Manufacturing method of printed circuit board of high-speed transmission line with graphene structure

Abstract

The invention relates to the technical field of circuit board manufacturing, and discloses a method for manufacturing a printed circuit board of a high-speed transmission line with a graphene structure, which comprises the following steps of: preparing a combined structure body with a temporary carrier and a printed circuit board outer layer pattern, the temporary carrier being used for supporting the processing of the printed circuit board outer layer pattern; and depositing a layer of conductor material on the outer pattern of the printed circuit board of the combined structure body by adopting a thin film deposition process. The manufacturing method of the printed circuit board of the high-speed transmission line with the graphene structure aims at providing a novel transmission line-to-body structure of the printed circuit board, a higher signal transmission speed can be provided through the conductor structure, RCdelay is minimized, high-speed terminal products such as a server for AI are improved, the highest transmission speed is achieved, and the product quality is improved. And the conductor energy loss is minimum, so that the transmission quality of the signal is optimized, and the signal integrity is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit board manufacturing, in particular to a printed circuit board manufacturing method with a high-speed transmission line having a graphene structure. BACKGROUND

[0002] With the continuous improvement of computing power demand, the requirement for transmission rate of terminal equipment is increasingly improved. As the core carrier of signal transmission, the performance of the transmission line conductor of the printed circuit board becomes a key factor affecting the overall transmission efficiency. At present, the transmission line of the printed circuit board mainly relies on traditional conductor materials (such as copper) to realize signal transmission. In the high-computing-power scene, the integration of active electrical components (such as chips and chip packages) is continuously improved, and the energy generated by the rapid switching of the crystal in the unit area is significantly increased, resulting in a faster temperature accumulation speed. At the same time, in the high-speed and high-frequency application, the skin effect reduces the effective signal transmission cross-sectional area of the transmission line conductor, and the actual current density is increased, which further aggravates the temperature rise under the action of Joule heat. Under this background, how to optimize the conductive performance of the transmission line to improve the transmission rate and improve the heat dissipation capacity to cope with temperature accumulation has become an important research direction for the development of high-computing-power printed circuit boards.

[0003] Although the existing printed circuit board transmission line technology has been widely applied, there are still significant defects in the high-computing-power and high-speed transmission scene: firstly, the conductivity and heat dissipation of the traditional conductor material (such as copper) have been difficult to meet the demand, and the limitation of the transmission line resistance on the signal transmission rate is increasingly obvious, which cannot adapt to the requirement of the terminal products such as AI servers for high-speed transmission, and is easy to cause signal defects due to RCdelay (resistance-capacitance delay), thereby reducing the signal integrity; secondly, the existing transmission line design is insufficient in terms of heat dissipation, and the accumulated heat in the unit area cannot be effectively dissipated in time, and the high temperature not only reduces the working efficiency of the chip, but also causes the chip to burn out and fail in serious cases; thirdly, the increase of current density under the skin effect further aggravates the energy loss and temperature problem, and the existing technology lacks a transmission line structure design that can simultaneously solve the problems of high conductivity, low resistance and high heat dissipation, which cannot meet the dual requirements of high-computing-power printed circuit boards for "high-speed transmission" and "high-efficiency heat dissipation", thereby restricting the performance improvement of high-computing-power terminal products. SUMMARY

[0004] The purpose of the present application is to provide a novel printed circuit board transmission line structure, which can provide faster signal transmission speed, minimize RCdelay, improve the fastest transmission speed of high-speed terminal products such as AI servers, minimize conductor energy loss, and optimize the transmission quality of signals to improve signal integrity. A printed circuit board manufacturing method with a high-speed transmission line having a graphene structure is proposed.

[0005] The technical scheme for solving the above technical problems is as follows: A printed circuit board manufacturing method of a high-speed transmission line with a graphene structure, comprising the following steps: S10, preparing a combined structure with a temporary carrier and a printed circuit board outer layer pattern, the temporary carrier being used to support the processing of the printed circuit board outer layer pattern; S20, depositing a layer of conductor material on the printed circuit board outer layer pattern of the combined structure by using a thin film deposition process, to form a composite transmission line structure; S30, laminating the printed circuit board outer layer pattern processed by S20 on a film and a printed circuit board with an inner layer structure, and laminating another film and a copper foil under the printed circuit board with an inner layer structure in sequence to form a laminated structure; S40, processing the laminated structure by using a printed circuit board hot pressing process, so that the outer layer pattern of the conductor material, the film, the passive device and the printed circuit board with an inner layer structure are bonded and solidified as a whole; S50, separating the printed circuit board processed by S40 from the temporary carrier to expose the surface of the outer layer pattern of the conductor material; S60, removing the exposed conductor material of the printed circuit board after separation by using a grinding process, and retaining the conductor material in the transmission line area; S70, manufacturing a Via hole that is conductive between the inner and outer layers in the printed circuit board outer layer pattern processed by S60, metalizing the Via hole, and completing the metalization of the other side Via hole and the manufacturing of the outer layer pattern to obtain a printed circuit board with a high-speed transmission line with a graphene structure.

[0006] On the basis of the above technical scheme, the application can also be improved as follows.

[0007] Further, the temporary carrier in S10 is a carrier copper foil, the carrier copper foil comprises a stripping layer and a copper layer, wherein the thickness of the copper layer is 2-3 μm; the stripping layer is made of a material with a strippable property, and the thickness thereof is 0.5-2 μm.

[0008] Further, the thin film deposition process in S20 is selected from at least one of screen printing, chemical vapor deposition or ultrasonic spraying; when the chemical vapor deposition process is used, the reaction gas is a carbon-containing gas, the reaction temperature is controlled at 800-1000 ℃, and the reaction pressure is 1-10 kPa; when the screen printing process is used, the concentration of the high-conductivity material in the printing paste is 50-80 wt%, and the printing speed is 1-5 m / min; when the ultrasonic spraying process is used, the spraying pressure is 0.2-0.5 MPa, and the nozzle moving speed is 2-6 mm / s.

[0009] Further, the conductor material in S20 is selected from graphene, nanobimetallic copper, or other pure conductor materials or combined materials with better conductivity and thermal conductivity than copper; when the material is graphene, it is a single-layer or multi-layer graphene film, and the carbon atom arrangement order degree of the graphene is ≥95%; when the material is nanobimetallic copper, the grain size is 5-50 nm, and the twin boundary density is ≥10 14 m -2 .

[0010] Further, the thickness of the high-conductivity, low-resistance, and high-heat-dissipation conductor material deposited in S20 is 0.34 nm-10 nm; when the material is graphene, the thickness is 0.34 nm-5 nm, and the number of layers is 1-15 layers; when the material is nanobimetallic copper, the thickness is 2-10 nm.

[0011] Further, the hot-pressing process parameters in S40 are: hot-pressing temperature 180-220℃, hot-pressing pressure 2-4 MPa, and hot-pressing time 60-120 min; during the hot-pressing process, a stepwise heating mode is adopted, first heating at a rate of 5℃ / min to 120℃ and keeping for 30 min, and then heating at a rate of 3℃ / min to the target temperature and keeping for a specified time.

[0012] Further, the grinding process in S60 is chemical mechanical grinding, the grinding liquid is an alkaline suspension containing silica abrasive, the abrasive particle size is 50-100 nm, the grinding pressure is 0.1-0.3 MPa, and the grinding rate is 10-20 μm / min.

[0013] Further, the Via hole for internal and external conduction in S70 is made by laser drilling process, the laser wavelength is 355 nm or 1064 nm, the drilling diameter is 50-200 μm, and the hole site accuracy is controlled within ±5 μm; the Via hole metallization treatment adopts a combination of chemical copper plating and electroplating copper, first forming a conductive layer with a thickness of 0.5-1 μm on the inner wall of the Via hole by chemical copper plating, and then increasing the thickness of the conductive layer to 5-10 μm by electroplating copper, to ensure the conductivity and connection reliability of the Via hole.

[0014] Further, the film in S30 is a modified epoxy resin film with a thickness of 20-50 μm, a glass transition temperature ≥180℃, and a thermal conductivity ≥0.3 W / (m・K); the copper foil is an electrolytic copper foil or a calendered copper foil with a thickness of 12-35 μm and a surface roughness Ra≤0.5 μm.

[0015] Further, the high-conductivity, low-resistance, high-heat-dissipation conductor material deposited in S20 is a composite layer of graphene and nanobimetallic copper, wherein the graphene layer is located on the side close to the outer layer pattern of the printed circuit board, with a thickness of 0.34-2 nm, and the nanobimetallic copper layer is located on the side away from the outer layer pattern of the printed circuit board, with a thickness of 2-8 nm; the composite layer realizes the close combination of graphene and nanobimetallic copper through an interface treatment process, and the interface bonding strength is ≥ 50 MPa.

[0016] Compared with the prior art, the technical scheme of the present application has the following beneficial technical effects: In the present application, a thin film deposition process is used to deposit a conductor material on the outer layer pattern of the printed circuit board to form a composite transmission line structure, which reduces the transmission line resistance through the characteristics of high conductivity and low resistance, reduces the RC delay (resistance-capacitance delay), thereby improving the signal transmission rate and signal integrity, meeting the demand for high-speed transmission of terminal products such as AI servers; at the same time, the high heat dissipation of the conductor material can enhance the heat dissipation capacity of the transmission line, and the composite transmission line structure provides a more effective way for heat dissipation, secondly, the high-conductivity, low-resistance conductor material can optimize the current distribution under the skin effect, reduce the impact of the reduction of the effective signal transmission cross-sectional area, and reduce the actual current density, thereby alleviating the temperature rise caused by Joule heat and reducing energy loss, in addition, the hot pressing process makes the outer layer pattern, the film, the passive device and the printed circuit board of the inner layer structure adhere to form a whole and solidify, ensuring the stable combination of the transmission line with high-performance conductor material and the overall structure of the printed circuit board, and guaranteeing the stable performance of the transmission line; through the grinding process, the high-performance conductor material in the transmission line area can be reserved to concentrate its performance advantages in the key transmission path, further improving the overall performance of the transmission line, and ultimately helping to improve the performance of high-performance terminal products. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a combination structure of a temporary carrier and an outer layer pattern of a printed circuit board. Figure 2 It is a structural schematic diagram of a process deposition of graphene or a thin film. Figure 3 It is a structural schematic diagram of a combination of a carrier, a printed circuit board and a copper foil. Figure 4 It is a structural schematic diagram of a printed circuit board with a Via hole for internal and external conduction in the outer layer pattern.

[0018] In the figure: 1, temporary carrier; 2, outer layer pattern of printed circuit board; 3, graphene; 4, film; 5, substrate; 6, copper foil; 7, Via hole. DETAILED DESCRIPTION

[0019] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0020] The application discloses a printed circuit board manufacturing method with a high-speed transmission line with a graphene structure, comprising the following steps: S10, preparing a combined structure with a temporary carrier 1 and a printed circuit board outer layer pattern 2, the temporary carrier 1 being used for supporting the processing of the printed circuit board outer layer pattern 2; The temporary carrier is generally a substrate with a 18um bottom copper layer, coated with an organic conductive ion type film (about 20nm), and then with a 5um copper foil; the 5um substrate is used for electroplating when the circuit pattern is manufactured, and the electroplating thickness / line width is designed by the customer; S20, depositing a layer of conductor material on the printed circuit board outer layer pattern 2 of the combined structure by using a thin film deposition process, to form a composite transmission line structure; S30, laminating the printed circuit board outer layer pattern 2 processed by S20 on a film 4 and a printed circuit board with an inner layer structure, and laminating another film 4 and a copper foil 6 under the printed circuit board with the inner layer structure in sequence, to form a laminated structure; S40, processing the laminated structure by using a printed circuit board hot pressing process, so that the outer layer pattern of the conductor material, the film 4, the passive device and the printed circuit board with the inner layer structure are bonded and solidified as a whole; S50, separating the printed circuit board processed by S40 from the temporary carrier 1, to expose the surface of the outer layer pattern of the conductor material; S60, removing the exposed conductor material of the printed circuit board after separation by using a grinding process, to reserve the conductor material in the transmission line area; S70, manufacturing a Via hole with internal and external conduction in the printed circuit board outer layer pattern 2 processed by S60, metalizing the Via hole, and completing the metalization of another Via hole and the manufacturing of the outer layer pattern, to obtain the printed circuit board with the high-speed transmission line with the graphene structure.

[0021] The temporary carrier 1 in S10 is a carrier copper foil 6, which includes a release layer and a copper layer, wherein the thickness of the copper layer is 2-3 pm; the release layer is made of a material with peelable properties, and the thickness is 0.5-2 pm, which is used to facilitate the separation of the temporary carrier 1 from the printed circuit board in S50, and avoid damage to the outer layer pattern 2 of the printed circuit board and the deposited high-conductivity material during the separation process. Compared with the traditional temporary carrier 1, this structure can not only ensure the supporting strength, but also reduce the separation difficulty and improve the production efficiency by precisely controlling the thickness and material properties of the release layer, which solves the problem of deformation of the conductor pattern caused by the separation of the existing temporary carrier 1. By limiting the temporary carrier 1 to be the carrier copper foil 6 containing the release layer and the copper layer, the precisely controlled thickness (0.5-2 pm) and peelable property of the release layer can provide stable support for the outer layer pattern 2 of the printed circuit board and the deposited high-conductivity material during the processing process, and facilitate the convenient and damage-free separation in the S50 separation step, avoiding mechanical damage to the transmission line structure, thereby ensuring the integrity of the high-conductivity material and the stability of the conductivity and heat dissipation performance of the transmission line. At the same time, the copper layer thickness of 2-3 pm reduces material consumption and improves production efficiency under the premise of ensuring supporting strength.

[0022] The release layer specifically adopts a modified polyimide material, which is pre-cured by ultraviolet light for 10-15 minutes under a wavelength of 365 nm ultraviolet light, so that the initial peel strength of the release layer is controlled at 1.0-1.2 N / cm, which not only meets the support requirements during the processing process, but also reduces the peel strength to 0.3-0.5 N / cm through heating (80-100°C) during separation, realizing stress-free separation. The copper layer of the carrier copper foil 6 adopts high-purity electrolytic copper (purity ≥ 99.99%), and the surface is subjected to nano-scale passivation treatment (passivation solution is chromate solution, concentration is 5-8 g / L, treatment time is 3-5 seconds), forming a passivation film with a thickness of 5-10 nm to prevent the copper layer from being oxidized and affecting the deposition adhesion of the subsequent high-conductivity material. In the S10 step, the combined structure needs to be subjected to a plasma cleaning process (using a mixture of argon and oxygen gas with a volume ratio of 9:1, power of 100-150 W, and cleaning time of 60-90 seconds), to remove surface organic contaminants and dust particles, so that the water contact angle of the surface of the outer layer pattern 2 of the printed circuit board is ≤10°, and the adhesion between the deposited material and the substrate is ≥20 N / m.

[0023] The thin film deposition process in S20 is selected from at least one of screen printing, chemical vapor deposition or ultrasonic spraying; wherein, when the chemical vapor deposition process is adopted, the reaction gas is carbon-containing gas, the reaction temperature is controlled at 800-1000℃, the reaction pressure is 1-10kPa, and the thickness uniformity of the deposited material is controlled by adjusting the reaction time, so that the thickness deviation of the deposited high-conductivity material is not more than ±0.5nm; when the screen printing process is adopted, the concentration of the high-conductivity material in the printing paste is 50-80wt%, and the printing speed is 1-5m / min, so as to ensure that a continuous and uniform coating is formed on the surface of the outer layer pattern 2 of the printed circuit board; when the ultrasonic spraying process is adopted, the spraying pressure is 0.2-0.5MPa, and the nozzle moving speed is 2-6mm / s, so as to avoid the phenomena of missing spraying or accumulation. The selection and parameter control of these processes can realize accurate deposition according to the characteristics of different high-conductivity materials, and compared with the traditional deposition process, can significantly improve the uniformity and bonding force of the material deposition, ensure the stability of the conductive and heat dissipation performance of the transmission line, the temperature and pressure control of the chemical vapor deposition process ensures the crystallization quality of materials such as graphene 3, and the parameter setting of screen printing and ultrasonic spraying avoids coating defects, so that the thickness deviation of the deposited material is controlled within ±0.5nm, and the uniformity of the conductive performance of the transmission line is significantly improved. This uniformity directly alleviates the problems of local resistance rise and heat dissipation dead angle caused by uneven material distribution in the background art, reduces RCdelay, and at the same time, enhances the bonding force of the material and the substrate, avoids signal interruption or heat dissipation failure caused by material falling off in high-speed transmission scenarios.

[0024] When the chemical vapor deposition process is adopted, in addition to carbon-containing gas, nitrogen gas is also needed as a diluent gas (carbon-containing gas to nitrogen gas volume ratio 1:20), and the gas flow rate is accurately controlled by a mass flow controller (total flow rate 50-100sccm) to ensure that the reaction cavity pressure is stable at 1-10kPa. Before deposition, the substrate needs to be pretreated: heated to 900℃ in a hydrogen atmosphere (flow rate 30sccm) for 30 minutes to remove the surface oxide layer. In the screen printing process, the screen used is stainless steel with a mesh size of 300-400 mesh and a photosensitive glue thickness of 10-15μm, and after printing, drying needs to be carried out under the protection of inert gas (nitrogen) (temperature 120-150℃, time 20-30 minutes) to avoid oxidation of the high-conductivity material. The ultrasonic spraying process uses a double-channel nozzle, one channel of which transports the paste (solid content 50-80wt%), and the other channel transports inert gas (argon, pressure 0.3MPa), which refines the droplets (particle size 5-10μm) through gas shear force to ensure the uniformity of the coating. After deposition, a four-probe tester is used to test the material square resistance (test point spacing 1mm) to ensure that the resistance deviation is ≤5%.

[0025] The conductor material in S20 is selected from graphene 3, nanobimetallic copper, or other pure conductor materials or combined materials with better conductivity and heat conductivity than copper; when the material is graphene 3, it is a single-layer or multi-layer graphene 3 film, and the carbon atom arrangement order degree of the graphene 3 is greater than or equal to 95%; when the material is nanobimetallic copper, the grain size is 5-50 nm, and the twin boundary density is greater than or equal to 1014 m-2. By selecting such high-performance materials and controlling the microstructure parameters, compared with the traditional copper conductor, the conductivity of the transmission line can be increased by 10-30%, and the heat dissipation coefficient can be increased by 15-40%, effectively solving the problem of large RC delay and poor heat dissipation of the existing transmission line due to insufficient material performance. The high-order carbon atom arrangement (greater than or equal to 95%) of graphene 3 and the ultra-fine grain size (5-50 nm) and high twin boundary density of nanobimetallic copper make the conductivity and heat dissipation coefficient of graphene 3 and nanobimetallic copper respectively increase by 10-30% and 15-40% compared with the traditional copper conductor, directly reducing the RC delay of the transmission line and enhancing the signal transmission rate. At the same time, the excellent heat dissipation performance accelerates the dissipation of the accumulated heat in the unit area, avoids the performance decline or burning of the chip caused by high temperature, and meets the dual requirements of “high-speed transmission” and “high-efficiency heat dissipation” in high-computing scenarios.

[0026] When the material is graphene 3, it is prepared by a chemical exfoliation method, the raw material is natural flake graphite (carbon content greater than or equal to 99.9%), and after oxidation and exfoliation, graphene 3 oxide is obtained, and then the graphene 3 oxide is reduced by hydrazine hydrate (reduction temperature 80°C, time 24 hours), so that the oxygen content of the graphene 3 is less than or equal to 2 at% (determined by X-ray photoelectron spectroscopy). The surface resistance of the graphene 3 film is tested by a four-probe method (less than or equal to 30 Ω / □), and the light transmittance (550 nm wavelength) is greater than or equal to 85%, which ensures the high conductivity of the graphene 3. When the material is nanobimetallic copper, it is prepared by electrodeposition, and the electrolyte composition is: copper sulfate 200 g / L, sulfuric acid 50 g / L, chloride ion 50 mg / L, and an organic additive (such as polyethylene glycol, molecular weight 8000, concentration 100 mg / L) is added to inhibit grain growth, and the deposition temperature is controlled at 25-30°C, and the current density is 2-5 A / dm2. The microstructure is characterized by transmission electron microscopy (TEM), so as to ensure that the twin boundary proportion is greater than or equal to 80%, and there is no obvious dislocation accumulation. Before use, the material needs to be vacuum annealed at 100°C (vacuum degree less than or equal to 1 Pa, time 2 hours) to eliminate internal stress and avoid structural deformation caused by stress release in subsequent processes.

[0027] The thickness of the high-conductivity, low-resistance, high-heat-dissipation conductor material deposited in S20 is 0.34 nm-10 nm; when the material is graphene 3, the thickness is 0.34 nm-5 nm, and the number of layers is 1-15 layers; when the material is nanobimetallic copper, the thickness is 2-10 nm. The selection of the thickness range is based on the skin effect principle, aiming at the characteristics that the current is mainly concentrated on the surface of the conductor under high-speed transmission, by controlling the thickness of the material, both the full play of the high-conductivity, high-heat-dissipation performance and the avoidance of material waste and the reduction of production cost can be ensured, at the same time, the difficulty of subsequent grinding process caused by excessive thickness is avoided, the balance between material thickness and performance, processing cost is solved, and the thickness range of 0.34 nm-10 nm accurately matches the characteristics that the current is concentrated on the surface of the conductor under high-speed transmission, ensuring that the high-conductivity material can fully play a role (such as graphene 3-15 layers which can ensure the conductivity and avoid the increase of resistance caused by too many layers). At the same time, reasonable thickness control reduces material consumption, reduces production cost, and avoids the increase of grinding process difficulty caused by excessive thickness of the material, ensures the flatness of the transmission line edge after grinding, further reduces signal transmission loss, and improves signal integrity in high-computing-power scenarios.

[0028] For high-frequency scenarios with a working frequency ≥28 GHz, the thickness of graphene 3 is preferably 0.34-2 nm (1-6 layers), at this time the skin depth is about 0.5-1 μm, and the conductive performance of single-layer graphene 3 can be maximized; for scenarios with a working frequency of 5-28 GHz, the thickness of graphene 3 can be increased to 2-5 nm (6-15 layers), and the conductive performance and cost are balanced by multiple layers. The thickness of nanobimetallic copper needs to be combined with the current density: when the current density of the transmission line design is ≥5×105 A / cm2, the thickness is controlled to be 5-10 nm to enhance the current carrying capacity; when the current density is <5×105 A / cm2, the thickness of 2-5 nm can meet the demand. The thickness is detected by an ellipsometer (measurement range 0.1-100 nm, accuracy ±0.01 nm), which is monitored in real time during the deposition process, and data is recorded every 10 seconds to ensure that the final thickness deviation is not more than ±0.3 nm. In addition, the uniformity of the material thickness along the length direction of the transmission line needs to meet: the thickness change in any 10 mm interval is ≤0.5 nm, to avoid impedance mismatch caused by thickness fluctuation.

[0029] The hot-pressing process parameters in S40 are: hot-pressing temperature 180-220℃, hot-pressing pressure 2-4MPa, hot-pressing time 60-120min; during the hot-pressing process, a stepwise heating mode is adopted, first heating at a rate of 5℃ / min to 120℃ and keeping for 30min, then heating at a rate of 3℃ / min to the target temperature and keeping for a specified time. This hot-pressing process can not only ensure that the film 4 is fully cured and the structures of each layer are firmly bonded, but also avoid the destruction of the structure of the deposited high-conductivity material (such as graphene 3) due to excessive temperature or pressure, solving the problem that the existing hot-pressing process is easy to cause damage to high-performance conductor materials, ensuring the electrical performance and structural stability of the transmission line. The temperature range of 180-220℃ and the stepwise heating (first slow and then stable) not only ensure the full curing of the modified epoxy resin film 4 (the glass transition temperature meets the standard), but also avoid the damage to the graphene 3 lattice structure (such as the decrease of carbon atom arrangement order) caused by high temperature. At the same time, the pressure control of 2-4MPa prevents the thickness unevenness of high-conductivity materials caused by excessive extrusion, ensuring the stability of the electrical performance of the transmission line, so that the printed circuit board can maintain high-speed transmission and high-efficiency heat dissipation ability for a long time in high-computing power scenarios.

[0030] The hot-pressing equipment adopts a full-automatic multi-layer hot-pressing machine equipped with an infrared temperature sensor (temperature measurement accuracy ±1℃) to monitor the surface temperature of the stacked structure in real time, ensuring that the deviation from the set temperature is ≤3℃. The surface of the hot-pressing mold is treated by chrome plating (hardness HRC50-55) and polishing (Ra≤0.02μm) to avoid the indentation of the stacked structure caused by the rough surface of the mold. Before hot-pressing, the stacked structure needs to be pretreated in vacuum (vacuum degree ≤10Pa, time 30min) to remove the air bubbles between the layers and prevent the appearance of voids affecting heat dissipation after hot-pressing. For the composite transmission line containing graphene 3, the maximum hot-pressing temperature is strictly controlled within 200℃, and after reaching the target temperature, pulse pressure maintaining is adopted (the pressure fluctuates between 2-4MPa with a range of 0.5MPa, the cycle is 30 seconds), which promotes the flow of the film 4 while avoiding the deformation of the graphene 3 layer under pressure. After hot-pressing, cold-pressing treatment is carried out (pressure 2MPa, temperature 25℃, time 30min) to reduce internal stress, and the curing degree of the film 4 is confirmed to be ≥95% (the storage modulus at 180℃ is ≥1GPa) through dynamic mechanical analysis (DMA) test.

[0031] The polishing process in S60 is chemical mechanical polishing, the polishing liquid is an alkaline suspension containing silica abrasive, the abrasive particle size is 50-100 nm, the polishing pressure is 0.1-0.3 MPa, and the polishing rate is 10-20 μm / min. Through this polishing process, the outer exposed high-conductivity material can be accurately removed, while avoiding damage to the material in the transmission line area and the printed circuit board base layer, ensuring the edge flatness and electrical performance stability of the transmission line, solving the problem of material residue or excessive polishing caused by traditional polishing processes. The alkaline suspension containing silica abrasive (50-100 nm) and the polishing pressure of 0.1-0.3 MPa can accurately remove the outer exposed high-conductivity material, while avoiding damage to the material in the transmission line area and the base layer. The polishing rate of 10-20 μm / min ensures the controllability of the polishing process, ensuring the edge flatness of the transmission line (Ra≤0.1 μm), reducing signal reflection and loss in signal transmission, and improving signal integrity under high-speed transmission. In addition, this process avoids chemical corrosion of the polishing liquid on the high-conductivity material, ensuring that the conductivity and heat dissipation performance of the transmission line are not affected.

[0032] The particle size distribution of the silica abrasive in the polishing liquid needs to meet: D50=70 nm, D90≤100 nm (detected by a laser particle size analyzer), the abrasive concentration is 10-15 wt%, and a dispersing agent (such as sodium hexametaphosphate, concentration 0.5 wt%) is added to prevent abrasive agglomeration. The pH value of the polishing liquid is controlled at 10-11 (adjusted by ammonia water), which can ensure the chemical activity of the abrasive and avoid corrosion of graphene 3 or nanometer bicrystal copper (72-hour immersion test, material mass loss rate ≤0.1%). The polishing process uses an online endpoint detection system: by monitoring the concentration change of carbon elements (for graphene 3) or copper elements (for nanometer bicrystal copper) in the polishing liquid, when the concentration decreases to less than 1% of the initial value, it is determined as the polishing endpoint, ensuring that the exposed material is completely removed. After polishing, the printed circuit board needs to go through three steps of cleaning: first, ultrasonic cleaning with deionized water (power 300 W, time 5 minutes), then immersion in dilute nitric acid (concentration 1 wt%) for 30 seconds to remove residual abrasive, and finally washing with deionized water and nitrogen blowing (pressure 0.5 MPa), and X-ray fluorescence spectrum detection confirms that there is no silicon residue on the surface (content ≤0.01 wt%).

[0033] The Via hole for internal and external conduction in S70 is made by laser drilling process, the laser wavelength is 355 nm or 1064 nm, the drilling diameter is 50-200 pm, and the hole position accuracy is controlled within ±5 pm; the Via hole metallization treatment adopts the combination of chemical copper plating and electroplating copper, first forms a conductive layer with a thickness of 0.5-1 pm on the inner wall of the Via hole, and then increases the thickness of the conductive layer to 5-10 pm by electroplating copper, to ensure the conductivity and connection reliability of the Via hole. Compared with traditional mechanical drilling and single electroplating, the Via hole manufacturing and metallization process has higher precision and conductivity, can meet the signal integrity requirements under high-speed transmission, and solves the problems of large processing difficulty and insufficient conductivity of small size Via hole. The 355 nm or 1064 nm wavelength laser ensures the processing accuracy of the 50-200 pm diameter Via hole (hole position deviation ±5 pm), avoiding the size error caused by drill wear in traditional mechanical drilling. The combination of chemical copper plating and electroplating copper (first form a 0.5-1 pm conductive layer, then thicken to 5-10 pm), not only ensures the uniform coverage of the hole wall, but also improves the conductivity of the Via hole (through-hole resistance ≤3 mΩ), meeting the signal integrity requirements under high-speed transmission. This high-precision and high-conductivity Via hole design ensures the stability of the printed circuit board interlayer signal transmission, and alleviates the signal delay problem caused by interlayer connection in high computing power scenarios.

[0034] The laser drilling adopts a Q-switched laser, the pulse width is controlled within 10-50 ns, the single pulse energy is 50-100 pJ, and the drilling is performed by multi-pulse superposition (50-100 pulses per hole), to avoid carbonization of the hole wall caused by high single pulse energy (the carbonized layer thickness on the hole wall is ≤0.5 pm observed by SEM). After drilling, plasma drilling pollution removal treatment is performed (oxygen atmosphere, power 200 W, time 60 seconds) to remove the residual resin debris on the hole wall. The chemical copper plating solution formula is: copper sulfate 10 g / L, formaldehyde 5 g / L, ethylenediaminetetraacetic acid disodium 25 g / L, sodium hydroxide 10 g / L, temperature 25-30°C, pH value 12-13, deposition time 15-20 minutes, to ensure 100% coverage of the hole wall. The electroplating copper adopts an acidic plating solution (copper sulfate 200 g / L, sulfuric acid 50 g / L), adds a brightener (such as 2-mercaptobenzimidazole, concentration 0.1 g / L), the current density is 1-2 A / dm2, and the plating uniformity is controlled by Hall tank test (thickness deviation ≤10%). After the Via hole is completed, a thermal shock test is performed (-55°C to 125°C, 100 cycles), and the through-hole resistance change rate after the test is ≤5%, to ensure stable conduction in the temperature fluctuation environment of high computing power equipment.

[0035] The film 4 in S30 is a modified epoxy resin film 4 with a thickness of 20-50 μm, a glass transition temperature ≥180℃, and a thermal conductivity ≥0.3 W / (m·K); the copper foil 6 is an electrolytic copper foil 6 or a rolled copper foil 6 with a thickness of 12-35 μm and a surface roughness Ra≤0.5 μm. By selecting such film 4 and copper foil 6, a good match can be formed with the deposited high-conductivity material, improving the heat resistance, heat dissipation, and signal transmission performance of the overall structure, solving the problems of insufficient heat resistance of traditional film 4 and large surface roughness of copper foil 6 leading to signal loss, making the printed circuit board more suitable for high-performance AI terminal products. By selecting high-performance modified epoxy resin film 4 and low-roughness copper foil 6, the problem of signal loss caused by insufficient heat resistance of traditional film 4 and large surface roughness of copper foil 6 is solved. The high glass transition temperature (≥180℃) and high thermal conductivity (≥0.3 W / (m·K)) of the film 4 ensure its stability under long-term high-temperature operation of high-performance equipment, avoiding deformation of the transmission line caused by softening of the film 4. The surface roughness Ra≤0.5 μm of the copper foil 6 reduces the skin effect loss in signal transmission, forms a good match with the deposited high-conductivity material, and improves the signal transmission performance and heat dissipation capacity of the overall structure. This material combination makes the printed circuit board more suitable for the harsh working environment of high-performance AI terminal products, ensuring the long-term reliability of the equipment.

[0036] In the modified epoxy resin film 4, 30-40 wt% of nano-boron nitride (BN) filler (particle size 50-100 nm) is added, which is dispersed by a ball mill (rotation speed 3000 rpm, time 2 hours) to form a continuous thermal conduction network in the film 4, and its thermal conductivity can reach 0.5-0.8 W / (m·K) by laser flash method. The curing shrinkage of the film 4 is controlled to ≤1% (tested by a thermal mechanical analyzer TMA), avoiding stress damage to the transmission line during curing. The copper foil 6 is a high-ductility rolled copper foil 6 (elongation ≥15%), and its surface is treated by electrolytic roughening, but the roughening particles are controlled to a height of 0.3-0.5 μm, and the surface roughness Ra≤0.3 μm is confirmed by atomic force microscopy (AFM) scanning. The bonding force between the copper foil 6 and the film 4 is verified by peeling test (test speed 50 mm / min) to ensure ≥1.8 N / mm, and the bonding force retention rate is ≥90% after aging at 150℃ for 1000 hours. In addition, the dielectric constant of the film 4 (at 1 GHz) is controlled to 3.0-3.2, and the dielectric loss is ≤0.002, further reducing the dielectric loss in signal transmission.

[0037] The high-conductivity, low-resistance, high-heat-dissipation conductor material deposited in S20 is a composite layer of graphene 3 and nanobimorph copper, wherein the graphene 3 layer is located on the side close to the outer layer pattern 2 of the printed circuit board, with a thickness of 0.34-2 nm, and the nanobimorph copper layer is located on the side away from the outer layer pattern 2 of the printed circuit board, with a thickness of 2-8 nm; the composite layer realizes the close combination of graphene 3 and nanobimorph copper through an interface treatment process, with an interface bonding strength ≥ 50 MPa. The composite layer combines the high conductivity of graphene 3 and the high thermal conductivity and mechanical strength of nanobimorph copper, and compared with a single material layer, can further reduce the transmission line resistance by 15-20%, improve the heat dissipation capacity by 20-25%, and at the same time, enhance the bending resistance of the transmission line, solve the performance limitations of a single material, significantly improve the comprehensive performance of the printed circuit board, and further improve the comprehensive performance of the transmission line through synergistic effect. The high conductivity of the graphene 3 layer (on the side close to the substrate) reduces the transmission resistance, the high thermal conductivity and mechanical strength of the nanobimorph copper layer (on the outer side) enhance the heat dissipation capacity and bending resistance, and the interface bonding strength ≥ 50 MPa ensures the synergistic effect of the two layers of materials. Compared with a single material, the composite structure further reduces the transmission line resistance by 15-20%, improves the heat dissipation capacity by 20-25%, and at the same time, the bending resistance (no fracture when the bending radius ≤ 1 mm) meets the mechanical stress requirements in the processing and use of the printed circuit board, and can better adapt to the extreme requirements of "high speed, high efficiency and high reliability" in high computing power scenarios.

[0038] The interface treatment of the graphene 3 layer and the nanobimorph copper layer adopts plasma activation technology: first, the surface of graphene 3 is treated with oxygen plasma (power 100 W, oxygen flow rate 20 sccm, time 60 seconds), to introduce hydroxyl (-OH) functional groups (detected by Fourier transform infrared spectroscopy FTIR, a hydroxyl characteristic peak appears at 3400 cm⁻ 1 The interface treatment of the graphene 3 layer and the nanobimorph copper layer adopts plasma activation technology: first, the surface of graphene 3 is treated with oxygen plasma (power 100 W, oxygen flow rate 20 sccm, time 60 seconds), to introduce hydroxyl (-OH) functional groups (detected by Fourier transform infrared spectroscopy FTIR, a hydroxyl characteristic peak appears at 3400 cm⁻ The composite layer is deposited by a step-by-step process: first, a graphene 3 layer is prepared by chemical vapor deposition, and then a nanobimorph copper layer is deposited by magnetron sputtering (target material: high-purity copper, purity 99.99%, sputtering power 200 W, argon pressure 0.5 Pa), to ensure that there is no oxide layer between the layers (observed by high-resolution transmission electron microscopy HRTEM, the interface transition zone thickness ≤ 2 nm). The mechanical properties of the composite layer are verified by nanoindentation testing (load 500 μN), with a hardness ≥ 2.5 GPa and an elastic modulus ≥ 120 GPa; after 1000 bending tests (bending angle 180°, bending radius 1 mm), the conductivity attenuation is ≤ 5% and the thermal conductivity attenuation is ≤ 8%, to ensure stable performance in long-term use.

[0039] The combination structure containing temporary carrier 1 and printed circuit board outer layer pattern 2 is prepared by S10 step, wherein the release layer adopts a modified polyimide material, which has stable supporting strength after ultraviolet pre-curing treatment, and can reduce the release strength by heating, laying a foundation for subsequent non-destructive separation, and ensuring the structural integrity of the outer layer pattern and the subsequent deposited material during processing.

[0040] In S20 step, high-conductivity, low-resistance, high-heat-dissipation material is precisely deposited on the printed circuit board outer layer pattern 2 by chemical vapor deposition, screen printing or ultrasonic spraying process: if it is graphene 3, the carbon atom ordering degree is ≥95%, and the mixed atmosphere of carbon-containing gas and nitrogen gas and the temperature control of 800-1000℃ during chemical vapor deposition ensure the crystalline quality; if it is nanometer bicrystal copper, the grain size of 5-50nm and the bicrystal boundary density of ≥1014m-2 are realized by electrodeposition process, which ensures that the electrical conductivity and heat dissipation coefficient are respectively increased by 10-30% and 15-40% compared with traditional copper. The thickness of the material is controlled in the range of 0.34nm-10nm, which precisely matches the skin effect under high-speed transmission, maximizes the utilization rate of material performance, and avoids the processing problems caused by excessive thickness.

[0041] S30 step stacks the deposited outer layer pattern with modified epoxy resin film 4, inner layer structure circuit board and copper foil 6. The high glass transition temperature and low dielectric loss of the film 4 cooperate with the low roughness of the copper foil 6 to reduce the dielectric loss and skin effect loss in signal transmission, forming a laminated structure suitable for high-speed transmission.

[0042] S40 uses a stepwise hot pressing process, first heating at 5℃ / min to 120℃ for 30min, then increasing the temperature to the target temperature at 3℃ / min, and avoiding the destruction of high-conductivity material structure by pulse pressure holding, while ensuring that the film 4 is fully cured, realizing firm adhesion of each layer, and protecting the stability of the overall structure.

[0043] S50 reduces the strength of the release layer of the temporary carrier 1 by heating, realizes non-destructive separation with the printed circuit board, and exposes the complete surface of the high-conductivity material; S60 uses chemical mechanical polishing to precisely remove the outer exposed high-conductivity material, leaving the material in the transmission line area, ensuring the flatness of the transmission line edge, and avoiding signal reflection and loss.

[0044] S70 makes Via holes by laser drilling, and combines the metallization treatment of chemical copper plating and electroplating copper to ensure the high conductivity and reliability of interlayer connection and reduce interlayer signal delay.

[0045] For the composite layer structure, the interface bonding strength is greater than or equal to 50 MPa by plasma activation treatment, the graphene 3 layers utilize high conductivity to reduce transmission resistance, the nanometer bicrystal copper layer enhances heat dissipation and bending resistance by virtue of high thermal conductivity and mechanical strength, and the two synergistically further reduce resistance by 15-20%, breaking through the performance limitations of single material.

[0046] It should be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another, without necessarily requiring or implying any actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0047] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a printed circuit board with a high-speed transmission line having a graphene structure, characterized in that, Includes the following steps: S10. Prepare a combined structure with a temporary carrier and a printed circuit board outer layer pattern, wherein the temporary carrier is used to support the processing of the printed circuit board outer layer pattern; S20. A layer of conductor material is deposited on the outer layer pattern of the printed circuit board of the combined structure using a thin film deposition process to form a composite transmission line structure. S30. The outer layer pattern of the printed circuit board processed by S20 is superimposed on a film and a printed circuit board with an inner layer structure, and another film and copper foil are sequentially superimposed below the printed circuit board with the inner layer structure to form a stacked structure. S40. The stacked structure is processed by a hot pressing process for printed circuit boards, so that the outer layer pattern of the conductor material, the film, the passive device and the printed circuit board with the inner layer structure are bonded together and cured. S50: Separate the printed circuit board processed by S40 from the temporary carrier to expose the outer patterned surface of the conductor material. S60. The exposed conductor material on the outer layer of the printed circuit board after separation is removed by a grinding process, while the conductor material in the transmission line area is retained. S70. In the outer layer pattern of the printed circuit board processed by S60, a Via hole with internal and external conductivity is made. The Via hole is metallized. The metallization of the Via hole and the outer layer pattern of the other side are completed to obtain a printed circuit board with a high-speed transmission line with a graphene structure.

2. The method for manufacturing a printed circuit board with a high-speed transmission line having a graphene structure according to claim 1, characterized in that, In S10, the temporary carrier is a carrier copper foil, which includes a release layer and a copper layer, wherein the thickness of the copper layer is 2-3 μm; the release layer is made of a material with peelable properties and has a thickness of 0.5-2 μm.

3. The method for fabricating a printed circuit board with a graphene structure for high-speed transmission lines according to claim 1, characterized in that, The thin film deposition process in S20 is selected from at least one of screen printing, chemical vapor deposition, or ultrasonic spraying; wherein, when using chemical vapor deposition, the reaction gas is a carbon-containing gas, the reaction temperature is controlled at 800-1000℃, and the reaction pressure is 1-10kPa; when using screen printing, the concentration of highly conductive material in the printing paste is 50-80wt%, and the printing speed is 1-5m / min; when using ultrasonic spraying, the spraying pressure is 0.2-0.5MPa, and the nozzle moving speed is 2-6mm / s.

4. The method for manufacturing a printed circuit board with a high-speed transmission line having a graphene structure according to claim 3, characterized in that, The conductor material in S20 is selected from graphene, nano-bicrystalline copper, or other pure conductor materials or combinations thereof with better electrical and thermal conductivity than copper; wherein, when the material is graphene, it is a single-layer or multi-layer graphene film, and the carbon atom arrangement order of graphene is ≥95%; when the material is nano-bicrystalline copper, its grain size is 5-50nm, and its grain boundary density is ≥10. 14 m -2 .

5. The method for manufacturing a printed circuit board with a graphene structure for high-speed transmission lines according to claim 4, characterized in that, The thickness of the highly conductive, low-resistance, and high-heat-dissipation conductive material deposited in S20 is 0.34nm-10nm; wherein, when the material is graphene, the thickness is 0.34nm-5nm and the number of layers is 1-15; when the material is nano-bicrystalline copper, the thickness is 2-10nm.

6. The method for manufacturing a printed circuit board with a graphene structure for high-speed transmission lines according to claim 1, characterized in that, The hot pressing process parameters in S40 are: hot pressing temperature 180-220℃, hot pressing pressure 2-4MPa, and hot pressing time 60-120min. During the hot pressing process, a stepped heating method is adopted, first heating to 120℃ at a rate of 5℃ / min and holding for 30min, and then heating to the target temperature at a rate of 3℃ / min and holding for a specified time.

7. The method for manufacturing a printed circuit board with a graphene structure for high-speed transmission lines according to claim 1, characterized in that, The grinding process in S60 is chemical mechanical grinding. The grinding fluid is an alkaline suspension containing silica abrasive, the abrasive particle size is 50-100nm, the grinding pressure is 0.1-0.3MPa, and the grinding rate is 10-20μm / min.

8. The method for manufacturing a printed circuit board with a high-speed transmission line having a graphene structure according to claim 1, characterized in that, The Via hole in S70, which provides internal and external conductivity, is created using laser drilling technology with a laser wavelength of 355nm or 1064nm. The drilling diameter is 50-200μm, and the hole position accuracy is controlled within ±5μm. The metallization treatment of the Via hole uses a combination of chemical copper plating and electroplating. First, a conductive layer with a thickness of 0.5-1μm is formed on the inner wall of the Via hole through chemical copper plating. Then, the thickness of the conductive layer is increased to 5-10μm through electroplating to ensure the conductivity and connection reliability of the Via hole.

9. A method for manufacturing a printed circuit board with a graphene structure for high-speed transmission lines according to claim 1, characterized in that, The film in S30 is a modified epoxy resin film with a thickness of 20-50 μm, a glass transition temperature ≥180℃, and a thermal conductivity ≥0.3 W / (m・K); the copper foil is an electrolytic copper foil or a rolled copper foil with a thickness of 12-35 μm and a surface roughness Ra≤0.5 μm.

10. A method for manufacturing a printed circuit board with a high-speed transmission line having a graphene structure according to claim 3, characterized in that, The highly conductive, low-resistance, and high-heat-dissipating conductor material deposited in S20 is a composite layer of graphene and nano-bicrystalline copper. The graphene layer is located on the side closer to the outer pattern of the printed circuit board, with a thickness of 0.34-2 nm, while the nano-bicrystalline copper layer is located on the side of the graphene layer away from the outer pattern of the printed circuit board, with a thickness of 2-8 nm. The composite layer achieves a tight bond between graphene and nano-bicrystalline copper through an interface treatment process, with an interface bonding strength ≥50 MPa.

Images