U.S. patent application number 11/959840 was filed with the patent office on 2008-05-01 for variation of conductive cross section and/or material to enhance performance and/or reduce material consumption of electronic assemblies.
Invention is credited to Michael Fein, Daniel P. Lawrence.
Application Number | 20080100421 11/959840 |
Document ID | / |
Family ID | 35929896 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080100421 |
Kind Code |
A1 |
Fein; Michael ; et
al. |
May 1, 2008 |
Variation of Conductive Cross Section and/or Material to Enhance
Performance and/or Reduce Material Consumption of Electronic
Assemblies
Abstract
An RFID antenna is fabricated according to varying current
density requirements of different regions of the antenna. A method
such as computer modeling is used to determine the current
densities of the antenna regions. In one aspect of the invention, a
conductive material is printed to a substrate at varying thickness
according to current density requirements of particular antenna
regions. In another aspect of the invention, materials of different
conductivity are printed to the substrate according to the current
density requirements. A material of higher conductivity is printed
at an antenna region that requires high current density, and a
material of lower conductivity is printed at antenna region that
requires lower current density.
Inventors: |
Fein; Michael; (Ann Arbor,
MI) ; Lawrence; Daniel P.; (Ann Arbor, MI) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Family ID: |
35929896 |
Appl. No.: |
11/959840 |
Filed: |
December 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10979874 |
Nov 2, 2004 |
7323993 |
|
|
11959840 |
Dec 19, 2007 |
|
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Current U.S.
Class: |
340/10.1 ;
427/58 |
Current CPC
Class: |
H01Q 9/16 20130101; G06K
19/07749 20130101; H01L 2924/01057 20130101; H01L 2924/00011
20130101; H01L 2224/16 20130101; H01L 2224/0401 20130101; H01Q
23/00 20130101; H01L 2924/00014 20130101; H01L 2224/0401 20130101;
H05K 3/245 20130101; H01L 2924/00011 20130101; H01L 2924/00014
20130101; G06K 19/07786 20130101; H01L 2924/3011 20130101; H05K
1/0263 20130101 |
Class at
Publication: |
340/010.1 ;
427/058 |
International
Class: |
H04B 7/00 20060101
H04B007/00; B05D 5/12 20060101 B05D005/12 |
Claims
1. An RFID tag, comprising: a substrate; an antenna formed on the
substrate that includes first and second conductive traces, a first
antenna region, and at least one second antenna region; and an
integrated circuit that is connected across the first and second
conductive traces, wherein the first antenna region is formed from
a first material having a first conductivity and the at least one
second antenna region is formed from a second material having a
second conductivity, and wherein the RFID tag further comprises a
third antenna region having a third conductivity, wherein said
first antenna region comprises an interconnect area, said second
antenna region comprises a main antenna area, and said third
antenna region comprises an intermediate antenna area, and wherein
said first conductivity is greater than either of said second and
third conductivity.
2. The RFID tag of claim 1 wherein the first antenna region is a
first distance from the integrated circuit and the at least one
second antenna region is a second distance from the integrated
circuit.
3. The RFID tag of claim 1 wherein the first antenna region has a
first current density and the at least one second antenna region
has a second current density.
4. The RFID tag of claim 2 wherein the second distance is greater
than the first distance.
5. The RFID tag of claim 1 wherein the first conductivity is
greater than the second conductivity.
6. The RFID tag of claim 1 wherein the at least one second antenna
region comprises a coil region.
7. An RFID tag, comprising: a substrate; an antenna formed on the
substrate that includes first and second conductive traces, a first
antenna region, and at least one second antenna region; and an
integrated circuit that is connected across the first and second
conductive traces, wherein the first antenna region is formed at a
first thickness and possesses a first conductivity, wherein the at
least one second antenna region is formed at a second thickness and
possesses a second conductivity, wherein the RFID tag further
comprises a third antenna region possessing a third conductivity,
wherein said first antenna region comprises an interconnect area,
said second antenna region comprises a main antenna area, and said
third antenna region comprises an intermediate antenna area, and
wherein said first conductivity is greater than either of said
second conductivity and said third conductivity.
8. The RFID tag of claim 7 wherein the first antenna region is a
first distance from the integrated circuit and the at least one
second antenna region is a second distance from the integrated
circuit.
9. The RFID tag of claim 8 wherein the second distance is greater
than the first distance.
10. The RFID tag of claim 7 wherein the first antenna region has a
first current density and the at least one second antenna region
has a second current density.
11. The RFID tag of claim 7 wherein the at least one second antenna
region comprises a coil region.
12. A method of printing an RFID antenna with varying conductivity
comprising: determining current densities of a first region and at
least one second region of the antenna; determining conductivity
requirements of the first and at least one second regions according
to the current densities; selecting a first material according to
the conductivity requirements of the first region and a second
material according to the conductivity requirements of the at least
one second region; and printing the first material to a substrate
at the first region and the second material to the substrate at the
at least one second region.
13. The method of claim 12 wherein the first antenna region has a
first current density and the at least one second antenna region
has a second current density, wherein said printing prints the
first material to a substrate at the first region and the second
material to the substrate at the at least one second region.
14. The method of claim 12, wherein the first material has a first
conductivity and the second material has a second conductivity,
wherein the first conductivity is greater than the second
conductivity, wherein said printing prints the first material to a
substrate at the first region and the second material to the
substrate at the at least one second region.
15. The method of claim 14 wherein the RFID antenna further
comprises a third antenna region made from a third material having
a third conductivity, wherein the first antenna region comprises an
interconnect area, the second antenna region comprises a main
antenna area, and the third antenna region comprises an
intermediate antenna area, and wherein said first conductivity is
greater than either the second and third conductivity, wherein said
printing prints the first material to a substrate at the first
region, the second material to the substrate at the at least one
second region, and the third material to the substrate at the at
least one third region.
16. The method of claim 14 wherein the RFID antenna further
comprises a third antenna region made from a third material having
a third conductivity, wherein the first antenna region comprises an
interconnect area, the second antenna region comprises a main
antenna area, and the third antenna region comprises an
intermediate antenna area, and wherein said first conductivity is
greater than either the second and third conductivity, wherein said
printing prints the first material to a substrate at the first
region at a first thickness according to the conductivity
requirements of the first region, the second material to the
substrate at the at least one second region at a second thickness
according to the conductivity requirements of the second region,
and the third material to the substrate at the at least one third
region at a third thickness according to the conductivity
requirements of the third region.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/979,874, filed Nov. 2, 2004, which is hereby incorporated
herein in its entirety by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to radio frequency
identification (RFID) antennas, and more particularly to a printing
process for RFID antennas.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits (ICs) are the basic building blocks that
are used to create electronic devices. Continuous improvements in
IC process and design technologies have led to smaller, more
complex, and more reliable electronic devices at a lower cost per
function. As performance has increased and size and cost have
decreased, the use of ICs has expanded significantly.
[0004] One particular type of IC that would benefit from
inexpensive mass production involves the use of radio frequency
identification (RFID) technology. RFID technology incorporates the
use of electromagnetic or electrostatic radio frequency (RF)
coupling. Traditional forms of identification such as barcodes,
cards, badges, tags, and labels have been widely used to identify
items such as access passes, parcels, luggage, tickets, and
currencies. However, these forms of identification may not protect
items from theft, misplacement, or counterfeit, nor do they allow
"touch-free" tracking.
[0005] More secure identification forms such as RFID technology
offer a feasible and valuable alternative to traditional
identification and tracking. RFID does not require physical contact
and is not dependent on line-of-sight for identification. RFID
technology is widely used today at lower frequencies, such as 13.56
MHz, in security access and animal identification applications.
Higher-frequency RFID systems ranging between 850 MHz and 2.5 GHz
have recently gained acceptance and are being used in applications
such as vehicular tracking and toll collecting, and in business
logistics such as manufacturing and distribution.
[0006] A printing process is used to print conductive traces on a
substrate to form a functional electronic structure such as an RFID
antenna. The RFID antenna absorbs, couples with, and/or reflects
radio frequency signals from a transmitter and provides a signal
and power to an attached integrated circuit. The conductance of the
antenna is determined by material properties of the antenna and the
thickness of the conductive traces. For example, some areas of the
antenna may need to conduct more current than other areas of the
antenna; therefore, a greater amount of conductive material must be
used when higher current density is required. However, a process
such as screen printing applies a single layer of film of
conductive ink at a generally constant thickness.
SUMMARY OF THE INVENTION
[0007] An RFID tag comprises a substrate. An antenna is formed on
the substrate that includes first and second conductive traces, a
first antenna region, and at least one second antenna region. An
integrated circuit is connected across the first and second
conductive traces. The first antenna region is formed from a first
material having a first conductivity and the at least one second
antenna region is formed from a second material having a second
conductivity.
[0008] In another aspect of the invention, an RFID tag comprises a
substrate. An antenna is formed on the substrate that includes
first and second conductive traces, a first antenna region, and at
least one second antenna region. An integrated circuit is connected
across the first and second conductive traces. The first antenna
region is formed at a first thickness and the at least one second
antenna region is formed at a second thickness.
[0009] In another aspect of the invention, a method of printing an
RFID antenna with varying conductivity comprises determining
current densities of a first region and at least one second region
of the antenna. Conductivity requirements of the first and at least
one second regions are determined according to the current
densities. A first material is selected according to the
conductivity requirements of the first region and a second material
is selected according to the conductivity requirements of the at
least one second region. The first material is printed to a
substrate at the first region and the second material is printed to
the substrate at the at least one second region.
[0010] In another aspect of the invention, a method of printing an
RFID antenna with varying conductivity comprises determining
current densities of a first region and at least one second region
of the antenna. Conductivity requirements of the first and at least
one second regions are determined according to the current
densities. A conductive material is printed to a substrate at the
first region at a first thickness according to the conductivity
requirements of the first region. The conductive material is
printed to the substrate at the at least one second region at a
second thickness according to the conductivity requirements of the
at least one second region.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0012] FIG. 1 is a cross-sectional view of an RFID antenna
according to the prior art;
[0013] FIG. 2A is a cross-sectional view of an RFID antenna
indicating general areas of the antenna pattern according to the
prior art;
[0014] FIG. 2B illustrates current density of different areas of an
RFID antenna;
[0015] FIG. 3A illustrates a printing process for an RFID antenna
according to the present invention;
[0016] FIG. 3B illustrates an alternative embodiment of a printing
process for an RFID antenna according to the present invention;
[0017] FIG. 4A illustrates a computer model of current density of
an RFID antenna according to the present invention;
[0018] FIG. 4B illustrates a computer model mesh used to calculate
current density according to the present invention;
[0019] FIG. 4C is a top-down view of an exemplary print of an RFID
antenna according to the present invention; and
[0020] FIG. 5 illustrates steps of a method for printing an RFID
antenna according to the present invention.
DETAILED DESCRIPTION
[0021] The following description of embodiments is merely exemplary
in nature and is in no way intended to limit the invention, its
application, or uses.
[0022] Referring now to FIG. 1, an RFID system 10 includes a
substrate 12 having an antenna 14 printed and/or otherwise attached
thereto. The antenna 14 includes first and second antenna
components 14A and 14B. A transmitter is typically implemented
using an integrated circuit (IC) 16 and is electronically
programmed with a unique identification (ID) and/or information
about the item. The IC 16 typically includes conductors 18 formed
on one side thereof that are connected by conductive adhesive 20 to
the antenna 14. In use, a transceiver containing a decoder
communicates with transmitters that are within range.
[0023] The antenna 14 is typically comprised of one or more general
areas, each with particular current density requirements, as shown
in FIGS. 2A and 2B. A particular antenna pattern may include only
one or all of the areas according to the antenna's frequency,
intended application, and size. For example, an interconnection
area 30 is located nearest the IC 16 and is often very sensitive to
ink conductivity. The interconnection area 30 requires conductive
lines and gaps that correspond with the features of the IC 16. Any
electrical shorting of the gaps renders the RFID system 10
ineffective. Therefore, to maintain the gaps at a particular width,
a single thick layer of conductive ink is printed at the
interconnection area 30. For example, the RFID system 10 may
require gaps narrower than 150 microns. A single thick layer of
conductive ink provides high conductance and effectual gaps.
Conversely, multiple applications of conductive ink may cause
overlaps in the registration of printed layers due to limitations
in the printing process. The overlaps result in printed layers that
are relatively coarse.
[0024] A main antenna area 32 is designed according to the
wavelength of the radio frequency that the antenna 14 is operable
to receive. For example, the main antenna area 32 usually includes
at least one dimension that is related to one, one half or one
quarter of the operating wavelength. The main antenna area 32
requires less current density than the interconnection area 30. The
conductive lines and gaps of the main antenna area 32 are typically
not as narrow as the corresponding features of the interconnection
area 30. For example, gaps of 200 microns may be sufficient for the
main antenna area 32. Additionally, the current density may vary
across the width of the main antenna area 32. The required current
density of the main antenna area 32 may decrease proportionately to
the distance from the IC 16. As current density changes across this
area, conductive ink of greater or lesser thickness may be used
accordingly to accommodate varying conductance requirements.
[0025] The antenna 14 may include an intermediate antenna area 34
that requires a low current density relative to the main antenna
area 32. For example, the antenna 14 may be designed to include a
thick, highly-conductive interconnect area 30, a thinner,
less-conductive main antenna area 32, and an even thinner
intermediate antenna area 34. The intermediate antenna area 34 may
function as a half-wave or an RF-reflective patch. Therefore, the
intermediate antenna area 34 does not require great thickness or
high conductivity in the printed material. In certain embodiments,
the intermediate antenna area 34 may be larger than one quarter, or
even one half, of the total antenna size.
[0026] A coil area 36 functions to tune the antenna 14 to the
capacitance or impedance of the integrated circuit 16.
Additionally, the coil area 36 may be designed to include
additional features, such as solid state or printed portions that
add various capabilities to the RFID system 10. The coil area 36 is
typically very sensitive to ink conductivity.
[0027] FIG. 2B illustrates the current density 38 of the antenna
RFID system 10 relative to the different areas of the antenna 14.
Generally, the current density is higher near the critical gap of
the antenna 14, which is visible as a gap 40 in the current
density. Further, current density is higher in the coil area, which
is not shown in FIG. 2B. The current density decreases further away
from the gap 40. Therefore, more conductive material may be used in
the areas of the antenna that require higher current density;
conversely, less conductive material may be used in areas that
require less current density. Alternatively, material of higher
conductivity may be used where more conductivity is required, and
material of lower conductivity may be used were less conductivity
is required. In this manner, the antenna can use less costly
material in areas where greater conductivity is not required.
[0028] Referring now to FIGS. 3A and 3B, the printing process
applies conductive material 50 according to the varying current
density 52. Materials of different conductive capabilities may be
printed according to the required current density of the particular
antenna area as shown in FIG. 3A. For example, a first material 54
with a relatively high conductivity is printed with a first process
in a first area 56, which requires relatively high current density.
A second material 58 that is less conductive than the first
material 54 is printed with a second process in a second area 60.
The second area 60 requires less current density than the first
area 56. A third material 62 is printed with a third process in a
third area 64. A fourth material 66 is printed with a fourth
process in a fourth area 68. The third area 64 requires less
current density than the second area 60, and the fourth area 68
requires less current density than the third area 64.
Correspondingly, the third material 62 is less conductive than the
second material 58, and the fourth material 66 is less conductive
than the third material 62.
[0029] Because the materials are printed consecutively, the process
may produce minimal overlap between the materials. For example, the
third material 62 may overlap the second material 58, or the fourth
material 66 may overlap the third material 62, resulting in overlap
regions 70. The varying printing processes used for the different
antenna areas may include, but are not limited to, gravure, offset
gravure, flexography, offset lithography, letterpress, ink jet,
flatbed screen, and/or rotary screen printing. A particular
printing process may be used for more than one area by further
varying elements within the process. For example, flexography may
be used for multiple processes by changing flexography units or
adjusting anilox volume.
[0030] Alternatively, a single material 72 may be printed at
varying thickness according to the required current density of the
particular antenna area as shown in FIG. 3B. For example, areas 74,
76, 78, and 80 require varying current density. The material 72 is
printed on all areas. However, the material 72 is printed using a
different print unit for each area to achieve varying thickness
across the entire process. The material 72 is printed using a first
print unit for area 74, a second print unit for area 76, a third
print unit for area 78, and a fourth print unit for area 80. The
process as described in FIG. 3B avoids the potential overlap
associated with using multiple print processes and multiple
materials.
[0031] These antennas can be manufactured using printing processes,
such as, but not limited to: gravure, offset gravure, flexography,
offset lithography, letterpress, ink jet, flatbed screen, and/or
rotary screen printing. Furthermore, the antenna can be patterned
using etching, stamping, or electrochemical deposition (such as
electrolysis or electroplating) of metals.
[0032] Referring now to FIGS. 4A, 4B, and 4C, computer simulation
can be used to identify the different areas of required current
density of the antenna 14. Further, computer simulation can be used
to assess the sensitivity to ink thickness and conductivity of each
antenna area. Through this process, a minimum conductivity level of
each antenna area is identified, thereby preserving the performance
of the device while minimizing the material cost.
[0033] For example, a computer model 82 may be used to demonstrate
the varying degrees of current density as shown in FIG. 4A. Lighter
areas of the computer model 82 indicate higher current density.
Similarly, a computer model mesh 84 may be used to calculate
current density as shown in FIG. 4B. The printing process is then
adapted according to the current density calculations to apply
thicker and/or more conductive material in the high current areas
of the structure. The resulting RFID antenna structure therefore
provides higher performance than a similar structure without proper
conductivity in high current density areas. Correspondingly, the
resulting RFID antenna structure can be manufactured at a lower
cost than an antenna structure that is printed at a uniform
thickness.
[0034] Although the above computer modeling method may be used to
determine the current densities of different antenna areas, it is
to be understood that other suitable methods may be used. A
top-down view of an exemplary print of an RFID antenna 14 used to
generate the computer model 82 and the computer model mesh 84 is
shown in FIG. 4C. The RFID antenna 14 includes the IC 16, the
interconnection area 30, the main antenna area 34, and the coil
area 36. The corresponding current densities of these areas of the
RFID antenna 14 are illustrated in FIGS. 4A and 4B.
[0035] Referring now to FIG. 5, steps of a method according to the
present invention are shown. In step 90, the current density
requirements of the antenna are determined. For example, computer
modeling may be used to calculate the current densities. The
conductivity requirements for each area based on the current
density calculations are determined at step 92. The proper
thickness and/or a suitable material for a given antenna area are
determined in step 94. The selected material is then printed to the
substrate at the proper thickness at the antenna area in step 96.
At step 98, the process is repeated for remaining antenna areas as
necessary.
[0036] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the current
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be so limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings, the
specification and the following claims.
* * * * *