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Practical Reliability Engineering 2009
Contents
� Why is reliability important?
� Assembleon Reliability program 2007 – 2008
� HALT and basic principles of Reliability
� HALT case overview (Temperature)
2
� HALT case overview (Temperature)
� Electrical Transients
� HALT case overview (Transients)
� Shock & Vibration
� Experience with HALT
� Mindset
Why is reliability so important?
�Unreliable products gives:
– Customer dissatisfaction
– Warranty Costs
– Rework of parts (€ )
– Loss of Reputation
3
– Loss of Reputation
– Loss of Repeat Business
Assembleon Reliability program 2007-20081/2
� Design reviews, FMEA, functional/duration testing are NOT sufficient.
We still had FP’s (Field Problems).
� A reliability program was set up determine if the HALT technique can
provide answers to the following questions:
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provide answers to the following questions:
– How can we provoke realistic failures during design?
– How to do this within a reasonable amount of time?
– What does reliability cost?
(HALT = High Accelerated Life Testing)
Assembleon Reliability program 2007-20082/2
� Engineering changes had to be made to various electronic boards
because of functionality expansion.
– This gave us the opportunity to try to simulate & solve known FP’s
using the HALT method.
� (Hitch-hike with the ongoing engineering process)
5
� (Hitch-hike with the ongoing engineering process)
Find an answer to the unanswered questions:
What is HALT ?� HALT is an engineering step-stress-to-fail process which can reveal
design flaws quickly (within hours of testing).
� HALT is not a compliance test and not limited by component or product
specifications.Failure
Evaluate the relevance of the failure.
Determine if stress-level is acceptible and
implement corrective action if necessary.
6Apply stress
(+/-15min/step)
Failure
Evaluate the relevance of the failure.
Determine if stress-level is acceptible and
implement corrective action if necessary. Increase stress
Basic principles of Reliability:
Reliability of a product is determined by:
– strength (product related)
– stress (user/environment related)
7
Reliability (Load & Strength interferences)
1
Excluding wear-out
8
Load Strength
Defect!
Ref. Patrick T.D. O’Connor – British Areospace
Reliability (HALT principle)
..
1 • Induce failure
• Find weak-spots
Design
• Improve design
9Load Strength
Ref. Patrick T.D. O’Connor – British Areospace
Design
Margin
HALT tests may include:
� Temperature stress
• under max. loading conditions
• In combination with power cycling
� Temperature cycling
� Voltage stress (in combination with temp.)
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� Voltage stress (in combination with temp.)
� Electric transient susceptibility stress (all cables)
� Shock & vibration
� RH%
HALT case overview – Temperature
+100C
+140C
ModifiedChange FET type Cost: approx. 10ct
ModifiedChange IC type Cost: approx. 10ct
ModifiedChange Diode type Cost: approx. 5ct
ModifiedChange FET type Add 10uF capacitor Cost approx. 20ct
120C
85C
130C140C
X20 PCB’s
80CX20PCB’s
Case 1(Tape cutter)
100C
140C
Case 6(ITBF-EFT) 120C
Modified
Solve in FPGA
Stop test.
100C
140C
Sprocket
140C
Modified2 x pull-down resistors.Cost: negligible
ModifiedChange the BIOS settings.Cost: negligible (Implementation)
ModifiedChange res. values Cost: negligible
140CX14 PCBs130C
80C
140C
11
-40C
Case 3(PCU-IC)
+50C
Re-active (learning – correlation with FP’s)
70C
Case 5(re-use F)
Case 2(PCU-FETs)
X20PCB’s
-10C
Case 8(AXPC)
Pro-active
CCB(tray
trolley)
Solve in FPGA
Cost: negligible
Case 7(BA-
Camera)
60C
Sprocket
detector
Case 9(TPR Liftcontroller)
70C
Case 4(PCU-diode)
70C
80C
Summary: Performing Temperature HALT
� Perform Infra-red measurements (Hot-spots)
before performing HALT.
� For HALT; (Rule of Thumb): ensure a margin of at least 40C above
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specification.• (This is NOT a continuous spec!)
� It’s important to analyze all failures and to decide on: • Root cause
• Evaluate the relevance of the failure
• What is the effort/cost for improvement
Electric transients
13
� Electronic circuits with cable connections can be affected by electric transients.
� Cables can be excellent antenna’s, depending on impedances, length etc. and can
pick up such transients:
� This phenomenon deals with electromagnetic disturbances inside equipment (intra-EMC)
� The EMC regulations often concern only inter-EMC and has a more legal goal & scope
� Additional EMC performance is often necessary for reliability
Example of an electric transient and effects
Relay switching off a load witha residue voltage.
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Possible resultant transient voltage which can be induced into nearby cables or locally on a PCB.
Possible resultant damage caused by a transient voltage disturbance.
HALT case overview – Transients
6kV
7kV
8kV
9kV
10kV
Modified
Add 10nF cap.
Cost: negligible
Modified
Gnd. connection
Cost: negligible
At approx. 8kV,
Cable isolation gets “tricky”
10kV10kV
Modified
Shield repeater
Cost: 5 euro
8kVdefect
Modified
Gnd. connection
Cost: 10ct
6kV
Modified
Add 2x10nF caps.
Cost: negligible
Case 6(BA-
Camera)
Design integration
EMC
Cost: negligible
Design integration
EMC
Cost: negligible
8kV
Case 8(TPR)
10kV
15
1kV
2kV
3kV
4kV
5kV
Re-active (learning – correlation with FP’s)
2kVCase 2
(ITBF)
mP reset
3kV3kV
3kVFET defect
Case 1
0.5kV
2.5kV
Case 4Fire-WireRepeater problem
1.5kVdefect
Case 3(Sprocket detector)
1kV
Pro-active
Camera)
4kV
0.6kV
2.8kV
Case 7(LED pcb)
Case 5(Tape cutter)
mP reset
2kV
Transient “Rule of thumb” targets
6kV
7kV
8kV
9kV
10kV
Soft errorsHard failureEither SW
or HW
16
1kV
2kV
3kV
4kV
5kV
Shock & Vibration (placement head)
Example: Placement Head (during operation)
Test:
Vibration:10-1000Hz; 0.1g; 0.2g;… 1g; 1.2g… etc
Shock: 25g; 3msec (Sys. Limit) 30, 60, 100%
17
Other tests: Non-operating; transport
Shock & Vibration
BA Camera
Representing Optics
18
Representing OpticsRepresenting Electronics
Experience with HALT: (electro.)
� A lot of Field Problems can be provoked using the concept of HALT
testing.
� HALT testing provides results quickly (within a few hours/days).
� Experience shows that realistic failures can be provoked with minimum
19
� Experience shows that realistic failures can be provoked with minimum
design impact.� Provided testing is performed early during development (pro-active).
� Now we are performing pro-active HALT testing with success.
Reliability engineering: a matter of mindset
� The principle behind HALT is quite simple and is usually easy to
perform. The biggest challenge is setting the right MINDSET and
applying the right strategy.
� Don’t test for approval but test to find potential failures and make the
necessary improvements (It’s not a Pass/Fail test).
20
� Determine HALT: plan/parameters depending on product type &
working environment.
� HALT is not a “magic solvent” but with a good test strategy and the right
mindset, it can be a very effective tool for improving the reliability of
design’s.
� Less failures gives satisfied customers
– Improved quality & less re-work