A PTFE foam copper-clad laminate and its preparation method

Abstract

This invention belongs to the field of electronic circuit technology and discloses a PTFE foam copper-clad laminate and its preparation method. The invention first prepares a foaming liquid by mixing a PTFE suspension with a thickener solution. Then, the foaming liquid is freeze-set, freeze-dried, and sintered to prepare PTFE foam. Finally, it is coated with an adhesive and hot-pressed with a metal material to prepare the PTFE foam copper-clad laminate. The PTFE foam copper-clad laminate prepared by this invention has high PTFE purity, low dielectric constant, low dielectric loss, isotropic material, good dimensional stability, and a mature technology, making it easy to achieve large-scale production of PTFE foam copper-clad laminates.

Description

Technical Field

[0001] This invention belongs to the field of electronic circuits, specifically relating to a PTFE foam copper-clad laminate and its preparation method. Background Technology

[0002] With the explosive growth of the global 5G market, the vision of transforming people's lifestyles through the Internet of Things, autonomous driving, and a smart society is becoming increasingly closer. 5G communication technology uses the millimeter-wave band, and the shorter the wavelength of electromagnetic waves, the worse their diffraction ability and the greater the attenuation during propagation. This results in poor signal interference resistance during propagation, placing more stringent requirements on copper-clad laminate (CCL) materials. Currently, conventional FR-4 CCLs are far from meeting the demands, and substrate materials are gradually developing towards high-precision and sophisticated technologies, giving rise to high-frequency CCLs.

[0003] There are many resin materials suitable for producing high-frequency copper-clad laminates, such as polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO / PPE), cyanate ester (CE), polyimide (PI), olefin resins, and liquid crystal polymers (LCP). Among them, PTFE molecular chains contain CF bonds and have a symmetrical structure. Furthermore, due to the large size of the fluorine (F) atoms, PTFE molecular chains exhibit a helical structure. These structural characteristics endow PTFE with excellent properties, such as excellent dielectric properties, insulation, high heat resistance, chemical stability, and weather resistance. Therefore, PTFE resin is the most suitable resin material for the production of high-frequency copper-clad laminates.

[0004] Because PTFE is a thermoplastic polymer material, it can be repeatedly heated and molded. However, PTFE has a high melting point (around 327°C) and extremely high melt viscosity (10). 11 -10 13 Therefore, conventional processes such as melt extrusion and injection molding are not suitable for molding PTFE high-frequency copper-clad laminates. Traditional FR-4 copper-clad laminates are produced using a glass cloth impregnation molding process, and similar processes are used in the copper-clad laminate industry to produce PTFE-based high-frequency copper-clad laminates. However, the viscosity of the PTFE dispersion is low, and the amount of adhesive applied by a single impregnation of the glass cloth can only reach 20-60 g / m². 2 Even with multiple applications of adhesive, the PTFE content is destined to be limited due to the maximum crack-breaking film thickness. Therefore, pure PTFE cutting film is typically used to further increase the adhesive content of the board. Furthermore, the presence of glass cloth still affects the dielectric properties of the board, and the dimensional stability of the board in all directions is also affected by the type of material.

[0005] Furthermore, with the increasing demand for PTFE-based high-frequency copper clad laminates, although several domestic companies are now capable of producing fiberglass-reinforced PTFE-based high-frequency copper clad laminates, these products are only considered low- to mid-range products in the high-frequency market. High-end high-frequency substrate materials are currently monopolized by American companies. It is hoped that domestic high-frequency copper clad laminate manufacturers will increase their R&D investment and actively innovate to revitalize the national information industry. Therefore, developing a PTFE-based high-frequency copper clad laminate with stable dielectric properties, low dielectric loss, and isotropy has significant practical implications. Summary of the Invention

[0006] In view of the problems and shortcomings of the existing technology, the purpose of this invention is to provide a PTFE foam copper clad laminate and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a PTFE foam copper clad laminate, the PTFE foam copper clad laminate comprising PTFE foam material, wherein a metal material layer is provided on the upper surface and / or lower surface of the PTFE foam material, and the metal material layer is connected to the PTFE foam material through an adhesive layer.

[0009] Preferably, the preparation method of the PTFE foam material is as follows: mixing PTFE suspension with thickener solution to obtain a mixture; stirring the mixture to foam it to obtain a foaming liquid; freezing the foaming liquid to set it; and then freeze-drying and sintering the set sample to obtain the PTFE foam material.

[0010] Preferably, the thickener is any one of polyethylene oxide, methylcellulose, and polyvinyl alcohol.

[0011] Preferably, the mass ratio of PTFE to thickener in the mixture is (5-20):1. More preferably, the mass ratio of PTFE to thickener in the mixture is 10:1.

[0012] Preferably, the molecular weight of the polyethylene oxide is between 100,000 and 5,000,000. More preferably, the molecular weight of the polyethylene oxide is between 500,000 and 3,000,000.

[0013] More preferably, the molecular weight of the methylcellulose is 454 and the molecular weight of the polyvinyl alcohol is 15,000.

[0014] Preferably, the thickener solution has a percentage concentration of 5wt%-15wt%.

[0015] More preferably, the solvent for both the PTFE suspension and the thickener solution is water.

[0016] More preferably, functional materials may be added to the mixture of the PTFE suspension and the thickener solution to give the resulting PTFE foam material a superior cell structure, resulting in better dielectric properties and thermal dimensional stability. These functional materials may be one or more ceramic materials such as boron nitride and aluminum nitride. In practical applications, functional materials can be added as needed.

[0017] In this invention, the particle size of the functional material affects the expansion ratio of the subsequently prepared PTFE, thereby affecting the density of the subsequent PTFE foam material. The functional material can be, but is not limited to, inorganic material particles, organic polymer material particles, composite material particles, or their precursors. Optionally, a particle size of 200-600 nm is beneficial for preparing PTFE foam materials.

[0018] Preferably, during the preparation of the PTFE foam material, the stirring rate of the stirring foaming process is 3000-5000 r / min, and the foaming ratio is 1-5 times.

[0019] Preferably, during the preparation of the PTFE foam material, the freeze-setting conditions are -200 to 0°C for 10-120 minutes. Further, the specific freeze-setting operation involves pouring the foaming liquid into a mold and rapidly freezing it at -200 to 0°C for 10-120 minutes for setting. More preferably, the freeze-setting temperature is -100 to 0°C.

[0020] More preferably, in the preparation process of the PTFE foam material, the freeze-drying temperature is -200℃ to 0℃, the time is 10-120 min, and the vacuum degree of the freeze dryer is -0.101 MPa. More preferably, the freeze-drying temperature is -100℃ to 0℃.

[0021] More preferably, the freeze-setting temperature and the freeze-drying temperature are the same.

[0022] Preferably, during the preparation of the PTFE foam material, the sintering conditions are 330-390℃ for 2-12 hours. More preferably, the sintering temperature is 330-370℃. This is because the freeze-dried sample still contains thickener, which needs to be removed by high-temperature sintering in a muffle furnace after demolding.

[0023] Preferably, the adhesive is a thermoplastic adhesive or a thermosetting adhesive. More preferably, the adhesive is at least one selected from epoxy resin, phenolic resin, PPO resin, and polyacrylate.

[0024] More preferably, the metal material includes a metal film or a metal sheet, and the shape and size of the metal material are not limited, and can be selected according to the actual application requirements. More preferably, the metal material is a copper foil with a thickness of 18 μm.

[0025] More preferably, the metal material can be disposed on one surface of the PTFE foam material or on two opposite surfaces of the PTFE foam material, without limitation.

[0026] The second aspect of the present invention provides a method for preparing the copper-clad laminate described in the first aspect above. The method comprises: coating an adhesive on the upper surface and / or lower surface of a PTFE foam material, bonding the adhesive-coated side of the PTFE foam material to a metal material, and then performing vacuum hot pressing to obtain the copper-clad laminate.

[0027] Preferably, the hot pressing temperature is 140-200℃, the pressure is 1-30MPa, and the time is 30min-180min. More preferably, the hot pressing pressure is 5-20MPa, and the time is 30min-120min.

[0028] The third aspect of the present invention provides the application of the copper-clad laminate described in the first aspect in electronic products.

[0029] A fourth aspect of the present invention provides an electronic component comprising a copper-clad laminate as described in the first aspect above.

[0030] In this invention, the electronic components include resistors, capacitors, connectors, electroacoustic devices, electronic display devices, optoelectronic devices, sensors, printed circuit boards, circuit boards, circuits, piezoelectric devices, etc. Specifically, the electronic components may be, but are not limited to, printed circuit boards, circuit boards, sensors, electronic circuits, etc. Specifically, the copper-clad laminate may be, but is not limited to, used in printed circuit boards. Each layer of the copper-clad laminate has low conductivity and low loss rate, which can improve the water and oxygen isolation performance of the electronic components; or when the PTFE foam material in the copper-clad laminate includes conductive fillers, the conductivity of the electronic components is improved; or when the PTFE foam material in the copper-clad laminate includes thermally conductive fillers, the thermal conductivity of the electronic components is improved.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) In this invention, a foaming liquid is prepared by first mixing a PTFE suspension with a thickener solution. Then, the foaming liquid is freeze-set, freeze-dried, and sintered to prepare PTFE foam. Finally, an adhesive is coated onto the foam, and it is hot-pressed with a metal material to prepare a PTFE foam copper-clad laminate. This invention overcomes the difficulty in processing PTFE by adjusting parameters such as the foaming ratio and the mass fraction of the thickener solution to adjust the porosity of the PTFE foam, thereby adjusting the dielectric constant, dielectric loss, and other performance parameters of the PTFE foam copper-clad laminate. Furthermore, the PTFE foam material prepared by this invention has uniform cell structure, good dielectric properties, and isotropic properties, which is more conducive to the dimensional stability of the copper-clad laminate. Moreover, the technology is mature and easily enables large-scale production of PTFE foam copper-clad laminates.

[0033] (2) The present invention can also add functional materials such as boron nitride and aluminum nitride to the mixture of PTFE suspension and thickener solution to make the PTFE foam material have better performance, such as better dielectric properties, electromagnetic shielding effectiveness, and thermal conductivity. Therefore, the technical method of the present invention has a large degree of operability and the technical process can be adjusted as needed to meet actual needs. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0036] Example 1: Discussion on the foaming ratio in the preparation method of PTFE foam copper clad laminate

[0037] To investigate the effects of foaming ratio on the average porosity of the prepared PTFE foam and the dielectric constant and dielectric loss of the PTFE foam copper clad laminate, the inventors conducted the following experiments, namely Examples 1-1 to 1-5 and Comparative Example 1-1, with corresponding foaming ratios of 1, 2, 3, 4, 5, and 0, respectively. The measurement results are shown in Table 1.

[0038] Example 1-1

[0039] This embodiment provides a PTFE foam copper-clad laminate, including the following steps:

[0040] (1) Dissolve polyethylene oxide (PEO) with a molecular weight of 1.5 million in deionized water to prepare an 8% PEO solution as a thickener for later use.

[0041] (2) Mix the PTFE suspension with the PEO solution obtained in step (1) to obtain a mixture; wherein the mass ratio of PTFE to PEO in the mixture is 10:1.

[0042] (3) The mixture obtained in step (2) is mechanically stirred and foamed until the foaming ratio is 1, and then the stirring is stopped to obtain foaming liquid; wherein the stirring speed is 3000r / min.

[0043] (4) Quickly pour the foaming liquid obtained in step (3) into a 20cm×20cm stainless steel mold and place it in a -80℃ freezer for 30 minutes to set the shape; after setting, place it in a freeze dryer for 24 hours to freeze dry. During the freeze drying process, the vacuum degree of the freeze dryer is -0.101MPa and the temperature is -80℃.

[0044] (5) The freeze-dried sample was demolded and placed in a muffle furnace at 356℃ for 4 hours. The heating rate of the muffle furnace was 20℃ / min. After sintering, PTFE foam was obtained.

[0045] (6) Coat the upper and lower surfaces of the PTFE foam with epoxy resin adhesive, and then cover them with 18μm copper foil and vacuum press them together to obtain the PTFE foam copper-clad laminate. The pressing conditions are 140℃ and 5MPa hot pressing for 30min.

[0046] Examples 1-2

[0047] The content of a PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the foaming ratio in step (3) is 2 times.

[0048] Examples 1-3

[0049] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the foaming ratio in step (3) is 3 times.

[0050] Examples 1-4

[0051] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the foaming ratio in step (3) is 4 times.

[0052] Examples 1-5

[0053] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the foaming ratio in step (3) is 5 times.

[0054] Comparative Example 1-1

[0055] The content of a PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the foaming liquid in step (3) is not prepared, and the mixture obtained in step (2) is directly poured into a stainless steel mold for freezing and shaping.

[0056] Table 1 Performance parameters of the copper-clad laminate samples prepared in Example 1

[0057]

[0058] As shown in Table 1, with the increase of foaming ratio, the porosity increases significantly, while the dielectric constant and dielectric loss decrease significantly. It is well known that air has a dielectric constant close to 1 and a dielectric loss close to 0. PTFE foam material, due to the introduction of air bubbles, has cells that act like cavities, reducing the material's dielectric constant and dielectric loss. However, the higher the foaming ratio, the worse the mechanical properties of the foam material. Therefore, considering mechanical properties, a foaming ratio of 1 is preferred for PTFE foaming; considering dielectric properties, a foaming ratio of 5 is preferred; and considering both dielectric and mechanical properties, a foaming ratio of 3 is preferred for PTFE foaming.

[0059] Example 2: Discussion on the mass fraction of PEO solution in the preparation method of PTFE foam copper clad laminate

[0060] To investigate the effect of PEO solution mass fraction on the average porosity of the prepared PTFE foam and the dielectric constant and dielectric loss of the PTFE foam copper clad laminate, the inventors conducted the following experiments, namely Examples 1-1 and 2-1 to 2-3, with corresponding PEO solution mass fractions of 8%, 5wt%, 10wt%, and 15wt%, respectively. The measurement results are shown in Table 2.

[0061] Example 2-1

[0062] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the mass fraction of the PEO solution in step (1) is 5 wt%.

[0063] Example 2-2

[0064] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the mass fraction of the PEO solution in step (1) is 10wt%.

[0065] Example 2-3

[0066] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the mass fraction of the PEO solution in step (1) is 15wt%.

[0067] Table 2 Performance parameters of the copper-clad laminate samples prepared in Example 2

[0068]

[0069] As shown in Table 2, with the increase of PEO solution mass fraction, the porosity slightly increases, while the dielectric constant and dielectric loss decrease. This is because the increased PEO solution mass fraction increases the viscosity of the mixed solution, resulting in greater surface tension and promoting more stable cell formation. Therefore, a PEO solution mass fraction of 15 wt% is preferred for preparing PTFE foam.

[0070] Example 3: Discussion on the molecular weight of PEO in the preparation method of PTFE foam copper clad laminate

[0071] To investigate the influence of PEO molecular weight on the average porosity of the prepared PTFE foam and the dielectric constant and dielectric loss of the PTFE foam copper clad laminate, the inventors conducted the following experiments, namely Examples 1-1 and 3-1 to 3-3, with corresponding PEO molecular weights of 1.5 million, 500,000, 1 million, and 3 million, respectively. The measurement results are shown in Table 3.

[0072] Example 3-1

[0073] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the molecular weight of PEO in step (1) is 500,000.

[0074] Example 3-2

[0075] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the molecular weight of PEO in step (1) is 1 million.

[0076] Example 3-3

[0077] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the molecular weight of PEO in step (1) is 3 million.

[0078] Table 3 Performance parameters of the copper-clad laminate samples prepared in Example 3

[0079]

[0080] As shown in Table 3, the porosity and dielectric properties did not change significantly with the increase of PEO molecular weight. This is because the porosity remained essentially the same at the same foaming ratio.

[0081] Example 4: Discussion on freezing temperature in the preparation method of PTFE foam copper clad laminate

[0082] To investigate the effects of freeze-setting and freeze-drying temperatures on the average porosity of the prepared PTFE foam and the dielectric constant and dielectric loss of the PTFE foam copper-clad laminate, the inventors conducted the following experiments, namely Examples 1-1 and 4-1 to 4-3, with corresponding freeze-setting and freeze-drying temperatures of -80℃, -100℃, -50℃, and 0℃, respectively. The measurement results are shown in Table 4.

[0083] Example 4-1

[0084] The content of a PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the freezing and freezing-drying temperatures in step (4) are both -100℃.

[0085] Example 4-2

[0086] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the freezing and freezing-drying temperatures in step (4) are both -50°C.

[0087] Example 4-3

[0088] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the freezing and freezing-drying temperatures in step (4) are both 0°C.

[0089] Table 4 Performance parameters of the copper-clad laminate samples prepared in Example 4

[0090]

[0091] Table 4 shows that porosity, dielectric constant, and dielectric loss remain relatively stable with increasing freeze-setting and freeze-drying temperatures. This is because freezing fixes the cell structure but does not alter it; however, lower temperatures result in faster production. Considering both production efficiency and effectiveness, a freeze-setting and freeze-drying temperature of -80℃ is preferred for preparing PTFE foam.

[0092] Example 5: Discussion on sintering temperature in the preparation method of PTFE foam copper clad laminate

[0093] To investigate the effects of sintering temperature on the average porosity of the prepared PTFE foam and the dielectric constant and dielectric loss of the PTFE foam copper-clad laminate, the inventors conducted the following experiments, namely Examples 1-1 and 5-1 to 5-2, with corresponding sintering temperatures of 356℃, 330℃, and 370℃, respectively. The measurement results are shown in Table 5.

[0094] Example 5-1

[0095] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the sintering temperature in step (5) is 330℃.

[0096] Example 5-2

[0097] The content of the PTFE foam copper clad laminate is basically the same as that of Example 1-1, except that the sintering temperature in step (5) is 370℃.

[0098] Table 5 Performance parameters of the copper-clad laminate samples prepared in Example 5

[0099]

[0100] Table 5 shows that with increasing sintering temperature, porosity increases, dielectric constant decreases slightly, and dielectric loss remains relatively stable. This is because higher sintering temperature allows for more complete PEO degradation and enables its degradation products to leave the material bulk more quickly, which slightly increases cell size and porosity. Considering both production efficiency and effectiveness, a sintering temperature of 356℃ is preferred for preparing PTFE foam.

[0101] In summary, this invention effectively overcomes the shortcomings of the prior art and has high industrial applicability. The above embodiments are intended to illustrate the substantive content of this invention, but are not intended to limit the scope of protection of this invention. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this invention without departing from the essence and scope of protection of this invention.

Claims

1. A PTFE foam copper-clad laminate, characterized in that, The PTFE foam copper clad laminate includes PTFE foam material, and a metal material layer is provided on the upper surface and / or lower surface of the PTFE foam material. The metal material layer is connected to the PTFE foam material through an adhesive layer. The preparation method of the PTFE foam material is as follows: PTFE suspension is mixed with thickener solution to obtain a mixture; the mixture is stirred and foamed to obtain a foaming liquid; the foaming liquid is freeze-dried and sintered sequentially to obtain PTFE foam material; The thickener is any one of polyethylene oxide, methylcellulose, and polyvinyl alcohol, and the percentage concentration of the thickener solution is 5wt% to 15wt%; the mass ratio of PTFE to thickener in the mixture is (5 to 20):

1.

2. The PTFE foam copper-clad laminate according to claim 1, characterized in that, The molecular weight of the polyethylene oxide is between 100,000 and 5 million.

3. The PTFE foam copper-clad laminate according to claim 1, characterized in that, During the preparation of the PTFE foam material, the foaming ratio of the stirring foaming treatment is 1 to 5 times.

4. The PTFE foam copper-clad laminate according to claim 1, characterized in that, During the preparation of the PTFE foam material, the freezing and shaping conditions are -200 to 0℃ for 10 to 120 minutes; the sintering conditions are 330 to 390℃ for 2 to 12 hours.

5. The method for preparing the copper-clad laminate according to any one of claims 1 to 4, characterized in that, The preparation method is as follows: an adhesive is coated on the upper surface and / or lower surface of the PTFE foam material, and the side of the PTFE foam material coated with adhesive is bonded to the metal material, and then hot pressing is performed to obtain the copper-clad laminate.

6. The preparation method according to claim 5, characterized in that, The adhesive is a thermoplastic adhesive or a thermosetting adhesive; the hot pressing temperature is 140-200℃, the hot pressing pressure is 1-30MPa, and the hot pressing time is 30-180min.

7. The application of the copper-clad laminate according to any one of claims 1 to 4 in electronic products.

8. An electronic component, characterized in that, Including the copper-clad laminate as described in any one of claims 1 to 4.

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