A w-aln-w layered substrate and a method for manufacturing the same

Abstract

The application discloses a W-AlN-W layered substrate and a preparation method thereof, and relates to the technical field of ceramic substrate precision preparation. The layered substrate structure is sequentially provided with a W surface layer, a gradient transition layer and an AlN core layer from the surface layer to the core layer. The W surface layer and the gradient transition layer are symmetrically arranged on the two sides of the AlN core layer, forming a symmetric structure of the W surface layer-gradient transition layer-AlN core layer-gradient transition layer-W surface layer. The gradient transition layer is a mixture of W and AlN. The layered substrate is prepared by powder metallurgy and integrated molding under pressure. The tungsten surface layer is symmetrically arranged, so that the tungsten surface layer can be directly combined with a copper layer without a titanium transition layer. The problems of bonding force attenuation and thermal conductivity reduction caused by the TiN layer are avoided, and the bonding strength of the copper layer is significantly improved. The gradient transition layer realizes the continuous transition of the composition and the thermal expansion coefficient of AlN and tungsten, effectively alleviates the interface stress concentration, and avoids the problem of cracking of the substrate during sintering or use.

Description

Technical Field

[0001] This invention relates to the field of precision ceramic substrate fabrication technology, specifically to a W-AlN-W layered substrate and its fabrication method. Background Technology

[0002] Aluminum nitride (AlN) ceramic is a core substrate for third-generation semiconductor packaging, possessing advantages such as a theoretical thermal conductivity of 320 W / (m·K), excellent electrical insulation properties, a thermal expansion coefficient matching that of semiconductor chips, and low dielectric loss. Compared to alumina ceramic and silicon carbide ceramic, it has irreplaceable application advantages in the heat dissipation of high-power devices. However, pure AlN ceramic has inherent technical defects that severely limit its high-end industrial applications.

[0003] On the one hand, pure AlN ceramics have weak mechanical properties, with a bending strength of only 300~400MPa. They are brittle and have poor impact resistance. During device packaging and welding, mechanical assembly, and high and low temperature thermal cycling, they are prone to chipping, cracking, and breakage. The substrate's load-bearing capacity cannot meet the long-term use requirements under high power and high vibration conditions.

[0004] On the other hand, poor compatibility with metallized packaging is a core technical bottleneck for AlN ceramic substrates. In practical packaging applications, a composite copper conductive layer is usually required on the surface of the AlN ceramic substrate to achieve power transmission and auxiliary heat dissipation. However, the wettability of molten copper and AlN ceramic is extremely poor, and a direct metallurgical bond cannot be formed. The copper layer is very easy to fall off and peel off. Therefore, the bonding strength between the metallic copper layer and the AlN ceramic layer is the core indicator that determines the reliability of the substrate.

[0005] The current industry-standard solution involves using active metal brazing (AMB), sputtering, and other processes to add a titanium (Ti) transition layer between the AlN ceramic and the copper layer. The TiN chemical bonding layer is generated by the high-temperature reaction of titanium with AlN, thus achieving an indirect bond between the ceramic and the copper.

[0006] This traditional titanium transition layer process has several inherent defects, making it difficult to balance processability and product performance: 1. Significantly reduced thermal conductivity: The thermal conductivity of the TiN layer formed by the titanium reaction is only 30~60W / (m·K), which is much lower than that of AlN ceramic substrate. This will form a thermal bottleneck at the substrate interface, significantly reducing the overall heat dissipation efficiency, resulting in increased operating temperature, performance degradation, and shortened lifespan of power devices. 2. Complex process and high production cost: The preparation of titanium transition layer requires precision equipment such as high-precision vacuum sputtering, evaporation coating, and precise temperature-controlled brazing. The process window is narrow and the requirements for vacuum degree, temperature and atmosphere are strict. It is very easy to have defects such as titanium layer oxidation, uneven coating and interface voids, resulting in low yield and high cost of large-scale production. 3. Poor interface reliability and short service life: The thermal expansion coefficients of TiN, AlN and copper are significantly different. During the long-term high and low temperature cycle operation of the device, stress concentration will continue to occur at the interface, and failure problems such as delamination, peeling and cracking will gradually occur, which cannot meet the service requirements of long life and high reliability of high-end devices. 4. Poor process compatibility: Traditional titanium transition layer processes have limited adaptability and cannot be compatible with some high-speed electroplating and low-temperature brazing processes, resulting in insufficient packaging flexibility.

[0007] In summary, existing AlN ceramic substrate technologies suffer from multiple problems, including poor mechanical properties, cumbersome metallization processes, high thermal conductivity losses, and low interface reliability. The industry urgently needs a new type of ceramic substrate and its preparation process that can simultaneously achieve high thermal conductivity, high strength, high interface stability, simple processing, and low cost. Summary of the Invention

[0008] This invention overcomes the shortcomings of the prior art by proposing a W-AlN-W layered substrate and its preparation method, which solves the problems of low mechanical strength of traditional AlN ceramic substrates and poor wettability between copper and AlN ceramics, which prevent direct bonding.

[0009] This invention is achieved through the following technical solution: A W-AlN-W layered substrate is disclosed, wherein the layered substrate structure consists of a W surface layer, a gradient transition layer, and an AlN core layer, arranged sequentially from the surface layer to the core layer. The W surface layer and the gradient transition layer are symmetrically arranged on both sides of the AlN core layer, forming a symmetrical structure of W surface layer-gradient transition layer-AlN core layer-gradient transition layer-W surface layer. The gradient transition layer is a mixture of W and AlN. From the W layers on both sides to the gradient transition layer and then to the AlN core layer, the W content gradually decreases from 100% to 0% by mass, while the AlN content gradually increases from 0% to 100% by mass.

[0010] Preferably, the thickness of the W surface layer is 5%-15% of the total thickness of the substrate, the thickness of the single-sided gradient transition layer is 5%-10% of the total thickness of the substrate, and the thickness of the AlN core layer is 30%-70% of the total thickness of the substrate; the total thickness of the substrate is 0.2-2.0 mm, wherein the thickness of the tungsten surface layer is controlled at 0.05-0.3 mm.

[0011] Preferably, the W surface layer, gradient transition layer, and AlN core layer are mixed with sintering aids.

[0012] Preferably, the sintering aid is Y2O3 or Sm2O3, and the amount of sintering aid added is 0.1%-2.0% of the total mass of the corresponding layer powder.

[0013] A method for preparing a W-AlN-W layered substrate, which employs powder metallurgy and pressure molding.

[0014] Preferably, the corresponding powders are first laid in layers according to the structural order, and then pressed to form a green substrate; then the green substrate is sintered at high temperature to obtain a densified substrate.

[0015] Preferably, before pressure molding, the W powder and AlN powder are vacuum dried separately, and W layer, gradient transition layer and AlN core layer powder are prepared separately. The mass ratio of W powder to AlN powder in the gradient transition layer is 1:1. The prepared powder layers are then ultrasonically dispersed and spheroidized.

[0016] Preferably, the vacuum drying temperature is 120-150℃, the time is 2-4 h; the ball-to-material ratio is 5:1-10:1, the rotation speed is 200-300 r / min, and the ball milling time is 2-6 h.

[0017] Preferably, the pressure molding is dry pressing, injection molding, or cold isostatic pressing, with a molding pressure of 50-200 MPa and a holding time of 1-5 min.

[0018] Preferably, the sintering method is vacuum or inert gas protected hot pressing sintering, the heating rate is 10-20℃ / min, the temperature is raised to 1600-2000℃, the holding temperature is 3-6 h, and the sintering pressure is 1-30MPa.

[0019] The beneficial effects of this invention compared to the prior art are as follows: 1. Thoroughly optimize thermal conductivity and eliminate heat dissipation bottlenecks: This invention abandons the low thermal conductivity TiN transition layer and utilizes the high thermal conductivity AlN core layer to ensure the basic heat dissipation performance of the substrate. Combined with a tungsten surface layer with excellent compatibility with copper, and an interface-free low thermal conductivity interlayer, the overall thermal conductivity of the substrate is greatly improved, effectively solving the problems of overheating and performance degradation of power devices. This invention, through the symmetrical arrangement of the tungsten surface layer, can be directly composited with the copper layer without the need for a titanium transition layer, avoiding the problems of adhesion attenuation and thermal conductivity reduction caused by the TiN layer. The bonding strength of the copper layer is significantly improved, and it is not easy to fall off or peel off under thermal cycling conditions, resulting in higher long-term reliability of the substrate.

[0020] 2. Significantly improved mechanical and thermal shock resistance: The introduction of a high-performance tungsten metal layer (tungsten bending strength ≥1000MPa) and a composite gradient transition structure increases the overall bending strength of the substrate to over 500MPa, far superior to pure AlN ceramic substrates; the gradient transition layer achieves a continuous transition in composition and thermal expansion coefficient between AlN and tungsten, effectively alleviating interface stress concentration and preventing the substrate from cracking during sintering or use; the finished substrate combines thermal conductivity, mechanical properties, and electrical conductivity; long-term service reliability is significantly enhanced.

[0021] 3. Simplified process and reduced mass production cost: It eliminates the need for complex metallization pretreatment processes such as titanium layer sputtering and brazing. It adopts a W-AlN-W functional gradient structure formed by powder metallurgy, eliminating the need for separate titanium layer cladding and metallization processes, thus shortening the process flow. The tungsten powder and AlN powder raw materials used are readily available, which reduces processing costs compared to the titanium transition layer process, making it suitable for large-scale mass production.

[0022] 4. Wide packaging adaptability and strong compatibility: The finished tungsten surface layer can be directly bonded to the copper layer with high strength metallurgy, perfectly compatible with existing mainstream packaging processes such as electroplating, hot-press copper cladding, and vacuum brazing. There is no need to adjust existing production equipment and process parameters. It can be widely used in a variety of high-requirement scenarios such as IGBT, SiC power modules, RF devices, and aerospace electronics, and has broad market application prospects. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the W-AlN-W layered substrate preparation method in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the W-AlN-W layered substrate in Embodiment 1 of the present invention; Figure 3 This is a SEM image of the fracture surface of the W-AlN-W layered substrate in Embodiment 1 of the present invention; Figure 4 This is a SEM image of the polished surface of the W-AlN-W layered substrate in Embodiment 1 of the present invention. Detailed Implementation

[0024] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0025] The technical solution of the present invention will be described in detail below through three sets of examples with different parameters and two sets of comparative examples. The purity, particle size and testing standards of the raw material powders in all examples and comparative examples are completely consistent.

[0026] Standardized experimental conditions: tungsten powder, AlN powder, and Y2O3 powder all had a purity of 99.9% and an average particle size of 1 μm; the test items included substrate density, room temperature thermal conductivity, bending strength, copper layer bonding strength, and number of thermal cycling failures; all sample sizes were standardized at 50mm × 50mm; and the test methods all adopted the national standard for testing electronic ceramic substrates. Example 1

[0027] This embodiment proposes a method for preparing a W-AlN-W layered substrate, which specifically includes the following steps: S1. Powder pretreatment: Tungsten powder, AlN powder and Y2O3 powder are vacuum dried at 120℃ for 3h to remove the moisture and impurities adsorbed on the powder surface, and then passed through a 200-mesh sieve for later use. Prepare W layer, transition sublayer, and AlN core layer powders according to the proportions in the table below: ; The prepared W layer, transition sublayer, and AlN core layer powders were added to three 100ml portions of anhydrous ethanol and ultrasonically dispersed for 30min each. Then, they were ball-milled in a planetary ball mill for 6h. The grinding balls were made of AlN, the ball-to-material ratio was 8:1, and the rotation speed was 250 r / min. After ball milling, the powders were vacuum dried at 120℃ for 3h and passed through a 200-mesh sieve to obtain uniformly dispersed W layer, transition sublayer, and AlN core layer powders. S2. Layered molding: The corresponding powders are laid in layers according to the structural sequence of "W layer - transition sublayer - AlN core layer - transition sublayer - W layer", and the green substrate is pressed by dry pressing process. The molding pressure is controlled at 120 MPa and the pressure is held for 3 min. During the molding process, it is ensured that the interfaces of each layer are tightly bonded and free from defects such as bubbles and cracks.

[0028] S3. Sintering and Densification: The green substrate is placed in a hot-pressing sintering furnace and sintered under argon protection at a heating rate of 15℃ / min until it reaches 1800℃. A pressure of 30 MPa is applied, and the temperature is held for 60 min. After cooling to room temperature, the sintered body is obtained. During sintering, the W layer diffuses and bonds with the adjacent transition sublayer, and the AlN core layer diffuses and bonds with the adjacent transition sublayer, achieving a continuous transition in composition and structure to form a gradient transition layer (see [link to relevant documentation]). Figure 3 This process ultimately forms a dense W-AlN-W layered substrate.

[0029] S4. Post-processing: The sintered body is cut into 50mm×50mm finished substrates and the surface is ground and polished to remove the surface oxide layer and impurities; the substrates can be cut and chamfered as required to obtain finished substrates of the target size.

[0030] In the finished substrate, from the W layers on both sides to the gradient transition layer, and then to the AlN core layer, the tungsten content gradually decreases from 100% to 0%; the AlN content gradually increases from 0% to 100% by mass percentage.

[0031] Depend on Figure 4 As can be seen, the interfaces of each layer of the finished substrate are clear and continuous, and the upper and lower W layers, transition sublayers and AlN core layers are tightly bonded without obvious cracks or other delamination defects. Stable metallurgical bonding is achieved between each layer, which verifies the interface reliability of the gradient structure under the preparation process of this invention.

[0032] Performance test results: The finished substrate has a density of 97.9%, a thermal conductivity of 143 W / (m·K), a bending strength of 542 MPa, and a copper layer bonding strength of 28.5 MPa; it showed no delamination, cracking, or failure after 1000 cycles of thermal cycling from -40℃ to 125℃. Example 2

[0033] This embodiment proposes a method for preparing a W-AlN-W layered substrate, which specifically includes the following steps: S1. Powder pretreatment: drying temperature 140℃, drying time 2.5h; Y2O3 addition amount of each layer 0.8%; ultrasonic dispersion 50min, ball-to-material ratio 10:1, rotation speed 280r / min, ball milling 5h, the remaining parameters are the same as in Example 1.

[0034] S2, Layered molding: Cold isostatic pressing is used, with a molding pressure of 180MPa and a holding pressure of 2min. The remaining parameters are the same as in Example 1.

[0035] S3. Sintering densification: Argon inert gas protection, heating rate 12℃ / min, sintering temperature 1900℃, holding time 5h, sintering pressure 20MPa.

[0036] S4. Post-processing: Precision polishing to ensure surface roughness ≤0.5μm.

[0037] Performance test results: substrate density 98.5%; thermal conductivity 148 W / (m·K); bending strength 498 MPa; copper layer bonding strength 27.8 MPa; no failure after 1000 thermal cycles. Example 3

[0038] This embodiment proposes a method for preparing a W-AlN-W layered substrate, which specifically includes the following steps: S1. Powder pretreatment: drying temperature 120℃, drying time 4h; Sm2O3 sintering aid addition amount of 1.5% in each layer; ultrasonic dispersion for 30min, ball-to-material ratio 5:1, rotation speed 220r / min, ball milling for 3h.

[0039] S2, Layered molding: Dry pressing, molding pressure 80MPa, holding pressure for 5min.

[0040] S3. Sintering densification: Vacuum sintering, heating rate 18℃ / min, sintering temperature 1750℃, holding time 3h, sintering pressure 20MPa.

[0041] S4. Post-processing: conventional grinding and polishing, and dimensional cutting.

[0042] Performance test results: substrate density 97.6%; thermal conductivity 122 W / (m·K); bending strength 568 MPa; copper layer bonding strength 29.2 MPa; no failure after 1000 thermal cycles.

[0043] Comparative Example 1 A 1.0 mm thick pure AlN ceramic substrate was prepared using industry-standard processes. A 0.5 μm titanium transition layer was then prepared on the surface by vacuum sputtering, followed by copper plating to prepare a metallized substrate. The entire process parameters were the best in the industry.

[0044] Performance test results: substrate density 96.2%; thermal conductivity 92 W / (m·K); bending strength 385 MPa; copper layer bonding strength 22.3 MPa; local delamination occurred after 620 thermal cycles.

[0045] Comparative Example 2 The total thickness of the substrate is 1.0 mm, and the overall thickness ratio is completely consistent with that of Example 1. The gradient transition layer is eliminated, and a sudden structure in which the tungsten layer and the AlN core layer are directly bonded is adopted. The preparation process, raw material parameters, and sintering conditions are completely consistent with those of Example 1.

[0046] Performance test results: substrate density 95.8%; thermal conductivity 115 W / (m·K); bending strength 452 MPa; copper layer bonding strength 24.6 MPa; interface microcracks appeared after 810 thermal cycles.

[0047] A comparison of the data from Examples 1-3 with Comparative Examples 1 and 2 clearly shows that: The gradient W-AlN-W layered substrate designed in this invention achieves significant improvements in all core performance aspects compared to traditional titanium transition layer processes and substrates without gradient abrupt structure. Specifically, thermal conductivity is improved by 32.6%~60.8%, bending strength by 29.4%~47.5%, copper layer bonding strength by 19.7%~30.9%, and thermal cycling life is improved by over 60%. Simultaneously, the gradient transition structure completely solves the problem of interlayer stress concentration, significantly optimizing substrate density and structural stability.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A W-AlN-W layered substrate, characterized in that, The layered substrate structure consists of a W surface layer, a gradient transition layer, and an AlN core layer, arranged sequentially from the surface layer to the core layer. The W surface layer and the gradient transition layer are symmetrically arranged on both sides of the AlN core layer, forming a symmetrical structure of W surface layer - gradient transition layer - AlN core layer - gradient transition layer - W surface layer. The gradient transition layer is a mixture of W and AlN. From the W layers on both sides to the gradient transition layer and then to the AlN core layer, the W content gradually decreases from 100% to 0% by mass, while the AlN content gradually increases from 0% to 100% by mass.

2. The W-AlN-W layered substrate according to claim 1, characterized in that, The thickness of the W surface layer is 5%-15% of the total substrate thickness, the thickness of the single-sided gradient transition layer is 5%-10% of the total substrate thickness, and the thickness of the AlN core layer is 30%-70% of the total substrate thickness; the total substrate thickness is 0.2-2.0 mm, of which the thickness of the tungsten surface layer is controlled at 0.05-0.3 mm.

3. The W-AlN-W layered substrate according to claim 1, characterized in that, Sintering aids are mixed in the W surface layer, gradient transition layer, and AlN core layer.

4. The W-AlN-W layered substrate according to claim 3, characterized in that, The sintering aid is Y2O3 or Sm2O3, and the amount of sintering aid added is 0.1%-2.0% of the total mass of the corresponding layer powder.

5. A method for preparing a W-AlN-W layered substrate according to any one of claims 1-4, characterized in that, It is formed by pressure molding using powder metallurgy.

6. The method for preparing a W-AlN-W layered substrate according to claim 5, characterized in that, First, the corresponding powders are laid in layers according to the structural order and then pressed to form a green substrate; then the green substrate is sintered at high temperature to obtain a densified substrate.

7. The method for preparing a W-AlN-W layered substrate according to claim 6, characterized in that, Before pressure molding, W powder and AlN powder are vacuum dried separately, and W layer, gradient transition layer and AlN core layer powder are prepared separately. The mass ratio of W powder to AlN powder in the gradient transition layer is 1:

1. The prepared powder layers are then ultrasonically dispersed and spheroidized.

8. The method for preparing a W-AlN-W layered substrate according to claim 7, characterized in that, The vacuum drying temperature is 120-150℃, and the time is 2-4 h; the ball-to-material ratio is 5:1-10:1, the rotation speed is 200-300 r / min, and the ball milling time is 2-6 h.

9. The method for preparing a W-AlN-W layered substrate according to claim 6, characterized in that, The pressure molding is dry pressing, injection molding, or cold isostatic pressing, with a molding pressure of 50-200 MPa and a holding time of 1-5 min.

10. The method for preparing a W-AlN-W layered substrate according to claim 6, characterized in that, The sintering method is vacuum or inert gas protected hot pressing sintering, with a heating rate of 10-20℃ / min, heating to 1600-2000℃, holding for 3-6 h, and a sintering pressure of 1-30MPa.

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