A paper-based microwave composite dielectric substrate and a preparation method thereof

Abstract

The application provides a paper-based microwave composite dielectric substrate and a preparation method thereof.The paper-based microwave composite dielectric substrate is prepared from the following raw materials in parts by weight: inorganic or organic short-cut fibers: 0-12 wt%; inorganic fiber cotton or organic fibrillation / precipitation fibers: 3-20 wt%; fluororesin: 68-97 wt%.The paper-based microwave composite dielectric substrate has low relative dielectric constant, low dielectric loss factor, excellent thickness uniformity and excellent relative dielectric constant uniformity, and the method is more economical and convenient and can be mass-produced.

Description

Technical Field

[0001] This invention belongs to the field of microwave composite dielectric substrate technology, and relates to a paper-based microwave composite dielectric substrate and its preparation method. Background Technology

[0002] Microwave composite dielectric substrates, also known as high-frequency substrate materials or high-frequency copper-clad laminates, are fundamental electronic materials used in the fabrication of printed circuit boards (PCBs) and various radio frequency / microwave functional components. They are widely used in commercial communications, integrated circuits, industrial equipment, and aerospace. With the increasing demands for data transmission rates and throughput in modern electronic information technology, the operating frequency, rated power, and integration density of electronic devices are constantly increasing. Therefore, it is essential to use microwave composite dielectric substrates with low relative permittivity, low dielectric loss factor, and high dielectric structure consistency to achieve low latency, low attenuation, and high reliability in end-applications.

[0003] Existing technologies often employ fiber-reinforced polymer resin composites to prepare the aforementioned dielectric substrates, which suffer from the following problems: 1) The types of fiber raw materials used are relatively limited, lacking innovative development and utilization of high-performance fibers; 2) The technical route for preparing prepregs is relatively simple, generally involving first preparing fiber base paper using wet forming technology, and then repeatedly impregnating / coating the fiber base paper with resin to prepare the prepreg, resulting in cumbersome and inefficient processes; 3) The fiber base paper mentioned in 2) has extremely poor strength and is easily damaged, therefore, a certain amount of adhesive is often sprayed during the wet paper web forming stage. While adhesives can improve the strength of fiber-based paper, they also reduce the porosity of the paper, directly affecting the amount of adhesive applied in subsequent impregnation / coating. Furthermore, the adhesive introduces impurities into the final dielectric substrate, severely impacting its dielectric properties. 4) Existing wet-forming processes produce prepregs with uneven fiber-resin distribution, affecting the dielectric and thickness uniformity, as well as high-frequency performance stability. 5) Cold-pressing sintering results in numerous pores and a lack of density within the dielectric substrate, leading to high water absorption and poor performance stability in practical applications. Therefore, vacuum hot-pressing sintering is commonly used in this field to prepare nearly completely dense dielectric substrates.

[0004] Therefore, the shortcomings of existing technologies in products include high dielectric loss factor, high relative permittivity, poor uniformity of relative permittivity, poor uniformity of thickness, and difficulty in continuous engineering fabrication. Summary of the Invention

[0005] To address the problems of poor dielectric properties and uniformity, complex fabrication processes, and inability to achieve stable mass production of paper-based microwave composite dielectric substrates prepared by existing technologies, this invention provides a paper-based microwave composite dielectric substrate and its fabrication method. The paper-based microwave composite dielectric substrate of this invention exhibits low relative permittivity, low dielectric loss factor, excellent thickness uniformity, and excellent relative permittivity uniformity. Furthermore, the method of this invention is more economical, convenient, and scalable for mass production.

[0006] The technical solution adopted in this invention is as follows:

[0007] On one hand, the present invention provides a paper-based microwave composite dielectric substrate, which is a short fiber reinforced fluororesin microwave composite dielectric substrate, made from the following raw materials by weight percentage:

[0008] Inorganic or organic chopped fibers: 0-12 wt%;

[0009] Inorganic fiber cotton or organic fibrillated / precipitated fiber: 3-20 wt%;

[0010] Fluoropolymer: 68-97 wt%.

[0011] Preferably, the content of the inorganic or organic chopped fibers is 0-10 wt%.

[0012] Preferably, the content of the inorganic fiber cotton or organic fibrillated / precipitated fiber is 3-17 wt%.

[0013] Preferably, the content of the fluororesin is 80-97 wt%.

[0014] Preferably, the inorganic chopped fibers are selected from alkali-free, low-dielectric, high-silica, high-strength hollow glass chopped fibers, quartz chopped fibers, boron nitride chopped fibers, etc., and the organic chopped fibers are selected from aromatic polyamide chopped fibers (including para- and meta-aramid chopped fibers), aromatic heterocyclic chopped fibers (including poly(p-phenylenebenzodioxazole) (PBO), polybenzimidazole, polyphenylenepyridinium diimidazole, aramid III, polyimide fibers, etc.).

[0015] Preferably, the inorganic chopped fibers have an average diameter of less than 10 micrometers and a length of 1-9 millimeters.

[0016] Preferably, the inorganic chopped fibers have an average diameter of 3-6 micrometers and a length of 5-7 millimeters.

[0017] Preferably, the organic chopped fibers have an average diameter of less than 15 micrometers and a length of 1-9 millimeters.

[0018] Preferably, the organic chopped fibers have an average diameter of 12-14 micrometers and a length of 2-7 millimeters.

[0019] Preferably, the inorganic fiber cotton is selected from alkali-free, low-dielectric, high-silica, high-strength glass wool fiber, quartz glass wool fiber, boron nitride cotton fiber, etc., and the organic fibrillated / precipitated fiber is selected from aromatic polyamide fibrillated / precipitated fibers (including para- and meta-aramid fibrillated / precipitated fibers), aromatic heterocyclic fibrillated / precipitated fibers (including poly(p-phenylenebenzodioxazole), polybenzimidazole, polyphenylenepyridinium diimidazole, aramid III, polyimide fibrillated / precipitated fibers, etc.

[0020] Preferably, the average diameter of the inorganic fiber cotton is less than or equal to 3 micrometers.

[0021] Preferably, the organic fibrillated / precipitated fiber is an organic short-cut fiber prepared by mechanical pulping or chemical precipitation to obtain a freeness of 25-85°SR.

[0022] More preferably, the organic fibrillated / precipitated fiber is an organic short-cut fiber prepared by mechanical pulping or chemical precipitation to obtain a freeness of 30-80°SR.

[0023] More preferably, the organic fibrillated / precipitated fiber is an organic short-cut fiber prepared by mechanical pulping or chemical precipitation to obtain a freeness of 50-70°SR.

[0024] Preferably, the fluororesin is selected from resins such as polytetrafluoroethylene, polyvinylidene fluoride, and perfluoroethylene propylene, and more preferably polytetrafluoroethylene resin.

[0025] Preferably, the fluororesin is in granular form with an average particle size of 0.15-0.35 micrometers.

[0026] Preferably, the fluororesin is in the form of a fluororesin suspension, which is a suspension formed by uniformly dispersing particulate fluororesin in an aqueous medium.

[0027] Preferably, in the fluororesin suspension, the content of the particulate fluororesin is 25-62 wt% (e.g., 60 wt%).

[0028] The paper-based microwave composite dielectric material prepared by this invention has the following characteristics:

[0029] 1) The relative permittivity is as low as 2.11, the dielectric loss factor is as low as 0.0006, and the range of relative permittivity of 9 points within a 500×600mm area is less than or equal to 0.04, and the range of thickness of 9 points within a 500×600mm area is less than 10 micrometers. It has excellent isotropy and can meet the requirements of high-performance and high-reliability dielectric substrates for RF, millimeter-wave and even terahertz frequency band applications to the greatest extent.

[0030] 2) It has excellent processability and performance characteristics under high humidity conditions, with a water absorption rate as low as 0.01%. It can withstand the corrosion of various commonly used acids, alkalis and organic solutions in PCB processing and 260℃ soldering processing while keeping the dielectric substrate from warping and its performance from degrading.

[0031] 3) Low density, which can effectively reduce the overall weight of electronic systems and expand their functionality in large-scale circuit design;

[0032] 4) The paper-based microwave composite dielectric substrate of the present invention uses a wide range of raw materials that are readily available, and the preparation process is more efficient than the prior art. It is also environmentally friendly and easy to mass-produce in the industrial sector.

[0033] This invention addresses the practical performance requirements of dielectric substrate materials for millimeter-wave and even terahertz frequency band applications. It optimizes the use of high-performance organic / inorganic fibers and fluororesins, and utilizes fiber blending techniques to control the overall performance of the dielectric substrate material. Simultaneously, it innovatively employs advanced wet papermaking technology to impart uniformity of fiber-resin distribution at the micro-nano scale and random orientation within the fiber plane, significantly avoiding the introduction of various impurities and additives. Therefore, the paper-based microwave dielectric substrate prepared by this invention possesses low relative permittivity and low dielectric loss factor, excellent thickness uniformity, excellent relative permittivity uniformity, high isotropy, and low water absorption. It shows promising application prospects in high-frequency, high-speed, and high-reliability fields such as RF / millimeter-wave / terahertz circuits, high-speed computers, consumer electronics, and industrial equipment.

[0034] On the other hand, the present invention provides a method for preparing a paper-based microwave composite dielectric substrate, the method comprising the following steps:

[0035] 1) Disperse inorganic or organic chopped fibers in deionized water to obtain a suspension in which the inorganic or organic chopped fibers are fully dispersed. This step is required if inorganic or organic chopped fibers are used; otherwise, this step is omitted.

[0036] 2) Disperse inorganic fiber cotton or organic fibrillated / precipitated fiber in deionized water to obtain a suspension in which inorganic fiber cotton or organic fibrillated / precipitated fiber is fully dispersed.

[0037] 3) Mix and stir the suspension of inorganic or organic short-cut fibers obtained in step 1) with the suspension of inorganic fiber cotton or organic fibrillated / precipitated fibers obtained in step 2) to obtain a fiber mixed suspension; if step 1) does not exist, this step is not required.

[0038] 4) Add flocculant to the fluororesin suspension for flocculation treatment to obtain flocculated fluororesin slurry;

[0039] 5) Add the flocculated fluororesin slurry from step 4) to the fiber mixed suspension from step 3) (or, if step 3 does not exist, add it to the suspension of inorganic fiber cotton or organic fibrillated / precipitated fibers from step 2) to obtain a mixed slurry.

[0040] 6) The mixed slurry from step 5) is subjected to wet papermaking and dried to obtain a paper-based semi-cured sheet;

[0041] 7) The paper-based prepreg from step 6) is heat-treated under high temperature conditions;

[0042] 8) The paper-based prepreg obtained in step 7) is stacked in single or multiple layers according to the required thickness, and finally copper foil is applied to the outermost single or double sides for vacuum hot pressing to prepare a paper-based microwave composite dielectric substrate.

[0043] Preferably, in step 1), the mass concentration of the suspension in which the inorganic or organic chopped fibers are fully dispersed is 0.01-1%.

[0044] Preferably, in step 1), inorganic or organic chopped fibers are dispersed in deionized water and decomposed in a hydraulic pulper at a speed of 1000-15000 r / min for 1-30 min to obtain a suspension in which inorganic or organic chopped fibers are fully dispersed.

[0045] Preferably, in step 2), the mass concentration of the inorganic fiber cotton or organic fibrillated / precipitated fiber fully dispersed suspension is 0.01-1%.

[0046] Preferably, in step 2), the inorganic fiber cotton or organic fibrillated / precipitated fiber is dispersed in deionized water and decomposed in a hydraulic pulper at a speed of 1000-25000 r / min for 1-25 min to obtain a suspension in which the inorganic fiber cotton or organic fibrillated / precipitated fiber is fully dispersed.

[0047] Preferably, in step 4), the fluororesin suspension is formed by dispersing particulate fluororesin in deionized water.

[0048] Preferably, in step 4), the mass fraction of the fluororesin suspension is 25-62%.

[0049] Preferably, in step 4), the fluororesin suspension is a polytetrafluoroethylene suspension with a mass fraction of 25-62%.

[0050] Preferably, the flocculant is selected from one or more of cationic branched starch, dopamine hydrochloride, chitosan, polyethylene oxide, polyethyleneimine, polyacrylamide, and natural polymer-acrylamide copolymers.

[0051] Preferably, in step 4), the amount of flocculant used is 0.01wt%-10wt% of the total dry weight of the raw materials.

[0052] Preferably, in step 6), the wet papermaking process refers to dehydrating and forming the mixed slurry obtained in step 5) on the wire section of a papermaking machine, and then drying it to obtain a paper-based semi-cured sheet.

[0053] Preferably, the paper machine can be selected from inclined wire, cylinder wire, super cylinder wire, long wire, clamp wire, and top wire paper machine.

[0054] Preferably, the drying method can be one or a combination of heat conduction, heat convection, and heat radiation; the drying environment can be atmospheric pressure or vacuum conditions.

[0055] Preferably, in step 7), the high temperature condition is a temperature of 180-320℃, and the equipment used can be a high temperature blower / vacuum oven, muffle furnace, tube furnace, etc., with no restrictions on the environmental atmosphere.

[0056] Preferably, in step 7), the heat treatment time is 2-6 hours.

[0057] Preferably, in step 8), the paper-based prepreg used in the multilayer stacking can be of the same type, or multiple types of prepreg can be selected for stacking.

[0058] Preferably, in step 8), the copper foil is selected from one or a combination of two of the following: electrolytic copper foil, reverse copper foil, or rolled copper foil, and has a thickness of 9 micrometers to 70 micrometers.

[0059] Preferably, in step 8), the vacuum hot pressing conditions are: pressure 2-8 MPa, temperature 365℃-400℃, vacuum degree 0.04-0.1 MPa, and hot pressing time 2-8 hours.

[0060] Preferably, in step 8), the thickness of the paper-based microwave composite dielectric substrate ranges from 0.05 to 10 mm.

[0061] Preferably, the paper-based microwave composite dielectric material prepared in step 8) can be directly used in the processing of single / double-sided flexible / rigid PCBs, multilayer boards and various microwave functional components.

[0062] Compared with the prior art, the preparation process of the present invention has the following advantages:

[0063] 1) This technology avoids the two-stage preparation route of first forming short fibers into base paper and then impregnating the base paper with resin in the existing technology. The technology has fast forming speed, high efficiency, high repeatability and high reliability, which is conducive to large-scale industrial production.

[0064] 2) The fiber / resin mass ratio can be adjusted easily and quickly, thereby flexibly adjusting the overall performance of the dielectric substrate and overcoming the disadvantage of the difficulty in controlling the amount of adhesive applied in the impregnation method.

[0065] 3) The fiber skeleton and resin matrix in the prepreg are formed simultaneously during the papermaking process. The uniformity of fiber-resin micro-distribution in the micro-nano scale is better than that of the impregnation method. Therefore, the dielectric properties of the prepared paper-based microwave composite dielectric substrate are more excellent. At the same time, due to the steric hindrance effect of the resin particles during the forming process, some fibers are distributed along the thickness direction of the paper, which helps to reduce the Z-direction thermal expansion coefficient of the dielectric substrate and improve the isotropy of the dielectric substrate.

[0066] 4) There are many types and forms of fibers that can be used, and they are abundant and easy to obtain, resulting in better overall performance of the prepared dielectric substrate. Detailed Implementation

[0067] The present invention will be further described below with reference to embodiments, which are as follows:

[0068] Example 1

[0069] Raw materials and their proportions:

[0070] Inorganic fiber cotton: 5wt% quartz glass wool fiber, average diameter 3 micrometers;

[0071] Fluoropolymer: 95wt% polytetrafluoroethylene resin, in aqueous dispersion suspension: the mass fraction of polytetrafluoroethylene particles is 60%, with an average particle size of 0.25 micrometers.

[0072] 1) Disperse quartz glass wool fibers at a concentration of 0.08 wt% in deionized water, and use a hydraulic pulper at a constant speed of 8000 r / min for 15 min to obtain a quartz glass wool fiber suspension.

[0073] 2) Add 0.1% of the total dry weight of cationic branched starch to the polytetrafluoroethylene suspension for flocculation treatment, and then mix it evenly with the quartz glass wool fiber suspension in step 1) to obtain a mixed slurry.

[0074] 3) Pump the mixed slurry from step 2) to the inclined wire paper machine. After being fully dispersed in the headbox, the slurry is dehydrated and formed in the forming wire section of the inclined wire paper machine to obtain a wet paper web. After drying, a paper-based semi-cured sheet is obtained.

[0075] 4) Treat the paper-based semi-cured sheet in an oven at 200-240℃ for 4-6 hours;

[0076] 5) The semi-cured sheets from step 4) are stacked, and an electrolytic copper foil is coated on each of the two surfaces. The paper-based microwave composite dielectric substrate is obtained by holding the substrate under vacuum of 0.08 MPa, temperature of 380℃, and pressure of 2.5 MPa for 2.5 hours.

[0077] Example 2

[0078] Raw materials and their proportions:

[0079] Inorganic chopped fibers: 8 wt% quartz glass chopped fibers, with an average diameter of 4-5 micrometers and an average length of 6 mm;

[0080] Inorganic fiber cotton: 3wt% alkali-free glass wool fiber, with an average diameter of 2 micrometers;

[0081] Fluoropolymer: 89wt% polytetrafluoroethylene resin, in aqueous dispersion suspension: the mass fraction of polytetrafluoroethylene particles is 60%, with an average particle size of 0.25 micrometers.

[0082] Preparation process steps:

[0083] 1) Disperse chopped quartz glass fibers at a concentration of 0.1 wt% in deionized water, and maintain the hydraulic pulper speed at a constant 3000 rpm.

[0084] The concentration was increased by r / min and the disintegration was carried out for 5 min to obtain a quartz glass short-cut fiber dispersion suspension.

[0085] 2) Disperse alkali-free glass wool fibers at a concentration of 0.2 wt% in deionized water, and use a hydraulic pulper with a fixed speed of 10,000 r / min to dissolve for 6 min to obtain an alkali-free glass wool fiber suspension.

[0086] 3) Mix the quartz glass chopped fiber suspension from step 1) with the alkali-free glass wool fiber suspension from step 2) evenly to obtain a fiber mixed suspension;

[0087] 4) Add 0.15% of the total dry weight of cationic branched starch to the polytetrafluoroethylene suspension for flocculation treatment, and then mix it evenly with the fiber suspension in step 3) to obtain a mixed slurry.

[0088] 5) Pump the mixed slurry from step 4) to the inclined wire paper machine. After being fully dispersed in the headbox, the slurry is dehydrated and formed in the forming wire section of the inclined wire paper machine to obtain a wet paper web. After drying, a paper-based semi-cured sheet is obtained.

[0089] 4) Treat the paper-based semi-cured sheet in an oven at 200-240℃ for 4-6 hours;

[0090] 5) The semi-cured sheets from step 4) are stacked, and an electrolytic copper foil is coated on each of the two surfaces. The paper-based microwave composite dielectric substrate is obtained by maintaining the temperature and pressure at 380°C and 0.08MPa for 3 hours.

[0091] Example 3

[0092] Raw materials and their proportions:

[0093] Inorganic fiber cotton: 3wt% high silica glass wool fiber, average diameter 2 micrometers;

[0094] 14wt% quartz glass wool fiber, average diameter 3 micrometers;

[0095] Fluoropolymer: 83wt% polytetrafluoroethylene resin, in aqueous dispersion suspension: the mass fraction of polytetrafluoroethylene particles is 60wt%, with an average particle size of 0.18 micrometers.

[0096] Preparation process steps:

[0097] 1) Disperse high-silica glass wool fibers and quartz glass wool fibers in deionized water at a concentration of 0.1 wt%, and dissolve them in a hydraulic pulper at a constant speed of 15000 r / min for 10 min to obtain a glass wool fiber suspension.

[0098] 2) Add 0.06% of the total dry weight of cationic branched starch to the polytetrafluoroethylene suspension for flocculation treatment, and then mix it evenly with the fiber mixed suspension in step 1) to obtain a mixed slurry;

[0099] 3) Pump the mixed slurry from step 2) to the inclined wire paper machine. After being fully dispersed in the headbox, the slurry is dehydrated and formed in the forming wire section of the inclined wire paper machine to obtain a wet paper web. After drying, a paper-based semi-cured sheet is obtained.

[0100] 4) Treat the paper-based semi-cured sheet in an oven at 200-240℃ for 4-6 hours;

[0101] 5) The semi-cured sheets from step 4) are stacked, and an electrolytic copper foil is coated on each of the two surfaces. The paper-based microwave composite dielectric substrate is obtained by holding the substrate under vacuum of 0.08 MPa, temperature of 385℃, and pressure of 4.5 MPa for 2 hours.

[0102] Example 4

[0103] Raw materials and their proportions:

[0104] Organic fibrillated / precipitated fiber: 3wt% poly(p-phenylenebenzodioxazole) fibrillated fiber, prepared by mechanical refining, with a freeness of 65°SR;

[0105] Fluoropolymer: 97wt% polytetrafluoroethylene resin, in aqueous dispersion suspension form: 60wt% polytetrafluoroethylene particles with an average particle size of 0.3 micrometers.

[0106] Preparation process steps:

[0107] 1) Disperse PBO fibrillated fibers at a concentration of 0.3 wt% in deionized water, and use a hydraulverizer with a fixed speed of 6000 r / min to dissolve for 6 min to obtain a PBO fibrillated fiber suspension;

[0108] 2) Add 0.1% of the total dry weight of polyethyleneimine to the polytetrafluoroethylene suspension for flocculation treatment, and then mix it evenly with the PBO fibrillated fiber suspension in step 1) to obtain a mixed slurry.

[0109] 3) Pump the mixed slurry from step 2) to the inclined wire paper machine. After being fully dispersed in the headbox, the slurry is dehydrated and formed in the wire section of the paper machine to obtain a wet paper web. After drying, a paper-based semi-cured sheet is obtained.

[0110] 4) Treat the paper-based prepreg in an oven at 240-260℃ for 2-4 hours;

[0111] 5) The prepreg from 4) is stacked, and a rolled copper foil is coated on each of the two surfaces. The paper-based microwave composite dielectric substrate is obtained by holding the substrate under vacuum of 0.08 MPa, temperature of 375℃, and pressure of 4 MPa for 4 hours.

[0112] Example 5

[0113] Raw materials and their proportions:

[0114] Organic chopped fiber: 6wt% poly(p-phenylenebenzodioxazole) chopped fiber, average diameter 13 micrometers, average length 6 mm;

[0115] Organic fibrillated / precipitated fiber: 4wt% poly(p-phenylenebenzodioxazole) fibrillated fiber, prepared by mechanical refining, with a freeness of 55°SR;

[0116] Fluoropolymer: 90wt% polytetrafluoroethylene resin, in aqueous dispersion suspension form: 60wt% polytetrafluoroethylene particles with an average particle size of 0.3 micrometers.

[0117] Preparation process steps:

[0118] 1) Disperse PBO chopped fibers at a concentration of 0.05 wt% in deionized water, and use a hydraulverizer with a fixed speed of 3000 r / min to dissolve for 1 min to obtain a PBO chopped fiber suspension;

[0119] 2) Disperse PBO fibrillated fibers at a concentration of 0.3 wt% in deionized water, and use a hydraulverizer with a fixed speed of 6000 r / min to dissolve for 6 min to obtain a PBO fibrillated fiber suspension;

[0120] 3) Mix the PBO chopped fiber suspension from step 1) with the PBO fibrillated fiber suspension from step 2) evenly to obtain a fiber mixed suspension.

[0121] 4) Polyethyleneimine, with a total dry weight of 0.06% of the raw materials in the polytetrafluoroethylene suspension, is subjected to flocculation treatment, and then mixed evenly with the fiber mixed suspension in step 3) to obtain a mixed slurry.

[0122] 5) Pump the mixed slurry from step 4) to a cylinder paper machine, dewater and form a wet paper web, and then dry it to obtain a paper-based semi-cured sheet;

[0123] 6) Treat the paper-based prepreg in an oven at 240-260℃ for 2-4 hours;

[0124] 7) The prepreg from 6) is stacked, and a rolled copper foil is coated on each of the two surfaces. The substrate is then kept at a vacuum of 0.08 MPa, a temperature of 370°C, and a pressure of 3.5 MPa for 3 hours to obtain a paper-based microwave composite dielectric substrate.

[0125] Example 6

[0126] Raw materials and their proportions:

[0127] Organic chopped fiber: 3wt% poly(p-phenylenebenzodioxazole) chopped fiber, average diameter 13 micrometers, average length 6 mm;

[0128] Inorganic fiber cotton: 8wt% alkali-free glass wool fiber, with an average diameter of 2 micrometers;

[0129] Fluoropolymer: 89wt% polytetrafluoroethylene resin, in aqueous dispersion suspension: the mass fraction of polytetrafluoroethylene particles is 60wt%, with an average particle size of 0.22 micrometers.

[0130] Preparation process steps:

[0131] 1) Disperse PBO chopped fibers at a concentration of 0.05 wt% in deionized water, and use a hydraulverizer with a fixed speed of 3000 r / min to dissolve for 3 min to obtain a PBO chopped fiber suspension;

[0132] 2) Disperse alkali-free glass wool fibers at a concentration of 0.2 wt% in deionized water, and use a hydraulic pulper with a fixed speed of 10,000 r / min to dissolve for 6 min to obtain an alkali-free glass wool fiber suspension.

[0133] 3) Mix the PBO chopped fiber suspension from step 1) with the alkali-free glass wool fiber suspension from step 2) evenly to obtain a fiber mixed suspension.

[0134] 4) Add 0.06% of the total dry weight of the raw materials of polyethyleneimine to the polytetrafluoroethylene suspension for flocculation treatment, and then mix it evenly with the fiber mixed suspension in step 3) to obtain a mixed slurry;

[0135] 5) Pump the mixed slurry from step 4) to a cylinder paper machine, dewater and form a wet paper web, and then dry it to obtain a paper-based semi-cured sheet;

[0136] 6) Treat the paper-based prepreg in an oven at 230-260℃ for 3-4 hours to thoroughly remove organic impurities;

[0137] 7) The prepreg from 6) is stacked, and an electrolytic copper foil is coated on each of the two surfaces. The substrate is kept at a vacuum of 0.08 MPa, a temperature of 380°C, and a pressure of 3.5 MPa for 2 hours to obtain a paper-based microwave composite dielectric substrate.

[0138] Example 7

[0139] Raw materials and their proportions:

[0140] Organic chopped fiber: 10wt% poly(p-phenylenebenzodioxazole) chopped fiber, average diameter 13 micrometers, average length 3mm;

[0141] Organic fibrillated / precipitated fiber: 10wt% poly(p-phenylenebenzodioxazole) fibrillated fiber, prepared by mechanical refining, with a freeness of 35°SR;

[0142] Fluoropolymer: 80wt% polytetrafluoroethylene resin, in aqueous dispersion suspension: the mass fraction of polytetrafluoroethylene particles is 60wt%, with an average particle size of 0.28 micrometers.

[0143] The preparation process steps are the same as in Example 5.

[0144] The performance test results of the paper-based microwave composite dielectric substrates in Examples 1-7 are shown in the table below:

[0145]

[0146] Note: The smaller the relative permittivity, the faster the signal transmission speed; the smaller the dielectric loss factor, the less signal transmission loss.

[0147] Comparative Example 1: Preparation of paper-based microwave composite dielectric substrates using the traditional impregnation method

[0148] Raw materials and their proportions:

[0149] Organic fibrillated / precipitated fiber: poly(p-phenylenebenzodioxazole) fibrillated fiber, prepared by mechanical pulping, with a freeness of 65°SR;

[0150] Fluoropolymer: Polytetrafluoroethylene resin, aqueous dispersion suspension: polytetrafluoroethylene particles with a mass fraction of 60 wt% and an average particle size of 0.3 micrometers.

[0151] Preparation process steps:

[0152] 1) PBO fibrillated fibers were dispersed in deionized water at a concentration of 0.3 wt%, and the mixture was pulped at a constant speed of 6000 r / min for 6 min to obtain a PBO fibrillated fiber suspension.

[0153] 2) The PBO fibrillated fiber suspension from step 1) is subjected to wet papermaking and dried to obtain fiber base paper.

[0154] 3) The fiber base paper is impregnated with a 60wt% solid content polytetrafluoroethylene emulsion using the standard impregnation process of existing technology, and then dried to obtain a paper-based semi-cured sheet.

[0155] 4) Treat the paper-based prepreg in an oven at 240-260℃ for 2-4 hours;

[0156] 5) The prepreg from 4) is stacked, and then a rolled copper foil is applied to each of the two surfaces. The paper-based microwave composite dielectric substrate is obtained by holding the substrate under vacuum of 0.08 MPa, temperature of 375℃, and pressure of 4 MPa for 4 hours.

[0157] The performance test results of the paper-based microwave composite dielectric substrate prepared in Comparative Example 1 are shown in the table below:

[0158]

[0159] The dielectric properties of the paper-based microwave composite dielectric substrate prepared by the present invention are superior to those of Comparative Example 1.

[0160] Comparative Example 2: An Exploration Experiment on Fiber Types

[0161] Raw materials and their proportions:

[0162] Inorganic fiber cotton: 5wt% alumina cotton fiber, average diameter 3 micrometers;

[0163] Fluoropolymer: 95wt% polytetrafluoroethylene resin, in aqueous dispersion suspension: the mass fraction of polytetrafluoroethylene particles is 60wt%, with an average particle size of 0.25 micrometers.

[0164] The preparation process is the same as in Example 1.

[0165] The performance test results of the paper-based microwave composite dielectric substrate prepared in Comparative Example 2 are shown in the table below:

[0166]

[0167]

[0168] The paper-based microwave composite dielectric substrate prepared by this invention has better performance than Comparative Example 2.

[0169] Comparative Example 3: Experimental Study on Fiber Length

[0170] Raw materials and their proportions:

[0171] Organic chopped fiber: 6wt% poly(p-phenylenebenzodioxazole) chopped fiber, average diameter 13 micrometers, average length 12 mm;

[0172] Organic fibrillated / precipitated fiber: 4wt% poly(p-phenylenebenzodioxazole) fibrillated fiber, prepared by mechanical refining, with a freeness of 55°SR;

[0173] Fluoropolymer: 90wt% polytetrafluoroethylene resin, in aqueous dispersion suspension form: 60% polytetrafluoroethylene particles by mass, with an average particle size of 0.3 micrometers.

[0174] The preparation process steps are the same as in Example 5.

[0175] Results: In Example 5, the chopped PBO fibers exhibited good dispersion uniformity, resulting in excellent paper-based prepreg forming quality. In Comparative Example 3, the PBO chopped fibers showed severe flocculation during the wet papermaking process, leading to poor uniformity in the paper-based prepreg forming. The performance test results of the paper-based microwave composite dielectric substrate prepared in Comparative Example 3 are shown in the table below.

[0176]

[0177] The dielectric properties of the paper-based microwave composite dielectric substrate prepared by this invention are superior to those of Comparative Example 3.

[0178] As can be seen from the above embodiments and comparative examples, the dielectric loss factor of the dielectric substrate prepared by the present invention is as low as 0.0006, which belongs to the ultra-low loss range. It is 30-40% lower than the dielectric loss factor of the prior art, which is a significant improvement. The relative permittivity reaches or exceeds that of the prior art, and has better relative permittivity and thickness uniformity, which can significantly improve signal transmission speed and antenna radiation efficiency. At the same time, the extremely low water absorption rate and low density reach or exceed the level of the prior art. Overall, it improves the manufacturing technology and comprehensive performance level of the existing paper-based microwave composite dielectric substrate, and has important practical application value.

Claims

1. A paper-based microwave composite dielectric substrate, comprising, by weight, the following raw materials: inorganic or organic chopped fibers: 0-12 wt%; Inorganic fiber cotton or organic fibrillated / precipitated fiber: 3-20 wt% Fluoropolymer: 68-97 wt% in, The preparation method of the paper-based microwave composite dielectric substrate includes the following steps: 1) Disperse inorganic or organic chopped fibers in deionized water to obtain a suspension in which the inorganic or organic chopped fibers are fully dispersed; 2) Disperse inorganic fiber cotton or organic fibrillated / precipitated fiber in deionized water to obtain a suspension in which inorganic fiber cotton or organic fibrillated / precipitated fiber is fully dispersed; 3) Mix and stir the suspension of inorganic or organic short-cut fibers obtained in step 1) with the suspension of inorganic fiber cotton or organic fibrillated / precipitated fibers obtained in step 2) to obtain a fiber mixed suspension; if step 1) does not exist, this step is not required. 4) Add flocculant to the fluororesin suspension for flocculation treatment to obtain flocculated fluororesin slurry; 5) Add the flocculated fluororesin slurry from step 4) to the fiber mixed suspension from step 3), or if step 3) is not present, add it to the suspension of inorganic fiber cotton or organic fibrillated / precipitated fibers that are fully dispersed in step 2) to obtain a mixed slurry. 6) The mixed slurry from step 5) is subjected to wet papermaking and dried to obtain a paper-based semi-cured sheet; 7) The paper-based prepreg from step 6) is heat-treated under high temperature conditions; 8) The paper-based prepreg obtained in step 7) is stacked in single or multiple layers according to the required thickness, and finally copper foil is applied to the outermost single or double sides for vacuum hot pressing to prepare a paper-based microwave composite dielectric substrate. The inorganic chopped fibers are selected from alkali-free glass chopped fibers, high-silica glass chopped fibers, and quartz glass chopped fibers; the organic chopped fibers are poly(p-phenylenebenzodioxazole) chopped fibers. The inorganic chopped fibers have an average diameter of less than 10 micrometers and a length of 1-9 millimeters; The organic chopped fibers have an average diameter of less than 15 micrometers and a length of 1-9 millimeters. The inorganic fiber cotton is selected from alkali-free glass wool fiber, high silica glass wool fiber, and quartz glass wool fiber, and the organic fibrillated / precipitated fiber is poly(p-phenylenebenzodioxazole) fibrillated / precipitated fiber. The average diameter of the inorganic fiber cotton is less than or equal to 3 micrometers; The organic fibrillated / precipitated fiber is an organic short-cut fiber prepared by mechanical pulping or chemical precipitation to obtain a freeness of 25-85︒SR. The fluororesin is polytetrafluoroethylene resin; the fluororesin is in particulate form with an average particle size of 0.15-0.35 micrometers; the fluororesin is in the form of a fluororesin suspension, which is a suspension formed by uniformly dispersing particulate fluororesin in an aqueous medium; and the content of particulate fluororesin in the fluororesin suspension is 25-62 wt%.

2. The paper-based microwave composite dielectric substrate according to claim 1, wherein, The content of the inorganic or organic short-cut fibers is 0-10 wt%; The content of the inorganic fiber cotton or organic fibrillated / precipitated fiber is 3-17 wt%; The content of the fluoropolymer is 80-97 wt%.

3. The paper-based microwave composite dielectric substrate according to claim 1 or 2, wherein, The inorganic chopped fibers have an average diameter of 3-6 micrometers and a length of 5-7 millimeters.

4. The paper-based microwave composite dielectric substrate according to claim 1 or 2, wherein, The organic chopped fibers have an average diameter of 12-14 micrometers and a length of 2-7 millimeters.

5. The paper-based microwave composite dielectric substrate according to claim 1 or 2, wherein, The organic fibrillated / precipitated fiber is an organic short-cut fiber prepared by mechanical pulping or chemical precipitation, with a freeness of 30-80︒SR.

6. The paper-based microwave composite dielectric substrate according to claim 1 or 2, wherein, The organic fibrillated / precipitated fiber is an organic short-cut fiber prepared by mechanical pulping or chemical precipitation to obtain a freeness of 50-70︒SR.

7. A method for preparing a paper-based microwave composite dielectric substrate according to any one of claims 1 to 6, the method comprising the following steps: 1) Disperse inorganic or organic chopped fibers in deionized water to obtain a suspension in which the inorganic or organic chopped fibers are fully dispersed; 2) Disperse inorganic fiber cotton or organic fibrillated / precipitated fiber in deionized water to obtain a suspension in which inorganic fiber cotton or organic fibrillated / precipitated fiber is fully dispersed; 3) Mix and stir the suspension of inorganic or organic short-cut fibers obtained in step 1) with the suspension of inorganic fiber cotton or organic fibrillated / precipitated fibers obtained in step 2) to obtain a fiber mixed suspension; if step 1) does not exist, this step is not required. 4) Add flocculant to the fluororesin suspension for flocculation treatment to obtain flocculated fluororesin slurry; 5) Add the flocculated fluororesin slurry from step 4) to the fiber mixed suspension from step 3), or if step 3) is not present, add it to the suspension of inorganic fiber cotton or organic fibrillated / precipitated fibers that are fully dispersed in step 2) to obtain a mixed slurry. 6) The mixed slurry from step 5) is subjected to wet papermaking and dried to obtain a paper-based semi-cured sheet; 7) The paper-based prepreg from step 6) is heat-treated under high temperature conditions; 8) The paper-based prepreg obtained in step 7) is stacked in single or multiple layers according to the required thickness, and finally copper foil is applied to the outermost single or double sides for vacuum hot pressing to prepare a paper-based microwave composite dielectric substrate.

8. The method according to claim 7, wherein, In step 1), the mass concentration of the suspension in which the inorganic or organic short-cut fibers are fully dispersed is 0.01-1%.

9. The method according to claim 7, wherein, In step 1), inorganic or organic chopped fibers are dispersed in deionized water and thawed in a hydraulic pulper at a speed of 1000-15000 r / min for 1-30 min to obtain a suspension in which inorganic or organic chopped fibers are fully dispersed.

10. The method according to any one of claims 7 to 9, wherein, In step 2), the mass concentration of the inorganic fiber cotton or organic fibrillated / precipitated fiber fully dispersed suspension is 0.01-1%.

11. The method according to any one of claims 7 to 9, wherein, In step 2), inorganic fiber cotton or organic fibrillated / precipitated fiber is dispersed in deionized water and thawed in a hydraulic pulper at a speed of 1000-25000 r / min for 1-25 min to obtain a suspension in which inorganic fiber cotton or organic fibrillated / precipitated fiber is fully dispersed.

12. The method according to any one of claims 7 to 9, wherein, In step 4), the fluororesin suspension is formed by dispersing particulate fluororesin in deionized water.

13. The method according to any one of claims 7 to 9, wherein, In step 4), the mass fraction of the fluororesin suspension is 25-62%.

14. The method according to any one of claims 7 to 9, wherein, In step 4), the fluororesin suspension is a polytetrafluoroethylene suspension with a mass fraction of 25-62%.

15. The method according to any one of claims 7 to 9, wherein, The flocculant is selected from one or more of the following: cationic branched starch, dopamine hydrochloride, chitosan, polyethylene oxide, polyethyleneimine, polyacrylamide, and natural polymer-acrylamide copolymers.

16. The method according to any one of claims 7 to 9, wherein, In step 4), the amount of flocculant used is 0.01 wt%-10 wt% of the total dry weight of the raw materials.

17. The method according to any one of claims 7 to 9, wherein, In step 6), the wet papermaking process refers to dewatering and forming the mixed slurry obtained in step 5) on the wire section of a papermaking machine to obtain a wet paper web, and then drying it to obtain a paper-based semi-cured sheet. The paper machine is selected from inclined wire, cylinder wire, super cylinder wire, long wire, clamp wire, and top wire paper machines; The drying method is selected from one or a combination of heat conduction, heat convection, and heat radiation; the drying environment is atmospheric pressure or vacuum conditions.

18. The method according to any one of claims 7 to 9, wherein, In step 7), the high temperature condition is a temperature of 180-320 ℃, and the equipment used is a high temperature blower / vacuum oven, muffle furnace, or tube furnace.

19. The method according to any one of claims 7 to 9, wherein, In step 7), the heat treatment time is 2-6 hours.

20. The method according to any one of claims 7 to 9, wherein, In step 8), the paper-based prepreg used in the multiple layers is of the same type, or multiple types of prepreg are selected for layering.

21. The method according to any one of claims 7 to 9, wherein, In step 8), the copper foil is selected from one or a combination of two of electrolytic copper foil, reverse copper foil, or rolled copper foil, and has a thickness of 9 micrometers to 70 micrometers.

22. The method according to any one of claims 7 to 9, wherein, In step 8), the vacuum hot pressing conditions are: pressure 2-8 MPa, temperature 365℃-400℃, vacuum degree 0.04-0.1 MPa, and hot pressing time 2-8 hours.

23. The method according to any one of claims 7 to 9, wherein, In step 8), the thickness of the paper-based microwave composite dielectric substrate ranges from 0.05 to 10 mm.

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