Reliability
Models for Failure Mechanisms
Hot Carrier Effects
Hot
carrier effects is a phenomenon involving the injection of highly energetic carriers
into the gate oxide layer and the silicon substrate, resulting
in volume charge build-up that can
shift transistor threshold voltages. This mechanism is
accelerated by low temperatures.
AF = tfuse / tftest
AF
= e([Ea/k]
[1/Tuse-1/Ttest] + C [Vtest-Vuse])
where:
V = voltage
accelerating the carriers
Ea = -0.2 eV
to -0.06 eV
C = constant
Bond/Solderability Failures
Bond/solderability failures related to
intermetallic growths, e.g.,
ball lifting due to Kirkendall voids, Cu-Sn intermetallic growths towards
the leadfinish surface, etc. are modeled as follows.
tf
= Ae(Ea/kT)
AF = tfuse / tftest
AF
=
e(Ea/k)
(1/Tuse-1/Ttest)
where:
A = constant
Ea = 1 eV for Au-Al bonds
Ea = 0.5-0.75 eV for Sn-based leadfinish
TC-induced Package Cracking
The
occurrence
of fracture anywhere in the package after it has undergone several
temperature cycles has also been modeled.
Since
the zero-stress condition of the package is at a high temperature (around
175 deg C) , the low temperature (cooling) cycle has the main effect on
this mechanism.
AF = (DTaccel/DTuse)m
where:
DTaccel =
Tmin(accel)
- Tneutral
DTuse =
Tmin(use)
- Tneutral
Tneutral =
zero stress temperature (approx. 175
deg C)
m = 20 (fracture property-dependent)
Fatigue Failures
Fatigue
failures are failures due to application of cyclical stresses.
AF = (DTaccel/DTuse)n
Nf = C(DT)-n
where:
Nf = cycles to failure
DT
= temperature difference
n = temperature difference factor
<Back to Page
1 - Intro to Reliability
Modeling>
<Back to Page
2 - Rel Models for
Electromigration, Corrosion, TDDB>
See also:
Reliability Engineering;
Failure
Analysis;
Process
Qualification;
Package
Failures;
Die
Failures
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