JP2010040633A - Film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film capacitor having a high thermal resistance, which can suppress the lowering of outer-layer cracks, withstand voltage drop and insulating resistance drop, even in flow soldering using lead free solder and reflow soldering. <P>SOLUTION: The film capacitor 1 includes a film capacitor element 10, where a conductor 18 and a dielectric film 20 are sequentially overlapped and wound, and with external electrodes 12 installed on both end faces of the film capacitor element 10. The dielectric film 20 has a first dielectric film 22 and a second dielectric film 24, having a lower thermal contraction coefficient, as compared to that of the first dielectric film 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a structure of a film capacitor.

  Film capacitors are basic electronic components used in various industrial devices, including small and large ones. Conventional film capacitors have a capacitor element using a conductor such as a metal foil and a dielectric film such as a polyethylene terephthalate film or a polypropylene film, or are placed in a resin container, and the gap in the container Is filled with resin (for example, see Patent Document 1).

  There are a flow soldering method and a reflow soldering method for mounting electronic components. In recent years, the solder temperature has become high with the lead-free soldering and the high melting point of the material. In addition, the temperature of preheating (preheating) of the electronic component and the substrate for easily performing the flow soldering and the reflow soldering is also high. When a conventional film capacitor is exposed to such a high temperature condition, the dielectric film in the film capacitor is thermally contracted and deformed, and various characteristics of the film capacitor such as outer layer cracking, lowering of withstand voltage, lowering of insulation resistance, etc. Will be adversely affected. Polypropylene films are mainly used as dielectric films for film capacitors used in high-frequency circuits (with a relatively small capacitance). Since the polypropylene film has a higher thermal shrinkage rate (lower heat resistance) than other dielectric films, cracks in the outer layer, a decrease in withstand voltage, a decrease in insulation resistance, and the like are remarkable.

  For this reason, conventional film capacitors cannot be soldered at the same time as other electronic components, and may be soldered by lowering the temperature conditions of flow soldering and reflow soldering from those of other electronic components. . Thus, the conventional film capacitor cannot perform the soldering operation simultaneously with other electronic components, and there is a possibility that the working efficiency is deteriorated.

Japanese Patent No. 2877364

  Therefore, an object of the present invention is to provide a high heat resistance film capable of suppressing outer layer cracking, lowering of withstand voltage, lowering of insulation resistance, etc. in both flow soldering and reflow soldering using lead-free solder. It is to provide a capacitor.

  The present invention is a film capacitor having a film capacitor element in which a conductor and a dielectric film are sequentially overlapped and wound, and external electrodes provided on both end faces of the film capacitor element, wherein the dielectric The film includes a first dielectric film and a second dielectric film having a thermal contraction rate lower than that of the first dielectric film.

  In the film capacitor, it is preferable that the conductor, the first dielectric film, and the second dielectric film are arranged in this order toward the radially outer side of the film capacitor element.

  In the film capacitor, it is preferable that the first dielectric film is a polypropylene film and the second dielectric film is a polyethylene terephthalate film.

  In the film capacitor, it is preferable that the conductor is not disposed at the winding end portion of the film capacitor element, and the dielectric film is disposed.

  In the film capacitor, it is preferable that the conductor is not disposed at the winding start portion of the film capacitor element, and the dielectric film is disposed.

  In the film capacitor, the conductor is preferably an aluminum foil.

  According to the film capacitor of the present invention, it is possible to suppress cracking of the outer layer, a decrease in withstand voltage, a decrease in insulation resistance, and the like in both flow soldering and reflow soldering using lead-free solder.

  Embodiments of the present invention will be described below.

  FIG. 1 is an exploded schematic perspective view showing an example of the configuration of a film capacitor according to an embodiment of the present invention. FIG. 2 is a schematic view of the material configuration of the film capacitor element before winding as viewed from the length direction. FIG. 3 is a schematic view of the material configuration of the film capacitor element before winding as viewed from the width direction. As shown in FIG. 1, the film capacitor 1 includes a film capacitor element 10, external electrodes 12 provided on both end faces of the film capacitor element 10, lead wires 14 provided on the external electrode 12, and the film capacitor element 10. And an exterior 16 to be covered.

  As shown in FIGS. 2 and 3, the film capacitor element 10 before winding is superposed in the order of the conductor 18, the dielectric film 20, the conductor 18, and the dielectric film 20. The dielectric film 20 includes a first dielectric film 22 and a second dielectric film 24 having a thermal contraction rate lower than that of the first dielectric film 22 (that is, high heat resistance). As shown in FIG. 3, the conductor 18 is arranged while being shifted in the width direction of the dielectric film 20. The film capacitor element 10 is formed by winding the conductor 18 and the dielectric film 20. The film capacitor element 10 may be formed into a flat shape by performing a molding process such as a heat press, or may be a cylindrical type without performing the molding process.

  As shown in FIG. 1, the conductor 18, the first dielectric film 22, and the second dielectric film 24 are arranged in this order toward the radially outer side of the film capacitor element 10. That is, the second dielectric film 24 is disposed so as to be the outermost periphery of the film capacitor element 10, but is not limited thereto. FIG. 4 is an exploded schematic perspective view showing an example of the configuration of a film capacitor according to another embodiment of the present invention. As shown in FIG. 4, for example, the conductor 18, the first dielectric film 22, and the second dielectric film 24 are directed toward the radially outer side of the film capacitor element 10, and the conductor 18 and the second dielectric film 24. The first dielectric film 22 may be arranged in the order. That is, the first dielectric film 22 may be disposed so as to be the outermost periphery of the film capacitor element 10. However, the second dielectric film 24 becomes the outermost periphery of the film capacitor element 10 in that the adhesion (adhesion) between the film capacitor element 10 and the outer covering 16 covering the film capacitor element 10 can be sufficiently secured. It is preferable to arrange | position.

  If the dielectric film 20 used in the present embodiment is composed of the first dielectric film 22 and the second dielectric film 24 having a thermal contraction rate lower than that of the first dielectric film 22, the dielectric film 20 There are no particular restrictions on the material that constitutes, and examples thereof include resin materials such as polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyphenylene sulfide (PPS). Although the heat shrinkage rate of the film varies slightly depending on the film production method, the heat shrinkage rate of a general polypropylene film is 3.6% to 8.0% at 140 ° C., and the heat shrinkage rate of the polyethylene terephthalate film is 150%. 0.7% to 1.5% at 190 ° C, 1.7% to 3.5 at 190 ° C, heat shrinkage of polyethylene naphthalate film is 0.4% or less at 150 ° C, 1.0% at 200 ° C The thermal shrinkage rate of the polyphenylene sulfide film is 0.2% or less at 150 ° C to 200 ° C.

  From the value of the thermal shrinkage rate, when the first dielectric film 22 is a PP film as a combination of the first dielectric film 22 and the second dielectric film 24 of the present embodiment, the second dielectric film 24 is PET. A film, a PEN film, a PPS film or the like is selected. With such a configuration, there is a high heat resistance film capacitor that can suppress outer layer cracking, lowering of withstand voltage, lowering of insulation resistance, etc. in both flow soldering and reflow soldering using lead-free solder. can get.

  For example, a PP film having a high heat shrinkage rate is mainly used for a film capacitor for a high frequency circuit. Therefore, in film capacitors for high-frequency circuits, flow layer soldering using lead-free solder and reflow soldering tend to cause outer layer cracking, reduced withstand voltage, reduced insulation resistance, and the like. However, by using a PET film, a PEN film, a PPS film, or the like having a thermal contraction rate lower than that of the PP film as the second dielectric film 24 as in this embodiment, the above problem is solved. In particular, it is preferable that the first dielectric film 22 is a PP film and the second dielectric film 24 is a PET film in that an inexpensive film capacitor can be manufactured.

  In the present embodiment, as shown in FIG. 2, the (longitudinal) length of the dielectric film 20 is made longer than the (longitudinal) length of the conductor 18, and the winding end portion of the film capacitor element 10 is It is preferable to dispose the dielectric film 20 without disposing the conductor 18. Moreover, it is preferable to arrange the dielectric film 20 at the winding start portion of the film capacitor element 10 without arranging the conductor 18. With the above configuration, the heat resistance, insulation, humidity resistance, and the like of the film capacitor 1 can be improved.

  The thickness, width, and the like of the dielectric film 20 used in the present embodiment are appropriately set according to the capacitance, rated voltage, and the like of the film capacitor 1 and are not particularly limited. The thickness of the first dielectric film 22 is preferably in the range of 4.0 μm to 20.0 μm, and the thickness of the second dielectric film 24 is preferably in the range of 3.0 μm to 12.0 μm. For example, the width of the first dielectric film 22 and the second dielectric film 24 is preferably in the range of 5.0 mm to 20.0 mm. Further, the length of the winding end portion and the length of the winding start portion of the dielectric film 20 used in the present embodiment are appropriately set depending on the dimensions of the film capacitor 1 and are not particularly limited. However, for example, the length of the winding end portion of the dielectric film 20 is preferably in the range of 65 mm to 100 mm, and the length of the winding start portion is preferably in the range of 5 to 15 mm.

  Examples of the conductor 18 used in the present embodiment include a metal foil such as an aluminum foil, and a deposited film obtained by depositing a metal such as aluminum on one surface of the dielectric film 20. However, when a deposited film is used, it is preferable to use a metal foil because a film capacitor having a small capacitance may be too small to make the capacitor difficult to manufacture. Moreover, it is more preferable that it is aluminum foil from the point of being cheap. The thickness and width of the conductor 18 are not particularly limited. For example, when a metal foil is used as the conductor 18, the thickness is preferably in the range of 5.0 μm to 12.0 μm, and the width is 3.5 mm to A range of 18.0 mm is preferred.

  The external electrode 12 formed on the end face of the film capacitor element 10 of the present embodiment is for ensuring electrical contact between the conductor 18 of the film capacitor element 10 and the lead wire 14. It is formed by the conductor 18 protruding from the film 20. Further, for example, the external electrode 12 may be formed of a metallized metal sprayed with a metal such as tin, zinc, or copper, or a solder pile.

  For the lead wire 14 used in the present embodiment, all the conventional wires used for film capacitors such as Cp wire and Cu wire are applied. The installation method of the lead wire 14 to the external electrode 12 is not particularly limited, such as spot welding or soldering.

  The exterior 16 of this embodiment is formed by a resin exterior method in which, for example, an insulating liquid resin is coated on the film capacitor element 10 and then the film capacitor element 10 is covered with a powder resin such as an epoxy resin. Further, for example, the film capacitor element 10 is accommodated in a plastic case such as polycarbonate (PC) or polybutylene terephthalate (PBT), and then formed by a case exterior method in which an epoxy resin or the like is injected.

  The film capacitor according to the present embodiment is used, for example, as a capacitor for electric power, electric equipment, various power supply circuits, communication equipment, and smoothing, filter, etc. used in a high frequency region for DC applications.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

Example 1
The aluminum foil (thickness 6.0 μm, width 5 mm), the PP film (thickness 12.0 μm, width 7.0 mm), and the PET film (thickness 6.0 μm, width 7.0 mm) are stacked in this order and shown in FIG. Thus, a film capacitor element was produced. The length of the PP film and PET film at the winding start part was 5 to 15 mm, and the length of the PP film and PET film at the winding end part was 65 to 100 mm. The external electrode was an aluminum foil that protruded from the dielectric film. A lead wire (Cp wire or Cu wire) was welded to the external electrode, and the outer electrode was coated with an epoxy resin to produce a film capacitor. This was designated Example 1. The film capacitor of Example 1 has a capacitance of 1000 pF and a rated voltage of 630 VDC.

(Examples 2 and 3)
In Example 2, a film capacitor was produced under the same conditions as in Example 1 except that metallicons were applied to both end faces of the capacitor element to form external electrodes. In Example 3, a film capacitor was produced under the same conditions as in Example 1 except that solder was applied to both end faces of the capacitor element to form external electrodes.

(Examples 4 to 6)
In Example 4, aluminum foil (thickness 6.0 μm, width 5.0 mm), PET film (thickness 6.0 μm, width 7.0 mm), PP film (thickness 12.0 μm, width 7.0 mm) in this order. A film capacitor was produced under the same conditions as in Example 1 except that the film capacitors were superposed and wound as shown in FIG. In Example 5, a fill capacitor was produced under the same conditions as in Example 4 except that the metal electrodes were applied to both end faces of the capacitor element to form external electrodes. In Example 6, a film capacitor was produced under the same conditions as in Example 4 except that both ends of the capacitor element were soldered to form external electrodes.

(Comparative Examples 1-3)
In Comparative Example 1, aluminum foil (thickness 5.0 μm, width 5.0 mm), PP film (thickness 15.0 μm, width 7.0 mm), PP film (thickness 15.0 μm, width 7.0 mm) in this order. A film capacitor was produced under the same conditions as in Example 1 except that the film capacitor element was produced by overlapping and winding. In Comparative Example 2, a film capacitor was produced under the same conditions as in Comparative Example 1 except that metallicon was applied to both end faces of the capacitor element to form external electrodes. In Comparative Example 3, a film capacitor was produced under the same conditions as in Comparative Example 1 except that external electrodes were formed by applying solder on both end faces of the capacitor element.

<High temperature storage test>
The film capacitors of Examples 1 to 6 and Comparative Examples 1 to 3 were put into a high-temperature bath and allowed to stand at 150 ° C. for 15 minutes, 160 ° C. for 15 minutes, 170 ° C. for 15 minutes, or 180 ° C. for 15 minutes. Then, it was evaluated whether or not the exterior resin of the film capacitor after being left was broken. Moreover, the withstand voltage test and the insulation resistance test of the film capacitor were also performed. 20 pieces (10 Cp lines and 10 Cu lines) were tested under each temperature-time condition. The evaluation of the exterior crack was NG when the exterior crack was visually observed. In the withstand voltage test, 1300 VDC was applied to the film capacitor for 1 minute, and the breakdown was determined as NG. The insulation resistance test was performed based on the insulation resistance measurement method defined in JIS C 5101-1, and 50,000 MΩ or less was determined as NG. The results of the exterior crack, withstand voltage test, and insulation resistance test were evaluated according to the following criteria, and are summarized in Table 1.
○: NG number / test number (20) = 0%
Δ: NG number / test number (20 pieces) = 1% to less than 50% X: NG number / test number (20 pieces) = 50% or more

  As can be seen from the results in Table 1, in the film capacitor of 2 PP films (Comparative Examples 1 to 3), after leaving at 160 ° C. for 15 minutes, an external crack occurred, and 170 ° C. for 15 minutes, 180 ° C. for 15 minutes. After standing for minutes, NG occurred in the withstand voltage test and the insulation resistance test. On the other hand, in the film capacitors of PP film-PET film (Examples 1 to 6), NG was not generated in the exterior cracking, withstand voltage test, and insulation resistance test even after being left at 180 ° C. for 15 minutes.

<Solder heat resistance test>
The film capacitors of Examples 1 to 6 and Comparative Examples 1 to 3 were put into a high temperature bath and preheated at 120 ° C. for 90 seconds, and then 260 ° C. for 5 seconds, 260 ° C. for 10 seconds, 260 C. for 15 seconds. The portion immersed in the solder bath was a part of the lead wire of the film capacitor (that is, the outer resin portion was not immersed). An evaluation was made as to whether or not the outer packaging resin of the film capacitor after the immersion was broken, and a withstand voltage test and an insulation resistance test of the film capacitor were performed. The evaluation of the external crack, the withstand voltage test, and the insulation resistance test were performed in the same manner as described above, and evaluated according to the same criteria as described above.

  As can be seen from the results in Table 2, with PP film 2-piece film capacitors (Comparative Examples 1 to 3), 120 ° C-90 seconds preheating and 260 ° C-10 seconds solder immersion, exterior cracking, withstand voltage test In the insulation resistance test, NG occurred. On the other hand, in the film capacitor of PP film-PET film (Examples 1 to 6), even in preheating at 120 ° C. for 90 seconds and solder immersion at 260 ° C. for 15 seconds, in the exterior crack, withstand voltage test, and insulation resistance test No NG occurred.

  As described above, even when a PP film with a high heat shrinkage rate (low heat resistance) is used, a film capacitor with high heat resistance can be obtained by combining with a PET film having a heat shrinkage rate lower than that of the PP film. It is.

It is an exploded model perspective view showing an example of the composition of the film capacitor concerning the embodiment of the present invention. It is the schematic diagram which looked at the material structure of the film capacitor element before winding from the length direction. It is the schematic diagram which looked at the material structure of the film capacitor element before winding from the width direction. It is a disassembled schematic perspective view which shows an example of a structure of the film capacitor which concerns on other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Film capacitor, 10 Film capacitor element, 12 External electrode, 14 Lead wire, 16 Outer casing, 18 Conductor, 20 Dielectric film, 22 1st dielectric film, 24 2nd dielectric film

Claims (6)

A film capacitor having a film capacitor element wound with a conductor and a dielectric film sequentially stacked and external electrodes provided on both end faces of the film capacitor element,
The dielectric film includes a first dielectric film and a second dielectric film having a thermal contraction rate lower than that of the first dielectric film.   2. The film capacitor according to claim 1, wherein the conductor, the first dielectric film, and the second dielectric film are arranged in this order toward a radially outer side of the film capacitor element. Film capacitor characterized by   3. The film capacitor according to claim 1, wherein the first dielectric film is a polypropylene film, and the second dielectric film is a polyethylene terephthalate film. 4.   It is a film capacitor of any one of Claims 1-3, Comprising: The said conductor is not arrange | positioned in the winding end part of the said film capacitor element, The said dielectric film is arrange | positioned. Film capacitor characterized by   5. The film capacitor according to claim 4, wherein the conductor is not disposed at the winding start portion of the film capacitor element, and the dielectric film is disposed.   The film capacitor according to claim 1, wherein the conductor is an aluminum foil.

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