MULTILAYER CERAMIC CAPACITORS/AXIAL
& RADIAL LEADED
Multilayer ceramic capacitors are available in a
variety of physical sizes and configurations, including
leaded devices and surface mounted chips. Leaded
styles include molded and conformally coated parts
with axial and radial leads. However, the basic
capacitor element is similar for all styles. It is called a
chip and consists of formulated dielectric materials
which have been cast into thin layers, interspersed
with metal electrodes alternately exposed on opposite
edges of the laminated structure. The entire structure is
fired at high temperature to produce a monolithic
block which provides high capacitance values in a
small physical volume. After firing, conductive
terminations are applied to opposite ends of the chip to
make contact with the exposed electrodes.
Termination materials and methods vary depending on
the intended use.
TEMPERATURE CHARACTERISTICS
Ceramic dielectric materials can be formulated with
Class III:
General purpose capacitors, suitable
a wide range of characteristics. The EIA standard for
for by-pass coupling or other applications in which
ceramic dielectric capacitors (RS-198) divides ceramic
dielectric losses, high insulation resistance and
dielectrics into the following classes:
stability of capacitance characteristics are of little or
no importance. Class III capacitors are similar to Class
Class I:
Temperature compensating capacitors,
II capacitors except for temperature characteristics,
suitable for resonant circuit application or other appli-
which are greater than ± 15%. Class III capacitors
cations where high Q and stability of capacitance char-
have the highest volumetric efficiency and poorest
acteristics are required. Class I capacitors have
stability of any type.
predictable temperature coefficients and are not
affected by voltage, frequency or time. They are made
KEMET leaded ceramic capacitors are offered in
from materials which are not ferro-electric, yielding
the three most popular temperature characteristics:
superior stability but low volumetric efficiency. Class I
C0G:
Class I, with a temperature coefficient of 0 ±
capacitors are the most stable type available, but have
30 ppm per degree C over an operating
the lowest volumetric efficiency.
temperature range of - 55°C to + 125°C (Also
known as “NP0”).
Class II:
Stable capacitors, suitable for bypass
X7R:
Class II, with a maximum capacitance
or coupling applications or frequency discriminating
change of ± 15% over an operating temperature
circuits where Q and stability of capacitance char-
range of - 55°C to + 125°C.
acteristics are not of major importance. Class II
Z5U:
Class III, with a maximum capacitance
capacitors have temperature characteristics of ± 15%
change of + 22% - 56% over an operating tem-
or less. They are made from materials which are
perature range of + 10°C to + 85°C.
ferro-electric, yielding higher volumetric efficiency but
less stability. Class II capacitors are affected by
Specified electrical limits for these three temperature
temperature, voltage, frequency and time.
characteristics are shown in Table 1.
SPECIFIED ELECTRICAL LIMITS
Parameter
Dissipation Factor: Measured at following conditions.
C0G – 1 kHz and 1 vrms if capacitance >1000pF
1 MHz and 1 vrms if capacitance 1000 pF
X7R – 1 kHz and 1 vrms* or if extended cap range 0.5 vrms
Z5U – 1 kHz and 0.5 vrms
Dielectric Stength: 2.5 times rated DC voltage.
Insulation Resistance (IR): At rated DC voltage,
whichever of the two is smaller
Temperature Characteristics: Range, °C
Capacitance Change without
DC voltage
* MHz and 1 vrms if capacitance
100 pF on military product.
Temperature Characteristics
C0G
X7R
2.5%
(3.5% @ 25V)
Z5U
0.10%
4.0%
Pass Subsequent IR Test
1,000 M
F
or 100 G
-55 to +125
0 ± 30 ppm/°C
1,000 M
F
or 100 G
-55 to +125
± 15%
1,000 M
or 10 G
F
+ 10 to +85
+22%,-56%
Table I
4
© KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
APPLICATION NOTES FOR MULTILAYER
CERAMIC CAPACITORS
ELECTRICAL CHARACTERISTICS
The fundamental electrical properties of multilayer
ceramic capacitors are as follows:
Polarity:
Multilayer ceramic capacitors are not polar,
and may be used with DC voltage applied in either direction.
Rated Voltage:
This term refers to the maximum con-
tinuous DC working voltage permissible across the entire
operating temperature range. Multilayer ceramic capacitors
are not extremely sensitive to voltage, and brief applications
of voltage above rated will not result in immediate failure.
However, reliability will be reduced by exposure to sustained
voltages above rated.
Capacitance:
The standard unit of capacitance is the
farad. For practical capacitors, it is usually expressed in
microfarads (10
-6
farad), nanofarads (10
-9
farad), or picofarads
(10
-12
farad). Standard measurement conditions are as
follows:
Class I (up to 1,000 pF):
Class I (over 1,000 pF):
Class II:
Class III:
1MHz and 1.2 VRMS
maximum.
1kHz and 1.2 VRMS
maximum.
1 kHz and 1.0 ± 0.2 VRMS.
1 kHz and 0.5 ± 0.1 VRMS.
The variation of a capacitor’s impedance with frequency
determines its effectiveness in many applications.
Dissipation Factor:
Dissipation Factor (DF) is a mea-
sure of the losses in a capacitor under AC application. It is the
ratio of the equivalent series resistance to the capacitive reac-
tance, and is usually expressed in percent. It is usually mea-
sured simultaneously with capacitance, and under the same
conditions. The vector diagram in Figure 2 illustrates the rela-
tionship between DF, ESR, and impedance. The reciprocal of
the dissipation factor is called the “Q”, or quality factor. For
convenience, the “Q” factor is often used for very low values
of dissipation factor. DF is sometimes called the “loss tangent”
or “tangent ”, as derived from this diagram.
Figure 2
ESR
DF = ESR
Xc
X
c
O
δ
Ζ
1
Xc
=
2πfC
Like all other practical capacitors, multilayer ceramic
capacitors also have resistance and inductance. A simplified
schematic for the equivalent circuit is shown in Figure 1.
Other significant electrical characteristics resulting from
these additional properties are as follows:
Figure 1
R
P
L
R
S
C
C = Capacitance
L = Inductance
R = Equivalent Series Resistance (ESR)
S
R = Insulation Resistance (IR)
P
Insulation Resistance:
Insulation Resistance (IR) is the
DC resistance measured across the terminals of a capacitor,
represented by the parallel resistance (Rp) shown in Figure 1.
For a given dielectric type, electrode area increases with
capacitance, resulting in a decrease in the insulation resis-
tance. Consequently, insulation resistance is usually specified
as the “RC” (IR x C) product, in terms of ohm-farads or
megohm-microfarads. The insulation resistance for a specific
capacitance value is determined by dividing this product by
the capacitance. However, as the nominal capacitance values
become small, the insulation resistance calculated from the
RC product reaches values which are impractical.
Consequently, IR specifications usually include both a mini-
mum RC product and a maximum limit on the IR calculated
from that value. For example, a typical IR specification might
read “1,000 megohm-microfarads or 100 gigohms, whichever
is less.”
Insulation Resistance is the measure of a capacitor to
resist the flow of DC leakage current. It is sometimes referred
to as “leakage resistance.” The DC leakage current may be
calculated by dividing the applied voltage by the insulation
resistance (Ohm’s Law).
Dielectric Withstanding Voltage:
Dielectric withstand-
ing voltage (DWV) is the peak voltage which a capacitor is
designed to withstand for short periods of time without dam-
age. All KEMET multilayer ceramic capacitors will withstand a
test voltage of 2.5 x the rated voltage for 60 seconds.
KEMET specification limits for these characteristics at
standard measurement conditions are shown in Table 1 on
page 4. Variations in these properties caused by changing
conditions of temperature, voltage, frequency, and time are
covered in the following sections.
Impedance:
Since the parallel resistance (Rp) is nor-
mally very high, the total impedance of the capacitor is:
2
2
Z=
Where
R
S
+ (X
C
- X
L
)
Z = Total Impedance
RS = Equivalent Series Resistance
X
C
= Capacitive Reactance =
1
2πfC
π
X
L
= Inductive Reactance = 2πfL
π
© KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
5
Application Notes
APPLICATION NOTES FOR MULTILAYER
CERAMIC CAPACITORS
TABLE 1
EIA TEMPERATURE CHARACTERISTIC CODES
FOR CLASS I DIELECTRICS
Significant Figure
of Temperature
Coefficient
PPM per
Degree C
Letter
Symbol
Multiplier Applied
to Temperature
Coefficient
Multi-
plier
Number
Symbol
Tolerance of
Temperature
Coefficient *
PPM per
Degree C
Letter
Symbol
0.0
0.3
0.9
1.0
1.5
2.2
3.3
4.7
7.5
C
B
A
M
P
R
S
T
U
-1
-10
-100
-1000
-100000
+1
+10
+100
+1000
+10000
0
1
2
3
4
5
6
7
8
9
±30
±60
±120
±250
±500
±1000
±2500
G
H
J
K
L
M
N
* These symetrical tolerances apply to a two-point measurement of
temperature coefficient: one at 25°C and one at 85°C. Some deviation
is permitted at lower temperatures. For example, the PPM tolerance
for C0G at -55°C is +30 / -72 PPM.
TABLE 2
EIA TEMPERATURE CHARACTERISTIC CODES
FOR CLASS II & III DIELECTRICS
Low Temperature
Rating
Degree
Celcius
Letter
Symbol
High Temperature Maximum Capacitance
Rating
Shift
Degree
Celcius
Number
Symbol
Percent
Letter
Symbol
+10C
-30C
-55C
Z
Y
X
+45C
+65C
+85C
+105C
+125C
+150C
+200C
2
4
5
6
7
8
9
±1.0%
±1.5%
±2.2%
±3.3%
±4.7%
±7.5%
±10.0%
±15.0%
±22.0%
+22 / -33%
+22 / -56%
+22 / -82%
A
B
C
D
E
F
P
R
S
T
U
V
+10
+20
+30
+40
+50
+60
+70
+80
6
© KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
APPLICATION NOTES FOR MULTILAYER
CERAMIC CAPACITORS
At higher AC voltages, both capacitance and dissipation factor
begin to decrease.
Typical curves showing the effect of applied AC and DC
voltage are shown in Figure 6 for KEMET X7R capacitors and
Figure 7 for KEMET Z5U capacitors.
Effect of Frequency:
Frequency affects both capaci-
tance and dissipation factor. Typical curves for KEMET multi-
layer ceramic capacitors are shown in Figures 8 and 9.
The variation of impedance with frequency is an impor-
tant consideration in the application of multilayer ceramic
capacitors. Total impedance of the capacitor is the vector of the
capacitive reactance, the inductive reactance, and the ESR, as
illustrated in Figure 2. As frequency increases, the capacitive
reactance decreases. However, the series inductance (L)
shown in Figure 1 produces inductive reactance, which
increases with frequency. At some frequency, the impedance
ceases to be capacitive and becomes inductive. This point, at
the bottom of the V-shaped impedance versus frequency
curves, is the self-resonant frequency. At the self-resonant fre-
quency, the reactance is zero, and the impedance consists of
the ESR only.
Typical impedance versus frequency curves for KEMET
multilayer ceramic capacitors are shown in Figures 10, 11, and
12. These curves apply to KEMET capacitors in chip form, with-
out leads. Lead configuration and lead length have a significant
impact on the series inductance. The lead inductance is
approximately 10nH/inch, which is large compared to the
inductance of the chip. The effect of this additional inductance
is a decrease in the self-resonant frequency, and an increase
in impedance in the inductive region above the self-resonant
frequency.
Effect of Time:
The capacitance of Class II and III
dielectrics change with time as well as with temperature, volt-
age and frequency. This change with time is known as “aging.”
It is caused by gradual realignment of the crystalline structure
of the ceramic dielectric material as it is cooled below its Curie
temperature, which produces a loss of capacitance with time.
The aging process is predictable and follows a logarithmic
decay. Typical aging rates for C0G, X7R, and Z5U dielectrics
are as follows:
C0G
X7R
Z5U
Effect of Temperature:
Both capacitance and dissipa-
tion factor are affected by variations in temperature. The max-
imum capacitance change with temperature is defined by the
temperature characteristic. However, this only defines a “box”
bounded by the upper and lower operating temperatures and
the minimum and maximum capacitance values. Within this
“box”, the variation with temperature depends upon the spe-
cific dielectric formulation. Typical curves for KEMET capaci-
tors are shown in Figures 3, 4, and 5. These figures also
include the typical change in dissipation factor for KEMET
capacitors.
Insulation resistance decreases with temperature.
Typically, the insulation resistance at maximum rated temper-
ature is 10% of the 25°C value.
Effect of Voltage:
Class I ceramic capacitors are not
affected by variations in applied AC or DC voltages. For Class
II and III ceramic capacitors, variations in voltage affect only
the capacitance and dissipation factor. The application of DC
voltage higher than 5 vdc reduces both the capacitance and
dissipation factor. The application of AC voltages up to 10-20
Vac tends to increase both capacitance and dissipation factor.
None
2.0% per decade of time
5.0% per decade of time
Typical aging curves for X7R and Z5U dielectrics are
shown in Figure 13.
The aging process is reversible. If the capacitor is heat-
ed to a temperature above its Curie point for some period of
time, de-aging will occur and the capacitor will regain the
capacitance lost during the aging process. The amount of de-
aging depends on both the elevated temperature and the
length of time at that temperature. Exposure to 150°C for one-
half hour or 125°C for two hours is usually sufficient to return
the capacitor to its initial value.
Because the capacitance changes rapidly immediately
after de-aging, capacitance measurements are usually delayed
for at least 10 hours after the de-aging process, which is often
referred to as the “last heat.” In addition, manufacturers utilize
the aging rates to set factory test limits which will bring the
capacitance within the specified tolerance at some future time,
to allow for customer receipt and use. Typically, the test limits
are adjusted so that the capacitance will be within the specified
tolerance after either 1,000 hours or 100 days, depending on
the manufacturer and the product type.
© KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
7
Application Notes
APPLICATION NOTES FOR MULTILAYER
CERAMIC CAPACITORS
POWER DISSIPATION
Power dissipation has been empirically determined for
two representative KEMET series: C052 and C062. Power dis-
sipation capability for various mounting configurations is shown
in Table 3. This table was extracted from Engineering Bulletin
F-2013, which provides a more detailed treatment of this sub-
ject.
Note that no significant difference was detected between
the two sizes in spite of a 2 to 1 surface area ratio. Due to the
materials used in the construction of multilayer ceramic capac-
itors, the power dissipation capability does not depend greatly
on the surface area of the capacitor body, but rather on how
well heat is conducted out of the capacitor lead wires.
Consequently, this power dissipation capability is applicable to
other leaded multilayer styles and sizes.
TABLE 3
POWER DISSIPATION CAPABILITY
(Rise in Celsius degrees per Watt)
Mounting Configuration
1.00" leadwires attached to binding post
of GR-1615 bridge (excellent heat sink)
0.25" leadwires attached to binding post
of GR-1615 bridge
Capacitor mounted flush to 0.062" glass-
epoxy circuit board with small copper traces
Capacitor mounted flush to 0.062" glass-
epoxy circuit board with four square inches
of copper land area as a heat sink
Power
Dissipation
of C052 & C062
90 Celsius degrees
rise per Watt ±10%
55 Celsius degrees
rise per Watt ±10%
77 Celsius degrees
rise per Watt ±10%
53 Celsius degrees
rise per Watt ±10%
capacitors may be operated with AC voltage applied without
need for DC bias.
RELIABILITY
A well constructed multilayer ceramic capacitor is
extremely reliable and, for all practical purposes, has an infi-
nite life span when used within the maximum voltage and
temperature ratings. Capacitor failure may be induced by sus-
tained operation at voltages that exceed the rated DC voltage,
voltage spikes or transients that exceed the dielectric with-
standing voltage, sustained operation at temperatures above
the maximum rated temperature, or the excessive tempera-
ture rise due to power dissipation.
Failure rate is usually expressed in terms of percent per
1,000 hours or in FITS (failure per billion hours). Some
KEMET series are qualified under U.S. military established
reliability specifications MIL-PRF-20, MIL-PRF-123, MIL-
PRF-39014, and MIL-PRF-55681. Failure rates as low as
0.001% per 1,000 hours are available for all capacitance /
voltage ratings covered by these specifications. These spec-
ifications and accompanying Qualified Products List should
be consulted for details.
For series not covered by these military specifications,
an internal testing program is maintained by KEMET Quality
Assurance. Samples from each week’s production are sub-
jected to a 2,000 hour accelerated life test at 2 x rated voltage
and maximum rated temperature. Based on the results of
these tests, the average failure rate for all non-military series
covered by this test program is currently 0.06% per 1,000
hours at maximum rated conditions. The failure rate would be
much lower at typical use conditions. For example, using MIL-
HDBK-217D this failure rate translates to 0.9 FITS at 50%
rated voltage and 50°C.
Current failure rate details for specific KEMET multilay-
er ceramic capacitor series are available on request.
MISAPPLICATION
Ceramic capacitors, like any other capacitors, may fail
if they are misapplied. Typical misapplications include expo-
sure to excessive voltage, current or temperature. If the
dielectric layer of the capacitor is damaged by misapplication
the electrical energy of the circuit can be released as heat,
which may damage the circuit board and other components
as well.
If potential for misapplication exists, it is recommended
that precautions be taken to protect personnel and equipment
during initial application of voltage. Commonly used precau-
tions include shielding of personnel and sensing for excessive
power drain during board testing.
STORAGE AND HANDLING
Ceramic chip capacitors should be stored in normal
working environments. While the chips themselves are quite
robust in other environments, solderability will be degraded
by exposure to high temperatures, high humidity, corrosive
atmospheres, and long term storage. In addition, packaging
materials will be degraded by high temperature – reels may
soften or warp, and tape peel force may increase. KEMET
recommends that maximum storage temperature not exceed
40˚ C, and maximum storage humidity not exceed 70% rela-
tive humidity. In addition, temperature fluctuations should be
minimized to avoid condensation on the parts, and atmos-
pheres should be free of chlorine and sulfur bearing com-
pounds. For optimized solderability, chip stock should be
used promptly, preferably within 1.5 years of receipt.
As shown in Table 3, the power dissipation capability of
the capacitor is very sensitive to the details of its use environ-
ment. The temperature rise due to power dissipation should not
exceed 20°C. Using that constraint, the maximum permissible
power dissipation may be calculated from the data provided in
Table 3.
It is often convenient to translate power dissipation capa-
bility into a permissible AC voltage rating. Assuming a sinu-
soidal wave form, the RMS “ripple voltage” may be calculated
from the following formula:
E=Zx
Where
P
MAX
R
E = RMS Ripple Voltage (volts)
P = Power Dissipation (watts)
Z = Impedance
R = ESR
The data necessary to make this calculation is included in
Engineering Bulletin F-2013. However, the following criteria
must be observed:
1. The temperature rise due to power dissipation
should be limited to 20°C.
2. The peak AC voltage plus the DC voltage must not
exceed the maximum working voltage of the
capacitor.
Provided that these criteria are met, multilayer ceramic
8
© KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
Download Centre
京公网安备 11010802033920号
EEWORLD
