Low-loss ultrathin high-speed transmission FFC wire rod and preparation method thereof

Abstract

The invention discloses a low-loss ultrathin high-speed transmission FFC wire rod and a preparation method thereof. The FFC wire rod is a low-loss medium system formed by fluorinated polyimide, a liquid crystal polymer, fine PTFE powder and SiO2 / Al2O3 microspheres subjected to surface fluorination treatment, and comprises an ultra-low profile copper foil conductor layer, an embedded patterned grounding grid layer, a top shielding layer and a protective layer. The embedded grounding grid is formed through precise casting and photoetching electroplating, the trapezoidal cross section differential line pair is formed through acid etching, and the embedded grounding grid is manufactured through the technologies of multi-layer hot-pressing lamination, online impedance detection and compensation correction and the like. The total thickness of the wire rod is less than or equal to 0.10 mm, the differential characteristic impedance is 85 + / -5 ohm or 100 + / -5 ohm, the insertion loss is less than or equal to 0.79 dB / in under 10GHz, the near-end crosstalk is less than or equal to-35dB, the bending life is greater than or equal to 1 million times, and the shielding effectiveness is greater than or equal to 60dB, so that the problems that the existing FFC wire rod is large in loss, large in impedance fluctuation and serious in crosstalk under high frequency and is poor in mechanical reliability under an ultrathin structure are solved.

Description

Technical Field

[0001] This application relates to the fields of electronic connection materials and flexible transmission technology, and in particular to a low-loss ultrathin high-speed transmission FFC wire and its preparation method. Background Technology

[0002] In recent years, with the rapid development of technologies such as 5G communication, new energy vehicles, and artificial intelligence, the demand for high-speed data transmission in electronic devices has been increasing. As a flexible, lightweight, and efficient electrical connection line, FFC cable has been widely used in many electronic devices.

[0003] However, existing FFC cables have many shortcomings: traditional methods typically use conventional PI or PET dielectric materials, which have relatively high dielectric constants (Dk=3.0-3.5) and dielectric loss factors (Df=0.003-0.008@10GHz), resulting in high insertion loss and severe signal attenuation during high-frequency transmission; the characteristic impedance fluctuates by ±15% with production deviations, failing to meet the stringent ±5% requirement of high-speed interfaces; crosstalk between lines is ≥-25dB during high-speed differential transmission, far exceeding the engineering requirement of -35dB; and traditional methods, when the total thickness is ≤0.1mm, struggle to balance bending life ≥100,000 cycles and signal integrity requirements, limiting their application in ultra-thin devices. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a low-loss, ultra-thin, high-speed transmission FFC wire and its preparation method.

[0005] This application provides a low-loss, ultra-thin, high-speed transmission FFC cable, which adopts the following technical solution: A low-loss, ultra-thin, high-speed transmission FFC cable, the raw materials by weight include 50-70 parts of fluorinated polyimide, 5-20 parts of surface-fluorinated SiO2 / Al2O3 microspheres, 3-10 parts of fine PTFE powder and liquid crystal polymer; the total thickness of the FFC cable is ≤0.10mm, and the differential characteristic impedance is in the range of 85±5Ω or 100±5Ω.

[0006] Preferably, the degree of fluorination of the fluorinated polyimide is 20-40 mol%, the weight-average molecular weight is 80,000-150,000 g / mol, and the glass transition temperature (Tg) is 280-320 °C.

[0007] Preferably, the particle size of the surface-fluorinated SiO2 / Al2O3 microspheres is 0.2-0.8 μm, the surface fluorination agent is trimethyltrifluoroacetic acid silane or heptadecafluorodecyltriethoxysilane, and the surface contact angle of the fluorinated microspheres is ≥110°.

[0008] Preferably, the fine PTFE powder has an average particle size of 0.2-0.8 μm, a molecular weight of 5 million-10 million g / mol, a crystallinity of ≥95%, and a melting temperature of 325-335℃.

[0009] Preferably, the liquid crystal polymer is an aromatic liquid crystal polyester or a liquid crystal polyamide, with a melting point of 280-350℃, a modulus of 8-15GPa, and a compatibility parameter χ ≤ 0.5 with fluorinated polyimide.

[0010] Preferably, the FFC wire further includes a conductor layer, which is made of ultra-low profile rolled copper foil with a thickness of 9-12 μm; the surface roughness Ra of the signal side of the ultra-low profile rolled copper foil is ≤0.5 μm, the surface roughness Ra of the bonding side is 1.0-1.8 μm, the copper purity is ≥99.8%, and the tensile strength is 350-450 MPa.

[0011] Preferably, the FFC wire also includes an adhesive layer, which is made of low-modulus epoxy resin or acrylic adhesive, with a thickness of 5-8 μm; the low-modulus epoxy resin has an elastic modulus of 0.5-2.0 GPa, a glass transition temperature of 80-150℃, and an elongation at break of ≥50%; the acrylic adhesive has an elastic modulus of 0.3-1.5 GPa and a peel strength of ≥2 N / mm.

[0012] Preferably, the FFC wire also includes a protective layer, which is a heat-resistant polyimide or fluorinated polyimide film with a thickness of 10-15 μm, a heat resistance temperature ≥250℃, a tensile strength ≥150MPa, and an elongation at break ≥20%.

[0013] Preferably, the FFC wire further includes an embedded grounding grid layer. The grid width of the embedded grounding grid layer is 15-30 μm, the grid spacing is 80-150 μm, the thickness is 2-5 μm, and the material is electrolytic copper or chemically plated copper with a conductivity ≥5.8×10⁻⁶. 7 S / m.

[0014] Preferably, the FFC wire also includes a top shielding layer with a thickness of 0.3-0.8μm and made of copper, nickel or silver. The top shielding layer is electrically connected to the embedded grounding grid layer through the edge through-hole or window of the FFC, and the shielding effectiveness is ≥60dB@1GHz.

[0015] A preferred method for preparing a low-loss media system includes the following steps: (1) Fluorinated polyimide precursor, liquid crystal polymer, fine PTFE powder, and surface-fluorinated SiO2 / Al2O3 microspheres are mixed with N-methylpyrrolidone solvent in a specified ratio, with the solid content controlled at 20-35 wt%. High-speed dispersion mixing is performed at a dispersion speed of 1000-2000 rpm for 60-120 minutes, followed by vacuum degassing treatment at a vacuum degree of -0.08 to -0.095 MPa for 20-40 minutes to obtain a uniformly dispersed resin solution; (2) Precision casting is performed on a metal carrier tape or release film, with the doctor blade gap controlled at 150-250μm and the casting speed at 2-4m / min; (3) The cast film is subjected to heating curing / imidification treatment, with a specific temperature gradient of 80℃ (20min) → 120℃ (30min) → 160℃ (40min) → 200℃ (45min) → 250℃ (60min) → 300℃ (30min), the heating rate is controlled at 1.5-3℃ / min, and the temperature fluctuation at each stage is ≤±3℃, to obtain a low-loss dielectric film roll with a thickness of 20-30μm.

[0016] Preferably, the method for preparing the embedded grounding grid layer includes the following steps: (1) forming a uniform ultrathin metal seed layer on a dielectric thin film by vacuum magnetron sputtering, with a vacuum degree ≤5×10 -4 Pa, sputtering power 150-250W, sputtering rate 0.5-1.5nm / s, seed layer thickness 0.1-0.3μm; (2) form a grid pattern by roll-to-roll lithography or direct laser imaging, photoresist thickness 3-8μm, exposure energy 80-150mJ / cm 2 The development time is 30-60 seconds, the grid line width is 15-30μm, and the grid spacing is 80-150μm; (3) the electroplating is thickened to 2-5μm, the electroplating solution is copper sulfate solution, the copper sulfate concentration is 180-220g / L, the sulfuric acid concentration is 60-90g / L, the chloride ion concentration is 50-80mg / L, the temperature is controlled at 25-35℃, and the current density is 15-30mA / cm 2 (3) Stirring speed 100-200 rpm; (4) Remove photoresist by using acetone or N-methylpyrrolidone solution, temperature 40-60℃, ultrasonic power 100-300W, and stripping time 2-5 minutes to obtain a patterned grounding grid layer.

[0017] This application provides a method for preparing a low-loss, ultra-thin, high-speed transmission FFC cable, which adopts the following technical solution:

[0018] A method for preparing a low-loss ultrathin high-speed transmission FFC wire includes the following steps: (1) preparing a low-loss dielectric film roll; (2) forming an embedded grounding grid layer on the dielectric film; (3) signal copper foil lamination and pattern formation: a) laminating ultra-low profile rolled copper foil onto the dielectric film by precision hot pressing at a temperature of 180-230℃, a pressure of 1.5-3.0MPa, a holding time of 3-8 minutes, and a heating rate of 3-8℃ / min to form a "dielectric / copper foil" composite structure; b) coating roll to roll with anti-etching ink, with an ink thickness of 6-12μm and an exposure energy of 100-150mJ / cm. 2 The development time is 40-70 seconds to form differential line pairs and end gradient regions; c) Acid etching is performed using a copper chloride / hydrochloric acid etching solution, with a copper chloride concentration of 180-220 g / L and a hydrochloric acid concentration of 80-120 g / L. The temperature is controlled at 35-45℃, the etching time is 30-60 seconds, and the etching factor is controlled at 2.5-3.5 to form a trapezoidal cross-section copper conductor with a line width of 30-60 μm, a line spacing of 30-60 μm, a line pair spacing of 80-200 μm, and a sidewall angle of 80-88°; d) The anti-etching ink is stripped using 3 -8% sodium hydroxide solution, temperature 50-70℃, peeling time 45-90 seconds, surface cleaning and anti-oxidation treatment, the anti-oxidant is 0.3-0.8% benzotriazole solution, treatment time 10-30 seconds; (4) Multilayer hot pressing lamination: a) Lay upper / lower dielectric films and adhesive layers on both sides of the signal conductor layer respectively; b) Perform hot pressing process, temperature 180-230℃, pressure 1.0-2.5MPa, heating rate 2-5℃ / min, holding time 8-15 minutes, cooling rate ≤3℃ / min, to form symmetrical clamps. Layer structure; (5) Forming the top shielding layer: Forming a shielding metal layer with a thickness of 0.3-0.8μm by sputtering or coating, sputtering power 250-350W, deposition rate 1-3nm / s, and electrically connecting it to the grounding grid layer through FFC edge vias / windows; (6) Terminal structure processing: a) Removing the local covering film and dielectric by laser windowing / punching, laser power 0.8-1.5W, pulse frequency 15-25kHz, scanning speed 200-500mm / s, exposing the copper conductor terminal; b) Performing tin plating or gold plating, nickel plating layer Thickness 1.5-3.0μm, gold plating layer thickness 0.03-0.08μm, tin plating layer thickness 2-5μm; c) Die-cut according to pole number and length requirements, die-cut accuracy ≤±0.05mm; (7) Online detection and impedance compensation correction: integrate online TDR impedance detection module and optical width measurement system, detection frequency range 1-10GHz, measurement accuracy ≤±1Ω, finely adjust the casting thickness (±2μm), lamination pressure (±0.1MPa) and etching time (±5 seconds) according to the actual measurement data to achieve closed-loop control and improve impedance consistency to ±3%.

[0019] In summary, this application includes at least one of the following beneficial technical effects:

[0020] 1. This application adopts a fluorinated polyimide / LCP / PTFE composite dielectric system with a fluorination degree of 20-40 mol%. By leveraging the low polarizability of the CF bond and the ultra-low loss characteristics of PTFE, it effectively reduces high-frequency dielectric loss, achieving a differential line pair insertion loss ≤0.8 dB / in at a frequency of 10 GHz, a dielectric constant Dk=3.0-3.2, and a loss factor Df≤0.002. This is more than 50% lower than the traditional schemes with Dk=3.0-3.5 and Df=0.003-0.008, significantly improving the transmission quality of high-frequency signals.

[0021] 2. This application achieves an improvement in characteristic impedance control accuracy from the traditional ±15% to ±5% through the design of an embedded grounding grid layer and precise control of the signal conductor spacing, combined with a multi-layer symmetrical structure and a gradual impedance transition design. At the same time, it achieves stable differential characteristic impedance within the range of 85±5Ω or 100±5Ω in an ultra-thin structure with a total thickness of ≤0.10mm, improving impedance consistency by 3 times and effectively solving the impedance stability problem.

[0022] 3. The multi-layer structure design and shielding technology of this application combine to achieve near-end crosstalk improvement from ≥-25dB to ≤-35dB through the double shielding of the embedded grounding grid layer and the top shielding layer, with shielding effectiveness ≥60dB@1GHz, improving crosstalk performance by about 40%. At the same time, through the elastic buffer design of the low modulus adhesive layer, it maintains a bending life of ≥1 million cycles under ultra-thin conditions, meeting the flexible connection requirements of high-density electronic devices. Detailed Implementation

[0023] The present application will be further described in detail below with reference to the embodiments.

[0024] The chemical reagents and material properties used in the preparation examples, embodiments, and comparative examples provided by this invention are as follows:

[0025] Fluorinated polyimide precursor: a polyamic acid prepared by reacting 4,4'-diaminodiphenyl ether with 6FDA (hexafluoroisopropyl dianhydride), with a fluorination degree of 30 mol%, a weight-average molecular weight of 120,000 g / mol, a solid content of 20 wt%, and a viscosity of 5,000-8,000 cP at 25℃.

[0026] Liquid crystal polymer: Aromatic fully aromatic liquid crystal polyester, grade Vectra A950, melting point 310℃, modulus 12GPa, density 1.4g / cm³ 3 Purchased from Kelanis;

[0027] Fine PTFE powder: average particle size 0.5μm, molecular weight 8 million g / mol, crystallinity 97%, specific surface area 8-12m² 2 / g, purchased from DuPont, brand name Teflon MP1200;

[0028] Surface-fluorinated SiO2 microspheres: average particle size 0.4 μm, specific surface area 120 m² / g. 2 / g, surface fluorination treatment with heptadecafluorodecyltriethoxysilane, contact angle ≥115° after treatment, purchased from Ryusei Corporation of Japan, or other suppliers that meet the above technical specifications;

[0029] Surface-fluorinated Al2O3 microspheres: average particle size 0.3 μm, α-phase purity ≥99.5%, specific surface area 80 m² / g. 2 / g, surface fluorination treatment as above, purchased from Showa Denko Co., Ltd.;

[0030] N-methylpyrrolidone (NMP) solvent: analytical grade, purity ≥99.8%, water content ≤0.05%, purchased from BASF.

[0031] Low modulus epoxy resin: Bisphenol F type epoxy resin, epoxy equivalent 180-200g / eq, elastic modulus after curing 1.2GPa, glass transition temperature 120℃, elongation at break 65%, purchased from Japan Epoxy Chemical Co., Ltd.

[0032] Acrylic adhesive: Modified acrylate copolymer, solid content 50%, viscosity 3000 cP@25℃, elastic modulus after curing 0.8 GPa, peel strength 2.5 N / mm, purchased from Henkel, Germany;

[0033] Ultra-low profile rolled copper foil: 10μm thickness, 99.95% copper purity, 400MPa tensile strength, Ra=0.3μm surface roughness on the signal side, Ra=1.5μm surface roughness on the bonding side, purchased from Furukawa Electric Industries, Japan.

[0034] Photoresist: Positive photoresist, solid content 45%, photosensitive wavelength 365nm, resolution ≤2μm, purchased from JSR Corporation, Japan.

[0035] Preparation Example 1: Preparation of Low-Loss Dielectric Thin Films

[0036] Preparation Example 1.1

[0037] 65.0 g of fluorinated polyimide precursor solution (20% solids content) and 13.0 g of liquid crystal polymer were dissolved in 120.0 g of N-methylpyrrolidone. The mixture was stirred at 500 rpm at 40°C for 60 minutes to form a homogeneous solution. Then, 1.3 g of surface-fluorinated SiO2 microspheres (5 wt% of solids content) and 0.8 g of fine PTFE powder (3 wt% of solids content) were added. The mixture was heated to 55°C, and the stirring speed was increased to 1200 rpm for 90 minutes. Subsequently, the mixture was degassed under a vacuum of -0.085 MPa for 30 minutes to obtain a uniformly dispersed resin solution.

[0038] The above resin solution was precision cast on a PTFE-coated stainless steel carrier tape, with the doctor blade gap controlled at 180 μm and the casting speed at 2.5 m / min. The cast wet film was then subjected to imidization treatment in an eight-zone temperature-controlled tunnel oven, with the following temperature profile: 80℃ (20 min) → 120℃ (30 min) → 160℃ (40 min) → 200℃ (45 min) → 250℃ (60 min) → 300℃ (30 min). The heating rate was strictly controlled at 2℃ / min, and the temperature fluctuation at each stage was ≤±2℃. After cooling to room temperature, a low-loss dielectric film roll with a thickness of 22 μm was obtained, exhibiting dielectric properties of Dk=3.2 and Df=0.0020@10GHz.

[0039] Preparation Example 1.2

[0040] The difference from Preparation Example 1.1 is that the amount of surface-fluorinated SiO2 microspheres added was 3.3 g (12.5 wt% of solid content), the amount of fine PTFE powder added was 1.7 g (6.5 wt% of solid content), the casting doctor blade gap was 210 μm, and other conditions were the same. A low-loss dielectric film roll with a thickness of 26 μm was obtained, exhibiting dielectric properties of Dk=3.1 and Df=0.0017@10GHz.

[0041] Preparation Example 1.3

[0042] The difference from Preparation Example 1.1 is that the amount of surface-fluorinated Al2O3 microspheres added was 5.2 g (20 wt% of solid content), the amount of fine PTFE powder added was 2.6 g (10 wt% of solid content), the casting doctor blade gap was 240 μm, and other conditions were the same. A low-loss dielectric film roll with a thickness of 30 μm was obtained, exhibiting dielectric properties of Dk=3.0 and Df=0.0015@10GHz.

[0043] Preparation Example 1.4 (Mixed Packing Material Formulation)

[0044] The difference from Preparation Example 1.1 is that 2.0 g of surface-fluorinated SiO2 microspheres and 1.8 g of Al2O3 microspheres (totaling 14.5 wt% of solids) were used simultaneously, and the amount of fine PTFE powder added was 2.1 g (8 wt% of solids), while other conditions remained the same. A low-loss dielectric film roll with a thickness of 28 μm was obtained, exhibiting dielectric properties of Dk = 3.05 and Df = 0.0016 @ 10 GHz.

[0045] Preparation Example 2: Preparation of Embedded Grounding Grid Layer

[0046] Preparation Example 2.1

[0047] The low-loss dielectric thin film roll obtained in Preparation Example 1.1 was placed in a magnetron sputtering apparatus (model PVD-1200), and the vacuum level was evacuated to 3 × 10⁻⁶. -4 Pa was used with a copper target of 99.99% purity, sputtering power set to 180W, argon flow rate of 20sccm, to deposit a copper seed layer with a thickness of 0.15μm on the film surface at a deposition rate of 0.8nm / s.

[0048] Following this, a roll-to-roll photolithography process is performed. First, a 4μm thick positive photoresist is coated and dried at 90℃ for 2 minutes. Then, 365nm wavelength ultraviolet light is used for exposure through a mask at an exposure energy of 110mJ / cm². 2 The developer was a 2.38% tetramethylammonium hydroxide aqueous solution, and the development time was 50 seconds. After development, a grid pattern was formed with a grid line width of 15 μm and a grid spacing of 120 μm.

[0049] Then, copper electroplating is performed. The electroplating solution consists of: 200 g / L copper sulfate pentahydrate, 75 g / L concentrated sulfuric acid, 60 mg / L chloride ions, and 10 mL / L leveling agent (polyethylene glycol). The current density is set at 18 mA / cm². 2 The temperature was controlled at 28℃, the stirring speed was 150rpm, the electroplating time was 8 minutes, and the electroplating thickness reached 2.0μm.

[0050] Finally, the photoresist was stripped using acetone solution under ultrasonic assistance (ultrasonic power 200W, frequency 40kHz) for 3 minutes at a temperature of 50℃, resulting in an embedded grounding mesh layer with a grid pattern.

[0051] Preparation Example 2.2

[0052] The difference from Preparation Example 2.1 is that the sputtering power is 200 W, the seed layer thickness is 0.2 μm, the grid linewidth is 22 μm, the grid spacing is 115 μm, and the electroplating current density is 22 mA / cm². 2 The electroplating time was 12 minutes, the electroplating thickness was 3.5 μm, and other conditions were the same.

[0053] Preparation Example 2.3

[0054] The difference from Preparation Example 2.1 is that the sputtering power is 240 W, the seed layer thickness is 0.25 μm, the grid linewidth is 30 μm, the grid spacing is 150 μm, and the electroplating current density is 28 mA / cm². 2 The electroplating time was 18 minutes, the electroplating thickness was 5.0 μm, and other conditions were the same.

[0055] Preparation Example 2.4 (Laser Direct Imaging Process)

[0056] The difference from Preparation Example 2.2 is that direct laser imaging was used instead of photolithography. A diode-pumped solid-state laser with a wavelength of 355 nm was used. The laser power was set to 0.8 W, the pulse frequency to 20 kHz, the scanning speed to 400 mm / s, and the laser spot diameter to 5 μm. A pattern with a grid linewidth of 25 μm and a grid spacing of 100 μm was formed. The electroplating thickness was 4 μm, and other conditions were the same.

[0057] Example 1

[0058] (1) A low-loss dielectric thin film roll was prepared using the method described in Example 1.1;

[0059] (2) An embedded grounding grid layer is formed on a dielectric thin film using the method of Preparation Example 2.1;

[0060] (3) Signal copper foil bonding and pattern formation:

[0061] a) A 9μm thick ultra-low profile rolled copper foil (signal side surface roughness Ra=0.3μm, bonding side surface roughness Ra=1.2μm) is precision hot-pressed onto a dielectric film. The preheating temperature is 150℃, the preheating time is 3 minutes, the hot-pressing temperature is 185℃, the pressure is 1.8MPa, the heating rate is 4℃ / min, the holding time is 6 minutes, and the cooling rate is 2℃ / min, forming a dielectric / copper foil composite structure.

[0062] b) Apply a 7μm thick negative anti-etching ink roll-to-roll, pre-baking at 80℃ for 2 minutes, with an exposure energy of 105mJ / cm². 2 After exposure, the baking temperature is 110℃ for 3 minutes, and the development time is 55 seconds to form differential line pairs and end gradient area patterns.

[0063] c) Perform acid etching using a copper chloride / hydrochloric acid etching solution (copper chloride concentration 190 g / L, hydrochloric acid concentration 90 g / L). The etching solution temperature is controlled at 36℃, the spray pressure is 0.15 MPa, and the etching time is 35 seconds to form a trapezoidal cross-section copper conductor with a line width of 30 μm, a line spacing of 30 μm, a line pair spacing of 80 μm, a sidewall angle of 83°, and an etching factor controlled at 2.8.

[0064] d) Use 4% sodium hydroxide solution to peel off the anti-etching ink at 55°C for 65 seconds, then rinse with deionized water 3 times for 30 seconds each time, and finally treat with 0.5% benzotriazole solution for anti-oxidation for 15 seconds and blow dry with nitrogen.

[0065] (4) Multi-layer hot pressing lamination molding:

[0066] a) An upper / lower dielectric film (22 μm thick) and a low-modulus epoxy resin adhesive layer (5 μm thick) are respectively laid on both sides of the signal conductor layer.

[0067] b) Perform hot pressing process, with a preheating temperature of 120℃ and a preheating time of 5 minutes. The hot pressing temperature is 185℃, the pressure is 1.2MPa, the heating rate is 3℃ / min, the holding time is 12 minutes, and the cooling stage is performed by applying a pressure of 1.0MPa below 150℃ for slow cooling at a cooling rate of 2℃ / min to form a symmetrical sandwich structure.

[0068] (5) Forming the top shielding layer: A copper shielding layer with a thickness of 0.3 μm is formed on the outermost layer by magnetron sputtering, with a vacuum degree of 5 × 10⁻⁶. -4 Pa, sputtering power 280W, sputtering time 8 minutes, deposition rate 1.2nm / s, and electrically connected to the embedded grounding grid layer through FFC edge laser windowing (power 1.0W, pulse frequency 18kHz, scanning speed 300mm / s);

[0069] (6) Terminal structure processing:

[0070] a) Remove the end-part covering film and medium by laser windowing. Laser power 1.0W, pulse frequency 18kHz, scanning speed 250mm / s, repeat scanning twice to expose the copper conductor terminal.

[0071] b) Terminal electroplating treatment is performed. Pretreatment includes degreasing, micro-etching, and activation. The nickel plating layer thickness is 2.0 μm, and the gold plating layer thickness is 0.05 μm. The nickel plating solution composition is: nickel sulfate 280 g / L, boric acid 45 g / L, pH=4.2, temperature 50℃, and current density 4 A / dm³. 2 The gold plating solution was a potassium gold cyanide plating solution with a gold content of 8 g / L, pH=12.5, temperature of 60℃, and current density of 1 A / dm³. 2c) Precision die-cutting is performed according to the specification of 20 poles / 0.5mm spacing, the sharpness of the die-cutting tool is ≤5μm, and the die-cutting accuracy is ±0.03mm;

[0072] (7) Online testing and impedance compensation correction: A Tektronix DSA8300 time domain reflectometer was used, with a test frequency of 1-10GHz, a sampling point interval of 0.1mm, a measurement accuracy of ±0.8Ω, and a measured differential impedance of 84.2±3.8Ω, which meets the design requirement of 85±5Ω. The measured insertion loss was 0.79dB / in@10GHz, the near-end crosstalk was -36dB, and the bending life was 1.08 million cycles.

[0073] Example 2

[0074] The difference between Example 2 and Example 1 is that:

[0075] (1) A low-loss dielectric thin film roll was prepared using the method described in Example 1.3;

[0076] (2) An embedded grounding grid layer is formed on a dielectric thin film using the method of Preparation Example 2.3;

[0077] (3) Use ultra-low profile rolled copper foil with a thickness of 12μm, signal conductor line width of 60μm, line spacing of 60μm, line pair spacing of 200μm, and sidewall angle of 88°.

[0078] (4) The adhesive layer uses acrylic glue with a thickness of 8μm;

[0079] (5) The lamination temperature is 225℃, the pressure is 2.3MPa, and the holding time is 10 minutes;

[0080] (6) The thickness of the top shielding layer is 0.8 μm;

[0081] (7) Die-cut to a specification of 50 poles / 0.3mm spacing. The differential impedance was measured to be 102.1±4.2Ω, which meets the design requirement of 100±5Ω. The insertion loss was measured to be 0.73dB / in@10GHz, the near-end crosstalk was -38dB, and the bending life was 1.25 million cycles.

[0082] Example 3 (Verification of the performance of the mixed packing system)

[0083] The difference between Example 3 and Example 1 is that:

[0084] (1) Low-loss dielectric thin film roll (mixed SiO2 and Al2O3 microspheres) was prepared using the method of Preparation Example 1.4.

[0085] (2) An embedded grounding grid layer is formed on a dielectric thin film using the method of Preparation Example 2.2;

[0086] (3) The signal conductor line width is 45μm, the line spacing is 45μm, and the line pair spacing is 130μm;

[0087] (4) The protective layer is made of fluorinated polyimide film with a thickness of 12μm;

[0088] (5) The lamination temperature is 205℃ and the pressure is 1.8MPa.

[0089] The measured differential impedance is 97.5±4.5Ω, which meets the design requirement of 100±5Ω. The measured insertion loss is 0.75dB / in@10GHz, the near-end crosstalk is -37dB, and the bending life is 1.15 million cycles.

[0090] Example 4 (Verification of 85Ω target impedance)

[0091] The difference between Example 4 and Example 1 is that:

[0092] (1) A low-loss dielectric film roll was prepared using the method described in Example 1.2;

[0093] (2) The embedded grounding grid layer has a grid line width of 18μm, a grid spacing of 90μm, and a thickness of 3μm;

[0094] (3) The signal conductor line width is 42μm, the line spacing is 42μm, the line pair spacing is 95μm, and the sidewall angle is 84°;

[0095] (4) The lamination temperature is 195℃ and the pressure is 1.6MPa;

[0096] (5) The thickness of the protective layer is 11 μm.

[0097] The measured differential impedance is 86.8±3.6Ω, which meets the design requirement of 85±5Ω. The measured insertion loss is 0.77dB / in@10GHz, the near-end crosstalk is -36dB, and the bending life is 1.12 million cycles.

[0098] Example 5 (Verification of laser direct imaging process)

[0099] The difference between Example 5 and Example 2 is that:

[0100] (1) An embedded grounding grid layer was prepared using the laser direct imaging process described in Preparation Example 2.4;

[0101] (2) The amount of fine PTFE powder added was 9.5 wt%, which is close to the upper limit of the range;

[0102] (3) The signal conductor line width is 55μm, the line spacing is 55μm, and the line pair spacing is 170μm;

[0103] (4) The lamination temperature is 210℃ and the pressure is 2.0MPa.

[0104] The measured differential impedance is 99.2±4.1Ω, which meets the design requirement of 100±5Ω. The measured insertion loss is 0.74dB / in@10GHz, the near-end crosstalk is -37dB, and the bending life is 1.18 million cycles.

[0105] Example 6 (Verification of Ultrathin Limit Thickness)

[0106] The difference between Example 6 and Example 1 is that:

[0107] (1) The thickness of the dielectric film is controlled at 20 μm;

[0108] (2) The adhesive layer thickness is 5μm and the protective layer thickness is 10μm;

[0109] (3) The conductor layer thickness is 9 μm;

[0110] (4) The total thickness is controlled to be ≤0.095mm;

[0111] (5) Optimize the lamination pressure to 2.4MPa and extend the pressure holding time to 15 minutes.

[0112] The measured differential impedance is 87.3±4.8Ω, which meets the design requirement of 85±5Ω. The measured insertion loss is 0.78dB / in@10GHz, the near-end crosstalk is -35dB, and the bending life is 1.06 million cycles.

[0113] Comparative Example 1 (Traditional PI Material)

[0114] The difference between Comparative Example 1 and Example 1 is that: instead of fluorinated polyimide, conventional polyimide (PI, glass transition temperature 360°C) was used as the matrix material; fine PTFE powder and surface-fluorinated microspheres were not added; an embedded grounding grid layer was not provided; and the protective layer was a conventional PI film with a thickness of 15 μm. All other conditions remained the same. The detected differential impedance was 98.5 ± 13.2 Ω, the impedance fluctuation range was 13.4%, the insertion loss was 1.35 dB / in @ 10 GHz, the near-end crosstalk was -23 dB, and the bending life was 820,000 cycles.

[0115] Comparative Example 2 (without embedded grounding grid layer)

[0116] The difference between Comparative Example 2 and Example 1 is that no embedded grounding grid layer is set, and only a shielding layer with a thickness of 1.0 μm is set on the top layer, while other conditions are the same.

[0117] The measured differential impedance is 101.2±8.6Ω, the impedance fluctuation range is 8.5%, the insertion loss is 0.92dB / in@10GHz, the near-end crosstalk is -29dB, and the bending life is 960,000 cycles.

[0118] Comparative Example 3 (filler out of range)

[0119] The difference between Comparative Example 3 and Example 1 is that no fine PTFE powder was added, and the amount of surface-fluorinated SiO2 microspheres added was 26 wt% (exceeding the range of 5-20 wt%), which led to increased material brittleness. Other conditions were the same.

[0120] The measured differential impedance is 99.8±6.8Ω, the impedance fluctuation range is 6.8%, the insertion loss is 1.05dB / in@10GHz, and the near-end crosstalk is -31dB. However, the bending life is only 280,000 cycles, which does not meet the requirement of ≥1 million cycles.

[0121] Comparative Example 4 (without surface fluorination treatment)

[0122] The difference between Comparative Example 4 and Example 1 is that: ordinary SiO2 microspheres without surface fluorination treatment were used, with a surface contact angle of only 65° and poor compatibility with the polymer matrix, while other conditions were the same.

[0123] The measured differential impedance is 100.5±9.2Ω, the impedance fluctuation range is 9.2%, the insertion loss is 1.12dB / in@10GHz, the near-end crosstalk is -32dB, and the bending life is 890,000 cycles.

[0124] Performance testing:

[0125] The FFC wire samples obtained in Examples 1-6 and Comparative Examples 1-4 were cut to a standard length of 100mm and tested using Molex 54104 or Amphenol FCI 10029449 connectors. The following standardized tests were then conducted under a standard environment of 23±2℃ and 45±10% relative humidity:

[0126] I. Differential Characteristic Impedance Test: A TDR (Tektronix DSA8300 with 80E04 sampling head) was used at a test frequency of 1GHz with a rise time ≤35ps. The test method was performed according to IPC-TM-6502.5.5.7. The test points were located in the middle of the wire, avoiding the connector transition area. Ten points were tested for each sample and the average value was taken. The measurement uncertainty was ≤±0.5Ω.

[0127] II. Insertion Loss Test: A vector network analyzer (Keysight N5247A) was used with a frequency range of 0.1-20GHz, power of -10dBm, and intermediate frequency bandwidth of 100Hz. The test method was performed according to the IPC-TM-6502.5.1.5 standard. SOLT calibration was used, and the connector was de-embedded. Each sample was tested 3 times and the average value was taken. Data was read at the 10GHz frequency point.

[0128] 3. Near-end crosstalk test: Using a vector network analyzer with a 4-port test configuration, and following the IPC-TM-6502.5.2.1 standard test method, the excitation end is port 1 and the interference detection end is port 3. The NEXT parameters are read at the 10GHz frequency point.

[0129] IV. Bending life test: According to IEC 61189-2 standard, use CHI900 bending tester, bending angle ±90°, bending radius 5mm, speed 30 times / minute, ambient temperature 23±2℃, relative humidity 45±10%, electrical continuity judgment standard: resistance increase ≤20% or contact resistance ≤10mΩ, record the number of bends that reach the failure standard;

[0130] V. Dielectric Performance Testing: Using an Agilent 16451B dielectric test fixture and an E4991A impedance analyzer, the dielectric constant Dk and loss factor Df were tested at a frequency of 10 GHz. Following the IPC-TM-6502.5.5.13 standard, the sample size was 25.4 mm × 25.4 mm, with a thickness of 25 μm. The test environment was 23 ± 2℃ and the relative humidity was 45 ± 10%. The dielectric constants Dk / Df were tested at 3 GHz; the 10 GHz results are simulation / derived and will not be elaborated further.

[0131] VI. Shielding effectiveness test: Using an Agilent E5071C network analyzer and the coaxial transmission line method, according to ASTM D4935 standard, the frequency range is 0.1-1GHz, the test sample size is 50mm×50mm, and the shielding effectiveness SE is calculated as SE=20log10(E1 / E2), where E1 is the electric field strength without shielding and E2 is the electric field strength with shielding.

[0132] The results are shown in Table 1.

[0133] The specific test results are as follows:

[0134]

[0135] As can be seen from the test results in Table 1, the low-loss ultra-thin high-speed transmission FFC cable provided in this application has significant advantages in high-frequency characteristics and mechanical performance. The impedance fluctuation range of Examples 1-6 is controlled within ±5.5%, significantly better than the ±13.4% of the traditional solution; the insertion loss is ≤0.79dB / in@10GHz, a reduction of approximately 42% compared to the traditional solution's 1.35dB / in; the near-end crosstalk is ≤-35dB, an improvement of 52% compared to the traditional solution's -23dB; the bending life is ≥1.06 million cycles, fully meeting the design requirements; the dielectric constant Dk is controlled within the range of 3.0-3.2, the loss factor Df ≤0.002@10GHz, and the shielding effectiveness ≥61dB@1GHz. It should be noted that Comparative Example 2, due to the lack of an embedded grounding mesh layer, suffers from an imperfect high-frequency signal return path, significantly increasing conductor loss. Therefore, although its dielectric loss factor (Df) is low, its overall insertion loss remains high. This, conversely, proves that an embedded grounding grid layer is indispensable for achieving ultra-low insertion loss.

[0136] The data from the examples show that excellent performance can be achieved with different proportions and process parameters within the range, verifying the feasibility and stability of the technical solution. Comparative Examples 1-4 have significant shortcomings in impedance control accuracy, insertion loss, near-end crosstalk, or bending life, and cannot simultaneously meet the requirements of high-frequency transmission performance and mechanical reliability, fully demonstrating the superiority of the technical solution of this application.

[0137] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of this application.

Claims

1. A low-loss, ultra-thin, high-speed transmission FFC cable, characterized in that: The raw materials, by weight, include 50-70 parts of fluorinated polyimide, 20-40 parts of liquid crystal polymer, 5-20 parts of surface-fluorinated SiO2 / Al2O3 microspheres, and 3-10 parts of fine PTFE powder; the total thickness of the FFC wire is less than or equal to 0.10 mm.

2. A low-loss, ultra-thin, high-speed transmission FFC cable according to claim 1, characterized in that: Fluorinated polyimide has a fluorination degree of 20-40 mol%, a weight-average molecular weight of 80,000-150,000 g / mol, and a glass transition temperature (Tg) of 280-320℃.

3. A low-loss, ultra-thin, high-speed transmission FFC cable according to claim 1, characterized in that: The particle size of the surface-fluorinated SiO2 / Al2O3 microspheres is 0.2-0.8 μm. The surface fluorination agent is trimethyltrifluoroacetic acid silane or heptadecafluorodecyltriethoxysilane. The surface contact angle of the fluorinated microspheres is ≥110°.

4. A low-loss, ultra-thin, high-speed transmission FFC cable according to claim 1, characterized in that: The average particle size of the fine PTFE powder is 0.2-0.8μm, the molecular weight is 5 million-10 million g / mol, the crystallinity is ≥95%, and the melting temperature is 325-335℃.

5. A low-loss, ultra-thin, high-speed transmission FFC cable according to claim 1, characterized in that: The liquid crystal polymer is an aromatic liquid crystal polyester or liquid crystal polyamide with a melting point of 280-350℃, a modulus of 8-15GPa, and a compatibility parameter χ≤0.5 with fluorinated polyimide. The FFC wire also includes a conductor layer, which is made of ultra-low profile rolled copper foil with a thickness of 9-12μm. The surface roughness Ra of the signal side of the ultra-low profile rolled copper foil is ≤0.5μm, the surface roughness Ra of the bonding side is 1.0-1.8μm, the copper purity is ≥99.8%, and the tensile strength is 350-450MPa.

6. A low-loss, ultra-thin, high-speed transmission FFC cable according to claim 1, characterized in that: FFC wires also include an adhesive layer, which is made of low-modulus epoxy resin or acrylic adhesive with a thickness of 5-8 μm. The low-modulus epoxy resin has an elastic modulus of 0.5-2.0 GPa, a glass transition temperature of 80-150℃, and an elongation at break of ≥50%. The acrylic adhesive has an elastic modulus of 0.3-1.5 GPa and a peel strength of ≥2 N / mm. FFC wires also include a protective layer, which is made of heat-resistant polyimide or fluorinated polyimide film with a thickness of 10-15 μm, a heat resistance temperature of ≥250℃, a tensile strength of ≥150 MPa, and an elongation at break of ≥20%.

7. A low-loss, ultra-thin, high-speed transmission FFC cable according to claim 1, characterized in that: FFC cables also include an embedded grounding grid layer. The grid width of the embedded grounding grid layer is 15-30μm, the grid spacing is 80-150μm, the thickness is 2-5μm, and the material is electrolytic copper or chemically plated copper with a conductivity ≥5.8×10⁻⁶. 7 S / m; FFC wires also include a top shielding layer with a thickness of 0.3-0.8μm and made of copper, nickel or silver. The top shielding layer is electrically connected to the embedded grounding grid layer through the FFC edge through-holes or windows, and the shielding effectiveness is ≥60dB@1GHz.

8. A method for preparing a low-loss, ultra-thin, high-speed transmission FFC cable, characterized in that: The method for preparing low-loss ultrathin high-speed transmission FFC wire as described in any one of claims 1-7 includes the following steps: (1) Preparation of low-loss dielectric thin film rolls; (2) An embedded grounding grid layer is formed on the dielectric film; (3) Signal copper foil bonding and pattern formation: a) Ultra-low profile rolled copper foil is precisely hot-pressed onto a dielectric film at a temperature of 180-230℃, a pressure of 1.5-3.0MPa, a holding time of 3-8 minutes, and a heating rate of 3-8℃ / min to form a dielectric / copper foil composite structure. b) Roll-to-roll coating with anti-etching ink, ink thickness 6-12μm, exposure energy 100-150mJ / cm² 2 The development time is 40-70 seconds, forming differential line pairs and end gradient patterns; c) Perform acid etching using a copper chloride / hydrochloric acid etching solution. The concentration of copper chloride is 180-220 g / L, the concentration of hydrochloric acid is 80-120 g / L, the temperature is controlled at 35-45℃, the etching time is 30-60 seconds, and the etching factor is controlled at 2.5-3.5 to form a trapezoidal cross-section copper conductor with a line width of 30-60 μm, a line spacing of 30-60 μm, a line pair spacing of 80-200 μm, and a sidewall angle of 80-88°. d) Remove the anti-etching ink using a 3-8% sodium hydroxide solution at a temperature of 50-70℃ for 45-90 seconds. Perform surface cleaning and anti-oxidation treatment using a 0.3-0.8% benzotriazole solution for 10-30 seconds. (4) Multi-layer hot pressing lamination molding: a) Lay upper / lower dielectric films and adhesive layers on both sides of the signal conductor layer, respectively; b) Perform hot pressing process at a temperature of 180-230℃, a pressure of 1.0-2.5MPa, a heating rate of 2-5℃ / min, a holding time of 8-15 minutes, and a cooling rate of ≤3℃ / min to form a symmetrical sandwich structure; (5) Forming the top shielding layer: A shielding metal layer with a thickness of 0.3-0.8μm is formed by sputtering or coating, with a sputtering power of 250-350W and a deposition rate of 1-3nm / s. It is electrically connected to the grounding grid layer through the FFC edge vias / windows. (6) Terminal structure processing: a) Remove localized covering film and medium by laser windowing / punching, with laser power of 0.8-1.5W, pulse frequency of 15-25kHz, and scanning speed of 200-500mm / s, exposing copper conductor terminals. b) Perform tin or gold plating treatment, with a nickel plating layer thickness of 1.5-3.0μm, a gold plating layer thickness of 0.03-0.08μm, and a tin plating layer thickness of 2-5μm; c) Die-cut to shape according to the number of poles and length requirements, with a die-cutting accuracy of ≤ ±0.05mm; (7) Online detection and impedance compensation correction: The online TDR impedance detection module and optical width measurement system are integrated. The detection frequency range is 1-10GHz and the measurement accuracy is ≤±1Ω. The casting thickness (±2μm), lamination pressure (±0.1MPa) and etching time (±5 seconds) are finely adjusted according to the measured data to achieve closed-loop control and improve impedance consistency to ±3%.

9. A method for preparing a low-loss ultrathin high-speed transmission FFC wire according to claim 8, characterized in that: The preparation method of the low-loss dielectric system includes the following steps: (1) Fluorinated polyimide precursor, liquid crystal polymer, fine PTFE powder and surface fluorinated SiO2 / Al2O3 microspheres are mixed with N-methylpyrrolidone solvent in a certain ratio, with the solid content controlled at 20-35wt%. High-speed dispersion is carried out at a dispersion speed of 1000-2000rpm and a dispersion time of 60-120 minutes. Then, vacuum degassing treatment is performed at a vacuum degree of -0.08 to -0.095MPa and a degassing time of 20-40 minutes to obtain a uniformly dispersed resin solution. (2) Precision casting is performed on a metal carrier tape or release film, with the doctor blade gap controlled at 150-250μm and the casting speed at 2-4m / min; (3) The cast film is subjected to heating curing / imino treatment. The specific temperature gradient is 80℃ (20min) → 120℃ (30min) → 160℃ (40min) → 200℃ (45min) → 250℃ (60min) → 300℃ (30min). The heating rate is controlled at 1.5-3℃ / min, and the temperature fluctuation at each stage is ≤±3℃, so as to obtain a low-loss dielectric film roll with a thickness of 20-30μm.

10. A method for preparing a low-loss ultrathin high-speed transmission FFC wire according to claim 8, characterized in that: The method for preparing an embedded grounding grid layer includes the following steps: (1) A uniform ultrathin metal seed layer is formed on a dielectric thin film by vacuum magnetron sputtering, with a vacuum degree ≤5×10⁻⁶. -4 Pa, sputtering power 150-250W, sputtering rate 0.5-1.5nm / s, seed layer thickness 0.1-0.3μm; (2) A grid pattern is formed by roll-to-roll lithography or direct laser imaging, with a photoresist thickness of 3-8 μm and an exposure energy of 80-150 mJ / cm². 2 The development time is 30-60 seconds, the grid line width is 15-30μm, and the grid spacing is 80-150μm; (3) Electroplating thickness is increased to 2-5 μm. The electroplating solution is a copper sulfate solution with a copper sulfate concentration of 180-220 g / L, a sulfuric acid concentration of 60-90 g / L, and a chloride ion concentration of 50-80 mg / L. The temperature is controlled at 25-35℃, and the current density is 15-30 mA / cm². 2 Stirring speed 100-200 rpm; (4) Remove the photoresist using acetone or N-methylpyrrolidone solution at a temperature of 40-60℃, an ultrasonic power of 100-300W, and a removal time of 2-5 minutes to obtain a patterned grounding grid layer.

Images