A transponder and a method for manufacturing it The present invention relates to a transponder comprising a substrate, which includes a circuitry pattern and an integrated circuit on a chip having a location on the substrate, and a cover layer attached to the substrate in such a manner that at the location of the chip there is a hole in the cover layer in which the chip is arranged to be located, and there is a free space outside the chip in the hole. The present invention also relates to a method for manufacturing such a card.

In the present application, transponders refer to cards, tags, labels, and the like comprising an RF-ID circuit (identification) or an RF-EAS circuit (electronic article surveillance). The transponder comprises a so-called radio frequency identification (RFID) circuit, which is typically used at a distance of some tens of centimetres from a reader antenna. A reader device and the card are coupled inductively. Such a transponder can be used for example as an electrical purse, as a ticket in public service vehicles, or for personal identification. The card may be for single use only.

In addition to the transponders having the inductive coupling to the reader device, also transponders having an antenna based on the dipole antenna technique and an electric coupling belong in the scope of the invention.

A problem related to transponders is that the chip is brittle and vulnerable to damages. Therefore the chip must be protected against impacts. One such arrangement is described in WO 99/41721. A web stock device comprises a sheet-like material, which has a cavity. A signaling device is at least partly contained in the cavity. The web stock material includes means for retaining the signaling device at least partly in the cavity.

The transponder of the invention is characterized in that the free space has been filled with ink. The manufacturing method of the invention is characterized in that the free space is filled at least partially with ink.

The invention has advantageous features. Excess layers are avoided in the product, and it is made simple and easy to manufacture. The process step comprising printing with ink can be integrated into the same production line in which other process steps to manufacture the card are made.

The transponder can be manufactured individually, as sheets comprising more than one transponder, or as a continuous web. The continuous web is a preferred choice. The transponder substrate in a web form comprises successive and/or adjacent circuitry patterns to which the chips are attached. The different layers of the transponder may include paper or plastic materials. The layers are attached to each other by a suitable adhesive, or by heat sealing. The adhesive is preferably a film, which can be laminated to another surface by transfer lamination.

The circuitry pattern of the transponder can be manufactured by printing a circuitry pattern with an electroconductive printing ink on a film, by etching the circuitry pattern on a metal film, by electroplating, by punching the circuitry pattern from a metal film, or by winding the circuitry pattern of for example a copper wire. The preferred manufacturing method is etching. The electrically operating radio frequency identification (RFID) circuit of the transponder is a simple electric oscillating circuit (RCL circuit) operating at a defined frequency.

The circuit consists of a coil, a capacitor and an integrated circuit on a chip. The integrated circuit comprises an escort memory and an RF part, which is arranged to communicate with a reader device. Also the capacitor of the RCL circuit can be integrated on the chip.

The integrated circuit on the chip is attached to the circuitry pattern for example by using the principle-of the flip-chip technique, which is known as such but also other techniques for the attachment are possible. The chip can be attached to a separate structural part as well, and thereafter attach the structural part to the substrate comprising the circuitry pattern. The transponder substrate may be provided with a thermoplastic anisotropically conductive film, which is attached to the surface on the transponder substrate to cover the surface including the

circuitry pattern. The anisotropically conductive film may cover the transponder substrate completely or partly. Since the anisotropically conductive film is thermoplastic it endures repetitive heating, which is necessary for making the film tacky. The attachment of the chip is made so that a suitable place in the transponder substrate is heated on the reverse side and the chip adheres slightly to the substrate. After that the chip is fixed firmly to the substrate. Suitable thermoplastic films for adhering the chip are for example anisotropic conductive films 8773 and 8783 (Z-Axis Adhesive Films 8773 and 8783,3M, USA).

In addition to anisotropically conductive films, also other suitable techniques for attaching the chip may be used. For example, isotropically conductive films, or crimping techniques can be used.

The transponder substrate comprising the circuitry pattern and the chip is attached to the cover layer, which includes a hole. The hole is intended for receiving the chip from underneath when the transponder substrate and the cover layer are attached together. The shape of the hole can be any, for example a square or a circle. The dimensions of the hole are larger than the dimensions of the chip, and hence there is a free space around the chip except the underside of the chip, which is firmly attached to the transponder substrate. The hole is at least partially filled with ink. The ink may be printed by conventional printing methods over the hole when the ink transfers into the hole. The ink may fill the hole as such, or it may comprise expandable components, which are expanded after printing. Inks, which are capable for filling the hole as such are for example inks intended for printing Braille alphabets. When the ink is expanded by using for example heat, substantially the rest of the hole volume not filled with the chip is filled with the expanded ink. A level of the ink may be even with the upper eve of the cover layer, or slightly lower. It is also possible that the expandable substance is other than the ink, and it is brought into the hole by using technique other than the printing. Some coating compositions and coating or injecting methods may be usable, too.

In a preferred embodiment, the transponder is manufactured as a continuous web, and all the layers of the transponder are attached to

each other on the same production line. It is possible that the ink is also filled in the hole and possibly expanded on the same production line as the layers are attached to each other.

In the following, the invention will be described with reference to the appended drawings, in which Fig. 1 shows a substrate of a transponder in a top view, and Fig. 2 shows a transponder of the invention in a cross-sectional view.

Figure 1 shows a transponder substrate 1, such as a smart card substrate, in a top view, including a circuitry pattern 3 and an integrated circuit on a chip 2 therein. In Fig. 1, the transponder substrate is separated from a continuous web. The transponder substrate 1 can be manufactured by printing the circuitry pattern on a film with an electroconductive printing ink, by etching the circuitry pattern on a metal film, by punching the circuitry pattern off a metal film, or by winding the circuitry pattern of e. g. a copper wire. The circuitry pattern is provided with an identification circuit, such as a radio frequency identification (RFID) circuit. The identification circuit is a simple electric oscillating circuit (RCL circuit) tuned to operate at a defined frequency.

The circuit consists of a coil, a capacitor and a circuit integrated on a chip, consisting of an escort memory and an RF part for communication with a reader device. The capacitor of the RCL circuit can also be integrated on the chip.

Figure 2 shows a transponder of the invention in a cross-sectional view. A transponder substrate 1 carries a chip 2 and a circuitry pattern (not shown in Fig.-2.). A cover layer 4 is attached to-the-transponder substrate 1. The cover layer 4 has a hole at a location of the chip 2, and dimensions of the hole are larger than those of the chip 2. The vertical walls of the hole form a protective arrangement for the chip 2 but excess protection is needed against perpendicular impacts. Thus, the hole is at least partially filled with ink 5, which fills the rest of the hole volume not filled with the chip 2 when the ink 5 has been cured,

for example by heat or ultraviolet radiation. Such inks include inks capable for forming Braille alphabets. An example of such ink is YK20- 9599 (Sun Chemical, USA). In general, the ink shall be such that its volume does not decrease essentially during drying. On the reverse side of the transponder substrate 1 may be an excess material layer 6 to bring some rigidity to the transponder.

Another possibility is to fill the hole by an expandable ink, and expand it by heat. The ink may comprise for example expandable microspheres, such as Expancel microspheres (Expancel Inc., USA).

The invention is not restricted to the description above, but it may vary within the scope of the claims.