U.S. patent application number 09/921064 was filed with the patent office on 2002-04-25 for resistor component with multiple layers of resistive material.
This patent application is currently assigned to GA-TEK Inc. (dba Gould Electronics Inc.). Invention is credited to Centanni, Michael A., Clouser, Sidney J., Wang, Jiangtao.
Application Number | 20020047773 09/921064 |
Document ID | / |
Family ID | 24677632 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047773 |
Kind Code |
A1 |
Wang, Jiangtao ; et
al. |
April 25, 2002 |
Resistor component with multiple layers of resistive material
Abstract
A resistor foil, comprised of a copper layer having a first side
and a second side. A tiecoat metal layer having a thickness of
between 5 .ANG. and 70 .ANG. is disposed on the first side of the
copper layer. A first layer of a first resistor metal having a
thickness of between 100 .ANG. and 500 .ANG. is disposed on the
tiecoat metal layer, and a second layer of a second resistor metal
having a thickness of between 100 .ANG. and 500 .ANG. is disposed
on the first layer of the first resistor metal. The first resistor
metal has a resistance different from the second resistor
metal.
Inventors: |
Wang, Jiangtao; (Cleveland
Heights, OH) ; Centanni, Michael A.; (Parma, OH)
; Clouser, Sidney J.; (Chardon, OH) |
Correspondence
Address: |
MARK KUSNER COMPANY LPA
HIGHLAND PLACE SUITE 310
6151 WILSON MILLS ROAD
HIGHLAND HEIGHTS
OH
44143
|
Assignee: |
GA-TEK Inc. (dba Gould Electronics
Inc.)
|
Family ID: |
24677632 |
Appl. No.: |
09/921064 |
Filed: |
August 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09921064 |
Aug 2, 2001 |
|
|
|
09667294 |
Sep 22, 2000 |
|
|
|
Current U.S.
Class: |
338/308 |
Current CPC
Class: |
H01C 7/18 20130101; H05K
2201/0355 20130101; Y10T 29/49082 20150115; H05K 2201/0317
20130101; Y10T 29/49156 20150115; H05K 2201/0391 20130101; Y10T
29/49101 20150115; H01C 17/07 20130101; H05K 2203/0723 20130101;
H05K 1/167 20130101; Y10S 29/016 20130101; H05K 2203/0361 20130101;
Y10T 29/49099 20150115 |
Class at
Publication: |
338/308 |
International
Class: |
H01C 001/012 |
Claims
Having described the Invention, the following is Claimed:
1. A resistor foil, comprised of: a copper layer having a first
side and a second side; a tiecoat metal layer having a thickness of
between 5 .ANG. and 70 .ANG. on said first side of said copper
layer; a first layer of a first resistor metal having a thickness
of between 100 .ANG. and 500 .ANG. on said tiecoat metal layer; and
a second layer of a second resistor metal having a thickness of
between 100 .ANG. and 500 .ANG. on said first layer of said first
resistor metal, said first resistor metal having a resistance
different from said second resistor metal.
2. A resistor foil as defined in claim 1, wherein said first
resistor metal is selected from the group consisting of aluminum,
zinc, nickel, nickel/chromium, nickel/chromium/aluminum/silicon
alloy, titanium, vanadium, chromium, tantalum, iron, manganese and
alloys, oxides, nitrides and silicides thereof.
3. A resistor foil as defined in claim 2, wherein said second
resistor metal is selected from the group consisting of aluminum,
zinc, nickel, nickel/chromium, nickel/chromium/aluminum/silicon
alloy, titanium, vanadium, chromium, tantalum, iron, manganese and
alloys, oxides, nitrides and silicides thereof.
4. A resistor foil as defined in claim 3, wherein said first
resistor metal is different from said second resistor metal.
5. A resistor foil as defined in claim 4, wherein said first
resistor metal is nickel/chromium/aluminum/silicon alloy.
6. A resistor foil as defined in claim 5, wherein said second
resistor metal is tantalum oxide.
7. A resistor foil, comprised of: a copper layer having a first
side and a second side; a tiecoat metal layer having a thickness of
between 5 .ANG. and 70 .ANG. on said first side of said copper
layer; a first layer of a first resistor metal on said tiecoat
metal layer; and a second layer of a second resistor metal on said
first layer of said first resistor metal, said first resistor metal
and said second resistor metal selected from the group consisting
of aluminum, zinc, nickel, nickel/chromium,
nickel/chromium/aluminum/silicon alloy, titanium, vanadium,
chromium, tantalum, iron, manganese and alloys, oxides, nitrides
and suicides thereof, and said first resistor metal having a
resistance different from said second resistor metal.
8. A resistor foil as defined in claim 7, wherein said first
resistor metal is different from said second resistor metal.
9. A resistor foil as defined in claim 8, wherein said first
resistor metal is nickel/chromium/aluminum/silicon alloy.
10. A resistor foil as defined in claim 9, wherein said second
resistor metal is tantalum oxide.
11. A resistor foil as defined in claim 7, wherein said first
resistor metal and said second resistor metal each have a thickness
between 100 .ANG. and 500 .ANG..
12. A resistor foil, comprised of: a copper layer having a first
side and a second side; a metal layer on said first side of said
copper layer; a first layer of a first resistor metal on said metal
layer; and a second layer of a second resistor metal on said first
layer of said first resistor metal, said first resistor metal
having a resistance different from said second resistor metal.
13. A resistor foil as defined in claim 12, wherein said first
resistor metal is selected from the group consisting of aluminum,
zinc, nickel, nickel/chromium, nickel/chromium/aluminum/silicon
alloy, titanium, vanadium, chromium, tantalum, iron, manganese and
alloys, oxides, nitrides and silicides thereof.
14. A resistor foil as defined in claim 13, wherein said second
resistor metal is selected from the group consisting of aluminum,
zinc, nickel, nickel/chromium, nickel/chromium/aluminum/silicon
alloy, titanium, vanadium, chromium, tantalum, iron, manganese and
alloys, oxides, nitrides and silicides thereof.
15. A resistor foil as defined in claim 14, wherein said first
resistor metal is different from said second resistor metal.
16. A resistor foil as defined in claim 15, wherein said first
resistor metal is nickel/chromium/aluminum/silicon alloy.
17. A resistor foil as defined in claim 16, wherein said second
resistor metal is tantalum oxide.
18. A resistor foil as defined in claim 12, wherein said first
resistor metal and said second resistor metal each have a thickness
between 100 .ANG. and 500 .ANG..
19. A resistor foil, comprised of: a copper layer having a first
side and a second side; a first layer of a first resistor material
on said copper layer; and a second layer of a second resistor
material on said first layer of said first resistor material, said
first resistor material having a resistance different from said
second resistor material.
20. A resistor foil as defined in claim 19, wherein said first
resistor material is selected from the group consisting of
aluminum, zinc, nickel, nickel/chromium,
nickel/chromium/aluminum/silicon alloy, titanium, vanadium,
chromium, tantalum, iron, manganese and alloys, oxides, nitrides
and silicides thereof.
21. A resistor foil as defined in claim 20, wherein said second
resistor material is selected from the group consisting of
aluminum, zinc, nickel, nickel/chromium,
nickel/chromium/aluminum/silicon alloy, titanium, vanadium,
chromium, tantalum, iron, manganese and alloys, oxides, nitrides
and silicides thereof.
22. A resistor foil as defined in claim 21, wherein said first
resistor material is different from said second resistor
material.
23. A resistor foil as defined in claim 22, wherein said first
resistor material is nickel/chromium/aluminum/silicon alloy.
24. A resistor foil as defined in claim 23, wherein said second
resistor material is tantalum oxide.
25. A resistor foil as defined in claim 19, further comprising a
tie coat layer between said copper layer and said first resistor
material.
26. A resistor foil as defined in claim 25, wherein said tie coat
layer is a metal selected from the group consisting of nickel,
palladium, titanium, tantalum, aluminum, iron, vanadium, chromium,
chromium-based alloys and nickel-based alloys.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to multi-layer printed circuit
boards and, more particularly, to a resistive component usable in
forming boards with embedded resistive layers.
BACKGROUND OF THE INVENTION
[0002] A basic component of a printed circuit board is a dielectric
layer having a sheet of copper foil bonded thereto. Through a
subtractive process that includes one or more etching steps,
portions of the copper foil are etched away to leave a distinct
pattern of conductive lines and formed elements on the surface of
the dielectric layer. Multi-layer printed circuit boards are formed
by stacking and joining two or more of the aforementioned
dielectric layers having printed circuits thereon. Many printed
circuit boards include conductive layers containing patterned
components that perform like specific, discreet components. One
such discreet component is a resistive element formed from a
resistor foil. A resistor foil is basically a copper foil having a
thin layer of resistive material, typically a metal or metal alloy
deposited onto one surface thereof. The resistor foil is attached
to a dielectric substrate with the resistive material adhered to
the dielectric substrate. Using conventionally known masking and
etching techniques, the copper foil and resistive material are
etched away to produce a trace line of copper with the resistive
material therebelow on the surface of the dielectric. A section of
the copper layer is removed leaving only the resistive material on
the surface connecting the two separated ends of the copper.
Because the material forming the resistive layer typically has a
conductivity less than copper, it essentially acts as a resistor
between the separated ends of the copper trace lines. The thickness
and width of the resistive layer, as well as the length of the
resistive layer disposed between the ends of the copper traces,
affect the resistance of the resistive element so formed.
[0003] The present invention represents an improvement over
resistor foils known heretofore and provides a resistor foil having
multiple layers of resistive material on a copper layer, thereby
facilitating the formation of a variety of different resistive
elements having a variety of resistance values.
SUMMARY OF THE INVENTION
[0004] In accordance with a preferred embodiment of the present
invention, there is provided a resistor foil, comprised of a copper
layer having a first side and a second side. A tiecoat metal layer
having a thickness of between 5 .ANG. and 70 .ANG. is provided on
the first side of the copper layer. A first layer of a first
resistor metal having a thickness of between 100 .ANG. and 500
.ANG. is on the tiecoat metal layer, and a second layer of a second
resistor metal having a thickness of between 100 .ANG. and 500
.ANG. is on the first layer of the first resistor metal. The first
resistor metal has a resistance different from the second resistor
metal.
[0005] In accordance with another embodiment of the present
invention, there is provided a method of forming a resistive
element on a printed circuit board, comprising the steps of:
[0006] a) adhering a resistor foil to a dielectric substrate, the
resistor foil comprised of:
[0007] a copper layer having a first side and a second side;
[0008] a tiecoat metal layer having a thickness of between 5 .ANG.
and 70 .ANG. on the first side of the copper layer;
[0009] a first layer of a first resistor metal on the tiecoat metal
layer; and
[0010] a second layer of a second resistor metal on the first layer
of the first resistor metal, the first resistor metal having a
resistance different from the second resistor metal, the resistor
foil adhered to the substrate with the second layer of the second
resistor metal facing the dielectric substrate;
[0011] b) forming a circuit trace line on the dielectric substrate
from the resistor foil; and
[0012] c) removing a portion of the copper layer and the tiecoat
metal layer from the circuit trace line to define a section of the
circuit trace line comprised of the first and second layer of
resistor metals.
[0013] These and other objects will become apparent from the
following description of a preferred embodiment taken together with
the accompanying drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention may take physical form in certain parts and
arrangement of parts, a preferred embodiment of which will be
described in detail in the specification and illustrated in the
accompanying drawings which form a part hereof, and wherein:
[0015] FIG. 1 is an enlarged, cross-sectional view of a resistor
foil illustrating a preferred embodiment of the present
invention;
[0016] FIG. 2 is an enlarged, cross-sectional view of a resistor
foil illustrating an alternate embodiment of the present
invention;
[0017] FIG. 3 is a cross-sectional view showing the resistor foils
shown in FIG. 2 attached to a dielectric substrate;
[0018] FIG. 4 is a perspective view of a resistive element formed
from a resistor foil shown in FIG. 2;
[0019] FIG. 4A is a schematic, electrical representation of the
resistive element shown in FIG. 4;
[0020] FIG. 5 is a partially sectioned, side elevational view of
another resistive element shown in FIG. 2;
[0021] FIG. 5A is a schematic, electrical representation of the
resistive element shown in FIG. 5;
[0022] FIG. 6 is a partially sectioned, side elevational view of a
still further type of resistive element formed using the resistor
foil shown in FIG. 2;
[0023] FIG. 6A is a schematic, electrical representation of the
resistive element shown in FIG. 6;
[0024] FIG. 7 is a cross-sectional view of a resistive element
formed from a resistor foil having three layers of resistive
material thereon, illustrating another embodiment of the present
invention;
[0025] FIG. 7A is a schematic, electrical representation of the
resistive element shown in FIG. 7; and
[0026] FIG. 8 is a perspective view of a resistive element formed
from the resistor foil shown in FIG. 2, illustrating another
embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0027] The present invention relates to a resistor foil for use in
forming embedded resistive elements in printed circuit boards.
Broadly stated, the resistor foil is formed of a resistive copper
foil having two or more layers of resistive material applied
thereto. The resistive materials are preferably formed of metal. As
used herein, the term "metal" refers to metals and alloys capable
of vacuum deposition by the methods discussed herein.
[0028] The copper foils used with this invention can be made using
one of two techniques. Wrought or rolled copper foil is produced by
mechanically reducing the thickness of a copper or copper alloy
strip or ingot by a process such as rolling. Electrodeposited foil
is produced by electrolytically depositing from solution copper
ions on a rotating cathode drum and then peeling the deposited foil
from the cathode. Electrodeposited copper foils find advantageous
application with this invention.
[0029] The copper foils typically have nominal thicknesses ranging
from about 0.0002 inch to about 0.02 inch. Copper foil thickness is
sometimes expressed in terms of weight and typically the foils of
the present invention have weights or thicknesses ranging from
about 1/8 to about 14 ounces per square foot (oz/ft.sup.2).
Especially useful copper foils are those having weights of 1/3,
1/2, 1 or 2 oz/ft.sup.2.
[0030] Electrodeposited copper foils have a smooth or shiny (drum)
side and a rough or matte (copper deposit growth front) side. The
side or sides of the foil, to which the layer applied by the
inventive process overlies, can be a "standard-profile surface,"
low-profile surface" or "very-low-profile surface." Useful
embodiments involve the use of foils with low-profile surfaces and
very low-profile surfaces. The term "standard-profile surface" is
used herein to refer to a foil surface having a R.sub.tm
(IPC-MF-150F) of greater than 10.2 .mu.. The term "low-profile
surface" refers to a foil surface having a R.sub.tm (IPC-MF-150F)
of less than 10.2 .mu.. The term "very-low-profile surface" refers
to a foil surface having a R.sub.tm (IPC-MF-150F) of less than 51
.mu.. R.sub.tm (IPC-MF-150F) is the mean of the maximum
peak-to-valley vertical measurements from each of five consecutive
sampling measurements, and can be measured using a SURTRONIC.RTM. 3
profilometer marketed by Rank Taylor Hobson, Ltd., Leicester,
England.
[0031] The present invention finds advantageous application with
copper foils of the type heretofore described.
[0032] Referring now to FIG. 1, a resistor foil 10, illustrating a
preferred embodiment of the present invention is shown in
cross-section. Resistor foil 10 is comprised of a copper layer 12.
A first layer 14 of a first resistive material is applied to one
side of copper layer 12. Layer 14 is preferably formed of a metal
or metal alloy that is deposited onto copper layer 12 by a
deposition process such as vacuum metalization, electrodeposition,
electroless deposition or combinations thereof. Layer 14 is
preferably applied to side 12a of copper layer 12 by an
electrodeposition process or vacuum metalization. Layer 14 is
formed of a metal having a resistivity greater than copper. Metals
such as aluminum, zinc, nickel, nickel/chromium,
nickel/chromium/aluminum/silicon alloy, titanium, vanadium,
chromium, tantalum, iron, manganese and alloys, oxides, nitrides
and suicides thereof, as well as any vapor depositable metal or
alloy, oxide, nitride and silicide whose electrical resistivity is
greater than that of copper, find advantageous application in
forming layer 14. In a preferred embodiment, layer 14 is formed of
a nickel/chromium/aluminum/silicon alloy. As layer 14 will
ultimately be used to form a resistive element, the thickness of
layer 14 will be based upon the resistivity of the metal forming
layer 14 as well as the desired resistance of the resistive element
to be formed. In this respect, layer 14 may have a thickness of
between 100 .ANG. and 500 .ANG., and more preferably between 100
.ANG. and351 .ANG..
[0033] A second layer 16 of a second resistive material is applied
onto layer 14. Layer 16 is preferably formed of a material
different from that forming layer 14. The material forming layer 16
preferably has a resistivity different from the material forming
layer 14, wherein layer 16 has a resistance different from layer
14.
[0034] Layer 16 may be formed from any of the same materials
identified above i.e., aluminum, zinc, nickel, nickel/chromium,
nickel/chromium/aluminum/silicon alloy, titanium, vanadium,
chromium, tantalum, iron, manganese and alloys, oxides, nitrides
and silicides thereof, as well as any vapor depositable metal or
alloy, oxide, nitride and silicide whose electrical resistivity is
greater than that of copper, subject to layer 16 having a
resistance different from layer 14. In preferred embodiments,
second layer 16 is formed of compounds of tantalum and oxygen,
e.g., Ta.sub.2O.sub.5, compounds of tantalum and nitrogen, e.g.,
Ta.sub.2N and TaN.sub.2, or compounds of chromium and silicon,
e.g., CrSi.
[0035] Layer 16 is preferably applied by a deposition process such
as vacuum metalization, electrodeposition, electroless deposition
or combinations thereof. Layer 16 is preferably applied to layer 14
by an electrodeposition process or vacuum metalization.
[0036] As with layer 14, the thickness of layer 16 will be based
upon the desired resistance of layer 16 and the resistance element
to be formed, as well as on the material forming layer 16. In this
respect, layer 16 may have a thickness of between 100 .ANG. and 500
.ANG., and more preferably between 100 .ANG. and 350 .ANG..
[0037] Referring now to FIG. 2, a resistor foil 20, illustrating an
alternate embodiment of the present invention is shown. Resistor
foil 20 is similar to resistor foil 10, and like elements are
designated with like reference numbers. Resistor foil 20 differs
from resistor foil 10 in that a tiecoat layer, designated 18, is
disposed between copper layer 12 and first layer 14. Tiecoat layer
18 is provided as an adhesion promoting layer to improve the
adhesion of layer 14 to copper layer 12.
[0038] Tiecoat 18 may be formed of the following metals: nickel,
palladium, titanium, tantalum, aluminum, iron, vanadium, chromium,
chromium-based alloys and nickel-based alloys. A metal tiecoat
layer 18 is applied to a clean surface of the copper. In a
preferred embodiment, tiecoat layer 18 is comprised of chromium.
The chromium tiecoat may be applied by a vacuum deposition process
such as sputtering, e-beam deposition or thermal evaporation.
Tiecoat 18 has a thickness greater than 5 .ANG.. Preferably, the
thickness of tiecoat 18 is between 5 .ANG. and 70 .ANG., and more
preferably, between about 10 .ANG. and about 20 .ANG..
[0039] Referring now to the use of resistor foil 10 or resistor
foil 20 in forming a resistive element, FIG. 3 shows resistor foil
20 adhered to a dielectric substrate 30. As will be appreciated
from a further reading of the specification, the following
discussion would also apply if resistor foil 10 is used. Resistor
foil 20 may be secured to dielectric substrate 30 using an adhesive
(not shown), or adhered to dielectric substrate 30 by a lamination
process, wherein dielectric substrate 30 is cured with resistor
foil 20 attached thereto. Methods of securing a resistor foil, such
as foils 10 and 20 are conventionally known, and the particular
method used in and of itself is not critical to the present
invention.
[0040] Resistor foil 20 is attached to dielectric substrate 30 with
second layer 16 closest to, and facing, substrate 30 (as shown in
FIG. 3), and with copper layer 12 exposed. Using conventionally
known processes of masking and etching, unwanted areas of resistor
foil 20 are etched away to leave a circuit pattern (not shown) on
the surface of dielectric substrate 30.
[0041] FIG. 4 is a perspective view of a portion of a circuit
showing a trace line 40 on substrate 30. A section, designated "X,"
of copper layer 12 is removed from trace line 40, by conventionally
known masking and etching techniques, to leave only first and
second layers 14, 16 of first and second resistor materials
connecting the spaced-apart ends of copper layer 12. In other
words, section X essentially forms a resistive element between the
spaced-apart ends of copper layer 12 of trace line 40. Any current
flow through trace line 40 must necessarily flow through first and
second layers 14, 16 of section X. Since first layer 14 has a
different resistance than second layer 16, the total resistance of
section X is a function of both layers 14, 16.
[0042] FIG. 4A is an electrical, schematic representation of the
resistance of section X. The resistive element shown in FIG. 4 is
the equivalent of two resistors R.sub.14, R.sub.16 in parallel,
where R.sub.14 is the resistance of first layer 14 in section X and
R.sub.16 is the resistance of second layer 16 in section X. The
total resistance, R.sub.TOTAL, of the resistive element shown in
FIG. 4 is determined by the following equation: 1 R TOTAL = ( R 14
) ( R 16 ) R 14 + R 16
[0043] FIG. 5 shows a variation to trace element 40, as shown in
FIG. 4, that produces a different resistive element. In the
embodiment shown in FIG. 5, first layer 14 is also etched away in
section X (by conventional masking and etching techniques), leaving
only second layer 16 in section X. The resistance of the element
shown in FIG. 5 is a function of resistance R.sub.16 of second
layer 16 in section X. The resulting resistive element is
equivalent to that schematically illustrated in FIG. SA. FIGS. 4-5A
thus show how two different resistive elements may be formed from
the same resistor foil 10 by merely changing the number of layers
removed, i.e., etched away, from trace line 40.
[0044] FIGS. 6 and 6A show still another embodiment of a resistive
element that may be formed from resistor foil 10. In the embodiment
shown in FIG. 6, resistor foil 10 has been masked and etched to
form a trace line (shown in cross-section in FIG. 6) and the trace
line masked and etched to form a resistive element having a central
section "X" and two sections "Y" adjacent thereto. In section X,
only second layer 16 remains. In sections Y, both first and second
layers 14 and 16 remain.
[0045] The resistance of the resultant structure is shown in FIG.
6A, wherein the resistance of sections Y are equivalent to two
resistors R.sub.14Y and R.sub.16Y in parallel, wherein R.sub.14Y is
the resistance of first layer 14 in section Y and R.sub.16Y is the
resistance of second layer 16 in section Y. The resistance of
section X is R.sub.16X which is the resistance of second layer 16
in section X. The total resistance of the structure shown in FIGS.
6 and 6A is the sum of the resistances of each section.
[0046] The resistive elements heretofore described were formed with
a resistor foil 10 having two layers of resistive materials
thereon, i.e., first layer 14 and second layer 16. FIG. 7 shows a
cross-sectional view of a resistive element formed from a resistor
foil 110 having three layers of resistor material thereon. Resistor
foil 110 has a copper layer 112, a first layer 114 of a first
resistive material, a second layer 115 of a second resistive
material and a third layer 116 of a third resistive material. Each
resistive material has a different resistivity such that each layer
114, 115 and 116 has a different resistance value. Resistor foil
110 is masked and etched to produce a central zone "X" comprised of
layer 116, intermediate sections "Y" comprised of layers 115 and
116 and outer sections "Z" comprised of layers 114, 115 and 116. As
shown in FIG. 7A, and like the structures previously discussed, the
resistance of the structure shown in FIG. 7 is the sum of
resistance of each of sections X, Y and Z, and the resistance of
sections Y and Z are determined by the respective resistances of
layers 114, 115 and 116 in parallel. FIG. 7 thus illustrates that a
resistor foil having more than two resistive layers may be formed
and a variety of different resistor values can be created.
[0047] Heretofore, single trace lines having resistive elements
formed therein have been described. FIG. 8 illustrates how a
circuit having a junction of three branches, designated A, B and C,
can be formed from resistor foil 10. FIG. 8 illustrates how
multiple branch trace lines having one or more branches with
different resistances may be formed.
[0048] The foregoing description discloses specific embodiments of
the present invention. These embodiments are described for purposes
of illustration only. Numerous alterations and modifications may be
practiced by those skilled in the art without departing from the
spirit and scope of the invention. It is intended that all such
modifications and alterations be included insofar as they come
within the scope of the invention as claimed or the equivalents
thereof.
* * * * *