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PDF AN830 Data sheet ( Hoja de datos )
| Número de pieza | AN830 | |
| Descripción | RFID Tag and COB Development Guide | |
| Fabricantes | Microchip | |
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AN830
RFID Tag and COB Development Guide with Microchip’s RFID Devices
Author: Youbok Lee, Ph.D.
Microchip Technology Inc.
INTRODUCTION
A passive RFID tag contains an RFID integrated circuit
(IC), resonant capacitor (C), and antenna (L), as shown
in Figure 1. The antenna and cap acitor form a parallel
LC resonant circuit. The LC circuit must be tuned to the
reader’s carrier frequency for maximum performance
(read range).
The two most common antenna types for RFID tagging
applications are: (a) wire-wound coil and (b) etched (or
printed/stamped) spiral inductor on a dielectric sub-
strate. The antenna types are typically determined by
carrier frequency , t ag’s p ackage type, performance,
and assembly cost factors. For example, low frequency
(< 400 kHz) tags need a few mH of induct ance. This
inductance is achieved with a few hundreds of turns of
wire. This kind of induct ance cannot be obtained eco-
nomically with etched antenna, but with a wire-wound
antenna. However , medium frequency (4 - 30 MHz)
tags need a few uH of inductance. This inductance can
be achieved with a few turns of wire or etched (or
printed/stamped) spiral inductor on dielectric substrate.
After the antenna type is chosen, the next step is to
attach the silicon device to the antenna. There are two
basic methods for the device att achment: (a) using a
chip-on-board (COB) or (b) direct die attachment to the
antenna. The COB is commonly used for wire-wound
antennas and the direct die attachment is for the
etched (printed/stamped) antenna types.
The COB is made by packaging a r esonant capacitor
and an RFID device together in the same p ackage. It
has two external terminals for antenna atat chment. The
inductance of the antenna is determined by the COB’ s
resonant cap acitor value and the reader ’s carrier
frequency. The antenna is att ached to the COB‘s two
external terminals by welding or soldering. Because
most of the COBs are used for ISO cards which need
to meet the ISO card st andard thickness (0.76 mm)
specification, typical thickness of the COB is approxi-
mately 0.4 mm. Although the CO B p ackage is
designed to protect the internal silicon device during
the card lamination process which involves mechanical
pressure with hot temperature, care is needed to pre-
vent mechanical cracks on the device. The two popular
COB package types are IOA2(MOA2) from IST in T ai-
wan and World II from HEI Inc. in the USA.
Since the direct die att achment reduces a step for
making the COB package, it is widely used for low cost
and high volume applications such as smart labels. The
direct die att achment can be achieved with two dif fer-
ent methods: (a) wire bonding or (b) flip-chip with
bumped die. For the flip-chip, it needs a special bump-
ing on the die’s bond pads. Typically the bump material
is made of gold with approximately 25 um of height.
The flip-chip assembly process att aches the bumped
area to the antenna tr aces. Several bumping and flip
chip assembly methods are available for RFID t ags.
The wire bonding method needs a relatively simple
process for the die attachment. The die is directly wire-
bonded to the antenna, and covers the wire bonded
area with a black colored epoxy glob top. For small vol-
ume pr oduction, the wir e-bonding method is still les s
expensive than using the flip-chip process. However, it
is less efficient for high volume production. The flip-chip
method is preferred for high volume production.
The read range of an RFID at g is greatly afected by the
tag’s size, tuning, circuit Q, de vice’s power consump-
tion and data modulation depth. The tag’s size must be
chosen depending on it s application and cost con-
straints. Tags must be tuned precisely to the reader ’s
carrier frequency for long range applications. Since the
tag’s antenna circuit consists of a combination of L and
C components, the tolerance of the component often
causes the variation in the read range between t ags.
Once the induct ance is designed, it s tolerance is typi-
cally within 1 ~ 2%. Therefore, a t ag’s tuning variation
is mostly due to the capacitance tolerance. The capac-
itance used for the antenna circuit or COB must be
chosen carefully. For example, the tolerance must be
kept within ~5% and the capacitor’s Q factor should be
greater than 100 at the operating frequency to maxi-
mize the read r ange performanc e. T he internal
resonant cap acitors of the MCRF451/452/455 and
MCRF360 devices are made with silicon oxide. Their
tolerance is approximately less than 5% for the devices
in the same wafer and within ~10% from dif ferent
wafers. Their Q factor is greater than 100 at
13.56 MHz. The cap acitance tolerance result s in
variations in the read range between tags. Therefore, if
the read range variation (about 10%) is a concern due
to the internal capacitor’s tolerance, the MCRF450 and
MCRF355 can be used with an external cap acitor that
has a smaller tolerance (within 2~5%).
2002 Microchip Technology Inc.
DS00830B-page 1
http://www.Datasheet4U.com
1 page  
AN830
DIE LAYOUT AND EXTERNAL
ANTENNA CIRCUITS FOR MCRF
DEVICES
Table 3 shows internal resonant cap acitance of the
13.56 MHz MCRF devices and their induct
ance
requirements. The external circuit configuration for
these devices are shown in Figure 1. The MCRF452
includes two 50 pF internal cap acitors in series (C1:
between antenna A and B, C2: between antenna B and
VSS). The device short s and un-short s C2 when it
sends data “Hi” and “Lo”, respectively . The MCRF452
needs only two connection points (antenna A and VSS)
to external antenna. When the MCRF452 is used for
the COB, it does not require the extra cap acitor. The
MCRF452 is a good candidate for both direct die
attachment and COB. Tag assembly processing step s
for various methods are shown in Figure 7.
The MCRF451, MCRF455 and MCRF360 requires
three connection point s to the external antenna
(antenna A, antenna B, V SS). These devices can be
used effectively for direct die attachment (wire bonding
or flip-chip) to the antenna.
Here is the summary for the 13.56 MHz devices:
For direct die att achment to antenna: MCRF 355,
MCRF360, MCRF450, MCRF451, MCRF452,
MCRF455.
For COB: MCRF355, MCRF450, MCRF452.
TABLE 1:
13.56 MHZ DEVICE FEATURES
Devices
Programming
Internal
Anti-collision Memory Resonant
Capacitor
Read
Range
Application
Availability
MCRF355
Contact or factory
programming
Yes (typically 20
tags/second and
as many as 50
tags/second)
154 bits
MCRF360
MCRF450
Contactless
Yes (read all 1K bits
energized tags)
MCRF451
MCRF452
MCRF455
No
100 pF
No
95 pF
30 pF
50 pF
up to 1.5
meters
Multiple reading of tags,
book store and library
book ID, toys/gaming
tools, airline baggage
tracking, access control
and asset tracking
Die, wafer,
wafer on frame,
bumped, SOIC,
PDIP
Multiple reading and writ-
ing of tags, book store
and library applications,
toys/gaming tools, airline
baggage tracking,
access control, asset
tracking and inventory
management
2002 Microchip Technology Inc.
DS00830B-page 5
5 Page 
AN830
FIGURE 9: EXTERNAL ANTENNA CIRCUITS FOR MCRF355 AND MCRF360
Interrogator
RF Carrier
Ant. A
C
Modulated
RF Data
(a)
L1
L2
L1 > L2
MCRF355
Ant. B
VSS
f0=
-----------1------------
2π CLT
Where:
LT = L1 + L2 + 2LM
LM = Mutual inductance
between L1 and L2
Interrogator
Interrogator
RF Carrier
L
Modulated
RF Data
(b)
Ant. A
C1
C2
C1 ≥ C2
MCRF355
Ant. B
VSS
f0
=
-----------1--------------------------------
2π L-C-C-1-1-+-C--C-2-2------------
RF Carrier
L1
Modulated
RF Data
L2
(c)
Ant. A
Ant. B
VSS
L1 > L2
100 pF
MCRF360
f0
=
-----------------------------1-----------------------------
2π (LT)(100x10–12)
Where:
LT = L1 + L2 + 2LM
LM = Mutual inductance
between L1 and L2
2002 Microchip Technology Inc.
DS00830B-page 11
11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet AN830.PDF ] | |
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