BURN-IN, RELIABILITY TESTING, AND
MANUFACTURING OF
SEMICONDUCTORS
Prepared By Cagatay Bozturk
C.Bozturk,School of Technology,KSU
Index
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What is BURN-IN?
Reliability of Semiconductors
What is Reliability&Life Testing
Semiconductor Manufacturing
C.Bozturk,School of Technology,KSU
What is BURN-IN?
Burn-In is the application of thermal and
electrical stress for the purposes of inducing the
failure of "marginal (microelectronic) devices,
those with inherent defects or defects resulting
from manufacturing aberrations which cause
time and stress dependant failures.
C.Bozturk,School of Technology,KSU
Reliability of Semiconductors
To evaluate the reliability of an electronic system,
reliability information on the components used in that
system is important. Failure rates are often used as an
index for reliability. A failure rate indicates how often a
failure occurs per unit time, and failure-rate values
generally change overtime as shown below
C.Bozturk,School of Technology,KSU
Early Failure Stage
During this stage, failures occur at a high rate
following the initial operation of semiconductor
devices. They occur very soon and thus the failure
rate declines rapidly over time. This Is because the
potential' failures that could not be removed through
a selective process are included and surface in a
short time if a stress such as temperature or voltage
is applied after use of the device is started. In the
case of semiconductors, these failures are usually
due to defects that could not be removed during
production, such an micro dust collecting on the
wafer, or to material defects.
C.Bozturk,School of Technology,KSU
Random Failure Stage
When early failures are eliminated, the
failure rate drops to an extremely low
value. However, there is always the
possibility of a potential failure accidentally
occurring after a long time. Consequently
the failure rate never decreases to zero. It
is almost constant because failures occur
sporadically
C.Bozturk,School of Technology,KSU
Wear-out Failure Stage
During this stage, failures occur with
increasing frequency over time and are
caused by age-related wear and fatigue. In
the case of a semiconductor device,
electronic migration or oxide film
destruction (TDDB) may occur.
C.Bozturk,School of Technology,KSU
What is Reliability & Life Testing?
The reliability of a semiconductor device is
determined by its ability to perform its
required functions under the stipulated
conditions for a finite period of time.
Quantifiable yardsticks such as the
reliability rate, failure rate, and mean time
to failure (MTTF) are used to measure
reliability.
C.Bozturk,School of Technology,KSU
Objective of Reliability Testing
The objective of reliability testing is to
confirm a semiconductor device's fault-free
operation and estimated useful life by
exposing the device to accelerated or
marginal stress, based on the amount of
stress (thermal stress, mechanical stress,
electrical stress etc) that the device is
estimated to undergo during manufacture,
shipping and normal use.
C.Bozturk,School of Technology,KSU
Semiconductor Manufacturing
Semiconductor manufacturing consists of
the following steps:
1) production of silicon wafers from very
pure silicon ingots
2) fabrication of integrated circuits onto
these wafers
3) assembly of every integrated circuit on
the wafer into a finished product
4) testing and back-end processing of the
finished products.
C.Bozturk,School of Technology,KSU
Wafer Fabrication
Wafer fabrication generally refers to the process of
building integrated circuits on silicon wafers. Prior
to wafer fabrication, the raw silicon wafers to be
used for this purpose are first produced from very
pure silicon ingots, through either the Czochralski
(CZ) or the Float Zone (FZ) method. The ingots are
shaped then sliced into thin wafers through a
process called wafering.
Wafer fab processes, allowing the device designer
to optimize his design by selecting the best fab
process for his device.
C.Bozturk,School of Technology,KSU
Assembly
1.
2.
3.
4.
The process of putting the integrated
circuit inside a package to make it
reliable and convenient to use is known
as semiconductor package assembly, or
simply 'assembly'.
In general, an assembly process would
consist of the following steps:
die preparation
die attach
bonding
encapsulation
C.Bozturk,School of Technology,KSU
Steps of Assembly
die preparation, which cuts the wafer into
individual integrated circuits or dice;
die attach, which attaches the die to the
support structure (e.g., the leadframe) of
the package;
bonding, which connects the circuit to the
electrical extremities of the package,
thereby allowing the circuit to be
connected to the outside world; and
encapsulation (usually by plastic molding),
which provides 'body' to the package of
the circuit for physical and chemical
protection.
C.Bozturk,School of Technology,KSU
Test
Once assembled, the integrated circuit is
ready to use. However, owing to the
imperfection of this world, assembled
devices don't always work. Many things
can go wrong to make a device fail, e.g.,
the die has wafer fab-related defects, or
the die cracked during assembly, or the
bonds were poorly connected or not
connected at all. Thus, prior to shipment to
the customer, assembled devices must first
be electrically tested.
C.Bozturk,School of Technology,KSU
Electrical Testing
Electrical testing of devices in big volumes
must be done fast and inexpensively.
Mass-production electrical testing therefore
requires an automated system for doing
the test. Equipment used to test devices
are called, well, testers, and equipment
used to handle the devices while
undergoing testing are called, well,
handlers. Tester/handler systems are also
known as automatic test equipment (ATE).
C.Bozturk,School of Technology,KSU
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.
C.Bozturk,School of Technology,KSU
BURN-IN
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.
C.Bozturk,School of Technology,KSU
Figure 1
Photo of Bare and Socketpopulated Burn-in Boards
Figure 2
Two examples of burn-in
ovens
Conclusion
Burn-in helps us to detect problem trends /
determine critical components in a system
failure (s), and, analyze the system for
Effective reliability. Thanks to burn-in, we
can predict reliability performance and Lifecycle of the products. It provides valid field
“failure data” and timely corrected actions.
C.Bozturk,School of Technology,KSU
References
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http://www.semiconfareast.com
http://www.reltech.co.uk
C.Bozturk,School of Technology,KSU