A copper-based composite material with interpenetrating graphite mesh framework and its preparation method

Abstract

This invention discloses a graphite mesh skeleton copper-based composite material and its preparation method, belonging to the field of thermal management materials. The composite material includes a vertical graphite mesh skeleton, copper pillar supports in the center of each mesh unit, and copper-based filler phases filling the gaps. The high thermal conductivity direction of the graphite surface is aligned with the material thickness direction, and its sidewalls have micropores. After sintering, the copper-based filler phases pass through the micropores, causing the copper in adjacent meshes to fuse together to form a three-dimensional through-network. The preparation method includes graphite cutting and drilling, skeleton assembly, introduction of copper pillars and copper powder filling, and sintering densification. This invention suppresses the collapse of vertical graphite during sintering through the central copper pillars and breaks the physical separation of the matrix through the physical riveting effect of the micropores, significantly improving interfacial bonding and macroscopic mechanical strength, while maintaining excellent out-of-plane continuous directional thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging and thermal management materials technology, specifically to a copper-based composite material with interpenetrating graphite mesh skeleton and its preparation method. In particular, it relates to a composite structure that improves the skeleton's shape retention during sintering, enhances the interfacial bonding force of each phase and the overall mechanical properties, and maintains the integrity of the directional thermal pathway by reconstructing the spatial orientation of graphite, setting copper pillar supports in the center of the unit of the vertical graphite mesh skeleton, and opening interconnecting micropores on the sidewall of the graphite mesh skeleton. Background Technology

[0002] As electronic devices evolve towards higher frequencies, higher power, and greater integration, higher demands are being placed on the heat dissipation performance of thermal management materials. Copper-based / graphite composite materials, combining the excellent thermal conductivity of copper with the low expansion and low density of graphite, have become one of the most promising next-generation electronic packaging and thermal management materials.

[0003] However, existing copper-based composite materials still face significant technical bottlenecks in structural design and fabrication processes. In copper-based composite materials prepared by traditional powder metallurgy, graphite (especially graphite sheets or films) tends to align in a direction perpendicular to the pressure (i.e., in the horizontal plane) during the pressing process. This two-dimensional orientation results in a high thermal conductivity in the in-plane direction, but a significant decrease in thermal conductivity in the thickness direction (Z-axis, i.e., out-of-plane direction), failing to meet the demands of modern high-power devices for rapid heat dissipation in the thickness direction. To improve thermal conductivity in the thickness direction, some existing technologies attempt to use three-dimensional sponge-like or randomly porous graphite as a framework to infiltrate molten metal, or to laminate mesh copper with graphite films. However, these methods cannot form a straight, continuous, and efficient heat conduction path in the thickness direction. Addressing the problem of tortuous heat paths, directly introducing vertically aligned graphite into the matrix to construct vertical heat paths presents insurmountable manufacturing challenges. Graphite films have extremely low out-of-plane stiffness. During the pre-compression and high-temperature sintering densification process of composite materials, the flow, extrusion, and sintering shrinkage of copper-based powder generate enormous internal stress. This can cause severe twisting, deformation, or even overall collapse of the originally vertically arranged film skeleton.

[0004] Furthermore, existing composite materials employing continuous graphite skeletons face another fatal flaw—severe physical separation and weak interfacial bonding. Due to the poor natural wettability between graphite and the copper matrix, and the fact that the continuously extending vertical graphite film acts as an insurmountable barrier, the internal copper matrix is ​​completely divided into isolated small units. This lack of three-dimensional connectivity in the microstructure makes the composite material highly susceptible to stress concentration at the smooth copper / graphite interface when subjected to external mechanical loads (such as shear force and compressive force) or thermal stress generated by thermal cycling. This leads to severe interlaminar delamination, cracking, or macroscopic structural damage, resulting in a sharp deterioration in the overall mechanical properties of the material.

[0005] In summary, the key technical challenge that urgently needs to be solved in the field of thermal management composite materials is how to construct straight, continuous out-of-plane preferential heat conduction pathways within the composite material during large-scale sintering densification processes, effectively overcoming the structural collapse problem of vertical graphite during sintering, while also breaking the physical fragmentation of the thin film to achieve three-dimensional connectivity of the copper matrix to improve interfacial bonding and mechanical properties. Summary of the Invention

[0006] The purpose of this invention is to provide a copper-based composite material with interpenetrating graphite mesh skeleton, its preparation method, and its application, so as to at least solve one or more of the following problems in the prior art:

[0007] 1. Solve the problem that ordinary graphite / copper composite materials are difficult to form a continuous thermally conductive skeleton in the thickness direction;

[0008] 2. To solve the problem of insufficient rigid structural support during the sintering of graphite mesh skeleton composite structures, where continuous vertical graphite breaks the matrix, resulting in weak interfacial bonding and poor macroscopic mechanical properties;

[0009] 3. A graphite composite material structure suitable for enhancing out-of-plane thermal conductivity is provided;

[0010] 4. Provide an integrated preparation method applicable to the above-mentioned composite structure.

[0011] To achieve the above objectives, the present invention provides a graphite mesh skeleton copper-based composite material, comprising a vertical graphite mesh skeleton, copper pillar supports disposed within the mesh skeleton grid units, and a copper-based filler phase filling the remaining gaps within the grid units; wherein, the graphite skeleton is formed by multiple sets of vertically perpendicular striped graphite arranged along the thickness direction of the composite material and staggered in the horizontal plane to form a mesh structure, the mesh structure comprising multiple grid units, the boundaries of each grid unit being composed of vertically striped graphite; and constituting the grid unit The vertical strip graphite at the boundary of the unit has micropores for connecting adjacent grid cells; the copper-based filling phase is filled with copper powder in the gap between the copper pillar support and the vertical strip graphite, and after sintering, it passes through the micropores to form a three-dimensional through-connecting phase; the copper pillar support is used to suppress the collapse of the vertical graphite into the grid cells during sintering, so as to maintain the structural integrity of the vertical graphite mesh skeleton; the in-plane high thermal conductivity direction of the graphite is consistent with the thickness direction of the composite material, so as to realize the construction of out-of-plane preferential thermal conduction path inside the composite material.

[0012] Preferably, the micropores are circular, elliptical, or polygonal in shape; the aperture or feature size of the micropores is smaller than the side length of the grid cell, and the micropores are filled with the copper-based filler phase, so that the copper-based materials in adjacent grid cells form a physically interlocked structure through the micropores.

[0013] Preferably, adjacent strips of graphite form a stable skeleton structure through insertion, fitting, snap-fit, slotting, or fixed connection.

[0014] Preferably, the strip graphite remains continuous in its respective extension direction and does not form a fused joint at the intersection.

[0015] Preferably, each grid cell contains a copper pillar support, which can be any one of a cylinder, a rounded square pillar, or a polygonal rounded pillar, and extends along the thickness direction of the composite material.

[0016] To achieve the above objectives, the present invention also provides a method for preparing a copper-based composite material with an interpenetrating graphite mesh framework, comprising the following steps:

[0017] (1) Prepare materials: copper powder, copper pillar support and graphite film;

[0018] (2) Graphite mesh skeleton processing: the graphite film is cut into strip-shaped units of predetermined size, and micropores penetrating the thickness direction are processed at predetermined positions of the strip-shaped units; the strip-shaped units are surface cleaned and modified using alkaline solution and organic solvent, and washed until neutral; the strip-shaped units are connected by insertion, fitting, snap-fit, slot fitting or fixed connection to form a stable skeleton structure, and a graphite mesh skeleton with micropores on each grid sidewall is obtained;

[0019] (3) Copper-based filling phase treatment: copper pillar supports are set in the central area inside the grid cell, and copper powder is filled into the gap between the copper pillar supports and the strip graphite.

[0020] (4) Sintering densification: The filled structure is pre-pressed and sintered to densify the copper powder and fill it into the micropores to obtain a graphite mesh skeleton copper-based composite material.

[0021] Preferably, in step (2), the strip-shaped units are connected by pre-made slots to form an interlaced mesh skeleton; the surface cleaning and modification treatment specifically involves immersing the strip-shaped units in a NaOH solution with a temperature of 80℃–90℃ and a mass concentration of 20% for 30 minutes, and immersing them in an acetone solution for 30 minutes.

[0022] Preferably, in step (3), the filling powder is filled into the grid space enclosed by the graphite film skeleton by one or more of the following methods: layered filling, vibration filling, scraping filling, and pre-compression filling.

[0023] Preferably, in step (4), the sintering and densification is carried out by spark plasma sintering, hot pressing sintering or pressure-assisted sintering; the sintering temperature of spark plasma sintering is 600℃–1100℃, the sintering pressure is 10MPa–80MPa, and the holding time is 1min–30min.

[0024] The beneficial effects of this invention are:

[0025] By vertically interlacing strips of graphite to form a mesh skeleton, the spatial reconstruction of the high thermal conductivity direction in the graphite plane to the thickness direction of the composite material is achieved, thus breaking through the limitation that traditional graphite is mainly used for planar heat diffusion.

[0026] By placing a copper pillar support in the center of each grid cell within the grid space enclosed by the graphite skeleton, local instability and collapse during the sintering process can be suppressed.

[0027] By creating micropores on the sidewalls of the vertical graphite grid, the independent copper matrices separated by the grid can fuse together through the micropores after sintering, forming a three-dimensional continuous copper-based network structure within the composite material. This perforated interlocking effect completely breaks down the physical separation of the matrix by the vertical graphite, firmly connecting the copper matrix phase and the graphite skeleton like countless rivets. This significantly improves the interfacial bonding force between the phases, substantially enhances the overall compressive and shear resistance of the composite material, and effectively prevents interlaminar delamination under thermal stress.

[0028] This collaborative design, which combines an out-of-plane continuous heat conduction path (graphite skeleton), an anti-collapse structure (central copper pillar), and a three-dimensional interlocking network (perforated copper base), offers designability of heat conduction direction, structural stability, and process feasibility. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0030] Figure 2 This is a schematic diagram of the graphite mesh skeleton of the present invention;

[0031] Figure 3 This is a schematic diagram of the skeleton after the copper base is filled in according to the present invention;

[0032] Figure 4 This is a schematic diagram of the composite material preparation process of the present invention;

[0033] Figure 5 This is a schematic diagram of the anti-collapse support and three-dimensional perforation interlocking mechanism in the sintering process of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly illustrate the purpose of the embodiments of the present invention. To make the objectives, features and advantages of the present invention more apparent and understandable, please refer to the accompanying drawings. It should be understood that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only used to complement the content disclosed in the specification, so as to enable those skilled in the art to understand and read, and are not intended to limit the implementation conditions of the present invention. Therefore, they have no substantial technical significance. Any modification to the structure, change in the proportional relationship or adjustment of the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0035] Example 1

[0036] This embodiment provides a graphite mesh skeleton copper-based composite material with interpenetrating networks, including a vertical graphite mesh skeleton, copper pillar supports disposed in the central region of each mesh unit, and a copper powder filler phase. The graphite volume fraction in the composite material is 20 vol%, the copper pillar supports volume fraction is 10 vol%, and the copper powder filler phase volume fraction is 70 vol%. The graphite film is cut into strip-shaped units with a thickness of 100 μm. Micropores are arrayed in predetermined areas of the strips using laser drilling technology. The micropore diameter is approximately 0.15 mm, and the surface opening ratio (the ratio of the total area of ​​the micropores to the area of ​​the wall surface) is controlled at 15%. Adjacent strips with micropores are interlocked through pre-fabricated slots to form a vertical mesh skeleton with a mesh feature size of approximately 1.0 mm. The copper pillar supports are pre-fabricated cylindrical copper pillars disposed in the central region of each mesh unit, with a pillar diameter of approximately 0.3 mm. Copper powder was then filled into the gap between the copper pillar support and the strip graphite. After filling, the mold was installed and lightly pre-pressed, at which point some fine copper powder had initially entered the micropores of the strip graphite. Densification was achieved using spark plasma sintering at 850℃, a sintering pressure of 30MPa, and a holding time of 10min. Under high temperature and pressure, the copper powder underwent plastic flow and completely filled the micropores, forming a three-dimensional, interconnected physical network between the grid units after sintering. After demolding, non-destructive testing and cross-sectional SEM observation showed no significant bending or collapse of the internal vertical strip graphite, and the copper matrix was tightly interlocked within the graphite skeleton, achieving a composite material density of 99.5%. Its out-of-plane (Z-axis) thermal conductivity was measured to be 605 W / (m·K), and its in-plane thermal conductivity was 425 W / (m·K). Thanks to the three-dimensional perforated interlocking structure, its compressive strength was significantly increased to 245MPa.

[0037] Example 2

[0038] The results were essentially the same as in Example 1, except that the graphite volume fraction was 15 vol%, the copper pillar support volume fraction was 10 vol%, the copper powder filler volume fraction was 75 vol%, the mesh feature size was 1.2 mm, and the graphite thickness was 80 μm. The micropore diameter was 0.25 mm, and the face wall porosity was adjusted to 20%. Test results showed that the graphite skeleton was intact after demolding, and the composite material density reached 99.6%. The measured out-of-plane (Z-axis) thermal conductivity was 535 W / (m·K), the in-plane thermal conductivity was 410 W / (m·K), and the compressive strength reached 258 MPa.

[0039] Example 3

[0040] The composite material was essentially the same as in Example 1, except that the volume fraction of graphite was 25 vol%, the volume fraction of the copper pillar support was 8 vol%, the volume fraction of the copper powder filler phase was 67 vol%, the mesh feature size was 0.8 mm, and the graphite thickness was 100 μm. To maintain extremely high Z-axis thermal conductivity with a high graphite content, the micropore size was reduced to 0.10 mm, and the face wall porosity was set to 10%. Test results: Cross-sectional observation after demolding showed that the graphite skeleton was intact without collapse, and the composite material density reached 99.2%. The out-of-plane (Z-axis) thermal conductivity was measured to be 675 W / (m·K), the in-plane thermal conductivity was 440 W / (m·K), and the compressive strength was 225 MPa.

[0041] Comparative Example 1 (lacking central support)

[0042] The composite material consists only of a vertical graphite mesh framework with micropores and a copper powder filler phase, without a central copper pillar support. Test results: Due to the lack of central rigid support, numerous thin-walled vertical graphite strips within the composite material experienced severe instability, bending, and localized collapse under sintering pressure, leading to the breakage of continuous directional heat conduction pathways. The composite material's density was only 94.5%, its out-of-plane thermal conductivity dropped sharply to 415 W / (m·K), and its compressive strength fell to 125 MPa.

[0043] Comparative Example 2 (Pure Copper Substrate)

[0044] It is merely a conventional pure copper sintered body, without a vertical graphite mesh framework. The density of this conventional pure copper sintered body was measured to be 99.0%, and its out-of-plane thermal conductivity was only 385 W / (m·K), while its in-plane thermal conductivity was 390 W / (m·K), which is completely insufficient to meet the requirement of preferential heat dissipation along the thickness direction for high-power devices.

[0045] Comparative Example 3 (Non-perforated partition frame)

[0046] The structure is identical to that of Example 1 (with a central copper pillar and a graphite mesh framework), but no interconnecting micropores are formed on the strip graphite walls. This comparative example is used to illustrate the influence of the micropore interlocking structure on macroscopic mechanical properties. Test results: The out-of-plane thermal conductivity of the composite material is 615 W / (m·K). However, because the continuous strip graphite completely severs the internal copper matrix into isolated units, lacking macroscopic physical connections, the material is prone to interface slippage and delamination under stress. Its compressive strength was measured to be only 185 MPa, about 24% lower than that of Example 1 (245 MPa). This fully demonstrates the necessity of constructing a three-dimensional interlocking network by forming interconnecting micropores.

[0047] Effect description

[0048] A comparison of the data from the above embodiments and comparative examples reveals that this invention successfully breaks down the three-dimensional spatial division of the copper matrix by the original mesh structure (Comparative Example 3) by creating interconnected micropores on the sidewalls of the vertical graphite mesh skeleton (Examples 1-3). During the sintering densification process, the copper matrix flows through the pores, forming numerous metal rivets that cross the graphite boundaries within the material. This physical interlocking effect increases the compressive strength of the composite material by more than 20% with minimal sacrifice (or even negligible impact) on the ultra-high thermal conductivity along the Z-axis, completely solving the industry problem of low macroscopic mechanical properties in graphite / copper composite materials due to weak interfacial bonding.

[0049] In general, this invention achieves integrated synergy of anti-collapse support, three-dimensional copper-based sintering connection and physical interlocking function by introducing a central copper column support in a vertical graphite mesh skeleton and constructing interconnected micropores on the wall surface. This greatly improves the interface reliability and structural stability of the high-performance thermal management composite material in practical applications.

Claims

1. A copper-based composite material with an interpenetrating graphite mesh skeleton, characterized in that, The composite material comprises a vertical graphite mesh skeleton, copper pillar supports disposed within the mesh skeleton grid units, and a copper-based filler phase filling the remaining gaps within the grid units. The graphite skeleton consists of multiple sets of vertically aligned strips of graphite arranged perpendicularly along the thickness direction of the composite material and staggered in a horizontal plane to form a mesh structure. The mesh structure includes multiple grid units, the boundaries of which are formed by vertical strips of graphite. Micropores for connecting adjacent grid units are formed on the vertical strips of graphite constituting the grid unit boundaries. The copper-based filler phase consists of copper powder filling the gaps between the copper pillar supports and the vertical strips of graphite, and after sintering, it passes through the micropores to form a three-dimensionally penetrating connecting phase. The copper pillar supports are used to suppress the collapse of the vertical strips of graphite into the grid units during sintering, thereby maintaining the structural integrity of the vertical strip graphite mesh skeleton. The in-plane high thermal conductivity direction of the strips of graphite is consistent with the thickness direction of the composite material, thereby creating an out-of-plane preferential thermal conduction pathway within the composite material.

2. The interpenetrating graphite mesh skeleton copper-based composite material according to claim 1, characterized in that, The micropores are circular, elliptical, or polygonal in shape; the aperture or feature size of the micropores is smaller than the side length of the grid cell, and the micropores are filled with the copper-based filler phase, so that the copper-based materials in adjacent grid cells form a physically interlocked structure through the micropores.

3. The interpenetrating graphite mesh skeleton copper-based composite material according to claim 1, characterized in that, Adjacent strips of graphite form a stable skeleton structure through insertion, fitting, snap-fit, slotting, or fixed connection.

4. The interpenetrating graphite mesh skeleton copper-based composite material according to any one of claims 1 to 3, characterized in that, The strip graphite remains continuous in its respective extension direction and does not form a fused joint at the intersection.

5. The interpenetrating graphite mesh skeleton copper-based composite material according to any one of claims 1 to 4, characterized in that, Each grid cell contains a copper pillar support, which can be any of the following: a cylinder, a rounded square pillar, or a polygonal rounded pillar. The copper pillar support extends along the thickness direction of the composite material.

6. A method for preparing a copper-based composite material with an interpenetrating graphite mesh framework, characterized in that, Includes the following steps: (1) Prepare materials: copper powder, copper pillar support and graphite film; (2) Graphite mesh skeleton processing: the graphite film is cut into strip-shaped units of a predetermined size, and micropores penetrating the thickness direction are processed at predetermined positions of the strip-shaped units; The strip-shaped units are surface-cleaned and modified using alkaline solutions and organic solvents, and then washed until neutral. The strip-shaped units are connected by insertion, fitting, snap-fitting, slotting, or fixed connection to form a stable skeleton structure, resulting in a graphite mesh skeleton with micropores on the sidewalls of each grid. (3) Copper-based filling phase treatment: copper pillar supports are set in the central area inside the grid cell, and copper powder is filled into the gap between the copper pillar supports and the strip graphite. (4) Sintering densification: The filled structure is pre-pressed and sintered to densify the copper powder and fill it into the micropores to obtain a graphite mesh skeleton copper-based composite material.

7. The preparation method according to claim 6, characterized in that, In step (1), the strip graphite is connected by pre-made slots to form an interlaced mesh skeleton; in step (2), the surface cleaning and modification treatment specifically involves immersing the strip unit in a NaOH solution with a temperature of 80℃–90℃ and a mass concentration of 20% for 30 minutes, and immersing it in an acetone solution for 30 minutes.

8. The preparation method according to claim 6, characterized in that, In step (3), the filling powder is filled into the grid space enclosed by the graphite skeleton by one or more of the following methods: layered filling, vibration filling, scraping filling, and pre-compression filling.

9. The preparation method according to claim 6, characterized in that, In step (4), the sintering and densification is carried out by spark plasma sintering, hot pressing sintering or pressure-assisted sintering; the sintering temperature of spark plasma sintering is 600℃–1100℃, the sintering pressure is 10MPa–80MPa, and the holding time is 1min–30min.

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