Flexible self-supporting diamond heat spreading film and method of making same

Abstract

The application discloses a flexible self-supporting diamond heat dissipation film and a preparation method thereof, and relates to the technical field of heat dissipation materials. In view of the problems of high heat flow density of power devices, 5G radio frequency and advanced packaging chips, strong anisotropy of traditional graphite films, poor insulation of metal foils, and easy aging and pumping out of silicone grease / gaskets to cause the increase of interface thermal resistance, the application provides the flexible self-supporting diamond heat dissipation film and the preparation method thereof. On the structure, 10-50 mu m nanocrystalline CVD diamond film is used as the main body, and 1-3 mu m polyimide surface modification layers are arranged on both sides to improve wet adhesion and environmental resistance. On the process, after the silicon substrate is cleaned and activated, a composite is formed through CVD deposition, self-supporting film is obtained by using the internal stress of the difference in thermal expansion of diamond / silicon, and the PI layer is coated and solidified on both sides. As a result, the flexible self-supporting diamond heat dissipation film has high thermal conductivity, thin and light weight, and can be repeatedly bent and mounted, reduces the interface thermal resistance, and improves the long-term heat dissipation reliability.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation materials technology, specifically to a flexible self-supporting diamond heat dissipation film and its preparation method. Background Technology

[0002] With the rapid development of high heat flux density devices such as power devices, 5G RF devices, advanced packaged chips, and lasers, these devices generate a large amount of heat within a small volume. If this heat cannot be dissipated in time, it can cause junction temperature rise, performance drift, decreased reliability, or even failure. Therefore, thermal management materials need to possess characteristics such as high thermal conductivity, low thermal resistance, and thinness, and be adaptable to various device morphologies and packaging structures.

[0003] Although graphite films have high in-plane thermal conductivity, they have limitations in terms of thickness, anisotropy, environmental resistance, and interfacial bonding stability; metal foils have good thermal conductivity but high density, poor insulation, and limited flexibility and resilience; thermal pads and silicone greases are susceptible to aging and pumping effects, resulting in increased interfacial thermal resistance during long-term use. Summary of the Invention

[0004] To achieve the above objectives, the present invention provides a technical solution as follows: a flexible self-supporting diamond heat dissipation film, wherein a polyimide surface modification layer is attached to both sides of the nanocrystalline CVD diamond film body, the nanocrystalline CVD diamond film body has a thickness of 10-50μm, an elongation at break of not less than 3%, and can be repeatedly bent 360° with a bending radius of not less than 5mm.

[0005] Furthermore, the grain size of the nanocrystalline CVD diamond film substrate is 50-200 nm, and the thermal conductivity is not less than 1600 W / (m·K).

[0006] Furthermore, the polyimide surface modification layer has a thickness of 1-3 μm and a surface contact angle of 85-95°.

[0007] Furthermore, the polyimide surface-modified layer is uniformly and continuously coated on both sides of the nanocrystalline CVD diamond film substrate.

[0008] Furthermore, the nanocrystalline CVD diamond film substrate does not crack after being folded at least 1000 times with a bending radius of 5mm.

[0009] The present invention also provides a technical solution: a method for preparing a flexible self-supporting diamond heat dissipation film, comprising the following steps: Step S1: Perform RCA cleaning on the single-crystal silicon wafer substrate and then perform plasma activation treatment under an argon atmosphere with a power of 200-300W for 10-15 minutes. Step S2: Using DC jet CVD process, a mixture of methane, hydrogen and argon gas is used as the reaction gas source. Deposition is carried out at 800-900℃ and 10-20kPa for 12-24h, with methane volume fraction of 2-5% and argon volume fraction of 5-10%, to form a nanocrystalline diamond film-silicon substrate composite with a thickness of 10-50μm. Step S3: Place the composite in an environment with a constant temperature of 25-30℃ and a constant humidity of 50-60% for 2-4 hours. Utilize the internal stress generated by the difference in thermal expansion coefficients between diamond and silicon to allow the diamond film to detach from the silicon substrate, thereby obtaining a self-supporting diamond film. The detachment time shall not exceed 10 minutes. Step S4: The polyimide precursor solution is uniformly coated onto both sides of the obtained self-supporting diamond film using a solution coating method, and cured at 150-200℃ for 1-2 hours to form a polyimide surface modification layer.

[0010] Furthermore, the single-crystal silicon wafer substrate in S1 is cleaned using RCA and then subjected to plasma activation treatment under an argon atmosphere. The plasma activation treatment has a power of 200-300W and a treatment time of 10-15min.

[0011] Furthermore, the DC jet chemical vapor deposition process in S2 uses a mixture of methane, hydrogen, and argon as the reaction gas source; the deposition temperature is 800–900°C, the deposition pressure is 10–20 kPa, and the deposition time is 12–24 h; wherein the volume fraction of methane is 2–5% and the volume fraction of argon is 5–10%, in order to form a nanocrystalline diamond film-silicon substrate composite with a thickness of 10–50 μm.

[0012] Furthermore, the temperature of the constant temperature and humidity environment in S3 is 25-30°C, the relative humidity is 50-60%, and the standing time is 2-4 hours; the internal stress generated by the difference in thermal expansion coefficients between the diamond film and the silicon substrate causes the diamond film to detach from the silicon substrate on its own, and the detachment time does not exceed 10 minutes.

[0013] Furthermore, in step S4, a polyimide precursor solution is uniformly coated onto both sides of the self-supporting diamond film using a solution coating method, and then cured at 150–200°C for 1–2 hours to form the polyimide surface modification layer.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The flexible self-supporting diamond heat dissipation film provided by this invention uses nanocrystalline CVD diamond thin film as the main body to achieve a balance between high thermal conductivity and thinness. It can quickly dissipate heat and reduce interfacial thermal resistance without significantly increasing the thickness and weight of the device, thereby suppressing performance drift and reliability degradation caused by junction temperature rise. At the same time, since the film is a self-supporting structure and has the flexibility to be bent repeatedly, it can adapt to various device morphologies such as planar, curved, and flexible packaging, improving the mounting adaptability and heat dissipation consistency in complex structures. It overcomes the problem that traditional heat dissipation materials cannot balance thermal conductivity and structural adaptability in high heat flux density and miniaturized packaging scenarios.

[0015] Furthermore, the present invention provides a polyimide surface-modified layer on both sides of the diamond film, which can significantly improve the wetting / compatibility and adhesion stability with encapsulating adhesives, polymer substrates, etc., and reduce the risk of increased contact thermal resistance due to interface instability. At the same time, the polyimide modified layer has wear-resistant and environmental-resistant properties, which can maintain the integrity of the interface during long-term thermal cycling and mechanical bending, avoiding the performance degradation caused by the easy aging and pumping out of thermal pads / silicone grease materials. In terms of comprehensive performance, it makes up for the defects of graphite film anisotropy and insufficient interface bonding stability, poor insulation of metal foil and limited flexibility and resilience, thereby achieving a more stable and reliable long-term heat dissipation effect. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the overall structure of the present invention; Figure 2 is a schematic flowchart of the method of the present invention.

[0017] In the figure: 1. Nanocrystalline CVD diamond film substrate; 2. Polyimide surface modification 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 flexible self-supporting diamond heat dissipation film and its preparation method are disclosed. The nanocrystalline CVD diamond film body 1 has polyimide surface modification layers 2 on both sides. The nanocrystalline CVD diamond film body 1 has a thickness of 10-50 μm, an elongation at break of not less than 3%, and can be repeatedly bent 360° with a bending radius of not less than 5 mm.

[0021] Furthermore, the grain size of the nanocrystalline CVD diamond film body 1 is 50-200 nm, and the thermal conductivity is not less than 1600 W / (m·K).

[0022] Furthermore, the polyimide surface modification layer 2 has a thickness of 1-3 μm and a surface contact angle of 85-95°.

[0023] Furthermore, the polyimide surface-modified layer 2 is uniformly and continuously coated on both sides of the nanocrystalline CVD diamond film body 1.

[0024] Furthermore, the nanocrystalline CVD diamond film body 1 does not produce cracks after being folded at least 1000 times with a bending radius of 5mm.

[0025] This embodiment presents the structural parameters and characterization method of a typical flexible self-supporting diamond heat dissipation film. The film body is nanocrystalline CVD diamond with a thickness of 20 μm, and each side is coated with a 2 μm PI layer. The nanocrystalline diamond particle size is approximately 100 nm, which can be characterized by SEM / TEM and estimated by XRD diffraction peak width. In-situ doping or subsequent annealing can slightly increase the grain size and improve the thermal conductivity. The in-plane thermal conductivity of this film at room temperature is measured to be approximately 1800 W / (m·K), close to the limit of single-crystal diamond and much higher than that of traditional heat dissipation materials. The thermal conductivity is determined by laser flash method: under known specific heat capacity and density conditions, the sample surface is heated by laser pulse and the back temperature response curve is measured. The thermal diffusivity is calculated and converted into thermal conductivity. Due to the high thermal conductivity of diamond, it is recommended to use a laser flash device with a high thermal conductivity range. Using a NETZSCH LFA-467 will yield accurate thermal conductivity values.

[0026] The double-sided PI modified layer uses a commercial thermosetting polyimide precursor solution, which is cured at 150–200°C for 1–2 hours after each spin coating to crosslink into a film. The cured PI layer is approximately 2 μm thick. Surface hydrophilicity / hydrophobicity is measured using a contact angle meter: the contact angle is typically measured with a water droplet at room temperature. Literature reports that the water contact angle of ordinary PI films is less than 90°, while in this embodiment, surface modification achieves a range of 85–95° to improve wettability with the encapsulating adhesive and ensure interfacial adhesion.

[0027] Nanocrystalline diamond possesses ultra-high lattice thermal conductivity, enabling rapid heat conduction. Although grain boundaries in the polycrystalline structure slightly reduce thermal conductivity, the film size is only a few micrometers, and the thermal resistance mainly originates from the interface, thus the overall thermal conductivity remains excellent. The nanocrystalline structure and extremely thin thickness make the film flexible: abundant grain boundaries and dislocations can slide during bending, and the thin geometry reduces bending stress concentration. It has been reported that submicron-thick diamond films can be bent 360°; although this embodiment is approximately 20 μm thick, it can still be bent multiple times with a radius of 5 mm without cracking. The polyimide layer provides flexible protection, scratch resistance, and interfacial bonding, while also possessing high-temperature resistance and insulation properties. The double-sided PI-modified layer improves the affinity between diamond and the external interface, prevents the increase of interfacial thermal resistance, and protects the film surface during thermal cycling and mechanical bending, enhancing the reliability of the heat dissipation device.

[0028] The grain size of nanocrystalline diamond films can be adjusted within the range of 50–200 nm; the film thickness can be selected from 10–50 μm. Kapton-type or high-temperature modified PI can be used; the PI layer thickness can be adjusted from 1–3 μm, but excessive thickness will increase thermal resistance. Other thermally stable polymers or silane coupling agents can be used as alternatives to polyimide for the interface layer, but PI is commonly used due to its superior temperature resistance, wear resistance, and compatibility. Organic solvents such as DMF and NMP can be selected as polymer solvents.

[0029] Example 2 The present invention also provides a technical solution: a method for preparing a flexible self-supporting diamond heat dissipation film, characterized by comprising the following steps: Step S1: Perform RCA cleaning on the single-crystal silicon wafer substrate and then perform plasma activation treatment under an argon atmosphere with a power of 200-300W for 10-15 minutes. Step S2: Using DC jet CVD process, a mixture of methane, hydrogen and argon gas is used as the reaction gas source. Deposition is carried out at 800-900℃ and 10-20kPa for 12-24h, with methane volume fraction of 2-5% and argon volume fraction of 5-10%, to form a nanocrystalline diamond film-silicon substrate composite with a thickness of 10-50μm. Step S3: Place the composite in an environment with a constant temperature of 25-30℃ and a constant humidity of 50-60% for 2-4 hours. Utilize the internal stress generated by the difference in thermal expansion coefficients between diamond and silicon to allow the diamond film to detach from the silicon substrate, thereby obtaining a self-supporting diamond film. The detachment time shall not exceed 10 minutes. Step S4: The polyimide precursor solution is uniformly coated onto both sides of the obtained self-supporting diamond film using a solution coating method, and cured at 150-200℃ for 1-2 hours to form a polyimide surface modification layer.

[0030] Furthermore, the single-crystal silicon wafer substrate in S1 is cleaned using RCA and then subjected to plasma activation treatment under an argon atmosphere. The plasma activation treatment has a power of 200-300W and a treatment time of 10-15min.

[0031] Furthermore, the DC jet chemical vapor deposition process in S2 uses a mixture of methane, hydrogen, and argon as the reaction gas source; the deposition temperature is 800–900°C, the deposition pressure is 10–20 kPa, and the deposition time is 12–24 h; wherein the volume fraction of methane is 2–5% and the volume fraction of argon is 5–10%, in order to form a nanocrystalline diamond film-silicon substrate composite with a thickness of 10–50 μm.

[0032] Furthermore, the temperature of the constant temperature and humidity environment in S3 is 25-30°C, the relative humidity is 50-60%, and the standing time is 2-4 hours; the internal stress generated by the difference in thermal expansion coefficients between the diamond film and the silicon substrate causes the diamond film to detach from the silicon substrate on its own, and the detachment time does not exceed 10 minutes.

[0033] Furthermore, in step S4, a polyimide precursor solution is uniformly coated onto both sides of the self-supporting diamond film using a solution coating method, and then cured at 150–200°C for 1–2 hours to form the polyimide surface modification layer.

[0034] S1: Use a 100mm or 150mm single-crystal silicon wafer as the substrate. First, clean according to RCA standards: immerse in deionized water with an NH4OH / H2O2 solution at 75–80℃ for 10–15 min to remove organic residues and particles; then remove metal ions with an HCl / H2O2 mixture. After cleaning, an oxide layer remains at the ends of the silicon wafer, which can be briefly immersed in a dilute HF solution to remove residual SiO2. Subsequently, perform plasma activation treatment in an argon atmosphere to remove trace surface impurities and increase surface energy, thereby improving the subsequent diamond nucleation density. Optional processes: After plasma activation, a nanoscale silicon oxide interface layer or silicon nitride interface layer can be grown on the silicon wafer surface to adjust self-peeling conditions; a thin oxide layer can also be formed using VOC plasma gas.

[0035] S2: Diamond deposition is performed in a DC-jet CVD reaction chamber. The commonly used gas source is a mixture of methane, high-purity hydrogen, and argon. Control conditions: temperature 800–900℃, total pressure 10–20 kPa. Gas flow rate: approximately 2–5% CH4, 5–10% Ar, with the remainder being H2. Deposition under these conditions for 12–24 hours yields a diamond film approximately 20 μm thick. The deposition apparatus features a cathode DC-jet plasma: using hot filament or cold cathode discharge, a localized high-temperature plasma is generated between the two electrodes and jetted onto the substrate for growth. Key controls: maintaining uniform flame temperature to prevent localized overheating and substrate bending; adjusting the CH4 content controls grain size and nitrogen doping content. Optional seeding nucleation: pre-coating a nanodiamond particle solution onto the silicon wafer or using a bias-assisted nucleation device to increase nucleation density; if bias jetting is used, a negative bias can be applied to the substrate to enhance ion bombardment and promote nucleation. After deposition, the system is slowly shut down and cooled to room temperature to avoid stress shock caused by rapid cooling.

[0036] S3: The deposited diamond-silicon composite is placed under constant temperature and humidity conditions of 25–30°C and 50–60%RH for 2–4 hours. This environment induces residual internal stress between the silicon wafer and the diamond due to the difference in their coefficients of thermal expansion: the diamond film experiences tensile stress upon cooling to room temperature, while the silicon substrate experiences compressive stress. Focusing on the edge or creating a microcrack trigger point allows the diamond film to self-peel off the substrate; the entire detachment process takes less than 10 minutes. Peeling mechanism: Similar to existing self-peeling substrate technologies, no additional layer is required; only the stress itself is utilized. Optional improvements: Fine slits are etched at the edge of the silicon wafer or on the film to promote stress concentration; or a thin layer of release agent is pre-sprayed at the diamond-silicon interface to regulate adhesion. The peeled self-supporting diamond film is then transferred to another platform using appropriate tools.

[0037] S4: The polyimide precursor solution is uniformly coated onto both sides of the obtained self-supporting diamond film using spin coating or dip coating methods. The spin coating speed and number of coats can adjust the PI layer thickness. After coating, the solvent is removed by soft drying in air, followed by thermal curing at 150–200℃ for 1–2 hours to crosslink into a thermally stable PI film. This process can be carried out in a vacuum or inert atmosphere to reduce porosity. Key factors: Ensure uniform PI coverage without air bubbles; control the temperature rise within the curing temperature range to avoid thermal shock cracking of the diamond film. Optional: Before coating, perform oxidation plasma treatment on the diamond surface to improve wettability, or add a coupling agent to increase adhesion; after PI coating, staged curing can be used to reduce internal stress. After curing, check the integrity of the PI film and characterize the surface quality using AFM / SEM. The final product is a flexible diamond heat dissipation film with double-sided PI coverage.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 flexible self-supporting diamond heat dissipation film, comprising a nanocrystalline CVD diamond film substrate (1) and a polyimide surface-modified layer (2), characterized in that: The nanocrystalline CVD diamond film body (1) has polyimide surface modification layers (2) on both sides. The nanocrystalline CVD diamond film body (1) has a thickness of 10-50 μm, an elongation at break of not less than 3%, and can be repeatedly bent at 360° with a bending radius of not less than 5 mm.

2. The flexible self-supporting diamond heat dissipation film according to claim 1, characterized in that: The nanocrystalline CVD diamond film substrate (1) has a grain size of 50-200 nm and a thermal conductivity of not less than 1600 W / (m·K).

3. The flexible self-supporting diamond heat dissipation film according to claim 1, characterized in that: The polyimide surface modification layer (2) has a thickness of 1-3 μm and a surface contact angle of 85-95°.

4. The flexible self-supporting diamond heat dissipation film according to claim 1, characterized in that: The polyimide surface-modified layer (2) is coated on both sides of the nanocrystalline CVD diamond film body (1) in a uniform and continuous manner.

5. The flexible self-supporting diamond heat dissipation film according to claim 1, characterized in that: The nanocrystalline CVD diamond film body (1) does not produce cracks after being folded at least 1000 times with a bending radius of 5 mm.

6. A method for preparing a flexible self-supporting diamond heat dissipation film, characterized in that: Includes the following steps: Step S1: Perform RCA cleaning on the single-crystal silicon wafer substrate and then perform plasma activation treatment under an argon atmosphere with a power of 200-300W for 10-15 minutes. Step S2: Using DC jet CVD process, a mixture of methane, hydrogen and argon gas is used as the reaction gas source. Deposition is carried out at 800-900℃ and 10-20kPa for 12-24h, with methane volume fraction of 2-5% and argon volume fraction of 5-10%, to form a nanocrystalline diamond film-silicon substrate composite with a thickness of 10-50μm. Step S3: Place the composite in an environment with a constant temperature of 25-30℃ and a constant humidity of 50-60% for 2-4 hours. Utilize the internal stress generated by the difference in thermal expansion coefficients between diamond and silicon to allow the diamond film to detach from the silicon substrate, thereby obtaining a self-supporting diamond film. The detachment time shall not exceed 10 minutes. Step S4: The polyimide precursor solution is uniformly coated onto both sides of the obtained self-supporting diamond film using a solution coating method, and cured at 150-200℃ for 1-2 hours to form a polyimide surface modification layer.

7. The flexible self-supporting diamond heat dissipation film and its preparation method according to claim 6, characterized in that: The single-crystal silicon wafer substrate in S1 is cleaned using RCA and then subjected to plasma activation treatment under an argon atmosphere. The power of the plasma activation treatment is 200-300W and the treatment time is 10-15min.

8. The flexible self-supporting diamond heat dissipation film and its preparation method according to claim 6, characterized in that: The DC jet chemical vapor deposition process in S2 uses a mixture of methane, hydrogen, and argon as the reaction gas source; the deposition temperature is 800–900℃, the deposition pressure is 10–20 kPa, and the deposition time is 12–24 h; wherein the volume fraction of methane is 2–5% and the volume fraction of argon is 5–10%, in order to form a nanocrystalline diamond thin film-silicon substrate composite with a thickness of 10–50 μm.

9. The flexible self-supporting diamond heat dissipation film and its preparation method according to claim 6, characterized in that: The constant temperature and humidity environment in S3 is 25-30℃, relative humidity is 50-60%, and the standing time is 2-4h. The internal stress generated by the difference in thermal expansion coefficients between the diamond film and the silicon substrate causes the diamond film to detach from the silicon substrate on its own, and the detachment time does not exceed 10min.

10. The flexible self-supporting diamond heat dissipation film and its preparation method according to claim 6, characterized in that: In step S4, a polyimide precursor solution is uniformly coated onto both sides of the self-supporting diamond film using a solution coating method, and then cured at 150–200°C for 1–2 hours to form the polyimide surface modification layer.

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