SOLID TANTALUM CHIP CAPACITORS
TANTALUM MnO
2
COMPONENT PERFORMANCE CHARACTERISTICS
(con’t.)
RELIABILITY
(1)
λ
V
=
λ
b
π
T
π
C
π
V
π
SR
π
Q
π
E
x 1000
19. Reliability Prediction
(2)
λ
b
= 0.00005
CWR
or 0.0004
CSR
Solid tantalum capacitors exhibit no degradation
-0.15
1
1
(3)
π
T
= exp
-5
failure mode during shelf storage and show a
8.617 • 10 T
Amb
298
constantly decreasing failure rate (i.e., absence
17
Application-Voltage
of any wear out mechanism) during life tests.
(4)
S=
π
V
= S
+1
Rated-Voltage
0.6
This failure rate is dependent upon three impor-
tant application conditions; DC Voltage, ambient
(5)
π
C
= 1.0 • C
.023
temperature, and circuit impedance. Additional
effects are attributable to the capacitance of the
(6)
π
SR
= Lookup Table
π
E
= Lookup Table
device and atmospheric and mechanical expo-
Pcs. Fail
sure of the assembled circuit. The 1000 multiplier
(7)
π
Q
=
Pcs. Tested x Hrs. Tested
x 100,000
at the end converts the failure rate to parts-per-
billion piece-hours. A prediction of the failure rate
FIGURE 11a. MIL-HDBK-217F Notice 2 formulas.
can be made using these application conditions
and the formulas and tables listed in MIL-HDBK-
217F (Notice 2).
Base Multiplier:
The first multiplier is the base
π
SR
CR (ΩV)
0.66
multiplier (2) established for the capacitor type.
>0.8
1.0
0.6-0.8
For “CWR-Chips” or surface mount components
1.3
0.4-0.6
the base multiplier is 0.00005, and for “CSR-
2.0
0.2-0.4
Leaded” devices, the base multiplier is 0.00040.
2.7
0.1-0.2
Temperature:
The temperature factor is given as
3.3
<0.1
(3). From this formula, it can be seen that the unity
FIGURE 11b. Table for circuit resistance multipiers.
factor, or 1, is derived at an ambient temperature
of +25 C (+298 K), and that at temperatures
below this the multiplier is decreasing and at tem-
peratures above this the multiplier is increasing.
Quality Factor:
All of these multipliers are
applied to the established or base failure rate of
Voltage:
The multiplier for application voltage (4)
the part. The T492 Series is qualified under U.S.
is a two step process: first, the application volt-
military specification MIL-PRF-55365. Failure
age is compared to 60% of rated voltage, and
rates as low as 0.001% kHr are available under
then this ratio is raised to an exponential power
this test program.
of 17 and added to unity. Consider applications
of 50%, 60%, 70%, 80% and 90% of rated volt-
For series not covered by military specifications,
age. The multipliers for these applications would
an internal sampling program is operated by
be 1.045, 2.00, 14.7, 134, and 986, respectively.
KEMET Quality Assurance whereby parts are put
From these results it is evident why manufactur-
on life test at rated voltage for 2000 hours. The
ers recommend application voltages not to
confidence level chosen for the reporting data is
exceed 50% rated voltages.
60%. (The cost of sampling each batch would be
prohibitive, and no claim is made to guarantee
Capacitance:
There is a factor (5) applied to the
the failure rate of each batch.) With this testing
capacitance (in µF) which effectively increases
and each new qualification test for new parts, the
the failure rate for increasing capacitance
average failure rate for all commercial Series lies
(increases in effective area resulting in increases
between 0.1% and 1.0% per thousand-
in possible faults).
piece-hours.
Series Resistance:
The series resistance is only
FIT Calculator
concerned with the resistance per application
bias (ohms per volt) external to the capacitor,
All of these factors are gathered into a Windows
and does not include the ESR as a factor.
based software, available free from the KEMET
web site (www.kemet.com). The “FIT Calculator”
Environmental:
The environmental factor is
software does all the calculations and look-ups
determined by the harshness of the ambient
based on information entered or selected by the
conditions beyond temperature. An explanation
operator. A manual may also be downloaded
of these ratings is included in the MIL specifica-
from the same web page to explain the controls
tion and are too extensive to be covered here. In
and displays The manual as well as a help
most cases, this factor is set to ground benign or
screen also detail the environmental conditions.
G
B
, with the resulting factor equal to “1”.
©KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
11
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Solid Tantalum Surface Mount
KEMET [ KEMET CORPORATION ]
