U.S. patent number RE41,563 [Application Number 12/396,691] was granted by the patent office on 2010-08-24 for radio frequency identification tag and method of making the same.
This patent grant is currently assigned to Michael Caron, Inc.. Invention is credited to Michael Roger Caron, John Paul Frazier, Samuel V. Nablo.
United States Patent |
RE41,563 |
Caron , et al. |
August 24, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Radio frequency identification tag and method of making the
same
Abstract
The present invention describes a process for manufacture of
RFID tags. The RFID tag of the present invention includes a
substrate, an antenna, and a die positioning structure disposed on
the substrate that is cast and cured specifically for receiving a
silicon die of the type typically used in RFID applications. The
substrate is selected from a number of materials, the properties of
which render it penetrable by electron beam radiation. The die
positioning structure is a second material which is electron beam
curable, and which is deposited and cured at high speed on the
substrate in a novel fashion in accordance with the present
invention in a highly efficient, reproducible and economical
manner.
Inventors: |
Caron; Michael Roger
(Cumberland Forside, ME), Nablo; Samuel V. (Acton, MA),
Frazier; John Paul (Scarborough, ME) |
Assignee: |
Michael Caron, Inc. (Westbrook,
ME)
|
Family
ID: |
36124993 |
Appl.
No.: |
12/396,691 |
Filed: |
March 3, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
10958699 |
Oct 5, 2004 |
07221277 |
May 22, 2007 |
|
|
Current U.S.
Class: |
340/572.1;
235/492 |
Current CPC
Class: |
G06K
19/0775 (20130101); G06K 19/07749 (20130101) |
Current International
Class: |
G08B
13/14 (20060101); G06K 19/06 (20060101) |
Field of
Search: |
;340/568.1-572.9
;235/492 ;29/592,592.1,600,601 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mehmood; Jennifer
Attorney, Agent or Firm: Pierce Atwood LLP Farrell; Kevin M.
Wrobel; Katherine A.
Claims
We claim:
1. A radio frequency identification (RFID) tag comprising: a
substrate material; an antenna disposed on the substrate; a die
positioning structure .Iadd.that is ebeam curable .Iaddend.disposed
on the substrate and defining a cavity for receiving a silicon die;
and a silicon die disposed in the die positioning structure, the
silicon die having at least one bond for connecting to the
antenna.
2. The RFID tag of claim 1 wherein the die positioning structure
defines a cavity, and further wherein the cavity defines a first
surface adjacent to the substrate and a second surface, the second
surface disposed at an angle relative to the first surface, the
angle being between 100 and 110 degrees.
3. The RFID tag of claim 1 wherein the antenna is selected from the
group consisting of gold, copper, silver, aluminum, zinc .[.or.].
.Iadd.and .Iaddend.tungsten.
.[.4. The RFID tag of claim 1 wherein the antenna is gold..].
.[.5. The RFID tag of claim 1 wherein the antenna is copper..].
6. The RFID tag of claim 1 wherein the antenna is silver.
.[.7. The RFID tag of claim 1 wherein the antenna is
aluminum..].
8. The RFID tag of claim 1 wherein the substrate is selected from
the group consisting of polyimide, polyester, polyethylene,
polypropylene, cotton-polyester blend, extrusion coated paper,
impregnated paper, .[.or.]. .Iadd.and .Iaddend.thermal label.
.[.9. The RFID tag of claim 1 wherein the substrate comprises
polyimide..].
.[.10. The RFID tag of claim 1 wherein the substrate comprises
polyester..].
.[.11. The RFID tag of claim 1 wherein the substrate comprises
polyethylene..].
.[.12. The RFID tag of claim 1 wherein the substrate comprises
polypropylene..].
.[.13. The RFID tag of claim 1 wherein the substrate comprises of
one of cotton-polyester blend..].
.[.14. The RFID tag of claim 1 wherein the substrate comprises
extrusion coated paper..].
.[.15. The RFID tag of claim 1 wherein the substrate comprises
impregnated paper..].
.[.16. The RFID tag of claim 1 wherein the substrate comprises
thermal label..].
.[.17. The RFID tag of claim 1 wherein the substrate is between
0.0025 and 0.0125 cm in thickness..].
.[.18. The RFID tag of claim 1 wherein the substrate is between
0.005 and 0.01 cm in thickness..].
.[.19. The RFID tag of claim 1 wherein the substrate is between
0.006 and 0.008 cm in thickness..].
.[.20. The RFID tag of claim 1 wherein the silicon die is one of a
read-only memory chip, an electrically programmable read-only
memory chip, or an electrically erasable programmable read-only
memory chip..].
.[.21. The RFID tag of claim 1 wherein the antenna is operable
between 915 and 920 Megahertz..].
.[.22. The RFID tag of claim 1 wherein the antenna is operable
between 868 and 869 Megahertz..].
.[.23. The RFID tag of claim 1 wherein the antenna is operable
between 100 and 150 kilohertz..].
.[.24. The RFID tag of claim 1 wherein the antenna is operable
between 950 and 960 Megahertz..].
.[.25. The RFID tag of claim 1 wherein the antenna is operable
between 2.4 and 2.5 Gigahertz..].
26. A method of manufacture for a radio frequency identification
(RFID) tag, the method comprising: providing a substrate; providing
an antenna preformed on the substrate; providing a second material
.Iadd.that is ebeam curable.Iaddend.; providing a negative cast of
a die positioning structure; pressing the second material between
the substrate and the negative cast, thereby providing a die
positioning structure; curing the second material .Iadd.with an
ebeam.Iaddend., thereby providing a cured die positioning
structure; and affixing a silicon die within the cured die
positioning structure, such that the silicon die is in contact with
the cured die positioning structure.
.[.27. The method of claim 26 wherein the step of curing the second
material comprises irradiating the second material with an electron
beam..].
28. The method of claim 26 wherein the step of curing the second
material comprises irradiating the second material with an electron
beam having an energy of between 100 and 300 kiloelectron
volts.
29. The method of claim 26 wherein the step of curing the second
material comprises irradiating the second material with an electron
beam having an energy of 200 kiloelectron volts.
30. The method of claim .[.25.]. .Iadd.26 .Iaddend.wherein the
substrate is selected from the group consisting of polyimide,
polyester, polyethylene, polypropylene, cotton-polyester blend,
extrusion coated paper, impregnated paper, .[.or.]. .Iadd.and
.Iaddend.thermal label.
.[.31. The method of claim 25 wherein the substrate comprises
polyimide..].
.[.32. The method of claim 25 wherein the substrate comprises
polyester..].
.[.33. The method of claim 25 wherein the substrate comprises
polyethylene..].
.[.34. The method of claim 25 wherein the substrate comprises
polypropylene..].
.[.35. The method of claim 25 wherein the substrate comprises
cotton-polyester blend..].
.[.36. The method of claim 25 wherein the substrate comprises
extrusion coated paper..].
.[.37. The method of claim 25 wherein the substrate comprises
impregnated paper..].
.[.38. The method of claim 26 wherein the substrate comprises
thermal label..].
39. The method of claim 26 wherein the substrate is between 0.0025
and 0.0125 cm in thickness.
.[.40. The method of claim 26 wherein the substrate is between
0.005 and 0.01 cm in thickness..].
.[.41. The method of claim 26 wherein the substrate is between
0.006 and 0.008 cm in thickness..].
42. The method of claim 26 wherein the step of providing a negative
cast of a die positioning structure comprises providing a
platen.
.[.43. The method of claim 42 wherein the platen is comprised of
brass..].
44. The method of claim 42 wherein the step of providing a negative
cast of a die positioning structure comprises providing a platen
disposed for repeated pressing of the negative cast of the die
positioning structure.
45. The method of claim 42 wherein the platen is a cylinder
disposed for continuous rolling.
.[.46. The method of claim 26 further comprising the step of
applying bonding adhesives to at least one antenna contact point,
the antenna contact point disposed in the die positioning
structure..].
.[.47. The method of claim 26 wherein the silicon die is one of a
read-only memory chip, an electrically programmable read-only
memory chip, or an electrically erasable programmable read-only
memory chip..].
.[.48. The method of claim 26 wherein the silicon die is an
electrically erasable programmable read-only memory chip..].
49. The method of claim 26 further comprising the step of providing
a non-conductive protective layer protecting the silicon die and
the die positioning structure.
.[.50. The method of claim 26 further comprising the step of
irradiating the antenna with electromagnetic radiation to test the
operability of the RFID tag..].
.[.51. The method of claim 26 further comprising the step of
introducing ultraviolet radiation blocking pigments into the second
material..].
.Iadd.52. The RFID tag of claim 1 wherein the die positioning
structure is curable by radiation from an electron
beam..Iaddend.
.Iadd.53. The RFID tag of claim 1 wherein the die positioning
structure is curable by radiation from an electron beam having an
energy of between 100 and 300 kiloelectron volts..Iaddend.
.Iadd.54. The RFID tag of claim 1 wherein the die positioning
structure is curable by radiation from an electron beam having an
energy of 200 kiloelectron volts..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of wireless
communications, and specifically to the use of radio frequency
transmissions to track the movement of commercial goods, as well as
other suitable applications.
2. Description of the Related Art
Consumers are familiar with electronic systems for recognizing,
tabulating, and indexing the movement of goods through the chain of
commerce. Everyday examples include bar codes combined with optical
scanners as found in a supermarket. More recently, some products
and their containers have been "tagged" with radio frequency
identification (RFID) transponders, which in combination with a
radio frequency reader and sophisticated computer systems, enable a
commercial enterprise to track inventory from a distance. An RFID
system includes a tag, a reader, and a computer network connected
to the reader for compiling the relevant data.
RFID tags generally consist of a substrate material in which an
antenna is located for receiving and transmitting radio signals.
The antenna is connected to a silicon chip, or die, which is
encoded with data concerning the object to which the tag is
attached. The die itself can be of several varieties, including
read-only memory (ROM), electronically programmable read-only
memory (EPROM), and electronically erasable programmable read-only
memory (EEPROM). Depending on the type of die used, a tag may be
able to store data, transmit data to the reader, and be
reprogrammed to adapt to new data inputs.
RFID tags come in two forms: active and passive. An active tag
includes a power supply, such as a battery, that provides enough
current to actively transmit the necessary data from the RFID
antenna to a distal receiver. A passive tag is generally smaller
than an active tag, and it does not include an independent power
source. Rather, a passive tag derives its power from incoming
radiation, such as that from an inquiring reader. Due to the
advantageous size, weight, and cost of a passive tag, they are
generally considered superior to active tags for use with highly
mobile retail items and containers, including, for example, books
and shipping boxes.
In spite of the advantages of the passive tag, there are numerous
problems encountered with their maintenance, operation, and
manufacture. In particular, given the sheer volume of commerce and
the potential market for RFID tags, there are currently severe
limitations in the manufacturing process that hinder the mass
production of suitable tags.
In the manufacture of an RFID tag, the silicon die must be
precisely placed and connected to the antenna. The placement of the
die is generally done through robotics via optical alignment, at
which time the bonds between the die and the antenna must be
formed. Once the antenna is bonded to the die, the bond is cured.
The curing process typically involves heat or ultraviolet (UV)
radiation that interacts with a chemical photoinitiator in the
bonding agent, thereby accelerating the hardening process. In a
typical process, an epoxy containing a UV sensitive photoinitiator
is used to bond the die to the antenna. The UV radiation then
illuminates the bond site with sufficient fluence of photons of
approximately 3 electron volts (eV) energy, and after several
seconds, the epoxy hardens and the bond is formed.
The process outlined above presents a number of complications that
hinder the large-scale production of RFID tags. First, as the
economic demand for RFID tags reaches into the billions of units
per year, the 8-10 second UV-curing process effectively limits the
supply that manufacturers can theoretically muster. Secondly, once
the die is bonded to the antenna, there is no simple method for
removing the die if it fails to perform in the pre-shipment tests.
Consequently, an estimated 20-40% of the RFID tags that fail the
tests are irrevocably lost, further limiting the supply and
increasing the cost of tags to businesses and consumers.
Given the foregoing, there is a need in the art for a reliable,
cost-effective, and easily produced RFID tag that is usable over a
range of commercial applications. Moreover, there is a need for a
novel production method that is capable of large-scale cost
effective production of RFID tags with reliable testing parameters
and a high production yield.
SUMMARY OF THE INVENTION
Accordingly, the present invention includes an efficient, reliable,
and high fidelity RFID tag and a method of making the same. The
RFID tag of the present invention includes a substrate, upon which
an antenna for receiving and transmitting radio frequency signals
may be printed. The RFID tag also includes a die positioning
structure disposed on the substrate that is cast and cured
specifically for receiving a silicon die of the type typically used
in RFID applications. The silicon die is electrically connected to
the antenna through at least one bond, which enables the RFID tag
to transmit, receive, and possibly update electronic data stored on
the silicon die through normal RFID protocols.
In varying embodiments, the RFID tag of the present invention is
operable over a range of frequencies that enable it to be operable
over a range of applications and jurisdictions. For example, the
antenna may be selected such that it is operable between 400 and
1000 Megahertz. More particularly, for improved operation in the
United States, the antenna may be selected to be operable between
915 and 920 Megahertz. For low frequency applications, the selected
antenna would be operable between 100 and 150 kilohertz, while for
microwave applications the antenna would be operable between 2.4
and 2.5 Gigahertz. Thus, the RFID tag of the present invention is
readily adapted to use over a range of frequencies, and thus may be
used in across a range of applications, from a variety of consumer
products to automotive components and animal identification
tags.
The novel RFID tag of the present invention is the result of an
improved method of manufacture in the RFID industry. The method
includes a number of acts, including providing a substrate with an
antenna printed thereon and a second material. The substrate is
generally of a dielectric material and hydrophobic, and should
preferably be of low stopping power for electron beam radiation.
The second material is curable by electron beam radiation, and is
disposed on the substrate through a pressing mechanism that forms
the die positioning structure discussed above. Once the die
positioning structure is cured and affixed to the substrate, a
silicon die is positioned within the die positioning structure and
connected to the antenna through at least one bonding point. At
this time, a manufacturer may provide a radio signal receivable by
the antenna to test the electrical connections of the RFID tag.
Once the operability of the RFID tag is confirmed, a protective cap
or coating is disposed over the silicon die and the die positioning
structure to increase the resiliency and abrasive resistance of the
RFID tag.
The foregoing is intended as a summary of the novel and useful
features of the present invention. Further aspects, features and
advantages of the invention will become apparent from consideration
of the following detailed description and the appended claims when
taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of an RFID tag in accordance with the present
invention.
FIG. 2 is a detailed plan view of a typical RFID tag in accordance
with the present invention.
FIG. 3 is an oblique perspective view of an RFID tag in accordance
with the present invention.
FIG. 4 is a perspective view of a typical silicon die in accordance
with the present invention.
FIG. 5 is a cross-sectional view of an RFID tag in accordance with
one embodiment of the present invention.
FIG. 6 is a flow chart depicting a method of making an RFID tag in
accordance with the present invention.
FIG. 7 is a schematic view of a method of making a die positioning
structure for an RFID tag in accordance with the present
invention.
FIG. 8 is a cross-section view of a negative cast usable in the
making of the die positioning structure in accordance with the
present invention.
FIG. 9 is a plan view of a negative cast usable in making the die
positioning structure in accordance with the present invention.
FIG. 10 is a schematic view of a method of making the die
positioning structure on a substrate in accordance with the present
invention.
FIG. 11 is a graph of electron penetration as a function of
energy.
DETAILED DESCRIPTION OF THE INVENTION
Two embodiments of the invention to accommodate the silicon die in
a normal (bond pads up) and flip chip (bond pads down) orientation
are presented here. In accordance with a preferred embodiment of
the present invention, FIG. 1 illustrates a plan view of an RFID
tag 10. The RFID tag 10 includes a substrate 12 and an antenna 14
that is located upon the substrate 12. The RFID tag 10 further
includes a die positioning structure 16 in which a silicon die 18
is disposed.
The details of the RFID tag 10 are shown in FIG. 2, which is a
detailed plan view of the present invention. As shown in FIG. 2,
the die positioning structure 16 is disposed on the substrate 12
such that it overlaps the antenna 14. The die positioning structure
16 is disposed such that it substantially overlaps antenna leads
20a, 20b. The die positioning structure 16 defines in part a die
positioning cavity 17, which is also located such that it
substantially overlaps the antenna leads 20a, 20b in such a manner
that one or both of the leads is available for (direct) bonding to
the die bond pads, 19A and 19B, as shown in FIG. 4.
FIG. 3 is a perspective view of an RFID tag 10 in accordance with a
preferred embodiment of the present invention. As shown in FIG. 3,
the die positioning structure 16 defines in part an outer slope 21
and an inner slope 23. Further, the die positioning structure 16 is
preferably disposed on the substrate 12 such that it overlaps the
antenna 14. The die positioning structure 16 is disposed such that
it substantially overlaps antenna leads 20a, 20b, and further such
that the die positioning cavity 17 substantially overlaps the
antenna leads 20a, 20b. The die positioning cavity 17 is adapted to
receive the silicon die 18, which may be dropped into the die
positioning cavity 17 in the direction of arrow 1.
FIG. 4 is an oblique perspective view of a silicon die 18
illustrating a pair of contact points 19a, 19b that are
electrically conductive and connectable to the antenna leads 20a,
20b shown as part of the RFID tag 10.
FIG. 5 is a cross-sectional view of an RFID tag in accordance with
the present invention. In a preferred embodiment, the die
positioning structure 16 defines the die positioning cavity 17. The
die positioning cavity 17 defines an inner slope 23 that is angled
relative to the surface of the substrate 12. Specifically, a first
line A is defined normal to the surface of the substrate 12. A
second line B is defined coplanar with the surface of the inner
slope 23, and the angle between A and B is designated .alpha.. In a
preferred embodiment, the angle .alpha. is between 10 and 20
degrees, and is most preferably about 15 degrees. The angled face
of the inner slope 23 allows for improved reliability and accuracy
when positioning the silicon die 18 into the die positioning cavity
17.
The die positioning structure 16 also defines at least one outer
surface 21 that is gradually sloped relative to the surface of the
substrate 12. A third line C is defined coplanar with the surface
of the outer surface 21. A fourth line D is defined coplanar with
the surface of the substrate 12, and the angle between C and D is
designated .beta.. In a preferred embodiment, the angle .beta. is
between 20 and 40 degrees, and is most preferably about 30 degrees.
The angled face of the outer surface 21 allows for improved
resistance to wear and tear to the RFID tag 10 or later coating and
print rolls, and reduces the probability that any shearing forces
or friction will dislodge the silicon die 18 from its connection to
the antenna 14.
As shown in FIG. 5, the RFID tag 10 also provides for an alternate
embodiment in which there is an underfill 24 disposed within the
die positioning cavity 17 prior to the silicon die 18. The silicon
die 18 is then bonded at bonds 26a, 26b to the die positioning
structure 16, which is conductively connected to the antenna 14. A
protective cap 22, preferably composed of non-conductive material,
is disposed over the die positioning structure 16, the silicon die
18, and the bonds 26a, 26b to increase the resiliency and abrasion
resistance of the RFID tag 10. Preferably, the protective cap 22 is
treated with a blocking pigment to optically shield the die from
photovoltaic action.
Referencing FIGS. 1-5 collectively, the RFID tag 10 is described in
a preferred embodiment. The antenna 14 of the RFID tag 10 is
produced from an electrically conductive material, such as a metal
or metal alloy. Commonly employed metals for use in antennas
include, for example, gold, copper, silver, aluminum, zinc or
tungsten. In a more preferred embodiment, the antenna 14 is one of
gold, copper, silver or aluminum. The antenna 14 is preferably
printed or prefabricated on a suitable substrate 12 that should
preferably be of low stopping power for electron beam
radiation.
The type of application for which the RFID tag 10 is selected
defines the antenna 14 specifications. In one embodiment, the
antenna 14 is operable over a frequency range from 400 to 1000
Megahertz. In another embodiment, the antenna is operable over a
frequency range from 915 to 920 Megahertz. For applications in
which lower frequency radio transmissions are customary, the
antenna 14 is operable over a frequency range of 100 to 150
kilohertz. For high frequency applications the antenna 14 is
operable at 13.56 Megahertz. For use in foreign countries with
differing frequency allocations, such as Europe, the antenna 14 is
operable over a frequency range of 868 to 869 Megahertz. In Japan,
however, it is proposed that the antenna 14 would be operable
between 950 and 960 Megahertz. For some applications the antenna 14
may be operable over a frequency range of 2.4 to 2.5 Gigahertz. It
should be evident from the foregoing that the type of antenna 14
selected for the RFID tag 10 will depend upon a number of factors,
including government allocation rights and the type of signal
needed for the particular application.
The substrate 12 can be any number of materials, but it is most
preferably selected from a group of materials including polyimide,
polyester, polyethylene, polypropylene, cotton-polyester blend,
extrusion coated paper, impregnated paper, or thermal label. As
noted, the substrate 12 should preferably be of low stopping power
for electron beam radiation, as well as adaptable to a plurality of
packaging options covering a wide range of commercial uses. In
order to satisfy these conditions, the substrate 12 is preferably
between 0.0025 and 0.0125 cm in thickness, thus being easily
penetrable by electron beam radiation. In a more preferred
embodiment, the substrate 12 is between 0.005 and 0.010 cm in
thickness; and in a yet more preferred embodiment, the substrate 12
is between 0.006 and 0.008 cm in thickness.
The die positioning structure 16 is comprised of a non-conductive
or dielectric material that is curable by electron beam (e-beam)
radiation. E-beam radiation is a non-thermal method that uses
high-energy electrons as the ionizing radiation to initiate
polymerization and crosslinking reactions at controlled dose rates
in polymeric materials. Electron curing has been employed in the
converting industry for several decades--typically for the high
speed curing of thin films, coatings or laminating adhesives. Some
polymers (e.g., polyethylene) naturally cross link via e-beam
treatment, while others such as most high-performance epoxies and
acrylated copolymers, require modification to initiate curing. It
has been shown that epoxies modified by the addition of
photoinitiators, so that the addition polymerization can be
initiated with ultraviolet radiation, can achieve electrical and
thermomechanical properties comparable to those typical of thermal
curing.
E-beam curing has several advantages over conventional thermal
curing methods including: improved product quality/performance;
reduced environmental, safety, and health concerns; improved
material handling; ability to combine various materials and
functions in a single operation; ability to utilize lower cost
tooling; capability to produce unique parts that cannot be
fabricated any other way; reduced energy consumption; and reduced
cure times. In the context of the present invention a particularly
important advantage is the ability to cure at near room
temperature. Current thermal curing techniques for connecting bond
pads to a substrate require exposure to temperatures within the
range of 150 to 160 degrees C. for several seconds. The fact that
this can be done quickly at room temperature using e-beam curing
enables the use of thermolabile substrates (e.g., coated or
impregnated papers or polymer films) as discussed above. Epoxy
Technology (Billerica, Mass. 01821) offers a line of products
described as UV-curable adhesives which, when modified, would be
suitable for use in connection with e-beam curing methods. More
specifically, the photoinitiator can be removed from the UV-curable
adhesive for use in connection with e-beam curing methods. One
skilled in the art would be familiar with a variety of other
suitable e-beam curable polymer formulations.
In a preferred embodiment, the die positioning structure 16 is
comprised of a material that is hydrophobic, and thus capable of
seating the silicon die 18 while preventing any electromagnetic or
moisture-caused interference with the operation of the RFID tag 10.
Suitable materials include resins and epoxies that undergo rapid
polymerization when exposed to electron beam radiation. In the
flip-chip (bond pads down) embodiment, the die positioning
structure 16 is preferably a strong insulator. A preferred
insulating material is acrylated urethane, which has the necessary
adhesive properties to properly bond to the substrate 14 while
maintaining a degree of flexibility suitable for receiving the
silicon die 18. In the normal (bond pads up) embodiment, shown in
FIG. 5, the die positioning structure 16 may be conductive to
permit ease of connection between the silicon die 18 and the
antenna 14 disposed on the substrate 12. In this embodiment, the
die positioning structure 16 is preferably a high-conductivity
epoxy that is loaded or doped with a sufficient quantity of metal
powder to lessen resistance. In each of the described embodiments,
the die positioning structure 16 is treated with blocking pigments
to optically shield the silicon die 18 from photovoltaic
action.
The silicon die 18 is selected from a group of silicon dies that
are adapted to coupling to an antenna 14 operable over a range of
frequencies. In one embodiment, the silicon die 18 is selected from
a group comprising a read-only memory chip (ROM), an electrically
programmable read-only memory chip (EPROM), or an electrically
erasable programmable read-only memory chip (EEPROM).
A second aspect of the present invention is a method for making the
improved RFID tag 10 described in detail above. FIG. 6 is a flow
chart depicting a method of making the RFID tag 10 in accordance
with the preferred embodiments of the present invention.
Starting at step S10, the method of the present invention provides
that a substrate 12 is selected in step S112. As discussed above,
with reference to the RFID tag 10, the substrate 12 can be any
number of materials, but it is most preferably selected from a
group of materials including polyimide polyester, polyethylene,
polypropylene, cotton-polyester blend, extrusion coated paper,
impregnated paper, or thermal label.
As previously noted, the substrate 12 should be a poor absorber of
electron beam radiation, as well as adaptable to a plurality of
packaging options covering a wide range of commercial uses. In
order to satisfy these conditions, the substrate 12 is preferably
between 0.0025 and 0.0125 cm in thickness, thus being penetrable to
electron beam radiation. In a more preferred embodiment, the
substrate 12 is between 0.005 and 0.010 cm in thickness; and in a
yet more preferred embodiment, the substrate 12 is between 0.006
and 0.008 cm in thickness. The substrate 12 should preferably have
an antenna 14 located thereon, or be readily adapted to receive an
antenna 14 of the like discussed above.
In step S114, a second material is selected, the second material
being adapted for use as the die positioning structure 16 discussed
above. The die positioning structure 16 is comprised of an
insulating or dielectric material that is curable by electron beam
radiation. The die positioning structure 16 is preferably comprised
of a material that is hydrophobic and capable of securely seating
the silicon die 18 while preventing any electromagnetic or moisture
interference with the operation of the RFID tag 10. Lastly, the die
positioning structure 16 is preferably treated with blocking
pigments to optically shield the silicon die 18 from photovoltaic
action.
In step S116, a negative cast of the die positioning structure is
positioned such that as the second material is disposed between the
substrate and the negative cast, a die positioning structure 16
will be formed following the filling of the engraving (negative
cast) with the second material step S118.
Once the second material is pressed into a die positioning
structure 16 in step S118, the second material is cured in step
S120. The curing step comprises using electron beam radiation to
polymerize the second material and render the die positioning
structure 16. In a preferred embodiment, the step of curing the
second material comprises using an electron beam with energy in the
range of 100 to 300 kilo-electron volts (keV). Most preferably, the
energy of the curing electron beam is approximately 200 keV.
Following the electron beam curing of the second material in step
S120, the silicon die 18 is bonded to the die positioning structure
16 and the antenna 14 in step S122. The functionality of the RFID
tag 10 can then be tested in step S123 by providing a sample radio
signal and measuring the response of the RFID tag 10.
After the RFID tag 10 has been successfully tested, a protective
coating is deposited over the silicon die 18 and the die
positioning structure 16 in step S124. The protective layer 22 is
preferably composed of non-conductive material and disposed over
the die positioning structure 16, the silicon die 18, and the bonds
26a, 26b to increase the resiliency of the RFID tag 10. Preferably,
the protective layer 22 is treated with a blocking pigment to
optically shield the silicon die 18 from photovoltaic action. Step
S126 represents the termination of the method of making the
improved RFID tag 10, but it is understood that the method can be
repeated continuously to generate a large stock of RFID tags
suitable for use across an array of commercial enterprises.
The method of making the RFID tag 10 of the present invention can
also be described with reference to a system that accomplishes the
method of making the same. FIG. 7 is a schematic view of one method
of making an RFID tag 10, including a substrate 12 and a second
material 15 suitable for use as a die positioning structure 16. In
this embodiment of the method, a negative cast 50 is shown directly
adjacent to the second material 15. A pressing mechanism 60 is
disposed above the substrate 12, second material 15, and negative
cast 50. The pressing mechanism 60 is movable with respect to the
negative cast 50, or the pressing mechanism 60 may be fixed
relative to the negative cast 50, such that a volume of the second
material 15 may be passed through the system.
As shown in FIG. 7, the pressing mechanism 60 is rotatable along a
central axis along arrow 2. The negative cast 50 is movable along
arrow 3, such that the pressing mechanism 60 is always pressing new
materials into the negative cast 50. Following the pressing step of
the present method, an electron beam generator 62 is provided for
generating electron beams 64 which cure the second material 15 into
the die positioning structure 16 as discussed above. In a preferred
embodiment, the electron beam has an energy in the range of 100 to
300 kiloelectron volts (keV). Most preferably, the energy of the
curing electron beam is approximately 200 keV.
FIG. 8 is a cross-sectional view of a preferred negative cast 50
usable in the making of an RFID tag 10. FIG. 9 is a plan view of
the preferred negative cast 50. The shape defined by the negative
cast 50 is the inverse of the shape defined by the die positioning
structure 16, discussed above in detail. The negative cast 50
defines an inner bank 54 and an outer bank 52. Line E is defined as
normal to the surface of the negative cast 50. Line F is defined as
coplanar with the surface of the inner bank 54, and the angle
between lines E and F is designated .delta.. The angle .delta. is
preferably between 10 and 20 degrees, and most preferably it is
approximately 15 degrees.
The outer bank 52 of the negative cast 50 is more gradually sloped
in order to cast a die positioning structure 16 that has an outer
slope 21 of the characteristics shown in FIG. 3. A line H is
defined as coplanar with the negative cast 50. A line G is defined
as coplanar with the outer bank 52, and the angle between lines G
and H is designated .phi.. The angle .phi. is preferably between 20
and 40 degrees, and is most preferably approximately 30
degrees.
FIG. 10 is a schematic view of a method 70 of making the die
positioning system on substrate in accordance with the present
invention. The schematic representation of the method 70 is not
intended to limit the scope of the claims herein, rather it is
intended as an example of a systematic method for the production of
RFID tags 10 in accordance with the present invention.
In one representation of the method 70, a substrate 12 is
continuously fed over a first cylinder 72, which rotates about a
central axis in the direction of arrow 4. The first cylinder 72 has
a plurality of negative casts 50 disposed on its surface in a
sequence matching the tag dimensions. The second material 15 is
disposed in a pan 78 in liquid form. A second cylinder 80a
(typically engraved) and third cylinder 80b (typically a rubber
roll), rotatable in opposing directions shown by arrows 5 and 6,
remove the second material 15 from the pan 78 and apply it to the
first cylinder 71. A doctor blade 82 cleans the first cylinder 72
of any excess second material 15.
The substrate 12 is disposed on the second material 15. A fourth
cylinder 74 rotatable in the direction of arrow 7 serves a pressing
mechanism for pressing the second material 15 into the negative
cast 50 on the surface of the first cylinder 72. An electron beam
generator 62 is disposed at a distance from the first cylinder 72
for generating electron beams 64 which cure the second material 15
into the die positioning structure 16, as discussed above. In a
preferred embodiment, the electron beam has an energy in the range
of 100 to 300 kilo-electron volts (keV). Most preferably, the
energy of the curing electron beam is approximately 200 keV. After
curing, a fifth idler cylinder 76 removes the cured second material
15 from the first cylinder 72. As described above, the newly formed
die positioning structure 16 and the substrate 12 are adapted for
the receipt of a silicon die 18 and the remaining steps of the
method claimed herein.
FIG. 11 is a graph illustrating relationship between the
penetration range (grams/meters.sup.2) and dosage penetration
percentage (%) as a function of electron beam energy. As previously
noted, an electron beam generator 62 is utilized for generating
electron beams 64 which cure the second material 15 into the die
positioning structure 16. In a preferred embodiment, the electron
beam has an energy in the range of 100 to 300 kilo-electron volts
(keV). in a most preferred embodiment, the energy of the curing
electron beam is approximately 200 keV.
The present invention as described in its preferred embodiments
thus improves the procedure of manufacture of RFID tags in addition
to providing a specific method for a novel RFID tag. In particular,
the formation of the die positioning structure by systematic and
reliable means on a selected substrate will provide a more reliable
and resilient RFID tag. Moreover, by electron beam curing the die
positioning structure, the pace of production of the RFID tags can
be significantly increased, permitting the use of RFID tags in an
ever broadening field of commercial applications.
It should be apparent to those skilled in the art that the
above-described embodiments are merely illustrative of but a few of
the many possible specific embodiments of the present invention.
Numerous and various other arrangements can be readily devised by
those skilled in the art without departing from the spirit and
scope of the invention as defined in the following claims.
* * * * *