Application
Information
Reliability:
Reliability for this capacitor style is considered poor in comparison to other
capacitor styles. The failure rate model is significantly different from the
non-button type mica capacitor.
Tolerance/Aging: Capacitor stability is very good with time and
highly reliable in circuits where ambient conditions can be closely controlled.
It is prone to failure from silver-ion migration when used under DC voltage
stress in high humidity and high temperature environments.
Frequency
Characteristics: The capacitor is intended for use up to 500
MHz.
Military
Considerations
Figure 5 specifies temperature-derating requirements for capacitors conforming to
MIL-C-10950 (Style CB).
Capacitors, Fixed,
Glass
This capacitor is a
small-sized, low capacitance value (1pf –
0.1 mf)
style, with good high frequency characteristics. The package is rugged and able
to withstand high temperatures. It is intended for applications where high
insulation resistance, low dielectric absorption, and fixed temperature
coefficients are important.
Construction
This capacitor is
composed of alternating layers of glass ribbon and electrode material
(pressurized sealed) monolithic block. It is not always hermetically sealed
because thermal expansion of case often does not match that of leads.
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum rated voltage when below TS, where
TS = TMAX –40oC. Linearly derate from
60% at TS to 30% at TD, as shown in Figure 6,
where TD = TMAX –15oC. Do not operate
within 15oC of maximum rated operating temperature.
Application
Information
Reliability:
This is a highly reliable capacitor style, especially at high temperatures. It
generally has the lowest failure rate of any capacitor style. This capacitor has
a strong tendency to fail in the short circuit mode.
Tolerance/Aging: This capacitor is very good at withstanding
extreme environmental conditions such as high shock, vibration, acceleration,
moisture, and vacuum. Its temperature coefficient is typically between 85 and
165 PPM/oC. It is highly stable with time, but in a severe operating
environment, the design should be able to withstand an additional 1% change in
capacitance value over a lifetime.
Frequency
Characteristics: The high frequency performance characteristics are superior
to most other capacitor styles. It exhibits a much higher Q factor than other
capacitor styles.
Military
Considerations
None.
Capacitors, Fixed,
Ceramic, General Purpose
This is a capacitor
designed for applications where a small physical size with comparatively large
electrical capacitance and high insulation resistance is required. Its primary
drawback is poor tolerance and stability over time.
Construction
Stacked layers of a
ceramic dielectric with a thin metallic film (usually silver) are fired onto the
ceramic at high temperatures. Terminal leads are attached by pressure contact or
soldering. The package is encapsulated to provide electrical insulation and
environmental protection. It is also called a ceramic disk.
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum rated voltage. Ambient operating temperature
should be limited to 15oC below maximum rated operating temperature
(TMAX), as shown in Figure 7.
Application
Information
The package is smaller
than paper or mica units of the same capacitance and voltage rating. It has the
largest capacitance-to-size ratios of all high-resistance
dielectrics.
Reliability:
The failure rate is very stable with temperature. It is capable of withstanding
high moisture conditions due to relative impermeability of ceramic to moisture.
The most common failure mode is a short circuit, but open circuits and parameter
drift are nearly as common.
Tolerance/Aging: The tolerance of this capacitor varies with grade
of dielectric. This capacitor is generally recommended only where large
variations in capacitance value can be tolerated (up to ±20%
through the life of capacitor). The cumulative effect of high voltage and
temperature tends to decrease capacitance value and dielectric constant with
time. It is relatively insensitive to moisture due to the non-hydrostropic
nature of ceramic. Storage under high humidity conditions may cause silver
migration problems and result in high leakage currents.
Frequency
Characteristics: Suitable as by-pass, filter, and non-critical coupling
elements in high frequency applications where moderate variations due to
temperature, voltage, and frequency will not affect proper functioning of the
circuit. Typical operating frequency range is 1kHz to 300MHz.
Military
Considerations
Figure 7 shows the derating temperature requirements for capacitors conforming to
MIL-PRF-39014 (Style CKR) and MIL-C-11015 (Style CK).
Capacitors, Fixed,
Ceramic, Temperature Compensating
This is a capacitor used
to compensate for temperature induced variance from other circuit elements. It
is used for highly accurate circuits where change in capacitance value cannot be
tolerated.
Construction
It is constructed with
multiple layers of conductive material sandwiched between ceramic
dielectric.
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum rated voltage below TS, where
TS = TMAX –40oC. Linearly derate from
60% at TS to 40% at TD as shown in Figure 8,
where TD = TMAX –10oC. Do not operate
within 10oC of maximum rated operating temperature.
Application
Information
Reliability:
This capacitor is highly reliable in high humidity conditions due to relatively
non-hydrotropic nature of ceramic, but insulation resistance may vary with
humidity and organic contamination on the ceramic chip surface. Electrical
leakage across the chip can occur due to silver migration under simultaneous
application of high humidity and high dc voltage conditions.
Tolerance/Aging: The individual capacitor specification must be
consulted for detailed temperature coefficient and linearity information. One
can expect this capacitor to remain within tolerance throughout life, except in
severe environments, where they should be able to tolerate an additional ±1%
change in capacitance value over lifetime.
Frequency
Characteristics: This capacitor style is typically intended for frequencies
between 1kHz and 300MHz.
Military
Considerations
Figure 8 shows the derating temperatures for capacitors conforming to MIL-PRF-20 (Style
CC and CCR).
Capacitors, Fixed,
Ceramic, Chip
This capacitor package is
intended for surface mount applications where a variation in capacitance with
respect to temperature, voltage, and life can be tolerated.
Construction
Multiple layers of
conductive material are sandwiched between ceramic dielectric
material.
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum rated voltage below TS, where
TS = TMAX –40oC. Linearly derate from
60% at TS to 40% at TD as shown in Figure 9,
where TD = TMAX –10oC. Do not operate
within 10oC of maximum rated operating temperature.
Application
Information
Reliability:
This capacitor is highly reliable in high humidity conditions due to the
relatively non-hydrotropic nature of ceramic, but insulation resistance may vary
with humidity and organic contamination on the ceramic chip surface. It is
historically prone to electrical leakage across the chip due to silver migration
under simultaneous application of high humidity and high DC voltage conditions.
However, special-manufacturing techniques can be used by the vendor to retard
the problem (i.e., addition of 20% palladium to the silver or completely
overcovering the silver terminations by tin-lead bonding).
Tolerance/Aging: This capacitor is available with many different
tolerances (typically ±1
to 10%). One can expect the capacitor to remain within tolerance throughout
life, except in severe environments where the capacitor should be able to
tolerate an additional ±1%
change in capacitance value.
Frequency
Characteristics: This capacitor is typically intended for frequencies
between 1kHz and 300MHz.
Military
Considerations
Figure 9 shows the derating temperatures for capacitors conforming to MIL-PRF-55681
(Style CDR).
Capacitors, Fixed,
Tantalum, Chip
This is a small-sized,
medium capacitance value (0.068 to 100mF)
chip capacitor intended for surface mount applications, including hybrid
circuits. It is designed to be mounted with reflow soldering equipment and
typically available with maximum voltage rating below 50V.
Construction
The surface is a porous
tantalum slab (anode) that is electrochemically converted to an oxide of
tantalum (dielectric) and then coated with an oxide semiconductor (solid
electrolyte).
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum rated voltage below TS, where
TS = TMAX –40oC. Linearly derate from
60% at TS to 50% at TD as shown in Figure 10, where TD = TMAX –10oC. Do
not operate within 10oC of maximum rated operating
temperature.
Reverse
Voltage: For polarized capacitors, derate reverse voltage to 2% of maximum
(forward) rated DC voltage (maximum allowable reverse voltage is typically 15%
of rated DC voltage).
Application
Information
Reliability:
This is a highly reliable style with a failure rate slightly lower than an
equivalent ceramic chip capacitor. It has a relatively constant failure rate
with stress level.
Tolerance/Aging: This capacitor is typically purchased with
tolerances of 10 and 20%. Its stability is considered good. Further recommend
designing with a series impedance of at least 1W/V
(or limit maximum current to 330 mA) to protect against excess damage to the
dielectric during self-healing process. This capacitor has excellent high
temperature characteristics with low capacitance-temperature
characteristic.
Frequency
Characteristics: This capacitor can be used over a wide range of operating
frequencies.
Special
Considerations: None.
Military
Considerations
Figure 10 shows the derating temperatures for capacitors conforming to MIL-PRF-55365
(Style CWR).
Capacitors, Fixed,
Electrolytic, Tantalum, Solid
This style is a general
purpose tantalum capacitor that is package in a leaded, metal/glass hermetic
package. Commercial versions of this part are also available in molded and
dipped plastic packages. It is available in high capacitance values (0.047 –
3000 mf).
The cost is generally higher than other electrolytic capacitors, and it has a
low reverse voltage tolerance.
Construction
The surface of a tantalum
pellet or wire (anode) is electrochemically converted to an oxide to create a
dielectric. The result is coated with manganese dioxide and a metal film to
serve as the cathode. It is available in lower voltage rating (typically 50V)
than aluminum electrolytics.
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum full rated voltage below TS, where
TS = TMAX –40oC. Linearly derate from
60% at TS to 10% at TD as shown in Figure 11, where TD = TMAX –10oC. Do
not operate within 10oC of maximum rated operating
temperature.
Reverse
Voltage: For polarized capacitors, derate reverse voltage to 2% of maximum
(forward) rated DC voltage (maximum allowable reverse voltage is typically 15%
of rated DC voltage).
Application
Information
Reliability:
This is the most reliable of the electrolytic capacitor styles. The capacitor
has a self-healing dielectric, but its capacitance decreases and leakage current
increases with age due to reformation of dielectric during the self-healing
process. Compared to aluminum electrolytics, it has a longer shelf life,
superior low temperature characteristics, freedom from electrolyte leakage, and
higher operating temperatures. It is capable of withstanding high ripple
currents for short periods, until heat-dissipation limit is
reached.
Tolerance/Aging: This capacitor is typically purchased with
tolerances of 10 and 20%. Its stability is considered good. Further recommend
designing with a series impedance of at least 1 W/V
(or limit maximum current to 330 mA) to protect against excess damage to the
dielectric during self-healing process. This capacitor has excellent high
temperature characteristics with low capacitance-temperature
characteristic.
Frequency
Characteristics: This capacitor can be used over a wide range of operating
frequencies.
Military
Considerations
Figure 11 shows derating temperature requirements for capacitors conforming to
MIL-PRF-39003 (Style CSR).
Capacitors, Fixed,
Electrolytic, Tantalum, Non-Solid (Wet and Foil)
This is a capacitor that
normally exhibits a high capacitance value (0.1 mf
to 3000 mf).
It is primarily used in low frequency filtering applications where high
capacitance density is needed but where wide tolerances can be tolerated. This
style has a high leakage current that increases with age. This category is
intended to cover plain foil, etched foil, and sintered slug types. This
capacitor style is not recommended for airborne applications.
Construction
In foil types, tantalum
foil acts as the anode and electrolyte acts as the cathode. The foil is
electrochemically treated to form a tantalum oxide, which acts as the
dielectric. Etched foil styles are similar, but foil is etched to increase
surface area and capacitive density. In sintered slug styles, a sintered slug
serves as the anode. Solderable leads are welded to tantalum lead wires in all
styles.
Derating
Requirements
Voltage:
Derate voltage to 60% of maximum full rated voltage below ambient temperature of
TS, where TS = TMAX –60oC.
Linearly derate from 60% at TS to 10% at TD as shown
in Figure 12, where TD = TMAX –10oC. Do
not operate within 10oC of maximum rated operating
temperature.
Reverse
Voltage: Derate reverse voltage to 2% of maximum (forward) rated DC
voltage.
Application
Information
This category covers
three non-solid tantalum capacitor types, discussed as follows:
Foil: The
most versatile of all electrolytic capacitors. It has the advantage of high
ripple current, good capacitance-tolerance characteristics, and a low power
factor. Packages available in both polarized and non-polarized
versions.
Etched Foil:
Capacitance density is up to 10X the capacitance/area of plain foil style, but
the capacitance values are highly variable.
Sintered
Slug: Use is limited to low voltage applications.
Reliability:
Reliability is better than aluminum electrolytic styles, but less reliable than
similar value dry slug tantalum capacitor. Shelf life characteristics are
considered excellent. Because this capacitor style is often used in power
rectification application, attention must be paid to the effect of ambient
temperature rise of nearby components.
Tolerance/Aging: The typical purchased tolerance is 20%, but
designs should be capable of withstanding an additional 10% tolerance through
life. Etched foil styles can have purchased tolerances as high as
+75%.
Frequency
Characteristics: This capacitor style is not intended for high frequency
characteristics. It is generally designed to be used below 1KHz, although
special processing techniques can increase high frequency
performance.
Special
Considerations: Compared to aluminum electrolytics, tantalums have higher
capacitance per unit area due to higher dielectric constant of tantalum oxide
(»24)
over aluminum oxide (»8).
Wet slug tantalum capacitors should not be used in airborne
systems.
Military
Considerations
Figure 12 shows temperature derating requirements for capacitors conforming to
MIL-PRF-39006 (Style CLR) and MIL-C-3965 (Style CL). Style CLR is rated at
125oC, and Style CL can be rated at either 85, 125, or
175oC, depending on the style.
Capacitors, Fixed,
Electrolytic, Aluminum, General Purpose
This capacitor possesses
high capacitance density, high voltmetric efficiency, low cost, and low
frequency filtering capacitor. This is the most common electrolytic capacitor
style. It is not recommended for airborne applications.
Construction
Similar to electrolytic
aluminum style capacitors, except it is considered a higher grade and made with
higher quality materials.
Derating
Requirements
Voltage:
Derate voltage to 70% of maximum rated voltage below TS, where
TS = TMAX –30oC. Linearly derate from
70% at TS to 40% at TD1 as shown in Figure 13, where TD1 = TMAX –20oC.
Linearly derate from 40% at TD1 to 20% at TD2,
where TD2 = TMAX –10oC. Do not operate
within 10oC of maximum rated operating temperature. Apply additional
derating in applications where high voltage surges are known to occur so maximum
voltage surge will remain below the maximum voltage rating.
Application
Information
Reliability:
This style is less reliable than tantalum styles, as it is susceptible to oxide
breakdown at small reverse biased voltages. A wear out failure mechanism,
resulting in decreased capacitance and increased equivalent series resistance,
is caused by electrolyte evaporation.
Tolerance/Aging: The initial purchased tolerance is high in
comparison to non-electrolytic styles. Aging, storage, and environmental effects
will cause further tolerance buildup. Low temperatures may cause capacitance to
decrease (20% to 50% at -40oC) and series resistance to increase.
High working voltage causes capacitance to decrease due to growth in the
thickness of the oxide layer. Long periods in storage without applied voltage
causes increase in leakage current (although low leakage electrolytic capacitors
can be purchased).
Frequency
Characteristics: This capacitor is not intended for high frequency
applications.
Special
Considerations: This capacitor is not recommended for airborne applications.
A safety vent hole is incorporated into the capacitor case and is designed to
open at dangerous pressure. Low barometric pressures may cause safety vent hole
to release and result in electrolyte dry out. Electrolyte is corrosive and can
cause damage to surrounding components and copper board traces if vent hole
releases. Explosion can result due to spark ignition or pressure buildup of free
oxygen and hydrogen liberated at the electrode.
Military
Considerations
Figure 13 shows the temperature derating requirements for capacitors conforming to
MIL-PRF-39018 (Style CU).
Capacitors, Fixed,
Electrolytic, Aluminum (Dry)
This capacitor style is
similar to an aluminum electrolytic capacitor GP, except with lower grade
materials. The derating requirements are similar, but TD1 is
15oC less than TMAX (rather than 20oC). A
non-aqueous electrolyte is used, thus the reference to "dry electrolyte
capacitor". This capacitor style is not recommended for airborne
applications.
A wear out failure
mechanism results in decreased capacitance, and increased equivalent series
resistance caused by electrolyte evaporation.
Construction
An aluminum foil is
rolled onto a porous space with impregnated electrolyte solution of ammonium
borate, boric acid, and glycol in a porous spacer. The aluminum plate is etched
to increase surface area and capacitance volume. A vent hole is incorporated
into the case as a safety precaution.
Derating
Requirements
Voltage:
Derate voltage to 70% of maximum rated voltage below TS, where
TS = TMAX –30oC. Linearly derate from
70% at TS to 40% at TD1 as shown in Figure 14, where TD1 = TMAX –15oC.
Linearly derate from 40% at TD1 to 20% at TD2,
where TD2 = TMAX –10oC. Do not operate
within 10oC of maximum rated operating temperature. Apply additional
derating in applications where high voltage surges are known to occur, such that
the maximum voltage surge will remain below the maximum voltage rating of the
capacitor.
Application
Information
Reliability:
This style is less reliable than tantalum styles. It is susceptible to oxide
breakdown at small reverse biased voltages. A wear out failure mechanism,
resulting in decreased capacitance and increased equivalent series resistance,
is caused by electrolyte evaporation.
Tolerance/Aging: The initial purchased tolerance is high in
comparison to non-electrolytic styles. Aging, storage, and environmental effects
will cause further tolerance buildup. Low temperatures cause capacitance to
decrease (20% to 50% at -40oC) and series resistance to increase.
High working voltage causes capacitance to decrease due to growth in the
thickness of the oxide layer. Long periods in storage without applied voltage
causes increase in leakage current (although low leakage electrolytic capacitors
can be purchased).
Frequency
Characteristics: This style is not intended for high frequency
applications.
Special
Considerations: This capacitor is not recommended for airborne applications.
A safety vent hole is incorporated into the capacitor case and designed to open
at dangerous pressure. Low barometric pressures may cause the safety vent hole
to release and may result in electrolyte dry out. Electrolyte is corrosive and
can cause damage to surrounding components and copper board traces if vent hole
releases. Explosion can result due to spark ignition or pressure buildup of free
oxygen and hydrogen liberated at the electrode.
Military
Considerations
Figure 14 show temperature-derating requirements for capacitors conforming to MIL-C-62
(Style CE).
Capacitors, Variable,
Ceramic
This is non-linearly
adjustable, small-sized trimmer capacitor designed for applications where
fine-tuning is periodically required during the life of an equipment.
Construction
The package consists of
stator with silver fired on surface and rotor. The rotor is usually made of
titanium dioxide. The overlap of stator and rotor determines capacitance
value.
Derating
Requirements
Voltage:
Derate to 60% of maximum rated voltage below TS, where
TS = TMAX –60oC. Linearly derate from
60% at TS to 40% at TD as shown in Figure 15, where TD = TMAX –60oC. Do
not operate within 10oC of maximum rated operating
temperature.
Application
Information
Reliability:
As with all variable capacitors, reliability is considered
poor.
Tolerance/Aging: This style should generally not be used in
applications that will experience large temperature variations because
capacitance value stability is non-linear and varies considerably with the
quality of the capacitor. It is relatively stable against shock and vibration
due to low mass, but not as stable as air trimmer variables. Capacitance drift
with age is generally less than 0.5 pf. this style is not recommended for
temperature compensation applications because capacitance value is non-linear
with temperature and varies greatly between units.
Frequency
Characteristics: Breakdown voltage remains steady up to about 2.5 MHz and
then decreases with increased frequency (decreases by about 10% at 30
MHz).
Military
Considerations
Figure 15 shows the temperature derating limits for capacitors conforming to MIL-PRF-81
(Style CV).
Capacitors, Variable,
Piston Style
This is a linearly
adjustable, small-sized trimmer capacitor designed for applications where fine
tuning is periodically required during the life of equipment. The package is
able to withstand higher ambient temperatures than variable ceramic
style.
Construction
Capacitance is achieved
by interleaving concentric cylindrical metal sleeves. Capacitance is varied by
adjusting the penetration of one set of sleeves into the other. Construction
materials will vary.
Derating
Requirements
Voltage:
Derate to 60% of maximum rated operating voltage at ambient temperature below
TS, where TS = TMAX –85oC.
Linearly derate from 60% at TS to 20% at TD1 as shown
in Figure 16, where TD1 = TMAX –25oC.
Above TD1, linearly derate to TD2, where
TD2 = TMAX -15oC.
Application
Information
Reliability:
This style exhibits the best reliability among the variable capacitor styles,
but is considerably worse than equivalent valued fixed capacitor. Its most
common failure mode is parameter drift.
Tolerance/Aging: This style is relatively stable against shock and
vibration due to low mass. Capacitance change is linear with respect to rotation
to about ±10%.
Frequency
Characteristics: This capacitor is capable of being used across a wide range
of operating frequencies up to RF.
Military
Considerations
Figure 16 gives the temperature derating requirements for capacitors conforming to
MIL-C-14409 (Style PC).
Capacitors, Variable,
Air Trimmer
This is a large capacitor
intended for line rectification applications.
Construction
The overlap of stator and
rotor determines capacitance value.
Derating
Requirements
Voltage:
Derate to 60% of maximum rated operating voltage at ambient temperature below
TS, where TS = TMAX –60oC.
Linearly derate from 60% at TS to 20% at TD as shown
in Figure 17, where TS = TMAX –10oC. Do
not operate within 10oC of maximum rated operating
temperature.
Application
Information
Reliability:
As with all variable capacitors, reliability is considered very
low.
Frequency
Characteristics: This capacitor is intended for low frequency applications
only.
Military
Considerations
Figure 17 shows the temperature derating requirements for capacitors conforming to
MIL-C-92 (Style CT).
Capacitors, Variable
and Fixed, Gas or Vacuum
This is a non-linear
fixed or variable capacitor intended for high power applications.
Construction
A heavy copper
construction minimizes stray inductance and provides an excellent heat
sink.
Derating
Requirements
Voltage:
Derate 60% of maximum rated voltage at ambient temperatures below
25oC. Linearly derate from 60% at 25oC to 40% at
TD as shown in Figure 18, where TD = TMAX
–10oC.
Application
Information
Reliability:
As with all variable capacitors, reliability is considered relatively poor. The
package is able to withstand repeated, heavy current overloads. The heat
dissipation factor is very low.
Frequency
Characteristics: This style will handle exceptionally high currents at very
high frequencies. Breakdown voltage is stable to about 2.5MHz, before
decreasing.
Military
Considerations
Figure 18 shows temperature-derating requirements for capacitors conforming to MIL-C-23183
(Style CG).