METHOD FOR MANUFACTURING A FILM CAPACITOR

Abstract: In manufacturing a film capacitor, an oxygen plasma etching of a laminated or stacked film capacitor body for making electrode connection is made by a two-stage application of radio frequency power, wherein a first stage application is at a larger power and a second stage application is at a smaller power of the radio frequency.

Description: 1. FIELD OF THE INVENTION The present invention relates to a method for manufacturing a film capacitor, and particularly to a method for manufacturing a film capacitor having a lamination or a stacked body of organic dielectric film having electrode layer thereon, as for instance known from EP-A-0158971. 2. DESCRIPTION OF THE RELATED ART Recently, decrease of size, decrease of weight, achieving of high characteristic performance, decrease of cost, and so on are demanded generally for electronics components, and hence, the same are demanded for film capacitors. That is, the film capacitors of small type and high characteristic performance are being developed extensively. The inventors have made research works for manufacturing the film capacitor element such as a stacked body or a lamination, whereof selective removal of organic dielectric substance is made at the electrode connection part. The art which was not disclosed to public, but was under research work before as prior stage to conceiving of the present invention is elucidated with reference to FIG.2 and FIG.3, for the sake of easy understanding of the present invention. FIG.3 shows an oxygen plasma processing apparatus and a state of manufacturing a film capacitor body by selective removal of the organic dielectric film in the stacked body or the lamination, for making electrode connecting part. In FIG.3, a film capacitor body 1 comprises a multiple layer lamination, stack or roll of plastic dielectric films, e.g. polyphenylene-sulfide (hereinafter is referred to being abbreviated as PPS) films, 1a and aluminum films 1b vapor-deposited on the PPS films as electrodes, forming alternate lamination of the dielectric film and the electrodes, in a form of a laminated body or a stacked body or wound into a roll-shape. The film capacitor 1 is placed on a water-cooled table-shaped lower electrode 5 disposed in a vacuum chamber 3. The vacuum chamber 3 further comprises an upper electrode 4, which has gas discharging perforations 41 on its lower surface for discharging O₂ gas in a chamber on the film capacitor body 1. And the upper electrode 4 is applied with a radio frequency power of 13.56 MHz from a radio frequency power source 2. The film capacitor body 1 is sandwiched between a pair of mask members 6,6 which covers upper and lower end faces of the film capacitor body 1 so as to isolate them from the low temperature oxygen plasma during the oxygen plasma processing. The masks are made, for instance, with aluminum sheets. The vacuum chamber 3 is connected to a known vacuum pump 7 for evacuating the air inside thereof. In the above-mentioned chamber, the O₂ plasma etching is made by discharging O₂ gas from the perforations 41 of the upper electrode 4 into the chamber and applying a radio frequency power from the upper electrode 4 and the lower electrode 5 to the O₂ gas in the chamber 3. Thus, the O₂ gas is excited to become oxygen plasma such that a reaction-active oxygen radicals against the organic film is produced in the oxygen plasma. And the exposed side surfaces of the laminated or stacked film capacitor body 1 is selectively etched and removed by contacting with the oxygen radicals, thereby making the end parts of the vapor deposited aluminum electrode 1b relatively to protrude from the oxygen-plasma-etched side faces of the PPS film 1a. Then, a known metalicon layer 8,8 are formed on the exposed protruding edges of aluminum electrodes so as to make connection to the electrodes. FIG.2 is a graph of curves which show relation between processing time (minutes) and amount (depth: µm) of the selective etching of PPS film at the side face, and also temperature rises for several radio frequency powers applied to the chamber. One example of other processing conditions were as follows: size of process chamber: As shown in FIG.2, it is observed that (1) the larger the applied radio frequency power is, the faster the etching speed (etching depth: µm) of the PPS film 1a is, and the higher the temperature rise late becomes, (2) after lapse of a predetermined time from an application of the radio frequency of a given intensity, the temperature rise becomes constant, (3) when the radio frequency power of 700 W or larger is used for etching 50 µm depthwise of PPS film from the side face, the temperature of the whole body of the PPS film capacitor body 1 rises too high above the threshold durable temperature; whereas when the radio frequency power is 500 W or lower for the same etching the temperature of the PPS film capacitor body 1 does not exceeds the threshold durable temperature, and the intended 50 µm depth etching of PPS film is made by processing for 45 minutes, and (4) when the radio frequency power is 300 W or lower, the processing time becomes 60 minutes or longer, which is too long. That is, in the non-disclosed prior stage method of the radio frequency etching of the PPS film capacitor body, the safe processing time is 45 minutes or longer at the radio frequency power of 500 W. In other word, when the applied radio frequency power is larger, the oxygen plasma density is raised much, and generation of the oxygen radicals which react with the PPS film 1a increases, and hence the etching speed for the PPS film 1a is increased. On the other hand, an excessively large radio frequency power application will unduly raise the temperature of the PPS film 1a above the durable threshold (melting point) of the PPS film 1a, thereby adversely melting the PPS film 1a at inside and as the whole. Accordingly, the applied radio frequency power must be limited under a safe threshold value, and thereby the etching speed has not been sufficient. OBJECT AND SUMMARY OF THE INVENTION The inventors consider the above-mentioned nature and conditions of the etching speed of the film capacitor body and the safe threshold power which does not to melt the inside and whole part of the PPS film capacitor body, and summarized as follows: (1) first, the non-disclosed prior stage application of the radio frequency power which power is lower the safe threshold limit results in insufficient small production of the active radicals of oxygen which makes reaction with the side surface of the film capacitor body of PPS dielectric substance, and results in an insufficiently low etching speed and hence undesirably long processing time; (2) generally, the higher the temperature in the processing is, the higher the etching speed of the organic substance such as PPS is; and (3) when the low and constant power of the radio frequency is applied, the temperature rise rate is very small, and therefor the time increase rate of the etching speed is insufficiently small, thereby resulting in an unduly long etching time of the side face of the PPS film capacitor body. Considering the above-mentioned, the inventors conceived the present invention which can shorten the processing time without undesirable melting of the inside and whole part of PPS film capacitor body. The above-mentioned object of the present invention is achieved by a method for manufacturing a film capacitor comprising the steps of: selectively etching side faces of a film capacitor body comprising a multiple layer lamination, stack or roll of plastic films and electrode layer, by contacting them with a reactive gas which is reactive to selected parts of the plastic films and thereafter forming connection metal members on the exposed protruding edges of the electrode layer to mutual and outward connections of plural exposed protruding edges to make edge terminal, wherein radio frequency power for generating reactive gas and to heat the film capacitor body are applied to the reactive chamber in a two-stage processing which comprises: a first stage of applying a larger intensity, whereby a sufficient amount of the reactive gas is generated and temperature of the film capacity body is raised to a predetermined temperature which is close to but below the welting point of the plastic film, and a second stage which is subsequent to the first stage, of applying a smaller intensity, whereby the film capacity body having its temperature raised in the first stage is maintained around the predetermined temperature but below the welting point. By means of the above-mentioned method, by application of a stronger radio frequency power in the first stage, much amount of component which is reactive with the organic substance is produced in the oxygen plasma, and thereby etch-removing-speed against the side face of the organic dielectric substance is accelerated and the process time is shortened. Therefore, the temperature of the laminated or stacked film capacitor body is raised to the temperature which is appropriately close to the threshold durable temperature within a short time period. Then, by application of the weaker radio frequency power in the second stage process, the etch-removing of the side face of the film capacitor body is carried out safely under the threshold temperature but close thereto, without fear of undesirable temperature rise above the safety threshold temperature. By adopting the above-mentioned two-staged process instead of the non-disclosed prior stage process of applying radio frequency power of constant intensity in a single stage, drastically expedited short time period, without fear of damaging the film capacitor body. BRIEF EXPLANATION OF THE DRAWINGS FIG.1 is a graph showing relations between processing time (minutes) and amount (depth: µm) of the selective etching of PPS film at the side face, and also temperature rises for radio frequency power applied to the chamber of the preferred embodiment made in accordance with the method of the present invention. FIG.2 is a graph of a prior stage non-disclosed art showing relations between processing time (minutes) and amount (depth: µm) of the selective etching of PPS film at the side face, and also temperature rises for several radio frequency powers applied to the chamber. FIG.3 is a sectional view showing a parallel type manufacturing apparatus which is common to the non-disclosed prior stage method and the embodiment. FIG.3A is a sectional view showing the film capacitor body whereon metalicon layers are provided on its plasma-etched side part. FIG.4 is a sectional view showing a barrel type manufacturing apparatus to be used for the method of the present invention. It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. DETAILED DESCRIPTION OF THE EMBODIMENT Hereafter the preferred embodiment is elucidated with reference to the accompanying drawings of FIG.1 and FIG.3. FIG.1 is a graph of curves which show relations between processing time (minutes) and amount (depth: µm) of the selective etching of PPS film at the side face, and also temperature rises for several radio frequency powers applied to the chamber, with respect to the preferred embodiment made in accordance with the present invention. The manufacturing apparatus of FIG.3 and conditions other than the below-mentioned two step application of the radio frequency power are applicable also to the present embodiment. An oxygen plasma processing apparatus as shown in FIG.3 is used by combining a program of applying radio frequency power in two stage manner. In FIG.3, a film capacitor body 1 comprises a multiple layer lamination, stack or roll of plastic dielectric films, e.g. polyphenylenesulfide (hereinafter is referred to being abbreviated as PPS) films 1a, and aluminum films 1b vapor-deposited on the PPS films as electrodes, forming alternate lamination of the dielectric film and the electrodes, in a form of a laminated body or a stacked body or wound into a roll-shape. In actual processing, a number of the film capacitor bodies 1 are placed on a water-cooled table-shaped lower electrode 5 disposed in a vacuum chamber 3. The vacuum chamber 3 further comprises an upper electrode 4, which has gas discharging perforations 41 on its lower surface for discharging O₂ gas in a chamber on the film capacitor body 1. And the upper electrode 4 is applied with a radio frequency power from a radio frequency power source 2. The film capacitor body 1 is sandwiched between a pair of mask members 6,6 which covers upper and lower end faces of the film capacitor body 1 so as to isolate them from the low temperature oxygen plasma during the oxygen plasma processing. The masks are made, for instance, with aluminum sheets. The vacuum chamber 3 is connected to a known vacuum pump 7 for evacuating the air inside thereof. In the above-mentioned chamber 3, the O₂ plasma etching is made by discharging O₂ gas from the perforations 41 of the upper electrode 4 into the chamber 3, and by applying a radio frequency power from the upper electrode 4 and the lower electrode 5 to the O₂ gas in the chamber 3 to excite the O₂ gas to become oxygen plasma and to the film capacitor body 1. And the exposed side surfaces of the laminated or stacked film capacitor body 1 is selectively etched and removed by contacting with the oxygen plasma, thereby making the end parts of the vapor deposited aluminum electrode 1b relatively to protrude from the oxygen-plasma-etched side faces of the PPS film 1a. The difference of manufacturing process of the preferred embodiment from the afore-mentioned non-disclosed prior stage method is adoption of a two-stage application of radio frequency powers to the reaction chamber, in that a first stage is of larger radio frequency power intensity and a second stage is of smaller radio frequency power intensity. Then, a known metalicon layer 8,8 are formed on the exposed protruding edges of aluminum electrodes so as to make connection to the electrodes. FIG.2 is a graph of curves which show relation between processing time (minutes) and amount (depth: µm) of the selective etching of PPS film at the side face, and also temperature rises for several radio frequency powers applied to the chamber. One example of other processing conditions were as follows: size of process chamber: In the present invention, the selective etching of side faces of a film capacitor body 1, which comprises a multiple layer lamination, stack or roll of plastic films and electrode layer, is made by contacting the film gas, wherein the first stage processing is made by applying radio frequency power of 700 W for 20 minutes, and the second stage processing is made by application of the radio frequency power of 500 W for 15 minutes. As mentioned above, the radio frequency power is applied in two-stage application with different power intensities, wherein in the first stage application of the larger radio frequency power of 700 W, the component which is reactive to the PPS film 1a is generated in oxygen plasma and speed of etching the PPS film 1a is accelerated thereby to shorten the processing time, and the temperature of the film capacitor body 1 is raised in the processing to 270°C which is close to but under the heat resistive threshold temperature of the film capacitor body 1 within the short time of 20 minutes in the first stage. And in the second stage processing, a smaller intensity of radio frequency power of 500 W is applied so that the temperature of the film capacitor body 1 is controlled not to exceeds 285 °C which is the heat resistive threshold temperature of the film capacitor body 1; that is, the process of etching the side face of the film capacitor body 1 is made by keeping the inside and surface temperatures of the film capacitor body 1 at about 270 °C. Thus by the two-stage power application, a more efficient processing can be made at a higher temperature region in comparison with the non-disclosed prior stage case where a constant radio frequency power of 500 W is applied. In other words, by heating with the larger radio frequency power of 700 W in the first stage, the side face of the PPS film capacitor body 1 is etched within a shorter time than processing with the constant lower radio frequency power of 500 W in the non-disclosed prior stage single stage processing. As shown in FIG. 1, since the combination of the applications of stronger radio frequency power in the first stage and weaker radio frequency power in the second stage is used, the side face etching of 50 µm depth of the PPS film 1a can be made within the total processing time of only 35 minutes wherein the first stage is 20 minutes and the second stage is 15 minutes. This total processing time of 35 minutes is shorter by 10 minutes than 45 minutes of the inventors' non-disclosed prior stage art method made in the same apparatus for the same film capacitor body. Preferable ratio of the high frequency powers of the second stage is between 30 % to 85 % of that of the first stage. Under 30% the etching speed is too low, and above 85 % the inside of the film capacity body is damaged such as to make voids or short circuit of electrode. In the above-mentioned embodiment, the plastic dielectric film was PPS film, but the present invention is applicable to film capacitor bodies using PET (polyethylenetelephthalate) film or PEN (polyethylenenaphthalate) film or PP (polypropylene) film or PC (polycarbonate) film quite similarly, since these plastic films has fundamentally similar thermal characteristics though their melting temperatures are different. Furthermore, as the processing apparatus, in place of the parallel electrode type plasma etching apparatus as shown in FIG.3, a barrel type plasma etching apparatus as shown in FIG.4 wherein a pair of electrodes 45,45 for applying the radio frequency power is provided on outside face of a vacuum thamber 3, can be similarly used in the method of the present invention. Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

Claims: A method for manufacturing a film capacitor comprising the steps of: placing a film capacity body comprising a multiple layer lamination, stack or roll of plastic films and electrode layers in a plasma etching chamber, selectively etching side faces of said film capacitor body by contacting them with a reactive gas which is excited to be reactive to selected parts of said plastic films by application of a radio frequency power to a gas discharge electrode of said plasma etching chamber, and thereafter forming connection metal members on said exposed protruding edges of said electrode layers to mutual and outward connections of plural exposed protruding edges to make edge terminations, wherein said radio frequency powers for exciting said reactive gas and to heat the film capacitor body are applied to said plasma etching chamber in a two-stage processing which comprises: a first stage of applying a larger intensity radio frequency power, whereby a sufficient amount of said reactive gas is generated and the temperature of said film capacity body is raised to a predetermined temperature which is close to but below the melting point of said plastic film, and a second stage which is subsequent to said first stage, of applying a smaller intensity of radio frequency power, whereby said film capacity body having its temperature raised in said first stage is maintained around said predetermined temperature but below said melting point. A method for manufacturing a film capacitor in accordance with claim 1, wherein said plasma etching chamber has a parallel type electrodes. A method for manufacturing a film capacitor in accordance with claim 1, wherein said plasma etching chamber has a barrel type electrodes. A method for manufacturing a film capacitor in accordance with claim 1, wherein said radio frequency power of said second stage is about 30-85 % of that of said first stage.

Inventors: IKEDA, TANEJIRO, KIMURA, TADASHI
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: H01G1
IPC codes: H01G4, H01L21, C08J7