WO1989005034A1

WO1989005034A1 - Z-folded capacitor construction

Info

Publication number: WO1989005034A1
Application number: PCT/AU1988/000448
Authority: WO
Inventors: David Robert Brooks; Robert Charles Gouldson
Original assignee: Magellan Corporation (Australia) Pty. Ltd.
Priority date: 1987-11-20
Filing date: 1988-11-18
Publication date: 1989-06-01
Also published as: ZA888680B; AU2780689A

Abstract

A capacitor comprising dielectric film (10), metal coated on both sides (11, 12) and Z-folded upon itself, which can have electrical components (16), such as resistors, inductors, VLSI chips etc. attached to it and electrically connected to each other by a wiring pattern (13) formed on part of the metal coated dielectric film. The components can be recessed via a hole (15) in the capacitor. The capacitor and components can be encased in a protective film coating to form a transponder, smart card, credit card, identification tag etc. A method of forming the capacitor with printed wiring pattern is disclosed.

Description

Z-FOLDED CAPACITOR CONSTRUCTION

The present invention relates to capacitor construction and in particular to an integral circuit formation. More particularly, the present invention relates to a capacitor construction which in combination with an electrical component may form a compact electrical circuit.

BACKGROUND ART

The use of a printed circuit board (PCB) in electronics assembly work is well known. The PCB in a simple form comprises a sheet of insulating material which may be either rigid or flexible coated on one or both sides with a pattern formed in thin metal foil or other electrically conductive material.

Electronic components are attached to this pattern, the pattern providing inter-connecting wiring. Where necessary holes may be formed in the PCB to provide connections between conductive material formed on both sides .

In some cases it is possible to form or utilise the small capacitances between the foil areas on the two sides. However the thickness and dielectric properties of the underlying insulating layer usually constrain the capacitors to be of very low value only. Therefore, for most circuit applications such as tuned circuits or noise suppression conventional capacitors must be used.

The manufacture of capacitors from thin plastic dielectric film coated with a metallic layer on one side is well known, whereby two or more such film composites are wound on to a mandrel. Optionally, the mandrel may afterwards be removed and the roll may then be pressed flat. This structure provides a large surface area, and therefore a relatively high capacitance value in a small volume.

U.S. 3,880,493 discloses a dual-in-line integrated circuit package and a PCB assembly. A capacitor is formed in the body of an IC package mounting socket. This, however, adds considerable expense to overall circuit cost and, moreover, results in a circuit layout cf larger bulk. G.B. 2,067,018 discloses a chip package in the form of a capacitor made of dielectric material which has incorporated therein an integrated circuit. This configuration, however, has limited use due in part to its bulk and is specifically manufactured for PCB use. AU 83181/79 discloses a Z-folded printed circuit board arrangement in order to facilitate cooling of the high density board module. The disclosure relates to a standard plastics circuit board having copper tracking thereon. However, the specification does not disclose a component part of a circuit forming a means to support other circuit elements. The specification does not disclose a capacitor adapted to permit direct mounting of an electrical component.

Further, capacitors produced in accordance with U.S. 4,694,283 (and also, in accordance with U.S. 4,369,557) will necessarily have at least two dielectric layers separating the two foil areas. To achieve a given capacitance value, this necessitates that the plate area be also doubled, resulting in a larger device than necessary. In U.S. 4,127,891, a Z-folded capacitor is described, having certain modifications introduced to facilitate the attachment of conventional lead-wires to the ends. In the present invention, there are no such lead-wires . Specification U.S. 3,482,194 describes a folding technique, specifically adapted to produce capacitors of small electrical value. This folding technique is not utilised in the present invention. OBJECTS OF INVENTION The present invention has as a principal objective the provision of a capacitor structure suitable for use with an integral wiring structure. An object of the present invention is to obviate the need for a printed circuit board and to provide a novel capacitor construction. A further object of the present invention is to provide a capacitor adapted to accommodate an electrical component or chip. A further object of the present invention is to provide for the manufacture, by low-cost automated means, of electrical circuits composed of a capacitance, which may have a variety of applications, such as in transponders, identification tags or smart cards. The methods and apparatus hereinafter described offer significant advantages in terms of a variety of possible electrical configurations, and of electrical efficiency and facilitate circuit miniaturisation. SUMMARY OF INVENTION The present invention provides, in one form, a capacitor comprising : metal coated dielectric film, Z-folded upon itself and being adapted to accommodate an electrical component. The electrical component may comprise one or more or a combination of integrated circuits, VLSI chips, resistors, inductors or other components.

The present invention also provides, in another form, a method of forming a capacitor comprising the steps of : 1. forming a metal coated dielectric film,

2. Z-folding the film upon itself, the film being substantially alignable to facilitate mounting of a component.

The above method may further comprise the step of providing at least one recess in the film for mounting the component.

The method above may further comprise, preceding step 2, the step of making a desired electrical circuit, such as interconnect wiring, inductances or resistances by forming a wiring pattern on at least a part of the metal coating.

Conveniently any number of layers may be so folded to achieve the desired capacitance value. The surfaces may be coated with adhesive to maintain the folded mass and/or may be encapsulated. An electronic component or components may be mounted on either face of the conductive film by conventional surface-mount techniques or by thermo compression bonding or wire bonding.

There is also provided according to the present invention, in another form, a circuit structure comprising a capacitor as hereinbefore described and including an electrical circuit having a predetermined wiring pattern formed on at least part of the metal coating and including means for supporting electronic component or components 0 thereon.

The circuit structure may form a tuned circuit. Capacitance can be provided by the capacitor of the present invention, the resistance and inductance can be conventional . - components mounted in the capacitor or, alternatively, the resistor can be printed on a surface of the capacitor, and the inductor can be etched on a surface of the capacitor. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS)

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, wherein :

Figure 1 shows, in partial cross-sectional view, a greatly enlarged circuit structure having an integrated circuit mounted in a capacitor of the present invention. __ς Figure la is a partial plan view looking from point

A.

Figure 2 is a partial sectional view greatly enlarged of a circuit and capacitor assembly, in accordance with a further embodiment of the present invention. ,_n Figure 3 shows a single sided metal coated dielectric.

The assembly includes a thin plastic dielectric film 10 metal coated on both sides 11, 12. The metal coating on the top fold 10a, is chemically etched by conventional means or some other process in printed circuit manufacture to form an inter-connected wiring pattern or patterns 13. After formation of a desired circuitry, the metal coated plastic film is preferably coated with contact adhesive and Z-folded upon itself as shown. This folding ensures that the metallic coating on either side contacts only itself, and contact with the opposite side (which would be the case with conventional rolling) is avoided. Of course the wiring patterns provided must take this into account, to ensure the integrity of the circuit, alternatively, an insulating layer 14 will be required. In most practical applications, it is envisaged that only the first one or two folds will carry circuit wiring leaving the rest of the metal coated film component to form the capacitance plates. It will be understood the circuit wiring layer or layers, may be located anywhere within the Z-folded assembly, to facilitate complete encapsulation of the circuit, and any or all electronic components .

Because of the configuration of the capacitor, the glued surfaces simply hold the same capacitor plate back to back, and therefore the thickness of the glue layer does not affect the capacitance value of the component.

The present invention includes circuits, in a form particularly adapted for operation at comparatively low AC frequencies. Such frequencies are preferable in many practical applications, due to the reduced level of spurious electromagnetic radiation.

The present invention permits the manufacture of products incorporating active electrical functions and even so-called "smart" features, by the provision of suitable logic and/or memory circuits. Such active circuitry will preferably be embodied in VLSI "chips".

The present invention also includes a means whereby all the necessary circuitry may be fabricated on a single side of the foil. This not only reduces the amount of processing required, but also eliminates the need for "via" or edge rolled connections between foils on opposite sides of the dielectric. Naturally, with only a single foil, the problem of maintaining mechanical registration between foils on opposite sides of the dielectric, also no longer exists.

The device of the present invention may be encapsulated in a protective plastic or other suitable material. This provides a more useful form of the device such as transponders, identification tags or smart cards. The coating should not unduly interfere with electrical signals within and to or from the encapsulated device. The present invention also allows for the production and supply of electronic devices as aforesaid, conveniently provided with a suitable adhesive backing, and provided on a strip of waxed paper or similar release material, said strip being supplied rolled, folded or in other suitable bulk-packaging format, whereby said electronic devices may be applied at the point of use, by suitable dispensing machinery (such machinery being well-known in the field of applying adhesive labels, etc.).

With reference to Figure 1 and Figure la, hole(ε) 15, may be cut through the dielectric layer(ε) to form, in a folded position, a substantially aligned aperture with wiring layer 13 being at the base of the aperture. Components such as an integrated circuit (chip 16) may be attached directly to the wiring layer through the aperture, with the aperture afterwards being filled with a known potting compound, or covered by further Z-folds , without holes, to encapsulate the chip, or both.

With reference to Figure 1, a through hole connection 17 (that is between the two circuit wiring sides of the dielectric film) is provided. Such connections may be also simply formed as shown in Figure 2, by rolling the film edge, thereby intentionally shorting the two sides and then ultrasonic welding or soldering the connections 18. Naturally, such a roll may be only performed over wiring patterns deliberately designed to avoid spurious side-to-εide connections. With reference to Figure 2, A, B and C form a Z-fold. Surface A forms the upper portion of the Z, surface C forms the lower portion of the Z, and surface B forms the surface interconnecting A and C.

The integral circuit structure, including the capacitor of the present invention enables easy production by continuous mass production techniques with provision for incorporating chip and surface mounted components 19.

A tuned circuit can be formed on the dielectric film by forming thereon a suitable inductance and connecting a resistor thereto.

Such assemblies are useful in low cost applications particularly transponders and smart card devices.

An alternative embodiment comprises a dielectric layer laminate, is shown in Figure 3. A sheet of plastic film 21 is coated (as previously) with a suitably patterned metal film 22, but on one side only. The reverse side 20 (i.e. remote from the metal film) of the plastic dielectric layer is so treated as to cause it to adhere to itself, if necessary under application of heat and/or pressure. The film laminate is then folded upon itself, about a fold line 24 of Figure 3, so that the metal-coated surfaces are outermost thereby forming a double sided metal coated dielectric. The inner surfaces (suitably treated, as aforesaid) are then adhered to each other, and the resulting laminate, which now comprises a dielectric sheet sandwiched between two patterned metal layers, is processed as previously; i.e. Z-folded to accommodate an electrical component( ε ) .

This method of forming the laminate results in a plastic layer of twice the previous thickness (it being folded upon itself). Accordingly, in order to approximate the required dielectric thickness, a laminate having less dielectric should be used. This is a slight disadvantage, but may, in certain applications, be outweighed by the following advantages : 1. Extremely thin dielectric films sometimes exhibit pinholeε, which may, were a εingle film to be used, short-circuit the two sides. With this embodiment, two pinholes must coincide on the two plastic layers, to form a short-circuit. This is an extremely improbable eventuality. Hence, the reliability of the device is enhanced.

2. Where connections between the two metal layers are required, the connection at 18 of Figure 2 or at 17 of Figure 1 is no longer required. It is sufficient to pattern the metal, before folding, with conductive, metal tracks passing as needed across the central fold line. When the laminate is folded, these tracks will provide the connections required, between the two sides.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A capacitor comprising : metal coated dielectric film, Z-folded upon itself and being adapted to accommodate an electrical component.

2. A capacitor as claimed in Claim 1, wherein the film has a recess therein adapted to accommodate the component.

3. A capacitor as claimed in Claim 1, wherein the film is a double sided metal coated dielectric.

4. A capacitor as claimed in Claim 1, wherein the film is a single sided metal coated dielectric, which when folded upon itself forms a double sided metal coated dielectric film.

5. A capacitor as claimed in Claim 1, wherein a wiring pattern is formed on at least a part of said metal coated dielectric film.

6. A capacitor as claimed in Claim 5, wherein inductors and/or resistors are also formed on or attached to said wiring pattern.

7. A capacitor as claimed in Claim 3, wherein electrical connection is formed between each side of said dielectric by rolling the film edge.

8. A capacitor as claimed in Claim 1, encapsulated in a protective film coating.

9. A capacitor as claimed in Claim 1, wherein the film is further Z-folded over an attached component.

10. A method of forming a capacitor comprising the steps of :

(a) forming a metal coated dielectric film

(b) Z-folding the film upon itself, the film being substantially alignable to facilitate mounting of an electrical component.

11. A method as claimed in Claim 10, further comprising the step of providing at least one recess in the film, wherein the component is mounted.

12. A method as claimed in Claim 10, further comprising the step of, preceding step (b) :

(c) making a desired electrical circuit by forming a wiring pattern on at least a part of the film.

13. A method as claimed in Claim 10, wherein step (a) includes obtaining a single sided metal coated dielectric, making a desired electrical circuit by forming a wiring pattern on at least a part of the metal coating and folding the uncoated dielectric side upon itself to form a double sized metal coated dielectric.

14. A method as claimed in Claim 10 or 13, wherein the dielectric iε coated with an adhesive, which iε curable upon folding the dielectric upon itself.

15. A capacitor made by the method as claimed in any one of Claims 10 to 14.

16. A device including a capacitor as claimed in Claims 1, 2, 5 or 10.

17. A device as claimed in Claim 16, wherein the electrical component iε a VLSI chip.

18. A device as claimed in Claim 17, in the form of a transponder, smart card, credit card or identification tag or card.

19. A device as claimed in Claim 18, provided with a suitable adhesive backing to facilitate attachment to an object.