JOHANSON DIELECTRICS INC.

15191 Bledsoe Street, Sylmar, Ca. 91342 Phone (818) 364-9800 Fax (818) 364-6100

5/21/2012 1

CERAMIC CAPACITOR AGING MADE SIMPLE

Christopher England Applications Engineer HVS Produc ts

Class II dielectrics experience a phenomenon called aging, and it is simply a decrease in

capacitance over time due to crystalline changes that occur in all Class II dielectrics

(X7R, X5R and Y5V). This is caused by the relaxation or realignment of the electrical

dipoles within the capacitor. This phenomenon is affected by time, temperature, voltage

(voltage has a minute effect).

As the relative “dielectric constant” or “ε

” of the material increases, this effect is

magnified. The ε

of the material determines the volumetric capacity of the capacitor. As

the ε

increases we are able to design capacitors with higher capacitance values. These

higher values have their drawbacks too. As the ε

increases so does capacitor aging and

capacitance loss in the capacitor due to temperature and voltage.

Class I dielectrics (NP0 – COG) do not exhibit this phenomenon as they are stable over

Time, Temperature and voltage. The drawback for these dielectrics is that the ε

relatively low as compared to the Class II dielectrics. This means the maximum

capacitance available in these stable parts is much lower than that of the Class II parts.

Typically these ε

are as follows: NP0 10-100, X7R 2000-5000 and Y5V can be as high

as 25000.

THE EFFECT OF TIME

The effect of time imposes a predictable loss of capacitance in Class II capacitors. For

X7R and X5R the loss is calcul ated at -2.5% per decade hour and for Y5 V it is -7% per

decade hour. After manufacturing the crystalline structure of the dielectric material is

reset. It is due to the realignment of these crystals after firing that the capacitor goes

through a logarithmic loss of capacitance. The aging rate for each of these materials is

listed below in Figure 1.

Cl ass I I Di el ect r i c agi ng

-30

-25

-20

-15

-10

-5

0.1 1 10 100 1000

TIME

% CHG

X7R

Y5V

Figure 1

JOHANSON DIELECTRICS INC.

15191 Bledsoe Street, Sylmar, Ca. 91342 Phone (818) 364-9800 Fax (818) 364-6100

5/21/2012 2

This aging rate is expressed in decade hours. This means after manufacturing the loss o f

capacitance is calculated at 1hr, 10hrs, 100hrs, 1000hrs etc….. This means at 10 hours

the capacitance changes the same percentage as it will when measured at 100 hours and

1000 hours. As time goes on the aging process slows.

REVERSING THE AGING EFFECT

The agin g process is rever sible. B y heatin g the c apacitors o ver the “C urie Point ” (approx

125

for Barium Titanate capacitors) the crystalline structure of the capacitor is returned

to its original state and the capacitance value observed after manufacturing. This process

is referred to as “De-Aging”. The amount of De-Aging is dependant on the level of

temperature and how long the cap aci to rs are expos ed t o it. Ex posure to 150

for 1.5 hours

is sufficient to return the capacitor to its original value. The soldering process is not

necessarily an effective De-Aging process but the capacitance value will be raised.

STORAGE AND INSPECTION

It should be noted that the longer the capacitor is stored after manufacturing the lower the

“Aged Capacitance” will be. This means that when the capacitor is inspected before

assembly the capacitance may appear to be out of specified tolerance. This capacitance

readin g do es not tak e into ac count the di electric aging and t he time si nce manufact uring.

Only by De-Aging can the “Initial Capacitance” be verified.

IN-PLANT TESTING

In the manufacturing process the test limits are adjusted so that the capacitance value is

withi n the speci fied to lerance at 1000h rs. Thi s is cr itical as the cap acitanc e chan ge in th e

first 1000 hours is the greatest. After 1000 hours (41 days) the capacitor has gone through

4 decades of aging (0-1, 1-10, 10-100, 100-1000). This effect is different for each

dielectric material as shown in Figure 1

TESTING AFTER ASSEMBLY

After the soldering process the capacitors have essentially been De-Aged. Capacitance

measurem ents m ay be er ratic in t he initial 10 hours after testing. This is due to the initial

capacitance value, dielectric type and the time between reflow and the capacitance

measurem ent. For this reason it may be necessary to wait for the capacitance to stabilize

after reflow before testing. In “High K” dielectrics the capacitance may also appear

slightly high after the soldering process. This is normal as the capacitance is intended to

be stabl e after 1000 hour s so that there is adequate capacitance throughout the life of the

circuit

Notice: Specifications are subject to change without notice. Contact your nearest Johanson Dielectrics,

Inc. Sales Office for the latest specifications. All statements, information and data given herein are

believed to be accurate and reliable, but are presented without guarantee, warranty, or responsibility of

any kind, expressed or implied. Statements or suggestions concerning possible use of our products are

made without representation or warranty that any such use is free of patent infringement and are not

recommendations to infringe any patents. The user should not assume that all safety measures are

indicated or that other measures may not be required. Specifications are typical and may not apply to all

applications.