The Manufacture of Transponders and Contactless Smart Cards - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 328

Table 12.1 Surface resistance of polymer thick
film pastes with different admixtures given a layer
thickness of 25 µ m (Anderson, 1998)

Conductor Surface resistance

Silver (Ag) 5-20m /

Copper (Cu) 30-120m /

Graphite (carbon) 20 000-100 000m /

Table 12.2 Typical properties of some polymer thick film pastes (Anderson, 1998)

Paste Dupont 5028 Dupont 5029

Surface resistance after drying 27-33m / 14-20m /

Surface resistance after lamination 8-10m / 4-5m /

Layer thickness after drying (200 µ m screen) 16-20m / 28-32 µ m

Viscosity (RVT UC&S 14 10 rpm) 15-30m / 35-50Pa.s

Antenna coils made of wire, i.e. wound or embedded coils, are connected to the chip
module using microwelding techniques. The lacquer enamelled antenna coil is bared in
the connection area of the chip module using a special tool and then welded to the termi-
nals (lead frames) of the chip module using ultrasound (Haghiri and Tarantino, 1999).
Contacting a printed coil to the chip or a module is problematic as conventional
soldering and welding techniques do not work for polymer pastes. The use of flip
chip technology, 2 in which fixing and contacting of the chip can take place using a
conductive adhesive, offers a solution. A second solution is the use of cut clamp tech-
nology (CCT). In this approach the metal terminals (lead frame) of the chip module are
punched through with a pointed tool, so that pointed crowns are formed (Figure 12.9).
The chip module is then pressed onto the carrier foil from below, so that the peaks of
the crown penetrate the foil and make contact with the antenna terminals. The crown
peaks are bent over using a flat stamp, making a permanent mechanical and electrical
connection between the chip module and the antenna coils.

Antenna
terminal

Antenna

PVC foil

Crowns

Contactless chip module

Figure 12.9 Contacting of a chip module to a printed or etched antenna by means of cut clamp
technology

2 The unhoused chip is placed directly upon the terminals of the coil with the contact areas (bond pads)
downwards.