TAP/TEP Technical Summary and
Application Guidelines
A commonly held misconception is that the leakage current
of a Tantalum capacitor can predict the number of failures
which will be seen on a surge screen. This can be disproved
by the results of an experiment carried out at AVX on 47μF
10V surface mount capacitors with different leakage
currents. The results are summarized in the table below.
An added bonus of increasing the derating applied in a
circuit, to improve the ability of the capacitor to withstand
surge conditions, is that the steady-state reliability is
improved by up to an order. Consider the example of a
6.3 volt capacitor being used on a 5 volt rail. The steady-
state reliability of a Tantalum capacitor is affected by three
parameters; temperature, series resistance and voltage
derating. Assuming 40°C operation and 0.1Ω/volt of series
resistance, the scaling factors for temperature and series
resistance will both be 0.05 [see Section 3.1 (page 154)]. The
derating factor will be 0.15. The capacitors reliability will
therefore be
Leakage Current vs Number of Surge Failures
Number tested Number failed surge
Standard leakage range
0.1 μA to 1μA
10,000
10,000
10,000
25
26
25
Over Catalog limit
5μA to 50μA
Failure rate = FU x FT x FR x 1%/1000 hours
= 0.15 x 0.05 x 1 x 1%/1000 hours
Classified Short Circuit
50μA to 500μA
-3
= 7.5% x 10 /hours
If a 10 volt capacitor was used instead, the new scaling factor
would be 0.017, thus the steady-state reliability would be
Again, it must be remembered that these results were
derived from a highly accelerated surge test machine,
and failure rates in the low ppm are more likely with the end
customer.
Failure rate = FU x FT x FR x 1%/1000 hours
= 0.017 x 0.05 x 1 x 1%/1000 hours
-4
= 8.5% x 10 / 1000 hours
AVX recommended derating table
So there is an order improvement in the capacitors steady-
state reliability.
Voltage Rail
Working Cap Voltage
3.3
5
6.3
3.3 RELIABILITY TESTING
AVX performs extensive life testing on tantalum capacitors.
10
10
12
15
≥24
20
■ 2,000 hour tests as part of our regular Quality Assurance
Program.
25
35
Test conditions:
Series Combinations (11)
■ 85°C/rated voltage/circuit impedance of 3Ω max.
■ 125°C/0.67 x rated voltage/circuit impedance of 3Ω max.
3.4 Mode of Failure
For further details on surge in Tantalum capacitors refer
to J.A. Gill’s paper “Surge in Solid Tantalum Capacitors”,
available from AVX offices worldwide.
This is normally an increase in leakage current which ultimately
becomes a short circuit.
MAY 2013 ■ 157
KYOCERA AVX [ KYOCERA AVX ]
