U.S. patent number RE35,064 [Application Number 08/060,877] was granted by the patent office on 1995-10-17 for multilayer printed wiring board.
This patent grant is currently assigned to Circuit Components, Incorporated. Invention is credited to Jorge M. Hernandez.
United States Patent |
RE35,064 |
Hernandez |
October 17, 1995 |
Multilayer printed wiring board
Abstract
A multilayer printed wiring board is presented for surface
mounting or through hole technology, which includes one or more
layers of a high capacitance flexible dielectric sheet material.
The dielectric sheet is comprised of a monolayer of multilayer or
single layer high dielectric constant (e.g. ceramic) chips or
pellets of relatively small area and thickness which are arranged
in a planar array. These high dielectric constant chips are spaced
apart by a small distance. The spaces between the chips are then
filled with a flexible polymer/adhesive to define a cohesive sheet
with the polymer binding the array of high dielectric (e.g.
ceramic) chips together. Next, the opposite planar surfaces of the
array (including the polymer) are electroless plated or electroded
by vacuum metal deposition, or sputtering, to define opposed
metallized surfaces. The board of the present invention alleviates
the need for decoupling capacitors, thus resulting in significant,
space savings on the board surface.
Inventors: |
Hernandez; Jorge M. (Mesa,
AZ) |
Assignee: |
Circuit Components,
Incorporated (Tempe, AZ)
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Family
ID: |
46247937 |
Appl.
No.: |
08/060,877 |
Filed: |
May 12, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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226619 |
Aug 1, 1988 |
4908258 |
|
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Reissue of: |
291531 |
Dec 29, 1988 |
05065284 |
Nov 12, 1991 |
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Current U.S.
Class: |
361/763; 174/255;
174/256; 174/260; 361/321.2; 361/761; 361/762; 361/780; 361/783;
361/794; 361/795 |
Current CPC
Class: |
H01G
4/20 (20130101); H05K 1/0353 (20130101); H05K
1/162 (20130101); H05K 1/0298 (20130101); H05K
3/4611 (20130101); H05K 2201/0187 (20130101); H05K
2201/09309 (20130101) |
Current International
Class: |
H01G
4/20 (20060101); H01G 4/018 (20060101); H05K
1/03 (20060101); H05K 1/16 (20060101); H05K
3/46 (20060101); H05K 1/00 (20060101); H05K
001/18 (); H05K 001/11 () |
Field of
Search: |
;29/830,832,846,849
;174/250,255,260,261,256 ;257/723,724,778,700,532
;361/313,321,322,328,329,760,761,762,763,765,766,777,779,780,792,793,794,807
;439/47,68,69,74 ;428/209,901 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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8078411 |
|
May 1983 |
|
JP |
|
63-52446 |
|
Mar 1988 |
|
JP |
|
297158 |
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May 1954 |
|
CH |
|
Other References
IBM Disclosure Bul. "Packaging Of Integrated Circuits" by McIntosh
et al. vol. 15 No. 6 Nov. 1972 pp. 1977-1980. .
IBM Disclosure Bul. "Internal Capacitors and Resistors for
Multilayer Ceramic Modules" by Lussow vol. 20 No. 9 Feb. 1978 pp.
3436-3437. .
IBM Disclosure Bul. "Stress Avoidanc in Cofired Two Material
Ceramics" by Brownlow vol. 22 No. 9 Feb. 1980 pp. 4256 and 4257.
.
IBM Disclosure Bul. "Low Capacitive Via Path Through High
Dielectric Constant Material" by Narken et al. vol. 22 No. 12 May
1980 pp. 5330-5331. .
Electron Design Report (ISSCC Review Communication) Feb. 14, 1991.
.
Electronics "Trying to Keep up with Fast-Moving Chips" Oct. 15,
1987. .
Electronics Design Report "ISSCC Review Communications" Feb. 14,
1991. .
Electronics Products "PC-board Capacitance Without a Capacitor" by
Spencer Chin Nov. 1992. .
E.P. Search Report. .
English Translation of pp. 15-23 from Swiss Pat 297158..
|
Primary Examiner: Picard; Leo P.
Assistant Examiner: Sparks; Donald A.
Attorney, Agent or Firm: Fishman, Dionne & Cantor
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation-in-bart of U.S. application Ser. No. 226,019
filed Aug. 1, 1988 now U.S. Pat. No. 4,908,258.
Claims
What is claimed is:
1. A multilayer circuit board comprising:
a first layer of insulating material having opposed first and
second surfaces;
a second layer of insulating material having opposed first and
second surfaces;
a first conductive layer on at least a portion of said first
surface of said first layer of insulating material;
a second conductive layer on at least a portion of said first
surface of said second layer of insulating material;
at least one high dielectric flexible sheet between .Iadd.and in
contact with .Iaddend.said second surfaces of said first and second
layers of insulating material, said high dielectric flexible sheet
including:
(a) an array of spaced high dielectric chips arranged in a single
layer, each of said chips having side, top and bottom surfaces;
(b) a flexible polymeric binder between said side surfaces of said
chips and binding said chips to define a cohesive sheet having
opposed first and second planar surfaces with said top and bottom
surfaces of said chips being exposed on said respective first and
second surfaces, said binder being selected from the group
consisting of flexible thermoplastics and flexibilized
thermosets;
(c) a first metallized layer defining a first voltage level plane
on said first planar surface; and
(d) a second metallized layer defining a second voltage level plane
on said second planar surface.
2. The board of claim 1 wherein:
said chips comprise a sintered ceramic material.
3. The board of claim 2 wherein:
said ceramic material is selected from the group consisting of
bariun titanate, lead magnesium niobate or iron tungsten
niobate.
4. The board of claim 1 wherein:
said chips have a shape which is selected from the group consisting
of cylindrical, rectangular or square.
5. The board of claim 1 including:
at least one groove formed in said chips to enhance mechanical
binding with said polymeric binder.
6. The board of claim 1 wherein:
said chips comprise multilayer capacitive elements having exposed
top and bottom electrodes which electrically contact respective of
said first and second metallized layers.
7. The board of claim 1 wherein:
said first and second metallized layers are comprised of a material
selected from the group consisting of copper, nickel or tin.
8. The board of claim 1 wherein:
said high dielectric chip has a dielectric constant of at least
10,000.
9. The board of claim 1 including:
at least one first via connecting said first conductive layer to
said first voltage level plane; and at least one second via
connecting said second conductive layer to said second voltage
level plane.
10. The board of claim 9 including:
an opening through said high dielectric flexible sheet; and
at least one of said first or second vias passing through said
opening.
11. The board of claim 1 including:
at least one plated through hole interconnecting said first and
second conductive layers, said plated through hole being out of
contact with said first and second voltage level planes.
12. The board of claim 1 including:
a plurality of adjacent high dielectric flexible sheets between
said first and second layers of insulating material.
13. The board of claim 1 wherein:
said first and second conductive layers each comprise respective
first and second conductive patterns.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a multilayer printed wiring
board, either for surface mounting or through hole technology.
More, particularly this invention relates to a multilayer printed
wiring board which incorporates a high dielectric constant sheet
material.
It wiil be apreciated that there is an ever increasing need for a
reliable, flexible high dielectric material which may be used for a
variety of applications in electronic circuitry design and
manufacture. Presently, flexible high dielectric materials of this
type are manufactured by mixing small particles (e.g. 1-3 microns)
of a high dielectric constant material into a flexible polymeric
matrix. Surprisingly, the resultant effective dielectric constant
of the dielectric impregnated polymer is relatively low. For
example, the dielectric constant of a Z5U BaTiO.sub.3 is in the
range of 10,000 to 12,000. However, when such Barium Titanate is
mixed with a flexible polymer such as polyimide, polyester,
polyetherimide and like materials, the effective dielectric
constant relizable is only on the order of 20 to 40 (depending on
the loading ratio of the dielectric in the polymer).
It will be further appreciated that a need exists for a multilayer
printed circuit board which provides power distribution free of the
need for decoupling capacitors. This is because decoupling
capacitors take up space on the surface of the surface of the
board. This space can be used for integrated circuit chips or other
functional components thereby increasing the amount of functional
area on the board. Attempts have been made to construct a board
which provides both power distribution and decoupling. One prior
art attempt involves reducing the thickness of the dielectric layer
between the voltage and ground planes. This attempt has proven
unsatisfactory because of manufacturing problems. Because of the
reduced thickness of the dielectric layer, pin holes are formed in
it thereby resulting in electrical shorting of the circuit board.
Also, the capacitance of the board varies with changes in the
thickness of the dielectric layer. Another prior art board uses as
a dielectric a suitable polymer filled with a high dielectric
constant material such as barium titantate. The filed polymer is
placed between the voltage and ground planes to create a capacitor
effect. This prior art multilayer board has proven ineffective
because the filled polymer has an effective dielectric constant of
no more than about 80-100, which is too low for adequate
results.
SUMMARY OF THE INVENTION
The above-discussed and other problems and deficiencies of the
prior art are overcome or alleviated by the multilayer circuit
board of the present invention which incorporates a high dielectric
constant flexible sheet material. In accordance with the present
invention, this high capacitance flexible dielectric material is
comprised of a monolayer of multilayer or single layer high
dielectric constant (e.g. ceramic) chips or pellets of relatively
small area and thickness which are arranged in a planar array.
These high dielectric constant chips are spaced apart by a small
distance. The spaces between the chips are then filled with a
flexible polymer/adhesive to define a cohesive sheet with the
polymer binding the array of high dielectric constant (e.g.
ceramic) chips together. Next, the opposite planar surfaces of the
array (including the polymer) are metallized (e.g. electroless
plated or metallized by vacuum deposition, sputtering, etc.) to
define opposed metailized surfaces. The end result is a relatively
flexible high capacitance dielectric film or sheet material which
is drillable, platable, printable, etchable, laminable and
reliable.
In a preferred embodiment, the small high dielectric chips are
cylindrical in shape. However, the chips may be any other suitable
shape including rectangular. Also, the high dielectric constant
chips may includes punches or cut-outs to improve mechanical
adhesion between the chips and the polymeric binding material.
Also as mentioned above, rather than using high dielectric constant
(ceramic) pellets, the discrete high dielectric monolayer may be
comprised of an array of multilayer ceramic chips such as those
disclosed at FIGS. 4 and 10 in U.S. Pat. No. 4,748,537 and at FIGS.
11-16 and U.S. Pat. No. 4,706,162, all of which are assigned to the
assignee hereof and incorporated herein by reference.
The high capacitance flexible dielectric sheet of the present
invention may be used in a large number of applications in the
electronic circuitry design and manufacturing fields. For example,
the high dielectric flexible sheet may be used for forming
multilayer circuit boards, or in the manufacture of decoupling
capacitors or bus bars.
The multilayer printed circuit board of the present invention
provides a circuit board which both decouples and distributes
power. The multilayer printed circuit board of the present
invention may be comprised of multiple layers of insulative
material with the central layer being comprised of the high
dielectric constant flexible sheet. The metallized surfaces of the
high dielectric constant sheet act as the voltage and ground planes
of the circuit board. On the surface of the board is provided a
printed metallic pattern which defines the circuit. Because this
board can be used free of decoupling capacitors, it provides the
user with a higher packing density of functional components on the
surface of the board.
The above discussed and other features and advantages of the
present invention will be appreciated and understood by those of
ordinary skill in the art from the following detafied description
and drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, wherein like elements are numbered
alike in the several FIGURES:
FIG. 1 is a perspective view of the high dielectric flexible sheet
material of the present invention;
FIG. 2 is a cross-sectional elevation view along the line 2--2 of
FIG. 1;
FIG. 3 is a perspective view, similar to FIG. 1 of a different
embodiment of the present invention;
FIG. 4 is a cross-sectional elevation view along the line 4-4 of
FIG. 3;
FIGS. 5A. 5B and 5C are perspective views of alternative high
dielectric constant pellet configurations which may be used in
accordance with the present invention;
FIG. 6 is a cross-sectional elevation view of still another
embodiment of the present invention utilizing multilayer capacitive
elements;
FIG. 7 is a cross-sectional elevation view similar to FIG. 6,
subsequent to metallization; and
FIG. 8 is a cross-sectional elevation view similar to FIG. 7, and
subsequent to additional metallization.
FIG. 9 is a cross-sectional plated side elevation view of the multi
layer pnnted circuit board of the present invention;
FIG. 10 is a prospective view with sections cut away of the board
of FIG. 9;
FIG. 11 is a cross-sectional partial side elevation view of the
circuit board of FIG. 9 with plated through holes;
FIG. 12 is a cross-sectional of the circuit board of FIG. 9 with a
surface mounted IC; and
FIG. 13 is a cross-sectional elevation view of the circuit board of
FIG. 9 incorporating a pair of internal high dielectric constant
flexible sheets.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention relates to a multilayer circuit board incorporating
a high dielectric constant sheet material. Referring first to FIGS.
1 and 2, the high dielectric constant flexible polymeric sheet
material is shown generally at 10. Flexible sheet 10 is comprised
of a monolayer of high dielectric constant pellets or chips 12
which are of relatively small area and thickness and are arranged
in a planar array. The chips are separated from each other by a
small distance to define spaces therebetween. The spaces between
the chips 12 are filled with a suitable polymeric material 14.
Polymeric material 14 will act as a binder to hold the array of
high dielectric constant pellets 12 together. Significantly,
polymeric material 14, will contact only the sides of pellets 12
and will be out of contact with the top and bottom surfaces 16 and
18 of each pellet 12. This will result in both end surfaces 16, 18
of high dielectric constant pellets 12 and end surfaces 20, 22 of
polymeric binder 14 being exposed. Next, these opposed and exposed
surfaces (comprised of surfaces 16 and 20 on the one hand and
surfaces 18 and 22 on the other hand) of the pellet array and
polymer are metalized to define a thin (e.g. about 10-50 micro
inches) metallized layer 24 and 26. These thin metallized layers 24
and 26 may then be plated up to higher thicknesses (e.g. about 1-2
mils) by well known electroplating techniques to define layers 28
and 30. The thin metallized layers may be produced using any known
method including by electroless plating or by vapor deposition
techniques including vacuum deposition, sputtering, etc.
The material used to produce high dielectric constant pellets 12
may be any suitable high dielectric constant material and is
preferably a high dielectric constant ceramic material such as
BaTiO.sub.3. In addition, other known high dielectric ceramic
materials may be utilized including lead magnesium niobate, iron
tungsten niobate, etc. It will be appreciated that by "high"
dielectric constant, it is meant dielectric constants of over about
10,000. As mentioned, the pellets are relatively small and are
preferably cylindrical in shape having a height of 0.015" and a
diameter of 0.020". If a ceramic is used, the pellets should be
fully sintered prior to being bonded together by the polymer.
Of course, while cylindrical configurations for the array of
pellets 12 are preferred, any other suitably shaped high dielectric
constant pellet may be used. For example, in FIG. 3, a flexible
high capacitance sheet is shown at 32 incorporating an array of
rectangularly shaped pellets 34 in a polymer matrix 36. Also, in
FIGS. 5A-5C, square shaped pellets are shown at 38,39 and 40
respectively which are provided with from two through eight slots
or grooves 42. It will be appreciated that these grooves or slots
will provide a stronger mechanical bond between the polymeric
binder and the pellet.
The pellet array is impregnated with a suitable polymer which may
be a either a flexible thermoplastic or a flexibilized thermoset
(epoxy, polyetherimide, polyester, etc.) to give the array
mechanical strength and electrical insulating stability with
temperature, moisture, solvents, etc. The polymeric material should
be a high temperature (approximately 350.degree. F.) polymer which
is somewhat flexible and has a dielectric constant of between about
4-9. Preferred materials include polyetherimides, polyimides,
polyesters and epoxies. It will be appreciated that the flexibility
is necessary to preclude cracking of the sheet under stress.
Preferably, the dielectric sheet is electroless plated with copper
or nickel.
The resultant sheet material will have an effective high dielectric
constant of better than 1,000, a small thickness (approximately
0.005"-0.015"), will be flexible, will be metallized on both sides
and will be drillable and platable.
EXAMPLES
A mathematical analysis can be made to determine the effective
dielectric constant of the combined pellet array and polymeric
matrix.
EXAMPLE 1
For example, using a dietecmc sheet as depicted in FIGS. 1 and 2
which incorporates cylindrical pellets measuring 0.020" in diameter
by 0.010" in length; and assuming a sheet of one square inch having
a total of about 2,500 cylinders. Capacitance of the dielectric
sheet is determined using the following formula:
where
C=total capacitance
.epsilon.=relative permitivity of the dielectric
.epsilon..sub.o =permitivity of free space
a=area of electroded part of dielectric
D=distance between two electrodes of dielectric
N=number of dielectric pellets
Assuming that the pellets are made of a Z5U dielectric with a
dielectric constant of 15,000, then the capacitance of such an
array would be:
.epsilon.=15,000
.epsilon..sub.o =8.85.times.10.sup.-12
a=2.827.times.10 .sup.-7 m.sup.2
D=3.times.10.sup.-4 m
N=2500
Thus: ##EQU1## or
C=312 nF/sq.-in, or 312,500 pF/sq in.
If an X7R dielectric with a dielectric constant of 4500) is
utilized, then using the above equation (1), the capacitance per
square inch would be about 93.6 nF/sq.in.
EXAMPLE 2
If a rectangular ceramic pellet (such as shown in FIG. 3) made from
lead magnesium niobate (having a dielectric constant of 17,000) is
selected with each pellet having surface area dimensions of
0.2041.times.0.30" and 0.015" in thickness; and with the array of
pellets being spaced apart 0.020", then, using the same
calculations as in Example 1, the capacitance will be 224 nF/sq in.
Alternately, if an internal boundary layer dielectric is selected
with a dielectric constant of approximately 60,000 [such as
(Sr.sub.0.4 Ba.sub.0.6) TiO.sub.3 +10H.sub.2 O] then the effective
capacitance per square inch will be equal to 759 n F./sq.in.
Still another embodiment of the present invention is shown in FIGS.
6-8. In this embodiment, rather than using high dielectric constant
pellets of homogeneous composition, a multilayer capacitive element
44 is utilized. Capacitive element 44 is a known multilayer ceramic
chip capacitor (such as disclosed in aforementioned U.S. Pat. Nos.
4,745,537 and 4,706,162) comprised of a plurality of metallized
layers 46 with alternating layers being connected to end electrodes
48 and 50. The top and bottom surfaces of multilayer chip 44
includes exposed electrodes 52 and 54 which are also connected to
opposed end electrodes 48 and 50, respectiveiy. Finally, an
insulating cap 56 is provided on each end electrode 48 and 50 to
prevent shorting between an exposed top or bottom electrode 52, 54
and one of the end electrodes 48 and 50. As in the previously
discussed embodiments of FIGS. 1-4, in this latter embodiment, a
plurality of multilayer capacitive elements 44 are arranged in a
monolayer array and a suitable polymeric adhesive 58 is used to
bind the side edges of the multilayer chips 44 together. As shown
in FIG. 6, this will typically result in an undulating surface
between the polymer 58 and each multilayer capacitive element 44.
As shown in FIG. 7, the array can then be electroless plated with
copper, nickel, tin or any other suitable plating material to
define thin metallized outer layers 60 and 62. Of course the
undulating surface features may be eliminated by sufficiently
building up the thickness of the plated electrodes and then
grinding or lapping them to define a planar outer surface as in
FIG. 8.
It will be appreciated that the capacitance per unit area for the
FIGS. 6-8 embodiment of the present invention will depend upon the
size of the chips, the number of the chips per unit area, the
capacitance of individual chips and the thickness of the chips.
EXAMPLE 3
As an illustration of the levels of capacitance achievable with the
embodiment of FIGS. 6-8, a flexible sheet of the type shown in FIG.
8 using multilayer capacitive elements 44 having length dimensions
of 0.35", width dimensions of 0.20" anti thickness dimensions of
0.018" will be discussed. The dielectric used in the capacitive
element is a lead magnesium niobate dielectric wherein capacitance
on an average of 1.0 micro F/chip is obtainable. Next, assuming a
0.030" gap between chips in the chip array, there would be 4.4
chips in the y direction and 3.03 chips in the x direction for a
total of 13.33 chips per square inch or a total capacitance of
13.33 micro F./sq.in. This is compared to the far lower capacitance
obtained from using the embodiment of FIG. 1 (see Example 1) of
0.312 micro F./sq. in.
Refernng now to FIGS. 9-12, a high capacitance multilayer printed
circuit board in accordance with the present invention is shown
generally at 90. Circuit board 90 comprises a pair of exterior
electrically insulative layers 92 and 94 which sandwich
therebetween a high dielectric flexible layer 96 of the type
described in detail with regard to FIGS. 1-8. Each insulative sheet
92 and 94 include circuit patterns 98 and 100 respectively thereon.
As described in detail above, flexible dielectric sheet 96
comprises a planar layer of spaced ceramic chips 102 separated by a
flexible polymeric material 104. Dielectric chips 102 and polymeric
material 104 include a planar or otherwise deposited upper
electrode 106 and lower electrode 108. Electrode layers 106 and 108
will act as the voltage and ground planes for the multilayer
circuit board 90. Thus, high dielectric flexible layer 96 will
function as a decoupling capacitor when a circuit component is
electrically attached to board 90. This important feature of the
present invention eliminates the need for discrete decoupling
capacitor elements and frees valuable board space on the surface of
board 90. Insulative layers 92 and 94, may comprise any suitable
insulative material including well known circuit board materials
FR-4, G-10, G-11 and the like.
High dielectric flexible sheet 96 may be altered to fine tune
physical parameters on board 90 for particular uses. Also, multiple
layers of sheet may be used to provide many voltage planes and
interconnections. The thickness of layers 96 may be altered to vary
the capacitance of board 90. Because of the design of flexible
sheet 96, the capacitance per unit area of the dielectric layer may
be varied to a predetermined level. The thickness of electrodes 106
and 108 may also be varied to change the current carrying capacity
of the voltage planes and the ground planes. The temperature
stability of sheet 96 may also be adjusted.
In addition to simultaneously providing both power distribution and
decoupling, and eliminating the need for discrete alecoupling
capacitors, the multilayer circuit board of the present invention
provides many other advantages. Board 90 eliminates the need for
expensive pick and place machinery for decoupling capacitors. It
also eliminates solder quality problems inherent with decoupling
capacitors. Moreover, flexible high dielectric sheet 96 makes
multilayer board 90 more dense, more reliable, less costly to
assemble, and also improves heat dissipation by virtue of ceramic
elements 102 in the flexible dielectric layers.
The multilayer circuit board incorporanng the flexible high
dielectric constant sheet in accordance with the present invention
may be used with either through hole technology or in surface mount
applications. For example, in FIG. 11, a dual-in-line integrated
circuit package 110 includes a plurality of leads 112 which are
mounted in plated through holes 114 in multilayer circuit board
90A. Circuit board 90A is substantially similar to circuit board 90
of FIGS. 9 and 10 with the exception that plated through holes 114
are provided to interconnect circuit patterns 98 and 100 on the two
outer surfaces of the board.
In FIG. 12, a surface mount integrated circuit package 116 is shown
on a multilayer circuit board 90B wherein vias 118 and 120 have
been provided to interconnect with the flexible dielectric sheet 96
withn circuit board 90B. Note that a hole 122 has been drilled
through flexible sheet 96 to permit attachment between the lower
electrode 108 and via 120.
Turning now to FIG. 13, as mentioned, a plurality of flexible
dielectric sheets 96 may be used in the multilayer circuit board of
the present invention. Thus, in FIG. 13, a pair of flexible
dielectric sheets 124 and 126 are mounted adjacent one another to
provide a pair of outer voltage planes 128 and 130 and an inner
ground plane 132. As in the embodiment of FIG. 12, holes are
drilled in the flexible high dielectric sheets to provide
attachment with the several voltage planes 128, 130 and ground
plane 132. Of course, any number of flexible dielectric sheets may
be stacked up within the circuit board so as to obtain relatively
high preselected capacitance values.
While preferred embodiments have been shown and described, various
modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustrations and not limitation.
* * * * *