TAP/TEP Technical Summary and
Application Guidelines
SECTION 3:
RELIABILITY AND CALCULATION OF FAILURE RATE
3.1 STEADY-STATE
Tantalum Dielectric has essentially no wear out mechanism
and in certain circumstances is capable of limited self
healing, random failures can occur in operation. The failure
rate of Tantalum capacitors will decrease with time and not
increase as with other electrolytic capacitors and other
electronic components.
Voltage Correction Factor
1.0000
0.1000
0.0100
Infant
Mortalities
0.0010
0.0001
0
0.9
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Applied Voltage / Rated Voltage
Figure 2. Correction factor to failure rate F for voltage
derating of a typical component (60% con. level).
Infinite Useful Life
Operating temperature
If the operating temperature is below the rated temperature
for the capacitor then the operating reliability will be improved
as shown in Figure 3. This graph gives a correction factor FT
for any temperature of operation.
Useful life reliability can be altered by voltage
derating, temperature or series resistance
Figure 1. Tantalum reliability curve.
Temperature Correction Factor
The useful life reliability of the Tantalum capacitor is affected
by three factors. The equation from which the failure rate can
be calculated is:
100.0
F = FU x FT x FR x FB
10.0
where FU is a correction factor due to operating voltage/
voltage derating
Tantalum
1.0
FT is a correction factor due to operating
temperature
0.1
FR is a correction factor due to circuit series
resistance
0.0
FB is the basic failure rate level. For standard
leaded Tantalum product this is 1%/1000hours
20 30 40 50 60 70 80 90 100 110 120 130
Temperature (C)
Figure 3. Correction factor to failure rate F for ambient
temperature T for typical component (60% con. level).
Operating voltage/voltage derating
If a capacitor with a higher voltage rating than the maximum
line voltage is used, then the operating reliability will be
improved. This is known as voltage derating. The graph,
Figure 2, shows the relationship between voltage derating
(the ratio between applied and rated voltage) and the failure
rate. The graph gives the correction factor FU for any
operating voltage.
MAY 2013 ■ 155
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