Multilayer circuit structure and its fabrication method

Abstract

This invention proposes a multilayer circuit structure and its fabrication method. The multilayer circuit structure includes a substrate and integrated circuits disposed on both sides of the substrate. Each integrated circuit includes a flexible insulating layer and two flexible conductive layers disposed on both sides of the flexible insulating layer. Each flexible conductive layer has a rough surface and a smooth surface, with each rough surface in contact with the flexible insulating layer. One side of the flexible conductive layer has a rough surface that contacts the flexible insulating layer, significantly increasing the contact area and improving the adhesion between the flexible conductive layer and the flexible insulating layer. This design helps reduce the risk of delamination and peeling, enhances the mechanical stability of the circuit structure, and maintains stable performance, especially when subjected to thermal cycling and mechanical stress during manufacturing. The multilayer circuit structure uses a material with a certain degree of flexibility, enabling it to withstand stress from mechanical operations during manufacturing. The combination of these two factors improves the manufacturing yield of the multilayer circuit structure.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor packaging technology, and particularly relates to a multilayer circuit structure and its fabrication method. Background Technology

[0002] Polypropylene (PP) is a resin-impregnated glass fiber material commonly used as an interlayer insulation material in multilayer PCB manufacturing, widely applied to the construction of both rigid and flexible circuit boards. PP is composed of glass fiber and epoxy resin, cured during hot pressing to form a robust, flexible insulating layer. PP is widely used in the lamination process of rigid PCBs to bond multiple circuits together, providing good mechanical strength and stable electrical performance.

[0003] ABF is an epoxy resin-based insulating film material, originally developed by Ajinomoto Co., Ltd. of Japan. It is mainly used in the manufacture of multilayer printed circuit boards (PCBs) and build-up layers in semiconductor packaging. In packaging technologies such as FCBGA, ABF is used for chip build-up layer insulation, providing high-performance insulation and electrical connection between the chip and the substrate.

[0004] Both PP and ABF are commonly used semiconductor packaging technologies, but they have the following problems. On the one hand, PP has relatively poor flexibility, making it unsuitable for very complex or frequently bending applications. Therefore, lamination technology is the only option for PCB manufacturing. Lamination requires simultaneously bonding multiple substrates and circuit layers, a complex process that makes it difficult to guarantee product quality and results in low yield. On the other hand, although ABF material has higher flexibility and can slightly improve yield during lamination, ABF material and processing technology are relatively expensive, leading to higher manufacturing costs for PCBs using ABF. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multilayer circuit structure and its preparation method, aiming to solve the problem of how to improve the yield of circuit structure manufacturing under the condition of low manufacturing cost.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows: a multilayer circuit structure applied in the field of semiconductor packaging, the multilayer circuit structure includes a substrate and integrated circuits disposed on both sides of the substrate, each integrated circuit includes a flexible insulating layer and two flexible conductive layers disposed on both sides of the flexible insulating layer, each flexible conductive layer has a rough surface and a smooth surface, and each rough surface is in contact with the flexible insulating layer.

[0007] In some embodiments of the present invention, the flexible conductive layer of the integrated circuit that is in contact with the substrate is a first circuit layer, and the flexible conductive layer of the integrated circuit that is away from the substrate is a second circuit layer, the second circuit layer including an electroplated layer disposed on the side away from the flexible insulating layer.

[0008] In some embodiments of the present invention, the substrate is provided with a first through hole, a first hole electrode is provided in the first through hole, the first circuit layer is electrically connected to the first hole electrode, and the substrate and the integrated circuit are coaxially provided with a second through hole that is not connected to the first through hole, a second hole electrode is provided in the second through hole, and the second hole electrode is electrically connected to the second circuit layer.

[0009] In some embodiments of the present invention, the substrate comprises at least one of glass, silicon, bismaleimide-triazine resin, polyimide, aluminum oxide, aluminum nitride, and silicon nitride.

[0010] This invention proposes a fabrication method for preparing the multilayer circuit structure described above, the fabrication method comprising the following steps:

[0011] S1, Modified insulating coating;

[0012] S2. The insulating coating is applied to a flexible conductive layer, cured to form a flexible insulating layer, and then wound up to form a spiral circuit.

[0013] S3. Electroplating is performed on the substrate to form the first circuit layer, thus obtaining the add-on board;

[0014] S4. Vacuum bonding is performed on the spiral wound circuit and the add-on board so that the first circuit layer is connected to the flexible insulating layer to obtain a multilayer circuit structure.

[0015] In some embodiments of the present invention, in step S1, the insulating coating comprises, by weight, 50-60 parts resin material, 20-25 parts curing agent, 10-15 parts filler, 0.5-1 part leveling agent, 0.1-0.5 parts defoamer, 0.1-0.3 parts wetting agent, and the balance being solvent.

[0016] The resin material includes at least one of epoxy resin, polyimide resin, cyanate ester resin, and polyphenylene ether resin.

[0017] The filler includes at least one of ceramic powder, silicon dioxide, and glass fiber.

[0018] In some embodiments of the present invention, step S1 includes:

[0019] S1.1 Place all components of the insulating coating in a mixing device and mix thoroughly;

[0020] S1.2. Vacuum degassing treatment is performed on the uniformly mixed insulating coating.

[0021] In some embodiments of the present invention, step S2 includes:

[0022] S2.1 The insulating coating is applied to the flexible conductive layer using a roller coating process;

[0023] S2.2 Place the coated flexible conductive layer into an oven or curing furnace for heating and curing. The heating temperature is 150~200℃ and the heating time is 30~60min.

[0024] S2.3 Place the flexible conductive layer with the solidified flexible insulating layer in the winding device, attach the release film on the flexible insulating layer, and wind it into a spiral circuit.

[0025] In some embodiments of the present invention, step S3 includes:

[0026] S3.1 After cleaning the substrate, place it in a reducing solution to carry out the activation reaction;

[0027] S3.2 Place the activated substrate in an electroplating solution to form a flexible conductive layer;

[0028] S3.3. The flexible conductive layer on the substrate is patterned to form the first circuit layer, thus obtaining the add-on board.

[0029] In some embodiments of the present invention, step S4 includes:

[0030] S4.1 Place the spiral wound circuit and the add-on board in a vacuum laminator for alignment and fixation, so that the flexible insulating layer of the spiral wound circuit faces the first circuit layer of the add-on board.

[0031] S4.2 Extract the air from inside the vacuum laminator until the air pressure reaches 0.01~0.05MPa;

[0032] S4.3 Maintain air pressure and increase bonding pressure, wherein the bonding pressure ranges from 0.5 to 1 MPa;

[0033] S4.4 Raise the temperature to the preset temperature and maintain it. After cooling, release the pressure and remove the device. The preset temperature is 80~150℃ and the holding time is 30~60min.

[0034] Compared with existing technologies, the multilayer circuit structure and its fabrication method in this invention have the following advantages:

[0035] One side of the flexible conductive layer has a rough surface that contacts the flexible insulating layer, significantly increasing the contact area and improving the adhesion between them. This design helps reduce the risk of delamination and peeling, enhancing the mechanical stability of the circuit structure, especially maintaining stable performance under thermal cycling and mechanical stress during manufacturing. Multilayer circuit structures using materials with a degree of flexibility (such as flexible insulating and conductive layers) can withstand stress from mechanical operations during manufacturing; the combination of these two aspects improves the manufacturing yield of multilayer circuit structures. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart of a method for fabricating a multilayer circuit structure according to an embodiment of the present invention;

[0037] Figure 2 This is a cross-sectional schematic diagram of a multilayer circuit structure in one embodiment of the present invention;

[0038] Figure 3 This is a cross-sectional schematic diagram of a multilayer circuit structure in another embodiment of the present invention;

[0039] Figure 4 This is a cross-sectional schematic diagram of a multilayer circuit structure in another embodiment of the present invention.

[0040] In the accompanying drawings, the reference numerals indicate:

[0041] 100. Multilayer circuit structure; 10. Substrate; 20. Integrated circuit; 21. First circuit layer; 22. Second circuit layer; 23. Flexible insulating layer; 24. Electroplated layer; 31. First hole electrode; 32. Second hole electrode; 41. First through hole; 42. Second through hole. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] This invention proposes a multilayer circuit structure 100 for application in the semiconductor packaging field. The multilayer circuit structure 100 includes a substrate 10 and integrated circuits 20 disposed on both sides of the substrate 10. Each integrated circuit 20 includes a flexible insulating layer 23 and two flexible conductive layers disposed on both sides of the flexible insulating layer 23. Each flexible conductive layer has a rough surface and a smooth surface, and each rough surface is in contact with the flexible insulating layer 23.

[0044] One side of the flexible conductive layer has a rough surface that contacts the flexible insulating layer 23, significantly increasing the contact area and improving the adhesion between the flexible conductive layer and the flexible insulating layer 23. This design helps reduce the risk of delamination and peeling, enhancing the mechanical stability of the circuit structure, especially maintaining stable performance under thermal cycling and mechanical stress during manufacturing. The multilayer circuit structure 100 uses materials with a certain degree of flexibility (such as the flexible insulating layer 23 and the flexible conductive layer), which can withstand stress from mechanical operations during manufacturing. The combination of these two aspects improves the manufacturing yield of the multilayer circuit structure 100.

[0045] The other side of the flexible conductive layer has a smooth surface. The smooth surface helps to reduce the resistance when current passes through, thereby reducing the overall resistance of the circuit and improving the conductivity.

[0046] The multilayer circuit structure 100, through the precise combination of flexible conductive layers and flexible insulating layers 23, optimizes the heat conduction path and enhances the heat dissipation effect inside the circuit. The roughened surface increases the contact interface between the flexible conductive layers and flexible insulating layers 23, promoting heat conduction, while the smooth surface helps to efficiently conduct heat to external heat dissipation areas. Due to the different surface treatments of the flexible conductive layers, the smooth surface can reduce signal interference and loss, improve signal integrity and transmission quality, and reduce the impact of electromagnetic interference (EMI) on the circuit.

[0047] Multilayer circuit structures 100 can provide higher integration within a limited package space. Multilayer designs enable high-density layouts of complex circuits, providing chips with more functionality and finer electrical connections, thus contributing to the development of miniaturized package designs.

[0048] In other embodiments, the multilayer circuit structure 100 can also be applied to the field of printed circuit boards (PCBs), which involves the design, manufacture, and application of circuit boards for electronic devices. PCBs mechanically and electrically connect electronic components through conductive paths, pads, and other features. PCBs are central to modern electronic devices and are used in a wide range of applications, from consumer electronics (such as mobile phones, computers, and televisions) to industrial equipment, medical devices, automotive electronics, and aerospace.

[0049] In multilayer circuit structures, the PCB industry typically stacks multiple layers of conductive and insulating materials to achieve higher electrical performance, density, and reliability. Multilayer circuit boards allow for complex circuit layouts within limited space, facilitate miniaturization, and better reduce signal interference, thereby improving the performance and stability of electronic products. Research and development of these multilayer structures focuses primarily on signal integrity, thermal management, and material compatibility, with wide applications, especially in high-frequency and high-power environments.

[0050] Specifically, the flexible conductive layer of the integrated circuit 20 that is in contact with the substrate 10 is the first circuit layer 21, and the flexible conductive layer of the integrated circuit 20 that is away from the substrate 10 is the second circuit layer 22. The second circuit layer 22 includes an electroplated layer 24 disposed on the side away from the flexible insulating layer 23.

[0051] The first circuit layer 21 is directly connected to the substrate 10, providing a stable electrical connection and mechanical support. Because it is directly connected to the substrate 10, the conductivity and contact performance of this layer are crucial to the overall circuit performance. By optimizing the design of the first circuit layer 21, a low-resistance connection with the substrate 10 can be ensured, thereby improving signal transmission efficiency. The second circuit layer 22 is located away from the substrate 10 and is typically used for external electrical connections or signal transmission. By adding an electroplated layer 24 to the side of the second circuit layer 22 away from the flexible insulating layer 23, the conductivity of this layer is further enhanced, allowing current to flow more smoothly within the layer and reducing resistance loss.

[0052] The second circuit layer 22 includes an electroplated layer 24, which is typically made of a highly conductive material such as gold, silver, or nickel. This design helps improve the surface conductivity of the second circuit layer 22, enhancing the reliability of electrical contacts, especially in connections to external components such as solder joints or electrical connectors. This not only improves conductivity but also enhances oxidation and corrosion resistance, thereby extending the circuit's lifespan.

[0053] During the packaging and soldering process, the electroplated layer 24 can significantly improve soldering performance. In particular, when using gold or nickel plating, it can reduce oxidation reactions during soldering, ensuring the reliability and consistency of the solder joints. This helps improve the efficiency and quality of the packaging process and reduces failures caused by poor soldering.

[0054] The substrate 10 has a first through hole 41 through it, and a first hole electrode 31 is provided in the first through hole 41. The first circuit layer 21 is electrically connected to the first hole electrode 31. The substrate 10 and the integrated circuit 20 have a second through hole 42 through it coaxially, which is not connected to the first through hole 41. The second through hole 42 has a second hole electrode 32 in it, and the second hole electrode 32 is electrically connected to the second circuit layer 22.

[0055] The design of the first via 41 and the first via electrode 31 allows the first circuit layer 21 to be electrically connected to other circuit layers via a vertical conductive path. This design effectively connects different layers of circuits on the substrate 10 and the integrated circuit 20 through via electrodes, allowing for more complex electrical path designs and meeting the requirements of high integration and high-density wiring. Similarly, the placement of the second via 42 and the second via electrode 32 enables the second circuit layer 22 to be independently electrically connected to other layers of the substrate 10. Since the second via 42 is not connected to the first via 41, signal and power transmission between different circuit layers is more independent, avoiding interference between circuits.

[0056] Different circuit layers are connected through the first via 41 and the second via 42, forming independent signal transmission channels. This reduces path detours in signal transmission, shortens the transmission path, and reduces signal delay and loss, especially in high-speed signal transmission and high-frequency applications, thereby improving signal integrity.

[0057] The first via 41 and the second via 42 each have independent via electrodes. This structure helps to effectively isolate signals from different circuit layers, avoiding electrical interference and crosstalk. This is crucial for high-frequency signal processing, helping to improve signal transmission quality, reduce electromagnetic interference (EMI) problems, and ensure system stability and reliability.

[0058] Specifically, the substrate 10 includes at least one of glass, silicon, bismaleimide-triazine resin, aluminum oxide, aluminum nitride, and silicon nitride.

[0059] In the field of semiconductor packaging, traditional packaging and advanced packaging represent different stages of technological development and application needs.

[0060] Conventional packaging typically includes several basic packaging methods, such as: Lead Frame Packages: This type of package connects the chip to the printed circuit board via a lead frame. It was widely used in early integrated circuits, with common examples being Dual In-line Packages (DIPs) and Small Outline Packages (SOPs). Ball Grid Array (BGA): BGA packaging is another traditional packaging type that connects the chip to the PCB via solder balls, offering higher density and better heat dissipation. Chip Scale Package (CSP): CSP packaging is a miniaturized packaging method that approximates chip size, commonly used in mobile devices to save space. Conventional packaging is generally used in applications where small size requirements are not high and heat dissipation requirements are moderate; it has a relatively simple structure and lower cost.

[0061] Advanced packaging refers to emerging and more complex packaging technologies that can meet the needs of high-performance computing and miniaturized devices, including: glass substrate packaging technology, flip-chip ball grid array packaging, fan-out panel-level packaging, etc.

[0062] Glass substrate 10 packaging technology uses glass as the substrate material for chip packaging. Glass has a low coefficient of thermal expansion, high flatness, and good electrical and mechanical properties, making it suitable for higher precision and higher density chip packaging. Glass substrate 10 can provide higher signal transmission rates and stability than traditional organic substrates 10, and is therefore widely used in high-frequency and high-performance computing chips. Glass has good thermal conductivity and is transparent, making it suitable for some optical and MEMS (microelectromechanical systems) applications.

[0063] Flip-chip ball grid array (FCBGA) directly bonds the chip to the substrate 10 via a flip-chip method. Key features include: Flip-chip design: The chip's contact points face the substrate 10, reducing signal path length, thereby lowering inductance and resistance, and improving electrical performance and data transmission speed; Thermal performance: The flip-chip structure facilitates thermal management, making this packaging method ideal for high-power, high-density applications; Application scenarios: FCBGA is commonly used in high-performance processors, graphics processing units (GPUs), network processors, and data center chips.

[0064] Fan-out panel-level packaging (FOPLP) is an advanced form of fan-out packaging, using a larger panel (instead of a circular wafer) as the packaging carrier. Compared to traditional fan-out wafer-level packaging (FOWLP), FOPLP uses a rectangular panel as the substrate 10, increasing the packaging area, reducing material waste, and lowering packaging costs. By directly packaging multiple chips on the panel-level substrate 10, high-density integration can be achieved, making it suitable for system-in-package (SoC). FOPLP effectively reduces thermal resistance and electrical resistance, and the fan-out design enables lower interconnect resistance and higher performance, making it suitable for high-performance, low-power mobile devices such as RF devices and mobile processors.

[0065] Glass has a very high surface flatness, which helps improve alignment accuracy during packaging and reduces the risk of chip misalignment. The coefficient of thermal expansion of glass is close to that of silicon, which helps reduce thermal stress generated during thermal cycling, thereby reducing the likelihood of package failure. Glass also has extremely high electrical insulation properties, making it suitable for maintaining signal integrity in high-frequency applications.

[0066] In the glass substrate 10 packaging technology, glass is directly used to package the substrate 10, thereby creating a multilayer circuit structure 100 with excellent dimensional stability, low electrical loss and excellent mechanical stability, suitable for high-frequency and high-speed devices.

[0067] Silicon possesses excellent thermal conductivity, effectively transferring heat and making it suitable for high-power applications. It also exhibits good mechanical strength, providing sufficient support and protection during packaging. Furthermore, silicon is highly compatible with semiconductor manufacturing processes, making it suitable for complex semiconductor packaging.

[0068] In FCBGA (Flip Chip Ball Grid Array Package), silicon as the substrate material 10 can improve the thermal management performance of the package, and the resulting multilayer circuit structure 100 is particularly suitable for high-power chips, such as power devices and server chips.

[0069] Silicon is typically used as an intermediate layer between the chip and the package in FOPLP (Fan-Out Panel-Level Packaging), providing mechanical support and helping the chip dissipate heat through its thermal conductivity.

[0070] Bismaleimide-triazine resin (BT resin) exhibits excellent thermal stability, withstands high-temperature soldering processes, and is suitable for packaging applications under high-temperature conditions. In high-frequency circuits, BT resin demonstrates good electrical properties, reducing signal loss and interference. Simultaneously, BT resin possesses good mechanical strength, providing long-term stable structural support for the package.

[0071] In FCBGA, BT resin has good heat resistance and electrical properties, and the multilayer circuit structure 100 made from it can support high-density packaging applications such as high-performance computing chips and server chips.

[0072] Alumina has excellent thermal conductivity, making it suitable for heat dissipation in high-heat environments. It also has good electrical insulation properties, making it suitable for providing electrical isolation in high-voltage and high-frequency applications.

[0073] Aluminum nitride is also suitable for packages with extremely high heat dissipation requirements. Furthermore, aluminum nitride has a low dielectric constant, making it suitable for signal transmission in high-frequency applications.

[0074] Silicon nitride has very high mechanical strength, providing strong mechanical protection for packaged chips. At the same time, silicon nitride has good thermal conductivity and insulation properties, making it suitable for packaging high-performance chips.

[0075] In FCBGA, aluminum oxide, aluminum nitride, and silicon nitride can all be used as substrate materials in high-power applications. The resulting multilayer circuit structure 100 has the function of rapid heat dissipation and maintains the operating stability of the chip.

[0076] In FOPLP, the multilayer circuit structure 100 made of alumina, aluminum nitride, and silicon nitride can be used for the heat dissipation part of high-power packaged chips, providing excellent thermal conductivity.

[0077] Example 1:

[0078] Embodiment 1 of the present invention proposes a fabrication method for fabricating a multilayer circuit structure 100. The fabrication method includes the following steps:

[0079] S1, Prepare insulating coating.

[0080] In step S1, the insulating coating comprises, by weight, 50 parts epoxy resin, 20 parts amine curing agent (e.g., aliphatic amine, aromatic amine), 10 parts ceramic powder, 0.5 parts polysiloxane leveling agent (e.g., organosilicon leveling agent), 0.1 parts organosilicon defoamer, 0.1 parts organosilicon wetting agent, and the balance solvent is toluene.

[0081] The curing agent reacts chemically with the resin material to form a cross-linked network, thereby providing high mechanical strength and thermal stability. Choosing a suitable curing agent ensures that the coating has good structural stability and heat resistance after curing.

[0082] Leveling agents help coatings spread evenly on the substrate surface, reduce surface defects, ensure a smooth and uniform coating surface, and help improve the appearance quality and functionality of insulating coatings.

[0083] The function of defoamers is to prevent air bubbles mixed in with the coating from remaining in the coating during the curing process. Air bubbles can affect the insulation properties and surface smoothness of the coating. Defoamers reduce surface tension, causing the air bubbles to burst and ensuring a dense and defect-free coating film.

[0084] Wetting agents can improve the wettability of coatings on substrates, ensuring that the coating can be evenly covered on the substrate surface, and improve the compatibility between coatings and fillers, preventing filler settling or aggregation, thereby ensuring the uniformity and insulation effect of the coating.

[0085] S1.1 Place each component of the insulating coating in a mixing device and mix them evenly.

[0086] Uniform mixing of the components of the insulating coating (such as epoxy resin, curing agent, filler, leveling agent, defoamer, wetting agent, and solvent) ensures that each component is evenly distributed throughout the coating system. Uniform mixing ensures the consistency of the resin and filler in the coating, thereby improving the coating's performance, including mechanical strength, insulation properties, and heat resistance. The mixing equipment used is a conventional technique known to those skilled in the art, and the preparation steps in this application are unrelated to the specific selection of the mixing equipment.

[0087] S1.2. Vacuum degassing treatment is performed on the uniformly mixed insulating coating.

[0088] During the mixing process, air may be introduced into the coating, forming bubbles. If these bubbles remain in the coating during subsequent coating and curing processes, it can lead to a decrease in the coating's mechanical strength and insulation properties. Vacuum degassing treatment, by placing the coating in a low-pressure environment, forces the bubbles to escape from the coating, eliminating residual air. This ensures a denser coating after curing, avoids defects caused by bubbles, and improves the coating's structural stability and insulation performance.

[0089] During vacuum degassing, tiny air bubbles in the coating are effectively removed. This not only prevents the formation of voids in the coating but also avoids defects such as "shrinkage cavities" and "bubbles" on the coating surface, thereby improving the surface smoothness and gloss of the coating and enhancing its appearance. By eliminating air bubbles, the uniformity of the coating surface is enhanced, which helps improve its application performance in high-precision electronic equipment and reduces the risk of potential electrical failures. The vacuum degassing equipment used for this process is a conventional technique known to those skilled in the art, and the preparation steps described in this application are unrelated to the specific equipment used.

[0090] S2. Apply insulating coating to a flexible conductive layer, cure to form a flexible insulating layer 23, and then roll it up to obtain a spiral circuit.

[0091] Step S2 includes:

[0092] S2.1 Apply the insulating coating onto the flexible conductive layer using a roller coating process.

[0093] Roll coating is a highly efficient and stable coating method that ensures the insulating coating is uniformly applied to the surface of the flexible conductive layer. Compared to other manual coating methods, roll coating guarantees consistent coating thickness, avoiding localized areas of excessive thickness or thinness. Roll coating is suitable for mass production, allowing for large-area coating operations to be completed in a shorter time, thus improving production efficiency. Due to the precise control of the roll coating process, the thickness and uniformity of the coating are optimized, reducing defects such as bubbles and uneven coating that may occur during subsequent curing, thereby improving the overall quality of the spiral wound circuit.

[0094] The roller coating equipment used in the roller coating process is a conventional technique known to those skilled in the art, and the preparation steps in this application are unrelated to the specific selection of equipment.

[0095] S2.2 Place the coated flexible conductive layer into an oven or curing furnace for heating and curing. The heating temperature is 180℃ and the heating time is 30 minutes.

[0096] By heating and curing at appropriate temperature and time, the resin material in the insulating coating undergoes complete cross-linking, forming a dense network structure, thereby significantly improving the mechanical strength and electrical insulation performance of the coating. Curing at suitable temperature and time allows the coating to bond tightly with the flexible conductive layer, enhancing the adhesion between the flexible insulating layer 23 and the flexible conductive layer, and avoiding the risk of coating peeling or detachment.

[0097] Temperature and time control are crucial. Excessive temperature or heating time can lead to over-curing or material decomposition, while insufficient temperature or time will result in incomplete curing. This application precisely controls the curing temperature within the range of 150~200℃, ensuring uniform curing and preventing heat damage.

[0098] S2.3 Place the flexible conductive layer with the solidified flexible insulating layer 23 in the winding device, attach the release film to the flexible insulating layer 23, and wind it into a spiral circuit.

[0099] Laminating a release film onto the flexible insulating layer 23 effectively protects the surface of the flexible insulating layer 23 from scratches, contamination, or dust, ensuring the surface quality of the roll-to-roll circuit during subsequent processing or storage. Rolling the cured circuit board into a roll structure effectively saves space and facilitates storage and transportation. The roll-to-roll structure also reduces physical damage, avoiding mechanical damage caused by bending or impact, as is common in flat structures.

[0100] Roll-up circuits are ideally suited for continuous production. Compared to the bonding method of traditional chip circuits, roll-up circuits can be continuously bonded using automated equipment. Combined with vacuum bonding technology, this significantly improves production efficiency, especially in mass production. Roll-up circuits reduce repetitive steps when laminating multiple circuit boards, simplifying the production process, reducing the workload for operators, thereby accelerating the production cycle and saving time and costs.

[0101] With the increasing demand for miniaturization and high performance in electronic devices, roll-to-roll circuitry combined with vacuum bonding technology can be adapted to the manufacture of high-density multilayer circuit boards. This process ensures uniform bonding of each layer and prevents performance degradation due to complex designs.

[0102] S3. Electroplating is performed on the substrate 10 to form the first circuit layer 21, thus obtaining the enhancement board.

[0103] Step S3 includes:

[0104] S3.1 After cleaning the substrate 10, place it in a reducing solution to carry out the activation reaction.

[0105] The cleaning step effectively removes impurities, oil, and oxide layers from the surface of substrate 10, providing a clean and activated surface for subsequent electroplating processes. The activation reaction in the reducing solution deposits an extremely thin catalyst layer on the surface of substrate 10. This catalyst layer enhances the adhesion between substrate 10 and the subsequent electroplated layer 24, promoting the uniform growth of the flexible conductive layer. Activation of the substrate 10 surface helps improve the uniformity and rate of metal deposition during subsequent electroplating, ensuring that the flexible conductive layer can uniformly and stably cover the entire substrate 10, improving the electroplating effect and the reliability of the circuit layer.

[0106] The reducing solution can be a mixture of palladium salts (such as palladium chloride and palladium nitrate) and reducing agents (such as formaldehyde and hypophosphite). The palladium-based solution deposits a palladium catalytic layer on the surface of substrate 10 through the reduction reaction of palladium ions. Palladium has good catalytic activity and can promote the electroplating reaction, making it particularly suitable for non-conductive substrates (such as plastics and ceramics) or substrates that require the formation of an initial flexible conductive layer on the surface.

[0107] S3.2. Place the activated substrate 10 in an electroplating solution to form a flexible conductive layer. The flexible conductive layer can be a copper layer.

[0108] Through electroplating, metal ions are deposited from the electroplating solution onto the surface of the substrate 10, forming a continuous, dense, flexible conductive layer. Electroplating can construct stable conductive paths on the surface of the substrate 10, providing a foundation for subsequent circuit patterning. The flexible conductive layer formed by electroplating has excellent conductivity, which can significantly improve the current carrying capacity of the circuits on the substrate 10, making it suitable for circuit applications involving high current or high-speed signal transmission. The electroplated metal layer not only provides excellent conductivity but also has high mechanical strength and wear resistance, improving the reliability and lifespan of the entire circuit board.

[0109] S3.3. The flexible conductive layer on the substrate 10 is patterned to form the first circuit layer 21, thus obtaining the add-on board.

[0110] Patterning processes (such as photolithography and etching) can be used to fabricate flexible conductive layers into desired circuit patterns. This step divides the flexible conductive layer on the circuit board into specific channels and functional areas, providing precise electrical connections and functional layouts for circuit design. Patterning allows for precise control of circuit linewidth and spacing, enabling the realization of high-density, multi-layer circuits. This is particularly important in modern electronic devices, supporting more compact circuit designs and improving integration. Photolithography and etching processes are techniques known to those skilled in the art and are unrelated to the steps involved in fabricating the multi-layer circuit structure 100 in this application.

[0111] By precisely controlling the size and layout of circuit paths, graphical processing can effectively reduce resistance and parasitic effects in signal transmission, optimize high-speed signal transmission performance, and improve the signal integrity of circuits.

[0112] S4. Vacuum bonding is performed on the spiral-wound circuit and the add-on board so that the first circuit layer 21 is connected to the flexible insulating layer 23, thereby obtaining a multilayer circuit structure 100.

[0113] Specifically, step S4 includes:

[0114] S4.1 Place the spiral wound circuit and the add-on board in a vacuum laminator for alignment and fixation, so that the flexible insulating layer 23 of the spiral wound circuit faces the first circuit layer 21 of the add-on board.

[0115] By precisely aligning the roll-to-roll circuit and the add-on board within a vacuum laminator, the flexible insulating layer 23 of the roll-to-roll circuit is ensured to accurately adhere to the first circuit layer 21 of the add-on board. This precise alignment guarantees correct electrical connections between circuit layers, preventing circuit misalignment or signal path interruptions. Alignment and fixation in a vacuum environment reduces errors caused by external environmental interference during operation, improves the processing accuracy of the multilayer circuit structure 100, and ensures interlayer matching.

[0116] S4.2 Extract the air from inside the vacuum laminator until the air pressure reaches 0.01MPa.

[0117] By reducing the air pressure inside the vacuum laminator to 0.01 MPa, the air in the lamination area is essentially evacuated, preventing air from remaining between the roll-to-roll circuitry and the add-on board during the lamination process and avoiding the formation of air bubbles. The presence of air bubbles leads to poor electrical connections between circuit layers, reducing electrical performance.

[0118] In a vacuum environment, there is no air barrier during the bonding process, and the flexible insulating layer 23 of the spiral wound circuit can be tightly bonded to the first circuit layer 21 of the add-on board, enhancing the adhesion between layers and improving the overall strength and reliability of the multilayer circuit structure 100.

[0119] S4.3 Maintain air pressure and increase bonding pressure, wherein the bonding pressure ranges from 0.5 to 1 MPa.

[0120] Maintaining vacuum conditions and applying a pressure of 0.5~1 MPa ensures a tight bond between the spiral wound circuit and the uplayer board. Appropriate pressure uniformly presses the flexible insulating layer 23 and the circuit layer together, ensuring uniformity and strength of the bond. Appropriate bonding pressure prevents separation between the spiral wound circuit and the uplayer board, ensuring that the bonded multilayer circuit structure 100 maintains interlayer stability over a long period, preventing delamination problems caused by thermal expansion and contraction or mechanical stress.

[0121] S4.4 Raise the temperature to the preset temperature and maintain it. After cooling, release the pressure and remove the device. The preset temperature is 100℃ and the holding time is 30 minutes.

[0122] Increasing the temperature to 80°C effectively promotes the curing of adhesives (such as epoxy resin or other adhesives) used between spiral wound circuits and overlay boards. By maintaining the temperature at the appropriate time for 30 minutes, the adhesives can fully crosslink, forming a stable bond and ensuring a tight bond between the circuit layers.

[0123] Precise control of temperature and time prevents overheating or underheating. Appropriate heating allows the adhesive to achieve optimal curing, avoiding excessive flow or incomplete curing, thus ensuring a high-strength bond between layers.

[0124] Temperature control within the range of 80~100℃ can prevent thermal damage or deformation of the substrate material and circuit layers due to excessively high temperatures, maintaining the integrity and accuracy of the circuit board. Releasing pressure after cooling prevents stress accumulation between layers, ensuring the stability of the final multilayer circuit structure 100.

[0125] Example 2:

[0126] Embodiment 2 of the present invention proposes a fabrication method for fabricating a multilayer circuit structure 100. The fabrication method includes the following steps:

[0127] S1, Prepare insulating coating.

[0128] In step S1, the insulating coating comprises, by weight, 60 parts of cyanate ester resin, 25 parts of anhydride curing agent such as hexahydrophthalic anhydride, 10 parts of silica, 0.5 parts of fluorocarbon leveling agent, 0.1 parts of polyether defoamer, 0.1 parts of polyester wetting agent, and acetone as solvent.

[0129] Step S1 includes:

[0130] S1.1 Place each component of the insulating coating in a mixing device and mix them evenly.

[0131] S1.2. Vacuum degassing treatment is performed on the uniformly mixed insulating coating.

[0132] S2. Apply insulating coating to a flexible conductive layer, cure to form a flexible insulating layer 23, and then roll it up to obtain a spiral circuit.

[0133] Step S2 includes:

[0134] S2.1 Apply the insulating coating onto the flexible conductive layer using a roller coating process;

[0135] S2.2 Place the coated flexible conductive layer into an oven or curing furnace for heating and curing. The heating temperature is 150℃ and the heating time is 60min.

[0136] S2.3 Place the flexible conductive layer with the solidified flexible insulating layer 23 in the winding device, attach the release film to the flexible insulating layer 23, and wind it into a spiral circuit.

[0137] S3. Electroplating is performed on the substrate 10 to form the first circuit layer 21, thus obtaining the enhancement board.

[0138] Step S3 includes:

[0139] S3.1 After cleaning the substrate 10, place it in a reducing solution to carry out an activation reaction. The reducing solution includes a mixed solution of sodium hypophosphite or potassium hypophosphite and a catalyst (such as nickel salt or cobalt salt).

[0140] Hypophosphite is a common chemical reducing agent that reacts with metal ions in solution to deposit a catalytic metal layer (such as nickel or cobalt). This reducing solution is often used in electroless plating to reduce nickel or cobalt ions with hypophosphite, forming a uniform catalytic metal layer. Hypophosphite reducing solutions provide a good initial flexible conductive layer, making subsequent electroplated layers 24 more uniform and possessing better adhesion. These solutions are commonly used in processes requiring metallization on non-metallic substrates 10.

[0141] S3.2 Place the activated substrate 10 in an electroplating solution to form a flexible conductive layer.

[0142] S3.3. The flexible conductive layer on the substrate 10 is patterned to form the first circuit layer 21, thus obtaining the add-on board.

[0143] Step S4 includes:

[0144] S4.1 Place the spiral wound circuit and the add-on board in a vacuum laminator for alignment and fixation, so that the flexible insulating layer 23 of the spiral wound circuit faces the first circuit layer 21 of the add-on board.

[0145] Specifically, step S4.1 includes:

[0146] S4.1.1 A heat-responsive intermediate layer material is uniformly coated onto the surface of the flexible insulating layer 23 of the spiral wound circuit. The heat-responsive intermediate layer material can be applied to the surface of the flexible insulating layer 23 in the form of coating, spraying, or film.

[0147] Thermally responsive interlayer materials can include paraffin wax, polymethyl methacrylate (PMMA), etc. Paraffin wax melts between 46 and 68°C, and different molecular weights of paraffin wax vaporize at around 100 to 150°C. It can gradually melt and vaporize after being heated to a certain temperature, making it suitable for interlayers requiring thermal responsiveness. Polymethyl methacrylate (PMMA) begins to decompose and vaporize at around 150°C.

[0148] The smooth properties of thermally responsive interlayer materials effectively protect the surface of the circuit layer during lamination, preventing scratches or other mechanical damage when high pressure and heat treatment are applied. This is crucial for high-precision, multilayer circuits, as even minor surface damage can affect conductivity or lead to electrical failures.

[0149] Adding a thermally responsive interlayer material between the spiral wound circuit and the overlay board helps balance the pressure distribution between the two layers during lamination. The thermally responsive interlayer material has a smooth surface that compensates for any minor unevenness that may exist on the surface of the circuit layers, ensuring a uniform interlayer structure free of bubbles or voids after lamination. This is crucial for high-performance circuits, helping to ensure both electrical performance and mechanical strength.

[0150] Adding a thermally responsive interlayer material between circuit layers can prevent electrical short circuits that may occur during lamination. Especially when the flexible conductive layer and flexible insulating layer 23 are bonded, the thermally responsive interlayer material can act as an effective isolation barrier to prevent any accidental contact. Furthermore, it can prevent contamination between different materials, ensuring the purity and performance stability of the circuit layers.

[0151] The removability of the thermally responsive interlayer material is crucial. After lamination, this material should be easily removed from between the spiral wound circuit and the overlay board, leaving no residue or affecting the mechanical and electrical properties of the circuit layer.

[0152] S4.1.2 Place the spiral wound circuit with a thermally responsive intermediate layer on the add-on board and align it precisely to ensure that the flexible insulating layer 23 of the spiral wound circuit faces the first circuit layer 21 of the add-on board.

[0153] Alignment methods can include: optical alignment, which uses optical equipment (such as an alignment microscope or camera system) to precisely align the circuit patterns or alignment marks between the roll-to-roll circuit and the add-on board; mechanical alignment, which uses alignment holes or other mechanical fixing devices to ensure the relative position of the roll-to-roll circuit and the add-on board. Both are designed with corresponding alignment holes or slots, which are inserted for fixing; and laser alignment systems, which use a precise laser beam for alignment. The laser scans the reference points or edges of the roll-to-roll circuit and the add-on board to ensure accurate alignment of the flexible insulating layer 23 with the first circuit layer 21.

[0154] S4.2 Extract the air from inside the vacuum laminator until the air pressure reaches 0.05MPa;

[0155] S4.3 Maintain air pressure and increase bonding pressure, wherein the bonding pressure ranges from 0.8 MPa;

[0156] S4.4 Raise the temperature to the preset temperature and maintain it. After cooling, release the pressure and remove the device. The preset temperature is 150℃ and the holding time is 60min.

[0157] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a multilayer circuit structure, characterized in that, The multilayer circuit structure includes a substrate and integrated circuits disposed on both sides of the substrate. Each integrated circuit includes a flexible insulating layer and two flexible conductive layers disposed on both sides of the flexible insulating layer. Each flexible conductive layer has a rough surface and a smooth surface, and each rough surface is in contact with the flexible insulating layer. The steps include: S1, Modified insulating coating; S2. The insulating coating is applied to a flexible conductive layer, cured to form a flexible insulating layer, and then wound up to form a spiral circuit. S3. Electroplating is performed on the substrate to form the first circuit layer, thus obtaining the add-on board; S4. Vacuum bonding is performed on the spiral-wound circuit and the add-on board so that the first circuit layer is connected to the flexible insulating layer to obtain a multilayer circuit structure. Step S4 includes: S4.1 Place the spiral wound circuit and the add-on board in a vacuum laminator for alignment and fixation, so that the flexible insulating layer of the spiral wound circuit faces the first circuit layer of the add-on board. Step S4.1 includes: S4.1.1 A heat-responsive intermediate layer material is uniformly coated on the surface of the flexible insulating layer of the spiral circuit. The heat-responsive intermediate layer material is placed on the surface of the flexible insulating layer in the form of coating, spraying, or film. The heat-responsive intermediate layer material includes at least one of paraffin wax and polymethyl methacrylate. S4.1.2 Place the spiral wound circuit with a thermally responsive intermediate layer on the add-on board and align it precisely to ensure that the flexible insulating layer of the spiral wound circuit faces the first circuit layer of the add-on board. S4.2 Extract the air from inside the vacuum laminator until the air pressure reaches 0.01~0.05MPa; S4.3 Maintain air pressure and increase bonding pressure, wherein the bonding pressure ranges from 0.5 to 1 MPa; S4.

4. Raise the temperature to the preset temperature and hold it. The thermally responsive intermediate layer vaporizes and is removed from between the spiral wound circuit and the add-on board. After cooling, release the pressure and remove it to obtain a multilayer circuit structure. The preset temperature is 80~150℃ and the holding time is 30~60min.

2. The method for fabricating a multilayer circuit structure according to claim 1, characterized in that, The flexible conductive layer of the integrated circuit that is in contact with the substrate is a first circuit layer, and the flexible conductive layer of the integrated circuit that is away from the substrate is a second circuit layer. The second circuit layer includes an electroplated layer disposed on the side away from the flexible insulating layer.

3. The method for fabricating a multilayer circuit structure according to claim 2, characterized in that, The substrate has a first through hole, and a first hole electrode is provided in the first through hole. The first circuit layer is electrically connected to the first hole electrode. The substrate and the integrated circuit have a second through hole that is not connected to the first through hole. The second through hole has a second hole electrode provided in the second through hole and is electrically connected to the second circuit layer.

4. The method for fabricating a multilayer circuit structure according to claim 1, characterized in that, The substrate comprises at least one of glass, silicon, bismaleimide-triazine resin, polyimide, aluminum oxide, aluminum nitride, and silicon nitride.

5. The method for fabricating a multilayer circuit structure according to any one of claims 1-4, wherein the steps of the fabrication method include: In step S1, the insulating coating comprises, by weight, 50-60 parts resin material, 20-25 parts curing agent, 10-15 parts filler, 0.5-1 part leveling agent, 0.1-0.5 parts defoamer, 0.1-0.3 parts wetting agent, and the balance being solvent. The resin material includes at least one of epoxy resin, polyimide resin, cyanate ester resin, and polyphenylene ether resin. The filler includes at least one of ceramic powder, silicon dioxide, and glass fiber.

6. The method for fabricating a multilayer circuit structure according to claim 1, characterized in that, Step S1 includes: S1.1 Place all components of the insulating coating in a mixing device and mix thoroughly; S1.

2. Vacuum degassing treatment is performed on the uniformly mixed insulating coating.

7. The method for fabricating a multilayer circuit structure according to claim 1, characterized in that, Step S2 includes: S2.1 The insulating coating is applied to the flexible conductive layer using a roller coating process; S2.2 Place the coated flexible conductive layer into an oven or curing furnace for heating and curing. The heating temperature is 150~200℃ and the heating time is 30~60min. S2.3 Place the flexible conductive layer with the solidified flexible insulating layer in the winding device, attach the release film on the flexible insulating layer, and wind it into a spiral circuit.

8. The method for fabricating a multilayer circuit structure according to claim 1, characterized in that, Step S3 includes: S3.1 After cleaning the substrate, place it in a reducing solution to carry out the activation reaction; S3.2 Place the activated substrate in an electroplating solution to form a flexible conductive layer; S3.

3. The flexible conductive layer on the substrate is patterned to form the first circuit layer, thus obtaining the add-on board.

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