Porous ceramic skeleton-PTFE (Polytetrafluoroethylene) composite membrane as well as preparation method and application thereof

Abstract

The invention relates to a porous ceramic skeleton-PTFE composite membrane as well as a preparation method and application thereof, and relates to the technical field of new materials. The porous ceramic skeleton-PTFE composite membrane comprises a ceramic skeleton and a PTFE layer, the PTFE layer is attached to the surface of the ceramic skeleton, and the ceramic skeleton has a network structure. The porous ceramic skeleton-PTFE composite membrane has a relatively low linear thermal expansion coefficient and a relatively high heat conductivity coefficient, the linear thermal expansion coefficient can be reduced to 50% or below of that of a conventional PTFE material, the heat conductivity coefficient can be increased to 15 times or above of that of the conventional PTFE material, and relatively low dielectric constant and dielectric loss are maintained.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to porous ceramic framework-PTFE composite membranes, their preparation methods, and applications. Background Technology

[0002] PTFE material has the characteristics of low dielectric constant and low loss, and has good application prospects in high-frequency and high-speed circuit boards. Common methods for producing PTFE base films are: directly coating the PTFE dispersion onto metal strips or release paper (casting method), or rolling it into a film using a calender.

[0003] However, due to the long-chain structure and high coefficient of thermal expansion of PTFE, its dimensional changes differ in the machining direction and the direction perpendicular to machining. PTFE materials produced directly using casting or calendering methods exhibit different expansion and contraction ratios in different directions during processing, leading to difficulties in machining alignment and component positioning. Furthermore, PTFE has a low thermal conductivity of only 0.25 W / (m·K), which is detrimental to heat dissipation. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a porous ceramic skeleton-PTFE composite membrane, which has a low linear thermal expansion coefficient, a high thermal conductivity, and a linear thermal expansion coefficient that can be reduced to less than 50% of that of conventional PTFE materials. The thermal conductivity can be increased to more than 15 times that of conventional PTFE materials, while maintaining a low dielectric constant and dielectric loss.

[0005] To achieve the above objectives, the present invention provides a porous ceramic skeleton-PTFE composite membrane, comprising a ceramic skeleton and PTFE, wherein the ceramic skeleton has a plurality of pores, making the ceramic skeleton have a network structure, and the PTFE fills the pores.

[0006] In the aforementioned porous ceramic skeleton-PTFE composite membrane, the ceramic skeleton is integral and has a network structure, rather than being formed into a slurry with other components in powder or particle form and then the mixture is used to form the membrane layer. Because of the integral and network structure of the ceramic skeleton, the porous ceramic skeleton-PTFE composite membrane can utilize the structural stability of the network skeleton to pin the PTFE. Simultaneously, the interconnected structures within the ceramic skeleton can form thermally conductive channels, thereby improving the material's thermal conductivity and reducing its linear coefficient of thermal expansion.

[0007] In one embodiment, the pore size increases gradually from the surface to the center of the ceramic skeleton.

[0008] The pore size gradient from the outside to the inside allows the PTFE dispersion to better wet the ceramic skeleton and fill the pores. The larger pore size at the center can prevent pore blockage inside the ceramic skeleton.

[0009] In one embodiment, the pores on the surface of the ceramic skeleton have a diameter of 1-2 μm, and the pores at the center of the ceramic skeleton have a diameter of 3-5 μm.

[0010] The present invention also provides a method for preparing the porous ceramic framework-PTFE composite membrane, comprising the following steps:

[0011] Preparation and pretreatment of ceramic framework: Ceramic framework is prepared from ceramic raw materials and treated with silane coupling agent and / or plasma;

[0012] Wetting: Immerse the ceramic skeleton in water and degas; immerse the ceramic skeleton in a solution so that the solution penetrates the pores inside the ceramic skeleton, dry to obtain an intermediate product, and polish; repeat the wetting steps until the surface of the intermediate product is free of voids; the solution includes a PTFE dispersion.

[0013] Sintering: Gradient sintering is carried out under an inert atmosphere to obtain a porous ceramic skeleton-PTFE composite membrane.

[0014] In the above preparation method, the impregnation step disperses the PTFE dispersion in a porous ceramic framework. The pores in the ceramic framework are macropores, which can provide sufficient binding force to ensure that the film layer formed by the PTFE dispersion is tightly bonded to the ceramic framework. Then, it is cured to form a porous ceramic framework-PTFE composite film. The porous ceramic can reduce the overall coefficient of thermal expansion and improve the thermal conductivity. In the above preparation and pretreatment steps of the ceramic framework, the porous ceramic framework is treated with a silane coupling agent, which can reduce the hydrophilicity of the ceramic and improve its compatibility with the PTFE dispersion. The porous ceramic framework surface is treated with plasma to clean the surface and introduce active groups such as -OH, which can enhance the physical anchoring of PTFE and the porous ceramic framework.

[0015] In one embodiment, the ceramic raw material includes at least one of Al2O3, SiC, and AlN.

[0016] In one embodiment, the nanoparticles include at least one of ZrO2, SiO2, AlN, BN, and SiC;

[0017] In the impregnation step, the solution is impregnated into the pores inside the ceramic skeleton by ultrasound and / or centrifugation;

[0018] The gradient sintering temperature is 120-360℃.

[0019] In addition to the PTFE dispersion, the above solution may also contain some nanoparticles. These nanoparticles may be added or not added depending on the product requirements. When not added, the porous ceramic framework-PTFE composite membrane mainly relies on the porous ceramic framework to reduce the linear thermal expansion coefficient and increase the thermal conductivity. When added, the nanoparticles can help to simultaneously reduce the thermal expansion coefficient of the material.

[0020] The present invention also provides a PTFE-based composite porous ceramic skeleton copper-clad laminate, comprising copper foil and the porous ceramic skeleton-PTFE composite film.

[0021] In one embodiment, the porous ceramic skeleton-PTFE composite membrane is sandwiched between the copper foil.

[0022] This invention also provides a method for preparing the aforementioned PTFE-based composite porous ceramic framework copper-clad laminate, comprising the following steps:

[0023] Copper foil is formed on both sides of the porous ceramic skeleton-PTFE composite film by sputtering a seed layer and electroplating, or by sandwiching the porous ceramic skeleton-PTFE composite film between two copper foils and hot pressing, or by using a low dielectric adhesive for a high-frequency substrate to bond the copper foil to both sides of the porous ceramic skeleton-PTFE composite film, thus forming a PTFE-based composite porous ceramic skeleton copper-clad laminate.

[0024] The present invention also provides a high-frequency, high-speed circuit board, which is prepared by using the porous ceramic skeleton-PTFE composite film or the PTFE-based composite porous ceramic skeleton copper-clad laminate.

[0025] The present invention also provides the application of the porous ceramic skeleton-PTFE composite film or the PTFE-based composite porous ceramic skeleton copper-clad laminate in high-frequency and high-speed circuit boards.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention relates to a porous ceramic skeleton-PTFE composite membrane, its preparation method, and its application. The porous ceramic skeleton-PTFE composite membrane has a low linear thermal expansion coefficient and a high thermal conductivity. The linear thermal expansion coefficient can be reduced to less than 50% of that of conventional PTFE materials, and the thermal conductivity can be increased to more than 15 times that of conventional PTFE materials, while maintaining a low dielectric constant and dielectric loss. Attached Figure Description

[0028] Figure 1 Flowchart of the preparation process for copper-clad laminate with PTFE-based composite porous ceramic framework;

[0029] Figure 2This is a schematic diagram of a copper-clad laminate based on a PTFE-based composite porous ceramic skeleton, where ① is copper foil and ② is a porous ceramic skeleton-PTFE composite film. Detailed Implementation

[0030] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0031] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] Unless otherwise specified, all reagents, materials, and equipment used in this embodiment are commercially available; unless otherwise specified, all test methods are conventional test methods in this field.

[0034] Example

[0035] A porous ceramic skeleton-PTFE composite membrane and a PTFE-based composite porous ceramic skeleton copper-clad laminate.

[0036] I. Preparation method of porous ceramic skeleton-PTFE composite membrane.

[0037] 1. A ceramic framework with gradient pore sizes is constructed by adding appropriate pore-forming agents to ceramic powders such as Al2O3, SiC, and AlN. The surface pore size is 1-2 μm, and the central pore size is 3-5 μm. The specific fabrication method is as follows:

[0038] 1) The surface slurry includes pore-forming agent powder (such as PMMA microspheres) with a particle size of 0.5-1.5μm, alumina powder, PVA solution and a certain amount of dispersant;

[0039] 2) The intermediate layer slurry consists of pore-forming agent powder (such as graphite powder) with a particle size of 3-4 μm, alumina powder, PVA solution and a certain amount of dispersant;

[0040] 3) Fill the slurry into the mold in sequence and pre-press at 10MPa. After filling all three layers (top layer + middle layer + top layer), press at 30MPa. During the filling process, spray anhydrous ethanol between the layers to prevent delamination.

[0041] 4) Degrease in stages at 25-400℃ and 400-600℃ to remove PMMA pore-forming agent and graphite powder pore-forming agent, and then sinter at a uniform temperature of 1600℃ to form a porous ceramic skeleton.

[0042] 2. The ceramic skeleton is treated with silane coupling agent or plasma to improve its compatibility with PTFE.

[0043] 3. Select a PTFE dispersion with a mass fraction of 40%-50%. Nano ZrO2, SiO2 and other particles can be mixed into the solution as needed.

[0044] 4. The ceramic skeleton is immersed in the PTFE dispersion. The immersion process is divided into several stages:

[0045] (1) Pre-soaking stage: Immerse the ceramic skeleton in deionized water and sonicate for 5 minutes to remove the gas;

[0046] (2) First immersion: Immerse the ceramic skeleton in PTFE dispersion in a vacuum environment for 20-30 minutes, with the aid of ultrasound. After removal, centrifuge to allow the dispersion to penetrate into the inner pores, and then dry.

[0047] (3) Secondary wetting: After each drying, polish the surface to prevent clogging, and then repeat steps (1) and (2) 2-3 times until there are no obvious gaps on the surface.

[0048] 5. The dried material is sintered in an inert gas environment (N2, Ar) at a gradient temperature of 120℃-360℃ to produce a porous ceramic skeleton-PTFE composite membrane.

[0049] II. Preparation method of PTFE-based composite porous ceramic skeleton copper-clad laminate.

[0050] The preparation method process is as follows: Figure 1 As shown; the structure of the PTFE-based composite porous ceramic skeleton copper-clad laminate is as follows. Figure 2 As shown, ① is copper foil and ② is a porous ceramic skeleton-PTFE composite membrane.

[0051] After the porous ceramic skeleton-PTFE composite film is fabricated, copper-clad laminate is made by sputtering a seed layer and electroplating, directly hot-pressing copper foil, or using a high-frequency substrate to bond copper foil with a low-dielectric adhesive.

[0052] Experimental example

[0053] Porous ceramic framework-PTFE composite membrane samples 1, 2, and 3 were prepared using the method described in the examples (the ceramic raw materials of samples 1, 2, and 3 included Al2O3, and no nanoparticles were added to the solution), and their performance was tested.

[0054] I. The ceramic pore filling rate was ≥80% as determined by Archimedes density method.

[0055] 2. The linear coefficient of thermal expansion of the material was measured according to ASTM E831-24 standard, and it can be reduced to less than 50% of that of PTFE material, from about 110 ppm / K to 50 ppm / K.

[0056] Third, the thermal conductivity of the material was tested according to ASTM E1461 standard, and the test result was about 5 W / (m·K), which is more than 15 times higher than that of pure PTFE.

[0057] IV. According to IPC-TM-6502.5.5.2, the dielectric constant (Dk) of the material was tested to be around 2.8@10GHz, and the dielectric loss (Df) was around 0.0007@10GHz.

[0058] The performance test results are shown in Table 1.

[0059] Table 1 Performance test results of samples 1, 2, and 3

[0060]

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A porous ceramic framework-PTFE composite membrane, characterized in that, It includes a ceramic skeleton and PTFE, wherein the ceramic skeleton has a plurality of pores, giving the ceramic skeleton a network structure, and the PTFE fills the pores.

2. The porous ceramic framework-PTFE composite membrane according to claim 1, characterized in that, The pore size increases gradually from the surface to the center of the ceramic skeleton.

3. The porous ceramic framework-PTFE composite membrane according to claim 2, characterized in that, The pores on the surface of the ceramic skeleton have a diameter of 1-2 μm, while the pores in the center of the ceramic skeleton have a diameter of 3-5 μm.

4. A method for preparing the porous ceramic framework-PTFE composite membrane according to any one of claims 1-3, characterized in that, Includes the following steps: Preparation and pretreatment of ceramic framework: Ceramic framework is prepared from ceramic raw materials and treated with silane coupling agent and / or plasma; Wetting: Immerse the ceramic skeleton in water and degas; immerse the ceramic skeleton in a solution so that the solution penetrates the pores inside the ceramic skeleton, dry to obtain an intermediate product, and polish; repeat the wetting steps until the surface of the intermediate product is free of voids; the solution includes a PTFE dispersion. Sintering: Gradient sintering is carried out under an inert atmosphere to obtain a porous ceramic skeleton-PTFE composite membrane.

5. The preparation method according to claim 4, characterized in that, The solution also includes nanoparticles, which include at least one of ZrO2, SiO2, AlN, BN, and SiC. In the impregnation step, the solution is impregnated into the pores inside the ceramic skeleton by ultrasound and / or centrifugation; The gradient sintering temperature is 120-360℃.

6. A PTFE-based composite porous ceramic skeleton copper-clad laminate, characterized in that, Includes copper foil and the porous ceramic skeleton-PTFE composite membrane as described in any one of claims 1-3.

7. The PTFE-based composite porous ceramic skeleton copper-clad laminate according to claim 6, characterized in that, The porous ceramic skeleton-PTFE composite membrane is sandwiched between the copper foil.

8. The method for preparing the PTFE-based composite porous ceramic skeleton copper-clad laminate according to any one of claims 6-7, characterized in that, Includes the following steps: Copper foil is formed on both sides of the porous ceramic skeleton-PTFE composite film by sputtering a seed layer and electroplating, or by sandwiching the porous ceramic skeleton-PTFE composite film between two copper foils and hot pressing, or by using a low dielectric adhesive for a high-frequency substrate to bond the copper foil to both sides of the porous ceramic skeleton-PTFE composite film, thus forming a PTFE-based composite porous ceramic skeleton copper-clad laminate.

9. A high-frequency, high-speed circuit board, characterized in that, It is prepared using the porous ceramic skeleton-PTFE composite membrane according to any one of claims 1-3 or the copper-clad laminate based on the PTFE-based composite porous ceramic skeleton according to any one of claims 6-7.

10. The application of the porous ceramic skeleton-PTFE composite film according to any one of claims 1-3 or the PTFE-based composite porous ceramic skeleton copper-clad laminate according to any one of claims 6-7 in high-frequency and high-speed circuit boards.

Images