Transcript Standardisation of Electronic Components

Reliability Engineering
1
Bath Tub curve
Infant
Mortality
Useful Life
Wear Out
Time
2
LIFE CHARACTERISTIC CURVE
Infant Mortality
 Due to gross built in flaws caused by faulty
workmanship
 Transportation damage or installation errors, etc.
Examples:
Poor seals or welds or solder joints
Poor connections
Dirt or contamination on surfaces or in materials
Chemical impurities in metals or insulation
Voids, cracks, thin spots insulation or protective
coatings
Incorrect positioning of parts
3
Useful Life Period
Characterised mainly by occurrence of stress
related failures
Exponential distribution, constant failure rate
Wear out
Due to deterioration of the design strength of
the device as a consequence of operation
and exposure to environmental fluctuations,
corrosion / oxidation / ionic migration, etc.
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Four Types of Part Failures
Type
Quality
Dependent upon
Unrelated to
stress or Time
Eliminated by
Inspection
Reliability Stress
Screening
Wear-out
Time
Design
May be stress
and/or time
dependent
Qualification (life)
testing or periodic
replacement
Proper application
and derating
5
Reliability
Reliability is the probability that an
item will perform its intended function
for a specified time interval under
stated conditions
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R(t) = e-t
R(t) is the probability that the item will
operate without failure for the time period t,
under specified operating conditions
e - base of natural logarithm = 2.71828
λ - failure rate in Fits
1 Fit = 1 Failure / 10-9 hours
Fit - Failure Unit , Failure in time
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MTBF and MTTR
Up
Ut
Dt
Down
Time
8
Availability
The probability that the system is operating
at time t.
MTBF.
Availability = ---------------------.
MTBF + MTTR.
MTBF … Mean time between failures.
MTBF = 1/ λ hours.
MTTR … Mean time to repair (expressed in
hours).
9
Maintainability
The measure of the ability of an item to be
retained in or restored to a specified
condition when maintenance is performed
by personnel having specified skill levels,
who use prescribed procedures and
resources at each level of maintenance and
repair.
10
Failure Distribution
Versus
Environment
VIBRATION
 TEMPERATURE
 MOISTURE
 SAND & DUST
 SALT
 ALTITUDE
 SHOCK

27%
40%
19%
6%
4%
2%
2%
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