A full nitride aluminum TEC direct bonding laser packaging structure and a preparation method thereof

Abstract

This invention relates to the field of semiconductor laser device packaging technology, specifically a direct-attach laser packaging structure for aluminum nitride ceramic TEC and its fabrication method. In terms of the packaging structure, the laser chip is sintered and fixed to the upper surface of a tungsten-copper heat sink via a gold-tin solder layer; an aluminum nitride thermally conductive insulating sheet is fixed to the lower surface of the tungsten-copper heat sink, and this sheet is flexibly encapsulated on the cold-end ceramic surface of the aluminum nitride ceramic TEC via an ultra-thin indium foil layer; or the lower surface of the tungsten-copper heat sink is directly flexibly encapsulated on the cold-end ceramic surface of the aluminum nitride ceramic TEC via an ultra-thin indium foil layer. This significantly simplifies the heat dissipation path and substantially reduces the overall system thermal resistance. By relying on the homogeneous thermal matching design of the aluminum nitride ceramic TEC and the aluminum nitride thermally conductive insulating sheet, precise matching of the interface thermal expansion coefficients is achieved, eliminating the potential for thermal stress concentration at the structural level. Combined with the ultra-thin indium foil layer as the sole flexible thermally conductive interface, residual stress can be released through plastic deformation to ensure tight interface contact.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser device packaging technology, and in particular to an all-aluminum nitride TEC direct-attach laser packaging structure and its preparation method. Background Technology

[0002] Semiconductor laser chips are widely used in industrial inspection, automotive lasers, precision instruments, military equipment and other fields. Most applications require adaptation to extreme environments with a wide temperature range of -50℃ to 80℃, and require the laser chip to work stably in a constant temperature range of 20℃ to 50℃ for a long time to ensure the consistency of laser wavelength and the stability of output power.

[0003] The mainstream laser packaging solution in the industry adopts a multi-stage transition heat dissipation structure. This involves soldering the laser chip to a tungsten-copper heat sink, and then bonding it to the TEC (thermal energy dissipation device) via a copper transition heat sink and multiple interfaces of thermally conductive silicone / indium foil. The initial design intention was to use the copper transition heat sink to alleviate the mismatch in thermal expansion coefficients between the tungsten-copper heat sink and the alumina ceramic TEC, preventing alternating thermal stress caused by high and low temperature cycling from leading to solder layer voids, delamination cracking, or even TEC ceramic fracture. However, the forced introduction of the copper transition heat sink inevitably adds at least two additional thermal interfaces to the heat dissipation path. Combined with the thermal resistance of the copper base itself, this significantly increases the total system thermal resistance. At 80°C, the TEC cooling load increases dramatically, making it unable to effectively suppress chip temperature rise, and easily leading to wavelength drift and power attenuation issues.

[0004] Existing technologies attempt to reduce additional thermal resistance by increasing the thermal conductivity of the copper transition heat sink and reducing its thickness. However, thinning the copper transition heat sink inevitably weakens its thermal stress buffering capacity, thus exacerbating the risk of interface failure. Furthermore, increasing the thermal conductivity of the copper transition heat sink itself cannot fundamentally eliminate the increase in thermal resistance it introduces. Some direct-mount TEC solutions use alumina ceramic TECs, whose thermal conductivity is only 20–30 W / (m²). Furthermore, it suffers from poor thermal matching, resulting in thermal stress concentration and insufficient heat dissipation efficiency, making it unsuitable for laser equipment requiring long-term continuous operation in a wide temperature range at high temperatures.

[0005] Therefore, it is imperative for those skilled in the art to solve the aforementioned problems. Summary of the Invention

[0006] The purpose of this invention is to provide an all-aluminum nitride TEC direct-attach laser packaging structure, which aims to solve the problem that existing multi-stage transition heat dissipation structures cannot simultaneously achieve thermal stress relief and low thermal resistance heat dissipation, and cannot adapt to long-term stable operation over a wide temperature range.

[0007] This invention relates to a direct-attach laser packaging structure for an all-aluminum nitride TEC, comprising a laser chip, a gold-tin solder layer, a tungsten-copper heat sink, an ultrathin indium foil layer, and an all-aluminum nitride ceramic TEC; The laser chip is fixed to the tungsten copper heat sink by sintering with a gold-tin solder layer; An aluminum nitride thermally conductive insulating sheet is fixed to the lower surface of the tungsten copper heat sink, and the aluminum nitride thermally conductive insulating sheet is flexibly encapsulated on the cold end ceramic surface of the all-aluminum nitride ceramic TEC through an ultra-thin indium foil layer; or the lower surface of the tungsten copper heat sink is directly flexibly encapsulated on the cold end ceramic surface of the all-aluminum nitride ceramic TEC through an ultra-thin indium foil layer.

[0008] As a further improvement to the technical solution disclosed in this invention, both the aluminum nitride thermally conductive insulating sheet and the cold end substrate of the all-aluminum nitride ceramic TEC are made of high thermal conductivity aluminum nitride ceramic with a thermal conductivity ≥180W / (m²). The coefficient of thermal expansion (K) ranges from 4.4 to 4.6 ppm / ℃, and the two values ​​are equal.

[0009] As a further improvement to the technical solution disclosed in this invention, the thickness of the aluminum nitride thermally conductive insulating sheet is 0.2 to 0.5 mm; the thickness of the cold end substrate of the all-aluminum nitride ceramic TEC is 0.3 to 0.6 mm.

[0010] As a further improvement to the technical solution disclosed in this invention, the hot end substrate of the all-aluminum nitride ceramic TEC is made of aluminum nitride ceramic material, the operating ambient temperature is -50℃~80℃, and the cooling power density is ≥15W / cm³. 2 The cooling efficiency of the all-aluminum nitride ceramic TEC decreases by ≤3% after 1000 hours of continuous operation at an ambient temperature of 80℃.

[0011] As a further improvement to the technical solution disclosed in this invention, the ultrathin indium foil layer is prepared using high-purity indium material with a purity of ≥99.99%, and has a thickness of 0.01~0.1mm.

[0012] As a further improvement to the technical solution disclosed in this invention, the tungsten-copper heat sink is made of a tungsten-copper alloy with a tungsten content of 80% to 90%, has a coefficient of thermal expansion of 7 to 8 ppm / ℃, and a thermal conductivity ≥190 W / (m²). K).

[0013] As a further improvement to the technical solution disclosed in this invention, the upper and lower surfaces of the tungsten copper heat sink are both mirror-polished, with a surface roughness Ra≤0.2μm and a flatness error≤0.01mm.

[0014] Furthermore, this invention also discloses a preparation method for forming the above-mentioned all-aluminum nitride TEC direct-attach laser packaging structure, comprising the following steps: S1. The bonding surfaces of the tungsten copper heat sink, aluminum nitride thermally conductive insulating sheet, and all-aluminum nitride ceramic TEC are mirror-polished, and then ultrasonically cleaned with acetone and anhydrous ethanol in sequence before drying; or the bonding surfaces of the tungsten copper heat sink and all-aluminum nitride ceramic TEC are mirror-polished, and then ultrasonically cleaned with acetone and anhydrous ethanol in sequence before drying. S2. Gold-tin eutectic solder is laid on the upper surface of the tungsten copper heat sink, a laser chip is placed, and it is sintered at a constant temperature of 270-290℃ to form a gold-tin solder layer with a void ratio of ≤0.5%. S3. Weld and fix the aluminum nitride thermally conductive insulating sheet to the lower surface of the tungsten copper heat sink. Lay an ultra-thin indium foil layer on the cold end ceramic surface of the all-aluminum nitride ceramic TEC. Use flexible packaging technology to align and press the aluminum nitride thermally conductive insulating sheet with the cold end ceramic surface of the all-aluminum nitride ceramic TEC. Alternatively, lay an ultra-thin indium foil layer on the cold end ceramic surface of the all-aluminum nitride ceramic TEC. Use flexible packaging technology to align and press the lower surface of the tungsten copper heat sink with the cold end ceramic surface of the all-aluminum nitride ceramic TEC. S4. After curing at room temperature, a full aluminum nitride TEC direct-attach laser encapsulation structure is obtained.

[0015] As a further improvement to the technical solution disclosed in this invention, in step S3, the flexible packaging technology adopts a constant pressure progressive pressing process, with a pressing pressure of 0.2 to 0.5 MPa, a holding time of 30 to 60 seconds, and a pressing temperature of 20 to 30°C. During the alignment pressing process, the alignment error between the aluminum nitride thermally conductive insulating sheet and the cold end ceramic surface of the all-aluminum nitride ceramic TEC is ≤0.05 mm, and the alignment error between the lower surface of the tungsten copper heat sink and the cold end ceramic surface of the all-aluminum nitride ceramic TEC is ≤0.05 mm.

[0016] As a further improvement to the technical solution disclosed in this invention, in step S3, the aluminum nitride thermally conductive insulating sheet is fixed to the lower surface of the tungsten copper heat sink by tin-silver-copper solder, and the welding temperature is 240-260℃, and the welding bond strength is ≥20MPa; before laying the ultrathin indium foil layer, the surface is deoxidized by argon plasma, and the treatment time is 10-30s, and the treatment power is 100-200W.

[0017] In practical applications, the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention can achieve at least the following beneficial technical effects, specifically: 1) The all-aluminum nitride ceramic TEC direct-mount laser packaging structure adopts a direct-mount design without a metal copper transition heat sink, thereby significantly simplifying the heat dissipation path and reducing the total thermal resistance of the system. Relying on the homogeneous thermal matching design of the all-aluminum nitride ceramic TEC and the aluminum nitride thermally conductive insulating sheet, precise matching of the interface thermal expansion coefficients is achieved, eliminating the potential for thermal stress concentration at the structural level. Combined with an ultra-thin indium foil layer as the only flexible thermally conductive interface, residual stress can be released through plastic deformation to ensure tight interface contact and improve thermal conductivity. 2) Two independently implemented parallel packaging structures can be flexibly selected according to actual needs: The first structure sets an aluminum nitride thermally conductive insulating sheet between the tungsten copper heat sink and the all-aluminum nitride ceramic TEC, which has both excellent electrical insulation performance and thermal conductivity; the second structure adopts a design of direct bonding between the tungsten copper heat sink and the all-aluminum nitride ceramic TEC, which further simplifies the number of structural layers and achieves a lower total system thermal resistance and a smaller package volume.

[0018] In terms of the preparation method, a complete packaging process system is formed through the synergistic effect of multiple steps, including interface pretreatment, temperature gradient process, flexible pressing and room temperature curing: the clean and flat interface obtained by mirror polishing and stepwise ultrasonic cleaning in step S1 provides the foundation for low-stress flexible pressing in step S3, which can maximize the effective contact area of ​​the interface; step S2 uses isothermal sintering to prepare a low-void gold-tin solder layer, and at the same time sets a clear temperature upper limit for subsequent processes, so that step S3 can adopt a reasonable sequence of chip welding first, followed by insulating sheet welding and TEC bonding, completely avoiding thermal damage to the chip and the already formed solder interface by subsequent processes; the flexible alignment pressing technology in step S3, combined with the room temperature curing process in step S4, further eliminates local stress concentration and residual thermal stress, and finally achieves high consistency and high reliability in the preparation of the all-aluminum nitride TEC direct-attach laser packaging structure. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a three-dimensional schematic diagram of the first embodiment of the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention; Figure 2 yes Figure 1 A magnified view of part of I.

[0021] Figure 3 This is a three-dimensional schematic diagram of the all-aluminum nitride ceramic TEC in the first embodiment of the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention; Figure 4 This is a three-dimensional schematic diagram of the second embodiment of the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention; Figure 5 yes Figure 4 A magnified view of part II.

[0022] Figure 6This is a three-dimensional schematic diagram of the all-aluminum nitride ceramic TEC in the second embodiment of the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention; 1-Laser chip; 2-First gold-tin solder layer; 3-Second gold-tin solder layer; 4-Tungsten copper heat sink; 5-Ultra-thin indium foil layer; 6-All-aluminum nitride ceramic TEC; 7-Aluminum nitride thermally conductive insulating sheet. Detailed Implementation

[0023] Laser chip 1 is the core light-emitting element of semiconductor laser devices. The stability of its operating temperature directly determines the consistency of laser wavelength and the stability of output power. It is also the key to the long-term continuous and reliable operation of the device in extreme environments with a wide temperature range of -50℃ to 80℃.

[0024] The all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention abandons the traditional multi-level heat dissipation architecture with copper transition heat sink, and adopts the design concept of aluminum nitride ceramic homogeneous thermal matching combined with flexible thermal interface, which takes into account both low thermal resistance heat dissipation performance and resistance to alternating thermal stress, can meet the usage requirements of wide temperature range semiconductor laser devices, and is also suitable for industrial mass packaging production.

[0025] The all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention includes two specific embodiments, which are described in detail below.

[0026] First implementation method (equipped with aluminum nitride thermally conductive insulating sheet) Figure 1 , Figure 2 The diagrams show a three-dimensional schematic and a partial enlarged view of the first embodiment of the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention. It can be seen that the structure mainly consists of a laser chip 1, a first gold-tin solder layer 2, a second gold-tin solder layer 3, a tungsten-copper heat sink 4, an ultra-thin indium foil layer 5, and an all-aluminum nitride ceramic TEC 6 (e.g., ...). Figure 3 It consists of several parts, including the aluminum nitride thermally conductive insulating sheet 7 shown in the figure.

[0027] The laser chip 1 is embedded inside the tungsten copper heat sink 4, and the two are fixed by sintering through the first gold-tin solder layer 2; the lower surface of the tungsten copper heat sink 4 is attached to the aluminum nitride thermally conductive insulating sheet 7, and a firm connection is achieved by means of the second gold-tin solder layer 3; the bottom surface of the aluminum nitride thermally conductive insulating sheet 7 is covered with an ultra-thin indium foil layer 5, and the aluminum nitride thermally conductive insulating sheet 7 is flexibly encapsulated on the cold end ceramic surface of the all-aluminum nitride ceramic TEC6 through the ultra-thin indium foil layer 5.

[0028] Furthermore, the tungsten-copper heat sink 4 is preferably made of a tungsten-copper alloy with a tungsten content of 80% to 90%, has a coefficient of thermal expansion of 7 to 8 ppm / ℃, and a thermal conductivity ≥190 W / (m²). K). Furthermore, both the upper and lower surfaces of the tungsten copper heat sink 4 are mirror-polished, resulting in a surface roughness Ra≤0.2μm and a flatness error ≤0.01mm after processing. This effectively reduces the interfacial contact thermal resistance while ensuring the assembly accuracy of the welding and pressing processes.

[0029] Both the aluminum nitride thermally conductive insulating sheet 7 and the cold-end substrate of the all-aluminum nitride ceramic TEC6 are made of high thermal conductivity aluminum nitride ceramic, and both have a thermal conductivity ≥80W / (m²). The coefficient of thermal expansion is uniformly set at 4.4–4.6 ppm / ℃ to achieve thermal matching of homogeneous materials. Specifically, the aluminum nitride thermally conductive insulating sheet 7 has a thickness of 0.2–0.5 mm, and the cold-end substrate of the all-aluminum nitride ceramic TEC6 has a thickness of 0.3–0.6 mm. This effectively eliminates alternating thermal stress generated during high and low temperature cycling, avoiding failure problems such as weld voids, structural delamination, and ceramic chipping.

[0030] The hot-end substrate of the all-aluminum nitride ceramic TEC6 is also made of aluminum nitride ceramic material, with an applicable operating temperature range of -50℃ to 80℃ and a cooling power density of ≥15W / cm³. 2 Tests have shown that the hot-end substrate of the all-aluminum nitride ceramic TEC6 exhibits a cooling efficiency decrease of ≤3% after 1000 hours of continuous operation at 80℃, demonstrating excellent high-temperature long-term working capability. This effectively suppresses the temperature rise of the laser chip and prevents faults such as wavelength drift and output power attenuation.

[0031] The ultrathin indium foil layer 5 is made of high-purity indium material with a purity of ≥99.99%, and its thickness is controlled between 0.01 and 0.1 mm. As the only flexible thermal interface inside the structure, the ultrathin indium foil layer 5 can release residual thermal stress through its own plastic deformation, while ensuring close contact between the interfaces of each layer, thereby simultaneously improving the overall thermal conductivity and the fatigue resistance of the structure.

[0032] Both the first gold-tin solder layer 2 and the second gold-tin solder layer 3 are sintered from gold-tin eutectic solder, with a porosity of ≤0.5%, ensuring a strong bond at the welding interface and uniform heat conduction, thus enabling long-term stable heat transfer.

[0033] The fabrication process steps for the all-aluminum nitride TEC direct-attach laser packaging structure are as follows: S1. Interface pretreatment: Mirror polishing is performed on all bonding surfaces of the tungsten copper heat sink 4, aluminum nitride thermally conductive insulating sheet 7, and all aluminum nitride ceramic TEC6. After polishing, the workpiece is placed in acetone and anhydrous ethanol for ultrasonic cleaning in sequence. After cleaning, it is thoroughly dried to remove surface oil, impurities and oxide layer.

[0034] S2. Chip welding and fixing: Gold-tin eutectic solder is laid in the chip embedding area of ​​the tungsten copper heat sink 4, and the laser chip 1 is embedded in the corresponding position. It is sintered under constant temperature conditions of 270-290℃ to form the first gold-tin solder layer 2 with a void ratio of ≤0.5%, thus completing the assembly and fixing of the laser chip 1 and the tungsten copper heat sink 4.

[0035] S3. Component Welding and Flexible Pressing: The aluminum nitride thermally conductive insulating sheet 7 is welded to the lower surface of the tungsten copper heat sink 4 using tin-silver-copper solder. The welding temperature is controlled at 240–260℃, and the bond strength after welding is ≥20MPa. The ultra-thin indium foil layer 5 undergoes argon plasma deoxidation treatment with a power of 100–200W and a treatment time of 10–30s. The treated ultra-thin indium foil layer 5 is then evenly laid on the cold end surface of the all-aluminum nitride ceramic TEC6. This process uses a constant pressure progressive pressing process for alignment pressing, with a pressing pressure of 0.2–0.5MPa, a holding time of 30–60s, and an ambient temperature of 20–30℃. During the operation, the alignment error between the aluminum nitride thermally conductive insulating sheet 7 and the cold end of the all-aluminum nitride ceramic TEC6 is strictly controlled to ≤0.05mm.

[0036] S4. Room temperature curing: After the pressing operation is completed, the overall structure is placed in a room temperature environment to cure naturally, and finally the packaged product is obtained.

[0037] This embodiment adds an aluminum nitride thermally conductive insulating sheet 7 between the tungsten copper heat sink 4 and the all-aluminum nitride ceramic TEC6. This simplifies the heat dissipation path, reduces system thermal resistance, and provides excellent electrical insulation performance. Combined with the homogeneous thermal matching of aluminum nitride and the flexible pressure-relieving structure of ultra-thin indium foil, the overall thermal stress resistance is outstanding, making it suitable for applications with high requirements for electrical insulation and equipment operational reliability.

[0038] The second implementation method (aluminum nitride-free thermally conductive insulating sheet, direct-attach structure) Figure 4 , Figure 5 The diagram shows a three-dimensional schematic diagram and a partial enlarged view of the second embodiment of the all-aluminum nitride TEC direct-attach laser packaging structure disclosed in this invention. It can be seen that it is mainly composed of several parts, including a laser chip 1, a first gold-tin solder layer 2, a tungsten copper heat sink 4, an ultra-thin indium foil layer 5, and an all-aluminum nitride ceramic TEC 6.

[0039] The laser chip 1 is embedded inside the tungsten copper heat sink 4, and the two are fixed by sintering through the first gold-tin solder layer 2; the lower surface of the tungsten copper heat sink 4 is directly covered with an ultra-thin indium foil layer 5, and is flexibly encapsulated on the cold end ceramic surface of the all-aluminum nitride ceramic TEC6 through the ultra-thin indium foil layer 5.

[0040] In this embodiment, the material selection, dimensional parameters, performance indicators, and surface processing requirements of the tungsten-copper heat sink 4, the ultra-thin indium foil layer 5, the all-aluminum nitride ceramic TEC 6, and the first gold-tin solder layer 2 are consistent with those of the first embodiment. The tungsten-copper heat sink 4 is a tungsten-copper alloy with a tungsten content of 80% to 90% and a thermal conductivity ≥190W / (m²). K), the surface is mirror-polished; both the hot and cold end substrates of the all-aluminum nitride ceramic TEC6 are high thermal conductivity aluminum nitride ceramics, with a thermal conductivity of ≥180W / (m²) for the cold end substrate. The thermal expansion coefficient is 4.4~4.6ppm / ℃, and it can work stably for a long time in a wide temperature range of -50℃~80℃; the ultra-thin indium foil layer 5 is made of high-purity indium material with a purity of ≥99.99% and a thickness of 0.01~0.1mm, which plays a role in flexible pressure relief and efficient heat conduction; the first gold-tin solder layer 2 has a void ratio of ≤0.5%, which ensures reliable connection between laser chip 1 and tungsten copper heat sink 4 and smooth heat transfer.

[0041] The fabrication process steps for the all-aluminum nitride TEC direct-attach laser packaging structure are as follows: S1. Interface pretreatment: The bonding surfaces of the tungsten copper heat sink 4 and the all-aluminum nitride ceramic TEC6 are mirror-polished. After polishing, the workpiece is placed in acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After cleaning, it is dried for later use.

[0042] S2. Chip welding and fixing: Gold-tin eutectic solder is laid in the chip embedding area of ​​the tungsten copper heat sink 4, the laser chip 1 is inserted, and sintering is carried out in a constant temperature environment of 270-290℃ to form the first gold-tin solder layer 2 with a void ratio ≤0.5%, thus completing the chip assembly and fixing.

[0043] S3. Flexible Alignment Pressing: The ultrathin indium foil layer 5 undergoes argon plasma deoxidation treatment with a power of 100–200W and a processing time of 10–30s. Subsequently, the ultrathin indium foil layer 5 is laid on the cold end ceramic surface of the all-aluminum nitride ceramic TEC6. A constant pressure progressive pressing process is used, with a pressing pressure of 0.2–0.5MPa, a holding time of 30–60s, and a pressing temperature of 20–30℃. The alignment error between the lower surface of the tungsten copper heat sink 4 and the cold end of the all-aluminum nitride ceramic TEC6 is controlled to be ≤0.05mm.

[0044] S4. Room temperature curing: After pressing, the structure is placed in a room temperature environment to cure naturally, and finally the packaged product is obtained.

[0045] Implementation method two omits the aluminum nitride thermally conductive insulating sheet 7 and the second gold-tin solder layer 3, resulting in fewer overall structural layers and a simpler assembly process. Compared to the first implementation method, it can further reduce the total system thermal resistance while effectively reducing the package size, making it suitable for applications with high requirements for heat dissipation efficiency and miniaturized equipment design, and without additional electrical insulation requirements.

[0046] In summary, both Implementation Method 1 and Implementation Method 2 abandon the traditional copper transition heat sink structure and rely on all aluminum nitride ceramics to achieve precise matching of the thermal expansion coefficient. Combined with the ultra-thin indium foil layer to release residual thermal stress, they fundamentally solve the problems of high thermal resistance and easy interface failure under high and low temperature cycling conditions in traditional multi-level heat dissipation structures. They can fully adapt to the packaging requirements of wide temperature range semiconductor laser devices under different operating conditions, so as to stabilize the laser wavelength and output power for a long time and extend the overall service life of the device.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A direct-attach laser encapsulation structure for aluminum nitride TEC, characterized in that, This includes laser chips, gold-tin solder layers, tungsten-copper heat sinks, ultra-thin indium foil layers, and all-aluminum nitride ceramic TEC; The laser chip is sintered and fixed to the tungsten copper heat sink via the gold-tin solder layer; An aluminum nitride thermally conductive insulating sheet is fixed to the lower surface of the tungsten copper heat sink, and the aluminum nitride thermally conductive insulating sheet is flexibly encapsulated on the cold end ceramic surface of the all-aluminum nitride ceramic TEC through the ultra-thin indium foil layer; or the lower surface of the tungsten copper heat sink is directly flexibly encapsulated on the cold end ceramic surface of the all-aluminum nitride ceramic TEC through the ultra-thin indium foil layer.

2. The all-aluminum nitride TEC direct-attach laser packaging structure according to claim 1, characterized in that, Both the aluminum nitride thermally conductive insulating sheet and the cold-end substrate of the all-aluminum nitride ceramic TEC are made of high thermal conductivity aluminum nitride ceramic with a thermal conductivity ≥180W / (m²). The coefficient of thermal expansion (K) ranges from 4.4 to 4.6 ppm / ℃, and the two values ​​are equal.

3. The all-aluminum nitride TEC direct-attach laser packaging structure according to claim 2, characterized in that, The thickness of the aluminum nitride thermally conductive insulating sheet is 0.2–0.5 mm; the thickness of the cold end substrate of the all-aluminum nitride ceramic TEC is 0.3–0.6 mm.

4. The all-aluminum nitride TEC direct-attach laser packaging structure according to claim 2, characterized in that, The hot end substrate of the all-aluminum nitride ceramic TEC is made of aluminum nitride ceramic material, with an operating ambient temperature of -50℃ to 80℃ and a cooling power density of ≥15W / cm³. 2 The cooling efficiency of the all-aluminum nitride ceramic TEC decreases by ≤3% after 1000 hours of continuous operation at an ambient temperature of 80℃.

5. The all-aluminum nitride TEC direct-attach laser packaging structure according to claim 1, characterized in that, The ultrathin indium foil layer is prepared using high-purity indium material with a purity of ≥99.99% and a thickness of 0.01–0.1 mm.

6. The all-aluminum nitride TEC direct-attach laser packaging structure according to claim 1, characterized in that, The tungsten-copper heat sink is made of a tungsten-copper alloy with a tungsten content of 80%–90%, has a coefficient of thermal expansion of 7–8 ppm / ℃, and a thermal conductivity ≥190 W / (m²). K).

7. The all-aluminum nitride TEC direct-attach laser packaging structure according to claim 6, characterized in that, The upper and lower surfaces of the tungsten copper heat sink are both mirror-polished, with a surface roughness Ra≤0.2μm and a flatness error≤0.01mm.

8. A preparation method for forming the all-aluminum nitride TEC direct-attach laser encapsulation structure as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. The bonding surfaces of the tungsten copper heat sink, the aluminum nitride thermally conductive insulating sheet, and the all-aluminum nitride ceramic TEC are mirror-polished, and then ultrasonically cleaned with acetone and anhydrous ethanol in sequence before drying; or the bonding surfaces of the tungsten copper heat sink and the all-aluminum nitride ceramic TEC are mirror-polished, and then ultrasonically cleaned with acetone and anhydrous ethanol in sequence before drying. S2. Gold-tin eutectic solder is laid on the upper surface of the tungsten copper heat sink, a laser chip is placed therein, and the heat sink is sintered at a constant temperature of 270-290°C to form a gold-tin solder layer with a void ratio of ≤0.5%. S3. The aluminum nitride thermally conductive insulating sheet is welded and fixed to the lower surface of the tungsten copper heat sink. The ultra-thin indium foil layer is laid on the cold-end ceramic surface of the all-aluminum nitride ceramic TEC. The aluminum nitride thermally conductive insulating sheet and the cold-end ceramic surface of the all-aluminum nitride ceramic TEC are aligned and pressed together using flexible packaging technology; or the ultra-thin indium foil layer is laid on the cold-end ceramic surface of the all-aluminum nitride ceramic TEC. The lower surface of the tungsten copper heat sink and the cold-end ceramic surface of the all-aluminum nitride ceramic TEC are aligned and pressed together using flexible packaging technology. S4. After curing at room temperature, the full aluminum nitride TEC direct-attach laser encapsulation structure is obtained.

9. The preparation method according to claim 8, characterized in that, In step S3, the flexible packaging technology adopts a constant pressure progressive pressing process, with a pressing pressure of 0.2 to 0.5 MPa, a holding time of 30 to 60 seconds, and a pressing temperature of 20 to 30 degrees Celsius. During the alignment and pressing process, the alignment error between the aluminum nitride thermally conductive insulating sheet and the cold end ceramic surface of the all-aluminum nitride ceramic TEC is ≤0.05mm, and the alignment error between the lower surface of the tungsten copper heat sink and the cold end ceramic surface of the all-aluminum nitride ceramic TEC is ≤0.05mm.

10. The preparation method according to claim 8, characterized in that, In step S3, the aluminum nitride thermally conductive insulating sheet is fixed to the lower surface of the tungsten copper heat sink by tin-silver-copper solder, and the welding temperature is 240-260℃, with a welding bond strength ≥20MPa; before the ultra-thin indium foil layer is laid, it is subjected to surface deoxidation treatment by argon plasma, and the treatment time is 10-30s, with a treatment power of 100-200W.

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