General Description
Typical Cap. Change vs. D.C. Volts
X7R
Capacitance Change Percent
2.5
0
-2.5
-5
-7.5
-10
25%
50%
Percent Rated Volts
75%
100%
Capacitance Change Percent
+1.5
0
-1.5
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.
Typical Curve of Aging Rate
X7R
-3.0
-4.5
Figure 4
Typical Cap. Change vs. Temperature
X7R
Capacitance Change Percent
+20
+10
0VDC
0
-10
-20
-30
-55 -35
-15
+5
+25 +45 +65 +85 +105 +125
-6.0
-7.5
1
10
100
1000 10,000 100,000
Hours
Characteristic
C0G (NP0)
X7R, X5R
Y5V
Max. Aging Rate %/Decade
None
2
7
Figure 6
Temperature Degrees Centigrade
Figure 5
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
Effects of Frequency –
Frequency affects capacitance
and impedance characteristics of capacitors. This effect is
much more pronounced in high dielectric constant ceramic
formulation than in 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.avx.com.
67
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