A drill bit coating for printed circuit boards and its preparation method

Abstract

The present invention relates to the technical field of plating of metal materials, and particularly to a drill bit coating applied to printed circuit boards and a preparation method thereof. The preparation method comprises the following steps: S1, ion etching the surface of the drill bit; S2, continuously ion etching the drill bit by using a pulsed negative bias voltage; S3, applying a pulsed negative bias voltage to the etched drill bit to obtain a ta-C layer by using a graphite target; S4, obtaining a composite target by using tantalum powder, solar-grade polysilicon, and carbon black; S5, applying a pulsed negative bias voltage and depositing a composite layer on the ta-C layer by using the composite target to obtain the drill bit coating. The drill bit coating prepared by the present invention has high hardness and strong bonding force, thereby being able to improve the service life of the drill bit.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material plating, and particularly relates to a drill bit coating for printed circuit boards and a preparation method thereof. Background Art

[0002] Printed circuit boards (PCBs) play an important role in various fields such as communication, industrial automation, automotive electronics, computers, consumer electronics, aerospace, and military electronics. With the development of consumer electronic products such as smart phones towards thinner, lighter, and more multifunctional directions, PCB products are also developing towards smaller, more refined, and more integrated directions, which has led to an increasing demand for micro-drilling technology. The micro-drilling process requires the use of drills with smaller diameters, especially micro-drills with high aspect ratios. In the manufacturing process of PCBs, drilling is a key step. The drill bit rubs against the board during high-speed rotation, generating high temperatures. At the same time, the notches formed during the processing will apply high stress to the cutting edge of the drill bit, resulting in drill bit fatigue and even fracture. The PCB industry consumes a large number of drill bits. Therefore, improving the durability of drill bits has become the main challenge faced by manufacturers. Traditional tungsten carbide (WC) drill bits are widely used due to their excellent cost performance, but they are prone to fracture, which reduces the service life of the drill bits and increases the production cost of PCBs. To solve this problem, researchers are exploring coated drill bit technology. By applying surface engineering technology and coating a special coating material on the cutting part of the drill bit, the drilling performance of WC drill bits can be improved, their service life can be extended, thereby reducing production costs, or by surface nitriding (carbonization), using high-hardness nitride hard coatings, coating low-friction coefficient coatings, etc. to improve the service life of drill pins.

[0003] Among them, the ta-C coating (tetrahedral amorphous carbon) has been proven to be a surface treatment technology that can effectively increase the service life of micro-drill pins. Tetrahedral amorphous carbon, like diamond and graphite, belongs to carbon materials. Its structural composition is between graphite and diamond. The ta-C coating is composed of carbon atoms, and its chemical structure is similar to that of diamond, with an sp 3 bond content of more than 80%. It has higher microhardness and thermal stability compared to ordinary DLC coatings. Generally, the anti-wear performance of materials is positively correlated with their hardness. Therefore, ta-C has better anti-wear performance than ordinary a-C. In addition, because ta-C does not contain hydrogen and has a high sp 3 -C content, it has excellent thermal stability. In other words, ta-C should be more suitable for harsh conditions such as high load, high speed, high temperature, and long life in modern industry. The ta-C coating for drill pins only needs to be a few hundred nanometers thick to achieve a good protection effect, and it is also beneficial to ensure the drilling accuracy.

[0004] CN110343998A discloses a method for preparing a ta-C coating on a printed circuit board drill bit, comprising the following steps: 1) introducing a mixed gas of argon and hydrogen under vacuum conditions and etching the drill bit using an ion source; 2) performing ion etching on the drill bit with argon using a negative bias voltage; 3) depositing a metal Cr bottom layer on the working surface of the drill bit; 4) applying a high-pulse negative bias voltage to the drill bit to inject carbon atoms generated by a graphite target into the Cr bottom layer; 5) reducing the negative bias voltage and continuing to deposit carbon atoms to form a ta-C functional layer. The ta-C coating on the printed circuit board drill bit and the preparation method thereof provided by the invention can increase the service life of the drill bit by 5-10 times, and in particular, can process ultra-thick printed circuit boards and high-hardness boards that are difficult to process with uncoated drill bits.

[0005] CN112267097A provides a composite coating for a printed circuit board drill bit and a preparation method thereof. The composite coating sequentially includes a bottom layer, a carbonitriding layer, a diamond-like carbon coating, and a heat-insulating layer from the surface of the drill bit outward. The bottom layer includes any one of a metal layer, an alloy layer, or a metal compound layer, and the heat-insulating layer is a metal nitride ceramic layer. In the composite coating of the present invention, through the design of a multi-layer coating structure, the diamond-like carbon coating can effectively improve the hardness and wear resistance of the drill bit, thereby increasing the service life of the drill bit. The carbonitriding layer can effectively improve the adhesion strength of the diamond-like carbon coating and avoid the problem that the diamond-like carbon coating is prone to peeling. The heat-insulating layer can delay the graphitization of the diamond-like carbon coating and further increase the service life of the drill bit. The drill bit of the present invention is deposited with a composite coating and is particularly suitable for drilling of high-frequency and high-speed printed circuit boards, and the obtained drilling quality and precision are high.

[0006] However, due to its relatively high hardness and internal stress, the ta-C coating is not easily attached to the surface of the substrate material. The high internal stress is likely to cause the coating to crack, peel off, or cause severe deformation of the substrate, restricting the further thickening and practical application of the coating. Therefore, it is necessary to adopt a co-doping or coating-increasing method to improve the adhesion of the coating. However, this method will affect the wear resistance while improving the adhesion. Summary of the Invention

[0007] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a drill bit coating for a printed circuit board and a preparation method thereof.

[0008] The ta-C layer has a low friction coefficient, high chemical stability and wear resistance, and can significantly reduce the friction coefficient, adhesive wear and cutting force. Therefore, it is widely used as a coating for drill bits. However, it has a high hardness and poor adhesion to the surface of the drill bit, so its wear life is relatively short. Therefore, in the present invention, tantalum powder is mixed with solar-grade polysilicon and carbon black and then combusted and synthesized to obtain a composite, and then hot-pressed into a target and deposited on the surface of the ta-C layer. Since tantalum nitride and tantalum carbide are carbides and nitrides known for their high melting points, high hardness and high thermal stability, and the addition of silicon elements can not only improve the hardness and thermal stability, but also enhance the oxidation resistance and friction resistance, the drill bit coating obtained after the deposition of the composite target can have higher hardness and better anti-friction properties, thereby protecting the underlying ta-C coating and not affecting the coating life due to its poor adhesion.

[0009] To achieve the above object, the present invention provides a method for preparing a coating for a drill bit used in a printed circuit board, comprising the following steps:

[0010] S1. Pass a mixed gas of an inert gas and hydrogen under vacuum to etch the surface of the drill bit;

[0011] S2. Continue to perform ion etching on the drill bit with the inert gas under a pulsed negative bias voltage;

[0012] S3. Apply a pulsed negative bias voltage to the etched drill bit to obtain a ta-C layer on the surface of the drill bit with a graphite target;

[0013] S4. Mix tantalum powder with solar-grade polysilicon and carbon black and then perform ball milling for mechanical activation. After ball milling for 20 - 30 min, combust and synthesize at 3000 - 3500 °C for 10 - 30 min, and then perform ball milling for 4 - 8 h to obtain a powder. The powder is added to a 20% hydrochloric acid solution and heated for 4 - 6 h to remove impurities, filtered, dried and then hot-pressed to obtain a composite target;

[0014] S5. Mix nitrogen and argon, apply a pulsed negative bias voltage, and deposit a composite layer on the ta-C layer in step S3 with the composite target to obtain the drill bit coating.

[0015] Further, the inert gas is argon.

[0016] Further, the flow rate ratio of the inert gas to hydrogen is 1:1 - 5 sccm.

[0017] Further, the negative bias voltage in step S2 is 100 - 300 V, and the duty cycle is 30 - 80%.

[0018] Further, the negative bias voltage in step S3 is 100 - 400 V, the duty cycle is 30 - 80%, and the current of the graphite target is 40 - 80 A.

[0019] Further, the mass ratio of the tantalum powder, solar-grade polysilicon, and carbon black is 50-60:30-40:5-10.

[0020] Further, the temperature range for heating in step S4 is 70-80 °C.

[0021] Further, the conditions for hot pressing are 1500-1800 °C, 20-40 MPa, and 5-15 min.

[0022] Further, in step S5, the flow rate ratio of nitrogen to argon is 1:1-10 sccm, the negative bias voltage is 100-500 V, the duty cycle is 30-80%, and the current of the composite target is 50-80 A.

[0023] The present invention also provides a drill bit coating for a printed circuit board, which is prepared by the above method.

[0024] Advantages of the present invention:

[0025] In the present invention, a composite is obtained by mixing tantalum powder with solar-grade polysilicon and carbon black and then burning and synthesizing, and then hot pressing into a target and depositing it on the surface of the ta-C layer. Since tantalum nitride and tantalum carbide are carbides and nitrides known for their high melting points, high hardness, and high thermal stability, and the addition of silicon elements can not only improve the hardness and thermal stability but also enhance the oxidation resistance and friction resistance, the drill bit coating obtained after depositing the composite target can have higher hardness and better anti-friction performance, thereby protecting the underlying ta-C coating and not affecting the coating life due to poor adhesion. Specific embodiments

[0026] Tantalum powder, purity: 3N grade, Yourong New Materials Technology, Zhuozhou.

[0027] Solar-grade polysilicon, Shandong Ruiyang Silicon Industry Technology.

[0028] Carbon black, N-330, Shandong Kepler Biotechnology.

[0029] Example 1

[0030] A preparation method for a drill bit coating for a printed circuit board includes the following steps:

[0031] S1. Pass a mixed gas of argon and hydrogen under vacuum to etch the surface of the drill bit, and the flow rate ratio of argon to nitrogen is 1:2 sccm;

[0032] S2. Continue to perform ion etching on the drill bit with argon under a pulsed negative bias voltage of 200 V, and the duty cycle is 30%;

[0033] S3. Apply a pulsed negative bias voltage of 400 V with a duty cycle of 50% to the etched drill bit to obtain a ta-C layer on the surface of the drill bit from a graphite target, with a target current of 60 A;

[0034] S4. Mix tantalum powder, solar-grade polysilicon, and carbon black in a mass ratio of 53.5:37.5:9, then perform ball milling for mechanical activation. After ball milling for 20 min, carry out combustion synthesis at 3500 °C for 20 min, and then perform ball milling for 6 h to obtain a powder. Add the powder to 20% hydrochloric acid, heat it to 80 °C, and treat it for 5 h to remove impurities. After filtration and drying, perform hot pressing at 1600 °C and 30 MPa for 10 min to obtain a composite target;

[0035] S5. Mix nitrogen and argon in a flow rate ratio of 1:5 sccm, apply a pulsed negative bias voltage of 450 V with a duty cycle of 60%, and use the composite target to deposit a composite layer on the ta-C layer in step S3. The current of the composite plate is 80 A, thus obtaining the drill bit coating.

[0036] Example 2

[0037] A preparation method for a drill bit coating applied to a printed circuit board, comprising the following steps:

[0038] S1. Pass a mixed gas of argon and hydrogen under vacuum to etch the surface of the drill bit, with a flow rate ratio of argon to nitrogen of 1:2 sccm;

[0039] S2. Continue to perform ion etching on the drill bit with argon under a pulsed negative bias voltage of 200 V, with a duty cycle of 30%;

[0040] S3. Apply a pulsed negative bias voltage of 400 V with a duty cycle of 50% to the etched drill bit to obtain a ta-C layer on the surface of the drill bit from a graphite target, with a target current of 60 A;

[0041] S4. Mix tantalum powder, solar-grade polysilicon, and carbon black in a mass ratio of 60:30:10, then perform ball milling for mechanical activation. After ball milling for 20 min, carry out ball milling at 3500 °C for 20 min, and then perform ball milling for 6 h to obtain a powder. Add the powder to 20% hydrochloric acid, heat it to 80 °C, and treat it for 5 h to remove impurities. After filtration and drying, perform hot pressing at 1600 °C and 30 MPa for 10 min to obtain a composite target;

[0042] S5. Mix nitrogen and argon in a flow rate ratio of 1:5 sccm, apply a pulsed negative bias voltage of 450 V with a duty cycle of 60%, and use the composite target to deposit a composite layer on the ta-C layer in step S3. The current of the composite plate is 80 A, thus obtaining the drill bit coating.

[0043] Example 3

[0044] A preparation method for a drill bit coating applied to a printed circuit board, comprising the following steps:

[0045] S1. Introduce a mixed gas of argon and hydrogen under vacuum to etch the surface of the drill bit, and the flow rate ratio of argon to nitrogen is 1:2 sccm;

[0046] S2. Continuously use argon to perform ion etching on the drill bit under a pulsed negative bias voltage of 200 V, and the duty cycle is 30%;

[0047] S3. Apply a pulsed negative bias voltage of 400 V to the etched drill bit, with a duty cycle of 50%, to obtain a ta-C layer on the surface of the drill bit from a graphite target, and the target current is 60 A;

[0048] S4. Mix tantalum powder, solar-grade polysilicon, and carbon black in a mass ratio of 50:40:10, then perform ball milling for mechanical activation. After ball milling for 20 min, carry out combustion synthesis at 3500 °C for 20 min, and then perform ball milling for 6 h to obtain a powder. Add the powder to 20% hydrochloric acid, heat it to 80 °C, and treat it for 5 h to remove impurities. After filtration and drying, perform hot pressing at 1600 °C and 30 MPa for 10 min to obtain a composite target;

[0049] S5. Mix nitrogen and argon in a flow rate ratio of 1:5 sccm, apply a pulsed negative bias voltage of 450 V, and the duty cycle is 60%. Use the composite target to deposit a composite layer on the ta-C layer in step S3, and the current of the composite plate is 80 A, thus obtaining the drill bit coating.

[0050] Example 4

[0051] A preparation method for a drill bit coating applied to a printed circuit board, comprising the following steps:

[0052] S1. Introduce a mixed gas of argon and hydrogen under vacuum to etch the surface of the drill bit, and the flow rate ratio of argon to nitrogen is 1:2 sccm;

[0053] S2. Continuously use argon to perform ion etching on the drill bit under a pulsed negative bias voltage of 200 V, and the duty cycle is 30%;

[0054] S3. Apply a pulsed negative bias voltage of 400 V to the etched drill bit, with a duty cycle of 50%, to obtain a ta-C layer on the surface of the drill bit from a graphite target, and the target current is 60 A;

[0055] S4. Mix tantalum powder, solar-grade polysilicon, and carbon black in a mass ratio of 55:40:5, then perform ball milling for mechanical activation. After ball milling for 20 min, carry out combustion synthesis at 3500 °C for 20 min, and then perform ball milling for 6 h to obtain a powder. Add the powder to 20% hydrochloric acid, heat it to 80 °C, and treat it for 5 h to remove impurities. After filtration and drying, perform hot pressing at 1600 °C and 30 MPa for 10 min to obtain a composite target;

[0056] S5. Mix nitrogen and argon in a flow rate ratio of 1:5 sccm, apply a pulsed negative bias voltage of 450 V, and a duty cycle of 60%. Use the composite target to deposit a composite layer on the ta-C layer in step S3. The current of the composite plate is 80 A, and then the drill bit coating is obtained.

[0057] Comparative Example 1

[0058] A preparation method for a drill bit coating applied to a printed circuit board includes the following steps:

[0059] S1. Introduce a mixed gas of argon and hydrogen under vacuum to etch the surface of the drill bit. The flow rate ratio of argon to nitrogen is 1:2 sccm;

[0060] S2. Continue to perform ion etching on the drill bit with argon under a pulsed negative bias voltage of 200 V, and the duty cycle is 30%;

[0061] S3. Apply a pulsed negative bias voltage of 400 V to the etched drill bit, and the duty cycle is 50%, so that a ta-C layer is obtained on the surface of the drill bit with a graphite target, and the target current is 60 A, and then the drill bit coating is obtained.

[0062] Test Example 1

[0063] Use a nanoindentation instrument to test the nano-hardness of the coatings of the examples and comparative examples by the indentation method. The indentation load is 8 mN to ensure that the indentation depth is less than 1 / 10 of the film thickness, and the test mode is the continuous stiffness mode. When testing, randomly select 6 clean and pollution-free places to test the hardness, and calculate the average value to obtain the nano-hardness value.

[0064] Table 1 Hardness of Drill Bit Coatings Applied to Printed Circuit Boards

[0065] Experimental Scheme Nano-hardness / GPa Example 1 38.9 Example 2 37.6 Example 3 38.1 Example 4 36.9 Control Example 1 27.4

[0066] It can be found through the comparison between the control examples and the examples that when the composite layer is not deposited on the surface of the ta-C layer, the hardness of the obtained drill bit coating is significantly worse. This is because tantalum nitride and tantalum carbide are carbides and nitrides known for their high melting points, high hardness, and high thermal stability, and the addition of silicon element can further improve the hardness. Therefore, the deposited composite coating can endow the drill bit with higher mechanical properties, so the hardness is greater than that of the control example 1 without the deposited composite coating. The differences between Examples 1 to 4 illustrate that tantalum powder, solar-grade polysilicon, and carbon black will affect the performance of the final composite coating. From the results, the ratio in Example 1 is better.

[0067] Test Example 2

[0068] The scratch method is used to characterize the bonding strength between the coatings of the examples and the control examples and the drill bits. During the test, a conical indenter slides on the coating at a certain speed for a certain distance, and the vertical pressure acting on the indenter gradually or continuously increases until the coating peels off. When the coating is subjected to the vertical pressure, it will go through two important load stages: the vertical load when the coating starts to crack is called the first critical load; while the vertical load when the coating first shows obvious peeling is called the second critical load. Since the initial formation position of the coating cracks is usually difficult to observe, the second critical load is regarded as an indicator of the bonding strength between the coating and the substrate. To test the bonding performance between the coating and the substrate, the scratch module of the friction testing machine is used. The experimental settings are as follows: the vertical load is gradually increased from 0 to 1 N and maintained at this load for 10 s. Subsequently, within 15 s, the load is gradually increased from 1 N to 30 N while a sliding displacement of 10 mm is carried out. The above experimental steps are repeated three times for each sample. Since the load increases linearly with the sliding distance, each point during the sliding process corresponds to a specific pressure value. By analyzing the relationship between the load and the displacement, the second critical load is obtained.

[0069] Table 2 Bonding Strength of Drill Bit Coatings Applied to Printed Circuit Boards

[0070] Experimental Scheme Second Critical Load / N Example 1 25.4 Example 2 23.2 Example 3 24.1 Example 4 22.3 Control Example 1 13.8

[0071] It can be found through the comparison between the control examples and the examples that the bonding force between the drill bit coatings prepared in the examples and the drill bit surface is stronger. This may be because although the ta-C coating in the control example 1 has higher hardness but is also more brittle, and its ability to resist plastic deformation under the action of vertical stress is low, resulting in earlier peeling. The addition of silicon element in the examples improves the anti-friction performance of the composite coating. Therefore, when facing the vertical stress, the coating is less likely to peel off, and the bonding strength between the coating and the drill bit surface is better.

[0072] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in this technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A method for preparing a drill needle coating for a printed circuit board, characterized in that: The steps include: S1. A mixed gas of inert gas and hydrogen is introduced under vacuum to etch the surface of the drill needle; S2, continue to use the inert gas to ion etch the drill needle under the pulse negative bias voltage; S3, applying a pulsed negative bias voltage to the drill needle after etching, so that the graphite target material obtains a ta-C layer on the surface of the drill needle; S4, mixing tantalum powder with solar grade polysilicon and carbon black and then ball milling for mechanical activation, ball milling for 20-30 minutes, combustion synthesis at 3000-3500°C for 10-30 minutes, and then ball milling for 4-8 hours to obtain powder, adding the powder to 20% hydrochloric acid solution and heating for 4-6 hours to remove impurities, filtering, drying and hot pressing to obtain a composite target; S5, using a mixture of nitrogen and argon, applying a pulsed negative bias, and using a composite target to deposit a composite layer on the ta-C layer in step S3, so as to obtain a drill needle coating; The mass ratio of the tantalum powder to solar-grade polysilicon and carbon black is 50-60:30-40:5-10.

2. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The inert gas is argon.

3. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The flow ratio of the inert gas to the hydrogen is 1:1-5 sccm.

4. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The negative bias voltage in step S2 is 100-300V, and the duty cycle is 30-80%.

5. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The negative bias voltage in step S3 is 100-400 V, the duty cycle is 30-80%, and the current of the graphite target is 40-80 A.

6. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The temperature range of the heating in step S4 is 70-80°C.

7. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The hot pressing conditions are 1500-1800° C., 20-40 MPa, and 5-15 min.

8. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: In the step S5, the flow ratio of nitrogen to argon is 1:1-10 sccm, the negative bias voltage is 100-500 V, the duty cycle is 30-80%, and the current of the composite target is 50-80 A.

9. The method for preparing a drill needle coating for a printed circuit board according to claim 1, characterized in that: The steps include: S1. A mixed gas of argon and hydrogen is introduced under vacuum to etch the surface of the drill needle, and the flow ratio of argon to nitrogen is 1:2 sccm; S2, continue to use argon gas to ion etch the drill needle under a pulsed negative bias voltage of 200V, with a duty cycle of 30%; S3, applying a pulsed negative bias voltage of 400V to the drill bit after etching, with a duty cycle of 50%, so that the graphite target obtains a ta-C layer on the surface of the drill bit, and the target current is 60A; S4, mixing tantalum powder with solar grade polysilicon and carbon black in a mass ratio of 50:40:10 and then ball milling for mechanical activation, ball milling for 20 minutes, combustion synthesis at 3500° C. for 20 minutes, and then ball milling for 6 hours to obtain powder, adding the powder to 20% hydrochloric acid and heating it to 80° C. for 5 hours to remove impurities, filtering, drying, and hot pressing at 1600° C. and 30 MPa for 10 minutes to obtain a composite target; S5. Nitrogen and argon are mixed at a flow ratio of 1:5 sccm, a pulsed negative bias of 450 V is applied, and a duty cycle of 60% is applied. A composite layer is deposited on the ta-C layer in step S3 using a composite target. The current of the composite plate is 80 A, and a drill needle coating is obtained.

10. A drill needle coating for a printed circuit board, characterized in that: Prepared by the method according to any one of claims 1 to 9.