Plasma surface activation pre-bonding-femtosecond laser connection integrated process

Abstract

The invention discloses a plasma surface activation pre-bonding-femtosecond laser connection integrated process, belongs to the technical field of advanced dissimilar material precision connection, and particularly relates to a multi-material interface efficient connection method based on plasma surface activation pre-bonding and femtosecond laser processing. The method is suitable for high-strength and low-thermal-damage heterogeneous bonding of transparent materials (such as glass, quartz and sapphire) and transparent materials or metal materials (such as titanium alloy, stainless steel and invar alloy). According to the method, interface atomic-scale cleaning and chemical activity regulation and control are achieved through plasma activation, interface connection of the two materials is induced by combining the femtosecond laser ultrafast nonlinear effect, and the bottlenecks that in a traditional connection technology, optical contact depends on a mechanical clamp, and heat input is uncontrollable are broken through; and an innovative solution is provided for cross-material interface functional manufacturing in the fields of photoelectric device packaging, optical-electronic integrated systems and the like.

Description

Technical Field

[0001] This invention belongs to the field of advanced precision joining technologies for dissimilar materials, specifically a method for efficiently joining multi-material interfaces based on plasma surface activation pre-bonding and femtosecond laser processing. This method is suitable for high-strength, low-thermal-damage heterojunctions between transparent materials (such as glass, quartz, and sapphire) and transparent or metallic materials (such as titanium alloys, stainless steel, and Invar alloys). This method achieves atomic-level cleaning and chemical activity control of the interface through plasma activation, combined with the ultrafast nonlinear action of a femtosecond laser to induce the interface connection between the two materials. This method overcomes bottlenecks in traditional joining technologies, such as the reliance on mechanical clamps for optical contact and uncontrollable heat input, and provides innovative solutions for the functionalized manufacturing of cross-material interfaces in fields such as optoelectronic device packaging and optical-electronic integrated systems. Background Art

[0002] With the rapid development of optoelectronics, micro-nano sensing, and aerospace technology, the demand for high-performance heterojunction between transparent materials and metals is becoming increasingly urgent. However, traditional technologies face three major challenges: (1) The surface of transparent materials is highly chemically inert, making it difficult to form effective chemical bonds with metal interfaces. Reliance on adhesives or intermediate layers can easily lead to interface aging and optical path distortion; (2) Thermal welding (such as laser welding and electron beam welding) can easily cause interface cracks and thermal stress mismatch due to the large difference in thermal expansion coefficients between transparent materials and metals; (3) Although mechanical clamps can maintain optical contact, the introduction of assembly stress can easily lead to local stress concentration, affecting the connection quality.

[0003] In recent years, plasma surface activation technology can generate active groups such as hydroxyl (-OH) and dangling bonds on the surface of transparent materials through ion bombardment and free radical reaction, significantly improving their surface energy and wettability with metals, laying the foundation for non-gelatinized interface bonding. At the same time, femtosecond laser with ultrashort pulse (10 -15 The high peak power characteristics of the plasma activation laser (s-level) and can induce nonlinear absorption effects within transparent materials, precisely triggering the transient diffusion and reaction of metal-nonmetal atoms in the interface micro-region, thus avoiding the thermal accumulation damage of traditional long-pulse lasers. However, existing research has focused on a single technology (plasma activation or femtosecond laser processing), and has not yet effectively synergized the advantages of both technologies: existing plasma activation bonding technology requires cumbersome process steps such as annealing, and the bond strength is not high, and fatigue performance is low; while the high-strength connection of femtosecond lasers can only be achieved when the interface optical contact conditions are achieved under assembly stress, but the introduction of assembly stress can easily lead to local stress concentration.

[0004] The present invention proposes an integrated process of "plasma surface activation-femtosecond laser connection". Through the timing coordination of plasma surface activation and femtosecond laser processing in a vacuum environment, optical contact is achieved between the transparent material and the metal interface without assembly stress, and high-efficiency and high-strength connection is achieved using femtosecond laser. Summary of the Invention

[0005] The purpose of the present invention is to provide an integrated process of plasma surface activation pre-bonding and femtosecond laser connection. In the face of the problem of stress concentration in the local connection area caused by the need to introduce assembly stress to achieve optical contact during the high-strength connection process of femtosecond laser, this problem is solved by replacing the assembly stress with plasma surface activation and bonding to achieve optical contact at the interface of transparent material / transparent material or transparent material / non-transparent material. On the one hand, the connection efficiency and connection strength of single plasma activation bonding are improved, and on the other hand, the stress concentration phenomenon of femtosecond laser connection is reduced, thereby improving the connection quality.

[0006] A plasma surface activation pre-bonding-femtosecond laser connection integrated process includes plasma surface activation of the material pre-connection surface, bonding after material interface activation, and femtosecond laser connection process.

[0007] Taking sapphire (Al2O3) / Invar alloy (Fe-36Ni) as an example, the working process of the present invention is described in detail.

[0008] 1) Step 1: Material surface pretreatment

[0009] Before plasma surface activation bonding, sapphire (Al2O3) and Invar alloy (Fe-36Ni) need to be ground and cleaned;

[0010] 2) Step 2: Plasma surface activation

[0011] After cleaning the surfaces of sapphire and Invar alloy, they are dried with a hair dryer and placed in a vacuum chamber of a plasma activation device. The gas in the vacuum chamber is ionized to produce a glow. The ionized gas, Ar or N2, generates plasma that bombards the surfaces of sapphire and Invar alloy, removing organic pollutants and particles from the surfaces and forming dangling bonds on the surfaces.

[0012] 3) Step 3: Optimize plasma surface activation parameters

[0013] The optimal activation parameter range was determined by studying the change in contact angle of water droplets on the surfaces of sapphire and Invar alloy after activation; the activation parameters were determined to be Ar / N2, bombardment power >70W, and plasma bombardment time >90s based on the change in contact angle.

[0014] 4) Step 4: Activated sapphire / Invar alloy pre-bonding

[0015] The sapphire and Invar alloy activated surfaces are stacked and pressed by a fixture for more than 30 seconds to pre-bond the activated interfaces of the two.

[0016] 5) Step 5: Femtosecond laser welding

[0017] Femtosecond laser parameters should include: average power of 7 to 15 W, pulse width of 263 to 5000 fs, pulse frequency of 100 to 1000 kHz, scanning speed of 30 to 60 mm / s, number of scans 3 times, and defocus less than 0.5 mm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Optical contact without assembly stress: Plasma-activated bonding replaces mechanical fixtures for forced alignment, enabling optical contact between the transparent material and the metal interface without external force. This reduces the impact of local stress concentration caused by fixture pressure in traditional femtosecond laser connection and improves the mechanical properties of the joint.

[0020] 2. Process synergy improves connection efficiency: After transparent materials and metal materials undergo plasma surface activation in a vacuum, they can be bonded at room temperature. The material interface achieves optical contact without annealing, and then femtosecond laser high-strength connection is performed, greatly reducing the time cost of the entire process and improving connection efficiency.

[0021] 3. Selective high-precision connection: During the annealing process of traditional plasma activated bonding, the connection accuracy of the activated area is low. However, the connection process combined with femtosecond laser bonding can achieve selective high-strength connection with micron-level precision, which is particularly suitable for stress-free assembly of curved lenses and metal brackets in optical devices.

[0022] 4. Broad-spectrum material compatibility: The process can be extended to various transparent material-metal combinations such as glass / titanium, quartz / aluminum, sapphire / stainless steel, as well as transparent material-transparent material combinations such as glass / glass and sapphire / sapphire. By regulating the plasma gas composition (such as oxygen, nitrogen, argon, etc.) and laser parameters, the interfacial reaction characteristics of different material systems can be adapted to provide a universal solution for heterogeneous integration in multiple scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 Schematic diagram of integrated plasma activation pre-bonding and femtosecond laser connection

[0025] Figure 2 Effect of different activation times on the contact angle of water droplets on the Invar alloy surface

[0026] Figure 3 Effect of different activation times on the contact angle of water droplets on sapphire surface

[0027] Figure 4 Effect of different activation powers on the contact angle of water droplets on the Invar alloy surface

[0028] Figure 5 Effect of different activation powers on the contact angle of water droplets on sapphire surface

[0029] Figure 6 Femtosecond laser bonding of sapphire / Invar alloy in a fixture assembly

[0030] Figure 7 Macroscopic diagram of plasma activated bonding and femtosecond laser connection

[0031] Figure 8 Schematic diagram of the confocal microscopy with femtosecond laser connection before activation and without clamp (control experiment) and after activation

[0032] Figure 9 Schematic diagram of the joint microstructure after plasma activation-femtosecond laser connection

[0033] Figure 10 Shear strength of femtosecond laser-bonded joints under fixture assembly (control experiment), without fixture and without activation (control experiment), and under activation conditions DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0035] It should be noted that unless defined otherwise, all technical and scientific terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0036] The application of the integrated process of plasma surface activation pre-bonding-femtosecond laser connection is not limited to transparent materials / metal materials, but should also include transparent materials / transparent materials and transparent materials / non-transparent materials.

[0037] The plasma surface activation pre-bonding process in the present invention only needs to ensure that the material interface achieves optical contact, so the gas used is not limited to the Ar or N2 single gas in the present invention and other available gases or mixed gases.

[0038] In order to make the present invention more specific and clear to be understood, the following will take sapphire (Al2O3) / Invar alloy (Fe-36Ni) as an example to explain the working process of the present invention in detail. Figure 1 As shown:

[0039] (1) Step 1: Material surface pretreatment

[0040] Before plasma surface activation bonding, sapphire (Al2O3) and Invar alloy (Fe-36Ni) must be ground and cleaned. The Invar alloy is first polished using a 2000# diamond grinding wheel, followed by fine grinding with 2500# and 3000# sandpaper. Finally, it is polished using 2.5# and 0.5# diamond polishing sprays until the surface is mirror-like. This is followed by an acetone cleaning process in an ultrasonic cleaner to remove surface oil and impurities, preventing uneven optical contact after plasma activation bonding. Sapphire is a commercially available single crystal Al2O3 with polished, transparent surfaces on both the top and bottom. This cleaning process also requires prior processing to ensure uniform optical contact.

[0041] (2) Step 2: Plasma surface activation

[0042] After cleaning the surfaces of sapphire and Invar alloy with acetone, dry them with a hair dryer and place them in the vacuum chamber of a plasma activation device. The gas in the vacuum chamber (Ar or N2 single gas, not mixed with other gases) is ionized to produce a red glow, such as Figure 1 The ionized gas generates plasma to bombard the surface of sapphire and Invar alloy, peeling off the organic pollutants and particles on the surface, forming a large number of dangling bonds on the surface, which can react with free radicals in the air to generate active groups such as hydroxyl (-OH) and dangling bonds, significantly improving their surface energy and wettability, which is beneficial to improving bonding efficiency and increasing the optical contact area. The principle is as follows Figure 1 shown.

[0043] (3) Step 3: Optimize plasma surface activation parameters

[0044] The optimal activation parameter range was determined by studying the changes in the contact angle of water droplets on the surfaces of sapphire and Invar alloy after activation. Figures 2 to 5 The results show that the longer the activation time, the longer the plasma bombardment time, the greater the density of dangling bonds and active groups generated with air, and the better the hydrophilicity; the greater the activation power, the greater the plasma density generated per unit time, the more intense the surface bombardment, the greater the density of dangling bonds and active groups generated with air, and the better the hydrophilicity.

[0045] The activation parameters can be determined from the change of contact angle as Ar / N2, >70W, >90s.

[0046] (4) Step 4: Pre-bonding of activated sapphire / Invar alloy

[0047] The sapphire and Invar alloy activated surfaces were stacked and pressed for 30 seconds by a fixture to pre-bond the activated interfaces of the two. The bonding effect was as follows: Figure 7As shown in the figure. The plasma activated sapphire / Invar alloy interface shows obvious Newton rings, with a zero-order dark fringe in the middle area. The optical contact effect is the best, and the interface gap between the two is about 0, which is conducive to high-strength connection by femtosecond laser. Compared with the activated bonded interface, the bonding effect under the unactivated and fixture-free condition is poor, the bonding is uneven, and there are unevenly distributed small areas with large gaps on the interface, such as Figure 7 As shown in (a).

[0048] (5) Step 5: Femtosecond laser welding

[0049] Femtosecond laser parameters should include average power (7-15W), pulse width (263-5000fs), pulse frequency (100-1000kHz), scanning speed (30-60mm / s), scanning times 3 times, and defocus (0-0.5mm). This is the optimal parameter range after femtosecond laser optimization under fixture assembly.

[0050] Macroscopic effects and confocal magnification of femtosecond laser welding of sapphire / Invar alloy plasma bonding and unactivated bonding, such as Figure 7 and Figure 8 As shown. Irregular solder joints appear on the welding interface without activation and fixture. This is because uneven bonding leads to large gaps inside the Newton rings, and irregular plasma eruption leads to irregular solder joints, which in turn leads to uneven stress distribution on the welding interface. Under the action of external force, stress concentration is likely to occur, which reduces the mechanical properties of the welded joint. However, the welding interface after activation is more regular, and the distribution of welded joints at the interface is regular. The internal sapphire and Invar alloy are mechanically mixed to form a nail-shaped mosaic structure, as shown. Figure 9 shown.

[0051] Example 1

[0052] Using sapphire / Invar alloy as the experimental material, an integrated experiment of plasma surface activation pre-bonding and femtosecond laser bonding was conducted using the above-mentioned plasma activation optimization parameters (selecting Ar, 70W, 90s) and femtosecond laser parameters (average power 7W, pulse width 800fs, pulse frequency 200kHz, scan speed 50mm / s, scan number 3, defocus distance -0.5mm). Finally, shear tests were conducted on the femtosecond laser-bonded joints under fixture assembly, unfixtured and activated conditions. It was found that the shear strength of the unfixtured joint was low, at 52MPa. This was due to the stress concentration caused by the irregular weld points at the welding interface, which reduced the mechanical properties. The shear strength of the joint under fixture assembly was as high as 185MPa, while the strength of the femtosecond laser-bonded joint after activation was as high as 220MPa, an increase of 18.9%. This is because the activation bonding replaced the fixture assembly, eliminating the local stress concentration caused by the assembly stress, further improving the welding quality and enhancing the mechanical properties of the joint.

Claims

1. Plasma surface activation pre-bonding-femtosecond laser connection integrated process, characterized by The following steps are involved: Step 1: Material surface pretreatment Before plasma surface activation bonding, the two materials to be bonded need to be polished and cleaned; Step 2: Plasma surface activation Step 2: Plasma surface activation After the surfaces of the two materials are cleaned, dried with a hair dryer and placed in the vacuum chamber of a plasma activation device. The gas in the vacuum chamber is ionized to produce a glow. Step 3: Optimize plasma surface activation parameters The contact angle changes of water droplets on the surfaces of the two materials were studied to determine the optimal activation parameter range. The results showed that the longer the activation time and the longer the plasma bombardment time, the greater the density of dangling bonds and active groups generated with air, and the better the hydrophilicity. Step 4: Pre-bonding of activated sapphire / Invar alloy The sapphire and Invar alloy activated surfaces are stacked and pressed by a fixture for more than 30 seconds to pre-bond the activated interfaces of the two. Step 5: Femtosecond laser welding.

2. The process according to claim 1, characterized in that When the materials to be bonded are sapphire and Invar alloy, the following steps are included: 1) Step 1: Material surface pretreatment Before plasma surface activation bonding, sapphire (Al2O3) and Invar alloy (Fe-36Ni) need to be ground and cleaned; 2) Step 2: Plasma surface activation After cleaning the surfaces of sapphire and Invar alloy, they are dried with a hair dryer and placed in a vacuum chamber of a plasma activation device. The gas in the vacuum chamber is ionized to produce a glow. The gas is Ar or N2. The ionized gas generates plasma that bombards the surfaces of sapphire and Invar alloy, stripping off organic pollutants and particles on the surface and forming dangling bonds on the surface. 3) Step 3: Optimize plasma surface activation parameters The optimal activation parameter range was determined by studying the change in contact angle of water droplets on sapphire and Invar alloy surfaces after activation. The activation parameters were determined to be Ar or N2, bombardment power greater than or equal to 70W, and plasma bombardment time greater than or equal to 90s based on the change in contact angle. 4) Step 4: Activated sapphire / Invar alloy pre-bonding The sapphire and Invar alloy activated surfaces are stacked and pressed by a fixture for more than 30 seconds to pre-bond the activated interfaces of the two. 5) Step 5: Femtosecond laser welding Femtosecond laser parameters should include: average power of 7 to 15 W, pulse width of 263 to 5000 fs, pulse frequency of 100 to 1000 kHz, scanning speed of 30 to 60 mm / s, number of scans 3 times, and defocus of 0 to -0.5 mm.

3. The process according to claim 1, characterized in that It is the bonding of transparent materials to transparent materials or the bonding of transparent materials to non-transparent materials.

4. The process according to claim 1, characterized in that The gas used is Ar or N2, or other gases and mixed gases.

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