Method for manufacturing low esr thin film capacitor

Abstract

The application discloses a low-ESR thin film capacitor and a preparation method thereof. The low-ESR thin film capacitor comprises a shell, a core arranged in the shell, and a lead-out electrode. The core is at least wound by a metalized film. The metalized film comprises a base film and a first metal layer arranged on the surface of the base film. The first metal layer comprises an edge region and a center region. The thickness of the edge region is greater than that of the center region. The base film comprises a plurality of primary microstructures and a plurality of secondary microstructures. The size of the secondary microstructure is smaller than that of the primary microstructure. The primary microstructure comprises a protrusion or a groove. The secondary microstructure comprises a protrusion or a groove. The first end of the lead-out electrode is connected with the core. The edge region with the highest current density has a lower ohmic resistance due to the thicker metal layer, thereby significantly reducing the overall ESR of the whole capacitor. While reducing the ESR, the capacitor can also have a certain self-healing ability.

Description

Technical Field

[0001] This application relates to the field of capacitor manufacturing, specifically to a method for preparing a low ESR thin-film capacitor. Background Technology

[0002] Thin-film capacitors are widely used in inverters, charging piles, and other equipment due to their good high-frequency characteristics and high voltage withstand capability. However, under high-frequency and high-current operating conditions, their ESR (equivalent series resistance) leads to increased power loss (P=I²×ESR), generates a large amount of heat, and affects service life and system stability. In existing technologies, methods to reduce ESR mostly focus on thickening the metal electrodes, but this leads to a sharp decline in self-healing performance. Summary of the Invention

[0003] This application provides a method for preparing a low-ESR thin-film capacitor, in order to overcome the problem in the prior art that reducing ESR leads to a sharp decline in self-healing ability.

[0004] This application solves the above-mentioned technical problems through the following technical solution:

[0005] A low ESR film capacitor, comprising:

[0006] case;

[0007] A core is disposed within the housing. The core is formed by winding at least two metallized films. The metallized films include a base film and a first metal layer disposed on the surface of the base film. The first metal layer includes an edge region and a central region. The central region is located inside the edge region. The thickness of the edge region is greater than the thickness of the central region. The base film includes multiple primary microstructures and multiple secondary microstructures. The size of the secondary microstructures is smaller than that of the primary microstructures. The primary microstructures include protrusions or grooves, and the secondary microstructures include protrusions or grooves.

[0008] The lead-out electrode has a first end connected to the core and a second end disposed outside the housing.

[0009] Preferably, the thickness of the edge region is 50-200 nm, and the thickness of the center region is 10-50 nm.

[0010] Preferably, the material of the first metal layer is an aluminum-copper alloy, wherein the mass percentage of copper is 5%-15%, and / or the base film is a polypropylene film with a thickness of 2-10 μm.

[0011] Preferably, the size of the primary microstructure is 0.1-0.5 μm.

[0012] Preferably, the secondary microstructure is disposed on the primary microstructure.

[0013] Preferably, the primary microstructure and the secondary microstructure are disposed only in the regions corresponding to the base film and the edge region.

[0014] Preferably, the metallized film further includes a second metal layer disposed in the central region. The second metal layer has a mesh structure including multiple cutouts, and the total thickness of the central region of the first metal layer and the second metal layer is less than the thickness of the edge region.

[0015] Preferably, it also includes a conductive coating, through which the lead-out electrode is connected to the core, and / or, the first end of the lead-out electrode has a serrated structure.

[0016] A method for fabricating a low-ESR thin-film capacitor, comprising:

[0017] S10: Pre-treat the base film to form the primary microstructure and the secondary microstructure;

[0018] S20: The first metal layer is formed on the base film in the edge region and the center region respectively by magnetron sputtering, wherein the sputtering time in the edge region is longer than the sputtering time in the center region;

[0019] S30: At least two metallized films are wound in an alternating stacked manner to form the core;

[0020] S40: Connect the first end of the lead-out electrode to the core, and install the core and the lead-out electrode into the housing.

[0021] Preferably, step S30 is preceded by step S25: forming a second metal layer with a grid structure on the central region.

[0022] The positive advancements of this application are as follows: The first metal layer adopts a gradient thickness structure, with the thickness of the edge region being greater than that of the central region. This design conforms to the skin effect of high-frequency current and the distribution law of current converging from the center to the edge. The edge region, with the highest current density, has a lower ohmic resistance due to its thicker metal layer, thereby significantly reducing the overall ESR (Equivalent Series Resistance) of the entire capacitor. While reducing ESR, it also possesses a certain degree of self-healing capability. The thickness of the first metal layer in the central region is relatively thin, allowing for easy and thorough vaporization of the metal surrounding the fault point when local breakdown occurs in the central region, forming an effective insulating isolation zone. Furthermore, since the surface of the base film includes multiple primary microstructures and multiple smaller secondary microstructures, this design provides a larger specific surface area and a complex surface morphology. The primary and secondary microstructures can form a strong mechanical interlocking effect with the first metal layer, greatly improving the bonding strength. This effectively suppresses the tendency of the first metal layer to crack and peel off from the base film under temperature cycling, mechanical vibration, or high-frequency stress, ensuring the long-term stability of the adhesion between the metal layer and the base film. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of a low ESR thin-film capacitor according to an embodiment of this application.

[0024] Figure 2 This is a schematic diagram of the axial structure of a low ESR thin film capacitor according to an embodiment of this application;

[0025] Figure 3 This is a schematic diagram of the core structure of a low ESR thin-film capacitor according to an embodiment of this application;

[0026] Figure 4 This is a schematic diagram of the first structure of the metallized film of a low ESR thin film capacitor according to an embodiment of this application.

[0027] Figure 5 This is a schematic diagram of the second structure of the metallized thin film of a low ESR thin film capacitor according to an embodiment of this application. Detailed Implementation

[0028] The present application is further illustrated below by way of embodiments, but this does not limit the present application to the scope of the embodiments.

[0029] like Figures 1-4As shown, this embodiment provides a low ESR thin-film capacitor, including a housing 4, a core 21, and lead-out electrodes 1. The core 21 is disposed within the housing 4 and is formed by winding at least two metallized films. The metallized films include a base film 210 and a first metal layer 220 disposed on the surface of the base film 210. The first metal layer 220 includes an edge region 221 and a central region 222, with the central region 222 located inside the edge region 221. The thickness of the edge region 221 is greater than the thickness of the central region 222. The base film 210 includes multiple primary microstructures (not shown) and multiple secondary microstructures (not shown). The secondary microstructures are smaller than the primary microstructures. The primary microstructures include protrusions or grooves, and the secondary microstructures also include protrusions or grooves. A first end of the lead-out electrode 1 is connected to the core 21, and a second end of the lead-out electrode 1 is disposed outside the housing 4. The first metal layer 220 is deposited on the base film 210 by vapor deposition.

[0030] like Figure 4 As shown, the first metal layer 220 has a structure where the thickness of the edge region 221 is greater than that of the central region 222. This design conforms to the skin effect of high-frequency current and the distribution law of current converging from the center to the edge. The edge region 221, with the highest current density, has a lower ohmic resistance due to its thicker metal layer, thus significantly reducing the overall ESR (equivalent series resistance) of the entire capacitor. While reducing ESR, not only is the temperature rise of the capacitor reduced, but it also possesses a certain degree of self-healing capability. The thickness of the first metal layer 220 in the central region 222 is relatively thin, and when a local breakdown occurs in the central region 222, it can easily and completely vaporize the metal around the fault point, forming an effective insulating isolation zone. In addition, since the surface of the base film 210 includes multiple primary microstructures and multiple smaller secondary microstructures, this design provides a larger specific surface area and a complex surface morphology. The primary and secondary microstructures can form a very strong mechanical interlocking effect with the first metal layer 220, greatly improving the bonding strength. This effectively suppresses the tendency of the first metal layer 220 to crack and peel off from the base film 210 under temperature cycling, mechanical vibration, or high-frequency stress, ensuring the long-term stability of the adhesion between the metal layer and the base film 210. In some embodiments, the thickness of the edge region 221 is 50-200 nm, and the thickness of the central region 222 is 10-50 nm.

[0031] Among them, the scheme of multiple primary microstructures and multiple secondary microstructures has a synergistic effect with the scheme of the edge region 221 having a greater thickness than the central region 222. The increase in the thickness of the edge region 221 will seriously affect the adhesion to the base film 210. Multiple primary microstructures and multiple secondary microstructures can solve the reliability risks (cracking, peeling) caused by the increased thickness of the edge region 221, thereby ensuring that the central region 222 has excellent self-healing ability while reducing ESR, and the film capacitor can still maintain long-term stability.

[0032] In some embodiments, the first metal layer 220 is made of an aluminum-copper alloy, wherein the mass percentage of copper is 5%-15%. Using an aluminum-copper alloy significantly improves the conductivity of the first metal layer 220 compared to pure aluminum (the resistivity of pure aluminum is approximately 2.82 × 10⁻⁻⁻⁻⁴). 8 Ω·m, copper is 1.68×10⁻ 8 (Ω·m). With the same thickness structure, the resistance of the first metal layer 220 itself is further reduced, thereby synergistically enhancing the effect of reducing ESR. In some embodiments, the base film 210 is a polypropylene film with a thickness of 2-10 μm. Specifically, the base film 210 is a biaxially oriented polypropylene film.

[0033] In some embodiments, the size of the primary microstructure is 0.1-0.5 μm.

[0034] In some embodiments, the secondary microstructure is disposed on the primary microstructure. The secondary microstructure being disposed on the primary microstructure results in a multilayer composite microstructure being formed on the surface of the base film 210, which can further increase the bonding strength between the first metal layer 220 and the base film 210.

[0035] In some embodiments, the primary and secondary microstructures are disposed only in the regions corresponding to the base film 210 and the edge region 221. Since the first metal layer 220 of the edge region 221 is relatively thick, it is easier for the first metal layer 220 of the edge region 221 to detach from the base film 210 compared to the central region 222. The primary and secondary microstructures help improve the bonding strength between the first metal layer 220 of the edge region 221 and the base film 210. Furthermore, disposing the primary and secondary microstructures only in the regions corresponding to the base film 210 and the edge region 221 also helps reduce costs.

[0036] In some embodiments, the central region 222 of the first metal layer 220 includes a grid structure with multiple hollowed-out portions. The grid structure divides the first metal layer 220 into multiple relatively independent small units. When a local breakdown occurs, the breakdown current tends to melt the conductive path of the small unit without causing a short circuit in the entire first metal layer 220, thereby achieving local isolation and self-healing protection. Compared with a single continuous thick film, the grid structure can more controllably limit the spread of faults while ensuring conductivity, thus improving self-healing capability.

[0037] In some embodiments, such as Figure 5 As shown, the metallized thin film also includes a second metal layer 230, which is disposed in the central region 222. The second metal layer 230 has a mesh structure including multiple hollow portions. The total thickness of the central region 222 of the first metal layer 220 and the second metal layer 230 is less than the thickness of the edge region 221. The mesh structure of the second metal layer 230 forms multiple parallel current channels in the central region 222, which can share the current density of the central region 222 of the first metal layer 220, and can reduce the local equivalent resistance of the central region 222 overall.

[0038] In some embodiments, such as Figure 3 As shown, the system also includes a conductive coating 31. The lead-out electrode 1 is connected to the core 21 through the conductive coating 31. The conductive coating 31 is specifically an epoxy resin conductive adhesive filled with gold or silver powder. The thickness of the conductive coating 31 is 10-50 μm. Using an epoxy resin conductive adhesive filled with silver powder as the conductive coating 31, the lead-out electrode 1 is connected to the core 21 through this adhesive layer. The silver-epoxy resin conductive adhesive possesses both the high conductivity of silver and the excellent adhesion of epoxy resin. Therefore, in this structure, the contact resistance between the lead-out electrode 1 and the core 21 is extremely low, and the mechanical strength of the connection is high, which can significantly improve the conductivity and reliability of the lead-out electrode 1 connection.

[0039] In some embodiments, the first end of the lead electrode 1 has a serrated structure. The serration depth is 0.5-2 mm. Designing the first end of the lead electrode 1 as a serrated structure increases the effective contact area. This structure can disperse the mechanical stress at the contact point, improve the strength of the weld or bond, and at the same time, the larger contact area reduces the contact resistance, improving the stability and current carrying capacity of the electrical connection.

[0040] like Figure 1 and Figure 2 As shown, in some embodiments, the low ESR film capacitor also includes potting compound 5 for filling the housing 4 to encapsulate the core 21 within the housing 4. Example 2

[0041] This embodiment provides a method for preparing a low ESR thin-film capacitor, used to prepare the capacitor of Example 1. The preparation method includes:

[0042] S10: Pre-treat the base film to form primary and secondary microstructures;

[0043] S20: A first metal layer is formed on the base film in the edge region and the center region respectively by magnetron sputtering, wherein the sputtering time in the edge region is longer than the sputtering time in the center region;

[0044] S30: At least two metallized films are wound in an interleaved manner to form a core;

[0045] S40: Connect the first end of the lead electrode to the core, and install the core and lead electrode into the housing.

[0046] In some embodiments, step S30 is preceded by step S25: forming a second metal layer 230 with a mesh structure on the central region.

[0047] Specifically, in step S10, the base film is an 8μm biaxially oriented polypropylene film, which is treated with 800W plasma for 20s to achieve a surface roughness of 0.3μm. The primary microstructure can be formed by textured rollers on a roll-to-roll device using hot or cold pressing embossing, while the secondary microstructure can be formed using either embossing or plasma roughening methods, or a combination thereof.

[0048] In step S20, an aluminum-copper alloy target (copper content 10%) is used for sputtering at a vacuum of 1×10⁻³Pa and an argon flow rate of 30sccm. The edge region is sputtered for 45s (thickness 120nm) and the center region is sputtered for 10s (thickness 30nm).

[0049] In step S30, the core is wound with a tension of 10N and a speed of 20m / min to form a core with a diameter of 50mm;

[0050] In step S40, the lead-out electrode is a sawtooth copper electrode (sawtooth depth 1mm) and coated with 30μm thick silver-epoxy resin conductive adhesive, which is cured at 100℃ for 2h.

[0051] Tests showed that the capacitor prepared by this method had an ESR of 5mΩ at a frequency of 10kHz, which is 37.5% lower than that of the traditional product (8mΩ). After working continuously with a current of 10A for 1 hour, the temperature was 45℃, while that of the traditional product was 68℃.

[0052] While specific embodiments of this application have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of this application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of this application, but all such changes and modifications fall within the scope of protection of this application. Furthermore, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined.

Claims

1. A method for fabricating a low-ESR thin-film capacitor, characterized in that, The low ESR film capacitor includes: case; A core is disposed within the housing. The core is formed by winding at least two metallized films. The metallized films include a base film and a first metal layer disposed on the surface of the base film. The first metal layer includes an edge region and a central region. The central region is located inside the edge region. The thickness of the edge region is greater than the thickness of the central region. The base film includes multiple primary microstructures and multiple secondary microstructures. The size of the secondary microstructures is smaller than that of the primary microstructures. The primary microstructures include protrusions or grooves. The secondary microstructures include protrusions or grooves and are disposed on the primary microstructures. The lead-out electrode has a first end connected to the core and a second end disposed outside the housing. The method includes: S10: The base film is pretreated to form the primary microstructure and the secondary microstructure, wherein the base film is a polypropylene film treated with plasma, the primary microstructure is formed by a textured roller, and the secondary microstructure is formed by embossing or plasma roughening. S20: The first metal layer is formed on the base film in the edge region and the center region respectively by magnetron sputtering, wherein the sputtering time in the edge region is longer than the sputtering time in the center region; S30: At least two metallized films are wound in an alternating stacked manner to form the core; S40: Connect the first end of the lead-out electrode to the core, and install the core and the lead-out electrode into the housing.

2. The method for preparing a low ESR thin-film capacitor as described in claim 1, characterized in that, The metallized film further includes a second metal layer, which is disposed in the central region. The second metal layer is a grid structure including multiple hollow portions, and the total thickness of the central region of the first metal layer and the second metal layer is less than the thickness of the edge region. Before step S30, step S25 is also included: forming a second metal layer with a grid structure on the central region.

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