Burn-in
Burn-in
is an electrical stress test that employs
voltage
and
temperature
to accelerate the electrical failure of a device. Burn-in
essentially simulates the
operating
life
of the
device, since the electrical excitation applied during burn-in may
mirror the worst-case bias that the device will be subjected to in
the course of its useable life. Depending on the burn-in
duration
used, the reliability information obtained may pertain to the
device's
early
life
or its
wear-out.
Burn-in may be used as a
reliability monitor
or as a
production screen
to weed out potential
infant
mortalities from the lot.
Burn-in
is usually done at
125 deg C,
with electrical excitation applied to the samples. The burn-in
process is facilitated by using
burn-in boards
(see Fig.
1) where the samples are loaded. These burn-in boards are then
inserted into the burn-in oven (see Fig. 2), which supplies the
necessary voltages to the samples while maintaining the oven
temperature at 125 deg C. The electrical bias applied may either be
static
or
dynamic,
depending on the failure mechanism being accelerated.
|
Figure 1. Photo of Bare and Socket-populated
Burn-in Boards |
The
operating life cycle distribution of a population of devices may be
modeled as a
bath tub
curve,
if the failures are plotted on the y-axis against the operating life
in the x-axis. The bath tub curve shows that the
highest
failure rates experienced by a population of devices occur during
the
early
stage of the life cycle, or early life, and during the
wear-out
period of the life cycle. Between the early life and wear-out
stages is a long period wherein the devices fail very sparingly.
Figure
2. Two examples of burn-in ovens
Early
life failure (ELF)
monitor burn-in, as the name implies, is performed to screen out
potential early life failures. It is conducted for a duration of 168
hours or less, and normally for only
48 hours.
Electrical failures after ELF monitor burn-in are known as early
life failures or infant mortality, which means that these units will
fail prematurely if they were used in their normal operation.
High Temperature Operating Life (HTOL)
Test is the opposite of ELF monitor
burn-in, testing the reliability of the samples in their wear-out
phase. HTOL is conducted for a duration of
1000 hours, with
intermediate read points at 168 H and 500 H.
Although
the electrical excitation applied to the samples are often defined
in terms of voltages, failure mechanisms accelerated by current
(such as electromigration) and electric fields (such as dielectric
rupture) are understandably accelerated by burn-in as well.
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