A cavity board

Abstract

The utility model relates to a kind of cavity circuit boards.The cavity circuit board includes first copper foil, first solidified sheet, second copper foil, integrated circuit packaging film, first double-layer copper-clad plate, second solidified sheet, second double-layer copper-clad plate, third solidified sheet, third copper foil, fourth solidified sheet and fourth copper foil in turn laminated, wherein:the first double-layer copper-clad plate and the second double-layer copper-clad plate each include first copper layer, glass fiber resin composite layer and second copper layer in turn laminated;And the first double-layer copper-clad plate and the second solidified sheet are partially removed to form a cavity inside the cavity circuit board.According to the technical scheme of the utility model, the integrated circuit (IC) packaging film is used for the manufacture of cavity circuit board, which solves the problem of concave after pressing in the traditional manufacturing method, and avoids the use of gasket, which is inconvenient to take and difficult to mass-produce, improves the quality and production efficiency of the circuit board manufacturing, and enhances the stability and reliability of the product.

Description

Technical Field

[0001] This utility model relates to the field of circuit board technology, specifically to a cavity circuit board. Background Technology

[0002] In the field of printed circuit board technology, with the booming development of portable electronic communication products, the market has placed higher demands on special printed circuit boards and special components. In order to achieve better assembly efficiency and smaller footprint, in addition to meeting specific customer performance requirements, other parts of special printed circuit boards need to be designed to be thinner. Their motherboards are often made with stepped positions for "embedding" components, such as buried capacitors, buried resistors circuit boards, stepped boards, and cavity boards, etc., with the aim of reducing the size of the assembled product and improving portability.

[0003] Cavity boards are constructed within the circuit board structure using either sealed or vented cavities. Currently, the mainstream method for creating cavities in the industry involves first partially hollowing out an FR4 substrate and its upper and lower surfaces with low-flow prepreg, then adding one or more pre-fabricated core boards at the top and bottom, and finally pressing them together using a steel plate and press (see patent publication number CN104168711B and utility model patent application number CN202022587023.0). While this method is theoretically feasible, it has revealed numerous problems in practical applications. Firstly, during the pressing process, there is no pressure pad to cushion the low-pressure areas of the cavity, and the low-flow prepreg used for interlayer bonding possesses a certain rigidity after riveting. This rigidity hinders tight local bonding, making delamination prone to occur near the bonding area between the low-flow prepreg and the cavity due to insufficient pressure. Delamination not only directly leads to circuit board processing interruptions but also causes a large number of products to be scrapped, severely impacting production efficiency and product quality. On the other hand, this method does not clearly define the types of the top and bottom core boards. In fact, only when the core board type is FR4 can a relatively qualified cavity board be produced; when the core board type is a flexible PI substrate, due to the thinness and softness of the PI material, the overall rigidity is severely insufficient before the interlayer bonding medium has cured. In the later stages of lamination, the rapid drop in temperature difference leads to a decrease in air pressure inside the cavity, causing large-area depressions, which greatly limits the application of this method under different material combinations.

[0004] In addition, to address the issues of lamination and delamination in the cavity plates mentioned above, the industry has attempted a process of embedding gaskets within the cavity before lamination. However, this process has significant drawbacks in practice. Both embedding and removing the gaskets require manual operation, resulting in extremely low efficiency and making it difficult to meet the demands of large-scale industrial production, severely hindering the mass production of cavity plates.

[0005] In summary, existing cavity circuit board manufacturing technologies face numerous challenges in practical applications, urgently requiring a new technical solution to address issues such as delamination near the cavity bonding area, depression in the cavity after lamination, and difficulties in mass production due to the inconvenience of gasket removal and placement. This would promote the further development of printed circuit board technology and meet the market demand for high-performance, low-cost cavity circuit boards. Utility Model Content

[0006] Based on the technical problems described above, the purpose of this utility model is to provide a cavity circuit board and its preparation method. The cavity circuit board uses an integrated circuit (IC) packaging film as the cavity circuit board, which solves the problems of concavity in the cavity and delamination near the cavity bonding area after lamination in traditional manufacturing methods. At the same time, it avoids the disadvantages of inconvenient placement and removal of gaskets and difficulty in mass production, improves the quality and production efficiency of circuit board manufacturing, and enhances the stability and reliability of the product.

[0007] Specifically, according to one aspect of the present invention, a cavity circuit board is provided, the cavity circuit board comprising, in sequence, a first copper foil, a first cured sheet, a second copper foil, an integrated circuit packaging film, a first double-layer copper clad laminate, a second cured sheet, a second double-layer copper clad laminate, a third cured sheet, a third copper foil, a fourth cured sheet, and a fourth copper foil, wherein:

[0008] The first double-layer copper-clad laminate and the second double-layer copper-clad laminate each comprise a first copper layer, a glass fiber resin composite layer, and a second copper layer stacked sequentially; and

[0009] The first double-layer copper-clad laminate and the second cured sheet are partially removed to form a cavity inside the cavity circuit board.

[0010] According to another aspect of the present invention, a method for preparing a cavity circuit board is provided, the method comprising the following steps:

[0011] S1: The first double-layer copper-clad laminate, the second prepreg, and the second double-layer copper-clad laminate are stacked sequentially to obtain a first laminate, and the first laminate is subjected to a first hot pressing to obtain a first pressed body.

[0012] S2: The first press body is milled to partially remove the first double-layer copper-clad laminate and the second prepreg.

[0013] S3: An integrated circuit packaging film and a second copper foil are sequentially bonded to the milled surface of the first press-fit body, and a third prepreg and a third copper foil are sequentially bonded to the unmilled surface of the first press-fit body to obtain a second laminate. Then, the second laminate is subjected to a second hot press to obtain the second press-fit body.

[0014] S4: A first prepreg and a first copper foil are sequentially bonded to the surface of the second copper foil of the second press body, and a fourth prepreg and a fourth copper foil are sequentially bonded to the surface of the third copper foil of the second press body to obtain a third laminate. Then, the third laminate is subjected to a third hot pressing to obtain a third press body. Attached Figure Description

[0015] In this invention, accompanying drawings are provided to better illustrate the contents of this invention; however, this invention is by no means limited thereto.

[0016] Figure 1 A schematic structural diagram of a cavity circuit board according to a specific embodiment of the present invention is shown;

[0017] Figure 2 A flowchart showing steps S1-S4 of a method for fabricating a cavity circuit board according to a specific embodiment of the present invention is displayed; and

[0018] Figures 3(a)-3(d) The diagram shows a step-by-step structural schematic of a method for preparing a cavity circuit board according to a specific embodiment of the present invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It will be understood that other embodiments may be implemented without departing from the scope or spirit of the present invention. Therefore, the following detailed description is non-limiting.

[0020] Unless otherwise specified, all figures used in this specification and claims to indicate feature dimensions, quantities, and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired properties using the teachings disclosed herein. The use of numerical ranges indicated by endpoints includes all numbers within that range and any range within that range; for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc.

[0021] As described above, this invention aims to solve a series of problems existing in the traditional cavity circuit board manufacturing process. Traditional manufacturing methods often result in depressions in the cavity after lamination, affecting the flatness and overall quality of the circuit board; after long-term storage, delamination is prone to occur near the cavity bonding area, reducing product stability and reliability; furthermore, the gaskets used in the manufacturing process are inconvenient to handle, hindering large-scale mass production. This invention effectively solves the above technical problems by using integrated circuit (IC) packaging film as the cavity circuit board, improving circuit board manufacturing quality and production efficiency, and enhancing product stability and reliability.

[0022] Specifically, according to one aspect of the present invention, a cavity circuit board is provided, the cavity circuit board comprising, in sequence, a first copper foil, a first cured sheet, a second copper foil, an integrated circuit packaging film, a first double-layer copper clad laminate, a second cured sheet, a second double-layer copper clad laminate, a third cured sheet, a third copper foil, a fourth cured sheet, and a fourth copper foil, wherein:

[0023] The first double-layer copper-clad laminate and the second double-layer copper-clad laminate each comprise a first copper layer, a glass fiber resin composite layer, and a second copper layer stacked sequentially; and

[0024] The first double-layer copper-clad laminate and the second cured sheet are partially removed to form a cavity inside the cavity circuit board.

[0025] Figure 1 A schematic structural diagram of a cavity circuit board 100 according to a specific embodiment of the present invention is shown. Figure 1 As shown, the cavity circuit board 100 includes a first copper foil 1, a first curing sheet 2, a second copper foil 3, an integrated circuit packaging film 4, a first double-layer copper clad laminate 5, a second curing sheet 6, a second double-layer copper clad laminate 7, a third curing sheet 8, a third copper foil 9, a fourth curing sheet 10, and a fourth copper foil 11 stacked sequentially, wherein: the first double-layer copper clad laminate 5 and the second double-layer copper clad laminate 7 each include a first copper layer 12, a glass fiber resin composite layer 13, and a second copper layer 14 stacked sequentially; and the first double-layer copper clad laminate 5 and the second curing sheet 6 are partially removed to form a cavity 15 inside the cavity circuit board 100.

[0026] In addition, such as Figure 1As shown, the cavity circuit board further includes: a through hole 16, which penetrates the entire cavity circuit board 100; a first outer blind via 17, which penetrates the first copper foil 1 and the first cured sheet 2 of the cavity circuit board 100; a second outer blind via 18, which penetrates the fourth copper foil 11 and the fourth cured sheet 10 of the cavity circuit board 100; a first inner blind via 19, which penetrates the second copper foil 3 and the integrated circuit packaging film 4 inside the cavity circuit board 100; a second inner blind via 20, which penetrates the third copper foil 9 and the third cured sheet 8 inside the cavity circuit board 100; and an inner drill hole 21, which penetrates the first double-layer copper clad laminate 5, the second cured sheet 6, and the second double-layer copper clad laminate 7 inside the cavity circuit board 100.

[0027] Specifically, the cavity circuit board of this utility model adopts a unique multi-layer structure design, consisting of, from the outside to the inside, a first copper foil, a first curing sheet, a second copper foil, an integrated circuit packaging film, a first double-layer copper-clad laminate, a second curing sheet, a second double-layer copper-clad laminate, a third curing sheet, a third copper foil, a fourth curing sheet, and a fourth copper foil. This structural design is the foundation for achieving the technical effects of this utility model, with each layer of materials working together to exert its function.

[0028] The first and second double-layer copper-clad laminates each comprise a first copper layer, a glass fiber resin composite layer, and a second copper layer stacked sequentially. The copper layer, as a conductive component, possesses excellent conductivity, effectively conducting current to form various circuits, enabling electrical connections between electronic components and ensuring normal current transmission throughout the circuit. The glass fiber resin composite layer acts as insulation, separating the upper and lower copper layers to prevent short circuits and ensure stable signal transmission between circuits. Simultaneously, it provides mechanical strength to the circuit board, supporting its overall structure. According to certain preferred embodiments of this invention, the copper layer of the double-sided copper-clad laminate is composed of pure copper foil, further improving conductivity; the dielectric layer (glass fiber resin composite layer) uses FR4 material, a hybrid structure of glass fiber and resin, possessing good insulation properties and a certain mechanical strength, allowing the upper and lower copper layers to bond firmly and ensuring the overall stability of the circuit board. In terms of electrical function, the circuits formed by the copper layers are responsible for transmitting electronic signals and distributing power, meeting the operational needs of different electronic components and ensuring normal circuit operation. In terms of mechanical function, copper-clad laminate (CCL), as the main structure of the circuit board, provides a foundation for the installation and fixation of other materials and components. Its strength and stability ensure that the circuit board is not easily deformed or damaged during production, transportation, and use. The thickness of the first copper layer and the second copper layer of both the first and second double-layer CCLs are each in the range of 10-50 μm, preferably 15-30 μm. The thickness of the glass fiber resin composite layer of both the first and second double-layer CCLs is in the range of 0.05-5 mm, preferably 0.1-3 mm.

[0029] Commercially available examples of double-sided copper-clad laminates that can be used in this invention include: FR-4 series double-sided copper-clad laminates produced by Guangdong Shengyi Technology Co., Ltd., Kingboard laminates produced by Kingboard Holdings Limited, and high-TG double-sided copper-clad laminates produced by Kingboard Holdings Limited, etc. Preferably, the integrated circuit packaging film is the SIF03 and SIF04 laminated insulating film products of Guangdong Shengyi Technology Co., Ltd.

[0030] The integrated circuit (IC) packaging film plays a core supporting role in the cavity circuit board of this invention and is an important aspect of solving the problems of traditional technologies. Its shear modulus needs to be in the range of 8-15 GPa, its tensile strength in the range of 100-150 MPa, and its glass transition temperature (Tg) above 200℃. These performance parameters are crucial to achieving the technical effects of this invention. When the shear modulus of the integrated circuit packaging film is less than 8 GPa, or when the tensile strength of the integrated circuit packaging film is less than 100 MPa, or when the glass transition temperature (Tg) of the integrated circuit packaging film is below 200℃, a depression will appear at the cavity after lamination. This is because the lower shear modulus and tensile strength cannot effectively resist the pressure during the lamination process, leading to deformation of the packaging film and thus depression at the cavity; while the lower glass transition temperature makes the packaging film less stable under temperature changes, also easily causing depression problems. When the shear modulus of the integrated circuit packaging film exceeds 15 GPa, or the tensile strength exceeds 150 MPa, the resulting cavity circuit board will delaminate after prolonged storage (temperature 20℃-30℃, relative humidity 40%-60%). This is because excessively high shear modulus and tensile strength cause stress mismatch between the packaging film and other layers, leading to delamination under long-term environmental conditions. Taking Guangdong Shengyi Technology Co., Ltd.'s SIF03 laminated insulating film as an example, its shear modulus is approximately 9 GPa, its tensile strength is approximately 120 MPa, and its glass transition temperature (Tg) measured by the TMA method is approximately 210℃. This product effectively avoids the problems of cavity depression after lamination and delamination after long-term storage in traditional manufacturing methods, improving the quality and stability of the circuit board.

[0031] The thicknesses of the first, second, third, and fourth copper foils are respectively within the range of 10-50 μm, preferably 15-30 μm. This thickness range is chosen by comprehensively considering conductivity and the overall thickness of the circuit board. Thinner copper foils can reduce the weight and cost of the circuit board, while also reducing signal transmission losses to some extent; while thicker copper foils can withstand greater current, ensuring the electrical performance of the circuit board. In this invention, the 10-50 μm thickness range meets the current transmission requirements of most electronic devices while also taking into account the requirement for a thinner and lighter circuit board.

[0032] The first, second, third, and fourth cured sheets are obtained by curing prepregs. Prepregs are commonly used materials in printed circuit board (PCB) manufacturing, typically composed of resin and reinforcing materials. In multilayer PCB fabrication, prepregs play a crucial bonding role. Under heat and pressure, the prepreg softens, tightly bonding different circuit layers (such as copper foil and core board) together; upon cooling, it cures, forming a stable structure that ensures strong connections between PCB layers, maintains overall structural stability, and guarantees reliable electrical performance. In this invention, its lamination and pressing with double-sided copper-clad laminates is essential for forming the inner layer structure. Commercially available prepregs that can be used in this invention include, but are not limited to, high-transparency epoxy fiberglass prepregs produced by Zhejiang Zhaoyi Technology Co., Ltd., S1170 series prepregs produced by Guangdong Shengyi Technology Co., Ltd., and KB series prepregs from Jiantao Chemical Co., Ltd. These prepregs have their own advantages in different application scenarios and can meet the requirements of this invention for PCB bonding performance and structural stability.

[0033] According to certain preferred embodiments of this utility model, the cavity circuit board of this utility model can optionally be designed with various hole structures, including through holes, outer blind vias, inner blind vias, and inner drill holes, etc. These hole structures play different functions in the circuit board, further improving the performance and applicability of the circuit board.

[0034] Through-holes run through the entire cavity circuit board, serving as crucial channels for electrical connections between different layers. In complex circuit designs, electronic components often need to connect to traces on different layers; through-holes provide direct electrical pathways, ensuring smooth current flow throughout the board. For example, in circuits requiring high power transmission, through-holes can transfer current from the power layer to various functional layers, providing a stable power supply for electronic components. Simultaneously, through-holes also serve a heat dissipation function, conducting heat generated inside the circuit board to the outside, thus improving the board's heat dissipation performance.

[0035] The outer blind via extends from the surface of the cavity circuit board into its interior. Depending on design requirements, it can penetrate the first copper foil and the first cured wafer, or it can penetrate the fourth copper foil and the fourth cured wafer. This blind via structure has important applications in surface mount technology (SMT). Through the outer blind via, surface-mount electronic components can be connected to the internal circuitry of the circuit board, reducing circuit length and signal transmission delay. For example, in some high-speed signal transmission applications, such as the radio frequency (RF) circuitry of mobile phones, the outer blind via can directly connect the RF chip to the internal RF circuitry, improving signal transmission quality and speed. Furthermore, the outer blind via can reduce the number of holes drilled on the circuit board, lowering production costs and improving production efficiency.

[0036] Internal blind vias extend from one layer to an adjacent layer within a cavity circuit board, such as penetrating the second copper foil and the integrated circuit packaging film, or penetrating the third copper foil and the third curing film. The presence of internal blind vias allows for more flexible and diverse interlayer connections within the circuit board. In some high-density wiring circuit designs, internal blind vias can avoid excessive space occupation by vias, increasing the wiring density of the circuit board. Simultaneously, internal blind vias can reduce interference during signal transmission, improving circuit performance. For example, in circuits with high electromagnetic compatibility requirements, by rationally designing the location and number of internal blind vias, crosstalk between signals can be effectively reduced, improving circuit stability.

[0037] Inner layer vias extend through three or more layers within a cavity circuit board, such as penetrating the first double-layer copper-clad laminate, the second bonding pad, and the second double-layer copper-clad laminate. Inner layer vias are primarily used to achieve complex electrical connections between multiple layers. In circuits requiring extensive signal transmission and complex logic control, inner layer vias can connect circuits on different layers to form complex circuit networks. For example, in high-end electronic products such as computer motherboards, inner layer vias can connect circuits of multiple functional modules, enabling high-speed data transmission and processing. The design and fabrication of inner layer vias require high-precision equipment and processes to ensure the positional accuracy of the vias and the quality of the via walls, thereby guaranteeing the performance and reliability of the circuit board.

[0038] Compared with traditional cavity circuit board manufacturing techniques, this invention has significant advantages. Firstly, by using an integrated circuit encapsulation film as the cavity support layer, the problem of cavity depression after lamination is effectively solved. In traditional methods, due to material and process limitations, depressions easily appear in the cavity after lamination, affecting the flatness and appearance quality of the circuit board, and consequently impacting the installation and performance of electronic components. However, the integrated circuit encapsulation film in this invention has suitable shear modulus and tensile strength, effectively resisting pressure during lamination and maintaining its shape and structural stability, thus ensuring that depressions do not occur in the cavity.

[0039] Secondly, this invention solves the problem of delamination near the cavity bonding area. In traditional manufacturing methods, delamination easily occurs near the cavity bonding area due to insufficient pressure in the low-flow prepreg, leading to circuit board quality problems and low production efficiency. The integrated circuit packaging film of this invention exhibits good compatibility and adhesion with other layer materials, maintaining a stable bond during long-term storage and use, thus preventing delamination. Under aging conditions of 85℃ and 85% relative humidity, circuit boards manufactured using traditional methods may delaminate within a short time, while the cavity circuit boards prepared by this invention show no delamination even after more than 500 hours, significantly improving product stability and reliability.

[0040] Furthermore, this invention avoids the drawbacks of inconvenient placement and removal of gaskets, and difficulties in mass production. In traditional processes, inserting and removing gaskets within the cavity requires manual operation, which is inefficient and prone to errors, making it difficult to meet the needs of large-scale industrial production. This invention, through its innovative structural design, eliminates the need for gaskets, simplifies the production process, improves production efficiency, reduces production costs, and makes large-scale production of cavity circuit boards possible.

[0041] In summary, the cavity circuit board and its preparation method of this utility model effectively solve the problems existing in traditional technologies through innovative structural design, material selection and hole structure design, improve the quality and production efficiency of circuit board manufacturing, enhance the stability and reliability of products, and have significant innovation and practicality, providing a new direction and solution for the development of printed circuit board technology.

[0042] According to another aspect of the present invention, a method for preparing a cavity circuit board is provided, the method comprising the following steps:

[0043] S1: The first double-layer copper clad laminate 5, the second semi-cured sheet 6' and the second double-layer copper clad laminate 7 are stacked in sequence to obtain a first laminate, and the first laminate is subjected to a first hot pressing to obtain a first pressed body.

[0044] S2: The first press body is milled to partially remove the first double-layer copper-clad laminate 5 and the second prepreg 6';

[0045] S3: An integrated circuit packaging film 4 and a second copper foil 3 are sequentially bonded to the milled surface of the first press-fit body, and a third prepreg 8' and a third copper foil 9 are sequentially bonded to the unmilled surface of the first press-fit body to obtain a second laminate. Then, the second laminate is subjected to a second hot press to obtain the second press-fit body.

[0046] S4: First prepreg 2' and first copper foil 1 are sequentially bonded to the surface of the second copper foil 3 of the second press body, and fourth prepreg 10' and fourth copper foil 11 are sequentially bonded to the surface of the third copper foil 9 of the second press body to obtain a third laminate. Then, the third laminate is subjected to a third hot pressing to obtain a third press body.

[0047] Figure 2 A flowchart illustrating the steps of a method for preparing a cavity circuit board according to a specific embodiment of the present invention is shown, which includes the steps S1, S2, S3 and S4 above.

[0048] Figures 3(a)-3(d) The diagram shows a step-by-step structural schematic of a method for preparing a cavity circuit board according to a specific embodiment of the present invention.

[0049] Specifically, in step S1, the first double-layer copper clad laminate 5, the second semi-cured sheet 6', and the second double-layer copper clad laminate 7 are stacked sequentially to obtain a first laminate, and the first laminate is subjected to a first hot pressing to obtain a first pressed body.

[0050] In step S2, the first laminate is milled to partially remove the first double-layer copper-clad laminate 5 and the second prepreg 6'. Additionally, the first laminate undergoes one or more of the following processes: drilling, plasma cleaning, electroplating, double-sided lamination, double-sided exposure, double-sided etching, and automated optical inspection.

[0051] In step S3, an integrated circuit packaging film 4 and a second copper foil 3 are sequentially bonded to the milled surface of the first press-fit body, and a third prepreg 8' and a third copper foil 9 are sequentially bonded to the unmilled surface of the first press-fit body to obtain a second laminate. Then, the second laminate is subjected to a second hot-pressing process to obtain the second press-fit body. Furthermore, the second press-fit body undergoes one or more of the following processes: X-ray punching of positioning holes, edge milling, laser drilling of blind holes, board brushing, board baking, plasma cleaning, chemical desmearing, automatic optical inspection of blind holes, horizontal electroplating of through holes, flash plating, hole-filling electroplating, full-board electroplating, outer layer circuitry construction, and automatic optical inspection.

[0052] In step S4, a first prepreg 2' and a first copper foil 1 are sequentially bonded to the surface of the second copper foil 3 of the second press body, and a fourth prepreg 10' and a fourth copper foil 11 are sequentially bonded to the surface of the third copper foil 9 of the second press body to obtain a third laminate. Then, the third laminate is subjected to a third hot press to obtain the third press body. Furthermore, the third press body undergoes one or more of the following processes: X-ray punching of positioning holes, edge milling, laser drilling of blind holes, outer layer mechanical drilling, board brushing, board baking, plasma cleaning, chemical adhesive removal, automatic optical inspection of blind holes, horizontal electroplating of through holes, flash plating, hole-filling electroplating, full-board electroplating, outer layer circuit construction, automatic optical inspection, solder resist, electroless nickel-gold plating, milling of the outline, ultrasonic hot water washing, UV laser drilling of vent holes, four-wire testing, final inspection, outgoing sampling inspection, nitrogen baking, packaging, and warehousing.

[0053] Specifically, in step S1, the first double-layer copper-clad laminate, the second prepreg, and the second double-layer copper-clad laminate are stacked sequentially to form the first laminate. In this process, the first and second double-layer copper-clad laminates serve as the key basic structures of the circuit board, providing support for subsequent circuit construction and electrical connections. Their copper layers are used to form conductive lines, enabling electrical connections between electronic components; the glass fiber resin composite layer provides insulation and mechanical support, ensuring stable signal transmission between lines and maintaining the overall structural stability of the circuit board.

[0054] Optionally, before stacking, the first double-layer copper-clad laminate can undergo one or more of the following processes: cutting, drilling, plasma cleaning, electroplating, inner layer lamination, inner layer exposure, single-sided etching, automated optical inspection (AOI), and micro-etching. Cutting involves cutting the large-sized copper-clad laminate into suitable specifications according to actual production needs; drilling is used to form the required vias or mounting holes; plasma cleaning removes impurities and organic matter from the surface of the board, enhancing surface activity and improving the adhesion of subsequent processing; electroplating forms a uniform metal plating layer on the copper layer surface, improving conductivity and corrosion resistance; processes such as inner layer lamination, inner layer exposure, and single-sided etching are used to create inner layer circuitry, transferring the designed circuit pattern onto the copper layer using photolithography and etching away unwanted copper foil to form a precise circuit layout; automated optical inspection (AOI) is used to inspect the quality of the processed circuitry and promptly detect circuit defects; micro-etching slightly etches the surface of the copper layer, increasing surface roughness and further improving adhesion to other materials.

[0055] Optionally, prior to stacking, the second double-layer copper-clad laminate can undergo one or more of the following processes: cutting, brushing, inner layer lamination, inner layer exposure, single-sided etching, automated optical inspection, and browning. Brushing removes dirt and oxide layers from the board surface; browning forms a brown oxide film on the copper layer surface, increasing the adhesion between the copper layer and the prepreg, and improving interlayer bonding strength.

[0056] After the stacking is completed, the first layer is subjected to a first hot press. The first hot press is performed at a temperature of 150-200°C for 60-120 minutes. Within this temperature and time range, the second prepreg softens, and the resin inside flows, tightly bonding the first and second double-layer copper clad laminates together.

[0057] In step S2, after the first lamination is completed, milling is performed. The purpose of this step is to partially remove the first double-layer copper-clad laminate and the second prepreg, thereby forming the initial shape of the cavity inside the cavity circuit board. Milling is performed using high-precision milling equipment, machining according to the pre-designed cavity shape and dimensions. During milling, milling parameters, such as the milling cutter's rotational speed, feed rate, and depth of cut, need to be strictly controlled to ensure machining accuracy and quality.

[0058] In step S3, the integrated circuit encapsulation film and the second copper foil are first pressed together to semi-cure the integrated circuit encapsulation film. The integrated circuit encapsulation film, as a key material of this invention, has a shear modulus in the range of 8-15 GPa, a tensile strength in the range of 100-150 MPa, and a glass transition temperature (Tg) above 200℃. These special properties enable it to play a crucial role in cavity circuit boards, effectively solving the problems of depression and delamination at the cavity after pressing in traditional processes.

[0059] During the pre-compression process, pressure and temperature are controlled to bring the integrated circuit packaging film to a semi-cured state. The semi-cured packaging film possesses both a certain degree of adhesion, facilitating subsequent bonding with other materials, and a degree of plasticity, adaptable to various processing requirements. The pre-compression pressure and temperature need to be adjusted according to the characteristics of the packaging film. Generally, the pressure is gradually increased within a certain range, while the temperature is maintained at an appropriate level to ensure uniform semi-curing of the packaging film and avoid uneven local curing.

[0060] Then, the exposed surface of the semi-cured integrated circuit packaging film is bonded to the first double-layer copper-clad laminate of the first laminate after milling, while the third semi-cured sheet and the third copper foil are sequentially bonded to the second double-layer copper-clad laminate of the first laminate without milling, thus obtaining the second laminate. During the bonding process, it is necessary to ensure tight adhesion between the layers to avoid air bubbles or gaps. To achieve tight adhesion, vacuum bonding technology or applying pressure during the bonding process can be used. Vacuum bonding technology can eliminate air between layers, improving the tightness of the bond; applying pressure helps promote adhesion between layers and enhances interlayer bonding strength. Furthermore, cleaning the surfaces of each layer before bonding to remove dust, oil, and other impurities can also improve the bonding quality.

[0061] Subsequently, a second hot-pressing process is performed on the second laminate, also at a temperature of 150-200°C for 60-120 minutes. During the hot-pressing process, the third prepreg softens, further and firmly bonding the integrated circuit packaging film, the second copper foil, the third copper foil, and the first and second double-layer copper clad laminates together. At this point, the integrated circuit packaging film not only serves as a support layer for the cavity but also fuses with the other layer materials to form a tight, integrated structure.

[0062] The bonding strength between the layers in the second laminate after hot pressing is significantly improved, meeting the mechanical performance requirements of subsequent processing and use. Simultaneously, the special properties of the integrated circuit packaging film are fully utilized after hot pressing, effectively preventing depressions and delamination at the cavities. Optionally, after the second hot pressing, the second laminate may undergo one or more of the following processes: X-ray punching of positioning holes, edge milling, laser drilling of blind holes, board brushing, board baking, plasma cleaning, chemical desmearing, automatic optical inspection of blind holes, horizontal electroplating of through holes, flash plating, hole-filling electroplating, full-board electroplating, outer layer circuitry construction, and automatic optical inspection.

[0063] These processing steps further refine the structure and performance of the circuit board. X-ray punching positioning holes are used to determine the precise position of the circuit board, providing a reference for subsequent processing; edge milling removes burrs and excess material from the edges of the circuit board, ensuring accurate dimensions and smooth edges; laser drilling of blind holes and outer layer mechanical drilling are used to form various types of hole structures to meet the needs of circuit connection and component installation; processes such as brushing, baking, plasma cleaning, and chemical desmearing are used to clean the surface of the circuit board, removing impurities and adhesive residues left over from processing and improving surface quality; automatic optical inspection of blind holes and automatic optical inspection are used to inspect the hole structure and circuitry for quality, ensuring product quality; processes such as horizontal electroplating through holes, flash plating, through-hole plating, and full-board electroplating are used to form metal plating layers on the hole walls and circuit surfaces, improving conductivity and corrosion resistance; outer layer circuitry construction involves creating complex circuit patterns on the circuit board surface according to design requirements to achieve electrical connections between electronic components.

[0064] In step S4, a first prepreg and a first copper foil are sequentially bonded to the surface of the second copper foil of the second laminate, and a fourth prepreg and a fourth copper foil are sequentially bonded to the surface of the third copper foil to obtain a third laminate. Then, the third laminate is subjected to a third hot-pressing process at 150-200°C for 60-120 minutes. Through this third hot-pressing, the first and fourth prepregs are cured, firmly bonding the layers together to form the final cavity circuit board structure.

[0065] In this step, temperature and time control during hot pressing are equally crucial. Appropriate temperature and time ensure the prepreg fully cures, achieving optimal adhesion strength between the circuit board layers. Simultaneously, during bonding, it's essential to maintain the alignment accuracy of each layer to prevent interlayer misalignment, which could negatively impact the circuit board's performance and appearance.

[0066] Optionally, after the third hot pressing, the third pressed body undergoes a series of subsequent processing, including X-ray punching of positioning holes, edge milling, laser drilling of blind holes, outer layer mechanical drilling, board brushing, board baking, plasma cleaning, chemical desmearing, automatic optical inspection of blind holes, horizontal electroplating of through holes, flash plating, hole-filling electroplating, whole board electroplating, outer layer circuit construction, automatic optical inspection, solder resist, electroless nickel-gold plating, milling of the outline, ultrasonic hot water washing, UV laser drilling of vent holes, four-line testing, final inspection, outgoing sampling inspection, nitrogen baking, packaging and warehousing, etc.

[0067] Specifically, the solder resist process involves coating the circuit board surface with a layer of solder resist to prevent short circuits during soldering, thus improving the accuracy and reliability of the soldering. Electroless nickel-gold plating forms a nickel-gold alloy coating on the circuit surface, improving not only conductivity and corrosion resistance but also soldering performance. Milling is used to process the circuit board into its final dimensions to meet practical application requirements. Ultrasonic hot water washing further cleans impurities and residues from the circuit board surface, improving surface cleanliness. UV laser drilling creates vent holes in specific locations to meet the needs of some special applications. Four-wire testing is used to test the electrical performance of the circuit board, ensuring normal circuit connections. Final inspection and outgoing sampling conduct comprehensive quality testing to ensure that the quality of products leaving the factory meets standards. Nitrogen baking removes moisture from the circuit board, preventing electrical faults caused by moisture during subsequent use. Packaging and warehousing ensure proper storage and management of the finished products, facilitating subsequent transportation and sales.

[0068] The cavity circuit board fabrication method of this invention has significant advantages over traditional processes. Firstly, by employing a specific performance integrated circuit packaging film and optimizing each process step, the problems of depression at the cavity after lamination and delamination near the cavity bonding area are effectively solved. Tests show that after storage for 3-5 years in a normal environment (temperature 20℃-30℃, relative humidity 40%-60%) and 500 hours under aging conditions of 85℃ and 85% relative humidity, no delamination was observed in the fabricated cavity circuit boards; furthermore, no depression occurred at the cavity after lamination, ensuring the flatness and appearance quality of the circuit board.

[0069] Secondly, this preparation method avoids the use of gaskets, simplifies the production process, improves production efficiency, reduces production costs, and is easier to scale up for industrial production. Throughout the preparation process, each step works in close coordination, and precise control of material properties, process parameters, and processing procedures ensures the stability and reliability of product quality. This not only meets the market demand for high-performance, low-cost cavity circuit boards but also promotes the further development of printed circuit board technology, providing strong support for the miniaturization and high-performance of electronic communication products, and possesses significant economic and technological value.

[0070] The following list of embodiments further illustrates various exemplary embodiments of the present invention, which should not be construed as unduly limiting the present invention:

[0071] Specific implementation scheme 1 is a cavity circuit board, which includes a first copper foil, a first cured sheet, a second copper foil, an integrated circuit packaging film, a first double-layer copper clad laminate, a second cured sheet, a second double-layer copper clad laminate, a third cured sheet, a third copper foil, a fourth cured sheet, and a fourth copper foil stacked sequentially, wherein:

[0072] The first double-layer copper-clad laminate and the second double-layer copper-clad laminate each comprise a first copper layer, a glass fiber resin composite layer, and a second copper layer stacked sequentially; and

[0073] The first double-layer copper-clad laminate and the second cured sheet are partially removed to form a cavity inside the cavity circuit board.

[0074] Specific implementation scheme 2 is based on the cavity circuit board described in 1, wherein the shear modulus of the integrated circuit packaging film is in the range of 8-15 GPa, the tensile strength is in the range of 100-150 MPa, and the glass transition temperature Tg is above 200℃.

[0075] Specific implementation scheme 3 is based on the cavity circuit board described in specific implementation scheme 1, wherein the integrated circuit packaging film is the SIF03 and SIF04 multilayer insulating film products of Guangdong Shengyi Technology Co., Ltd.

[0076] Specific implementation scheme 4 is a cavity circuit board according to specific implementation scheme 1, wherein the thicknesses of the first copper foil, the second copper foil, the third copper foil and the fourth copper foil are respectively in the range of 10-50μm.

[0077] Specific implementation scheme 5 is based on the cavity circuit board described in specific implementation scheme 1, wherein the first curing sheet, the second curing sheet, the third curing sheet and the fourth curing sheet are obtained by curing semi-curing sheets.

[0078] Specific implementation scheme 6 is a cavity circuit board according to specific implementation scheme 1, wherein the thickness of the first copper layer and the second copper layer of the first double-layer copper clad board and the second double-layer copper clad board are each in the range of 10-50μm.

[0079] Specific implementation scheme 7 is a cavity circuit board according to specific implementation scheme 1, wherein the thickness of the glass fiber resin composite layer of the first double-layer copper clad board and the second double-layer copper clad board is in the range of 0.05-5mm.

[0080] Specific implementation scheme 8 is a cavity circuit board according to specific implementation scheme 1, wherein the cavity circuit board further includes one or more of the following:

[0081] A through-hole, which penetrates the entire cavity circuit board;

[0082] An outer blind via extends from the surface of the cavity circuit board into the interior of the cavity circuit board;

[0083] Internal blind vias, the internal blind vias extending from one layer inside the cavity circuit board to an adjacent layer; and

[0084] Inner layer drilling, wherein the inner layer drilling extends through more than three layers inside the cavity circuit board.

[0085] Specific implementation scheme 9 is based on the cavity circuit board described in specific implementation scheme 8, wherein:

[0086] The outer blind via penetrates the first copper foil and the first cured sheet of the cavity circuit board; and / or

[0087] The outer blind via penetrates the fourth copper foil and the fourth curing sheet of the cavity circuit board.

[0088] Specific implementation scheme 10 is the cavity circuit board according to specific implementation scheme 8, wherein:

[0089] The internal blind via penetrates the second copper foil and the integrated circuit packaging film within the cavity circuit board; and / or

[0090] The internal blind hole penetrates the third copper foil and the third curing sheet inside the cavity circuit board.

[0091] Specific implementation scheme 11 is a cavity circuit board according to specific implementation scheme 8, wherein the inner layer drill hole penetrates the first double-layer copper-clad laminate, the second curing sheet and the second double-layer copper-clad laminate inside the cavity circuit board.

[0092] Specific implementation scheme 12 is a method for fabricating a cavity circuit board, the method comprising the following steps:

[0093] S1: The first double-layer copper-clad laminate, the second prepreg, and the second double-layer copper-clad laminate are stacked sequentially to obtain a first laminate, and the first laminate is subjected to a first hot pressing to obtain a first pressed body.

[0094] S2: The first press body is milled to partially remove the first double-layer copper-clad laminate and the second prepreg.

[0095] S3: An integrated circuit packaging film and a second copper foil are sequentially bonded to the milled surface of the first press-fit body, and a third prepreg and a third copper foil are sequentially bonded to the unmilled surface of the first press-fit body to obtain a second laminate. Then, the second laminate is subjected to a second hot press to obtain the second press-fit body.

[0096] S4: A first prepreg and a first copper foil are sequentially bonded to the surface of the second copper foil of the second press body, and a fourth prepreg and a fourth copper foil are sequentially bonded to the surface of the third copper foil of the second press body to obtain a third laminate. Then, the third laminate is subjected to a third hot pressing to obtain a third press body.

[0097] Specific implementation scheme 13 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S1, before the stacking:

[0098] The first double-layer copper-clad laminate is subjected to one or more of the following processes: blanking, drilling, plasma cleaning, electroplating, inner layer lamination, inner layer exposure, single-sided etching, automated optical inspection, and micro-etching; and / or

[0099] The second double-layer copper clad laminate is subjected to one or more of the following processes: blanking, brushing, inner layer lamination, inner layer exposure, single-sided etching, automatic optical inspection, and browning.

[0100] Specific implementation scheme 14 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S1, the first hot pressing is performed at a temperature of 150-200°C for 60-120 minutes.

[0101] Specific implementation scheme 15 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S1, after the first hot pressing, the first pressed body is subjected to one or more of the following processes: drilling, plasma cleaning, electroplating, double-sided lamination of outer layer, double-sided exposure, double-sided etching and automatic optical inspection.

[0102] Specific implementation scheme 16 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein step S3 includes:

[0103] S3-1: Press the integrated circuit packaging film and the second copper foil together to make the integrated circuit packaging film semi-cured;

[0104] S3-2: The exposed surface of the integrated circuit packaging film is bonded to the first double-layer copper-clad laminate of the first laminate from step S2 after milling, and the third prepreg and the third copper foil are sequentially bonded to the second double-layer copper-clad laminate of the first laminate from step S2 without milling, to obtain the second laminate; and

[0105] S3-3: Perform a second hot pressing on the second laminate.

[0106] Specific implementation scheme 17 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S3, the second hot pressing is performed at a temperature of 150-200°C for 60-120 minutes.

[0107] Specific implementation scheme 18 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S3, after the second hot pressing, the second pressed body is subjected to one or more of the following processes: X-ray punching of positioning holes, edge milling, laser drilling of blind holes, board brushing, board baking, plasma cleaning, chemical desmearing, automatic optical inspection of blind holes, horizontal electroplating of through holes, flash plating, hole filling electroplating, whole board electroplating, outer layer circuit construction, and automatic optical inspection.

[0108] Specific implementation scheme 19 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S4, the third hot pressing is performed at a temperature of 150-200°C for 60-120 minutes.

[0109] Specific implementation scheme 20 is a method for preparing a cavity circuit board according to specific implementation scheme 12, wherein in step S4, after the third hot pressing, the third pressed body is subjected to one or more of the following processes: X-ray punching of positioning holes, edge milling, laser drilling of blind holes, outer layer mechanical drilling, board brushing, board baking, plasma cleaning, chemical desmearing, automatic optical inspection of blind holes, horizontal electroplating of through holes, flash plating, hole filling electroplating, whole board electroplating, outer layer circuit construction, automatic optical inspection, solder resist, chemical nickel-gold plating, milling of the outline, ultrasonic hot water washing, UV laser drilling of vent holes, four-wire testing, final inspection, outgoing sampling inspection, nitrogen baking, packaging and warehousing.

[0110] Specific implementation scheme 21 is the method for preparing a cavity circuit board according to specific implementation scheme 12, wherein the shear modulus of the integrated circuit packaging film is in the range of 8-15 GPa, the tensile strength is in the range of 100-150 MPa, and the glass transition temperature Tg is above 200℃.

[0111] Specific implementation scheme 22 is the method for preparing a cavity circuit board according to specific implementation scheme 12, wherein the integrated circuit packaging film is the SIF03 and SIF04 multilayer insulating film products of Guangdong Shengyi Technology Co., Ltd.

[0112] Specific implementation scheme 23 is the method for preparing a cavity circuit board according to specific implementation scheme 12, wherein the thicknesses of the first copper foil, the second copper foil, the third copper foil and the fourth copper foil are respectively in the range of 10-50 μm.

[0113] Specific implementation scheme 24 is the method for preparing a cavity circuit board according to specific implementation scheme 12, wherein the first semi-cured sheet, the second semi-cured sheet, the third semi-cured sheet and the fourth semi-cured sheet are respectively cured to form a first cured sheet, a second cured sheet, a third cured sheet and a fourth cured sheet.

[0114] Specific implementation scheme 25 is the method for preparing a cavity circuit board according to specific implementation scheme 12, wherein the thickness of the first copper layer and the second copper layer of the first double-layer copper clad board and the second double-layer copper clad board are each in the range of 10-50μm.

[0115] Specific implementation scheme 26 is the method for preparing a cavity circuit board according to specific implementation scheme 12, wherein the thickness of the glass fiber resin composite layer of the first double-layer copper clad board and the second double-layer copper clad board is in the range of 0.05-5mm.

[0116] Specific implementation scheme 27 is a method for preparing a cavity circuit board according to specific implementation scheme 24, wherein the cavity circuit board further includes one or more of the following:

[0117] A through-hole, which penetrates the entire cavity circuit board;

[0118] An outer blind via extends from the surface of the cavity circuit board into the interior of the cavity circuit board;

[0119] Internal blind vias, the internal blind vias extending from one layer inside the cavity circuit board to an adjacent layer; and

[0120] Inner layer drilling, wherein the inner layer drilling extends through more than three layers inside the cavity circuit board.

[0121] Specific implementation scheme 28 is the method for preparing a cavity circuit board according to specific implementation scheme 27, wherein:

[0122] The outer blind via penetrates the first copper foil and the first cured sheet of the cavity circuit board; and / or

[0123] The outer blind via penetrates the fourth copper foil and the fourth curing sheet of the cavity circuit board.

[0124] Specific implementation scheme 29 is the method for preparing a cavity circuit board according to specific implementation scheme 27, wherein:

[0125] The internal blind via penetrates the second copper foil and the integrated circuit packaging film within the cavity circuit board; and / or

[0126] The internal blind hole penetrates the third copper foil and the third curing sheet inside the cavity circuit board.

[0127] Specific implementation scheme 30 is the method for preparing a cavity circuit board according to specific implementation scheme 27, wherein the inner layer drilling penetrates the first double-layer copper-clad laminate, the second curing sheet and the second double-layer copper-clad laminate inside the cavity circuit board.

[0128] Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the spirit and scope of this disclosure. Therefore, if such modifications and variations fall within the scope of the claims of this utility model and their equivalents, this disclosure is also intended to include such modifications and variations.

Claims

1. A cavity circuit board, characterized in that, The cavity circuit board comprises, in sequence, a first copper foil, a first cured sheet, a second copper foil, an integrated circuit packaging film, a first double-layer copper clad laminate, a second cured sheet, a second double-layer copper clad laminate, a third cured sheet, a third copper foil, a fourth cured sheet, and a fourth copper foil, wherein: The first double-layer copper-clad laminate and the second double-layer copper-clad laminate each comprise a first copper layer, a glass fiber resin composite layer, and a second copper layer stacked sequentially; and The first double-layer copper-clad laminate and the second cured sheet are partially removed to form a cavity inside the cavity circuit board.

2. The cavity circuit board according to claim 1, characterized in that: The integrated circuit packaging film has a shear modulus in the range of 8-15 GPa, a tensile strength in the range of 100-150 MPa, and a glass transition temperature (Tg) above 200℃; and / or The integrated circuit packaging film is the SIF03 and SIF04 multilayer insulating film products of Guangdong Shengyi Technology Co., Ltd.

3. The cavity circuit board according to claim 1, characterized in that, The thicknesses of the first copper foil, the second copper foil, the third copper foil, and the fourth copper foil are all in the range of 10-50 μm.

4. The cavity circuit board according to claim 1, characterized in that, The first cured sheet, the second cured sheet, the third cured sheet, and the fourth cured sheet are obtained by curing semi-cured sheets.

5. The cavity circuit board according to claim 1, characterized in that, The thicknesses of the first copper layer and the second copper layer of the first double-layer copper clad laminate and the second double-layer copper clad laminate are each in the range of 10-50 μm.

6. The cavity circuit board according to claim 1, characterized in that, The thickness of the glass fiber resin composite layer in the first double-layer copper clad laminate and the second double-layer copper clad laminate is in the range of 0.05-5mm.

7. The cavity circuit board according to claim 1, characterized in that, The cavity circuit board also includes one or more of the following: A through-hole, which penetrates the entire cavity circuit board; An outer blind via extends from the surface of the cavity circuit board into the interior of the cavity circuit board; Internal blind vias, the internal blind vias extending from one layer inside the cavity circuit board to an adjacent layer; and Inner layer drilling, wherein the inner layer drilling extends through more than three layers inside the cavity circuit board.

8. The cavity circuit board according to claim 7, characterized in that: The outer blind via penetrates the first copper foil and the first cured sheet of the cavity circuit board; and / or The outer blind via penetrates the fourth copper foil and the fourth curing sheet of the cavity circuit board.

9. The cavity circuit board according to claim 7, characterized in that: The internal blind via penetrates the second copper foil and the integrated circuit packaging film within the cavity circuit board; and / or The internal blind hole penetrates the third copper foil and the third curing sheet inside the cavity circuit board.

10. The cavity circuit board according to claim 7, characterized in that, The inner layer drilling penetrates the first double-layer copper-clad laminate, the second curing sheet, and the second double-layer copper-clad laminate inside the cavity circuit board.

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