A femtosecond laser welding method and equipment for packaging optoelectronic devices

Abstract

This invention provides a femtosecond laser welding method and equipment for packaging optoelectronic devices, specifically including: stacking samples with a transparent material on top and a ceramic material on the bottom, and clamping them with a fixture to ensure that the interface gap reaches a non-optical contact condition; the laser beam passes sequentially through a reflector, an aperture, and a dustproof system before entering a galvanometer system, and after being modulated by a scanning galvanometer and focused by a lens, it exits and scans along a preset path; the laser energy first generates internal plasma inside the transparent material, and the remaining energy is transferred to the interface to trigger the generation of interface plasma; the interface plasma continues to grow upward, enhancing local melting and wetting of the ceramic surface; after rapid quenching, the penetrated molten transparent material re-solidifies, and the dual plasmas work synergistically to form a mechanically interlocked and partially mixed interface layer. After the heterogeneous materials complete the process, a stable, low-crack, high-shear-strength welded joint can be obtained.

Description

Technical Field

[0001] This invention patent relates to the field of optoelectronics, specifically to a femtosecond laser welding method and equipment for packaging optoelectronic devices. Background Technology

[0002] Optoelectronic integrated chip technology has achieved leapfrog development, and its application scenarios have expanded from the traditional transceiver field to many important fields such as optical computing, biomedical sensing, optical interconnection and consumer electronics.

[0003] As the demand for optical solutions from artificial intelligence and machine learning hardware continues to rise, coupled with the increasingly urgent need for high-speed data processing and transmission from high-performance semiconductors, quantum computing, and data centers, the field of optoelectronic device packaging is facing severe challenges. These challenges are particularly concentrated in key areas such as increasing integration density, expanding bandwidth, and developing cost-effective processes suitable for mass production.

[0004] As a key development direction in the manufacturing field, optoelectronic packaging technology is the core means to achieve efficient integration of optical components. This technology has outstanding advantages in high-speed data transmission, broadband communication, low-latency processing, and high energy efficiency. Its core lies in the efficient integration of various heterogeneous materials and devices, thereby comprehensively improving the overall performance and application value of the system.

[0005] However, in the packaging process of optoelectronic devices, the reliable connection between the transparent material cover and the ceramic substrate has become a technical bottleneck: traditional welding processes have problems such as ultraviolet degradation and thermal aging, which lead to a shortened device life; anodic bonding and brazing processes require high temperature and high pressure or solder assistance, which can easily cause thermal damage to the chip and a decline in optical performance.

[0006] In this regard, the utility model patent (CN217086582U) employs a cooling medium circulation and double-sealing packaging method. However, due to the need for additional circulation power and storage devices, it suffers from drawbacks such as low system integration, complex operation and maintenance, and the fact that the process precision of flow channel processing and assembly welding directly affects packaging performance. Currently, in practical applications, it exhibits problems such as high risk of cooling medium leakage, susceptibility to mechanical damage to the chip, and poor consistency in heat dissipation and sealing among different packaged samples. Therefore, its application is limited, especially in the packaging of miniaturized, integrated optoelectronic devices or under complex operating conditions.

[0007] The utility model patent (CN217428511U) employs a multi-mechanical mechanism—lifting, resetting, cleaning, and drawer-linked collaborative packaging method. This method is structurally complex, difficult to assemble and debug, and the operational stability of each mechanism directly impacts packaging performance. In practical applications, it suffers from inconsistent packaging pressure, drawer movement jamming, and unstable cleaning effects, leading to significant differences in the tightness of different packaged samples and fluctuating ease of removing electronic devices. Therefore, its application is limited, particularly in mass production or the packaging of large or irregularly shaped laser optoelectronic devices.

[0008] In addition, the invention patent (CN119260171A) involves stacking double-sided polished transparent materials and metallic materials sequentially on a three-dimensional motion platform. A fixture is used to clamp and adjust the focal plane to the contact surface of the two workpieces. A high-repetition-rate ultrafast laser is employed, and after three scans, the laser energy is confined to the vicinity of the weld, gradually increasing the amount of material melted to achieve joint strengthening. This method of large-spacing heterogeneous welding using multi-scan coordination requires high matching of scanning parameters, complex process control, and the cumulative effect of thermal stress directly affects welding performance. Currently, in practical applications, problems exist such as transparent materials being prone to cracking after more than three scans, significant differences in welding strength in different areas, and poor consistency in welding large-format and curved workpieces. Therefore, its practical application is limited, especially in welding applications requiring high welding efficiency or complex-shaped heterogeneous materials.

[0009] In existing technologies, ultrafast femtosecond laser welding has been used to join brittle heterogeneous materials, but it still has shortcomings in the heterogeneous welding of ceramics and transparent materials for optoelectronic device packaging. The most important reason is that in traditional laser welding, the internal plasma generated within the transparent material cannot maintain a constant vertical position during the welding process, and the interfacial plasma between the two materials exhibits a teardrop structure that continuously grows upwards, making it difficult to maintain sustained energy deposition and melting at the interface. This makes it difficult to form a stable molten region during welding, thus compromising the weld strength in non-optical contact applications. In addition, firstly, there are significant differences in the thermophysical properties of ceramics and transparent materials, such as melting point, thermal conductivity, and coefficient of thermal expansion, which easily lead to thermal stress cracking after welding. Secondly, under non-optical contact conditions (interfacial gap > 10 μm), the weld joint formed by traditional laser welding methods has insufficient sealing, making it difficult to achieve a stable connection. Thirdly, uneven energy distribution during welding leads to a high defect rate at the joint, affecting the hermeticity and light transmittance of the packaging. Therefore, there is an urgent need to develop a high-strength, high-stability heterogeneous material welding method suitable for optoelectronic devices. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention provides a femtosecond laser welding method and equipment for optoelectronic device packaging. The laser beam enters the galvanometer system through the optical path, and after being modulated by the scanning galvanometer and focused by the lens, it is emitted. The transparent material first nonlinearly absorbs part of the energy inside, inducing internal plasma, called plasma one; the remaining energy is transmitted and deposited at the interface, triggering the formation of interface plasma, called plasma two. The two plasmas are plasma one and plasma two. The energy density of plasma two is lower than that of plasma one, but it is sufficient to trigger local melting. Both plasmas maintain their morphology and high stability, which is also the key to forming a high-strength and stable weld joint.

[0011] The radial pressure generated by plasma one propels the molten transparent material towards the ceramic interface, while the heat causes the transparent material to melt rapidly in localized areas, forming characteristic teardrop-shaped molten regions. Meanwhile, plasma two continues to extend upwards, enhancing the localized melting of the protruding areas on the ceramic surface and improving the wettability between the molten transparent material and the ceramic surface. The two material elements diffuse into each other, and after rapid quenching, the molten transparent material that has penetrated to the interface re-solidifies, forming a mechanically interlocked and partially mixed interfacial bonding layer.

[0012] The dual plasmas reflect, refract, and absorb the incident laser beam, achieving a self-regulating equilibrium through energy confinement. The pressure and heat provided by plasma one push the molten transparent material toward the interface, while plasma two enhances the wettability of local melting and ceramic rough spots. Their synergistic effect provides thermodynamic and kinetic conditions for the interfacial reaction. Through the dual action of physical and chemical processes, the formation of a welded joint with good stability, low crack rate, and high shear strength is ultimately promoted.

[0013] To achieve the above objectives, the present invention provides a femtosecond laser welding method and equipment for packaging optoelectronic devices, comprising the following steps:

[0014] (1) Select a ceramic substrate and a transparent material cover plate, clean them with ethanol and wipe them dry with dust-free lens paper. Stack the ceramic and transparent material on the stage from bottom to top and fix them with a custom clamp so that the interface gap between the two reaches the non-optical contact condition. Adjust the lifting stage to make the interface at a suitable height so that the laser beam is finally focused on the interface of the stacked ceramic and transparent material.

[0015] (2) Turn on the laser. The laser beam enters the galvanometer system through the preset optical path. After being modulated by the scanning galvanometer and focused by the lens, it is emitted from above the transparent material and scans along the preset path. During the scanning process, the transparent material first nonlinearly absorbs the laser energy and generates internal plasma. After the beam is transmitted into the interface, the remaining energy is deposited in the interface between the ceramic and the transparent material, triggering the generation of interface plasma.

[0016] (3) Rapid evolution of plasma plume leads to non-uniform spatial energy distribution, which modifies local areas. The internal plasma maintains a constant vertical position during welding, while the interface plasma exhibits stable upward growth. The pressure and heat generated by the internal plasma promote the flow of molten transparent material to the interface, while the interface plasma enhances the local melting and wetting of ceramic roughness. Through the synergistic effect of the two plasmas, high-strength and high-stability welding is achieved.

[0017] (4) After rapid quenching, the penetrated molten transparent material resolidifies to form a mechanically interlocked and partially mixed interface layer. After the heterogeneous materials complete the process, a stable, low-crack, high-shear-strength heterogeneous welded joint can be obtained.

[0018] Furthermore, the transparent material is double-polished quartz, sapphire, or soda-lime glass, and the ceramic substrate is alumina, aluminum nitride, or yttrium-stabilized zirconium oxide (YSZ), with an original surface roughness of 2-5 μm and a thickness of 1-5 mm for both.

[0019] Furthermore, the interface gap between the ceramic substrate and the transparent material is maintained at more than 10 μm, which is suitable for non-optical contact welding applications.

[0020] Furthermore, the lifting platform is a single-degree-of-freedom motion platform that can move along the Z-axis, thereby enabling the adjustment of the workpiece's position and posture in terms of height.

[0021] Furthermore, the laser parameters are set as follows: femtosecond laser wavelength 500~1100nm, pulse width 200~950fs, repetition rate 100~1200kHz, laser power 5~30W, scanning speed 1~50mm / s, defocus distance -0.8~+0.8μm, scanning line spacing 0.01~0.10mm, and scanning path 3×3mm. 2 ~150×150mm 2 A rectangular area, or an annular area with a diameter of 5mm to 150mm.

[0022] Furthermore, plasma one maintains a constant vertical position at approximately 20-80µm from the interface during the welding process, ensuring high stability in shape and height. Meanwhile, the height difference h between the two plasmas, namely plasma one and plasma two, remains stable at approximately 10-20µm, providing a core guarantee for the formation of a high-strength and stable welded joint.

[0023] Furthermore, the plasma was observed using a high-speed imaging system: at 0.111 ms, a small elliptical bright spot appeared at the interface, marking the generation of plasma; at 0.666 ms, the bright spot expanded significantly, indicating that the plasma began to extend in the opposite direction of the laser propagation and grow vertically upwards perpendicular to the interface; from 1.211 ms to 1.665 ms, plasma one gradually formed and stabilized inside the transparent material, which is the teardrop-shaped molten area that can be observed on one side of the transparent material after welding; plasma two gradually formed and stabilized at the non-optical contact interface, which is the heterojunction that can be observed at the interface after welding.

[0024] Furthermore, the coexistence of the two plasmas forms a stable local thermal field, driving the molten transparent material to migrate towards the interface and enhancing the interfacial melting and diffusion. Elements on the transparent material side, such as Si, Al, or Na, diffuse towards the ceramic side with a penetration depth of about 20-30 µm. At the same time, elements on the ceramic side, such as Al, N, or Zr, diffuse towards the transparent material side with a penetration depth of about 60-70 µm.

[0025] Furthermore, the dual-plasma synergy between the ceramic and the transparent material has a positive impact on the strength of the welded joint: during the welding process, elements diffuse between the transparent material and the ceramic, but the elemental composition of the joint remains essentially unchanged after welding, and the oxygen content at the joint after welding is as high as 45%~55%, indicating that a local oxidation reaction occurred at the interface. This confirms the stable energy coupling of elemental interpenetration and reaction at the interface, promoting the formation of a dense interpenetrating interface. After rapid cooling, the permeated molten transparent material re-solidifies, forming a stable mechanical interlocking structure, ultimately producing a welded joint with an average shear strength of 12~15 MPa.

[0026] Furthermore, a femtosecond laser welding method and equipment for optoelectronic device packaging includes a femtosecond laser, a collimating optical path, a galvanometer and lens system, and a lifting platform. The method is characterized by including an optical component for adjusting the laser beam emitted by the laser to be perpendicular to the surface of the workpiece to be processed, and a fixture for clamping stacked samples, wherein the fixture can adjust the interface gap between the transparent material and the ceramic.

[0027] In summary, compared with existing technical solutions, the above technical solutions of the present invention have the following main advantages:

[0028] This method is a welding method under non-optical contact conditions, with excellent optical performance, no obvious optical defects in the welding area, and supports micron-level weld precision control. It meets the high-density packaging requirements of miniaturized optoelectronic devices, and the connection strength of heterogeneous materials is high. The average shear strength of the weld joint reaches 12~15MPa, which meets the mechanical reliability requirements of the packaging.

[0029] Compared to traditional processes, this invention does not add organic materials and does not require solder or adhesives, so the resulting heterogeneous material has good thermal stability, is resistant to high temperatures and ultraviolet radiation, and the device life is increased to more than three times that of traditional processes. It also avoids pollution and subsequent cleaning processes, meeting the requirements of green manufacturing. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the femtosecond laser welding system of the present invention.

[0031] Figure 2 The strengthening mechanism of femtosecond laser welding.

[0032] [Explanation of Labels in the Attached Image]

[0033] 1. Femtosecond laser; 2. Reflector; 3. Aperture; 4. Lifting platform; 5. Dustproof device; 6. Galvanometer and lens system; 7. Beam; 8. Sample; 9. Stage; 10. Main control computer. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Example 1

[0036] It is known that high-repetition-rate femtosecond lasers can achieve adhesive-free, high-strength welding of ceramics and transparent materials under non-optical contact conditions. To guide the selection of femtosecond laser action parameters, it is necessary to further measure the effect of femtosecond lasers on the samples.

[0037] In this embodiment, the ceramic substrate is 20mm×10mm×2mm in size, and the quartz cover plate is 10mm×5mm×2mm in size. The ceramic substrate and quartz are ultrasonically cleaned with anhydrous ethanol for 15 minutes to remove surface oil and impurities. After being dried with nitrogen, they are wiped with dust-free lens paper. The ceramic substrate is fixed on the stage, and the deep ultraviolet LED chip is die-bonded to the cavity of the ceramic substrate. The quartz is then stacked, and the interface gap is controlled to be 13μm.

[0038] The laser parameters were set as described in claim 4. Welding of a 3×3mm area was completed using a galvanometer scan. After welding, a shear strength test was performed using a PY-880B tensile tester, and the average shear strength was measured to be 13.75 MPa. Ultraviolet spectrophotometry showed a transmittance of 92% in the 265nm band. After 500 hours of high-temperature aging at 100℃, the joint showed no cracking, and the transmittance attenuation rate was 3.2%.

[0039] Example 2

[0040] Under non-patent-limited parameters, such as different laser energies or scanning speeds, it is difficult to form the synergistic effect of dual plasmas, making it impossible to achieve high-strength, high-stability welding, and at most forming low-strength weld joints.

[0041] For example, under the following parameters: femtosecond laser wavelength of 1030nm, pulse width of 200~1000fs, repetition frequency of 25~5000 kHz, laser power of 3~5W, scanning spacing of 0.2mm, scanning speed of 0.5~100mm / s, and a scanning path of 5mm×5mm square area, laser welding is performed using the same material according to the steps described in claim 1.

[0042] It was found that although plasma was formed simultaneously inside the material and near the interface of the heterogeneous material, the stability was insufficient due to the incomplete formation of the molten region. The plasma escaped and was prone to insufficient or excessive accumulation of plasma, which led to a weak bonding layer that was not enough to maintain the overall connection, or material cracking and sputtering. All of these resulted in a decrease in welding strength, and the highest welded joint with a shear strength of about 2 MPa could only be obtained.

Claims

1. A femtosecond laser welding method for packaging optoelectronic devices, characterized in that, Includes the following steps: Step 1: Select a ceramic substrate and a transparent material cover plate. After cleaning with ethanol, wipe them dry with dust-free lens paper. Stack the ceramic and transparent material on the stage from bottom to top and fix them with a custom clamp to make the interface gap between the two reach a non-optical contact condition. Adjust the lifting stage to make the interface at a suitable height so that the laser beam is finally focused on the interface of the stacked ceramic and transparent material. Step 2: Turn on the laser. The laser beam enters the galvanometer system through the preset optical path. After being modulated by the scanning galvanometer and focused by the lens, it is emitted from above the transparent material and scans along the preset path. During the scanning process, the transparent material first nonlinearly absorbs the laser energy and generates internal plasma. After the beam is transmitted into the interface, the remaining energy is deposited in the interface between the ceramic and the transparent material, triggering the generation of interface plasma. Step 3: Rapid evolution of plasma plume leads to non-uniform spatial energy distribution, which modifies local areas. The internal plasma maintains a constant vertical position during the welding process, while the interfacial plasma exhibits stable upward growth. The pressure and heat generated by the internal plasma promote the flow of molten transparent material to the interface, while the interfacial plasma enhances the local melting and wetting of ceramic roughness. Through the synergistic effect of the two plasmas, high-strength and high-stability welding is achieved. Step 4: After rapid quenching, the penetrated molten transparent material re-solidifies, forming a mechanically interlocked and partially mixed interface layer. After the heterogeneous materials complete the process, a stable, low-crack, high-shear-strength heterogeneous welded joint can be obtained.

2. The femtosecond laser welding method for packaging optoelectronic devices according to claim 1, characterized in that, The transparent material is double-polished quartz, sapphire, or soda-lime glass, and the ceramic substrate is alumina, aluminum nitride, or yttrium-stabilized zirconia (YSZ). The original surface roughness is 2~5μm, and the thickness of both is 1~5mm.

3. The femtosecond laser welding method for packaging optoelectronic devices according to claim 1, characterized in that, In step one, the interface gap between the ceramic substrate and the transparent material is maintained at more than 10 μm, which is a non-optical contact welding application scenario.

4. The femtosecond laser welding method for packaging optoelectronic devices according to claim 1, characterized in that, The lifting platform mentioned in step one is a motion platform with one degree of freedom, which can move along the Z-axis, thereby realizing the adjustment of the workpiece's position and posture in terms of height.

5. The femtosecond laser welding method for packaging optoelectronic devices according to claim 1, characterized in that, The laser parameters in step two are set as follows: femtosecond laser wavelength 500~1100nm, pulse width 200~950fs, repetition rate 100~1200kHz, laser power 5~30W, scanning speed 1~50mm / s, defocus distance -0.8~+0.8μm, scanning line spacing 0.01~0.10mm, and scanning path 3×3mm. 2 ~150×150mm 2 A rectangular area, or an annular area with a diameter of 5mm to 150mm.

6. The femtosecond laser welding method for packaging optoelectronic devices according to claim 5, characterized in that, Under the parameter conditions described in claim 5, when the laser beam is incident on the transparent material in step two, relying on high peak power irradiation, the transparent material absorbs the laser energy and generates internal plasma, called plasma one, through multiphoton absorption and avalanche ionization mechanism, nonlinear absorption within it. During the welding process, it maintains a constant vertical position 20~80µm away from the interface, maintaining high stability in shape and height. At the same time, the portion of energy not completely absorbed by the transparent material penetrates the plasma inside the transparent material and undergoes energy deposition at the non-optical contact interface, inducing the generation of plasma at the non-optical contact interface, called plasma two, which has the characteristics of continuous existence and maintaining high stability in shape and height. The dual plasmas, namely Plasma I and Plasma II, have a stable height difference h of 10~20µm, providing a core guarantee for the formation of high-strength and stable welded joints.

7. The femtosecond laser welding method for packaging optoelectronic devices according to claim 6, characterized in that, The plasma was observed using a high-speed imaging system: at 0.111 ms, a small elliptical bright spot appeared at the interface, marking the generation of plasma. At 0.666 ms, the bright spot expanded significantly, indicating that the plasma began to extend in the opposite direction of laser propagation and grow vertically upwards perpendicular to the interface. From 1.211 ms to 1.665 ms, plasma one gradually formed and stabilized inside the transparent material, which is the teardrop-shaped molten area that can be observed on one side of the transparent material after welding. Plasma two gradually formed and stabilized at the non-optical contact interface, which is the heterojunction that can be observed at the interface after welding.

8. The femtosecond laser welding method for packaging optoelectronic devices according to claim 1, characterized in that, The coexistence of the two plasmas forms a stable local thermal field, driving the molten transparent material to migrate towards the interface and enhancing the melting and diffusion at the interface. Elements on the transparent material side, including Si, Al, and Na, diffuse towards the ceramic side with a penetration depth of 20-30µm. At the same time, elements on the ceramic side, including Al, N, and Zr, diffuse towards the transparent material side with a penetration depth of up to 60-70µm.

9. The femtosecond laser welding method for packaging optoelectronic devices according to claim 1, characterized in that, The synergistic effect of dual plasma between ceramics and transparent materials has a positive impact on the strength of welded joints: During the welding process, elements diffuse between the transparent material and the ceramic, but the elemental composition of the joint remains basically unchanged after welding. Moreover, the oxygen content at the joint after welding is as high as 45%~55%, indicating that a local oxidation reaction occurred at the interface. This confirms that the elements at the interface interpenetrate and react with stable energy coupling, promoting the formation of a dense interpenetrating interface. After rapid cooling, the permeated molten transparent material re-solidifies, forming a stable mechanical interlocking structure, ultimately producing a welded joint with an average shear strength of 12~15MPa.

10. The femtosecond laser welding equipment for the packaging of the optoelectronic device, characterized in that, The femtosecond laser welding method for packaging optoelectronic devices as described in claim 1 is used to obtain stable, low-crack, and high-shear-strength heterogeneous material weld joints.

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