GB2372012A

GB2372012A - Forming a high frequency contact-less smart card with an antenna coil

Info

Publication number: GB2372012A
Application number: GB0101319A
Authority: GB
Inventors: Chi Keung Lee; Kwok Lam Kwan
Original assignee: Pioneer Oriental Engineering Ltd
Current assignee: Pioneer Oriental Engineering Ltd
Priority date: 2001-01-18
Filing date: 2001-01-18
Publication date: 2002-08-14
Also published as: TW525094B; GB0101319D0; HK1049904A1; KR20020062199A; CN1365083A

Abstract

An antenna coil formed by wire 14 is first embedded by means of ultrasonic transducer (22, Fig 1) on upper surface 16 of core sheet 12 and then the card is embedded with an integrated circuit (IC). A cavity 32 for receiving part of the IC is provided on the core sheet and adhesive tape 30 retains the IC in place temporarily after it is placed in the cavity by way of the lower surface (36, Fig 3) of the core sheet. The IC is electrically connected to the antenna coil by thermo compression bonding while the core sheet rests on platform 40. The card can then be laminated with base sheets (44, 46, Fig 6).

Description

A Method of Forming an IC Card This invention relates to a method of forming a card embedded with at least one integrated circuit, generally known as an"IC Card"or"Smart card".

Cards have long been used as a data carrier. Ordinary cards may carry data visually, e. g. having information or the like printed or written on one or both major surfaces of the card. Cards may also act as magnetic data carriers in the form of magnetic cards. In magnetic cards, a magnetic strip is pressed on a particular location of a card. The magnetic strip carries data which are readable by a magnetic data reader. Magnetic cards may be used as train tickets, bank cards etc.. Such magnetic cards, however, suffer from the drawback that the amount of data which can be carried or stored by a magnetic strip is small. In addition, magnetic cards can only be over-written a relatively small number of times, and are easily damaged. Magnetic cards are also prone to be affected by magnetic fields in the environment, and may even lose the data stored therein.

As an improvement over the above conventional data-carrying cards,"smart cards"or "IC cards"have been provided. Such are cards embedded with an integrated circuit (IC) for

storing data. With existing technology, an IC can store over 30k byte of data, and can be over-written and read for over 100, 000 times. As the IC can contain both the data and the programme, the smart cards can be used remote of a computer terminal. IC cards are used as telephone cards or credit cards. Such cards sometimes also include a magnetic strip, thus providing two interfaces.

IC cards may be generally classified as contact cards and contact-less cards. For contact cards, at least a major surface of the IC with a read/write interface is exposed to the outside environment. When in use, the read/write interface of the IC card is in direct physical contact with a read/write head of a computer terminal or processor, whereby data may be written into and/or read from the IC in the card. On the other hand, a contact-less card is provided with a coil of a copper wire, which is secured at or adjacent to its two ends with the IC, which is fully embedded within the IC card. The coil of copper wire acts as an antenna for transmitting and/or receiving radio frequency signals. The IC may then be coupled to an external system, e. g. a computer system, by radio frequency (RF) transmission. In this case, the IC needs not be in direct contact with any read/write head of the external computer system.

If a contact IC card is frequently used, say once or twice a day or more, the IC embedded in it will be easily damaged. In certain circumstances, the use of contact cards will also be more time-consuming. For example, for paying highway toll, the use of contact cards will mean that each car passing through a toll counter will have to stop for processing payment. Contact-less cards are thus appropriate for use in transactions which are relatively frequent but involve relatively small amount of money.

Contact-less IC cards may be further classified as high-frequency contact-less IC cards and low-frequency contact-less IC cards. The operating frequency of a high-frequency contact-less IC card (also called a high-frequency card) is 13. 56MHz, while that of a lowfrequency contact-less IC card (also called a low-frequency card) is 125kHz. A high frequency card is provided with a coil of 4 to 5 rounds of copper wire, and the operation distance is within roughly 10cm. The chance of a high-frequency card accidentally affecting, or being affected by, the operation of other nearby high-frequency cards is small, and is thus very reliable. For a low-frequency card, such is provided with a coil of 250 to 300 rounds of a copper wire. While the manufacture of low-frequency cards is rather complicated and not readily susceptible to automation, its main advantage is that its operation distance may be up to 3m.

High-frequency cards are usually adopted for personal use, e. g. for travelling on trains or buses. As to low-frequency cards, such may be used for paying highway tolls, as the radio frequency signals can be transmitted through a long distance and it is relatively easy to differentiate between different cars.

For high-frequency cards, there are mainly three ways of providing a coil in the card, namely by printing, by etching, and by embedding. In the printing method, electricallyconductive ink is printed on a core sheet to form a coil of several rounds. Such a method is quick and requires relatively inexpensive equipment. However, such a method suffers from the shortcoming that the printed"wire"is easily broken. In addition, the electrical resistance is not uniform as the electrical conductivity depends on the mixing between some electrically-conductive metal powder and ink. The circuit so printed out is also very thin, and cannot pass the bending test required under the relevant International Standard. Furthermore, in the printing method, the adjacent rounds of wire cannot get too close to each other, and such significantly reduces the effectiveness of radio frequency transmission. Due to the above various problems, this method is now seldom used.

Turning to the etching method, such is similar to that used in producing circuit boards.

However, as the adjacent rounds of wire cannot get too close to each other, the effectiveness of radio frequency transmission is compromised. In addition, there is the problem of pollution to the environment during production. Neither can the card so produced pass the bending test. This method is thus also seldom used.

As to the embedding method, such is very versatile and two adjacent rounds of wire can virtually contact each other, the effectiveness of radio frequency transmission is greatly enhanced. Such a method is susceptible to automation, with no adverse effect to the environment. A card produced by such a method can also pass the bending test.

In the conventional method of producing a high-frequency contact-less IC card, the substrate with a cavity for receiving the IC is adhered to a filler sheet. A layer of adhesive glue is then applied on the area of the filler sheet exposed through the cavity of the substrate.

An IC chip is then positioned in the cavity and held therein by the adhesive glue. A wire is then laid on the substrate, with two ends of the wire secured to the IC chip by thermo compression bonding. However, such a conventional method suffers from the following shortcomings :a. As the IC chip is supported by the relatively soft filler sheet, when pressure is applied thereon during bonding, some of the force will be absorbed by the filler sheet. The effect of bonding may thus be compromised.

b. If IC chips are in short supply, only the sheets can be cut out, but the rest of the manufacturing process has to be held up until new supply of IC chips arrives.

It is thus an object of the present invention to provide a method of forming an IC card in which the aforesaid shortcomings are mitigated, or at least to provide a useful alternative to the public.

According to the present invention, there is provided a method of forming a card embedded with at least one integrated circuit and an antenna coil, said method including the steps of (a) providing a base sheet with at least a cavity for receiving at least part of said integrated circuit; (b) providing said antenna coil on said base sheet; (c) positioning said integrated circuit into said cavity of said base sheet; and (d) securing said integrated circuit with said antenna coil, wherein said step (c) is carried out after said step (b).

An embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings : Fig. 1 shows part of a wiring machine and a core sheet used in a method according to the present invention; Fig. 2 shows an adhesive tape as attached to the core sheet shown in Fig. 1;

Fig. 3 shows the positioning of an IC into the core sheet shown in Fig. 2 ; Fig. 4 shows a sectional view of a core sheet with an IC ready for bonding according to the present invention; Fig. 5 shows part of a bonding process according to the present invention; Fig. 6 shows the putting together of various base sheets for lamination according to the present invention; and

Fig. 7 is a cross section of a conventional contact-less high-frequency IC card ; and Fig. 8 shows the product IC card as punched out according to the present invention.

To produce an IC card according to the present method, two guide holes are punched out on a core sheet 12. The guide holes assist in aligning the core sheet 12 relative to various machines for future processing. A cavity is also provided, e. g. by punching, for housing a part of an IC, in a manner to be discussed below.

A part of a wiring machine 10 and a core sheet 12 are shown in Fig. 1. The core sheet 12 is usually made of a thermoplastic material (e. g. plexiglass, polyvinyl chloride, polypropylene and acrylonitrile butadiene-styrene), or a heat resistant material (e. g. epoxyfiberglass) coated with a thin layer (e. g. about half the diameter of the wire 14) of a partially cured thermoset adhesive. A wire 14 is delivered from a spool (not shown) into a wire feed mechanism 15, which feeds the wire 14 on to an upper surface 16 of the core sheet 12. The wiring machine 10 includes an ultrasonic generator 18 which activates a drive coil 20. The drive coil 20 can thus drive an ultrasonic transducer 22, which is provided with a stylus 24 at its end. The stylus 24 includes a groove (not shown) which fits the shape of the wire 14.

Two leaf spring suspensions 26 are also provided for supporting the ultrasonic transducer 22 within the machine 10.

With this arrangement, the stylus 24 may be set into up-and-down vibrational movement at an ultrasonic frequency. Such a vibration creates heat which melts the material on the upper surface 16 of the core sheet 12 under the wire 14. Downward force on the stylus 24 will push the wire 14 into the upper surface 16. The softened thermoplastic material will quickly harden when the stylus 24 moves upward, thus locking the wire 14 in place in the core sheet 12. Patterns may be formed of the wire 14 by periodically stopping the wire feed mechanism 15 and rotating the wire feed mechanism 15, and thus to turn the wire 14 in a new direction. At the end of the path, the wire 14 is then cut with a small shear 28 near the tip of the stylus 24. The wire 14 so embedded will form an antenna coil for reception and transmission of radio frequency signals, whereby data may be written into and/or read from the IC.

The advantage of ultrasonic bonding is that heat is generated within the substrate (i. e. the core sheet 12) itself by the mechanical stresses of the vibration. This produces heat very rapidly at exactly the place it is required, namely in a small volume underneath the wire 14.

Since the heating is very localized and occurs only in the substrate, the material solidifies again as soon as the stylus 24 has passed. The ultrasonic heating is so rapid that the substrate under the wire 14 melts before any heat can be conducted away. Adjacent substrate, even as close as a single wire diameter, is completely unaffected. This enables the bonding to proceed at a linear speed of several inches per second without affecting the wires 14 already bonded.

The wire 14 is usually of solid copper with a tough and elastic insulating coating, e. g. polyimide, polyester and polyurethane. Polyimide is particular suitable for complex patterns because it resists mechanical breakdown at cross-overs. A thin (e. g. 0.0005 to 0.01 inch) coating of bonding material may be added to the wire 14 to allow more than one layer of wire 14 to be bonded. The wire 14 may be applied onto the upper surface 16 of the core sheet 12 at a rate of 5 to 15 feet per minute, depending on the application.

As shown in Fig. 2, after the embedding of the wire 14 onto the upper surface 16 of the core sheet 12, an adhesive tape 30 is then adhered onto the upper surface 16, with the adhesive side facing downward (in the sense as shown in Fig. 2). The adhesive tape 30 extends across a cavity 32 for receiving part of the IC. It can be seen that two ends 34 of the wire 14 also extend across the cavity 32. The adhesive tape 30 may be stationery adhesive tape available from stationery stores. Although only roughly one round of wire 14 is shown in Fig. 2, it should be understood that, for a high-frequency contact-less IC cards, there are normally four to five rounds of wire 14.

The core sheet 12 is then turned upside down (as shown in Fig. 3) with a lower surface

36 facing upward. An Integrated Circuit (IC) 38 is then placed into the cavity 32. The adhesive tape 30 thus comes into contact with the IC 38 and serves the purpose of temporarily retaining the IC 38 in this position. The core sheet 12 is turned upside down again, as shown in Fig. 4, so that the ends 34 of the wire 14 face upwardly. The core sheet 12 is then placed on a rigid platform 40, and the ends 34 of the wire 14 secured to and electrically connected with the IC 38 by thermo compression bonding. In particular, during the bonding process, an impulse current is delivered to the wire 14 to melt the insulating layer of the wire 14 and to bond the copper wire onto the IC 38. As the core sheet 12 rests on a rigid support, namely the platform 40, during bonding, the result of the bonding is significantly improved.

As shown in Fig. 5, after bonding by a bonder 42, the adhesive tape 30 is removed. The

core sheet 12 embedded with the wire 14 and the IC 38 may then be used in the subsequent process for manufacturing IC cards. As shown in Fig. 6, the core sheet 12 is positioned among other base sheets 44,46 for lamination. The core sheet 12 and the other base sheets 44,46 are piled together. As the core sheet 12 and the base sheets 44,46 are all provided with guide holes, they can be easily and accurately aligned with one another. These sheets will then be spot-welded to ensure that they remain at their correct relative position during the lamination process. During lamination, the core sheet 12 and the other base sheets 44,46 are secured to each other under pressure and high temperature. After lamination, product IC cards 47 are punched out from the laminated base sheets, as shown in Fig. 8, ready for use.

Fig. 7 shows a cross-sectional view of a conventional contact-less high-frequency IC card, including, in addition to the IC 38 secured to the core sheet 12, a filler sheet 48, two protective sheets 50, two graphical printing sheets 52, and two outer transparent sheets 54.

The total thickness of such an IC card is roughly 0. 84mm. In an alternative construction, there is no protective sheet. In a further alternative construction, while there is no protective sheet, there is provided an additional layer of filler sheet.

An additional advantage of the present invention is that, even during short supply of IC chips, the wire can still be embedded onto the core sheet. As the procedure for embedding

the wire takes more time than the procedure for placing the IC into the cavity and subsequently bonding the IC with the antenna coil, a manufacturer may carry out the wireembedding procedure, and once the IC chips are available, the subsequent relatively less time-consuming process can be carried out for producing the final product.

It should be understood that the above only illustrates an example whereby the present invention may be carried out, and that various modifications and/or alterations may be made thereto without departing from the spirit of the invention.

It should also be understood that various features of the invention which are, for brevity, described in the context of a single embodiment, may be provided separately or in any appropriate sub-combinations.

Claims

CLAIMS :- 1. A method of forming a card embedded with at least one integrated circuit and an antenna coil, said method including the steps of (a) providing a sheet with at least a cavity for receiving at least part of said integrated circuit; (b) providing said antenna coil on said sheet; (c) positioning said integrated circuit into said cavity of said sheet; and (d) electrically connecting said integrated circuit with said antenna coil, wherein said step (c) is carried out after said step (b).
2. A method according to Claim 1 wherein said integrated circuit is secured with said antenna coil.
3. A method according to Claim 1 and 2 further including a step (e) of providing means for temporarily retaining said integrated circuit in said cavity of said sheet.
4. A method according to Claim 3 wherein said retaining means comprises an adhesive tape.
5. A method according to any of the preceding claims further including a step (f) of reversing said sheet for allowing said integrated circuit to be positioned into said cavity.
6. A method according to Claim 5 further including a step (g) of further reversing said sheet to carry out step (d) above.
7. A method according to any of the preceding claims wherein said integrated circuit is secured with said antenna coil by thermo compression bonding.
8. A method according to any of the preceding claims wherein said sheet rests directly on a rigid support during step (d) above.
9. A method according to any of one of Claims 3 to 8 further including a step (h) of removing said retaining means.
10. A method according to any of the preceding claims further including a step (i) wherein, after step (d), said sheet is positioned between at least two outer sheets for lamination.
11. A method according to Claim 10 further including a step CD of punching a product card out of said laminated sheets.