U.S. patent application number 09/911977 was filed with the patent office on 2002-03-07 for circuit module.
Invention is credited to Brown, Robert Walter, Letkomiller, Joseph Michael, Pollack, Richard Stephen.
Application Number | 20020027531 09/911977 |
Document ID | / |
Family ID | 24041690 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027531 |
Kind Code |
A1 |
Brown, Robert Walter ; et
al. |
March 7, 2002 |
Circuit module
Abstract
Circuit modules having one, two or three double-sided printed
circuit boards (PCBs). Each PCB can have coils formed as spiral
traces on both sides thereof. The coils can all be connected
together, in series or in parallel, to function as a coil antenna.
Alternatively, selected ones of the spiral traces can be connected
to function as one winding of a transformer, the other coils
functioning as another winding of the transformer and connected to
an external antenna. Electronic components can be mounted to a
lower one of the PCBs, and in embodiments having two or three PCBs,
the PCB overlying the lower PCB has a central opening to
accommodate the electronic components. A ferrite rod antenna may be
disposed in the opening, aligned parallel to the PCBs, to provide a
dual-directional antenna system.
Inventors: |
Brown, Robert Walter;
(Medina, OH) ; Pollack, Richard Stephen; (Boulder,
CO) ; Letkomiller, Joseph Michael; (Thornton,
CO) |
Correspondence
Address: |
Patent & Trademark Dept. D/823
The Goodyear Tire & Rubber Company
1144 East Market Street
Akron
OH
44309-3531
US
|
Family ID: |
24041690 |
Appl. No.: |
09/911977 |
Filed: |
July 25, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09911977 |
Jul 25, 2001 |
|
|
|
09513050 |
Feb 24, 2000 |
|
|
|
6304232 |
|
|
|
|
Current U.S.
Class: |
343/895 ;
343/700MS |
Current CPC
Class: |
H05K 1/165 20130101;
G06K 19/07749 20130101; H04B 1/72 20130101; H01Q 1/38 20130101;
H05K 3/4611 20130101; H01Q 9/27 20130101; H05K 1/183 20130101; H01Q
1/2241 20130101 |
Class at
Publication: |
343/895 ;
343/700.0MS |
International
Class: |
H01Q 001/36 |
Claims
What is claimed is:
1. A circuit module comprising: a first printed circuit board
having a first surface and a second surface; electronic components
mounted to the first surface of the first printed circuit board;
characterized by: a first long conductive trace disposed on the
first surface of the first printed circuit board, said first long
conductive trace having two ends; and a second long conductive
trace disposed on the second surface of the first printed circuit
board, said second long conductive trace having two ends; wherein:
the second long conductive trace is connected in series or in
parallel with the first long conductive trace; and each of the
first and second long conductive traces forms a portion of a coil
which is connected to selected ones of the electronic
components.
2. Circuit module, according to claim 1, characterized by: a second
printed circuit board having a first surface and a second surface;
a third long conductive trace (230, 330) disposed on the first
surface of the second printed circuit board, said third long
conductive trace having two ends; wherein: the third long
conductive trace is connected in series or in parallel with the
first and second long conductive traces; and each of the first,
second and third long conductive traces forms a portion of a coil
which is connected to selected ones of the electronic
components.
3. Circuit module, according to claim 2, characterized in that: the
second printed circuit board is in the form of a ring, having an
opening; and the opening forms a cavity for containing the
electronic components.
4. Circuit module, according to claim 2, characterized by: a third
printed circuit board, positioned on the opposite side of the
second printed circuit board as the first printed circuit board,
having a first surface and a second surface; a fourth long
conductive trace disposed on the first surface of the third printed
circuit board, said fourth long conductive trace having two ends;
wherein: the fourth long conductive trace is connected in series or
in parallel with the first, second and third long conductive
traces; and each of the first, second, third and fourth long
conductive traces forms a portion of a coil which is connected to
selected ones of the electronic components.
5. Circuit module, according to claim 1, characterized by: a second
printed circuit board having a first surface and a second surface;
a third long conductive trace disposed on the first surface of the
second printed circuit board, said third long conductive trace
having two ends; wherein: a coil formed by the connected first and
second long conductive traces functions as a first winding of a
transformer; and the third long conductive trace functions as a
second winding of the transformer.
6. Circuit module, according to claim 5, characterized in that: the
second printed circuit board is in the form of a ring, having an
opening; and the opening forms a cavity for containing the
electronic components.
7. Circuit module, according to claim 5, characterized by: an
antenna connected to the third long conductive trace.
8. Circuit module, according to claim 7, characterized in that: the
circuit module is an RF transponder; and the antenna is disposed
circumferentially around an inner surface of a pneumatic tire.
9. Circuit module, according to claim 7, characterized in that: the
second printed circuit board is in the form of a ring having an
opening; where the opening forms a cavity for containing the
electronic components.
10. Circuit module, according to claim 5, characterized by: a third
printed circuit board disposed between the first printed circuit
board and the second printed circuit board.
11. Circuit module, according to claim 10, characterized in that:
the third printed circuit board is in the form of a ring having an
opening; and the opening forms a cavity for containing the
electronic components.
12. Circuit module, according to claim 5, characterized by: a
fourth long conductive trace disposed on the second surface of the
second printed circuit board, said fourth long conductive trace
having two ends; wherein: the fourth long conductive trace is
connected in series or in parallel with the third long conductive
trace; a coil formed by the connected first and second long
conductive traces functions as a first winding of a transformer;
and a coil formed by the connected third and fourth long conductive
traces functions as a second winding of the transformer.
13. Circuit module, according to claim 12, characterized by: a
third printed circuit board disposed between the first printed
circuit board and the second printed circuit board.
14. Circuit module, according to claim 13, characterized in that:
the third printed circuit board is in the form of a ring having an
opening; and the opening forms a cavity for containing the
electronic components.
15. Circuit module, according to claim 14, characterized by: an
antenna connected to the coil formed by the connected third and
fourth long conductive traces.
16. Circuit module, according to claim 1, characterized in that: a
second printed circuit board is in the form of a ring, having an
opening; a third printed circuit board having a first surface and a
second surface; a third long conductive trace disposed on the first
surface of the third printed circuit board, said third long
conductive trace having two ends; a fourth long conductive trace
disposed on the second surface of the third printed circuit board,
said fourth long conductive trace having two ends; wherein: the
second printed circuit board is positioned between the first
surface of the first printed circuit board and the second surface
of the third printed circuit board with the opening in the second
printed circuit board forming a cavity for containing the
electronic components; the ends of the first, second, third and
fourth long conductive traces are connected to each other in series
or in parallel; and each of the first, second, third and fourth
long conductive traces forms a portion of a coil which is connected
to selected ones of the electronic components.
17. Circuit module, according to claim 16, characterized by: a
ferrite antenna (410) comprising a coil of wire wound about a
ferrite rod disposed within the cavity formed by the opening in the
second printed circuit board.
18. Circuit module, according to claim 17, characterized by: the
ferrite rod being oriented so that its axis is parallel to the
first surface of the second printed circuit board.
19. An RF transponder circuit module comprising at least one
printed circuit board (102) with electronic components on a surface
thereof, characterized by: an antenna coil comprised of a long
conductive trace on at least one surface of the at least one
printed circuit board; and a molding material disposed on all
external surfaces of the circuit module.
20. An RF transponder, according to claim 19, characterized in
that: the molding material is selected from the group consisting of
essentially Ethylene Propylene Diene Monomer (EPDM) rubber, butyl
rubber, synthetic rubber, natural rubber, neoprene and mixtures
thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/513,050 entitled CIRCUIT MODULE having a
filing date of Feb. 24, 2000.
TECHNICAL FIELD OF THE INVENTION
[0002] The invention relates to the interconnection and packaging
of electronic components and, more particularly, to a circuit
module such as an RF transponder for monitoring a condition within
a pneumatic tire.
BACKGROUND OF THE INVENTION
[0003] As used herein, the term "circuit module" refers to an
interconnection substrate such as a printed circuit board (PCB)
having electronic components mounted thereto. A PCB is a
multi-layer substrate, having alternate layers of insulating
material and conductive material. The conductive material is
patterned to have conductive "lines" or "traces" for routing
signals (and power) from one location on the PCB to another
location on the PCB. Electronic components are interconnected with
one another by the conductive traces. Conductive traces may be
disposed on both sides (surfaces) of the PCB. Examples of
electronic components which may be incorporated in a circuit module
include:
[0004] (a) "active" electronic components such as integrated
circuit (IC) devices, and the like;
[0005] (b) "passive" electronic components such as resistors,
capacitors, and inductors (including transformers), and the
like;
[0006] (c) switches, relays and the like; and
[0007] (d) sensors, transducers and the like.
[0008] In some cases, a circuit module is intended to be disposed
in a "harsh" environment, and it is desirable to isolate the
electronic components of the circuit module from such an
environment. An example of such an application for a circuit module
is an RF transponder which is disposed within a pneumatic tire of a
vehicle. In such applications, it is generally desirable to
encapsulate or otherwise package the circuit module to isolate the
electronic components from the environment.
[0009] As used herein, a "transponder" is an electronic apparatus
(device) capable of monitoring a condition such as air pressure
within a pneumatic tire, and transmitting information (a signal)
indicative of the monitored condition to an external device. The
external device can be either an RF (radio frequency)
reader/interrogator or, simply an RF receiver. A simple receiver
can be used when the transponder is "active", and has its own power
source. A reader/interrogator would typically be used when the
transponder is "passive" and is powered by an RF signal from the
reader/interrogator. In either case, in conjunction with the
external device, the transponder forms a component of an overall
tire-condition monitoring/warning system.
[0010] In order to send and receive RF signals, a transponder must
have an antenna. The antenna may either be incorporated into the
transponder module itself, or it may be external to the transponder
module and electrically connected or coupled to it in a suitable
manner.
[0011] U.S. Pat. No. 4,724,427 (Carroll; 1988), incorporated in its
entirety by reference herein, discloses a transponder device. FIG.
9 of the patent, shows a topographical representation of a
transponder chip (100) in an embodiment that includes an antenna
coil (104) as part of a monolithic chip (102). As disclosed
therein, the coil (104) is etched around the periphery of the
monolithic chip also known as the chip substrate (102). In the
center of the coil (104) are found a custom logic circuit (106), a
programmable memory array (108), and a memory control logic (110).
Using the chip topography shown in this figure, a functionally
complete transponder may be realized on a single semiconductor
chip. (see column 11, lines 7-22; numbers edited)
[0012] In a similar manner, U.S. Pat. No. 5,345,231 (September
1994) discloses a contactless inductive data-transmission system.
FIG. 7 of this patent shows components of a chip having a substrate
(52) which can be photolithographically deposited along with
antenna coils (50) which can be in a plane above the semiconductor
topography (51) of the chip. (column 7, lines 14-17) In both this
patent and the aforementioned U.S. Pat. No. 4,724,427, the antenna
coils are disposed around the periphery of the IC chip, surrounding
the components and periphery of the IC chip.
[0013] U.S. Pat. No. 5,574,470 (de Vall; 1996), incorporated in its
entirety by reference herein, discloses a radio frequency
identification transponder apparatus and method. A transponder is
formed of a very thin flexible dielectric substrate (10) on
opposite sides of which are formed first (26) and second (31)
series-connected halves of a single antenna coil having ends
connected to an integrated circuit die (50) mounted to a die bond
site (46) at a corner of the substrate (10). Conductive vias
(22,24) extend through the substrate (10) to effect connection
between the antenna halves (26,31), from one side of the substrate
to the other side of the substrate. Protective laminates (58,60) on
either side of the substrate (10) are bonded to one another around
the substrate edges, and also are bonded to one another at interior
portions through a slot (20) formed in the substrate (10).
[0014] The following patents, all of which are incorporated in
their entirety by reference herein, are cited as being of interest:
5,923,300; 5,894,006; 5,879,502; 5,870,066; 5,854,480; 5,461,545;
5,420,757; 5,345,231; 5,313,365; 5,250,843; 5,223,851; 5,218,861;
5,214,410; 5,181,975; 4,911,217; 4,851,855; 4,795,693; 4,724,427;
4,628,148; 4,524,324; and 4,092,487.
SUMMARY OF THE INVENTION
[0015] According to the invention, a circuit module comprises a
first printed circuit board (PCB) having a first surface and a
second surface, electronic components mounted to its first surface,
a first long conductive spiral trace on its first surface and a
second long conductive spiral trace on its second surface, wherein
the second long conductive trace is connected in series with the
first long conductive trace to form a coil which is connected to
the electronic components.
[0016] In a second embodiment, other PCBs are stacked parallel to
the first PCB, each having a first surface and a second surface,
and each having a long spiral conductive trace on its first surface
and/or on its second surface. Still other PCBs having no traces may
be stacked between the PCBs having traces in order to separate a
long trace of one PCB from a long trace of another PCB. A PCB
adjacent to, but not possessing, the electronic components may be
in the form of a ring having an opening, wherein the opening forms
a cavity for containing the electronic components. The long
conductive traces are attached all in series with each other to
form a single air core antenna coil, and the circuit module
functions as a RF transponder.
[0017] In a third embodiment, the long conductive traces can be
attached in two separate series to form two windings of a coupling
transformer, in which one winding (comprised of one or more traces
connected in series) is connected to the electronic components, and
the other winding (also comprised of one or more traces connected
in series) is connected to an external antenna. The external
antenna can be a coil of wire disposed circumferentially
(360-degrees) around an inner surface of a pneumatic tire, and the
circuit module functions as a RF transponder.
[0018] In a variation of the second embodiment, a ferrite antenna
comprising a coil of wire wound about a ferrite rod is disposed
within the cavity formed by the opening in one of the PCBs. The
ferrite antenna is aligned parallel with the PCBs, and thus
perpendicular with respect to the axis of the coil formed by the
long traces, to provide a dual-polarized antenna system.
[0019] In a variation of any of the embodiments, the long spiral
conductive traces of some or all of the PCBs can be attached to
each other in parallel, to improve performance by way of reduced
electrical resistance if the spiral coils are made of very fine
pitched traces.
[0020] Any of the above embodiments of an RF transponder circuit
module can be encapsulated within molding material disposed on all
external surfaces of the circuit module. The molding material can
be any rubber, ethylene propylene diene monomer (EPDM) rubber,
butyl rubber, natural rubber, neoprene and mixtures thereof, a
mixture of chlorobutyl rubber and natural rubber, or a mixture of
styrene-butadiene rubber (SBR) and natural rubber.
[0021] Other objects, features and advantages of the invention will
become apparent in light of the following description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Reference will be made in detail to preferred embodiments of
the invention, examples of which are illustrated in the
accompanying drawings. The drawings are intended to be
illustrative, not limiting. Although the invention will be
described in the context of these preferred embodiments, it should
be understood that it is not intended to limit the spirit and scope
of the invention to these particular embodiments.
[0023] Certain elements in selected ones of the drawings may be
illustrated not-to-scale, for illustrative clarity. The
cross-sectional views, if any, presented herein may be in the form
of "slices", or "near-sighted" cross-sectional views, omitting
certain background lines which would otherwise be visible in a true
cross-sectional view, for illustrative clarity.
[0024] Elements of the figures are typically numbered as follows.
The most significant digits (hundreds) of the reference number
usually corresponds to the figure number. Elements of FIG. 1 are
typically numbered in the range of 100-199. Elements of FIG. 2 are
typically numbered in the range of 200-299. Similar elements
throughout the drawings may be referred to by similar reference
numerals. For example, the element 199 in a figure may be similar,
and possibly identical to the element 299 in an other figure. In
some cases, similar (including identical) elements may be referred
to with similar numbers in a single drawing. For example, each of a
plurality of elements 199 may be referred to individually as 199a,
199b, 199c, etc. Such relationships, if any, between similar
elements in the same or different figures will become apparent
throughout the specification, including, if applicable, in the
claims and abstract.
[0025] The structure, operation, and advantages of the present
preferred embodiment of the invention will become further apparent
upon consideration of the following description taken in
conjunction with the accompanying drawings, wherein:
[0026] FIG. 1 is a cross-sectional view of a circuit module
comprising one PCB, according to the invention;
[0027] FIG. 1A is a top view of the circuit module of FIG. 1,
according to the invention;
[0028] FIG. 2 is an exploded, cross-sectional view of a circuit
module comprising two PCBs, according to the invention;
[0029] FIG. 2A is an exploded, cross-sectional view of a circuit
module comprising two PCBs, according to the invention, connected
to an antenna;
[0030] FIG. 3 is an exploded, cross-sectional view of a circuit
module comprising three PCBs, according to the invention;
[0031] FIG. 3A is an exploded, cross-sectional view of another
circuit module comprising three PCBs, according to the
invention;
[0032] FIG. 4 is an exploded, cross-sectional view of another
circuit module comprising three PCBs, according to the invention,
connected to a ferrite rod antenna;
[0033] FIG. 5A is an exploded, cross-sectional view of an injection
molding process for encapsulating a circuit module, according to
the invention;
[0034] FIG. 5B is a cross-sectional view of a further step in the
injection molding process for encapsulating a circuit module,
according to the invention; and
[0035] FIG. 5C is an exploded, cross-sectional view of a further
step in the injection molding process for encapsulating a circuit
module, according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] FIGS. 1 (side cross-sectional view) and 1A (top view)
illustrate a circuit module 100 comprising a printed circuit board
(PCB) 102 having conductive traces on both its top surface 102a and
its bottom surface 102b, and electronic components 104, 106 and 108
mounted to its top surface 102a and interconnected with one
another.
[0037] A long conductive trace 110 is in the form of a spiral
having a one end 110a and another end 110b, and is disposed around
a peripheral area of the top surface 102a of the PCB 102. In the
views of FIGS. 1 and 1A, TEN complete turns can be seen.
[0038] In a similar manner, a one long conductive trace 112 is in
the form of a spiral having a one end 112a and another end 112b,
and is disposed on the bottom surface 102b of the PCB 102. In the
cross-sectional view of FIG. 1, TWENTY turns can be seen.
[0039] The conductive traces 110 and 112 are connected in series
with one another, and each of the conductive traces 110 and 112
forms a portion of an overall coil antenna for the circuit module
100. For example, the component 104 is connected to the end 110a of
the trace 110. The end 110b of the trace 110 is connected by a via
114 through the PCB 102 to the end 112a of the trace 112. The end
112b of the trace 112 is connected by a via 116 through the PCB 102
to the component 106.
[0040] The conductive traces 110 and 112, and those discussed
hereinbelow, are in the form of loops having many turns. These
loops can be characterized as a planar coil which lays flat on the
surface of the respective PCB in a form such as a spiral. As is
known for coil antennas, the direction of current flow around the
coil determines the direction of the radiated magnetic field, and
vice-versa for a receiving antenna. Therefore, for the example
hereinabove wherein traces 110 and 112 are connected in series to
form at least part of an overall coil antenna, the spirals for the
two traces 110 and 112 must be laid out so that the current flows
in the same direction in the trace 110 and in the trace 112 portion
of the antenna. For example, if the trace 110 spirals from end 110a
to end 110b in a clockwise direction (looking down at the top PCB
surface 102a), then the trace 112 must also spiral in the same
clockwise direction from end 112a to end 112b.
[0041] It is within the scope of this invention that an overall
coil antenna may be formed by connecting coils such as trace 110
and trace 112 in parallel with each other. This may be desirable in
cases where, for example, very fine-pitched traces 110 and 112 are
used, producing high electrical resistance in each coil. For a
parallel connection, ends 110a and 112b would be connected together
and to one antenna end connection such as component 106, and ends
110b and 112a would be connected together and to the other antenna
end connection such as component 104. Such a parallel connection is
not illustrated in FIG. 1, but can be seen in the
parallel-connected traces 350 and 352 of FIG. 3. Known techniques
could be employed to connect component 104 to trace end 110b (e.g.,
extending an insulated wire between the two, preferably crossing
the turns of trace 110 at right angles, as illustrated for wire 227
of FIG. 2 which crosses the turns of trace 230). Now, in order to
maintain proper current direction in a parallel-connected antenna
formed from traces 110 and 112, if the trace 110 spirals from end
110a to end 110b in a clockwise direction (looking down at the top
PCB surface 102a), then the trace 112 must also spiral in the same
clockwise direction from end 112b to end 112a.
[0042] For a transmitting loop, the driving point voltage and
current is proportional to radiation resistance (Rr) of the loop
and is given by the following equation (eqn 1):
Rr=[6/(Mo/Eo)].sup.2 (2 L).sup.4 (NA).sup.2
[0043] where:
[0044] (Mo/Eo).sup.-2 is the wave impedance of the space
[0045] 2/L is the propagation constant in the space
[0046] N is the number of turns in the loop
[0047] A is the area of the loop
[0048] For a receiving loop, the voltage (Vr) developed at its
open-circuited terminals is given by the following equation (eqn
2):
Vr=jwNAbhd z
[0049] where:
[0050] j is the square root of minus 1;
[0051] w is angular frequency (2f);
[0052] N is the number of turns in the loop;
[0053] A is the area of the loop; and
[0054] bhd z is the component of incident magnetic density normal
to the plane of the loop.
[0055] As can be seen by the expressions above, whether the
conductive traces 110, 112 serve as a transmitting loop or a
receiving loop, the RF transmission and receiving strength is
directly related to the number of turns and the area circumscribed
by the turns.
[0056] FIG. 2 illustrates a circuit module 200 comprising two
printed circuit boards (PCBs) 202 and 222. The PCB 202 (compare
102) has conductive traces on both its top surface 202a and its
bottom surface 202b, and electronic components 204, 206 and 208
mounted to its top surface 202a and interconnected with one
another.
[0057] A one long conductive trace 210 (compare 110) is in the form
of a spiral having a one end 210a and another end 210b, and is
disposed around a peripheral area of the top surface 202a of the
PCB 202. In the cross-sectional view of FIG. 2, TEN turns can be
seen.
[0058] In a similar manner, a one long conductive trace 212
(compare 112) is in the form of a spiral having a one end 212a and
another end 212b, and is disposed on the bottom surface 202b of the
PCB 202. In the cross-sectional view of FIG. 2, TWENTY turns can be
seen.
[0059] The PCB 222 is in the form of a ring, having a central
opening 224, and has a top surface 222a and a bottom surface 222b.
A one long conductive trace 230 (compare 210) is in the form of a
spiral having a one end 230a and another end 230b, and is disposed
around a peripheral area of the top surface 222a of the PCB 222. In
the cross-sectional view of FIG. 2, TEN turns can be seen.
[0060] The conductive traces 210, 212 and 230 may be connected in
parallel (not shown) or in series with one another (as illustrated)
so that each forms a portion of a single overall coil antenna for
the circuit module 200. For example, the component 204 is connected
to the end 210a of the trace 210. The end 210b of the trace 210 is
connected by a via 214 through the PCB 202 to the end 212a of the
trace 212. The end 212b of the trace 212 is connected by a via 216
through the PCB 202 to a surface trace 217 which contacts a via 226
through the PCB 222 to the end 230a of the trace 230. The end 230b
of the trace 230 is connected by a wire 227 to via 228 through the
PCB 222 to connect with a surface trace 207 and thereby to the
component 206. For clarity of illustration, the trace 207 is shown
as if it were raised above trace 217, whereas in reality the traces
207 and 217 would usually be of equivalent height and separated
horizontally, such as trace 207 being behind trace 217 in the view
of FIG. 2. The wire 227 is suitably insulated from the spiral turns
of trace 230 and preferably crosses the turns at right angles.
Suitable insulation includes, for example, an air gap, enamel or
PVC coating on the wire 227, an/or an insulating coating over the
PCB 222 surface 222a and over the trace 230.
[0061] One having ordinary skill in the art to which the invention
most nearly pertains will understand how, in this and other
embodiments of the invention presented herein, connections are made
between PCBs (from one PCB to another), using pins, connectors and
the like. Generally, in this and other embodiments of the invention
presented herein, when PCBs are stacked one atop the other, they
preferably have approximately the same outside dimensions. In other
words, they are preferably the same size and shape as one
another.
[0062] Alternatively to the embodiment illustrated in FIG. 2, FIG.
2A illustrates the circuit module 200', having conductive traces
210' and 212' (compare 110 and 112) on the lower PCB 202' (compare
102) which may be series-connected with one another and connected
to the electronic components 204' and 206', respectively, in the
manner described for the circuit module 100, to form a winding of
an air-gap transformer ("air-gap" is commonly understood to include
non-conductive, non-magnetic materials such as the PCB material
filling the transformer gap), with the conductive trace 230' on the
upper PCB 222' not being connected to the traces 210' and 212' but
rather serving as the other winding of the air-gap transformer.
Such a transformer can serve as a coupling transformer which is
connected to an antenna 260 for the circuit module. The ends 230a'
and 230b' of the conductive trace 230' are shown connected to the
antenna 260. The circuit module 200' is suitably an RF transponder,
and the antenna 260 is suitably a coil of wire disposed
circumferentially (360-degrees) around an inner surface of a
pneumatic tire (not shown).
[0063] The lower PCB 202' has an upper surface 202a' and a lower
surface 202b'. The upper PCB 222' has an upper surface 222a' and a
lower surface 222b', and a central opening 224'. The trace 210' has
two ends 210a' and 210b', and the trace 212' has two ends 212a' and
212b40 .
[0064] FIG. 3 illustrates a circuit module 300 comprising three
circuit boards (PCBs) 302, 322 and 342.
[0065] The lower PCB 302 (compare 102) has conductive traces on
both its top surface 302a and its bottom surface 302b, and
electronic components 304, 306 and 308 mounted to its top surface
302a and interconnected with one another.
[0066] A one long conductive trace 310 (compare 110) is in the form
of a spiral having a one end 310a and another end 310b, and is
disposed around a peripheral area of the top surface 302a of the
PCB 302. In the cross-sectional view of FIG. 3, TEN turns can be
seen.
[0067] In a similar manner, a one long conductive trace 312
(compare 112) is in the form of a spiral having a one end 312a and
another end 312b, and is disposed on the bottom surface 302b of the
PCB 302. In the cross-sectional view of FIG. 3, TWENTY turns can be
seen.
[0068] In this example, the conductive traces 310 and 312 are
connected in series with one another, and each form a portion of a
transformer winding for the circuit module 300. For example, the
component 304 is connected to the end 310a of the trace 310. The
end 310b of the trace 310 is connected by a via 314 through the PCB
302 to the end 312a of the trace 312. The end 312b of the trace 312
is connected by a via 316 through the PCB 302 to the component
306.
[0069] The middle PCB 322 is in the form of a ring, having a
central opening 324, and has a top surface 322a and a bottom
surface 322b. In this example, the PCB functions primarily as a
spacer, having no electrical functionality associated therewith.
(Compare the ring-like PCB 222 which has conductive traces on a
surface thereof).
[0070] The top PCB 342 has an upper surface 342a and a lower
surface 342b, and is disposed atop the PCB 322 so as to cover the
opening 324 in the middle of the PCB 322.
[0071] A one long conductive trace 350 (compare 112, 110) is in the
form of a spiral having a one end 350a and another end 350b, and is
disposed on the top surface 342b of the PCB 342. In the
cross-sectional view of FIG. 3, TWENTY turns can be seen.
[0072] In a similar manner, a one long conductive trace 352
(compare 112) is in the form of a spiral having a one end 352a and
another end 352b, and is disposed on the bottom surface 342b of the
PCB 342. In the cross-sectional view of FIG. 3, TWENTY turns can be
seen.
[0073] In this example, the conductive traces 350 and 352 are
connected in parallel with one another, and each form a portion of
a transformer winding for the circuit module 300. For example, an
antenna 360 (compare 260) is connected to the end 350a of the trace
350 and also to the end 352b of the trace 352 by way of a via 356
(compare 316) through the PCB 342. The other end of the antenna 360
is connected to the end 350b of the trace 350 and also to the end
352a of the trace 352 by way of a via 354 (compare 314) through the
PCB 342. In this manner, an air-gap transformer is formed, one
winding comprising the series-connected traces 310 and 312, the
other winding comprising the parallel-connected traces 350 and 352.
The circuit module 300 is suitably an RF transponder, and the
antenna 360 is suitably a coil of wire disposed circumferentially
(360-degrees) around an inner surface of a pneumatic tire (not
shown).
[0074] FIG. 3A illustrates a circuit module 300' comprising three
printed circuit boards (PCBs) 302', 322' and 342'.
[0075] The lower PCB 302' (compare 202) has conductive traces on
both its top surface 302a' and its bottom surface 302b', and
electronic components 304', 306' and 308' mounted to its top
surface 302a' and interconnected with one another.
[0076] A one long conductive trace 310' (compare 210) is in the
form of a spiral having a one end 310a' and another end 310b', and
is disposed around a peripheral area of the top surface 302a' of
the PCB 302'. In the cross-sectional view of FIG. 3A, TEN turns can
be seen.
[0077] In a similar manner, a one long conductive trace 312'
(compare 212) is in the form of a spiral having a one end 312a' and
another end 312b', and is disposed on the bottom surface 302b' of
the PCB 302'. In the cross-sectional view of FIG. 3A, TWENTY turns
can be seen.
[0078] The middle PCB 322' (compare 222) is in the form of a ring,
having a central opening 324', and has a top surface 322a' and a
bottom surface 322b'. A one long conductive trace 330 (compare 230)
is in the form of a spiral having a one end 330a and another end
330b, and is disposed around a peripheral area of the top surface
322a' of the PCB 322'. In the cross-sectional view of FIG. 3A, TEN
turns can be seen. The end 330a is connected to a contact pad 331,
and the end 330b is connected to a via 326. A second via 328 passes
through the PCB 322' somewhere near the edge of the central opening
324' and does not make electrical contact with any part of the
trace 330.
[0079] The top PCB 342' has an upper surface 342a' and a lower
surface 342b', and is disposed atop the PCB 322' so as to cover the
opening 324' in the middle PCB 322'.
[0080] A one long conductive trace 350' (compare 350) is in the
form of a spiral having a one end 350a40 and another end 350b@',
and is disposed on the top surface 342a40 of the PCB 342'. In the
cross-sectional view of FIG. 3A, TWENTY turns can be seen.
[0081] The conductive traces 310', 312', 330, and 350' may be
connected in parallel (not shown) or in series with one another (as
illustrated) so that each forms a portion of a single overall coil
antenna for the circuit module 300'. For example, the component
304' is connected to the end 310a40 of the trace 310'. The end
310b40 of the trace 310 is connected by a via 314' through the PCB
302' to the end 312a40 of the trace 312'. The end 312b40 of the
trace 312' is connected by a via 316' (compare 216) through the PCB
302' to a surface trace 317 which contacts the via 326 (compare
226) through the PCB 322' to the end 330b of the trace 330. The end
330a of the trace 330 is connected to a contact 331 which connects
to a via 354' through the PCB 342' to the end 350a40 of the trace
350'. The end 350b40 of the trace 350' is connected by a via 356'
through the PCB 342' to a surface trace 357 with an end 357a which
is placed to connect with via 328 through the PCB 322' to connect
with a surface trace 307 and thereby to the component 306. For
clarity of illustration, the trace 307 is shown as if it were
raised above trace 317, whereas in reality the traces 307 and 317
would usually be of equivalent height and separated horizontally,
such as trace 307 being behind trace 317 in the view of FIG.
3A.
[0082] It is within the scope of this invention that any or all of
the circuit boards in the module 300' have long (elongate)
conductive traces on one or both of their surfaces, and that these
elongate conductive traces may be in the form of spirals, including
square spirals, and that the conductive traces may be connected
with one another in any manner, such as in series or in parallel
with one another, or such as some functioning as a one winding of a
coupling transformer and the others acting as the other winding of
a coupling transformer, however a particular application for the
circuit module may dictate.
[0083] The circuit modules 300 and 300' of FIGS. 3 and 3A,
respectively, each have three PCBs stacked one atop the other. In
both cases, the middle PCB 322, 322' is in the form of a ring,
having a central opening 324, 324', respectively. As is evident
from the illustrations, the top PCB 342, 342' covers the opening
324, 324', respectively. The opening 324, 324' thus forms a cavity
wherein the components 304, 306, 308 (and 304', 306', 308') are
contained within the assembly of three PCBs. With the exception
that it is not covered, the opening 224, 224' in the PCB 222, 222'
of the circuit module 200, 200' shown in FIGS. 2 and 2A also forms
a cavity for containing the electronic components 204, 206, 208,
204', 206', 208' mounted to the lower PCB 202, 202'. These openings
224, 224', 324, 324' are suitably disposed in the center of the
respective PCBs 222, 222', 322, 322', but it is within the scope of
the invention that the openings 224, 224', 324, 324' are disposed
other than at the center of the respective PCBs 222, 222', 322,
322'.
[0084] Coils, whether they be antenna coils or transformer
windings, formed by the elongate traces (110, 112, 210, 210', 212,
212', 230, 230', 310, 310', 312, 312', 330, 350, 350') on the PCBs
(102, 202, 202', 222, 222', 302, 302', 322, 322', 342, 342') have
an axis which is normal to the surface of the PCB on which they are
disposed. As viewed in the figures, the axis would be vertical on
the sheet. Also, as described hereinabove, the spiraling direction
of each of these coils formed by the elongate traces 110, 112, 210,
210', 212, 212', 230, 230', 310, 310', 312, 312', 330, 350, 350' is
suitably determined in order to maintain parallel, same-direction
current in adjacent connected coils, taking into account whether
the coils are connected in series or in parallel.
[0085] With particular regard to elongate traces forming an antenna
for the respective circuit module, it is within the scope of the
invention that an additional antenna or transformer element may be
included in the circuit module.
[0086] FIG. 4 illustrates a circuit module 400 which is
substantially identical to the previously-described circuit module
300' of FIG. 3A. Where features of FIG. 4 are identical to
corresponding features in FIG. 3A, the reference numbers for those
features will be the same in the two figures. Features which have
been added in FIG. 4 have reference signs in the 400 series, and
modified features have a reference number which is the same as in
FIG. 3A except for a double prime.
[0087] FIG. 4 illustrates an alternative embodiment of the coil
placement, wherein the coil formed from trace 330" (compare 330) is
placed on the bottom surface 342b40 of the top PCB 342' so that the
middle PCB 322' has no traces on it and serves mainly as an
insulator/spacer between the bottom PCB 302' and the top PCB 342'.
The vias 326 and 328 remain in the middle PCB 322' in order to
carry current between the bottom PCB 302' and the top PCB 342'. The
via 326 is now only connected to the end 330b41 of the trace 330"
by way of contact pad 431 when the PCBs are assembled together, and
the end 330a41 of the trace 330" is now fixedly connected to the
via 354', thereby eliminating the contact pad 331.
[0088] A ferrite rod antenna 410 comprising a coil of wire 412
wound about a generally-cylindrical ferrite rod 414 is disposed
within the cavity formed by the opening 324'. The rod 414 is
oriented so that its axis 420 (hence the axis of the coil of wire
412) is parallel to the surface 302a40 of the PCB 302'. The coil of
wire 412 has two ends 416 and 418 which are connected to respective
terminals 426 and 428 on the PCB 302'. The ferrite rod antenna 410
may be used in lieu of the antenna coils formed by the elongate
traces 310', 312', 330", 350' on the PCBs 302', 322', 342', but
preferably is used in conjunction with the antenna coils formed by
the elongate traces 310', 312', 330", 350'.
[0089] It is within the scope of the invention that the wire 412 is
replaced by conductive traces on the surfaces 302a40 and 342b40 of
the lower and upper PCBs 302' and 342', respectively, and,
optionally, conductive traces on the sidewall(s) of the cavity
formed by the opening 324' in the middle PCB 322'. This can be
structured with or without the ferrite rod.
[0090] As mentioned above, the coils formed by the elongate traces
310', 312', 330", to 350' on the PCBs 302', 322', 342' have an axis
422 which is normal to the surfaces of the PCBs on which they are
disposed. Therefore, the axis 420 of the ferrite rod antenna 410 is
orthogonal to the axis 420 of the antenna coils formed by spiral
elongate traces 310', 312', 330", 350' on the PCBs. In this manner,
using the ferrite rod antenna 410 in conjunction with the antenna
coil(s) formed by the elongate traces 310', 312', 330", 350', an
omni-directional (or, dual-polarized or directional) antenna system
is provided for the transponder.
[0091] Various benefits will accrue when using such an
omni-directional or dual-directional antenna system in a circuit
module (400) serving as an RF transponder disposed within a
pneumatic tire. Preferably, the transponder (circuit module 400)
would be mounted within the tire so that the axis 420 of the
ferrite rod antenna 410 extends axially (from bead-to-bead) across
the tread of the tire, i.e., is parallel to the axis of the
tire.
[0092] Commonly-owned U.S. Pat. No. 5,181,975 and U.S. Pat. No.
5,218,861, incorporated in their entirety by reference herein,
disclose improving coupling to a tire-mounted transponder by
utilizing an annular bead of the tire as the primary winding of a
transformer. A transponder is disposed near the annular bead, and
has a coil antenna that is loosely electromagnetically coupled to
the annular bead, and acts as the secondary winding of the
transformer.
[0093] Despite the "360-degree" readability of a transponder which
can result from using an annular bead or the like in the tire as a
coupling element, it is suspected that coupling from a transponder
in a rotating tire, via an annular bead or the like, to an
externally fixed antenna can result in non-uniform coupling,
including phase shifts. It is, of course, generally desirable to
ensure uniform, or at least adequate, coupling of RF signals
between an on-board interrogator and a tire-mounted transponder,
irrespective of the orientation of the wheel vis-a-vis the
vehicle-mounted antenna. By using the omni-directional antenna
system of the present invention in a circuit module (400) serving
as an RF transponder disposed within a pneumatic tire, as described
hereinabove, coupling can be enhanced and rendered more
uniform.
ENCAPSULATING THE CIRCUIT MODULE
[0094] U.S. Pat. No. 5,420,757 (Eberhardt, et al.; 1995),
incorporated in its entirety by reference herein, discloses a
method of producing a RF transponder with a molded environmentally
sealed package. The components are mounted on a lead-type substrate
frame, and are encapsulated in a plastic housing using a
conventional plastic molding process utilizing a suitable plastic
or epoxy (column 6, lines 56-62). The leads which support the
transponder in the mold during the molding process are eventually
severed to provide a leadless package. As disclosed in the patent,
the frame may be a PCB formed to have supporting arms which are
severed at the periphery of the respective plastic molded
housings.
[0095] Injection molding is a well-known process. Typically, a
two-part mold of an injection molding machine has a cavity which is
in the shape of the desired final product. Molten or fluid material
is injected into the cavity via gates to fill the cavity, and
encapsulate any object which was previously inserted into the
cavity.
[0096] FIGS. 5A, 5B and 5C illustrate an injection molding process
for encapsulating any of the circuit modules described
hereinabove--for example, the circuit module 300.
[0097] FIG. 5A shows a mold 500 while open. The mold 500 comprises
two mold halves, an upper mold half 502 and a lower mold half 504.
An inner surface 502a of the upper mold half 502 has a recess 506.
An inner surface 504a of the lower mold half 504 has a recess 508.
When the mold halves 502 and 504 are brought together, as indicated
by the arrows in FIG. 5A, the recesses 506 and 508 form a cavity.
The circuit module 300 is disposed in any suitable manner, such as
supported by pins or posts 510, within the cavity.
[0098] FIG. 5A shows the mold 500 when closed. The circuit module
300 is smaller than the cavity, there being spaces between the
circuit module and the walls of the cavity.
[0099] The lower mold half 504 is provided with a gate 512 for
injecting molding material into the mold cavity, as indicated by
the arrow 514. The upper mold half 502 is provided with a vent hole
516 for venting gas (e.g., air) from the mold cavity, as indicated
by the arrow 518. This is best viewed in FIG. 5B which shows the
mold cavity partially (approximately half, e.g., the left half as
viewed in the figure) filled with molding material 520, and the
circuit module 300 partially encapsulated. Once the cavity is
filled, the molding material is molded to shape and allowed to
solidify, by cooling or curing to a desired degree prior to removal
from the mold. Heat can be applied to the mold if necessary
(depending on the material used).
[0100] FIG. 5C shows the mold 500 opened up upon completion of the
molding process. At the completion of the molding process, the
circuit module 300 is fully and completely encapsulated with
molding material 520, and the mold halves 502 and 504 are
separated, as indicated by the arrows in FIG. 5C, resulting in the
encapsulated circuit module 530 illustrated in FIG. 5C which has
molding material on all of its external (exposed) surfaces.
[0101] Suitable molding materials for encapsulating the circuit
module include rubber selected from the group consisting of
essentially ethylene propylene diene monomer (EPDM) rubber, butyl
rubber, natural rubber, synthetic rubbers, neoprene and mixtures
thereof, such as, for example, a mixture of halobutyl rubber and
natural rubber, poul-butadiene rubber and natural rubber or a
mixture of styrene-butadiene rubber (SBR) and natural rubber. These
rubber compositions can typically be cured by heating to a desired
temperature in the order of 150 degrees (C.) and for a period of
time depending upon the curing system used, accelerators, and the
degree of curing desired prior to removal of the product from the
mold.
[0102] While the invention has been described in combination with
embodiments thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications and
variations as fall within the spirit and scope of the appended
claims.
* * * * *