U.S. patent application number 13/567822 was filed with the patent office on 2012-11-29 for high voltage capacitors.
This patent application is currently assigned to VISHAY SPRAGUE, INC.. Invention is credited to JOHN BULTITUDE, JOHN JIANG, JOHN ROGERS.
Application Number | 20120297596 13/567822 |
Document ID | / |
Family ID | 40381922 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120297596 |
Kind Code |
A1 |
BULTITUDE; JOHN ; et
al. |
November 29, 2012 |
HIGH VOLTAGE CAPACITORS
Abstract
In a method of manufacturing a multilayer ceramic component, a
ceramic capacitor body is formed from electrode layers and
dielectric layers. First and second external terminals are attached
on opposite ends of the ceramic capacitor body. The ceramic
capacitor body is coated to assist in increasing breakdown voltage.
The electrode layers include active electrode layers configured in
an alternating manner such that a first end of the active
electrodes extends from one end of the ceramic capacitor body
inwardly and a next internal active electrode extends from an
opposite end of the ceramic capacitor body inwardly. The active
electrode layer includes side shields to provide additional
shielding.
Inventors: |
BULTITUDE; JOHN; (MONROE,
CT) ; JIANG; JOHN; (MILFORD, CT) ; ROGERS;
JOHN; (SEYMOUR, CT) |
Assignee: |
VISHAY SPRAGUE, INC.
SANFORD
ME
|
Family ID: |
40381922 |
Appl. No.: |
13/567822 |
Filed: |
August 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12189492 |
Aug 11, 2008 |
8238075 |
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13567822 |
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11359711 |
Feb 22, 2006 |
7336475 |
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12189492 |
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Current U.S.
Class: |
29/25.42 |
Current CPC
Class: |
Y10T 29/435 20150115;
H01G 4/012 20130101; H01G 4/30 20130101; H01G 4/232 20130101 |
Class at
Publication: |
29/25.42 |
International
Class: |
H01G 4/12 20060101
H01G004/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2006 |
US |
PCT/US06/23338 |
Claims
1. A method of manufacturing a multilayer ceramic component,
comprising: forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
and coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises layers of active electrodes and layers of shielding
electrodes and wherein the layers of active electrodes are
configured in an alternating manner such that a first of the
plurality of active electrodes extends from one end of the ceramic
capacitor body inwardly and a next internal active electrode
extends from an opposite end of the ceramic capacitor body
inwardly; wherein the layers of shielding electrodes comprise a top
internal electrode shield and an opposite bottom internal electrode
shield wherein the top internal electrode shield and the opposite
bottom internal electrode shield are on opposite sides of the
plurality of active electrodes and each electrode shield extends
inwardly to or beyond a corresponding external terminal to provide
shielding; wherein the layers of active electrodes further comprise
layers of side shields on opposite sides of the active electrodes
to provide additional shielding.
2. The method of claim 1 wherein the coating comprises depositing a
polyimide on an outer surface of the ceramic capacitor body.
3. The method of claim 1 wherein the coating is spin coated.
4. A method of manufacturing a multilayer ceramic component,
comprising: forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
and coating the ceramic capacitor body; wherein the plurality of
electrode layers comprises layers of active electrodes and layers
of shielding electrodes and wherein the layers of active electrodes
are configured in an alternating manner such that a first of the
plurality of active electrodes extends from one end of the ceramic
capacitor body inwardly and a next internal active electrode
extends from an opposite end of the ceramic capacitor body
inwardly; wherein the layers of active electrodes further comprise
layers of side shields on opposite sides of the active electrodes
to provide shielding.
5. The method of claim 4 wherein the coating comprises depositing a
polyimide on an outer surface of the ceramic capacitor body.
6. The method of claim 4 wherein the coating is spin coated.
7. A method of manufacturing a multilayer ceramic component,
comprising: forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
and coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises layers of active electrodes and layers of shielding
electrodes and wherein the layers of active electrodes are
configured in an alternating manner such that a first of the
plurality of active electrodes extends from one end of the ceramic
capacitor body inwardly and a next internal active electrode
extends from an opposite end of the ceramic capacitor body
inwardly; wherein the layers of shielding electrodes comprise a top
internal electrode shield and an opposite bottom internal electrode
shield wherein the top internal electrode shield and the opposite
bottom internal electrode shield are on opposite sides of the
plurality of active electrodes and each electrode shield extends
inwardly to or beyond a corresponding external terminal to provide
shielding; wherein the layers of active electrodes further comprise
side shields to provide additional shielding.
8. A method of manufacturing a multilayer ceramic component,
comprising: forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
and coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises active electrodes and shielding electrodes and wherein
the active electrodes are configured in an alternating manner such
that a first of the plurality of active electrodes extends from one
end of the ceramic capacitor body inwardly and a next active
electrode extends from an opposite end of the ceramic capacitor
body inwardly; wherein the layers of active electrodes further
comprise side shields to provide shielding.
9. A method of manufacturing a multilayer ceramic component,
comprising: forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
and coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises a plurality of active electrode layers being configured
in an alternating manner such that a first end of the plurality of
active electrodes extends from one end of the ceramic capacitor
body inwardly and a next internal active electrode extends from an
opposite end of the ceramic capacitor body inwardly; wherein the
active electrode layer further comprises side shields to provide
additional shielding.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/189,492, filed Aug. 11, 2008, now U.S. Pat.
No. 8,238,075, and a continuation-in part of PCT Application No.
PCT/US06/23338, filed Jun. 15, 2006, which claims priority to U.S.
patent application Ser. No. 11/359,711 filed Feb. 22, 2006, now
U.S. Pat. No. 7,336,475, which are incorporated by reference as if
fully set forth.
BACKGROUND
[0002] Multilayer ceramic capacitors generally have alternating
layers of ceramic dielectric material and conductive electrodes.
Various types of dielectric materials can be used and various types
of physical configurations have been used. Capacitors for high
voltage performance have been produced for many years using a
"series design". In the series design the charge is stored between
the floating electrode and electrodes connected to the terminals on
either side as shown for a single floating electrode designs in
FIG. 1. This compares to a standard capacitor design shown in FIG.
2 in which the electrodes alternatively connect to different
terminals and the charge is stored between these electrodes. The
capacitance for these designs is given by:
C=.epsilon..sub.o.epsilon..sub.rAN./T
Where C=Capacitance in F
[0003] .epsilon..sub.o=Permittivity of Free
Space=8.854.times.10.sup.-12 Fm.sup.-1 [0004]
.epsilon..sub.r=Permittivity of the Ceramic Material, a material
dependent dimensionless constant [0005] A=Effective Overlap Area of
Electrodes m.sup.2 [0006] N=Number of electrodes-1 [0007] T=Fired
Active Thickness of Ceramic Separating the Layers
[0008] However, in the case of the series design the effective
overlap area is significantly reduced. The advantage of the series
design is that the internal voltage acting on the electrodes is
halved for the single floating electrode. It is possible to further
separate the floating electrode to give more than one floating
electrode per layer to reduce the internal voltage but this also
lowers the effective overlap area reducing capacitance. The average
voltage breakdowns (n=50) for 27 lots of case size 1812 MLCCs, 47
nF.+-.10% standard designs and the same number of case size 1812,
22 nF.+-.10% single floating electrode series designs are shown in
FIG. 3. In all these cases the fired active thickness separating
the electrodes was 0.0023'', 58 microns with an overall thickness
of 0.051.+-.0.003'' (1.30.+-.10 0.08 mm) for the standard design
and 0.068.+-.0.003'' (1.73.+-.0.08 mm) for the series capacitors.
The length and width dimensions were 0.177.+-.0.0 10''
(4.50.+-.0.25 mm) and 0.126.+-.0.008'' (3.20.+-.0.20 mm)
respectively for all these 18 12 case size capacitors.
Cross-sections of the 1812 standard design and the single electrode
series design are shown in FIGS. 4 and 5 respectively.
[0009] In addition to the internal voltage withstanding capability
of these MLCCs it is also critical that these parts are resistant
to arc-over from the capacitor terminals. U.S. Pat. No. 4,731,697,
to McLarney discloses a surface electrode with portions of the
margin covered by a further dielectric layer to prevent arc over
that requires laser trimming. However, it is important to note that
exposed electrodes are subject to corrosion. Also the properties of
exposed electrodes are significantly impacted by the environment
factors, such as humidity, limiting the applications in which these
capacitors can be used.
[0010] U.S. Pat. No. 6,627,509 to Duva discloses a method for
producing surface flashover resistant capacitors by applying a
para-poly-xylylene coating to the surface of multilayer ceramic
capacitors followed by trimming the excess material from the
terminals. In this case significant costs are associated with
coating of the capacitors. Furthermore, the coating may not be
compatible with the circuit board assembly processes and the
presence of organic coatings in some electronic application such as
satellites is limited because of out gassing concerns.
[0011] Thus, despite various efforts to reduce produce capacitors
with high voltage breakdown and which minimize occurrence of arc
over, problems remain. What is needed is an improved high voltage
capacitor.
SUMMARY
[0012] Therefore, it is a primary object, feature, or advantage of
the present invention to improve upon the state of the art.
[0013] It is a further object, feature, or advantage of the present
invention to provide a multilayer ceramic capacitor which is
resistant to arc-over.
[0014] It is a still further object, feature, or advantage of the
present invention to provide a multilayer ceramic capacitor with
high voltage breakdown in air.
[0015] A still further object, feature, or advantage of the present
invention is to provide a multilayer ceramic capacitor with a
design which retains high capacitance.
[0016] Another object, feature, or advantage of the present
invention is to minimize the occurrence of unwanted disruptions due
to arc-over when the capacitor is incorporated into an electronic
circuit.
[0017] Yet another object, feature, or advantage of the present
invention is to provide a capacitor with high voltage withstanding
capability with a smaller case size allowing for miniaturization of
circuits.
[0018] A further object, feature, or advantage of the present
invention is to provide an improved capacitor which can be
manufactured conveniently and economically.
[0019] One or more of these and/or other objects, features, or
advantages of the present invention will become apparent from the
specification and claims that follow.
[0020] According to one aspect of the present invention, a
multilayer ceramic capacitor component is provided. The capacitor
component includes a ceramic capacitor body having opposite ends
and comprised of a plurality of electrode layers and dielectric
layers. The capacitor component further includes first and second
external terminals attached to the ceramic capacitor body. The
capacitor component also includes a plurality of internal active
electrodes within the ceramic capacitor body configured in an
alternating manner such that a first of the plurality of internal
active electrodes extends from one end of the ceramic capacitor
body inwardly and a next internal active electrode extends from an
opposite end of the ceramic capacitor body inwardly. There is also
a plurality of internal electrode shields within the ceramic
capacitor body to thereby assist in providing resistance to
arc-over. The plurality of internal electrode shields include a top
internal electrode shield and an opposite bottom internal electrode
shield wherein the top internal electrode shield and the opposite
bottom internal electrode shield are on opposite sides of the
plurality of internal active electrodes and each internal electrode
shield extends inwardly to or beyond a corresponding external
terminal to thereby provide shielding. There are also side shields.
Each side shield extends inwardly from one end of the capacitor
body and the side shields are configured to further shield an
active electrode to thereby further resist arc over between active
electrodes and terminals. A coating is on the ceramic capacitor
body to assist in increasing breakdown voltage.
[0021] According to another aspect of the present invention, a
multilayer ceramic capacitor component for providing improved high
voltage characteristics is provided. The capacitor includes a
ceramic capacitor body having opposite ends and comprised of a
plurality of electrode layers and dielectric layers. First and
second external terminals are attached to the ceramic capacitor
body. The plurality of electrode layers include a top layer having
an electrode shield extending inwardly to or beyond the first
terminal, a bottom layer having an electrode shield extending
inwardly to or beyond the second terminal, and a plurality of
alternating layers of active electrodes extending inwardly from
alternating ends of the ceramic capacitor body. Each of the
alternating layers of active electrodes also includes side shields.
A coating on the ceramic capacitor body assists in increasing
breakdown voltage.
[0022] According to another aspect of the present invention a
method of manufacturing a multilayer ceramic component is provided.
The method includes forming a ceramic capacitor body from a
plurality of electrode layers and dielectric layers and attaching
first and second external terminals on opposite ends of the ceramic
capacitor body. The plurality of electrode layers comprises layers
of active electrodes and layers of shielding electrodes and wherein
the layers of active electrodes are configured in an alternating
manner such that a first of the plurality of active electrodes
extends from one end of the ceramic capacitor body inwardly and a
next internal active electrode extends from an opposite end of the
ceramic capacitor body inwardly. The layers of shielding electrodes
include a top internal electrode shield and an opposite bottom
internal electrode shield wherein the top internal electrode shield
and the opposite bottom internal electrode shield are on opposite
sides of the plurality of active electrodes and each electrode
shield extends inwardly to or beyond a corresponding external
terminal to thereby provide shielding. The layers of active
electrodes also include layers of side shields on opposite sides of
the active electrodes to thereby provide additional shielding. A
coating on the ceramic capacitor body assists in increasing
breakdown voltage.
[0023] A multilayer ceramic capacitor component comprising a
ceramic capacitor body having opposite ends and comprised of a
plurality of electrode layers and dielectric layers; first and
second external terminals attached to the ceramic capacitor body; a
plurality of internal active electrodes within the ceramic
capacitor body configured in an alternating manner such that a
first of the plurality of internal active electrodes extends from
one end of the ceramic capacitor body inwardly and a next internal
active electrode extends from an opposite end of the ceramic
capacitor body inwardly; a plurality of internal electrode shields
within the ceramic capacitor body to thereby assist in providing
resistance to arc-over; the plurality of internal electrode shields
comprising a plurality of side shields, each side shield extending
inwardly from one end of the capacitor body and the side shields
configured to shield a corresponding active electrode to thereby
resist arc over between active electrodes and terminals; and a
coating on the ceramic capacitor body to assist in increasing
breakdown voltage.
[0024] A method of manufacturing a multilayer ceramic component,
comprising forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
coating the ceramic capacitor body; wherein the plurality of
electrode layers comprises layers of active electrodes and layers
of shielding electrodes and wherein the layers of active electrodes
being configured in an alternating manner such that a first of the
plurality of active electrodes extends from one end of the ceramic
capacitor body inwardly and a next internal active electrode
extends from an opposite end of the ceramic capacitor body
inwardly; wherein the layers of active electrodes further comprise
layers of side shields on opposite sides of the active electrodes
to thereby provide shielding.
[0025] A multilayer ceramic capacitor component comprising a
ceramic capacitor body having opposite ends and comprised of a
plurality of electrode layers and dielectric layers; first and
second external terminals attached to the ceramic capacitor body; a
plurality of internal active electrodes within the ceramic
capacitor body configured in an alternating manner such that a
first of the plurality of internal active electrodes extends from
one end of the ceramic capacitor body inwardly and a next internal
active electrode extends from an opposite end of the ceramic
capacitor body inwardly; a plurality of internal electrode shields
within the ceramic capacitor body to thereby assist in providing
resistance to arc over; each of the internal electrode shield
extends inwardly to or beyond a corresponding external terminal to
thereby provide shielding; the plurality of internal electrode
shields comprising a plurality of side shields, each side shield
extending inwardly from one end of the capacitor body and the side
shields configured to shield the internal active electrode to
thereby further resist arc over between the internal active
electrodes and the terminals; and a coating on the ceramic
capacitor body to assist in increasing breakdown voltage.
[0026] A multilayer ceramic capacitor component for providing
improved high voltage characteristics, comprising a ceramic
capacitor body having opposite ends and comprised of a plurality of
electrode layers and dielectric layers; first and second external
terminals attached to the ceramic capacitor body; wherein the
plurality of electrode layers comprise a top layer having an
electrode shield extending inwardly to or beyond the first
terminal, a bottom layer having an electrode shield extending
inwardly to or beyond the second terminal, and a plurality of
alternating layers of active electrodes extending inwardly from
alternating ends of the ceramic capacitor body; a plurality of side
shields disposed within the plurality of alternating layers of
active electrodes to provide shielding; and a coating on the
ceramic capacitor body to assist in increasing breakdown
voltage.
[0027] A method of manufacturing a multilayer ceramic component,
comprising forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises layers of active electrodes and layers of shielding
electrodes and wherein the layers of active electrodes being
configured in an alternating manner such that a first of the
plurality of active electrodes extends from one end of the ceramic
capacitor body inwardly and a next internal active electrode
extends from an opposite end of the ceramic capacitor body
inwardly; wherein the layers of shielding electrodes comprise a top
internal electrode shield and an opposite bottom internal electrode
shield wherein the top internal electrode shield and the opposite
bottom internal electrode shield are on opposite sides of the
plurality of active electrodes and each electrode shield extends
inwardly to or beyond a corresponding external terminal to thereby
provide shielding; wherein the layers of active electrodes further
comprise side shields to thereby provide additional shielding.
[0028] A multilayer ceramic capacitor component comprising a
ceramic capacitor body having opposite ends and comprised of a
plurality of electrode layers and dielectric layers; first and
second external terminals attached to the ceramic capacitor body; a
plurality of internal active electrodes within the ceramic
capacitor body configured in an alternating manner such that a
first of the plurality of internal active electrodes extends from
one end of the ceramic capacitor body inwardly and a next internal
active electrode extends from an opposite end of the ceramic
capacitor body inwardly; a plurality of internal electrode shields
within the ceramic capacitor body to thereby assist in providing
resistance to arc over; the plurality of internal electrode shields
comprising a plurality of side shields, each side shield extending
inwardly from one end of the capacitor body to thereby resist arc
over between active electrodes and terminals; and a coating on the
ceramic capacitor body to assist in increasing breakdown
voltage.
[0029] A method of manufacturing a multilayer ceramic component,
comprising forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises active electrodes and shielding electrodes and wherein
the active electrodes being configured in an alternating manner
such that a first of the plurality of active electrodes extends
from one end of the ceramic capacitor body inwardly and a next
active electrode extends from an opposite end of the ceramic
capacitor body inwardly; wherein the layers of active electrodes
further comprise side shields to thereby provide shielding.
[0030] A method of manufacturing a multilayer ceramic component,
comprising forming a ceramic capacitor body from a plurality of
electrode layers and dielectric layers; attaching first and second
external terminals on opposite ends of the ceramic capacitor body;
coating the ceramic capacitor body to assist in increasing
breakdown voltage; wherein the plurality of electrode layers
comprises a plurality of active electrode layers being configured
in an alternating manner such that a first end of the plurality of
active electrodes extends from one end of the ceramic capacitor
body inwardly and a next internal active electrode extends from an
opposite end of the ceramic capacitor body inwardly; wherein the
active electrode layer further comprise side shields to thereby
provide additional shielding.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a diagram of a cross-section through a series
capacitor design with a single floating electrode.
[0032] FIG. 2 is a diagram of a cross-section through a standard
capacitor sign.
[0033] FIG. 3 shows an average voltage breakdown of series and
standard capacitor 10 designs.
[0034] FIG. 4A shows a cross-section photograph of 1812 MLCC
standard design.
[0035] FIG. 4B shows an end view photograph of an 1812 MLCC
standard design.
[0036] FIG. 5A is a cross-section photograph of 1812 MLCC single
floating electrode series design.
[0037] FIG. 5B shows an end view photograph of an 1812 MLCC single
floating electrode series design.
[0038] FIG. 6 is a diagram of capacitor designs according to
several embodiments of the present invention.
[0039] FIG. 7 is a table showing the average capacitance and
dimensions for the capacitor designs of FIG. 6.
[0040] FIG. 8A is a side view cross-section drawing of Example
1.
[0041] FIG. 8B is an end view cross-section drawing of Example
1.
[0042] FIG. 9A is a side view cross-section drawing of Example
2.
[0043] FIG. 9B is an end view cross-section drawing of Example
2.
[0044] FIG. 10A is a side view cross-section drawing of Example
3.
[0045] FIG. 10B is an end view cross-section drawing of Example
3.
[0046] FIG. 11 shows a voltage breakdown of Examples 1, 2 and
3.
[0047] FIG. 12A is a photograph of a cross-section of Example
1.
[0048] FIG. 12B is a photograph of an end view of the cross-section
of Example 1.
[0049] FIG. 13A is a photograph of a cross-section of Example
2.
[0050] FIG. 13B is a photograph of an end view of the cross-section
of Example 2.
[0051] FIG. 14A is a photograph of a cross-section of Example
3.
[0052] FIG. 14B is a photograph of an end view of the cross-section
of Example 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0053] This invention describes a novel arrangement of internal
electrodes that results in an arc resistant multilayer ceramic
capacitor with very high voltage breakdown in air. Furthermore
these designs retain a high capacitance. To assist in describing
the present invention, each of three designs and MLCC performance
is described and then a more detailed description of each example
is provided with reference to the drawings. The designs and MLCC
performance is described in the following examples.
EXAMPLE 1
[0054] A standard case size 1206 capacitor design was manufactured
using a production MLCC X7R materials system C-153.
EXAMPLE 2
[0055] A case size 1206 capacitor design was manufactured using a
production MLCC X7R materials system C-153 with shield electrodes
on top and bottom. The purpose of these shield electrodes is to
prevent an arc-over between the terminal and the internal electrode
of opposite polarity or across the top or bottom surface of the
capacitor between terminals of opposite polarity. For this reason
it is only necessary to have one shield electrode present in the
case where the active below is of opposite polarity. However,
during the course of manufacturing capacitors of different values
by shielding both terminal areas at the top and bottom of the
capacitor there is no need to change the screens for different
numbers of electrodes improving manufacturability.
EXAMPLE 3
[0056] A case size 1206 capacitor design was manufactured using a
production MLCC X7R materials system C-153 with side shield
electrodes on either side of the active in additions to shield
electrodes on top and bottom. The purpose of the side shield
electrode is to prevent an arc-over between the terminal and
different internal electrode layers of opposite polarity or across
the sides of the capacitor between terminals of opposite polarity.
As for the top and bottom side shield electrodes, two side shield
electrodes on each side were used but it is only necessary to have
one side shield electrode at the side of each layer with terminal
of opposing polarity. The two side shield electrodes on each side
allow to accurately check alignment of the electrode stack.
[0057] The design and electrode pattern for all three examples is
shown in FIG. 6. Terminals were applied to these examples
consisting of a thick film fired silver paste and these were then
over plated with nickel followed by tin. The pasts were screened
through a 1000V Hi-Pot and IR verified. The average capacitances
(n=100) and dimensions (n=5) were measured as shown in FIG. 7.
[0058] It can be seen that the Number of Electrodes-1 (N) are
almost the same for all these examples, 27.+-.1. The Fired Active
Thickness of Ceramic Separating the Layers (T) is also the same for
all three examples and since the same ceramic material system was
used to manufacture all the capacitors the Permittivity (Er) is the
same. The only variable affecting capacitance is therefore the
Effective Overlap Area of Electrodes (A). This is lower for Example
3 because of the presence of the side-shields. The actual
cross-sections of Examples 1, 2 and 3 are shown in FIGS. 12A and
12B (Example 1), FIGS. 13A and 13B (Example 2) and FIGS. 14A and
14B (Example 3).
[0059] A sample of 50 capacitors for examples 1, 2 and 3 were
tested to failure by applying voltage at a ramp rate of 500 V/s per
method 103 of EIA 198-2-E. The results are shown in FIG. 11. The
instrument used for testing was the Associated Research 75 12 DT
HiPot. Data of FIG. 11 represents dielectric breakdown voltage
levels, which include arc-over and or physical destruction. Post IR
testing of Example 1 parts had 13/50 Insulation Resistance (IR)
failures, Examples 2 and 3 had 48/50 and 50/50 IR failures
respectively indicating that failures due to arc-over were not
observed in Example 3. It is also important to note that repeated
arc-over occurrences on applying voltage would eventually cause IR
failure.
[0060] It can clearly be seen that Example 3 has the highest
average voltage breakdown >2.5 kV of the examples cited. The
voltage breakdown and capacitance of the 1206 case size capacitor
in Example 3 are similar to the 1812 1000V rated single floating
electrode serial capacitors described in the prior art. The
capacitors described in Example 3 therefore allow the circuits
required to handle high voltages to be significantly
miniaturized.
[0061] FIG. 1 illustrates a prior art capacitor design. In FIG. 1,
a capacitor 10 is shown with a first terminal 12 and an opposite
second terminal 14 on the opposite end of the capacitor body 16.
Floating electrodes 18 are shown. FIG. 2 illustrates another prior
art capacitor design. In FIG. 2, instead of floating electrodes,
the electrodes alternate. FIG. 3 compares the series and standard
designs. In particular, FIG. 3 shows the average voltage breakdowns
(n=50) for 27 lots of case size 1812 MLCCs, 47 nF.+-.10 percent
standard designs and the same number of case size 1812, 22 nF.+-.10
percent single floating electrode series designs. In all these
cases the fired active thickness separating the electrodes was
0.0023'', 58 microns with an overall thickness of 0.051.+-.0.003''
(1.30.+-.0.08 mm) for the standard design and 0.068.+-.0.003''
(1.73.+-.0.08 mm) for the series capacitors. The length and width
dimensions were 0.177.+-.0.010'' (4.50.+-.0.25 mm) and
0.126.+-.0.008'' (3.20 .+-.0.20 mm) respectively for all these 1812
case size capacitors. Cross-sections of the 1812 standard design
and the single electrode series design are shown in FIGS. 4A-4B and
5A-10 5B, respectively.
[0062] FIG. 6 is a table which shows three different capacitor
design examples. The first example is a standard design used for
comparison purposes. The second example is one embodiment of the
present invention where top and bottom shields are used. The third
example is another embodiment of the present invention where both
top and bottom shields as well as side shields are used.
[0063] As shown in FIG. 6, in the standard design, the fired active
thickness of the capacitor is 0.0020 inches or 51 microns. The
standard design includes 26 active electrodes. In the top/bottom
shield design, the fired active thickness of the capacitor is also
0.0020 inches or 51 microns. The top/bottom shield design includes
27 active 20 electrodes. In the top/bottom and side shield design,
the fired active thickness is 0.0020 inches or 51 microns. In the
top/bottom side shield design there are 28 active electrodes.
[0064] FIG. 6 also shows the electrode layout plans for the various
types of design. According to the standard design there is a first
electrode 20 and a staggered second electrode 22. A third electrode
24 is aligned with the first electrode 20. A fourth electrode 26 is
aligned with the second electrode 22. This alternating pattern
continues, with additional alternating electrodes until the second
to last electrode, N-1, and the last electrode 30.
[0065] In the top/bottom shield design the first electrode layer
includes a first top shield 32 and a second top shield 34 as well
as a first bottom shield 36 and a second bottom shield 38. It is of
particular note that only the first top shield 32 and the second
bottom shield 38 are active-the other shields need not even be
present. The first top shield 32 and second bottom shield 38 are
necessary to prevent arc-over from terminations of opposed polarity
and shields 34 and 26 are present for manufacturing
convenience.
[0066] In the top/bottom and side shields embodiment, there is a
first top shield 32 and a second top shield 34 as well as a first
bottom shield 36 and a second bottom shield 38. For each active
electrode there are also side shields 40, 42, 44, 46, 48, 50, 52,
54, 56, 58, 60, 62, 64, 66, 68, and 70. The side shields 40, 42,
52, 54, 56, 58, 68, and 70 are required to protect the inner active
electrodes from arc over from the termination of opposed polarity
whereas the other side shields were included to test the electrode
alignment within the parts.
[0067] The designs shown in FIG. 6 are further illustrated in FIGS.
8A to 10B. FIG. 8A is a cross-section of Example 1 (standard
design) while FIG. 8B is an end view of the cross-section of
Example 1. In FIG. 8A, a multilayer ceramic capacitor component 48
is shown with a first terminal 12 and a second terminal 14 on
opposite ends of a multilayer ceramic capacitor component 16. The
internal active electrodes of the ceramic capacitor body are
configured in alternating manners such that a first internal active
electrode 20 extends from one end of the ceramic capacitor body
inwardly toward the terminal on the opposite end of the ceramic
capacitor body. The next internal active electrode 22 extends from
the opposite end of the ceramic capacitor body inwardly toward the
terminal on the opposite end of the ceramic body. A coating 17 may
be used to further assist in increasing breakdown voltage. The end
view cross-section of FIG. 8B illustrates the electrodes.
[0068] FIG. 9A is a side view cross-section of Example 2
(top/bottom shields) while FIG. 9B is an end view of the
cross-section of Example 2. In FIG. 9A, a multilayer ceramic
capacitor component 50 is shown. Note the presence of the internal
electrode shields within the ceramic capacitor body which assist in
providing resistance to arc-over between the terminals and internal
electrodes. The internal electrode shields shown include a top
internal electrode shield 32 and an opposite bottom internal
electrode shield 38. The top internal electrode shield 32 and the
opposite bottom internal electrode shield 38 are on opposite sides
of the multilayer ceramic capacitor body 16. Each internal
electrode shield 32, 38 extends inwardly to or beyond a
corresponding terminal 12, 14 to thereby provide shielding. As
previously mentioned, additional structures 34, and 36 are provided
but are not required as they do not provide actual shielding due to
the polarity of the terminals. They are included for convenience in
the manufacturing process. In addition, a coating 17 may be used to
further assist in increasing breakdown voltage.
[0069] FIG. 10A is a side view cross-section of Example 3
(top/bottom shields and side shield) while FIG. 10B is an end view
of the cross-section of Example 3. The multilayer ceramic capacitor
60 of FIG. 10A includes not only the top shield 32 and opposite
bottom shield 38, but also side shields. The side shields are best
shown in FIG. 10B that depicts a cross-section through the
capacitor. The side shield in question depends on the depth of the
cross-section hence the side shields shown are 40, 42, 48, and
50.
[0070] FIG. 7 provides a table for comparing the standard design to
two designs according 10 to the present invention. The table shows
the average capacitance and dimensions for the capacitor designs of
FIG. 6.
[0071] FIG. 11 shows a voltage breakdown of Examples 1, 2 and 3.
Note that in FIG. 11, the top/bottom shield embodiment (Example 2)
provides increased voltage break down relative to the standard
design (Example 1). The top/bottom and side shield embodiment
(Example 3) provides further increased break down voltage. Thus,
the present invention can be used to create multi-layer ceramic
capacitors having voltage breakdowns above 1000V, 1500V, 2000V,
2500V, or even 3000V.
[0072] The present invention further contemplates that a coating
may be used to further improve voltage breakdown performance. In
particular, a coating such as a polyimide coating may be used for
improved voltage breakdown performance. The coating may be spin
coated. Testing may be performed by subjecting the capacitor to
voltage breakdown testing in air after applying and curing a
polyimide coating on the ceramic surface. The use of the coating
assists in increasing breakdown voltage. As standard multilayer
ceramic capacitor component of 100 nf capacitance and 1812 package
size was subjected to voltage breakdown testing in air both with
and without coating with polyimide using spin coating techniques.
The uncoated capacitors had an average voltage breakdown of 1.27
RVDC while the coated capacitors had an average breakdown voltage
of 2.46 RVDC. Thus, the use of the polyimide resulted in a
significant improvement in breakdown voltage.
[0073] Therefore an improved high voltage capacitor has been
disclosed. The present invention is not to be limited to the
specific embodiments shown in here. For example, the present
invention contemplates numerous variations in the types of
dielectric used, types of conductors used, sizes, dimensions,
packaging, and other variations.
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