An introduction to HALT, HASS,
HASA, and CALT
July 2, 2012
Why accelerated life testing?
► Traditional testing methods are time consuming and
► Manufacturers were not able to improve product
reliability dramatically with traditional testing
HALT — What is it?
Halt is a process to discover product design limitations
by subjecting products to step stresses.
• Halt is a design tool owned by engineering.
• To find product defects in design stage, not to pass
• To stimulate defects, not to simulate environmental
HALT — Equipment
Example: Qualmark Typhoon 2.5
Liquid nitrogen cooled
• Maximum thermal ramp rate: 200 °C/min
• Temperature range: -100°C to +200°C
Repetitive shock vibration
• Degrees of freedom: 6
• Acceleration: over 50G
Thermal and vibration
HALT — Step stress approach model
Temperature step stress
Vibration step stress
Rapid thermal transitions
HALT — How it works?
• Increase the stress, and repeat the process.
HALT — Why it works?
S-N Diagram (Aluminum 7075-T6)
(stress vs. number of cycles)
• 40KSI 2,000,000 cycles to failure
• 80KSI 2,000 cycles to failure
Number of cycles
HALT — Why it works?
100 200 300 400
Number of Thermal Cycles
Rate of change vs. number of cycles
18 °C/min 10 cycles
10 °C/min 55 cycles
5 °C/min 400 cycles
HALT — Summary of results
Failure Percentage by Stress Type
HALT — Early fault detection is key
The cost of finding and fixing a product fault:
$46 — during design phase
$228 — before procurement
$480 — before production
$22,000 — before shipment
$900,000 — on customer site
~ Hiroshi Hamada, Ricoh’s chairman
HALT — BenefitsSpending
MR — Manufacturing Release.
HASS — General rules
• Screening of 100% of production
• Screening stress level — the 80/50 rule
80% of the temperature operating limits found in HALT.
50% of the vibration operating limits found in HALT.
• An effective yet safe screening profile
Effective: A singe application of the screen.
Safe: Remove less than 5% of the total life.
Highly Accelerated Stress Auditing
The same as HASS, only operated on an audit basis instead
Calibrated Accelerated Life Testing
CALT — What is it?
A test process that allows time compression in life testing
while retaining correlation in resulting life predictions.
Statistical model for CALT:
• Statistic distribution
The scatter in product life under a constant stress
• Relationship between life and stress
CALT — Failure distribution
A mathematical model that describes the probability of failures
occurring over time.
Exponential distribution Normal distribution
Lognormal distribution Weibull distribution
CALT — Weibull distribution
Weibull probability density
where k>0 is the shape parameter,
λ>0 is the scale parameter.
λ — the characteristic life (63.2%).
CALT — Life and stress relationship
Usually the mean of the life distribution is expressed as a
function of the accelerating stress.
• Arrhenius relationship
where s is the stress, L is the mean of the life distribution, C, B, k, n are
• Inverse power model
CALT — Complications
Find the most suitable failure distribution model and
• Graphical data analysis
• Least squares analysis
• Maximum likelihood methods
Competing failure modes
GMW8287 Highly Accelerated Life Testing, February
GMW8758 Calibrated Accelerated Life Testing (CALT),
W. Nelson, Accelerated Testing: Statistical Methods, Test
Plans, and Data Analysis, John Wiley & Sons, 2004.
H. W. Mclean, Halt, Hass, and Hasa Explained, Revised
Edition, ASQ Quality Press, 2009.