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High Q Capacitors

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Ageing of Ceramic Capacitors

Capacitor ageing is a term used to describe the negative,

logarithmic capacitance change which takes place in ceramic

capacitors with time. The crystalline structure for barium

titanate based ceramics changes on passing through its Curie

temperature (known as the Curie Point) at about 125ºC. The

domain structure relaxes with time and in doing so, the

dielectric constant reduces logarithmically; this is known as the

ageing mechanism of the dielectric constant. The more stable

dielectrics have the lowest ageing rates.

The ageing process is reversible and repeatable. Whenever the

capacitor is heated to a temperature above the Curie Point the

ageing process starts again from zero.

The ageing constant, or ageing rate, is defined as the

percentage loss of capacitance due to the ageing process of

the dielectric which occurs during a decade of time (a tenfold

increase in age) and is expressed as percent per logarithmic

decade of hours. As the law of decrease of capacitance is

logarithmic, this means that for a capacitor with an ageing rate

of 1% per decade of time, the capacitance will decrease at a

rate of:

a) 1% between 1 and 10 hours

b) An additional 1% between the following 10 and 100

hours

c) An additional 1% between the following 100 and 1000

hours

d) An additional 1% between the following 1000 and

10000 hours

e) The ageing rate continues in this manner throughout

the capacitor’s life.

Typical values of the ageing constant for our MLCCs are

Tight Tolerance

One of the advantages of Syfer’s unique ‘wet process’ of

manufacture is the ability to offer capacitors with exceptionally

tight capacitance tolerances.

The accuracy of the printing screens used in the fully

automated, computer controlled manufacturing process allows

for tolerance as close as ± 1% on C0G/NP0 parts greater than

or equal to 10pF. For capacitance value less than 4.7pF

tolerances can be as tight as ± 0.05pF.

Periodic Tests Conducted and Reliability Data

For standard surface mount capacitors components are

randomly selected on a sample basis and the following routine

tests conducted:

• Load Test. 1,000 hours @ 125˚C (150˚C for X8R).

Applied voltage depends on components tested

• Humidity Test. 168 hours @ 85˚C/85%RH

• Board Deflection (bend test)

Test results are available on request.

Conversion Factors

From

FITs

FITs

To

MTBF (hours)

MTBF (years)

Operation

109 ÷ FITs

109 ÷ (FITs × 8760)

FIT = Failures In Time. 1 FIT = 1 failure in 109 hours

MTBF = Mean Time Between Failure

Dielectric Class

Ultra Stable C0G/NP0

Typical Values

Negligible capacitance loss

through ageing

Example of FIT Data Available

Stable X7R

<2% per decade of time

Capacitance Measurements

Because of ageing it is necessary to specify an age for

reference measurements at which the capacitance shall be

within the prescribed tolerance. This is fixed at 1000 hours,

since for all practical purposes there is not much further loss of

capacitance after this time.

All capacitors shipped are within their specified tolerance at the

standard reference age of 1000 hours after having cooled

through their Curie temperature.

The ageing curve for any ceramic dielectric is a straight line

when plotted on semi-log paper.

Capacitance vs. Time

(Ageing X7R @ 1% per decade)

Component type:

Testing Location:

Results based on:

0805 (C0G/NP0 and X7R)

Syfer reliability test department

16,622,000 component test hours

© Knowles 2014

HighQDatasheet Issue 6 (P110506) Release Date 25/08/15 Page 5 of 7

Tel: +44 1603 723300 | Email SyferSales@knowles.com | www.knowlescapacitors.com/syfer

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