Thin film capacitor and method for manufacturing thin film capacitor

Abstract

A thin film capacitor includes a wound body having a pair of dielectric thin films stacked in a thickness direction and having a metal deposited on a surface thereof, and a pair of end surface electrodes formed at both ends of the wound body, a void portion is formed between the pair of dielectric thin films, and the wound body has a gap between the pair of dielectric thin films in a cross-section in a direction along a surface in which the end surface electrodes extend. The winding body has a shape in which the dimension in the first direction is shorter than the dimension in the second direction orthogonal to the first direction, and the ratio of the thickness of the void in the height direction of the winding body in the first direction to the thickness of the dielectric film is 0.003-0.029.

Description

Technical Field

[0001] The present invention relates to a film capacitor and a method for manufacturing the film capacitor. Background Art

[0002] For example, Patent Document 1 describes a film capacitor including a body including a plurality of dielectric films and a first electrode film and a second electrode film wound thereon, with a gap between the dielectric film and the first electrode film or the second electrode film.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2021 / 125006 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] The thin film capacitor of Patent Document 1 still has room for improvement in terms of reducing the degree of anodic oxidation.

[0008] The present invention provides a film capacitor with reduced anodic oxidation degree and a method for manufacturing the film capacitor.

[0009] Technical solutions to solve problems

[0010] The film capacitor of the present invention comprises:

[0011] A wound body of a pair of dielectric thin films on which metal is deposited and overlapped in the thickness direction; and

[0012] A pair of end surface electrodes are formed at both ends of the wound body,

[0013] forming a gap between the pair of dielectric films,

[0014] The winding body has a shape in which a dimension in a first direction is shorter than a dimension in a second direction orthogonal to the first direction in a cross-section along a surface extending along the end face electrode, and a ratio of a thickness of the gap portion in the first direction to a thickness of the dielectric film is greater than 0.003 and less than 0.029.

[0015] The method for manufacturing a film capacitor of the present invention comprises:

[0016] A step of overlapping a pair of dielectric films on the surfaces of which metal is vapor-deposited, in a thickness direction, and winding the films to form a wound body;

[0017] a step of pressing the wound body; and

[0018] The step of forming end surface electrodes at both ends of the wound body,

[0019] In the step of pressing the wound body, the thickness of the gap formed between the pair of dielectric films is controlled to be 0.003 or more and 0.029 or less relative to the thickness of the dielectric films by controlling the pressing pressure within a given range.

[0020] Effects of the Invention

[0021] According to the present invention, a thin film capacitor having a reduced degree of anodic oxidation can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a perspective view showing a thin film capacitor according to Embodiment 1 of the present invention.

[0023] Figure 2 It is a perspective view showing a wound body with the protective winding member omitted.

[0024] Figure 3 It is schematically shown Figure 2 A cross-sectional view of a wound body.

[0025] Figure 4 1 is a flowchart showing a method for manufacturing a thin film capacitor according to Embodiment 1 of the present invention.

[0026] Figure 5 It is shown Figure 1 Schematic diagram of a pair of dielectric films of a film capacitor.

[0027] Figure 6 It is shown that the winding Figure 5 A schematic three-dimensional diagram of the state of the dielectric film.

[0028] Figure 7 It shows suppression Figure 6 A schematic cross-sectional view of a process for winding a dielectric film.

[0029] Figure 8 It shows suppression Figure 6 A schematic cross-sectional view of a process for winding a dielectric film.

[0030] Fig. 9 This is a table showing the measurement results of capacitance loss and degree of anodic oxidation.

[0031] Fig.10 This is a schematic diagram for explaining anodization of a film capacitor. DETAILED DESCRIPTION

[0032] (Process of realizing the present invention)

[0033] In the film capacitor described in Patent Document 1, it is proposed that the diameter of the effective part of the winding body perpendicular to the winding axis is made larger than the diameter of the metal spraying electrode, the volume ratio of the metal spraying electrode is reduced, and the film capacitor is miniaturized and has a higher capacitance. In the film capacitor of Patent Document 1, a gap is formed between the dielectric films by expanding the gas such as air remaining in the body in which the dielectric film, the first electrode film, and the second electrode film are wound, thereby increasing the diameter of the effective part.

[0034] On the other hand, in a thin film capacitor in which dielectric thin films are stacked or wound, when voltage is applied, an electrode film formed on the thin film reacts with moisture or ionic impurities contained in the thin film, thereby sometimes causing anodic oxidation on the surface of the electrode film.

[0035] Fig.10 This is a schematic diagram for explaining anodization in a film capacitor. Fig.10 As shown, anodic oxidation is a phenomenon in which water (H2O), ionic impurities (Ion), etc. contained in the dielectric film 110 react with the electrode film 120 formed of aluminum or the like to form an oxide film 121 on the surface. When anodic oxidation occurs, the effective electrode area of ​​the electrode film 120 formed on the dielectric film 110 is reduced, and there is a problem that the capacitance of the film capacitor decreases or the ESR increases. In order to reduce anodic oxidation, it is studied to provide gaps between the dielectric films 110.

[0036] The inventors of the present invention have found that if the gap between dielectric films is too large, the capacitance of the film capacitor becomes smaller than the designed value, and therefore it is important to appropriately control the size of the gap.

[0037] In the film capacitor described in Patent Document 1, voids are formed by expanding gas such as air remaining in the film, so it is difficult to control the size of the voids. As a result, the voids become larger than a desired size, and the electrostatic capacitance of the film capacitor decreases.

[0038] Therefore, the inventors of the present invention studied the appropriate thickness of the gaps, studied a film capacitor capable of reducing the degree of anodic oxidation and suppressing a decrease in electrostatic capacitance, and achieved the following invention.

[0039] Hereinafter, Embodiment 1 according to the present invention will be described with reference to the drawings. In each drawing, each element is exaggeratedly shown for ease of description.

[0040] (Implementation method 1)

[0041] [Overall structure]

[0042] Figure 11 is a perspective view showing a thin film capacitor according to Embodiment 1 of the present invention. In addition, the X, Y, and Z directions in the figure respectively represent the lateral direction, the longitudinal direction, and the height direction of the thin film capacitor 1 .

[0043] like Figure 1 As shown, the film capacitor 1 includes a pair of dielectric film wound bodies 10 and a pair of end surface electrodes 20 formed at both ends of the wound bodies 10 .

[0044] The wound body 10 is formed by stacking a pair of dielectric films having metal vapor-deposited electrodes on their surfaces in the thickness direction, and then winding and pressing them into a flat shape. Alternatively, the wound body 10 may be formed by stacking and pressing a plurality of dielectric films.

[0045] The wound body 10 has a shape in which a dimension τ1 in a first direction (Z direction) is shorter than a dimension d1 in a second direction (Y direction) in a cross section along a plane (YZ plane) along which the end surface electrode 20 extends. In other words, the wound body 10 is formed into a columnar shape having an oblong cross section.

[0046] Figure 2 1 is a perspective view showing a winding body with the protective winding member omitted. In this embodiment, a protective winding member is formed on the surface of the winding body 10 to protect the dielectric film. Figure 2 As shown, the wound body 10 is formed by overlapping and winding a pair of dielectric films 31 and 32 in the thickness direction. More specifically, after overlapping one dielectric film 31 and the other dielectric film 32, the pair of dielectric films 31 and 32 are rolled up and pressed into a flat shape, thereby forming the wound body 10 having an oblong cross-section.

[0047] As the dielectric film, for example, a plastic film containing a thermoplastic resin such as polyethylene terephthalate, polypropylene, polyphenylene sulfide, or polyethylene naphthalate, or a plastic film containing a thermosetting resin such as a cured product obtained by reacting a hydroxyl group (OH group) of a first organic material with an isocyanate group (NCO group) of a second organic material can be used. As the metal vapor-deposited electrode formed on the surface of the dielectric film, for example, a metal such as aluminum or zinc can be used.

[0048] The end surface electrodes 20 can be formed by thermally spraying a metal such as zinc on both end portions of the wound body 10 .

[0049] Figure 3 It is schematically shown Figure 2 A cross-sectional view of a wound body. Figure 3As shown, a gap 41 is provided between the pair of dielectric films 31 and 32. For example, the gap 41 can be formed by overlapping and winding the pair of dielectric films 31 so that an air layer is included between the dielectric films 31 and 32. By forming the gap 41 between the dielectric films 31 and 32, stress when an external force is applied to the wound body 10 can be reduced, and anodic oxidation of the metal vapor-deposited electrodes formed on the surfaces of the dielectric films 31 and 32 can be suppressed.

[0050] In the first direction (Z direction), the ratio of the thickness of the void portion in the height direction of the wound body 10 to the thickness of the dielectric films 31 and 32 is 0.003 or more and 0.029 or less.

[0051] The thickness of the dielectric films 31 and 32 indicates the total of the thicknesses f1 to f7 of the dielectric films 31 and 32 stacked in the first direction (Z direction) of the wound body 10. In addition, the thickness of the void portion 41 in the height direction (Z direction) of the wound body 10 indicates the total of the thicknesses s1 to s6 of the void portion 41 in the first direction. That is, the ratio of the thickness of the void portion to the thickness of the dielectric films 31 and 32 indicates the ratio of the sum of the thicknesses s1 to s6 of the void portion 41 to the sum of the thicknesses f1 to f7 of the dielectric films 31 and 32. In other words, the size of the void portion 41 is set so that the sum of the thicknesses s1 to s6 of the void portion 41 is greater than or equal to 0.003 and less than or equal to 0.029 relative to the sum of the thicknesses f1 to f7 of the dielectric films 31 and 32.

[0052] In addition, the gap portion 41 does not necessarily need to be formed to have a uniform thickness, and there may be a portion where the dielectric thin films 31 and 32 are in contact with each other.

[0053] [Manufacturing method]

[0054] Figure 4 1 is a flowchart showing a method for manufacturing a thin film capacitor according to Embodiment 1 of the present invention. Figure 5 It is shown Figure 1 Schematic diagram of a pair of dielectric films of a film capacitor. Figure 6 It is shown that the winding Figure 5 A schematic three-dimensional diagram of the state of the dielectric film. Figure 7 It shows suppression Figure 6 A schematic cross-sectional view of a process for winding a dielectric film. Figure 8 It shows suppression Figure 6 A schematic cross-sectional view of a process for winding a dielectric film. Figures 4 to 8 , a method for manufacturing the film capacitor 1 is described.

[0055] In step S1, a wound body 10 is formed. Regarding the formation of the wound body 10, first, Figure 5 As shown in the figure, a pair of dielectric films 31 and 32 on which metal is deposited are overlapped in the thickness direction. The dielectric films 31 and 32 are films in which metal vapor-deposited electrodes 31a and 32a are formed on the surface of a strip-shaped dielectric film having a length L. The metal vapor-deposited electrodes 31a and 32a are formed on the surface of the dielectric films 31 and 32 except for the insulating margins 31b and 32b. In addition, a pattern margin (not shown) on which metal is not vapor-deposited may be formed on the metal vapor-deposited electrodes 31a and 32a.

[0056] like Figure 5 As shown, a pair of dielectric films 31 and 32 are overlapped with each other at a length As in the width direction W. By overlapping the dielectric films 31 and 32 in this way, it is possible to suppress a short circuit between the metal vapor-deposited electrodes 31a and 32a and the end surface electrode 20 after the end surface electrode 20 is formed in a subsequent step.

[0057] Next, if the pair of dielectric films 31 and 32 overlapping each other are rolled up, Figure 6 As shown in FIG. 1 , a cylindrical winding body 10 is formed. Figure 7 As shown, in the wound body 10 formed in step S1, the dimension h1 in the first direction (Z direction) and the dimension h2 in the second direction (Y direction) in the cross section (YZ plane) perpendicular to the winding axis are approximately the same, and the wound body 10 has a cylindrical shape with a substantially circular cross section.

[0058] In step S2, the wound body 10 is pressed. Figure 7 as well as Figure 8 As shown in FIG. 2 , the side of the cylindrical winding body 10 is pressed to form a flat winding body 10. For example, the cylindrical winding body 10 is placed in a pressing device, and pressure is applied in the direction of arrow P to form a flat winding body 10. By adjusting the pressing pressure, the thickness of the gap 41 between the dielectric films 31 and 32 can be adjusted. More specifically, the greater the pressing pressure, the smaller the thickness of the gap 41. By pressing the winding body 10 in step S2, as shown in FIG. 2 , the winding body 10 is formed into a flat shape. Figure 8 As shown, the dimension h3 in the first direction in the cross section (YZ plane) perpendicular to the winding axis is relatively smaller than the dimension h4 in the second direction.

[0059] In step S3, the end surface electrodes 20 are formed on the pressed winding body, and the Figure 1 The film capacitor 1 shown in the figure can be formed by thermally spraying a metal such as zinc on both ends of the wound body 10 to form the end surface electrodes 20 .

[0060] [Example]

[0061] In the film capacitor described in the first embodiment, the step of pressing the wound body 10 ( Figure 4 The thickness of the gap 41 was changed by changing the pressing pressure in step S2), and the deviation of the film capacitor 1 from the designed capacitance value and the degree of anodization were measured. Fig. 9 Like that.

[0062] <Film capacitors>

[0063] In the examples, a film capacitor in which the ratio of the thickness of the cavity 41 to the thickness of the dielectric films 31 and 32 was changed from 0 to 0.06 by changing the pressing pressure in 11 steps was used to measure the deviation from the designed capacitance value and the degree of anodization.

[0064] <Thickness of the Gap>

[0065] The ratio of the thickness of the air gap to the thickness of the dielectric film of each film capacitor was calculated by the following method.

[0066] First, the height τ1 of the film capacitor in the first direction is measured (refer to Figure 1 ). Next, the film capacitor is decomposed to find the number of windings of the dielectric film. The obtained number of windings is set as T film , the film thickness of the dielectric film is set to d film . In addition, the film thickness of the dielectric film also includes the thickness of the metal vapor-deposited electrode. The number of turns of the pre-wound part and the protective winding part other than the dielectric film in the film capacitor is also calculated in the same way. The so-called pre-wound part is the part that becomes the core when the dielectric film is wound, and the so-called protective winding part is the part wound on the periphery to protect the dielectric film and the metal vapor-deposited electrode. The number of turns of the pre-wound part is set to T in , set the film thickness to d in , set the winding number of the protective winding member to T out , set the film thickness to d out .

[0067] The height τ0 of the thin film capacitor in the first direction when no cavity is formed is calculated by equation (1).

[0068] τ0=d in ×T in ×2+d out ×T out ×2+T film ×d film ×4 … (1)

[0069] In addition, regarding the pre-wound material and the protective wound material, if wound once, they include two layers in the first direction, so the thickness in the first direction is calculated as "number of windings × film thickness × 2". Regarding the dielectric film, two sheets are wound as a pair, so they include four layers in the first direction after one winding, so the thickness in the first direction is calculated as "number of windings × film thickness × 4".

[0070] By subtracting τ0 from τ1, that is, by using equation (2), the thickness D of the void portion included in the thin film capacitor can be calculated.

[0071] D = τ1 - τ0 … (2)

[0072] The thickness d of the gap per dielectric film air It is calculated by formula (3).

[0073] d air =D / (4*T film ) … (3)

[0074] Therefore, the ratio R of the thickness of the cavity portion to the thickness of the dielectric thin film is calculated by equation (4).

[0075] R=d air / d film … (4)

[0076] <Designed Capacitance Value>

[0077] The design capacitance value of the film capacitor can be calculated as follows.

[0078] The film capacitor was disassembled and the dielectric film was taken out. The film width A0, effective electrode width A, insulation margin width Am, and length L of the dielectric film were measured (refer to Figure 5 ). The effective electrode width A represents the width of the metal vapor-deposited electrode that actually functions as a capacitor. Let the dielectric constant of a vacuum be ε0 and the relative dielectric constant of a dielectric film be ε film , let the effective electrode area ratio be N. The effective electrode area ratio N represents the ratio of the area of ​​the effective electrode calculated by "effective electrode width A×length L of dielectric film" minus the area of ​​the pattern margin and the like. Specifically, the effective electrode area ratio N can be calculated by "N=(L×A-Sp) / (L×A)". In addition, Sp represents the area of ​​the pattern margin and the like where no metal is evaporated. In addition, the effective electrode width A can be calculated by "A=A0-2Am-As". The design capacitance value C0 of the film capacitor can be calculated by formula (5).

[0079] C0=ε0ε film ×L×A×N / d film … (5)

[0080] <Capacitance loss relative to the designed capacitance value>

[0081] The capacitance loss ΔC of each film capacitor relative to the designed capacitance value C0 can be calculated by using the actually measured capacitance value C1 and the designed capacitance value C0 of each film capacitor using equation (6).

[0082] ΔC=(C0-C1) / C0×100…(6)

[0083] <Determination of Anodic Oxidation Degree>

[0084] The film capacitors with the thickness of the gap 41 adjusted at various pressing pressures were subjected to a high temperature and high humidity test, and the degree of anodization after the high temperature and high humidity test was measured. The degree of anodization was measured by finding the ratio of the area where the metal vapor-deposited electrodes 31a and 32a of the dielectric films 31 and 32 changed color to white.

[0085] In the high temperature and high humidity test, a voltage of 500 V was applied for 1000 hours in an environment of a temperature of 85°C and a humidity of 85% RH.

[0086] After the high temperature and high humidity test, the film capacitor was disassembled and the proportion of the area that changed color to white due to anodic oxidation in the effective electrode area was calculated. In addition, the part that changed color to white due to anodic oxidation was determined visually. In addition, the difference between the discolored area and the non-discolored area is clear by visual inspection, and the result of the area ratio does not produce a substantial difference compared to the case where image processing technology is used.

[0087] Effective electrode area A all The calculation is done by "dielectric film length L x effective electrode width A". If the area of ​​the part that turns white due to anodization is A ox , then the degree of anodic oxidation O can be calculated by formula (7).

[0088] O=A ox / A all ×100 … (7)

[0089] <Measurement Results>

[0090] Fig. 9 TABLE 2 is a table showing the measurement results of capacitance loss and degree of anodic oxidation. Fig. 9 , the preferred range of the thickness of the gap portion 41 is studied.

[0091] When the ratio R of the thickness of the gap to the thickness of the dielectric film is less than 0.029, the capacitance loss ΔC, which indicates the degree to which the measured capacitance value C1 of the film capacitor decreases relative to the designed capacitance value C0, converges within 10%. This is because the greater the thickness of the gap between the dielectric films, the greater the capacitance loss ΔC. In the product standard of film capacitors, the capacitance loss ΔC relative to the designed capacitance value C0 is required to be within 10%, so the ratio R of the thickness of the gap should be less than 0.029.

[0092] In addition, when the ratio R of the thickness of the void portion to the thickness of the dielectric film is greater than 0.003, the degree of anodic oxidation can be suppressed to less than 5%. If the degree of anodic oxidation increases, the equivalent series resistance (ESR) when a voltage is applied to the film capacitor will increase. In the product standard of film capacitors, the increase rate of ESR is required to be within 50%. By keeping the degree of anodic oxidation within 5%, the product standard can be more reliably met. Therefore, it is preferable that the ratio R of the thickness of the void portion is greater than 0.003. In addition, the increase rate of ESR is an indicator that shows the extent to which the ESR has increased, for example, before and after a high temperature and high humidity test.

[0093] Based on the above results, the ratio R of the thickness of the cavity portion to the thickness of the dielectric thin film can be 0.003 or more and 0.029 or less.

[0094] [Effect]

[0095] According to the above-mentioned embodiment, the following effects can be achieved.

[0096] The film capacitor 1 includes a winding body 10 and a pair of end surface electrodes 20. The winding body 10 is a winding body obtained by winding a pair of dielectric films 31 and 32 on which metal is vapor-deposited and overlapped in the thickness direction. The end surface electrodes 20 are formed at both ends of the winding body 10. A gap portion 41 is formed between the pair of dielectric films 31 and 32. The winding body 10 has a shape in which a dimension τ1 in a first direction (Z direction) is shorter than a dimension d1 in a second direction (Y direction) orthogonal to the first direction in a cross section along the direction of the surface (YZ plane) along which the end surface electrodes 20 extend. In the first direction, the ratio of the thickness of the gap portion 41 in the height direction of the winding body 10 to the thickness of the dielectric films 31 and 32 is greater than 0.003 and less than 0.029.

[0097] With such a structure, it is possible to suppress anodic oxidation of the film capacitor 1. By providing the gap 41 between the dielectric films 31 and 32, it is possible to prevent anodic oxidation of the metal vapor-deposited electrodes 31a and 32a. On the other hand, by setting the ratio of the thickness of the gap 41 to be greater than or equal to 0.003 and less than or equal to 0.029, it is possible to suppress the capacitance loss of the film capacitor 1. Therefore, it is possible to provide a film capacitor 1 that is less susceptible to anodic oxidation and has a small capacitance loss.

[0098] Furthermore, when the designed capacitance value of the film capacitor 1 is C0 and the measured capacitance value is C1, (C0-C1) / C0×100 is 10% or less.

[0099] With such a structure, it is possible to provide the film capacitor 1 having a small capacitance loss.

[0100] The method for manufacturing the film capacitor 1 includes the steps of forming a winding body, pressing the winding body, and forming an end surface electrode. The step of forming the winding body includes overlapping and winding a pair of dielectric films 31 and 32 on the surfaces of which metal is evaporated. The step of pressing the winding body includes controlling the thickness of the gap 41 formed between the pair of dielectric films 31 and 32 by controlling the pressing pressure within a given range.

[0101] With such a structure, it is possible to provide the thin film capacitor 1 in which a cavity portion having an appropriate thickness is formed.

[0102] (Overview of Implementation Methods)

[0103] (1) The film capacitor of the present invention comprises: a wound body having a pair of dielectric films on which metal is vapor-deposited and overlapped in a thickness direction; and a pair of end surface electrodes formed at both ends of the wound body, a gap portion being formed between the pair of dielectric films, the wound body having a shape in which a dimension in a first direction is shorter than a dimension in a second direction orthogonal to the first direction in a cross-section along a plane extending from the end surface electrodes, and a ratio of a thickness of the gap portion in a height direction of the wound body in the first direction to a thickness of the dielectric film is greater than 0.003 and less than 0.029.

[0104] (2) In the film capacitor of (1), when a designed capacitance value of the film capacitor is C0 and an actually measured capacitance value is C1, (C0-C1) / C0×100 may be 10% or less.

[0105] (3) The method for manufacturing a film capacitor of the present invention comprises: a step of overlapping a pair of dielectric films on the surfaces of which metal is vapor-deposited in a thickness direction and winding them to form a wound body; a step of pressing the wound body; and a step of forming end surface electrodes at both ends of the wound body, wherein in the step of pressing the wound body, the thickness of the gap formed between the pair of dielectric films is controlled to be greater than 0.003 and less than 0.029 relative to the thickness of the dielectric films by controlling the pressing pressure within a given range.

[0106] Industrial Applicability

[0107] The present invention is useful in film capacitors used in various electronic devices, electrical equipment, industrial equipment, vehicle devices, and the like.

[0108] Description of Reference Numerals

[0109] 1 Film capacitor

[0110] 10 Winding

[0111] 20 End electrode

[0112] 31, 32 Dielectric film

[0113] 31a, 32a Metal vapor deposition electrode

[0114] 31b, 32b Insulation margin

[0115] 41 gap.

Claims

1. A film capacitor comprising: A wound body of a pair of dielectric thin films on which metal is deposited and overlapped in the thickness direction; and A pair of end surface electrodes are formed at both ends of the wound body, forming a gap between the pair of dielectric films, The winding body has a shape in which a dimension in a first direction is shorter than a dimension in a second direction orthogonal to the first direction in a cross-section along a surface extending along the end face electrode, and a ratio of a thickness of the gap portion in the first direction to a thickness of the dielectric film is greater than 0.003 and less than 0.

029.

2. The film capacitor according to claim 1, wherein: When the designed capacitance value of the film capacitor is C0 and the measured capacitance value is C1, (C0-C1) / C0×100 is less than 10%.

3. A method for manufacturing a film capacitor, comprising: A step of overlapping a pair of dielectric films on the surfaces of which metal is vapor-deposited, in a thickness direction, and winding the films to form a wound body; a step of pressing the wound body; and The step of forming end surface electrodes at both ends of the wound body, In the step of pressing the wound body, the thickness of the space formed between the pair of dielectric films is controlled to be 0.003 or more and 0.029 or less relative to the thickness of the dielectric films by controlling the pressing pressure within a given range.

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