Reliability of Aluminum Electrolytic
Capacitors
| |
[1] Drift of Aluminum Electrolytic
Capacitors Over Time
.gif)
|
|
The aluminum electrolytic
capacitor has a limited life span.
This occurs because the electrolyte
in the element eventually dissipates.
The changes in
performance over
time can be described
as follows:
|
|
(1) |
Eventually, the capacitance
begins to drop off.
|
|
(2) |
The tangent of the
loss angle begins to increase.
|
|
(3) |
Generally, when voltages
are applied, the leakage current
begin to drop.
|
|
(4) |
Finally, at the end
of the life span, the capacitor
enters an open-circuit mode as
the dielectric dries up.
|
|
|
[2] Criteria for Defining Failures in
Aluminum Dielectric Capacitors
|
|
The criteria for defining
failures are established for each individual
product series. In general, the standards
for establishing the guaranteed life span
are as follows:
|
|
(1) |
Changes in capacitance:
A failure is defined as a change in capacitance
from the initial capacitance level beyond
the specified range. The change is generally ±20%
to ±30%.
|
|
(2) |
Changes in the tangent
of the loss angle: A failure is defined
as the component exceeding the specified
range. Usually, this range is 1.5 to 3.0
times the initial value.
|
|
(3) |
Change in leakage current:
The definition of failure occurs when there
is an excess of the specification values. |
[3] Definitions of Life Span for the Aluminum
Electrolytic Capacitor
|
|
The following five
life span definitions of aluminum
electrolytic capacitors are used
at Elna, Ltd.:
|
|
(1) |
Guaranteed Life Span
The life span that is set in the
product transactions. (The
period of time where the specified
performance will be maintained.)
|
|
(2) |
Design Life Span
A targeted life span specified
at the design stage.
|
|
(3) |
Practical Life Span
A precursory period of time where
the component enters into the
burnout failure phase.
|
|
(4) |
Effective Life Span
The period of time where the capacitor
has gone beyond the infant
mortality stage and has entered
the burnout failure stage.
At this stage, the number of
failures are less than the
specified values.
|
|
(5) |
Average Life Span
The average of the five life spans
prior to the burnout failures.
|
|
|
|
|
There are five different
definitions for "life span." These definitions
share a relationship in terms of the length
of their life spans: guaranteed life span < design
life span < practical life span < effective
life span < average life span. |
[4] Typical Aluminum Electrolytic Capacitor
Failure Modes and Their Causes
|
|
The failure mode and cause
analysis diagram is shown below: |
[5] Various Types of Reliability Data
|
|
The reliability data for
typical Elna aluminum dielectric capacitors
are shown below:
|
|
<1> |
RVK Series: 125°C vertical
chip aluminum electrolytic capacitor |
| |
(1) Durability (high temperature
charge) |
|
| |
(2) High temperature and
low temperature characteristics |
|
| |
(3) Frequency characteristic |
|
|
<2> |
RYK Series: 125°C horizontal
chip aluminum electrolytic capacitor |
| |
(1) Durability (high temperature
charge) |
|
| |
(2) High temperature and
low temperature characteristics |
|
| |
(3) Frequency characteristic |
|
|
<3> |
RK Series: 125°C small
footprint aluminum electrolytic capacitor |
| |
(1) Durability (high temperature
charge) |
|
| |
(2) High temperature and
low temperature characteristics |
|
| |
(3) Frequency characteristic |
|
|
<4> |
RJB
Series: 105°C small footprint high
reliability low impedance aluminum electrolytic
capacitor
|
| |
(1) Durability (high temperature
charge) |
|
| |
(2) High temperature and
low temperature characteristics |
|
| |
(3) Frequency characteristic |
|
|
|
|
