Coverlay film composition, coverlay film, embedded capacitor, circuit board and method of manufacturing the same

Abstract

The present application provides a kind of covering film composition for embedded capacitor, covering film, embedded capacitor, circuit board and its preparation method. By weight parts, covering film composition includes 30-70 parts of main resin, 5-25 parts of epoxy resin, 10-50 parts of inorganic filler and 10-30 parts of flame retardant. The present application reaches the electrical design of high dielectric constant / low loss by the design of resin composition and the optimal amount of inorganic filler, and has good adhesion, which can be directly adhered to copper circuit layout layer, reduces the thickness of circuit board of covering film; also can simultaneously by the end point electrode design of circuit board, attach single layer high dielectric / low loss covering film between parallel electrodes of circuit board to form an embedded capacitor without additional embedding other passive components, which can greatly reduce the overall thickness of circuit board, reduce manufacturing cost, and improve the overall circuit board manufacturing yield, suitable for application in the design of increasingly miniaturized electronic products.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed circuit board, in particular to a cover film composition for embedded capacitor, cover film, embedded capacitor, circuit board and preparation method thereof. BACKGROUND

[0002] With the development of electronic components towards high functionality and miniaturization, the proportion of passive devices in electronic systems is increasing. Currently, passive devices mainly use surface mounting method, which occupies a large space of the substrate, and the length of surface interconnection and the number of soldering points are large, which greatly reduces the electrical properties and reliability of materials and systems. Therefore, in order to provide electronic systems that are lighter, better in performance, cheaper in price and stronger in reliability, the past surface mounting is converted to embedded system, which is the only choice.

[0003] Traditional PCB embedding technology is to directly embed passive components into PCB, for example, directly embedding passive components such as capacitors, inductors and resistors into the substrate. Due to the height limitation of passive components, it is difficult to truly achieve thin and small design and meet the demand for thinness. Among all passive devices, capacitors are the most numerous and are particularly concerned. In order to obtain high-value embedded capacitors, the dielectric material needs to have high capacitance value, high voltage strength, high peeling strength between the electrode of the substrate, and excellent heat resistance. As is known to all, as embedded capacitors, the dielectric layer needs to have thin thickness and high dielectric constant, and the dielectric constant depends on the addition of high dielectric filler. High amount of filler has certain negative effects on the dielectric layer, such as reducing the peeling strength between the metal electrode, and the material becomes brittle, etc. Especially when the dielectric layer is designed to be thinner, the shortcomings are more obvious.

[0004] Taiwanese patent TW203677B describes a method for manufacturing an internal capacitor, using two conductive foils and a dielectric layer therebetween, and applying heat and pressure treatment to become a circuit board, but the patent does not mention what material is used as the dielectric layer, and the lines on the dielectric layer need to be etched into a line pattern before the lamination of the multi-layer board, which is more wasteful in wiring area, and is not suitable for manufacturing multi-layer printed circuit boards with low line width, line spacing and embedded blind holes.

[0005] US Patent 5796587A discloses a method for embedding capacitors in a circuit board. The method uses a mixture of 85% by weight barium titanate powder and epoxy resin. This material is applied to pre-drilled conductors, then gradually stacked and laminated to create a circuit board with embedded capacitors. This method has a limitation: the ceramic powder (barium titanate) requires high-temperature (1300°C) or low-temperature (750°C) co-sintering to achieve a high dielectric constant. It is not suitable for use in printed circuit boards (processing temperatures not exceeding 250°C). Furthermore, adding a high proportion of ceramic powder to increase the dielectric constant can easily make the material brittle and prone to cracking, making it unsuitable for use in printed circuit boards, especially flexible circuit boards. Summary of the Invention

[0006] The main objective of this invention is to provide a cover film composition, cover film, embedded capacitor, circuit board, and preparation method thereof for use with embedded capacitors, so as to solve the problems of large thickness, poor dielectric properties, and high manufacturing cost of embedded capacitors in printed circuit boards in the prior art.

[0007] To achieve the above objectives, according to one aspect of the present invention, a cover film composition for use in embedded capacitors is provided, comprising, by weight, 30 to 70 parts of a host resin, 5 to 25 parts of an epoxy resin, 10 to 50 parts of an inorganic filler and 10 to 30 parts of a flame retardant.

[0008] Further, by weight, the cover film composition comprises: 55-60 parts of a base resin, 5-10 parts of an epoxy resin, 10-20 parts of an inorganic filler, and 15-25 parts of a flame retardant.

[0009] Further, the main resin includes one or more of polyimide resin, polyester resin and polybutadiene; and / or the epoxy resin is one or more of difunctional epoxy resin, trifunctional epoxy resin and tetrafunctional epoxy resin; preferably, the epoxy equivalent of the epoxy resin is 100 to 300 g / eq; more preferably, the epoxy resin is a tetrafunctional epoxy resin.

[0010] Further, the inorganic filler includes ceramic filler; optionally, the inorganic filler also includes other fillers, including one or more of carbon black, carbon nanotubes, metals and metal oxides; preferably, the ceramic filler is one or more of barium titanate, strontium titanate, barium strontium titanate, barium calcium titanate and lead zirconium titanate, more preferably barium titanate and / or strontium titanate; more preferably, the D50 of the ceramic filler is 0.80 to 1.50 μm; even more preferably, the inorganic filler is further surface-treated by a coupling agent, the coupling agent being a silane coupling agent and / or a titanate ester coupling agent.

[0011] Further, the flame retardant is a phosphorus-based flame retardant and / or a metal compound flame retardant; preferably, the phosphorus-based flame retardant is one or more of bisphenol biphenyl phosphate, ammonium polyphosphate, hydroquinone-bis-(biphenyl phosphate), potassium phosphite, sodium phosphite and diethyl aluminum phosphate; preferably, the metal compound flame retardant is a metal oxide and / or a metal hydroxide, the metal oxide is antimony trioxide, and the metal hydroxide is aluminum hydroxide and / or magnesium hydroxide; more preferably, the average particle size of the metal oxide is 1 to 5 μm.

[0012] According to another aspect of the present invention, a cover film is provided, comprising a single-layer cover film, a release film disposed on one surface of the single-layer cover film, and a release paper disposed on the other surface of the single-layer cover film; wherein the single-layer cover film is made from the cover film composition of the present invention described above.

[0013] Further, the adhesion between the release film and the single-layer cover film is 700-1100 mN / 25 mm, and the adhesion between the release paper and the single-layer cover film is 250-600 mN / 25 mm; preferably, the adhesion between the release film and the single-layer cover film is 800-1000 mN / 25 mm, and the adhesion between the release paper and the single-layer cover film is 250-500 mN / 25 mm.

[0014] According to another aspect of the present invention, an embedded capacitor is provided, comprising electrodes and a capacitor dielectric, wherein the capacitor dielectric comprises the cover film described above in the present invention.

[0015] According to another aspect of the present invention, a circuit board is provided having at least one embedded capacitor as described above.

[0016] According to another aspect of the present invention, a method for manufacturing the circuit board described above is provided, comprising the following steps:

[0017] Step S1: Take a copper-clad laminate, which includes a substrate layer and a copper foil layer; etch the copper foil layer into a circuit pattern to form a circuit layer; the circuit layer has a first electrode and a second electrode, and the first electrode and the second electrode are parallel to each other; Step S2: Fill a cover film between the first electrode and the second electrode, the upper surface of the cover film is flush with the upper surfaces of the first electrode and the second electrode, and the first electrode, the second electrode and the cover film together form an embedded capacitor R; Step S3: Fill and cover the part of the copper-clad laminate in the circuit layer except for the embedded capacitor R and the functional part with a solder resist film to obtain a circuit board; the functional part includes a soldering part.

[0018] In the capping film composition of this invention, the main resin material provides dielectric / low-loss properties, and the addition of epoxy resin enables the capping film composition to form a cross-linked network structure after curing, improving structural stability and breakdown voltage resistance. The high dielectric constant inorganic filler further enhances the overall dielectric value, while the addition of flame retardants improves the flame retardancy of the composition. This invention, through the synergistic effect of a few components in specific proportions, allows each component to not only fully exert its own function but also achieve a synergistic effect, resulting in a capping film with excellent high dielectric constant Dk and low dielectric loss Df characteristics, suitable for embedded capacitor design in passive devices.

[0019] The capping film composition of this invention achieves a high dielectric constant / low loss electrical design through the design of the resin composition and the optimal addition of inorganic fillers, and has good adhesion. When applied to the circuit design of flexible circuit boards, it can be directly adhered to the copper circuit layer using traditional fast pressing methods, without the need for additional adhesive layers to bond with the circuit board, thereby effectively reducing the thickness of the circuit board. In addition to protecting the metal circuits, the high dielectric capping film of this invention can also be used to form an embedded capacitor by attaching a single layer of high dielectric / low loss capping film between the parallel electrodes of the circuit board through the design of the circuit board's endpoint electrodes, without the need for additional embedded passive components. This can significantly reduce the overall thickness of the circuit board, reduce manufacturing costs, and improve the overall circuit board manufacturing yield, making it suitable for increasingly miniaturized electronic product designs. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 A schematic diagram of a sandwich structure of a cover film according to an embodiment of the present invention is shown;

[0022] Figure 2 A flowchart of circuit board fabrication according to an embodiment of the present invention is shown; and

[0023] Figure 3 A circuit board structure diagram according to an embodiment of the present invention is shown.

[0024] The above figures include the following reference numerals:

[0025] 1. Release film; 2. Single-layer cover film; 3. Release paper; 4. Embedded capacitor; 100. Substrate layer; 101. First copper foil layer; 102. Second copper foil layer; 201. First circuit layer; 202. Second circuit layer; 203. First electrode; 204. Second electrode; 30. Single-layer cover film; 40. Solder resist film. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] As described in the background section of this invention, existing technologies suffer from problems such as large thickness, poor dielectric properties, and high manufacturing costs of embedded capacitors in printed circuit boards. To address these issues, in a typical embodiment of this invention, a cover film composition for embedded capacitors is provided. By weight, the cover film composition comprises: 30-70 parts of a base resin, 5-25 parts of epoxy resin, 10-50 parts of inorganic filler, and 10-30 parts of flame retardant. The base resin is any resin other than epoxy resin.

[0028] In the capping film composition of this invention, the main resin material provides dielectric / low-loss properties, and the addition of epoxy resin enables the capping film composition to form a cross-linked network structure after curing, improving structural stability and breakdown voltage resistance. The high dielectric constant inorganic filler further enhances the overall dielectric value, while the addition of flame retardants improves the flame retardancy of the composition. This invention, through the synergistic effect of a few components in specific proportions, allows each component to not only fully exert its own function but also achieve a synergistic effect, resulting in a capping film with excellent high dielectric constant Dk and low dielectric loss Df characteristics, suitable for embedded capacitor design in passive devices.

[0029] The capping film composition of this invention achieves a high dielectric constant / low loss electrical design through the design of the resin composition and the optimal addition of inorganic fillers, and has good adhesion. When applied to the circuit design of flexible circuit boards, it can be directly adhered to the copper circuit layer using traditional fast pressing methods, without the need for additional adhesive layers to bond with the circuit board, thereby effectively reducing the thickness of the capping film on the circuit board. In addition to protecting the metal circuits, the high dielectric capping film of this invention can also be used to form an embedded capacitor by attaching a single layer of high dielectric / low loss capping film between the parallel electrodes of the circuit board through the design of the circuit board's endpoint electrodes, without the need for additional embedded passive components. This can significantly reduce the overall thickness of the circuit board, reduce manufacturing costs, and improve the overall circuit board manufacturing yield, making it suitable for the increasingly miniaturized electronic product design.

[0030] To further improve the overall performance of the composition, in a preferred embodiment, the cover film composition comprises, by weight, 55-60 parts of a base resin, 5-10 parts of an epoxy resin, 10-20 parts of an inorganic filler, and 15-25 parts of a flame retardant. Specifically, when the base resin is in the above-mentioned weight proportions, the cover film composition exhibits better dielectric properties and peel strength; when the curing agent is in the above-mentioned weight proportions, the cover film composition exhibits better structural stability, puncture resistance, and peel strength; when the inorganic filler is in the above-mentioned weight proportions, the cover film composition exhibits better dielectric properties; when the flame retardant is in the above-mentioned weight proportions, the cover film composition exhibits better flame resistance; and when the inorganic filler, flame retardant, and curing agent are all in the above-mentioned weight proportions, the cover film composition exhibits better bending properties.

[0031] In a preferred embodiment, the host resin comprises one or more of polyimide resin, polyester resin, and polybutadiene. The aforementioned host resin material can provide better dielectric / low-loss properties and also has better flame retardant properties. Preferably, the host resin is a polyimide resin, which can provide a lower dielectric constant (Df) and, being a polyimide host structure, has even more superior flame retardant properties.

[0032] For example, polyimide resins such as PI-315B and PI-380G manufactured by Jin Yi Chemical, PIAD manufactured by Arakawa Chemical, and P260 manufactured by Ube Industries, Japan can be used; polyester resins such as TOYOBO, BX-39SS, and UR-3500 can be used; and polybutadiene such as polybd hydroxyl-terminated polybutadiene manufactured by Sartomer and NA-5400-10MA manufactured by Struktol can be used.

[0033] As mentioned above, the main function of epoxy resin in the cover film composition is to form an effective cross-linked network structure with a high cross-linking density with the host resin, thereby improving the heat resistance and breakdown voltage of the composition. Simultaneously, the selection of epoxy resin also needs to consider the adhesiveness of the composition. Therefore, in a preferred embodiment, the epoxy resin is one or more of difunctional, trifunctional, and tetrafunctional epoxy resins, where difunctional, trifunctional, and tetrafunctional refer to the number of epoxy end groups. Preferably, the epoxy equivalent of the epoxy resin is 100–300 g / eq; more preferably, the epoxy resin is a tetrafunctional epoxy resin.

[0034] As an example, a bifunctional epoxy resin can have the following structure, where n is a non-zero integer:

[0035]

[0036] As an example, trifunctional epoxy resins can have the following structure, where n is 1:

[0037]

[0038] For example, tetrafunctional epoxy resins can have the following structures:

[0039]

[0040] As a further example, difunctional epoxy resins can use the CNE200 series manufactured by Changchun Company, trifunctional epoxy resins can use the TFE2000 series manufactured by Changchun Company and the TPNE5501 series manufactured by Jiashengde Materials, and tetrafunctional epoxy resins can use the TNE190A70 series manufactured by Changchun Company and the JD919 series products manufactured by Jiashengde Materials.

[0041] In a preferred embodiment, the inorganic filler includes ceramic filler; the cover film composition of the present invention is mainly used in embedded capacitors and requires excellent dielectric properties, therefore ceramic filler with a large dielectric constant is a necessary filler; in addition to ceramic filler, for requirements such as color and mechanical properties, the inorganic filler may optionally include other fillers, including one or more of ceramic filler, carbon black, carbon nanotubes, metals and metal oxides.

[0042] Preferably, the ceramic filler is one or more of barium titanate, strontium titanate, barium strontium titanate, barium percalotitanate, and lead zirconium titanate, more preferably barium titanate and / or strontium titanate; the above-mentioned ceramic fillers have higher dielectric strength and dielectric constant, and can be more uniformly dispersed in the resin composition. In order to reduce the impact of increased leakage current that may be caused by excessively large particle size, preferably, the D50 of the ceramic filler is 0.80 to 1.50 μm; most preferably, electronic grade barium titanate is used as a high dielectric inorganic filler with a particle size distribution D50 of 0.80 to 1.50 μm.

[0043] To further enhance the wetting effect between the inorganic filler and the resin, preferably, the inorganic filler is also surface-treated with a coupling agent, which is a silane coupling agent and / or a titanate coupling agent.

[0044] Flame retardants are used to provide flame retardancy when the composition is applied to a circuit board. Commonly used flame retardants in circuit boards in the prior art can all be considered for application in this invention. To further improve the overall flame retardancy of the cover film composition while maintaining good Df value and adhesive strength, in a preferred embodiment, the flame retardant is a phosphorus-based flame retardant and / or a metal compound flame retardant. Preferably, the phosphorus-based flame retardant is one or more of bisphenol biphenyl phosphate, ammonium polyphosphate, hydroquinone-bis-(biphenyl phosphate), potassium phosphite, sodium phosphite, and diethylaluminum phosphate. Preferably, the metal compound flame retardant is a metal oxide and / or a metal hydroxide, where the metal oxide is antimony trioxide and the metal hydroxide is aluminum hydroxide and / or magnesium hydroxide. More preferably, the average particle size of the metal oxide is 1–5 μm.

[0045] In another typical embodiment of the present invention, a cover film is also provided, comprising a single-layer cover film, a release film disposed on one surface of the single-layer cover film, and a release paper disposed on the other surface of the single-layer cover film; wherein the single-layer cover film is made from the cover film composition of the present invention. The above-mentioned cover film has the advantages of being lightweight, thin, short, and small, making it suitable for application in the increasingly miniaturized design of electronic products.

[0046] Specifically, the main resin, inorganic filler, and flame retardant are first mixed, stirred, and ball-milled to disperse them, obtaining a mixed solution. Then, epoxy resin is added and stirred to obtain a colloid of the cover film composition. The viscosity of the prepared colloid is controlled at 1500–2500 cps, and the solid content is controlled at 45–55%. The prepared colloid is then coated onto a release film, dried, and heated to remove the solvent, resulting in a single-layer cover film. Release paper is then attached to the surface of the formed single-layer cover film, and hot-pressed to form a well-protected single-layer high-dielectric / low-loss cover film stack for later use.

[0047] The aforementioned release film is primarily composed of polyethylene terephthalate (PET), providing a coating carrier for the composition used as a single-layer cover film. After the composition is coated, release paper is applied to the surface to prevent contamination or damage from the external environment. This single-layer high-dielectric / low-loss cover film product has a sandwich structure consisting of a release film, a single-layer cover film, and release paper. During use, the release paper must first be removed, then the single-layer high-dielectric / low-loss cover film is adhered to the copper wiring layer and pressed together, followed by heat curing. Finally, the release film is removed, thus achieving the transfer of the single-layer high-dielectric / low-loss cover film.

[0048] Given the usage process, the matching of release forces between the release paper and the release film is even more important. The release force of the release paper needs to be light, and the release force of the release film needs to be heavy. In a preferred embodiment, the adhesion force between the release film and the single-layer cover film is 700-1100 mN / 25 mm, and the adhesion force between the release paper and the single-layer cover film is 250-600 mN / 25 mm; preferably, the adhesion force between the release film and the single-layer cover film is 800-1000 mN / 25 mm, and the adhesion force between the release paper and the single-layer cover film is 250-500 mN / 25 mm.

[0049] During their research, the inventors unexpectedly discovered that when the release force of the release paper exceeds 600mN / 25mm, the cover film composition easily transfers to the release paper when it is peeled off, a phenomenon known as adhesive tearing, causing inconvenience in use. If the release force of the release paper is too light, it cannot adhere smoothly to the single-layer cover film, causing it to detach and failing to achieve a protective effect. When the release force of the release film is below 700mN / 25mm, adhesive tearing also easily occurs when the release paper is peeled off. When the release force exceeds 1100mN / 25mm, the cover film composition, after curing, cannot be smoothly transferred to the circuitry of the printed circuit board.

[0050] The release film thickness is 25–50 μm, preferably 38–50 μm, to facilitate the coating of the cover film composition. The release paper thickness is 90–120 μm, preferably 110–120 μm. Since the cover film provided by this invention is a single-layer design, it has a thinner advantage than the traditional double-layer structure. However, the thinness advantage can also easily cause insufficient stiffness when the cover film is used to create windows or punches on the flexible circuit board, making the process difficult. Therefore, by designing the release paper thickness, the problem of insufficient stiffness in window punching can be further improved.

[0051] In another typical embodiment of the present invention, an embedded capacitor is also provided, including electrodes and a capacitor dielectric, wherein the capacitor dielectric includes the covering film described above.

[0052] As described above, in addition to protecting the metal circuits, the high-dielectric cover film of the present invention can also form an embedded capacitor by attaching a single layer of high-dielectric / low-loss cover film between the parallel electrodes of the circuit board through the terminal electrode design of the circuit board, without the need to embed other passive components. This can significantly reduce the overall thickness of the circuit board, reduce manufacturing costs, and improve the overall circuit board manufacturing yield, making it suitable for applications in the increasingly miniaturized electronic product design.

[0053] In yet another typical embodiment of the present invention, a circuit board is also provided having at least one embedded capacitor as described above.

[0054] In another typical embodiment of the present invention, a method for preparing the above-mentioned circuit board is also provided, comprising the following steps: Step S1, taking a copper-clad laminate, the copper-clad laminate comprising a substrate layer and a copper foil layer; etching the copper foil layer into a circuit pattern to form a circuit layer; the circuit layer having a first electrode and a second electrode, the first electrode and the second electrode being parallel to each other; Step S2, filling a cover film between the first electrode and the second electrode, the upper surface of the cover film being flush with the upper surfaces of the first electrode and the second electrode, the first electrode, the second electrode and the cover film together forming an embedded capacitor R; Step S3, filling and covering the portion of the copper-clad laminate in the circuit layer excluding the embedded capacitor R and the functional part with a solder resist film to obtain a circuit board; the functional part includes a soldering part.

[0055] First, a copper-clad laminate is taken. According to the required circuitry, the copper foil layer is etched into a circuit pattern to form a circuit layer. The circuit layer has at least two parallel electrode endpoints, serving as the first electrode and the second electrode, respectively. Then, a cover film is attached and filled between the first and second electrodes. The first electrode, the second electrode, and the cover film together form an embedded capacitor R. Finally, according to the circuitry, a windowed solder resist film is attached to the circuitry to form the final product circuit board. In this invention, the cover film serves as both a protective layer and, together with the electrodes on both sides, as an embedded capacitor. This significantly reduces the thickness of the circuit board, conforming to the trend of lighter and thinner electronic products. Furthermore, it allows for the use of less material and simpler process steps, greatly reducing the production cost of the circuit board. The solder resist cover film can be any conventional cover film in the art; those skilled in the art can choose according to their needs, which will not be elaborated further here.

[0056] It should be noted that the copper-clad laminate described above can be either single-sided or double-sided. As long as it has a substrate layer and a copper foil layer, and the copper foil layer is etched into a circuit pattern to form a structure resembling two parallel electrodes, with the cover film described above in this invention in the middle, the effect of embedded capacitors can be achieved. The copper-clad laminate described above can be either flexible or rigid.

[0057] When the aforementioned copper-clad laminate is a flexible double-sided laminate, its preparation method can be as follows: (e.g.) Figure 2 As shown, firstly, a flexible copper-clad double-sided board is taken, which includes a substrate layer 100, a first copper foil layer 101, and a second copper foil layer 102. According to the required circuit, the first copper foil layer 101 and the second copper foil layer 102 are etched into circuit patterns to form a first circuit layer 201 and a second circuit layer 202, respectively. The first circuit layer 201 has at least two parallel electrode endpoints, which serve as the first electrode 203 and the second electrode 204, respectively. Then, a single-layer cover film 30 is attached and filled between the first electrode 203 and the second electrode 204. The first electrode 203, the second electrode 204, and the single-layer cover film 30 together form an embedded capacitor R. Finally, according to the circuit, the windowed solder mask 40 is attached to the circuit to form the final product, a flexible circuit board.

[0058] Typical, but not limiting, components of the covering film composition include, among which, the main resin is 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, or any two of these ranges; the epoxy resin is 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, or any two of these ranges; the inorganic filler is 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, or any two of these ranges; and the flame retardant is 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, or any two of these ranges.

[0059] Typical, but not limiting, adhesive strengths of release film and single-layer cover film are 700mN / 25mm, 750mN / 25mm, 800mN / 25mm, 850mN / 25mm, 900mN / 25mm, 950mN / 25mm, 1000mN / 25mm, 1050mN / 25mm, 1100mN / 25mm, or boundary values ​​consisting of any two of these ranges; adhesive strengths of release paper and single-layer cover film are 250mN / 25mm, 300mN / 25mm, 350mN / 25mm, 400mN / 25mm, 450mN / 25mm, 500mN / 25mm, 550mN / 25mm, 600mN / 25mm, or boundary values ​​consisting of any two of these ranges.

[0060] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0061] Preparation of glue solution for single-layer cover film

[0062] Example 1

[0063] The measured main resin (PI-380G, 30 parts by weight), inorganic filler (barium titanate, 50 parts by weight), and flame retardant (OP-935, 5 parts by weight; H-42M, 5 parts by weight) were added to a container equipped with a stirrer and stirred to dissolve at room temperature. Then, the mixture was dispersed by ball milling. After ball milling and dispersion, the mixed solution was removed, and epoxy resin (JD-919, 10 parts by weight) was added. The mixture was stirred again for approximately 2.0 hours to obtain the final coating film composition colloid. The viscosity of the prepared colloid was controlled at 1500–2500 cps, and the final solids content was controlled at 45–55%.

[0064] Examples 2 to 8

[0065] The difference between Examples 2 to 8 and Example 1 is that the composition of the covering film is different, as detailed in Table 1.

[0066] Comparative Examples 1 to 6

[0067] The difference between Comparative Examples 1 to 6 and Example 1 is that the composition of the covering film is different, as detailed in Table 1.

[0068] Table 1

[0069]

[0070]

[0071] PI-380G: Polyimide resin, Jin Yi Chemical

[0072] BX-39SS: Polyester resin, Toyobo, Japan.

[0073] CNE-200: Bifunctional epoxy resin, Changchun Chemical Industry, epoxy equivalent 198g / eq

[0074] TPNE5501: Trifunctional epoxy resin, Jiashengde Materials, epoxy equivalent 171g / eq

[0075] JD919: Tetrafunctional epoxy resin, manufactured by Jiasheng Materials, epoxy equivalent 110g / eq

[0076] HPBT-04C: Barium titanate, Hubei Tianci, D50 is 0.8~1.5μm

[0077] OP-935: Diethylaluminum phosphate, Klein Chemical Company

[0078] H-42M: Aluminum hydroxide, Showa Chemical Industry

[0079] Cover film production

[0080] Covering membrane structure such as Figure 1 As shown. The cover film compositions of the above examples and comparative examples were colloidally coated onto a release film (the adhesion strength of the single-layer cover film formed with the cover film composition was 1000 mN / 25 mm). After drying and desolventizing at 120°C for about 20 minutes, a single-layer film material with a solvent residue rate of ≤1% was obtained on the release film, and the thickness of the single-layer cover film was 10 μm. Then, release paper (the adhesion strength of the single-layer cover film formed with the cover film composition was 300 mN / 25 mm) was attached to the single-layer film material, and the film was pressed at 70-85°C to form the cover film to be used. The performance test results of the cover films of the above examples and comparative examples are shown in Tables 2 and 3.

[0081] Example 9

[0082] The difference between Example 9 and Example 1 is that the adhesion of the single-layer cover film formed by the release film and cover film composition is 700mN / 25mm, and the adhesion of the single-layer cover film formed by the release paper and cover film composition is 250mN / 25mm. There is no adhesive tearing phenomenon, and the single-layer cover film formed by the cover film composition can be smoothly transferred to the circuit of the printed circuit board.

[0083] Example 10

[0084] The difference between Example 10 and Example 1 is that the adhesion of the single-layer cover film formed by the release film and cover film composition is 800mN / 25mm, and the adhesion of the single-layer cover film formed by the release paper and cover film composition is 250mN / 25mm. There is no adhesive tearing phenomenon, and the single-layer cover film formed by the cover film composition can be smoothly transferred to the circuit of the printed circuit board.

[0085] Example 11

[0086] The difference between Example 11 and Example 1 is that the adhesion of the single-layer cover film formed by the release film and cover film composition is 1000mN / 25mm, and the adhesion of the single-layer cover film formed by the release paper and cover film composition is 500mN / 25mm. There is no adhesive tearing phenomenon, and the single-layer cover film formed by the cover film composition can be smoothly transferred to the circuit of the printed circuit board.

[0087] Example 12

[0088] The difference between Example 12 and Example 1 is that the adhesion of the single-layer cover film formed by the release film and cover film composition is 1100mN / 25mm, and the adhesion of the single-layer cover film formed by the release paper and cover film composition is 600mN / 25mm. There is no adhesive tearing phenomenon, and the single-layer cover film formed by the cover film composition can be smoothly transferred to the circuit of the printed circuit board.

[0089] Comparative Example 7

[0090] The difference between Comparative Example 7 and Example 1 is that the adhesive strength of the single-layer cover film formed by the release film and cover film composition is 600mN / 25mm, while the adhesive strength of the single-layer cover film formed by the release paper and cover film composition is 200mN / 25mm, resulting in adhesive tearing. The single-layer cover film formed by the cover film composition can be successfully transferred to the circuit of the printed circuit board.

[0091] Comparative Example 8

[0092] The difference between Comparative Example 8 and Example 1 is that the adhesive strength of the single-layer cover film formed by the release film and cover film composition is 1200mN / 25mm, while the adhesive strength of the single-layer cover film formed by the release paper and cover film composition is 700mN / 25mm, resulting in adhesive tearing. The single-layer cover film formed by the cover film composition can be successfully transferred to the circuit of the printed circuit board.

[0093] Evaluation method

[0094] 1. Measurement of dielectric constant (Dk) and dielectric loss (Df)

[0095] The capping films obtained in the examples and comparative examples were dried at 150°C for 30 min, and the dielectric constant and dielectric loss of each composite dielectric layer were measured using a resonator (Agilent E5071BENA) by the Split Dielectric Resonator (SPDR) method at 25°C and RH 50%.

[0096] 2. Peel strength

[0097] The peel strength referred to here is tested by attaching a single-layer cover film to a copper substrate to measure its peel strength against the copper substrate. First, the single-layer cover film is attached to the copper substrate using a thermo-pressing method, and then cured at 185°C for 2 hours to obtain a test piece. Next, the test piece is cut into test strips 1 cm wide and 10 cm long. These test strips are then pulled at a speed of 50 mm / min in a 180-degree direction to measure the tensile force resisted when the single-layer cover film peels off from the substrate.

[0098] 3. Solder solder heat resistance

[0099] Refer to IPC-TM650.2.6.8 standard. The sample preparation method is the same as the peel strength test specimen. The sample is cut into 5 cm × 5 cm pieces, and then immersed in a solder bath at 288°C for 30 seconds. After removing the specimen, observe whether there are phenomena such as blistering, discoloration, floating and peeling on the surface. Evaluate the changes in appearance according to the following criteria.

[0100] ○: No delamination and no discoloration.

[0101] ×: Delamination and discoloration.

[0102] 4. Flame resistance

[0103] The flame retardancy referred to here is based on the UL-94VTM-0 standard. Specifically, a single-layer cover film is subjected to two 10-second burning tests. If the flame extinguishes within 10 seconds and no burning material falls, the flame retardancy is considered good. Conversely, if it fails to extinguish within 10 seconds, the flame retardancy is considered poor. The specific evaluation criteria are as follows:

[0104] ○: The flame extinguishes within 10 seconds without any burning material falling, indicating excellent flame retardancy.

[0105] ×: The flame did not extinguish within 10 seconds, or burning material fell, indicating poor flame resistance.

[0106] 5. Breakdown voltage

[0107] The single-layer cover film sample was cut into 10×10cm sizes and cured at 150℃ for two hours to obtain the breakdown voltage test sample. The voltage was increased using a pulse voltage generator (EMCSOSIN, WVT255) until the voltage reached the breakdown voltage, which caused a short circuit on the surface of the single-layer cover film. This voltage is the maximum withstand breakdown voltage.

[0108] 6. Bending ability

[0109] A single-layer cover film was hot-pressed onto a copper substrate, similar to the method used for peel strength test pieces. The test pieces were then cut to 30mm x 5mm sizes. The MIT method was followed, using a grooved film flexural fatigue testing machine (model: 549) manufactured by Toyo Seiki Co., Ltd. as the MIT flexural fatigue testing device. The test pieces were repeatedly bent with a bending radius of 0.38mm and a load of 500g until the circuit could no longer conduct. A higher number of bends indicates better flexural strength.

[0110] Table 2

[0111]

[0112]

[0113] Table 3

[0114]

[0115] Tables 2 and 3 compare the characteristics of single-layer cover films under different formulation ratios. The film thickness of the examples and comparative examples is 10 μm. It can be seen that, according to the composition and ratio of the present invention, the high-dielectric / low-loss cover films in each example have a dielectric constant between 4.5 and 11.2, and a Df loss value between 0.0025 and 0.0065, exhibiting high dielectric and low-loss electrical properties. The peel strength to copper is at least over 0.70 N / cm, and the heat resistance and flame retardancy meet the specifications. The flexibility (at least 4000 cycles in the MIT test) is excellent, meeting the requirements for cover films used in flexible circuit boards.

[0116] The main resin content of Comparative Examples 1-3 exceeded the proportion of the present invention. Comparative Example 1 showed a significant increase in Df (displacement factor), and its peel strength was less than 0.7 N / cm. Comparative Example 2 had a main resin content exceeding 70 parts by weight, with reduced epoxy resin and barium titanate content, resulting in significantly worse overall properties, especially a decrease in Dk (displacement factor) to 3.3. This prevented the formation of an effective cross-linked network structure, thus affecting heat resistance, flame retardancy, and breakdown voltage. Comparative Example 3 showed a significant increase in Df, with excessive barium titanate content, resulting in poor flexibility. Comparative Example 4 had an epoxy resin content exceeding the proportion of the present invention, primarily affecting the degree of cross-linking of the main component, thereby impacting the material's flexibility. Comparative Examples 5 and 6 had flame retardant proportions exceeding the proportion of the present invention. Comparative Example 5 had an excessively low flame retardant content, resulting in poor flame retardancy and a low breakdown voltage. Comparative Example 6 had an excessively high content of flame retardant. Although it had good flame retardant performance, the amount of H-42M also affected the overall material Df value, causing Df to exceed the range. Furthermore, the excessive powder addition affected the adhesion strength between the cover film and the copper foil.

[0117] Single-layer cover film as embedded capacitor for flexible circuit board

[0118] A flexible copper-clad double-sided board is taken, which includes a substrate layer 100, a first copper foil layer 101 and a second copper foil layer 102. According to the required circuit, the first copper foil layer 101 and the second copper foil layer 102 are etched into circuit patterns to form a first circuit layer 201 and a second circuit layer 202, respectively. The first circuit layer 201 has at least two parallel electrode endpoints, which serve as the first electrode 203 and the second electrode 204, respectively. Then, a single-layer cover film 30 is attached and filled between the first electrode 203 and the second electrode 204. The first electrode 203, the second electrode 204 and the single-layer cover film 30 together form an embedded capacitor R. Finally, according to the circuit, the windowed solder resist film 40 is attached to the surface to form the final product, a flexible circuit board.

[0119] The fabrication process of a flexible circuit board with a single-layer cover film as an embedded capacitor is described in [link to documentation]. Figure 2 S1 represents the circuit pattern, S2 represents the lamination of the single-layer cover film, and S3 represents the lamination of the solder resist film. A diagram of the flexible circuit board structure using the single-layer cover film as an embedded capacitor is shown below. Figure 3 .

[0120] As can be seen from the above, traditional PCB embedding technology directly embeds passive components into the PCB. However, the size and height of the embedded passive components limit the achievement of a thin and compact design. The high-dielectric / low-loss cover film of this invention can be directly applied to the circuit protection of flexible circuit boards. Furthermore, due to its single-layer high-dielectric properties, it can directly form a capacitor assembly between the two electrodes in the circuit, achieving embedded components and a thin design. In this invention, the two electrodes of the embedded capacitor are co-constructed by the circuit, eliminating the need for additional embedded passive components. The use of a single-layer high-dielectric / low-loss cover film as the high-dielectric material to form the capacitor assembly significantly reduces the circuit board thickness. Moreover, the combination of an etching process and a single-layer high-dielectric / low-loss cover film reduces the manufacturing cost of flexible circuit boards.

[0121] As can be seen from the above, compared with the comparative examples, the cover film compositions of the various embodiments of the present invention achieve a high dielectric constant / low loss electrical design through the design of the resin composition and the optimal addition of inorganic fillers, and have good adhesion. When applied to the circuit design of flexible circuit boards, they can be directly adhered to the copper circuit layer using the traditional fast pressing method, without the need for additional adhesive layers to bond with the circuit board, thereby effectively reducing the circuit board thickness of the cover film. In addition to protecting the metal circuits, the high dielectric cover film of the present invention can also form an embedded capacitor by attaching a single layer of high dielectric / low loss cover film between the parallel electrodes of the circuit board through the design of the terminal electrodes of the circuit board, without the need for additional embedded passive components. This can significantly reduce the overall thickness of the circuit board, reduce manufacturing costs, and improve the overall circuit board manufacturing yield, making it suitable for the increasingly miniaturized electronic product design. Furthermore, it can be seen that the material performance is better when all parameters are within the preferred range of the present invention.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An embedded capacitor, comprising electrodes and a capacitor dielectric, characterized in that, The capacitor dielectric includes a single-layer cover film, wherein the single-layer cover film is made from a cover film composition, which, by weight, includes: 30-70 parts of a main resin, 5-10 parts of an epoxy resin, 10-50 parts of an inorganic filler and 10-30 parts of a flame retardant. The main resin is polyimide resin and / or polyester resin; The epoxy resin is one or more of difunctional epoxy resin, trifunctional epoxy resin, and tetrafunctional epoxy resin. The inorganic filler includes ceramic filler; the ceramic filler is one or more of barium titanate, strontium titanate, barium strontium titanate, barium percalotitanate, and lead zirconium titanate. The flame retardant is a phosphorus-based flame retardant and / or a flame retardant containing a metal compound.

2. The embedded capacitor according to claim 1, characterized in that, The cover film composition comprises, by weight, 55-60 parts of the main resin, 5-10 parts of the epoxy resin, 10-20 parts of the inorganic filler and 15-25 parts of the flame retardant.

3. The embedded capacitor according to claim 1, characterized in that, The epoxy equivalent of the epoxy resin is 100~300g / eq.

4. The embedded capacitor according to claim 1, characterized in that, The epoxy resin is a tetrafunctional epoxy resin.

5. The embedded capacitor according to claim 1 or 2, characterized in that, The inorganic filler also includes other fillers, including one or more of carbon black, carbon nanotubes, metals, and metal oxides.

6. The embedded capacitor according to claim 5, characterized in that, The ceramic filler has a D50 of 0.80~1.50 μm.

7. The embedded capacitor according to claim 6, characterized in that, The inorganic filler is further surface-treated with a coupling agent, which is a silane coupling agent and / or a titanate coupling agent.

8. The embedded capacitor according to claim 1, characterized in that, The phosphorus-based flame retardant is one or more of bisphenol biphenyl phosphate, ammonium polyphosphate, hydroquinone-bis-(biphenyl phosphate), potassium phosphite, sodium phosphite, and diethylaluminum phosphate; The metal-containing flame retardant is a metal oxide and / or a metal hydroxide, wherein the metal oxide is antimony trioxide and the metal hydroxide is aluminum hydroxide and / or magnesium hydroxide.

9. The embedded capacitor according to claim 8, characterized in that, The average particle size of the metal oxide is 1~5μm.

10. A circuit board, characterized in that, It has at least one embedded capacitor as described in any one of claims 1 to 9.

11. A method for manufacturing a circuit board according to claim 10, characterized in that, Includes the following steps: Step S1: Take a copper-clad laminate, the copper-clad laminate comprising a substrate layer and a copper foil layer; etch the copper foil layer into a circuit pattern to form a circuit layer; the circuit layer has a first electrode and a second electrode, and the first electrode and the second electrode are parallel to each other; Step S2: A single-layer cover film is filled between the first electrode and the second electrode. The upper surface of the single-layer cover film is flush with the upper surfaces of the first electrode and the second electrode. The first electrode, the second electrode, and the single-layer cover film together form an embedded capacitor. Step S3: Fill and cover the copper-clad laminate in the circuit layer except for the embedded capacitor R and the functional part with solder mask to obtain the circuit board; the functional part includes the solder part.

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