Engineering" refers to the development of technology, processes, and
standards to ensure the reliability of semiconductor devices during
application. It encompasses a vast set of engineering disciplines that
ensure the continuous improvement in the reliability of every device.
Reliability is defined as the ability of a
device to conform to its
electrical and visual/mechanical specifications over a specified period
of time under specified conditions at a specified confidence
level. Reliability engineering employs a wide variety of
tests (see menu on the left for descriptions of some reliability
tests) to achieve continuous reliability improvement throughout the entire life cycle of the
semiconductor device - from design, to manufacturing, to its usage, and until after its
Since it is often more
difficult to improve the reliability of a semiconductor device after it
has been released, as much effort as possible must be exerted to design
units that are inherently reliable. This concept is known
as "Designing for Reliability", or DFR. This consists of
following all known design rules for making a device reliable, not only
electrically, but visually and mechanically as well. These design rules
must be updated regularly, to reflect the best known practices that
ensure maximum reliability for a device. Building reliability
into a device as early as the 'design phase' is a 'must', especially
now that semiconductor devices reach obsolescence more quickly than in previous years.
an integrated circuit has been designed and the first silicon comes out,
reliability tests at wafer level are done to assess the reliability of
the die. This is known as
wafer-level reliability testing. Any reliability issues identified
at this level must be corrected, since these will surely manifest even
at package level. Note that the possibility of encountering wafer-level
problems will be greatly minimized by diligently following the concept
If the new circuit passes
wafer-level reliability testing, the wafer is assembled into its
intended package. The packaged device will then undergo
package-level reliability testing.
refers to the assessment of the over-all
reliability of the device in packaged form. This consists of
subjecting packaged samples to reliability tests that expose the various
sample sets to different stress conditions, after which the samples are
tested for any degradation in
quality after the stress. Since reliability stresses are often
destructive, only a sample population is used for reliability
testing. As such, the assessment of the reliability of the rest of
the population is essentially statistical and probabilistic in nature.
are many industry-standard package-level reliability tests already available.
The reliability test employed is chosen based on the failure mechanism
of interest to the engineer, as different stress tests accelerate
different failure mechanisms. Nonetheless, most reliability tests
utilize one or more of the following stress factors to accelerate
failure: temperature, moisture or humidity, current, voltage, and
pressure. The most popular industry-standard reliability tests for
semiconductors are shown in the
menu on the left.
to the official release of a new device for mass manufacturing, it must undergo full qualification.
device qualification is operationally the same as
package-level reliability testing, except that it is systematized with
the objective of generating official reliability data that would justify
the mass manufacturing of the new device. New device qualification
most often requires several sets of samples for different reliability
the final semiconductor device has successfully completed the qualification process,
it may be released for mass manufacturing and consumption. To ensure
that no major process deviations occur in the manufacturing line, a regular
monitoring of the reliability of the manufactured units is performed.
Reliability monitoring, as this activity is often referred to,
consists of getting finished samples from the line and
subjecting these to reliability testing. Valid reliability
failures should undergo root cause analysis for reliability improvement.
an excellent semiconductor reliability engineering system would have all
of the following components: 1) design for reliability; 2)
wafer-level reliability testing; 3) package-level reliability testing;
4) new device/process qualification; and 5) reliability monitoring.
Test or PCT;
Heat Resistance Test (SHRT);
www.EESemi.com. All Rights Reserved.