GB2094061A

GB2094061A - Multilayer capacitors and methods and apparatus for making them

Info

Publication number: GB2094061A
Application number: GB8205130A
Authority: GB
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 1981-02-27
Filing date: 1982-02-22
Publication date: 1982-09-08
Also published as: AT386296B; ES8303810A1; IT1149778B; DK151424C; CA1173123A; FI820707L; GB2143087B; IE53253B1; DE8227050U1; PT74140B; IE820435L; ATA30282A; CH645748A5; JPH0474848B2; FI78795C; GB2143087A; NO157000B; NL191547B; NL8105732A; FI78795B

Abstract

A capacitor comprises a plurality of layers 18a, 18b each layer comprising a dielectric substrate 6a and a metallic film 8a extending from one edge to the other but including a zone 10 free of said metallic film and adjacent to but spaced from one edge to leave a narrow marginal metal film band 24 at said edge. The layers are disposed alternately offset and reversed laterally, such that alternate edges 33 of layers 18a lie beyond the marginal band edged 36 of the layers 18b, and vice versa at the opposite side of the capacitor. The outwardly lying edges 33, of the layers are coated with electrically- conductive material 40a to connect electrically the alternate metal film layers in two groups. The capacitors are made by laser- scribing parallel metal-free zones onto webs A and B. The webs are slit into ribbons by blades 21a prior to winding onto a drum 20 on offset and laterally reversed fashion, to produce a plurality of side-by-side annular layered members. Rollers 16a, 16b and said slitting blades 21a are close to the drum 20, such that the slit ribbons are supported over substantially their full lengths prior to winding onto said drum. The annular members are separated and individually cut transversely to the ribbons, to form stacked capacitors. <IMAGE>

Description

SPECIFICATION Capacitors and methods and apparatus for making them This invention relates to layer or stack wound capacitors and to methods and apparatus for making them.

One such method and apparatus is shown and described in U.S Patent No. 3 670 378. In that patent the process for the production of the capacitors comprises first forming capacitor bodies by winding alternate metallic and dielectric films on a drum, contemporaneously winding separating layers between the capacitor bodies to form a parent winding having alternate layers of capacitor bodies and separating layers, then applying a metallic spray coating to the edges of the parent winding to connect metallic films, and thereafter severing the parent winding perpendicular to the separating layers to form the individual capacitor bodies. These resultant capacitor bodies have interwoven metallic layers which are separated by dielectric layers.The layers of one group comprising dielectric substrates and metallic films project outwardly from one side of the capacitor body while another group of substrates and films, alternating with the first group, project from the other side of the capacitor body. The metallic coating is applied such that it connects electrically together the metallic films on the outwardly projected group of layers. Thus, there are provided two electrodes or sets of capacitor "plates" which are dielectrically isolated from one another but which are interwoven.

In the foregoing arrangement it sometimes happens that during the winding process the beingwound layers will weave or depart from their intended paths, resulting in one or more layers being improperly located with respect to the adjacent layers. If the lateral offset between the groups of layers is not sufficient, the capacitor may be shortcircuited or it may have a lower than intended dielectric strength at one or more regions. If the lateral offset is excessive, the resulting capacitance of the capacitor is reduced.

An object of this invention is to provide a high quality commercial capacitor of the general type stated, but which is different in structure and wherein the manufacturing process is considerably lower in cost.

A further object of this invention is to provide an arrangement of the type stated which materially reduces the possibility of short-circuiting of the being-wound capacitor as a result of improper disposition of the metallic and dielectric films.

Another object of this invention is to provide an arrangment of the type stated in which the production of capacitors is much faster than it is possible with the presently available equipment.

Another object of this invention is to provide apparatus of the type stated which functions to apply the layers forming the capacitor to a drum or transfer wheel directly from laminating or lay-on rollers.

Such an arrangement prevents the supply material from travelling unsupported in space, thereby reducing weave and consequent misalignment of the capacitor layers.

In accordance with one aspect of this invention, a capacitor comprises a plurality of layers having opposed edges, each layer comprising a dielectric substrate and a metallic film, the metallic film extending from one edge towards the other edge, each layer including a zone free of said metallic film, said zone being adjacent to but spaced from said other edge to leave a narrow marginal metal film band at said other edge which is spaced by said zone from the remainder of said metallic film, said layers being disposed with the layers in a first group of layers alternating with the layers of a second group of layers, with the metal film of one layer being separated by dielectric material from the metal film of the adjacent layer, said layers being relatively reversed laterally and also offset, such that at one side of the capacitor said edges of the first group of layers lie outwards beyond said other edges of the second group of layers, and at the opposite side of the capacitor said edges of the second group of layers lie outwards beyond said other edges of the first group of layers, and the outwardly lying edges of the layers in each group being coated with electrically-conductive material to connect electrically the metal film layers of each group. Said narrow marginal metallic film band thereby separates the adjacent coating material from the metal-free zone.

In accordance with another aspect of this invention, a method of making a capacitor comprises: providing first and second webs of material each having a dielectric substrate, a metallic film coating, and narrow parallel longitudinal metal - free zones; slitting said webs along parallel lines that are offset from said metal-free zones to form ribbons each of which has a narrow marginal metal film band extending inwards from one longitudinal edge of the ribbon to said metal-free zone; winding said ribbons from said first and second webs alternately on a drum while relatively reversed laterally, and in said winding offsetting the ribbons of one web from the ribbons of the other web to form a plurality of adjacent rings of capacitance structure each having alternately disposed metal and dielectric layers, with there being in each structure the layers from the ribbons of each web respectively projecting laterally outwards from said marginal metal film bandsfrom the ribbons of the other web; removing the structures from the drum and separating the structures from each other; coating the laterally projected parts of each structure with a metal substance to connect electrically the metal films of the respective webs of the structure; and severing the structure transversely of the ribbons to form capacitors.

In accordance with another aspect of this invention, apparatus for making capacitors comprises: first and second supply rolls of webs, each web having a dielectric substrate with a metallic film coating; a rotatable drum spaced from said supply rolls; first and second laminator rollers, said rollers being circumferentially spaced with respect to the periphery of said drum; a tension-sensing roller associated with each laminator roller and in spaced parallel relation thereto to constitute with its associ ated laminator roller a roller pair, one web being strained and tensioned over each roller pair; and means for slitting the webs into ribbons prior to winding said ribbons onto said drum to provide alternate layers of metallic and dielectric material; said laminating rollers being sufficiently close to said drum, and said slitting means being sufficiently close to said laminating rollers, such that the ribbons are supported over substantially their full lengths prior to winding onto said drum.

Preferably in a capacitor said metal-free zone and said narrow marginal metal film band have a combined width which is a minor fractional part of the width of the associated layer.

The method may also include the application to both of the webs of a thin film of adhesive in at least a portion of the electric fieid regions of a capacitor, but the adhesive is not applied in the region of slitting of the web nor in the laterally projected parts of the structure where a spray contact is made with the metallic coating. The purpose of the adhesive is, to the extent needed, to lock the lamination so that the wound capacitor structure can be handled without delamination.

Preferably each of the webs is passed through a station where a number of laser beams can burn off the metal to form precisely spaced demetalized zones. These demetalized zones may be made much narrower by laser beam burn-off than would be obtainable by material commercially available with conventional demetalized zones, which are much wider than is necessary for capacitors with low voltage ratings.

The accompanying drawings show examples of capacitors and apparatus embodying the invention.

In these drawings: Figure lisa diagrammatic view of the apparatus; Figure 2 is a fragmentary enlarged sectional view taken along the Ine 2-2 of Figure 1; Figure 3 is a fragmentary top-plan view of the structure of Figure 2; Figure 4 is a further enlarged fragmentary sectional view taken along the line 4-4 of Figure 3; Figure is an enlarged diagrammatic view, partially in section taken along the line 5-5 of Figure 1; Figure 6 is a much enlarged fragmentary sectional view, on the same scale as Figure 4, of parts of a capacitor; Figure 7 is an enlarged fragmentary portion of Figure 2 and showing a modification for applying adhesive to the web; and Figure 8 is a diagrammatic showing of a modification including a laser burn-off station which forms the demetalized zones as a web is withdrawn from its supply roll.

Referring now in more detail to the drawings, in Figure 1 there is shown a pair of supply rolls 1,4 from which webs A and B are withdrawn. Each of the webs A, B comprises a dielectric substrate 6 and a metallic film 8 (Figure 4). The substrate 6 may be of a suitable plastics material such as the resin sold under the tradmark "Mylar". The film 8 may be of vapour-deposited aluminium, and both the substrate 6 and metallic film 8 are exceedingly thin. By way of example but not of limitation, the substrate 6 may be of the order of 0.001 inches (0.025 mm) or less in thickness while the thickness of the metalized film 8 may be of the order of 500 angstrom units. Each web A, B has a plurality of parallel demetalized or metal-free zones 10. These are best seen in Figures 3 and 4 with respect to the web B, but it is understood that a like series of demetalized zones are provided on the web A.The webs A, B may have the demetalized zones 10 preformed thereon, or these zones may be formed by a laser burn-off method as will later be described. In any case the webs pass over a series of rollers respectively, for slitting into ribbons and for interleaved or alternate winding onto a large diameter drum or transfer wheel 20.

In particular, the web A passes over an idler roller 1 2a, the axis of rotation of which is shiftable to control weave ofthe web A. The idler roller 12a moves parallel to its axis as a unit with the supply roll 2 under the control of a conventional edge guide sensor (not shown) to control the weave. From the idler roller 12a, the web passes by the aforementioned edge guide sensor to a tension-sensing roller 14a. The tension-sensing roller sends a signal to a variable-drag clutch (not shown) on which the supply roll 2 is mounted. This closed loop control maintains the tension at any preset value. The apparatus also includes a laminating or lay-on roller 16a.Between the rollers 14a, 16a is a web-slitting station at which the web A is slit into a plurality of ribbons prior to passage around the lay-on roller 16a and wrapping onto the drum or transfer wheel 20.

Similarly, the web B passes over a shifting idler roller 1 2b and from there to a tension-sensing roller 14b, past the slitting station and onto a laminating or lay-on roller 1 6b, and the idler roller 1 2b responds to a second edge guide sensor (not shown) to control the weave of web B while the tension-sensing roller 14b again sends a signal to a variable-drag clutch (not shown) on which the supply roll 4 is mounted, to maintain the tension ata presetvalue.

The tension sensing and edge guide control system employed are available from Advanced Web Systems, Inc, 4793 Colt Road, P.O. Box 6025, Rockford, Illinois 61125, United States of America.

The slitting station for the web B comprises a plurality of spaced parallel cutters such as razor blades 21b which cooperate with a polished web support bar 22b over which the web B passes.

Likewise, for the web A the slitting station comprises spaced parallel razor blades 21a (Figure 7) which cooperate with a web support bar. For each web the slitting station forms a plurality of ribbons which immediately pass onto the roller 1 6a or 16b, as the case may be, and then onto the drum 20. The result is that the ribbons are supported substantially throughouttheirfull length priortowinding onto the drum 20. Because the ribbons do not travel unsupported in space, weave is eliminated and the ribbons can be accurately deposited onto the drum 20. This is in contrast to prior art arrangements which rely upon edge guides, sometimes unsatisfactorily, to prevent weave of the web.

The laminating or lay-on rollers press against the drum or transfer wheel 20, and the razor blades may operate directly in narrow slits on the rollers 16a, 166. In any event, the arrangement for slitting the webs provides smooth cuts by the razor blades without causing the web material to wrinkle. This is particularly important as it is difficult to obtain smooth cuts without wrinkling in web material as thin as that utilized in the present invention. In the present apparatus, the rollers 16a, 16b may be located either 90 apart as shown in Figure 1, or 180 apart.

The web B is slit into the plurality of ribbons 18b, as seen in Figures 2 to 4. The web A is also slit to provide ribbons 1 8a which, like the ribbons 1 8b, ultimately will become capacitor layers, as seen in Figure 6. The slit lines for the web B are offset from the demetalized zones 10 so as to form marginal metal film bands 24 at one edge of eachribbon 18b.

A like slitting takes place for the web A except, however, that the slit line for each blade 21a is in laterally reversed position from that in Figure 3 to form marginal film bands 24 on the ribbons 18a.

Thus, if each blade 21b is located to the left of the adjacent demetalized zone 10 in cutting the web B (reference to Figure 3) then for the web A each blade 21a will be to the right of the adjacent demetalized zone, as indicated by arrows 21aa in Figure 3.

The ribbons are disposed simultaneously upon the drum 20 to produce the layered pattern shown in Figure 5. There are formed a plurality of hoops or rings 30 of capacitor structure from which individual capacitors may be formed. In Figure 5 only one of the rings 30 is shown in cross section for purposes of clarity of illustration. Moreover, the sources of the various ribbons, namely from the supply web A or B, is indicated on one of the rings 30 in Figure 5. It will also be apparent that the ribbons are not illustrated to scale, but rather the thickness is greatly exaggerated. In any case, there is an initial winding of layers of web A adjacent to the drum 20, as shown by the lower five such layers designated in Figure 5.

Thereafter, the ribons are interleaved and offset from each other as they are simultaneously wound onto the drum 20 to form the pattern indicated by the A and B alternate layers in Figure 5. In the A layers, the demetalized zone is near the right-hand edge 37, while in the B layers the demetalized zone is near the left-hand edge 36. That is to say the layers are identical but relatively reversed laterally. Thereafter, another group of A layers are wound over the group of A and B alternate layers. The inner and outer A layers serve as reinforcement on the faces of the capacitors, while the interweaved A and B layers or ribbons provide the active portion of the capacitor structure.

Each of the separate rings 30 is removed from the drum 20, and the sides 32,34 thereof then coated in a conventional manner with a metallic spray coating 40 (Figure 6). That is to say, one coating 40a is applied to the outwardly lying left-hand edges 33 of the A layers 8a 6a, and the other coating 40b is applied to the outwardly lying right-hand edges 35 of the B layers 8b, 6b. The ring 30 may then be cut perpendicular to the edges 32, to form a length of capacitor structure. That length can then be cut again transversely to form individual capacitor units.

Figure 6 shows an enlarged sectional view through several interleaved layers of the capacitor. It will be seen that, at the left side of the capacitor, layers from portions of the ribbon 1 8a comprising the metalized film 8a and of the substrate 6a project laterally outwardly of the adjacent edges 36 of the layers from portions of the ribbon 18b. The metal ized spray coating 40a electrically connects the metalized films 8a to form a set of capacitor electrodes or plates, this being made possible by the spaces between the layers from ribbon 18a. The space between the left-hand metallic coating 40a of the top portion of Figure 6 and the metalized film 8b of the layers from ribbon 18b is at least the width of the demetalized zone 10 plus the width of the marginal metal film band 24.In general, the coating 40a does not penetrate to the edges 36, and so does not make any electrical connection with the bands 24. Thus, in effect, each band 24 is a "floating" electrode. By providing for the floating electrode formed by the band 24, the full width of the demetalized zone 10 is utilized for dielectric separation along the surfaces of the layers, thereby reducing the possibility of short-circuiting or changing the capacitance of the capacitor from its prescribed value. If by chance the coating 40a does penetrate to any of the edges 36, the relevant band 24 acts as a barrier, so that the full width of the demetalized zone 10 is preserved as insulation between the band 24 and the respective film 8b.

On the right side of the capacitor, as shown by the lower portion of Figure 6, the layers from portions of the ribbon 18b project outwards from the margin 37 of the layers from the ribbon 18a for receiving the right-hand metal spray coating 40b, shown in the bottom portion of Figure 6. Each marginal metal film band 24 is, in the lower portion of Figure 6, located on a layer from ribbon 18a, and likewise serves as a "floating" electrode or as a barrier, so that full advantage is taken of the demetalized zones 10, as previously described.

In a modified form of the invention shown in Figure 7 any suitable thin adhesive may be deposited on both of the webs A and B by applicators 50 positioned just before the slitting operation occurs.

Epoxy resin is one type of adhesive that may be used, but the invention is not limited thereto. The adhesive is not applied in the region of slitting or in the extension area of the web where the metallic spray is to be applied. The purpose of the adhesive, if needed, is to lock the laminations together after being wound onto the drum 20 so that the rings 30 can be handled without delamination. The adhesive can be deposited and spread in a film thickness substantially less than one micron, and the adhesive may thus be used without materially reducing an efficient capacitance-to-volume ratio.

The web material used in the present invention may be purchased with the demetalized zones.

However, these demetalized zones are usually somewhat wider than is necessary for low voltage capacitors. Accordingly, as shown in Figure 8, it is possible to form the demetalized zones 10 as the web A or B is being withdrawn from the supply roll. This may be accomplished by running the web through a laser burn-off station 52 at which laser beams 53 may be utilized to burn off the deposited metal and form extremely narrow demetalized zones 10, much narrower than are provided on commercially available webs. Consequently, material cost is reduced along with the size of the capacitor. For example, the width of the zones 10 may be about 200 microns.

Claims

1. A capacitor comprising a plurality of layers having opposed edges, each layer comprising a dielectric substrate and a metallicfilm,the metallic film extending from one edge towards the other edge, each layer including a zone free of said metallic film, said zone being adjacent to but spaced from said other edge to leave a narrow marginal metal film band at said other edge which is spaced by said zone from the remainder of said metallic film, said layers being disposed with the layers in a first group of layers alternating with the layers of a second group of layers with the metal film of one layer being separated by dielectric material from the metal film of the adjacent layer, said layers being relatively reversed laterally and also offset, such that at one side of the capacitor said edges of the first group of layers lie outwards beyond said other edges of the second group of layers, and at the opposite side of the capacitor said edges of the second group of layers lie outwards beyond said other edges of the first group of layers, and the outwardly lying edges of the layers in each group being coated with electrically-conductive material to connect electrically the metal film layers of each group

2. A capacitor according to claim 1, in which said metal-free zone and said narrow marginal metal film band have a combined width which is a minor fractional part of the width of the associated layer.

3. A capacitor according to claim 2, further including reinforcing layers on opposite faces of said assembled first and second groups of layers.

4. A method of making capacitors, comprising: providing first and second webs of material each having a dielectric substrate, a metallic film coating, and narrow parallel longitudinal metal-free zones; slitting said webs along parallel lines that are offset from said metal-freezonestoform ribbons each of which has a narrow marginal metal film band extending inwards from one longitudinal edge of the ribbon to said metal-free zone; winding said ribbons from said first and second webs alternately on a drum while relatively reversed laterally, and in said winding offsetting the ribbons of one web from the ribbons of the other web to form a plurality of adjacent rings of capacitance structure each having alternately disposed metal and dielectric layers, with there being in each structure the layers from the ribbons of each web respectively projecting laterally outwards from said marginal metal film bands from the ribbons of the other web; removing thestruc- tures from the drum and separating the structures from each other; coating the laterally projected arts of each structure with a metal substance to connect electrically the metal films of the respective webs of the structure; and severing the structure transverse Iyofthe ribbons to form capacitors.

5. A method according to claim 4, comprising placing the webs in tension over a length of each web, and slitting the webs at said tensioned lengths.

6. A method according to claim 5, further comprising interposing adhesive between the beingwound ribbons of each structure.

7. Apparatus for making capacitors, comprising: first and second supply rolls of webs, each web having a dielectric substrate with a metallic film coating; a rotatable drum spaced from said supply rolls; first and second laminator rollers, said rollers being circumferentially spaced with respect to the periphery of said drum; a tension-sensing roller associated with each laminator roller and in spaced parallel relation thereto to constitute with its associated laminator roller a roller pair, one web being strained and tensioned over each roller pair; and means for slitting the webs into ribbons prior to winding said ribbons onto said drum to provide alternate layers of metallic and dielectric material; said laminating rollers being sufficiently close to said drum, and said slitting means being sufficiently close to said laminating rollers, such that the ribbons are supported over substantially their full lengths prior to winding onto said drum.

8. Apparatus according to claim 7, in which said laminator rollers are approximately 90 apart at the periphery of the drum.

9. Apparatus according to claim 7, in which said laminator rollers are approximately 180 apart at the periphery of the drum.

10. Apparatus according to any of claims 7 to 9, including means being the rollers of each pair for applying adhesive to the surface of the respective web.

11. Apparatus according to claim 10, in which each adhesive-applying means is between the respective tension-sensing roller and slitting means.

12. Apparatus according to any of claims 7 to 11, including laser means for forming a plurality of longitudinal parallel metal-free zones on each web priorto slitting oftheweb.

13. A capacitor according to claim 1, substantially as described with reference to Figure 6 of the accompanying drawings.

14. A method according to claim 4, substantially as described with reference to Figures 1 to 6 of the accompanying drawings, or modified as described with reference to Figure 7 or Figure 8.

15. Apparatus according to claim 7, substantially as described with reference to Figures 1 to 4 of the accompanying drawings, or modified as described with reference to Figure 7 or Figure 8.