The Manufacture of Transponders and Contactless Smart Cards - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 324

Filling

Overlay foil

Stamped out foil

Connection
method

Antenna
Carrier foil

Contactless
chip module

Overlay foil

Figure 12.4 Foil structure of a contactless smart card

process (see Section 12.2.3) from collapsing around the chip module and to give a
smooth and even card surface (Haghiri and Tarantino, 1999).

12.2.1 Coil manufacture

Winding In the winding technique the transponder coil is wound upon a winding
tool in the normal way and affixed using baked enamel. After the chip module has been
welded onto the antenna, the semi-finished transponder is placed on the inlet sheet and
mechanically affixed using cemented joints (Figure 12.5).
For contactless smart cards in the frequency range < 135 kHz the winding technique
is the only procedure that can be used for the manufacture of transponder coils due to
the high number of windings (typically 50-1500 windings).
Embedding Inlet manufacture using the embedding technique (Figures 12.6 and 12.7)
is a relatively new procedure that is nevertheless increasing significantly in importance.
In this technique, the chip module is first affixed in its intended location on a PVC
foil. The wire is then embedded directly into the foil using a sonotrode. The sonotrode
consists of an ultrasonic emitter with a passage in its head through which the wire is
guided onto the foil. The ultrasound emitter is used to locally heat the wire to such a
degree that it melts into the foil and is thus fixed in shape and position. The sonotrode
is moved across the inlet foil in a similar manner to an X-Y plotter, while the wire
is fed through, so that the transponder can be 'drawn' or embedded. At the start and
the end of the coil a spot welding machine is used to make the electrical connection
to the transponder module.
Screen printing The screen printing technique is a common printing technique in
industrial production and is used, for example, in the production of wallpaper, (PVC)
stickers, signs, and also in textile printing. A screen mesh made of synthetic or natural
fibres or metal wires is stretched over a frame. The fineness of the screen mesh and
the strength of the fibres are selected on the basis of the resolution of the print and
the viscosity of the paint. The template is applied to the screen mesh manually or
photomechanically. The actual print motif, in our case a coil, remains free. The template
material may, for example, be a light-sensitive emulsion that is applied to the screen.
If this coated screen is illuminated through a printing film, the emulsion hardens at
the illuminated points. The points that have not been illuminated are washed out with
water. Colour drawn over the screen with a rubber squeegee is pressed through these