JPS637449B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a small film capacitor that is heat resistant and has excellent electrical characteristics. In today's world where energy saving and space saving have become social demands, it can be said that electronic and electrical equipment have particularly severe demands. For this reason, high-density packaging of electronic circuits is even becoming the basis of circuit design. What has made such high-density packaging possible is none other than the miniaturization of individual electronic components. Under these circumstances, chip technology is rapidly penetrating the capacitor industry for capacitors made of materials such as tantalum and ceramics. However, in the case of film capacitors, which have excellent electrical properties, there is a limit to how thin the film can be made because plastic film is used as the dielectric, and there are manufacturing constraints due to the film's low heat resistance, as well as the need for miniaturization. The response was not adequate. As prior art, there are capacitors constructed of polyether sulfone or polyimide resin, which is soluble in solvents and has a heat distortion temperature of 200° C. or higher, on a conductor. However, this capacitor requires 300°C to obtain strong adhesion.
It is necessary to bake at a temperature above 0.9 °C, which complicates the manufacturing process and causes deformation of the aluminum foil.If left at high temperatures for a long time, since it is only a thermoplastic resin, there is a problem that the dielectric strength may decrease due to the creep phenomenon. The object of the present invention is to eliminate the drawbacks of the conventional technology, make the plastic film as thin as possible, and obtain a compact film capacitor that is heat resistant, has excellent electrical characteristics, and is miniaturized. The present invention will be explained based on the drawings. FIG. 1 is a sectional view of a strip of a film capacitor according to the present invention. In the film capacitor of the present invention, a thin aluminum foil serves as one of the opposing electrodes and plays an important role in manufacturing and structure. In particular, for miniaturization, it is better for the foil to be as thin as possible, but mainly due to manufacturing limitations, a foil with a thickness of 6 μm to 30 μm is suitable, and this is also used in the present invention. In the present invention, as shown in FIG. 1, a photocurable resin film 2 is applied as a first layer onto an aluminum foil (hereinafter referred to as aluminum foil) 1. Desirable properties for this photocurable resin are (1) strong adhesion to aluminum foil 1, (2) small curing shrinkage, and (3) several μm
(4) Good thermal stability.
(5) The dielectric strength after curing is strong. As examples, epoxy and modified acrylic prepolymers (hereinafter simply referred to as prepolymers) are suitable. After adding a photoinitiator to these prepolymers and coating them on aluminum foil 1, a second dielectric layer 3 is formed on the first dielectric layer 2 which is cured by ultraviolet irradiation. This second layer must (1) be heat resistant, (2) be soluble in solvents, (3) have good film-forming properties, (4) have excellent electrical properties, and (5) It must satisfy properties such as elongation at break of 10% or more. Applicable materials include polysulfone, polyethersulfone, polyphenylene oxide, and the like.
The second layer 3 is formed by coating the first layer 2 with a lacquer obtained by dissolving these polymers in a solvent, and drying it. After the first and second dielectric layers 2 and 3 are thus formed on the aluminum foil 1, aluminum is deposited to a thickness of about 1000 Å as a counter electrode 4 to the aluminum foil 1. Note that the first layer 2 is inferior to the second layer 3 in terms of electrical properties, so it is better to make the film as thin as possible, but if you take into account the occurrence of defects during coding, it should be 0.5~
4μ is appropriate. The thickness of the second layer 3 may be increased depending on the required capacitance per unit area, but a minimum thickness of 1μ is required.
Thicker is desirable. In this way, a capacitor is completed on a single piece of aluminum foil 1. Tokukaisho
54-94463 and 54-127201, the central part of the aluminum foil is sandwiched between two lead wires with solder balls formed in advance, and the lead wires 5 and 5 are wound around the axis. 2 by heating
Lead wires 5, 5 are soldered to the aluminum foil 1 and the aluminum evaporated electrode 4, respectively. By packaging this element, the plastic film capacitor according to the present invention is completed. Figure 2 shows a conceptual diagram before exterior packaging. Here, the roles of the first and second dielectric layers 2 and 3 will be explained. The features of the first layer 2 as a dielectric include (1) very strong adhesion to aluminum foil, and (2) no creep at temperatures below the heat distortion temperature. On the other hand, it is not very suitable as a dielectric material alone because it has drawbacks such as (1) generally a rather high dielectric loss tangent, (2) a large increase in capacitance upon absorption of moisture, and (3) somewhat brittleness. On the other hand, although the second dielectric layer 3 has excellent electrical properties, it has weak adhesion to aluminum.
It has the disadvantage that if it is left continuously at high temperatures, a creep phenomenon occurs and the withstand voltage tends to drop, and even if this alone is used, it tends to lack reliability as a dielectric. However, when these first and second layers are combined, the defects of the first layer are covered by the second layer, and due to the presence of the first layer,
As a result, the second layer adheres homogeneously and strongly onto the aluminum foil. Furthermore, the first layer prevents the second layer from freezing when left at high temperatures, thereby preventing a decisive drop in withstand voltage. As mentioned above, the first
The film capacitor of the present invention, which has a combination of a layer of photocurable resin and a second layer of heat-resistant thermoplastic resin, has good thermal stability and excellent electrical properties. In addition, since a high withstand voltage can be achieved even with a thin film thickness, the advantages of the manufacturing methods of JP-A-54-94463 and JP-A-Sho 54-127201 are fully utilized, making it possible to significantly reduce the size. The present invention will be specifically explained below using examples. Example 1 A mixture of epoxy acrylate (Viscoat 540 Osaka Organic Chemical Industry Co., Ltd.) with 2% benzoin isopropyl ether (hereinafter referred to as BIPE) was dissolved in methyl ethyl ketone (hereinafter referred to as MEK).
% solution. This was gravure coated on 20μ aluminum foil and then dried at 80° to 100°C for 1 minute. After drying, it was irradiated with ultraviolet rays for 30 seconds from a distance of 30 cm using a 1 KW lamp to cure and form a 2 μ thick film. Next, a second layer was coated on top of this using a 15% solution of polysulfone in dimethylformamide, and dried at 150°C for 1 minute to form a 2μ thick polysulfone layer. On this derivative, a width of 4 mm and a length of 10 cm is placed.
Aluminum was deposited to a thickness of 1000 Å on the area. Aluminum foil was slit into strips with a total width of 5 mm and length of 101 mm, leaving a non-deposited part of 0.5 mm around each of the evaporated areas. As shown in Figure 3, with a mold sandwiching this strip, two lead wires (wire diameter 0.5
After winding the aluminum foil around the lead wire from the center of the aluminum foil, a current of 25 amperes was applied to each lead wire to melt the solder, and the solder was bonded to the aluminum foil and the vapor-deposited electrode. 54−94463,
54−127201). The element after winding looks like the one shown in FIG. The initial characteristics of a film capacitor completed by covering this element with powdered resin are shown in the table.

[Table] Example 2 A 20μ aluminum foil on which a 2μ layer of Viscoat 540 was formed by the method of Example 1 was coated with a 20% dimethylformamide solution of polyethersulfone as the second layer, and heated at 150°C for 1 minute. It was dried to form a 2μ film. Aluminum was deposited on top of this to a size of 4 mm x 100 mm, and a capacitor was completed in the same manner as in the example below. The initial characteristics are shown in the table. Example 3 A 20μ aluminum foil on which a 2μ layer of Viscoat 540 was formed by the method of Example 1 was coated with a 15% trichlene solution of polyphenylene oxide as a second layer, dried at 150°C for 1 minute, and then coated with a 2μ layer. A film was formed. From above, add 4mm x 100 pieces of aluminum.
mm, and a capacitor was completed in the same manner as in the example below. The initial characteristics are shown in the table. In the present invention, the dielectric is composed of two layers: a heat-resistant photocurable resin and a heat-resistant thermoplastic resin, which mutually compensate for the shortcomings in their properties. It has the following effects: high voltage resistance, lower baking temperature than conventional methods, better thermal safety, and the advantages of prior art manufacturing methods.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a sheet of a film capacitor of the present invention, Fig. 2 is a perspective view of a wound film capacitor of the present invention, and Fig. 3 is an arrangement of lead wires before winding of the film capacitor of the present invention. , is shown. 1: aluminum foil, 2: second layer of photocurable resin,
3: second layer of heat-resistant thermoplastic resin, 4: vapor-deposited aluminum electrode, 5: lead wire.

Claims (1)

[Scope of Claims] 1. A first layer in which a thin heat-resistant photocuring resin that has strong adhesion to the aluminum foil is coated on an aluminum foil serving as one electrode, and a thin coating is applied on the first layer. A second layer of heat-resistant thermoplastic resin and a vapor-deposited aluminum electrode were sequentially provided on the second layer, and a lead wire was provided at the center of the strip and the aluminum foil electrode and the vapor-deposited electrode were wound. A small film capacitor with lead wires soldered to aluminum foil electrodes and evaporated electrodes. 2. The small film capacitor according to claim 1, wherein the photocurable resin is epoxy and modified acrylic resin. 3. The small film capacitor according to claim 1 or 2, wherein the heat-resistant thermoplastic resin is one or a combination of polysulfone, polyethersulfone, and polyphenylene oxide.