GB2115213A - Laminated bus bar with dielectric inserts - Google Patents

Abstract

The capacitance of the bar is substantially increased by separating each pair of conductors (12, 22, 32, 82) by a thin, flexible layer (42) of plastics dielectric insulation having a resin coating thereon and which has incorporated in an opening (43) therein a ceramic insert (44) e.g. barium titanate, opposite sides of which are metallized, or coated with a thin layer of metal. The layer (42) of insulation is then partially cured to cause part of the resin coating on the insulation to flow and fix the insert in the opening in the insulation. This permits the partially cured insulation to be manipulated during its incorporation into a bus bar assembly where it is interposed between two strip conductors (Figs. 1 and 2 not shown). The assembly is thereafter laminated in a dielectric jacket (40') in such manner that opposite sides of each dielectric ceramic insert will be engaged with the confronting surfaces of adjacent conductors. Alternate conductors can be connected to each other through their projecting terminals (14, 24, 34, 84) to increase the capacitance between various conductors in a bar. <IMAGE>

Description

SPECIFICATION Laminated bus bar with dielectric ceramic inserts and method of making same THIS INVENTION relates to laminated bus bars, and more particularly to a method of making a laminated bar of the type in which thin dielectric ceramic wafers or inserts are incorporated in its insulation to increase its electrical capacitance.

Laminated bus bars of the type described are frequently employed for transmitting power to a variety of circuits, including circuits which utilize AC or DC signals, or combinations of both. Preferably these bus bars have low characteristic impedance and high capacitance. Recent technology in the area of thin layered ceramic capacitors has reached a level in which it has been possible to produce extremely thin metallized layers or wafers of ceramic dielectric materials which are suitable for incorporation directly into a laminated bus bar.

For example, U.S. Patent No. 3,778,735 teaches the desirability of inserting a plurality of ceramic wafers, each with a metallized coating on each side thereof, between the surfaces of a pair of metal conductor strips, which are encapsulated in an insulating sheath. And each of U.S. patents No.

4,236,046 and No. 4,266,091 suggests using an electrically conductive adhesive for securing such metallized ceramic wafers or chips to the faces of the conductors between which they are sandwiched. U.S. patent No.

4,236,038, on the other hand, suggests using a non-conductive adhesive for this purpose.

One of the problems with known methods of producing high capacity bus bars has been the difficulty in assemblying the bars with the metallized ceramic wafers properly secured between adjacent conductor strips. Another problem is the fact that adhesives previously used between the chip and adjacent conductor interferred with the desired contact between a metallized surface of the chip and the confronting conductor, or, if the adhesive was of the electrically-conductive variety, tended to cause undesirable shorting between adjacent conductors.

A primary object of this invention, therefore is to provide a novel method for manufacturing laminated bus bars of the type described in which no adhesive, conductive or otherwise, is used between the confronting surfaces of the capacitor chips and the adjacent conductor strips. To this end the bars are produced from special layers of insulation, which are coated with a partially cured resin and which are provided with spaced openings.

Thin ceramic capacitors or inserts are then placed in these openings and the assembly is partially cured, as by heating at 150-250"F, so as to cause part of the resin to melt and flow into fixing engagement with the marginal edge portions, only, of the ceramic inserts, thereby to secure the inserts in the insulation.

Thereafter the insulation, with the inserts secured therein, is placed between conductors and laminated in a plastic jacket to complete the bar.

In this way the opposed faces of the inserts are held in direct contact with the confronting surfaces of the conductors, and without having any adhesive interposed between the metallized faces of the inserts and the confronting conductor surfaces.

Other objects and features of the invention will be apparent hereinafter from the following specification and claims, particularly when read in conjunction with the accompanying drawings, wherein: Figure 1 is a fragmentary plan view of a special layer of insulation which is adapted to be incorporated into laminated bus bars of the type made according to this invention; Figure 2 is a fragmentary plan view of an assembly fixture and illustrating the manner in which special laminating layers of the type shown in Fig. 1 are adapted to be incorporated into bus bars made according to this invention; Figure 3 is a fragmentary side elevational view of a bus bar after it has been assembled and laminated in accordance with one embodiment of this invention, a portion of the bar being broken away and shown in section;; Figure 4 is a view similar to Fig. 3 but showing a modified form of this bus bar; and Figure 5 is a fragmentary sectional view similar to Fig. 4, but showing only a portion of still another form of this bus bar.

Referring now to the drawings by numerals of reference, 40 denotes generally an insulator blank or laminate which comprises a pair of spaced side webs 41, which are interconnected by parallel, transversely extending insulator strips 42, each of which is adapted to be incorporated into a bus bar as noted hereinafter. Each of the insulator strips 42, which in the embodiment illustrated is about 7 mils thick, has therein a plurality of spaced, longitudinally extending, rectangular openings 43.

Secured in each opening 43 in a manner noted hereinafter is a thin capacitor made from a dielectric ceramic material such as, for example, a barium titanate composition sold by Minnesota Mining 8 Manufacturing Co.

under the trademark "Al Si Mag 1 283".

Each insert 44 in the embodiment illustrated has a thickness in the range of 7 to 10 mils, and preferably is at least as thick, or thicker, than the strip 42 of insulation in which it is housed. Although not illustrated in the drawings, it is to be understood that the opposed plane surfaces of each insert 44 are metallized, or coated with an extremely thin layer of metal, for example by vapor deposi tion or the like.

Each blank 40 may be prepared by cutting or punching it from a thin layer of flexible, plastic insulating material, such as for example the type sold by E. I. DuPont deNemours 8 Co., Inc. under the trade name "NOMEX", and which material has been previously coated with a partially cured resin.

This punching operation not only forms the rectangular openings 43 in the blanks, but also the circular openings 46 which are utilized later during assembly operations. In the embodiment illustrated each opening 43 is approximately 3/4" in length, and has a width approximately equal to half the width of respective strip 42.

After the cutting or punching operation, each blank 40 is sent to a sub-assembly point where the dielectric inserts or capacitors 44 are placed in the openings 43. The inserts fit snugly in the openings 43, but not so snugly that they will remain in the openings without further treatment. Therefore, in order to secure the wafers 44 in openings 43, at least so that the blanks can thereafter be manipulated during assembly of the bus bars without causing the wafers to drop from the openings, each blank 40 with the inserts 44 assembled therein is subjected to a relatively low termperature treatment, for example by placement in a heating unit maintained at a temperature in the range of 150"F to 250"F. This treatment causes some of the still uncured coating, on each blank 40 to melt and flow to engagement with the marginal edges of the inserts 44, thus securing the inserts in the associated blank 40. Each partially cured subassembly 40 with its inserts 44 can now be manipulated by an operator for assembly in the final bars as noted hereinafter.

It is important to note that the low temperature heat treatment (150"F to 250"F) of the sub-assembly 40 with inserts 44 does not result in the complete curing of the resin coating on the blank 40. It merely permits a portion of the resin to flow into contact with the inserts 44. Obviously when the sub-assemblies are withdrawn from the low temperature ambient the resin cools and secures the inserts 44 in the associated blank.

In order to assemble the blanks 40 with the attached inserts 44 into bus bars, the procedures as set forth in the U.S. Patent No.

3,886,654 may be followed. For example, using the assembly fixture 50 (Fig. 2) and a plurality of metal blanks 10, 20 and 30, an initial layer 40' of insulation, which is similar in configuration to the blank 40 except that it does not have therein any of the openings 43 or inserts 44, is located by means of its openings 46 over the mounting pins 52 on the fixture 50. Thereafter the side webs 11 of the blank 10 are mounted over the pins 52 to position this metal blank on the lower-most insulating blank 40', after which one of the sub-assemblies 40, containing the inserts 44 is mounted over the blank 10 in such manner that its inserts 44 will register with the midportions of the parallel conductor strips 1 2 which extend between the webs 11 of blank 10.Thereafter, as will be apparent from an examination of Fig. 2 herein, the blank 20 is assembled on top of the first insulating layer 40' which is similar to the bottom or initial insulating layer 40'.

After the above assembly steps have been completed, the assembly is partially laminated as explained in the above-noted U.S. Patent No. 3,886,654, the side webs of the insulating and conducting blanks are removed, and the final lamination step takes place to complete the lamination of each bar. This final lamination step also completes the curing of the resin coatings on the insulating layers 40, 40'.

Referring now to Fig. 3, which illustrates fragmentarily and partially in section a laminated bus bar made in accordance with the above-described process, it will be noted that in each such bar the opposed metallized surfaces of the inserts 44 are in direct contact with the adjacent confronting surfaces of the metal strips 12, 22 and 32 at longitudinally spaced points therealong. When the middle conductor 22, for example, is used as the grounded conductor, extremely high capacitance exists between it and the adjacent conductors 12, 32, as compared to prior bus bars of this type. Moreover, even in those instances when a bar of this type has been flexed to a point which could cause fracture of one or more of the ceramic inserts 44 contained in the bar, it has been found that the characteristically high capacitance of the bar is not substantially altered.

In the embodiment shown in Fig. 3, it will be noted that the various tabs or terminals 14, 24, and 34 of the respective strip conductors 12, 22 and 32 have been purposely offset from each other longitudinally of the bar to prevent any undesirable shorting of one upon the other. It has been found, however, that if the tabs 14, 34, of, for example, the strips 1 2 and 32 are deliberately placed in longitudinal registry with each other, and the registering tabs 14 and 34 are then deliberately connected to each other as shown in Fig. 4, the capacitance of the resulting bar, as between strip 22, and the now interconnected strips 1 2 and 32, is increased even further as compared to the bar shown in Fig. 3.

Still another type of bar is shown in Fig. 5, wherein like numerals are employed to denote elements similar to those shown in the preceding embodiments. In this bar a fourth metal conductor strip 82 has been added and is separated from strip 32 by a strip 42 of insulation which contains a plurality of the inserts 44, of the opposed, metallized surfaces of which are in contact with the con fronting surfaces of the conductor strips 82 and 32, respectively. Also in this embodiment strip 82 has the usual, spaced tabs 84 projecting from at least one edge thereof, and which in this embodiment register with, and are connected to, the tabs 24 of the conductor strip 22.This manner of interconnecting strips 24 and 84, which are arranged in alternating relationship with strips 1 2 and 32, also increased significantly the capacitance as between the respective conductors 1 2 and 32 relative to the interconnected strips 22 and 82 when the latter function, for example, as the ground strips.

In connection with the illustrations of the bus bars in Figs. 3 to 5, it will be appreciated that the relative sizes of the components have been exaggerated merely for purposes of illustration.

The distributed capacitance, which is incorporated in applicants' novel bus bars by use of the insulation layer containing the inserts 44, enables the production of extremely compact and reliable bus bars, and obviates the need to employ any adhesive directly between the confronting surfaces on the inserts and conductor strips, respectively. By selection of the quantity and disposition of the ceramic capacitors or inserts 44 in the layers of insulation, it is possible to design a respective bar to have a predetermined capacitance. Furthermore, this capacitance can be readily altered during the manufacture of the bars merely by placing in registry, and connecting, the projecting side tabs 14, 24, 34, etc. of the various conductior strips in a bar, thereby substantially to increase its capacitance when necessary or desirable.

It should also be noted that high capacitance insulation sub-assemblies of the type denoted at 40, or at least the strips 42 thereof which contain the ceramic dielectric inserts 44, in effect constitute capacitor elements, which are incorporated in the bus bar.

Referring to Fig. 3, for example, when the metal conductor strip 22 functions as the ground conductor, the adjacent insulator strips 42 containing the inserts 44 filter out any electronic noise which might otherwise be developed during current flow in the adjacent conductors 1 2 and 32. In this sense, therefore, applicants' sub-assembly 40 or 42 literally functions as a capacitor when utilized in the manner disclosed herein; and could be used in the manufacture of condensers.

While certain dimensions of the sub-assembly 40 and associated inserts 44 have been suggested, it will be apparent that these dimensions are cited merely by way of example, and that they could be changed without departing from this invention. Likewise, the configuration of the inserts 44 could be altered, as could be the number and configurations of the conductor strips employed in the illustrated embodiments. The embodiment shown in Fig. 5, for example, could be manufactured with the tabs 14 registering with, and connected to, the tabs 34 of conductor 32, whereby alternate conductors 1 2 and 32 would be interconnected and interleaved with the intervening metal strips 22 and 82, which are interconnected by their respective tabs 24 and 84. Thus, depending upon the number of conductor strips in a bar, there are several different ways in which the metal strips can be connected to provide the desired capacitance. Moreover, instead of heating a subassembly 40 to secure the inserts 44 in its openings 43, a liquid solvent could be applied to its surface around each opening 43 to cause part of the resin thereon to flow into fixing engagement with the marginal edges of the inserts 44.

Claims (5)

1. A method of manufacturing a high capacitance laminated bus bar, comprising preparing from a resin-coated layer of plastic, dielectric material a thin, flexible strip of insulation having at least one opening therein, positioning in said opening, a thin, wafer-like dielectric ceramic insert, opposite sides of which are metallized, partially curing said strip to cause part of the coating thereon to flow into engagement with the marginal edges of said insert, thereby to secure the latter in said opening in generally coplanar relation to said strip, placing said strip between two metal strip conductors to insulate said conductors from each other, and then laminating said conductors in a plastic insulating jacket, and with the metallized sides of said insert directly in contact with the confronting surfaces of said conductors.

2. A method as defined in claim 1, including preparing from said dielectric material a blank comprising a plurality of said strips extending in spaced, parallel relation to each other, and transversely between two, spaced side portions of said blank, each of said strips having therein a plurality of like openings spaced from each other longitudinally of the strip, placing one of said inserts in each of said openings in said strips and partially curing said blank to secure the inserts therein, placing said partially cured blank between and in registry with two metal blanks having configurations similar to said partially secured blank; laminating the assembled blanks between two, outer insulating jackets which also have configurations similar to said partially cured blank, and thereafter separating said laminated strip by removing the registering side portions of said blanks and jackets.

3. A laminated bus bar, comprising at least three flat, metal strip conductors, each having a plurality of circuit-connecting projections extending from at least one edge thereof, a first plurality of layers of dielectric insulation eachof which is laminated between a different pair of said conductors to insulate one from the other, additional layers of dielectric insulation laminated over and enclosing the outside surfaces of said conductors except in the areas of said circuit-connecting projections, a ceramic insert incorporated in each of said first layers of insulation to have opposite sides thereof directly engaged with the confronting surfaces of the two conductors which flank the insert, and means connecting at least certain of the projections on one of a first pair of said conductors with certain of the projections on the other of said first pair of conductors thereby further to increase the capacitance as between said first pair of conductors and a third conductor in said bar.

4. A laminated bus bar as defined in claim 3, wherein there are four conductors laminated in said additional layers of insulation and separated from each other by said first plurality of layers of insulation, and said first pair of conductors are disposed in alternating relation to the remaining conductors in said bar.

5. For use in a method of the type defined in claim 1, a strip of dielectric insulation comprising a thin, flexible dielectric layer of plastic having at least one opening therein, and having thereon a partially cured resin coating, a thin, ceramic insert which is similar in configuration to, and slightly smaller than, said opening and means securing said insert in said opening and in substantially coplanar registry with said layer of plastic, said means comprising a portion of said resin coating which has been caused to flow into fixing engagement with marginal edge portions only of said insert.

5. For use in a method of the type defined in claim 1, a strip of dielectric insulation comprising a thin, flexible, dielectric layer of plastic having at least one opening therein, and having thereon a partially cured resin coating, a thin, ceramic-insert which is similar in configuration to, and slightly smaller than, said opening, and means securing said insert in said opening and in substantially coplanar registry with said layer of plastic, said means comprising a portion of said resin coating which has been caused to flow into fixing engagement with marginal edge portions only of said insert.

6. A strip of dielectric insulation as defined in claim 5, wherein said insert is a thin wafer-like layer of barium titanate composition, and opposed surfaces of which waferlike layer have been metallized.

7. A strip of dielectric insulation as defined in either claim 5 or 6, wherein said insert has a thickness slightly greater than that of said layer of plastic so that said insert projects slightly from said opening.

8. A method of manufacturing a laminated bus bar substantially as described herein with reference to the accompanying drawings.

9. A laminated bus bar substantially as described herein with reference to the accompanying drawings.

10. Any novel feature or combination of features described herein.

CLAIMS (9 Sept 1982)

3. A laminated bus bar made according to the method defined in claim 1, including at least three of said metal strip conductors each having a plurality of circuit-connecting projections extending from at least one edge thereof, a plurality of said strips of insulation each of which is laminated between a different pair of said conductors to insulate one from the other, and with the ceramic inserts in said strips of insulation having opposite sides thereof directly engaged with the confronting surfaces of the two conductors between which they are positioned, said insulating jacket being laminated over and enclosing the outside surfaces of the outer conductors except in the areas of said circuit-connecting projections, and means connecting at least certain of the projections on one of a first pair of said conductors with certain of the projections on the other of said first pair of conductors, thereby further to increase the capacitance as between said first pair of conductors and a third conductor in said bar.

4. A laminated bus bar as defined in claim 3, wherein there are four conductors laminated in said insulating jacket and separated from each other by said strips of insulation, and the two conductors of said first pair thereof are disposed in alternating relation to the remaining conductors in said bar.