GB2462287A

GB2462287A - Printed touch switch

Info

Publication number: GB2462287A
Application number: GB0813978A
Authority: GB
Inventors: Kate Jessie Stone
Original assignee: Novalia Ltd
Current assignee: Novalia Ltd
Priority date: 2008-07-31
Filing date: 2008-07-31
Publication date: 2010-02-03
Anticipated expiration: 2028-07-31
Also published as: GB2462287B; GB0813978D0

Abstract

printed article (1) comprises a substrate (4) and first and second coplanar pads (5, 6) of conductive ink disposed on the substrate for providing terminals of a switch which are bridgeable by a finger of a user. The pads are separated by a gap (9) of wherein the area covered by the first or second pad is much larger than the area of the gap between the first and second pads.

Description

Printed article

Description

The present invention relates to a printed article, such as a book or greeting card.

An electronic circuit can be integrated into a printed article. Generally, a circuit includes at least one switch for activating the circuit or providing user input.

GB-A-2 440 730 proposes a book comprising sheets having printed switches which allow a user to access and control digital information.

In GB-A-2 440 730 supra., a switch generally takes the form of a pair of conductive comb-shaped terminals printed on a sheet and arranged so that the fingers of the combs are interdigitated. The switch is arranged so that it is normally open.

However, the switch can be closed by a user touching the terminals so that the user's finger acts as a bridge.

GB-A-2 440 730 supra. illustrates several test structures in which comb finger parameters, such as the spacing between fingers, the width of each finger and the number of fingers, are changed with the aim of reducing the resistance of the switch when closed. The test structures show that increasing the number of fingers, reducing spacing between fingers and increasing the width of the fingers help to reduce resistance.

The present invention seeks to provide an improved switch.

According to a first aspect of the present invention there is provided a printed article comprising a substrate and first and second coplanar pads of conductive ink disposed on the substrate for providing terminals of a switch which are bridgeable Jo by a finger of a user, wherein the pads are separated by a gap wherein the area covered by the first or second pad is much larger than the area of the gap between the first and second pads.

This can help to lower the total resistance of the switch when closed.

The area covered by the first or second pad may be at least five times the area of the gap, at least ten times the area of the gap or at least twenty times the area of the gap.

The gap may have an approximately constant width.

Each pad may be generally a solid block so that when the finger bridges the gap contact of the finger with each pad is substantially uninterrupted by gaps between different parts of the same pad.

At least one of pads may be teardrop-shaped, a semicircle or a rectangle.

The or each pad may have a width and length across the substrate defining an aspect ratio and the aspect ratio may lie between about 0.3 and about 3. The area of each pad may be at least about 4 mm2, at least about 10 mm2 or at least about 25 mm2. Each pad may have an area no more than about 25 mm2 or no more than about 50 mm2 or 100 mm2.

The article may further comprise first and second elongate conductive tracks disposed on the substrate connected to and integrally formed with the first and second pads respectively.

The article may be a book and the substrate may be page in the book. The article may be a greeting card or packaging for a product.

The substrate may comprise paper, card or a plastics material.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a first switch in accordance with the present invention; Figure 2 is a cross-sectional view of the first switch shown in Figure 1 taken along the line A-A'; Figure 3 illustrates operation of a switch in accordance with the present invention; Figure 4 is a plan view of a second switch in accordance with the present invention; Figure 5 is a plan view of a third switch in accordance with the present invention; Figure 6 is a plan view of a fourth switch in accordance with the present invention; Figure 7 is perspective view of a printed article in accordance with the present invention; Figure 8 illustrates a circuit including a switch in accordance with the present invention and a controller is in the form of a processor; and Figure 8a illustrates an alternative controller in the form of a transistor.

Referring to Figures 1 and 2, a part of (p/o) of a printed article I in accordance with the present invention is shown.

The printed article I includes a switch 2 formed on a flat surface 3, e.g. upper or outward facing surface, of a substrate 4. The substrate 4 comprises card, although other materials may be used such as paper, a plastics material or some other suitable print media. The substrate 4 may be a laminate of materials.

The switch 2 includes first and second coplanar pads 3, 6 disposed on the substrate 4 which provide contact terminals of the switch 2. First and second elongate conductive tracks 7, 8 are connected to the first and second conductive pads 5, 6 respectively, in this example, on opposite sides of the switch 2. For clarity, the conductive pads 5, 6 are shown shaded in Figure 1.

The conductive pads 5, 6 and tracks 7, B are formed at the same time during manufacture. However, they may be formed at different times.

The conductive pads 5, 6 and tracks 7, B comprise a silver-based conductive ink.

Suitable conductive inks are available from Sun Chemical Corporation, Parsippany, New Jersey, USA. Other forms of conductive ink can be used, such as a copper- based conductive ink or some other metallic-based conductive ink, or a carbon-based conductive ink.

Different conductive inks can be used for the pads 5, 6 and the conductive tracks 7, 8. The conductive pads 5, 6 and conductive tracks 7, 8 are formed using a printing process, such as screen printing, ink jet printing, flexography or offset printing.

The conductive pads 5, 6 and/or tracks 7, 8 may comprise metallic foil, e.g. aluminium. The conductive pads 5, 6 and conductive tracks 7, 8 may be formed by defining an etch mask and etching unwanted regions of metallic foil from the substrate 4.

The pads 5, 6 are separated by a gap 9 of approximately constant width, s.

As shown in Figure 3, the switch 2 has suitable si2e and configuration so that the gap 9 can be bridged by a finger 10 so as to form a connection between the conductive pads 5, 6. Herein, the term "finger" is intended to encompass any digit of a hand including a thumb.

Under usual ambient conditions, the resistance between the conductive pads 5, 6 is at least of the order of I GQ. When the user touches the switch 2 SO as to form a bridge between the conductive pads 5, 6 using their finger 10, the resistance drops to about 4 MQ or so.

As shown in Figure 1, the gap 9 has a length, s, of about 0.5 to 3 mm and the conductive pads 5, 6 have a diameter, d, of about 10 mm.

The si2e of the conductive pads 5, 6 may be varied. For example, the conductive pads 5, 6 may each have an area of at least about 4 mm2, at least about 10 mm2, at least about 25 mm2 or at least about 50 mm2.

One or both of the conductive pads 5, 6 generally takes the form of a solid block or conglomerate, e.g. grouped or formed into a compact body, so that contact between the finger 10 and the conductive pad 5, 6 is substantially or minimally uninterrupted by gaps between different parts of the same conductive pad 5. Gaps between different parts of the same conductive pad 5, 6 may occur if, for example, a comb arrangement is used. In a comb arrangement, a gap lies, for example, on a (shortest) straight line between distal ends of adjacent fingers.

The conductive pads 5, 6 have respective areas, A1,1, A2, and the gap 9 has an area, AG, between the pads 5, 6. Thus, the switch 2 has an area, As, which is the sum of the areas of the conductive pads 5, 6 and gap 9, i.e. A -A1, + A2 + AG. The area covered by the pads 5, 6 is much bigger than the area of the area of the gap 9, e.g. at least an order or magnitude greater than the areas of the pads. Thus, if c is the ratio between the area, A, covered by a pad 5, 6 (in this case A A1, A2) and the area of the gap 9 between the pads (i.e. c -A/A0), then c >> 1. It is preferable that c is at least about 5. It is more preferable that c is at least about 10.

It is even more preferable that c is at least about 20. In some embodiments, the gap 9 is made as narrow as possible and/or the pads 5, 6 are made as large as possible. The area of the pads 5, 6 may be limited to the area of typically-si2ed fingerprint.

The present invention is based, at least in part, on the insight that the total resistance of the switch 2 when closed is dominated by a contact resistance between a conductive pad 5, 6 and the finger 10. Thus, in embodiments of the present invention, the area of a conductive pad 5, 6 is increased relative to the area of the gap 9 so as to reduce the contact resistance and, thus, lower the total resistance of the switch 2 when closed.

To maximise the area of a pad 5, 6, the pad 5, 6 can take the form of a solid block.

Thus, larger conductive pads 5, 6 can be used compared with a switch of the same si2e (i.e. taking up the same footprint or general outline) in which, for example, only comb-shaped electrodes are used. This is because, in a switch having comb-shaped electrodes, the gap between the electrodes takes up more of the area of the switch and so the electrodes are smaller.

Figures 4 and 5 illustrate differently-shaped switches 2', 2" having conductive pads which generally take the form of solid blocks.

In Figure 4, the conductive pads 5', 6' are solid semicircles in plan view. Similar to the switch 2 shown in Figure 1, the conductive pads 5', 6' have a diameter, d, and are separated by a gap 9' of width, s.

In Figure 5, the conductive pads 5", 6" are solid rectangles in plan view. The conductive pads 5", 6" have a width, w, and a length, 1. In this example, the length, 1, of a pad 5", 6" is about half the width, w, of the padS", 6", i.e. 1 0.5 w. The conductive pads 5", 6" are separated by a gap 9" of width, s In the switches hereinbefore described, the conductive pads in a switch have substantially the same area and are substantially the same shape. However, the conductive pads need not have the same area and need not be the same shape or symmetrical. However, it will be appreciated that the resistance is likely to be dominated by the si2e of the smaller pad and so it is preferred that the pads have the same area.

For example, Figure 6 shows a switch 2" having one conductive pad 5" which generally takes the form of a solid block, in particular a solid circle or disc, and another conductive pad 6" which is closely configured around it, in particular a coaxial broken ring.

Solid blocks may have aspect ratio between I and about 5 (or I to about 0.2), preferably between I and about 3 (or between I and about 0.33).

Referring to Figure 7, the printed article I takes the form of a greeting card I. As explained earlier, the substrate 4 is formed of card. The surface 3 is the face of the card for displaying to a user. The face 3 of the card includes text and/or graphics (not shown).

The card 1 supports a circuit 11 which includes the switch 2, conductive tracks 7, 8, other conductive tracks 12 and one or more light emitting diodes 13 or other output devices. The light emitting diodes 13 can be attached directly onto the card I using conductive glue or ink. The circuit 11 includes a portion 14 which includes a pull-up resistor 15 and a processor 16.

In this example, the circuit portion 14 is formed on a circuit board (not shown) and is glued to a reverse face (not shown) of the card I or to another card, so as to be sandwiched between the cards. However, the circuit portion 14 can be formed directly, e.g. printed, on the substrate 4. A battery 17 is used to provide power to the circuit 11, for example in the form of a thin lithium polymer battery.

Referring to Figure 8, the circuit 11 is shown in more detail. The switch 2 and resistor 15 are arranged a potential divider between a supply and ground rails 18, 19.

The supply rail 18 is about 3V. A tap 20 between the switch 2 and resistor 15 is fed, via input 21, into a microcontroller 16, for example a PIC(RTM) microcontroller available from Microchip Technology Inc., Chandler, Ari2ona, USA. As shown in Figure 8, the battery 17 also provides power to the microcontroller 16.

When the switch 2 is open, the input 21 to the processor 16 is close to the supply voltage. Thus, the light emitting diode 13 is not activated.

When the switch 2 is closed, the input 21 is pulled towards the ground rail 19. The processor 16 detects that the input 21 has passed a threshold voltage, Vh, closes a switch 22 and causes current to flow through the light emitting diode 13. Thus, the light emitting diode 13 is activated.

To achieve this operation, the pull up resistor 15 has a value of about 68 MQ.

However, a resistor having a value of about 40 to 100 MQ can be used, for example 82 MQ. However, the value of the pull up resistor 15 and the resistance of the switch 2 can be found through routine experiment, e.g. by using pull up resistors of different values, checking that the light emitting diode 13 is off under ambient conditions, touching the switch 2 and checking that the light emitting diode 13 turns on. Typically, the pull-up resistor 14 has a value of the order of 10 MQ, about times larger than the value of the switch 2 when it is in a low resistive state, i.e. closed.

The processor 16 can be used to control more than one light emitting diode, or other output device, either collectively, e.g. by connecting the light emitting diode in series, or independently via separate lines. The processor 16 can be programmed to activate the light emitting diodes in a predetermined pattern, e.g. to flash on and off, and to continue to operate the light emitting diodes after the user has ceased to close the switch 2. Thus, the processor 16 can be used to provide effects, such as candles flickering and/or playing a tune.

Referring to Figure 8a, a simpler arrangement can be used in which the processor 16 is replaced by another controlling means 16' comprising switching means in the form of a transistor 18'. The transistor 18 can be printed directly onto the card I (Figure 1) and may take the form of an organic field effect transistor.

It will be appreciated that many modifications may be made to the embodiments hereinbefore described. For example, other forms of audio/visual output devices may be used, such as thermochromic displays and bu2zers. The resistor 9 (Figure 1) can be printed on the substrate. The tracks 5 (Figure 1) may be formed from foil.

The printed article may be a book (including, for example, a hardback book, a paperback, a board book, etc.), a greeting card, a postcard, a poster, a calendar (e.g. a wall calendar or triangular desk calendar), packaging for a product (e.g. primary, secondary or tertiary packaging), a board game, a folder or file, an in-store display or consumer promotional item (e.g. a triangular table-top display card or beer mat).

The printed article can be formed from paper, card, cardboard or plastic. The substrate may be a laminate. The tracks may be covered by other layers of ink providing text or graphics. The surface need not be flat, but can be, for example, gently concave or convex.

Claims

Claims 1. A printed article comprising: a substrate; and first and second coplanar pads of conductive ink disposed on the substrate for providing terminals of a switch which are bridgeable by a finger of a user, wherein the pads are separated by a gap and wherein the area covered by the first or second pad is much larger than the area of the gap between the first and second pads.
2. A printed article according to claim 1, wherein the area covered by the first or second pad is at least five times the area of the gap.
3. A printed article according to claim I or 2, wherein the area covered by the first or second pad is at least ten times the area of the gap.
4. A printed article according to any preceding claim, wherein the gap has a approximately constant width.
5. A printed article according to any preceding claim, wherein each pad is generally a solid block so that, when the finger bridges the gap, contact of the finger with each pad is substantially uninterrupted by gaps between different parts of the same pad.
6. A printed article according to any one of claims I to 5, wherein at least one of pads is teardrop-shaped.
7. A printed article according to any one of claims I to 5, wherein at least one of pads is a semicircle.
8. An article according to any one of claims I to 5, wherein at least one of pads is a rectangle.

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9. An article according to any preceding claim, wherein the pad had a width and length across the substrate defining an aspect ratio and the aspect ratio lies between about 0.3 and about 3.
10. An article according to any preceding claim, wherein the area of each pad is at least about 4 mm2.
11. An article according to any preceding claim, wherein the area of each pad is at least about 10 mm2.
12. An article according to any one of claims I to 11, wherein the area of each pad is at least about 25 mm2.
13. An article according to any one of claims I to 11, wherein each pad has an area no more than about 25 mm2.
14. An article according to any preceding claim, further comprising first and second elongate conductive tracks disposed on the substrate connected to the first and second pads respectively.
15. An article according to any one of claims I to 14, wherein the article is a book and the substrate is a page in the book.
16. An article according to any one of claims I to 14, wherein the article is a greeting card.
17. An article according to any one of claims I to 14, wherein the article is packaging for a product.
18. An article according to any one of claims I to 17, wherein the substrate comprises paper.
19. An article according to any one of clsinis I to 17, wherein the substrate comprises card.
20. An article according to any one of ckinis I to 17, wherein the substrate comprises plastics material.