T491V108K035AT View Datasheet(PDF) - KEMET

Part Name

Description

Manufacturer

T491V108K035AT

Surface Mount Capacitors

KEMET 

SOLID TANTALUM CHIP CAPACITORS

TANTALUM MnO2 COMPONENT PERFORMANCE CHARACTERISTICS (con’t.)

RELIABILITY

(1) λV = λbπTπCπVπSRπQπE x 1000

19. Reliability Prediction

(2) λb = 0.00005CWR or 0.0004CSR

Solid tantalum capacitors exhibit no degradation

failure mode during shelf storage and show a

constantly decreasing failure rate (i.e., absence

of any wear out mechanism) during life tests.

This failure rate is dependent upon three impor-

tant application conditions; DC Voltage, ambient

temperature, and circuit impedance. Additional

effects are attributable to the capacitance of the

device and atmospheric and mechanical expo-

sure of the assembled circuit. The 1000 multiplier

at the end converts the failure rate to parts-per-

billion piece-hours. A prediction of the failure rate

can be made using these application conditions

and the formulas and tables listed in MIL-HDBK-

217F (Notice 2).

[ ( )] (3)

πT = exp

-0.15

8.617 • 10-5

1

TAmb

1

298

(4) S = Application-Voltage

Rated-Voltage

( ) πV =

S

0.6

17

+1

(5) πC = 1.0 • C.023

(6) πSR = Lookup Table

πE = Lookup Table

( ) Pcs. Fail

(7) πQ = Pcs. Tested x Hrs. Tested x 100,000

FIGURE 11a. MIL-HDBK-217F Notice 2 formulas.

Base Multiplier: The first multiplier is the base

CR (ΩV) πSR

multiplier (2) established for the capacitor type.

>0.8

0.66

For “CWR-Chips” or surface mount components

the base multiplier is 0.00005, and for “CSR-

Leaded” devices, the base multiplier is 0.00040.

Temperature: The temperature factor is given as

0.6-0.8

1.0

0.4-0.6

1.3

0.2-0.4

2.0

0.1-0.2

2.7

<0.1

3.3

(3). From this formula, it can be seen that the unity

factor, or 1, is derived at an ambient temperature

FIGURE 11b. Table for circuit resistance multipiers.

of +25ЊC (+298ЊK), 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

Voltage: The multiplier for application voltage (4)

applied to the established or base failure rate of

is a two step process: first, the application volt-

the part. The T492 Series is qualified under U.S.

age is compared to 60% of rated voltage, and

military specification MIL-PRF-55365. Failure

then this ratio is raised to an exponential power

rates as low as 0.001% kHr are available under

of 17 and added to unity. Consider applications

this test program.

of 50%, 60%, 70%, 80% and 90% of rated volt-

age. The multipliers for these applications would

be 1.045, 2.00, 14.7, 134, and 986, respectively.

From these results it is evident why manufactur-

ers recommend application voltages not to

exceed 50% rated voltages.

For series not covered by military specifications,

an internal sampling program is operated by

KEMET Quality Assurance whereby parts are put

on life test at rated voltage for 2000 hours. The

confidence level chosen for the reporting data is

60%. (The cost of sampling each batch would be

Capacitance: There is a factor (5) applied to the

prohibitive, and no claim is made to guarantee

capacitance (in µF) which effectively increases

the failure rate of each batch.) With this testing

the failure rate for increasing capacitance

and each new qualification test for new parts, the

(increases in effective area resulting in increases

average failure rate for all commercial Series lies

in possible faults).

between 0.1% and 1.0% per thousand-

Series Resistance: The series resistance is only

piece-hours.

concerned with the resistance per application

FIT Calculator

bias (ohms per volt) external to the capacitor,

and does not include the ESR as a factor.

All of these factors are gathered into a Windows

based software, available free from the KEMET

Environmental: The environmental factor is

web site (www.kemet.com). The “FIT Calculator”

determined by the harshness of the ambient

software does all the calculations and look-ups

conditions beyond temperature. An explanation

based on information entered or selected by the

of these ratings is included in the MIL specifica-

operator. A manual may also be downloaded

tion and are too extensive to be covered here. In

from the same web page to explain the controls

most cases, this factor is set to ground benign or

and displays The manual as well as a help

GB, with the resulting factor equal to “1”.

screen also detail the environmental conditions.

©KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300

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