Composite connection structure for packaging thermoelectric device and preparation method of composite connection structure

Abstract

The invention discloses a composite connection structure for packaging a thermoelectric device and a preparation method of the composite connection structure. The composite connection structure comprises a thermoelectric conversion substrate, and the upper surface of the thermoelectric conversion substrate is provided with a metalized bonding pad. The high-conductivity nano material and the high-plasticity / low-modulus material are compounded in space, the contradiction that a traditional material is strong but not conductive and is conductive but not strong is broken through, the plastic deformation and pore collapse of the buffer layer, the slip system starting of the high-entropy alloy and the flowing of the liquid metal are utilized, the multi-stage stress dissipation from microcosmic to macroscopic is realized, and the mechanical property of the material is improved. Through micro-nano structuring, active element doping and introduction of the diffusion barrier layer, interface element mutual diffusion and cavity growth are remarkably inhibited, the service life of the device under high temperature and large current is prolonged, the requirements of workers are met, and the production efficiency is improved. Therefore, the composite connection structure provided by the invention perfectly solves the technical problem that low resistance and high reliability in thermoelectric device packaging are difficult to achieve at the same time, and has extremely high industrial application value.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric device packaging technology, specifically to a composite connection structure for thermoelectric device packaging and its preparation method. Background Technology

[0002] Thermoelectric conversion technology is a solid-state energy technology that enables the direct conversion between thermal energy and electrical energy, and it has broad application prospects in fields such as waste heat recovery, solid-state refrigeration, and deep space exploration. The core of thermoelectric devices typically consists of N-type and P-type thermoelectric legs, which need to be electrically and mechanically connected to a ceramic or metal substrate via metallized pads.

[0003] However, existing thermoelectric device packaging and connection technologies have two main contradictions: 1. Contact Resistance and Electrical Loss Issues: To ensure device conversion efficiency, the interconnect layer needs to have extremely low resistivity (low impedance). While traditional solders (such as Sn-Ag-Cu) have mature manufacturing processes, their relatively high resistivity generates significant Joule heating during high-current operation, reducing the system's net output power. Although using highly conductive materials such as nano-silver (Nano-Ag) can reduce resistance, they are inherently brittle and require high pressure and temperature during sintering.

[0004] 2. Thermal Stress and Reliability Issues: There is a significant difference in the coefficient of thermal expansion (CTE) between thermoelectric materials (such as Bi₂Te₃ and PbTe) and substrate materials (such as Al₂O₃ and AlN). When thermoelectric devices undergo repeated heating-cooling cycles (thermal shock), enormous shear and thermal stresses are generated at the interface. This stress can lead to fatigue cracking of the bonding layer, interface delamination, and ultimately open-circuit failure of the device. While traditional pure metal buffer layers can alleviate stress, they often come at the cost of reduced conductivity or excessive creep under long-term high-temperature operation, resulting in loose connections. Summary of the Invention

[0005] To solve the above-mentioned technical problems, a composite connection structure for thermoelectric device packaging and its preparation method are provided. This technical solution solves the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect of the present invention, a composite connection structure for thermoelectric device packaging is provided, comprising: Thermoelectric conversion substrate, with metallized pads on its upper surface; A thermoelectric leg assembly includes an N-type thermoelectric leg and a P-type thermoelectric leg, with one end of the thermoelectric leg assembly corresponding to the metallized pad; A low-impedance connection layer is disposed between the metallized pad and the thermoelectric leg assembly to reduce contact resistance. The low-impedance connection layer comprises a highly conductive nanocrystalline metal or amorphous alloy material. A stress relief buffer layer is embedded in or covers the contact interface between the low-impedance connection layer and the thermoelectric leg assembly, or is located between the low-impedance connection layer and the metallized pad. The stress relief buffer layer is made of a conductive material with high plastic deformation capacity or low Young's modulus. The low-impedance connection layer provides the main current transmission channel, and the stress relief buffer layer is used to absorb the shear stress and thermal stress caused by the mismatch between the thermoelectric leg and the substrate due to the thermal expansion coefficient.

[0007] Preferably, the low-impedance connection layer has a gradient composite structure, with the grain size increasing or decreasing in a gradient distribution from the side near the thermoelectric leg assembly to the side near the metallized pad, and the material of the layer is selected from nano-silver, nano-copper or copper-graphene composite coating.

[0008] Preferably, the low-impedance connection layer is doped with trace amounts of active elements, including titanium, chromium, zirconium, or the rare earth element cerium, with a total doping amount of 0.1% to 5% by mass, which is used to enhance the interfacial bonding force and oxidation resistance between the low-impedance connection layer and the thermoelectric leg material.

[0009] Preferably, the thickness of the low-impedance connection layer is controlled within to Between, and its resistivity at 25℃ is lower than This is to ensure that Joule heating generated when a large current passes through is minimized.

[0010] Preferably, the surface of the metallized pad is roughened or micro / nano-structured to form micropores or pits, and a portion of the material of the low-impedance connection layer fills the micropores or pits.

[0011] Preferably, the stress relief buffer layer is a porous foam metal structure or a corrugated metal foil, and the material is selected from pure indium, pure tin, or an indium-tin alloy, with a porosity of 10% to 40%, or a corrugation amplitude of [missing information]. This provides deformation space perpendicular to the interface direction.

[0012] Preferably, the stress relief buffer layer comprises a high-entropy alloy material, the general formula of which is: , where 0≤ ≤1.5, this layer has a face-centered cubic (FCC) or body-centered cubic (BCC) solid solution structure, which utilizes its lattice distortion effect to hinder crack propagation and release stress through the slip system.

[0013] Preferably, the stress relief buffer layer is a liquid metal composite material, which is composed of liquid gallium indium tin alloy Galinstan microcapsules dispersed in a solid conductive polymer matrix. During thermal cycling, the liquid microcapsules undergo reversible deformation to dissipate accumulated thermal stress. Preferably, it further includes an interface diffusion barrier layer disposed between the low-impedance connection layer and the stress relief buffer layer, or disposed between the metallized pad and the low-impedance connection layer. The diffusion barrier layer material is selected from titanium nitride, tungsten carbide or molybdenum, and is used to prevent tellurium or bismuth elements in the thermoelectric leg material from diffusing into the metal layer.

[0014] In a second aspect of the present invention, a method for preparing a composite connection structure for thermoelectric device packaging is also provided, comprising: S1. Substrate pretreatment: Plasma cleaning and micro-etching are performed on the metallized pads of the thermoelectric conversion substrate to remove the surface oxide layer and increase the surface roughness. S2. Stress buffer layer preparation: On the metallized pad or thermoelectric leg contact surface, a stress release buffer layer material is deposited by magnetron sputtering, electrochemical deposition or 3D printing technology, and pre-forming treatment is performed, such as corrugation or foaming to create pores. S3. Low-impedance layer co-deposition: On the surface of the stress relief buffer layer, a low-impedance bonding layer material is deposited using pulsed electrodeposition or vacuum thermal evaporation technology, and the deposition parameters are controlled to form a nanocrystalline or amorphous structure. S4. Component assembly: Place the hot end of the thermoelectric leg assembly with the low-resistance connection layer and apply a certain pre-pressure. S5. Heat treatment bonding: Hot pressing sintering or spark plasma sintering is carried out in a protective atmosphere or vacuum environment. The sintering temperature is lower than the melting point of the thermoelectric leg material but higher than the recrystallization temperature of the low impedance layer material. The holding time is 5 min to 60 min, so that the low impedance bonding layer forms a metallurgical bond with the two side interfaces. At the same time, the stress buffer layer undergoes plastic rheological filling of the interface microvoids. S6. Cooling: Slowly cool the furnace or control the cooling rate to release residual stress and complete the encapsulation.

[0015] Compared with the prior art, the present invention provides a composite connection structure for thermoelectric device packaging and its preparation method, which has the following beneficial effects: This invention breaks the traditional material contradiction of "strong but not conductive, conductive but not strong" by spatially compositing highly conductive nanomaterials with highly ductile / low modulus materials. Utilizing the plastic deformation of the buffer layer, pore collapse, the activation of the slip system of the high-entropy alloy, and the flow of liquid metal, it achieves multi-level stress dissipation from the microscopic to the macroscopic level. Through micro-nano structuring, active element doping, and the introduction of diffusion barrier layers, it significantly suppresses inter-diffusion of interfacial elements and void growth, extending the service life of the device under high temperature and high current, thus meeting the needs of personnel. Therefore, the composite connection structure proposed in this invention perfectly solves the technical challenge of achieving both "low resistance" and "high reliability" in thermoelectric device packaging, possessing extremely high industrial application value. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the composite connection structure for the thermoelectric device encapsulation in this invention; Figure 2 This is a flowchart illustrating the preparation method of the composite connection structure for thermoelectric device encapsulation in this invention. Detailed Implementation

[0017] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0018] Example 1 Please refer to Figure 1 As shown, in a first aspect of the present invention, a composite connection structure for thermoelectric device packaging is provided, comprising: Thermoelectric conversion substrate 1, with metallized pads provided on its upper surface; Thermoelectric leg assembly 2 includes an N-type thermoelectric leg and a P-type thermoelectric leg, with one end of the thermoelectric leg assembly 2 corresponding to the metallized pad; A low-impedance connection layer 3 is disposed between the metallized pad and the thermoelectric leg assembly 2 to reduce contact resistance. The low-impedance connection layer 3 contains highly conductive nanocrystalline metal or amorphous alloy material. The stress relief buffer layer 4 is embedded or covers the contact interface between the low impedance connection layer 3 and the thermoelectric leg assembly 2, or is located between the low impedance connection layer 3 and the metallized pad. The stress relief buffer layer 4 is made of a conductive material with high plastic deformation capacity or low Young's modulus. Among them, the low-impedance connection layer 3 provides the main current transmission channel, and the stress relief buffer layer 4 is used to absorb the shear stress and thermal stress caused by the mismatch between the thermoelectric leg and the substrate due to the thermal expansion coefficient.

[0019] The low-impedance connection layer 3 has a gradient composite structure. From the side near the thermoelectric leg assembly 2 to the side near the metallized pad, the grain size is distributed in a gradient increasing or decreasing pattern. The material of this layer is selected from nano-silver, nano-copper or copper-graphene composite coating.

[0020] The low-impedance bonding layer 3 is doped with trace amounts of active elements, including titanium, chromium, zirconium or rare earth element cerium, with a total doping amount of 0.1% to 5% by mass percentage, which is used to enhance the interfacial bonding force and oxidation resistance between the low-impedance bonding layer 3 and the thermoelectric leg material.

[0021] The thickness of the low-impedance interconnect layer 3 is controlled within to Between, and its resistivity at 25℃ is lower than This is to ensure that Joule heating generated when a large current passes through is minimized.

[0022] The surface of the metallized pads is roughened or micro / nano-structured to form micropores or pits, and a portion of the material of the low-impedance interconnect layer 3 fills the micropores or pits.

[0023] The stress relief buffer layer 4 is a porous foam metal structure or a corrugated metal foil, made of pure indium, pure tin, or an indium-tin alloy, with a porosity of 10% to 40%, or a corrugation amplitude of [missing information]. This provides deformation space perpendicular to the interface direction.

[0024] The stress relief buffer layer 4 contains a high-entropy alloy material, the general formula of which is: , where 0≤ ≤1.5, this layer has a face-centered cubic (FCC) or body-centered cubic (BCC) solid solution structure, which utilizes its lattice distortion effect to hinder crack propagation and release stress through the slip system.

[0025] The stress relief buffer layer 4 is a liquid metal composite material, consisting of liquid gallium indium tin alloy Galinstan microcapsules dispersed in a solid conductive polymer matrix. During thermal cycling, the liquid microcapsules undergo reversible deformation to dissipate accumulated thermal stress. It also includes an interface diffusion barrier layer 5, which is disposed between the low impedance connection layer and the stress relief buffer layer, or between the metallized pad and the low impedance connection layer 3. The diffusion barrier layer 3 is made of titanium nitride, tungsten carbide or molybdenum, and is used to prevent tellurium or bismuth elements in the thermoelectric leg material from diffusing into the metal layer.

[0026] Please refer to Figure 2 As shown, in a second aspect of the present invention, a method for preparing a composite connection structure for thermoelectric device packaging is also provided, comprising: S1. Substrate pretreatment: Plasma cleaning and micro-etching are performed on the metallized pads of the thermoelectric conversion substrate to remove the surface oxide layer and increase the surface roughness. S2. Stress buffer layer preparation: On the metallized pad or thermoelectric leg contact surface, a stress release buffer layer material is deposited by magnetron sputtering, electrochemical deposition or 3D printing technology, and pre-forming treatment is performed, such as corrugation or foaming to create pores. S3, Low-impedance layer co-deposition: On the surface of the stress relief buffer layer, a low-impedance connection layer 3 material is deposited using pulsed electrodeposition or vacuum thermal evaporation technology, and the deposition parameters are controlled to form a nanocrystalline or amorphous structure. S4. Component assembly: Place the hot end of thermoelectric leg assembly 2 with the low impedance connection layer and apply a certain pre-pressure. S5. Heat treatment bonding: Hot pressing sintering or spark plasma sintering is carried out in a protective atmosphere or vacuum environment. The sintering temperature is lower than the melting point of the thermoelectric leg material but higher than the recrystallization temperature of the low impedance connection layer 3 material. The holding time is 5 min to 60 min, so that the low impedance connection layer 3 forms a metallurgical bond with the two side interfaces. At the same time, the stress buffer layer undergoes plastic rheological filling of the interface microvoids. S6. Cooling: Slowly cool the furnace or control the cooling rate to release residual stress and complete the encapsulation.

[0027] Example 2 Performance tests were conducted on the composite connection structure of the thermoelectric device package. (1) Experimental Example 1: Gradient nanosilver / indium foil composite structure S1, Substrate Pretreatment: ... The ceramic substrate is placed in a plasma cleaner and treated with Ar gas for 10 minutes to remove surface organic contaminants; then it is treated with a micro-etching solution (ammonium persulfate + sulfuric acid) for 30 seconds to form a micron-level rough surface, and then cleaned and dried. S2. Stress buffer layer preparation: A 20μm thick pure indium foil is placed on the metallized pad, and a corrugated structure with an amplitude of 10μm is pressed on the surface of the indium foil using a mechanical rolling mill. S3. Low-resistivity co-deposition: A low-resistivity interconnect layer is deposited on the surface of indium foil using pulsed electrodeposition. Gradient control: In the initial stage, a high current density (10A / dm²) is used. 2 Fine-grained silver nanoparticles (~20 nm) were obtained; the current density was then linearly reduced to 1 A / dm³. 2 Coarse-grained silver nanoparticles (~200 nm) were obtained. The total thickness was controlled at 8 μm. Doping: 1 wt% titanium nanoparticles were added to the electrodeposition solution and co-deposited by ultrasonic dispersion; S4, Component Assembly: ... The hot end of the thermoelectric leg is placed aligned with the low-resistivity layer, and a pre-pressure of 1 MPa is applied. S5. Heat treatment bonding: Place in an SPS sintering furnace, heat to 280°C at 100°C / min under a N2 protective atmosphere, hold for 15 minutes, and maintain a pressure of 2MPa, which is lower than the melting point of the thermoelectric leg and higher than the recrystallization temperature of silver. S6. Cooling: Cool to room temperature in the furnace at a rate of 5℃ / min to complete the encapsulation.

[0028] (2) Experimental Example 2: High-entropy alloy / liquid metal composite structure S1-S2: Same as Example A, but in S2, magnetron sputtering is used to deposit a 2μm thick layer on the pad. The high-entropy alloy layer serves as a buffer layer; S3: Preparation of liquid metal composite material - Disperse liquid Galinstan microcapsules (average particle size 20μm) in epoxy resin / silver powder mixed conductive adhesive, screen print them on a high entropy alloy layer with a thickness of 15μm, and then vacuum evaporate a 5μm thick amorphous copper layer on it as a low impedance layer. S4-S6: Cured by hot pressing in a vacuum environment at 250℃ for 30 minutes.

[0029] (3) Comparative example: Traditional Sn-Ag-Cu brazing Reflow soldering was performed at 250°C using Sn-3.0Ag-0.5Cu solder.

[0030] Experimental Data and Performance Analysis To verify the advantages of the present invention, we conducted three key tests on the above experimental examples and comparative examples: contact resistivity, shear strength, and thermal cycling life.

[0031] Table 1: Comparison of Electrical and Thermal Properties

[0032] Data Analysis: The contact resistivity of Example 1 is only 1.85 μΩ·cm. 2 This is far lower than the comparative example's 8.60 μΩ·cm. 2 This demonstrates that the nanocrystalline / gradient structure effectively reduces contact resistance.

[0033] Although slightly higher than bulk silver (blank group), this value is already excellent considering the interfacial bonding strength and stress release capability.

[0034] After doping with Ti and introducing a buffer layer, the thermal conductivity remains at a high level, which is beneficial to the thermoelectric conversion efficiency.

[0035] Table 2: Mechanical Strength and Stress Relief Capacity

[0036] Test conditions: thermal cycling range -40℃ ~ 200℃, holding time 15min, heating / cooling rate 10℃ / min.

[0037] Data Analysis: In Example 1, the shear strength showed almost no decrease after 300 severe thermal shocks. This is because the corrugated indium foil underwent plastic deformation, absorbing the shear stress caused by CTE mismatch.

[0038] In the comparative example, under the same conditions, due to the large difference between Sn-Ag-Cu solder and ceramic CTE, and the formation of brittle IMC (intermetallic compound), the strength dropped sharply, and a large number of cracks appeared at the interface.

[0039] 4. Experimental Conclusions Low impedance verification: By employing nanocrystalline / amorphous structures and gradient design, the contact resistivity was successfully controlled at 2.0 × 10⁻⁶. -6 Below Ω·cm, it is significantly superior to traditional brazing.

[0040] Stress relief verification: The introduced corrugated indium foil, porous foam metal or high-entropy alloy buffer layer (claims 6, 7) exhibits excellent plastic deformation capability in thermal cycling, enabling the device to retain more than 90% of the interfacial bonding force after 500 cycles from -40°C to 200°C.

[0041] Reliability verification: The micro-nano structured pads and active element doping generated strong mechanical interlocking and chemical bonding; the diffusion barrier layer effectively suppressed element interdiffusion.

[0042] In summary, this invention breaks the traditional material contradiction of "strong but not conductive, conductive but not strong" by spatially compositing highly conductive nanomaterials with highly ductile / low modulus materials. Utilizing the plastic deformation of the buffer layer, pore collapse, the activation of the slip system of the high-entropy alloy, and the flow of liquid metal, it achieves multi-level stress dissipation from the microscopic to the macroscopic level. Through micro-nano structuring, active element doping, and the introduction of diffusion barrier layers, it significantly suppresses inter-diffusion of interfacial elements and void growth, extending the service life of the device under high temperature and high current, thus meeting the needs of personnel. Therefore, the composite connection structure proposed in this invention perfectly solves the technical challenge of achieving both "low resistance" and "high reliability" in thermoelectric device packaging, possessing extremely high industrial application value.

[0043] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A composite connection structure for thermoelectric device encapsulation, characterized in that, include: Thermoelectric conversion substrate (1) has metallized pads on its upper surface; Thermoelectric leg assembly (2) includes N-type thermoelectric leg and P-type thermoelectric leg, one end of the thermoelectric leg assembly (2) is correspondingly disposed with respect to the metallized pad; A low-impedance connection layer (3) is disposed between the metallized pad and the thermoelectric leg assembly (2) to reduce contact resistance. The low-impedance connection layer (3) contains a highly conductive nanocrystalline metal or amorphous alloy material. A stress relief buffer layer (4) is embedded or covers the contact interface between the low impedance connection layer (3) and the thermoelectric leg assembly (2), or is located between the low impedance connection layer (3) and the metallized pad. The stress relief buffer layer (4) is made of a conductive material with high plastic deformation capacity or low Young's modulus. The low-impedance connection layer (3) provides the main current transmission channel, and the stress relief buffer layer (4) is used to absorb the shear stress and thermal stress caused by the mismatch between the thermoelectric leg and the substrate due to the thermal expansion coefficient.

2. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The low-impedance connection layer (3) is a gradient composite structure. From the side near the thermoelectric leg assembly (2) to the side near the metallized pad, the grain size is distributed in a gradient increasing or decreasing pattern. The material of this layer is selected from nano-silver, nano-copper or copper-graphene composite coating.

3. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The low-impedance connecting layer (3) is doped with trace amounts of active elements, including titanium, chromium, zirconium or rare earth element cerium, with a total doping amount of 0.1% to 5% by mass percentage, which is used to enhance the interfacial bonding force and anti-oxidation performance between the low-impedance connecting layer (3) and the thermoelectric leg material.

4. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The thickness of the low-impedance connection layer (3) is controlled at... to Between, and its resistivity at 25℃ is lower than This is to ensure that Joule heating generated when a large current passes through is minimized.

5. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The surface of the metallized pad is roughened or micro / nano-structured to form micropores or pits, and a portion of the material of the low-impedance connection layer (3) is filled in the micropores or pits.

6. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The stress relief buffer layer (4) is a porous foam metal structure or a corrugated metal foil, the material of which is selected from pure indium, pure tin or indium-tin alloy, and its porosity is 10%~40%, or the corrugation amplitude is This provides deformation space perpendicular to the interface direction.

7. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The stress relief buffer layer (4) comprises a high-entropy alloy material, the general formula of which is: , where 0≤ ≤1.5, this layer has a face-centered cubic (FCC) or body-centered cubic (BCC) solid solution structure, which utilizes its lattice distortion effect to hinder crack propagation and release stress through the slip system.

8. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, The stress relief buffer layer (4) is a liquid metal composite material, which is composed of liquid gallium indium tin alloy Galinstan microcapsules dispersed in a solid conductive polymer matrix. During thermal cycling, the liquid microcapsules undergo reversible deformation to dissipate the accumulated thermal stress.

9. The composite connection structure for thermoelectric device encapsulation according to claim 1, characterized in that, It also includes an interface diffusion barrier layer (5), which is disposed between the low impedance connection layer (3) and the stress relief buffer layer (4), or between the metallized pad and the low impedance connection layer (3). The diffusion barrier layer (5) is made of titanium nitride, tungsten carbide or molybdenum, and is used to prevent tellurium or bismuth elements in the thermoelectric leg material from diffusing into the metal layer.

10. A method for preparing a composite connection structure for thermoelectric device encapsulation, comprising: S1, substrate Pretreatment: The metallized pads of the thermoelectric conversion substrate are subjected to plasma cleaning and micro-etching to remove the surface oxide layer and increase the surface roughness; S2. Stress buffer layer preparation: On the metallized pad or thermoelectric leg contact surface, a stress release buffer layer material is deposited by magnetron sputtering, electrochemical deposition or 3D printing technology, and pre-forming treatment is performed, such as corrugation or foaming to create pores. S3, Low impedance layer co-deposition: On the surface of the stress relief buffer layer, a low impedance connection layer (3) material is deposited using pulse electrodeposition or vacuum thermal evaporation technology, and the deposition parameters are controlled to form a nanocrystalline or amorphous structure. S4. Component assembly: Place the hot end of the thermoelectric leg assembly (2) with the low impedance connection layer and apply a certain pre-pressure. S5. Heat treatment bonding: Hot pressing sintering or discharge plasma sintering is carried out in a protective atmosphere or vacuum environment. The sintering temperature is lower than the melting point of the thermoelectric leg material but higher than the recrystallization temperature of the low impedance connection layer (3) material. The holding time is 5min~60min, so that the low impedance connection layer (3) forms a metallurgical bond with the two side interfaces. At the same time, the stress buffer layer undergoes plastic rheological filling of the interface microvoids. S6. Cooling: Slowly cool the furnace or control the cooling rate to release residual stress and complete the encapsulation.

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