This document provides an overview of reliability in complex systems. It discusses how systems reliability cannot be determined by examining parts alone due to interactions. LED systems are given as an example of a complex system where lifetime prediction requires understanding effects of temperature, electrical configurations, and other factors. The document recommends modern reliability approaches like MOEST testing, Bayesian Networks, and using big data from real-world use to better predict failure of complex systems.

1. Reliability of Complex Systems
A concise overview
Jan Eite Bullema – ASQ Certified Reliability Engineer

2. Outline
Reliability of Complex Systems
Jan Eite Bullema
Reliability of Complex Systems
2
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Overview of Reliability Science
What are Complex Systems?
Challenges in LED System complexity
Limitations in part based lifetime predictions
Modern reliability approaches,
e.g. MOEST, Bayesian Networks, Big Data
Conclusions

3. What is Reliability
Definitions of Quality and Reliability
Jan Eite Bullema
Reliability of Complex Systems
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1996, Lewis
Quality
The ability of a product to fulfil its intended purpose
Reliability
The ability of a product to fulfil its intended purpose
for a certain period of time under stated conditions

4. Why is Reliability Important?
Business Issues
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Reputation
Customer Satisfaction
Warranty Costs
Repeat Business
Cost Analysis
Customer Requirements
Competitive Advantage

5. The bath-tub curve
Reliability Life-Model
Jan Eite Bullema
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Source: R. Crowe, Design for Reliability, CRC Press 2001

6. First Reliability Models were developed for the V1 rocket
V1 was 100% Unreliable.
Fixed weakest link - still unreliable
Jan Eite Bullema
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Source: MIL-HDBK-338B ELECTRONIC RELIABILITY DESIGN HANDBOOK

7. Later Reliability Models were more successful
Voyager 2 flies already 40 years with no problems
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The Voyager 2 was launched on August 20, 1977. Its initial purpose
was to explore Jupiter and Saturn, with an operational life of 5 years
Currently, after 35 years the Voyager 2 is about 15.000.000.000 km
from the earth and the electronics still function satisfactory
Bullema, Reliable and Durable Microjoining, Mikrocentrum Reliability Seminair, December 2012

8. Reliability Models go beyond parts reliability
Challenger disaster in 1986: a wake up call
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1987: R.P. Feynman, Personal observations on the reliability of the Shuttle, Appendix F
The Space Shuttle Challenger disaster occurred on January 28, 1986, when
Space Shuttle Challenger broke apart 73 seconds into its flight.
Management estimated a failure probability 1 in 1000 000 => safe system
Engineers estimated a failure probability 1 in 100 => not so safe system

9. Systems are becoming more complex
Parts based testing is no longer a solution
Jan Eite Bullema
Reliability of Complex Systems
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1962, Herbert Simon, The Architecture of Complexity

10. What is a Complex System?
Complex means difficult to predict from parts
A system composed of interconnected parts that as a whole exhibit one
or more properties (behaviour among the possible properties) not
obvious from the properties of the individual parts.
A system’s complexity may be one of two forms,
disorganized complexity and organized complexity
In essence disorganized complexity is a matter of very large number of
parts and organized complexity is a matter of the subject system
Jan Eite Bullema
Reliability of Complex Systems
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Weaver and Warren, Science and Complexity, American Scientist, 36, p. 536 (1948)

11. Outline
Reliability of Complex Systems
Jan Eite Bullema
Reliability of Complex Systems
12
------------------------------
Overview of Reliability Science
e.g. Complex Systems
Challenges in LED reliability
i.e. Lifetimes > 50.000 hrs.
Modern reliability approaches,
e.g. MOEST, Bayesian Networks, Big Data
Conclusions

12. Reliability Basics
What is the reliability of a single LED
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http://rl.omslighting.com/ledacademy/694/led-academy
LED manufacturer claims that
50% of their LEDs (from any
batch) will emit at least 70% of
the initial lumens after 50,000
hours of operation

13. Reliability Basics
What is the reliability of a single LED
Jan Eite Bullema
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http://rl.omslighting.com/ledacademy/694/led-academy
LED manufacturer claims that
50% of their LEDs (from any
batch) will emit at least 70% of
the initial lumens after 50,000
hours of operation
this implies that 50% of the
LEDs will not perform to the
required levels

14. Reliability Basics
What is the reliability of a single LED
Jan Eite Bullema
Reliability of Complex Systems
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http://rl.omslighting.com/ledacademy/694/led-academy
this implies that 50% of the
LEDs will not perform to the
required levels
in all practical terms, the
lifetime of the LEDs will
depend on the requirement(s)
of the application

15. Reliability Basics
What is the reliability of a single LED
E.g. the Mean Time Between Failures
Jan Eite Bullema
Reliability of Complex Systems
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ETAP White Paper: LED Lifetime in Practice

16. Reliability Basics
What is the reliability of a single LED
e.g. Temperature Dependence of MTBF
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LumiLED High Flux High Power Reliability Data

17. Reliability Basics
What is the reliability of a single LED?
e.g. Temperature Dependence of MTBF
Jan Eite Bullema
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LumiLED High Flux High Power Reliability Data

18. Durability of LED Systems
Lifetimes > 50.000 hrs
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Life time of a LED System has to be 25 000 – 50 000 hrs.
Gielen et al, Development of an intelligent integrated LED system-in-package, EPMC 2011

19. Durability of LED Systems
System behaviour is more than the sum of
component behaviour
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http://www.ledsmagazine.com

20. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example:
Reliability of a a single LED component
MTBF = 3E +12 e- 0.037x ( x = junction temperature in Kelvin)
R(LED) = e - (time/MTBF LED)
LED

21. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
LEDDriver
Example:
The LED needs a Driver
System reliability: R(Driver) x R(LED) = e - (time/MTBF Driver) x e - (time/MTBF LED)

22. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
LED 1Driver
LED 2
The LEDs are in a string to ensure lumen output: Parallel case
System reliability: R(Driver) x R(LED String)
= e - (time/MTBF Driver) x e - (time x {1 / [MTBF LED1 + MTBF LED2]})

23. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
LED 1Driver LED 2
The LEDs are in a string to ensure lumen output: Serial case
System reliability: R(Driver) x R(LED String)
= e - (time/MTBF Driver) x e - (time x 1 / MTBF LED1) x e – (time x 1 / MTBF LED2)

24. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
LED 1Driver
LED 2
Example:
The LEDs are in a string to ensure lumen output
System reliability: R(Driver) x R(LED String)
= e - (time/MTBF Driver) x e - (time x {1 / [MTBF LED1 + MTBF LED2]})
MTBF of a Component depends on environment
(e.g. Temperature, humidity, mechanical loading, position heat sink, etc.)
Temperature 1
Temperature 2
Temperature 3

25. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
LED 1Driver
LED 2
Resistor
Capacitor
De Driver needs additional electronics to perform well
System reliability: R (Electronics) x R(Driver) x R(LED String)
= e - (time/MTBF Electronics) x e - (time/MTBF Driver) x e - (time x (1 / [MTBF LED String))

26. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
LED 1Driver
LED 2
Resistor 1
Capacitor 1
LED 3
LED 4
LED 5
LED 6
Resistor 2
Capacitor 2
De Driver needs additional electronics to perform well
Can become complicated

27. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:
compact LED system with integrated driver and string of six LEDs
LED
die
Driver
chip
Thermal
Pad
IO leads
Silicone
lens/filler
Moulding
compound
LED
die
Driver
chip
Thermal
Pad
IO leads
Silicone
lens/filler
Moulding
compound

28. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:

29. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:
Failure tree for electrical defects and reduced lumen output

30. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:
Calculation R(t) for not cooled and heat pipe cooled (T = T not cooled - 20 C) Design
ESIP with and
without heat pipe

31. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:
Predicted Survival Rate R(t) of LV @ 25 ºC
Continuous,1xSwitch/day,10xSwitch/day
Green line = 10 x switching / day
Red line = 1 x switched / day
Blue line = No switching

32. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:
ESIP with and
without heat pipe
CSSL Design A, B
At Low and High Temp

33. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
34
Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:

34. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The CSSL Demonstrator:

35. LED Systems are Complex
Knowing the behaviour of parts is not sufficient
Jan Eite Bullema
Reliability of Complex Systems
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LED Luminaire Lifetime, Solid State Lighting Product Quality Initiative, 2010
Parts / Elements
- LED
- Optics
- Printed Circuit Board
- Mechanical
- Thermal / Heat Sink
- Housing
- Gaskets / Sealants
- Electrical Conductors
- Electrical Drivers
- Manufacturing Process

36. Outline
Reliability of Complex Systems
Jan Eite Bullema
Reliability of Complex Systems
37
-------------------------
Overview of Reliability Science
e.g. Complex Systems
Challenges in LED reliability
i.e. Lifetimes > 50.000 hrs.
Modern reliability approaches,
e.g. MOEST, Bayesian Networks, Big Data
Conclusions

37. MEOST: a jump into the future
Multiple Over Stress Testing: finding the weak spot
Jan Eite Bullema
Reliability of Complex Systems
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Keki R. Bhote , World Class Reliability, ISBN 0-8144-0792-7
Various stresses and their action

38. Bayesian Networks
Failure Prediction of LED systems over time
Jan Eite Bullema
Reliability of Complex Systems
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Bullema, Combination of Bayesian Networks and FEM models to Predict Reliability of LED Systems, ECTS 2012
Example: The ESIP Demonstrator:
ESIP with and
without heat pipe
CSSL Design A, B
At Low and High Temp

39. Big Data
Measuring all lamps real time during use: advanced prognostics
Jan Eite Bullema
Reliability of Complex Systems
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http://www.smartindustry.nl/

40. Outline
Reliability of Complex Systems
Jan Eite Bullema
Reliability of Complex Systems
41
MIL-HDBK-338B
Overview of Reliability Science
e.g. Complex Systems
Challenges in LED reliability
i.e. Lifetimes > 50.000 hrs.
Modern reliability approaches,
e.g. MOEST, Bayesian Networks, Big Data
Conclusions