MULTILAYER CERAMIC CAPACITORS/AXIAL
& RADIAL LEADED
Multilayer ceramic capacitors are available in a edges of the laminated structure. The entire structure is
variety of physical sizes and configurations, including fired at high temperature to produce a monolithic
leaded devices and surface mounted chips. Leaded block which provides high capacitance values in a
styles include molded and conformally coated parts small physical volume. After firing, conductive
with axial and radial leads. However, the basic terminations are applied to opposite ends of the chip to
capacitor element is similar for all styles. It is called a make contact with the exposed electrodes.
chip and consists of formulated dielectric materials Termination materials and methods vary depending on
which have been cast into thin layers, interspersed the intended use.
with metal electrodes alternately exposed on opposite
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 - 55C to + 125C (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 - 55C to + 125C.
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 + 10C to + 85C.
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
TemperatureCharacteristics
Parameter
C0G X7R Z5U
Dissipation Factor: Measured at following conditions.
C0G 1 kHz and 1 vrms if capacitance >1000pF
2.5%
1 MHz and 1 vrms if capacitance 1000 pF 0.10% 4.0%
(3.5% @ 25V)
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. Pass Subsequent IR Test
Insulation Resistance (IR): At rated DC voltage, 1,000 M F 1,000 M F 1,000 M F
whichever of the two is smaller or 100 G or 100 G or 10 G
Temperature Characteristics: Range, C
-55 to +125 -55 to +125 + 10 to +85
Capacitance Change without
0 30 ppm/C 15% +22%,-56%
DC voltage
* MHz and 1 vrms if capacitance 100 pF on military product.
Table I
4 KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300APPLICATION NOTES FOR MULTILAYER
CERAMIC CAPACITORS
The variation of a capacitors impedance with frequency
ELECTRICAL CHARACTERISTICS
determines its effectiveness in many applications.
The fundamental electrical properties of multilayer
ceramic capacitors are as follows: Dissipation Factor: Dissipation Factor (DF) is a mea-
sure of the losses in a capacitor under AC application. It is the
Polarity: Multilayer ceramic capacitors are not polar,
ratio of the equivalent series resistance to the capacitive reac-
and may be used with DC voltage applied in either direction.
tance, and is usually expressed in percent. It is usually mea-
Rated Voltage: This term refers to the maximum con-
sured simultaneously with capacitance, and under the same
tinuous DC working voltage permissible across the entire
conditions. The vector diagram in Figure 2 illustrates the rela-
operating temperature range. Multilayer ceramic capacitors
tionship between DF, ESR, and impedance. The reciprocal of
are not extremely sensitive to voltage, and brief applications
the dissipation factor is called the Q, or quality factor. For
of voltage above rated will not result in immediate failure.
convenience, the Q factor is often used for very low values
However, reliability will be reduced by exposure to sustained
of dissipation factor. DF is sometimes called the loss tangent
voltages above rated.
or tangent d, as derived from this diagram.
Capacitance: The standard unit of capacitance is the
farad. For practical capacitors, it is usually expressed in ESR
Figure 2
-6
-9
microfarads (10 farad), nanofarads (10 farad), or picofarads
-12
(10 farad). Standard measurement conditions are as
O
ESR
follows:
DF =
X
c
Class I (up to 1,000 pF): 1MHz and 1.2 VRMS
maximum.
X
c
Class I (over 1,000 pF): 1kHz and 1.2 VRMS
maximum.
1
X =
Class II: 1 kHz and 1.0 0.2 VRMS.
c
2fC
Class III: 1 kHz and 0.5 0.1 VRMS.
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
Insulation Resistance: Insulation Resistance (IR) is the
these additional properties are as follows:
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
R
capacitance, resulting in a decrease in the insulation resis-
Figure 1
P
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
R
L
S
the capacitance. However, as the nominal capacitance values
become small, the insulation resistance calculated from the
C
RC product reaches values which are impractical.
C = Capacitance R = Equivalent Series Resistance (ESR)
Consequently, IR specifications usually include both a mini-
S
mum RC product and a maximum limit on the IR calculated
L = Inductance R = Insulation Resistance (IR)
P
from that value. For example, a typical IR specification might
read 1,000 megohm-microfarads or 100 gigohms, whichever
is less.
Impedance: Since the parallel resistance (Rp) is nor-
Insulation Resistance is the measure of a capacitor to
mally very high, the total impedance of the capacitor is:
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
22
Z = R + (X - X )
resistance (Ohms Law).
S C L
Dielectric Withstanding Voltage: Dielectric withstand-
Where Z = Total Impedance ing voltage (DWV) is the peak voltage which a capacitor is
designed to withstand for short periods of time without dam-
RS = Equivalent Series Resistance
age. All KEMET multilayer ceramic capacitors will withstand a
test voltage of 2.5 x the rated voltage for 60 seconds.
1
X = Capacitive Reactance =
C
2fC
KEMET specification limits for these characteristics at
standard measurement conditions are shown in Table 1 on
X = Inductive Reactance = 2fL
L
page 4. Variations in these properties caused by changing
conditions of temperature, voltage, frequency, and time are
covered in the following sections.
KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300 5
Application Notes