Selective etching method for composite-material-based metal coating with femtosecond laser assisted by temperature field

Abstract

The invention discloses a temperature field-assisted femtosecond laser composite material-based metal coating selective etching method. The method comprises the following steps: placing a composite material on a three-dimensional precision displacement platform; the Z axis of the three-dimensional precise displacement platform is regulated and controlled through a computer, and femtosecond laser is focused to the surface of the composite through a focusing lens; adjusting the focus of the auxiliary heat source laser to enable the auxiliary heat source laser and the femtosecond laser to be at the same position and on the same focal plane; refrigerating the composite material by using a semiconductor refrigerating table; adjusting the laser power of the auxiliary heat source through a computer, monitoring the surface temperature of the composite material at the same time, so that the surface temperature does not exceed the phase transition temperature of resin in the composite material, and preheating the metal coating by using the auxiliary heat source laser; the femtosecond laser power is regulated and controlled by adjusting the deflection angle of a polaroid in the power attenuator; all parameters are set through a computer, and machining is conducted on the surface of the composite through a set program. The method aims at solving the problems that an existing metal film patterning processing method is low in precision, selective etching is difficult, and damage to a substrate is serious.

Description

Technical Field

[0001] The present invention relates to the field of frequency selective surfaces, in particular to a method for selectively etching a composite metal coating assisted by a temperature field using femtosecond laser. Background Art

[0002] A frequency selective surface (FSS) is a periodic structure with specific electromagnetic responses, capable of reflecting, transmitting, or absorbing electromagnetic waves of specific frequencies, and is widely used in fields such as radar, communication, and stealth technology. Traditional FSS mostly uses pure metal materials, but they are heavy and costly, making it difficult to meet the requirements of modern industry for lightweight and multifunctional integration. Composite materials, due to their excellent properties such as lightweight, high strength, and corrosion resistance, have become key materials in fields such as aerospace, communication, and automotive. However, the insulating properties of composite materials themselves limit their applications in high-frequency electromagnetic fields, such as frequency selective surfaces (FSS), electromagnetic shielding structures, etc. To solve this problem, it is usually necessary to introduce a metal coating on the surface of the composite material and form a specific structure through patterning removal technology to achieve the desired electromagnetic functions. Existing radar design theories indicate that combining metal and composite materials to form a metal / composite material system can improve stealth performance while also taking into account its mechanical durability and robustness.

[0003] Existing preparation processes for metal / composite material systems include the film transfer method and the mechanical in-situ processing method. The film transfer method is divided into two steps: metal circuit fabrication and film transfer. Qi Cheng et al. first cleaned the surface of the dielectric substrate through ultrasonic waves to make its surface free of impurities and stains; then coated a conductive ink on its surface and heated it to remove some of the solvents contained in the ink; finally, set the movement trajectory and drove the laser head to move through the movement device to sinter the metal into metal wires, thereby completing the processing of the frequency selective surface. Lv Mingyun et al. from Beihang University built a mechanical processing system, conducted process tests on the built equipment, compared the transmission characteristics of the processed parts with the ideal simulation curves, and finally verified that it is feasible to process the frequency selective surface using a CNC robot. However, mechanical processing is a traditional processing method and belongs to contact processing. There will be tool wear during the processing, and it is impossible to ensure the consistency of accuracy after processing a large number of FSS units.

[0004] Compared with the above preparation processes, the method of selectively removing the metal coating pattern on the surface, that is, selectively removing the metal coating on the surface of the composite material to form a periodic structure, has become an ideal preparation scheme for frequency selective surfaces.

[0005] In the field of metal coating patterning removal technology on the surface of composite materials, femtosecond laser processing has become a research hotspot due to its characteristics such as ultra-short pulses, high precision, and low thermal impact. However, the local high temperature during femtosecond laser processing may still cause thermal damage to the composite material substrate, such as resin carbonization or fiber fracture. In addition, problems such as uniform removal on complex curved surfaces and protection of the interface between the metal layer and the matrix also need to be solved urgently. Therefore, developing an efficient, precise, and reliable metal coating patterning removal technology on the surface of composite materials has important theoretical significance and engineering value. Summary of the Invention

[0006] To solve the problems of low precision, difficult selective etching, and serious damage to the substrate in the current metal thin film patterning processing methods, the present invention provides a method for selective etching of metal coatings on composite materials assisted by a temperature field and femtosecond laser, which can achieve selective removal of metal coatings on the surface of composite materials. At the same time, compared with the case without an external temperature field, a lower laser power can be used to achieve a better processing effect, avoiding the problem of ablation of the substrate composite material during the removal of the metal coating.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In an embodiment of the present invention, a method for selective etching of metal coatings on composite materials assisted by a temperature field and femtosecond laser is proposed. The method includes:

[0009] In a super-clean environment, use a temperature field assisted femtosecond laser processing system;

[0010] Place the composite material on a three-dimensional precision displacement platform;

[0011] Through the computer, adjust the Z-axis of the three-dimensional precision displacement platform to focus the femtosecond laser on the surface of the composite material through a focusing lens;

[0012] Adjust the focus of the auxiliary heat source laser so that it is in the same position and the same focal plane as the femtosecond laser;

[0013] Turn on the semiconductor refrigeration table to reduce its temperature to -30°C and refrigerate the composite material under the metal coating;

[0014] Through the computer, adjust the output power of the auxiliary heat source laser, and at the same time monitor the temperature of the surface of the composite material to ensure that it does not exceed the phase change temperature of the resin in the composite material, and use the auxiliary heat source laser to preheat the metal coating of the composite material;

[0015] Import the pattern pre-drawn in CAD into the computer, and the three-dimensional precision displacement platform moves according to the path of the preset CAD pattern; turn on the processing optical path system, and adjust the deflection angle of the polarizer in the power attenuator to finely control the output power of the femtosecond laser;

[0016] The repetition frequency, power of the femtosecond laser, and the processing speed of the three-dimensional precision displacement platform are set by a computer, and then the processing is carried out on the surface of the composite material according to the preset CAD pattern by the program set by the computer.

[0017] Furthermore, the temperature field assisted femtosecond laser processing system includes: a femtosecond laser, a processing optical path system, an illumination optical path, a long-pulse laser, a calculator, a thermometer, a three-dimensional precision displacement platform, and a semiconductor refrigeration table. The processing optical path system includes a reflector, a focusing lens, and a power attenuator, which are used to regulate the propagation path of the femtosecond laser in the optical path and the laser power; the illumination optical path is used to transmit an image to the computer to observe the surface topography of the processing area to judge the processing effect; the long-pulse laser is used as an auxiliary heat source laser to preheat the metal coating of the composite material; the thermometer is used to monitor the temperature of the metal coating of the composite material and feedback to adjust the heating or cooling power; the three-dimensional precision displacement platform is used to drive the composite material to move according to the preset pattern imported by the computer to achieve patterned etching; the semiconductor refrigeration table is used to continuously refrigerate the composite material above; the data between the femtosecond laser, the power attenuator, the illumination optical path, the long-pulse laser, the thermometer, the three-dimensional precision displacement platform, and the semiconductor refrigeration table are interconnected through the computer via transmission cables.

[0018] Furthermore, in the processing optical path system, the reflector is adjusted to ensure that the beam incident on the focusing lens is collimated.

[0019] Furthermore, the semiconductor refrigeration table is equipped with a temperature circulation system, which can continuously keep the cold end of the semiconductor refrigeration table at a preset low temperature.

[0020] Beneficial effects:

[0021] 1. Traditional mechanical processing methods introduce residual stress to the material, and at the same time, due to tool wear, the accuracy during the processing will inevitably decrease. Chemical etching and masks also have problems such as low accuracy. The femtosecond laser processing technology has the characteristics of non-contact processing, high precision and high efficiency, and low thermal damage, resulting in less damage to the composite material under the metal coating, avoiding the thermal damage to the composite material and the damage to the substrate in traditional processing methods or long-pulse laser processing methods, and can initially realize the selective removal preparation process of the frequency selective surface.

[0022] 2. Compared with the femtosecond laser processing and etching method without applying an auxiliary temperature field, the introduction of a high-temperature field can significantly preheat the surface free electrons of the metal coating and significantly reduce the ablation threshold of the metal coating. The introduction of a low-temperature field reduces the overall temperature of the lower-layer composite material and increases its ablation threshold. With the reduction of the ablation threshold of the metal coating and the increase of the ablation threshold of the composite material, a better selective removal effect can be achieved under the same laser parameters. Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of the temperature field composite femtosecond laser processing system of the present invention;

[0024] In the figure: 1 - femtosecond laser, 2 - power attenuator, 3 - mirror, 4 - illumination optical path, 5 - focusing lens, 6 - long pulse laser, 7 - calculator, 8 - thermometer, 9 - three-dimensional precision displacement platform, 10 - semiconductor refrigeration stage, 11 - sample to be processed;

[0025] Figure 2 is a schematic diagram of temperature field-assisted femtosecond laser selective removal of the present invention;

[0026] In the figure: 10 - semiconductor refrigeration stage, 12 - composite material, 13 - femtosecond laser, 14 - auxiliary heat source laser, 15 - metal coating;

[0027] Figure 3 is a schematic diagram of the temperature field-assisted improvement of the selective removal effect of the present invention;

[0028] Figure 4 is a schematic diagram of the frequency selective surface of the temperature field-assisted selective patterning etching of the present invention;

[0029] Figure 5 is a comparison diagram of the processing effects of two patterns, namely the horizontal line and the vertical line, of the square ring resonator structure array of the same frequency selective surface in an embodiment of the present invention. Detailed Embodiments

[0030] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are given only to enable those skilled in the art to better understand and then design the present invention, and do not limit the scope of the present invention in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to be able to convey the scope of the present disclosure completely to those skilled in the art.

[0031] Those skilled in the art know that the embodiments of the present invention can be designed as a structure, a device, a preparation method, or a computer program product. Therefore, the present disclosure can be specifically designed in the following forms, namely: completely hardware, completely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software.

[0032] According to an embodiment of the present invention, a method for selectively etching a metal coating on a composite material assisted by a femtosecond laser with a temperature field is proposed. An external heating temperature field is used to reduce the ablation threshold of the metal coating, and an external cold temperature field is used to increase the ablation threshold of the bottom composite material. By using an external heating device and a cooling device, a specific temperature field distribution is constructed in the femtosecond laser etching area. The temperature of the processing area is monitored in real time by a thermometer, and the heating or cooling power is feedback-regulated to ensure that the temperature is stably within the set range (low temperature -30°C, high temperature 262°C), that is, to increase the local temperature of the metal coating (reduce the laser ablation threshold of the metal coating: 0.51 J / cm 2 ), and reduce the local temperature of the composite material substrate (increase the laser ablation threshold of the composite material: 1.26 J / cm 2 ), so as to achieve the purpose of protecting the composite material substrate and improving the etching efficiency and accuracy.

[0033] Next, with reference to several representative embodiments of the present invention, the principles and spirit of the present invention will be elaborated in detail.

[0034] The overall solution adopted by the present invention includes two parts: the construction of a temperature field-assisted femtosecond laser processing system and the method for selectively etching a metal coating on a composite material assisted by a femtosecond laser with a temperature field.

[0035] 1. Construction of the temperature field-assisted femtosecond laser processing system

[0036] As Figure 1 shown, the temperature field-assisted femtosecond laser processing system includes: a femtosecond laser 1, a processing optical path system, an illumination optical path 4, a long-pulse laser 6, a calculator 7, a thermometer 8, a three-dimensional precision displacement platform 9, and a semiconductor refrigeration stage 10. The power of the femtosecond laser 1 is 20 W, the pulse width is 250 fs, and the repetition frequency is 100 kHz - 1 MHz. The processing optical path system includes a mirror 3, a focusing lens 5, a power attenuator 2, etc., which are used to control the propagation path of the femtosecond laser in the optical path and the laser power; the illumination optical path 4 consists of a light source and an industrial CCD camera, which is used to transmit the image to the computer 7 to observe the surface morphology of the processing area to judge the processing effect; the long-pulse laser (power 100 W) 6 is used as an auxiliary heat source laser to preheat the metal coating of the sample to be processed 11 (composite material); the thermometer 8 is used to monitor the temperature of the area to be processed and feedback-regulate the heating or cooling power; the three-dimensional precision displacement platform 9 is used to drive the sample to be processed 11 to move according to the preset pattern imported by the computer 7 to achieve patterned etching; the semiconductor refrigeration stage 10 is used to continuously cool the sample to be processed 11 above. The data between the femtosecond laser 1, the power attenuator 2, the illumination optical path 4, the long-pulse laser 6, the thermometer 8, the three-dimensional precision displacement platform 9, and the semiconductor refrigeration stage 10 are interconnected through the computer 7 via transmission cables.

[0037] 2. Method for Selectively Etching Metal Coating on Composite Material by Femtosecond Laser Assisted with Temperature Field

[0038] As Figure 2 shown, the specific process is as follows:

[0039] (1) Place the composite material 12 on the three-dimensional precision displacement platform;

[0040] (2) Through the computer, adjust the Z-axis of the three-dimensional precision displacement platform, and focus the femtosecond laser 13 on the surface of the composite material 12 through the focusing lens to make a clear image appear;

[0041] (3) Adjust the focus of the auxiliary heat source laser 14 to be at the same position and the same focal plane as the femtosecond laser 13;

[0042] (4) Turn on the semiconductor refrigeration stage 10 to reduce its temperature to -30 °C and refrigerate the composite material 12 under the metal coating 15;

[0043] (5) Through the computer, adjust the output power of the auxiliary heat source laser 14, and at the same time monitor the temperature on the surface of the composite material 12 to make it not exceed the phase change temperature of the resin in the composite material 12, and use the auxiliary heat source laser 14 to preheat the metal coating 15 of the composite material 12;

[0044] (6) Import the pattern pre-drawn in CAD into the computer, and the three-dimensional precision displacement platform moves along the path of the preset CAD pattern; turn on the processing optical path system, and adjust the deflection angle of the polarizer in the power attenuator to finely control the output power of the femtosecond laser 13;

[0045] (7) Set the repetition frequency, power of the femtosecond laser 13 and the processing speed of the three-dimensional precision displacement platform through the computer, and then process on the surface of the composite material 12 according to the preset CAD pattern through the program set by the computer, and finally obtain a frequency selective surface as Figure 4 shown.

[0046] In order to ensure the processing accuracy and accuracy, the above processing process is carried out in a super clean environment without stopping until the processing is completed.

[0047] By applying the temperature field to assist the femtosecond laser, the selective removal effect on the metal coating on the composite material surface is significantly improved, as Figure 3 shown.

[0048] It should be noted that although the operations of the preparation method of the present invention are described in a specific order in the above embodiments and accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step for execution, and / or one step may be decomposed into multiple steps for execution.

[0049] In order to more clearly explain the method for regulating the surface resistance value of the composite material induced by femtosecond laser in situ, the following will be described in conjunction with a specific embodiment. However, it should be noted that this embodiment is only for better explaining the present invention and does not constitute an improper limitation of the present invention. Specific Embodiment

[0050] To prove the beneficial effect of the temperature field on the processing effect, in this embodiment, a frequency selective surface square loop resonator structure array was processed into two patterns, as Figure 5 shown.

[0051] 1. Removal situation without temperature field assistance

[0052] The composite material used in this embodiment is a cyanate ester resin composite material with a copper plating layer of about 10 μm on the surface. The plated composite material sample was cut into a 10 cm × 10 cm plate, and the particulate contaminants on the surface of the sample were blown away with nitrogen. Subsequently, it was rinsed successively with anhydrous ethanol and deionized water, and finally placed in a vacuum drying oven at 30 °C to dry the moisture under normal pressure for standby. Another composite material without a metal plating layer on the surface was prepared to calculate the ablation thresholds of the two.

[0053] Check the optical path system, adjust the mirrors in the optical path system to ensure the collimation of the beam incident on the focusing lens. Adjust the Z-axis of the three-dimensional precision displacement platform to find the focal plane of the sample. Turn on the power supply and key of the femtosecond laser, import the femtosecond laser parameters, keep the pulse width at 250 fs and the repetition frequency at 400 kHz, and then adjust the power of the femtosecond laser to 20% through the computer. Record the power at this time using a laser power meter. Turn on the femtosecond laser to scan the coated sample and the uncoated sample, and calculate the damage thresholds of the two according to the following formula:

[0054]

[0055] where D is the diameter of the ablation area, E is the energy of the incident laser, E th is the ablation threshold, and r0 is the distance from the center of the incident light spot to the 1 / e 2 point of the energy. In this embodiment, when the femtosecond laser power reached 20% without applying a temperature field, damage began to appear in the metal film layer, and the ablation threshold of the metal plating layer was 0.6 J / cm 2, at this time, serious damage appears on the composite material substrate.

[0056] Import the pattern drawn in CAD into the processing software of the computer. First, import the processing pattern (vertical line pattern) without applying the temperature field assistance, and perform processing as Figure 5 shown. From the macroscopic morphology, the substrate of the vertical line part turns black. Under the microscope, it can be seen that there are metal debris and substrate debris on the substrate without applying the temperature field assistance. The removal effect of the surface metal coating is poor, and the substrate is severely damaged.

[0057] 2. Preparation of Temperature Field Assistance

[0058] Turn on the power of the long-pulse laser, adjust the position of the mirror so that the laser irradiates the area to be processed, adjust the power to 35W on the computer, and at the same time use a thermometer to measure the temperature of the metal coating in the area irradiated by the long-pulse laser of the sample. The temperature of this area is measured to be 262°C, and this temperature is lower than the phase change temperature of the substrate resin material.

[0059] Turn on the power of the semiconductor refrigeration table. The semiconductor refrigeration table is equipped with a temperature cycling system, which can continuously refrigerate the cold end of the semiconductor refrigeration table, and set the temperature to the lowest temperature of -30°C.

[0060] After applying the thermal temperature field and the cold temperature field to the processing area at the same time, reduce the output power of the femtosecond laser to 15%, and process the pattern (horizontal line pattern) with the applied temperature field. As Figure 5 shown, the results show that the metal film layer on the surface is completely removed after applying the temperature field, and at the same time the substrate material is intact. In this working condition, the ablation threshold of the surface metal film layer is reduced to 0.51 J / cm 2 , and the ablation threshold of the composite material is 1.26 J / cm 2 .

[0061] By comparing the processing effects of the horizontal and vertical lines of the same square annular structure, applying the temperature field can reduce the ablation threshold of the metal coating and protect the substrate material from ablation damage, realizing the selective etching and removal of the metal film layer on the surface of the composite material.

[0062] The selective etching method of the composite material-based metal coating by the temperature field-assisted femtosecond laser proposed by the present invention has the following advantages:

[0063] 1. Traditional machining methods introduce residual stress to the material. At the same time, due to tool wear, the machining accuracy will inevitably decline during the machining process. Chemical etching and masking also have problems such as low accuracy. The femtosecond laser processing technology causes less damage to the composite material under the metal coating due to its non-contact machining, high precision and efficiency, and low thermal damage characteristics, avoiding the thermal damage to the composite material and the damage to the substrate in traditional machining methods or long-pulse laser machining methods, and can initially realize the selective removal preparation process of the frequency selective surface.

[0064] 2. Compared with the femtosecond laser processing and etching method without applying an auxiliary temperature field, the introduction of a high-temperature field can significantly preheat the free electrons on the surface of the metal coating and significantly reduce the ablation threshold of the metal coating. The introduction of a low-temperature field reduces the overall temperature of the lower composite material and increases its ablation threshold. With the reduction of the ablation threshold of the metal coating and the increase of the ablation threshold of the composite material, a better selective removal effect can be achieved under the same laser parameters.

[0065] Although the spirit and principle of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the disclosed specific embodiments, and the division of each aspect does not mean that the features in these aspects cannot be combined for benefit. This division is only for the convenience of expression. The present invention aims to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0066] Regarding the limitations on the protection scope of the present invention, those skilled in the art should understand that based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A method for selectively etching a composite-based metal coating assisted by a femtosecond laser with a temperature field, characterized in that, The method includes: In a clean environment, use a temperature field assisted femtosecond laser processing system; Place the composite material on a three-dimensional precision displacement platform; Through the computer to control the Z-axis of the three-dimensional precision displacement platform, and focus the femtosecond laser on the surface of the composite material through a focusing lens; Adjust the focus of the auxiliary heat source laser so that it is in the same position and on the same focal plane as the femtosecond laser; Turn on the semiconductor refrigeration table and reduce its temperature to -30°C to refrigerate the composite material under the metal coating; Adjust the output power of the auxiliary heat source laser through the computer, and at the same time monitor the temperature of the composite material surface to ensure that it does not exceed the phase change temperature of the resin in the composite material, and use the auxiliary heat source laser to preheat the metal coating of the composite material; Import the pattern pre-drawn in CAD into the computer, and the three-dimensional precision displacement platform moves according to the path of the preset CAD pattern; turn on the processing optical path system, and adjust the deflection angle of the polarizer in the power attenuator to finely control the output power of the femtosecond laser; Set the repetition frequency, power of the femtosecond laser and the processing speed of the three-dimensional precision displacement platform through the computer, and then process on the surface of the composite material according to the preset CAD pattern through the program set by the computer.

2. The selective etching method of the composite matrix metal coating assisted by a femtosecond laser with a temperature field according to claim 1, characterized in that The temperature field assisted femtosecond laser processing system includes: a femtosecond laser, a processing optical path system, an illumination optical path, a long pulse laser, a calculator, a temperature measuring instrument, a three-dimensional precision displacement platform and a semiconductor refrigeration table. The processing optical path system includes a mirror, a focusing lens and a power attenuator, which are used to control the propagation path and laser power of the femtosecond laser in the optical path; the illumination optical path is used to transmit the image to the computer to observe the surface topography of the processing area to judge the processing effect; the long pulse laser is used as the auxiliary heat source laser to preheat the metal coating of the composite material; the temperature measuring instrument is used to monitor the temperature of the metal coating of the composite material and feedback to adjust the heating or cooling power; the three-dimensional precision displacement platform is used to drive the composite material to move according to the preset pattern imported through the computer to realize patterned etching; the semiconductor refrigeration table is used to continuously refrigerate the composite material above; the data between the femtosecond laser, the power attenuator, the illumination optical path, the long pulse laser, the temperature measuring instrument, the three-dimensional precision displacement platform and the semiconductor refrigeration table are interconnected through the computer via transmission cables.

3. The method for selectively etching the composite matrix metal coating assisted by a femtosecond laser with a temperature field according to claim 1, wherein In the processing optical path system, adjust the mirror to ensure that the beam incident on the focusing lens is collimated.

4. The method for selectively etching the composite matrix metal coating assisted by a femtosecond laser with a temperature field according to claim 1, wherein The semiconductor refrigeration table is equipped with a temperature circulation system, which can continuously keep the cold end of the semiconductor refrigeration table at a preset low temperature.

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