1. An introduction to HALT, HASS,
HASA, and CALT
Winson Mao
July 2, 2012

2. Page 2
Why accelerated life testing?
► Traditional testing methods are time consuming and
expensive.
► Manufacturers were not able to improve product
reliability dramatically with traditional testing
methods.

3. Page 3
Highly Accelerated Life Testing
HALT

4. Page 4
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
tests.
• To stimulate defects, not to simulate environmental
stresses.
Different
purpose
Different
Methods
Different
Equipment

5. Page 5
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
Combined environment
Thermal and vibration

6. Page 6
HALT — Step stress approach model
Temperature step stress
Vibration step stress
Rapid thermal transitions
Combined environment

7. Page 7
HALT — How it works?
• Increase the stress, and repeat the process.

8. Page 8
HALT — Stress limits

9. Page 9
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
Stress(KSI)

10. Page 10
HALT — Why it works?
20
15
10
5
100 200 300 400
TemperatureRateofChange°C/Min.
Number of Thermal Cycles
(18, 10)
(10, 55)
(5, 400)
Rate of change vs. number of cycles
18 °C/min 10 cycles
10 °C/min 55 cycles
5 °C/min 400 cycles

11. Page 11
HALT — Summary of results
Failure Percentage by Stress Type
Cold Step
Stress
14%
Combined
Environment
20%
Vibration Step
Stress
45%
Rapid Thermal
Transition
4%
Hot Step
Stress
17%

12. Page 12
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

13. Page 13
HALT — BenefitsSpending
Time
MR
MR
MR — Manufacturing Release.

14. Page 14
Highly Accelerated Stress Screening
HASS

15. Page 15
HASS
A screening operation to detect weakness in
manufacturing.
• Equipment and parameters from HALT
• A mixed thermal cycle/vibration stress pattern

16. Page 16
HASS — Screen profile
For example

17. Page 17
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.

18. Page 18
Highly Accelerated Stress Auditing
HASA

19. Page 19
HASA
The same as HASS, only operated on an audit basis instead
of 100%.

20. Page 20
Calibrated Accelerated Life Testing
CALT

21. Page 21
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

22. Page 22
CALT — Failure distribution
A mathematical model that describes the probability of failures
occurring over time.
Exponential distribution Normal distribution
Lognormal distribution Weibull distribution

23. Page 23
CALT — Weibull distribution
Weibull probability density
,)()(
1
et
tk
tf
k
k
k 


 0t
where k>0 is the shape parameter,
λ>0 is the scale parameter.
λ — the characteristic life (63.2%).

24. Page 24
CALT — Life and stress relationship
Usually the mean of the life distribution is expressed as a
function of the accelerating stress.
• Arrhenius relationship
es
B
CL 
where s is the stress, L is the mean of the life distribution, C, B, k, n are
unknown parameters.
• Inverse power model
s
n
k
L


1
s
BCL
1
lnln 
snkL lnlnln 

25. Page 25
CALT — Approach

26. Page 26
CALT — Complications
 Find the most suitable failure distribution model and
life—stress relationship
• Graphical data analysis
• Least squares analysis
• Maximum likelihood methods
 Competing failure modes

27. Page 27
References
 GMW8287 Highly Accelerated Life Testing, February
2002.
 GMW8758 Calibrated Accelerated Life Testing (CALT),
October 2004.
 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.

28. Page 28
The End
Thank you!