Life Testing
A Reliability Engineering
Concept
By: Nicole Panaccio
Life Testing Overview
•
•
•
•
•
•
•
What is Life Testing?
Life Testing in Organizations
How Does Life Testing Work?
Who Uses Life Testing?
Motorola’s Process
Paper Clip Life Testing
Summary
What is Life Testing?
• A process done under controlled
conditions to determine how
and when a product will fail in
its intended environment
• Improves a product’s reliability
• Finds the weakest and strongest
points of a product
Life Testing in
Organizations
• Design Life Cycle:
–
–
–
–
–
–
Have an idea
Design it
Make a prototype
Final definition
Design and evaluation
implementation
Life Testing in
Organizations
• Life testing design cycle:
Idea
Design
Prototype
• Prototype is tested for failures
• Design cycle stops with
prototypes
Life Testing in
Organizations
• Customers believe that quality is
inherent is all product
• Life testing validates this
assumption.
• Specific directions are followed
in a uniform fashion
Three Types of Tests
• Type of tests performed:
– Qualitative Tests
– ESS (Environmental Stress
Screening)
– Accelerated Life Testing
Qualitative Tests
• Gives the product tested the
most failures
• Failures produced by high and
low stresses
• To pass the product must live
through the entire test without
failure ¹
ESS-Environmental
Stress Screening
• Applies environmental stimulus
to products
• Goal: ¹
– To find latent defects and eliminate
them
– To find defects not found with
inspection or electrical testing
Accelerated Life Testing
• Similar to Life Testing
– Testing moves at a faster pace
• Uses quantitative data
• End results yield times-to-failure
data
– Times-to-failure: how long it takes
till a failure is made
Accelerated Life Testing
• Life distributions show how fast
a product will fail ¹
• Two methods used to get timesto-failure information:
– Usage rate acceleration
– Overstress acceleration
Usage Rate
Acceleration
• A test used for products that
only operate for small amounts
of time ¹
• It increases the time to make
failures happen quicker than if it
were used normally
Overstress Acceleration
• Backup to usage rate
• Used if usage rate is not
appropriate means ¹
• Tests products that are
constantly used
• Uses stress levels that it would
not normally encounter
How Does Life Testing
Work?
• Majority of tests done on small
sample
– 4 to 6 units
• Begin test with lowest level of
the product
• Failures must be documented as
they happen
How Does Life Testing
Work?
• Soft failures occur when there is
damage made but the product
returns to its normal state
• Hard failures are permanent
damages done to the product
Margins and Reliability
• The difference
between soft and
hard failures is the
margin for stress ¹
• Once the failures
are found and fixed,
the margins have
reached their max
• Maximized margins
increase reliability
and the life of the
product
Who Uses Life Testing?
• Motorola
– Mission to produce cell phones
with “virtually no defects”
– Use accelerated life testing to
accomplish mission
– Helps to validate their six sigma
corporate standard
Motorola’s Process
• Determine environment
• Perform life testing in all
environments.
– Four to six weeks of testing is
required ¹
Motorola’s Process
• Drop Testing ¹
– Samples are dropped on different
surfaces of the phone multiple
times.
• Hot and Cold Temperatures ²
• The phones receive extreme
temperatures of hot and cold.
– Testing simultaneously with audio
quality and simulated calls
Motorola’s Process
• Electro-Static Discharge ¹
– Zap products with an electric pulse
at “discharge” points
• Dust Exposure ²
– Products are placed in dust
chamber
– Dust is shaken all over the product
and then left to settle
Motorola’s Process
• Vibration Testing ¹
– Horizontal and vertical vibration testing.
– Placed into vibration table and controlled
by tester
– The tests vary in the extremes of
vibrations given
– During the test it places a call and must
be stable throughout the process
Motorola’s Process
• Environmental Aging Tests ¹
– Temperature cycling: moving from low to
high heat and cold
– Temperature shock
• Certification Testing ²
–
–
–
–
Sudden Impact Testing
Endurance Testing
Package Drop Testing
Transport Simulation
Motorola Summary
• Life testing cuts Motorola’s
costs
• Less return of products that fail
for the customer
• Their design exceeds customer
satisfaction with “virtually no
defects”
Paper Clip Life Testing
• Follow these directions to
determine how fast a paper clip
will break using the life testing
methods. ¹
Follow These Steps
• With one hand, hold
the clip by the
longer, outer loop.
• With the thumb and
forefinger of the
other hand, grasp
the smaller, inner
loop.
• Pull the smaller,
inner loop out and
down 90 degrees
so that a right
angle is formed as
shown.
Follow These Steps
• With one hand,
continue to hold
the clip by the
longer, outer loop.
• With the thumb and
forefinger of the
other hand, grasp
the smaller, inner
loop.
Follow These Steps
• Push the smaller
inner loop up and in
90 degrees so that
the smaller loop is
returned to the
original upright
position in line with
the larger, outer
loop as shown.
Follow These Steps
• This completes one cycle.
• Repeat until the paper clip
breaks. Count and record the
cycles-to-failure for each clip.
Summary
• Quality is inherent in most products
• Life Testing allows the consumer to
have reliable information because it
is consistent throughout the testing
• Some life testing can cause
permanent damage, and some
aspects of the testing do not
• Prototypes are used to test because
it is cheaper and easier to run tests
on samples
Summary
• Life Testing can be done with
ease or tremendous detail
• Any way it is done it will yield
the same information
• The tester must document what
and how they do things