Introduction
The new buzz word in the card industry is "transponder" or
in simple technical terms "contactless radio frequency identification
device" and is emerging as a very important technology in the next
generation of ISO cards. There are two distinctive types of transponders
namely "active" and "passive" transponders whereby
the former requires a battery in order to transmit data.
Passive transponders, the subject of this article, obtain their energy
from being present in an electromagnetic field generated by a reader
system which can read and write data in handshake with the transponder
at a maximum distance which does not interfere with other electronic
equipment.
Passive transponders operate at two main frequencies, namely 125 kHz
and 13.56 Mhz.
The operating frequency of the transponder determines primarily the
maximum distance in which the transponder can receive and transmit data.
With low-frequency transponders (125 kHz) the coupling with the reader
is typically between 50 cm and 100 cm. With high-frequency transponders
(13.56 Mhz), the coupling is close with the reader and the distance
is internationally standardized at below 10 cm.
Transponders comprise of a microchip encapsulated for protection in
a wire bonded module and connected to an antenna.
The microchip has an analogue input which processes the radio signal
containing the digital data, an EEPROM memory which stores and erases
data and operational features such as anti collision, encryption and
special coding which offers the customer ease of use and security. The
physical characteristics of the antenna is determined by the operating
frequency of the microchip.
Low-frequency transponders have an antenna which is an oval shaped
wound coil having several hundred turns of fine copper wire. High frequency
transponders have an antenna which can be made from a multiple of different
technologies as the number of turns of wire is between four and six.
Applications
Transponder technology has been in use for a number of years in applications
such as: access control using plastic cards slightly thicker than ISO;
animal identification using glass tube transponders and immobilizers;
as an automobile anti-theft device, located in the car keys; and general
industrial radio-frequency identification (RFID) using disc tags.
In the past the transponders were read-only devices. Due to advanced
developments in low voltage EEPROM technology and full-custom optimization
of the chip area, resulting in higher yields and lower silicon cost,
read/write transponders have moved into the above applications. To further
complicate the issue, the above transponders were and are low-frequency
devices.
The early 1990s saw the emergence of the high-frequency transponders
with an operating distance of 10 cm, having a large size EEPROM memory,
encryption coding and anti-collision function which matched the exact
specification of the electronic ticket required in automatic fare collection.
Although many pilot projects were launched around the world, the first
real application for the contact-less card using a high-frequency transponder
was the electronic airline ticket used by the Lufthansa frequent travellers
in Germany.
At same time there was much controversy over the transit project in
Hong Kong, but perhaps the most successful mass transit project was
the use of contactless cards in buses in Seoul, Korea.
The use of contactless cards is not limited to automatic fare collection
applications, Japan's NTT decided in 1997 to use contactless cards as
a means of payment when using the telephone, and there are numerous
satellite card applications such as affinity and loyalty schemes, student
identification, electronic passport, vending machines, parking, access
control, toll payment - in short for applications replacing small amounts
of money (coins).
The advantages of contactless cards over the traditional contact card
is one of ease of use, speed, less maintenance on the readers as there
are no mechanical parts and lower operational costs for the transit
authorities.
The Combi Card or Dual Interface Card is a combination of contact and
contactless function integrated in an ISO card. The word "contact"
refers to the physical contacting of the chip module when the card is
entered into the slot of a reader in a telephone or an ATM. The chip
is microprocessor based with EEPROM, RF analogue inputs and peripherals
on a single chip solution. However, the chip size area is substantially
greater than the pure contactless microchip and so the overall cost
of the card is higher.
At the moment several semiconductor companies are investigating an
alternative to EEPROM technology such as FRAM, as it offers enhanced
data transmission speeds required in multi-media and image processing
applications like the electronic passports.
Unlike the contactless cards which are distributed by several types
of companies, such as transit authorities, systems providers, integrators
etc., the Combi Card is primarily distributed by the banks.
The main uses for Combi Cards in contact mode, where a high degree
of security is desired, are electronic cash, cybercash and credit card
facility. In contactless mode, the same applications apply as described
above, namely replacing small change especially in automatic fare collection.
The Combi Card is not as price sensitive as contactless cards and competition
is less aggressive as the number of secure card manufacturers is limited.
Manufacturing technology
The manufacturing of contactless and Combi Cards is not as simple as
it may seem. Achieving excellent card surface quality, high yields,
good warping and bending characteristics and durability at a competitive
price is not an easy task.
In contactless cards, the antenna and the chip module are embedded
into the card body by a cold or a hot lamination process. The former
method is basically gluing and little pressure is exerted on the chip
module, however, under environmental tests especially humidity and temperature
cycling, the life span of the card is reduced.
In the hot lamination process, temperature and pressure is exerted
on the chip module and at the interconnection points of the antenna
which causes yield loss if precautions are not taken. The antenna in
the low-frequency transponders is a wound coil and there is no economical
alternative to the traditional coil winding. The antenna in the high-frequency
transponders can be an etched antenna, a wound wire antenna, an embedded
wire antenna or a printed antenna. The mechanical and electrical characteristics
of a wound or embedded antenna is basically the same; insulated copper
wire forms the antenna and the wire ends are connected to the chip module
by way of thermo-compression bonding.
The intermetallic connection between the copper wire and the lead frame
module or epoxy glass module gives a bond force greater than 250 cN
and hence the interconnection cannot be degraded during the hot lamination
process.
The copper wire with a diameter between 100 and 150 microns has a stabile
high temperature enamel as insulation so that no short circuiting of
the copper wires is possible during the lamination.
An etched antenna has electrical characteristics inferior to that of
a copper wire antenna, as the cross sectional area of the etched copper
is less than 35 microns. Etched antennas are supplied in sheet format
and the card manufacturer can use a pick-and-place machine to position
the chip modules on the sheet for connection. Soldering seems to be
the preferred method of interconnection using a solder paste.
However, there are a number of reliability issues which have restricted
the use of etched antennas in contactless cards. Etching requires the
use of acids to remove the copper from the continuous sheet passing
through an acid bath. By using masks and photolithography, etched antennas
are created in a format by removing 90% of the copper around the antennas.
As the material loses its binding ability caused by the aggressive acids,
a primer is needed to ensure adhesion between the layers of the ISO
card and the etched coil.
Handling of the etched sheets with the chip module attached is critical
if the sheets have to be transported over rolls, drums or convex surfaces
before entering the lamination machine. As the etched copper is very
thin and delicate, there are yield losses before, during and after the
hot lamination process. Bending or warping of the ISO card at the position
of the module is critical. Oxidization of the etched antenna especially
at the points of interconnection with the module is a long-term reliability
issue. Finally, storing of etched antennas in sheet format is not advised
as the material curves at the sides making alignment difficult. In the
manufacturing process this curving is caused by a one-sided inner tension
in the material and can be avoided by back etching the copper on both
sides of the material.
Although the etched antenna has a number of defaults, it is an alternative
technology to the copper wire antenna and if the contactless card requires
several integrated circuits and discrete components, then the etched
antenna with circuitry offers great potential.
There is no reliable data on printed antennas, but there is one distinct
advantage in that the antenna can be applied to a card material which
is more suitable for the card manufacturing process. The reliability
of this additive process is dependent on the stability of the filler
material in the antenna, as well as the interconnection method with
the chip module.
The transponder inlay
The inlay is the principle component of the contactless card containing
the antenna and attached chip module, correctly speaking the "transponder
inlay".
The inlay is supplied to the card manufacturer in a transponder array
such as 3 x 6, whereby the overall size of the transponder inlay sheet
and the pitch between the antennas correlates respectively with the
size of the lamination plates and the alignment markings on the printed
sheets required for punching of the cards.
Handling and transport of the naked transponder inlays in which the
antenna and the chip module are exposed, leads to the question of quality
assurance at outgoing inspection and at incoming inspection at the card
manufacturing site.
As the transponder inlays have to be adapted to each individual card
manufacturer and as the top sheets having the punched opening or window
to accommodate the chip module mould compound must also be adapted and
aligned accurately with the transponder inlay, the card market has demanded
the so-called prelaminated transponder inlays.
By integrating the technologies of antenna wire embedding, thermo-compression
bonding and soft pressure lamination, it has become possible to create
a high quality semi-finished product, namely the "prelaminated
transponder inlay" which can be easily handled and processed by
the traditional card manufacturer. It enables excellent yields to be
achieved by using existing equipment with virtually no financial investment
required.
The picture is not much different for the production of Combi Cards,
however, unlike the contactless card production, capital investment
is required in new machinery and process technology especially in handling
sheets and interconnecting the combi-chip module with the embedded antenna.
In this case, the card manufacturer can source pre-laminated antenna
inlays adapted to the size of their lamination plates and the alignment
markings on their printed sheets.
Low frequency prelaminated transponder inlays are also available on
the market using silicon from various semiconductor suppliers for the
exact same reasons as described above.
For additional information on prelaminated transponder and antenna
inlays and equipment, please contact:
AmaTech Corporate Headquarters
Rossbergweg 2
87459 Pfronten, Germany
Telephone: 49 - 8363 - 91050
Facsimile: 49 - 8363 - 910539
E-mail: ecm@amatech.de
Web site: http://www.amatech.de
Contact: Paul Holloway