08055C datasheet(14/20 Pages) AVX

14 / 20 page

General Description

Typical Cap. Change vs. D.C. Volts

X7R

Typical Cap. Change vs. Temperature

X7R

Effects of Time – Class 2 ceramic capacitors change

capacitance and dissipation factor with time as well as tem-

perature, voltage and frequency. This change with time is

known as aging. Aging is caused by a gradual re-alignment

of the crystalline structure of the ceramic and produces an

exponential loss in capacitance and decrease in dissipation

factor versus time. A typical curve of aging rate for semi-

stable ceramics is shown in Figure 6.

If a Class 2 ceramic capacitor that has been sitting on the

shelf for a period of time, is heated above its curie point,

(125°C for 4 hours or 150°C for 1⁄2 hour will suffice) the part

will de-age and return to its initial capacitance and dissi-

pation factor readings. Because the capacitance changes

rapidly, immediately after de-aging, the basic capacitance

measurements are normally referred to a time period some-

time after the de-aging process. Various manufacturers use

different time bases but the most popular one is one day

or twenty-four hours after “last heat.” Change in the aging

curve can be caused by the application of voltage and

other stresses. The possible changes in capacitance due to

de-aging by heating the unit explain why capacitance

changes are allowed after test, such as temperature cycling,

moisture resistance, etc., in MIL specs. The application of

high voltages such as dielectric withstanding voltages also

tends to de-age capacitors and is why re-reading of capaci-

tance after 12 or 24 hours is allowed in military specifica-

tions after dielectric strength tests have been performed.

Effects of Frequency – Frequency affects capacitance

and impedance characteristics of capacitors. This effect is

much more pronounced in high dielectric constant ceramic

formulation that is low K formulations. AVX’s SpiCap soft-

ware generates impedance, ESR, series inductance, series

resonant frequency and capacitance all as functions of

frequency, temperature and DC bias for standard chip sizes

and styles. It is available free from AVX and can be down-

loaded for free from AVX website: www.avxcorp.com.

25%

50%

75%

100%

Percent Rated Volts

2.5

-2.5

-5

-7.5

-10

0VDC

-55 -35

-15

+25 +45 +65 +85 +105 +125

Temperature Degrees Centigrade

+20

+10

-10

-20

-30

Figure 4

Figure 5

100

1000 10,000 100,000

Hours

+1.5

-1.5

-3.0

-4.5

-6.0

-7.5

Characteristic

Max. Aging Rate %/Decade

C0G (NP0)

X7R, X5R

Y5V

None

Figure 6

Typical Curve of Aging Rate

X7R

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