Gradient composite diamond cooling fin and preparation method thereof

Abstract

The invention discloses a gradient composite diamond cooling fin and a preparation method thereof, and relates to the technical field of thermal management, in particular to the gradient composite diamond cooling fin and the preparation method thereof. The problems of high thermal resistance and easy layering caused by thermal expansion mismatch of diamond and a metal matrix and poor interface wetting in heat dissipation of high-heat-flux devices such as power devices and lasers are solved. The invention provides a gradient composite diamond cooling fin and a preparation method thereof. The cooling fin sequentially comprises a polycrystalline CVD diamond functional layer, a Ti-W-Ni component gradient transition layer and a metal heat dissipation base layer with a micron-sized groove from a heat source side to a heat dissipation side, and a continuous gradient layer is formed by magnetron sputtering and is subjected to brazing composite in vacuum; and the diamond layer is deposited through microwave plasma CVD and is subjected to periodic secondary nucleation / etching and polishing. The structure integrates mechanical occlusion and metallurgical bonding, interface thermal resistance can be reduced, and bonding strength and thermal cycle reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of thermal management technology, specifically to a gradient composite diamond heat sink and its preparation method. Background Technology

[0002] As electronic devices such as power devices, lasers, LED packages, CPUs, and GPUs develop towards higher power density and miniaturization, the heat generated per unit area of ​​these devices continues to increase. If the heat cannot be quickly diffused and dissipated from the heat source area, it will lead to increased junction temperature, thermal stress accumulation, performance degradation, or even failure.

[0003] Diamond materials possess extremely high thermal conductivity, which can significantly enhance heat conduction and diffusion capabilities when used as heat sinks or heat spreaders. However, the large difference in thermal expansion coefficients between diamond and commonly used metal substrates, interfacial wetting, and bonding difficulties make direct bonding prone to problems such as interfacial cracking, delamination, and peeling under thermal cycling or impact conditions. Furthermore, using simple metallization or a single transition layer for bonding often introduces additional interfacial thermal resistance, making it difficult to achieve both high-strength bonding and low-thermal-resistance heat transfer. Summary of the Invention

[0004] To achieve the above objectives, the technical solution provided by the present invention is as follows: a gradient composite diamond heat sink, wherein the Ti element content in the Ti-W-Ni gradient alloy layer varies from high to low along the thickness direction, and the Ni element content varies from low to high; the metal heat dissipation base layer has a micron-level groove structure on one side opposite to the Ti-W-Ni gradient transition layer for forming a mechanical interlock with the Ti-W-Ni gradient transition layer.

[0005] Furthermore, the diamond functional layer is a polycrystalline CVD diamond material with a thickness of 5–50 μm, a thermal conductivity of not less than 1800 W / (m·K), and a surface roughness of not more than 1 μm.

[0006] Furthermore, the groove depth in the micron-level groove structure on the surface of the metal heat dissipation substrate is 50–200 μm, and the groove width is 100–300 μm.

[0007] Furthermore, the thickness of the Ti-W-Ni gradient transition layer is 50–200 μm.

[0008] Furthermore, the metal heat dissipation base layer is made of aluminum alloy and has a thickness of 1-5 mm.

[0009] Furthermore, the Ti element content decreases from about 60% to about 10%, and the Ni element content increases from about 10% to about 60%.

[0010] The present invention also provides a technical solution: a method for preparing a gradient composite diamond heat sink, comprising the following steps: S1: Preparation of diamond functional layer: Polycrystalline diamond film is deposited on substrate using microwave plasma CVD process; S2: Preparation of gradient transition layer: A Ti-W-Ni alloy layer is deposited stepwise on the surface of the diamond functional layer by magnetron sputtering, so that the Ti content in the gradient transition layer gradually decreases and the Ni content gradually increases along the thickness direction; S3: Composite molding: The stacked structure with the deposited diamond functional layer and gradient transition layer is brazed to the metal heat dissipation substrate with pre-fabricated micron-level grooves in a vacuum to obtain the gradient composite diamond heat sink.

[0011] Furthermore, during the deposition process of S1, a secondary nucleation treatment is periodically performed. The secondary nucleation treatment includes increasing the methane flow rate to 30-40 sccm and continuing for 15-20 min, while simultaneously performing hydrogen / argon plasma etching for 8-10 min.

[0012] Furthermore, the sputtering atmosphere pressure of S2 is controlled at 0.3 to 0.5 Pa, the deposition temperature is controlled at 200 to 300 °C, and the Ti content is gradually reduced and the Ni content is gradually increased by adjusting the power of the titanium target and the nickel target in stages, thereby forming a continuous compositional gradient structure along the thickness direction.

[0013] Furthermore, in step S3, the vacuum brazing temperature is 850–950°C, the holding time is 30–60 min, and the temperature is cooled at a rate of 5–10°C / min after brazing.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves a smooth transition in thermal expansion properties and interfacial compatibility by setting a Ti-W-Ni composition gradient transition layer between the diamond functional layer and the metal heat dissipation substrate, so that the Ti content gradually decreases and the Ni content gradually increases along the thickness direction. At the same time, the continuous gradient structure is obtained by magnetron sputtering and metallurgical bonding is achieved by vacuum brazing. This effectively reduces the interfacial thermal resistance and contact instability caused by the abrupt interface at the diamond-metal interface, so that heat can be conducted more efficiently from the diamond high thermal conductivity layer to the metal substrate and further diffused, resulting in higher overall heat dissipation efficiency and lower temperature rise.

[0015] This invention prefabricates a micron-level groove structure on the surface of a metal heat dissipation substrate, enabling the gradient transition layer and the metal substrate to form a stable composite interface of mechanical interlocking and metallurgical bonding after brazing. This enhances the interface's shear resistance and peel resistance. Furthermore, the stress relief effect of the gradient transition layer reduces stress concentration caused by thermal expansion mismatch during thermal cycling, reducing the risk of failures such as interface cracking, delamination, and peeling. This improves the structural reliability and service life of the heat sink under high temperature, thermal shock, and long-term thermal cycling conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the heat sink structure of the present invention; Figure 2 This is a flowchart of the heat sink preparation method of the present invention.

[0017] In the figure: 1. Diamond functional layer; 2. Ti-W-Ni gradient alloy transition layer; 3. Metal heat dissipation base layer. Detailed Implementation

[0018] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed merely to enable those skilled in the art to better understand and implement the subject matter described herein, and are not intended to limit the scope, applicability, or examples set forth in the claims. The function and arrangement of the elements discussed may be changed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the various examples. For example, the described methods may be performed in a different order than described, and steps may be added, omitted, or combined. Furthermore, features described in some examples may be combined in other examples.

[0019] As used herein, the term "comprising" and its variations are open terms meaning "including but not limited to". The term "based on" means "at least partially based on". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other definitions, whether explicit or implicit, may be included below. Unless explicitly indicated by the context, the definition of a term shall remain consistent throughout the specification.

[0020] Example 1 Please see Figure 1-2 The present invention provides a technical solution: a gradient composite diamond heat sink, wherein the Ti element content in the Ti-W-Ni gradient alloy layer varies from high to low along the thickness direction, and the Ni element content varies from low to high; the metal heat dissipation base layer has a micron-level groove structure on one side opposite to the Ti-W-Ni gradient transition layer for forming a mechanical interlock with the Ti-W-Ni gradient transition layer.

[0021] Furthermore, the diamond functional layer is a polycrystalline CVD diamond material with a thickness of 5–50 μm, a thermal conductivity of not less than 1800 W / (m·K), and a surface roughness of not more than 1 μm.

[0022] Furthermore, the groove depth in the micron-level groove structure on the surface of the metal heat dissipation substrate is 50–200 μm, and the groove width is 100–300 μm.

[0023] Furthermore, the thickness of the Ti-W-Ni gradient transition layer is 50–200 μm.

[0024] Furthermore, the metal heat dissipation base layer is made of aluminum alloy and has a thickness of 1-5 mm.

[0025] Furthermore, the Ti element content decreases from about 60% to about 10%, and the Ni element content increases from about 10% to about 60%.

[0026] The schematic diagram shows the structure from top to bottom as follows: a diamond functional layer, a Ti-W-Ni gradient transition layer, and a metal heat dissipation base layer. The diamond functional layer uses polycrystalline CVD diamond, with a thickness of 50–500 μm, a thermal conductivity ≥1800 W / (m·K), and a surface roughness ≤1 μm; this layer is responsible for efficient heat conduction and direct contact with the chip. The transition layer is a Ti-W-Ni gradient alloy, with the Ti content gradually decreasing from 60% to 10% and the Ni content gradually increasing from 10% to 60% along the thickness direction. A suitable amount of W is present to smooth the differences in thermal expansion coefficients. The metal heat dissipation base layer is a 1–5 mm thick metal plate with micron-level grooves machined on the side opposite the Ti-W-Ni layer to enhance mechanical bonding. The grooves can be a unidirectional strip array or an interlaced grid, allowing the solder to solidify within the grooves to form a spike structure, thereby dispersing interfacial shear stress.

[0027] The gradual variation in titanium and nickel in the gradient transition layer ensures a smooth transition in the coefficient of thermal expansion between the diamond layer and the metal substrate, significantly reducing interfacial stress generated during thermal cycling. The groove structure allows the solder to form metal spikes after curing, engaging with the transition layer and geometrically dispersing the shear load at the interface. This, combined with metallurgical diffusion, results in enhanced interfacial bonding strength and significantly improved shear strength. The overall structure substantially reduces the thermal resistance of traditional diamond / metal interfaces, improving thermal conductivity and reliability.

[0028] To ensure that the structure of the embodiment meets the requirements, the following items are tested and judged according to the standards in Table 1.

[0029]

[0030] Table 1 The testing items and judgment criteria are shown in Table 2. Measurements of diamond layer thickness, surface roughness, and thermal conductivity are required; SEM / EDS scanning of the gradient layer composition along the thickness direction is necessary; XRD analysis of the interface is required; and interfacial thermal resistance and tensile / shear strength tests are required for the brazed composite.

[0031]

[0032] Table 2 The metal substrate can be made of high thermal conductivity aluminum alloy; the grooves can be in the form of parallel strips or interlaced grids; the Ti-W-Ni layer can also be replaced by magnetron sputtering by co-target sputtering or chemical plating.

[0033] Example 2 This invention also provides a technical solution: a method for preparing a gradient composite diamond heat sink, comprising the following steps: S1: Preparation of diamond functional layer: Polycrystalline diamond film is deposited on substrate using microwave plasma CVD process; S2: Preparation of gradient transition layer: A Ti-W-Ni alloy layer is deposited stepwise on the surface of the diamond functional layer by magnetron sputtering, so that the Ti content in the gradient transition layer gradually decreases and the Ni content gradually increases along the thickness direction; S3: Composite molding: The stacked structure with the deposited diamond functional layer and gradient transition layer is brazed to the metal heat dissipation substrate with pre-fabricated micron-level grooves in a vacuum to obtain the gradient composite diamond heat sink.

[0034] Furthermore, during the deposition process of S1, a secondary nucleation treatment is periodically performed. The secondary nucleation treatment includes increasing the methane flow rate to 30-40 sccm and continuing for 15-20 min, while simultaneously performing hydrogen / argon plasma etching for 8-10 min.

[0035] Furthermore, the sputtering atmosphere pressure of S2 is controlled at 0.3 to 0.5 Pa, the deposition temperature is controlled at 200 to 300 °C, and the Ti content is gradually reduced and the Ni content is gradually increased by adjusting the power of the titanium target and the nickel target in stages, thereby forming a continuous compositional gradient structure along the thickness direction.

[0036] Furthermore, in step S3, the vacuum brazing temperature is 850–950°C, the holding time is 30–60 min, and the temperature is cooled at a rate of 5–10°C / min after brazing.

[0037] Based on the heat sink structure shown in Example 1, this example uses the following process to prepare the heat sink: 1. S1 - Preparation of diamond functional layers: 1.1 Cleaning the substrate: Use a 250μm thick molybdenum or silicon wafer as the substrate, ultrasonically clean it and dry it in an inert atmosphere.

[0038] 1.2 CVD Deposition: The substrate was placed in a microwave plasma CVD system, and the vacuum was evacuated to ≤5×10^-4 Pa. H2 gas was introduced at 400 sccm to establish hydrogen plasma. The substrate was then heated to approximately 850℃.

[0039] 1.3 Deposition Preparation: The microwave source was activated, and CH4 gas was introduced at 30–40 sccm to deposit a polycrystalline diamond film. During deposition, a secondary nucleation was performed every 60–90 minutes: the CH4 flow rate was increased to 30–40 sccm and maintained for 15–20 minutes to generate more diamond nuclei; simultaneously, a hydrogen / argon mixed plasma was activated for etching for 8–10 minutes to remove amorphous carbon and improve film density. Then, the normal deposition atmosphere was restored, and deposition continued. This cycle was repeated until the desired thickness was obtained.

[0040] 1.4 Post-processing: After deposition, turn off the CVD power and allow the furnace to cool to room temperature. Remove the sample and polish the diamond film surface sequentially with a diamond polishing disc until the roughness Ra ≤ 1 μm. Use SEM to measure the film thickness and microstructure to ensure that the diamond layer is intact and free of macroscopic cracks.

[0041] 2. S2 - Depositional gradient transition layer: 2.1 Clean the polished diamond film sample and mount it onto the multi-target magnetron sputtering system. Evacuate to ≤5×10^-4 Pa, introduce Ar gas, and control the working pressure at 0.3–0.5 Pa. Heat the sample stage to 200–300℃ and maintain the sample temperature to improve film quality.

[0042] 2.2 Stepwise Power Deposition: Ti and Ni-10%W alloy targets were loaded. Initially, only the Ti target was activated: the Ti target power was set to 150 W, and the NiW target power was set to 10–20 W, depositing an approximately 2 μm Ti-rich layer. Subsequently, the Ti target power was gradually reduced to 100 W, while the NiW target power was increased to 100 W, continuing deposition for another 2–3 μm to reduce the Ti content to approximately 30%. In the final stage, the Ti target power was reduced to 50 W, while the NiW target power remained at 100 W, depositing a 4–5 μm Ni-rich layer to increase the Ni content to approximately 60%. The total thickness of the deposited Ti-W-Ni layer was approximately 8–10 μm. Throughout the process, the deposition thickness was monitored in real time, and offline EDS point analysis was performed to verify that the Ti / Ni content gradient along the thickness conformed to the design range.

[0043] 3. S3-Vacuum Brazing Composite Molding: 3.1 Clean the surface of the metal heat dissipation base layer. Oxygen-free copper plates do not require pre-plating, while aluminum plates should be pre-plated with nickel or tin to improve wettability. Pre-fabricate micron-level grooves. Align and stack the diamond / transition layer composite sheet with the metal base layer, with the groove direction parallel to the diamond. A small amount of active solder can be placed at the interface.

[0044] 3.2 Place the stacked components in a vacuum brazing furnace, evacuate to ≤1×10^-3 Pa, and heat to a brazing temperature of 900℃ at a rate of 8–10℃ / min. Hold at 900℃ for 30–60 minutes to allow the brazing filler metal to fully melt and wet the groove. Then slowly cool to room temperature at a rate of 5–10℃ / min. The process time / temperature curves are shown in Table 3.

[0045] Table 3 By employing the "stepwise target power adjustment" strategy in step S2 above, a continuous gradient is achieved, with Ti content decreasing from 60% to 10% and Ni content increasing from 10% to 60%. If pulse-alternating deposition is used, Ti and NiW targets can be switched on and off alternately, forming ultrafine layers over time, thereby obtaining a compositional distribution that resembles a continuous transition.

[0046] Throughout the process, the pretreatment of the silicon / molybdenum substrate, CVD deposition rate, diamond film thickness, sputtering power, and atmosphere parameters must be monitored. The final wafer should undergo all the tests listed in Table 2 above. Specifically, after S2, the transition layer profile should be inspected using SEM / EDS to confirm the Ti / Ni gradient distribution; after S3, the brazing fill, groove filling, and the presence of cracks or voids at the bonding interface should be checked. If the test results are inconsistent, the corresponding process parameters must be readjusted.

[0047] Those skilled in the art will understand that the various embodiments disclosed above can be modified and altered in various ways without departing from the spirit of the invention. Therefore, the scope of protection of this invention should be defined by the appended claims.

[0048] It should be noted that not all steps and units in the above processes are necessary; some steps or units can be omitted as needed. The execution order of each step is not fixed and can be determined as required. The device structure described in the above embodiments can be a physical structure or a logical structure. That is, some units may be implemented by the same physical entity, or some units may be implemented by multiple physical entities, or they may be jointly implemented by certain components in multiple independent devices.

[0049] The specific embodiments described above are exemplary embodiments, but do not represent all embodiments that can be implemented or fall within the scope of the claims. The term "exemplary" as used throughout this specification means "serving as an example, instance, or illustration" and does not imply that it is "preferred" or "advantageous" compared to other embodiments. Specific details are included to provide an understanding of the described techniques. However, these techniques can be practiced without these specific details. In some instances, well-known structures and apparatuses are shown in block diagram form to avoid obscuring the concepts of the described embodiments.

[0050] The foregoing description of this disclosure is provided to enable any person skilled in the art to implement or use this disclosure. Various modifications to this disclosure will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations without departing from the scope of this disclosure. Therefore, this disclosure is not limited to the examples and designs described herein, but is consistent with the widest scope of the principles and novel features disclosed herein.

Claims

1. A gradient composite diamond heat sink, comprising a diamond functional layer (1), a Ti-W-Ni gradient transition layer (2), and a metal heat dissipation base layer (3), characterized in that: The Ti element content in the Ti-W-Ni gradient alloy layer (1) varies from high to low along the thickness direction, and the Ni element content varies from low to high. The metal heat dissipation base layer (3) has a micron-level groove structure on one side opposite to the Ti-W-Ni gradient transition layer (2) for forming a mechanical engagement with the Ti-W-Ni gradient transition layer (2).

2. The gradient composite diamond heat sink according to claim 1, characterized in that: The diamond functional layer (1) is a polycrystalline CVD diamond material with a thickness of 5 to 50 μm, a thermal conductivity of not less than 1800 W / (m·K), and a surface roughness of not more than 1 μm.

3. The gradient composite diamond heat sink according to claim 1, characterized in that: The groove depth in the micron-level groove structure on the surface of the metal heat dissipation base layer (3) is 50-200μm, and the groove width is 100-300μm.

4. The gradient composite diamond heat sink according to claim 1, characterized in that: The thickness of the Ti-W-Ni gradient transition layer (2) is 50-200 μm.

5. The gradient composite diamond heat sink and its preparation method according to claim 1, characterized in that: The metal heat dissipation base layer (3) is made of aluminum alloy and has a thickness of 1 to 5 mm.

6. The gradient composite diamond heat sink according to claim 1, characterized in that: The Ti content decreases from about 60% to about 10%, and the Ni content increases from about 10% to about 60%.

7. A method for preparing a gradient composite diamond heat sink, characterized in that: Includes the following steps: S1: Preparation of diamond functional layer: Polycrystalline diamond film is deposited on substrate using microwave plasma CVD process; S2: Preparation of gradient transition layer: A Ti-W-Ni alloy layer is deposited stepwise on the surface of the diamond functional layer by magnetron sputtering, so that the Ti content in the gradient transition layer gradually decreases and the Ni content gradually increases along the thickness direction; S3: Composite molding: The stacked structure with the deposited diamond functional layer and gradient transition layer is brazed to the metal heat dissipation substrate with pre-fabricated micron-level grooves in a vacuum to obtain the gradient composite diamond heat sink.

8. The method for preparing a gradient composite diamond heat sink according to claim 7, characterized in that: During the deposition process of S1, a secondary nucleation treatment is periodically performed. The secondary nucleation treatment includes increasing the methane flow rate to 30-40 sccm and continuing for 15-20 min, while performing hydrogen / argon plasma etching for 8-10 min.

9. The method for preparing a gradient composite diamond heat sink according to claim 7, characterized in that: The sputtering atmosphere pressure of S2 is controlled at 0.3 to 0.5 Pa, the deposition temperature is controlled at 200 to 300 °C, and the Ti content is gradually reduced and the Ni content is gradually increased by adjusting the power of the titanium target and the nickel target in stages, thereby forming a continuous compositional gradient structure along the thickness direction.

10. The method for preparing a gradient composite diamond heat sink according to claim 7, characterized in that: In step S3, the vacuum brazing temperature is 850–950°C, and the holding time is 30–60 min. After brazing, the temperature is cooled at a rate of 5–10°C / min.

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