1) in an acid etching solution composed of 60 mL nitric acid, 120 mL hydrochloric acid and 600 mL deionized water for 10 seconds, and then soak in deionized water for 2 minutes.

Step (3): The micro drill bit processed in step (2) is etched with alkali formed by mixing V(K3Fe(CN)6):V(KOH):V(H2O)=1:1:10 in a volume ratio Soak in the solution for 4 minutes, then soak in deionized water for 2 minutes.

Step (4): Soak the micro drill bit processed in step (3) in the same acid etching solution as in step (2) for 30 seconds, and then soak in deionized water for 2 minutes.

Step (5): Put the micro drill bit processed in step (4) into a suspension with a concentration of 0.35g diamond powder (particle size is about 4 μm)/1000mL absolute ethanol, and oscillate ultrasonically to perform seed crystal planting treatment , the crystal planting time is 10min.

Step (6): Place the micro drill bit processed in step (5) in the CVD chemical vapor deposition equipment. The hot wire temperature is 2100°C, the hot wire-substrate distance is 20 μm, the substrate temperature is 800°C, and CH4 and H2 are each The flow rate is 60 sccm and 18000 sccm, the air pressure is 5 mbar, and the deposition time is 8 hours. Micro drills containing micron crystal diamond coating (MCD) are obtained. head.

The surface morphology of the pretreated micro drill bit in this embodiment is shown in Figures 1 and 2. It can be seen from Figures 1 and 2 that there are many holes on the surface, which provide nucleation sites for the subsequent diamond coating coating process, and this method has a good Co removal effect and improves the bonding between the coating and the substrate. force.

The micro drill bit containing diamond coating was observed through a scanning electron microscope and it was found that the coating was uniformly deposited on the surface of the micro drill bit, with good crystallinity, and diamond crystals with clear edges and corners could be clearly seen.

The pretreated micro drill bit was subjected to a fracture strength test experiment, and the fracture strength was found to be 29N. The micro drill bit was tested for drilling. When the number of holes was 4,000, the back cutter of the micro drill bit was observed through a scanning electron microscope. It was found that the bonding between the coating and the substrate was good, and no signs of coating peeling were found (as shown in Figure 3).

Example 2

Step (1): Soak the micro drill bit (WC-8wt%Co, drill diameter is 0.75mm, grain size is 0.5-0.7μm) in acetone, ultrasonically clean it at 40°C for 40 minutes; then use 99.99% purity Nitrogen for drying.

Step (2): Soak the micro drill bit processed in step (1) in an acid etching solution composed of 60 mL nitric acid, 240 mL hydrochloric acid and 600 mL deionized water for 30 seconds, and then soak in deionized water for 2 minutes.

Step (3): The micro drill bit processed in step (2) is etched with alkali formed by mixing V(K3Fe(CN)6):V(KOH):V(H2O)=1:1:10 in a volume ratio Soak in the solution for 6 minutes, then soak in deionized water for 2 minutes.

Step (4): Soak the micro drill bit processed in step (3) in the same acid etching solution as in step (2) for 50 seconds, and then soak in deionized water for 2 minutes.

Step (5): Put the micro drill bit processed in step (4) into diamond powder with a concentration of 0.5g (particle size is about 3μm)/1000mL of absolute ethanol suspension under ultrasonic vibration, and seed crystal planting was performed. The crystal planting time was 15 minutes.

Step (6): Place the micro drill bit processed in step (5) in the CVD chemical vapor deposition equipment. The hot wire temperature is 2100°C, the hot wire-substrate distance is 20 μm, the substrate temperature is 800°C, and CH4 and H2 are each The flow rate is 30 sccm and 9000 sccm, the air pressure is 1 mbar, and the deposition time is 8 hours, to obtain a micro drill bit containing nanocrystalline diamond coating (NCD).

Observing the diamond-coated micro drill bit through a scanning electron microscope, it was found that the coating was uniformly deposited on the surface of the micro drill bit, and the diamond grains were small in size and gathered in clusters, which gave them a cauliflower-shaped appearance.

The micro drill was subjected to a fracture strength test and the fracture strength was 25N. Another sample was taken for a micro drill drilling test. When the number of holes was 4,000, the flank surface of the micro drill was observed and it was found that there was a gap between the coating and the substrate. Bonded well and no signs of coating peeling were noted.

Example 3

Step (1): Soak the micro drill bit (WC-4wt%Co, drill diameter is 0.35mm, grain size is 0.8-1.0μm) in isopropyl alcohol, ultrasonically clean it at 60°C for 20 minutes; then use a drill with a purity of 99.99 % nitrogen for drying.

Step (2): Soak the micro drill bit processed in step (1) in an acid etching solution composed of 60 mL nitric acid, 120 mL hydrochloric acid and 900 mL deionized water for 20 seconds, and then soak in deionized water for 2 minutes.

Step (3): The micro drill bit processed in step (2) is etched with alkali formed by mixing V(K3Fe(CN)6):V(KOH):V(H2O)=1:1:10 in a volume ratio Soak in the solution for 2 minutes, then soak in deionized water for 2 minutes.

Step (4): Soak the micro drill bit processed in step (3) in the same acid etching solution as in step (2) for 10 seconds, and then soak in deionized water for 2 minutes.

Step (5): Put the micro drill bit processed in step (4) into a suspension with a concentration of 0.4g diamond powder (particle size is about 1 μm)/1000mL absolute ethanol, and oscillate ultrasonically to carry out seed crystal planting treatment. , the crystal planting time is 15min.

Step (6): Place the micro drill bit processed in step (5) in the CVD chemical vapor deposition equipment. The hot wire temperature is 2100°C, the hot wire-substrate distance is 20 μm, the substrate temperature is 800°C, and the air pressure is 1/ 5mbar, the deposition time is 8h, the flow rates of CH4 and H2 are 30sccm and 9000sccm respectively in the early stage, and the CH4 flow rate is adjusted to 165sccm later to obtain a micro drill bit containing gradient diamond coating (GCD).

The micro drill bit containing diamond coating was observed through a scanning electron microscope and it was found that the coating was uniformly deposited on the surface of the micro drill bit, and the coating surface showed a cauliflower-shaped surface morphology.

The micro drill bit was subjected to a fracture strength test experiment. Through the test, it was found that the fracture strength of the micro drill bit was 26N. Another sample was taken for a micro drill bit drilling test. When the number of holes was 4,000, the flank surface of the micro drill bit was observed to be coated. The bond between the layer and the substrate was good and no signs of coating peeling were found.

Example 4

The difference between this embodiment and Embodiment 1 is that the volume ratio of nitric acid, hydrochloric acid and water in the acid etching solution is 1:3:14.

The pretreated micro drill bit was subjected to a fracture strength test experiment, and the fracture strength was found to be 32N. The micro drill bit was tested for drilling. When the number of holes was 4,000, the back cutter of the micro drill bit was observed through a scanning electron microscope. It was found that the bonding between the coating and the substrate was good, and no signs of coating peeling were found.

Example 5

The difference between this embodiment and Embodiment 1 is that: the first acid etching time is 20s; the alkali etching time is 2min; the second The secondary acid etching time is 40s.

The pretreated micro drill bit was subjected to a fracture strength test experiment, and the fracture strength was found to be 25N. The micro drill bit was tested for drilling. When the number of holes was 4,000, the back cutter of the micro drill bit was observed through a scanning electron microscope. It was found that the bonding between the coating and the substrate was good, and no signs of coating peeling were found.

Comparative example 1

The difference between this comparative example and Example 1 is that: the first acid etching time is 1 min; the alkali etching time is 4 min; and the second acid etching time is 2 min.

The micro drill was subjected to a fracture strength test experiment, and the test showed that the fracture strength of the micro drill was 16N. Another sample was taken for a micro drill drilling test. When the number of holes was 600, needle breakage occurred.

Comparative example 2

The difference between this comparative example and Example 1 is that the alkali etching time is 15 minutes.

The micro drill bit was subjected to a fracture strength test experiment. The test showed that the fracture strength of the micro drill bit was 18N. Another sample was taken for a micro drill bit drilling test. When the number of holes was 1,000, the coating peeled off at the chisel edge. and severe sticky debris, as shown in Figure 4.

Comparative example 3

The difference between this comparative example and Example 1 is that the alkali etching time is 1 minute.

The micro drill bit was subjected to a fracture strength test experiment. The test showed that the fracture strength of the micro drill bit was 24N. Another sample was taken for a micro drill bit drilling test. When the number of holes was 2000, the coating peeled off at the chisel edge. .

Comparative example 4

The difference between this comparative example and Example 1 is that the first acid etching time is 5 seconds.

The micro drill bit was subjected to a fracture strength test experiment. The test showed that the fracture strength of the micro drill bit was 22N. Another sample was taken for a micro drill bit drilling test. When the number of holes was 2000, the coating peeled off at the chisel edge. .

Comparative example 5

The difference between this comparative example and Example 1 is that the first acid etching time is 1 minute.

The micro drill was subjected to a fracture strength test experiment, and the test showed that the fracture strength of the micro drill was 21N. Another sample was taken for a micro drill drilling test. When the number of holes was 2,000, needle breakage occurred.

Comparative example 6

The difference between this comparative example and Example 1 is that the second acid etching time is 5 seconds.

Comparative example 7

The difference between this comparative example and Example 1 is that the second acid etching time is 2 minutes.

The micro drill was subjected to a fracture strength test experiment, and the test showed that the fracture strength of the micro drill was 22N. Another sample was taken for a micro drill drilling test. When the number of holes was 1,000, needle breakage occurred.

Comparative example 8

The difference between this comparative example and Example 1 is that the diameter of the micro drill bit is 0.25 mm.

The micro drill was subjected to a fracture strength test, and the test showed that the fracture strength of the micro drill was 18N. Another sample was taken for a micro drill drilling test. When the number of holes was 1,000, needle breakage occurred.

Comparative example 9

The difference between this comparative example and Example 1 is that the diameter of the micro drill bit is 0.8 mm.

Comparative example 10

The difference between this comparative example and Example 1 is that the grain size of the micro drill is 0.1 μm.

The micro drill bit was subjected to a fracture strength test experiment. The test showed that the fracture strength of the micro drill bit was 25N. Another sample was taken for a micro drill bit drilling test. When the number of holes was 2,000, the coating peeled off at the chisel edge. .

Comparative example 11

The difference between this comparative example and Example 1 is that the grain size of the micro drill is 2 μm.

Comparative example 12

The difference between this comparative example and Example 1 is that the cobalt content of the micro drill bit is 2wt%.

The micro drill bit was subjected to a fracture strength test experiment. The test showed that the fracture strength of the micro drill bit was 16N. Another sample was taken for a micro drill bit drilling test. When the number of holes was 1,000, the coating peeled off at the chisel edge. .

Comparative example 13

The difference between this comparative example and Example 1 is that the cobalt content of the micro drill bit is 10 wt%.

The micro drill was subjected to a fracture strength test, and the test showed that the fracture strength of the micro drill was 24N. Another sample was taken for a micro drill drilling test. When the number of holes was 1,000, the coating peeled off at the chisel edge. .

In summary, the CVD diamond coating pretreatment process suitable for micro drill bits provided by this application can improve the fracture strength of micro drill bits and coatings without significantly weakening the fracture strength of micro drill bits through an optimized three-step chemical etching process. The adhesion performance between the substrate and the diamond coating enhances the mechanical bite force between the substrate and the diamond coating. Compared with traditional chemical etching methods, the optimized three-step etching process can effectively shorten the processing time and improve etching efficiency.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

A method for preparing a diamond-coated micro drill bit, which is characterized by including the following steps:

Chemically pretreating micro-fine drill bits before depositing the diamond coating;

The diameter of the micro drill bit is 0.35-0.75mm, the grain size is 0.3-1.0μm, and the cobalt content is 4-8wt%;

Chemical pretreatment includes the first acid etching, alkali etching and the second acid etching in sequence;

Wherein, the acid etching liquid used for the first acid etching and the acid etching liquid used for the second acid etching independently include nitric acid, hydrochloric acid and water in a volume ratio of 1:2-4:10-15; The alkali etching solution used in alkali etching includes potassium ferricyanide, potassium nitrate and water in a volume ratio of 1:1:10;

The first acid etching time is 10-30s; the alkali etching time is 2-6min; the second acid etching time is 10-50s.
The preparation method according to claim 1, characterized in that the material of the micro drill bit is cemented carbide, preferably WC cemented carbide;

And/or, the diamond grains contained in the diamond coating include micron crystals, nanocrystals or gradient crystals composed of micron crystals and nanocrystals.
The preparation method according to claim 1, characterized in that, before chemical pretreatment, it also includes cleaning the micro drill bit;

Preferably, the micro drill bit is placed in an organic solvent for ultrasonic cleaning;

Preferably, the organic solvent includes at least one of absolute ethanol, acetone and isopropyl alcohol;

Preferably, ultrasonic cleaning is performed at 40-60°C for 20-40 minutes;

Preferably, before the chemical pretreatment, it also includes drying the ultrasonic cleaned micro drill bit;

Preferably, drying is performed under a nitrogen atmosphere with a purity of not less than 99.99%.
The preparation method according to claim 1, characterized in that, before depositing the diamond coating, it also includes seeding the chemically pretreated micro drill bit;

Preferably, the seed crystal planting treatment includes: subjecting the chemically pretreated micro drill bit to ultrasonic vibration treatment in a treatment solution containing diamond powder;

Preferably, the treatment solution is prepared from anhydrous alcohol and nanodiamond powder in a ratio of 1L: 0.3-0.5g;

Preferably, the particle size of the nanodiamond powder is 1-4 μm;

Preferably, the time for planting seed crystals is 10-15 minutes.
The preparation method according to claim 1 or 2, characterized in that the deposition of the diamond coating is carried out by chemical vapor deposition.
The preparation method according to claim 5, characterized in that when the crystal grains of the diamond coating to be deposited are micron crystals, the deposition conditions include: the hot wire temperature is 2000-2200°C, and the hot wire-substrate distance is 18 -22mm, the substrate temperature is 800-850℃, the flow rate of CH4 is 50-70sccm, the flow rate of H2 is 17000-19000sccm, the air pressure is 5-10mbar, and the deposition time is 8-20h.
The preparation method according to claim 5, characterized in that when the crystal grains of the diamond coating to be deposited are nanocrystals, the deposition conditions include: the hot wire temperature is 2000-2200°C, and the hot wire-substrate distance is 18 -22mm, the substrate temperature is 800-850℃, the flow rate of CH4 is 20-40sccm, the flow rate of H2 is 8000-10000sccm, the air pressure is 1-5mbar, and the deposition time is 8-20h.
The preparation method according to claim 5, characterized in that when the grains of the diamond coating to be deposited are gradient crystals, the deposition conditions include: the hot wire temperature is 2000-2200°C, and the hot wire-substrate distance is 18 -22mm, the substrate temperature is 800-850℃, the flow rate of CH4 is 30-165sccm, the flow rate of H2 is 8000-10000sccm, the air pressure is 1-5mbar, sink The accumulation time is 8-20h.
A diamond-coated micro drill bit, characterized in that it is prepared by the preparation method described in any one of claims 1 to 8.
The application of the diamond-coated micro drill bit according to claim 9, characterized in that the diamond-coated micro drill bit is used for circuit board processing;

Preferably, the circuit board is a 5G communication PCB circuit board containing copper foil and/or PTFE and/or ceramic filler.