OVERVIEW OF HIGHLYOVERVIEW OF HIGHLY ACCELERATED LIFEACCELERATED LIFE
TESTChet Haibel
©2011 ASQ & Presentation ChetPresented live on Jan 18th, 2012
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Chet Haibel ©2012 Hobbs Engineering Corp.
OVERVIEW OF HIGHLY ACCELERATED LIFE TEST
Chet Haibel Hobbs Engineering Corporation
www.hobbsengr.com (303) 465-5988
Chet Haibel ©2012 Hobbs Engineering Corp. 1
What Is Reliability?
CLASSICAL DEFINITION
Reliability is the probability that a component,
subassembly, instrument, or system will perform
its specified function for a specified period of time
under specified environmental and use conditions.
Chet Haibel ©2012 Hobbs Engineering Corp. 2
What is a Product Failure?
Failure is the inability of a device to perform its intended functions
under stated environmental conditions for a specified time.
Failures are classified into three types based on time:
• Early-Life (Infant Mortality)
• Useful-Life (Random-in-time)
• Wear-Out (End of useful life)
Each failure type has different kinds of causes and therefore different
tests to discover them and different methods of correction / prevention.
Chet Haibel ©2012 Hobbs Engineering Corp. 3
What is a Product Failure?
Failures are also classified into three types based on their persistence:
• Hard Failure (Persistent)
Typically a component must be replaced, but trouble-shooting may be
done at room temperature with no vibration or other stimulus
• Soft Failure (Temporary)
Often merely removing the environmental stimulus clears the problem,
but sometimes it is necessary to cycle power, clear fault logs, etc.
Product must be stressed to duplicate and trouble-shoot soft failures
Many very important reliability issues are SOFT FAILURES.
• Intermittent Failure (Elusive)
This is permanent but the failure mode must be put into a detectable state
Chet Haibel ©2012 Hobbs Engineering Corp. 4
What Causes Product Failure?
A component fails when applied load exceeds design strength.
Applied Load Design Strength
Failure
Units of Applied Load, Strength
Chet Haibel ©2012 Hobbs Engineering Corp. 5
Applied Loads
Examples of applied load might be:
Force
Torque
Tension
Shear
Pressure
Voltage
Current
Wattage
Clock Speed
Electrostatic Discharge
Electromagnetic Interference
Chet Haibel ©2012 Hobbs Engineering Corp. 6
Design Strength
Examples of design strength:
Torque rating of a bolt
Voltage rating of a capacitor
Current rating of a diode
Power rating of a resistor
Shear strength of solder
Tensile rating of plastic
Temperature rating of transformer insulation
Chet Haibel ©2012 Hobbs Engineering Corp. 7
Load / Strength Interference
Desirable
Obvious
More Subtle
Load Strength
Load Strength
LoadStrength
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Early-Life
Useful-Life
Wear-Out
Load Strength
Load Strength
Load Strength
with time
Load / Strength Interference
Chet Haibel ©2012 Hobbs Engineering Corp. 9
Bathtub Curve
Operating Time (t)
Haza
rd R
ate
- h
(t)
Useful-Life
Failures
Early-Life
Failures
Wear-Out
Failures
Life to the Beginning of Wear-Out
Random-in-Time Failures
Chet Haibel ©2012 Hobbs Engineering Corp. 10
Wear-Out Failures
Hazard
Rate
Time
h(t)Increasing Hazard Rate
Failures due to cycle fatigue
Corrosion
Frictional wear
Shrinkage, cracking in plastic components
Typical of mechanical systems
StrengthLoad
with time
Chet Haibel ©2012 Hobbs Engineering Corp. 11
Cycle Fatigue
Cycled by:
• Product Operation
• Thermal Cycling
• Vibration
• Shock
• Etc.
Stresses:
• Pressure
• Tension
• Torsion
• Shear
• Etc.
Use up Fatigue Life
Chet Haibel ©2012 Hobbs Engineering Corp. 12
Observed Failure Behavior
For a given stress level, the number of cycles to failure in a sample
will occur in a distribution due to specimen variation
0
2
4
6
8
10
12
14
16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Cycles to Failure
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Observed Failure Behavior
Higher stress level requires fewer cycles to failure
0
2
4
6
8
10
12
14
16
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Cycles to Failure
Higher Stress Lower Stress
Chet Haibel ©2012 Hobbs Engineering Corp. 14
Observed Failure Behavior
For the same failure mode, stress level and the number of cycles
to failure are related by a straight line on log scales
S - N Diagram
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
0 1 2 3 4 5
Log N, Cycles to Failure
Lo
g S
, S
tress
S1 N1
S2 N2
Chet Haibel ©2012 Hobbs Engineering Corp.
One Failure Mode: Fatigue Damage
Vibration Analysis of Electronic Equipment by Dave Steinberg, Wiley, 1973
D n b, where
• D is the Miner’s Criterion fatigue damage accumulation,
• n is the number of cycles of stress,
• is the stress in force per unit area,
• b is the negative, inverse slope of the S-N diagram for the material.
For wrought Aluminum, doubling the stress decreases the
fatigue cycles by a factor of 1000 b is approximately 10
15
Chet Haibel ©2012 Hobbs Engineering Corp. 16
S-N Diagram for 7075 Aluminum
Vibration Analysis of Electronic Equipment by Dave Steinberg, Wiley, 1973
~ 2 thousand cycles at 80 KSI, but at 40 KSI it takes 2 million cycles
O
O
Chet Haibel ©2012 Hobbs Engineering Corp.
Assume a resonance at 1,000 Hz
At 40,000 psi, failure would occur at 2 million cycles
2 million ÷ 1 kHz = 2000 seconds or 33 minutes
At 80,000 psi, failure would occur in 2 seconds
Doubling the G rms level would achieve a time compression
factor of 1,000.
This TIME COMPRESSION is normal for HALT
Fatigue Damage from Vibration
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Chet Haibel ©2012 Hobbs Engineering Corp.
Time Compression
Reference: GE Lighting, private telecon with Jim Harsa in 2000
D t v b
t is time
v is the voltage
b =13 for incandescent lights
b = 8 for fluorescent lights
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Increased voltage stress shortens
time to see the same dominant
Wear-Out failure mode
Chet Haibel ©2012 Hobbs Engineering Corp. 19
Discovering Wear-Out Failures Without Using HALT
If possible, set up a repetitive “cycle test” which removes the “dead
time” between cycles. But brainstorm what test artifact may be
added and / or what the test may be concealing
Test until a minimum of five failures are produced [Haibel’s rule]
Use Weibull Analysis to fit a distribution to the failure data
If life is not sufficient, determine the reservoir of material and the
process consuming the reservoir. Increase the reservoir of material
and / or slow down the process consuming it
If necessary, replace the reservoir of material periodically with a
scheduled preventive maintenance program
Chet Haibel ©2012 Hobbs Engineering Corp. 20
Discovering Wear-Out Failures Without Using HALT
Electromigration
(photo courtesy Alcatel-Lucent)
Standard test for
electromigration in
MIL-STD-883 is
Dynamic Burn-In:
125°C for 160 hours
with all voltages,
currents, and clock
speed maximized
Chet Haibel ©2012 Hobbs Engineering Corp. 21
Useful-Life Failures
Hazard
Rate
Time
h(t)Constant Hazard Rate
Random-in-time failures
Parts are new until they fail
Strength-Load interference
Insufficient design margin
Typical of electronic hardware
StrengthLoad
Chet Haibel ©2012 Hobbs Engineering Corp. 22
Quantifying Strength / Load Interference
2/122 )( LS
LS MMSM
Subtracting two Normal
distributions produces
another Normal
distribution whose mean
is the difference of the
means, but whose
standard deviation is the
root-sum-square of the
two standard deviations
We define Safety Margin
Chet Haibel ©2012 Hobbs Engineering Corp. 23
Useful-Life Failures
For simple mechanical products with few parts, we can calculate
reliability one part at a time using Safety Margin for Normal
distributions, or using Monte Carlo simulations for non-Normal
distributions.
For electro-mechanical products with thousands of components
(each of which may have several relevant strength characteristics),
we need an efficient technique to catch the few component
applications that have marginal strength / load relationships. So far,
the most efficient technique is Highly Accelerated Life Test (HALT).
Load Strength
Chet Haibel ©2012 Hobbs Engineering Corp.
Highly Accelerated Life Test
Used in the Design Phase
HALT
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HALT Finds Useful-Life Failures
Load Strength
Load Strength
constantly
increasing load
Increase probability of seeing an existing failure mode
Chet Haibel ©2012 Hobbs Engineering Corp. 26
HALT is the method of seeing the existing failure modes
with the minimum number of prototypes (4 or 8)
in the minimum time (typically a week)
By experience with early prototypes or with similar
products, determine which environmental factors will
“stimulate” the relevant failure modes
Many failure modes in typical electromechanical
products are well stimulated by temperature and
rapid temperature cycling simultaneous with six
degree-of-freedom random vibration
HALT
Chet Haibel ©2012 Hobbs Engineering Corp. 27
G rms
Temperature (Celsius)
20
40
60
80
-20
0
-40
15 20 25 30
ENV2
ENV1
10 5
Goal “limit of technology”
Goal “limit of technology”
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HALT
Every stimulus of potential value is used during New Product Development to find the weak links in the product design
These stresses are not meant to simulate field environments but to find the weak links in the design using only a few units in a very short period of time
Stress levels are taken well beyond the normal mission profile
Sometimes one kind of stress will produce a failure mode in HALT, but a different kind of stress will produce that same failure mode in the hands of customers
Focus on fixing the failure mode, don’t focus on the stimulus
Crossover Effect
Chet Haibel ©2012 Hobbs Engineering Corp. 29
Crossover Effect
Chet Haibel ©2012 Hobbs Engineering Corp.
Thermal
Cycle
Vibration
Voltage
Cycle
High Temp
Burn in
All Combined
Margining
Reference: “Flaw-Stimulus Relationships”, G. K. Hobbs, Sound and Vibration, August 1986
Stimulus-Flaw Precipitation Relationships
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Chet Haibel ©2012 Hobbs Engineering Corp.
More than one failure mode may be affected by the same stress
Failure modes will not necessarily be exposed according to the field Pareto chart, but maybe in some other order
The time compression factor for the failure modes will be different
Perhaps a Different Order
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Field
Pareto
HALT
Order
Chet Haibel ©2012 Hobbs Engineering Corp.
Order of application and discovery:
Cold Step Stress 14%
Hot Step Stress 17%
Temperature Transition 4%
6-Axis Vibration 45%
Combined Temp and Vibe 20%
Without simultaneous, all axis vibration,
65% would have been missed!
“Summary of HALT and HASS Results at an Accelerated Reliability Test Center” by Mike Silverman
Based on 49 products from 19 different industries
Failure % by Stress Type
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Chet Haibel ©2012 Hobbs Engineering Corp.
Where Design Flaws Were Discovered
Cold Step Stress 10%
Hot Step Stress 12%
Rapid Thermal Cycling 4%
Vibration Step Stress 43%
Combined Temp and Vibe 31%
74% of the flaws would have been missed
without simultaneous, all axis vibration!
Chuck Laurenson, Parker Hannifin 1999 Hobbs Engineering ARTS USA Award Winning Paper
“Our Path to Reliability Using HALT”
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Chet Haibel ©2012 Hobbs Engineering Corp.
Let’s Focus on Vibration Swept Sine, Single Axis
Random, Single Axis
Six Degree of Freedom
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ElectroDynamic Shaker
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Chet Haibel ©2012 Hobbs Engineering Corp.
Z-Axis Mode of Vibration
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Chet Haibel ©2012 Hobbs Engineering Corp.
Driven Harmonic Motion
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Z-axis
excitation
A cos 2πft
ftAzdt
dz
dt
zd2cosKDM
2
2
0.001
0.01
0.1
1
10
1 10 100 1000
Transfer Function
Shaker frequency in Hz
Chet Haibel ©2012 Hobbs Engineering Corp.
Swept Sine Vibration
Essentially one frequency at a time,
sweeping at one octave per minute
Typically uses a Hydraulic shaker (limited upper frequency) or an
ElectroDynamic shaker (high powered voice coil)
Using a Stroboscope, one can observe behavior at resonance
But can only see one resonance at a time, in one translation
axis at a time; must mount the product for X, Y, & Z
Miss interactions between resonances at different
frequencies or in different directions
No guarantee of stimulating rotational resonances at all !
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Chet Haibel ©2012 Hobbs Engineering Corp.
Voice Coil Can be Rotated to Drive the Slip Table for X or Y
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Chet Haibel ©2012 Hobbs Engineering Corp.
An Oil Bearing Supports the Slip Table
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Chet Haibel ©2012 Hobbs Engineering Corp.
Random Vibration
Broadband, Pseudo Random (noise-like)
vibration generated by a computer
Typically uses an ElectroDynamic shaker, therefore one translation
axis at a time; still have to mount the product three times for X, Y,
& Z and that doesn’t stimulate rotational resonances very well
But this is a major improvement to see all frequencies at once,
therefore see the interaction of resonances in one direction
Crest factor (ratio of peak to average acceleration) is around 3
Major advantage is to shape the spectrum for qualifying to some
external standard (e.g., RCTA/DO-160D Category U Helicopter)
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Chet Haibel ©2012 Hobbs Engineering Corp.
Random Vibration Shaped Spectrum
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0.001
0.010
0.100
1.000
10 100 1000
Po
we
r S
pe
ctr
al D
en
sit
yg
2/H
z
Freqency (Hz)
Vertical axis is
Power Spectral
Density in units
of g2/Hz
To convert to G
rms, integrate
the power (g2)
over frequency
and take the
square root
Shown is approximately 5G rms
Chet Haibel ©2012 Hobbs Engineering Corp. 43
TIME COMPRESSORTM TC-1 Ocelot by
HALT & HASS Systems Corporation
Chet Haibel ©2012 Hobbs Engineering Corp.
44
Temperature change rates of plus or minus 120 Celsius degrees per
minute, the highest in the industry, from -100°C to +200°C
Vibration will start and run anywhere from 0.1 to 150 G rms
Low G levels are important for executing Modulated Excitation™
which is a breakthrough for detecting intermittent failures
X, Y, and Z acceleration balance is near 1:1:1
Sound level is only 50 dBA at 30 G rms, the lowest in the industry,
no ear protection is necessary, can be used on production lines
Will operate on 110 volts, 50-60 Hz with reduced heating for trouble
shooting – this is important for duplicating soft failures
Features of the TC-1 Ocelot
Chet Haibel ©2012 Hobbs Engineering Corp.
TC-1 Ocelot Vibration System
45
These are
pneumatically-
driven pistons
which generate
six-axis (6 DoF)
vibration from
approximately
20Hz to 10kHz
(one spring is
removed to
show the table
construction
detail) Bottom View
Chet Haibel ©2012 Hobbs Engineering Corp.
Repetitive Shock Spectrum
46
Time in seconds
T d
Mathematically, a string of
rectangular pulses of period T and
duration d in the Time Domain
Transforms into a “comb” of
frequencies whose fundamental
frequency is 1/T with harmonics
weighted by in the
Frequency Domain πdf
dfSin
0.00001
0.0001
0.001
0.01
0.1
1
Frequency in Hz
Chet Haibel ©2012 Hobbs Engineering Corp.
Six-Axis Random Vibration
Using several pneumatic pistons, with air flow modulated in a
proprietary fashion, produces overlapping smeared spectrums
The different angles of the pneumatic pistons generate a feedback
controlled, broadband level of random vibration in X, Y, and Z
translational directions and yaw, pitch, and roll angular directions
Feedback for the control system is provided from one z-direction
accelerometer on the bottom (piston side) of the table
This results in all frequencies in all directions, simultaneously
exciting all resonances for complete failure mode stimulus
The Crest Factor, the ratio of peak to average acceleration is ~10,
which rapidly precipitates design and manufacturing flaws
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Chet Haibel ©2012 Hobbs Engineering Corp.
Poorly mounted components
Poorly formed leads
Poor solder joints
Fretting Corrosion
Loose hardware
Loose wires
Adjacent parts contacting
Wires over sharp edges
Stacked resonances
Some Defects Precipitated by Vibration
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Some Defects Precipitated by Vibration
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Poorly matched expansion coefficients
• Boards and components should match
• Structures should match
Poor solder joints
Improperly formed leads
Improper crimps
PCB shorts, opens
Plated through hole defect
Some Defects Precipitated by Thermal Cycling
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Some Defects Precipitated by Thermal Cycling
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Effect of Temperature Rate on Number of Cycles
“Effective and Economics-Yardsticks for ESS Decisions”, S. A. Smithson, IES, 1990
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Chet Haibel ©2012 Hobbs Engineering Corp. 53
Time Compression for Data from the Previous Slide
Calculations by G. K. Hobbs
At a Ramp Rate of 5⁰C per minute, 400 cycles with a range of 165⁰C
(with no dwells) would take 440 hours
At a Ramp Rate of 25⁰C per minute, 4 cycles with a range of 165⁰C
(with no dwells) would take less than 60 minutes
(At a Ramp Rate of 40⁰C per minute, 1 cycle with a range of 165⁰C
(with no dwells) would take less than 10 minutes)
This is real TIME COMPRESSION !
Chet Haibel ©2012 Hobbs Engineering Corp. 54
Stresses Used in HALT
Wide range temperature
High rate temp. cycling
All axis random vibration
Power cycling
Power voltage and frequency
Secondary voltage
Digital clock frequency
Humidity
Dimensional parameters
Viscosity of a fluid
Vary pH of a fluid
Salinity of a fluid
Add particulates to the fluid
Back Pressure
Chet Haibel ©2012 Hobbs Engineering Corp. 55
More Stresses Used in HALT
Inject electrical noise
Mistune the channel
Radiation (E & M)
Nuclear radiation
Multiple sterilizations
Whatever else makes
sense for the
particular product
Vary magnetic tape thickness
Vary gear diameter
Off axis alignment
Mismatch / Overload
Imbalance
Off-track
Higher RPM
Chet Haibel ©2012 Hobbs Engineering Corp.
A flaw may be exposed by a different stress in HALT than the stress which exposes the flaw in the field environment
Focus on the failure modes and mechanisms, not the stresses used to expose them or the margin beyond field environment
Focusing on margin may lead to missing an opportunity for improvement followed by field failures of the same mode
This is a frequent, serious mistake in HALT!
Crossover Effect
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Chet Haibel ©2012 Hobbs Engineering Corp. 57
What Level of Stresses to Use
Chet Haibel ©2012 Hobbs Engineering Corp.
Vibration
• All modes excited
• Second modes are very important
Thermal
• All sites reach the desired temperatures
• All sites reach the desired rates of change
Voltage
Humidity
Current density
Other stresses or parameters
Product Response is of Prime Importance, the Inputs Are Not
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In HALT, one must go beyond customer-specified stress level to
compress the time to see the dominant failure modes
Stress level has been substituted for sample size!
This is one of the MAJOR BENEFITS of HALT
We do not need many units to HALT (four is good)
We can HALT a few at each stage of development and manufacturing.
• Prototype (as early as feasible)
• Pre-production (after corrections)
• Early production (after design transfer)
• Ongoing production (re-HALT)
59
What Level of Stresses to Use
Chet Haibel ©2012 Hobbs Engineering Corp.
Understand First
Again, the key is to focus on the failure mode, not the stress type used, or the margin beyond the field environment
Through failure analysis, gain root cause understanding first and then decide if the weakness would cause field failures or whether the weakness would put limitations on manufacturing screening
It’s often easier to fix it than prove it’s not a customer issue!
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Every weakness found represents an opportunity for improvement
HALT is proactive, but no action means no improvement
We try to break the product in order to find its weak links
This is discovery testing compared to qualification (success) testing
This is a total paradigm shift!
Opportunities not taken will probably lead to field failures much
more expensive than the improvement would have been. This fact
has been documented in thousands of cases
If you find it in HALT, it is probably relevant !
HALT Attitude
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Chet Haibel ©2012 Hobbs Engineering Corp.
Boeing 777 was the first
commercial airplane
ever certified for Extended
Twin-engine Operations
(ETOPS) at the outset of
service
Example of Success
Ed Minor, Boeing, in a presentation at a Hobbs Engineering Seminar
63
“Dispatch reliability after only two months of service was
better than the next best commercial airliner after six years”
Chet Haibel ©2012 Hobbs Engineering Corp. 64
Accelerometers
Analysis &Test Equipment
ASICs / Processors / Drives
Land / Air / Water Craft
A/V Products & Systems
Avionics / Aerospace
Compressors/Generators
PCs to Mainframes
Lipstick
Electronics / Electrical
Gears / Transmissions
Instruments / Gauges
Magnetic Resonance Scanners
Medical Products
Military / NASA (mixed)
Monitors / Displays / TVs
Ovens
Pneumatic Vibration
Point of Sale Systems
Power Supplies
Radar / GPS Systems
Telecommunications
Thermal Controls
Jet Engines / Missiles
Some Product Types Successfully Improved by HALT
Chet Haibel ©2012 Hobbs Engineering Corp.
HALT consists of:
• Precipitation
– Stresses
– Stress Levels
• Detection
– Detectable State
– Coverage
• Failure Analysis
• Corrective Action
– Corrective Action Verification
The Complete HALT Process
65
All must be present or no
improvement happens !
Chet Haibel ©2012 Hobbs Engineering Corp.
Achieve a Detectable State, the “Magic Level” or the “Sweet Spot”
where the intermittent is detectable
• Detection Screens are a well established technique commonly
practiced by the experts
• Requires equipment designed for HALT and HASS for best results
• Modulated ExcitationTM frequently improves detection by two
orders of magnitude, sometimes even more
The First Part of Detection
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Some damage from the HALT stresses may not be
immediately discernable – it may be LATENT !
HAST (Highly Accelerated Stress Test -- Pressure Cooker) may
precipitate latent damage, making it patent -- discernable
• Cracked component bodies (e.g. MLCC)
• Other long term failure modes not yet completed
If feasible, expose all HALT units to HAST
Or perform a biased (power on with signals toggling) exposure
to 60°C and 90% RH for one week
Detection Excellence
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Chet Haibel ©2012 Hobbs Engineering Corp. 68
Multi-Layer Ceramic Capacitor
CALCE Electronic Products and Systems Center, University of Maryland
PCBA Flexing
Chet Haibel ©2012 Hobbs Engineering Corp.
Combined all-axis, broad-band vibration and high-rate thermal cycling. Low frequencies must be present in sufficient amplitude to precipitate the defects.
Electrical stressing (power supply, clock frequency, loads)
Monitoring with high coverage is absolutely essential
Temperature, pressure, and humidity (HAST) equipment Traditional 85/85 takes 1,000 to 5,000 hours HAST takes only 48 hours!
Other stressors (such as corrosive atmosphere or radiation) as appropriate for the product and its environments
Equipment Required
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Appreciating HALT
To Appreciate
HALT, let’s look at
prototype test
quantities required
under normal
conditions
Chet Haibel ©2012 Hobbs Engineering Corp. 71
Reasonable Example
Suppose an R&D project has a product reliability
goal to have less than 5% Annual Failure Rate.
(this is not a lofty goal)
How many prototype units would have to be put
on test to have 70% probability of seeing all the
problems that must be resolved to be successful?
Chet Haibel ©2012 Hobbs Engineering Corp. 72
Infinite, Decreasing, Geometric Series
Mathematical Model for a Pareto
F1 , F1R , F1R2 , F1R
3 , ...
Sum = F1 / (1 - R) 0 < R < 1
Example:
If sum = 5%, R = 0.8, solve for F1
Answer:
(Sum)(1 - R) = F1 = (5%)(0.2) = 1%
Chet Haibel ©2012 Hobbs Engineering Corp. 73
Infinite, Decreasing, Geometric Series
0
1
2
3
4
A B C D E F G H I J K L M N O P
FAILURE MODE
PE
RC
EN
T
“allowed”
failure
modes
Chet Haibel ©2012 Hobbs Engineering Corp. 74
10
100
1000
0.001 0.01 0.1
Nu
mb
er o
f u
nit
s on
tes
t
Failure mode's failure probability
0.99 0.90 0.50 0.70
O
70% Chance of Seeing Failures for 5% Annual Failure Rate
Chet Haibel ©2012 Hobbs Engineering Corp. 75
Minimum Prototypes and Time
To see the failure modes that must be eliminated
for even mediocre reliability (5% AFR),
Test 120 units for a year at normal mission (customer, field) conditions,
or
HALT 4 units for a week
Chet Haibel ©2012 Hobbs Engineering Corp. 76
There are “Accelerated Reliability Test Centers” where you can take
some products to try a HALT chamber
The persons at the ARTC will run the chamber, but you have to
run your product using diagnostic software
Take an existing (currently shipping) product for which you know
the failure modes experienced by your customers
This is an excellent way to prove that HALT will find the relevant
failure modes in YOUR product
How to Prove that HALT Works
Chet Haibel ©2012 Hobbs Engineering Corp.
HALT WORKSHOP
Preparing to HALT a Product
Preparing a Product for HALT
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Chet Haibel ©2012 Hobbs Engineering Corp.
Preparing to HALT a Product
In any test we have to stimulate the product and look for a response
from it. HALT is no different, we need inputs and outputs which
we can control and observe from outside the HALT chamber.
Ideally, we want to check all functions of the product so we can see
any (soft) failures.
We often figure out a “quick test” which we can run at each condition
of voltage, temperature, vibration, etc. This might be the power-on
self-test (POST), so we power cycle the product at each condition.
Then occasionally, we will take the time to do a thorough checkout.
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Preparing to HALT a Product
Many products (especially software driven products) detect power
supply voltage and will shut down outside an upper and lower limit.
Some products detect temperature and will shut down outside an
upper and lower limit.
These protections must be disabled, either with special HALT
software (firmware) or by modifying the hardware (supplying a
stable voltage to the temperature and / or voltage comparators).
We want to see the underlying (raw) performance of the circuits.
These voltage and temperature limits will improve design margin.
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Preparing to HALT a Product
Some products have rubber feet on them to reduce skidding and
scratching, and take out minor irregularities in the support surface.
These will tend to dampen the vibration we are trying to drive into the
product. We must overcome this dampening by removing the feet
or supporting the product next to the feet on the chassis.
Similarly, inside the product there may be elastomer material to dampen
vibration. These dampeners must be defeated to transmit vibration.
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Preparing to HALT a Product
Most products have covers to protect the electronics from foreign
(conductive) material and protect the user from coming in contact
with live voltages.
Some products have fans to circulate air to cool the hot components
(and heat the cool components).
These covers and fans will get in the way of the turbulent airflow in the
HALT chamber, which is trying to impose a temperature on the
components. It makes a convection oven look tame!
Unless these covers are structural, they should be removed. If they are
structural, they must have holes drilled in them to let the airflow in.
81
Chet Haibel ©2012 Hobbs Engineering Corp.
OVERVIEW OF HIGHLY ACCELERATED LIFE TEST
Chet Haibel Hobbs Engineering Corporation
www.hobbsengr.com (303) 465-5988