A PBO fiber-based heat-conducting layer, a copper-clad plate, and a preparation method and application thereof

Abstract

The application discloses a kind of based on PBO fiber's heat-conducting layer, copper-clad plate and its preparation method and application, belong to high-performance electrical technical field.PBO fiber is used as base material, it is successively made by weaving, modification, impregnation, drying, at least meet the following conditions: ordinary PBO fiber or special-shaped PBO fiber, the cross section of ordinary PBO fiber is circular, the cross section of special-shaped PBO fiber is 3-10-blade multilobal, special-shaped degree>22%;Thermal conductivity: 20-50W / (m·K);Coefficient of thermal expansion:‑20-0ppm / ℃;Tensile modulus: 160GPa-280GPa.The application mainly aims at the problems, such as insufficient heat dissipation capacity of existing computing center PCB, limited temperature resistance and flame retardance, etc., by selecting PBO fiber (circular or multilobal special-shaped structure) with specific index system as base material, to further optimize and improve the thermal conductivity of the material, realize the synchronous upgrading of heat-conducting performance, mechanical strength, structural stability and safety performance, so as to meet the use requirements of super-high power density computing equipment.

Description

Technical Field

[0001] This invention relates to a thermally conductive layer based on PBO fibers, a copper-clad laminate, its preparation method, and its application. Specifically, it relates to a high thermal conductivity material prepared from ordinary PBO fibers or irregularly shaped PBO fibers, a copper-clad laminate containing the thermally conductive material, its preparation method, and its application in electrical performance fields (such as PCBs), belonging to the field of high-performance electrical technology. Background Technology

[0002] With the explosive growth of the digital economy and artificial intelligence industry, computing centers, as the core of digital infrastructure, are rapidly developing towards ultra-high power density, high-density integration, and long-term continuous operation. As a key carrier of core components such as server motherboards, AI accelerator cards, and high-speed interconnect backplanes, the PCB of a computing center undertakes multiple functions, including massive data signal transmission, heat dissipation of high-power devices, and support for precision components. Its performance directly determines the computing speed, stability, and energy consumption level of the computing center.

[0003] The core technological bottlenecks currently facing PCBs in computing centers are concentrated in four main areas: thermal management, structural compatibility, signal integrity, and long-term reliability. Specific issues are as follows:

[0004] (1) Exceeding the limit of heat dissipation pressure, the risk of thermal failure is prominent: The power of a single rack in the computing center has soared from the traditional 5-10kW to more than 50kW, the power consumption of a single AI server card has exceeded 700W, and the heat flux density of the chip is as high as 1000W / cm². The mainstream PCB currently uses FR-4 substrate, which has a vertical thermal conductivity of 0.2-0.3W / (m·K). Even the thermal conductivity of conventional high thermal conductivity PCB is only 1-3W / (m·K). Heat cannot be dissipated quickly, resulting in local hot spots around the chip, with temperatures reaching more than 150℃. This causes the chip to reduce frequency, lose computing power, and even suffer from thermal failure problems such as solder melting and substrate delamination, which seriously restricts the improvement of computing power and the stable operation of equipment.

[0005] (2) Traditional thermal conductive materials are difficult to achieve composite performance: In the existing improvement schemes, although the thermal conductivity of ceramic substrates is high, they are brittle and have poor vibration resistance, which cannot adapt to the mechanical stress during transportation and operation of computing equipment; metal substrates are heavy and have poor dielectric properties, which can easily generate electromagnetic interference; conventional fiber-reinforced substrates are mostly circular cross-sections, and the bonding force between them and the matrix interface is limited, and the thermal conductive network is prone to "disconnection", which makes it difficult to fully utilize the thermal conductivity potential of fibers and cannot meet the synergistic requirements of computing center PCBs for thermal conductivity and structural stability.

[0006] (3) Insufficient structural stability under high-density integration: The hole density and line density of the PCB in the computing center continue to increase, and the wiring spacing is reduced to less than 50μm. At the same time, it needs to support a large number of precision chips and components. The coefficient of thermal expansion (CTE) of traditional PCB substrates, copper foils and packaging materials do not match. Under long-term high-temperature operation and thermal cycling, interface stress concentration is prone to occur, resulting in faults such as via cracking, line warping and substrate delamination, which significantly reduces the service life and operational reliability of the PCB.

[0007] (4) Insufficient weather resistance and safety performance under high temperature environment: The computing center equipment operates continuously for 24 hours, and the ambient temperature of the computer room is often maintained at 30-40℃. The PCB is under high temperature load for a long time. The upper limit of the temperature resistance of traditional PCB substrates is mostly below 130℃, and the flame retardant rating is difficult to meet the UL94 V-0 standard. It is easy to burn under overload or short circuit conditions; and it is easy to experience performance degradation under long-term high temperature, which affects the integrity of signal transmission and the safety of equipment operation.

[0008] Therefore, developing a computing center PCB that can fundamentally overcome the existing bottlenecks in heat dissipation and structural stability has become an urgent need for the high-quality development of the computing power industry.

[0009] Poly(p-phenylenebenzodioxazole), abbreviated as PBO, is a heterocyclic aromatic polymer with rigid molecular chains. Its solution can exhibit a liquid crystal state under certain conditions. The fibers produced by spinning PBO are high-strength, high-modulus, high-thermal-stability, and high-chemical-stability high-performance fibers, and are considered the best-performing organic fibers to date. PBO fibers possess better thermal conductivity and thermal dimensional stability than ordinary fibers, a lower dielectric constant, and excellent mechanical strength, making them a highly promising reinforcing material for PCB (Printed Circuit Board) substrates. In the prior art, Chinese patent CN120676528A discloses a copper-clad laminate (CCL) and its interlayer, along with its preparation method and applications. This method involves orthogonally weaving PBO fibers and glass fibers in a certain proportion to form a blended fiber, followed by modification, impregnation, and drying steps to obtain the interlayer of the CCL. This method effectively combines the advantages of PBO and glass fibers, enabling the CCL to possess both low dielectric loss and thermal expansion coefficient, as well as excellent peel strength, heat resistance, and flexibility.

[0010] However, facing the severe heat dissipation challenges brought about by the development of ultra-high power density in computing center equipment (local hotspot temperatures on a single board can reach 150°C, and chip heat flux density can reach 1000W / cm²), existing technologies mainly focus on using PBO fibers to improve the dielectric properties and mechanical strength of copper-clad laminates, failing to fully utilize their excellent thermal conductivity. Therefore, how to leverage the thermal conductivity advantages of PBO fibers to construct efficient heat conduction paths in copper-clad laminates to match the heat dissipation requirements in high heat flux density scenarios currently lacks targeted systematic research and practical exploration. Summary of the Invention

[0011] To address the problems of insufficient heat dissipation capacity, unbalanced composite performance, poor structural stability, and limited temperature resistance and flame retardancy of existing computing center PCBs, this invention provides a thermally conductive layer based on PBO fibers, a copper-clad laminate, its preparation method, and its application. By selecting PBO fibers (circular or multi-lobed irregular structures) with specific index systems as the substrate, the thermal conductivity of the material is further optimized and improved, achieving simultaneous upgrades in thermal conductivity, mechanical strength, structural stability, and safety performance, thus meeting the usage requirements of ultra-high power density computing equipment.

[0012] This invention is achieved through the following technical solution: a method for preparing a thermally conductive layer based on PBO fiber, using PBO fiber as the substrate, and obtaining it through sequential spinning, modification, impregnation, and drying.

[0013] The PBO fiber must meet at least the following conditions:

[0014] (I) Ordinary PBO fiber or irregular PBO fiber, wherein the cross-section of the ordinary PBO fiber is circular, and the cross-section of the irregular PBO fiber is multi-leaf shaped with 3 to 10 leaves, and the irregularity is >22%;

[0015] (II) Thermal conductivity: 20–50 W / (m·K);

[0016] (III) Coefficient of thermal expansion: -20~0ppm / ℃;

[0017] (IV) Tensile modulus: 160 GPa~280 GPa.

[0018] The diameter of the PBO fiber (ordinary PBO fiber or irregular PBO fiber) is 6 to 18 μm.

[0019] The PBO fiber is produced by extruding a polymer solution through a spinneret with circular or irregular holes, followed by stretching, shaping, washing, drying, and heat treatment.

[0020] Preferably, the PBO fibers are spun into a fabric, and the fabric form is one or a combination of unidirectional, plain weave, and spread weave.

[0021] Preferably, the PBO fibers are woven into pure PBO fabric or into a blended fabric made of one or more of glass fiber, quartz, polyimide, and aramid.

[0022] The fabric spun from the PBO fibers is modified to obtain a modified fabric, wherein the modification treatment is selected from at least one of plasma treatment, irradiation treatment, and silane coupling agent treatment.

[0023] The modified fabric obtained by the modification is impregnated in an impregnation solution containing resin to obtain a fiber prepreg. The resin content in the impregnation solution is 35-70%, and the resin is selected from one of epoxy resin, hydrocarbon resin, cyanate ester, PPO resin, polyimide, phenolic resin and PTFE.

[0024] The impregnated fiber resin prepreg is dried at 100-200°C for 2-10 minutes, mainly to remove solvent and pre-cur it to obtain a thermally conductive layer for copper-clad laminates.

[0025] Furthermore, the present invention provides a thermally conductive layer based on PBO fibers, obtained by the above preparation method, wherein the thermally conductive layer meets the following indicators:

[0026] In-plane thermal conductivity: 6–20 W / (m·K);

[0027] Coefficient of thermal expansion: -15~10ppm / ℃;

[0028] Flexural modulus: 10 GPa~40 GPa;

[0029] Tensile modulus: 160 GPa~280 GPa.

[0030] Furthermore, the present invention provides a copper-clad laminate based on PBO fibers, comprising a first copper foil layer, a thermally conductive layer as described above, and a second copper foil layer stacked sequentially from top to bottom.

[0031] The thickness of the first copper foil layer is 18–105 μm;

[0032] The thickness of the thermally conductive layer is 50–4000 μm;

[0033] The thickness of the second copper foil layer is 18–105 μm.

[0034] Preferably, the copper-clad laminate meets the following specifications:

[0035] Peel strength: ≥0.8 N / mm;

[0036] Solder heat resistance: 288℃, immersion in tin for 10 seconds, 6 cycles, meets the requirement of no blistering or delamination abnormalities;

[0037] Drilling performance: No obvious burrs.

[0038] The present invention also provides a method for preparing the above-mentioned copper-clad laminate, wherein a first copper foil layer, a thermally conductive layer and a second copper foil layer are stacked sequentially from top to bottom, a surface protective layer precursor is then covered on the surface of the first copper foil layer, and the laminate is then placed in a hot press and hot-pressed to obtain the copper-clad laminate.

[0039] Furthermore, the present invention also provides the application of the above-mentioned copper-clad laminate in the preparation of a high thermal conductivity computing center PCB board, wherein the copper-clad laminate is used to prepare a high thermal conductivity computing center PCB board.

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] (1) This invention first prepared a PBO multi-leaf fiber with high specific surface area. Taking advantage of the characteristics of PBO liquid crystal spinning, PBO has a high molecular weight and high solid content, and is in liquid crystal state, which is easy to orient. Moreover, the oriented molecules are not easy to deorient. The PBO molecules oriented in the spinneret channel enter the coagulation bath to remove the solvent after being extruded from the channel. After the internal solvent is removed, the fiber skin shrinks further inward. Due to the external water pressure, the indentation of the fiber is deeper until the skin hardens and the irregular shape is completely fixed.

[0042] (2) This invention uses circular PBO fibers or PBO fibers with multi-lobed irregular structures to prepare the thermally conductive layer, which significantly improves the specific surface area of ​​the fibers and the interfacial bonding strength with the resin matrix, thus constructing a continuous and efficient three-dimensional thermally conductive network. Tests show that the in-plane thermal conductivity of the copper-clad laminate (or PCB) of this invention can reach over 5 W / (m·K).

[0043] It should be noted that traditional FR-4 substrates (vertical thermal conductivity 0.2–0.3 W / (m·K)) and conventional high thermal conductivity PCBs (vertical thermal conductivity 1–3 W / (m·K)) mainly rely on the isotropic thermal conductivity of resin or fillers. Their in-plane thermal conductivity is usually roughly equivalent to that in the vertical direction, making it difficult to achieve directional heat dissipation. However, the heat generated by actual chips needs to be conducted vertically to the outer surface and also rapidly diffused along the board surface. This invention addresses this practical heat dissipation requirement.

[0044] By using PBO fibers (circular or irregular shapes) to construct high-speed heat conduction channels in the plane, the heat generated by the chip is rapidly spread along the board surface, transforming the original local "point heat source" into a large-area "surface heat source". This significantly increases the heat dissipation area, reduces the local heat flux density, and the dispersed heat can be quickly conducted to heat dissipation structures such as copper pillars in the board, and then vertically conducted to the outer surface for final dissipation, thereby achieving efficient thermal management of "in-plane diffusion + vertical conduction".

[0045] Testing revealed that the in-plane thermal conductivity of the copper-clad laminate of this invention is more than an order of magnitude higher than that of the traditional FR-4 substrate, and 2 to 3 times higher than that of conventional high thermal conductivity PCBs. This unique anisotropic thermal design can reduce the temperature of local hot spots by more than 60°C, effectively preventing frequency reduction or computing power loss caused by heat accumulation in the chip, and ensuring the long-term stable operation of computing center equipment under high heat flux density (up to 1000W / cm²).

[0046] (3) This invention weaves circular PBO fibers or multi-lobed PBO shaped fibers (because the PBO main chain is highly oriented, the transverse thermal vibration will produce a greater "pulling" effect in the fiber axis when heated, resulting in significant axial shrinkage and a complex coefficient of thermal expansion) into a fabric, so that the thermal conductive layer has both high thermal conductivity and high rigidity, and has a unique coefficient of thermal expansion (-15 to 10 ppm / ℃), which is highly matched with the chip packaging material (which requires a lower coefficient of thermal expansion, about 5 ppm / ℃); and can withstand the mechanical vibration and installation stress of computing equipment. After 1000 thermal shocks in an environment of -40 to 125℃, there is no cracking or delamination. The structural stability is significantly better than that of traditional PCBs, greatly improving the long-term operational reliability under high-density integration conditions.

[0047] (4) This invention utilizes the advantage of the ultra-high tensile modulus (160-280GPa) of the irregular PBO fiber, combined with its irregular structure (multi-leaf cross section) and stable anchoring with the resin matrix, so that the thermally conductive layer has excellent mechanical load-bearing capacity, and its bending modulus can reach 10-40GPa, giving the copper-clad laminate extremely high rigidity and deformation resistance, which can effectively withstand the complex mechanical stress generated by the AI ​​server during transportation, installation and operation, which is significantly better than the brittle ceramic substrate or the conventional organic substrate with insufficient rigidity.

[0048] (5) This invention makes full use of the excellent dielectric properties of PBO fiber to ensure the integrity of high-frequency signal transmission. The dielectric loss Df of the PCB made can be reduced to below 0.002 at 10GHz, effectively reducing signal attenuation and crosstalk, and perfectly matching the stringent requirements of computing centers for high-speed and high-fidelity data transmission.

[0049] (6) The copper-clad laminate of this invention exhibits extremely high thermal shock resistance. The solder heat resistance test (288℃, immersion in solder for 10 seconds, 6 cycles) meets the following requirements: no blistering or delamination abnormalities, which is comparable to the thermal shock resistance of traditional PCB boards. It can cope with long-term high temperature (30-40℃ computer room environment) and instantaneous overload conditions in computing centers. At the same time, the product's flame retardant rating meets the UL94V-0 standard, ensuring the inherent safety of equipment operation from the material level. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the spinning holes of the spinneret used in this invention.

[0051] Figure 2 This is a scanning electron microscope image of the five-lobed irregular PBO fiber described in this invention. Detailed Implementation

[0052] The invention's objective, technical solution, and beneficial effects will be further explained in detail below.

[0053] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the claimed invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0054] This invention relates to a thermally conductive layer based on PBO fibers, a copper-clad laminate containing the thermally conductive layer, its preparation method, and its application. In addition to ordinary PBO fibers (with a circular cross-section), the cross-sectional shape of the PBO fibers is designed to be irregular (diameter of 6-18 μm, cross-section of 3-10 blades, and irregularity > 22%), resulting in a thermally conductive reinforcing material with ultra-high thermal conductivity, low coefficient of thermal expansion, and high mechanical strength. This material is then applied to copper-clad laminates, thereby solving the problems of heat dissipation difficulties and poor structural stability in computing center PCBs in the prior art.

[0055] Furthermore, the technical solution of the present invention can be summarized in detail as follows:

[0056] (a) Ordinary PBO fibers or irregularly shaped PBO fibers

[0057] The ordinary PBO fiber and the shaped PBO fiber used in this invention are high-performance fibers with circular or multi-leaf cross sections prepared by a specific spinning process. The preparation process involves multiple steps such as extrusion, coagulation, stretching, washing, drying and heat treatment of polymer solution. By adjusting the spinneret structure and process parameters, the fiber morphology and performance can be precisely controlled.

[0058] If ordinary PBO fibers are used, such as round PBO fibers, their fiber diameter can be set to 6-18 μm; if irregularly shaped PBO fibers are used, such as multi-leaf fibers with a cross-section of 3-10 leaves, their fiber diameter can be set to 6-18 μm, and the irregularity is greater than 22%. The high irregularity greatly increases the specific surface area of ​​the fiber.

[0059] In a preferred embodiment, the preparation process is as follows:

[0060] Polyphosphoric acid (PPA) was used as a solvent, and PBO fibers were prepared by dry-jet wet spinning in liquid crystal spinning. The solid content of the PBO polymer solution was 10-16%, and the intrinsic viscosity ranged from 18 to 30 dL / g. The spinning solution was extruded through a spinneret with irregularly shaped holes (e.g., ...). Figure 1The extrusion temperature is 160–210℃, and the spinneret has three to ten leaflets (irregular structures as shown). The spinneret orifices are multi-leaf structures with a blade length L of 0.08–0.40 mm and a blade width W of 0.04–0.20 mm. After initial stretching and shaping, the extruded nascent filaments enter a coagulation bath with a phosphoric acid concentration of 0–30%. In the coagulation bath, the PPA solvent in the filaments diffuses into the coagulation bath, and the fiber morphology gradually becomes fixed. Figure 2 The image shown is a scanning electron microscope (SEM) image of PBO profiled fibers prepared using a five-hole spinneret (due to the extremely high strength of PBO, a smooth cross-section could not be obtained through sectioning, and observation was only possible from the outside). It is evident that the fibers exhibit distinct grooves and protruding ridges along their longitudinal extension, indicating successful preparation of the profiled PBO fibers. The maximum fiber diameter is approximately 18 μm, while the diameter of a circular PBO fiber with the same linear density is approximately 14 μm (since the minimum fiber diameter cannot be measured but is less than 14 μm, 14 μm is used here as an approximation).

[0061] PBO fiber irregularity = =(1-14 / 18)×100%>22%

[0062] Furthermore, the coagulated fibers undergo multi-stage washing to remove residual phosphoric acid from the fibers, followed by multi-stage drying. Each stage of the dryer is equipped with multiple hot rollers with a temperature of 60–400°C. The fiber bundle is sequentially wound around the multiple hot rollers and dried in stages at 60–150°C (first stage), 150–250°C (second stage), and 250–450°C (third stage) until the fiber moisture content is ≤5%.

[0063] After drying, the fibers undergo heat treatment under nitrogen protection to remove residual moisture and phosphoric acid and further improve the aggregated structure of the fibers. The heat treatment is carried out in a tube furnace, with the fiber bundle running slowly under a certain tension at a speed of 20–250 m / min. The heat treatment and nitrogen temperature is 450–650 °C, and the treatment tension is 1–3 cN / dtex.

[0064] The resulting PBO fibers must meet the following key indicators to ensure their excellent overall performance:

[0065] Thermal conductivity: The thermal conductivity of a single fiber is 20-50 W / (m·K), which is the basis for achieving high in-plane thermal conductivity of the thermal conductive layer.

[0066] Coefficient of thermal expansion: The coefficient of thermal expansion of a single fiber is -20 to 0 ppm / ℃. Its negative thermal expansion characteristics enable it to effectively control the overall thermal expansion behavior of the composite material after being combined with the resin matrix.

[0067] Tensile modulus: The tensile modulus of a single fiber is 160-280 GPa. The extremely high modulus provides excellent rigidity and dimensional stability to the final product.

[0068] (ii) Thermal conductive layer

[0069] The thermally conductive layer of the present invention is a composite material layer prepared from the above-mentioned PBO fibers through steps such as spinning, modification, impregnation, and drying.

[0070] The specific preparation method is as follows:

[0071] First, the prepared PBO fibers are woven into a fabric. The fabric structure can be selected from one or a combination of unidirectional, plain, and spread fabrics, depending on the needs. Unidirectional refers to fibers that are all in the same direction, which can reduce the thickness of a single layer of fabric. Plain weave refers to a weaving method where the warp and weft yarns interweave every other yarn in the perpendicular warp and weft directions, resulting in a more stable structure. Spread fabric refers to fabric made by spreading and thinning large bundles of fibers using airflow, ultrasound, and mechanical methods to obtain a thin layer of yarn before weaving, which also reduces the thickness of a single layer of fabric. The choice of fabric type affects the thermal conductivity of the heat-conducting layer and the thickness of the single layer.

[0072] In a practical case, the prepared PBO fibers can be woven into pure PBO fabric or into blended fabrics with one or more of glass fiber, quartz, polyimide, and aramid.

[0073] Secondly, the woven fabric is modified to enhance the interfacial bonding between the fiber and the resin matrix. The modification treatment is selected from at least one of plasma treatment, irradiation treatment, and silane coupling agent treatment. For example, plasma treatment can employ online corona treatment with a power of 1–7 kW and a linear velocity of 3–20 m / min; irradiation treatment can use gamma rays or electron beams with a dose controlled at 50–300 KGy; silane coupling agent treatment involves immersing the fiber fabric in a solution containing a silane coupling agent (such as at least one of KH-550, KH-560, and KH-570) for 30 minutes while the solution is stirred to ensure uniformity, followed by air drying and baking at 120°C for 10–120 minutes. These treatments can introduce polar groups or increase surface roughness on the fiber surface, thereby improving the wettability and bonding strength between the fiber and the resin.

[0074] The modified fabric is then impregnated in an impregnation solution containing resin to obtain a fiber prepreg. The solid content of the resin in the impregnation solution is 35-70%. The resin used can be selected from epoxy resin, hydrocarbon resin, cyanate ester resin, PPO resin, polyimide, phenolic resin, and PTFE, depending on the requirements for dielectric properties, heat resistance, and bonding strength. In addition to resin, the impregnation solution may also contain curing agents (such as amine curing agents, acid anhydrides, or polythiols), fillers (such as silica or aluminum hydroxide), flame retardants (such as bromine-containing flame retardants, phosphorus-containing flame retardants, or aluminum hydroxide), accelerators (such as imidazole, thiourea, or triethylamine), and solvents (such as methyl ethyl ketone, acetone, or DMF), etc. The added substances or amounts are usually determined according to the physical property requirements of the actual application.

[0075] Finally, the impregnated fiber prepreg is dried at 100–200°C for 2–10 minutes (drying time can be determined according to thickness, resin type, and solvent) to remove the solvent and bring the resin to a specific state before semi-curing or complete curing, thereby obtaining a thermally conductive layer for copper-clad laminates. More specifically, the drying process employs a multi-stage oven, controlling the temperature of each stage at 60–100°C (stage 1), 100–150°C (stage 2), and 150–200°C (stage 3).

[0076] The thermally conductive layer prepared by the above method has the following performance indicators:

[0077] In-plane thermal conductivity: 6–20 W / (m·K), which is due to the continuous thermal conductivity pathway formed by PBO fibers in the in-plane direction.

[0078] Coefficient of thermal expansion: -15~10ppm / ℃. By combining with PBO fiber with a negative coefficient of thermal expansion, the thermal expansion performance can be controlled, and it can achieve good thermal matching with chip packaging materials.

[0079] Flexural modulus: 10-40 GPa. The high modulus ensures the rigidity of the thermal conductive layer and even the entire copper clad laminate.

[0080] Tensile modulus: 160~280GPa, this index mainly inherits the high modulus characteristics of PBO fiber.

[0081] (iii) Copper Clad Laminate

[0082] The present invention provides a copper-clad laminate based on the above-mentioned PBO fiber thermal conductive layer, the structure of which includes a first copper foil layer, the thermal conductive layer and the second copper foil layer as described in the present invention, which are stacked sequentially from top to bottom.

[0083] First copper foil layer: thickness is 18-105um.

[0084] Thermal conductive layer: The thickness is 50~4000um. This layer serves as the core reinforcement and thermal conductive layer, and its thickness can be adjusted according to the current carrying and heat dissipation requirements of the final PCB board.

[0085] The second copper foil layer has a thickness of 18–105 μm.

[0086] The preparation method of this copper-clad laminate is as follows: A first copper foil layer, a thermally conductive layer, and a second copper foil layer are stacked sequentially. Then, a surface protective layer precursor (such as kraft paper or a three-layer composite material) is applied to the outer surface of the first copper foil layer for cushioning and shaping. The stacked laminate is placed in a hot press and subjected to hot-pressing composite under specific temperature (170–280℃), pressure (1–6 MPa), and vacuum (-0.1 MPa) conditions. This ensures a tight bond between the layers and full resin curing, ultimately yielding the copper-clad laminate.

[0087] The resulting copper-clad laminate meets the following performance indicators:

[0088] Peel strength: ≥0.8N / mm, indicating that the copper clad laminate made using PBO has good adhesion.

[0089] Solder heat resistance: After immersing in a tin bath at 288℃ for 10 seconds and repeating 6 times, it meets the requirement of no blistering or delamination, proving that it has excellent thermal shock resistance.

[0090] Drilling performance: The hole wall is smooth after drilling, with no obvious burrs, indicating that the material has good machinability.

[0091] Dielectric constant Dk: 2.5~3.8, which meets the performance requirements of the computing board.

[0092] Dielectric loss Df: ≤0.002@10GHz, indicating that it has extremely low loss and can be used in computing boards.

[0093] (iv) PCB board

[0094] The present invention further provides the application of the above-mentioned copper-clad laminate in the preparation of a high thermal conductivity computing center PCB board. The application is to use the copper-clad laminate through conventional PCB manufacturing processes (such as blanking, drilling, copper plating, electroplating, outer layer circuitry, solder masking, surface treatment, etc.) to finally prepare a high thermal conductivity computing center PCB board.

[0095] In a preferred embodiment, high-precision drilling (hole diameter tolerance ±0.01mm) is performed by ultraviolet laser drilling, and the vias are chemically deposited copper (copper layer thickness ≥0.8μm) and electroplated copper (plating layer thickness 15~25μm). After processes such as circuit etching, solder resist curing, and surface anti-oxidation treatment, an irregular A-fiber reinforced high thermal conductivity computing center PCB is produced.

[0096] In summary, this invention successfully overcomes the limitations of traditional fibers in constructing efficient thermal conductive networks by using ordinary PBO fibers or irregularly shaped PBO fibers with specific multi-leaf cross-sections (3-10 leaves, irregularity >22%) as the reinforcing substrate for the thermally conductive layer. This structural design significantly improves the specific surface area of ​​the fibers and the interfacial bonding strength with the resin matrix, constructing a continuous and stable three-dimensional thermally conductive skeleton in the in-plane direction of the copper-clad laminate, thereby fully utilizing the potential of the excellent thermal conductivity of PBO fibers (single fiber thermal conductivity 20-50 W / (m·K)). Tests have shown that the in-plane thermal conductivity of the thermal conductive layer of this invention can reach 6-20 W / (m·K). The in-plane thermal conductivity of copper-clad laminates and PCBs prepared from it can reach more than 5 W / (m·K), which is more than an order of magnitude higher than that of traditional FR-4 substrates and 2-3 times higher than that of conventional high thermal conductivity PCBs. This achieves the thermal management effect of efficiently expanding the local "point heat source" generated by the chip into a large-area "surface heat source", and can effectively reduce the hot spot temperature by more than 60°C.

[0097] Meanwhile, this invention utilizes the negative thermal expansion characteristics (-20 to 0 ppm / ℃) and ultra-high tensile modulus (280 GPa at 160℃) of PBO fibers to create a thermally conductive layer that possesses both an adjustable negative thermal expansion coefficient (-15 to 10 ppm / ℃) and high rigidity (flexural modulus 10 to 40 GPa). This achieves a high degree of matching with the thermal expansion coefficient of the chip packaging material, significantly improving structural stability and long-term operational reliability under high-density integration conditions. Furthermore, by combining the excellent dielectric properties of PBO fibers with the material selection of the intermediate dielectric layer, the resulting PCB board can achieve a dielectric loss Df as low as below 0.002 at a 10 GHz frequency, and exhibits excellent thermal shock resistance (passing 288℃ / 10s / 6 soldering tests) and processing performance (no burrs during drilling).

[0098] Therefore, this invention systematically solves the core technical problems faced by existing computing center PCBs in ultra-high power density scenarios, such as heat dissipation bottlenecks, thermal expansion mismatch, and insufficient signal integrity, by introducing PBO fibers with specific index systems. It provides the computing industry with a high-performance copper-clad laminate solution that combines high thermal conductivity, low expansion, high rigidity, and low loss characteristics, and has significant practical value and broad application prospects.

[0099] The specific embodiments of the present invention are described below with reference to examples. Of course, the scope of protection of the present invention is not limited to the following embodiments. In the following embodiments, the fiber preparation, modification treatment, impregnation process, hot pressing composite and other operations are all carried out using conventional technical means in the art unless otherwise specified.

[0100] (a) The test methods for the product performance indicators involved in each embodiment and comparative example are as follows:

[0101] Fiber thermal conductivity: measured using laser flare method.

[0102] In-plane thermal conductivity: measured using the laser flare method.

[0103] Coefficient of thermal expansion: Tested using TMA equipment.

[0104] Tensile modulus: The test method is described in ASTM D3039 / D3039M-17.

[0105] Flexural modulus: The test method is described in ASTM D790-17.

[0106] Peel strength: For testing methods, please refer to IPC-TM-650 2.4.8.

[0107] Solder heat resistance: For testing methods, please refer to IPC-TM-650 2.4.13.1.

[0108] Drilling performance: Tested using mechanical drilling.

[0109] Dielectric constant Dk: Detected using the SPDR method.

[0110] Dielectric loss Df: Detected using the SPDR method.

[0111] (II) The main raw materials used in the various embodiments and comparative examples of the present invention are as follows:

[0112] Fiberglass E-cloth: Commercially available electronic-grade fiberglass cloth (Shanghai Honghe Electronic Materials Co., Ltd. 2116).

[0113] Fiberglass Q cloth: Commercially available quartz fiber cloth (Shanghai Honghe Electronic Materials Co., Ltd. FQW).

[0114] Ordinary circular PBO: prepared according to the aforementioned method of the present invention, with a diameter of about 12 μm and a circular cross-section, and its fiber thermal conductivity, coefficient of thermal expansion and tensile modulus all meet the performance indicators of the PBO fiber described in the present invention.

[0115] Five-lobed irregular PBO: Prepared according to the aforementioned method of the present invention, its cross-section is five-lobed with a diameter of approximately 18 μm, and its irregularity is calculated to be 22.22%, meeting the requirement of >22%. Its fiber thermal conductivity, coefficient of thermal expansion, and tensile modulus all meet the performance indicators of the PBO fiber described in the present invention.

[0116] Five-lobed irregular PBO and glass fiber blend: Five-lobed irregular PBO with a cross-section of about 18 μm in diameter and irregularity >22% and glass fiber are blended together in a plain weave. Its single fiber thermal conductivity is 34 W / (m·K), thermal expansion coefficient is -16 ppm / ℃, and tensile modulus is 160~280 GPa, all of which meet the performance indicators of the irregular PBO fiber described in this invention.

[0117] (III) The main processing technology involved in this invention is as follows:

[0118] Modification treatment: γ-irradiation treatment was carried out in air at room temperature with a dose of 100 KGy; corona treatment was performed using an online corona treatment machine with a power of 3 KW and a line speed of 5 m / min; in the silane coupling agent treatment, KH-560 or KH-570 was used, and the mixture was soaked for 30 min, then removed and dried, and baked at 120℃ for 60 min.

[0119] Resin system: Epoxy resin system (bicycloisoprene epoxy resin) or hydrocarbon resin system (Ricon resin), with the resin content controlled at 60%. Filler: 60% BN ceramic filler or 60% silica (% is the solid percentage of filler in the resin, excluding solvent).

[0120] Preparation of thermal conductive layer: The modified fabric is immersed in the corresponding resin solution, the resin content is controlled, and then it is sent into a multi-stage drying oven and dried at 100-200℃ for 10 minutes to obtain the thermal conductive layer.

[0121] Copper-clad laminate preparation: The thermally conductive layer obtained above is used as the core layer, and an 18μm layer of electrolytic copper foil is placed on the top and bottom. The core layer is placed in a vacuum hot press and hot-pressed for 2 hours under the conditions of 210℃, 4MPa pressure and -0.1MPa vacuum to allow the resin to fully cure and obtain the copper-clad laminate.

[0122] PCB board preparation: The copper-clad laminate obtained above is used to prepare a high thermal conductivity computing power PCB board using conventional PCB processes.

[0123] (iv) Examples and Comparative Examples

[0124] According to the fiber type, modification method, weaving method, resin system and filler listed in Table 1, thermal conductive layer, copper clad laminate and PCB board were prepared, and their performance was tested according to the above test methods. The results are shown in Table 2.

[0125] Table 1. Preparation process parameters for each embodiment and comparative example

[0126]

[0127] Table 2 Performance test results of thermally conductive layers / copper clad laminates prepared in each embodiment and comparative example

[0128]

[0129] The test results in Table 2 show that:

[0130] (1) Effect of modification treatment on interfacial bonding

[0131] Comparing Examples 6 to 9, it can be seen that different modification treatments were applied to ordinary circular PBO fibers. Among these, irradiation treatment (Example 7) increased the peel strength of the copper-clad laminate from 0.63 N / mm (Example 6) to 1.09 N / mm, an increase of 73%, significantly better than the 40% increase achieved by corona treatment (Example 9). Furthermore, after irradiation treatment followed by silane coupling agent treatment (Example 8), the peel strength (1.06 N / mm) showed no significant difference compared to irradiation treatment alone, indicating that irradiation treatment itself effectively improved the interfacial bonding between the fiber and the resin.

[0132] (2) Effect of PBO fiber on thermal conductivity

[0133] Comparing the various embodiments with the comparative examples, it can be seen that the copper-clad laminates prepared using ordinary circular PBO fibers or five-lobed irregular PBO fibers have significantly improved in-plane thermal conductivity compared with the comparative examples without added PBO fibers. This indicates that the introduction of PBO fibers in the present invention can effectively enhance the thermal conductivity of the composite material.

[0134] Comparing Examples 1 and 7, it can be seen that, under the same epoxy resin system and irradiation treatment conditions, the copper-clad laminate prepared using five-lobed irregular PBO fibers (Example 1) has an in-plane thermal conductivity of 11.6 W / (m·K), which is about 23.4% higher than that of ordinary round PBO fibers (Example 7) of 9.4 W / (m·K). This indicates that the irregular structure helps to build a more efficient thermal conductivity network inside the composite material.

[0135] (3) The effect of filler on thermal conductivity

[0136] Comparing Example 1 and Example 2, it can be seen that adding BN ceramic filler (Example 2) to the five-lobed PBO fiber can further increase the thermal conductivity to 14.5 W / (m·K), which reflects the synergistic effect of fiber and thermally conductive filler.

[0137] (4) The effect of different resin systems on dielectric properties

[0138] Comparison of the various embodiments and comparative examples shows that after adopting the hydrocarbon resin system, the dielectric loss Df of the copper clad laminate is significantly reduced from 0.011-0.016 to below 0.001, and the dielectric constant Dk is also reduced, making it more suitable for high-frequency applications.

[0139] (5) Regulation of thermal expansion coefficient by PBO fiber

[0140] Comparison of the various embodiments and comparative examples shows that the coefficient of thermal expansion (CTE) of the copper clad laminate significantly decreased after the introduction of PBO fibers. Using pure PBO fibers (Examples 2, 3, and 10), composite materials with negative CTEs (-3.5 to -4.5 ppm / °C) can even be obtained, which is extremely advantageous for thermal matching with chip packaging materials. The CTE of the hybrid woven fabrics (Examples 4 and 5) falls between that of pure PBO and pure glass fiber, providing the possibility for on-demand performance control.

[0141] In summary, this invention, by employing circular or five-lobed PBO fibers with specific index systems, combined with appropriate modification treatments and resin systems, can produce copper-clad laminates that possess high thermal conductivity, low expansion, high rigidity, and low dielectric loss. Example 2 demonstrates outstanding performance in achieving high thermal conductivity, with a thermal conductivity coefficient of 14.5 W / (m·K); while Example 3, while maintaining high thermal conductivity (11.4 W / (m·K)), achieves extremely low dielectric loss (Df < 0.001 @ 10 GHz) and an ultra-low negative coefficient of thermal expansion (-3.7 ppm / ℃), representing a superior overall performance implementation. Furthermore, the PCB board made from the copper-clad laminate described in this invention can precisely meet the stringent requirements of computing centers for high-performance motherboards, accelerator cards, and other core components. This board can rapidly diffuse the heat generated by localized hot spots from chips along the board surface, thereby effectively reducing hot spot temperatures. Its coefficient of thermal expansion is highly compatible with the chip packaging material, which significantly improves the interconnect reliability under high-density packaging conditions, while effectively ensuring the integrity and low attenuation of high-frequency signals during transmission.

[0142] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a thermally conductive layer based on PBO fibers, characterized in that: The PBO fiber is prepared by using PBO fiber as the base material and sequentially undergoing spinning, modification, impregnation, and drying. The PBO fiber must at least meet the following conditions: (I) Ordinary PBO fibers or irregularly shaped PBO fibers, wherein the ordinary PBO fibers have a circular cross-section, and the irregularly shaped PBO fibers have a multi-leaf cross-section with 3 to 10 leaves, and the irregularity is >22%. The degree of irregularity is calculated according to the following formula: PBO fiber irregularity = ; (II) Thermal conductivity: 20–50 W / (m·K); (III) Coefficient of thermal expansion: -20~0ppm / ℃; (IV) Tensile modulus: 160 GPa~280 GPa.

2. The preparation method according to claim 1, characterized in that: The diameter of the PBO fiber is 6–18 μm.

3. The preparation method according to claim 1, characterized in that: The PBO fiber is produced by extruding a polymer solution through a spinneret with circular or irregular holes, followed by stretching, shaping, washing, drying, and heat treatment.

4. The preparation method according to claim 3, characterized in that: The PBO fibers are woven into a fabric, which may be unidirectional, plain weave, or a combination thereof.

5. The preparation method according to claim 3, characterized in that: The PBO fibers are woven into pure PBO fabric or into a blended fabric made with one or more of glass fiber, quartz, polyimide, and aramid.

6. The preparation method according to claim 1, characterized in that: The fabric spun from the PBO fibers is modified to obtain a modified fabric, wherein the modification treatment is selected from at least one of plasma treatment, irradiation treatment, and silane coupling agent treatment.

7. The preparation method according to claim 1, characterized in that: The modified fabric obtained by the modification is impregnated in an impregnation solution containing resin to obtain a fiber prepreg. The resin content in the impregnation solution is 35-70%, and the resin is selected from one of epoxy resin, hydrocarbon resin, cyanate ester, PPO resin, polyimide, phenolic resin and PTFE.

8. The preparation method according to claim 1, characterized in that: The impregnated fiber resin prepreg is dried at 100-200℃ for 2-10 minutes to obtain a thermally conductive layer for copper clad laminate.

9. A thermally conductive layer based on PBO fibers, characterized in that: The thermally conductive layer obtained by the preparation method according to any one of claims 1 to 8 satisfies the following properties: In-plane thermal conductivity: 6–20 W / (m·K); Coefficient of thermal expansion: -15~10ppm / ℃; Flexural modulus: 10–40 GPa; Tensile modulus: 160~280GPa.

10. A copper-clad laminate based on PBO fiber, characterized in that: It includes a first copper foil layer, a heat-conducting layer as described in claim 9, and a second copper foil layer stacked sequentially from top to bottom, wherein the thickness of the first copper foil layer is 18 to 105 μm; The thickness of the thermally conductive layer is 50–4000 μm; The thickness of the second copper foil layer is 18–105 μm.

11. The copper-clad laminate according to claim 10, characterized in that: The copper-clad laminate meets the following specifications: Peel strength: ≥0.8 N / mm; Solder heat resistance: 288℃, immersion in tin for 10 seconds, 6 cycles, meets the requirement of no blistering or delamination abnormalities.

12. The method for preparing copper-clad laminate as described in claim 10, characterized in that: The first copper foil layer, the thermally conductive layer, and the second copper foil layer are stacked sequentially from top to bottom. Then, a surface protective layer precursor is covered on the surface of the first copper foil layer. The material is then placed in a hot press and hot-pressed to obtain a copper-clad laminate.

13. The application of the copper-clad laminate as described in claim 10 in the fabrication of a high thermal conductivity computing center PCB board, characterized in that: The copper-clad laminate is used to prepare a high thermal conductivity computing power PCB board.

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